Machine Design

Adding another inert gas makes better welds

Ternary Gas Plasma Welding Torch

A new welding technique developed at NASA's Marshall Space Flight Center gives engineers a faster, more efficient means of joining thick materials with relatively low heat. The new technique, ternary-gas plasma arc welding, uses a special welding torch and three gases, primary and secondary inert plasma gases, and an inert shielding gas.

The primary inert gas flows through the torch body and across the tip of a welding electrode at the tip of the torch. The secondary gas flows through a lengthwise hole in the electrode. It interacts with the arc to produce defect-free welds in ferrous and nonferrous metals with less total heat per inch of weld, compared to other methods. This makes for deeper, narrower welds at any given current setting, thereby producing a more effective heat-affected zone and welds with higher ultimate tensile strengths. The secondary gas complements the primary gas as well, creating a "stiffer" arc, or one less subject to skewing or asymmetry. This eliminates weld cutting defects. The third inert gas, the shielding gas, circulates around the head of the torch next to the electrode tip.

The choice of gasses depends on the materials being welded and the results desired. The overall process works with current straight polarity and variable polarity welding modes. The new method is also less dependent on a welder's skill. The ternary torch has been developed, built, and used at NASA, and the space agency is looking to license the technology to commercial firms.

TAGS: Fasteners
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