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Int J Adv Manuf Technol (2001) 17:453461 2001 Springer-Verlag London LimitedThree-Dimensional Kernel Development for Injection MouldDesignT. L. Neo and K. S. LeeDepartment of Mechanical and Production Engineering, National University of Singapore, SingaporeToday, many software “plug-ins” have been developed onhigh-level 3D modelling platforms to facilitate processes suchas FEM analysis, CAM, injection mould design, simulationand visualisation. Such an arrangement is advantageous inmany ways. However, it is not without shortcomings. Ideally,these “plug-ins” could also be developed using low-level 3Dkernels for higher flexibility and better portability. This paperexamines the various issues and methodologies related to thedevelopment of such 3D-based applications. The emphasis isplaced on the software aspect. First, a methodology for thedevelopment of 3D-based applications is proposed. The ideais then implemented by developing an injection mould designapplication using a low-level 3D kernel called Parasolid. Basedon design concepts used in an established mould design appli-cation, IMOLD, the development of a mould base designmodule is illustrated. An object-oriented programming langu-age has been chosen for the development of the software ona Windows NT platform.Keywords: 3D kernel; Computer-aided design (CAD); Injec-tion mould design; Parasolid1.IntroductionThree-dimensional CAD systems have increasingly been usedto speed up the product realisation process. One of the firststeps involved in the automation of the product design processis the creation of the component parts in a 3D modellingapplication. The 3D model, upon creation, is called the digitalmaster copy. This 3D digital model forms the key to a widespectrum of process automation.Creating the 3D digital model of component parts is onlythe very first step. There are several other secondary tasks thatmust to be done before the part can be manufactured. Suchtasks include finite-element analysis, jigs and fixtures design,injection mould design, computer-aided manufacturing, simul-Correspondence and offprint requests to: K.-S. Lee, Department ofMechanical and Production Engineering, National University of Singa-pore, 119260 Singapore. E-mail: mpeleeksK.sgation, and visualisation. Today, many application Plug-ins havebeen developed on high-level 3D modelling platforms to facili-tate these secondary tasks. The 3D-modelling platform providesthe plug-in software with a library of functions as well as anestablished user interface and style of programming. As aresult, the development times for these plug-ins are signifi-cantly reduced.Such an arrangement is advantageous in many ways. How-ever, it has its shortcomings, especially in the long run. Inorder to develop a plug-in for established software, the devel-opers must adhere to the many constraints imposed. There isa need to be consistent with the style of the parent software.The developers must be able to achieve any functionality theyneed with only the set of library functions provided. Mostend-users need both the parent software and the plug-in. Inmany cases, however, they may be more interested in usingonly the plug-in software. An example of such a situation isin injection mould design. These users, however, must purchasethe entire software package which includes many features andfunctions that they do not need. Such a large program is oftenvery demanding on the hardware, which also means higher cost.The plug-in software is also very dependent on developments inthe parent software. Whenever a new version is updated forthe parent software, the plug-in developers have to follow-upon the changes. These shortcomings may not exist if theseapplications were developed on a low-level platform. Ideally,these plug-ins could be developed using low-level 3D kernelsfor higher flexibility and better portability. In many instances,such a move is both feasible and advantageous.Traditionally, injection mould design is carried out directlyon a CAD system. The entire injection mould, consisting ofperhaps hundreds of components, is modelled and assembledon CAD systems such as AutoCAD, Pro/Engineer, and Uni-graphics. As the injection mould design process is recursive,it is very time-consuming to re-model and re-assemble thedesign. In this aspect, 3D CAD systems such as Pro/Engineerand Unigraphics, which are feature-based, have a significantadvantage over 2D CAD systems such as AutoCAD. To furtherspeed up the injection mould design process, plug-ins weredeveloped on these 3D systems to automate certain stages ofthe design process. Examples of such add-on applicationsinclude IMOLD (Intelligent Mold Design and Assembly Sys-454T. L. Neo and K. S. Leetem, developed at the National University of Singapore, basedon Unigraphics), Expert Mold Designer (based on CADKEY)and Moldmaker (based on EUCLID). As each is based on aspecific CAD system, there is no plug compatibility.In 1994, Mok and Cheung 1 presented work on the devel-opment of an injection mould design application based onUnigraphics. In 1997, Shah 2 proposed a 3-tier architecturefor standardising communications between geometric modellingkernels and applications that require geometric modelling ser-vices. His objective is to achieve plug compatibility between3D applications that are based on Parasolid 3 (a 3D kernel,developed at the University of Cambridge) and ACIS. This,however, involved an extensively developed 3-tier modellinghusk. In this paper, the author attempts to develop a lightweightinjection mould design application using a low-level 3D kerneldirectly. The focus is on the flexibility and speed of thesoftware development. Design concepts and procedures weretaken from IMOLD 4,5, a complete mould design andassembly 3D application. Although the discussion is limited toinjection mould design only, the methodology applied caneasily be applied in other 3D-based applications that are of asimilar nature.A combination of developer tools was chosen for this pur-pose. Before the methodology is discussed, brief introductionsto some of these tools are first presented. They are, IMOLD,Parasolid version 10.1, Visual C+ version 6.0, and theMicrosoft Foundation Classes.2.IMOLD as a Mould Design ApplicationIMOLD (Intelligent Mold Design and Assembly) is an estab-lished 3D-based application that is dedicated to injection moulddesign. It is developed on top of an advanced CAD systemcalled Unigraphics. The development is carried out using theapplicationsprogramminginterface(API)provided.Thesoftware enables mould designers to create a design rapidlyby providing the tools that are commonly needed. Standardcomponents parts, that are often required in the design, havebeen pre-created in the software and can be readily used bythe designer. This reduces the design time significantly. Themould design process is divided into several stages, providingthe designer with a consistent method of creating the moulddesign. They are, namely:1. Data preparation.2. Filling system design.3. Mould base design.4. Inserts and parting design.5. Cooling system design.6. Slider and lifter design.7. Ejection system design.8. Standard parts library.Each stage can be considered as an independent module ofthe program. The 3D-based requirements for each module varyonly slightly. The success in developing the mould base moduleimplies feasibility in developing all the other modules.3.Parasolid as a 3D KernelParasolid is designed to be the centre or “kernel” of anysystem that is based on 3D model data. It is essentially a solidmodeller, which can be used to:1. Build and manipulate solid objects.2. Calculate mass and moments of inertia, and perform clashdetection.3. Output the objects in various ways, including pictorially.4. Store the objects in some sort of database or archive, andretrieve them later.Parasolid is one of the most advanced 3D kernels among CADapplications. It is the 3D kernel of Unigraphics and Solid-Works. Its unique tolerant modelling functionality enables itto accept data stored in other modeller formats. Parasolidmodel files are thus very potable. It is, therefore, a superiorplatform for the development of stand-alone applications.The 3D-based application interacts with Parasolid throughone of its three interfaces (see Fig. 1). These are called theParasolid kernel (PK) interface, the kernel interface (KI) andthe downward interface. The PK interface and the kernelinterface sit “on top” of the modeller (side-by-side), and arethe means by which the application models and manipulatesthe objects, as well as controls the functioning of the modeller.The downward interface lies “beneath” the modeller, and iscalled by the modeller when it needs to perform data-intensiveor system type operations. It consists of three parts: frustrum;graphical output (GO); and foreign geometry. These are brieflyexplained below.3.1The KI and PK InterfaceThe KI and the PK are interfaces for the programmer to accessthe modelling capabilities in the Parasolid kernel. They arestandard libraries of modelling functions. The programmer callsthese modelling functions in their programs. As the KI is tobe phased out soon, we chose to use the PK interface.Fig. 1. Parasolid components.3D Kernel Development for Injection Mould Design4553.2The FrustrumThe frustrum is a set of functions, which must be written bythe applications programmer. The kernel calls them when datamust be saved or retrieved. When using Parasolid, the appli-cations programmer must first decide how to manage thestorage of data, which Parasolid outputs through the frustrum.Transferring data through the frustrum usually involves writingto, or reading from, files. The format and location of the filesis determined when writing the frustrum functions.3.3The Graphical Output (GO)The graphical output is another set of functions, which is tobe written by the applications programmer. When a call is madeto the PK rendering functions, the graphical data generated areoutput through the GO interface. The graphical data are thenpassed to a 3D rendering package. OpenGL, a software inter-face to graphic cards, is a rendering package that is used forour purpose.3.4The Foreign GeometryThe foreign geometry provides functionality for the develop-ment of customised geometrical types such as in-house curvesand surfaces. These are used together with the standard geo-metrical types for modelling within Parasolid.4.Object-Oriented Programming UsingVisual C+ and the Microsoft FoundationClassesObject-oriented programming (OOP) has been the undisputedoption for software developers. It is among the most advanceddevelopmental tools available. The Microsoft Visual Studio issuch a software package. It features several developmentaltools that are meant for Internet-based and Windows-basedprogramming. Among these tools are the Visual C+ (VC+)and the Microsoft Foundation Classes (MFC). The VC+ is apowerful development tool for object-oriented programming,whereas the MFC is a framework of C+ classes that arededicated to Windows-based programming. Together, theseprovided the applications programmer with powerful develop-ment features and functionalities such as auto-code generation,and wizard-based operations. These greatly improved pro-ductivity.Theentireuser-interfaceforourprogramisdeveloped using the VC+ and the MFC.5.System DesignThe direct development of a 3D-based add-on application usinga 3D kernel requires several issues to be addressed. Theyconsist of 3 main stages at the highest level. First, the identifi-cation of the crucial features and functions required for theplug-in application. Secondly, the development of the designfor the application framework. Lastly, the design and develop-ment of the individual modules in the framework with appropri-ate developmental tools.5.1Identification of Essential ModulesParasolid, as a 3D kernel, provides only a number of librariesand a conceptual framework for 3D application development.It is thus necessary for the developers to identify and developthe other essential facilities that are provided in a 3D CADsystem. In order to identify the required facilities, it isimportant to understand the discrepancies between the two.Table 1 summarises the main differences in the facilitiesprovided by a 3D kernel and a 3D CAD system. Some ofthese facilities, such as features and parametric modelling, areboth time-consuming and technically demanding to develop.As most plug-ins do not use all the facilities of the parentsoftware, it is possible to develop only those required bythe plug-ins using low-level 3D kernels, producing a stand-alone version.Items 7 to 9 in Table 1 are prerequisites for the developmentof 3D-based applications using Parasolid. By studying therequirements of the plug-in application, other essential facilitiescan be identified. A framework for the application is thenproposed, based on the facilities provided by the Parasolid ker-nel.5.2Framework for 3D-Based ApplicationsA frameworkis developed with reference to the facilitiesprovided by the developmental tools and the requirements ofthe application. It is designed so that there are minimumdependencies between individual code modules. This may resultin a small degree of code duplication. In exchange, there isbetter portability of the program codes, greater ease of mainte-nance and a better prospect for future expansion. The overviewof this framework is illustrated in Fig. 2. The details of thevarious modules are discussed in the following sections.5.2.1Windows-Based User-Interface (A)Parasolid does not provide the programmer with a user-interface. Thus, the development of the 3D-based applicationat every single stage will involve designing the user-interfacefrom scratch. The necessary developments involve:1. Environmental setting and display of the 3D-based appli-cation.2. Interactive graphical interface and execution procedure forall application functionality.5.2.23D Developer Layer (B)Since different 3D-based applications require 3D-facilities todifferent extent, the framework must provide for these vari-ations. A 3D developer layer (See Fig. 2, Item B) is conceptual-ised to handle such variations. It is a library of objects orclasses that are developed, based on the Parasolid kernel. Theextent of development depends on the requirements of the456T. L. Neo and K. S. LeeTable 1. Summary of facilities provided by a 3D kernel and a CAD system.Facilities3D kernel3D CAD system1.Basic 3D modellingLow-level and general functions providedHigh-level and specific functions provided2.AssembliesSeveral library functions providedComplete system provided3.Feature-based modellingNot providedEstablished feature set provided4.Parametric modellingNot providedOften provided5.Free-form modellingLow-level functions providedOften provided6.DraftingNot providedComplete system provided7.Interactive user-interfaceNot providedAlways provided8.Visualisation of 3D objectsConceptual framework and several libraryCompletely developedfunctions provided9.File management systemConceptual framework and several libraryCompletely developedfunctions providedFig. 2. Overview of 3D-based application.application identified in the previous section. Besides cateringfor variations in application requirements, the 3D developerlayer also acts as a programming interface for non-Parasoliddevelopers. Such an interface can also be re-used for sub-sequent development of other 3D-based applications. The 3Ddeveloper layer essentially consists of three main sections.They are used for 3D modelling and assembly, 3D visualisationand 3D data management, respectively.I.3D Modelling and Assembly.The 3D modelling andassembly module is the most important and elaborate of allthree sections. It is analogous to the application-programminginterface (API) provided by most CAD systems. The moduleconsists of a library of 3D-based objects or classes, which areused for the development of the core application modules. Thebasic 3D functionality that is required by most 3D applicationsmust be developed first. Depending on the requirements of theindividual 3D-based application, other more advance featuresare subsequently added.II.3DVisualisation.Thedisplayof3DobjectsinaWindows client area requires a software graphics interface. Thegraphical output together with a selected graphical interface, areused for the rendering of 3D objects in the 3D-based appli-cation, as well as the management of the viewing projectionsand transformations. Here, a library of classes is developed forsuch purposes.III.3DDataManagement.The3Ddatamanagementmodule is developed on top of the frustrum. The frustrum isthe module in the Parasolid kernel that facilitates archivingand access of 3D part files. A library of classes are developedusing the frustrum for handling:1. 3D object file format.2. File management operations such as opening and saving a3D object file.5.2.3Application Modules (C)These are the actual 3D-based application modules that sitbetween the 3D developer layer and the application user-interface. The design of these modules depends mainly on thenature of the applications and often differs greatly. The mainbulk of the developmental work is carried out in this area.The ease of the development, however, depends on the capabili-ties of the 3D developer layer.5.2.4Other Software Modules (D)Very often, the 3D-based application may require functionalityfrom other existing software modules or application modules.Therefore, such a link may exist. An example of such arequirement is illustrated in the implementation section ofthis paper.5.3Development of Individual ModulesEach module to be developed is studied and analysed beforea suitable design is produced. The ease of development dependsgreatly on the design of the framework and the developer toolsselected. The next section illustrates the implementation of the3D Kernel Development for Injection Mould Design457Fig. 3. Overview of the injection mould base design application.above methodology on a 3D-based injection mould base designand assembly application.6.ImplementationsApplying the system design, a 3D-based injection mould designapplication is developed. This is achieved using the develop-mental tools mentioned in the earlier sections. The mould basemodule is chosen for illustration, as it requires the widest rangeof 3D functionality, including the generation of assemblies.6.1Framework of Application and theRequirements of Each ModuleA framework for the application is designed with reference tothe developmental work identified. Figure 3 illustrates theFig. 4. Windows-based interface.Fig. 5. Details of the mould base module.framework for the Mold Base design application. The detailsof the requirements in each module are discussed as follows:6.1.1Windows NT User-Interface (A)Mould base design is an iterative process. The Mould designerfirst selects a standard mould base from the catalogue, andthen repeatedly makes modifications to the dimensions of themould base until all the design requirements are met. It is,therefore, necessary to consider an interactive user-interfacefor such purpose. Using the Visual C+ and the MFC, aWindows-based interface is developed. These include:1. Creation, display and management of menu bar items, con-text menu items and toolbar buttons for easy access tofunctionality of the application.2. Creation, display and management of dialogue boxes toguide the user or to obtain user input.458T. L. Neo and K. S. LeeFig. 6. Cavity plate B.Fig. 7. A “Hoppt” two-plate mould base.3. Creation, display, and management of various views in thedisplay area, for illustration.4. Mouse driven interaction.5. The design of the sequence of operation (including userinteraction) for each function.The resulting application, as shown in Fig. 4, is a typicalWindows-based application with a user-friendly interface.6.1.23D Developer Layer (B)The 3D-based requirements of mould base design is analysedand the modules to be developed are identified. The modellingrequirements for 3D-based mould base design are:1. Creation of primitives such as blocks, cylinders, cones,prisms, and toruses.2. Creation of blends and chamfers.3D Kernel Development for Injection Mould Design459Fig. 8. Customisation of bottom screw dimensions.3. Boolean operations: unite and subtract.4. Transformation operations: translation and rotation.5. Management of object attributes such as name and colour.6. Creation of instances.7. Creation of assemblies and subassemblies.As these are not too extensive, it is possible to develop abasic modelling set. With the detailed development of theindividual modules, more functions are then added to the 3Ddeveloper layer. The overall requirements in each module areillustrated in the following sections.I.3D Modelling and Assembly.A mould base is essentiallyan assembly of many components such as plates, bushes, pins,and screws. To facilitate mould base design, the designermust be provided with a library of ready-made mould basecomponents. By selecting a particular dimension, a standardmould base will be generated. To facilitate these, a library of3D-based functions, corresponding to the requirements men-tioned in Section 6.1.2, are identified and developed. As thecodes are object-oriented, they can easily be expanded toaccommodate other mould design modules when required.II.3D Visualisation.Using the functions provided in thegraphical output, together with OpenGL as the graphical inter-face, several functions are developed for 3D rendering, viewprojections and view transformations. These include:1. Rendering 3D parts with selected colours (Fig. 6).2. Rendering 3D assemblies with selected colours (Figs 7 and 8for rendering in shaded and wireframe modes, respectively).3. Rendering other 3D entities on screen with selected colours.4. Rendering individual components with a different colour ina mould base assembly.5. Interactive view transformation such as rotation, translation,and zoom.6. Assembly tree display and manipulation.III.3D Data Management.Portability is one of the benefitsof developing a stand-alone application. It is thus important toadopt an open format for maximum portability. The nativeParasolid file format (.xmtFtxt) is thus used instead of a newfile format. Data management requirements of a mould basemodule include the following:1. Open, Save, Save As and Close Parasolid part files.2. Open, Save, Save As and Close Parasolid assembly files.3. Import and Export part files.6.1.3Mould Base Modules (C)In order to facilitate the automatic generation of standardmould base assemblies, the application must provide a libraryof mould base components, whose dimensions depend on stan-dard values found in catalogues. To facilitate design, sub-sequent modifications to these dimensions have been enabled.The details of this module will be discussed in Section .4Database Support (D)A standard mould base requires almost a hundred parametersto completely represent the dimensions and positions of theindividual components. Many of these parameters are inter-related and can be derived from others. A database file is thusrequired to store the catalogue-based parameters of standardmould bases. Microsoft Access database format is used, asthere are facilities in the MFC for direct access to AccessDatabase files. Using the Data Access Objects (DAO) in theMFC, a set of functions is developed for the extraction andmanagement of these relevant parameters from the database.460T. L. Neo and K. S. LeeFig. 9. Sample code for the mould base designer.6.2Development of the Mould Base Design ModuleThe mould base module consists of three major sections,namely, the mould base component library generator, the mouldbase assembly generator, and the mould base selection andcustomisation module. A fourth section, called the mould baseparameters manager, is also developed to provide databasesupport for the application. These are illustrated in Fig. 5. The3D Kernel Development for Injection Mould Design461details of each section are discussed in the following.I.Component Library Generator.With support from the3D developer layer, standard components for mould bases arecreated and stored in the component library. By specifying theappropriate dimensions, these components can be generatedand used by the mould base assembly generator when required.Figure 6 illustrates a cavity plate created by the componentslibrary generator.II.Assembly Generator.Using the 3D developer layer andthe component library generator, standard mould bases areassembled and stored in the assembly library. When suppliedwith a particular parameter set from the database support,specific standard mould base assembly can be automaticallygenerated. Figure 7 shows a “HOPPT” two-plate mould basecreated by the assembly generator.III.Parameters Manager.The parameters manager acts asa link between the mould base application module and thedatabase support. When a specific standard mould base isselected, the corresponding parameter set for the mould baseassembly is extracted from the database file and sent to thecomponentlibrarygeneratorandtheassemblygenerator.Besides this, the parameters manager also allows the parametersto be modified by the users for design purposes. Figure 8illustratesthemodificationsofbottomscrewdimensionsthrough the interactive user-interface.IV.MouldBaseDesigner.Themouldbasedesignerserves two main purposes. First, to allow the user to selectstandard mould bases from the assembly generator. Sec-ondly, to facilitate mould base design, by allowing themould designer to modify dimensions of the selected mouldbase. The sample code for the function call to generate themould base in this
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