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The process capability of gas metal arc welding (GMAW) processes is mainly determined by the arc properties and the material transfer. In recent years, numerical methods are being used increasingly in order to understand the complex interactions between the arc and material transfer in gas metal arc welding. In this paper, we summarize a procedure to describe the interaction between an arc and a melting and vaporizing electrode. Thereafter, the presented numerical model is used to investigate the arc properties and the metal transfer for a pulsed GMAW process of mild steel in argon. The results of the numerical simulation are compared with OES measurements as well as high-speed images at different times in the pulse cycle and show excellent agreement. The results illustrate the high influence of the changing vaporization rate on the arc attachment at the wire electrode in the high current phase. It could be shown that a substantial part of the current does not participate in the constriction of the wire electrode via the resulting lorentz force which explains the nearly spatter-free droplet detachment in pulsed GMAW processes of mild steel in argon shielding gas.

Abstract. Experimental and theoretical investigations on fibre-laser assisted plasma arc welding (LAPW) have been performed. Welding experiments were carried out on aluminium and steel sheets. In case of a highly focused laser beam and a separate arrangement of plasma torch and laser beam, high-speed video recordings of the plasma arc and corresponding measurements of the time-dependent arc voltage revealed differences in the process behaviour for both materials. In case of aluminium welding, a sharp decline in arc voltage and stabilization and guiding of the anodic arc root was observed whereas in steel welding the arc voltage was slightly increased after the laser beam was switched on. However, significant improvement of the melting efficiency with the combined action of plasma arc and laser beam was achieved for both types of material. Theoretical results of additional numerical simulations of the arc behaviour suggest that the properties of the arc plasma are mainly influenced not by a direct interaction with the laser radiation but by the laser induced evaporation of metal. Arc stabilization with increased current densities is predicted for moderate rates of evaporated metal only whereas metal vapour rates above a certain threshold causes a destabilization of the arc and reduced current densities along the arc axis.

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Results of an experimental study are presented in which the impact of a low power laser beam on the stability behaviour of plasma arcs was investigated. Both heat sources were arranged in a recently developed coaxial set-up. Bead on plate welding trials on AISI 304 stainless steel sheets demonstrated that the additional laser beam is capable of extending existing limitations of low current plasma arc welding processes with respect to realisable welding speeds. In particular, an effective stabilisation of the anodic arc attachment under conditions of direct current electrode negative plasma arc welding was achieved by use of a laser beam with only 100 W output power. As a result of a performed stability analysis, the particular conditions for arc stabilisation are specified and co nclusions about the most probable physical reasons for the stabilising action of the laser beam are drawn