parts. If an unbalanced flow pattern existed, that would lead to (over-) packing difficulties and part warpage [7]. Also, the appropriate selection of gate position would help to reduce the filling time and balance the moulded parts' temperature distribution [8]. The incorrect selection of process conditions may result in undesirable shrinkage, warpage [9], unbalanced fill or deterioration of mechanical or optical properties [10]. Among the aforementioned moulding problems, the present paper focuses on part warpage and injection pressure. Prior to discussing warpage, it is necessary to describe the principle difference of shrinkage characteristics of thermoplastic materials. The Pressure–Volume–Temperature (PVT) diagrams provide information with respect to change in specific volume as a function of melt processing temperature and pressure applied on the melt. For amorphous and crystalline materials the specific volume in the melt range varies linearly with the temperature. When pressure is applied on the melt, the specific volume decreases, hence its reciprocal value, the density increases. Upon reaching the transition temperature below which the material is considered solid, amorphous and crystalline materials differ in shrinkage characteristics. Amorphous materials exhibit a linear variation, while crystalline grades show an exponential dependence of specific volume on temperature just below the transition temperature. Owing to the fact the crystalline grades consist of crystalline and amorphous phases, the crystallization phenomenon during solidification causes an orderly, consequently more densely packed microstructure. The formation of the …