Modelling of Resin Transfer Moulding

Resin Transfer Moulding (RTM) is a manufacturing process in which resin is injected into a fibre filled tool cavity to produce composite components. The RTM process is highly repeatable and is particularly suited to components requiring tight dimensional control, and the recurring costs for complex shapes are less than hand lay-up techniques.

The costs for the design and manufacture of an RTM tool are high, and so it is vital to understand how the tool will perform and how the component design affects manufacturability. Simulation of the manufacturing process when introduced at an early stage in the component and tool design, reduces the number of iterations required to produce an acceptable manufacturing tool. The ultimate objective is to provide an integrated simulation capability, enabling the transfer of data from the draping, resin injection and cure, through to a performance analysis and life cycle assessment.

The modelling techniques used for the simulation of Resin Transfer Moulding are based around a Smoothed Particle Hydrodynamics code, that enables the simulation of the resin flow, heat transfer and resin cure within a single simulation. SPH is ideal for this type of analysis because it naturally tracks the free surface of the resin and the movement of resin so that the degree of cure and the resin viscosity can be assessed at any time. The code has been validated against experimental data and has been used to predict the resin flow patterns in real compoenents.

The figures show the results of a simulation for a component, where the tool is not shown. The component is an aerospace geometry that is geometrically complex. The resin is injected at the inlet gate at a temperature of 80 degrees into a tool that has been preheated to a temperature of 120 degrees. Initially the resin flow rates into the tool are high and there is little time for heat transfer and so resin temperatures remain around 80 degrees. As the resin heats up, its viscosity reduces, but simultaneously it begins to cure and the viscosity increases through this mechanism. As more resin is injected into the tool, the flow rates reduce, and the temperature of the resin furthest from the inlet gate rises towards the tool temperature. By the end of the simulation, most of the resin is at the tool temperature and the resin has filled the tool. Using this predictive capability, resin injection points can be tested to determine their best location before committing to tool manufacture. Any unfilled parts of the tool can also be identified enabling the modification of the filling strategy.