The use of the right material at the right place plays a leading role in lightweight efforts. The realization of those multi-material components depends strongly on joining technology as a key manufacturing process, especially for materials with opposed properties, e. g. metals and plastics. Thereby, thermal joining is a potential technology for manufacturing thermoplastic-metal joints without using a filler material (e. g. adhesive) or a joining element (e. g. screw, rivet).
In thermal joining, both materials are in contact at the boundary layer. The metal sheet is heated by an energy source, e. g. a laser beam or an inductor, and the plastic material gets molten due to the heat transfer between both materials. The molten plastic wets the metal surface and thus penetrates the surface structures. A solid joint is formed after solidification of the thermoplastic material.
The penetration of surface structures is a key parameter for forming the joint. The state of the art shows numerous investigations in the field of surface preparation techniques, e. g. laser-based preparation. However, the penetration of the structures in in causal relation to the temperature distribution in the joining zone, the chemical structure of the polymer and the effect of time is not given yet.
Within this paper, those different mechanisms were investigated by experiments and numerical simulations in laser-based thermal joining. As plastic joining partners, PA 6 and PP were used to gain information about polymer structure’s effect. As metal joining partners, aluminium (EN AW 6082) and stainless steel (X5CrNi18-10) were used. The metal surface was structured by a laser-based process to provide microscopic structures which were penetrated by molten plastic. Based on different joining times, the experimental results were correlated to the temperature distribution in the joining zone. Thereby, a causal relation of the required minimum temperature was identified as material-dependent parameter, when full penetration occurred and joining times became subordinate.