Overmolding could be one way of improving production speed and enhancing the properties of a thermoplastic composite part. Manufacturers heat an organosheet, which is a reinforced composite blank, and form a part in a press. The part is then injection molded as well. This process produces thermoplastic composite parts with complex geometries and integrated assemblies.
Hybrid additive manufacturing also has the potential for increasing production speeds. In this production method, manufacturers use 3D printing to add features to a larger substrate.
“By printing features like clips or retainers onto a larger substrate you can add complex functions to a simple part without the challenges of complex injection molding tooling,” explains Halsband. “Additionally, 3D printing features onto a larger substrate allows you to relatively easily utilize different resins on the same part. In one area you may need a stiff reinforcement rib or feature to secure a mechanical fastener, while in another area you may want to use a flexible material to mold clips to secure a wiring harness.”
With hybrid additive manufacturing it’s possible to produce relatively large parts with a mix of functional features. The process would simplify production and assembly through parts consolidation and optimized packaging.
Halsband believes that case studies demonstrating structural thermoplastics’ mass cost performance benefits will drive more opportunities. “Nothing beats the validation of success,” he says. “In the meantime, leading material, process and design firms must actively engage the market and share the successful development work that is ongoing now.”
Small Steps in Aerospace
Thermoplastic composite manufacturer TxV Aero Composites, which is part of polymer provider Vitrex, and parts producer SFS Intec are working cooperatively to develop thermoplastic composite parts for the aerospace industry. They have re-engineered metal aircraft storage bin clip brackets and are using an overmolding process to produce a thermoplastic composite version using VICTREX AE™ 250 composites and VICTREX™ polyether ether ketone polymer.
The part is being produced using rapid manufacturing techniques that have reduced cycle time to minutes versus hours. An automated tape placement process produces the thermoplastic sheets tailored to meet the part’s requirements. The sheets are consolidated into laminates, press formed and machined into parts. Continuous fiber composite inserts are placed in an injection molding tool where a PEEK polymer is added. “This provides additional geometry and may functionalize that laminate in a way that cannot be done with composite material alone,” explains Jonathan Sourkes, TxV commercial manager.