AUTOMATIC SIDE CORE CREATION FOR DESIGNING SLIDER/LIFTER OF INJECTION MOULDS

Abstract

Injection moulding is one of the most popular manufacturing technologies in production. Nowadays, dramatic changes are happening in the domain of mould design where the traditional design method is being completely changed by the use of CAD/CAM/CAE technologies. However, mature computer systems to automate mould design process are still far from being realised due to increasing complexity of products themselves and of the whole moulding cycle. There have been several reports of research effort towards automation of mould design. But practical implementation of these results in the mould industry is rarely reported. To bridge the apparent gap between academia and practice, an intelligent mould design and assembly system (IMOLD system) is under development at the National University of Singapore. As part of its slider/lifter module, an algorithm is presented in this thesis to establish a novel framework automating the design process of sliders and lifters. As sliders and/or lifters are only necessary when undercuts exist after the parting direction and parting surfaces have been decided, emphasis is placed on automatic detection of undercuts and creation of slider/lifter heads (e.g. side cores) to clear out the undercuts. The algorithm takes the 3-D part model and its virtual core and cavity as the input. It firstly extracts all the edges (U-edges) on the part which cause the undercut problems. Next, faces of undercuts (U-faces) are derived from the identified U-edges and grouped to form individual undercuts. The undercuts are then classified into depressions and protrusions, considering their different geometric properties and the ways to· generate slider/lifter heads for them respectively. For undercuts of depression, a set of Boolean operations are used to create the heads; while sweeping operation is used to create heads for undercuts of protrusion. Finally, heads intersection are resolved so as to reduce the number of required sliders/lifters.

The developed algorithms have been implemented on Unigraphics platform by using User-Functions and have been applied to sample parts with different types of undercuts. The result indicates that the proposed geometric reasoning method is a viable way towards automatic mould design.