The subject of the work was the assessment of the possibility of using Cadmould 3D-F software based on numerical analysis to design complex injection moulding cavities with plasticised polymer feed channels on the example of an element requiring special dimensional accuracy. The overarching goal of the design process was to create the most advantageous geometry of the injection moulding cavity model and the dedicated material supply channels, which will minimize the effect of problems occurring during injection moulding process, such as processing shrinkage, surface collapse, warpage and mouldings deformation. As an additional criterion, the smallest possible degree of complexity of the designed system was adopted for economical reasons and elimination of subsequent production problems resulting from the complex geometry of the designed mould.