Progress in High Performance Cladding Processes Tandem-Gas-Metal-Arc-Welding and Plasma-MIG Hybrid Welding

High performance cladding processes are characterized by a high deposition rate, in combination with a low dilution. In this work, two different high performance cladding processes, using two welding arcs, were investigated and their characteristics are compared.

Tandem-Gas-Metal-Arc-Welding (tandem GMAW) uses two, linked, independent power sources and electrically isolated electrodes with two separate arcs. With this setup, 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 speed of each individual wire. 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 cladding, optimized 3-dimensional graded platings with flexible properties can be produced in a highly efficient way.

The second high performance cladding process combines the two processes plasma welding and gas metal arc welding (plasma MIG welding). This advanced hybrid welding process with two concentric arcs again ensures a high deposition rate in combination with a low dilution. In this work, special focus is put on a newly designed prototype welding torch with a flat wire filler (4mm 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.