Development and Evaluation of a Dynamic Mould Temperature Control System with Electric Heating for Variotherm Injection Moulding

Variotherm injection moulding process is a new injection moulding technology. In this process, the mould cavity surface is heated up to a high temperature, before the filling stage, usually higher than the glass transition temperature (Tg) of the polymer. When the filling stage is finished, the shaped polymer melt will be cooled down quickly for mould opening. It is used for producing plastic parts with no weld lines, no flow marks and a shiny surface (up to 98% light reflecting), even for fibre-reinforced plastics. In this study, a new dynamic mould temperature control system with electric heating and coolant cooling for variotherm injection moulding was proposed and studied. The temperature control principle and moulding process for this new technology were explored, and an electric heating mould structure with electric heating rods and cooling channels was developed. The thermal response efficiency of the system and temperature uniformity of the mould surface was also evaluated by transient thermal analysis with a commercial software package, ANSYS. The cooling efficiency of the new variotherm injection moulding was compared with that of conventional injection moulding by calculating the cooling time of the two moulding techniques for plastic parts with different thickness. Finally, an electric heating mould for a 32-inch LCD panel was designed and manufactured, based on the simulation results. With the new proposed dynamic mould temperature control system, a variotherm injection moulding production line for the LCD panel was constructed. The test production results showed that the dynamic mould temperature control systems could efficiently and accurately control the mould temperature. The LCD panels produced with this new variotherm injection moulding process had a high surface gloss, without defects such as weld lines, sink marks, flow marks, etc. which usually occur in conventional moulding.