Mesoscale Simulation Of The Mold Filling Process Of Sheet Molding Compound PDF Download

In Compression Resin Transfer Molding (CRTM), the fiber preform is placed in the mold; the top of the mold is lowered until there is a small gap between the preform and the mold. The measured amount of resin is injected through one or more gates into this highly permeable gap. Then the resin injection is switched off and the mold is closed by moving the mold platen towards the preform until it reaches the desired thickness. This action compresses the preform and pressurizes the resin to flow into the preform and occupy the empty regions between the fibers. This process is very attractive for high volume production of net shape composite structures and is being considered by automobile manufacturing industry for structural components. The challenge is to create void free structures with reasonable applied force with filling times of the order of a few minutes. A model and simulation of the process can help identify the important parameters in the process that will aid in achieving this goal. An existing numerical simulation that can model the RTM process has been modified to accommodate the presence of gap elements, compression of preform and reduction of mesh size during the process. The process is modeled in three stages: (i) resin injection into the gap, (ii) closing of the gap with negligible compression of the preform and (iii) preform compaction. An analysis of the process has been conducted to identify the important non-dimensional parameters that influence the process. A parametric study reveals the relationship between the material, process and the geometric variables in this process. To validate the numerical model, an experimental set-up was constructed. The set-up includes a semi cylindrical transparent mold which is compressed using pressurized water in a collapsible tube. Independent experiments are conducted to measure the permeability of the fabric and the force required for compression. Various process parameters such as the location of the resin front during the compression, the rate of compression and the force are recorded as a function of time. These results are compared with the simulation to gauge the accuracy of the model and the reliability in the characterization of the material parameters. This simulation should prove useful in development of process inputs for large scale structures to produce void free parts with optimal compression rates and pressures.