Advanced Simulation of the Rotational Moulding Process

Large hollow seamless and essentially stress-free plastic products of various size is the hallmark of the rotational moulding process. Relatively longer cooling time and warpage problems insisted researchers develop simulation models for optimisation of the polymer process to achieve better productivity. The work aimed to develop process simulation, and simulation models for direct mould heating and shrinkage-warpage. It was discovered from the literature survey that simulation works were scarce, and no simulation models existed for direct mould heating and prediction of warpage in rotomoulding. Main components of rotational moulding process simulation for modern time requires simulation models of direct mould heating and the cooling accounting shrinkage-warpage phenomenon. As a result, the simulation model work was split into three components: complete rotomoulding cycle (process) simulation, direct mould heating and shrinkage-warpage models. Development of shrinkage-warpage simulation model forms a major piece of work. It was identified that Discrete Element Modelling (DEM) has the potential for process simulation with further work. All the simulation models were developed in FE based Abaqus software. For the first time, developed simulation model of direct electric mould heating showed controlled heating could be achieved, peak internal air temperature of 223 °C matches closely with 225°C of experiment value. A novel thermal expansion coefficient model was built for warpage simulation modelling for the first time in rotational moulding. The main conclusions of simulation models are that the cooling rate has a significant effect on warpage magnitude and results are in good agreement with experimental values of literature, and in-mould pressure of 10 kPa controlled the warpage growth by 75% for a given part. The external cooling rate was found to be directly proportional to warpage growth in parts, uniform cooling of mould controls the temperature gradient in the polymer part. Temperature dependent polymer properties were readily not available and were derived from literature data. Density, expansion coefficient and Young`s modulus values are significantly important for warpage prediction as determined by sensitivity simulation investigation. Industrial application of the shrinkage-warpage model on fuel tank mould showed qualitative agreement with experimental rotomoulding data. Successfully developed simulation models for direct mould heating and warpage prediction can be exploited for optimization of the process, and feedback for mould designer and moulder. Further work on DEM, measurement of polymer properties, and cohesive parameters, different forms of pressure and more validation work helps in development of advanced rotomoulding process simulation model.