Laser welding process for the production of a semi-finished sheet of hardenable steel with an aluminum or aluminum-silicon based coating

摘要

The invention relates to a method for producing a custom-made thermoformable sheet metal semifinished product, in which at least two steel sheets (1, 2 ') of different material quality and / or thickness are joined in the butt joint by laser welding, wherein at least one of the sheets is made of press-hardenable steel and a metallic coating (1.1, 2.1) on aluminum or aluminum-silicon base, wherein the laser welding by supplying additional wire (8) into the exclusively by means of at least one laser beam (4) generated welding melt (6), wherein the additional wire (8) in Is substantially free of aluminum and contains at least one alloying element favoring the formation of austenite, present in the filler wire (8) with at least 0.1 wt% greater mass fraction than in the press - hardenable steel, and wherein the filler wire (8) prior to Feeding into the welding melt (6) is heated by means of a heating device. To ensure that during hot forming (press hardening) the weld reliably transforms into a martensitic structure (eg with a MnB-MnB connection) or a mixed structure (eg when connecting MnB steel to microalloyed steel) and, in order to obtain an optimized weld geometry, the steel sheets (1, 2 ') according to the invention with one bounded by their edges to be welded together, an average width (b) of at least 0.15 mm having gap (G) welded together, wherein in the gap (G) so much material of the additional wire (8) is introduced, that the ratio of introduced into the gap (G) additional wire volume to the volume of molten steel sheet by means of laser beam material is at least 20%. The method according to the invention requires no prior stripping of the edge of the sheet metal edges to be welded and thus offers considerable cost advantages.