Argon‐arc surfacing with pulsed filler wire feed in repair of components

Abstract

Surfacing can be used to eliminate various service defects. These can be wear, burning or melting of the working surfaces or edges of blades, labyrinth seals and other important components in aircraft engines produced from creep-resisting, chromium-nickel cast and deformed alloys. Service defects can be repaired by various methods of arc fusion welding as well as by diffusion bonding and brazing. However, fusion welding is the simplest and most universal process, which does not require complicated equipment, a large number of operators and large production areas. At the same time, the method is suitable for processing a wide range of components and sections. When surfacing components of aviation engines (such as seals, blade, edges, discs, etc), problems occur because the dimensions of surfaced elements are small, the space between them is not large and components are often load-carrying. Therefore, the quality of welding must be very high. Taking these conditions into account, it is necessary to meet the volume of deposited metal in surfacing using miniature surfacing beads and multipass surfacing of layers of the required height must also be carried out. The materials used (high-strength, chromium-nickel alloys with intermetallic hardening) are characterised by limited weldability and, consequently, cracks may form in the weld zone during arc surfacing. Comparison of different methods of fusion welding (usually with a non-consumable electrode with small diameter filler wire, pulsed arc TIG welding, plasma welding), different gas mixtures and combinations of all these variants shows that the best results, as regards the efficiency of surfacing and adhering to the given requirements, are obtained by welding with pulsed filler wire feed with a pulsation frequency of 3 to 11 per second.1 Surfacing with pulsed filler wire feed is an automatic process in which the filler wire is fed into the molten pool in pulses (not continuously). The pulsating wire reaches the heat source rapidly (tens of millimetres per second), whereas the filler wire fed in a stable manner approaches the pool slowly (tens of millimetres per minute). The slowly moving wire is heated by radiation from the welding arc, melts prematurely and forms large droplets whose size and behaviour become unpredictable.