If you’re repairing an old car, then you’ll almost certainly need to weld rusted sheet metal at some point. Rusted body panels need to be repaired. Not only do they look horrible, but they make the metal structurally weak and less safe.
They can also cause costly future repairs if the rust spreads to vital components and damages them.
Which Type of Welding?
When you’re welding body panels you can either MIG weld or TIG weld. MIG welding is the easiest process to learn that has revolutionized autobody repair. It produces good quality results and is usually the preferred method for autobody repair unless you’re a very experienced welder. Sheet metal is only thin, so you won’t need a very powerful welder, just check the metal thickness of your sheet metal with the welder specifications to get the best one for your needs.
Cut out the rust
The first thing you’ll need to do is cut out the rust from the body panel. A plasma cutter is my favorite tool for cutting metal. Start by identifying all the areas that contain rust and mark the area that you’re going to cut out with a pen. To keep the structural stability in the metal you’ll want to leave as much of the original metal as you can, but you still need to cut out all the rust. If you leave rust it could spread and ruin all your hard work. When you mark out the area to cut out, remember that basic shapes with straight lines will be much easier to replace and cut out than ones with curves or many sides.
Replacing the metal
One you’ve cut out you’re piece of rusty metal then you’ll need to replace it with another piece that’s exactly the same size. Place the metal that you’ve cut out on top of your sheet metal and mark around the edge with a metal scribe. Then cut out an exact replica of the metal. Make the replacement metal is not larger than the original metal or it will not fit. It doesn’t matter as much it it’s a bit smaller because if there’s a very small gap this can be filled with filler metal.
Tack weld in place
Tack welding is the best way to hold the metal in place before you fully weld it to the original metal. Tack welds are simply small welds that barely penetrate the metal and aren’t pushed or pulled to form a bead. Tack weld different areas of the joint about an inch apart. This will hold it in place and allow you to weld it properly.
Complete the weld
Let the tack welds cool off before jumping into the full weld. You need to let it cool because overheating is very common when repairing body panels, which leads to warping. If your sheet metal is thin then you’ll have to be extremely careful. Don’t simply run a bead across the whole joint, work slowly into different areas around the joint, keeping a distance with the area you just welded. Do this until you’ve welded all the way round the joint and there are no gaps.
Finally, once the replacement metal is firmly in place, you’ll need to grind the metal and clean it up. Use a grinder to remove any slag and excess filler metal. Hold the grinder so the face is perfectly flat on the surface of the metal to make it as smooth as possible.
A coat of paint
That’s it, if you’ve made it this far then you’ll have successfully learned how to weld sheet metal on a car and you’ve repaired your rusty body panel. Now you can paint your new structurally secure metal and make it look great.