Spot welding may be done with either ac or DCEN. Sequencing controls automatically establish the preweld gas and water flow, start the arc, time the arc duration, and provide the required postweld gas and water flow.
A variation of the gas tungsten arc welding process, often done manually with a pistol-like holder that has a vented, water-cooled gas nozzle, a tungsten electrode that is concentrically positioned relative to the gas nozzle, and a trigger switch for controlling the operation. Figure S-22 illustrates manual gas tungsten arc spot welding.