A rapid Design for Manufacturing tool for injection over-moulded composite parts
Topic(s) : Special Sessions
Co-authors :
Anatoly KOPTELOV (UNITED KINGDOM), Xun WU (UNITED KINGDOM), Will DARBY , Andrew PARSONS (UNITED KINGDOM), Ole T. THOMSEN (UNITED KINGDOM), Stephen HALLETT (UNITED KINGDOM), Lee HARPER , Jonathan P.-H. BELNOUE (UNITED KINGDOM)Abstract :
Thermoplastic injection overmoulding is being explored for structural applications within the automotive and aerospace sectors. Low-cost fibre-filled injection moulding polymers are typically combined with high stiffness, high strength continuous fibre organosheets (see Figure 1.a). In this way, manufacturing can be simplified such that the continuous fibre material requires only a moderate change in shape during forming, while the discontinuous material is used to generate complex geometrical features via injection moulding.
Overmoulded parts have several design and manufacturing challenges. An abrupt transition from insert to overmoulding material results in stress concentrations at the interface due to the mismatch in stiffness, therefore the efficiency of the insert is low. This transition must be managed through a combination of laminate design rules and geometrical solutions. Discrete inserts also cause potential problems in terms of manufacturing, such as fibre wash, as it is difficult to constrain them when subjected to considerable pressure during the overmoulding process [1]. Injection moulded parts also tend to have heterogeneous fibre architectures due to flow-induced alignment (see Figure 1.b), which can have a significant effect on the variability of the bond strength for overmoulded parts [2].
This contribution introduces a numerical tool that can efficiently support the design and manufacture of thermoplastic overmoulded parts of industrial scale (see Figure 1.a). The tool is set to predict process induced fibre angle deviation in the continuous fibre insert, caused by a differential of pressure across the surface as the mould tool closes. This work builds on the physics-based DefGen material model developed at the Bristol Composites Institute. Whilst the model was originally developed to capture the visco-elastic response of thermoset composites, it is also appropriate to model the compaction response of thermoplastics [3] [4]. The main restriction for the analysis of full-size models is the large computational cost of traditional ply-by-ply modelling. To tackle this, a previously developed homogenisation scheme [5] has been used for the analysis. A series of compaction tests have been performed to extract adequate material properties for PA66. Model validation was then performed on feature components tested in a lab environment and then on a real-sized overmoulded panel (see Figure 1.b).
The results show the potential of the proposed approach for rapidly predicting the deformation in the organosheet during the overmoulding process (see Figure 1.c-1.d). This work can potentially improve the Design for Manufacturing processes in industry and the suppression of many of the costly physical trials currently required to optimise the manufacturing conditions of injection overmoulded components.
Overmoulded parts have several design and manufacturing challenges. An abrupt transition from insert to overmoulding material results in stress concentrations at the interface due to the mismatch in stiffness, therefore the efficiency of the insert is low. This transition must be managed through a combination of laminate design rules and geometrical solutions. Discrete inserts also cause potential problems in terms of manufacturing, such as fibre wash, as it is difficult to constrain them when subjected to considerable pressure during the overmoulding process [1]. Injection moulded parts also tend to have heterogeneous fibre architectures due to flow-induced alignment (see Figure 1.b), which can have a significant effect on the variability of the bond strength for overmoulded parts [2].
This contribution introduces a numerical tool that can efficiently support the design and manufacture of thermoplastic overmoulded parts of industrial scale (see Figure 1.a). The tool is set to predict process induced fibre angle deviation in the continuous fibre insert, caused by a differential of pressure across the surface as the mould tool closes. This work builds on the physics-based DefGen material model developed at the Bristol Composites Institute. Whilst the model was originally developed to capture the visco-elastic response of thermoset composites, it is also appropriate to model the compaction response of thermoplastics [3] [4]. The main restriction for the analysis of full-size models is the large computational cost of traditional ply-by-ply modelling. To tackle this, a previously developed homogenisation scheme [5] has been used for the analysis. A series of compaction tests have been performed to extract adequate material properties for PA66. Model validation was then performed on feature components tested in a lab environment and then on a real-sized overmoulded panel (see Figure 1.b).
The results show the potential of the proposed approach for rapidly predicting the deformation in the organosheet during the overmoulding process (see Figure 1.c-1.d). This work can potentially improve the Design for Manufacturing processes in industry and the suppression of many of the costly physical trials currently required to optimise the manufacturing conditions of injection overmoulded components.