Automatic determination of 3-D parting lines and surfaces in plastic injection mould design

In this paper, a methodology to generate the 3-D parting lines and parting surfaces is presented based on the optimal parting direction, the geometrical characteristics and topological relationships of injection moulded parts. The moulding surfaces are first classified into three main groups according to their orientation to the parting direction and their topological relationships. The largest edge-loop of the surface group is then defined and the algorithm to generate the edge-loop in different surface groups is proposed. The method to calculate the projected area of an edge-loop on the plane perpendicular to the optimal parting direction is also introduced. The 3-D parting lines are generated based on the proposed criterion of considering the above projected areas of edge-loops. After the parting lines are determined, the parting surfaces are generated by extruding the parting lines perpendicularly outwards to the parting direction. The case studies show that the methodology is efficient in determining the parting lines and the parting surfaces automatically in an intelligent mould design system.