autobody 101 MiG welder set up for car bodywork

today on this guys garage we start off with some basics of MiG welding for doing autobody work

wire size
technique

amazon links
USA
Lincoln MiG https://amzn.to/3wuZWMD
.023 MiG wire https://amzn.to/3gzOQiX
panel crimper https://amzn.to/35pH8mg


Canada
lincoln welder https://amzn.to/3cFWLtK
.023 mig wire https://amzn.to/2TAc5Bk
panel crimper https://amzn.to/3gtlfsu
This has become the most common type of repair and custom auto-body welding. Its name derives from the term metal inert gas, which is really a misnomer. After all, so-called TIG welding (for tungsten inert gas) is also a metal-inert-gas welding process. Properly, what is called MIG should be called according to the American Welding Society (AWS) GMAW for gas metal arc welding. TIG is properly designated as GTAW, for gas tungsten arc welding. I’m glad to get all of that sorted out, thank you. Now, please forgive me, while I continue to use the vernacular terms, MIG and TIG, for no better reason than that everyone uses and understands them.

In the MIG process, a welding wire is continuously fed into the weld area the puddle as it is drawn along the weld seam. The wire carries current, and is surrounded at the weld, by an inert shielding gas that is fed there through the welding hose and gun, along with the wire. C-25 is the most common gas used for sheetmetal welding, in a 25-percent CO2 and 75-percent argon mixture. The gas acts like the heat-vaporized rod coating in stick welding. It shields the weld puddle and the cooling weld from most of the oxidation corrosion that would occur if the weld was made and cooled in a normal air environment.

The actual MIG process involves a cycle. As the mechanically fed wire contacts the puddle, it creates a direct short circuit with the grounded work piece. The heat generated by the short melts off the wire’s end, into the puddle, ending the short circuit. However, it is quickly reestablished, as more wire is fed into the puddle, creating the short arc cycle that is the basis of MIG welding. This all occurs at about 100 to 150 cycles/second, and produces the famously characteristic frying egg sound that is associated with MIG welding.

The most-often botched aspect of MIG welding is fit-up, the distance between the edges of the metal pieces that are being joined. In lap and offset lap joints, fit-up is not an issue because the joints are overlaps. But in butt welding, it is critical to leave adequate fit-up distance between butted edges. This space is consistently in the range between the thickness of a dime and a nickel. It may sound more difficult to carry a weld puddle down such a gap than down two more closely fitted edges. However, this is not the case.

What is beyond difficult, in fact all but impossible, is to get a good MIG butt weld when edges are fitted up too closely or in actual contact with each other. This is because the expansion from welding heat inevitably distorts too-closely-fitted metal edges so badly that it is very hard to weld them. It is also very difficult to straighten out panels welded that way.