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1、Int J Adv Manuf Technol (2003) 21:807819Ownership and Copyright 2003 Springer-Verlag London LimitedA Parametric-Controlled Cavity Layout Design System for aPlastic Injection MouldM. L. H. Low and K. S. LeeDepartment of Mechanical Engineering, National University of Singapore, SingaporeToday, the tim
2、e-to-market for plastic products is becomingshorter, thus the lead time available for making the injectionmould is decreasing. There is potential for timesaving in themould design stage because a design process that is repeatablefor every mould design can be standardised. This paperpresents a method
3、ology for designing the cavity layout forplastic injection moulds by controlling the geometrical para-meters using a standardisation template. The standardisationtemplate for the cavity layout design consists of the configur-ations for the possible layouts. Each configuration of the layoutdesign has
4、 its own layout design table of all the geometricalparameters. This standardisation template is pre-defined at thelayout design level of the mould assembly design. This ensuresthat the required configuration can be loaded into the mouldassembly design very quickly, without the need to redesign thela
5、yout. This makes it useful in technical discussions betweenthe product designers and mould designers prior to the manu-facture of the mould. Changes can be made to the 3D cavitylayout design immediately during the discussions, thus savingtime and avoiding miscommunication. This standardisation tem-p
6、late for the cavity layout design can be customised easily foreach mould making company to their own standards.Keywords: Cavitylayoutdesign;Geometricalparameters;Mould assembly; Plastic injection mould design; Standardis-ation template1.IntroductionPlastic injection moulding is a common method for t
7、he massproduction of plastic parts with good tolerances. There are twomain items that are required for plastic injection moulding.They are the injection-moulding machine and the injectionmould. The injection-moulding machine has the mould mountedCorrespondence and offprint requests to: K. S. Lee, De
8、partment ofMechanical Engineering, National University of Singapore, 10 KentRidgeCrescent,Singapore119260.E-mailaddress:mpeleeksnus.edu.sgReceived 8 January 2002Accepted 16 April 2002on it and provides the mechanism for molten plastic transferfrom the machine to the mould, clamping the mould by thea
9、pplication of pressure and the ejection of the formed plasticpart. The injection mould is a tool for transforming the moltenplastic into the final shape and dimensional details of theplastic part. Today, as the time-to-market for plastic parts isbecoming shorter, it is essential to produce the injec
10、tion mouldin a shorter time.Much work had been done on applying computer techno-logies to injection mould design and the related field. Knowl-edge-based systems (KBS) such as IMOLD 1,2, IKMOULD3, ESMOLD 4, the KBS of the National Cheng KangUniversity, Taiwan 5, the KBS of Drexel University 6, etc.we
11、re developed for injection mould design. Systems such asHyperQ/Plastic 7, CIMP 8, FIT 9, etc. are developed forthe selection of plastic materials using a knowledge-basedapproach. Techniques have also been developed for partingdesign in injection moulding 1012.It has been observed that although mould
12、-making industriesare using 3D CAD software for mould design, much time iswasted in going through the same design processes for everyproject. There is great potential for timesaving at the moulddesign stage if the repeatable design processes can be standard-ised to avoid routine tasks. A well-organi
13、sed hierarchical designtree in the mould assembly is also an important factor 13,14.However, little work has been done in controlling the para-meters in the cavity layout design; thus this area will be ourmain focus. Although there are many ways of designing thecavity layout 15,16, mould designers t
14、end to use only conven-tional designs, thus there is a need to apply standardisation atthe cavity layout design level.This paper presents a methodology for designing the cavitylayout for plastic injection moulds by controlling the parametersbased on a standardisation template. First, a well-organise
15、dmould assembly hierarchy design tree had to be established.Then, the classification of the cavity layout configuration hadto be made to differentiate between those with standard con-figurations and those with non-standard configurations. Thestandard configurations will be listed in a configuration
16、databaseand each configuration has its own layout design table thatcontrols its own geometrical parameters. This standardisation808M. L. H. Low and K. S. LeeFig. 1. Front insert (cavity) and back insert (core).template is pre-defined at the layout design level of the mouldassembly design.2.Cavity La
17、yout Design for a PlasticInjection MouldAn injection mould is a tool for transforming molten plasticinto the final shape and dimensional details of a plastic part.Thus, a mould contains an inverse impression of the final part.Most of the moulds are built up of two halves: the front insertand the bac
18、k insert. In certain mould-making industries, thefront insert is also known as the cavity and the back insert isknown as the core. Figure 1 shows a front insert (cavity) anda back insert (core). Molten plastic is injected into theimpression to fill it. Solidification of the molten plastic thenforms
19、the part. Figure 2 shows a simple two-plate mouldassembly.Fig. 2. A simple mould assembly.2.1Difference Between a Single-Cavity and aMulti-Cavity MouldVery often, the impression in which molten plastic is beingfilled is also called the cavity. The arrangement of the cavitiesis called the cavity layo
20、ut. When a mould contains more thanone cavity, it is referred to as a multi-cavity mould. Figures 3(a)and 3(b) shows a single-cavity mould and a multi-cavity mould.A single-cavity mould is normally designed for fairly largeparts such as plotter covers and television housings. For smallerparts such a
21、s hand phone covers and gears, it is always moreeconomical to design a multi-cavity mould so that more partscan be produced per moulding cycle. Customers usually deter-mine the number of cavities, as they have to balance theinvestment in the tooling against the part cost.2.2Multi-Cavity LayoutA mult
22、i-cavity mould that produces different products at thesame time is known as a family mould. However, it is notusual to design a mould with different cavities, as the cavitiesmay not all be filled at the same time with molten plastic ofthe same temperature.On the other hand, a multi-cavity mould that
23、 produces thesame product throughout the moulding cycle can have a bal-anced layout or an unbalanced layout. A balanced layout isone in which the cavities are all uniformly filled at the sametime under the same melt conditions 15,16. Short mouldingcan occur if an unbalanced layout is being used, but
24、 this canbe overcome by modifying the length and cross-section of therunners (passageways for the molten plastic flow from thesprue to the cavity). Since this is not an efficient method, itis avoided where possible. Figure 4 shows a short mouldingsituation due to an unbalanced layout.A balanced layo
25、ut can be further classified into two categor-ies: linear and circular. A balanced linear layout can accommo-date 2, 4, 8, 16, 32 etc. cavities, i.e. it follows a 2nseries. Abalanced circular layout can have 3, 4, 5, 6 or more cavities,but there is a limit to the number of cavities that can beaccomm
26、odated in a balanced circular layout because of spaceconstraints. Figure 5 shows the multi-cavity layouts that havebeen discussed.3.The Design ApproachThis section presents an overview of the design approach forthe development of a parametric-controlled cavity layout designsystem for plastic injecti
27、on moulds. An effective workingmethod of mould design involves organising the various subas-semblies and components into the most appropriate hierarchydesign tree. Figure 6 shows the mould assembly hierarchydesign tree for the first level subassembly and components.Other subassemblies and components
28、 are assembled from thesecond level onwards to the nth level of the mould assemblyhierarchy design tree. For this system, the focus will be madeonly on the “cavity layout design”.A Cavity Layout Design System809Fig. 3. (a) A single cavity mould. (b) A multi-cavity mould.Fig. 4. Short moulding in an
29、unbalanced layout.3.1Standardisation ProcedureIn order to save time in the mould design process, it isnecessary to identify the features of the design that are com-monly used. The design processes that are repeatable for everymould design can then be standardised. It can be seen fromFig. 7 that ther
30、e are two sections that interplay in the stan-dardisation procedure for the “cavity layout design”: componentassembly standardisation and cavity layout configuration stan-dardisation.810M. L. H. Low and K. S. LeeFig. 5. Multi-cavity layouts.Fig. 6. Mould assembly hierarchical design tree.Fig. 7. Int
31、erplay in the standardization procedure.3.1.1Component Assembly StandardisationBefore the cavity layout configuration can be standardised,there is a need to recognise the components and subassembliesthat are repeated throughout the various cavities in the cavitylayout. Figure 8 shows a detailed “cav
32、ity layout design” hier-archy design tree. The main insert subassembly (cavity) in theFig. 8. Detailed “cavity layout design” hierarchical design tree.second level of the hierarchy design tree has a number ofsubassemblies and components that are assembled directly toit from the third level onwards o
33、f the hierarchy design tree.They can be viewed as primary components and secondarycomponents. Primary components are present in every moulddesign. The secondary components are dependent on the plasticpart that is to be produced, so they may or may not be presentin the mould designs.As a result, putt
34、ing these components and subassembliesdirectly under the main insert subassembly, ensures that everyrepeatable main insert (cavity) will inherit the same subas-semblies and components from the third level onwards of thehierarchy design tree. Thus, there is no need to redesignsimilar subassemblies an
35、d components for every cavity in thecavity layout.3.1.2Cavity Layout Configuration StandardisationIt is necessary to study and classify the cavity layout configur-ations into those that are standard and those that are non-standard. Figure 9 shows the standardisation procedure of thecavity layout con
36、figuration.A cavity layout design, can be undertaken either as a multi-cavity layout or a single-cavity layout, but the customersalways determine this decision. A single-cavity layout is alwaysconsidered as having a standard configuration. A multi-cavitymould can produce different products at the sa
37、me time or theA Cavity Layout Design System811Fig. 9. Standardisation procedure of the cavity layout configuration.same products at the same time. A mould that producesdifferent products at the same time is known as a familymould, which is a non-conventional design. Thus, a multi-cavity family mould
38、 has a non-standard configuration.A multi-cavity mould that produces the same product cancontain either a balanced layout design or an unbalanced layoutdesign. An unbalanced layout design is seldom used and, as aresult, it is considered to possess a non-standard configuration.However, a balanced lay
39、out design can also encompass eithera linear layout design or a circular layout design. This dependson the number of cavities that are required by the customers.It must be noted, however, that a layout design that has anyother non-standard number of cavities is also classified ashaving a non-standar
40、d configuration.After classifying those layout designs that are standard, theirdetailed information can then be listed into a standardisationtemplate. This standardisation template is pre-defined in thecavity layout design level of the mould assembly design andsupports all the standard configuration
41、s. This ensures that therequired configuration can be loaded very quickly into themould assembly design without the need to redesign the layout.3.2Standardisation TemplateIt can be seen from Fig. 10 that there are two parts in thestandardisation template: a configuration database and a layoutFig. 10
42、. The standardization template.design table. The configuration database consists of all thestandard layout configurations, and each layout configurationhas its own layout design table that carries the geometricalparameters. As mould-making industries have their own stan-dards, the configuration data
43、base can be customised to takeinto account those designs that are previously considered asnon-standard.3.2.1Configuration DatabaseA database can be used to contain the list of all the differentstandard configurations. The total number of configurations inthis database corresponds to the number of la
44、yout configur-ations available in the cavity layout design level of the moulddesign assembly. The information listed in the database is theconfiguration number, type, and the number of cavities. Table 1shows an example of a configuration database. The configur-ation number is the name of each of the
45、 available layoutconfigurations with the corresponding type and number ofcavities. When a particular type of layout and number ofcavities is called for, the appropriate layout configuration willbe loaded into the cavity layout design.3.2.2Layout Design TableEach standard configuration listed in the
46、configuration databasehas its own layout design table. The layout design tablecontains the geometrical parameters of the layout configurationand is independent for every configuration. A more complexlayout configuration will have more geometrical parameters tocontrol the cavity layout.Figures 11(a)
47、and 11(b) show the back mould plate (coreplate) with a big pocket and four small pockets for assemblingthe same four-cavity layout. It is always more economical andeasier to machine a large pocket than to machine individualsmaller pockets in a block of steel. The advantages of machin-ing a large poc
48、ket are:812M. L. H. Low and K. S. LeeFig. 11. The back mould plate with pocketing.Table 1. Sample of the configuration database.Configuration numberTypeNumber of cavitiesS01Single1L02Linear2L04Linear4L08Linear8L16Linear16L32Linear32L64Linear64C03Circular3C04Circular4C05Circular5C06Circular61. More s
49、pace between the cavities can be saved, thus asmaller block of steel can be used.2. Machining time is faster for creating one large pocketcompared to machining multiple small pockets.3. Higher accuracy can be achieved for a large pocket thanfor multiple smaller pockets.As a result, the default value
50、s of the geometrical parametersin the layout design table results in there being no gap betweenthe cavities. However, to make the system more flexible, thedefault values of the geometrical parameters can be modifiedto suit each mould design where necessary.3.3Geometrical ParametersThere are three va
51、riables that establish the geometrical para-meters:1. Distances between the cavities (flexible). The distancesbetween the cavities are listed in the layout design tableand they can be controlled or modified by the user. Thedefault values of the distances are such that there are nogaps between the ca
52、vities.2. Angle of orientation of the individual cavity (flexible). Theangle of orientation of the individual cavity is also listedin the layout design table which the user can change. Fora multi-cavity layout, all the cavities have to be at the sameangle of orientation as indicated in the layout de
53、sign table.If the angle of orientation is modified, all the cavities willbe rotated by the same angle of orientation without affectingthe layout configuration.3. Assembly mating relationship between each cavities (fixed).The orientation of the cavities with respect to each other ispre-defined for ea
54、ch individual layout configuration and iscontrolled by the assembly mating relationship betweencavities. This is fixed for every layout configuration unlessit is customised.Figure 12 shows an example of a single-cavity layout con-figuration and its geometrical parameters. The origin of themain inser
55、t/cavity is at the centre. The default values of X1and Y1 are zero so that the cavity is at the centre of thelayout (both origins overlap each other). The user can changethe values of X1 and Y1, so that the cavity can be offset appro-priately.Figure 13 shows an example of an eight-cavity layout con-
56、figuration and its geometrical parameters. The values of X andY are the dimensions of the main insert/cavity. By default, thevalues of X1 and X2 are equal to X, the value of Y1 is equalto Y, and thus there is no gap between the cavities. The valuesof X1, X2, and Y1 can be increased to take into acco
57、unt thegaps between the cavities in the design. These values are listedin the layout design table.If one of the cavities has to be oriented by 90, the rest ofthe cavities will be rotated by the same angle, but the layoutdesign remains the same. The user is able to rotate the cavitiesby changing the
58、parameter in the layout design table. Theresultant layout is shown in Fig. 14.Fig. 12. Single-cavity layout configuration and geometrical parameters.A Cavity Layout Design System813Fig. 13. Eight-cavity layout configuration and geometrical parameterswithout cavity rotation.Fig. 14. Eight-cavity layo
59、ut configuration and geometrical parameterswith cavity rotation.A complex cavity layout configuration, which has moregeometrical parameters, must make use of equation to relatethe parameters.4.System ImplementationA prototype of the parametric-controlled cavity layout designsystem for a plastic inje
60、ction mould has been implementedusing a Pentium III PC-compatible as the hardware. Thisprototype system uses a commercial CAD system (SolidWorks2001) and a commercial database system (Microsoft Excel)as the software. The prototype system is developed using theMicrosoft Visual C+ V6.0 programming lan
61、guage and theSolidWorks API (Application Programming Interface) in aWindows NT environment.SolidWorks is chosen primarily for two reasons:1. The increasing trend in the CAD/CAM industry is to movetowards the use of Windows-based PCs instead of UNIXworkstations mainly because of the cost involved in
62、purchas-ing the hardware.2. The 3D CAD software is fully Windows-compatible, thusit is capable of integrating information from Microsoft Excelfiles into the CAD files (part, assembly, and drawing)smoothly 17.This prototype system has a configuration database of eightstandard layout configurations th
63、at are listed in an Excel file.This is shown in Fig. 15(a). Corresponding to this configurationdatabase, the layout design level, which is an assembly filein SolidWorks (layout.sldasm), has the same set of layoutconfigurations. The configuration name in the Excel file corre-sponds to the name of the
64、 configurations in the layout assemblyfile, which is shown in Fig. 15(b).Every cavity layout assembly file (layout.sldasm) for eachproject will be pre-loaded with these layout configurations.When a required layout configuration is requested via the userinterface, the layout configuration will be loa
65、ded. The userinterface shown in Fig. 16 is prior to the loading of therequested layout configuration. Upon loading the requestedlayout configuration, the current layout configuration infor-mation will be listed in the list box.The user is then able to change the current layout configur-ation to any
66、other available layout configurations that are foundin the configuration database. This is illustrated in Fig. 17.The layout design table for the current layout configurationthat contains the geometrical parameters can be activated whenthe user triggers the push button at the bottom of the userinter
67、face. When the values of the geometrical parameters arechanged, the cavity layout design will be updated accordingly.Figure 18 shows the activation of the layout design table ofthe current layout configuration.5.A Case StudyA CAD model of a hand phone cover, shown in Fig. 19, isused in the following
68、 case study.Prior to the cavity layout design stage, the original CADmodel has to be scaled according to the shrinkage value ofthe moulding resin to be used. The main insert is then createdto encapsulate the shrunk part. This entire subassembly isknown as the main insert subassembly (xxx cavity.slda
69、sm),814M. L. H. Low and K. S. LeeFig. 15. The configuration database and layout template for prototype system.Fig. 16. The user interface prior to loading of the requested configuration.where “xxx” is the project name. Figure 20 shows the maininsert subassembly. After the main insert subassembly is
70、cre-ated, the cavity layout design system can be used to preparethe cavity layout of the mould assembly.5.1Scenario 1: Initial Cavity Layout DesignIn a mould design, the number of cavities to be built in amould is always suggested by the customers, as they have tobalance the investment in the toolin
71、g against the part cost.Initially, the customers had requested a two-cavity mould tobe designed for this hand phone cover. After the creation ofthe main insert subassembly, the mould designer loads a layoutconfiguration that is of a linear type which has two cavitiesusing this cavity layout design s
72、ystem. The correspondingconfiguration name is L02 and is listed in the user interfaceas shown in Fig. 21.5.2Scenario 2: Modification in the Cavity LayoutDesignTechnical discussion sessions between the customers and moulddesigners are common. This enables changes to be made tothe 3D CAD files of both
73、 the product and mould as soon aspossible, prior to mould manufacture. Changes are almostalways inevitable and mould designers are never given anyextension in the lead time.In this case, during a technical discussion session, the cus-tomers changed their minds and needed a linear four-cavitymould in
74、stead of a two-cavity mould so that the productionA Cavity Layout Design System815Fig. 17. The user interface after loading of the requested configuration.Fig. 18. The user interface with the layout design table.816M. L. H. Low and K. S. LeeFig. 19. The CAD model of a hand phone.rate of the hand pho
75、ne covers can be increased. The moulddesigner can use the cavity layout design system to modifythe existing cavity layout design to a linear four-cavity mould.The required new layout configuration can be selected fromthe available layout configurations that are listed in the con-figuration database.
76、 This is shown in Fig. 22.Fig. 21. A linear two-cavity configuration.Fig. 20. The main insert encapsulating the shrunk part.5.3Scenario 3: Gap is Required Between CavitiesFinally, in another technical discussion session, the moulddesigner is required to introduce a gap of 20 mm between thecavities i
77、n the longitudinal direction, as shown in Fig. 23.A Cavity Layout Design System817Fig. 22. A linear, four-cavity layout configuration (after a change in the layout configuration).Fig. 23. The introduction of a gap between the cavities.818M. L. H. Low and K. S. LeeFig. 24. Modifying the value of Y1 i
78、n the layout design table.Fig. 25. The final design after the addition of the gap.A Cavity Layout Design System819In the cavity layout subassembly level, the mould designeruses the cavity layout system to activate the layout designtable of the current layout configuration. The value of Y1 ischanged
79、from 50 mm to 70 mm to introduce a gap of 20 mmbetween the cavities in the longitudinal direction. Figure 24shows the change of the value of Y1 in the layout designtable. The result of the final design, after addition of the gap,is shown in Fig. 25.6.ConclusionsIn this paper, an approach using a sta
80、ndardisation template isproposed for the development of a parametric-controlled cavitylayout design system. Since this approach makes use of stan-dardisation, it can be further applied to other components formould assembly design if their design processes are repeatableor they have features that are
81、 commonly used for every moulddesign. The advantages of the developed cavity layout systemare as follows:1. The developed system has user-friendly interfaces.2. Since it makes use of databases, it is highly flexible, andmould-making industries that have their own standards cancustomise the databases
82、 to suit their needs.3. Because a pre-defined standardisation template is availablein the layout design level of the mould assembly design,the required layout configuration can be loaded very quicklyinto the mould assembly design without the need to redesignthe layout.4. This system enables product
83、designers and mould designersto have more useful technical discussions prior to mouldmanufacture as changes to the layout can be made immedi-ately during the discussions.5. This system saves time in the mould design process becauseit removes redundant work. This is very important for themould-making
84、 industries since the lead time for mouldmaking is decreasing.The developed system has some limitations. Although thedatabases and layout design tables can be customised, customis-ation will be more difficult for more complex non-standardconfigurations because the correct geometrical parameters have
85、to be determined. We are currently working on applying astandardisation template for other components in mould design.References1. K. S. Lee, J. Y. H, Fuh, Y. F. Zhang, A. Y. C. Nee and Z. Li,“IMOLD: an intelligent plastic injection mold design and assemblysystem”, Proceedings of the 4th Internation
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