64 International Journal of Engineering & Technology Research Volume-1, Issue-1, July – September, 2013, pp. 64-76, © IASTER 2013 www.iaster.com, ISSN Online: 2347-4904, Print: 2347-8292 Optimization of Injection Moulding Process for Multiple Quality Characteristics of Reprocessed ABS Products via the Integration of Taguchi Method and Grey Relational Analysis Ng Chin Fei 1 , Nik Mizamzul Mehat 1,2 , Shahrul Kamaruddin 1 1 School of Mechanical Engineering, Universiti Sains Malaysia, Engineering Campus, 14300, Nibong Tebal, Penang, Malaysia 2 Department of Mould Technology, Kolej Kemahiran Tinggi MARA, Balik Pulau,Genting, 11000, Balik Pulau, Penang, Malaysia ABSTRACT Determining the optimal parameters setting is performed routinely in the plastic injection moulding industry as it has a direct and dramatic influence on product quality and costs. This study emphasizes on the optimization of processing parameters to enhance multiple quality characteristics of the injection-moulded ring stopper, including hoop tensile strength, elongation at break and shrinkage. The specimens were prepared under different injection moulding conditions according to the design of experiments based on the Taguchi’s L 9 orthogonal array, by varying the melt temperature, packing switchover, injection pressure and packing pressure at second progressive stroke. Grey relational analysis is integrated with main effects analysis to obtain the optimal parameters setting. From the analysis, the optimal parameters setting which statistically result in the maximum hoop tensile strength and elongation at break, as well as minimum shrinkage for the ring stopper, are predicted to be the combination of melt temperature of 240°C, 80% of packing switchover, 1600MPa of injection pressure and 800MPa of packing pressure at second progressive stroke. On the other hand, the results also revealed that the melt temperature was found to be the most decisive factor whereas the packing pressure at second progressive stroke has the least influence in affecting the hoop tensile strength, elongation at break and shrinkage of the ring stopper in this study. Keywords: Grey Relational Analysis, Taguchi Method, Optimization, Multiple Quality Characteristics, Hoop Tensile Strength. 1. INTRODUCTION Injection moulding is the most important manufacturing process in the plastics industry as more than 1/3 of all thermoplastic materials are injection moulded and more than half of all polymer processing equipments are for injection moulding [1]. This is because the injection moulding process has the highest efficiency, largest yield, and highest dimensional accuracy among all the processing methods [2]. In addition, the injection-moulded products which exhibit good dimensional accuracy and excellent surface finish, has further proven the value of injection moulding process [3]. However, the complexity of injection moulding process has created a very intense effort to keep the quality characteristics under control. There are many factors contributing to the occurrence of defects that affect the quality of injection-moulded parts during the production such as material selection, part and mould designs and processing parameters. Inappropriate combination of material selection, part and mould design and the processing parameters can cause numerous production problems (e.g. product defects, long lead time, much scrap, high production costs, etc.), reduce the competitive price advantage, and decrease the company’s profitability.