Page 19 - MetalForming June 2010

“Sure, there’s parts in there nobody sees, but I know they’re there,” Webb says. “When you leave a perfect stacked- dime weld on every joint, you know the car is done right, and that’s something Harry Miller would have done.”
Attention to detail? Webb deposited welds on similar parts at exactly the same length; identical welds repeated on oppo- site sides of the car have the same number of ripples; and each ripple is spaced equally apart. On brackets, for instance, with
How to Select a GTAW Power Supply
Gas-tungsten-arc welding (GTAW) is a highly skilled and precise welding process, frequently used for cosmetic appli- cations or those involving thin sheetmetal that require strict control of heat input. Selecting the right power supply for your application is easy if you follow the right criteria.
Amperage range
A GTAW machine with too narrow an amperage range can limit the variety of materials that can be welded. A machine with a range of 5 to 230 A provides the flexibility needed to weld on thin materials like 24-gauge stainless as well as alu- minum alloys to 1⁄4 to 3⁄16 in. Aluminum requires higher amper- ages compared to steels, so purchasing a welding machine that cannot reach at least 200 A will limit the maximum thick- ness of aluminum to 3⁄16 in. The wider the range, the more applications you can perform without having multiple machines.
Low-amperage welding performance
Select a power supply that offers good arc stability at below 10 A. This provides easier arc starts and better arc control, critical when welding on thin materials, as well as opti- mum crater-fill capability at the end of each weld. Beware of machines that only will produce hot starts, which can cause workpiece burnthrough.
AC and DC welding
To weld a variety of materials—ferrous and nonferrous including aluminum alloys—select a welding machine that offers AC and DC power. AC finds use on self-oxidizing soft alloys like aluminum and magnesium, while DC gets the call for welding carbon and stainless steels and deoxi- dized copper.
The right controls
Heat control represents a critical success factor for suc- cessful GTAW, to minimize workpiece distortion. One way to control heat input into the weld without sacrificing weld pene- tration is to pulse weld—the machine alternates between a higher peak current and a lower background current. This maintains the arc while allowing the weld joint to cool.
Quality Design
Many GTAW machines include a number of features that will optimize durability and lifespan. These include environmen- tally coated PC boards and double-dip varnished transformer windings.
Submitted by Jim Harris, product manager, Lincoln Electric.
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