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Journal of Materials Processing Technology 171 2006 259 267 Abstract the in Unigraphics using distrib results at K 1 industries Almost usage by molding to at There are tion appropriate system This with ity pack e 0924 0136 doi 10 1016 j jmatprotec 2005 06 075 Design and thermal analysis of plastic injection mould S H Tang Y M Kong S M Sapuan R Samin S Sulaiman Department of Mechanical and Manufacturing Engineering Universiti Putra Malaysia 43400 Serdang Selangor Malaysia Received 3 September 2004 accepted 21 June 2005 This paper presents the design of a plastic injection mould for producing warpage testing specimen and performing thermal analysis for mould to access on the effect of thermal residual stress in the mould The technique theory methods as well as consideration needed designing of plastic injection mould are presented Design of mould was carried out using commercial computer aided design software Version 13 0 The model for thermal residual stress analysis due to uneven cooling of the specimen was developed and solved a commercial finite element analysis software called LUSAS Analyst Version 13 5 The software provides contour plot of temperature ution for the model and also temperature variation through the plastic injection molding cycle by plotting time response curves The show that shrinkage is likely to occur in the region near the cooling channels as compared to other regions This uneven cooling effect different regions of mould contributed to warpage 2005 Elsevier B V All rights reserved eywords Plastic Injection mould Design Thermal analysis Introduction by cooling stage where the mould is cooled until the part is sufficiently rigid to be ejected The last step is the ejection Plastic industry is one of the world s fastest growing ranked as one of the few billion dollar industries every product that is used in daily life involves the of plastic and most of these products can be produced plastic injection molding method 1 Plastic injection process is well known as the manufacturing process create products with various shapes and complex geometry low cost 2 The plastic injection molding process is a cyclic process are four significant stages in the process These stages filling packing cooling and ejection The plastic injec molding process begins with feeding the resin and the additives from the hopper to the heating injection of the injection plastic injection molding machine 3 is the filling stage in which the mould cavity is filled hot polymer melt at injection temperature After the cav is filled in the packing stage additional polymer melt is ed into the cavity at a higher pressure to compensate the xpected shrinkage as the polymer solidifies This is followed Corresponding author E mail address saihong eng upm edu my S H Tang stage after 4 meric nated actual the core and f mould gating to stresses de molded conducti molten e 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 of tooling Among the task of mould design designing mould specific supplementary geometry usually on the side is quite complicated by the inclusion of projection depression 5 In order to design a mould many important designing actors must be taken into consideration These factors are size number of cavity cavity layouts runner systems systems shrinkage and ejection system 6 In thermal analysis of the mould the main objective is analyze the effect of thermal residual stress or molded in on product dimension Thermally induced stresses velop principally during the cooling stage of an injection part mainly as a consequence of its low thermal vity and the difference in temperature between the resin and the mould An uneven temperature field xists around product cavity during cooling 7 260 Processing ences channel e Significant fore of understanding tion be producing mal residual 2 2 1 specimen that thin uct the moulded shell 120 material w temperature respecti duced 2 2 testing erations testing injection carbon the iii i imen design sion is machine The Therefore not reserv setting up S H Tang et al Journal of Materials During cooling location near the cooling channel experi more cooling than location far away from the cooling This different temperature causes the material to xperience differential shrinkage causing thermal stresses thermal stress can cause warpage problem There it is important to simulate the thermal residual stress field the injection molded part during the cooling stage 8 By the characteristics of thermal stress distribu deformation caused by the thermal residual stress can predicted In this paper the design of a plastic injection mould for warpage testing specimen and for performing ther analysis for the mould to access on the effect of thermal stress in the mould is presented Methodology Design of warpage testing specimen This section illustrates the design of the warpage testing to be used in plastic injection mould It is clear warpage is the main problem that exists in product with shell feature Therefore the main purpose of the prod development is to design a plastic part for determining effective factors in the warpage problem of an injection part with a thin shell The warpage testing specimen is developed from thin plastics The overall dimensions of the specimen were mm in length 50 mm in width and 1 mm in thickness The used for producing the warpage testing specimen as acrylonitrile butadiene stylene ABS and the injection time and pressure were 210 C 3 s and 60 MPa vely Fig 1 shows the warpage testing specimen pro Design of plastic injection mould for warpage specimen This section describes the design aspects and other consid involved in designing the mould to produce warpage specimen The material used for producing the plastic Fig 1 Warpage testing specimen produced imum base fitted lo sions ha reaction the respecti on space with Therefore T Mould Components T Ca Core Side Ejector Ejector Bottom Technology 171 2006 259 267 mould for warpage testing specimen was AISI 1050 steel Four design concepts had been considered in designing of mould including i Three plate mould Concept 1 having two parting line with single cavity Not applicable due to high cost ii Two plate mould Concept 2 having one parting line with single cavity without gating system Not applicable due to low production quantity per injection Two plate mould Concept 3 having one parting line with double cavities with gating and ejection system Not applicable as ejector pins might damage the product as the product is too thin v Two plate mould Concept 4 having one parting line with double cavities with gating system only used sprue puller act 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 Various considerations had been applied in the design Firstly the mould was designed based on the platen dimen of the plastic injection machine used BOY 22D There a limitation of the machine which is the maximum area of platen 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 should exceed this distance Furthermore 4 mm space had been ed between the two tie bars and the mould for mould and handling purposes This gives the final max width of the mould as 250 mm The standard mould with 250 mm 250 mm is employed The mould base is to the machine using Matex clamp at the upper right and wer 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 pressure ving clamping force higher than the internal cavity force force 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 cavities core plate to be placed horizontally as there is enough while the cavity plate is left empty and it is only fixed sprue bushing for the purpose of feeding molten plastics it is only one standard parting line was designed at able 1 plates dimensions Size mm width height thickness op clamping plate 250 250 25 vity plate 200 250 40 plate 200 250 40 plate support plate 37 250 70 retainer plate 120 250 15 plate 120 250 20 clamping plate 250 250 25 Processing the released opening is land only w for runner ing case more type This the diameter or same the air and flashing in or that occurring ca e ca cient sho core the Fig 2 Cavity layout with air vents and cooling channels plate The sprue puller located at the center of core plate not only functions as the puller to hold the product in position when the mould is opened but it also acts as ejector to push the product out of the mould during ejection stage No addi tional ejector is used or located at product cavities because the product produced is very thin i e 1 mm Additional ejec tor in the product cavity area might create hole and damage to 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 wireframe modeling of the mould developed using Unigraphics S H Tang et al Journal of Materials surface of the product The product and the runner were in a plane through the parting line during mould Standard or side gate was designed for this mould The gate located between the runner and the product The bottom of the gate was designed to have 20 slanting and has 0 5 mm thickness for easy de gating purpose The gate as also designed to have 4 mm width and 0 5 mm thickness the entrance of molten plastic In the mould design the parabolic cross section type of was selected as it has the advantage of simpler machin in one mould half only which is the core plate in this However this type of runner has disadvantages such as heat loss and scrap compared with circular cross section This might cause the molten plastic to solidify faster problem was reduced by designing in such a way that runner is short and has larger diameter which is 6 mm in It is important that the runner designed distributes material molten plastic into cavities at the same time under the pressure and with the same temperature Due to this cavity layout had been designed in symmetrical form Another design aspect that is taken into consideration was vent design The mating surface between the core plate the cavity plate has very fine finishing in order to prevent from taking place However this can cause air to trap the cavity when the mould is closed and cause short shot incomplete part Sufficient air vent was designed to ensure air trap can be released to avoid incomplete part from The cooling system was drilled along the length of the vities and was located horizontally to the mould to allow ven cooling These cooling channels were drilled on both vity and core plates The cooling channels provided suffi cooling of the mould in the case of turbulent flow Fig 2 ws cavity layout with air vents and cooling channels on plate In this mould design the ejection system only consists of ejector retainer plate sprue puller and also the ejector 3 3 1 testing run short air Fig 3 3D solid modeling and wireframe Technology 171 2006 259 267 261 Results and discussion Results of product production and modification From the mould designed and fabricated the warpage specimens produced have some defects during trial The defects are short shot flashing and warpage The shot is subsequently eliminated by milling of additional vents at corners of the cavities to allow air trapped to modeling of the mould 262 Processing escape packing by injection ity little the eliminate 3 2 of tion the directed the 35 men sure selected ing finite and core formed Fig 5 Model for thermal analysis T Material Carbon Density Y Poisson Y T Thermal Conducti Specific S H Tang et al Journal of Materials Fig 4 Extra air vents to avoid short shot Meanwhile flashing was reduced by reducing the pressure of the machine Warpage can be controlled controlling 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 required finishing by de gating Fig 4 shows modifications of mould which is machining of extra air vents that can short shot Detail analysis of mould and product After the mould and products were developed the analysis mould and the product was carried out In the plastic injec moulding process molten ABS at 210 C is injected into mould through the sprue bushing on the cavity plate and into the product cavity After cooling takes place product is formed One cycle of the product takes about s including 20 s of cooling time The material used for producing warpage testing speci was ABS and the injection temperature time and pres were 210 C 3 s and 60 MPa respectively The material for the mould was AISI 1050 carbon steel Properties of these materials were important in determin temperature distribution in the mould carried out using element analysis Table 2 shows the properties for ABS AISI 1050 carbon steel The critical part of analysis for mould is on the cavity and plate because these are the place where the product is Therefore thermal analysis to study the temperature distrib performed called 2D of modeling side together analysis and element response duration analysis Basically the the the 3 3 analysis time able 2 properties for mould and product Steel AISI 1050 mould 7860 kg m 3 oung s modulus E 208 GPa s ratio 0 297 ield strength S Y 365 4 MPa ensile strength S UTS 636 MPa expansion 11 65 10 6 K 1 vity k 49 4 W m K heat c 477 J kg K Technology 171 2006 259 267 ution and temperature at through different times are using commercial finite element analysis software LUSAS Analyst Version 13 5 A two dimensional thermal analysis is carried out for to study the effect thermal residual stress on the mould at different regions Due to symmetry the thermal analysis was performed by only the top half of the vertical cross section or view of both the cavity and core plate that were clamped during injection Fig 5 shows the model of thermal analyzed with irregular meshing Modeling for the model also involves assigning properties process or cycle time to the model This allowed the finite solver to analyze the mould modeled and plot time graphs to show temperature variation over a certain and at different regions For the product analysis a two dimensional tensile stress was carried using LUSAS Analyst Version 13 5 the product was loaded in tension on one end while other end is clamped Load increments were applied until model reaches plasticity Fig 6 shows loaded model of analysis Result and discussion for mould and product For mould analysis the thermal distribution at different intervals was observed Fig 7 shows the 2D analysis ABS Polymer product Density 1050 kg m 3 Young s modulus E 2 519 GPa Poisson s ratio 0 4 Yield strength S Y 65 MPa Thermal expansion 65 10 6 K 1 Conductivity 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 259 267 263 Fig 6 Loaded model for analysis of product contour plots of thermal or heat distribution at different time interv are the products Fig 8 shows nodes selected for plotting time response graphs Figs 9 17 show temperature distribution curves for dif ferent nodes as indicated in Fig 8 From the temperature distribution graphs plotted in Figs 9 17 it is clear that every node selected for the graph plotted experiencing increased in temperature i e from the ambient temperature to a certain temperature higher than the ambient temperature and then remained constant at this temperature for a certain period of time This increase in tem perature was caused by the injection of molten plastic into the cavity of the product After a certain period of time the temperature is then further increased to achieve the highest temperature and remained ature als in one complete cycle of plastic injection molding For the 2D analysis of the mould time response graphs plotted to analyze the effect of thermal residual stress on Fig 7 Contour plots of heat distribution constant at that temperature Increase in temper was due to packing stages that involved high pressure at different time intervals 264 Fig S H Tang et al Journal of Materials Processing 8 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 which remains reduction at absence plastic plotted be ysis Technology 171 2006 259 267 Fig 11 Temperature distribution graph for Node 302 Fig 12 Temperature distribution graph for Node 290 caused the temperature to increase This temperature constant until the cooling stage starts which causes in mould temperature to a lower value and remains this value The graphs plotted were not smooth due to the of function of inputting filling rate of the molten as well as the cooling rate of the coolant The graphs only show maximum value of temperature that can achieved in the cycle The most critical stage in the thermal residual stress anal is during the cooling stage This is because the cooling Fig 13 Temperature distribution graph for Node 278 stage glass ential in Figs cooling S H Tang et al Journal of Materials Processing Fig 14 Temperature distribution graph for Node 1838 Fig 15 Temperature distribution graph for Node 1904 causes the material to cool from above to below the transition temperature The material experiences differ shrinkage that causes thermal stress that might result warpage From the temperature after the cooling stage as shown in 9 17 it is clear that the area node located near the channel experienced more cooling effect due to fur Fig 16 Temperature distribution graph for Node 1853 ther cooling ing is 284 channel product middle stress more that cooling is mould cooling analyze on dimensional equi maximum v this in in is load to the stress tion purposes sis vice may loading Technology 171 2006 259 267 265 Fig 17 Temperature distribution graph for Node 1866 decreasing in temperature and the region away from the channel experienced less cooling effect More cool effect with quite fast cooling rate means more shrinkage occurring at the region However the farthest region Node experience more cooling although far away from cooling due to heat loss to environment As a result the cooling channel located at the center of the cavity caused the temperature difference around the of the part higher than other locations Compressive was developed at the middle area of the part due to shrinkage and caused warpage due to uneven shrinkage happened However the temperature differences after for different nodes are small and the warpage effect not very significant It is important for a designer to design a that has less thermal residual stress effect with efficient system For the product analysis from the steps being carried out to the plastic injection product the stress distribution product at different load factor is observed in the two analysis Figs 18 21 show the contour plots of valent stress at different load increments A critical point Node 127 where the product experiences tensile stress was selected for analysis The stress ersus strain curve and the load case versus stress curves at point were plotted in Figs 22 and 23 From the load case versus stress curves at this point plotted Fig 23 it is clear that the product experiencing increased tensile load until it reached the load factor of 23 which 1150 N This means that the product can withstand tensile until 1150 N Load higher