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Journal of Materials Processing Technology 139 (2003) 8189 A Windows-native 3D plastic injection mold design system L. Kong, J.Y.H. Fuh, K.S. Lee, X.L. Liu, L.S. Ling, Y.F. Zhang, A.Y.C. Nee Department of Mechanical Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Singapore Abstract 3D solid-modeling revolution has reached the design mainstream. While high-end 3D solid-modeling systems have been on engineers workstation at large aerospace, consumer products, and automobile companies for years, many smaller companies are now making the switch from workstations to PC. One reason for the shift is that the fl exibility and advancement of Windows-native/NT has let software developers create applications that are affordable and easy to use. High-end users are fi nding that mid-range solid modelers, such as SolidWorks, have met their needs. SolidWorks was chosen as the platform due to the Windows-native design environment, powerful assembly capabilities, ease-of-use, rapid learning curve, and affordable price. A Windows-native 3D plastic injection mold designs system has been implemented on an NT through interfacing Visual C+ codes with the commercial software, SolidWorks 99 and API. The system provides a designer with an interactive computer-aided design environment, which can both speed up the mold design process and facilitate standardization. 2003 Elsevier Science B.V. All rights reserved. Keywords: Plastic injection mold; Windows; CAD; Parting 1. Introduction With the broader use of plastics parts in a wide product range, from consumer products to machinery, cars and air- planes, the injection molding process has been recognized as an important manufacturing process. The mold design process is generally the critical path of a new product de- velopment. Conventionally, mold design has always been a much “mystifi ed” art, requiring years of experience before one can be relatively profi cient in it. Due to the initial diffi - culty in learning this art, less and less people are benefi ting from the experience and knowledge of the experts in this fi eld. To change the current situation, one way is to use a computer-aided design (CAD) system. CAD as an everyday term has grown to a broad range of capabilities and has applications in fi elds ranging from edu- cation for school teaching to three-dimensional mechanical design. At the present time, most CAD systems provide only the geometric modeling functions that facilitate the drafting operations of mold design, and do not provide mold designers with the necessary knowledge to design the molds. Thus, much “add-on” software, e.g. IMOLD, have been developed on high-level 3D modeling platforms to Corresponding author. Fax: +65-67791459. E-mail address: .sg (J.Y.H. Fuh). facilitate the mold design processes. Such an arrangement is advantageous in many ways. The 3D modeling platform provides plug-in software with a library of functions as well as an established user interface and style of programming. As a result, the development time for these “add-ons” is signifi cantly reduced. IMOLD(intelligent mold design) 1 is a knowledge- based software application, which runs on the Unigraphics SolidWorks platform and is carried out by using the User Function provided. It is available on the UNIX and windows operation system. For years, mold design engineers have had to deal with two different systems, UNIX and PC. The former is widely used in engineering applications whilst the latter is used mainly in small and medium companies. Engineers also need to run corporate offi ce applications such as word processing, spreadsheets, and project management tools, but these were not on their UNIX workstations. Fortunately, the remarkable development of computer technology in the last decade has provided a way to change this situation. The most signifi cant change has been in the area of computer hardware, i.e. the actual electronic components associated with data processing, information storage, and display technology, in terms of both speed and memory. These have resulted in the more effi cient use of the solid-modeling functions in a PC-based CAD/CAM system. With the increased availability of sophisticated, low-cost software for Windows, more and more engineers 0924-0136/03/$ see front matter 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0924-0136(03)00186-9 82L. Kong et al./Journal of Materials Processing Technology 139 (2003) 8189 are using PC applications to get their jobs done. Thus the development of a new mold design application based on the Windows platforms is in high demand. High-end users are fi nding that mid-range solid modelers, such as SolidWorks, have met their needs. Developed from the beginning as a native Windows application, SolidWorks is one of the 3D mechanical design softwares for Win- dows. Its unique combination of production-level power, ease-of-use, and affordability is unmatched. SolidWorks 99, the seventh major release of the companys mechan- ical design software for Windows NT, Windows 98 and beyond provides an increased power and functionality in a fully integrated solid modeler. Familiar conventions such as point-and-click, drag-and-drop, cut-and-paste, and seamless data sharing with other Windows software lead to produc- tivity gains. The ease-of-use without extensive training and at affordable pricing enables companies to install the sys- tem on every engineers desktop. One of its applications is for mold design in the plastics industry. This latest appli- cation technology has added an entirely new dimension to the mold design process. 2. Injection mold design Injection molding uses temperature-dependent changes in material properties to obtain the fi nal shapes of discrete parts to fi nish or near-fi nish dimensions through the use of molds. In this type of manufacturing process, liquid material is forced to fi ll and solidify inside the cavity of the mold 2. Firstly, the creation of a mold model requires a design model and a containing box. The design model represents the fi nished product, whereas the containing box represents the overall volume of the mold components. Fig. 1. Relationship among user applications, SolidWorks, Unigraphics and Parasolid. Injectionmolddesigninvolvesextensiveempiricalknowl- edge (heuristic knowledge) about the structure and the func- tions of the components of the mold. The typical process of a new mold development can be organized into four ma- jor phases: product design, moldability assessment, detailed part design, insert/cavity design, and detailed mold design. In Phase 0, a product concept is pulled together by a few people (usually a combination of marketing and engi- neering). The primary focus of Phase 0 is to analyze the market opportunity and strategic fi t. In Phase I the typical process-related manufacturing information is then added to the design to produce a detailed geometry. The concep- tual design is transformed into a manufacturable one by using appropriate manufacturing information. In Phase II the parting direction and parting lines location are added to inspect the moldability. Otherwise, the part shape is again modifi ed. In Phase III, the part geometry is used to establish the shape of the mold core and cavity that will be used to form the part. Generally shrinkage and expansions need to be considered so that the molding will be the correct size and shape at the processing temperature. Gates, runners, overfl ows, and vents also need to be added. The association between geometric data and parting information is critical at this point. Phase IV is related to the overall mechanical structure of the mold including the connection of the mold to the injection machine, a mechanisms for fi lling, cooling, and for ejection and mold assembly. 3. Methodology For the reasons described above, SolidWorks 99 has been used as the platform for the new mold design application. Fig. 1 shows a Windows-native 3D injection mold design L. Kong et al./Journal of Materials Processing Technology 139 (2003) 818983 system compared with IMOLD. Users applications can be created and run as a standalone exe fi le or as a User DLL or Extension DLL in SolidWorks. The SolidWorks Add-In Manager allows users to control which third party software is loaded at any time during their SolidWorks session. More than one package can be loaded at once, and the settings will be maintained across SolidWorks sessions. 3.1. SolidWorks SolidWorksrecentlyemergedasoneofthe3Dproductde- sign software for Windows, providing one of the most pow- erful and intuitive mechanical design solution in its class. In SolidWorks, parts are created by building a “base feature,” and adding other features such as bosses, cuts, holes, fi l- lets, or shells. The base feature may be an extrusion, revo- lution, swept profi le, or loft. To create a base feature, sketch a two-dimensional geometric profi le and move the profi le through space to create a volume. Geometry can be sketched on construction planes or on planar surfaces of parts. Feature-basedsolid-modelingprogramsaremaking two-dimensional design techniques obsolete. However, Unix-based solid-modeling software are expensive. With the introduction of SolidWorks for Microsoft Windows, the cost is less than the price of earlier dimension driven solid-modeling programs 3. 3.2. Parasolid as a 3D kernel SolidWorks uses Parasolid as a 3D kernel. Parasolid ker- nel modeling toolkit, is recognized as a worlds leading, production-proven core solid modeler. Designed as an exact Fig. 2. SolidWorks API objects. boundary-representation solid modeler, Parasolid provides robust solid-modeling, generalized cellular modeling and in- tegrated surface/sheet modeling capabilities and is designed for easy integration into CAD/CAM/CAE systems to give rapid time to market. Its extensive functionality is supplied as a library of routines with an object-oriented program- ming interface. It is essentially a solid modeler, which can be used to 4: (i) build and manipulate solid objects; (ii) calculate mass and moments of inertia, and perform inter- ference detection; (iii) output the objects in various picto- rial ways; (iv) store the objects in some sort of database or archive and retrieve them later; and (iv) support freeform surfaces. 3.3. API 5 The SolidWorks application programming interface (API) is an OLE programming interface to SolidWorks. The API containshundredsoffunctionsthatcanbecalledfromVisual Basic, VBA (Excel, Access, etc.), C, C+, or SolidWorks macro fi les. These functions provide the programmer with direct access to SolidWorks functionality such as creating a line, extruding a boss, or verifying the parameters of a surface. The API interface uses an object-oriented approach. All the API functions are methods or properties that apply to an object. Fig. 2 is one particular view of the SolidWorks API objects. SolidWorks exposes functionality through OLE automa- tion using Dispatch and also through standard COM objects. The Dispatch interface 6 will package arguments and re- turn values as Variants so that languages such as Basic can 84L. Kong et al./Journal of Materials Processing Technology 139 (2003) 8189 handle them. A COM implementation gives your applica- tion more direct access to the underlying objects, and sub- sequently, increased performance. 4. Implementations The facts that SolidWorks API interface uses an object- oriented approach and the API functions allows one to Fig. 3. System infrastructure for the mold design application. choose an object-oriented language, e.g. Visual C+, as the programming language. Using this methodology, a Windows-based 3D injection mold design application is de- veloped on Windows NT through interfacing of the Visual C+ code with a commercial software, SolidWorks 99. In this application the mold design process is divided into sev- eral stages, providing the mold designer with a consistent method of creating the mold design. The overview of this framework is shown in Fig. 3. Each stage can be considered L. Kong et al./Journal of Materials Processing Technology 139 (2003) 818985 as an independent module of the program. Several modules have been successfully developed using SolidWorks. Two of them, mold base module and parting module are shown below. 4.1. Mold base module The mold base module can automatically create parame- tric standard mold bases, with all its components and accessories, like HASCO, DME, HOPPT, LKM and FUTABA. This module allows easy customization of mold bases commonly used by designers. Key features in- clude availability of standard mold base components like support pillars and sprue bushings, 2-plate and 3-plate mold bases, and customization of non-standard mold bases. The mold base module consists of four main sections, namely, the component library (including standard and non-standard part library), the design table, the dimension driven functionality, and structure relation management. Here, the dimension driven functionality is provided by SolidWorks to support for the application. The details for the mold base module are shown in Fig. 4. (1) Component library In order to strengthen the mold design capability in this increasingly competitive world, lowering the design cost and cycle time, reducing the man-power, and au- tomation are major factors in achieving this purpose. In other words, it is necessary to have computer software that is able to easily create, modify, and analyze the mold design components, and update the changes in a design model. To achieve this, a 3D component library is provided to store standard and non-standard parts data, whose dimensions are stored in Microsoft Excel. By specifying the appropriate dimensions, these com- ponents can be generated and inserted into the assembly structure. This library is completely customizable and designers are able to add their own parts into the library. (2) Dimension driven SolidWorks provides strong dimension driven func- tionality to support parametric design. It is the logi- cal relationship between the dimension sets stored in Microsoft Excel and the geometry. When a set of di- mension is integrated with the corresponding parameter set of the geometry of an object, the exact model can be then obtained. (3) Design table A design table allows a designer to build multiple confi gurations of parts by specifying parameters in an embedded Microsoft Excel spreadsheet. The design table is saved in the part fi le and is used to store the dimensions, the suppression of features and the con- fi guration properties, including part number in a bill of materials, comments, and customer requirements. When appropriate dimensions are added, the design Fig. 4. Details of the mold base module. table will contain all the information needed to create an accurate model of the assembly. (4) Structure relation management This section records the structure relations between mold base components. When supplied with certain parameter set from the design table, this sub-module helps the mold designer to insert these components into the assembly structure, thus a specifi c mold base assembly can be automatically generated. 4.2. Parting module Some of the parting algorithms 710 have been reported previously.Inthisdevelopment,partingmoduleisdeveloped to handle the creation of cores and cavities. It is one of the most important modules in a computer-aided injection mold design system 11. The creation of a mold model needs to have a design model, a containing box, and parting surfaces available. The design model represents the fi nished product, whereas the containing box represents the overall volume 86L. Kong et al./Journal of Materials Processing Technology 139 (2003) 8189 Fig. 5. Parting design module. of the mold components. In order to split the box into the core and cavity, the design model is fi rst subtracted from the box. The parting surfaces are then used to separate the containing box into mold halves, often referred as the core and cavity. When melt plastics is injected into the cavity, the fi nished product is formed by the two opposing mold halves. After solidifi cation, both mold halves move away from the part along the parting directions d and d, respectively. The actual part is then obtained. Fig. 5 shows the parting design process. (1) Determination of the parting direction The pair of opposite directions along which the core and cavity open are the parting directions (Fig. 6(a). L. Kong et al./Journal of Materials Processing Technology 139 (2003) 818987 Fig. 6. Parting design process: (a) determination of parting direction; (b) generation of patching surfaces; (c) determination of parting lines and extruding directions; (d) swept parting surfaces; (e) radiated parting surfaces; (f) creation of containing box; (g) generation of the core and cavity. 88L. Kong et al./Journal of Materials Processing Technology 139 (2003) 8189 To generate the parting lines, the parting direction should be determined fi rst. The parting direction in- fl uences the orientation of the parting line that de- termines the complexity of the mold. In most cases, partingdirectionsaredeterminedbyconsidering both geometry and manufacturing issues at the same time. (2) Recognition and patching the “through” holes When there are some through holes in a product, the designers must indicate the parting location of the holes and generate the parting surfaces in these holes. This is called “patching” in this paper. Surfaces are needed and used to patch the through holes. Because the upper mold and the lower mold are connected at the through hole, a mold cannot be separated and the core and the cavity cannot be created automatically without patching those holes fi rst (see Fig. 6(b). (3) Determination of parting lines and the extruding directions In molding, one gro