Process monitoring for overmoulding using tool-mounted sensors combining infrared temperature and piezoelectric pressure measurement: Validation and application to PP-GF and PPS-CF

An in situ process monitoring approach for overmoulding of short glass fibre reinforced thermoplastics onto continuous fibre laminates is presented. The approach is based on novel tool-mounted sensors that combine infrared (IR)-based temperature with piezoelectric pressure measurement. Applying the sensors, parameter studies are performed with the target to investigate influences on the interfacial bond strength of short-glass fibre reinforced polypropylene (PP-GF) on corresponding laminates. In a first step, a full-factorial parametric study with rib-on-plate specimens was performed to identify process parameters significantly affecting interfacial bond strength, which was measured by rib-pull-off tests. These were found to be the melt temperature, the laminate surface temperature, the cavity pressure and the local filling velocity. A second study focused on these parameters, and applied a V-shaped demonstrator geometry with a rib connecting both flanges. Mechanical performance was determined, by pulling on the flanges of the V-structure thereby causing joint failure. For both geometries the in situ sensor data proved highly repeatable and enabled direct correlation of the investigated parameters with the mechanical joint performance. The results show that both higher thermal input and faster filling improve the bond strength. In a further study the V-structures were manufactured with short carbon fibre reinforced polyphenylene sulfide (PPS-CF), thereby showing functionality of the sensors also for these higher temperatures. Overall, the study demonstrates that the novel integrated IR/pressure sensor systems enable reliable cavity-level process monitoring and provide a robust foundation for data-driven quality assessment in thermoplastic composite overmoulding.