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Mould Flow

SMC/BMC materials offer exceptional flexibility to the designer: for example a design based on mouldable SMC/BMC can produce a highly complex, multi-functional part

First stage in the design process is to create a computer aided design (CAD), using numerical modelling such as finite element analysis (FEM). To create an accurate and representative design model, good knowledge of the materials¡¯ behaviour and capabilities are needed. SMC/BMC properties are well known, which makes it a avourable choice for designers. With the mechanical properties,, a designer can create a CAD model and simulate mechanical reliability using FEA and can rework the design as necessary. We¡¯ve used the example of a virtual car bumper beam to illustrate this process. The CAD model is transferred into a meshed structure, which consists of 3-dimensional geometrical elements and forms the basis for flow simulation. Each element owns specific physical properties, which are linked. The diagram shows the result of the flow simulation of the bumper beam. In the blue area the SMC is placed in the mould and, with simulation of the filling-process, showing the time evolution of the flow front during the filling process ¡®Flow simulation predicts cavity filling behaviour¡¯ the application of moulding pressure, starts to flow. The red colour indicates the flow front, which reaches , the edges of the cavity. The main results obtained via the flow simulation, are firstly the filling time and secondly whether the cavity is completely filled and if there are weld lines, where the material meets. Weld lines should be avoided, especially on visible parts.

The flow simulation (below) also importantly shows the fibre orientation within the part. In terms of mechanical behaviour, correct fibre orientation is essential, since the fibres bear the loadings and stresses. In a successful SMC part, the design has to enable the fibres to flow along the load direction - so the design must include the right flow characteristics.

Simulation of the filling-process,showing the time evolution of the flow front during the filling process

Correct fibre orientation is essential to cope with mechanical loadings and stresses¡¯Structural analysis Structural analysis can then be performed. By adjusting reference conditions, the impact of dynamic and static forces and excitations can be calculated. The simulation below shows the mechanical behaviour of the bumper beam under a single static load. The deformation is clearly shown and the colours indicate the resulting tension within the material. Now the designer can decide whether the stresses are acceptable or if the design needs modification.
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