How To Weld Sheet Metal

Most farmers have spent a lot of time fusing metal with a welder in the farm shop. The jobs they most often have to tackle are repairing structural components on an implement or fabricating corral gates. That usually involves some reasonably thick metal. But dealing with thin sheet metal is a little different.

There is a lot of sheet metal around the farm. Panels on livestock trailers, truck boxes or fenders and hoods on tractors, are places where it’s typically used. And all of those components are subject to rusting, dents and other damage, which can easily be repaired if you know how. This should get you started.


The trusty arc welder that does most of the work around the farm just won’t do the trick this time. Welding sheet metal requires maintaining an arc for very short periods of time and starting them precisely on the joint, which is nearly impossible with an arc welder. Also, typical arc welding electrodes are just too thick and require too much heat.

Sheet metal repair is a job for a MIG — or TIG welder, if you are lucky enough to have one. If you don’t have a MIG, buying one that will do all the welding work around the farm will set you back over $2,000. But a small 110-volt machine will easily weld sheet metal up to one-sixteenth of an inch, and you’ll pay less than half the cost of a larger welder.

A good angle grinder is also important. It will clean paint or rust off the base surfaces to ensure a good arc and prevent incorporating impurities into the weld. It can also be used to fine tune the fit up of pieces and to grind down the finished weld.


“Use the smallest wire diameter feasible,” reads the American Welding Society’s (AWS)Tips for successfully welding sheet metal. “Smaller wire takes less heat to melt, which, in turn, heats the metal less. A smaller wire also allows for more control over the weld bead and a better chance of recovering from mistakes because it has a lower deposition rate.”

That means using .023-gauge welding wire shielded with a 75-25 argon-CO2 gas mixture. Don’t use flux-core wire for thin steel. It uses more heat, which can increase the likelihood of distorting the base metal. Avoiding excess heat is the biggest challenge when welding thin-gauge material.

Fitting up the joint is critical. Pieces should fit tightly without any gaps. Even very small gaps will increase the possibility of burning through. “Gaps cause nothing but trouble,” mentions the AWS. “To avoid rework caused by melt-through, adhere to the old saying ‘Measure twice, cut once.’”

The AWS also recommends clamping a thicker piece of a dissimilar metal (like copper) behind a joint to help dissipate heat and reduce burn-through, but that may not always be possible, depending on the location and shape of the joint.

To demonstrate the process, these photographs and captions will walk you through welding a 20-gauge, mild-steel panel. The pictures show an old truck fender that was previously used to donate metal for other patches. In this case a patch is welded back onto the fender.

This sequence shows a butt-joint weld, which is the most demanding type, yes, however it creates a high-quality repair that can be made invisible from both sides. This type of joint requires the edges of the repair patch to exactly fit the panel without any gaps. And the welder setting must be precise. Too much heat can easily cause a burn-through, creating more work to fix.

As is usually the case with welding, practice makes perfect. Honing your skills on pieces of scrap metal first is a better idea than jumping right into an important repair. Now, go practise and melt some steel!


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About the author


Scott Garvey

Scott Garvey is a freelance writer and video producer. He is also the former machinery editor at Grainews.



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