Rapid Thermal Cycling of Injection Molds: An Overview on Technical Approaches and Applications

A heated mold with temperature above the polymer-softening temperature is highly desired in precision injection molding. The elevated mold temperature reduces unwanted freezing during the injection stage, thus improving moldability and enhancing part quality. The resulting advantages include, but are not limited to, longer flow path, improved feature replication and surface transcription, reduced molecular orientations and residual stresses, smoother surfaces of composites, better control of crystallization, stronger weld lines, etc. However, the heated mold needs to be rapidly cooled during the cooling stage to maintain a short cycle time. Despite the large body of available literature, mold rapid heating and cooling does not represent a well-developed area of practice. Development of capable techniques for rapidly heating and cooling a mold with a relatively large mass is technically challenging because of the constraints set by the heat transfer process and the endurance limits set by the material properties. This article attempts to offer a constructive overview on the state of the art in mold rapid heating and cooling, with the goal of explaining the working mechanisms and providing unbiased accounts of the pros and cons of existing processes and techniques. Successful applications of existing processes are highlighted and potential improvements of these processes are suggested. The article further intends to provide a fundamental understanding of the constituent elements and corresponding building blocks needed in a workable mold with a rapid heating and cooling capability. An increased understanding of these elements will facilitate the development of more capable new processes. (C) 2009 Wiley Periodicals, Inc. Adv Polym Techn 27: 233-255, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20136