Recognition of pass features for automatic parting surface generation in injection moulds

Abstract

This paper proposes a topology-based algorithm for recognizing passage features using the concept of a multiface hole loop. The multiface hole loop is a conceptual hole loop that is formed over several connected faces and serves as an entrance or an exit of a passage. A passage feature is thus recognized by identifying two multiface hole loops corresponding to its entrance and exit. To generate the core and the cavity of an injection mould for a part with passage features, either the entrance or the exit of each passage must be covered by a surface, and this surface constitutes the parting surfaces. The algorithm proposed in this paper checks the connectivity of the two multiface hole loops to recognize passage features. The total number of passage features in a part is calculated from the Euler equation, and the identification procedure continues until the number of identified passage features equals this number. To find all of the multiface hole loops in a part, the proposed approach considers all of the combinations of connected faces. The edge convexity is used to judge the validity of multiface hole loops. By using the algorithm proposed in this paper, the passage features could be recognized effectively. The approach proposed is illustrated with several example cases.