Manufacture of Production Quality Injection Mold Tools Using SLS and HSM

Abstract

The use of a rapid manufacturing method to create injection mould tools offers the opportunity to create conformal cooling channels in the core/cavity inserts. Conformal cooling channels allow for better thermal management of the injection mold tool through the cycle, with the potential to reduce cycle times and/or improve product quality. However, currently available rapid manufacturing methods do not deliver the levels of accuracy and surface finish required to meet typical injection mould tool specifications. This paper reports on a hybrid approach to developing the mold inserts, which uses the rapid manufacturing process of indirect selective laser sintering (SLS), using the 3D Systems LaserForm process, to create a near net shape insert with conformal cooling channels, and then produces the net shape inserts by using high speed machining (HSM) as a finishing process. This approach to injection mold tool development has been tested through three industrial case studies. In each study existing injection mold inserts have been redesigned to give a conformally cooled tool. These have then been manufactured to near net shape in a steel/bronze metal composite through indirect SLS, and finished to production specification using HSM, EDM and polishing. Within the case studies the main aim has been to improve productivity, and the inserts have been evaluated in industrial trials in order to assess their performance in terms of cycle time, energy usage, durability and quality. The results show that significant productivity improvements and energy use reductions in injection molding are possible through the implementation of conformal cooling. Consistency of part quality and material durability have been assessed through extended molding trials, and in some cases there is a clear economic benefit to using the inserts. However, the importance of up front modelling to understand the impact of conformal cooling channels, the need for careful planning in manufacture to ensure that the required internal geometry is created, and the need for multiple representations of the required geometry to inform the different stages of the manufacture process are highlighted.