CO2-LASER WELDING OF ZINC-COATED STEEL SHEETS

Welding of zinc-coated steel sheets for the automotive industry has be en investigated experimentally and theoretically, using a continuous w ave 2 kW CO2 laser. The specimens of 0.8, 1. 0 and 1.2 tnm thickness w ere welded as butt joint and lap joint. Argon gas was shielded co -axi ally to reduce the plasma and to protect the molten pool from atmosphe re. The mechanical tests of specimens were carried out to investigate the ductility of welds in butt joint and lap joint, using the Erichsen test, ball punch test and tensile shear test. The value of transverse weld pattern is higher than others. The fatigue life of longitudinal weld is superior, but that of circular weld pattern is inferior due to the high tensile residual stresses in the weld. The maximum Erichsen value was obtained as 96% and the deformability of zinc-coated steel b utt-welded was found to be 80% in the ball punch test. The high pressu re formed by vaporization of zinc with the low boiling temperature dur ing laser lap-joint welding splattered the molten pool and created por osities in the weld. The optimum gap vas calculated to be 0.1 mm in th e Iap joint welding of zinc-coated steel sheet which was a good agreem ent with the experimental result.