Transcript Motorsports Welding - College of Engineering Resources

Motorsports Welding
Tig and Mig welding
By: Luke Woroniecki
Table of Contents
•
•
•
•
•
•
•
•
•
Welding Certification and Qualification
Codes
Safety
Cutting Processes
Welding Processes
Weld Joint Geometry and Welding Symbols
Welding Metallurgy
Welding Discontinuities
Inspection and NDE
Certification
• Certified Welder- An individual which has proven he or she can
weld acceptable specimens to a procedure, and produce acceptable
results according to a welding code by welding a test specimen.
• Certifications have time limits, usually 6 months before you need to
recertify unless the welder is producing unsatisfactory results.
• The certification is only valid when applied to the company hosting the
weld test, to a prequalified code, or their proprietary code.
• The certification is limited to the specific criteria in the procedure, and
to the code. Things like process, thickness, rod or filler metal, heat,
position and Joint.
• Certifications will have traceability, an engineer, certified weld
inspector, or manager will administer and monitor the test. The test
will be destructively and non-destructively tested and the results
maintained by the company for audit.
• Certifications do not transfer from one company to another.
Qualification
• A Qualified Welder – Someone who has taken and passed a
weld test administered by an individual from a company or
organization.
• Qualification proves the welder is producing welds that satisfy
the companies standard. This is usually done to obtain a job.
• Qualification tests are typically harder then a certification test.
They are deemed acceptable by the company not a set of
standards in a code.
• Qualification does not qualify a welder to be certified, or visa
versa. The basic difference is the documentation associated with
the certification.
• All welders in the motorsports industry are qualified, most are
not certified, few know the difference.
Codes
• Codes are applied to ensure the mechanical integrity of
a welded member. This prevents buildings from falling
and bridges from collapsing. It also keeps the welding
practices the same no matter where the construction is
taking place. Codes also have legal status – a biggie!
• The largest organization governing welding codes is the
AWS- American Welding Society. Two others are:
ASME- American Society of Mechanical Engineers, and
API – American Petroleum Institute.
• Each organization has several different codes to
address welding in various situations.
Code Examples
• AWS Codes:
– AWS D1.1 Structural Welding Code – Steel
– AWS D15.1 Railroad Welding Specifications
– AWS D1.5 Bridge Welding Code
• ASME Codes:
– ASME B31.1 Power piping
– ASME B31.3 Process piping
• API Code:
- API 1104 Welding of pipelines
Each organization has codes for training, testing, design, materials,
safety, and about anything you could get sued for.
Safety
• The dangers of welding and cutting include
but, aren’t limited to the following:
– Grinding particulate inhalation
– UV light
– Heat
– Electrical shock
– Fumes and gasses
– Loud noises
Cutting Processes -Plasma
• Plasma Cutting – A plasma cutting machine inserts a spark
into a stream of inert gas traveling through a constricted
orifice to produce high density plasma. This stream of
plasma is typically about 40,000 degrees F. It can cut
through ferrous or non ferrous materials with hand held
control or automation.
• The process requires compressed air, or a readily available
inert gas to be delivered at 60 to 80 PSI, and when the
trigger is depressed a “pilot arc” made of high voltage and
low current is projected off an electrode. As the arc
projects off the electrode, it passes through a constricting
orifice with the air. At that moment most of the gas is
converted into high density plasma. It will cut through
anything it can maintain an electrical connection with.
Cutting Processes OXY-Fuel Cutting
• Oxy fuel cutting – A cutting process used to cut ferrous materials. It
uses fuel and pure oxygen to cut through material by rapidly
oxidizing the material when a critical temperature is reached. In
steel this is above 2500 degrees F. The fuel and oxygen are mixed in
the torch body, the result is a neutral flame producing a 5600
degree F flame. A lever on the torch will open a valve allowing pure
oxygen to flow from a large orifice to actually cut the material.
• Various fuels can be used. Some include: natural gas, MAPP gas,
propane, butane, propylene, and the Mac daddy of them all
acetylene. Acetylene is currently the industry standard because it is
cost effective to produce, it has the highest specific energy, and
easy to source. The downfall to acetylene is safety. It is unstable
when in an un-dissolved state and compressed above 15 PSI.
Welding Processes
• Welding and joining are made up of several
processes.
• In Motorsports the two primary processes are
Tig, and Mig.
• Mig – “Metal Inert Gas” Official process name
is GMAW- Gas Metal Arc Welding.
• TIG – “Tungsten Inert Gas” Official process
name is GTAW – Gas Tungsten Arc Welding.
Anatomy of the torch parts
• Torch- device you hold to manipulate the arc and weld pool.
• Cup- the cup is made from silica, and is pink in color. It absorbs heat
from the electrode and directs an inert gas over the weld pool.
• Diffuser- the diffuser can also be called a collet body and hold the
collet in place, transfers current to the collet, directs the gas.
• Collet- the collet hold the electrode in place and helps make the
electrical connection.
• Back cap- this surrounds the electrified electrode and seals in the
gas.
• Electrode- this focuses the electrical arc to a usable concentration
to create a weld pool. It is has a specific tip shape and thickness. Tig
electrodes are made of tungsten. Depending on the material your
attempting to weld you select a perticular type of alloyed tungsten.
Some alloying elements are: Thorium, cerium, Zirconium, lanthium,
and tungsten can come pure with no alloys as well.
Tig torch assembly
Various back caps
Various cups
Examples of tungsten
Process details
• Tig can be used in all three polarity options; A/C, DCEN,
and DCEP.
• Steel is almost exclusivly used with DCEN.
• DCEN = 1/3rd of the heat concentration on the
electrode, 2/3rds on the work.
• DCEN = exactly the opposite of the above.
• A/C = is usually a balance 50% to the positive and
negative, but almost always not the case. This polarity
is used for aluminum welding.
• Tig uses inert gas to schield atmosphere. 100% argon is
commonly used, sometimes 100% helium. A mixture
can also be used.
Process details cont.
• Tig is a non consumable electrode process. This means you can
have current flowing and no filler material being deposited.
• Tig is a constant current process. This means you set the amps you
want on the machine and when welding that stays the amps stay
the same and what adjusts by operator input is voltage. (moving
closer or further from the weld pool)
• Tig is a slow process, low deposition rates, takes a high degree or
operator skill and high equipment costs.
• Tig is a high penetration process, can weld all materials in all
positions.
• Tig is a full manual process. This means you control the current
amount, control of the electrode position, and feed rate of the filler
material.
Process details cont.
• What makes the Tig process so desirable is
because of the arrangement of the polarity and
variable foot control of delivered current, it can
be a high or low penetration process.
• You can change easily control the size of the
welds and accuracy of their placement.
• It is a clean process and does not leave behind
spatter or flux slag.
• It is easy to change materials, all that is needed is
to change the filler rod.
Tig drawbacks
•
•
•
•
High operator skill
Expensive initial equipment costs
Slow
Can easily overheat base material and remove
or reduce base metal heat treat.
Samples
Mig torch parts
• Torch- hand held gun that has a trigger. When
depressed inert gas flows to cup, and
simultaniously electrically charged wire feeds.
• Cup- the cup directs the gas to provide
atmospheric coverage around the weld pool.
• Tip- the tip guides the wire out of the torch
and provides electrical contact.
• Diffuser- allows the gas to flow into the cup
and holds the tip.
Mig torch assembly
Cup, tips, diffusers, and drive wheels
Process details
• Mig is a semi-automatic process. This means one of the
variable is done for you. In Mig this is the feeding of
the filler material. When you press the trigger, the feed
rate in inches/ min. will deposite.
• Mig is a process run in DCEP polarity. This limits the
short arc process to 3/16” material or thinner. On the
plus side this polarity allows for easy welding on thin
materials like body panels.
• Mig is conatant voltage process. This means you set the
votage you want on the machine and as electrode stick
out changes your dynamically changing resistance. (less
stick our = more penetration, and the inverse is true)
Process details cont.
• Mig uses inert gasses like Tig for schielding.
Unlike Tig, when you change materials you want
to weld you have to change gasses. This is a
drawback from a cost and time standpoint.
• Mig filler material is fed into the machine from a
spool. The actual feeding is done through a set of
drive wheels controlled by a motor.
• There are many verisons of the wire fed Mig
process mostly changes in filler metal transfer.
Some include: globular, spray, plused, flux cord,
metal cored, and submerged arc welding.
Mig drawbacks
• When you change base materials you need to
change wire and schielding gas.
• Low penetration, limited on thickness
• Weld spatter all around weld bead
• Poor control of weld size and placement
• Easy to have flaws and discontinuties
• Produces smoke and sparks
• Its easy to do, so it’s easy to do a bad job