The Surface-Tension-Transfer Power Source A New, Low-Spatter Arc Welding Machine
By Elliott K. Stava, Senior Research Engineer, Advanced Welding Technology, The Lincoln Electric Company, Cleveland, Ohio.

This new power source is said to be the first one developed in accordance with the physics of of the welding arc.

The surface-tension-transfer or STT power source is a new concept in arc-welding machine design. It operates neither in the constant current (CC) nor constant voltage (CV) mode. Rather, it is a high-frequency (wide-bandwidth), current-controlled machine wherein the power to the arc is based on the instantaneous arc requirements, not on an "average DC voltage." In principle, it is a power source that is capable of delivering and changing the electrode current in the order of microseconds. Furthermore, it is designed for semiautomatic applications, where travel, speed and electrode extension lengths will vary. It operates in the short circuiting welding mode. The applications are identical to those associated with the the standard short-circuiting processes. Various shielding gases, including 100 % carbon dioxide and blends of carbon dioxide and argon for mild steel as well as gas blends with helium for stainless steel, may be used with this new power source. The major benefits are substantially reduced spatter , ease of welding (a feature which maintains arc stability for variations in extension length), lower arc radiation and fume generation, and reduced heat input on thin-gauge material.

Reducing the spatter means less "cleanup" required of the weld surface area prior to final surface preparation. Also, much longer periods of welding are realized before having to clear the gun nozzle of accumulated spatter, especially when the shielding gas is 100% carbon dioxide. The maintenance of assembly fixtures, including the apparatus associated with robotic applications, benefit by this reduced spatter process. In addition to these benefits, the welder should be more comfortable by not having to work in an environment of flying molten metal. Also, since the current is precisely controlled during all phases of the welding process, optimum arc characteristics are maintained, even with variations in the electrode extension. This type of control relieves the welder from having to maintain exact extension lengths and welding gun angles in order to produce a low-spatter weld. Another benefit of this control method is a reduction in arc radiation and fumes. This results from an overall shortening if the arc length and minimizing the overheating of the electrode.


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