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

Abstract

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).

Influence of self-organizing microstructures on the wettability of molten plastic on steel for hybrid plastic-metal joints

“…For this method, high joint strengths between different materials of approx. 25 MPa have already been proven in previous works [1,2]. This process can be used for joining plastics and metals for different applications like structural parts like doors, car body parts, and seating structures, or small parts like valves, housings, and bearings.…”

“…Within the first process step the metal surface is microstructured with laser radiation to create undercut structures for the interlocking of polymer and metal and to enlarge the boundary surface and create undercut structures [1][2][3]. In a second heat conduction joining process step, the metal is heated up and by thermal contact of polymer and metal the thermoplastic composite material melts [1][2][3]. Applying an external clamping force, the plasticized material flows into the structures.…”

“…The combination of different materials, such as plastics and metals, adapted to local loads allows new approaches for weight optimization [1]. Whereas on the one hand, polymers are characterized by low weight, attractive price, and nearly endless shaping possibilities, metals on the other hand can withstand significantly higher loads due to their very good mechanical properties [1][2][3]. However, a direct and firm joint between both materials fails due to their physical and chemical diversity.…”

“…However, a direct and firm joint between both materials fails due to their physical and chemical diversity. Nowadays, joining material combinations of fiberreinforced polymers (FRP) and metals (steel, aluminum) is mostly based on mechanical fastening or adhesive joining [1][2][3]. Since mechanical fasteners have a punctual load transfer, destroy fibers, and weaken the material's mechanical properties, they are not suitable for the use of fiber-reinforced plastics.…”

“…In order to realize the multi-material lightweight approach, suitable joining techniques are required. A promising approach to overcome these problems is a laser-based two-step process consisting of metal surface microstructuring and direct thermal joining [1][2][3]. For this method, high joint strengths between different materials of approx.…”