Increasing rigidity and strength using local effects of bead-on-plate laser welding seams

In order to achieve graded strength properties and to improve the rigidity of metallic materials, side effects of the laser joining process are used. Local physical and geometrical effects which have only been observed as side effects are to be used purposefully. The investigations take place in context of the SFB 675 "high-strength metallic structures and joints by setting up scaled local material properties". The energy needed to produce bead-on-plate welding seams can be limited to a small area of the workpiece by using a focused laser beam with a diameter of tenths of a millimetre. The heat affected zone of a laser beam is very small. In comparison to other welding procedures, lower heat input is the main reason that basic material characteristics remain unaffected after welding. The progressive development of laser beam sources to higher available laser output power has extended their spectrum of use in the field of joining technologies [1, 2]. It should be pointed out that local physical and geometrical effects can be used to achieve specific material characteristics. Bead-on-plate laser welding seams were produced to demonstrate that strength and rigidity can be increased in metal sheets. First investigations are carried out on the micro-alloyed high-strength steel H340LAD. The sheets were tested using tensile tests and also with 3-point and 4-point bending tests. Six different specimens were investigated, one without welding seams and five with different laser based welding seam types. The tensile and bending tests showed that higher forces were needed to rupture or to bend the laser welded specimens. Furthermore, the investigations showed that the strength of the specimens was increased in comparison to the specimens without welding seam.