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Welding Sheetmetal - Oh Sheet!

Posted in How To: Body Chassis on June 18, 2014 Comment (0)
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Welding Sheetmetal - Oh Sheet!

Welding sheetmetal together makes burning thick metal together seem like a smiley walk in your favorite off-road shop. Welding sheetmetal is scary and daunting. Why, you may ask. Well, there are usually several things going against you when reattaching two bits of thin, old metal. Older Jeeps will probably have rust and may have 15 different layers of paint made from 20 different potentially noxious chemicals, while newer Jeeps may also have rust, zinc coatings, and/or super thin sheetmetal right from the factory. This means burning never-ending holes is easy, as are laying down welds filled with porosity and imperfections. Generally speaking, taking your time and making sure your materials are as clean as possible will help make the finished product a high-end repair rather than a botched booger-welded nightmare that takes hours to grind down. Here are a few tips we’ve learned the over the years that should help save you time and make your bodywork repair go a bit better.

Generally speaking, you want to match the MIG wire thickness to the metal you are welding together. If you are doing a lot of dedicated sheetmetal work, you should stick to thinner wire such as 0.023-inch diameter wire. Since we use our welder for everything from rollcages to sheetmetal, we’ve found 0.030-inch diameter wire to be a pretty good compromise for both.

Welding thin sheetmetal is a real pain. One of the worst spots we’ve encountered in a while was when we trimmed the rear wheelwells of our WJ’s Unitbody. The steel here was galvanized and super thin after been stamped in the die at the factory. Still, we were able to tack weld the two trimmed pieces of metal together. Just be sure to turn down the power on the welder and the wire feed speed. Then make small tacks a few inches apart. Once things have cooled down, you can go back and make another tack weld. Following this pattern you can stitch the two pieces of metal back together.

Cracks in thin sheet metal must be cleaned thoroughly before tack welding them closed. Here we used a grinder with a wire-wheel to clean the stress crack before welding. If rust has eaten away most of the metal’s thickness, welding just may not happen. In that case, you can only cut the thin metal out and replace it.

A large variety of clamps and locking pliers can be very useful for sheetmetal work. We’ve modified locking pliers for special jobs using our welder. There are also special pliers that can create a recessed flange for patching sheetmetal. We also have a pair of locking pliers with a wide jaw (about three inches) that is great for folding sheetmetal.

One other tool that you have to have for welding sheetmetal is a hammer. We can’t count the number of times we’ve tack welded metal together and then tapped or pounded away with a hammer before the next weld trying to get the metal to line up. Also, a grinder with a flap wheel is great for cleaning up rusty or zinc-plated metal. We also love having a second grinder with a metal wire wheel nearby to clean up seams and cracks before, during, and after welding. The key to nice welds is a clean surface.

Another great tool to have for an old Jeep is a copper or brass spoon. You can hold it on the back of a small hole in sheetmetal and use it to tack weld the hole closed. The liquid steel won’t stick to the copper or brass, but it will conduct electricity and cools the steel quickly, making filling holes in bodywork easier. Also, an oxyacetylene torch can be used with a skilled hand, some bailing wire, or an old steel coat hanger to fill holes in thin sheetmetal.

Butt-welding thick steel together is relatively easy. You should use a grinder to taper the edges so you get more penetration with the weld. With thinner metals like sheet metal, you have to make small tack welds a few inches apart. Take your time as rushing will only make more work for you if the metal gets hot and warps or you blow a hole in the metal.

If you end up burning a hole in the metal you are working on, turn the welder down a little, and slow the wire speed a touch. Then make one quick, small tack weld on edge of the hole (on the top of the hole if the piece of metal is vertical). Wait for the tack to cool and then repeat the process. Eventually you should be able fill the hole. If you do this too quickly, you can create a hot spot that could cause shrinkage that could later warp the sheetmetal.

When welding two different thicknesses of metals together, start on the thicker piece and then draw the weld bead down to the thinner metal briefly before returning to the thicker metal.

Safe and Healthy
Burning metal together can be a disaster waiting to happen, but it also can be done safely. There are a few safe practices that should always be followed when melting steel. The first few should be obvious but need repeating. First, make sure you have a functional fire extinguisher close by. Also, make sure to remove any and all flammable items from near the area you are welding. That means old rags (especially oily ones), cardboard, leaves, carpeting, and so on. Additionally, make sure any spare gas is far away from where you are going to be welding. For a list of potentially dangerous situations you may encounter during welding, check out this web site from OSHA on welding health hazards: (osha.gov/doc/outreachtraining/htmlfiles/weldhlth.html)

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Alternatives to Liquid Metal
Welding with MIG, stick, TIG or an oxyacetylene torch can all, when used correctly, help join two pieces of metal. Unfortunately, not all have access to a welder, or even a torch. Luckily, there are other alternatives for any Jeeper without a way to liquefy steel, and sometimes they are better than welding. We’ve used everything from glues, screws, and rivets to help hold parts of Jeeps together, and all can work well.

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