(Victrex)
Overmoulding of thermoplastic composites is a technology in which a thermoplastic composite is thermoformed and subsequently injection overmoulded. The near-net-shape manufacturing process is well suited for automated large series production of complex 3D structures with excellent structural performance and a high level of function integration. The innovation features a typical grid stiffened panel that can be found in larger numbers in aero engine applications. The stiffness and strength performance combined with extreme dimensional accuracy puts high demands on the manufacturing process.The panel consists of a thermoplastic composite insert that was press formed using TenCate Cetex® TC1225 engineered C/PAEK, which was then overmoulded with VICTREXTM PEEK90HMF40. The relatively low melting temperature of the composite’s PAEK polymer enables overmoulding with PEEK at a 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 combinations extremely suitable for a two-step overmoulding process. Numerical models were developed to predict two important aspects that are involved: 1.) Development of the interface between the composite insert and injected polymer during injection moulding, and 2.) Part warpage and spring-forward as a function of process-induced and shrinkage stresses. The models were validated on simplified test geometries as well as the grid stiffened demonstrator part. The project was established with the aim to create (numerical) design tools based on the basic mechanisms that underlay the overmoulding of thermoplastic composites using commercially available software packages. The work was carried out by the TPRC and funded by industrial partners from both the aerospace and automotive industry.