Transcript WELDING/BRAZING/TORCH - Area10FFA

ELECTRIC ARC / WIRE
WIRE WELDING
ARC/WIRE WELDING
OBJECTIVES
I can identify the main parts of the arc welding
process.
I can associated the terms with welding.
I can describe the difference between AC, DC
power input
I can compare and contrast transformers,
rectifiers and AC welding equipment.
I can identify electrodes and their application
I can identify welding equipment, positions and
equipment.
WELDING BASIC
WORK ANGLE
TRAVEL ANGLE
SMAW
SMAW is the AWS name used by the American
Welding Society for Shielded Metal Arc Welding.
Stick is the most commonly used name for
SMAW. This is because the electrode resembles
a stick. It is also, often referred to as manual
welding.
The SMAW process uses constant current power
sources.
SMAW is the most widely used arc welding
process in the world.
All electrode polarities are used: DC-, DC+ and
AC
SMAW PROCESS
SMAW is a process in which an electric arc is
established between the electrically grounded
work piece and a 9”-18” length of covered
consumable metal rod, called the electrode.
The heat of the arc melts the base metal in the
immediate area, the electrode’s metal core, and
any metallic elements in the coating of the
electrode.
It also melts, vaporizes or breaks down
chemically non-metallic substances in the
coating to shield the arc, protect the weld, and
add alloys or properties to the weld deposit
Terms:
Arc-flow of current across a small gap
Base Metal -metal to be welded to
Bead --Weld made by one pass of the
electrode
Crater --depression at the end of the weld
Penetration --depth of weld into the base
metal
Bevel --cutting the edge of the metal at an
angle
Welding --joining of two or more metal by
fusion
TERMS
Electrode --Metal wire or rod covered
with a chemical coating
Flux --Chemical coating to protect the
bead, can be a solid or gas.
Speed --how fast you are traveling.
Slag --left over carbon on a bead
made by an arc welder. Protects and
cools the bead.
Summary of Shielded Metal
Arc Welding—Why Do IT?
SMAW welding has grown tremendously in
popularity due to all of its advantages
It is still the most popular welding process in North
America.
SMAW is the most difficult welding process in
which to train welders, but it is the foundation of
electric arc welding processes.
The equipment is fairly basic and inexpensive
comparatively to any other arc welding process.
A wide variety of base materials, including both
ferrous and non-ferrous, can be welded using the
SMAW process along with a variety of applications
including sheet metal and thick sections of
material.
Summary of Shielded Metal Arc
Welding—Why Do IT? 2
The process produces a protective
slag that will need to be removed for
cleanliness and to prevent slag
inclusions in multiple pass welds.
The process also produces spatter,
which is a visual defect. However,
the spatter can be easily removed
with a grinder.
ARC WELDING
There are several advantages to SMAW.
Low Start Up Costs - SMAW welding machines are relativity
inexpensive
Portability - SMAW is a very portable process because it does not
require any external shielding gas and equipment due to the
ability of the electrode to produce its own shielding gases.
Outdoor Weldability - SMAW welding can be done outdoors. The
shielding of the weld puddle from the coating of the electrode is
not susceptible to winds and draft, and therefore, is an excellent
choice for outdoor welding.
All Position Welding - SMAW can be done in all welding positions,
which eliminates the need for expensive fixtures or manipulation
of the part being welded.
Variety of Materials - Many base materials and alloys can be
welded with the SMAW process.
DISADVANTAGES
Low Efficiency - The efficiency of a SMAW electrode can be
defined as the percentage of the electrode that is consumed
and becomes part of the weld. SMAW electrodes are 60%65% efficient. The primary reason for this low efficiency is
stub loss, or the portion of the electrode that is unused and
discarded. .
Operating Factor - Operating factor can be defined as the
amount of arc on time in a shift of work, labeled as a
percentage. SMAW welding has an operating factor of
approximately 25% - 30%--workday is spent arc welding.
Restarts - SMAW electrodes are only 9”-18” in length. When
the electrode is consumed in the arc, it needs to be replaced
with a new one. This means that welding stops, and time is
taken to replace each electrode.
Operator Skill - SMAW welding requires a high level of
operator skill. This process is one of the hardest arc welding
processes to learn.
Slag & Spatter .
Welding Equipment
Welders
AC (Alternating Current)--Current alternates
direction, between positive & negative.
DC (Direct Current)--Current flows in one
direction
a. DC Positive (STRAIGHT)
– Electrode negative, work positive
b. DC Negative(REVERSE)
– Electrode positive, work negative
AC/DC Rectifiers
TRANSFORMER
The transformer in a power supply is a step-down
transformer that takes high-voltage, low-amperage
AC input supplied from power companies and
changes it to low-voltage, high-amperage AC welding
current.
For example, your input power may be 230 volts on a
50-amp branch circuit. This voltage is much too high
and the amperage is much too low for welding
applications.
The transformer takes this condition and reverses it to
a much lower voltage, in the range of 13-45 volts
(most applications 15-35 volts) and increases the
amperage to a much higher level appropriate for
welding.
RECTIFIER
In power supplies that deliver DC and/or AC and DC current to
the arc, there needs to be a device that changes this now lowvoltage, high-amperage AC into DC.
This device is called a rectifier. A rectifier converts AC to DC.
They are very efficient and very reliable.
A rectifier is a device that allows current to flow in only one
direction.
If we remember the path that alternating current takes, it takes
one of a sine wave path. This represents one cycle in which
current flows in one direction for ½ of the cycle, stops at the
zero line, and reverses it’s direction of flow for the other ½
cycle. This cycle repeats itself over and over again at a
frequency of 60 Hz or 60 times a second in the United States.
A rectifier does not allow current to reverse itself. It only
allows current to flow in one direction. In essence, it directs
current in the same direction rather that allowing it to change
direction. This is called direct current of DC. The direction of
current flow determines whether the polarity is DC+ or DC-.
DUTY CYCLE
The duty cycle of a power source is the
percentage of a ten-minute period that it
operates at its rated output current setting.
If a power source is rated at 300 amps at a 60%
duty cycle, it means that the machine can be
operated safely at 300 amps welding current for
6 out of every 10 minutes.
If this duty cycle is reduced in actual operation,
the maximum permissible current is increased.
Thus, at a 35% duty cycle, this same 300 amp
power source could be operated at 375 amps
Direct Current Electrode Negative
(Straight)
A rectifier allows current to flow in one direction only.
The direction of the current flow determines the
DC polarity.
DC- or direct current electrode negative is the
arrangement of direct current arc welding
cables/leads in which the electrode is the negative
pole and the workpiece is the positive pole of the
welding arc.
When using DC- polarity, the majority of the heat is
directed at the electrode.
The electrodes designed for DC- polarity produce
weld deposits with shallow penetration. Primary
applications are fast travel speeds on sheet metal.
Direct Current Electrode
Positive (Reverse)
DC+ or direct current electrode positive is the
opposite of DC- or direct current electrode
negative.
In this case, the electrode is the positive pole and
the workpiece is the negative pole.
When using DC+ polarity, the majority of the heat
is directed at the work piece.
The electrodes designed for DC+ polarity produce
weld deposits with deep penetration.
Primary applications are for pipe welding, general
purpose and maintenance welding, deep
penetration applications, and on base material with
surface contaminants.
STRAIGHT
POLARITY DC—ELECTRODE
IS NEGATIVE;
WORK IS
POSITIVE
REVERSE
POLARITY
DC+ —
ELECTRODE
IS POSITIVE;
WORK IS
NEGATIVE
Effect of Polarity on Welds
Alternating Current
Alternating current is a current that reverses
regularly in recurring intervals of time 1/120th
(60Hz) of a second..
AC is the type of power used in the United States
as the standard for input power to run any
electrical equipment or apparatus. It has
alternating positive and negative values. In other
words, it switches from DC+ to DC-, and it
switches back and forth very rapidly.
An AC sine wave and the frequency of current flow
through one sine wave is 60 Hz or 60 times a
second in the U.S.
Comparison of Penetration
Contours
Equipment
Electrode holder—holds the rods
Ground clamp
Amp Adjustment--sets the heat to adjust the
penetration.
– Greater the heat, the more penetration
– Usually 110-125 amps
Helmet--Number 10 lens—Eye protection
– Flip down or automatic
Leather Gloves
Chipping Hammer--remove the slag
Wire Brush--Cleans the metal
LENS NUMBERS
Filter plates come in varying shades.
The shade required depends on the maximum
amount of amperage to be used.
The recommended shade number for SMAW is 10
or 11. The lowest shade number recommended is
a shade 7.
To determine the correct shade to use, start with
the darkest shade number. If it is difficult to see
the arc, reduce the shade number by one and so
on until the appropriate shade is found to provide
both shielding and visibility of the welding arc.
Electrode Holders/ Chipping
Hammer
Welding Positions
Sit or Stand in a relax position
Weld with both hand
Move across your body.
Right handed person—Left to right.
Lean electrode to the right a little bit
Start Arc by
Tapping
Scratching.
Move electrode either in circles or half moon
Adjusting the Current
Heat is adjusted by:
Thickness of metal
Size of Electrode
Speed of Travel
Position of weld
Bead should have deep and even
penetration.
Molten Puddle
When welding—watch your bead, not ahead
of the arc.
Molten Puddle should tell you:
1—Width of bead
2—Depth of penetration
3—Height of bead
Flux
Used Around the Electrode
Purposes:
Forms a gaseous shield
Gathers impurities
Keep weld from cooling to fast
Stabilizers and directs the arc.
Wire Welding—this is the argon/carbon
dioxide gas
ELECTRODE HOLDER
Electrode holders are also rated at a given amperage and
duty cycle similar to power supplies.
The EH 200, EH 300, and EH 400. Each are rated at 200
amps, 300 amps, and 400 amps respectively.
The primary function of the electrode holder is to hold the
electrode and to provide electrical contact of the electrode to
the work piece while insulating the operator and the jaws
from the power supply and from the work piece.
Copper jaws provide the best electrical contact.
The large insulated handle is designed for operator comfort.
Insulated jaws prevent accidental grounding. Jaws open
wide for quick release of electrode stubs.
The positive grip handle remains cool after steady welding
at rated current and is impact resistant for long life.
WORK CLAMPS
Work clamps are also rated at a given amperage
and duty cycle. The GC 300 and GC 500 are
rated at 300 amps and 500 amps respectively.
The work clamp completes the electrical circuit
from the electrode as it strikes the arc either to or
from the power supply. This depends upon
welding polarity.
A heavy spring tightly clamps the jaws to promote
positive electrical contact with the work piece.
Work clamps provide for quick connection to the
work piece. They have easy operation. Just
squeeze, slip the jaws over the work and let go.
The jaws open to a full 2 ½” (63mm).
CABLES
The ground cable from the power source to the
electrode carries current to the electrode and
from the arc to the workpiece and back to the
power source. These conductors are very
important to the efficiency of welding as well as
the arc characteristics or vice-versa depending
upon welding polarity.
Cables must also be the proper size to deliver the
appropriate amount of current to the welding arc.
Sizing of the cable is also dependent upon the
length of cable being used.
The conductors in the welding cable are made up
of strands of copper or aluminum. The cables are
wrapped in a paper wrapping. Next, rubber
insulates and covers the jacket wrapping. The
paper wrapping is for cable flexibility.
Electrode
A.
B.
C.
Carries Current to the Metal
Small end goes into electrode holder.
Identification of Electrode, Example 6013
1st 2 numbers (60) strength in 10,000 psi---60,000 psi
3rd number (1) Welding Position
1—All position-flat, horizontal, vertical, overhead.
2—Flat & horizontal
3—Flat
Last two number—chemical makeup of the flux, that
determines polarity, AC or DC
10—DC Reverse
11—AC/DC Reverse
12—DC Straight
13—AC/DC Straight
14—DC either polarity
15—Low Hydrogen
16—AC/DC Reverse.
SMAW - AWS Classification
The American Welding Society or AWS sets guidelines
for SMAW electrodes with which manufacturers have to
comply.
These guidelines include chemistry and mechanical
properties, and usability tests.
Each letter and digit stands for something very specific.
The E stands for electrode. AWS defines an electrode
as the current carrying device, not necessarily the
consumable that becomes the weldment. In the case of
SMAW, the electrode core is consumed as well as any
metallic elements in the coating to become the weld
deposit.
The 70 stands for minimum tensile strength in 10,000
psi. The weld deposit made by this SMAW electrode
must consistently meet a minimum tensile strength
requirement of 70,000 pounds per square inch (psi).
SMAW - AWS Classification
The next digit is either a 1 or a 2 and indicates
welding position.
A “1” indicates that the electrode is an all
position electrode-- (flat, horizontal, vertical up,
vertical down, and overhead).
While the 2 stands for welds that can only be
made in the flat/horizontal position.
The 3rd and 4th digit combined indicates the
type of current the electrode operates on and
the type of coating.
ELECTRODE ANGLE
Electrode angle can also affect the weld bead profile.
When welding a fillet weld, the electrode should be held in
the weld joint at approximately a 45 angle from the
horizontal base plate.
The travel angle will be a drag angle of approximately 1520. The electrode is then dragged down the weld joint at
the appropriate travel speed.
Travel speed is determined by the size of the electrode
being used, the type of electrode, the welding amperage
and the desired weld bead size and shape.
If the electrode angle is too severe and exceeds the
recommended 45, the weld will favor the horizontal plate
and inadequate fusion can take place, and perhaps burn
through on the bottom plate. The opposite effect can occur
for too small of an electrode angle of the electrode in the
weld joint.
STARTING THE ARC
When starting the arc, strike the electrode
like a match on the work surface by gently
and quickly moving it along the weld metal.
Next, withdraw the electrode to form an arc
length from the work piece of approximately
1/8”.
Reduce the arc length to the approximate
length required to produce the desired
weld.
ARC LENGTH
Arc length is arc voltage.
As the arc length is shortened, the arc voltage is
lowered. If the arc length is too close to the work
piece, the arc will go out or create a dead short. In
this situation, the voltage drops to 0 and the
amperage rises significantly. This may cause the
coating on the electrode to break down or even
catch on fire if it has an organic coating.
Arc length is dependent upon the type of electrode
used. Arc length can vary in height from just a drag
to 3/16” distance from the work piece.
Too long of an arc length will cause the arc to go
out. This situation is called a “pop out”.
DETERMING THE AMPERAGE
When determining electrode amperages, be sure
to consider:
Position of the weld.
Thickness of the weld metal.
The type of joint being fabricated.
Diameter of core wire will be another variable to
consider - when determining electrode
amperages.
The polarity will determine the actual amperage
setting.
Causes of Difficulties
Welder or metal is improper grounded
Improver electrode contact
Electrode is placed to high in electrode holder
Flux is Chipped on end.
Burn end off
Wrong Amps
Heat seating is too high or low
Adjust.