Thicknesses

Predicting local thickening of a laminate.

High geometric tolerances of the final product can be achieved by forming a thermoplastic laminate with two-sided rigid tooling. The high quality finish and the mechanical strength of the final product depend on the consolidation during the forming cycle. Deformations during the forming process introduce changes in the blank thickness resulting in areas with high and low compression forces. Low compression results in poorly consolidated spots, whereas high compression could lead to tearing and degradation.


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Figure 1: AniForm PrePost screenshot with tooling and laminate.

Figure 1 shows the tooling of a product geometry from automotive industry. When predicting the forming process of this part with AniForm, a thickness distribution over the entire blank will be calculated. This information can be used for cavity design or for cavity modifications of existing tooling. In this way, the above-mentioned problems can be avoided. This yields less trial & error, thereby achieving a cost reduction in the product development phase.

The forming process is modelled in AniForm PrePost. Meshes for tooling and blank are imported after which the properties for these can be assigned via the tree view. A laminate plan is assigned to the laminate, which defines the lay-up, the constitutive models and their related material properties. The constitutive models describe the in-plane, out-of-plane, and interface deformations. Examples of such deformations are intra-ply shear, bending, and friction respectively. These data can be determined by conducting material characterisation programmes. The laminate comprises four woven layers, each layer having a family of fibres in the x-direction and a family of fibres in the y-direction.


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Figure 2: Animation of the predicted forming process, showing the developing shear angle distribution.

Figure 2 shows the predicted deformations. The design engineer obtains a good impression of the phenomena that occur during the process. The shear angle distribution is plotted in figure 2 as well. The shearing, together with other in-plane deformations, determine the thickness distribution in the blank, which is shown in figure 3.


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Figure 3: Predicted thickness distribution of the formed laminate.

Figure 3 shows that the blank thickness after forming deviates from the nominal blank thickness of 0.15 mm. Large thickness increments in red are predicted near corners involving strong double curvature. These spots can be used to modify the initially uniform mould cavity, thereby preventing process induced defects such as bad consolidation in low compression, and damage in high compression areas.


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Figure 4: Predicted fibre stresses and directions in the final forming stage.

Figure 4 shows the stresses and the fibre directions of one family of fibres in the top ply. The fibre paths are affected by the deformation, which contribute significantly to the ultimate mechanical performance of the part. Concentrated stresses in the fibre directions develop due to the bridging effect. During the forming process, the laminate is spanned over some geometrical features in the tooling. Further closing the tooling pushes the spanned material inwards, which is accompanied by the development of the stresses indicated in red. These areas can affect the final product quality. Based on such information, the design engineer is able to conduct modifications to product and process design.