Influence of remote-laser-welding parameters for an 8 kW fibre laser on the seam quality of steels

This paper renders the research for contactless welding with long focal distances without supply of shielding gas or welding filler material from the welding head called Remote-Laser-Welding (RLW). Typical values for the distances between the focusing optic system and the workpiece are within a range of 400 mm to 1200 mm depending on the beam quality of the used laser source. Due to its high flexibility and reduced auxiliary process time RLW has been established in industry replacing conventional resistance spot welding processes in various applications. Nevertheless, problems regarding the quality of the welding process have to be solved. This paper discusses the influence of RLW process parameters, e.g. high velocity of welding, Rayleigh length, longitudinal and lateral beam inclination, on the seam quality of steels. These parameters are influenced by boundary conditions such as specifications of the work piece to be welded, e.g. coatings or thickness of the substrate, and additionally the optical and mechanical characteristics of the joining equipment. For the research described in this paper a brilliant 8 kW multi-mode fibre laser with a beam parameter product of less than 4 mm^*mrad was used. Methodological approaches are outlined to increase the seam quality and to reduce metal spatters because of high beam intensity. Experimental evidence for steel materials is discussed by virtue of metallurgical cross sections, surface magnifications and tensile tests.