What Size MIG Wire Should Be Used for Mild Steel?
The diameter of electrode and filler wire for metal inert gas (MIG) welding of mild or carbon steel is determined by the thickness of the metal you are welding and whether you are using flux or solid-core MIG wire.
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Wire Type
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When MIG welding mild steel, two wire type options are available. The first is a solid carbon steel wire (ER70S-6) that is best for thinner sheets of mild steel. The second option is a flux-core/solid steel welding wire (E71T-GS) that is intended for welding on painted or rusty mild steel and can weld thicker gauges of metal. The diameter of the MIG wire is determined by the thickness (gauge) of the mild steel you are welding and whether you are using solid-core or flux MIG wire.
The gauge of the MIG wire is measured in hundredths of an inch. Therefore, MIG wire that is 1/33 of an inch in diameter is .030.
Wire Diameter for Thinner Mild Steel
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A 22-gauge sheet of mild steel should be MIG welded with .023 or .030 solid MIG wire; 18-gauge mild steel can be welded with .023, .030 or .035 solid MIG wire, or .030 or .035 flux wire. For welding 16-gauge mild steel, you can use .030 or .035 solid MIG wire or .030, .035 or .045 flux wire.
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Wire Diameter for Thicker Mild Steel
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The thickest sheet a home welder is likely to use is 1/4 inch mild steel. For this heavy welding application you should use .035 solid MIG wire or .045 flux cored MIG wire. For 3/16 inch mild steel you should use .035 solid MIG wire or either .035 or .045 flux cored MIG wire. If you are welding 1/8 inch mild steel, you can use either .030 or .035 solid MIG wire or .035 or .040 flux cored MIG wire.
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References
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