Overmoulding of consolidated fibre-reinforced thermoplastics - increasing the bonding strength by physical surface pre-treatments

Fibre-reinforced thermoplastic materials enable an automated and economical manufacturing of lightweight structures in series-production. By combining different material-configurations, highly stressable components can be designed. Previous studies have shown that the combination of continuous fibre-reinforced hollow profiles and injection moulding compounds is suitable even for crash-relevant automotive parts. During the overmoulding process, the pre-consolidated hollow profile must remain cold in order to withstand high injection pressures. However, this leads to a poor adhesion between the profile and the overmoulding material. To increase the bonding strength, the interface can be pre-treated using laser and plasma technology. In this work, fibre-laser and atmospheric pressure plasma treatment are applied to glass fibre reinforced polyamide 6 composite (PA6/GF) sheets. The resulting surface properties are investigated by wettability and microscopy analysis. Afterwards, single-lap-shear specimens and special rib specimens are manufactured by overmoulding the sheets with PA6-66/GF bulk material. The resulting bonding strengths are characterised in tensile shear tests as well as pull-off tests of the ribs. The effects of different pre-treatment parameters on the bonding strength are analysed. Additionally, the effect of sheet temperature on the bonding strength is investigated, also including specimens without pre-treatment. Finally, the results are discussed with regard to the surface treatment of composite hollow profiles, considering bonding strength, manufacturing environment and processing times.