Joining by using pin-like structures in welding processes

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The use of pin-like structures for the generation of form-fit joints in welding processes represents an innovative approach to combine adhesion incompatible polymers and thus broadens the possible polymer combination spectrum. Without the use of additives or extensive surface pre-treatments, locally adapted part properties can be achieved by joining incompatible semi-crystalline thermoplastics. In addition, the use of pin-like structures allows the combination of semi-crystalline and amorphous thermoplastics, to enable for example a permanent functionalization by an optically transparent element. Besides joining adhesion incompatible polymers, the benefits of the process can be applied on bonds with low weld strength, e.g. fibre-reinforced thermoplastics. In this case, the pin-like structures could contribute to a modification of the fibre orientation, perpendicular to the joining plane, and thus to higher bond strengths.The aim of the proposed project is the fundamental investigation of interdependencies of the joining mechanism by means of pin-like structures in welding processes. For this purpose, vibration welding as well as ultrasonic welding technology are applied, which are both based on energy input by means of friction. Despite the high potential, interdependencies between material, process and resulting bond properties are currently unknown for this novel joining technique. The comprehensive experimental investigations within the research project, in combination with a model-based analysis, enable the development of general requirements for the material combinations as well as for the process handling. Therefore, the effects of decisive process parameters, of the structure geometry as well as of the occurring thermomechanical interactions on the resulting joint are fundamentally analysed.In comparison to the vibration welding technology, the use of the ultrasonic welding technology enables the production of smaller pin structures whereby the load capacity of the joint can be increased and the process can also be made accessible for smaller parts. Furthermore, ultrasonic welding continues to differentiate itself from the vibration welding principle since different oscillation directions are used for the energy input and the structure generation. This allows an improved identification of process-specific interactions during structuring.With the help of the knowledge gained within this project, a comprehensive understanding of the joining by means of pin-like structures as well as general structuring and joining strategies can be established. These allow the transfer of the methodology to further materials and joining processes.