Fast mold surface temperature evolution: Challenges and opportunities

Fast mold temperature evolution allows obtaining injection molded parts with lower filling pressure, better surface finishing, more accurate surface replication and reduced frozen-in orientation. Recently proposed, thin heating devices, with very low thermal inertia, located just below the mold cavity surface, allow obtaining high surface temperature during filling and low surface temperature during cooling stage. Several tests have been carried out injecting isotactic polypropylene into a rectangular cavity with the aim of analyzing the effects of heating temperature and heating time (equal or larger to the filling time) on both part quality and process evolution. As far as the part quality is concerned, a relevant improvement of the surface micro features replication and a lower orientation level have been attained by increasing heating temperature and time. From the point of view of the process, a significant reduction of filling pressure and pressure drops have been reached by increasing the mold surface temperature. The cycle time increases when the surface heating time increases. However, this increase has been found not much different from the surface heating time, if thin heating devices located at a short distance from the mold surface are adopted. Some secondary effects on the pressure evolutions related to the in-mold cooling and solidification have been also observed during the process and have been discussed with reference to the heating elements activity.