Microprocessor control of arc starting for gas tungsten arc welding (GTAW)

The development of a microprocessor-based controller which uses an adaptive touch-starting algorithm to ignite an arc on a gas tungsten arc welding system (GTAW) is described. By controlling the torch position and the welding current the arc is started without any use of high voltage. A servo-controlled displacement mechanism is used to move the electrode incrementally down to the workpiece until the controller detects the touching of the electrode to the workpiece. The electrode is heated to a certain point (resistive heating), by setting the welding current to a low value. The torch is driven up, but since the electrode has reached a high temperature, the thermionic emission will start an arc ramping up the current as the electrode-to-workpiece distance is increased, and a stable arc can be established. This approach eliminates the use of the conventional high-voltage, high-frequency ignition, which is known to cause problems due to high-voltage spikes and radiofrequency transmission in the starting procedure. The controller has been calibrated to begin the procedure with minimum possible output power to ignite the arc, and will adaptively adjust to the correct timing so that the torch will be driven up soon enough to prevent any overheating of the electrode, and without melting the workpiece, but still maintaining the arc. The arc starting controller has been implemented, and test results for touch starting on a stainless steel workpiece are presented