PREVENTIVE MAINTENANCE CHECKS AND SERVICES (PMCS), INCLUDING
LUBRICATION INSTRUCTIONS Continued
MIG WELDING METHOD.
MIG (Metal-Inert-Gas) welding. This process uses a DC power source, control panel, and a welding gun. The
gun feeds a consumable bare electrode at a given rate into a molten pool beneath a blanket of inert gas. When
an arc is struck, a molten pool forms at once. Move the welding gun along the joint line at a rate that shapes
the right size bead. The covering inert gas keeps air from polluting the welding zone. No flux is needed.
Lead angle and cant angle. Place gun at a lead angle of 10 deg to 15 deg off vertical. Point gun in direction of
weld travel for good gas coverage, cleaning, and preheating of material. Place gun at a cant angle of 90 deg. to
parent metal so filler wire and arc are directed towards apex of groove. This will give equal fusion on both
sides of material, even weld buildup, good gas coverage, and equal penetration.
Nozzle clearance. Keep nozzle clearance of 1/2 to 5/8 inch (12 to 16mm) for good gas coverage. Wrong
nozzle clearance will cause the following:
Oxide deposits in the weld bead.
Force gas bubbles into the weld.
Prevent cleaning action on the material in front of the weld pool.