外文翻译--注塑模具的设计及其热分析 英文版.pdf

Journal of Materials Processing Technology 171 (2006) 259267AbstracttheinUnigraphics,usingdistribresultsatK1.industries,AlmostusagebymoldingtoatTherearetionappropriatesystemThiswithitypacke0924-0136/$doi:10.1016/j.jmatprotec.2005.06.075Design and thermal analysis of plastic injection mouldS.H. Tang, Y.M. Kong, S.M. Sapuan, R. Samin, S. SulaimanDepartment of Mechanical and Manufacturing Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, MalaysiaReceived 3 September 2004; accepted 21 June 2005This paper presents the design of a plastic injection mould for producing warpage testing specimen and performing thermal analysis formould to access on the effect of thermal residual stress in the mould. The technique, theory, methods as well as consideration neededdesigning of plastic injection mould are presented. Design of mould was carried out using commercial computer aided design softwareVersion 13.0. The model for thermal residual stress analysis due to uneven cooling of the specimen was developed and solveda commercial finite element analysis software called LUSAS Analyst, Version 13.5. The software provides contour plot of temperatureution for the model and also temperature variation through the plastic injection molding cycle by plotting time response curves. Theshow that shrinkage is likely to occur in the region near the cooling channels as compared to other regions. This uneven cooling effectdifferent regions of mould contributed to warpage.2005 Elsevier B.V. All rights reserved.eywords: Plastic Injection mould; Design; Thermal analysisIntroduction by “cooling stage” where the mould is cooled until the part issufficiently rigid to be ejected. The last step is the “ejectionPlastic industry is one of the worlds fastest growingranked as one of the few billion-dollar industries.every product that is used in daily life involves theof plastic and most of these products can be producedplastic injection molding method 1. Plastic injectionprocess is well known as the manufacturing processcreate products with various shapes and complex geometrylow cost 2.The plastic injection molding process is a cyclic process.are four significant stages in the process. These stagesfilling, packing, cooling and ejection. The plastic injec-molding process begins with feeding the resin and theadditives from the hopper to the heating/injectionof the injection plastic injection molding machine 3.is the “filling stage” in which the mould cavity is filledhot polymer melt at injection temperature. After the cav-is filled, in the “packing stage”, additional polymer melt ised into the cavity at a higher pressure to compensate thexpected shrinkage as the polymer solidifies. This is followedCorresponding author.E-mail address: .my (S.H. Tang).stage”after4mericnatedactualthecoreandfmouldgatingtostressesdemoldedconductimoltene see front matter 2005 Elsevier B.V. All rights reserved.in which the mould is opened and the part is ejected,which the mould is closed again to begin the next cycle.The design and manufacture of injection molded poly-parts with desired properties is a costly process domi-by empiricism, including the repeated modification oftooling. Among the task of mould design, designingmould specific supplementary geometry, usually on theside, is quite complicated by the inclusion of projectiondepression 5.In order to design a mould, many important designingactors must be taken into consideration. These factors aresize, number of cavity, cavity layouts, runner systems,systems, shrinkage and ejection system 6.In thermal analysis of the mould, the main objective isanalyze the effect of thermal residual stress or molded-inon product dimension. Thermally induced stressesvelop principally during the cooling stage of an injectionpart, mainly as a consequence of its low thermalvity and the difference in temperature between theresin and the mould. An uneven temperature fieldxists around product cavity during cooling 7.260 Processingenceschannel.eSignificantfore,ofunderstandingtion,beproducingmalresidual2.2.1.specimenthatthinuctthemouldedshell120materialwtemperature,respectiduced.2.2.testingerationstestinginjectioncarbontheiii.iimen,designsionismachineTheTherefore,notreservsetting-upS.H. Tang et al. / Journal of MaterialsDuring cooling, location near the cooling channel experi-more cooling than location far away from the coolingThis different temperature causes the material toxperience differential shrinkage causing thermal stresses.thermal stress can cause warpage problem. There-it is important to simulate the thermal residual stress fieldthe injection-molded part during the cooling stage 8.Bythe characteristics of thermal stress distribu-deformation caused by the thermal residual stress canpredicted.In this paper the design of a plastic injection mould forwarpage testing specimen and for performing ther-analysis for the mould to access on the effect of thermalstress in the mould is presented.MethodologyDesign of warpage testing specimenThis section illustrates the design of the warpage testingto be used in plastic injection mould. It is clearwarpage is the main problem that exists in product withshell feature. Therefore, the main purpose of the prod-development is to design a plastic part for determiningeffective factors in the warpage problem of an injection-part with a thin shell.The warpage testing specimen is developed from thinplastics. The overall dimensions of the specimen weremm in length, 50 mm in width and 1 mm in thickness. Theused for producing the warpage testing specimenas acrylonitrile butadiene stylene (ABS) and the injectiontime and pressure were 210C, 3 s and 60 MPa,vely. Fig. 1 shows the warpage testing specimen pro-Design of plastic injection mould for warpagespecimenThis section describes the design aspects and other consid-involved in designing the mould to produce warpagespecimen. The material used for producing the plasticFig. 1. Warpage testing specimen produced.imumbasefittedlosionsha(reactiontherespectionspacewithTherefore,TMouldComponentsTCaCoreSideEjectorEjectorBottomTechnology 171 (2006) 259267mould for warpage testing specimen was AISI 1050steel.Four design concepts had been considered in designing ofmould including:i. Three-plate mould (Concept 1) having two parting linewith single cavity. Not applicable due to high cost.ii. Two-plate mould (Concept 2) having one parting line withsingle cavity without gating system. Not applicable dueto low production quantity per injection.Two-plate mould (Concept 3) having one parting linewith double cavities with gating and ejection system. Notapplicable as ejector pins might damage the product asthe product is too thin.v. Two-plate mould (Concept 4) having one parting line withdouble cavities with gating system, only used sprue pulleract as ejector to avoid product damage during ejection.In designing of the mould for the warpage testing spec-the fourth design concept had been applied. Variousconsiderations had been applied in the design.Firstly, the mould was designed based on the platen dimen-of the plastic injection machine used (BOY 22D). Therea limitation of the machine, which is the maximum area ofplaten is given by the distance between two tie bars.distance between tie bars of the machine is 254 mm.the maximum width of the mould plate shouldexceed this distance. Furthermore, 4 mm space had beened between the two tie bars and the mould for mouldand handling purposes. This gives the final max-width of the mould as 250 mm. The standard mouldwith 250 mm 250 mm is employed. The mould base isto the machine using Matex clamp at the upper right andwer left corner of the mould base or mould platen. Dimen-of other related mould plates are shown in Table 1.The mould had been designed with clamping pressureving clamping force higher than the internal cavity forceforce) to avoid flashing from happening.Based on the dimensions provided by standard mould set,width and the height of the core plate are 200 and 250 mm,vely. These dimensions enabled design of two cavitiescore plate to be placed horizontally as there is enoughwhile the cavity plate is left empty and it is only fixedsprue bushing for the purpose of feeding molten plastics.it is only one standard parting line was designed atable 1plates dimensions.Size (mm) width height thicknessop clamping plate 250 250 25vity plate 200 250 40plate 200 250 40plate/support plate 37 250 70-retainer plate 120 250 15plate 120 250 20clamping plate 250 250 25Processingthereleasedopening.islandonlywforrunneringcase.moretype.Thisthediameterorsametheairandflashinginorthatoccurring.caecacientshocoretheFig. 2. Cavity layout with air vents and cooling channels.plate. The sprue puller located at the center of core plate notonly functions as the puller to hold the product in positionwhen the mould is opened but it also acts as ejector to pushthe product out of the mould during ejection stage. No addi-tional ejector is used or located at product cavities becausethe product produced is very thin, i.e. 1 mm. Additional ejec-tor in the product cavity area might create hole and damageto the product during ejection.Finally, enough tolerance of dimensions is given consid-eration to compensate for shrinkage of materials.Fig. 3 shows 3D solid modeling as well as the wireframemodeling of the mould developed using Unigraphics.S.H. Tang et al. / Journal of Materialssurface of the product. The product and the runner werein a plane through the parting line during mouldStandard or side gate was designed for this mould. The gatelocated between the runner and the product. The bottomof the gate was designed to have 20slanting and has0.5 mm thickness for easy de-gating purpose. The gateas also designed to have 4 mm width and 0.5 mm thicknessthe entrance of molten plastic.In the mould design, the parabolic cross section type ofwas selected as it has the advantage of simpler machin-in one mould half only, which is the core plate in thisHowever, this type of runner has disadvantages such asheat loss and scrap compared with circular cross sectionThis might cause the molten plastic to solidify blem was reduced by designing in such a way thatrunner is short and has larger diameter, which is 6 mm in.It is important that the runner designed distributes materialmolten plastic into cavities at the same time under thepressure and with the same temperature. Due to this,cavity layout had been designed in symmetrical form.Another design aspect that is taken into consideration wasvent design. The mating surface between the core platethe cavity plate has very fine finishing in order to preventfrom taking place. However, this can cause air to trapthe cavity when the mould is closed and cause short shotincomplete part. Sufficient air vent was designed to ensureair trap can be released to avoid incomplete part fromThe cooling system was drilled along the length of thevities and was located horizontally to the mould to allowven cooling. These cooling channels were drilled on bothvity and core plates. The cooling channels provided suffi-cooling of the mould in the case of turbulent flow. Fig. 2ws cavity layout with air vents and cooling channels onplate.In this mould design, the ejection system only consists ofejector retainer plate, sprue puller and also the ejector3.3.1.testingrun.shortairFig. 3. 3D solid modeling and wireframeTechnology 171 (2006) 259267 261Results and discussionResults of product production and modificationFrom the mould designed and fabricated, the warpagespecimens produced have some defects during trialThe defects are short shot, flashing and warpage. Theshot is subsequently eliminated by milling of additionalvents at corners of the cavities to allow air trapped tomodeling of the mould.262 Processingescape.packingbyinjectionitylittletheeliminate3.2.oftionthedirectedthe35mensureselectedingfiniteandcoreformed.Fig. 5. Model for thermal analysis.TMaterialCarbonDensityYPoissonYTThermalConductiSpecificS.H. Tang et al. / Journal of MaterialsFig. 4. Extra air vents to avoid short shot.Meanwhile, flashing was reduced by reducing thepressure of the machine. Warpage can be controlledcontrolling various parameters such as the injection time,temperature and melting temperature.After these modifications, the mould produced high qual-warpage testing specimen with low cost and requiredfinishing by de-gating. Fig. 4 shows modifications ofmould, which is machining of extra air vents that canshort shot.Detail analysis of mould and productAfter the mould and products were developed, the analysismould and the product was carried out. In the plastic injec-moulding process, molten ABS at 210C is injected intomould through the sprue bushing on the cavity plate andinto the product cavity. After cooling takes place,product is formed. One cycle of the product takes abouts including 20 s of cooling time.The material used for producing warpage testing speci-was ABS and the injection temperature, time and pres-were 210C, 3 s and 60 MPa respectively. The materialfor the mould was AISI 1050 carbon steel.Properties of these materials were important in determin-temperature distribution in the mould carried out usingelement analysis. Table 2 shows the properties for ABSAISI 1050 carbon steel.The critical part of analysis for mould is on the cavity andplate because these are the place where the product isTherefore, thermal analysis to study the temperaturedistribperformedcalled(2D)ofmodelingsidetogetheranalysisandelementresponsedurationanalysisBasicallythethethe3.3.analysistimeable 2properties for mould and productSteel (AISI 1050), mould, 7860 kg/m3oungs modulus, E 208 GPas ratio, 0.297ield strength, SY365.4 MPaensile strength, SUTS636 MPaexpansion, 11.65 106K1vity, k 49.4 W/(m K)heat, c 477 J/(kg K)Technology 171 (2006) 259267ution and temperature at through different times areusing commercial finite element analysis softwareLUSAS Analyst, Version 13.5. A two-dimensionalthermal analysis is carried out for to study the effectthermal residual stress on the mould at different regions.Due to symmetry, the thermal analysis was performed byonly the top half of the vertical cross section orview of both the cavity and core plate that were clampedduring injection. Fig. 5 shows the model of thermalanalyzed with irregular meshing.Modeling for the model also involves assigning propertiesprocess or cycle time to the model. This allowed the finitesolver to analyze the mould modeled and plot timegraphs to show temperature variation over a certainand at different regions.For the product analysis, a two dimensional tensile stresswas carried using LUSAS Analyst, Version 13.5.the product was loaded in tension on one end whileother end is clamped. Load increments were applied untilmodel reaches plasticity. Fig. 6 shows loaded model ofanalysis.Result and discussion for mould and productFor mould analysis, the thermal distribution at differentintervals was observed. Fig. 7 shows the 2D analysisABS Polymer, productDensity, 1050 kg/m3Youngs modulus, E 2.519 GPaPoissons ratio, 0.4Yield strength, SY65 MPaThermal expansion, 65 106K1Conductivity, k 0.135 W/(m K)Specific heat, c 1250 J/(kg K)S.H. Tang et al. / Journal of Materials Processing Technology 171 (2006) 259267 263Fig. 6. Loaded model for analysis of product.contour plots of thermal or heat distribution at different timeintervarethe products. Fig. 8 shows nodes selected for plotting timeresponse graphs.Figs. 917 show temperature distribution curves for dif-ferent nodes as indicated in Fig. 8.From the temperature distribution graphs plotted inFigs. 917, it is clear that every node selected for the graphplotted experiencing increased in temperature, i.e. from theambient temperature to a certain temperature higher thanthe ambient temperature and then remained constant at thistemperature for a certain period of time. This increase in tem-perature was caused by the injection of molten plastic intothe cavity of the product.After a certain period of time, the temperature is thenfurther increased to achieve the highest temperature andremainedatureals in one complete cycle of plastic injection molding.For the 2D analysis of the mould, time response graphsplotted to analyze the effect of thermal residual stress onFig. 7. Contour plots of heat distributionconstant at that temperature. Increase in temper-was due to packing stages that involved high pressure,at different time intervals.264Fig.S.H. Tang et al. / Journal of Materials Processing8. Selected nodals near product region for time response graph plots.Fig. 9. Temperature distribution graph for Node 284.Fig. 10. Temperature distribution graph for Node 213.whichremainsreductionatabsenceplasticplottedbeysisTechnology 171 (2006) 259267Fig. 11. Temperature distribution graph for Node 302.Fig. 12. Temperature distribution graph for Node 290.caused the temperature to increase. This temperatureconstant until the cooling stage starts, which causesin mould temperature to a lower value and remainsthis value. The graphs plotted were not smooth due to theof function of inputting filling rate of the moltenas well as the cooling rate of the coolant. The graphsonly show maximum value of temperature that canachieved in the cycle.The most critical stage in the thermal residual stress anal-is during the cooling stage. This is because the coolingFig. 13. Temperature distribution graph for Node 278.stageglassentialinFigs.coolingS.H. Tang et al. / Journal of Materials ProcessingFig. 14. Temperature distribution graph for Node 1838.Fig. 15. Temperature distribution graph for Node 1904.causes the material to cool from above to below thetransition temperature. The material experiences differ-shrinkage that causes thermal stress that might resultwarpage.From the temperature after the cooling stage as shown in917, it is clear that the area (node) located near thechannel e