Mig spot welding is a process which uses a timed Mig arc to join two thicknesses of metal by penetrating through one into the other one to form a cast weld nugget. It may be used where resistance spot welding is inaccessible or would not be practical. Applications of this process in the automotive, truck cab and related industries may take advantage of a number of benefits it offers, as follows:
a. Welds can be made in joints where there is accessibility to only one side.
b. The weld need not necessarily mark the reverse side of the joint.
c. Special metal preparation is not necessary so long as the surface is free from contaminants.
d. Operator skill is minimal.
e. The welding machines are less expensive than resistance spot welding machines.
f. The welding gun can be portable and there is no "throat depth" limitation as with resistance welders.
Some process limitations must also be considered.
a. On material greater than 1/16-inch thick the process is only practical in the flat position.
b. The two thicknesses of material must be in tight contact to insure correct thermal distribution during welding.
c. Welds cannot be made through adhesives or sealants.
d. Quality and strength of welds is dependent on consistent performance of the wire feed system. Thus, regular checking and maintenance of the equipment is essential.