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New process involving injection moulding produces eco-friendly geometries for complex machine parts

04 December 2020

IMCOLOR developed a new manufacturing process that combined a multi-shot injection moulding process with the integration of continuous carbon fiber reinforcements. Together with the use of an expendable core material, a lightweight, eco-friendly air cycle machine part was produced. 

The synergy formed between injection moulding and thermoplastic automated fiber placements with in-situ consolidation (TP-AFPisc) will power future designs that are lightweight yet perform at a high mechanical level, with automated, easy-to-reproduce production techniques. The TP-AFPisc is different from current state-of-the-art procedures, where composite structures are typically built within process chains. 

Injection moulding is widely used in thermoplastic processing today, but its use is restricted to short-fibre material only. Traditionally, continuous fibres have not been used in injection moulding due to casting process issues. But IMCOLOR successfully closes this gap, resulting in highly efficient use of the material. The fiber architecture is precisely adapted to the user’s needs by engaging TP-AFPisc manufactured inserts, and an added bonus is that effort in trimming of composite parts is minimized and scrap is reduced.

A major environmental benefit of this new procedure is that no hexavalent chromium ion (Cr6+) treatments are necessary in the manufacturing process. Cr6+ is the most toxic form of chromium. It is produced during many industrial processes and it has a strongly negative impact on the environment. What’s more, aircraft efficiency will be increased while fuel and emissions will be decreased thanks to the lightweight structures that result from this new process. And last but not least, parts will be easier to recycle because of the use of thermoplastics and environmentally-friendly process auxiliaries. 

Some of the challenges faced by the IMCOLOR project included finding a suitable cavity design and injection parameters for encapsulating carbon fibre reinforced polymer (CFRP) inserts into the injection moulding polymer – further it was difficult to find a suitable material combination to facilitate good binding between the CFRP inserts and polymers. CFRP inserts also had to be fixed correctly during the high-pressure injections, so that no deformation or misalignment occurred. 

Salt cores were also implemented in the Poly-Ether-Ether-Ketone (PEEK) injection moulding. PEEK is one of the most versatile materials to use in injection moulding, and salt cores are ideal as they are both expendable and environmentally friendly. The results with salt cores were quite promising, as cross sections with good salt core quality could withstand the injection loads. They achieved proof-of-concept.

One unexpected finding was out-of-plane wrinkling defects on 23 plies inserts (thickness 3mm) of the model part. This is probably due to the play fit between the mould core and the insert. However, this effect did not occur for the 70 plies inserts (thickness 10mm) of the demonstrator part.   

Next steps for the topic manager will be further investigation of the new material combination and assessment of the new process in-house. The consortium will also investigate the potential of salt cores for composite production and metal casting processes, both in-house and in follow-up projects. 

Partners involved in this project included Liebherr Aerospace Toulouse SAS, the Technische Universitaet Muenchen (TUM), ThermoPlastic composites Research Center (TPRC), Apppex Gmbh, and Fischer Advanced Composite Components (FACC). The total EU contribution was €254 775.

IMCOLOR PROCESS (source: TUM, apppex)
IMCOLOR PROCESS (source: TUM, apppex)