Metal Inert Gas (MIG) welding is also called Gas Metal Arc Welding (GMAW). The process involves using a welding gun which automatically spools welding wire through a contact tip. While the trigger is pulled, wire passes through the gun and comes into contact with the contact tip. An electrical charge on the tip melts the wire to form a spot of metal called the weld pool. The gun also pumps an inert gas such as helium or argon over the weld pool to dispel the atmospheric gases which can damage the weld.
Select your wire type based on the metal being welded to. Welding wire is labeled by metal and includes steel, aluminum and stainless steel wires.
Select the wire size based on the thickness of the metal. If the material is 16 gauge or thicker, use a .045-inch wire. For thinner materials, convert your material thickness to inches and select a wire that is approximately that width.
Select your shielding gas. If you are welding steel, use carbon dioxide (CO2) for thicker steels and a 75 percent argon, 25 percent carbon dioxide mixture for thinner steels.
Replace the contact tube, gun liner and drive rolls to match the wire size.
Clean the gun and machine. Especially keep the gun nozzle free of any splattered metal. The gun liner and drive rolls should be kept clean.
Switch the power source to reverse polarity (DCEP).
Lead the wire from the gun by ¼ to ¾ inch. This length provides an evenly rounded weld.
Adjust the wire feeder hub tension and drive roll pressure so the wire feeds at a steady rate.
Hold the welding gun with both hands to steady the bead and keep the gun straight.
Tilt the gun 10 degrees forward or back or keep the gun perpendicular with the welding surface. A tilt back or “push” makes a shallow, wide and round fillet. A tilt forward or “pull” makes a narrow, deep and flat fillet. Keeping the gun perpendicular makes a deep rounded fillet.
Move the wire along the welding line, keeping the wire pointing to towards the front edge of the pool of metal. A proper fillet has a “leg” or width that is the same as the material thickness.
If welding in an awkward position such as overhead, weld using a small weld pool and the smallest wire size available. This prevents a lot of material dropping down from the weld pool.
Always wear proper protective equipment when welding. Molten metal and sparks can cause serious burns and electrical shock from the welding machine can be fatal. Read all safety documents before using any equipment.