Identification and quantitation of processing parameters controlling the surface quality of carbon fibre-reinforced composites

The paper investigates the effect of essential manufacturing parameters on the surface quality of uncoated carbon fibre-reinforced composites used as car body panels with visible surfaces (Class A properties). A series of carbon fibre-reinforced composites laminates were prepared by the resin transfer moulding technique varying the fibre volume content (30 to 60 %), reinforcement material (woven fabrics vs. unidirectional fibre reinforcements), curing temperatures (40℃ to 120℃), additives (SiO2 nanoparticles as matrix fillers) and using a surface finish applied as an in-mould coating. Laminate surfaces were characterised by roughness analysis (white-light interferometry) and wave-scan measurement to quantify the influence of the different manufacturing parameters on the surface quality. Especially, the used resins were intensively characterised concerning thermal properties and total resin shrinkage. These results correlate very well with the performed analysis of surface roughness. It is found that the fibre print through effect is significantly reduced by realising low total resin shrinkage and an even distribution of resin and fibres at the surface. Thus, using of unidirectional fibre reinforcement (no weft or sewing threads; very fine filaments), low curing temperatures (slow curing processes) and an in-mould coating are most successful for reduction of fibre print through effect and getting surface similar to Class A properties. In addition, the surface quality is quite positively affected by the application of nanoparticles and also strongly controlled by roughness of tooling.