Why do you need shielding gas for a mig welder? Answered

I thought the flux was burned at the tip of the weld, making a cloud of gas around the weld site.

"Gas-less" MIGs in fairness, use hollow wire with a flux filler - a bit like electronic solder contains flux. You end up with a result like a standard MMA (stick) weld, needing chipping.

Steve

It's to prevent / reduce oxidation / burning. The gas is usually held outside the welding unit - Argon, or on the cheap carbon dioxide.

L

 usually the gas is held in an outside tank. the gas is thiwer to create a bubble around the weld to protect the joint as you are working. it is imperative that the joint be "clean" when you weld, so they use the bubble to protect it.