Robotic tow placement for local reinforcement of glass mat thermoplastics (GMTs)
A process has been developed where multiple yarns of commingled glass and polypropylene are heated and placed to a desired geometry. The placed unidirectional (UD) tow is then encapsulated by over-moulding with glass mat thermoplastics (GMTs). The effects of both force (2080 N), with an equivalent pressure range of 846 bar, and the displacement rate (20100 mm/s) during tow placement on void content and flexural modulus were investigated for nine placement conditions. Placement rate affected the tow quality measured before overmoulding. Void contents were reduced after over-moulding. The volume fraction of UD tow (vol. O8 composite/vol. total composite) in the manufactured multi-material structure was 21.5%. Corresponding tensile tests showed a factor of 2 increase in modulus and a factor of 3 increase in strength relative to GMT. Tow placement rate had no significant effect on tensile properties after over-moulding. Tensile behaviour as a function of the UD tow volume fraction was modelled and predicted values agreed with the experimental results. Additionally, the predicted tensile performance of UD tow reinforced GMT has been compared with possible competitive materials using merit indices.