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Going over the mat'l first with the torch etches the metal. Do me a favour, the next time you are TIG welding contaminate your electrode by touching the metal while welding. Now go regrind your electrode and go over the dirty mess left by the contaminated weld. Where does all the nastiness go? I'm no scientist but maybe the impurities on the surface (ie:oils, oxides)are changed to gases and are then shielded from the area to be welded. All I know is that it works.



First of all, TIG is more susceptible to contamination than any other form of welding. That said, its critical that the surfaces be cleaned BEFORE any welding begins. And not by running your torch over the area !

Second, what you're doing is burning the contaminants with heat - the gas itself is doing nothing to "clean" the area. You may think you're "etching" the metal but in reality you're just contaminating the area by melting the surface and allowing the dirt into the molten metal (as minute as that may be). The heat generated by the TIG is about as hot as the sun so its stands to reason that just about any oil will burn of but oxidation doesn't melt so it flows right into the molten metal. Aluminum is a great example as it oxidizes almost instantly. If you don't clean it well and weld it right away it will be contaminated. Running your torch over it prior to welding wouldn't do squat to improve the final weld.

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The instructor who taught my welding class didn't have a problem with it. But, he was only a AWS/ASME certified welder with 20+ years in the iron workers union



I know welding technologists that don't have a problem with it. The point is that there's no advantage to it. No additional strength, just additional time and materials. Learn to weld properly - particularly if you want to make any money at it !