Innovative design and simulation study of a mould for rapid temperature control in micro-injection moulding

Precise temperature control of the mould surface is a key factor for optimising product quality in micro-injection moulding. The ability to rapidly rise or decrease the temperature during the moulding cycle adds further processing benefits including increased productivity, increased freedom of design, and increased quality levels in the finished part. In this work, an innovative concept of mould design was developed for the rapid temperature control in micro-injection moulding. A mould cavity geometry of area equal to 40 mm² and a thickness of 200 µm was created in a small and removable insert. Temperature control was implemented using very thin heating layers and thermocouples that can be attached near the surface of the cavity. In order to minimize the thermal dispersion, a push-pull system for the cavity seat was created. When the mould plates are in the open position, the push-pull system allows a quick separation of the cavity seat from the rest of the mould. For the temperature control, two steps are considered: the heating and the cooling. When the mould is in the open position and the cavity seat is pulled from the mould, the heating step is activated. Because of the air gap between the mould and the cavity, large increases in cavity temperature are feasible in a few seconds. When the mould is closed, conversely, the cavity seat is pushed toward the mould reducing the air gap and permitting a rapid cooling. This step involves also the injection of the polymer in the cavity. In addition, an evaluation of the heat transfer, by means of simulations was carried out. The study demonstrates that during the heating step, the use of the system allows the reduction of the thermal dispersion and the achievement of a temperature increase of the order of several hundred degrees at the cavity surfaces. Furthermore, the high thermal conductivity of the cavity permits to obtain a fast cooling when the mould is closed.