Composite Compression Co-moulding: a Warpage Reduction Investigation
Abstract
To accommodate the increasing need for vehicle emission reduction, automotive manufacturers are presently looking at the next generation of lightweight materials. Glass fibre-reinforced thermoplastic composites belong to this group and exhibit mechanical properties that resemble traditional metals but at a reduced weight and with improvements on other characteristics. Unfortunately, they are affected by processing-related warpage, especially when fabricated by means of the Long Fibre-reinforced Thermoplastics – Direct (LFT-D) manufacturing process, a technology that is valuable because of its high throughput and flow lengths. This occurs for many reasons but reinforcing LFT-D with Glass Mat Thermoplastics (GMT) – another material format with higher fibre content and isotropy – may overcome these issues altogether.
To validate this hypothesis, a complex demonstrator geometry was first selected. Then, the moulding of LFT-D was examined via thermography and moulding simulation to find thermal-related issues caused by the geometry and material. Following this investigation, LFT-D was co-moulded with GMT and the resulting warpage was compared to both LFT-D and GMT by means of a deformation energy-based warpage metric as well as an image correlation metric used for warpage pattern similarity assessment. Nearly 25% LFT-D volume replacement with GMT provided warpages similar to the base GMT material with minimal changes to the warpage pattern. Though, subsequent mechanical tests yielded inconclusive results – most likely due to the confounding effect of specimen warpage – the overall results suggest a good bonding, fusion and mixing of the two co-moulded materials. Further investigation of other warpage reduction methods could be considered in the future.