Journal of Materials Processing Technology
187–188 (2007) 690–693
Adaptive system for electrically driven thermoregulation
of moulds for injection moulding
B.Nardin a,∗,B.ˇZagar a,∗,A.Glojek a,D.Kriˇz aj b
a TECOS,Tool and Die Development Centre of Slovenia,Kidriˇc eva Cesta25,3000Celje,Slovenia
b Faculty of Electrical Engineering,Ljubljana,Slovenia
Abstract
One of the basic problems in the development and production process of moulds for injection moulding is the control of temperature con-ditions in the mould.Preci study of thermodynamic process in moulds showed,that heat exchange can be manipulated by thermoelectrical means.Such system upgrades conventional cooling systems within the mould or can be a stand alone application for heat manipulation within it.
In the paper,the authors will prent results of the rearch project,which was carried out in three phas and its results are patented in A686\2006 patent.The testing stage,the prototype stage and t
he industrialization pha will be prented.The main results of the project were total and rapid on-line thermoregulation of the mould over the cycle time and overall influence on quality of plastic product with emphasis on deformation control.
Prented application can prent a milestone in thefield of mould temperature and product quality control during the injection moulding process.© 2006 Elvier B.V. All rights rerved.
Keywords:Injection moulding;Mould cooling;Thermoelectric modules;FEM simulations
1.Introduction,definition of problem
Development of technology of cooling moulds via thermo-electrical(TEM)means derives out of the industrial praxis and 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 analys(FEA)simulation packages but not com-pletely avoided.Results of a diver state of the art analys revealed that all existing cooling systems do not provide con-trollable heat transfer capabilities adequate tofit into demand-ing technological windows of current polymer processing technologies.
Polymer processing is nowadays limited(in term of short-ening the production cycle time and within that reducing costs) only with heat capacity manipulation capabilities.Other produc-tion optimization capabilities are already driven to mechanical and polymer processing limitations[3].榆林旅游
∗Corresponding authors.Tel.:+3863490920;fax:+38634264612.
E-mail address:Blaz.Nardin@tecos.si(B.Nardin).1.1.Thermal process in injection moulding plastic processing
Plastic processing is bad on heat transfer between plastic material and mould cavity.Within calculation of heat transfer one should consider two major facts:first is all ud energy which is bad onfirst law of thermodynamics—law of energy conrvation[1],cond is velocity of heat transfer.Basic task at heat transfer analys 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 bad as heat conduction,convection and radiation[1].
1.2.Cooling time
Complete injection moulding process cycle compris of mould closing pha,injection of melt into cavity,packing pres-sure pha for compensating shrinkage effect,cooling pha, mould opening pha and part ejection pha.In most cas,the longest time of all phas 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].
0924-0136/$–e front matter© 2006 Elvier B.V. All rights rerved. doi:10.1016/j.jmatprotec.2006.11.052虎虎相配吗
B.Nardin et al./Journal of Materials Processing Technology 187–188 (2007) 690–693
691
Fig.1.Mould temperature variation across one cycle[2].
The main aim of a cooling process is to lower additional cooling time which is theoretically needless;in praxis,it extends from45up to67%of the whole cycle time[1,4].
From literature and experiments[1,4],it can be en,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.1where temperature varies from average value through whole cycle time.
2.Cooling technology for plastic injection moulds
As it was already described,there are already veral differ-ent technologies,enabling the urs to cool the moulds[5].The most conventional is the method with the drilling technology, i.e.producing holes in the mould.Through the holes(cooling lines),the cooling media isflowing,removing the generated and accumulated heat from the mould[1,2].It is also very convenient to build in different materials,with different thermal conductiv-ity 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 prop-erties.With such approach,the one can control the heat transfer with the time and space variable,what means,that the temper-ature 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.
2.1.Thermoelectric modules(TEM)
For the needs of the thermal manipulation,the TEM module was integrated into mould.Interaction between the heat and elec-trical variables for heat exchange is bad on the Peltier effect. The phenomenon of Peltier effect is well known,but it was
until
Fig.2.TEM block diagram.
now never ud in the injection moulding applications.TEM module(e Fig.2)is a device compod of properly arranged pairs of P and N type miconductors 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 inrting TEM module into walls of the mould cavity rving as a primary heat transfer unit.知行合一演讲稿
Such basic asmbly can be en in Fig.3.Secondary heat transfer is realized via conventionalfluid cooling system that allows heatflows in and out from mould cavity thermodynamic system.
Device prented in Fig.3compris of thermoelectric modules(A)that enable primarily heat transfer from or to tem-perature controllable surface of mould cavity(B).Secondary heat transfer is enabled via cooling channels(C)that deliver constant temperature conditions inside the mould.Thermoelec-tri
c modules(A)operate as heat pump and as such manipulate with heat derived to or from the mould byfluid cooling sys-tem(C).System for condary 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.Structure of TEM cooling asmbly.
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Technology 187–188 (2007) 690–693
Fig.4.Structure for temperature detection and regulation.小寒问候
The whole application consists of TEM modules,a temper-ature nsor and an electronic unit that controls the complete system.The system is described in Fig.4and compris 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 nsor loop information are attached to a control unit that acts as an exe-cution unit trying to impo predefined temperate/time/position relations.Using the Peltier effect,the unit can be ud for heating or cooling purpos.
The condary heat removal is realized viafluid cooling media en as heat exchanger in Fig.4.That unit is bad on current cooling technologies and rves as a sink or a source of a heat.This enables complete control of process in terms of temperature,time and position through the whole cycle. Furthermore,it allows various temperature/time/position pro-files within the cycle also for starting and ending procedures. Described technology can be ud for various industrial and rearch purpos where preci temperature/time/position con-trol is required.
The prented systems in Figs.3and4were analyd from the theoretical,as well as the practical point of view.The theoretical aspect was analyd by the FEM simulations,while the practical one by the development and the implementation of the prototype into real application testing.
英语专业介绍3.FEM analysis of mould cooling
Current development of designing moulds for injection moulding compris of veral phas[3].Among them is also design and optimization of a cooling system.This is nowa-days performed by simulations using customized FEM packages (Moldflow[4])that can predict cooling system capabilities and especially its influence on plastic.With such simulations,mould designers gather information on product rheology and deforma-tion due to shrinkage as ell as production time cycle information.
This thermal information is usually accurate but can still be unreliable in cas of insufficient rheological material informa-tion.For the high quality input for the thermal regulation of TEM,it is needed to get a picture about the temperature distri-bution during the cycle time and throughout the mould surface and throughout the mould thickness.Therefore,different process simulations are
needed.
Fig.5.Cross-ction of a prototype in FEM environment.
3.1.Physical model,FEM analysis
Implementation of FEM analys 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.Whole prototype cooling system was designed in FEM environment(e Fig.5)through which temperature distribution in each part of prototype cooling system and contacts between them were explored.For simulating physical properties inside a developed prototype,a simulation model was constructed using COMSOL Multiphysics software.Result was a FEM model identical to real prototype(e Fig.7)through which it was possible to compare and evaluate results.
FEM model was explored in term of heat transfer physics taking into account two heat sources:a water exchanger with fluid physics and a thermoelectric module with heat transfer physics(only conduction and convection was analyd,radiation was ignored due to low relative temperature and therefore low impact on temperature).
Boundary conditions for FEM analys were t with the goal to achieve identical working conditions as in real test-ing.Surrounding air and the water exchanger were t at stable temperature of20◦
C.男生节是什么时候
Fig.6.Temperature distribution according to FEM analysis.
B.Nardin et al./Journal of Materials Processing Technology 187–188 (2007) 690–693
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Fig.7.Prototype in real environment.
Results of the FEM analysis can be en in Fig.per-ature distribution through the simulation area shown in Fig.5. Fig.6reprents steady state analysis which was very accurate in comparison to prototype tests.In order to simulate the time respon also the transient simulation was performed,showing very positive results for future work.It was possible to achieve a temperature difference of200◦C in a short period of time(5s), what could cau veral problems in the TEM structure.Tho problems were solved by veral solutions,such as adequate mounting,choosing appropriate TEM material and applying intelligent electronic regulation.
3.2.Laboratory testing
As it was already described,the prototype was produced and tested(e Fig.7).The results are showing,that the t assump-tions were confirmed.With the TEM module it is possible to control the temperature distribution on different parts of the mould throughout the cycle time.With the laboratory tests,it was proven,that the heat manipulation can be practically regu-lated with TEM modules.The test were made in the laboratory, simulating the real industrial environment,with the injection mouldin
g machine Krauss Maffei KM60C,temperature n-sors,infrared cameras and the prototype TEM modules.The temperature respon in1.8s varied form+5up to80◦C,what reprents a wide area for the heat control within the injection moulding cycle.
4.Conclusions
U of thermoelectric module with its straightforward con-nection between the input and output relations reprents a milestone in cooling applications.Its introduction into moulds for injection moulding with its problematic cooling construction and problematic processing of preci and high quality plastic parts reprents high expectations.
The authors were assuming that the u of the Peltier effect can be ud for the temperature control in moulds for injection moulding.With the approach bad 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 class surfaces and its conquence of plastic part appear-ance can be solved.Problems offilling thin long walls can
小小意外be solved with overheating some surfaces at injection time.Further-more,with such application control over rheological properties of plastic materials can be gained.With the proper thermal regulation of TEM it was possible even to control the melt flow in the mould,during thefilling stage of the mould cav-ity.This is done with the appropriate temperature distribution of the mould(higher temperature on the thin walled parts of the product).
With the application of TEM module,it is possible to signif-icantly reduce the cycle time in the injection moulding process. The limits of possible time reduction lies in the frame of10–25% of additional cooling time,describe in Section1.2.
With the application of TEM module it is possible to actively control the warping of the product and to regulate the amount of product warpage in the way to achieve required product tol-erances.
The prented TEM module cooling application for injection moulding process is a matter of priority note for the patent,held and owned by TECOS.
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