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Journal of Materials Processing Technology 187188 (2007) 690693 Adaptive system for electrically driven thermoregulation of moulds for injection B. Nardin a, ,B. Zagar a, , A Slovenia, Abstract ditions means. mould it. w patent. on-line influence control. 2006 Elsevier B.V. All rights reserved. K simulations 1. Development of technology of cooling moulds via thermo- electrical (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 finite pletely re trollable ing technologies. ening only tion and 1.1. pr 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 0924-0136/$ doi: limitations can be located and predicted in advance with element analyses (FEA) simulation packages but not com- avoided. Results of a diverse state of the art analyses vealed that all existing cooling systems do not provide con- heat transfer capabilities adequate to fit into demand- technological windows of current polymer processing Polymer processing is nowadays limited (in term of short- the production cycle time and within that reducing costs) with heat capacity manipulation capabilities. Other produc- optimization capabilities are already driven to mechanical polymer processing limitations 3. Corresponding authors. Tel.: +386 3 490920; fax: +386 3 4264612. E-mail address: Blaz.Nardintecos.si (B. Nardin). which is based on first law of thermodynamicslaw of energy conservation 1, 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. 1.2. Cooling time Complete injection moulding process cycle comprises of mould closing phase, injection of melt into cavity, packing pres- sure 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 1. see front matter 2006 Elsevier B.V. All rights reserved. 10.1016/j.jmatprotec.2006.11.052 a TECOS, Tool and Die Development Centre of b Faculty of Electrical Engineering One of the basic problems in the development and production process in the mould. Precise study of thermodynamic processes in moulds Such system upgrades conventional cooling systems within the In the paper, the authors will present results of the research project, which The testing stage, the prototype stage and the industrialization phase thermoregulation of the mould over the cycle time and overall Presented application can present a milestone in the field of mould temperature eywords: Injection moulding; Mould cooling; Thermoelectric modules; FEM Introduction, definition of problem moulding . Glojek a ,D.Krizaj b Kidriceva Cesta 25, 3000 Celje, Slovenia , Ljubljana, Slovenia of moulds for injection moulding is the control of temperature con- showed, that heat exchange can be manipulated by thermoelectrical or can be a stand alone application for heat manipulation within as carried out in three phases and its results are patented in A6862006 will be presented. The main results of the project were total and rapid on quality of plastic product with emphasis on deformation and product quality control during the injection moulding process. Thermal processes in injection moulding plastic ocessing B. Nardin et al. / Journal of Materials Processing Technology 187188 (2007) 690693 691 cooling from mould and temperature from 2. ent most i.e. lines), accumulated to ity in to alter lik inte the erties. with ature independent done from simulation. TEM 2.1. w trical The Fig. 2. TEM block diagram. 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 current. 2.2. into unit. transfer allo system. modules perature heat constant tric with tem channels controllable mould Fig. 1. Mould temperature variation across one cycle 2. The main aim of a cooling process is to lower additional time which is theoretically needless; in praxis, it extends 45 up to 67% of the whole cycle time 1,4. From literature and experiments 1,4, it can be seen, that the temperature has enormous influence on the ejection time therefore the cooling time (costs). Injection moulding process is a cyclic process where mould varies as shown in Fig. 1 where temperature varies average value through whole cycle time. Cooling technology for plastic injection moulds As it was already described, there are already several differ- technologies, enabling the users to cool the moulds 5. The conventional is the method with the drilling technology, producing holes in the mould. Through these holes (cooling the cooling media is flowing, removing the generated and heat from the mould 1,2. It is also very convenient build in different materials, with different thermal conductiv- with the aim to enhance control over temperature conditions the mould. Such approaches are so called passive approaches wards the mould temperature control. The challenging task is to make an active system, which can the thermal conditions, regarding to the desired aspects, e product quality or cycles time. One of such approaches is grating thermal electrical modules (TEM), which can alter thermal conditions in the mould, regarding the desired prop- With such approach, the one can control the heat transfer the time and space variable, what means, that the temper- can be regulated throughout the injection moulding cycle, of the position in the mould. The heat control is by the control unit, where the input variables are received the manual input or the input from the injection moulding With the output values, the control unit monitors the module behaviour. Thermoelectric modules (TEM) For the needs of the thermal manipulation, the TEM module as integrated into mould. Interaction between the heat and elec- variables for heat exchange is based on the Peltier effect. phenomenon of Peltier effect is well known, but it was until the magnitude and the polarity of the supplied electric Application for mould cooling The main idea of the application is inserting TEM module walls of the mould cavity serving as a primary heat transfer Such basic assembly can be seen in Fig. 3. Secondary heat is realized via conventional fluid cooling system that ws heat flows in and out from mould cavity thermodynamic Device presented in Fig. 3 comprises of thermoelectric (A) that enable primarily heat transfer from or to tem- controllable surface of mould cavity (B). Secondary transfer is enabled via cooling channels (C) that deliver temperature conditions inside the mould. Thermoelec- modules (A) operate as heat pump and as such manipulate heat derived to or from the mould by fluid cooling sys- (C). System for secondary heat manipulation with cooling work as heat exchanger. To reduce heat capacity of area thermal insulation (D) is installed between the cavity (F) and the mould structure plates (E). Fig. 3. Structure of TEM cooling assembly. 692 B. Nardin et al. / Journal of Materials Processing Technology 187188 (2007) 690693 ature system. input and information cution relations. or media current of of Furthermore, files Described research trol theoretical, aspect one into 3. moulding design days (Moldflo especially designers tion unreliable tion. TEM, b and simulations Fig. 5. Cross-section of a prototype in FEM environment. 3.1. Physical model, FEM analysis Implementation of FEM analyses into development project was done due to authors long experiences with such packages 4 and possibility to perform different test in the virtual envi- ronment. en in them de COMSOL identical possible taking fluid physics w impact goal ing. temperature Fig. 4. Structure for temperature detection and regulation. The whole application consists of TEM modules, a temper- sensor and an electronic unit that controls the complete The system is described in Fig. 4 and comprises of an unit (input interface) and a supply unit (unit for electronic power electronic supplyH bridge unit). The input and supply units with the temperature sensor loop are attached to a control unit that acts as an exe- unit trying to impose predefined temperate/time/position Using the Peltier effect, the unit can be used for heating cooling purposes. The secondary heat removal is realized via fluid cooling seen as heat exchanger in Fig. 4. That unit is based on cooling technologies and serves as a sink or a source a heat. This enables complete control of processes in terms temperature, time and position through the whole cycle. it allows various temperature/time/position pro- within the cycle also for starting and ending procedures. technology can be used for various industrial and purposes where precise temperature/time/position con- is required. The presented systems in Figs. 3 and 4 were analysed from the as well as the practical point of view. The theoretical was analysed by the FEM simulations, while the practical by the development and the implementation of the prototype real application testing. FEM analysis of mould cooling Current development of designing moulds for injection comprises of several phases 3. Among them is also and optimization of a cooling system. This is nowa- performed by simulations using customized FEM packages w 4) that can predict cooling system capabilities and its influence on plastic. With such simulations, mould gather information on product rheology and deforma- due to shrinkage as ell as production time cycle information. This thermal information is usually accurate but can still be in cases of insufficient rheological material informa- For the high quality input for the thermal regulation of it is needed to get a picture about the temperature distri- ution during the cycle time and throughout the mould surface throughout the mould thickness. Therefore, different process are needed. Whole prototype cooling system was designed in FEM vironment (see Fig. 5) through which temperature distribution each part of prototype cooling system and contacts between were explored. For simulating physical properties inside a veloped prototype, a simulation model was constructed using Multiphysics software. Result was a FEM model to real prototype (see Fig. 7) through which it was to compare and evaluate results. FEM model was explored in term of heat transfer physics into account two heat sources: a water exchanger with physics and a thermoelectric module with heat transfer (only conduction and convection was analysed, radiation as ignored due to low relative temperature and therefore low on temperature). Boundary conditions for FEM analyses were set with the to achieve identical working conditions as in real test- Surrounding air and the water exchanger were set at stable of 20 C. Fig. 6. Temperature distribution according to FEM analysis. B. Nardin et al. / Journal of Materials Processing Technology 187188 (2007) 690693 693 ature Fig. in response v temperature what problems mounting, intelligent 3.2. tested tions control mould w lated simulating moulding sors, temperature represents moulding 4. nection milestone in cooling applications. Its introduction into moulds for injection moulding with its problematic cooling construction and problematic processing of precise and high quality plastic parts represents high expectations. The authors were assuming that the use of the Peltier effect can be used for the temperature control in moulds for injection moulding. With the approach based on the simulation work and the real production of laboratory equipment proved, the assump- tions were confirmed. Simulation results showed a wide area of possible application of TEM module in the injection moulding process. With mentioned functionality of a temperature profile across cycle time, injection moulding process can be fully controlled. Industrial problems, such as uniform cooling of problematic A ance solv more, of re flo ity of product). icantly The of control of erances. moulding and Refer 1 2 3 Fig. 7. Prototype in real environment. Results of the FEM analysis can be seen in Fig. 6, i.e. temper- distribution through the simulation area shown in Fig. 5. 6 represents steady state analysis which was very accurate comparison to prototype tests. In order to simulate the time also the transient simulation was performed, showing ery positive results for future work. It was possible to achieve a difference of 200 C in a short period of time (5 s), could cause several problems in the TEM structure. Those were solved by several solutions, such as adequate choosing appropriate TEM material and applying electronic regulation. Laboratory testing As it was already described, the prototype was produced and (see Fig. 7). The results are showing, that the set assump- were confirmed. With the TEM module it is possible to the temperature distribution on different parts of the throughout the cycle time. With the laboratory tests, it as proven, that the heat manipulation can be practically regu- with TEM modules. The test were made in the laboratory, the real industrial environment, with the injection machine Krauss Maffei KM 60 C, temperature sen- infrared cameras and the prototype TEM modules. The response in 1.8 s varied form +5 up to 80 C, what a wide area for the heat control within the injection cycle. Conclusions Use of thermoelectric module with its straightforward con- between the input and output relations represents a 4 5 class surfaces and its consequence of plastic part appear- can be solved. Problems of filling thin long walls can be ed with overheating some surfaces at injection time. Further- with such application control over rheological properties plastic materials can be gained. With the proper thermal gulation of TEM it was possible even to control the melt w in the mould, during the filling stage of the mould cav- . This is done with the appropriate temperature distribution the mould (higher temperature on the thin walled parts of the With the application of TEM module, it is possible to signif- reduce the cycle time in the injection moulding process. limits of possible time reduction lies in the frame of 1025% additional cooling time, describe in Section 1.2. With the application of TEM module it is possible to actively the warping of the product and to regulate the amount product warpage in the way to achieve required product tol- The presented TEM module cooling application for injection process is a matter of priority note for the patent, held owned by TECOS. ences I. Catic, Izmjena topline u kalupima za injekcijsko presanje plastomera, Drustvo plasticara i gumaraca, Zagreb, 1985. I. Catic, F. Johannaber, Injekcijsko presanje polimera i ostalih materiala, Drustvo za plastiku i gumu, Biblioteka polimerstvo, Zagreb, 2004. B. Nardin, K. Kuzman, Z. Kampus, Injection moulding simulation results as an input to the injection moulding process, in: AFDM 2002: The Sec- ond International Conference on Advanced Forming and Die Manufacturing Technology, Pusan, Korea, 2002. TECOS, Slovenian Tool and Die Development Centre, Moldflow Simulation Projects 19962006. S.C. Chen, et al., Rapid mold surface heating/cooling using electromag- netic induction technology: ANTEC 2004, Conference CD-ROM, Chicago, Illinois, 1620 May, 2004.