Induction-based joining of titanium with thermoplastics: Creation and examination of titanium-thermoplastic connections

The importance of hybrid composites is increasing, particularly with regard to structural lightweight construction. Therefore, a joining process for the production of hybrid bonds using induction technology is examined in this paper. An appropriate test rig was developed, assembled, commissioned and characterized for this purpose. Heating tests with titanium Ti6Al4V were carried out with this device to determine the influence of the process parameters on the temperature level and the temperature field. This applies in particular to the feed rate, the sample geometry, the relative positioning between sample and inductor as well as to the inductor setting like induction frequency and pulse width modulation. Based on the results of these examinations, a two-stage heating process was developed, which allows the formation of a homogeneous temperature field in the range of the melting and degradation temperature of the used polymer (PPS; Ten-Cate Cetex TC1100) and thus to achieve optimized bond strengths. More specifically, a short phase with a high energy input was used for quick and intensive warming and a longer time period was deployed to reach an even distribution of temperature. Subsequently, joints with CFRP were produced with a specimen geometry suitable for tensile shear tests according to DIN EN 1465 (Adhesives—determination of tensile lap-shear strength of bonded assemblies; German version EN 1465:2009, 2009). The analysis of the tensile shear strength and the fractured surfaces shows that the metal is much more difficult to heat up due to the melting enthalpy of the plastic than preliminary tests indicated. Further tests were carried out, which revealed a threshold value for heating where the temperature was sufficiently high to achieve a complete coating of the plastic on the metal can be achieved. In summary, the investigations showed that the presented method as well as the design of the test rig is generally suitable for bonding metal to thermoplastic polymers. The influence of various parameters on heating and bond strength could be identified. Moreover a process has been established, which allows industrially useful bonding forces. This not only proves that further investigations are useful, but also laid the foundation for further experiments.