Drillling & Tapping MIG Weld

gzig5 said

If the part can handle the heat, getting it cherry red and then slow cooling it should soften it and make it drill/tap easier. Quality cobalt drills and a good tap will make a difference too.

Maybe a question for another thread, but.....Is there a "soft" MIG wire or is the hardness a product of the process? TIG welds are workable, why are MIG such a bear?

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I've seen talk from old timers and farmers about using 'hay wire' (iron wire) to make 'soft' welds. No idea whether it's a good idea or what, but the lack of alloying materials seems to make the welds easier to deal with. I wouldn't do it for anything that's strength-critical obviously.

Mig welds use the heat of the filler metal to fuse to the surrounding metal. Versus TIG or torch which melt the base metal and heat the filler using the base metal and/or arc/flame. In a Mig weld, the material being welded will draw heat away from the weld and cause a faster temperature drop which can cause harder deposits or hardening of the base metal due to the relatively 'quick' cooling.

I remember reading years ago some guidance from the FAA on homebuilt aircraft that post weld normalizing of mig welds (heat with oxy/acetylene until red, let air cool, do not force cool) should be practiced by most any fabricator for tough joints. Also that MIG is the least reliable method of welding high-strength joints and is a method of last resort (they cited lack of penetration, fusion rarely exceeding more than 40% of the joint, etc). Their guidance was being given as a 'best practices' type deal recognizing that people will use Mig even when they shouldn't and were trying to help make things less-bad.