Sensing of weld pool surface using non-transferred plasma charge sensor

Gas tungsten arc welding (GTAW) is the primary process for precision joining of metals due to its capability for accurate control of heat input. As a close relative and modification of GTAW, plasma arc welding (PAW) has higher energy density and can penetrate thicker workpieces while maintaining the desired capability for accurate control of heat input. In order to produce quality welds consistently using PAW, in addition to accurate control of heat input, the sensing and control of the weld pool surface are also critical. It has been found that the non-transferred plasma arc, in the absence of the transferred arc or the main plasma arc for welding, can establish a plasma charge potential which is indicative of the arc length. In order to take good advantage of this intrinsic characteristic of the non-transferred arc and eliminate the influence of the transferred arc in a normal PAW process, a power module is used to cut off the main arc current periodically for a very short period of time to acquire accurate information for monitoring the weld pool surface. A non-transferred plasma charge sensor is proposed based on this mechanism and experiments verified its effectiveness.