How to MIG Weld Auto Body Panels

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MIG welding body panels can be tricky because they are so thin. Thinner metals require lower welder settings and some technique. With some practice, however, welding auto body panels becomes much easier. The trick is to get a solid, strong weld without warping or burning through the material. It is a very good idea to practice on some scrap sheet metal if you have any. That way, the mistakes you make while learning won't be evident on an important project.

Things You'll Need

  • MIG welder
  • Auto body sheet metal
  • Welding hood and leather gloves
  • Grinder
  • Tin snips
  • Primer
  • Cut the sheet metal precisely. One of the most important things to do when welding thin metals is to make sure the gap is as small as possible, and the pieces fit together extremely well. A quality pair of tin snips can make the job a lot easier. Bridging a large gap is not fun while doing any sort of welding, but it is next to impossible when MIG welding on auto body material. You can use an angle grinder to finely shape the pieces so that they fit as exactly as possible.

  • Tack weld everything first. Never attempt to simply completely weld up any body panels, because the heat will warp them quickly. Instead, tack weld them together every few inches, allowing everything to cool between arcs. To tack weld them, simply pull the trigger on the MIG gun for only two seconds or so. The goal is to stick them together well enough so that the panels won't separate, while at the same time avoiding burning through or warping the sheet metal. Do not bother grinding the tack welds once they are completed, because you will be welding more on the panels.

  • Fill the gaps with weld. Now that the body panels are tacked together, you can slowly connect them by welding the seams. It is important to go very slowly, welding only two to three inches at a time. "Pull" the gun away from the weld at a 45-degree angle to avoid deep penetration. Let the entire weld cool before striking another arc to avoid warping. If you can access the back side of the body panels, check to make sure there is no burn through from there. Sometimes it is very hard to see what is happening from the front side only. If the back of the sheet metal is turning black or you are seeing holes, turn the settings down on the welder a bit and try again.

  • Grind the welds down. Once the body panels are completely welded, it will be necessary to smooth the welds down so that they are flush with the rest of the sheet metal, and no longer visible. After the welds are ground down and the body panel is straight, you can coat the area with primer to prevent rust from forming.

References

  • "Welder's Handbook, RevisedHP1513: A Guide to Plasma Cutting, Oxyacetylene, ARC, MIG and TIG Welding;" Richard Finch; 2007
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