Laser-based plastic-metal-joining with self-organizing microstructures considering different load directions

Innovative multi-material lightweight construction enables reducing dead weight while maintaining and preferably boosting the components' performance. The implementation of multi-material parts (e.g., plastic-metal-components) requires reliable joining processes since a direct connection between these materials is not feasible due to their different physical and chemical properties. In order to avoid additional weight through adhesive bonding, riveting or fasteners, thermal direct joining with a modified metal surface is a promising approach. Within a first process step, the metal surface is modified by laser-microstructuring. To enlarge the boundary surface and create undercut structures, random self-organizing micro- and nanostructures are generated with ultrashort pulsed laser radiation on stainless steel samples. In the subsequent direct thermal joining process, both joining partners are clamped together. The metal is heated up with diode laser radiation, and through heat conduction, the polymer melts and flows into the generated cavities. After cooling-down, a firm joint between both materials is created, which is based on mechanical interlocking and increased specific adhesion between the joining partners. The mechanical strength of the joint depends strongly on the load direction. In the presented contribution, the strength of the joint between stainless steel and glass-fiber-reinforced and non-reinforced thermoplastics (PP) is investigated for three different load directions (tensile shear, tensile and peel).