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You never butt weld sheet metal with a mig welder. Mig weld a piece like that and give it two bends and it will break. Butt welds are for tig welding.

You can bend a tig weld all day and it won't break. Mig welds are brittle and should only be used on a overlap or on heavy steel.

Mig weld? If you can bend it you will break it. But not tig welds they are strong and are not brittle one reason the are used on moly steel cages. Moly steel is more ridgid and mig welds will not hold up do to less flex and more weld movement