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1Tig and Mig welding By: Luke Woroniecki Motorsports WeldingTig and Mig weldingBy: Luke Woroniecki
2Table of Contents Welding Certification and Qualification Codes Safety Cutting ProcessesWelding ProcessesWeld Joint Geometry and Welding SymbolsWelding MetallurgyWelding DiscontinuitiesInspection and NDE
3CertificationCertified 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.
4QualificationA 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.
5CodesCodes 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.
6Code Examples AWS Codes: ASME Codes: API Code: AWS D1.1 Structural Welding Code – SteelAWS D15.1 Railroad Welding SpecificationsAWS D1.5 Bridge Welding CodeASME Codes:ASME B31.1 Power pipingASME B31.3 Process pipingAPI Code:- API 1104 Welding of pipelinesEach organization has codes for training, testing, design, materials, safety, and about anything you could get sued for.
7SafetyThe dangers of welding and cutting include but, aren’t limited to the following:Grinding particulate inhalationUV lightHeatElectrical shockFumes and gassesLoud noises
8Cutting 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.
9Cutting 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.
10Welding ProcessesWelding 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.
12Anatomy 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.
17Process detailsTig 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.
18Process 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.
19Process 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.
20Tig drawbacks High operator skill Expensive initial equipment costs SlowCan easily overheat base material and remove or reduce base metal heat treat.
22Mig torch partsTorch- 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.
25Process detailsMig 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)
26Process 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.
27Mig drawbacksWhen you change base materials you need to change wire and schielding gas.Low penetration, limited on thicknessWeld spatter all around weld beadPoor control of weld size and placementEasy to have flaws and discontinutiesProduces smoke and sparksIts easy to do, so it’s easy to do a bad job