Contribution to mechanical fasteners for composite structures - An automated industrial approach

Current fastening technologies implemented in the composite structures of car body applications show various disadvantages compared to an interference-fit joint. For example, adhesive bonding requires clean and pre-treated surfaces and metallic fasteners are prone to galvanic corrosion. This work investigates the process of an interference-fit joint (connection) comprising a fiber-reinforced thermoplastic insert pressed into a pre-drilled hole in a polymeric composite structure. With the insert being oversized and the hole undersized, interface pressure is generated. Pressure in radial direction is leading to friction which in turn is giving the insert resistance against pull out. The connection is functionally evaluated by comparing both the pullout force curves and the injection force curves for three different levels of interference. Major target is a prediction of the resulting pull out force based on the injection process. Furthermore, a process capability evaluation of the connection is presented. Since the environmental conditions of a car manufacturer's body shop require highly automated processes, the connection should be implemented in a fully automated manner. The process is conducted by a robot controlled device fulfilling relevant targets of process reliability, capability and reproducibility. Additionally, the whole equipment is designed with regards to body shop facilities allowing to transfer the test equipment into a production environment.