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2.1. Thermoelectric modules (TEM)
For the needs of the thermal manipulation, the TEM module was integrated into mould. Interaction between the heat and electrical variables for heat exchange is based on the Peltier effect. The phenomenon of Peltier effect is well known, but it was until now never used in the injection moulding applications. TEM module (see Fig. 2) is a device composed of properly arranged pairs of P and N type semiconductors that are positioned between two ceramic plates forming the hot and the cold thermoelectric
cooler sites. Power of a heat transfer can be easily controlled through the magnitude and the polarity of the supplied electric current.
2.2. Application for mould cooling
The main idea of the application is inserting TEM module into walls of the mould cavity serving as a primary heat transfer unit.
Such basic assembly can be seen in Fig. 3. Secondary heat transfer is realized via conventional fluid cooling system that allows heat flows in and out from mould cavity thermodynamic system.
Device presented in Fig. 3 comprises of thermoelectric modules (A) that enable primarily heat transfer from or to temperature controllable surface of mould cavity (B). Secondary heat transfer is enabled via cooling channels (C) that deliver constant temperature conditions inside the mould. Thermoelectric modules (A) operate as heat pump and as such manipulate with heat derived to or from the mould by fluid cooling system (C). System for secondary heat manipulation with cooling channels work as heat exchanger. To reduce heat capacity of controllable area thermal insulation (D) is installed between the mould cavity (F) and the mould structure plates (E). Fig. 3.
The whole application consists of TEM modules, a temperature sensor and an electronic unit that controls the complete system. The system is described in Fig. 4 and comprises of an input unit (input interface) and a supply unit (unit for electronic
and power electronic supply—H bridge unit).
The input and supply units with the temperature sensor loop information are attached to a control unit that acts as an execution unit trying to impose predefined
temperate/time/position relations. Using the Peltier effect, the unit can be used for heating or cooling purposes.
The secondary heat removal is realized via fluid cooling media seen as heat exchanger in Fig. 4. That unit is based on current cooling technologies and serves as a sink or a source of a heat. This enables complete control of processes in terms of temperature, time and position through the whole cycle. Furthermore, it allows various temperature/time/position profiles within the cycle also for starting and ending procedures. Described technology can be used for various industrial and research purposes where precise temperature/time/position control is required. The presented systems in Figs. 3 and 4 were analysed from the theoretical, as well as the practical point of view. The theoretical aspect was analysed by the FEM simulations, while the practical one by the development and the implementation of the prototype into real application testing.
3. FEM analysis of mould cooling
Current development of designing moulds for injection moulding comprises of several phases . Among them is also design and optimization of a cooling system. This is nowadays performed by simulations using customized FEM packages (Moldflow ) that can predict cooling system capabilities and especially its influence on plastic.With such simulations, mould designers gather information on product rheology and deformation due to shrinkage as ell as production time cycle information.
This thermal information is usually accurate but can still be unreliable in cases of insufficient rheological material information. For the high quality input for the thermal regulation of TEM, it is needed to get a picture about the temperature distribution during the cycle time and throughout the mould surface and throughout the mould thickness. Therefore, different process simulations are needed.