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1. Introduction, definition of problem Development of technology of cooling moulds via thermoelectrical (TEM) means derives out of the industrial praxis and problems, i.e. at design, tool making and exploitation of tools.Current cooling technologies have technological limitations.Their limitations can be located and predicted in advance with finite element analyses (FEA) simulation packages but not completely avoided. Results of a perse state of the art analyses revealed that all existing cooling systems do not provide controllable heat transfer capabilities adequate to fit into demanding technological windows of current polymer processing technologies.35497
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Polymer processing is nowadays limited (in term of shortening the production cycle time and within that reducing costs) only with heat capacity manipulation capabilities. Other production optimization capabilities are already driven to mechanical and polymer processing limitations.
1.1. Thermal processes in injection moulding plastic processing
Plastic processing is based on heat transfer between plastic material and mould cavity. Within calculation of heat transfer one should consider two major facts: first is all used energy which is based on first law of thermodynamics—law of energy conservation , second is velocity of heat transfer. Basic task at heat transfer analyses is temperature calculation over time and its distribution inside studied system. That last depends on velocity of heat transfer between the system and surroundings and velocity of heat transfer inside the system. Heat transfer can be based as heat conduction, convection and radiation .
1.2. Cooling time
Complete injection moulding process cycle comprises of mould closing phase, injection of melt into cavity, packing pressure phase for compensating shrinkage effect, cooling phase, mould opening phase and part ejection phase. In most cases, the longest time of all phases described above is cooling time.
Cooling time in injection moulding process is defined as time needed to cool down the plastic part down to ejection temperature.
The main aim of a cooling process is to lower additional cooling time which is theoretically needless; in praxis, it extends from 45 up to 67% of the whole cycle time.
From literature and experiments, it can be seen, that the mould temperature has enormous influence on the ejection time and therefore the cooling time (costs).
Injection moulding process is a cyclic process where mould temperature varies as shown in Fig. 1 where temperature varies from average value through whole cycle time.
2. Cooling technology for plastic injection moulds
As it was already described, there are already several different technologies, enabling the users to cool the moulds. The most conventional is the method with the drilling technology, i.e. producing holes in the mould. Through these holes (cooling lines), the cooling media is flowing, removing the generated and accumulated heat from the mould. It is also very convenient to build in different materials, with different thermal conductivity with the aim to enhance control over temperature conditions in the mould. Such approaches are so called passive approaches towards the mould temperature control.
The challenging task is to make an active system, which can alter the thermal conditions, regarding to the desired aspects, like product quality or cycles time. One of such approaches is integrating thermal electrical modules (TEM), which can alter the thermal conditions in the mould, regarding the desired properties. With such approach, the one can control the heat transfer with the time and space variable, what means, that the temperature can be regulated throughout the injection moulding cycle, independent of the position in the mould. The heat control is done by the control unit, where the input variables are received from the manual input or the input from the injection moulding simulation.With the output values, the control unit monitors the TEM module behaviour.