Statistical test planning for ultrasonic welding of dissimilar materials using the example of aluminum‐carbon fiber reinforced polymers (CFRP) joints

This paper is focused on statistical test planning methods to increase process stability by means of reproducibility in comparison to a stepwise empirical variation of each process parameter during solid state joining as well as the significant reduction of experimental time and costs. The methodology will be presented for the specific challenges of ultrasonic welding. This pressure welding technology was investigated systematically for joining aluminum sheet metals to carbon fiber reinforced thermoplastic polymers (CFRP). In this study two aluminum wrought alloys were investigated to be welded onto CFRP with PA66 matrix. To evaluate suitable process parameters, the statistical model named “central composite design circumscribed (CCC)” was used to prove the weldability of the Al/CFRP‐joints. An important advantage of the CCC‐model is the description of the mutual dependence of the three central welding parameters: oscillation amplitude, welding force and energy in relation to the achievable mechanical properties of the joints. It allows the reduction of the number of necessary welds at a factor of seven in comparison to a conventional empirical investigation. All combinations of the welding parameters were proved in tensile shear tests. Additional microstructural analysis helped to understand the mechanical behaviour of ultrasonically welded hybrid joints in detail.