掛鉤底座注塑模具設(shè)計(jì)【塑料掛鉤底座注塑模具設(shè)計(jì)】,塑料掛鉤底座注塑模具設(shè)計(jì),掛鉤,底座,注塑,模具設(shè)計(jì),塑料 西安工業(yè)大學(xué)北方信息工程學(xué)院畢業(yè)設(shè)計(jì)（論文） 西安工業(yè)大學(xué)北方信息工程學(xué)院 畢業(yè)設(shè)計(jì)(論文)開題報(bào)告 題目：掛鉤底座注塑模具設(shè)計(jì) 系 別 專 業(yè) 班 級(jí) 姓 名 學(xué) 號(hào) 導(dǎo) 師 年 月 日 題　目 掛鉤底座注塑模具設(shè)計(jì) 姓　名 學(xué)　號(hào) 一、本課題的研究目的和意義 目的：以社會(huì)實(shí)際產(chǎn)品為課題，真題假做，設(shè)計(jì)一副能夠生產(chǎn)所給的塑件、結(jié)構(gòu)合理、能保證制品的精度、表面質(zhì)量的塑料模具，能熟練使用PROE、AUTOCAD等繪圖軟件。使學(xué)生在塑料結(jié)構(gòu)設(shè)計(jì)、塑料成型工藝分析、塑料模具數(shù)字化設(shè)計(jì)、塑料模具零件的選材、熱處理、塑料模具零件的制造，以及資料檢索、英文翻譯等方面獲得綜合訓(xùn)練，為縮短工作適應(yīng)期奠定堅(jiān)實(shí)的基礎(chǔ)。 意義：隨著塑料制品在機(jī)械、電子、交通、國(guó)防、建筑、農(nóng)業(yè)等各行業(yè)廣泛應(yīng)用，對(duì)塑料模具的需求日益增加，塑料模在國(guó)民經(jīng)濟(jì)中的重要性也日益突出。模具作為一種高附加值和技術(shù)密集型產(chǎn)品，其技術(shù)水平的高低已經(jīng)成為一個(gè)國(guó)家制造業(yè)水平的重要標(biāo)志之一。 二、本課題的主要研究?jī)?nèi)容（提綱） 1、 對(duì)實(shí)體進(jìn)行測(cè)量，自行設(shè)計(jì)出掛鉤底座的三維及CAD二維模型 2、 塑件成型工藝性（產(chǎn)品原材料、結(jié)構(gòu)、尺寸精度、表面質(zhì)量的）分析； 3、 計(jì)算塑件的體積和質(zhì)量（包括初選注射機(jī)型號(hào)）； 4、 塑件注射工藝參數(shù)的確定； 5、 利用PROE軟件生成模具的開模效果圖 6、 注射模的結(jié)構(gòu)設(shè)計(jì)及校核 （1）確定分型面及型腔數(shù)目以及排列方式 （2）選擇合適的模架 （3）澆注系統(tǒng)和澆口位置及澆口形式的確定 （4）冷卻系統(tǒng)的選定 （5）脫模推出機(jī)構(gòu)的設(shè)計(jì) （6）側(cè)向抽芯的結(jié)構(gòu)設(shè)計(jì) 7、出模具三維總裝圖、二維裝配圖及各重要零件的CAD圖 8、完成設(shè)計(jì)說(shuō)明書 三、文獻(xiàn)綜述（國(guó)內(nèi)外研究情況及其發(fā)展） 1. 國(guó)內(nèi)研究現(xiàn)狀及發(fā)展趨勢(shì)： 我國(guó)在注塑模技術(shù)開發(fā)研究與應(yīng)用方面起步較晚。從20世紀(jì)80年代中期開始，國(guó)內(nèi)部分大中型企業(yè)先后引進(jìn)了一些國(guó)外知名度較高的注塑模系統(tǒng)。同時(shí)，某些高等學(xué)校和科研院所也開始了注塑模系統(tǒng)的研制與開發(fā)工作，我國(guó)注塑模CAD/CAE/CAM研究始于07年代末，發(fā)展較為迅速多年來(lái),我國(guó)對(duì)注塑模設(shè)計(jì)制造技術(shù)及其開發(fā)應(yīng)用十分重視，在“八五”期間,由北京航空航天大學(xué)、華中理工大學(xué)、四川聯(lián)合大學(xué)等單位聯(lián)合進(jìn)行了國(guó)家重點(diǎn)科技攻關(guān)課題“注塑模CAD/CAE/CAM集成系統(tǒng)”，并于1996年通過(guò)鑒定，部分成果己投入實(shí)際應(yīng)用，使我國(guó)的注塑模研究和應(yīng)用水平有了較大提高。目前，我國(guó)經(jīng)濟(jì)仍處于高速發(fā)展階段。一方面，國(guó)內(nèi)模具市場(chǎng)將繼續(xù)高速發(fā)展，另一方面，模具制造也逐漸向我國(guó)轉(zhuǎn)移以及跨國(guó)集團(tuán)到我國(guó)進(jìn)行模具采購(gòu)趨向也十分明顯。因此，放眼未來(lái)，模具技術(shù)的發(fā)展趨勢(shì)主要是模具產(chǎn)品向著更大型、更精密、更復(fù)雜及更經(jīng)濟(jì)的方向發(fā)展，模具產(chǎn)品的技術(shù)含量不斷提高，模具制造周期不斷縮短，模具生產(chǎn)朝著信息化、無(wú)圖化、精細(xì)化、自動(dòng)化的方向發(fā)展，模具企業(yè)向著技術(shù)集成化、設(shè)備精良化、產(chǎn)批品牌化、管理信息化、經(jīng)營(yíng)國(guó)際化的方向發(fā)展。這對(duì)我們新時(shí)代的年輕人來(lái)說(shuō)是一個(gè)巨大的機(jī)會(huì)也是一次強(qiáng)大的挑戰(zhàn)。 2.國(guó)外研究現(xiàn)狀及發(fā)展趨勢(shì)： 近二十多年間，國(guó)外注塑模技術(shù)發(fā)展相當(dāng)迅速。70年代許多研究者對(duì)一維流動(dòng)進(jìn)行了大量研究，由最初的CAD技術(shù)和CAM技術(shù)以圖紙為媒介傳遞信息向CAD/CAM一體化方向發(fā)展。80年代初開展三維流動(dòng)與冷卻分析并把研究擴(kuò)展到保壓分子取向以及翹曲預(yù)測(cè)等領(lǐng)域。80年代中期注塑模進(jìn)入實(shí)用階段，出現(xiàn)了許多商品化注塑模CAD/CAE軟件，比較著名的有:1.澳大利亞MOLDFLOW公司的MOLDFLOW系統(tǒng)；2.美國(guó)PTC公司的Pro/Engineer 軟件；3.美國(guó)UG公司的UGllUNIGRAPHICSl系統(tǒng)等等.這些先進(jìn)軟件的熟練掌握極大地促進(jìn)了國(guó)外模具行業(yè)的發(fā)展。因此，未來(lái)的一段時(shí)間內(nèi)，他們將朝著大型、精密、復(fù)雜與長(zhǎng)壽命模具的方向發(fā)展。 3.綜述： 參閱了多本資料書籍，注塑成型是現(xiàn)代塑料工業(yè)中的一種重要的加工方法 ,世界上注塑模的產(chǎn)量約占塑料成型模具總產(chǎn)量的50%以上。注塑成型能一次成型形狀復(fù)雜、尺寸精確的制品 ,適合高效率、大批量的生產(chǎn)方式 ,以發(fā)展成為熱塑性塑料和部分熱固性塑料最主要的成型加工方法，一般需要經(jīng)過(guò)反復(fù)調(diào)試和修模才能正式投入生產(chǎn) ,這種傳統(tǒng)的生產(chǎn)方式不僅使產(chǎn)品的生產(chǎn)周期延長(zhǎng) ,生產(chǎn)成本增加 ,而且難以保證產(chǎn)品的質(zhì)量。要解決這些問(wèn)題,必須以科學(xué)分析的方法 ,研究各個(gè)成型過(guò)程的關(guān)鍵技術(shù),為實(shí)現(xiàn)注塑產(chǎn)品的更新?lián)Q代,提高企業(yè)的競(jìng)爭(zhēng)能力 ,必須進(jìn)行注塑模具設(shè)計(jì)與制造，及成型過(guò)程分析的CAD/CAM/CAE集成技術(shù)的研究。國(guó)外注塑模CAD/CAM/CAE 技術(shù)研究的成果有關(guān)統(tǒng)計(jì)數(shù)據(jù)表明:采用注塑模CAD/CAE/CAM 技術(shù)能使設(shè)計(jì)時(shí)間縮短50%,制造時(shí)間縮短30%,成本下降10%,塑料節(jié)省7% 注塑模計(jì)算機(jī)模擬技術(shù)正朝著與CAD/CAE無(wú)縫整體集成化方向發(fā)展 ,注塑CAD所構(gòu)造的幾何模型為實(shí)現(xiàn)注塑模CAE技術(shù)提供了基本的幾何拓?fù)湫畔⒑吞卣餍畔?注塑模 CAE的目標(biāo)是通過(guò)對(duì)塑料材料性能的研究和注射成型工藝過(guò)程的模擬和分析,為塑料制品的設(shè)計(jì)、材料選擇、模具設(shè)計(jì)、注射成型工藝的制定及注射成型工藝過(guò)程的控制提供科學(xué)依據(jù) ?，F(xiàn)時(shí)國(guó)際上占主流地位的注射模CAD軟件有Pro/E、I-DEAS、UG等；結(jié)構(gòu)分析軟件有MSC、Analysis等；注射過(guò)程數(shù)值分析軟件有MoldFlow等；數(shù)控加工軟件有MasterCAM、Cimatron等。總體說(shuō)來(lái)，國(guó)內(nèi)的模具設(shè)計(jì)與制造技術(shù)與發(fā)達(dá)國(guó)家相比有很大的差距，這也是中國(guó)現(xiàn)在只是制造大國(guó)而非制造強(qiáng)國(guó)的主要原因之一。 四、擬解決的關(guān)鍵問(wèn)題 1、 塑件成型工藝性（產(chǎn)品原材料、結(jié)構(gòu)、尺寸精度、表面質(zhì)量的）分析 2、 注射模的結(jié)構(gòu)設(shè)計(jì) （1）確定分型面及型腔數(shù)目及型腔的排布 （3）澆注系統(tǒng)和澆注口位置的確定 （4）脫模推出機(jī)構(gòu)的設(shè)計(jì) （4）側(cè)向抽芯的結(jié)構(gòu)設(shè)計(jì) 五、研究思路和方法 1、根據(jù)塑件制品分型面的設(shè)計(jì)與選擇原則，分型面應(yīng)該設(shè)計(jì)在零件截面最大的部位，且不影響零件的外觀。盡量在開模時(shí)使塑件包緊在動(dòng)模型芯一側(cè)，留在動(dòng)模側(cè)，從而使模具的結(jié)構(gòu)變得簡(jiǎn)單。 同時(shí)，考慮到掛鉤底座上各孔間的距離，為了方便其加工，選擇以鑲件的形式來(lái)配合完成。 2.根據(jù)塑件的實(shí)際結(jié)構(gòu)，采用一模兩腔的排布方式。 3、 澆口又稱進(jìn)料口，是連接分流道與型腔之間的一段細(xì)短流道。澆口形式有直澆口、側(cè)澆口、點(diǎn)澆口和潛伏式澆口等，據(jù)分析，側(cè)澆口通常開設(shè)在型腔側(cè)邊，是一種廣泛應(yīng)用于單分型面多模腔普通澆注系統(tǒng)的澆口形式，適用于各種塑料，所以本次設(shè)計(jì)選用側(cè)澆口較為合理。 4、出機(jī)構(gòu)的選用是為了保證制件在頂出時(shí)不受損壞以及制件的外觀。在設(shè)計(jì)時(shí)必須正確分析制件對(duì)模具的黏附力的大小和作用位置，以及選用合適的脫模方式和恰當(dāng)?shù)耐瞥鑫恢?，使制件平穩(wěn)脫出。同時(shí)推出時(shí)應(yīng)盡量使制件外表面不留痕跡。推出機(jī)構(gòu)盡量設(shè)在動(dòng)模一側(cè)，機(jī)構(gòu)簡(jiǎn)單、動(dòng)作簡(jiǎn)單，合模時(shí)能正確復(fù)位。根據(jù)本次采用的是一模兩腔以及制件的結(jié)構(gòu)特點(diǎn)、推出的要求，所以優(yōu)先采用推桿推出。 考慮到推桿加工的問(wèn)題，以及零件的壁厚問(wèn)題，可以采用階梯型圓形推桿。 5、通過(guò)查閱相關(guān)手冊(cè)，測(cè)抽芯結(jié)構(gòu)的類型有以下幾種： 1、彎銷側(cè)抽芯機(jī)構(gòu) 2、斜導(dǎo)槽側(cè)抽芯機(jī)構(gòu) 3、齒輪齒條側(cè)抽芯機(jī)構(gòu) 4、液壓或氣動(dòng)側(cè)抽芯機(jī)構(gòu) 5、斜滑塊側(cè)抽芯機(jī)構(gòu) 6、斜導(dǎo)柱側(cè)抽芯機(jī)構(gòu) 其中，斜導(dǎo)柱側(cè)抽芯機(jī)構(gòu)是應(yīng)用最為廣泛的也是相對(duì)方便實(shí)行的一種，本次設(shè)計(jì)可以選用斜導(dǎo)柱式側(cè)抽芯機(jī)構(gòu)。 六、本課題的進(jìn)度安排 1.搜集資料寫開題報(bào)告。 第1周第2周 2. 掛鉤底座的三維建模。 第3周第4周 3.凸凹模型面設(shè)計(jì)。 第5周第6周 4.注塑模具系統(tǒng)設(shè)計(jì)。 第7周第8周 5.繪制圖紙撰寫畢業(yè)論文。 第9周 第12周 7、 參考文獻(xiàn) [1] 編委會(huì). 中國(guó)模具設(shè)計(jì)大典[Z]. 江西科學(xué)技術(shù)出版社出版，2003.1 [2]宋玉恒. 塑料注射模具設(shè)計(jì)實(shí)用手冊(cè)［K］. 北京：航空工業(yè)出版社，1998 [3] 陳劍鶴.模具設(shè)計(jì)基礎(chǔ)[M].北京：機(jī)械工業(yè)出版社，2003.6 [4] 屈華昌.塑料成型工藝與模具設(shè)計(jì)[M].北京：高等教育出版社，2006.7 [5] 李銀萍. 電樞支架成型工藝及模具［J］. 模具工業(yè)，2005，31（4）：38-40 [6] 王文廣.塑料注射模設(shè)計(jì)技巧與實(shí)例[M].北京：化學(xué)工業(yè)出版社，2004.5 [7] 宋滿倉(cāng).注塑模具設(shè)計(jì)與制造實(shí)踐[M].北京：機(jī)械工業(yè)出版社，2003.7 [8] 李學(xué)鋒.模具設(shè)計(jì)與制造實(shí)訓(xùn)教程[M].北京：化學(xué)工業(yè)出版社，2004 [9] 劉礦陵、徐萍. 光盤盒注射模設(shè)計(jì)［J］. 模具工業(yè)，2007，33（3）：38-40 39～41 [10]史鐵梁. 模具設(shè)計(jì)指導(dǎo)［M］. 北京：機(jī)械工業(yè)出版社，2005 [11] 柳舟通、余立剛.模具制造工藝學(xué)[M].北京：科學(xué)出版社.2005.11 [12] 中國(guó)塑料模具網(wǎng) http://cn.plasticmould.net/ [13] 馮孝中. 普通澆注系統(tǒng)多層多腔注射模設(shè)計(jì)［J］. 模具工業(yè)，2002，28（12）： [14] 周四新.Pro/ENGINEER Wildfire實(shí)用設(shè)計(jì)百例[M].北京：清華大學(xué)出版社，2005 [15]翁其金. 塑料模塑成型技術(shù)［M］. 北京：機(jī)械工業(yè)出版社，2001 [16] 李恩學(xué)，翁史振，曹偉. 裝飾環(huán)注射模設(shè)計(jì)與制造［J］. 模具工業(yè)，2008，34 [17]Taylan Atlan, Blaln Liny and Y. C. Yen. Manufacturing of dies and molds. Ann. C, 50(2001) No. 2. P405． [18] F. Ilinca, J.-F. Hetu, and A. Derdouri, Proc. MOLDING 2001, Exec. Conf. Managem., 10 p. 2001:36-145 [19] Gao F and Yang Y. Multi-variable Interaction Analysis and a Proposed Quality Control System for Thermoplastics Injection Molding[C]. ANTEC’97,480-486 [20] Hanser publishers . Product design and process engineering . New York :Harold . 2002.4 指導(dǎo)教師意見（對(duì)課題的深度、廣度及工作量的意見） 指導(dǎo)教師： 年 月 日 所在系審查意見： 系 主管領(lǐng)導(dǎo)： 年 月 日 6 第 22 頁(yè) 共 23 頁(yè) 桂林電子科技大學(xué)畢業(yè)設(shè)計(jì)用紙 Automated Assembly Modelling for Plastic Injection Moulds An injection mould is a mechanical assembly that consists of product-dependent parts and product-independent parts. This paper addresses the two key issues of assembly modelling for injection moulds, namely, representing an injection mould assembly in a computer and determining the position and orientation of a product-independent part in an assembly. A feature-based and object-oriented representation is proposed to represent the hierarchical assembly of injection moulds. This representation requires and permits a designer to think beyond the mere shape of a part and state explicitly what portions of a part are important and why. Thus, it provides an opportunity for designers to design for assembly (DFA). A simplified symbolic geometric approach is also presented to infer the configurations of assembly objects in an assembly according to the mating conditions. Based on the proposed representation and the simplified symbolic geometric approach, automatic assembly modelling is further discussed. Keywords: Assembly modelling; Feature-based; Injection moulds; Object-oriented 1. Introduction Injection moulding is the most important process for manufacturing plastic moulded products. The necessary equipment consists of two main elements, the injection moulding machine and the injection mould. The injection moulding machines used today are so-called universal machines, onto which various moulds for plastic parts with different geometries can be mounted, within certain dimension limits, but the injection mould design has to change with plastic products. For different moulding geometries, different mould configurations are usually necessary. The primary task of an injection mould is to shape the molten material into the final shape of the plastic product. This task is fulfilled by the cavity system that consists of core, cavity, inserts, and slider/lifter heads. The geometrical shapes and sizes of a cavity system are determined directly by the plastic moulded product, so all components of a cavity system are called product-dependent parts. (Hereinafter, product refers to a plastic moulded product, part refers to the component of an injection mould.) Besides the primary task of shaping the product, an injection mould has also to fulfil a number oftasks such as the distribution of melt, cooling the molten material, ejection of the moulded product, transmitting motion, guiding, and aligning the mould halves. The functional parts to fulfil these tasks are usually similar in structure and geometrical shape for different injection moulds. Their structures and geometrical shapes are independent of the plastic moulded products, but their sizes can be changed according to the plastic products. Therefore, it can be concluded that an injection mould is actually a mechanical assembly that consists of product-dependent parts and product-independent parts. Figure 1 shows the assembly structure of an injection mould. The design of a product-dependent part is based on extracting the geometry from the plastic product. In recent years, CAD/CAM technology has been successfully used to help mould designers to design the product-dependent parts. The Fig. 1. Assembly structure of an injection mould automatic generation of the geometrical shape for a product-dependent part from the plastic product has also attracted a lot of research interest [1,2]. However, little work has been carried out on the assembly modelling of injection moulds, although it is as important as the design of product-dependent parts. The mould industry is facing the following two difficulties when use a CAD system to design product-independent parts and the whole assembly of an injection mould. First, there are usually around one hundred product-independent parts in a mould set, and these parts are associated with each other with different kinds of constraints. It is time-consuming for the designer to orient and position the components in an assembly. Secondly, while mould designers, most of the time, think on the level of real-world objects, such as screws, plates, and pins, the CAD system uses a totally different level of geometrical objects. As a result, high-level object-oriented ideas have to be translated to low-level CAD entities such as lines, surfaces, or solids. Therefore, it is necessary to develop an automatic assembly modelling system for injection moulds to solve these two problems. In this paper, we address the following two key issues for automatic assembly modelling: representing a product-independent part and a mould assembly in a computer; and determining the position and orientation of a component part in an assembly. This paper gives a brief review of related research in assembly modelling, and presents an integrated representation for the injection mould assembly. A simplified geometric symbolic method is proposed to determine the position and orientation of a part in the mould assembly. An example of automatic assembly modelling of an injection mould is illustrated. 2. Related Research Assembly modelling has been the subject of research in diverse fields, such as, kinematics, AI, and geometric modelling. Lib-ardi et al. [3] compiled a research review of assembly modelling. They reported that many researchers had used graph structures to model assembly topology. In this graph scheme, the components are represented by nodes, and transformation matrices are attached to arcs. However, the transformation matrices are not coupled together, which seriously affects the transformation procedure, i.e. if a subassembly is moved, all its constituent parts do not move correspondingly. Lee and Gossard [4] developed a system that supported a hierarchical assembly data structure containing more basic information about assemblies such as “mating feature” between the components. The transformation matrices are derived automatically from the associations of virtual links, but this hierarchical topology model represents only “part-of” relations effectively. Automatically inferring the configuration of components in an assembly means that designers can avoid specifying the transformation matrices directly. Moreover, the position of a component will change whenever the size and position of its reference component are modified. There exist three techniques to infer the position and orientation of a component in the assembly: iterative numerical technique, symbolic algebraic technique, and symbolic geometric technique. Lee and Gossard [5] proposed an iterative numerical technique to compute the location and orientation of each component from the spatial relationships. Their method consists of three steps: generation of the constraint equations, reducing the number of equations, and solving the equations. There are 16 equations for “against” condition, 18 equations for “fit” condition, 6 property equations for each matrix, and 2 additional equations for a rotational part. Usually the number of equations exceeds the number of variables, so a method must be devised to remove the redundant equations. The Newton–Raphson iteration algorithm is used to solve the equations. This technique has two disadvantages: first, the solution is heavily dependent on the initial solution; secondly, the iterative numerical technique cannot distinguish between different roots in the solution space. Therefore, it is possible, in a purely spatial relationship problem, that a mathematically valid, but physically unfeasible, solution can be obtained. Ambler and Popplestone [6] suggested a method of computing the required rotation and translation for each component to satisfy the spatial relationships between the components in an assembly. Six variables (three translations and three rotations) for each component are solved to be consistent with the spatial relationships. This method requires a vast amount of programming and computation to rewrite related equations in a solvable format. Also, it does not guarantee a solution every time, especially when the equation cannot be rewritten in solvable forms. Kramer [7] developed a symbolic geometric approach for determining the positions and orientations of rigid bodies that satisfy a set of geometric constraints. Reasoning about the geometric bodies is performed symbolically by generating a sequence of actions to satisfy each constraint incrementally, which results in the reduction of the object’s available degrees of freedom (DOF). The fundamental reference entity used by Kramer is called a “marker”, that is a point and two orthogonal axes. Seven constraints (coincident, in-line, in-plane, parallelFz, offsetFz, offsetFx and helical) between markers are defined. For a problem involving a single object and constraints between markers on that body, and markers which have invariant attributes, action analysis [7] is used to obtain a solution. Actionanalysis decides the final configuration of a geometric object, step by step. At each step in solving the object configuration, degrees of freedom analysis decides what action will satisfy one of the body’s as yet unsatisfied constraints, given the available degrees of freedom. It then calculates how that action further reduces the body’s degrees of freedom. At the end of each step, one appropriate action is added to the metaphorical assembly plan. According to Shah and Rogers [8], Kramer’s work represents the most significant development for assembly modelling. This symbolic geometric approach can locate all solutions to constraint conditions, and is computationally attractive compared to an iterative technique, but to implement this method, a large amount of programming is required. Although many researchers have been actively involved in assembly modelling, little literature has been reported on feature based assembly modelling for injection mould design.Kruth et al. [9] developed a design support system for an injection mould. Their system supported the assembly design for injection moulds through high-level functional mould objects (components and features). Because their system was based on AutoCAD, it could only accommodate wire-frame and simple solid models. 3. Representation of Injection Mould Assemblies The two key issues of automated assembly modelling for injection moulds are, representing a mould assembly in com- puters, and determining the position and orientation of a product-independent part in the assembly. In this section, we present an object-oriented and feature-based representation for assemblies of injection moulds. The representation of assemblies in a computer involves structural and spatial relationships between individual parts. Such a representation must support the construction of an assembly from all the given parts, changes in the relative positioning of parts, and manipulation of the assembly as a whole. Moreover, the representations of assemblies must meet the following requirements from designers: 1. It should be possible to have high-level objects ready to use while mould designers think on the level of real-world objects. 2. The representation of assemblies should encapsulate operational functions to automate routine processes such as pocketing and interference checks. To meet these requirements, a feature-based and object-oriented hierarchical model is proposed to represent injection moulds. An assembly may be divided into subassemblies, which in turn consists of subassemblies and/or individual components. Thus, a hierarchical model is most appropriate for representing the structural relations between components. A hierarchy implies a definite assembly sequence. In addition, a hierarchical model can provide an explicit representation of the dependency of the position of one part on another. Feature-based design [10] allows designers to work at a somewhat higher level of abstraction than that possible with the direct use of solid modellers. Geometric features are instanced, sized, and located quickly by the user by specifying a minimum set of parameters, while the feature modeller works out the details. Also, it is easy to make design changes because of the associativities between geometric entities maintained in the data structure of feature modellers. Without features, designers have to be concerned with all the details of geometric construction procedures required by solid modellers, and design changes have to be strictly specified for every entity affected by the change. Moreover, the feature-based representation will provide high-level assembly objects for designers to use. For example, while mould designers think on the level of a real- world object, e.g. a counterbore hole, a feature object of a counterbore hole will be ready in the computer for use. Object-oriented modelling [11,12] is a new way of thinking about problems using models organised around real-world concepts. The fundamental entity is the object, which combines both data structures and behaviour in a single entity. Object- oriented models are useful for understanding problems and designing programs and databases. In addition, the object- oriented representation of assemblies makes it easy for a“child” object to inherit information from its “parent”. Figure 2 shows the feature-based and object-oriented hier- archical representation of an injection mould. The representation is a hierarchical structure at multiple levels of abstraction, from low-level geometric entities (form feature) to high-level subassemblies. The items enclosed in the boxes represent “assembly objects” (SUBFAs, PARTs and FFs); the solid lines represent “part-of” relation; and the dashed lines represent other relationships. Subassembly (SUBFA) consists of parts (PARTs). A part can be thought of as an “assembly” of form features (FFs). The representation combines the strengths of a feature-based geometric model with those of object-oriented models. It not only contains the “part-of” relations between the parent object and the child object, but also includes a richer set of structural relations and a group of operational functions for assembly objects. In Section 3.1, there is further discussion on the definition of an assembly object, and detailed relations between assembly objects are presented in Section 3.2 Fig. 2. Feature-based, object-oriented hierarchical representation 3.1 Definition of Assembly Objects In our work, an assembly object, O, is defined as a unique, identifiable entity in the following form: O = (Oid, A, M, R) (1) Where: Oid is a unique identifier of an assembly object (O). A is a set of three-tuples, (t, a, v). Each a is called an attribute of O, associated with each attribute is a type, t, and a value, v. M is a set of tuples, (m, tc1, tc2, %, tcn, tc). Each element of M is a function that uniquely identifies a method. The symbol m represents a method name; and methods define operations on objects. The symbol tci(i= 1, 2, %, n) specifies the argument type and tc specifies the returned value type. R is a set of relationships among O and other assembly objects. There are six types of basic relationships between assembly objects, i.e. Part-of, SR, SC, DOF, Lts, and Fit. Table 1 shows an assembly object of injection moulds, e.g. ejector. The ejector in Table 1 is formally specified as: (ejector-pinF1, {(string, purpose, ‘ejecting moulding’), (string, material, ‘nitride steel’), (string, catalogFno, ‘THX’)}, {(checkFinterference(), boolean), (pocketFplate(), boolean)}, {(part-of ejectionFsys), (SR Align EBFplate), (DOF Tx, Ty)}). In this example, purpose, material and catalogFno are attributes with a data type of string; checkFinterference and pocketFplate are member functions; and Part-of, SR and DOF are relationships. 3.2 Assembly Relationships There are six types of basic relationships between assembly objects, Part-of, SR, SC, DOF, Lts, and Fit. Part-of An assembly object belongs to its ancestor object. SR Spatial relations: explicitly specify the positions and orientations of assembly objects in an assembly. For a component part, its spatial relationship is derived from spatial constraints (SC). SC Spatial constraints: implicitly locate a component part with respect to the other parts. DOF Degrees of freedom: are allowable translational/ rotational directions of motion after assembly, with or without limits. Lts Motion limits: because of obstructions/interferences, the DOF may have unilateral or bilateral limits. Fit Size constraint: is applied to dimensions, in order to maintain a given class of fit. Among all the elements of an assembly object, the relation-ships are most important for assembly design. The relationships between assembly objects will not only determine the position of objects in an assembly, but also maintain the associativities between assembly objects. In the following sub-sections, we will illustrate the relationships at the same assembly level with the help of examples. 3.2.1 Relationships Between Form Features Mould design, in essence, is a mental process; mould designers most of the time think on the level of real-world objects such as plates, screws, grooves, chamfers, and counter-bore holes. Therefore, it is necessary to build the geometric models of all product-independent parts from form features. The mould designer can easily change the size and shape of a part, because of the relations between form features maintained in the part representation. Figure 3(a) shows a plate with a counter-bore hole. This part is defined by two form features, i.e. a block and a counter-bore hole. The counter-bore hole (FF2) is placed with reference to the block feature FF1, using their local coordinates F2and F1, respectively. Equations (2)–(5) show the spatial relationships between the counter-bore hole (FF2) and the block feature (FF1). For form features, there is no spatial constraint between them, so the spatial relationships are specified directly by the designer. The detailed assembly relationships between two form features are defined as follows: Fig. 3. Assembly relationships. F2k= F1k (4) r2F= r1F+ b22*F1j+ AF1*F1i (5) DOF: ObjFhasF1FRDOF(FF2, F2j) The counter-bore feature can rotate about axis F2j. LTs(FF2, FF1): AF1, b11? 0.5*b21 (6) Fit (FF2, FF1): b22= b12 (7) Where F and r are the orientation and position vectors of features. F1= (F1i, F1j, F1k), F2= (F2i, F2j, F2k). bij is the dimension of form features, Subscript i ifeature number, j is dimension number. AF1is the dimension between form features. Equations (2)–(7) present the relationships between the form feature FF1 and FF2. These relationships thus determine the position and orientation of a form feature in the part. Taking the part as an assembly, the form feature can be considered as “components” of the assembly. The choice of form features is based on the shape characteristics of product-independent parts. Because the form features provided by the Unigraphics CAD/CAM system [13] can meet the shape requirements of parts for injection moulds and the spatial relationships between form features are also maintained, we choose them to build the required part models. In addition to the spatial relationships, we must record LTs, Fits relationships for form features, which are essential to c