The ThermoPlastic Composites Research Centre (TPRC) has successfully closed a two year collaborative project on the overmoulding of thermoplastic composites with the design and manufacture of an advanced demonstrator part.
According to TPRC, the part was realised as the result of a two year collaboration between TPRC, its members and renowned companies contributing from different areas of expertise: Autodesk, Harper Engineering, KraussMaffei, Safran, Samvardhana Motherson Peguform (SMP) and Victrex.
TPRC explains that the part features a typical grid stiffened panel that can be found in larger numbers in aerostructure applications. The stiffness and strength performance combined with extreme dimensional accuracy puts high demands on the manufacturing process.
The thermoplastic composite insert was press formed using TenCate Cetex TC1225 engineered C/PAEK and subsequently overmoulded with Victrex PEEK90HMF40. The relatively low melting temperature of the composite material enables overmoulding with PEEK at moderate insert temperature. The heat of the injected polymer is used to melt the surface of the solid insert upon contact. This makes the material combination extremely suitable for a two-step overmoulding process.
The overmoulding process combines the best of press forming and injection moulding: A continuous fibre reinforced shell with relatively simple geometry was stiffened with a complex injection moulded grid. However, tool design for injection moulding is complex, and becomes even more challenging when the process is combined with continuous fibre reinforced thermoplastics. Numerical process design tools are indispensable for the composite engineer who more and more needs to take manufacturability into account in an early stage.
TPRC researchers Mark Bouwman, Thijs Donderwinkel and Jeroen Houwers worked on the experimental validation and modelling of the mechanisms underlying the overmoulding process. They translated these to numerical models using a thermoforming software package (AniForm) combined with Autodesk Moldflow to predict interface strength and warpage caused by process-induced residual stresses.
Franco Costa, Senior Research Leader at Autodesk Moldflow, explains, “We have been very impressed with the quality of composites research at TPRC. The team at TPRC has demonstrated a great mix of practical process knowledge and a robust approach to modelling techniques and model development. The TPRC has also been very successful in bringing together into a collaborative project a broad range of companies which have each contributed from their own domain either equipment, materials expertise, process knowledge, modelling knowledge and software modelling. None of the partner company would have been able to achieve as much if they had been working alone – What has been achieved in collaboration is greater than the sum of the individual parts.”