Analysis of the Interfacial Bond Strength in Overmoulded Thermoplastic Composites

Overmolding of thermoplastic composites (TPC) combines the mechanical performance of continuous fiber laminates with the formability and ease of manufacturing complex shapes of short fiber‐reinforced thermoplastic compounds, offering lightweight parts with integrated structural and functional features. The reliability of these hybrid structures is largely governed by fusion bonding at the interface between insert and overmolded material. This study investigates the bonding behavior of glass‐fiber‐reinforced bio‐based polyamide (PA410‐GF) composites using a combination of controlled heating, process simulation and mechanical testing. Insert temperature and melt flow length were varied in an industrially representative demonstrator geometry. Infrared and mold heating trials revealed non‐uniform surface temperatures, while flow simulations highlighted the role of viscous shear heating in maintaining high melt temperatures along long flow paths, with a melt temperature increase of approximately 6°C along the flow path, partially compensating for heat losses to the mold. Rib pull‐off testing revealed a transition from adhesive to cohesive failure as interface temperature increased, with pull‐off strength increasing by approximately a factor of two from low (211°C) to intermediate (238°C) interface temperatures, approaching the bulk polymer yield stress. Further increases in interface temperature (257°C) resulted in < 5% additional strength improvement, indicating a plateau governed by interlaminar failure within the laminate, with the interlaminar strength of the laminate insert becoming the limiting factor rather than the interface between the insert and the overmolded compound.