Investigation into micro-tungsten inert gas arc behaviour and weld formation

Abstract

Current pulsing patterns are defined for the micro-tungsten inert gas welding apparatus developed and are described as: no pulsation (NP), high frequency pulsation (HFP), slightly hybrid pulsation (SHP), and heavily hybrid pulsation (HHP). The characteristics of the microarc behaviour and weld formation are then investigated in detail for these patterns. The parameters and pattern of the pulsating current dominate arcing power and arc stiffness at a given average current, thus affecting arc state and bead formation. The arc image analysis shows that the HFP and HHP arcs can burn more steadily even at an average current of 2 A because of the arc stabilising effect from the superimposed high frequency components. During the on time of the pulse, the state of the hybrid pulsating (HP) arc varies successively from an apple like shape to a cone with an increased taper. Furthermore, this HP arc shrinks owing to the decreases in the peak current and arcing power with increasing frequency of the base pulse, but is still much greater in size than the NP and HFP arcs. Finally, welding experimental results demonstrate that the HP welds are the widest and become narrow with an increase in the pulse frequency, and the NP and HHP beads are somewhat wider than the HFP and SHP beads respectively.