The article describes an optimization methods analysis in the technological process of plastic injection using the simulation tool Autodesk Moldflow Adviser. The Polyethylene 120J was the material used in production of the plastic part analyzed. Following the simulations, deficiencies affecting the quality of the final part were identified. Modifications were gradually made both in the cover's design and as changes in the process parameters so as to eliminate the deficiencies identified. In the first step, the value of the injection time was modified based on the results of the analysis of the determination of the ratio of solidified layers at the end of the process of filling the mold cavity. The second type of adjustment required a change in the molding's design. Based on the result of the simulation of forecasting cooling quality, we proposed a change in the wall thickness of selected model elements, specifically the adjustment of the wall thickness of the bolted joint column from 3 to 4 mm. The last adjustment consisted of adjusting the additional pressure profile.