The development of weight-optimized structures uses increasingly a multi material design. This approach uses the concept that the right material is used in the right place. Based on this idea the connection between different materials gains in importance. Depending on the joining partners and the processing chain different approaches can be applied. This contribution focuses on direct (adhesive-free) adhesions between thermoplastic polymers and thermosetting polymers. The polymer-to-polymer connection is realized by mechanical interlocking which consists of different scales – a micro-scale such as the surface roughness and a macro-scale like structural elements on the surface. The thermoplastic join partner is produced by injection molding. This large scale production process is suitable for this application because the surface structure is casted directly onto the part. There is no need for a subsequent processing step to form the mechanical interlocking. The thermosetting join partner is a fibre reinforced plastic which is produced by an injection process, the resin transfer molding. This process is also used for a high-volume production. It uses a liquid resin that is inserted into a mold where the reinforcing fibres and the before-mentioned thermoplastic join partner are located. The resin forms the adhesion between the polymers by interlocking on the surface structure of the thermoplastic part. This contribution treats the production and the design of different surface structures on thermoplastic parts and their ability to transmit forces on the interface to other materials. Thus a way to produce cost-effective multi-material components without additional adhesives is presented.