Rigid moulds

RTM has received the greatest amount of attention with regards to process simulation, as it presents the most simple case due to the constant cavity thickness. The CRTM process presents a more complex case due to the changing cavity thickness during the secondary compaction stage. 

Very little work has been presented in the literature on the monitoring of tooling forces during RTM or LCM processes. While a load cell can easily be mounted on the hydraulic ram of a press, the local forces and ratio of reinforcement stress and fluid pressure are often ignored. By using a distributed pressure sensor placed inside the mould, Walbran and co-workers [72, 89, 99] were able to measure spatial variation in the normal stresses applied to the mould during the process cycles for RTM and CRTM, and to isolate the fluid forces from forces due to preform compaction. 

The LCM operator usually has very little scope for influencing or controlling the process once initiated. While this may produce a more repeatable process than traditional open-mould techniques, it also puts more emphasis on the process design. Owing to the cost of materials used in LCM, process 

5 Force and injection pressure traces during the manufacturing process of a sample flat geometry using (a) RTM, (b) velocity-controlled CRTM, and (c) force-controlled CRTM. 

Research is also on-going to simulate the CRTM process [107-112] this process adds complication as compared to the RTM process in that part of the flow results from the reinforcement compaction. A controlled force may be employed instead of a controlled displacement during the compression flow phase, which provides an additional challenge for simulation [71, 113-116]. When the initial closing of the mould is such that an air gap remains between 

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As for rigid mould processes, one of the main goals of simulation is to minimise the trial and error development for manufacturing new parts. 

Journal paper concerning rigid mould processes... 

Kelly PA, Bickerton S. A comprehensive filling and tooling force analysis for rigid mould LCM processes. Composites Part A Applied Science and Manufacturing, 2009 40(11) 1685-1697. DOl 10.1016/j.compositesa.2009.07.013. 

Two types of ultrasonic seal are possible, ie contact or near field such as with high frequency welding, where the electrode or applicator is applied directly to the material where the weld is to be made, and remote or far field which is suitable for joining rigid mouldings. With the latter, the tip of the work horn is applied to a point of the work which may be some inches away from the faces to be welded, and the vibrations are transmitted through the material. 

The development of materials other than polyethylene and plasticised PVC will open up further market possibilities. Rigid mouldings should find acceptance in the furniture... 

The most commercially successful graft copolymerisation of NR is that with poly(methyl methacrylate)(PMMA). The resulting derivative is usually referred to as MG rubber. It is a hard rubber which blends well with NR in all proportions and is use as a reinforcing agent and in rigid mouldings. 

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