The growth of injection moulding  as a manufacturing process has led to the development of more products resulting in an increase in the focus on product quality, as manufacturers try to lower production costs, reduce product weight and eliminate defects. Of particular concern is the flow  behavior of molten resin in the mould cavities during the production process. Inconsistencies in the flow of the melt tend to result in uneven or incomplete filling of the mould, resulting in production of defects (short shots). In the paper the Taguchi method is used to determine the optimum values of the injection moulding process parameters for High Density Polyethylene (HDPE.) plastic parts. A moulding processing window in which the process will achieve maximum quality, with major focus being on mould filling is developed.