Page 9 - MetalForming March 2010

tungsten-arc (TIG) welding is known as a more precise procedure, it also requires a more advanced level of skill (see arti- cle beginning on page 14). When weld- ing thin sheetmetal panels, the main objective is to achieve optimal penetra- tion while avoiding warping and burn- through, and delivering a quality weld with a clean appearance.
Here we offer proper gas-metal-arc (MIG) welding tips and techniques.
Preparation
Always consider safety first. Make sure welders wear the appropriate pro- tective equipment such as a welding hel- met, safety glasses with side shields, gloves and long sleeves.
The welder must properly secure the ground clamp, and position the ground clamp as close as possible to the area where welding is being conducted to avoid damaging sensitive equipment such as wiring and sensors. Ensure the ground clamp is connected to clean sheetmet- al free of paint and rust, electrical insu- lators that impede the proper flow of weld- ing current and resulting in an unstable welding arc.
Equipment
Choose the thinnest-diameter welding wire possible to minimize heat input to the base material and helping to avoid burnthrough. With less filler metal, the welder has improved control over the weld bead, delivering an overall cleaner weld appearance.
Use a welding machine that pro- vides a short-circuit transfer process, and develop the welding procedure so that wire-feed speed is 150 to 250 in./min. at 15 to 22 V. These parameters allow the welder to weld on thick and thin materials in all positions with a con- trolled current, making it easier to pro- duce clean welds. Dependable current control minimizes spatter while deliv- ering optimal penetration for low-heat- input applications.
Use a shielding-gas blend of 75 Ar-25 CO2, which helps to reduce penetra- tion on thinner sheet since argon dis-
tributes less heat than 100 percent CO2. Having the proper wire and gas com- bination will minimize overall consum- able costs.
Application
Avoid long welds. Use only short tack welds when possible to evenly dissipate heat. For long seams or when continuous
welds are necessary, begin tack welding at the middle of the weld joint, and skip weld (or backstep) to evenly dis- tribute heat and avoid stress buildup, warping and distortion.
Information provided by Lon Damon, welding-school instructor, The Lincoln Electric Co., Cleveland, OH: 216/481- 8100; www.lincolnelectric.com.
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