Stability of keyhole in plasma arc welding

Stability of the keyhole plays a fundamental role in producing quality welds in keyhole plasma arc welding. Some studies have assumed that keyhole diameter is a stability measurement. However, recent experimental observation by the authors revealed that width is not correlated with stability. To measure stability, this study uses the keyhole width as the lower limit of the weld pool width required to prevent keyhole collapse. Because the maximal width of the weld pool before burn-through is approximately fixed for particular applications, it can be used as the upper limit of the weld pool width for preventing burn-through. Hence, the margins of the keyhole process from collapse and burn-through can be measured based on how close the pool width is to its upper and lower limits. The stability distance and stability factor are then defined based on the margins to quantify the state of the stability of the keyhole process.