This paper applies a Genetic Algorithm (GA) method to optimize injection moulding conditions, such as melt temperature, mould temperature and injection time. A GA is very suitable for moulding conditions optimization where complex patterns of local minima are possible. Existing work in the literature has limited versatility because the optimization algorithm is hard-wired with specific objective function. However, for most of the practical applications, the appropriateness of optimization objective functions depends on each specific moulding problem. The paper develops a multi-objective GA optimization strategy, where the objective functions may be defined by the designers, including using different criteria and/or weights. For parts with general quality requirements, an objective function is also recommended with some quality measuring criteria, which are either more accurately represented or cover more moulding defects than those from existing simulation-based optimization approaches. The paper also elaborates on the effective GA attributes suited to moulding conditions optimization, such as population size, crossover rate and mutation rate. A case study demonstrates the effectiveness of the proposed approach and algorithm. The optimization results are compared with those from an exhaustive search method to determine the algorithm's accuracy in finding global optimum. It is found to be favourable.
IntroductionInjection moulding conditions such as melt temperature, mould temperature and injection time are important parameters in injection moulding process design. The determination of appropriate moulding conditions is a nontrivial task (Pandelidis and Zou 1990). Increasing melt temperature can reduce viscosity, which results in the desired lower cavity pressure and shear stress. Yet it also increases cooling time which lowers productivity. Besides, too high a melt temperature may cause material degradation. Mould temperature has the similar effect but of much lower significance. Compared to melt temperature and mould temperature, injection time is the most important parameter affecting pressure and shear stress. Shorter injection time contributes to shorter cycle time, but it increases cavity pressure and shear stress. Excessive increase in injection time, however, will lead to an excessive decrease in melt temperature and increase in viscosity, causing cavity pressure and shear stress to increase significantly. Thus, it is necessary to optimize these parameters in order to produce a high quality part at minimum cost.There are generally two approaches in deriving optimal moulding conditions. The first is using artificial intelligence (AI) and knowledge-based system (KBS),