Transcript Document

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METAL JOINING
• Even the simplest object is an assembly of
components
• Complex ones - greater number of partssubassemblies joined to perform the function
• METHODSWELDING,
BRAZING,
SOLDERING,
ADHESIVE BONDING,
MECHANICAL JOINING
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WHY JOINING?
• IMPOSSIBLE TO MAKE AS ONE PIECE
• EASINESS AND ECONOMY IN
MANUFACTURE
• EASY IN REPAIRS AND MAINTENANCE
• FUNCTIONAL PROPERTIES DIFFERe.g.: Carbide tips of tools,corrosion resistant
parts, tungsten carbide tip of pens, brake shoes to
metal backing etc…
• TRANSPORTING SITE/ CUSTOMER
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CLASSIFICATION
• According to the STATE of the materials being
joined
• Extent of external heating- PRESSURE
• Use of FILLER materials
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Joining Processes
LIQUID
SOLID
CHEMICAL CUTTING ARC
CONSUMABLE
Oxy-fuel
Thermit
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SMAW
SAW
GMAW
FCAW
EGW
ESW
RESISTANCE
NON CONSUMABLE
Forge
Cold
Spot
GTAW
Ultrasonic
Seam
PAW
Friction
Projection Explosion
EBW
Flash
LBW
Diffusion
Stud
Dr. N. RAMACHANDRAN,
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percussion
MECH.
JOINING
LIQUIDSOLID
Brazing
Soldering
Adhesive
Bonding
Fastening
Crimping
Seaming
Stitching
5
History of welding
And
American Welding Society
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Vulcan –
The Roman
Fire God
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• Welding Heat
Exchanger
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• Thermite Welding
Patent 729573
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• 1948
  The Ohio State University Board of Trustees established
the Department of Welding Engineering on January 1 as
the first of its kind for a Welding Engineering cirriculum
at a University. OSU pioneered the Welding Engineering
through an emphasis in the Industrial Engineering
Department the previous nine years. The advantages of
this engineering degree is 1) Enable satisfactory
administration of problems relating to education and
research in the welding field. 2) Recognition is given to the
Welding Engineer as an entity among applied sciences. 3)
A degree is authorized which is descriptive of a particular
discipline imposed in training for professional work in the
field.
  Air Reduction Company develops the Inert-Gas MetalArc (MIG) process.
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 SIGMA Welding (Shielded Inert Gas Metal Arc) was developed to weld
plate greater than1/8 inch instead of the "Heli-Arc" welding process. The arc
is maintained in a shield of argon gas between the filler metal electrode and
the workpiece. No flux is used. Licensed by Linde Air Products Co.
•1948-1949
 Curtiss-Wright Corporation looks at brazing as a strong, lightweight
process for durable assemblies.
•1949
 American Westinghouse introduces and markets welding machines using
Selenium Rectifiers.
 US Navy uses inert-gas metal arc welding for aluminum hulls of 100 feet in
length.
•1950
 The Kurpflaz Bridge in Germany was built as the first welded orthotropic
deck.
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•1950s
 Electron Beam (EB) welding process developed in France by J. A.
Stohr of the French Atomic Energy Commission. First Public disclosure
was 1957.
 Wave soldering is introduced to keep up with the demand of Printed
Wiring Boards used in the electronics age.
 Research on testing of brazed joint begins as serious endeavor for the
next ten years.
•1950
 Electroslag Welding (ESW) is developed at the E. O. Paton Welding
Institute, Ukraine USSR.
 Third Edition of the Welding Handbook is printed by AWS.
 Flash Butt Welding is the standard for welding rail line construction.
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•1951
 Russia use Electroslag Welding (ESW) process in production.
 The Philip Roden Co. of Milwaukee Wisconsin announces the
DryRod electrode oven. This oven is intended to provide a
controlled moisture environment of 0.2% moisture standard set
forth by the government. This oven provides adjustable
temperature control of 200-550 F, vented and holding 350 pounds
of electrodes.
•1953
 Modifying the Gas Metal Arc Welding (GMAW) process,
Lyubavskii and Novoshilov used CO2 with consumable electrodes.
Resulted in hotter arc, uses higher current, and larger diameter
electrodes.
 The Ohio State University established a Welding Engineering
College curriculum out of the Industrial Engineering Department.
•
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•1957
 Flux Cored-Arc Welding (FCAW) patented and reintroduced by National
Cylinder Gas Co.
 Plasma Arc Welding (PAW) Process developed by Robert M. Gage
 Russia, Britain, and USA independently develop a short-circuiting transfer
for low-current low-voltage welding in a carbon dioxide atmosphere.
 Braze repair process for cracks in jet engine combustion chambers and
transition ducts.
1958
 The Soviet Union introduced the Electroslag Welding (ESW) Process at the
Brussels World Fair in Belgium. This welding process had been used since
1951 in the USSR which was based on the concept and work of an American,
R. K. Hopkins. Perfected at the Paton Institute Laboratory in Kiev, Ukraine,
USSR and the Welding Research Laboratory in Braitislava, Czechoslovakia.
 AWS Committee on Brazing and Soldering is formed to develop a test for
evaluating strength of brazed joints. Robert Peaslee proposes a test in the
Welding Journal.
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• 1959
  Electroslag welding process was first used at the Electromotive
Division of General Motors in Chicago and was called the
"Electro-Molding Process".
  Development of Inside-Outside Electrode which did not require
an external gas shielding - Innershield from Lincoln Electric Co.
• 1958-1959
  Short Arc (Micro-wire Short Arc) developed from refined power
supplies and smaller diameter wires.
• 1960s
  Pulsed Arc Welding...(more to follow)
  Space Program is underway...(more to follow)
  Difficult to stabilize GTAW at below 15 amps, Microplasma is
developed to overcome the limitation.
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1960
 Development of a cold wall vacuum furnace.
 First laser beam produced using a ruby crystal for the Light Amplification
Stimulated Emission Radiation (LASER).
 Explosive welding is developed in USA.
 Hughes Aircraft Company (Mainar) develops the first ruby laser
(springtime).
 Bell Telephone Laboratories (Ali Javan) developed and presented the first
gas laser using neon and helium (fall time)
1962
 The Mercury Space Capsule is formed using inner and outer titanium shell,
seam welded together using a three-phase resistance welder by Sciaky.
1963
 U.S.S. Thresher sinks off the coast of New Hampshire and by December,
the U.S. Navy charters the Submarine Safety Program (SUBSAFE) to
control the fabrication, inspection and quality control of submarine
construction. The presumed failure was with a silver-brazed piping joint, but
after the investigation, the whole welding and brazing program was suspect.
Included was the material properties of the welding and brazing filler metals.
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• 1965-1967
  CO2 lasers are developed for cutting and welding.
• 1967
  H. J. Clarke makes the following Predictions during the AWS Plummer
Lecture in Houston as he ties the current state of technology of welding to
the future of progress:
  World's Population would be greater than 5 Billion.
  Large scale farming of the ocean and fabrication of synthetic protein.
  Controlled thermonuclear power as a source of energy.
  General immunization against bacteria and virile infections, perfected
and available.
  Primitive forms of life will created in the lab.
  Automation will have advance for performance of menial chores and
complicated functions.
  Housewives would be ordering groceries and everyday items from
central stores linked to the home electronically. (!!!)
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 
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• Children will be receiving education at home - "either by television or
with personal teaching machines and programmed instructions"
  Moon - mining and manufacture of propellant and on Mars,
permanent unmanned research stations.
  Weather manipulation by the military.
  Effective anti-ballistic missile defense in the form of air-launched
missiles and directed energy beams.
  Libraries will be "computer-run"
  Gravity welding is introduced in Britain after its initial discovery by
Japan.
• 1969
  The Russian Welding Program in Space began by producing Electron
Beam welds on SOYUZ-6. Welding an AMG6 and DM-20 aluminum
alloys with the Vulkan process. Sponsored by the E. O. Paton Welding
Institute Academy of Science.
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• 1970
  As miniaturization developed from the pressure to increase component
densities, Surface Mount Technology is developed. This required new ways to
make soldered joints, including the development of vapor phase, infrared, hot
gas and other re-flow technologies.
  First AWS International Brazing Conference including 24 papers presented
created much interest in the brazing process.
  BP discovers oil off the coast of Scotland.
• 1971
  British Welding Institute (Houldcroft) adds oxidizing gas jet around laser
beam to develop laser cutting.
• 1973
  The American Astronauts used Electron Beam welding process in June
1973 welding Aluminum Alloy 2219-T87, Stainless 304 and Pure Tantalum.
  Welding equipment manufacturers concentrate on equipment refinement
instead of new processes.
  Two Supertankers, Globtik Tokyo and Globtik London (476025 DWT) were
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built
for carrying 153 million
gallons
(3 millionNITC
barrels) of crude oil.
• 1976
  First automotive production application of lasers weld begins with General
Motors Corporation, Dayton Ohio using two 1.25 kW CO2 lasers. for welding
valve assemblies for emission control systems.
• 1977
  The US Federal Highway Administration issues a moratorium of Electroslag
Welding (ESW) when cracks are discovered during an inspection of a bridge in
Pittsburgh, Pennsylvania on an interstate highway. Failure analysis was
conducted by Lehigh University on Interstate 79.
• 1980
  The Fort McHenry tunnel contract, for 750 Million Dollars, is awarded to
begin construction, completing Intestate 95 through Baltimore, Maryland. This
is the largest tunnel of its kind, 180 feet at the bottom with two separate four
lane immersed tunnels removing 3.5 million cubic yards of dredge.
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• 1983
  Homopolar pulse welding variation of the upset welding process research
begins at the University of Texas at Austin at the Center for
Electromechanics.
• 1987
  Laser research begins a unique method for depositing complex metal alloys
(Laser Powder Fusion).
• 1991
  TWI of Cambridge England develops the Friction Stir Weld (FSW)
process in its laboratory. This process differs from conventional rotary
technology whereby a hard, non consumable, cylindrical tool causes friction,
plasticizing two metals into a Solid-State Bond. No shielding gas or filler
metal is required. Metals joined successfully include, the 2XXX, 6XXX and
7XXX series aluminum. NASA is the first US venture which welded the
massive fuel tank for the Space Shuttle.
  Brazing Handbook (Fourth Edition) shows the data of the filler metal/base
metal failure transitions between 1T and 2T overlap and is the key for the
design data (factor of safety).
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1996
 Over 7,00,000 brazements are produced for the aircraft industry in the US
and Canada.
 Over 132,010,00 units of brazed automotive parts are produce.
1999
 The Edison Welding Institute develops a solution to obtaining deeper
penetration of a GTA weld by introducing FLUX onto the surface of the weld.
This FLUX helps drive the welding arc heat deeper into the weld joint and
permits 300 percent more penetration.
2000
 Magnetic Pulse Welding (MPW) is introduced by Pulsar Ltd. of Israel using
capacitive power as a solid state welding process. Discharging 2 Million amps
in less than 100 microseconds this process can create a metallurgical, a nonmetallurgical or a mechanical lock, depending on the substrate involved. No
heat affected zone (HAZ) is created since only a rise of 30oC occurs.
 Tailored welded blanks of aluminum are used where spot welding was once
performed.

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2000
Researchers from Argonne National Laboratory use the energy of the x-ray to
weld metal-matrix composite (Ti or Al / Al2O3 or SiC) materials.
 Diode laser welding, once limited to compact disks, laser printers, and laser
pointers, are now making their way to the manufacturing floor. Welding Type
304 Stainless steel (0.024 inch), Titanium foil (0.005 inch thick) and laser
brazing with a silicon-bronze brazing wire.
 Conductive heat resistance seam welding (CHRSEW) is developed. The
process uses steel cover sheets placed on top of aluminum butted together.
Using conventional seam welding, the heat generated from the steel forms a
molten interface on the aluminum and fusion is made at the butt joint. The
steel covers are then removed.
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• 2001
 AWS D17.1, "Specification for Fusion Welding for Aerospace
Applications" is published in March. The efforts of approximately 50
individuals from a cross-section of the Aviation Industry and government
produces the first commercial aviation welding specification.
 Flame brazing 5XXX aluminum alloys using non-corrosive flux.
 Sulzar Elbar introduces laser powder welding technology. Permits
rebuilding of substrate material (High Creep Resistance) and reproduction
of the single crystal structure.
•
2002
 From Linde Gas in Germany, a Diode laser using process gases and "active-gas
components" is investigated to enhance the "key-holing" effects for laser welding.
The process gas, Argon-CO2, increases the welding speed and in the case of a diode
laser, will support the transition of heat conductivity welding to a deep welding, i.e.,
'key-holing'. Adding active gas changes the direction of the metal flow within a weld
pool and produces narrower, high-quality weld.
 CO2 Lasers are used to weld polymers. The Edison Welding Institute is using
through-transmission lasers in the 230-980 nm range to readily form welded joints.
Using silicon carbides embedded in the surfaces of the polymer, the laser is capable
of melting the material leaving a near invisible joint line.
2003 2004 2005 Future developments.
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ABOUT AWS
The American Welding Society (AWS) was founded in 1919 as a
multifaceted, nonprofit organization with a goal to advance the
science, technology and application of welding and related
joining disciplines
• The Engineering
Societies Building (left)
in New York City was the
home of AWS until 1961
when the Society moved
to the United Engineering
Center, also in New York
City.
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From factory floor to high-rise construction, from
military weaponry to home products, AWS continues
to lead the way in supporting welding education and
technology development to ensure a strong,
competitive and exciting way of life for all Americans.
• The Society
moved its
headquarters to
Miami in 1971
(left).
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• The American Welding Society, in
conjunction with the Department of
Energy, has put together a vision that will
carry the welding industry through 2020.
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• Technical Publications
• AWS offers over 300 books, charts, videos,
replicas, proceedings, and software. 160 AWSdeveloped codes, recommended practices, and
guides are produced under strict American
National Standards Institute (ANSI) procedures,
including one of the most consulted codes in the
world, D1.1 Structural Welding Code - Steel.
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Foundation
• Founded in 1989, to support research and
education in welding and related technologies. It
is committed to annually awarding fellowships to
deserving graduate students for important
research in areas important to the requirements
of industry. Accordingly, each year the AWS
Foundation administers six $20,000 grants matched in kind by the participating
universities. The award of scholarships to
vocational and undergraduate college students is
also a high priority and a student loan program
has also been developed to prepare students for
welding relatedDr. careers.
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• The Professional Program
The AWS Professional Program offers a broad
spectrum of Technical Papers describing the
latest findings in welding research, processes and
applications. Special sessions and gatherings
exploring the boundaries of industry issues are
also significant features of the convention.
Subjects cover an entire range of industry
concerns from the joining of space age materials
to production management techniques, testing,
quality assurance and more.
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Which welding process(es) will see an
increase in use and which will see a
decrease in use during the next decade?
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• There was much speculation, but
almost unanimously the process
chosen for decline was shielded metal
arc welding (SMAW). A very few
speculated a decline in the use of gas
metal arc (GMAW) and gas tungsten arc
welding (GTAW). A significant group
felt the continuous wire processes
(FCAW, GMAW) would experience the
most use. The GTAW process was the
next most mentioned. One of the
reasons stated for its increase was "the
need for high-quality work on thin
materials." NITC
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Welding Forges into the
Future
Where do you see the use of welding automation
heading in your industry?
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• In what areas of welding do we need more
knowledge?
• Safety and Health. The industry needs more knowledge and
awareness regarding the hazards of welding, according to the
respondents.
  Welding of the newer grades of high-strength steels,
high- alloy steels and heat treatable steels.
• We need to "keep up the 'how to weld' information with the increase in
'new' alloys, which are becoming more difficult to weld."
  Automation. A variety of topics relating to automation. These
included training in computerization and automation; information on
short-run automation; and the need to create standard platforms for
welding equipment, robot controllers, sensing devices and other
automation peripherals.
  The basics While universities and institutions are doing basic
research, they cannot tell you the best process and fastest speed for a
1Ž4-in. fillet weld."
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• What are the strengths of the welding
industry? What are its weaknesses?
• What business improvements during the
next ten years would be in your company's
best interests?
• What has to be done in the future to keep
the welding industry healthy?
More than 50% of the respondents believe
improving the image of welding so top students
will be drawn to the industry and bettering training
methods for welders and welding engineers are the
keys to welding's future.
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• Are you optimistic or pessimistic about the
future of your particular industry?
92% of respondents indicated they are at least
optimistic about the future.
One respondent summed up his reasons this
way:
Metallics will be around for a long time and
they will need to be joined.
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• Since time machines still exist only in the stories of H.
G. Wells and other works of science fiction, no one can
tell us exactly how welding will fare in the 21st century.
However, the people who responded to the Welding
Journal survey represent a cross section of fabricators
of welded products and producers of welding
equipment and related products. Together they offer a
wide range of experience and knowledge. Answering
the questions separately, in their respective cities, they
still formed a consensus. They agree the future looks
promising for welding. It remains and will continue to be
a productive, cost-effective manufacturing method.
However, steps must be taken to bring more skilled
personnel into the industry, or changes must be made
to accommodate for the lack of skilled personnel (e.g.,
welding automation). They also indicated the welding
industry must embrace all of the modern-day
technological tools to keep pace with the rest of the
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world.
.
LIQUID STATE PROCESSES
• Partial melting and fusion of joint
• Physical and mechanical changes taking place
• Can be with application of pressure or by addition
of filler material
• Prior to joining, PREPARATION TO BE DONE
STANDARDS- AWS; ASTMTYPES OF GROOVES, JOINTS
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Types of welds and symbols
•
•
•
•
•
•
•
•
FILLET, SQUARE BUTT, SINGLE V,
DOUBLE V, SINGLE U, DOUBLE U,
SINGLE BEVEL BUTT, DOUBLE BEVEL BUTT,
SINGLE J BUTT, DOUBLE J BUTT,
STUD, BEAD(EDGE OR SEAL), PLUG,
SPOT, SEAM, MASHED SEAM,
STITCH, PROJECTION,
FLASH, UPSET etc. (REFER sketches supplied)
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Standard location of elements of weld symbol
G- Grind C- Chip
F-File M-Machine
Size
Specification
process.
R- Rolling
Length of weld
Unwelded length
Finish symbol
S
Weld all around
L
P
No tailSMAW
Field weld
Reference line
Other side of arrow
Near side of Arrow
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Arrow connecting reference
line to arrow side of joint /to
edge prepared /member or
both
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Groove face
GROOVE ANGLE
Joint angle
ROOT
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Root Face
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WELD POSITIONS
•
•
•
•
FLAT
HORIZONTAL
VERTICAL
OVERHEAD
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WELD MOVEMENTS
•H
•O
•C
•J
•U
• ZIGZAG
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WELDING TERMINOLOGY
Slide 2 of 18
ELECTRODE COATING INGREDIENTS
• Slag forming ingredients- silicates of sodium, potassium, Mg,
Al, iron oxide, China clay, mica etc.
• Gas shielding- cellulose, wood, starch, calcium carbonate
• De-oxidising elements- ferro manganese, ferro silicon- to
refine molten metal
• Arc stabilizing – calcium carbonate, potassium silicate,
titanates, Mg silicate etc.
• .Alloying elements- ferro alloys, Mn, Mo., to impart special
properties
• Iron powder- to improve arc behaviour, bead appearance
• Other elements - to improve penetration, limit spatter,
improve metal deposition rates,
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PURPOSE OF COATING
• Gives out inert or protective gas- shields
• Stabilizes the arc- by chemicals
• Low rate consumption of electrode- directs arc and
molten metal
• Removes impurities and oxides as slag
• Coatings act as insulators- so narrow grooves welded
• Provide means to introduce alloying elements
Bare electrodes - carbon- more conductive- slow
consumption in welding
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WELDING TECHNIQUES
FOREHAND
BACKHAND
THIN
Same direction torch
Heat concentrated away from
bead
THICK
Opposite direction torch
Heat concentrated on bead
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Even
Broad bead
48
WELD MOVEMENTS
I
L
O
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STRAIGHT
Z
ZIGZAG
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ASME P Material Numbers Explained
ASME has adopted their own designation for welding processes,
which are very different from the ISO definitions adopted by
EN24063.
Designation
Description
OFW
Oxyfuel Gas Welding
SMAW
Shielded Metal Arc Welding (MMA)
SAW
Submerged Arc Welding
GMAW
Gas Metal Arc Welding (MIG/MAG)
FCAW
Flux Cored Wire
GTAW
Gas Tungsten Arc Welding (TIG)
PAW
Plasma Arc Welding
Straight polarity = Electrode -ve
Reverse polarity = Electrode +ve
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ASME F Numbers
F Number
General Description
1
Heavy rutile coated iron powder electrodes :- A5.1 : E7024
2
Most Rutile consumables such as :- A5.1 : E6013
3
Cellulosic electrodes such as :- A5.1 : E6011
4
Basic coated electrodes such as : A5.1 : E7016 and E7018
5
High alloy austenitic stainless steel and duplex :- A5.4 : E316L-16
6
Any steel solid or cored wire (with flux or metal)
2X
Aluminium and its alloys
3X
Copper and its alloys
4X
Nickel alloys
5X
Titanium
6X
Zirconium
7X
Hard Facing Overlay
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Note:- X represents any number 0 to 9
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ASME A Numbers
These refer to the chemical analysis of the deposited weld and not
the parent material. They only apply to welding procedures in
steel materials.
A1
Plain unalloyed carbon manganese steels.
A2 to A4
Low alloy steels containing Moly and Chrome Moly
A8
Austenitic stainless steels such as type 316.
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ASME Welding Positions
Note the welding progression, (vertically upwards or downwards),
must always be stated and it is an essential variable for both
procedures and performance qualifications.
Welding Positions For Groove welds:Test Position
ISO and EN
Flat
1G
PA
Horizontal
2G
PC
Vertical Upwards Progression
3G
PF
Vertical Downwards Progression
3G
PG
Overhead
4G
PE
Pipe Fixed Horizontal
5G
PF
Pipe Fixed @ 45 degrees Upwards
6G
HL045
Pipe Fixed @ 45 degrees Downwards
6G
JL045
Welding Position
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G
for Groove
Welds
F
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for Fillet
Welds
54
G
for Groove
Welds
F
for Fillet
Welds
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Welding Positions For Fillet welds:Test Position
ISO and EN
Flat (Weld flat joint at 45
degrees)
1F
PA
Horizontal
2F
PB
2FR
PB
Vertical Upwards
Progression
3F
PF
Vertical Downwards
Progression
3F
PG
Overhead
4F
PD
Pipe Fixed Horizontal
5F
PF
Welding Position
Horizontal Rotated
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Multiple-pass layers.
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Weld layer sequence
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Welding Positions
QW431.1 and
QW461.2
Basically there are three
inclinations involved.
Flat, which includes
from 0 to 15 degrees
inclination
15 - 80 degrees
inclination
Vertical, 80 - 90 degrees
For each of these
inclinations the weld
can be rotated from the
flat position to
Horizontal to overhead.
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Effects of expansion and
contraction
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CONTROLLING DISTORTION
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HEAT AFFECTED ZONE
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LIQUID STATE PROCESSES
• Partial melting and fusion of joint
• Physical and mechanical changes taking place
• Can be with application of pressure or by addition
of filler material
• Prior to joining, PREPARATION TO BE DONE
STANDARDS- AWS; ASTMTYPES OF GROOVES, JOINTS
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OXY ACETYLENE WELDING (OAW)
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Oxyacetylene Welding (OAW)
The oxyacetylene welding process
uses a combination of oxygen and
acetylene gas to provide a high
temperature flame.
Oxyacetylene Welding (OAW)
• OAW is a manual process in which the
welder must personally control the the torch
movement and filler rod application
• The term oxyfuel gas welding outfit refers
to all the equipment needed to weld.
• Cylinders contain oxygen and acetylene gas
at extremely high pressure.
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Typical Oxyacetylene Welding
(OAW) Station
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STEPS for OAW
1. PREPARE THE EDGES AND MAINTAIN
PROPER POSITION………………………….(USE OF FIXTURES, CLAMPS)
2. OPEN ACETYLENE AND IGNITE
3. OPEN OXYGEN AND ADJUST FLAME
4. HOLD TORCH AT ABOUT 45O AND
FILLER METAL AT 30 TO 40 O
5. TOUCH FILLER ROD TO JOINT AND
CONTROL MOVEMENT
6. SINGLE BEAD MADE
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• FOR DEEP JOINTS, MULTIPLE PASSES
• CLEANING EACH WELD BEAD IS
IMPORTANT
• EQUIPMENT- WELDING TORCHVARIOUS SIZES AND SHAPES
• CYLINDERS DIFFERENT THREADS,
ANCHORED AND NOT DROPPED
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CAPABILITIES
• LOW COST. MANUAL AND HENCE SLOW
• PORTABLE, VERSATILE AND ECONOMICAL
FOR LOW QUANTITY AND REPAIR WORKS
• FOR ALL FERROUS AND NONFERROUS
METALS
LIMITATIONS THICKNESS < 6 MM
• SKILL ESSENTIAL---FOR PIPE, PRESSURE
VESSELS, LOAD BEARING STRUCTURAL
MEMBERS
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Oxygen Cylinders
• Oxygen is stored within cylinders of various
sizes and pressures ranging from 20002640 PSI. (Pounds Per square inch)
• Oxygen cylinders are forged from solid
armor plate steel. No part of the cylinder
may be less than 1/4” thick.
• Cylinders are then tested to over 3,300 PSI
using a (NDE) hydrostatic pressure test.
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Oxygen Cylinders
• Cylinders are regularly
re-tested using
hydrostatic (NDE)
while in service
• Cylinders are regularly
chemically cleaned
and annealed to relieve
“jobsite” stresses
created by handling .
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Cylinder Transportation
• Never transport cylinders without the safety
caps in place
• Never transport with the regulators in place
• Never allow bottles to stand freely. Always
chain them to a secure cart or some other
object that cannot be toppled easily.
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Oxygen Cylinders
• Oxygen cylinders
incorporate a thin metal
“pressure safety disk”
made from stainless steel
and are designed to
rupture prior to the
cylinder becoming
damaged by pressure.
• The cylinder valve should
always be handled
carefully
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Pressure Regulators for
Cylinders
• Reduce high storage
cylinder pressure to
lower working
pressure.
• Most regulators have a
gauge for cylinder
pressure and working
pressure.
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Pressure Regulators for
Cylinders
• Regulators are shut off
when the adjusting screw
is turn out completely.
• Regulators maintain a
constant torch pressure
although cylinder pressure
may vary
• Regulator diaphragms are
made of stainless steel
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Pressure Regulators Gauges
Using a “Bourdon” movement
• Gas entering the gauge fills a
Bourdon tube
• As pressure in the semicircular
end increases it causes the free
end of the tube to move
outward.
• This movement is transmitted
through to a curved rack which
engages a pinion gear on the
pointer shaft ultimately
showing pressure.
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Regulator Hoses
• Hoses are are fabricated from
rubber
• Oxygen hoses are green in
color and have right hand
thread.
• Acetylene hoses are red in
color with left hand thread.
• Left hand threads can be
identified by a grove in the
body of the nut and it may
have “ACET” stamped on it
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Check Valves &
Flashback Arrestors
• Check valves allow gas
flow in one direction only
• Flashback arrestors are
designed to eliminate the
possibility of an explosion
at the cylinder.
• Combination Check/
Flashback Valves can be
placed at the torch or
regulator.
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Acetylene Gas
• Virtually all the acetylene distributed for welding and cutting use
is created by allowing calcium carbide (a man made product) to
react with water.
• The nice thing about the calcium carbide method of producing
acetylene is that it can be done on almost any scale desired.
Placed in tightly-sealed cans, calcium carbide keeps indefinitely.
For years, miners’ lamps produced acetylene by adding water, a
drop at a time, to lumps of carbide.
• Before acetylene in cylinders became available in almost every
community of appreciable size produced their own gas from
calcium
carbide.
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Acetylene Cylinders
• Acetylene is stored in cylinders specially designed
for this purpose only.
• Acetylene is extremely unstable in its pure form at
pressure above 15 PSI (Pounds per Square Inch)
• Acetone is also present within the cylinder to
stabilize the acetylene.
• Acetylene cylinders should always be stored in the
upright position to prevent the acetone form
escaping thus causing the acetylene to become
unstable.
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Acetylene Cylinders
• Cylinders are filled with a
very porous substance
“monolithic filler” to help
prevent large pockets of
pure acetylene form
forming
• Cylinders have safety
(Fuse) plugs in the top and
bottom designed to melt at
212° F (100 °C)
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Acetylene Valves
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• Acetylene cylinder shut
off valves should only be
opened 1/4 to 1/2 turn
• This will allow the
cylinder to be closed
quickly in case of fire.
• Cylinder valve wrenches
should be left in place on
cylinders that do not
have a hand wheel.
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Oxygen and Acetylene Regulator
Pressure Settings
• Regulator pressure may vary with different
torch styles and tip sizes.
• PSI (pounds per square inch) is sometimes shown as
PSIG (pounds per square inch -gauge)
• Common gauge settings for cutting
– 1/4” material Oxy 30-35psi Acet 3-9 psi
– 1/2” material Oxy 55-85psi Acet 6-12 psi
– 1” material Oxy 110-160psi Acet 7-15 psi
• Check the torch manufactures data for
optimum pressure
settings NITC
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Regulator Pressure Settings
• The maximum safe working pressure for
acetylene is 15 PSI !
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Typical torch styles
•
A small welding torch, with throttle valves
located at the front end of the handle. Ideally
suited to sheet metal welding. Can be fitted
with cutting
•
attachment in place of the welding head
shown. Welding torches of this general design
are by far the most widely used. They will
handle any oxyacetylene welding job, can be
fitted with multiflame (Rosebud) heads for
heating applications, and accommodate
cutting attachments that will cut steel 6 in.
thick.
•
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A full-size oxygen cutting torch which has all
valves located in its rear body. Another style of
cutting torch, with oxygen valves located at
the front end
of its handle.
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Typical startup procedures
• Verify that equipment visually appears safe IE: Hose
condition, visibility of gauges
• Clean torch orifices with a “tip cleaners” (a small wire
gauge file set used to clean slag and dirt form the torch
tip)
• Crack (or open) cylinder valves slightly allowing
pressure to enter the regulators slowly
• Opening the cylinder valve quickly will “Slam” the
regulator and will cause failure.
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Typical startup procedures
• Never stand directly in the path of a regulator
when opening the cylinder
• Check for leaks using by listening for “Hissing” or
by using a soapy “Bubble” solution
• Adjust the regulators to the correct operating
pressure
• Slightly open and close the Oxygen and
Acetylene valves at the torch head to purge any
atmosphere from the system.
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Typical startup procedures
• Always use a flint and steel spark lighter to light the
oxygen acetylene flame.
• Never use a butane lighter to light the flame
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Flame Settings
• There are three distinct types of oxy-acetylene
flames, usually termed:
– Neutral
– Carburizing (or “excess acetylene”)
– Oxidizing (or “excess oxygen” )
• The type of flame produced depends upon the
ratio of oxygen to acetylene in the gas mixture
which leaves the torch tip.
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TYPES of FLAMES
• Neutral- with inner cone(30400C-33000C), outer envelope,
(21000C near inner cone, 12600C at tip)- high heating
• Reducing- Bright luminous inner cone, acetylene feather,
blue envelope
– Low temperature, good for brazing, soldering, flame
hardening
Hydrogen, methyl acetylene, propadiene also used as fuel.
• Oxidising- pointed inner cone, small and narrow outer
envelope
– Harmful for steels, good for Cu- Cu based alloys
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OXY ACETYLENE WELDING
(OAW)
Types of Flames
Neutral
Reducing
high heating
low temperature
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Oxidising
good for Cu- Cu alloys
97
Pure Acetylene and Carburizing
Flame profiles
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Neutral and Oxidizing Flame
Profiles
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Flame definition
• The neutral flame is produced when the ratio of oxygen to acetylene,
in the mixture leaving the torch, is almost exactly one-to-one. It’s
termed ”neutral” because it will usually have no chemical effect on the
metal being welded. It will not oxidize the weld metal; it will not cause
an increase in the carbon content of the weld metal.
• The excess acetylene flame as its name implies, is created when the
proportion of acetylene in the mixture is higher than that required to
produce the neutral flame. Used on steel, it will cause an increase in
the carbon content of the weld metal.
• The oxidizing flame results from burning a mixture which contains
more oxygen than required for a neutral flame. It will oxidize or
”burn” some of the metal being welded.
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Quiz time
• The regulator diaphragm is often made from
_______?
A: reinforced rubber
B: malleable iron
C: tempered aluminum
D: stainless steel
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Quiz time
• The hose nuts for oxygen and acetylene
differ greatly, because the acetylene hose
nut has.
A: a left hand thread.
B: has a grove cut around it.
C: may have ACET stamped on it.
D: All of the above.
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Quiz time
• An oxygen cylinder must be able to
withstand a ________ pressure of 3300 psi
(22753 kPa) to be qualified for service.
A: atmospheric
B: hydrostatic
C: hydroscopic
D: vapor
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Quiz time
• Why is the area above 15 psig often marked
with a red band on a acetylene low pressure
regulator ?
• Answer
– Acetylene pressure above 15 psig is unstable
and should not be used
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Quiz time
• True or False ?
– A flint and steel spark lighter is the generally
used to light the oxyacetylene flame.
• Answer: True
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Quiz time
• Acetylene cylinder fuse plugs melt at a
temperature of ________° F or 100°C
• Answer
– 212°F
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Quiz time
• What is the maximum safe working gauge
pressure for acetylene gas?
A: 8 psig (55 kPa)
B: 15 psig (103 kPa)
C: 22 psig (152 kPa)
D: 30 psig (207 kPa)
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Quiz time
• The color of and oxygen hose on a
oxyacetylene welding outfit is ______?
• Answer
– Green/Blue
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Quiz time
• The type of safety device is used on a
oxygen cylinder.
A: A fusible plug
B: A check valve
C: A pressure safety disk
D: A spring loaded plug
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Quiz time
• True or False ?
– The regulator is closed when the adjusting
screw is turned out.
• Answer: True
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Quiz time
• The color of acetylene hose on a
oxyacetylene welding outfit is ______?
• Answer
– Red
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Quiz time
• No part of an oxygen cylinder walls may be
thinner than _______?
A: 1/4”in (6.4 mm)
B: 3/8”in (9.5 mm)
C: 3/16”in (4.8 mm)
D: 7/32”in (5.6 mm)
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Quiz time
• To prevent the occurrence of flashbacks, a
________ should be installed between
either the torch and hoses or regulators and
hoses.
A: a two way check valve.
B: flame screen.
C: flashback arrestor.
D: three way check valve.
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Quiz time
• What type of safety device is used on a
acetylene cylinder.
A: A spring loaded plug
B: A pressure safety disk
C: A fusible plug
D: A check valve
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Quiz time
• Mixing _______ and water will produce
acetylene gas.
A: calcium carbide
B: potassium carbonate
C: carbon dioxide
D: acetylene carbide
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LIQUID STATE PROCESS
PARTIAL MELTING
BY STRIKING AN ARC
AFTER THE INVENTION OF ELECTRICITY
HOW ARC STRUCK?
ARC COLUMN THEORY
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ARC WELDING
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• ARC WELDING
ELECTRIC ARC
WITHOUT ADDITIONAL
AUTOGENEOUS
EXTERNAL SOURCE
NONCONSUMABLE- CONSUMABLE
CARBON ARC WELDING (CAW) - OLDEST
METALLIC ARC WELDING (MAW)
COATING MATERIALS
ARC TO BE CREATED BY ELECTRICITY
WHEN? WITH THE INVENTION OF AC DYNAMO IN 1877
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BEGINNING IN 1881- TO CONNECT PLATES OF STORAGE BATTERY
1886- BUTT WELDING TECHNIQUE WAS DEVELOPED
BUTTED, CLAMPED HIGH CURRENT PASSED
AT THE JOINT, RESISTANCE OF METAL TO ELECTRIC CURRENT
PRODUCES HIGH HEAT- PIECES FUSED
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ARC WELDING- MELTING AND FUSING OF METAL BY ELECTRODES
1ST BY N.V. BERNADO USING CARBON ELECTRODES
CONSISTANTLY IMPROVED
1895 N.G. SLAVIANOFF USED METALLIC ELECTRODES
1905 BARE ELECTRODES COATED—SHIELDING--- (SAW)
PORTABLE AND AUTOMATIC WELDING MACHINES
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ARC WELDING PROCESSES
USE OF CONSUMABLE ELECTRODES
SHIELDED METAL ARC WELDING
(SMAW)
• SIMPLEST AND MOST VERSATILE
• ABOUT 50% OF INDUSTRIAL WELDING
BY THIS PROCESS
• CURRENT- 50 TO 300 A, < 10 KW
• AC/DC USED
• FOR THICKNESSES UPTO 19 –20 MM
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SHIELDED METAL ARC WELDING
(SMAW)
•Shielded metal arc welding (SMAW),
•Also known as Manual Metal Arc (MMA) welding
• Informally as stick welding
is a manual arc welding process that uses a
consumable electrode coated in flux to lay the weld.
•An electric current, in the form of either alternating
current or direct current from a welding power supply, is
used to form an electric arc between the electrode and
the metals to be joined.
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ARC COLUMN THEORY
ELECTRICAL / IONIC THEORY
IONS FROM ANODE TO CATHODE,
AS METAL IONS ARE +VE CHARGED
•TOUCH AND THEN ESTABLISH A GAP
TO BALANCE THE ATOMIC STRUCTURE
ANODE +
•IONS COLLIDE WITH GAS MOLECULES
•PRODUCES A THERMAL IONISATION LAYER
DC
CATHODE -
•IONISED GAS COLUMN – AS HIGH
RESISTANCE CONDUCTOR
•ON STRIKING CATHODE, HEAT GENERATED
•TERMED AS IONIC THEORY
•NOT COMPLETE IN EXPLAINING ARC
COLUMN THEORY
•THUS, ELECTRON THEORY
ELECTRON THEORY
ARC COLUMN THEORY
IONS FROM ANODE TO CATHODE
AS METAL IONS ARE +VE
CHARGED
-VELY CHARGED ELECTRONS
DISSOCIATED FROM CATHODE
MOVE OPPOSITE WITH HIGH
VELOCITY
ANODE +
DC
CATHODE -
(MASS- 9.1x 10-28 gm)
CAUSES HEAT IN ARC COLUMN
RELEASES HEAT ENERGY IN
STRIKING THE ANODE
CALLED
ELECTRON IMPINGEMENT
AND
IONIC BOMBARDMENT
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ANODE+
HIGH HEAT
ELECTRON IMPINGEMENT
LOW HEAT
MEDIUM HEAT
IONIC BOMBARDMENT
CATHODE
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MAGNETIC FLUX THEORY
• THE COLUMN NOT FLAIRING
DUE TO THE FLUX LINES AROUND
THE ARC COLUMN.
(Right hand Thumb Rule)
THIS COMPLETES THE ARC COLUMN THEORY
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POLARITY
AC
1.
2.
3.
4.
5.
6.
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Currents higher than
those of DCRP can be
employed (400 A to 500
Afor 6 mm electrode)
Arc cleaning of the base
metal
Normal penetration
Equal heat distribution
at electrode and job
Electrode tip is colder
as compared to that in
DCRP
Average arc voltage in
argon atmosphere is
16V
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DCRP
1.
2.
3.
4.
5.
6.
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Currents generally less
than 125 amps (upto 6
mm dia electrodes) to
avoid overheating
2/3rd heat at electrode
and 1/3rd at the job
Least penetration
Average arc voltage on
argon atmosphere is
19V
Chances of electrode
overheating, melting and
losses
Better arc cleaning
action
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DCSP
1.
2.
3.
4.
5.
6.
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Welding currents upto
1000 amps can be
employed for 6 mm
electrodes
33.33% heat is generated
at the electrode and
66.66% at the job.
Deep penetration
Average arc voltage in an
argon atmsphere is 12 V
Electrode runs colder as
compared to AC or DCRP
No arc cleaning of base
metal
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METALLURGY OF WELDING
During joining, localized heating occurs.
This leads to metallurgical and physical changes in materials welded.
Hence, study of:
. 1. Nature of welded joint
2.
3.
4.
5.
6.
Quality and property of welded joint
Weldability of metals
Methods of testing welds
Welding design
Process selection- important
(3) Heat Affected Zone (HAZ)
(2) Fusion Zone
1) Base Metal
(
Structures: (1) SMALL (2) MEDIUM (3) LARGE
Properties of (2) and (3) important
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• Cooling of Beadsimilar to a casting in mould, which is metallic here.
Cooling is slow Hence the structure is coarse and
Strength toughness and ductility low.
But use of proper electrodes improves these.
• The purpose of coating the electrode is to
achieve the improved properties. If without,
nitrides and oxides of base metal form and
these result in weak and brittle nature.
• With coating, properties comparable with base metal
achieved.
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Gas shield
Arc column makes CRATER on
striking the surface- Temperature
above 1500 C
Flux + impurities- less dense. Floats as SLAG
Slag prevents heat loss- makes an evenly distribution
of heat radiation.
Preheating to receive the molten metal at an elevated temperature and
modify the structure. Not for M.S.
Locked in stresses due to heating and cooling- to be relieved by
PEENING, or other heat treatment processes.
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MAGNETIC ARC BLOW -- FOR AC SUPPLY.
Current through conductor- magnetic Flux lines perpendicular to
current flow- apply Right hand Thumb Rule.
Three areas of magnetic field
1. Arc; 2. Electrode; 3. Work piece, when ground.
Forward pull of Arc column results, called as Magnetic Arc Blow.
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EQUIPMENT
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• As the weld is laid, the flux coating of
the electrode disintegrates, giving off
vapors that serve as a shielding gas
and providing a layer of slag, both of
which protect the weld area from
atmospheric contamination.
• Because of the versatility of the
process and the simplicity of its
equipment and operation, shielded
metal arc welding is one of the world's
most popular welding processes.
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PURPOSE OF COATING
• Gives out inert or protective gas- shields
• Stabilizes the arc- by chemicals
• Low rate consumption of electrode- directs arc and
molten metal
• Removes impurities and oxides as slag
• Coatings act as insulators- so narrow grooves welded
• Provide means to introduce alloying elements
Bare electrodes - carbon- more conductive- slow
consumption in welding
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ELECTRODE COATING INGREDIENTS
• Slag forming ingredients- silicates of sodium, potassium, Mg,
Al, iron oxide, China clay, mica etc.
• Gas shielding- cellulose, wood, starch, calcium carbonate
• De-oxidising elements- ferro manganese, ferro silicon- to
refine molten metal
• Arc stabilizing – calcium carbonate, potassium silicate,
titanates, Mg silicate etc.
• .Alloying elements- ferro alloys, Mn, Mo., to impart special
properties
• Iron powder- to improve arc behaviour, bead appearance
• Other elements - to improve penetration, limit spatter,
improve metal deposition rates,
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WELD POSITIONS
• FLAT
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HORIZONTAL
VERTICAL
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OVERHEAD
142NITC
WELD MOVEMENTS
I
L
O
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STRAIGHT
Z
ZIGZAG
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WELDING TECHNIQUES
FOREHAND
BACKHAND
THIN
Same direction torch
Heat concentrated away from
bead
THICK
Opposite direction torch
Heat concentrated on bead
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Even
Broad bead
144
• It dominates other welding processes in the
maintenance and repair industry, used
extensively in the construction of steel
structures and in industrial fabrication.
• The process is used primarily to weld iron
and steels (including stainless steel) but
aluminum, nickel and copper alloys can also
be welded with this method.
• Flux-Cored Arc Welding (FCAW) , a
modification to SMAW is growing in
popularity
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Various
andNITC
an electrode holder
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SAFETY PRECAUTIONS
• Uses
an open electric arc, so
risk of burns – to be prevented
by protective clothing in the
form of heavy leather gloves
and long sleeve jackets.
•The brightness of the weld area
can lead arc eye, in which
ultraviolet light causes the
inflammation of the cornea and
can burn the retinas of the eyes.
•Welding helmets with dark face
plates to be worn to prevent this
exposure
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• New helmet models have been produced that
feature a face plate that self-darkens upon
exposure to high amounts of UV light
• To protect bystanders, especially in
industrial environments, transparent welding
curtains often surround the welding area.
• These are made of a polyvinyl chloride
plastic film, shield nearby workers from
exposure to the UV light from the electric arc,
but should not be used to replace the filter
glass used in helmets.
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ARC EYE
Arc eye, also known as arc flash or welder's flash or
corneal flash burns, is a painful condition sometimes
experienced by welders who have failed to use adequate
eye protection.
It can also occur due to light from sunbeds, light
reflected from snow (known as snow blindness), water
or sand. The intense ultraviolet light emitted by the arc
causes a superficial and painful keratitis.
Symptoms tend to occur a number of hours
after exposure and typically resolve
spontaneously within 36 hours.
It has been described as having sand poured
into the eyes.
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Signs
Intense lacrimation
Blepharospasm
Photophobia
Fluorescein dye staining will reveal corneal ulcers
under blue light
Management
• Instill topical anaesthesia
• Inspect the cornea for any foreign body
• Patch the worse of the two eyes and prescribe analgesia
• Topical antibiotics in the form of eye drops or eye
ointment or both should be prescribed for prophylaxis
against infection
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SUBMERGED ARC WELDING (SAW)
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CONTROL PANEL
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Submerged Arc Welding (SAW)
• Is a common arc welding process.
• A continuously fed consumable solid or tubular
(metal cored) electrode used.
• The molten weld and the arc zone are protected
from atmospheric contamination by being
“submerged” under a blanket of granular fusible
flux.
• When molten, the flux becomes conductive, and
provides a current path between the electrode
and the work
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• Normally operated in the automatic or
mechanized mode.
• Semi-automatic (hand-held) SAW guns with
pressurized or gravity flux feed delivery are
available.
• The process is normally limited to the 1F, 1G, or
the 2F positions (although 2G position welds
have been done with a special arrangement to
support the flux). Deposition rates approaching
45 kg/h have been reported — this compares to
~5 kg/h (max) for shielded metal arc welding.
• Currents ranging from 200 to 1500 A are
commonly used; currents of up to 5000 A have
been used (multiple arcs).
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• Single or multiple (2 to 5) electrode wire
variations of the process exist
• SAW strip-cladding utilizes a flat strip
electrode (e.g. 60 mm wide x 0.5 mm
thick).
• DC or AC power can be utilized, and
combinations of DC and AC are common
on multiple electrode systems.
• Constant Voltage welding power supplies
are most commonly used, however
Constant Current systems in combination
with a voltage sensing wire-feeder are
available.
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SAW
•
•
•
•
•
•
•
•
•
Fusion Welding Process
Automatic / Semi Automatic
Arc Between Consumable Electrode And Work
Arc Covered Under granular Flux
Wire / Electrode Continuously Fed To Weld Pool
Wire / Arc Under Flux Moves Along The Groove
Wire, BM & Flux Close to Arc Melt Under Flux
On Cooling Weld Metal Solidifies
Molten Flux Forms Thick Slag Coating On Weld
SAW
Hopper
Flux
Wire
Flux
Power Source
+
+
Slag
Weld
••••••••••••••••
•••
Arc
Base Metal
–
Flux For SAW
•
•
•
•
•
Sodium Chloride
Potassium Chloride
Titanium Dioxide
Sodium Silicate
Deoxidizing Agents
Types Of Flux
• Fused Flux
• Agglomerated Flux
» Neutral Flux
» Active Flux
Types Of Flux
• Neutral Flux
-Wire compatible to base metal
- Single flux suitable for several material
• Active Flux
- Single flux suitable for specific application
- Wire may be different from basemetal
- To be welded within the recommended parameters
Function Of Flux In SAW
•
•
•
•
•
•
•
•
•
•
Stabilizes Arc
Prevents contamination of weld metal
Cleans the weld from unwanted impurities
Increases Fluidity of molten metal
Generates inert gas shielding while metal transfers
Forms slag after melting & covers weld
Allows deposited metal to cool slowly
Compensates alloying elements Within the weld
Eliminates spatter generation
Helps in even & uniform bead finish
Baking Requirements For Flux
•
•
•
•
•
•
Spread the loose Flux in a Tray Of baking Oven
Identify The Tray With The Quality/Grade Of Flux
Bake Tray in an Oven Between 300° C to 350° C
Baking Time 2 Hrs to 3 Hrs
Reduce the temperature to 100 ° C to 150 ° C
Hold the Flux at this temperature till use
Why Baking Flux?
• To remove the moisture (H2O)
• To avoid possible cracking of weld
due to H2
How Does Moist Flux Generate
Crack Within Weld?
• Moist Flux introduce atomic hydrogen at high
temperature in weld
• On cooling, atomic hydrogen try to form
molecules
• The reaction results in stresses and fine cracks
• Cracks occur within hardened metal - HAZ
• Known as “Hydrogen Embrittlement” or
“Under Bead Crack” or Delayed Crack
Reuse Of Flux
• Flux May Be Reused Provided
- Weld Not Highly Critical In Impact / Chemistry
- Reuse Limited To Maximum Twice
- All Slag Particles Are sieved & Removed
- Rebaked If not Remained In Hot
- Minimum 50% Fresh Flux Well Mixed
- Customer Spec. Doesn't Prohibit The Same
Types Of Power Source
• Thyrester – DC
• Rectifier – DC
• Motor Generator – DC
• Transformer - AC
Characteristic Of Power Source
Machine welding
Drooping – Cons. A
Linear – Cons. V
V
V
V1
V1
V2
V2
A1 A2
A
A1
A2
A
SAW Wire - Electrode
•
•
•
•
•
•
•
Consumable Electrode / Wire
Layer Wound On Spool / Coil
CS & LAS Wires Coated with Cu
Conducts Current and generates Arc
Chemistry Compatible To Base Metal
Grade Of Flux Can Be Same For CS & LAS
Wire melts & deposited as filler in joint
Typical Welding Parameter
Sr
no
Wire
Ø mm
Current A
Voltage
V
Speed
mm/min
Dep. Rate
Per Arc Hr
1
1.6
200-300
22-26
750-1500
3 – 4 kgs
2
2
250-350
24-26
750-1250
3- 4.5 kgs
4
2.5
300-350
25-27
750-1250
4 –4.5 kgs
5
3
400-500
28-30
500-100
5 – 5.5 kgs
6
4
550-650
30-32
400-750
5.5 - 7 kgs
7
5
600-800
30-34
350-700
6 - 8 kgs
Wire & Flux
CS wire
+
Neutral
Flux
Important Terminology used in
Critical SAW
•
•
•
•
•
Preheating
Post Heating or Dehydrogenation
Intermediate Stress leaving
Inter pass Temperature
Post Weld Heat Treatment
What Is Preheating?
• Heating the base metal along the weld joint to a
predetermined minimum temperature
immediately before starting the weld.
• Heating by Oxy fuel flame or electric resistant
coil
• Heating from opposite side of welding wherever
possible
• Temperature to be verified by thermo chalks
prior to starting the weld
Why Preheating?
• Preheating eliminates possible cracking of weld and
HAZ
• Applicable to
-Hardenable low alloy steels of all thickness
-Carbon steels of thickness above 25 mm.
-Restrained welds of all thickness
• Preheating temperature vary from 75°C to 200°C
depending on hardenability of material, thickness &
joint restrain
How does Preheating Eliminate
Crack?
• Preheating promotes slow cooling of weld and
HAZ
• Slow cooling softens or prevents hardening of
weld and HAZ
• Soft material not prone to crack even in
restrained condition
What Is Post Heating?
• Raising the pre heating temperature of the weld joint to
a predetermined temperature range (250° C to 350° C)
for a minimum period of time (3 Hrs) before the weld
cools down to room temperature.
• Post heating performed when welding is completed or
terminated any time in between.
• Heating by Oxy fuel flame or electric resistant coil
• Heating from opposite side of welding wherever
possible
• Temperature verified by thermo chalks during the period
Why Post Heating?
• Post heating eliminates possible delayed cracking
of weld and HAZ
• Applicable to
-Thicker hardenable low alloy steels
-Restrained hardenable welds of all
thickness
• Post heating temperature and duration depends
on hardenability of material, thickness & joint
restrain
How does Post Heating Eliminate
Crack?
• SAW introduces hydrogen in weld metal
• Entrapped hydrogen in weld metal induces
delayed cracks unless removed before cooling to
room temperature
• Retaining the weld at a higher temperature for a
longer duration allows the hydrogen to come out
of weld
What Is Intermediate Stress
Relieving?
• Heat treating a subassembly in a furnace to a
predetermined cycle immediately on completion
of critical restrained weld joint / joints without
allowing the welds to go down the pre heat
temperature. Rate of heating, Soaking
temperature, Soaking time and rate of cooling
depends on material quality and thickness
• Applicable to
Highly restrained air hardenable material
Why Intermediate Stress
Relieving?
• Restrained welds in air hardenable steel highly
prone to crack on cooling to room temperature.
• Cracks due to entrapped hydrogen and built in
stress
• Intermediate stress relieving relieves built in
stresses and entrapped hydrogen making the joint
free from crack prone
What Is Inter- Pass Temperature?
• The temperature of a previously layed weld bead
immediately before depositing the next bead over
it
• Temperature to be verified by thermo chalk prior
to starting next bead
• Applicable to
Stainless Steel
Carbon Steel & LAS with minimum impact
Why Inter Pass Temperature?
• Control on inter pass temperature avoids over
heating, there by
-Refines the weld metal with fine grains
-Improves the notch toughness properties
-Minimize the loss of alloying elements in
welds
-Reduces the distortion
What Is Post Weld Heat
Treatment?
• Heat treating an assembly on completion of all
applicable welding, in an enclosed furnace with
controlled heating/cooling rate and soaking at a
specific temperature for a specific time.
• Rate of heating, Soaking temperature, Soaking
time and rate of cooling depends on material
quality and thickness
• Applicable to
-All type of CS & LAS
Material applications
• Carbon steels (structural and vessel
construction);
• Low alloy steels;
• Stainless Steels;
• Nickel-based alloys;
• Surfacing applications (wearfacing, buildup, and corrosion resistant overlay of
steels).
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Advantages of SAW
• High deposition rates (over45 kg/h) have been
reported;
• High operating factors in mechanized
applications;
• Deep weld penetration;
• Sound welds are readily made (with good
process design and control);
• High speed welding of thin sheet steels at over
2.5 m/min is possible;
• Minimal welding fume or arc light is emitted.
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Limitations of SAW
• Limited to ferrous (steel or stainless steels) and
some nickel based alloys;
• Normally limited to the 1F, 1G, and 2F positions;
• Normally limited to long straight seams or
rotated pipes or vessels;
• Requires relatively troublesome flux handling
systems;
• Flux and slag residue can present a health &
safety issue;
• Requires inter-pass and post weld slag removal.
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Key SAW process variables
•
•
•
•
•
Wire Feed Speed (main factor in welding current control);
Arc Voltage;
Travel Speed;
Electrical Stick-Out (ESO) or Contact Tip to Work (CTTW);
Polarity and Current Type (AC or DC).
Other factors
•
•
•
•
Flux depth/width;
Flux and electrode classification and type;
Electrode wire diameter;
Multiple electrode configurations.
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GAS TUNGSTEN ARC WELDING (GTAW)
GTAW
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GTAW
• Fusion Welding Process
• Arc Between Non-Consumable Tungsten
Rod And Work
• Arc & Weld Pool Shielded By Argon/Gas
• Filler Wire Separately Added To Weld Pool
• Welding Torch & Tungsten Rod Cooled by
Flow OF Argon / Cooling Water
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GAS TUNGSTEN ARC WELDING (GTAW)
• ELECTRODE NOT CONSUMED
• TUNGSTEN ELECTRODES USED
• ARGON- HEAVIER FOR NARROW AND LIMITED
EXPANSION,WIDER, DEEPER PUDDLE
• HELIUM FOR EVEN EXPANSIONLIMITED
STRESS BUILDUP
• MORE He, MORE HEAT IN ARC
• Ar-He MIX FOR AUTOMATIC GTAW
• Ar- CO2 FOR CARBON STEELS, ECONIMICAL,
INCREASES WETTING ACTION
• GTAW TORCH- WATER OR AIR COOLED
CONSTANT CURRENT SOURCE.(IIIr TO SMAW)
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GTAW Equipment & Accessories
• Power Source – Inverter, Thyrister, Rectifier,
•
•
•
•
•
•
•
Generator
High Frequency Unit
Water Cooling System
Welding Torch- (Ceramic Cup, Tungsten Rod, Collet,
Gas-lens)
Pedal Switch
Argon Gas Cylinder
Pressure Gauge, Regulator, Flow Meter
Earthing Cable With Clamp
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Equipment & Accessories
Pressure Regulator
Flow Meter
Tungsten Rod
Argon Gas In
Cooling Water In
Solenoid
Valve
Argon Cylinder
Gas Lens
Ceramic Cup
Welding Cable & Cooling
Water In Tube
Cooling Water Out
Argon Shielding
Arc
+
HF Unit &
Water Cooling
System
High Frequency
Connection
Work
Pedal Switch
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Power Source
Dr. N. RAMACHANDRAN, NITC
–
+
196
Equipment
GTAW torch with various
electrodes, cups, collets and gas
diffusers
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GTAW torch, disassembled
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Gas tungsten arc welding (GTAW),
commonly known as Tungsten Inert Gas
(TIG) welding
• Is an arc welding process that uses a
nonconsumable tungsten electrode to produce
the weld.
• The weld area is protected from atmospheric
contamination by a shielding gas (usually an
inert gas such as argon), and a filler metal is
normally used, though some welds, known as
autogenous welds, do not require it.
• A constant current welding power supply
produces energy which is conducted across the
arc through a column of highly ionized gas and
metal vapors known
as a plasma.
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• Most commonly used to weld thin sections
of stainless steel and light metals such as
aluminum, magnesium, and copper alloys.
• The process grants the operator greater
control over the weld than competing
procedures such as shielded metal arc
welding and gas metal arc welding, allowing
for stronger, higher quality welds.
• GTAW is comparatively more complex and
difficult to master, and furthermore, it is
significantly slower than most other welding
techniques.
• A related process, plasma arc welding, uses
a slightly different welding torch to create a
more focused welding arc and as a result is
often automated.
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GTAW system setup
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Applications
•
•
•
•
•
•
Aerospace industry is one of the primary users of gas
tungsten arc welding, the process is used in a number of other
areas.
Many industries use GTAW for welding thin workpieces,
especially nonferrous metals.
It is used extensively in the manufacture of space vehicles, and
is also frequently employed to weld small-diameter, thin-wall
tubing.
Is often used to make root or first pass welds for piping of
various sizes.
In maintenance and repair work, the process is commonly used
to repair tools and dies, especially components made of
aluminum and magnesium.
Because the welds it produces are highly resistant to corrosion
and cracking over long time periods, GTAW is the welding
procedure of choice for critical welding operations like sealing
spent nuclear fuel canisters before burial.
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GTAW ranks the highest in terms of the
quality of weld produced.
Operation must be with free from oil,
moisture, dirt and other impurities, as
these cause weld porosity and
consequently a decrease in weld
strength and quality.
To remove oil & grease, alcohol or
similar commercial solvents used, while
a stainless steel wire brush or chemical
process remove oxides from the
surfaces of metals like aluminum.
Rust on steels removed by first grit
blasting the surface and then using a
wire brush to remove imbedded grit.
These steps important when DCEN
used, because this provides no cleaning
during the welding process, unlike
DCEPor AC.
To maintain a clean weld pool during welding, the shielding gas flow should be
sufficient and consistent so that the gas covers the weld and blocks impurities in
the atmosphere. GTA welding in windy or drafty environments increases the
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amount
of shielding gas necessary
protect the weld,
increasing the cost and 202
making the process unpopular outdoors.
Quality
• Because of GTAW's relative difficulty and the
importance of proper technique, skilled
operators are employed for important
applications.
• Low heat input, caused by low welding
current or high welding speed, can limit
penetration and cause the weld bead to lift
away from the surface being welded.
• If there is too much heat input, the weld
bead grows in width while the likelihood of
excessive penetration and spatter increase.
• If the welder holds the welding torch too far
from the workpiece, shielding gas is wasted
and the appearance of the weld worsens.
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• If the amount of current used exceeds the
capability of the electrode, tungsten
inclusions in the weld may result. Known as
tungsten spitting, it can be identified with
radiography and prevented by changing the
type of electrode or increasing the electrode
diameter.
• If the electrode is not well protected by the
gas shield or the operator accidentally allows
it to contact the molten metal, it can become
dirty or contaminated. This often causes the
welding arc to become unstable, requiring
that electrode be ground with a diamond
abrasive to remove the impurity.
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• GTAW welding torches designed for either automatic
or manual operation and are equipped with cooling
systems using air or water. The automatic and
manual torches are similar in construction, but the
manual torch has a handle while the automatic torch
normally comes with a mounting rack.
• The angle between the centerline of the handle and
the centerline of the tungsten electrode, known as
the head angle, can be varied on some manual
torches according to the preference of the operator.
• Air cooling systems are most often used for lowcurrent operations (up to about 200 A), while water
cooling is required for high-current welding (up to
about 600 A).
• The torches are connected with cables to the power
supply and with hoses to the shielding gas source
and where used, the water supply.
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• The internal metal parts of a
torch are made of hard alloys
of copper or brass in order to
transmit current and heat
effectively.
• The tungsten electrode must
be held firmly in the center of
the torch with an
appropriately sized collet,
and ports around the
electrode provide a constant
flow of shielding gas.
• The body of the torch is
made of heat-resistant,
insulating plastics covering
the metal components,
providing insulation from
heat and electricity to protect
the welder.
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GTAW TORCH
Torch Handle
Cap with collet For
Holding Tungsten
Cooling Water Outlet
Argon Gas Inlet
Cooling Water Inlet Tube with cable
Ceramic Cup
Argon Shielding Gas
Tungsten Rod
Base Metal
Earthing Cable
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Arc
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• The size of the welding torch nozzle depends
on the size of the desired welding arc, and
the inside diameter of the nozzle is normally
at least three times the diameter of the
electrode.
• The nozzle must be heat resistant and thus is
normally made of alumina or a ceramic
material, but fused quartz, a glass-like
substance, offers greater visibility.
• Devices can be inserted into the nozzle for
special applications, such as gas lenses or
valves to control shielding gas flow and
switches to control welding current.
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Power supply
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• GTAW uses a constant
current power source,
meaning that the current (and
thus the heat) remains
relatively constant, even if
the arc distance and voltage
change.
• This is important because
most applications of GTAW
are manual or semiautomatic,
requiring that an operator
hold the torch.
• Maintaining a suitably steady
arc distance is difficult if a
constant voltage power
source is used instead, since
it can cause dramatic heat
variations and make welding
more difficult.
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• The preferred polarity of the GTAW system depends largely on
the type of metal being welded.
• DCEN is often employed when welding steels, nickel, titanium,
and other metals. It can also be used in automatic GTA welding
of aluminum or magnesium when helium is used as a shielding
gas. The negatively charged electrode generates heat by
emitting electrons which travel across the arc, causing thermal
ionization of the shielding gas and increasing the temperature
of the base material. The ionized shielding gas flows toward the
electrode, not the base material, and this can allow oxides to
build on the surface of the weld.
• DCEP is less common, and is used primarily for shallow welds
since less heat is generated in the base material. Instead of
flowing from the electrode to the base material, as in DCEN,
electrons go the other direction, causing the electrode to reach
very high temperatures. To help it maintain its shape and
prevent softening, a larger electrode is often used. As the
electrons flow toward the electrode, ionized shielding gas flows
back toward the base material, cleaning the weld by removing
oxides and other impurities and thereby improving its quality
and appearance.
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• AC commonly used when welding aluminum and
magnesium manually or semi-automatically, combines
the two direct currents by making the electrode and
base material alternate between positive and negative
charge. This causes the electron flow to switch
directions constantly, preventing the tungsten electrode
from overheating while maintaining the heat in the base
material. This makes the ionized shielding gas
constantly switch its direction of flow, causing
impurities to be removed during a portion of the cycle.
• Some power supplies enable operators to use an unbalanced
alternating current wave by modifying the exact percentage of time
that the current spends in each state of polarity, giving them more
control over the amount of heat and cleaning action supplied by
the power source.
• In addition, operators must be wary of rectification, in
which the arc fails to reignite as it passes from straight
polarity (negative electrode) to reverse polarity (positive
electrode).
• To remedy the problem, a square wave power supply
can be used, as can
high frequency voltage to
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encourage ignition.
Tungsten Rod
Tungsten Rod
• Non Consumable Electrode.
• Maintains Stable Arc
• Tip to be Ground to a cone Shape of 60º to 30º
angle
• Thoriated Tungsten for General Application,
Zerconiated Tungsten for Aluminium Welding
• Sizes :- 2, 2.4 & 3 mm Ø
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Ground to
50º ankle
212
•The electrode used in GTAW is
ISO
made of tungsten or a tungsten alloy,
ISO Color
Class
because tungsten has the highest
melting temperature among metals,
at 3422 °C.
WP
Green
• The electrode is not consumed
WC20
Gray
during welding, though some erosion
WL10
Black
(called burn-off) can occur.
WL15
Gold
•Electrodes can have either a clean
finish or a ground finish—clean finish WL20 Sky-blue
electrodes have been chemically
WT10
Yellow
cleaned, while ground finish
WT20
Red
electrodes have been ground to a
WT30
Violet
uniform size and have a polished
surface, making them optimal for
WT40
Orange
heat conduction.
WY20
Blue
•The diameter of the electrode can
WZ3
Brown
vary between 0.5 mm and 6.4 mm,
White
and their length can range from 75 to WZ8
610
mm .
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Dr. N. RAMACHANDRAN, NITC
AWS Class
AWS
Color
Alloy [18]
EWP
Green
None
EWCe-2
Orange
~2% CeO2
EWLa-1
Black
~1% LaO2
EWLa-1.5
Gold
~1.5% LaO2
EWLa-2
Blue
~2% LaO2
EWTh-1
Yellow
~1% ThO2
EWTh-2
Red
~2% ThO2
~3% ThO2
~4% ThO2
~2% Y2O3
EWZr-1
Brown
~0.3% ZrO2
~0.8% ZrO2
213
•
A number of tungsten alloys have been standardized by the International
Organization for Standardization and the American Welding Society in ISO
6848 and AWS A5.12, respectively, for use in GTAW electrodes- refer table
•
Pure tungsten electrodes (classified as WP or EWP) are general purpose
and low cost electrodes. Cerium oxide (or ceria) as an alloying element
improves arc stability and ease of starting while decreasing burn-off. Using
an alloy of lanthanum oxide (or lanthana) has a similar effect. Thorium oxide
(or thoria) alloy electrodes were designed for DC applications and can
withstand somewhat higher temperatures while providing many of the
benefits of other alloys.
However, it is somewhat radioactive, and as a replacement, electrodes with
larger concentrations of lanthanum oxide can be used. Electrodes
containing zirconium oxide (or zirconia) increase the current capacity while
improving arc stability and starting and increasing electrode life.
•
•
•
Electrode manufacturers may create alternative tungsten alloys with
specified metal additions, and these are designated with the classification
EWG under the AWS system.
Filler metals are also used in nearly all applications of GTAW, the major
exception being the welding of thin materials. Filler metals are available with
different diameters and are made of a variety of materials. In most cases,
the filler metal in the form of a rod is added to the weld pool manually, but
some applications call for an automatically fed filler metal, which is fed from
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214
rolls.
shielding gases
• Necessary in GTAW to protect the welding area from atmospheric
gases such as nitrogen and oxygen, which can cause fusion
defects, porosity, and weld metal embrittlement if they come in
contact with the electrode, the arc, or the welding metal. The gas
also transfers heat from the tungsten electrode to the metal, and it
helps start and maintain a stable arc.
• The selection of a shielding gas depends on several factors,
including the type of material being welded, joint design, and desired
final weld appearance.
• Argon is the most commonly used shielding gas for GTAW,
since it helps prevent defects due to a varying arc length. When
used with alternating current, the use of argon results in high
weld quality and good appearance.
• Another common shielding gas, helium, is most often used to
increase the weld penetration in a joint, to increase the welding
speed, and to weld conductive metals like copper and
aluminum.
• A significant disadvantage is the difficulty of striking an arc
with helium gas, and the decreased weld quality associated
with a varying arc length.
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Shielding Gas
•
•
•
•
•
•
•
•
Inert Gas - Argon , Helium
Common Shielding Gas – Argon
When Helium Is Used – Called Heli – Arc Welding
When Argon Is Used – Called Argon Arc Welding
Inert Gas Prevents Contamination Of Molten Metal
It Prevents Oxidation Of Tungsten Rod
It Ionizes Air Gap and Stabilizes Arc
It Cools Welding Torch & Tungsten Rod
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Shielding Gas
• Argon - Purity 99.95%
• Impure Argon Results In Porosities
• Purity Verified by Fusing BQ CS plate
• Leakage of Argon in Torch Results in
Porosity.
• Check Leakage by Closing the Ceramic Cup
With Thump
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Argon Gas Cylinder
• Light Blue In Colour
• Full Cylinder Pressure: 1800 psi ( 130 Kgs / Cm2 )
• Volume Of Argon In Full Cylinder: 7.3 M3
• Commercial Argon (99.99%) Cost: Rs 70/- Per M3
• High Purity Argon (99.999) Cost: Rs 87/- Per M3
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Back Purging
Purging Gas Commercial Argon or• Applicable to Single
Nitrogen
Sided full penetration
• Prevents oxidation of
Filler Wire
Welding Torch
root pass from opposite
side of weld
• Essential for high alloy
steels, nonferrous
Purging
Purging Gas In
Gas Out
metals and alloys
Root Pass
Purging
• Desirable For All
chamber
Material
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• Argon-helium mixtures are also frequently utilized in
GTAW, since they can increase control of the heat input
while maintaining the benefits of using argon. Normally,
the mixtures are made with primarily helium (often about
75% or higher) and a balance of argon. These mixtures
increase the speed and quality of the AC welding of
aluminum, and also make it easier to strike an arc.
• Argon-hydrogen, is used in the mechanized welding of
light gauge stainless steel, but because hydrogen can
cause porosity, its uses are limited.
• Nitrogen can sometimes be added to argon to help
stabilize the austenite in austentitic stainless steels and
increase penetration when welding copper. Due to
porosity problems in ferritic steels and limited benefits,
however, it is not a popular shielding gas additive.
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Materials
• Most commonly used to weld stainless steel
and nonferrous materials, such as aluminum
and magnesium, but it can be applied to
nearly all metals, with notable exceptions
being lead and zinc.
• Its applications involving carbon steels are
limited not because of process restrictions,
but because of the existence of more
economical steel welding techniques, such
as gas metal arc welding and shielded metal
arc welding.
• GTAW can be performed in a variety of otherthan-flat positions, depending on the skill of
the welder and the materials being welded.
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A TIG weld showing an
accentuated AC etched zone
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Closeup view of an
aluminium TIG weld AC etch zone
Dr. N. RAMACHANDRAN, NITC
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• Aluminum and magnesium are most often welded using
alternating current, but the use of direct current is also
possible, depending on the properties desired. Before
welding, the work area should be cleaned and may be
preheated to 175-200 °C for aluminum or to a maximum
of 150 °C for thick magnesium workpieces to improve
penetration and increase travel speed.
• AC current can provide a self-cleaning effect, removing
the thin, refractory aluminium oxide (sapphire) layer that
forms on aluminium metal within minutes of exposure to
air. This oxide layer must be removed for welding to
occur. When alternating current is used, pure tungsten
electrodes or zirconiated tungsten electrodes are
preferred over thoriated electrodes, as the latter are
more likely to "spit" electrode particles across the
welding arc into the weld.
• Blunt electrode tips are preferred, and pure argon
shielding gas should be employed for thin workpieces.
Introducing helium allows for greater penetration in
thicker workpieces, but can make arc starting difficult.
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• Direct current of either polarity, positive or negative,
can be used to weld aluminum and magnesium as
well.
• DCEN allows for high penetration, and is most
commonly used on joints with butting surfaces, such
as square groove joints. Short arc length (generally
less than 2 mm or 0.07 in) gives the best results,
making the process better suited for automatic
operation than manual operation. Shielding gases
with high helium contents are most commonly used
with DCEN, and thoriated electrodes are suitable.
• DCEP is used primarily for shallow welds, especially
those with a joint thickness of less than 1.6 mm.
While still important, cleaning is less essential for
DCEP than DCEN, since the electron flow from the
workpiece to the electrode helps maintain a clean
weld. A large, thoriated tungsten electrode is
commonly used, along with a pure argon shielding
gas.
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Steels
• For GTA welding of carbon and stainless steels, the
selection of a filler material is important to prevent
excessive porosity. Oxides on the filler material and
workpieces must be removed before welding to prevent
contamination, and immediately prior to welding, alcohol
or acetone should be used to clean the surface.
• Preheating is generally not necessary for mild steels less
than one inch thick, but low alloy steels may require
preheating to slow the cooling process and prevent the
formation of martensite in the heat-affected zone.
• Tool steels should also be preheated to prevent cracking
in the heat-affected zone. Austenitic stainless steels do
not require preheating, but martensitic and ferritic
chromium stainless steels do. A DCEN power source is
normally used, and thoriated electrodes, tapered to a
sharp point, are recommended. Pure argon is used for
thin workpieces, but helium can be introduced as
thickness increases.
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Dissimilar metals
• Welding dissimilar metals often introduces new difficulties to
GTA welding, because most materials do not easily fuse to form
a strong bond. Welds of dissimilar materials have numerous
applications in manufacturing, repair work, and the prevention
of corrosion and oxidation. In some joints, a compatible filler
metal is chosen to help form the bond, and this filler metal can
be the same as one of the base materials (eg:, using a stainless
steel filler metal stainless steel and carbon steel as base
materials), or a different metal (such as the use of a nickel filler
metal for joining steel and cast iron). Very different materials
may be coated or "buttered" with a material compatible with a
particular filler metal, and then welded. In addition, GTAW can
be used in cladding or overlaying dissimilar materials.
• When welding dissimilar metals, the joint must have an
accurate fit, with proper gap dimensions and bevel angles. Care
should be taken to avoid melting excessive base material.
Pulsed current is particularly useful for these applications, as it
helps limit the heat input. The filler metal should be added
quickly, and a large weld pool should be avoided to prevent
dilution of the base materials.
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Process variations
Pulsed-current
• In the pulsed-current mode, the welding current rapidly
alternates between two levels.
• The higher current state is known as the pulse current,
while the lower current level is called the background
current.
• During the period of pulse current, the weld area is
heated and fusion occurs. Upon dropping to the
background current, the weld area is allowed to cool and
solidify.
• Pulsed-current GTAW has a number of advantages,
including lower heat input and consequently a reduction
in distortion and warpage in thin workpieces. In addition,
it allows for greater control of the weld pool, and can
increase weld penetration, welding speed, and quality. A
similar method, manual programmed GTAW, allows the
operator to program a specific rate and magnitude of
current variations,Dr.making
it useful
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NITCfor specialized
227
applications.
Dabber
• The Dabber variation is used to precisely place
weld metal on thin edges. The automatic
process replicates the motions of manual
welding by feeding a cold filler wire into the weld
area and dabbing (or oscillating) it into the
welding arc. It can be used in conjunction with
pulsed current, and is used to weld a variety of
alloys, including titanium, nickel, and tool steels.
Common applications include rebuilding seals in
jet engines and building up saw blades, milling
cutters, drill bits, and mower blades
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Heat-affected zone
The cross-section of a welded butt joint, with the
darkest gray representing the weld or fusion zone,
the medium gray the heat affected zone, and
the lightest gray the base material.
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• The heat-affected zone (HAZ) is the area of base
material, either a metal or a thermoplastic, which has
had its microstructure and properties altered by welding.
The heat from the welding process and subsequent recooling causes this change in the area surrounding the
weld. The extent and magnitude of property change
depends primarily on the base material, the weld filler
metal, and the amount and concentration of heat input
by the welding process.
• The thermal diffusivity of the base material plays a large
role – if the diffusivity is high, the material cooling rate is
high and the HAZ is relatively small. Alternatively, a low
diffusivity leads to slower cooling and a larger HAZ. The
amount of heat inputted by the welding process plays an
important role as well, as processes like oxyfuel welding
use high heat input and increase the size of the HAZ.
Processes like laser beam welding give a highly
concentrated, limited amount of heat, resulting in a small
HAZ. Arc welding falls between these two extremes, with
the individual processes varying somewhat in heat input
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• To calculate the heat input for arc welding
procedures, the formula used is:
where Q = heat input (kJ/mm), V = voltage (V), I =
current (A), and S = welding speed (mm/min). The
efficiency is dependent on the welding process used,
with shielded metal arc welding having a value of
0.75, gas metal arc welding and submerged arc
welding, 0.9, and gas tungsten arc welding, 0.8.
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Types Of GTAW Power Source
• Inverter- DC
• Thyrister – DC
• Motor Generator – DC
• Rectifier – DC
• Transformer – AC (For Aluminium Welding Only)
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Power Source
• Provides Electric Energy – Arc – Heat
• Drooping Characteristic
• OCV – Appx. 90V,
• Current Range 40 A to 300 A ( Capacity Of M/s)
• Arc Voltage 18V to 26V
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Characteristic Of GTAW
Power Source
Drooping – Constant Current
V
V1
V2
Vertical
Curve
A
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A1 A2
Dr. N. RAMACHANDRAN, NITC
234
High Frequency Unit
• Provides High Voltage Electric Energy With Very
high Frequency – 10000 Cycles / Sec.
• Initiates low energy Arc / Spark & Ionize Air Gap.
• Electrically charges Air Gap For welding Current to
Jump Across the Tungsten Tip & BM to Form An
Arc.
• HF Gets Cut Off, Once Welding Arc Struck.
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Water Cooling System
• Provides Cooling Water To Welding Torch.
• Cools Tungsten Rod, Torch handle & Welding
Cable.
• Cooling Water Returns through Flexible Tube Which
Carries welding cable within.
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Pedal Switch
When Pedal Pressed
• Solenoid valve opens, Argon gas flows
• High Frequency current jumps from
tungsten rod generating sparks
• Welding current flows generating an
Switches system
arc across tungsten rod and work.
on And off in sequence
• High frequency gets cut off from the
system & welding continues.
When Pedal Released
1 Current gets cut off, Arc extinguishes
2 Gas flow remains for few more
seconds before it stops.
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Argon Gas Cylinder- Pressure Regulator +
Flow Meter
Cylinder Valve
Pressure gauges
Flow Meter
Flow Regulator
• Cylinder Stores Argon At
High Pressure
• Regulator Regulates
Cylinder Pressure to
Working Pressure
Pressure Regulator
Connection To Torch
• Flow Meter Controls Flow
Rate
Argon Cylinder
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Tools For GTAW
• Head Screen
• Hand gloves
• Chipping Hammer
• Wire Brush
• Spanner Set
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Filler Wire
• Added Separately to the weld pool.
• Compatible to base metal
• Used in cut length for manual welding.
• Used from layer wound spool for automatic
welding.
• Sizes :- 0.8, 1, 1.2, 1.6, 2, 2.4 & 3 mm
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ASME Classification Of Filler Wire
SS Filler Wire:
SFA-5.9, ER 308, 308L, 316, 316L, 347, 309
LAS Filler Wire:
SFA 5.28, ER 70S A1, ER 80S B2, ER90S D2,
ER 80S Ni2
CS Filler Wire:
SFA- 5.18 , ER 70S2
C = 0.07%, Mn = 0.9% – 1.4%, Si = 0.4 – 0.7%, P = 0.025%, S = 0.035%
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Dos & Don'ts In GTAW
Don’ts
Dos
• Always Connect
Electrode – Ve
• Keep Always Flow
Meter Vertical
• Check & Confirm
Argon Purity
• Clean Groove & Filler
wire With Acetone
• Grind Tungsten Tip to
Point
7/7/2015
• Don’t Strike Arc With
Electrode + Ve
• Don’t strike Arc Without
Argon Flow
• Don’t Strike Arc By
touching Tungsten Rod
• Don’t Touch Weld Pool
With Tungsten Rod
• Don’t Lift and break Arc
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242
Dos & Don'ts In GTAW
Don’ts
Dos
• Break The Arc Only By
Pedal Switch
• Lift The Torch only After
5 Sec Of Arc Break.
• Ensure Pre Purging &
Post Purging of 5Sec
• Ensure Argon Flow &
Water Circulation To
Torch
7/7/2015
• When Arc is Stopped Don’t
Lift Torch immediately.
• Don’t Weld With Blend
Tungsten Rod
• Don’t Weld With Argon
Leaking Torch
• Don’t Weld Without Water
Circulation
Dr. N. RAMACHANDRAN, NITC
243
Dos & Don'ts In GTAW
Don’ts
Dos
• Provide Back Purging For
Single Sided Full
Penetration Welds
• Use N2 or Argon as Back
Purging Gas For CS &
LAS
• Use Argon As Back
Purging Gas For SS &
Non Ferrous Alloys
7/7/2015
• Don’t Weld Single Sided
Full Penetration Welds
Without Back Purging
• Don’t Use N2 As Back
Purging Gas For Non
Ferrous Alloys
• Don’t Empty Ag Cylinders
Fully.
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244
Defects In GTAW
1. Cracks
2. Lack Of Fusion
3. Porosity
4. Undercut
5.Lack Of Penetration
6. Excess Penetration
7.Overlap
8. Suck Back
9. Under Flush
10. Burn Through
11. Tungsten Inclusion 11.Stray Arcing
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Crack
1)
2)
3)
4)
Cause
Wrong Consumable
Wrong Procedure
Improper Preheat
Inadequate Thickness
In Root Pass
1)
2)
3)
4)
Remedy
Use Right Filler Wire
Qualify Procedure
Preheat Uniformly
Add More Filler Wire
in root Pass
crack
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Lack Of Fusion
Cause
Remedy
1) Inadequate Current
1) Use Right Current
2) Wrong Torch angle
2) Train /Qualify welder
3) Improper bead placement 3) Train/Qualify Welder
Lack Of Fusion
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Porosity
Cause
1) Impure Argon Gas
2) Argon Leak Within Torch
3) Defective Filler Wire
4) Wet surface of BM
5) Rusted / Pitted Filler wire
6) Improper Flow Of Argon
Porosity
7/7/2015
Remedy
1) Replace Argon Cylinder
2) Replace Leaking Torch
3) Replace Filler Wire
4) Clean & Warm BM
5) Clean Filler Wire
6) Provide Gas lens
. .
Dr. N. RAMACHANDRAN, NITC
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Undercut
Cause
1) Excess Current
2) Excess Voltage
3) Improper Torch angle
Remedy
1) Reduce the Current
2) Reduce Arc length
3) Train & Qualify the Welder
Under cut
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Lack Of Penetration*
Cause
1) Excess Root Face
2) Inadequate Root opening
3) Over size Filler Wire
4) Wrong Direction of Arc
5) Improper bead placement
6) Improper weaving technique
Remedy
1) Reduce Root Face
2) Increase Root Opening
3) Reduce Filler Wire size
4) Train / Qualify Welder
5) Train / Qualify Welder
6) Train & Qualify Welder
* Applicable to SSFPW
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250
Excess Penetration*
Cause
1)Excess root opening
2) Excess Current
3) Inadequate root face
4) Excess Weaving
5) Wrong Direction Of Arc
1)
2)
3)
4)
5)
Remedy
Reduce root gap
Reduce Current
Increase Root face
Train Welder
Train Welder
* Applicable to SSFPW
Excess Penetration Dr. N. RAMACHANDRAN, NITC
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251
Overlap
Cause
1) Wrong Direction Of Arc
2) Inadequate Current
3) Excess Filler Wire
Remedy
1) Train & Qualify Welder
2) Increase Current
3) Reduce Filler Metal
Overlap
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Suck Back*
Cause
Remedy
1) Excess weaving in root
2) Excess Current
3) Inadequate root face
4) Wrong Electrode angle
1) Reduce weaving
2) Reduce Current
3) Increase root face
4) Train / Qualify Welder
* Applicable to SSFPW in 4G, 3G & 2G
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Suck Back
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253
Under flush
Cause
Remedy
1) Weld some more beads
1) Inadequate weld beads in
final layer
in final layer
2) Inadequate understanding on 2) Train / Qualify welder
weld reinforcement
3) Wrong selection of filler wire 3) Train / Qualify Welder
size
Under flush
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Burn through*
Cause
1) Excess Current
2) Excess Root opening
3) Inadequate Root face
4) Improper weaving
Remedy
1) Reduce the Current
2) Reduce root opening
3) Increase root face
4) Train / Qualify Welder
*Applicable to root pass
Burn trough
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Tungsten Inclusion
Cause
1) Ineffective HF
2) Improper Starting of Arc
3) Tungsten Tip Comes in
Contact With Weld
Remedy
1) Rectify HF Unit
2) Never Touch Weld
With Tungsten Rod
3) Train / Qualify welder
Tungsten Inclusion
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Stray Arcing
Cause
Remedy
1) HF Not In Operation
1) Rectify HF Unit
2) Inadequate Skill of Welder 2) Train the Welder
Arc Strikes
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Gas Metal Arc Welding
What Is GMAW ?
• A Fusion Welding Process – Semi Automatic
• Arc Between Consumable Electrode &Work
• Arc Generated by Electric Energy From a Rectifier
/ Thyrester / Inverter
• Filler Metal As Electrode Continuously fed From
Layer Wound Spool.
• Filler Wire Driven to Arc By Wire Feeder through
Welding Torch
• Arc & Molten Pool Shielded by Inert Gas through
Torch / Nozzle
Gas Metal Arc Welding
• MIG – Shielding Gas Ar / Ar + O2 / Ar + Co2
• MAG – Shielding Gas Co2
• FCAW – Shielding Gas Co2 With Flux cored
Wire
Note:- Addition of 1 – 5% of O2 or 5 – 10% of Co2 in Ar.
increases wetting action of molten metal
Power Source For MIG / MAG
•
•
•
•
Inverter- DC
Thyrister – DC
Motor Generator – DC
Rectifier – DC
Characteristic Of GMAW Power
Source
Constant V / Linear Characteristic
V
Appx. Horizontal
Curve
V1
V2
A1
A2
A
Current & Polarity
DC- Electrode +Ve
Stable Arc
Smooth Metal Transfer
Relatively Low Spatter
Good Weld Bead Characteristics
–
DC- Electrode Ve, Seldom
Used
AC- Commercially Not In use
Accessories Of GMAW
•
•
•
•
•
•
Power Source
Wire Feed Unit
Shielding Gas Cylinder, Pressure gauges/
Regulator, Flow meter (Heater For Co2 )
Welding Torch
Water Cooling System (For Water cooled Torch)
Earthing Cable With Clamp
Tools For GMAW
•
•
•
•
•
•
•
•
•
Head Screen With DIN 13 / 14 Dark Glass
Hand Wire Brush / Grinder With Wire Wheel
Cutting Pliers
Hand Gloves
Chipping Hammer / Chisel & hammer
Spanner Set
Cylinder Key
Anti-spatter Spray
Earthing Cable With Clamp
GMAW Torch
On / Off Switch
Shielding Gas
Torch Handle
Spring Conduit
Gas Cup
Arc
Nozzle Tip
Filler Wire - Electrode
Job
Equipment & Accessories
Pressure Regulator
Flow Meter
Shielding Gas
Switch
Heater
(Only For
Co2)
Solenoid
Valve
Shielding Gas
Cylinder
Copper Cup
Electrode /
Wire
Arc
–
Welding Torch
Wire Inside Spring Lining
Contact Tip
Argon / Co2
Shielding
Work
Torch With Cable Max. 3Mtr
Wire Feeder
Wire
Spool
Power Source
With Inductance
+
–
GAS METAL ARC WELDING (GMAW)
ALMOST REPLACING SMAW, FASTER, INTRODUCED IN 1940’S,
DCRP GENERALLY EMPLOYED, CONTINUOUS WIRE FEEDING
MODES OF METAL TRANSFER
1
2
3
4
5
SPRAY
SHORT
GLOBULAR
BURIED ARC PULSED
CIRCUIT
ARC
HIGH
VOLTAGE
HIGH
AMPERAGE
(WIRE FEED)
VERY LOW
VOLTAGE
MODERATE
WIRE FEED
DROPLETSDEEP Penet.
FOR THICK
COOLEST
MODE,
LEAST
Penetration.
ARGON ST.
(FOR
NARROW)
75 % Ar +
25% CO2
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BETWEEN 1&2
FOR CARBON
STEELS, 6 TO
12 MM
UNIQUE IN
GMAW,
HIGHER WIRE
FEED
PULSING
BETWEEN
MODES
HIGH SPPED,
LOW SPATTER,
DEEP Penet.,
FOR MS AND SS
NO GUN
OSCILLATI
ON
90%Ar + 7.5%
CO2 +2.5% He
FOR
THICK TO
THIN,
Dr. N. RAMACHANDRAN, NITC
DISSIMILAR
268
GASES
• PUROPOSE1.TO SHIELD MOLTEN PUDDLE FROM CONTAMINATION
2.CREATE A SMOOTH ELECTRICAL CONDUCTION
PATH FOR ELECTRONS IN ARC
• SOME GASES (ARGON)MAKE SMOOTH PATH, BUT SOME
RESISTS (CO2) PATH.
• STRAIGHT ARGON FOR NARROW BEADS
• 98% Ar+ 2 OXYGEN FOR SPRAY,
• He FOR COPPER, THICK Al (WITH Ar).
• 75 % Ar + 25% CO2 FOR SHORT CIRCUIT.,
• STRAIGHT CO2 ECONOMICAL, BUT SPATTERING.
• 90%Ar + 7.5% CO2 +2.5% He FOR BURIED ARC, SS.
• 90% Ar + 10% He FOR AUTOMATIC V, WIRE FEED SYSTEMS
• A CONSTANT VOLTAGE POWER SOURCE USED.
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ABOUT THE POWER SOURCE
• DCRP, DCSP, ACHF USED
• ELECTRODES OF 0.25 mm TO 6.4 mm FOR
DIFFERENT APPLICATIONS
• ELECTRODES CODED, WITH COLOR STRIPS
• BEST FOR ALUMINIUM, SINCE OXIDE FILM BREAKS
BY PENETRATION
Frequent cleaning and shaping of electrode tip to be done
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+ POINTS OF GMAW
• HIGH WELDING SPEED
• NO NEED TO CHANGE ELECTRODES (ONLY WIRE SPOOL
IN GMAW)
• HAZ SMALL
• VERY LITTLE SMOKE AND VERY LIGHT SiO2
SLAG(CALLED GLASS SLAG)
• LEAST DISTORTION
• EASE OF OPERATION (QUICK LEARNING)
• GUN MANIPULATION EASIER
• MOST FLEXIBLE PROCESS- VERSATILE
• VERY FEW MACHINE ADJUSTMENTS FOR THICK TO THIN
CHANGE
• MS, MCS, TOOL STEEL GRADES, SS, COPPER, Al, Mg
WELDED
• FCAW, SAW, ESW- OTER FORMS OF GMAW
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Types Of Wire Feeding In
GMAW
• Push Type
– Wire fed in to The torch by Pushing through Flexible
Conduit From A Remote Spool
• Pull Type
– Feed Rollers Mounted on The Torch Handle Pulls the
Wire From A Remote spool
• Self Contained
– Wire Feeder & The Spool On the Torch
Function Of Shielding Gas In
GMAW
• Prevents Air contamination of weld Pool
• Prevents Contamination During Metal
Transfer
• Increases fluidity of molten metal
• Minimizes the spatter generation
• Helps in even & uniform bead finish
Shielding Gases For GMAW
• MIG:
•
•
•
•
Argon Or Helium
For SS, CS, LAS & Non-ferrous Mt & Al
MIG: Ar + 1 to 2 % O2, Wire With Add. Mn & Si
For SS, CS, LAS & Non-ferrous Mt & Al
MIG: Ar + 5 to 20 % Co2 Wire With Add. Mn & Si
For SS, CS, LAS & Non-ferrous Mt & Al
MAG: Co2 With Solid Wire
For CS & LAS
FCAW: Co2 With Flux Cored Wire
For CS, LAS & SS Overlay
ASME Classification For CS
GMAW Wire
• SFA 5.18 : - CS Solid Wire
ER 70 S – 2, ER 70 S – 3
ER 70 S – 6, ER 70 S – 7
• SFA 5.20 :- CS Flux Cored Wire
E 71 T-1,
E 71 T-2 ( Co2 Gas )
E 71 T-1M, E 71 T-2M ( Ar + Co2 Mix)
GMAW CS Wire
• Generally Copper Coated
– Prevents Oxidation / rusting in Storage
– Promotes Electric Conductivity in Arcing
• Available In Solid & Flux Cored
– Size in mm 0.8, 1, 1.2, 1.6, 2, 2.4, 3
• Manganese & Silicon ( Mn 1 – 2 %, Si Max 1%)
– Act As Deoxidizing Agents
– Eliminate Porosity
– Increase Wetting Of Molten Pool
Metal Transfer In MIG
• Short-Circuiting / Dip Transfer
• Globular Transfer
• Spray Transfer
Metal Transfer In MIG
Up to 120A
CS Solid Wire 1.2 mm Φ
120 to 250A
14 – 22V
Dip/Short Circuiting
Co2 or Ar
16 – 24 V
Globular
Co2 or Ar
Above230A
24 – 35 V
Spray
Only Ar / Ar+O2
Short-Circuiting / Dip Transfer
• Wire In Contact With Molten Pool 20 to 200 times per
Second
• Operates in Low Amps & Volts – Less Deposition
• Best Suitable for Out of Position Welding
• Suitable for Welding Thin Sheets
• Relatively Large opening of Root Can be Welded
• Less Distortion
• Best Suitable for Tacking in Set up
• Prone to Get Lack of Fusion in Between Beads
Globular Transfer
• Metal transferred in droplets of Size grater than
wire diameter
• Operates in Moderate Amps & Volts – Better
Deposition
• Common in Co2 Flux Cored and Solid Wire
• Suitable for General purpose Welding
Spray Transfer
•
•
•
•
•
Metal transferred in multiples of small droplets
100 to 1000 Droplets per Second
Metal Spray Axially Directed
Electrode Tip Remains pointed
Applicable Only With Inert Gas Shielding
–
Not With Co2
• Operates in Higher Amps & Volts – Higher
Deposition Rate
• Not Suitable for Welding in Out of Position.
• Suitable for Welding Deep Grooves
Pulsed Spray Welding
• Power Source Provides Two different
Current Levels“Background” and “Peak”at
regular interval
• “Background” & “Peak” are above and
below the Average Current
• Best Suitable for Full Penetration Open
Root Pass Welding
• Good Control on Bead Shape and Finish
Synergic Pulse GMAW
• Parameters of Pulsed Current (Frequency,
Amplitude, Duration, Background Current)
Related to Wire feed Rate
• One Droplet detaches with each pulse
• An Electronic Control unit synchronizes wire feed
Rate with Pulse Parameters
• Best Suitable for Most Critical Full Penetration
Open Root Pass Welding
• Good Control on Open Root penetration, Bead
Shape and Finish
GMAW Process Variables
•
•
•
•
•
•
•
•
Current
Voltage
Travel Speed
Stick Out / Electrode Extension
Electrode Inclination
Electrode Size
Shielding Gas & Flow Rate
Welding Position
Parameter For 1.2 ф FC Wire
•
•
•
•
•
•
Current – 200 to 240 A
Voltage – 22-24
Travel Speed 150 to 250 mm / min
Stick Out / Electrode Extension – 15 to 20 mm
Electrode Inclination – Back Hand Technique
Shielding Gas – Co2, 12 L/Min
Parameter For 1.2 ф Solid Wire
•
•
•
•
•
•
Current – 180 to 220 A
Voltage – 20-22
Travel Speed 150 to 200 mm / min
Stick Out / Electrode Extension – 10 to 20 mm
Electrode Inclination – Back Hand Technique
Shielding Gas – Co2 – 12 L/Min
Results In Change Of Parameters
• Increase In Current
– More deposition, More Penetration, More BM Fusion
• Increase In Voltage
– More Weld Bead Width, Less Penetration, Less
Reinforcement, Excess Spatter
• Increase In Travel Speed
– Decrease in Penetration, Decrease in Bead Width,
• Decrease In Gas Flow rate
– Results In porosity
• Long Stick Out / Electrode Extension
– Excess Weld Deposit With Less Arc intensity, Poor Bead
Finish, Shallow Penetration
Common Defects In GMAW
1. Porosity
3. Lack Of Fusion
5. Over Lap
7. Crack
9. Burn Through
11. Unstable Arc
2. Spatters
4. Under Cut
6. Slag
8. Lack Of Penetration
10. Convex Bead
12. Wire Stubbing
Porosity
Cause
Remedy
1) Less Mn & Si In Wire
2) Rusted / Unclean BM / Groove
3) Rusted wire
4) Inadequate Shielding Gas
1) Use High Mn & Si Wire
2) Clean & warm the BM
3) Replace the Wire
4) Check & Correct Flow Rate
Porosity
. .
Spatters
Cause
Remedy
1) Low Voltage
2) Inadequate Inductance
3) Rusted BM surface
4) Rusted Core wire
5) Quality Of Gas
1) Increase Voltage
2) Increase Inductance
3) Clean BM surface
4) Replace By Rust Free wire
5) Change Over To Ar + Co2
Spatters
•
••
Lack Of Fusion
Cause
Remedy
1) Inadequate Current
1) Use Right Current
2) Inadequate Voltage
3) Wrong Polarity
4) Slow Travel Speed
5) Excessive Oxide On Joint
2) Use Right Voltage
3) Connect Ele. + Ve
4) Increase Travel speed
5) Clean Weld Joint
Lack Of Fusion
Undercut
Cause
1) Excess Voltage
2) Excess Current
3) Improper Torch angle
4) Excess Travel Speed
Under cut
Remedy
1) Reduce Voltage
2) Reduce Current
3) Train & Qualify the Welder
4) Reduce Travel Speed
Overlap
Cause
Remedy
1) Too Long Stick Out
1) Reduce Stick Out
2) Inadequate Voltage
2) Increase the Voltage
Overlap
Slag
Cause
1) Inadequate Cleaning
2) Inadequate Current
3) Wrong Torch angle
4) Improper bead placement
Slag
Remedy
1) Clean each bead
2) Use Right Current
3) Train / Qualify welder
4) Train / Qualify Welder
Crack
Cause
Remedy
1) Incorrect Wire Chemistry 1) Use Right Wire
2) Increase wire Feed
2) Too Small Weld Bead
3) Preheat Uniformly
3) Improper Preheat
4) Post heating or ISR
4) Excessive Restrain
crack
Lack Of Penetration*
Cause
1) Too Narrow Groove Angle
2) Inadequate Root opening
3) Too Low Welding current
4) Wrong Torch angle
5) Puddle Roll In Front Of Arc
6) Long Stick Out
* Applicable to SSFPW
LOP
Remedy
1) Widen The Groove
2) Increase Root Opening
3) Increase Current
4) Train / Qualify Welder
5) Correct Torch Angle
6) Reduce Stick Out
Burn through*
Cause
1) Excess Current
2) Excess Root opening
3) Inadequate Root face
4) Too Low Travel Speed
5) Quality Of Gas
Burn trough
Remedy
1) Reduce the Current
2) Reduce root opening
3) Increase root face
4) Increase Speed
5) Use Ar + Co2
*Applicable to root pass
Convex Bead Finish
Cause
1) Low Current
2) Low Voltage
3) Low Travel Speed
4) Low Inductance
5) Too Narrow Groove
Uneven bead finish
Remedy
1) Increase Current
2) Increase Voltage
3) Increase Travel Speed
4) Increase Inductance
5) Increase Groove Width
Unstable arc
Cause
1) Improper Wire Feed
2) Improper Gas Flow
3) Twisted Torch Conduit
Remedy
1) Check Wire Feeder
2) Check Flow Meter
3) Straighten Torch Cab
Wire Stubbing
Cause
1) Too Low Voltage
2) Too High Inductance
3) Excess Slope
4) Too Long Stick Out
Remedy
1) Increase Voltage
2) Reduce Inductance
3) Adjust Slope
4) Reduce Stick Out
Important Terminology used in
Critical Welding
•
•
•
•
•
Preheating
Post Heating or Dehydrogenation
Intermediate Stress leaving
Inter pass Temperature
Post Weld Heat Treatment
What Is Preheating?
• Heating the base metal along the weld joint to a
predetermined minimum temperature immediately
before starting the weld.
• Heating by Oxy fuel flame or electric resistant
coil
• Heating from opposite side of welding wherever
possible
• Temperature to be verified by thermo chalks prior
to starting the weld
Why Preheating?
• Preheating eliminates possible cracking of weld and HAZ
• Applicable to
Hardenable low alloy steels of all thickness
Carbon steels of thickness above 25 mm.
Restrained welds of all thickness
• Preheating temperature vary from 75°C to 200°C
depending on hardenability of material, thickness & joint
restrain
How does Preheating Eliminate Crack?
• Preheating promotes slow cooling of weld and
HAZ
• Slow cooling softens or prevents hardening of
weld and HAZ
• Soft material not prone to crack even in
restrained condition
What Is Post Heating?
• Raising the pre heating temperature of the weld joint to a
predetermined temperature range (250° C to 350° C) for
a minimum period of time (3 Hrs) before the weld cools
down to room temperature.
• Post heating performed when welding is completed or
terminated any time in between.
• Heating by Oxy fuel flame or electric resistant coil
• Heating from opposite side of welding wherever possible
• Temperature verified by thermo chalks during the period
Why Post Heating?
• Post heating eliminates possible delayed cracking
of weld and HAZ
• Applicable to
Thicker hardenable low alloy steels
Restrained hardenable welds of all thickness
• Post heating temperature and duration depends on
hardenability of material, thickness & joint
restrain
How does Post Heating Eliminate
Crack?
• SMAW introduces hydrogen in weld metal
• Entrapped hydrogen in weld metal induces
delayed cracks unless removed before cooling to
room temperature
• Retaining the weld at a higher temperature for a
longer duration allows the hydrogen to come out
of weld
What Is Intermediate Stress Relieving?
• Heat treating a subassembly in a furnace to a
predetermined cycle immediately on completion of
critical restrained weld joint / joints without
allowing the welds to go down the pre heat
temperature. Rate of heating, Soaking temperature,
Soaking time and rate of cooling depends on
material quality and thickness
• Applicable to
Highly restrained air hardenable material
Why Intermediate Stress Relieving?
• Restrained welds in air hardenable steel highly
prone to crack on cooling to room temperature.
• Cracks due to entrapped hydrogen and built in stress
• Intermediate stress relieving relieves built in stresses
and entrapped hydrogen making the joint free from
crack prone
What Is Inter- Pass Temperature?
• The temperature of a previously layed weld bead
immediately before depositing the next bead over
it
• Temperature to be verified by thermo chalk prior
to starting next bead
• Applicable to
Stainless Steel
Carbon Steel & LAS with minimum impact
Why Inter Pass Temperature?
• Control on inter pass temperature avoids over
heating, there by
Refines the weld metal with fine grains
Improves the notch toughness properties
Minimize the loss of alloying elements in
welds
Reduces the distortion
What Is Post Weld Heat Treatment?
• Heat treating an assembly on completion of all
applicable welding, in an enclosed furnace with
controlled heating/cooling rate and soaking at a
specific temperature for a specific time.
• Rate of heating, Soaking temperature, Soaking time
and rate of cooling depends on material quality and
thickness
• Applicable to
All type of CS & LAS
Why Post Weld Heat Treatment?
• Welded joints retain internal stresses within the
structure
• HAZ of welds remains invariably hardened
• Post Weld Heat Treatment relieves internal stresses
and softens HAZ. This reduces the cracking
tendency of the equipment in service
Weldability
• The weldability of a material refers to its
ability to be welded. Many metals and
thermoplastics can be welded, but some
are easier to weld than others. It greatly
influences weld quality and is an important
factor in choosing which welding process
to use.
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• Steels
• The weldability of steels is inversely
proportional to a property known as the
hardenability of the steel, which measures the
ease of forming martensite during heat
treatment. The hardenability of steel depends on
its chemical composition, with greater
quantities of carbon and other alloying elements
resulting in a higher hardenability and thus a
lower weldability. In order to be able to judge
alloys made up of many distinct materials, a
measure known as the equivalent carbon
content is used to compare the relative
weldabilities of different alloys by comparing
their properties to a plain carbon steel.
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• The effect on weldability of elements like
chromium and vanadium, while not as
great as carbon, is more significant than
that of copper and nickel, for example. As
the equivalent carbon content rises, the
weldability of the alloy decreases. The
disadvantage to using plain carbon and
low-alloy steels is their lower strength—
there is a trade-off between material
strength and weldability. High strength,
low-alloy steels were developed especially
for welding applications during the 1970s,
and these generally easy to weld materials
have good strength, making them ideal for
many welding applications.
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• Stainless steels, because of their high chromium
content, tend to behave differently with respect
to weldability than other steels. Austenitic grades
of stainless steels tend to be the most weldable,
but they are especially susceptible to distortion
due to their high coefficient of thermal
expansion. Some alloys of this type are prone to
cracking and reduced corrosion resistance as
well. Hot cracking is possible if the amount of
ferrite in the weld is not controlled—to alleviate
the problem, an electrode is used that deposits a
weld metal containing a small amount of ferrite.
Other types of stainless steels, such as ferritic
and martensitic stainless steels, are not as
easily welded, and must often be preheated and
welded with special electrodes.
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• Aluminum
• The weldability of aluminum alloys varies significantly,
depending on the chemical composition of the alloy used.
Aluminum alloys are susceptible to hot cracking, and to
combat the problem, welders increase the welding speed to
lower the heat input. Preheating reduces the temperature
gradient across the weld zone and thus helps reduce hot
cracking, but it can reduce the mechanical properties of the
base material and should not be used when the base
material is restrained. The design of the joint can be
changed as well, and a more compatible filler alloy can be
selected to decrease the likelihood of hot cracking.
Aluminum alloys should also be cleaned prior to welding,
with the goal of removing all oxides, oils, and loose particles
from the surface to be welded. This is especially important
because of an aluminum weld's susceptibility to porosity due
to hydrogen and dross due to oxygen.
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• References
• Lincoln Electric (1994). The Procedure Handbook
of Arc Welding. Cleveland: Lincoln Electric. ISBN
9994925822.
• Residual stresses are stresses that remain after
the original cause of the stresses has been
removed. Residual stresses occur for a variety of
reasons, including inelastic deformations and heat
treatment. Heat from welding may cause localized
expansion, which is taken up during welding by
either the molten metal or the placement of parts
being welded. When the finished weldment cools,
some areas cool and contract more than others,
leaving residual stresses. Castings may also have
large residual stresses due to uneven cooling.
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• While un-controlled residual stresses are undesirable,
many designs rely on them. For example, toughened
glass and pre-stressed concrete depend on them to
prevent brittle failure. Similarly, a gradient in martensite
formation leaves residual stress in some swords with
particularly hard edges (notably the katana), which can
prevent the opening of edge cracks. In certain types of
gun barrels made with two tubes forced together, the
inner tube is compressed while the outer tube stretches,
preventing cracks from opening in the rifling when the
gun is fired. Parts are often heated or dunked in liquid
nitrogen to aid assembly.
• Press fits are the most common intentional use of
residual stress. Automotive wheel studs, for example are
pressed into holes on the wheel hub. The holes are
smaller than the studs, requiring force to drive the studs
into place. The residual stresses fasten the parts
together. Nails are another example.
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Resistance Welding
Commonly used resistance welding processes:
• Resistance Spot Welding (RSW),
• Resistance Seam Welding (RSEW),&
• Resistance Projection Welding (PW) or
(RPW)
• Resistance welding uses the application of
electric current and mechanical pressure to
create a weld between two pieces of
metal. Weld electrodes conduct the electric
current to the two pieces of metal as they are
forged together.
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• The welding cycle must first develop sufficient
heat to raise a small volume of metal to the
molten state. This metal then cools while under
pressure until it has adequate strength to hold
the parts together. The current density and
pressure must be sufficient to produce a weld
nugget, but not so high as to expel molten metal
from the weld zone.
• High Frequency Resistance Welding (HFRW)
Percussion Welding (PEW) and Stud Welding
(SW), too.
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H = I2 R t
K
Electrode
K- energy losses through radiation &
conduction
Weld
Nugget
•resistances of the electrodes
•electrode- w/p contact resistance
•resistance of the individual parts to
be welded
•w/p-w/p contact resistance
(maintained high)
Resistance Welding
Benefits
•
High speed welding
•
Easily automated
•
Suitable for high rate
production
•
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Economical
HAZ
Electrode
Dr. N. RAMACHANDRAN, NITC
325
• Resistance Welding Limitations
• Initial equipment costs
• Lower tensile and fatigue strengths
• Lap joints add weight and material
Common Resistance Welding Concerns
•Optimize welding process variables.
•Evaluate current welding parameters and
techniques.
•And
thus eliminate
common welding problems and
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discontinuities - such as
Resistance Welding Problems and
Discontinuities
•
•
•
•
•
•
•
•
•
Cracks
Electrode deposit on work
Porosity or cavities
Pin holes
Deep electrode indentation
Improper weld penetration
Surface appearance
Weld size
Irregular shaped welds
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RESISTANCE SPOT WELDING
•
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AIR OPERATED ROCKER
ARM SPOT WELDING
MACHINE
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NITC
328
RESISTANCE SPOT WELDING
ELECTRODE DESIGNS FOR EASY ACCESS INTO COMPONENTS
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RESISTANCE SEAM WELDING
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RESISTANCE PROJECTION WELDING
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HIGH FREQUENCY BUTT WELDING OF TUBES
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FLASH WELDING
POOR
FOR SOLID RODS & TUBES
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GOOD
DESIGN GUIDELINES
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RESISTANCE STUD WELDING
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DISTORTION
• Welding involves highly localized heating of the
metal being joined together.
• The temperature distribution in the weldment is
nonuniform.
• Normally, the weld metal and the heat affected zone
(HAZ) are at temperatures substantially above that of
the unaffected base metal.
• Upon cooling, the weld pool solidifies and shrinks,
exerting stresses on the surrounding weld metal and
HAZ.
• If the stresses produced from thermal expansion and
contraction exceed the yield strength of the parent
metal, localized plastic deformation of the metal
occurs.
• Plastic deformation results in lasting change in the
component dimensions and distorts the
structure. This causes distortion of weldments.
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Types of distortion
•
•
•
•
•
•
Longitudinal shrinkage
Transverse shrinkage
Angular distortion
Bowing
Buckling
Twisting
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Factors affecting distortion
•
If a component were uniformly heated and cooled
distortion would be minimized. However, welding
locally heats a component and the adjacent cold metal
restrains the heated material. This generates stresses
greater than yield stress causing permanent distortion
of the component. Some of the factors affecting the
distortion are:
1. Amount of restraint
2. Welding procedure
3. Parent metal properties
4. Weld joint design
5. Part fit up
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• Restraint - to minimize distortion. Components welded
without any external restraint are free to move or distort
in response to stresses from welding. It is not unusual
for many shops to clamp or restrain components to be
welded in some manner to prevent movement and
distortion. This restraint does result in higher residual
stresses in the components.
• Welding procedure impacts the amount of distortion
primarily due to the amount of the heat input
produced. The welder has little control on the heat input
specified in a welding procedure. This does not prevent
the welder from trying to minimize distortion. While the
welder needs to provide adequate weld metal, the
welder should not needlessly increase the total weld
metal volume added to a weldment.
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• Parent metal properties, which have an effect on
distortion, are coefficient of thermal expansion and
specific heat of the material. The coefficient of thermal
expansion of the metal affects the degree of thermal
expansion and contraction and the associated stresses
that result from the welding process. This in turn
determines the amount of distortion in a component.
• Weld joint design will effect the amount of distortion in a
weldment. Both butt and fillet joints may
experience distortion. However, distortion is easier to
minimize in butt joints.
• Part fit up should be consistent to fabricate foreseeable
and uniform shrinkage. Weld joints should be
adequately and consistently tacked to minimize
movement between the parts being joined by welding.
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Welding Discontinuities
Some examples of welding discontinuities are
shown below.
Evaluation of the discontinuity will determine if the
discontinuity is a defect or an acceptable condition
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Incomplete Fusion - A weld discontinuity in
which fusion did not occur between weld metal
Dr. N. RAMACHANDRAN,
NITC
and fusion faces
or adjoining weld
beads.
340
Undercut - A groove melted into the base metal adjacent to the weld toe or
weld root and left unfilled by weld metal.
Overlap - The protrusion of weld metal beyond the weld toe or weld root.
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Underfill - A condition in which the weld face or root surface extends below the
adjacent surface of the base metal.
Incomplete Joint Penetration - A joint root condition in a groove weld in which
weld metal does not extend through the joint thickness
•Partial joint penetration groove welds are commonly specified in lowly loaded
structures. However, incomplete joint penetration when a full penetration joint is
required, as depicted above, would be cause for rejection. A fix for an
incomplete penetration joint would be to back gouge and weld from the other
side. Another acceptable partial penetration joint is shown below.
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Partial penetration joint on the left without discontinuities is an
acceptable condition.
Appropriate engineering decisions need to be applied to
determine what type of joint should be specified for a given
application.
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Several different representations of weld Cracking
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Representation of a convex fillet weld without discontinuities
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SOLID STATE PROCESSES
• Joining without fusion of work pieces
• No liquid (molten ) phase present in joint
• Principle: If two clean surfaces are brought into
atomic contact with each other - made with
sufficient pressure -(in the absence of oxide film
and other contaminents) they form bonds and
produce strong joint
• To improve strength, heat and some movement of
mating surfaces by plastic deformation employed.
Eg: USW, Friction Welding (FRW)
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FORGE WELDING (FOW)
• Both elevated temperature and pressure applied
to form strong bond between members
• Components heated and pressed/ hammered
with tools, dies or rollers
• Local plastic deformation at interface breaks up
the oxide films – improves bond strength.
• Not for high load bearing applications.
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COLD WELDING (CW)
• Pressure applied to work pieces either through dies
or rolls
• One (or both) of the mating parts must be ductile
• Interface cleaned prior to welding- brushing etc.
Rolling metal
Roll
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Bare metal
348
Explosive welding
• Solid state bonding process
• Joining by the cohesive force between atoms of two
intimate contact surfaces
High pressure waves- thousands of MPa created• To weld dissimilar metals, thick to thin, high difference
in Melting Point metals.
• Not a costly process
• Extremely large surfaces can be joined (2m X 10 m)
• Welding of heat treated metals without affecting the
process
• No HAZ
• Incompatible metals joined(thin foils to heavy plates)
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severe deformation
needed for joining.
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• Principle:
Explosive Impulse used to produce
extremely high normal pressure and a slight
shear or sliding pressure ( uses a detonator for
this)
Two properly laid metal surfaces brought together with high
relative velocity at high pressure and with proper
orientation
Large amount of plastic interaction between surfaces
results.
TWO WAYS
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(1)Contact technique
(2) Impact technique
• (1). Plastic interaction by positioning
explosive charge to deliver shock waves at
an oblique angle to parts to be welded- Less
frequently used.
• (2). Two pieces explosively projected
towards each other.
• Impact with high velocity (200 – 400 m/s)
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(1)Contact technique
•Plastic interaction by positioning explosive charge to deliver shock
waves at an oblique angle to parts to be welded- Less frequently
used.
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(2) Impact technique
Two pieces explosively projected towards each other.
Impact with high velocity (200 – 400 m/s)
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• Detonation velocity approx. 7000 m/s in the
detonation front.
• Produces pressure at interface 7000 to 70,000
atms. Parts driven at an angle Velocity of impact
and angle of collapse selected. Joining as s result
of intense plastic flow at the surface called
“surface jetting”
• For good joint, surface to be free from
contaminants
• Pressure sufficient to bring surfaces within
interatomic distances of each other [ In a range of
speed and angle of impact, a high velocity metal
jet forms. Removes surface contamination. Speed,
angle(10 to 100) of detonation important]
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• Bond as strong as the weaker of the two
obtained. 100 % efficient joint, (eg. In sheet
forming in aerospace industries)
• At the interface, microhardness slightly
increased. (because of plastic deformation
and strain hardening- a very thin hardness
zone)
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• Titanium cladding common
• Others- Ni, SS(50 mm), tantalum, carbon steels,
for heat exchangers, tubes, pressure vessels, etc.
• No change in chemical and physical properties
of parent metal
• But, not for brittle alloys. Metal must possess
some ductility.
• [Quantity of charge, detonation velocity, and
deformation characteristics of flyer plate decide
the weld]
• Also spot welding by small charge. Handy
explosive spot welding sets available (for 10mm
to 12 mm spots)
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• Minus points: Severe deformation needed
for joining (minimum 40 to 60%), as
welding is by pressure.
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THERMIT WELDING
• THERMITE- based on Therm, meaning heat
• Involves exothermic reactions between metal oxides and metallic reducing
agents
• Heat of reaction used for welding.
•
• Fine particles of iron oxide, aluminium oxide, iron & aluminium
• Reactions are:
(3/4) Fe3 O4 + 2 Al --- (9/4) Fe + Al2O3 + Heat
3 FeO + 2 Al --- 3 Fe + Al2O3 + Heat
Fe2O3 + 2Al --- 2Fe + Al2O3+ Heat
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THERMIT WELDING
THERMIT WELDING
Slide 13 of 18
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• Mixture is non explosive. Produces temperature of
32000 C within a minute
• Practically about 22000- 24000 C. Other materials to
impart special properties added. Applying a Mg fuse of
special compounds of peroxides, chlorates/ chromates.
• Welding copper, brasses, bronzes and copper alloys to
steel using oxides of copper, nickel, aluminium,
manganese – temperatures of 50000 C obtained
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PLASMA
WELDING
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Gas
MIG/TIG
Weldi
ng
Plasma Arc
Weldi
ng
Laser
Laser
Weldi
ng
Cuttin
g
Plasma
Cuttin
g
Acetylene
Oxy-Fuel
Cuttin
g
X
Air
Alumaxx Plus
X
Argon
X
X
Argon/hydrogen
TIG
X
Carbon dioxide
MAG
X
X
X
X
X
X
X
X
X
X
Carbon monoxide
X
Cooling
X
Ferromaxx Plus
MAG
Ferromax 15
MAG
Ferromaxx 7
MAG
Helium
TIG
X
X
X
Hydrogen
X
Inomaxx Plus
MAG
Inomaxx 2
MAG
Inomaxx TIG
TIG
X
Nitrogen
X
Nitrogen/hydrogen
mixes
X
Oxygen
X
X
Propane
Propylene
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Thermal
Spraying
Dr. N. RAMACHANDRAN, NITC
X
X
X
X
X
X
X
366
Arc Spraying
Arc spraying is the highest
productivity thermal spraying
process.
A DC electric arc is struck between
two continuous consumable wire
electrodes which form the spray
material.
Compressed gas (usually air)
atomises the molten spray material
into fine droplets and propels them
towards the substrate
The process is simple to operate- Can be used manually or in an automated manner.
Possible to spray a wide range of metals, alloys and metal matrix composites
(MMCs) in wire form.
A limited range of cermet coatings (with tungsten carbide) can also be sprayed in
cored wire form, where the hard ceramic phase is packed into a metal sheath as a
fine powder.
The combination of high arc temperature (6000 K) and particle velocities in excess of
100 m.sec-1 gives arc sprayed coatings superior bond strengths and lower porosity
levels when compared with flame sprayed coatings.
However,
air for dropletNITC
atomization and propulsion
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Dr. N. RAMACHANDRAN,
367
gives rise to high coating oxide content.
PLASMA SPRAYING PROCESS
•Uses a DC electric arc to generate a
stream of high temperature ionised
plasma gas, which acts as the
spraying heat source.
•The arc is struck between two nonconsumable electrodes, a tungsten
cathode and a copper anode within the
•
torch.
•The torch is fed with a continuous
flow of inert gas, which is ionised by
•
the DC arc, and is compressed and
accelerated by the torch nozzle so that
it issues from the torch as a high
velocity (in excess of 2000 m/sec),
high temperature (12000–16000 K)
plasma jet.
•
•The coating material, in powder form,
is carried in an inert gas stream into
the plasma jet where it is heated and
propelled towards the substrate.
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Because of the high temperature and
high thermal energy of the plasma jet,
materials with high melting points
can be sprayed.
Plasma spraying produces a high
quality coating by a combination of a
high temperature, high energy heat
source, a relatively inert spraying
medium and high particle velocities,
typically 200–300 m.sec-1.
However, inevitably some air
becomes entrained in the spray
stream and some oxidation of the
spray material may occur. The
surrounding atmosphere also cools
and slows the spray stream.
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Applications
• Plasma spraying is widely applied in the production of high
quality sprayed coatings.
• Spraying of seal ring grooves in the compressor area of
aeroengine turbines with tungsten carbide/cobalt to resist
fretting wear.
• Spraying of zirconia-based thermal barrier coatings (TBCs) onto
turbine combustion chambers.
• Spraying of wear resistant alumina and chromium oxide ceramic
onto printing rolls for subsequent laser and diamond
engraving/etching.
• Spraying of molybdenum alloys onto diesel engine piston rings.
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HIGH VELOCITY OXYFUEL SPRAYING
The most recent addition to the thermal
spraying family, high velocity oxyfuel
spraying (HVOF SPRAYING) has
become established as an alternative to
the proprietary, detonation (D-GUN)
flame spraying and the lower velocity,
air plasma spraying processes for
depositing wear resistant tungsten
carbide-cobalt coatings.
This differs from conventional flame spraying in that the combustion process is
internal, and the gas flow fates and delivery pressures are much higher than
those in the atmospheric burning flame spraying processes.
The combination of high fuel gas and oxygen flow rates and high pressure in the
combustion chamber leads to the generation of a supersonic flame with
characteristic shock diamonds.
Flame speeds of 2000ms-1 and particle velocities of 600–800ms-1 are claimed by
HVOF equipment suppliers.
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range of gaseous fuels is currently
used, including
Dr. N. RAMACHANDRAN,
NITC propylene, propane, 370
hydrogen and acetylene.
• Although similar in principle, potentially
significant details, such as powder feed
position, gas flow rates and oxygen to fuel
ratio, are apparent between each system.
• The HVOF process produces exceptionally
high quality cermet coatings (e.g., WC-Co), but
it is now also used to produce coatings of
metals, alloys and ceramics. Not all HVOF
systems are capable of producing coatings
from higher melting point materials, e.g.,
refractory metals and ceramics. The capability
of the gun is dependent upon the range of fuel
gases used and the combustion chamber
design.
• A liquid fuel (kerosene) HVOF system, has just
been launched, which is capable of much
higher deposition rates than the conventional
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gas-fuelled units.
Applications
HVOF spraying is a very recent process development, yet the high
quality of the coatings produced at competitive cost has already seen its
introduction in a number of very significant industries. Potential
applications overlap with plasma and D-gun spraying, particularly for
WC-Co coatings.
Tungsten carbide-cobalt coatings for fretting wear resistance on
aeroengine turbine components.
Wear resistant cobalt alloys onto fluid control valve seating areas.
Tungsten carbide-cobalt coatings on gate valves.
Various coatings for printing rolls, including copper, alumina, chromia.
NiCrBSi coatings (unfused) for glass plungers.
NiCr coatings for high temperature oxidation/corrosion resistance.
Alumina and alumina-titania dielectric coatings.
Biocompatible hydroxylapatite coatings for prostheses.
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Schematic of High Velocity Oxyfuel (HVOF) Spraying System
Process
Particle
Velocity
(m/s)
Adhesion (MPa)
Oxide Content
(%)
Porosity (%)
Deposition Rate
(kg/hr)
Typical Deposit
Thicknes
s (mm)
Flame
40
<8
10–15
10–15
1–10
0.2–10
Arc
100
10–30
10–20
5–10
6–60
0.2–10
Plasma
200–300
20–70
1–3
1–8
1–5
0.2–2
HVOF
600–800
>70
1–2
1–2
1–5
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Comparison of Thermal Spraying Processes and Coating
Characteristics
Typical Deposit
Thickness
(mm)
Particle Velocity (m/s)
Adhesion (MPa)
Oxide Content (%)
Porosity (%)
Deposition Rate
(kg/hr)
Flame
40
<8
10–15
10–15
1–10
0.2–10
Arc
100
10–30
10–20
5–10
6–60
0.2–10
Plasma
200–300
20–70
1–3
1–8
1–5
0.2–2
HVOF
600–800
>70
1–2
1–2
1–5
Process
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Thermal Spraying Gases
Process
Fuels that can be used
Other gases
HVOF
Acetylene, hydrogen, propylene, propane, or liquid
kerosene depending on material type
Oxygen and argon
Arc spraying
Flame spraying
Normally compressed air but can use nitrogen or argon
Mainly acetylene, but sometimes propane depending on
material
Plasma spraying
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Oxygen
Argon and hydrogen
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ELECTROGAS WELDING
Slide 14 of 18
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ELECTRON BEAM WELDING
•The electron beam gun has a
tungsten filament which is
heated, freeing electrons.
•The electrons are accelerated
from the source with high
voltage potential between a
cathode and anode.
•The stream of electrons then
pass through a hole in the
anode. The beam is directed
by magnetic forces of
focusing and deflecting coils.
This beam is directed out of
the gun column and strikes
the workpiece.
•The potential energy of the
electrons is transferred to
heat upon impact of the
workpiece and cuts a perfect
hole at the weld joint. Molten
metal fills in behind the beam,
• The electron beam stream and
workpiece are manipulated by
means of precise, computer
driven controls, within a vacuum
welding chamber, therefore
eliminating oxidation,
contamination.
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• How an Electron Beam Machine Works
The EB system is composed of an
electron beam gun, a power supply,
control system, motion equipment and
vacuum welding chamber. Fusion of base
metals eliminates the need for filler metals.
The vacuum requirement for operation of
the electron beam equipment eliminates
the need for shielding gases and fluxes.
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ELECTRON BEAM WELDING
Slide 15 of 18
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ELECTRON BEAM WELDING
Slide 16 of 18
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Electron Beam Welding
• Electron Beam Welding joins ferrous metals, light
metals, precious metals, and alloys, to themselves or
each other.
• Multi-axis EB control
• High ratio of depth-to-width
• Maximum penetration with minimal distortion
• Exceptional weld strength
• Ability to weld components up to 10 feet in diameter
• High precision and repeatability with virtually 0% scrap
• Versatility from .002" depth to 3.00" depth of
penetration
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Electron Beam Welding Facts
• Electron Beam Welding Advantages
• Maximum amount of weld penetration with the least amount of heat
input reduces distortion
• Electron beam welding often reduces the need for secondary
operations
• Repeatability is achieved through electrical control systems
• A cleaner, stronger and homogeneous weld is produced in a
vacuum
• The electron beam machine's vacuum environment eliminates
atmospheric contaminates in the weld
• Exotic alloys and dissimilar materials can be welded
• Extreme precision due to CNC programming and magnification of
operator viewing
• Electron beam welding frequently yields a 0% scrap rate
• The electron beam process can be used for salvage and repair of
new and used components
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Electron Beam Welding Speeds/Depth of Penetration
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• Electron Beam
Welding
Limitations
• The necessity of an
electron beam
welding vacuum
chamber limits the
size of the workpiece
— EBTEC's
maximum chamber
size is 11' 4" wide x
9' 2" high x 12' deep
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Electron Beam Welding Speeds/Depth of Penetration
385
LASER BEAM WELDING(LBW)
• LASER- Light Amplification by Stimulated
Emission of Radiation
• Focusing of narrow monochromatic light into
extremely concentrated beams (0.001 mm even)
• Used to weld difficult to weld materials, hard to
access areas, extremely small components, In
medical field to weld detached retinas back into
place
• Laser Beam- coherent
Laser production- complex process.
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The LASER, an
acronym for "Light
Amplification by
Stimulated Emission
of Radiation," is a
device that produces
a concentrated,
coherent beam of
light by stimulating
molecular or
electronic transitions
to lower energy
levels, causing the
emission of photons.
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Al2O3 + 0.05% Chromium
• solid state RubyLaser- Neon flash tube emits light
into specially cut ruby crystals- absorbs light electrons of chromium atoms get stimulated• Increase in stimulation ---- electrons increase from
normal(ground) orbit to an exited orbit. More
energy input- energy absorbed exceeds thermal
energy- no longer to heat energy.
• Electrons drop back to intermediate orbit- emits
PHOTONS (light) called spontaneous emission
• With continued emission, released photons
stimulate other exited electrons to release photonscalled stimulated emission
• Causes exited electrons to emit photons of same
wave length. Dr. N. RAMACHANDRAN, NITC
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388
• Power intensities > 10 kw/cm2
• No physical contact between work and welding
equipment
• 2 mirrors- coherent light reflected back and forth,
becomes dense, penetrates partially reflective mirror,
focused to the exact point
• Very little loss of beam energy
• Solid state, liquid, semiconductor and gas lasers used.
• Solid state uses light energy to stimulate electrons
Ruby, Neodymium, YAG
• Gas lasers use electrical charge to stimulate electrons
Gas lasers- higher wattage outputs. Used for thicker
sections - CO2, N2, He
• 7/7/2015
Liquid- nitrobenzene;
Gas- based on gallium arsenide
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Laser Welding Facts
• Laser Welding Advantages
• Processes high alloy metals without difficulty
• Can be used in open air
• Can be transmitted over long distances with a
minimal loss of power
• Narrow heat affected zone
• Low total thermal input
• Welds dissimilar metals
• No filler metals necessary
• No secondary finishing necessary
• Extremely accurate
• Welds high alloy metals without difficulty
• CO2 Laser Welding Speeds
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• The solid-state laser utilizes a single
crystal rod with parallel, flat ends. Both
ends have reflective surfaces. A highintensity light source, or flash tube
surrounds the crystal. When power is
supplied by the PFN (pulse-forming
network), an intense pulse of light
(photons) will be released through one end
of the crystal rod. The light being released
is of single wavelength, thus allowing for
minimum divergence
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• One hundred percent of the laser light will be
reflected off the rear mirror and thirty to fifty
percent will pass through the front mirror,
continuing on through the shutter assembly to
the angled mirror and down through the focusing
lens to the workpiece.
• The laser light beam is coherent and has a high
energy content. When focused on a surface,
laser light creates the heat used for welding,
cutting and drilling.
• The workpiece and the laser beam are
manipulated by means of robotics. The laser
beam can be adjusted to varying sizes and heat
intensity from .004 to .040 inches. The smaller
size is used for cutting, drilling and welding and
the larger, for heat treating
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Laser Welding Limitations
• Rapid cooling rate may cause
cracking in certain metals
• High capital cost
• Optical surfaces easily damaged
• High maintenance cost
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LASER WELDING
Slide 17 of 18
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LASER WELDING
Slide 18 of 18
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Laser beam cutting
•
Along with beam, oxygen used to help
cutting. Ar, He, N, CO2 also for steel, alloys
etc.
Two ways to weld
1. Work piece rotated or moved past beam
2. Many pulses of laser (10 times/sec)used.
Narrow HAZ., speeds of 40 mm/sec to 1.5 m/sec
Cooling system to remove the heatgas and liquid cooling used
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• Klyston tubes (glass to metal sealing),
capacitor bank, triggering device, flash
tube, focusing lens, etc. in the setup.
• Cathode of molybdenum, tantalum or
titanium used.
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1987
Laser research begins a unique method for depositing complex
metal alloys (Laser Powder Fusion).
2002
 From Linde Gas in Germany, a Diode laser using process gases
and "active-gas components" is investigated to enhance the "keyholing" effects for laser welding. The process gas, Argon-CO2,
increases the welding speed and in the case of a diode laser, will
support the transition of heat conductivity welding to a deep
welding, i.e., 'key-holing'. Adding active gas changes the direction
of the metal flow within a weld pool and produces narrower, highquality weld.
 CO2 Lasers are used to weld polymers. The Edison Welding
Institute is using through-transmission lasers in the 230-980 nm
range to readily form welded joints. Using silicon carbides
embedded in the surfaces of the polymer, the laser is capable of
melting
the material leaving
a near invisible joint line.
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Soldering and Brazing
•Soldering and Brazing are joining
processes where parts are
joined without melting the base
metals.
•Soldering filler metals melt
below 450 °C.
•Brazing filler metals melt
above 450 °C.
(De)soldering a contact from a wire
•Soldering is commonly used for electrical connection or
mechanical joints, but brazing is only used for mechanical
joints due to the high temperatures involved
Soldering
• A method of joining metal parts using an alloy of
low melting point (solder) below 450 °C (800 °F).
• Heat is applied to the metal parts, and the alloy
metal is pressed against the joint, melts, and is
drawn into the joint by capillary action and
around the materials to be joined by 'wetting
action'.
• After the metal cools, the resulting joints are
not as strong as the base metal, but have
adequate strength, electrical conductivity, and
water-tightness for many uses.
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Soldering and Brazing Benefits
•
•
•
•
•
•
Economical for complex assemblies
Joints require little or no finishing
Excellent for joining dissimilar metals
Little distortion, low residual stresses
Metallurgical bond is formed
Sound electrical component connections
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Soldering can be done in a number of
ways
Including passing parts over a bulk container of melted
solder, using an infrared lamp, or by using a point
source such as an electric soldering iron, a brazing
torch, or a hot-air soldering tool.
A flux is usually used to assist in the joining process.
Flux can be manufactured as part of the solder in single
or multi-core solder, in which case it is contained
inside a hollow tube or multiple tubes that are
contained inside the strand of solder.
Flux can also be applied separately from the solder,
often in the form of a paste.
In some fluxless soldering, a forming gas that is a
reducing atmosphere rich in hydrogen can also serve
much the same purpose as traditional flux, and
provide the benefits of traditional flux in re-flow ovens
through which electronic parts placed on a circuit
card are transported
for a carefully timed period of 402
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time.
• One application of
soldering is making
connections between
electronic parts and
printed circuit boards.
• Another is in plumbing.
Joints in sheet-metal
objects such as cans
for food, roof flashing,
and drain gutters were
also traditionally
soldered.
• Jewelry and small
mechanical parts are
often assembled by
soldering.
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Soldering can
also be used as a
repair technique
to patch a leak in
a container or
cooking vessel.
403
• Soldering is distinct from welding in that
the base materials to be joined are not
melted, though the base metal is dissolved
somewhat into the liquid solder much as a
sugar cube into coffee - this dissolution
process results in the soldered joint's
mechanical and electrical strengths.
• A "cold solder joint" with poor properties
will result if the base metal is not warm
enough to melt the solder and cause this
dissolution process to occur.
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• Due to the dissolution of the base metals into the
solder, solder should never be reused
• Once the solder's capacity to dissolve base
metal has been achieved, the solder will not
properly bond with the base metal and a cold
solder joint with a hard and brittle crystalline
appearance will usually be the result.
• It is good practice to remove solder from a joint
prior to resoldering - desoldering wicks or
vacuum desoldering equipment can be used.
• Desoldering wicks contain plenty of flux that will
lift the contamination from the copper trace and
any device leads that are present. This will leave
a bright, shiny, clean
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• The lower melting point of solder
means it can be melted away from the
base metal, leaving it mostly intact
through the outer layer.
• It will be "tinned" with solder.
• Flux will remain which can easily be
removed by abrasive or chemical
processes.
• This tinned layer will allow solder to
flow into a new joint, resulting in a new
joint, as well as making the new solder
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flow very quickly
and easily.
Common joining problems and
discontinuities:
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No wetting
Excessive wetting
Flux entrapment
Lack of fill (voids, porosity)
Unsatisfactory surface appearance
Base metal erosion
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• Basic electronic soldering techniques
All solder pads and device terminals must be clean for
good wetting and heat transfer.
The soldering iron or gun must be clean, otherwise
components may heat up excessively due to poor heat
transfer.
The devices must then be mounted on the circuit board
properly.
One technique is to elevate the components from the board
surface (a few millimeters) to prevent heating of the
circuit board during circuit operation.
After device insertion, the excess leads can be cut leaving
only a length equal to the radius of the pad.
Plastic mounting clips or holders are used for large devices
to reduce mounting stresses.
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• Heat sink the leads of sensitive devices to prevent heat
damage.
• Apply soldering iron or gun to both terminal lead and
copper pad to equally heat both.
• Apply solder to both lead and pad but never directly to the
tip of soldering iron or gun.
• Direct contact will cause the molten solder to flow over the
gun and not over the joint.
• The moment the solder melts and begins to flow, remove
the solder supply immediately.
• Do not remove the iron yet. The remaining solder will then
flow over the junction of the lead and pad, assuming both
are free of dirt.
• Let the iron heat the junction until the solder flows and then
remove the iron tip. This will ensure a good solid junction.
• Remove the iron from the junction and let the junction cool.
Solder flux will remain
and should NITC
be removed.
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• Be sure not to move the joint while it is cooling.
Doing so will result in a fractured joint.
• Do not blow air onto the joint while it is cooling;
Instead, let it cool naturally, which will occur fairly
rapidly.
• A good solder joint is smooth and shiny. The lead
outline should be clearly visible. Clean the soldering
iron tip before you begin on a new joint. It is
absolutely important that the iron tip be free of
residual flux.
• Excess solder should be removed from the tip. This
solder on the tip is known as keeping the tip tinned.
It aids in heat transfer to the joint.
• After finishing all of the joints, remove excess flux
residue from the board using alcohol, acetone, or
other organic solvents.
• Individual joints can be cleaned mechanically.
• The flux film fractures easily with a small pick and
can be blown away
with canned air.
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• In solder formulations with water-soluble fluxes,
• Traditional solder for electronic joints is a
60/40 Tin/Lead mixture with a rosin based
flux that requires solvents to clean the
boards of flux.
• Environmental legislation in many countries, and
the whole of the European Community area,
have led to a change in formulation.
• Water soluble non-rosin based fluxes have been
increasingly used since the 1980's so that
soldered boards can be cleaned with water or
water based cleaners. This eliminates
hazardous solvents from the production
environment, and
effluent.
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Lead-free electronic soldering
• More recently environmental legislation
has specifically targeted the wide use of
lead in the electronics industry. The
directives in Europe require many new
electronic circuit boards to be lead free by
1st July 2006, mostly in the consumer
goods industry, but in some others as well.
• Many new technical challenges have
arisen, with this endeavour.
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• For instance, traditional lead free solders have a
significantly higher melting point than lead based
solders, which renders them unsuitable for use with heat
sensitive electronic components and their plastic
packaging. To overcome this problem solder alloys with
a high silver content and no lead have been developed
with a melting point slightly lower than traditional solders.
• Not using lead is also extended to components pins and
connectors. Most of those pins were using copper
frames, and either lead, tin, gold or other finishes. Tinfinishes is the most popular of lead-free finishes.
However, this poses nevertheless the question of tinwhiskers. Somehow, the current movement brings the
electronic industry backs to the problems solved 40
years ago by adding lead.
• A new classification to help lead-free electronic
manufacturers decide what kind of provisions they want
to take against whiskers, depending upon their
application criticity.
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Stained glass soldering
• Historically soldering tips were copper, placed in
braziers. One tip was used; when the heat had
transferred from the tip to the solder (and depleted the
heat reserve) it was placed back in the brazier of
charcoal and the next tip was used.
• Currently, electric soldering irons are used; they consist
of coil or ceramic heating elements, which retain heat
differently, and warm up the mass differently, internal or
external rheostats, and different power ratings - which
change how long a bead can be run.
• Common solders for stained glass are mixtures of tin
and lead, respectively:
• 60/40: melts between 361°-376°F
• 50/50: melts between 368°-421°F
• 63/37: melts between 355°-365°F
• lead-free solder (useful in jewelry, eating containers, and
other environmental uses): melts around 490°F
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Pipe/Mechanical soldering
• Sometimes it is necessary to use solders of different melting points
in complex jobs, to avoid melting an existing joint while a new joint is
made.
• Copper pipes used for drinking water should be soldered with a
lead-free solder, which often contains silver. Leaded solder is not
allowed for most new construction, though it is easier to create a
solid joint with that type of solder. The immediate risks of leaded
solder are minimal, since minerals in municipal or well water
supplies almost immediately coat the inside of the pipe, but lead will
eventually find its way into the environment.
• Tools required for pipe soldering include a blowtorch (typically
propane), wire brushes, a suitable solder alloy and an acid paste
flux, typically based on zinc chloride. Such fluxes should never be
used on electronics or with electronics tools, since they will cause
corrosion of the delicate electronic part.
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Soldering defects
• Soldering defects are solder joints that are not soldered
correctly.
• These defects may arise when solder temperature is too low.
• When the base metals are too cold, the solder will not flow and
will "ball up", without creating the metallurgial bond.
• An incorrect solder type (for example, electronics solder for
mechanical joints or vice versa) will lead to a weak joint.
• An incorrect or missing flux can corrode the metals in the joint.
Without flux the joint may not be clean.
• A dirty or contaminated joint leads to a weak bond. A lack of
solder on a joint will make the joint fail.
• An excess of solder can create a "solder bridge" which is a
short circuit. Movement of metals being soldered before the
solder has cooled will make the solder appear grainy and may
cause a weakened joint.
• Soldering defects in electronics can lead to short circuits, high
resistance in the joint, intermittent connections, components
overheating, and damaged circuit boards. Flux left around
integrated circuits' leads will lead to inter-lead leakage.
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mount components
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Dr. N. RAMACHANDRAN,
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improper device operation as moisture absorption rises. In
Soldering processes
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Wave soldering
Reflow soldering
Infrared soldering
Induction soldering
Ultrasonic soldering
Dip soldering
Furnace soldering
Iron soldering
Resistance soldering
Torch soldering
Silver soldering/Brazing
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Brazing
• Is similar to soldering but uses higher melting
temperature alloys, based on copper, as the filler metal.
• "Hard soldering", or "silver soldering" (performed with
high-temperature solder containing up to 40% silver) is
also a form of brazing, and involves solders with melting
points above 450 C. Even though the term "silver
soldering" is more often used than silver brazing, it is
technically incorrect.
• Since lead used in traditional solder alloys is toxic, much
effort in industry has been directed to adapting soldering
techniques to use lead-free alloys for assembly of
electronic devices and for potable water supply piping.
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Brazing
• Brazing is a joining process whereby a non-ferrous filler
metal and an alloy are heated to melting temperature
(above 450°C;) and distributed between two or more
close-fitting parts by capillary action.
• At its liquid temperature, the molten filler metal interacts
with a thin layer of the base metal, cooling to form an
exceptionally strong, sealed joint due to grain structure
interaction. T
• he brazed joint becomes a sandwich of different layers,
each metallurgically linked to each other.
• Common brazements are about 1/3 as strong as the
materials they join, because the metals partially dissolve
each other at the interface, and usually the grain
structure and joint alloy is uncontrolled.
• To create high-strength brazes, sometimes a brazement
can be annealed, or cooled at a controlled rate, so that
the joint's grain structure and alloying is controlled.
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• In Braze Welding or Fillet Brazing, a bead of
filler material reinforces the joint. A braze-welded
tee joint is shown here.
• In another common specific similar usage,
brazing is the use of a bronze or brass filler rod
coated with flux, together with an oxyacetylene
torch, to join pieces of steel. The American
Welding Society prefers to use the term Braze
Welding for this process, as capillary attraction
is not involved, unlike the prior silver brazing
example.
• Braze welding takes place at the melting
temperature of the filler (e.g., 870 °C to 980 °C
for bronze alloys) which is often considerably
lower than the melting point of the base material
(e.g., 1600 °C for mild steel).
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• A variety of alloys of metals, including silver, tin,
zinc, copper and others are used as filler for
brazing processes.
• There are specific brazing alloys and fluxes
recommended, depending on which metals are
to be joined. Metals such as aluminum can be
brazed though aluminum requires more skill and
special fluxes. It conducts heat much better than
steel and is more prone to oxidation.
• Some metals, such as titanium cannot be brazed
because they are insoluble with other metals, or
have an oxide layer that forms too quickly at
intersoluble temperatures.
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• Although there is a popular belief that brazing is
an inferior substitute for welding, this is false.
• For example, brazing brass has a strength and
hardness near that of mild steel, and is much
more corrosion-resistant.
• In some applications, brazing is indisputably
superior. For example, silver brazing is the
customary method of joining high-reliability,
controlled-strength corrosion-resistant piping
such as a nuclear submarine's seawater coolant
pipes.
• Silver brazed parts can also be precisely
machined after joining, to hide the presence of
the joint to all but the most discerning observers,
whereas it is nearly impossible to machine welds
having any residual slag present and still hide
joints.
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• In order to work properly, parts must be closely fitted
and the base metals must be exceptionally clean and
free of oxides for achieving the highest strengths for
brazed joints.
• For capillary action to be effective, joint clearances
of 0.002 to 0.006 inch (50 to 150 µm) are
recommended. In braze-welding, where a thick bead
is deposited, tolerances may be relaxed to 0.5 mm.
• Cleaning of surfaces can be done in several ways.
Whichever way is selected, it is vitally important to
remove all grease, oils, and paint. For custom jobs
and part work, this can often be done with fine sand
paper or steel wool.
• In pure brazing (not braze welding), it is vitally
important to use sufficiently fine abrasive. Coarse
abrasive can lead to deep scoring that interferes with
capillary action and final bond strength. Residual
particulates from sanding should be thoroughly
cleaned from pieces.
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In assembly line Dr.
work,
a "pickling
N. RAMACHANDRAN,
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423
to dissolve oxides chemically. Dilute sulfuric acid is
• In most cases, flux is required to prevent oxides from
forming while the metal is heated. The most common
fluxes for bronze brazing are borax-based. T
• he flux can be applied in a number of ways. It can be
applied as a paste with a brush directly to the parts to be
brazed. Commercial pastes can be purchased or made
up from powder combined with water (or in some cases,
alcohol). Alternatively, brazing rods can be heated and
then dipped into dry flux powder to coat them in flux.
• Brazing rods can also be purchased with a coating of
flux. In either case, the flux flows into the joint when the
rod is applied to the heated joint. Using a special torch
head, special flux powders can be blown onto the
workpiece using the torch flame itself.
• Excess flux should be removed when the joint is
completed. Flux left in the joint can lead to corrosion.
• During the brazing process, flux may char and adhere to
the work piece. Often this is removed by quenching the
still-hot workpieceDr.inN.water
(to loosen the flux scale), 424
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followed by wire brushing the remainder.
• Brazing is different from welding, where
even higher temperatures are used, the base
material melts and the filler material (if used at all)
has the same composition as the base material.
• Given two joints with the same geometry, brazed
joints are generally not as strong as welded joints.
Careful matching of joint geometry to the forces
acting on the joint, however, can often lead to very
strong brazed joints.
• The butt joint is the weakest geometry for tensile
forces. The lap joint is much stronger, as it resists
through shearing action rather than tensile pull and
its surface area is much larger. To get joints roughly
equivalent to a weld, a general rule of thumb is to
make the overlap equal to 3 times the thickness of
the pieces of metal being joined.
• The "welding" of cast iron is usually a brazing
operation, with a filler rod made chiefly of nickel
being used although
true welding with cast iron rods
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is also available.
• Vacuum brazing is another materials joining technique,
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one that offers extremely clean, superior, flux free braze joints while
providing high integrity and strength.
The process can be expensive because it is performed inside a
vacuum chamber vessel however, the advantages are significant.
For example, furnace operating temperatures, when using
specialized vacuum vessels, can reach temperatures of 2400 °C.
Other high temperature vacuum furnaces are available ranging from
1500 °C and up at a much lesser cost.
Temperature uniformity is maintained on the work piece when
heating in a vacuum, greatly reducing residual stresses because of
slow heating and cooling cycles.
This, in turn, can have a significant impact on the thermal and
mechanical properties of the material, thus providing unique heat
treatment capabilities.
One such capability is heat treating or age hardening the work piece
while performing a metal-joining process, all in a single furnace
thermal cycle.
Reference: M.J.Fletcher, “Vacuum Brazing”. Mills and Boon
Limited: London, 1971.
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Advantages over welding
• The lower temperature of brazing and brass-welding is less
likely to distort the work piece or induce thermal stresses.
For example, when large iron castings crack, it is almost
always impractical to repair them with welding. In order to
weld cast-iron without recracking it from thermal stress, the
work piece must be hot-soaked to 1600 °F. When a large
(more than fifty kilograms (100 lb)) casting cracks in an
industrial setting, heat-soaking it for welding is almost
always impractical. Often the casting only needs to be
watertight, or take mild mechanical stress. Brazing is the
premium, preferred repair method in these cases.
• The lower temperature associated with brazing vs. welding
can increase joining speed and reduce fuel gas
consumption.
• Brazing can be easier for beginners to learn than welding.
• For thin workpieces (e.g., sheet metal or thin-walled pipe)
brazing is less likely to result in burn-through.
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• Brazing can also be a cheap and effective technique
for mass production. Components can be assembled
with preformed plugs of filler material positioned at
joints and then heated in a furnace or passed
through heating stations on an assembly line. The
heated filler then flows into the joints by capillary
action.
• Braze-welded joints generally have smooth
attractive beads that do not require additional
grinding or finishing.
• The most common filler materials are gold in
colour, but fillers that more closely match the
color of the base materials can be used if
appearance is important.
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Possible problems
• A brazing operation may cause defects in the
base metal, especially if it is in stress. This can
be due either to the material not being properly
annealed before brazing, or to thermal
expansion stress during heating.
• An example of this is the silver brazing of
copper-nickel alloys, where even moderate
stress in the base material causes intergranular
penetration by molten filler material during
brazing, resulting in cracking at the joint.
• Any flux residues left after brazing must be
thoroughly removed; otherwise, severe
corrosion may eventually occur.
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Brazing processes
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Block Brazing
Diffusion Brazing
Dip Brazing
Exothermic Brazing
Flow Brazing
Furnace Brazing
Induction Brazing
Infrared Brazing
Resistance Brazing
Torch Brazing
Twin Carbon Arc Brazing
Vacuum Brazing
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