WELDING METHOD OF SANDWICH STEEL PLATE

PURPOSE:To reduce the weight and cost in welding a sandwich steel plate, by moving a laser beam along the line deviated slightly to the side of an ordinary steel plate from the joint line between the sandwich steel plates and the ordinary steel plate and welding both steel plates. CONSTITUTION:Sandwich steel plates 11, 11 are butted via an ordinary steel plate 10 and a laser beam 8 is moved along the line deviated by 0.1-0.5mm. to the steel plate 10 side from the joint line of both steel plates. Gaseous Ar 9 is blown from a nozzle to the weld zone in order to blow off the gas generated during welding in a transverse direction in this stage. As a result, the generation of the gas by the combustion of a resin as in the prior art in the stage of sandwiching the steel plates is eliminated and the thermal effect and heating time in the welding are reduced. The formation of a structural member such as front floor or the like of an automobile shown in the figure is made possible by the above- mentioned method.