MIG Welding

Safety

Arc eye is a UV burn — helmet down before you strike, and warn people nearby. Fumes: ventilate, never weld galvanised without extraction. Sparks travel metres; clear the area of anything flammable. The workpiece is hot for a long time.

Steps

Grind the joint to bright metal and clamp it; earth clamp on clean metal.

Set wire speed and voltage from the chart for the thickness, then fine-tune by sound — a steady sizzle like frying bacon.

Hold the gun at 10–15° push, 10 mm stick-out.

Strike, let the puddle form, then travel at a speed that keeps the puddle a consistent oval.

Weave slightly on thicker stock; straight on thin.

Stop, chip and brush; inspect the back for penetration.

The Science

The arc is a plasma at around 6,000 K carrying 100–200 A; it melts the wire and a puddle in the parent metal, which freeze together as one piece. Ohm's law and Joule heating in the arc column set the heat; the shielding gas keeps oxygen and nitrogen out of the molten pool, which would otherwise make it porous and brittle. Wire feed speed sets current; voltage sets arc length.

How It Fails

Porosity (holes) from wind, dirty metal or too little gas. Lack of fusion — a bead sitting on top — from too little heat or moving too fast. Burn-through on thin metal from too much. Spatter everywhere from voltage too high or a long stick-out.

Summary

Fusing steel with an electric arc from a continuously fed wire, shielded by argon–CO₂ gas — the easiest process to start and the hardest to do well.