Abstract-This paper presents a study in which an attempt has been made to improve the quality characteristic (shrinkage) of an injection molding product (plastic tray) made from blends plastic (75% polypropylene (PP) and 25% low density polyethylene (LDPE)) by optimizing the injection molding parameters using the Taguchi method. The performance of the plastic trays is evaluated in terms of its shrinkage behavior. An orthogonal array (OA), main effect, signal-to-noise (S/N) ratio and analysis of variance (ANOVA) are employed to analyze the effect of injection molding parameters on the shrinkage behavior of the product. The analysis of the results shows that the optimal combination for low shrinkage are low melting temperature, high injection pressure, low holding pressure, long holding time and long cooling time. Using Taguchi method for design of experiment (DOE), other significant effects such as interaction among injection molding parameters are also investigated.Index Terms-Taguchi method, optimization, injection moulding, low density polyethylene (LDPE), Polypropylene (PP), shrinkage test
I. INTRODUCTIONProducts made from plastic range from sophisticated products, such as prosthetic hip and knee joints, to disposable food utensils. One of the reasons for enormous popularity of plastics in a wide variety of industrial applications is the tremendous range of properties exhibited by plastics and their ease of processing [1]. Injection moulding is the most important method for manufacturing varieties of plastic components. It is based on the ability of thermoplastic materials to be softened by heat and to harden when cooled [2]. The injection moulding is conceptually simple. In the process of producing plastic tray, the plastic in the form of pellets or granules is melted and then forced into the cavity of a closed mold which gives shape to the plastic. After sufficient time for plastic to solidify (usually by cooling), the Manuscript received August 19, 2010. This work was supported by the fund from the Short Term Grant Universiti Sains Malaysia.S. Kamaruddin is with the School of Mechanical Engineering, Engineering Campus Universiti Sains Malaysia, 14300, Nibong Tebal, Pulau Pinang, Malaysia (Phone: 604-5996382; Fax: 604-5941025; e-mail: meshah@eng.usm.my mold is opened and the part is ejected from the mould and the mold is closed again to repeat the cycle [3]. The process parameters such as injection speed, injection pressure, holding pressure, melting temperature, holding time, cooling time and etc. need to be optimized in order to produce finished plastic parts with good quality. Various studies have been carried out to improve or to optimise the quality characteristic so as to produce high quality commercial plastic product on injection moulding machine [4]- [7]. However, most of the researchers did not consider the effect of interaction between parameters on the quality characteristic of the products although, it could be quite significant.This paper attempts to describe the optimisation of the injection...
