QUALITY EDGE BUILD-UP BY AUTOMATIC PULSED MICRO-PLASMA ARC WELDING

Abstract

Edge build-up by welding has been a common repair technique for high value-added aero-engine components. This project investigates the influence of welding parameters on the quality of edge build-up process on AISI 410 martensitic stainless steel by means of automatic pulsed micro-plasma arc welding. Firstly, fundamental work was carried out to study the influence of welding parameters, namely, welding current, welding speed and wire feed rate (WFR), on build-up height and weld bead geometry because they are the two main quality factors. The results show that, for coupons of constant thickness, the build-up height (H) increases linearly with decreasing welding current (I) and to a lesser extent, with increasing welding speed (u) and wire feed rate (WFR), other things being equal. However, too low a welding current coupled with a high WFR will cause the machine to chatter, while too high a u coupled with a low WFR will cause the weld beads to become discontinuous. Tests with tapered coupons show that a linearly increasing/decreasing welding current works fine for the edge weld build-up on tapered samples. The process zones comprising sets of welding current-thickness (I-T) line functions for quality edge weld build-up of tapered sample are provided, one for each welding direction from thin-to-thick and thick-to-thin respectively. The results of a confirmation test further show that the I-T algorithms developed based on tapered coupons work adequately well for the edge weld build-up on parts composed of various tapered segments, on the condition that appropriate transitions from one tapered segment to the other, hence from one I-T algorithm to the other, be exercised to ensure minimum disturbance in the welding process at the transition point.