A 3D CAD knowledge-based assisted injection mould design system1 IntroductionIn recent years the plastic product manufacturing industry has been growing rapidly. A very popular moulding process for making plastic parts is injection moulding. The injection mould design is critically important to product quality and efficient product processing. Mould-making companies, who wish to maintain the competitive edge, desire to shorten both design and manufacturing leading times by automating the design process. Thus, the development of a computeraided injection mould design system (CAIMDS) is becoming a focus of research in both industry and academia.Recently published papers show that research in automatic mould design focuses on individual components of the mould process. For example Ong et al. and Ravi focused their research on the feeding system. Wang et al. focused their research on the ejection system. Others focus their research on the general design. Most research done on the general injection mould system can be classified into two areas:(a) functional, conceptual and initial mould designs;and (b) algorithms to automate mould generation.Functional, conceptual and initial designs of the injection mould are applied mainly to the pre-mould design. Such design involves selecting a suitable mould base, arranging the cavity layout, designing the runner and designing the gate. The objective is to come up with a large number of very different product ideas for a certain requirement. Britton et al. addressed injection mould design from a functional perspective by presenting the Function-Environment-Behaviour-Structure (FEBS) model.The study fostered a wide range of design alternatives. Costa and Young proposed a product range model (PRM) to support the reuse of design information in variant design cases. The general structure of a PRM is defined in terms of design functions linked with sets of design solutions, interactions between potential solutions and knowledge links. Ye et al. presented an approach to automatic initial design with algorithms that calculate the cavity number and automatically lay out the cavity. The initial injection mould design involves extensive empirical knowledge of the structure and functions of the mould components. Thus, a lot of researchers adopt a knowledge-based approach. Several knowledge-based systems (KBSs) were developed to advise plastic material selection, capture injection mould part design features, analyse mouldability, automate the mould design process and develop mould design for manufacture. Examples of such systems are GERES (Nielsen), PLASSEX(Agrawal and Vasudevan), EIMPPLAN-1 (Chin and Wong), CADFEED ( Ong et al.), ICAD (Cinquegrana), IKMOULD (Mok et al. ) and KBS of Drexel University (Tseng et al.). However, these KBSs consider only certain aspects of the total design.As for the automatic generation of an injection mould, a number of theoretical research works were conducted to automatically determine the parting direction, to determine the parting line, to generate the parting surface, to recognise undercut features and to generate the core/cavity. Ravi and Srinivasan presented nine rules that can be used by the mould design engineer to develop a suitable parting line in the product. These rules are projected area, flatness, draw, draft, undercuts, dimensional stability, flash, machined surfaces and directional solidification. Hui and Tan proposed the sweep method to form the cavity and core. The cavity and core are generated in a number of steps. Sweeping the mould part in the draw direction generates a solid. One end of the swept solid is subtracted from the first mould block. The other end of the mould block is subtracted from the mould part. The results of the above steps are subtracted with the part at the closed position to obtain the cavity and core. Shin and Lee proposed a method of core and cavity development so that the side cores and corresponding core and cavity plates can be generated. This method is composed of 3 steps. The designer determines the parting line that separates the product into 2 groups of faces. Each group face has the parting surface attached to it. Then external faces are added to each group face. Shin added that a mould could be made up of many pieces in addition to the cavity, core and side cores. Hui studied the mouldability of an injection mould based on an external and internal undercut analysis only for polyhedral solids. A blockage concept is presented to determine the main parting direction and a subdivision technique is developed to evaluate the geometry of an undercut. Chen et al. introduced the concept of visibility maps (V-maps) of the pockets to determine the parting direction. The method did not take into account internal undercuts. Fu et al. and Nee et al. gave a new classification of undercuts according to the external loops and the internal loops of a moulded part. The parting direction is then determined based on the proposed parting direction criteria considering the directions, location, number and volumes of undercut features. Fu et al. proposed an approach to generate the parting surface by extruding the parting line edges and create the core/cavity block using the Boolean regularised difference operation (BRDO). A methodology that generates non-planar parting lines and surfaces is presented by Nee et al. Wong et al. proposed a method to determine the cutting plane of a complex shaped product. Their method uses an algorithm that slices the product. The parting line and surfacesformed by this method are planar.Current research on automatic mould design is on going. However, some methods can be quite theoretical and the mould design can have a complicated product geometry. Most mould development activities involve a high level of skill, a wide variety of design expertise and knowledge. Due to the fact that automatic mould development is still far beyond the current technology, it is more reasonable to provide intelligentrules or guidelines that prevent the design from conflicting with design constraints. These rules also provide interactive tools in the detailed mould design environment. This paper presents an interactive knowledge based injection mould design system (IKB-MOULD).This system integrates the initial mould design and detailed mould design with both knowledge base and interactive commercial CAD/CAM software.The next section of this paper outlines an analysis of the injection mould design process based on the mould designers point of view. A later section introduces the basic structure of our IKB-MOULD for injection mould design. A case study of the injection mould design for a plastic product in IKB-MOULD is then presented. The conclusion and future work is located in the last section.2 The injection mould design process requirement analysisAn injection mould design is composed of two steps: the initial design and the detailed design. The initial design is composed of decisions made at the early stage of the mould design, such as the type of mould configuration, the number of cavities, the type of runner, the type of gate and the type of mould base. The detailed design is composed of the insert (core/cavity) design, the ejection system design, the cooling and venting component design, the assembly analysis and the final drafting. To develop a good CAIMDS, an analysis of what they have and what they want needs to be performed.What they have: The customers requirements for the product. This includes the detailed geometry and dimension requirements of the product. An existing mould design library. This library covers the standard or previously designed components and assemblies of the mould design, for example, the mould base (the fixed half and the moving half) and the pocket (the fixed half and the moving half). An expert knowledge in injection mould design. Expert knowledge of both initial and detailed designs for the injection mould is obtained mainly from experienced mould designers. Such knowledge includes material selection, shrinkage suggestion, cavity layout suggestion and others.What they want: An intelligent and interactive mould design environment. Mould design is often composed of a series of design procedures. These procedures usually require certain mould parts to be created and existing mould parts to be assembled. Such a mould design environment need not be fully automatic, especially for complicated products with many undercuts. An intelligent and interactive environment will be a good choice to integrate some useful automation algorithms, heuristic knowledge and on-line interaction by the experienced mould designer. Standard/previous designed components/ assemblies(product-independent parts) management. Apart from the core and cavity, an injection mould has many other parts that are similar in structure and geometrical shape that can be used in other injection mould designs. These parts are independent of the plastic mould products. They are mostly standard components that can be reused in different moulddesigns and mould sets. Useful tools (including solid design and analysis calculation) in the core and the cavity (product dependent parts) design. Geometrical shapes and the sizes of the core and cavity system are determined directly by the mould product. All components in such a system are product dependent. Also, these parts are the critical components in the mould design. Their geometrical requirements may be complicated. Thus, some tools developed to design the core and the cavity based on partial automation and partial interaction can be quite useful. Design for assembly. In conventional CAD/CAM systems, moulds are represented and stored as a complete geometric and topological solid model. This model is composed of faces, edges and vertices in a three dimensional (3D) Euclidean space. Such a representation is suitable for visual display and performing geometrically computation-intensive taskssuch as engineering analysis and simulation. However, this form is not appropriate for tasks that require decision-making based on high-level information about product geometric entities and their relationships. Mould designers prefer a design for assembly environment instead of a simple solid model environment. This idea is also presented in Ye et al.swork. A design for manufacture. A complete injection mould design development cycle can be composed of the mould design and mould manufacturing process. To integrate CAD/CAM into the mould design, the manufacturing features on the mould should be abstracted and analysed for the specific NC machine.Both the process plan and the NC code should be automatically generated to enable the final designed mould to be manufactured. A design for engineering drawings. For many companies, the injection mould design has to be represented in the form of engineering drawingswith detailed dimensions. CAD/CAM tools that are able to automatically generate these engineering drawings from the final injection mould design will be useful.Based on the above analysis, our research focus is to develop techniques to represent what they have and what they want.Representing what they want is actually the representation of the knowledge and injection mould object. Developing what they want means to integrate the representation with intelligent and interactive tools for the injection mould design into a completed design environment. Therefore, an IKB-MOULD is proposed for mould designers to realise the above two requirements.三維CAD知識付諸注射模具設(shè)計系統(tǒng)一、介紹近年來，塑料制品制造行業(yè)迅猛發(fā)展。注塑成型是一種非常受歡迎的塑料零件成型方法，注塑模具對于產(chǎn)品質(zhì)量和高效的制品加工有著十分重要的意義。想要保持競爭優(yōu)勢的模具制造公司，希望通過實(shí)現(xiàn)設(shè)計過程的自動化來縮短模具設(shè)計和制造的周期。因此，計算機(jī)輔助注塑模具設(shè)計系統(tǒng)（CAIMDS）的發(fā)展正逐漸成文工業(yè)界和學(xué)術(shù)界研究的焦點(diǎn)。最近發(fā)表的論文表明，自動化模具設(shè)計的研究主要集中于單個組件的模具工藝。例如，翁等人以及拉維集中研究送料系統(tǒng)；王等人主要研究噴射系統(tǒng)；其他人研究的重點(diǎn)是總體設(shè)計。一般注塑模具系統(tǒng)的研究大多數(shù)可以分為兩個領(lǐng)域：功能、概念和初步模具設(shè)計以及自動化模具生成算法。注塑模具的功能、概念和初步設(shè)計主要用于前模設(shè)計。此類設(shè)計包括選擇一個合適的模架、安排型腔布局、設(shè)計分流道以及設(shè)計澆口，目的是為了對于一個特定的要求提出大量不同的產(chǎn)品理念。布里頓等人通過提出功能-環(huán)境-行為-結(jié)構(gòu)模型，從功能的角度解決了注塑模具設(shè)計的問題。這項研究制造出了很多設(shè)計的互換件?？扑顾蜅钐岢隽水a(chǎn)品范圍模型，以支持不同設(shè)計案例中設(shè)計信息的再利用。產(chǎn)品范圍模型的總體結(jié)構(gòu)大致是從設(shè)計功能方面定義的，該功能的設(shè)計與各系列設(shè)計方案以及潛在方案與知識鏈之間的內(nèi)在聯(lián)系息息相關(guān)。葉等人提出了一種自動化初始設(shè)計的算法，能夠計算出型腔數(shù)并自動化地設(shè)計出型腔。注塑模具的初始設(shè)計涉及對模具組件廣泛的實(shí)驗(yàn)知識。因此，許多研究人員采用以實(shí)驗(yàn)知識為基礎(chǔ)的方法。他們開發(fā)了一些以實(shí)驗(yàn)知識為基礎(chǔ)的系統(tǒng)，用來建議塑料材料的選擇、捕獲注塑模具零件的設(shè)計特征、分析可塑性、自動生成模具設(shè)計工藝以及開發(fā)產(chǎn)品的模具設(shè)計。這樣的系統(tǒng)有諸如GERES (尼爾森), PLASSEX（阿格拉沃爾和瓦蘇德萬),EIMPPLAN-1（秦和王),CADFEED(翁等人),ICAD (辛魁格蘭那),IKMOULD(莫克等人)以及卓克索大學(xué)的知識庫系統(tǒng)(曾等人)。但是，這些知識庫系統(tǒng)只考慮吧了總體設(shè)計的某些方面，作為一個注塑模具的自動生成系統(tǒng)，需要做大量的理論研究工作，以自動地確定分型方向和分型面、生成分型面、識別削弱特征以及生成型腔。拉維和斯利瓦尼桑提出了九個規(guī)則，工程師可以用它們在制品中開發(fā)合適的分型面。這些規(guī)則分別是投影面積、平整度、收縮力、同軸度、削弱力、尺寸穩(wěn)定性、流動率、加工表面和定向凝固。惠和譚提出了行程型腔和型芯的掃描方法。型腔和型芯是經(jīng)過一系列的步驟生成的，在拉伸方向掃描生成一個實(shí)體，這個實(shí)體的一端是從第一個模塊中去除得到的，模塊的另一端是從模具中減去的。上述步驟的結(jié)果被去除的部分在閉合位置得到型腔和型芯。信和李提出了一種型芯和型腔發(fā)展的方法，因此可以生成側(cè)型芯以及相應(yīng)的型芯和型腔板。該方法由三個步驟組成，設(shè)計者確定分型線，它把制品分為兩組表面，每組表面都有分型面連接到它，然后，外部的表面再與每組的表面接觸。信說，一個模具由多個型腔、型芯和側(cè)芯組成?；莼诙嗝骟w外部和內(nèi)部的削弱分析，研究了注塑模具的的可塑性。堵塞概念的提出確定了主脫模方向，而且，細(xì)分技術(shù)被開發(fā)用來評估幾何方法削弱。陳等人引入了可視映射的概念，確定了分型的方向。但這個方法沒有考慮到內(nèi)部削弱力。付等人和倪等人根據(jù)外環(huán)槽和成型件的內(nèi)環(huán)槽，提出了一種削弱力的新分類?？紤]到方向、位置、數(shù)量和削弱力特征量，他們提出了分型方向的標(biāo)準(zhǔn)，而分型方向正是基于此確定的。付等人通過擠壓分型線邊緣和使用布爾查運(yùn)算創(chuàng)造型芯/型腔塊，提出了一種生成分型面的方法。倪等人還提出了生成非平面的分型線和分型線的方法論。王等人提出了一種確定復(fù)雜形狀制品的分割面的方法，他們的方法是，使用一種算法分開制品。通過這種方法形成的分型線和分型面是平面內(nèi)的。目前，對于自動化模具設(shè)計的研究還仍然在進(jìn)行中。然而，有一些方法是相當(dāng)?shù)睦碚摶?，而模具設(shè)計卻可能有著相當(dāng)復(fù)雜的制品幾何形狀。大多數(shù)模具開發(fā)活動要有很高的技術(shù)水平，以及各種專業(yè)設(shè)計經(jīng)驗(yàn)和知識。由于自動化模具設(shè)計技術(shù)的發(fā)展仍然遠(yuǎn)遠(yuǎn)超出了當(dāng)前的技術(shù)，所以它更適合用于提供只能規(guī)則或指導(dǎo)方針，防止設(shè)計過程中與約束