Investigating intermediate shapes for multi-stage forming of cranial implants: The influence of two intermediates stages

Abstract. This study investigates the use of two intermediate shapes, constructed with an automatic design strategy, in Single Point Incremental Forming (SPIF) to improve thickness distribution and geometric accuracy for cranial implants. Previous work showed a trade-off between these two factors when using only one intermediate stage. In this research, five three-stage experiments were conducted, along with both a two-stage and a single-stage control. The intermediate shapes are constructed using z-scaling and z-translation techniques and the design is based on the outcome of experiments with only one intermediate shape. Building further upon these previous results, the last intermediate stage is selected for optimal geometric accuracy and kept constant for all experiments for comparison purposes. An earlier stage is added and optimized further to improve the thickness distributions. Results show that while multi-stage forming improved the thickness distributions in the last intermediate stage, this benefit vanished in the final forming stage. Geometric accuracy was slightly better in the two-stage process compared to the three-stage experiments.