Task
More and more often parts have to meet different requirements that cannot be fulfilled by a single material. In future, tailored multi-material combinations of plastics and metals are becoming increasingly important. The broad profile of properties of plastics can be specifically extended by the combination with metals. The overall properties of the part can be improved by the best of both materials. Thereby, the main challenge is the realization of customized joining techniques for hybrid lightweight components that are taking the different material properties of the different materials into account.

Approach
A promising approach is the laser-based hot-melt bonding of thermoplastic-metal composites. The flexibility and wear-free operation of the laser beam and the possibility of local, non-contact energy input are ideal for material-adapted heating and joining of thermoplastic metal hybrids without the use of an additional adhesive. Thereby, laser radiation is absorbed by the metal surface which leads to an increase in the temperature of the material. Positioned below the metal, the thermoplastic melts as a result of heat transfer. The thermoplastic melt wets the metal surface and acts as hot-melt adhesive. After cooling, the dissimilar materials are joined together. Investigations are conducted to analyze the influence of the surface topography of the used metal and the used laser parameters as well as the melting and wetting behavior of the thermoplastic joining partner on the joint quality. At the end of the project, a guideline for the industrial implementation of the process is created.

Results
The tensile-shear strength depends on the surface pre-treatment of the metallic specimen. Cleaned and degreased stainless steel specimens joined to polyamide reach a tensile shear strengths of about 8 MPa. The tensile shear strength can be increase above 20 MPa due to an additional mechanical interlocking caused by laser structuring of the metal. To illustrate the potential for using the new approach a strong carrier made of stainless steel and thermoplastic composite and a media-tight made of stainless steel and polyamide are realized and tested successfully.