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This study presents an optimization of injection moulding parameters on mechanical properties of plastic part using Taguchi method and Grey Relational Analysis (GRA) approach. The orthogonal array with L9 was used as the experimental design. Grey relational analysis for ultimate tensile strength, modulus and percentage of elongation from the Taguchi method can convert optimization of the multiple performance characteristics into optimization of a single performance characteristic called the grey relational grade (GRG). It is found that mould temperature of 62oC, melt temperature of 280oC, injection time of 0.70s and cooling time 15.4s are found as the optimum process setting. Furthermore, ANOVA result shows that the cooling time is the most influenced factor that affects the mechanical properties of plastic part followed by mould temperature and melt temperature.

This study focuses on the analysis of fill time by optimizing the injection molding parameters to reduce the defects that are always found on the plastics part such as poor weld line and part not completely filling which can contribute to mechanical properties of the plastic part. The parameters selected for this study are melting temperature, mold temperature, injection time, and the number of gate positions. Response Surface Method (RSM) was used to determine the most significant and optimum parameters on the fill time. From the result analysis, it is found that the injection time is the most significant parameter that affected the fill time with a 99% contribution. The result shows that there is no interaction between process parameters toward fill time which the injection time is the only major factor that affects the fill time. The improvement increases by 0.07% after the optimization process from 4.278s to 4.281s. The most optimum parameters to longer the injection time are mold temperature at 60°C, injection time at 4s, and the number of the gate with two gates position. Thus, the longer the injection time, it can reduce the defect of molded part in the injection molding process.

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This study modified a two-plate family plastic injection mould to become interchangeable by changing the core and cavity plates using an existing mould base. The plastic parts produced in the modified two-plate family plastic injection mould included tensile, hardness, impact and flexural test specimens. The cavities of the plastic parts were machined at the parting surface of core plate. Meanwhile, the feeding systems including runner and gate system were machined at the cavity plate to ensure molten plastic can be injected in the cavity area. Various factors have been considered during the designing and fabricating process. This is to ensure the process of assembly between mould plate and standard mould parts can be done perfectly. The plastic parts in the family mould were successfully injected after mould was completed assembled and mould trial was performed. The plastic parts which had been ejected from the family injection mould are purposely produced for future research to study the mechanical properties of plastic materials.