.Welding is a means of joining metals by concentrating heat or pressure or both at the joint to cause coalescence of the adjoining areas. Electric-arc, gas torch, energy-ray, and Thermit® welding are fusion processes wherein the filler metal is essentially the same as the parent metal in the parts being joined. Braze welding, brazing, and soldering use filler metals different from and melting at lower temperatures than the base metal, which is not melted. The main types of plastic metal joining processes are resistance, pressure, and forge welding. Welding is done in manual, semi-automatic, or automatic operations, depending largely upon the quantity and variety of work. Welding processes utilize different sources of energy. Thermal, chemical, electrical, and mechanical sources of energy generate a temperature that is high enough to produce a weld. The distortion in the welded joints caused by the stresses and heat on the part being welded, in addition to the misuse or lack of operator training, result in weld defects. A comparison is made of the various welding methods.