Conformal cooling channels design for rapid plastic injection mould

Abstract

Cooling design in thermoplastic injection moulding (PIM) process is of paramount importance to the performance of the mould, influencing both the quality and productivity of the part being produced. However, cooling channel design and its fabrication processes are limited to respectively simple configurations as well as conventional machining processes, such as straight-line drilling, and milling, etc. The advancement of rapid tooling (RT) technologies and solid freeform fabrication (SFF) techniques have provided the capability to produce rapid tool or injection mould with complex geometric design of cooling channel, which are conformal to the contour of the mould core or cavity surfaces. The shape conformance between the cooling channels and mould surface cavity can achieve a nearer uniform cooling performance and thus with fewer defect formations. However, method with sound theoretical base for the design and verification of cooling channel corresponding to mould cavity (or core) surface in the PIM process is still lacking, especially for the complex geometric design in conformal cooling channel (CCC.) In this research, the cooling process of thermoplastic injection moulding is first reviewed from the heat transfer viewpoint. The most effective heat transfer that can be achieved in practice is then formulated in terms of visibility concepts of computational geometry. Feasibility checks for both conventional straight-line drilled cooling channels and conformal ones are then analyzed with light illumination. Conformal cooling channel generation is re-examined and a more appropriate equidistant cooling channel generation methodology is explained. In addition, variable radius conformal cooling channel (VRCCC,) conformal porous pocket cooling (CPPC,) and conformal pocket cooling (CPC) are proposed to test their heat transferrabilities, and benchmarked against the straight-line drilled cooling channel. The output results of industrial case studies are visualized by 3D rendering using computer-aided industrial design (CAID) tool and validated with the aid of meltflow analysis. It is found that further improvement in heat transferrability between the cooling channel surface and the mould surface can be realized with VRCCC and CPPC. Finally, the limitations of the visibility based methodologies to rapid PIM of zero defect parts are discussed and possible future works suggested.