Process Design for Optimal Mold Cooling

Process control has been recognized as an important means of improving the performance and consistency of thermoplastic parts. However, no single control strategy or process design has been universally accepted, and molding systems continue to produce defective components during production. The capability of the injection molding process is limited by the thermal and flow dynamics of the heated polymer melt. This paper develops a fundamental approach to process design for optimal mold cooling. Specifically, a viscoelastic constitutive model is utilized with process and quality models to develop theoretical and feasible limits for mold cooling. The analysis drives the development of a composite thermal structure consisting of 1) a thin layer with high density and specific heat, 2) a thin layer with low thermal conductivity, and 3) a conventional mold base with high thermal diffusivity. When pre-heated via gas convection, the resulting process enables isothermal mold-filling and improved polymer solidification. Numerical results indicate that the proposed system will reduce residual stress by 30% compared to conventional molding for equivalent cycle times.