Composite engineering will become increasingly complex to provide strong structural parts for aerospace and automotive load applications.
A good example comes from the ThermoPlastic Composites Research Center (TPRC) in Enschede, the Netherlands. TPRC is a testbed for advanced composite development involving academic and industry.
In a two-year collaborative project, a continuous fiber-reinforced shell with relatively simple geometry was stiffened with a sophisticated injection molded grid. The injection tool is complex, and the process becomes more challenging when combined with continuous fiber-reinforced thermoplastics.
The thermoplastic composite insert was press formed using TenCate Cetex TC1225 engineered C/PAEK. It is then overmolded with a high melt flow (40) Victrex PEEK. The beauty of the engineered PAEK is its relatively low melting temperature, allowing overmolding with PEEK at moderate insert temperature. The heat of the injected plastic melts the surface of the insert.
Design is one thing; manufacturability is another.
According to the TPRC researchers, the stiffness and strength performance combined with extreme dimensional accuracy stresses the manufacturing process.
Corporate collaborators were Autodesk, Harper Engineering Co., KraussMaffei, Safran S.A., Samvardhana Motherson Peguform (SMP) and Victrex PLC.
The injection molding machine used was a KM 750CX with 160 metric tons of clamping force and a stroke volume of 318 cc (19.4 cubic inches).
TPRC researchers Mark Bouwman, Thijs Donderwinkel and Jeroen Houwers worked on the experimental validation and modelling of the mechanisms underlying the overmolding 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.