10 Tips for TIG Welding Sheet Metal

Delta Air Lines Technical Operations Center in Atlanta (Delta TechOps; 866-MRO-Delta or TechSales.Delta@delta.com ) is the largest airline MRO in North America. In addition to providing maintenance and engineering support for Delta’s fleet of aircraft...

Lens crafter
Always use a TIG torch with a gas lens. The lens, a screen inserted inside the cup, smoothes gas flow and prevents turbulence, which in turn widens the area of gas coverage. If necessary, it allows increasing electrode extension from 1/4- to 3/4-inch beyond the cup. Extending the electrode permits reaching into corners and better visibility of the weld area.

Mind the gap
To perform maintenance on some parts, Delta TechOps must cut them apart to gain access and then re-weld the part … while maintaining the part’s original dimensions. All parts shrink when welded, so plan ahead. Good R&D work, good fixturing, and experience can provide an indication of how much to “pre-gap” a part prior to welding. In other instances, if possible, create parts that are slightly larger than required and cut off or machine away excess material after welding.

To the point
Electricity likes to come off a point. Nothing focuses an arc more than a needle-sharp tungsten. A sharp tungsten directs the heat where you want it (and away from areas you don’t). Also, don’t weld with contaminated tungsten; it’s a recipe for rework.

Note that Delta TechOps has standardized on lanthenated electrodes for all applications. It holds a sharp point for low-amperage welding, works well with AC TIG on aluminum and magnesium, and works well for high-speed pulsed DC TIG.

Invert your thinking
High-speed pulsed DC TIG welding (100 to 150 pulses per second (PPS) or greater), stiffens and narrows the arc cone, greatly increasing a welder’s directional control over the weld puddle. Further, high-speed pulsing reduces total heat input. With conventional TIG technology and welding near an edge, welders have to stay on their toes to prevent the weld puddle from wicking over and melting the edge; there’s simply no extra metal to conduct the heat.

Note that conventional TIG welders cannot pulse faster than 10 PPS, where welders such as Miller Electric Mfg. Co.’s Maxstar and Dynasty inverters permit high-speed pulsing (500 or 5,000 PPS, depending on the model). As budget permits, Delta TechOps is adding more TIG inverters to its fleet for pulsed welding in many DC TIG applications. Collier concludes that, “Any tool that gives you more control over heat input is a good tool, especially in the high-precision world of aircraft maintenance.”

Brush up
Keep separate brushes for different metals to prevent cross contamination. Write the metal type on the handle of every brush. Stainless steel won’t be stainless and aluminum won’t be nonferrous if you clean the weld with a brush impregnated with carbon steel particles.

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