Progress in high performance hardfacing processes tandem-gas-metal-arc- welding and plasma-MIG hybrid welding

High performance hardfacing processes are characterized by a high deposition rate, in combination with a low dilution. In this work, two different high performance hardfacing processes, using two welding arcs, were investigated. With tandem gas metal arc welding (GMAW), deposition rates up to 16 kg/h were reached. For this work, two metal powder cored wires differing in chemical composition were combined. As a consequence, weld pool viscosity and chemical composition of the deposit can be adjusted during the welding process by controlling the feeding rate of each wire individually. Weld pool viscosity affects the final shape and thickness of the hardfacing. The chemical composition determines the microstructure, hardness and, therefore, the cracking susceptibility. By using tandem GMAW for hardfacing, optimized 3-dimensional graded hard surfacing layer with flexible properties can be produced in a highly efficient way. In the second part, special focus is put on a newly designed plasma-GMAW prototype welding torch that uses a rectangular flat filler wire (4 mm x 0.6 mm). Characteristics of the torch and the welding process are discussed as well as the advantages and disadvantages of this setup are given. First welding tests were performed using Fe-based wires. The melting behavior and droplet transfer were investigated using a high speed video analysis system. Observations revealed that the inner GMAW arc burns continuously across the entire wire cross-section. This allows a stable welding process with a steady droplet transfer and a deposition rate up to 25 kg/h.