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Journal of Materials Processing Technology 187188 (2007) 690693Adaptive system for electrically driven thermoregulationof moulds for injectionB. Nardina,B.Zagara, ASlovenia,Abstractditionsmeans. mouldit.wpatent.on-line influencecontrol. 2006 Elsevier B.V. All rights reserved.K simulations1.Development of technology of cooling moulds via thermo-electrical (TEM) means derives out of the industrial praxis andproblems, i.e. at design, tool making and exploitation of tools.Current cooling technologies have technological limitations.Theirfinitepletelyretrollableingtechnologies.eningonlytionand1.1.prPlastic processing is based on heat transfer between plasticmaterial and mould cavity. Within calculation of heat transferone should consider two major facts: first is all used energy0924-0136/$doi:limitations can be located and predicted in advance withelement analyses (FEA) simulation packages but not com-avoided. Results of a diverse state of the art analysesvealed that all existing cooling systems do not provide con-heat transfer capabilities adequate to fit into demand-technological windows of current polymer processingPolymer 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 mechanicalpolymer 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 energyconservation 1, second is velocity of heat transfer. Basic taskat heat transfer analyses is temperature calculation over timeand its distribution inside studied system. That last depends onvelocity of heat transfer between the system and surroundingsand velocity of heat transfer inside the system. Heat transfer canbe based as heat conduction, convection and radiation 1.1.2. Cooling timeComplete injection moulding process cycle comprises ofmould 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, thelongest time of all phases described above is cooling time.Cooling time in injection moulding process is defined astime needed to cool down the plastic part down to ejectiontemperature 1. see front matter 2006 Elsevier B.V. All rights reserved.10.1016/j.jmatprotec.2006.11.052aTECOS, Tool and Die Development Centre ofbFaculty of Electrical EngineeringOne of the basic problems in the development and production processin the mould. Precise study of thermodynamic processes in mouldsSuch system upgrades conventional cooling systems within theIn the paper, the authors will present results of the research project, whichThe testing stage, the prototype stage and the industrialization phasethermoregulation of the mould over the cycle time and overallPresented application can present a milestone in the field of mould temperatureeywords: Injection moulding; Mould cooling; Thermoelectric modules; FEMIntroduction, definition of problemmoulding. Glojeka,D.KrizajbKidriceva Cesta 25, 3000 Celje, Slovenia, Ljubljana, Sloveniaof moulds for injection moulding is the control of temperature con-showed, that heat exchange can be manipulated by thermoelectricalor can be a stand alone application for heat manipulation withinas carried out in three phases and its results are patented in A6862006will be presented. The main results of the project were total and rapidon quality of plastic product with emphasis on deformationand product quality control during the injection moulding process.Thermal processes in injection moulding plasticocessingB. Nardin et al. / Journal of Materials Processing Technology 187188 (2007) 690693 691coolingfrommouldandtemperaturefrom2.entmosti.e.lines),accumulatedtoityintoalterlikintetheerties.withatureindependentdonefromsimulation.TEM2.1.wtricalTheFig. 2. TEM block diagram.now never used in the injection moulding applications. TEMmodule (see Fig. 2) is a device composed of properly arrangedpairs of P and N type semiconductors that are positioned betweentwo ceramic plates forming the hot and the cold thermoelectriccooler sites. Power of a heat transfer can be easily ounit.transferallosystem.modulesperatureheatconstanttricwithtemchannelscontrollablemouldFig. 1. Mould temperature variation across one cycle 2.The main aim of a cooling process is to lower additionaltime which is theoretically needless; in praxis, it extends45 up to 67% of the whole cycle time 1,4.From literature and experiments 1,4, it can be seen, that thetemperature has enormous influence on the ejection timetherefore the cooling time (costs).Injection moulding process is a cyclic process where mouldvaries as shown in Fig. 1 where temperature variesaverage value through whole cycle time.Cooling technology for plastic injection mouldsAs it was already described, there are already several differ-technologies, enabling the users to cool the moulds 5. Theconventional is the method with the drilling technology,producing holes in the mould. Through these holes (coolingthe cooling media is flowing, removing the generated andheat from the mould 1,2. It is also very convenientbuild in different materials, with different thermal conductiv-with the aim to enhance control over temperature conditionsthe mould. Such approaches are so called passive approacheswards the mould temperature control.The challenging task is to make an active system, which canthe thermal conditions, regarding to the desired aspects,e product quality or cycles time. One of such approaches isgrating thermal electrical modules (TEM), which can alterthermal conditions in the mould, regarding the desired prop-With such approach, the one can control the heat transferthe 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 isby the control unit, where the input variables are receivedthe manual input or the input from the injection mouldingWith the output values, the control unit monitors themodule behaviour.Thermoelectric modules (TEM)For the needs of the thermal manipulation, the TEM moduleas 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 untilthe magnitude and the polarity of the supplied electricApplication for mould coolingThe main idea of the application is inserting TEM modulewalls of the mould cavity serving as a primary heat transferSuch basic assembly can be seen in Fig. 3. Secondary heatis realized via conventional fluid cooling system thatws heat flows in and out from mould cavity thermodynamicDevice presented in Fig. 3 comprises of thermoelectric(A) that enable primarily heat transfer from or to tem-controllable surface of mould cavity (B). Secondarytransfer is enabled via cooling channels (C) that delivertemperature conditions inside the mould. Thermoelec-modules (A) operate as heat pump and as such manipulateheat derived to or from the mould by fluid cooling sys-(C). System for secondary heat manipulation with coolingwork as heat exchanger. To reduce heat capacity ofarea thermal insulation (D) is installed between thecavity (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) 690693aturesystem.inputandinformationcutionrelations.ormediacurrentofofFurthermore,filesDescribedresearchtroltheoretical,aspectoneinto3.mouldingdesigndays(Moldfloespeciallydesignerstionunreliabletion.TEM,bandsimulationsFig. 5. Cross-section of a prototype in FEM environment.3.1. Physical model, FEM analysisImplementation of FEM analyses into development projectwas done due to authors long experiences with such packages4 and possibility to perform different test in the virtual envi-ronment.eninthemdeCOMSOLidenticalpossibletakingfluidphysicswimpactgoaling.temperatureFig. 4. Structure for temperature detection and regulation.The whole application consists of TEM modules, a temper-sensor and an electronic unit that controls the completeThe system is described in Fig. 4 and comprises of anunit (input interface) and a supply unit (unit for electronicpower electronic supplyH bridge unit).The input and supply units with the temperature sensor loopare attached to a control unit that acts as an exe-unit trying to impose predefined temperate/time/positionUsing the Peltier effect, the unit can be used for heatingcooling purposes.The secondary heat removal is realized via fluid coolingseen as heat exchanger in Fig. 4. That unit is based oncooling technologies and serves as a sink or a sourcea heat. This enables complete control of processes in termstemperature, 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 andpurposes where precise temperature/time/position con-is required.The presented systems in Figs. 3 and 4 were analysed from theas well as the practical point of view. The theoreticalwas analysed by the FEM simulations, while the practicalby the development and the implementation of the prototypereal application testing.FEM analysis of mould coolingCurrent development of designing moulds for injectioncomprises of several phases 3. Among them is alsoand optimization of a cooling system. This is nowa-performed by simulations using customized FEM packagesw 4) that can predict cooling system capabilities andits influence on plastic. With such simulations, mouldgather 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 bein cases of insufficient rheological material informa-For the high quality input for the thermal regulation ofit is needed to get a picture about the temperature distri-ution during the cycle time and throughout the mould surfacethroughout the mould thickness. Therefore, different processare needed.Whole prototype cooling system was designed in FEMvironment (see Fig. 5) through which temperature distributioneach part of prototype cooling system and contacts betweenwere explored. For simulating physical properties inside aveloped prototype, a simulation model was constructed usingMultiphysics software. Result was a FEM modelto real prototype (see Fig. 7) through which it wasto compare and evaluate results.FEM model was explored in term of heat transfer physicsinto account two heat sources: a water exchanger withphysics and a thermoelectric module with heat transfer(only conduction and convection was analysed, radiationas ignored due to low relative temperature and therefore lowon temperature).Boundary conditions for FEM analyses were set with theto achieve identical working conditions as in real test-Surrounding air and the water exchanger were set at stableof 20C.Fig. 6. Temperature distribution according to FEM analysis.B. Nardin et al. / Journal of Materials Processing Technology 187188 (2007) 690693 693atureFig.inresponsevtemperaturewhatproblemsmounting,intelligent3.2.testedtionscontrolmouldwlatedsimulatingmouldingsors,temperaturerepresentsmoulding4.nectionmilestone in cooling applications. Its introduction into mouldsfor injection moulding with its problematic cooling constructionand problematic processing of precise and high quality plasticparts represents high expectations.The authors were assuming that the use of the Peltier effectcan be used for the temperature control in moulds for injectionmoulding. With the approach based on the simulation work andthe real production of laboratory equipment proved, the assump-tions were confirmed. Simulation results showed a wide area ofpossible application of TEM module in the injection mouldingprocess.With mentioned functionality of a temperature profile acrosscycle time, injection moulding process can be fully controlled.Industrial problems, such as uniform cooling of problematicAancesolvmore,ofrefloityofproduct).icantlyTheofcontroloferances.mouldingandRefer123Fig. 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 accuratecomparison to prototype tests. In order to simulate the timealso the transient simulation was performed, showingery positive results for future work. It was possible to achieve adifference of 200C in a short period of time (5 s),could cause several problems in the TEM structure. Thosewere solved by several solutions, such as adequatechoosing appropriate TEM material and applyingelectronic regulation.Laboratory testingAs 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 tothe temperature distribution on different parts of thethroughout the cycle time. With the laboratory tests, itas 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 injectionmachine Krauss Maffei KM 60 C, temperature sen-infrared cameras and the prototype TEM modules. Theresponse in 1.8 s varied form +5 up to 80C, whata wide area for the heat control within the injectioncycle.ConclusionsUse of thermoelectric module with its straightforward con-between the input and output relations represents a45class surfaces and its consequence of plastic part appear-can be solved. Problems of filling thin long walls can beed with overheating some surfaces at injection time. Further-with such application control over rheological propertiesplastic materials