Abstract
Computer numerical control (CNC) machining of polymeric resins, such as those based on epoxy or polyurethane, to produce prototype tooling still has a number of important advantages over new layer manufacturing technologies. However, some machining limitations, mainly related to geometric details that cannot be easily milled, can pose challenges for tooling manufacturers. For metals, some of these difficulties are overcome by using electrical discharge machining which significantly increases the manufacturing time. Unfortunately, this technique cannot be used with polymeric resins. This paper investigates the main milling limitations for prototype tooling using polymeric resin board and proposes a procedure for their solution. The proposed solution consists of breaking the challenging features down into simpler ones that can be obtained solely using milling and then assembling the new features in the main mould inserts. A test part was manufactured to test the proposed procedure from the design of the insert to the injection moulding stage. With the mould inserts obtained 100 polypropylene prototype parts were injection moulded using an industrial injection moulding machine. The results show that, provided adequate tooling skills are available, the proposed systematic approach allows prototype tooling using polymeric resins containing challenging features to be obtained solely using milling operations, and this is achieved together with a considerable time and cost savings, when compared to traditional methods and materials. Therefore, it increases the competitiveness of CNC machining in this sector.