Abstract: A spot weld controller includes a current transformer, a current amplitude detector, a keypad data entry, a solenoid, an air valve and pneumatic cylinder, welding electrodes, a connection to an electric power supply, a source of pressurized air, and programmed logic that controls the sequential operation of the equipment. The controller performs a weld cycle that includes a preheat period, during which inorganic material that bonds metal laminas together is heated and forced away from the electrodes, and a weld period, during which electric current at welding amplitude produces the weld after the metal lamina contact one another.

Abstract: A spot weld control senses differences in welding current required to produce an optimum weld by determining the time rate of change of resistance during the increasing resistance portion of the weld cycle. The weld control can reduce the welding current if the time rate of resistance change exceeds a maximum value and increase the current if the resistance change is less than a minimum value. The weld current may be terminated when a decrease in resistance from the peak resistance value has reached a predetermined percentage of the peak resistance value or terminated after a predetermined number of current cycles.