Gas Metal Arc Welding - Lincoln Electric

1 Gas Metal Arc WeldingProduct and Procedure gas Metal arc process is dominant today as ajoining process among the world s Welding fabrica-tors. Despite its sixty years of history, research anddevelopment continue to provide improvements tothis process, and the effort has been rewarded withhigh quality results. This publication s purpose is to provide the readerwith the basic concepts of the gas Metal arc Welding (GMAW) process, and then provide an examination ofmore recent process developments. Additionally, thereader will find technical data and direction, providingthe opportunity to optimize the operation of theGMAW process and all of its DefinitionGas Metal Arc Welding (GMAW), by definition, is anarc Welding process which produces the coalescenceof metals by heating them with an arc between a con-tinuously fed filler Metal electrode and the work.

2 Theprocess uses shielding from an externally suppliedgas to protect the molten weld pool. The applicationof GMAW generally requires DC+ (reverse) polarity tothe non-standard terminology, GMAW is commonlyknown as MIG ( Metal Inert Gas) Welding and it is lesscommonly known as MAG ( Metal Active Gas) either case, the GMAW process lends itself to welda wide range of both solid carbon steel and tubularmetal-cored electrodes. The alloy material range forGMAW includes: carbon steel, stainless steel,aluminum, magnesium , copper, nickel, silicon bronze and tubular Metal -cored surfacing alloys . The GMAW process lends itself to semiautomatic,robotic automation and hard automation of GMAWThe GMAW process enjoys widespread use becauseof its ability to provide high quality welds, for a widerange of ferrousand non-ferrous alloys , at a low also has the following advantages: The ability to join a wide range of material types andthicknesses.

3 Simple equipment components are readily availableand affordable. GMAW has higher electrode efficiencies, usually between93% and 98%, when compared to other Welding processes. Higher welder efficiencies and operator factor, when comparedto other open arc Welding processes. GMAW is easily adapted for high-speed robotic, hardautomation and semiautomatic Welding applications. All-position Welding capability. Excellent weld bead appearance. Lower hydrogen weld deposit generally less than5 mL/100 g of weld Metal . Lower heat input when compared to other Welding processes. A minimum of weld spatter and slag makes weld clean up fastand easy. Less Welding fumes when compared to SMAW (ShieldedMetal Arc Welding ) and FCAW (Flux-Cored Arc Welding ) of GMAW Generally, lower cost per length of weld Metal deposited whencompared to other open arc Welding processes.

4 Lower cost electrode. Less distortion with GMAW-P (Pulsed Spray Transfer Mode),GMAW-S (Short-Circuit Transfer Mode) and STT (SurfaceTension Transfer ). Handles poor fit-up with GMAW-S and STT modes. Reduced Welding fume generation. Minimal post-weld of GMAW The lower heat input characteristic of the short-circuitingmode of Metal transfer restricts its use to thin materials. The higher heat input axial spray transfer generally restricts itsuse to thicker base materials. The higher heat input mode of axial spray is restricted to flator horizontal Welding positions. The use of argon based shielding gas for axial spray andpulsed spray transfer modes is more expensive than 100%carbon dioxide (CO2).Gas Metal Arc Welding :Jeff Nadzam, Senior Application EngineerContributors:Frank Armao, Senior Application EngineerLisa Byall, Marketing GMAW ProductsDamian Kotecki, , Consumable Research and DevelopmentDuane Miller, Design and Engineering ServicesGas Metal Arc Welding GuidelinesImportant Information on our WebsiteConsumable AWS Safety Data Sheets (MSDS) Safety in Welding and Cutting and Arc WeldingSafety E205 Safety of Gas Metal Arc Welding (GMAW).

5 6 Modes of Metal Transfer..7-10 Short-Circuit Transfer ..7 Globular Transfer ..8 Axial Spray Transfer ..9 Pulsed Spray Transfer ..10 Components of the Welding Arc..11 Shielding Gases for GMAW..12-15 Inert Shielding Gases ..12 Reactive Shielding Gases ..12-13 Binary Shielding Gas Blends ..13-14 Ternary Shielding Gas Blends ..14 GMAW Shielding Gas Selection Guide ..15 Effects of Variable..16-17 Current Density ..16 Electrode Efficiencies ..16 Deposition Rate ..16-17 Electrode Extension and CTWD ..17 Advanced Welding Processes for GMAW..18-19 Waveform Control Technology ..18-19 The Adaptive Loop..20-21 Advanced Waveform Control Technology ..20 Surface Tension Transfer ..20-21 Tandem GMAW..22-23 Features of Tandem GMAW ..22 Modes of Metal Transfer for Tandem GMAW ..22-23 Equipment for GMAW..24-31 The Power Source.

6 25 The Wire Drive System ..26-27 Special Wire Feeding Considerations ..28-29 Shielding Gas Regulation ..28 Bulk Electrode Packaging ..29 Typical GMAW Systems ..30-31 Semiautomatic GMAW System ..30 Automatic GMAW System ..30 Portable Engine Driven GMAW System ..31 GMAW Torches..31-33 For Semiautomatic GMAW Welding ..31-32 For Hard and Robotic Automation .. of Carbon and Low Alloy ..34-39 Selecting Carbon and Low Alloy Electrodes ..34 Types of GMAW Carbon and Low Alloy Steel Electrodes ..35-36 Mechanical Properties ..36 Chemical Composition ..37 AWS Specifications for Manufacturing GMAW Wires ..38 Selecting Carbon and Low Alloy Electrodes for GMAW ..38-39 GMAW of Stainless Steels..40-57 Types of Stainless Steels ..40-42 Sensitization ..43-44 Hot Cracking ..44-45 Precipitation Hardening ..46 Duplex Stainless Steels.

7 47 Physical and Mechanical Properties ..47-49 Selecting Stainless Steel ..49 Corrosion Resistance of Stainless Steels in Various Environments ..50 Design for Stainless Steels ..51 Selecting Stainless Steel Electrodes for GMAW ..52-54 GMAW of Stainless Steels ..54-56 GMAW of Aluminum alloys ..57-64 Properties of Aluminum ..57 Aluminum GMAW Modes of Metal Transfer ..57 Power Supplies and Wire Drives for Aluminum GMAW ..58-59 Shielding Gases for Aluminum GMAW ..60 Filler Alloy for Aluminum GMAW ..60 Aluminum GMAW Welding Techniques ..60-61 Filler Metal Selection ..62-63 Chemical Composition for Aluminum Wires ..63 Selecting Aluminum Electrodes for GMAW ..63 Aluminum Filler Metal Guide ..64 General Welding Guidelines..65-77 Current vs. Wire Feed Speed ..65-66 General Welding Guidelines ..67-77 STT II Welding Guidelines.

8 78-81 For Carbon Steel ..78-79 For Stainless Steel ..80 For Nickel Alloy and Silicon Bronze ..81 For Pipe Root Pass ..81 Rapid-Arc Welding Guidelines..82-87 ForSolid Wire ..82-84 For Metal -Cored Wire ..84-86 Application Notes ..86-87 Glossary..88-89 Safety Precautions.. of GMAW, gas Metal arc Welding , had its industrialintroduction in the late 1940 s. The site was the BattelleMemorial Institute, and it was there that Hobart and Devers,sponsored by the Air Reduction Company, researched anddeveloped the first use of a continuously fed aluminum wireelectrode, shielded with 100% argon gas. Axial spray transfer for aluminum was the earliest Metal transfermode for the process. This eventually led to the use of argonplus small additions of oxygen. The oxygen improved arc stabilityand finally permitted the use of axial spray transfer on ferrousmaterials.

9 The process was limited because of the high energylevel of axial spray transfer to plate thickness material. In the early 1950 s, the work of Lyubavshkii and Novoshilovinitiated the development of the GMAW process to include theuse of large diameters of steel electrode shielded with carbondioxide, a reactive gas. The process development at this stagewas high in weld spatter, and the level of heat generated by thearc made the process uninviting to welders. In the late 1950 s improvements in power source technologyand the interface of small diameter electrodes, in the " " ( - mm) diameter range, permitted the implemen-tation of the discrete mode known as short-circuiting development permitted the use of lower heat input weldingon thin sections of base material, and it provided the opportunityfor all-position Welding .

10 In the early 1960 s, power source research and development ledto the introduction of pulsed spray in the GMAW mode. Theidea for pulsed spray transfer, GMAW-P, occurred in the 1950 sand it conceptually involved the use of a high-speed transitionbetween a high-energy peak current to a low backgroundcurrent. The motivation behind the idea was the need todecrease spatter and eliminate incomplete fusion defects. Thepulsed arc process incorporated the benefits of axial spraytransfer clean, spatter-free welds having excellent fusion,with lower heat input. The lower average current provided byGMAW-P allowed for out-of-position Welding capability withimproved weld quality, when compared with 1970 s introduced power source technology, which furtherenhanced the development of the GMAW process and GMAW-Pin particular.