手機(jī)后蓋注塑模設(shè)計(jì)-后殼外殼件

喜歡這套資料就充值下載吧。。。資源目錄里展示的都可在線預(yù)覽哦。。。下載后都有，，請(qǐng)放心下載，，文件全都包含在內(nèi)，圖紙為CAD格式可編輯，【有疑問咨詢QQ:414951605 或 1304139763】 畢業(yè)設(shè)計(jì)（論文）中期檢查表（指導(dǎo)教師） 指導(dǎo)教師姓名：郭中玲 　　 填表日期： 2014年 4 月 20 日 學(xué)生學(xué)號(hào) 1000110110 學(xué)生姓名 譚鑫 題目名稱 手機(jī)保護(hù)殼注塑模設(shè)計(jì) 已完成內(nèi)容 開題并做調(diào)研，進(jìn)行翻譯； 確定其方案設(shè)計(jì)； 完成結(jié)構(gòu)設(shè)計(jì)； 繪制結(jié)構(gòu)草圖； 完成相關(guān)計(jì)算； 完成英文翻譯； 繪制裝配圖； 繪制零件圖； 撰寫論文； 完成畢業(yè)設(shè)計(jì)。 檢查日期：2014-4-20 完成情況 t全部完成 □按進(jìn)度完成 □滯后進(jìn)度安排 存在困難 　 解決辦法 　查閱相關(guān)資料，并且與指導(dǎo)老師和同學(xué)們一起討論解決方案。 預(yù)期成績(jī) □優(yōu) 秀 t良 好 □中 等 □及 格 □不及格 建 議 教師簽名： 教務(wù)處實(shí)踐教學(xué)科制表 說明：1、本表由檢查畢業(yè)設(shè)計(jì)的指導(dǎo)教師如實(shí)填寫；2、此表要放入畢業(yè)設(shè)計(jì)（論文）檔案袋中； 3、各院(系)分類匯總后報(bào)教務(wù)處實(shí)踐教學(xué)科備案 編號(hào)： 　畢業(yè)設(shè)計(jì)(論文)任務(wù)書 題 目： 手機(jī)后蓋注塑模設(shè)計(jì) 學(xué)　　院： 國(guó)防生學(xué)院 專 業(yè)：機(jī)械設(shè)計(jì)制造及其自動(dòng)化 學(xué)生姓名： 譚鑫 學(xué) 號(hào)： 1000110110 指導(dǎo)教師單位： 機(jī)電工程學(xué)院 姓 名： 郭中玲 職 稱： 高級(jí)工程師 題目類型：¨理論研究 ¨實(shí)驗(yàn)研究 t工程設(shè)計(jì) ¨工程技術(shù)研究 ¨軟件開發(fā) 2013年12月9日 一、 畢業(yè)設(shè)計(jì)（論文）的內(nèi)容 1、塑件的分析 2、塑件材料的選用與性能分析（特性及成型工藝參數(shù)） 3、擬定模具的結(jié)構(gòu)形式（型腔的數(shù)目及排布） 4、澆注系統(tǒng)的設(shè)計(jì) 5、分流道的設(shè)計(jì) 6、澆口的設(shè)計(jì) 7、冷料穴和拉料桿的設(shè)計(jì) 8、成型零件的設(shè)計(jì) 9、導(dǎo)向機(jī)構(gòu)的設(shè)計(jì) 10、脫模推出機(jī)構(gòu)的設(shè)計(jì) 11、側(cè)向分型與抽心機(jī)構(gòu)設(shè)計(jì) 12、排氣系統(tǒng)的設(shè)計(jì) 13、溫度調(diào)節(jié)系統(tǒng)的設(shè)計(jì) 14、限位釘設(shè)計(jì) 二、畢業(yè)設(shè)計(jì)（論文）的要求與數(shù)據(jù) 1、外型尺寸及配合精度必須標(biāo)注 2、使用環(huán)境-10℃~40℃ 3、電氣性能符GB標(biāo)準(zhǔn) 4、外觀要求美觀堅(jiān)固 5、根據(jù)實(shí)際情況確定脫模斜度 6、ABS主要技術(shù)指標(biāo)及工藝參數(shù) 7、設(shè)計(jì)中的計(jì)算 8、安裝尺寸的校核 三、畢業(yè)設(shè)計(jì)（論文）應(yīng)完成的工作 1、完成二萬字左右的畢業(yè)設(shè)計(jì)說明書（論文）；在畢業(yè)設(shè)計(jì)說明書（論文）中必須包括詳細(xì)的300-500個(gè)單詞的英文摘要； 2、獨(dú)立完成與課題相關(guān)，不少于四萬字符的指定英文資料翻譯（附英文原文）； 3、對(duì)于純機(jī)械類課題，繪圖工作量折合A0圖紙3張以上，其中必須包含兩張A3以上的計(jì)算機(jī)繪圖圖紙； 四、應(yīng)收集的資料及主要參考文獻(xiàn) [1] 李學(xué)峰.塑料模設(shè)計(jì)及制造[M].北京：機(jī)械工業(yè)出版社.2001 [2] 翁其金.塑料模塑成型技術(shù). [M].北京：機(jī)械工業(yè)出版社.2002 [3] 錢泉森.塑料成型工藝及模具設(shè)計(jì). [M].濟(jì)南：山東科學(xué)技術(shù)出版社，2004 [4] 《塑料模設(shè)計(jì)手冊(cè)》編著組.塑料設(shè)計(jì)手冊(cè).北京：機(jī)械工業(yè)出版社.2002 [5] 陳劍鶴.模具設(shè)計(jì)基礎(chǔ). [M].北京：機(jī)械工業(yè)出版社，2004 [6] 王文廣等.塑料注塑模具設(shè)計(jì)技巧與實(shí)例[M].北京：化學(xué)工業(yè)出版社，2004 [7] 章飛.型腔模具設(shè)計(jì)與制造.[M].北京：化學(xué)工業(yè)出版社，2003 [8] 譚雪松，林曉新，溫利編.新編塑料模設(shè)計(jì)手冊(cè).北京：人民郵電出版社，2007.1 [9] 朱光.塑料注塑模中小型模架及其技術(shù)條件[M].北京：清華大學(xué)出版社，2003,1 [10] cunha,L,et.al.,performance of chromium nitride and titanium nitride coatings during platics injection moulding. Surface and coating Technology, 2002.153(2-3):p.160-165. 五、試驗(yàn)、測(cè)試、試制加工所需主要儀器設(shè)備及條件 計(jì)算機(jī)(autoCAD,及pro/E,protel軟件) 任務(wù)下達(dá)時(shí)間： 2013年12月4日 畢業(yè)設(shè)計(jì)開始與完成時(shí)間： 2013年12月7日至 2014年05 月26日 組織實(shí)施單位： 教研室主任意見： 簽字： 2013年12月10日 院領(lǐng)導(dǎo)小組意見： 簽字： 2013年12月12日 編號(hào)： 　畢業(yè)設(shè)計(jì)(論文)開題報(bào)告 題 目： 手機(jī)后蓋注塑模設(shè)計(jì) 院 （系）： 國(guó)防生學(xué)院 專 業(yè)： 機(jī)械設(shè)計(jì)制造及其自動(dòng)化 學(xué)生姓名： 譚鑫 學(xué) 號(hào)： 1000110110 指導(dǎo)教師單位： 機(jī)電工程學(xué)院 姓 名： 郭中玲 職 稱： 高級(jí)工程師 題目類型：¨理論研究 ¨實(shí)驗(yàn)研究 t工程設(shè)計(jì) ¨工程技術(shù)研究 ¨軟件開發(fā) 2013年12月23日 開題報(bào)告填寫要求 ? 1．開題報(bào)告作為畢業(yè)設(shè)計(jì)（論文）答辯委員會(huì)對(duì)學(xué)生答辯資格審查的依據(jù)材料之一。此報(bào)告應(yīng)在指導(dǎo)教師指導(dǎo)下，由學(xué)生在畢業(yè)設(shè)計(jì)（論文）工作前期內(nèi)完成，經(jīng)指導(dǎo)教師簽署意見審查后生效。 ?2．開題報(bào)告內(nèi)容必須用黑墨水筆工整書寫，或按教務(wù)處統(tǒng)一設(shè)計(jì)的電子文檔標(biāo)準(zhǔn)格式打印，禁止打印在其它紙上后剪貼，完成后應(yīng)及時(shí)交給指導(dǎo)教師簽署意見。 ?3．學(xué)生查閱資料的參考文獻(xiàn)應(yīng)在5篇及以上（不包括辭典、手冊(cè)）。 ?4．有關(guān)年月日等日期的填寫，應(yīng)當(dāng)按照國(guó)標(biāo)GB/T 7408—94《數(shù)據(jù)元和交換格式、信息交換、日期和時(shí)間表示法》規(guī)定的要求，一律用阿拉伯?dāng)?shù)字書寫。如“2004年4月26日”或“2004-04-26”。 ? ? 1. 本課題的研究?jī)?nèi)容、重點(diǎn)及難點(diǎn) 本次研究設(shè)計(jì)了塑料手機(jī)保護(hù)殼的材料特點(diǎn)以及相關(guān)內(nèi)容，主要描述該手機(jī)保護(hù)殼的成型加工工藝，包括注射模結(jié)構(gòu)，各大系統(tǒng)和機(jī)構(gòu)的設(shè)計(jì)，以及各零部件參數(shù)的校核。此次設(shè)計(jì)中有許多地方需要仔細(xì)研究，其重點(diǎn)難點(diǎn)如下： 1、脫模推出機(jī)構(gòu)和側(cè)抽芯機(jī)構(gòu)的設(shè)計(jì)； 2、塑件的合理性設(shè)計(jì)及結(jié)構(gòu)工藝性分析； 3、材料選擇，收縮率計(jì)算。模具強(qiáng)度及剛度分析； 4、塑件壁厚成型工藝考慮及保證塑件的外觀要求； 5、模具型腔數(shù)的確定，模具結(jié)構(gòu)、分型面和進(jìn)料口形式的選擇； 6、保證塑件成型時(shí)無變形，注出的制件表面光滑，無氣泡和其它缺陷，無飛邊或少飛邊； 7、繪制模具總裝圖、零件圖及尺寸標(biāo)注。 2. 準(zhǔn)備情況（查閱過的文獻(xiàn)資料及調(diào)研情況、現(xiàn)有設(shè)備、實(shí)驗(yàn)條件等） 隨著我國(guó)制造業(yè)的迅速發(fā)展，一些新興產(chǎn)業(yè)業(yè)取得了長(zhǎng)足的進(jìn)步。模具是工業(yè)生產(chǎn)的基礎(chǔ)工藝裝備，在機(jī)械、電子、汽車、航空以及通信等領(lǐng)域有著廣泛的應(yīng)用。隨著人民生活水平的不斷提高，日常生活中使用的物品越來越多地用到了模具，特別是現(xiàn)代社會(huì)，人們對(duì)于手機(jī)的需求越來越高，手機(jī)已經(jīng)從生活的調(diào)味品變成了必需品，手機(jī)后蓋的生產(chǎn)主要以注塑模具生產(chǎn)，注塑模生產(chǎn)具有生產(chǎn)效率高，成本低等特點(diǎn)，非常適合手機(jī)后蓋的生產(chǎn)。 當(dāng)前，計(jì)算機(jī)技術(shù)和網(wǎng)絡(luò)技術(shù)取得了突破性的成就，CAD/CAM技術(shù)、數(shù)控加工技術(shù)以及快速成型技術(shù)為模具技術(shù)的發(fā)展提供了強(qiáng)大的技術(shù)支持。同時(shí)，以高分子塑料為主的模具材料不斷被開放出來。這些材料種類繁多，性能優(yōu)良，價(jià)格低廉，這更為模具產(chǎn)業(yè)的發(fā)展提供了有力的幫助。本設(shè)計(jì)主要是為了夠清楚地闡述塑料注射模的設(shè)計(jì)過程，能夠?qū)δ＞咴O(shè)計(jì)過程中所使用的各種基本工具，例如UG/Pro/ENGINEER，Moldflow Plastics Insight等等，具有一個(gè)基本的了解。本次主要是對(duì)手機(jī)的后蓋進(jìn)行設(shè)計(jì)，從零件的尺寸確定，到模具設(shè)計(jì)、模架設(shè)計(jì)，全面闡述了手機(jī)后蓋注塑模具的整個(gè)設(shè)計(jì)過程。 到目前，已經(jīng)做了十足的準(zhǔn)備，認(rèn)真閱讀了解了許多相關(guān)資料，其中包括 [1] 郭新玲編著.塑料模具設(shè)計(jì)[M］.北京:清華大學(xué)出版社,2006. [2] 2006 HERBERT W.YANKEE MANUFACTURING PROCESSES Prentice-Hall, Inc. [3] 張信群.塑料成型工藝與模具結(jié)構(gòu)[M］.北京:人民郵電出版社,2008 [4] 竇召領(lǐng).模具機(jī)械加工技術(shù)[M］.武漢:科技大學(xué)出版社,2008 [5] 張信群.模具制造技術(shù)[M］.北京:人民郵政出版社,2009 [6] 謝琴香.模具設(shè)計(jì)及計(jì)算機(jī)應(yīng)用[M］.華南理工出版社,2008 [7] 程志遠(yuǎn).實(shí)用注塑模設(shè)計(jì)手冊(cè)[M］.中國(guó)輕工業(yè)出版社 [8] 楊叔子.機(jī)械加工工藝師手冊(cè)[M］.北京:機(jī)械工業(yè)出版社 [9] 機(jī)械設(shè)計(jì)手冊(cè)[M］.北京:機(jī)械工業(yè)出版社 [10] 黃義俊.模具CAD/CAM技術(shù)[M］.北京:人民郵電出版社,2009. [11] 李小敏.計(jì)算機(jī)輔助設(shè)計(jì)-CAD/CAE/CAPP/CAM[M］.北京:清華大學(xué)出版社.2008.4 [12] 顏智偉編著.塑料模具設(shè)計(jì)與機(jī)構(gòu)設(shè)計(jì)[M］.北京: 國(guó)防工業(yè)出版社.2006. [13] 張中元.塑料成型工藝與模具設(shè)計(jì)[M]. 北京：航空工業(yè)出版社，2006. [14] 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. [15] 李云程.模具制造工藝學(xué)[M］.機(jī)械工業(yè)出版社，2005 3. 實(shí)施方案、進(jìn)度實(shí)施計(jì)劃及預(yù)期提交的畢業(yè)設(shè)計(jì)資料 2013年12月17日至2013年12月30日，閱讀執(zhí)行畢設(shè)任務(wù)書要求并收集整理資料文獻(xiàn)，根據(jù)畢設(shè)內(nèi)容完成并交開題報(bào)告； 2013年1月6日至2014年1月13日，開展調(diào)研，了解塑件結(jié)構(gòu)，對(duì)原材料進(jìn)行分析，考慮塑件的成型工藝性、模具的總體結(jié)構(gòu)的形式，并完成部分英文摘要翻譯； 2014年3月4日至2013年3月31日，查閱資料，熟悉注射模的結(jié)構(gòu)及有關(guān)計(jì)算，擬定模具的方案設(shè)計(jì)、總體設(shè)計(jì)及主要零件設(shè)計(jì)，擬定成型工藝過程，查閱有關(guān)手冊(cè)確定適宜的工藝參數(shù)，注射機(jī)的選擇及確定注射設(shè)備及型號(hào)規(guī)格； 2014年4月1日至2014年4月21日，完成設(shè)計(jì)計(jì)算任務(wù)，總體結(jié)構(gòu)的設(shè)計(jì)和完成總裝配圖及零件圖的設(shè)計(jì)； 2014年4月22日至2014年5月5日，完成設(shè)計(jì)，圖紙繪制任務(wù)，工藝規(guī)程說明書的編寫； 2014年5月6日至2014年5月20日，完善設(shè)計(jì)并完成論文的撰寫； 2014年5月20日至2014年5月26日，修改并打印畢業(yè)論文及整理相關(guān)資料，交指導(dǎo)老師評(píng)閱，準(zhǔn)備論文答辯。 指導(dǎo)教師意見 指導(dǎo)教師： 年 月 日 開題小組意見 開題小組成員簽字： 年 月 日 院系審核意見 院系主管領(lǐng)導(dǎo)簽字： 年 月 日 桂林電子科技大學(xué)畢業(yè)設(shè)計(jì)（論文）外文翻譯（譯文） 編號(hào)： 　畢業(yè)設(shè)計(jì)（論文）外文翻譯 （原文） 學(xué) 院： 國(guó)防生學(xué)院 專 業(yè)：機(jī)械設(shè)計(jì)制造及其自動(dòng)化 學(xué)生姓名： 譚鑫 學(xué) 號(hào)： 1000110110 指導(dǎo)教師單位： 機(jī)電工程學(xué)院 姓 名： 郭中玲 職 稱： 高級(jí)工程師 2014年3月9日 contents Rapid Prototyping Versus Virtual Prototyping in Product Design and Manufacturing 1 prolonging lifetime ofservice life of die based on deform 13 桂林電子科技大學(xué)畢業(yè)設(shè)計(jì)（論文）外文翻譯（原文） 第 28 頁(yè) 共 29 頁(yè) Rapid Prototyping Versus Virtual Prototyping in Product Design and Manufacturing C. K. Chua1, S. H. Teh1 and R. K. L. Gay2 School of Mechanical & Production Engineering; and 2Gintic Institute of Manufacturing Technology, Nanyang Technological University, Singapore Abstract Rapid prototyping (RP) is the production of a physical model from a computer model without the need for any jig or fixture or numerically controlled (NC) programming. This technology has also been referred to as layer manufacturing, material deposit manufacturing, material addition manufacturing, solid freeform manufacturing and three-dimensional printing. In the last decade, a number of RP techniques has been developed. These techniques use different approaches or materials in producing prototypes and they give varying shrinkage, surface finish and accuracy. Virtual prototyping (VP) is the analysis and simulation carried out on a fully developed computer model, therefore performing the same tests as those on the physical prototypes. It is also sometimes referred to as computer-aided engineering (CAE) or engineering analysis simulation. This paper describes a comparative study of the two prototyping technologies with respect to their relevance in product design and manufacture. The study investigates the suitability and effectiveness of both technologies in the various aspects of prototyping, which is part and parcel of an overall design and manufacturing cycle. Keywords: Product design; Rapid prototyping; Virtual prototyping 1. Introduction Rapid prototyping (RP) is emerging as a key prototyping technology with its ability to produce even complicated parts virtually overnight. It enables product designers to shorten the product design and development process. The coming-of-age of this technology is clearly reflected in the inclusion of a stereolithography (STL) file generator in most, if not all, CAD. systems today. The STL file is the de facto standard used by RP systems in the representation of the solid 3D CAD models. While RP is a relatively young technology, virtual prototyping (VP) has been in steady development since the 1970s in many guises. Virtual prototyping is taken to mean the testing and analysis of 3D solid models on computing platforms. Today, VP is often tightly integrated with CAD/CAM software and sometimes referred to as CAE packages. It provides the ability to test part behaviour in a simulated context without the need to manufacture the part first [1]. 2. Definitions of RP and VP Rapid prototyping (RP) is a widely used term in engineering, particularly in the computer software industry where it was first coined to describe rapid software development. This term has also been adopted by the manufacturing industry to characterise the construction of physical prototypes from a solid, powder, or liquid in a short period of time when compared to “traditional” subtractive machining methods. This technology has also been variously referred to as layer manufacturing, material deposit manufacturing, material addition manufacturing, solid freeform manufacturing and threedimensional printing [2]. Virtual prototyping (VP) refers to the creation of a model in the computer, often referred to as CAD/CAM/CAE. Virtual or computational prototyping is generally understood to be the construction models of products for the purpose of realistic graphical simulation [1]. In this paper, VP will refer to thesimulation, virtual reality and manufacturing process design domains [3]. Nevertheless, there are many areas where the distinction between RP and VP is blurred. As RP systems rely on CAD systems to generate the files needed to produce the prototype, it would seem that RP is a downstream process from VP in the product or part development cycle. Indeed, Pratt’s definition of VP reveals the fact that VP is a term which is loosely used in the prototyping community. As such, it would be appropriate to clearly define both RP and VP. Rapid prototyping will be taken to mean, as above, the production of a physical model from a computer model without the need of any jig or fixture or NC programming. This also includes other related processes and applications which use RP-produced objects, such as rapid tooling. Similarly, VP is defined as the subsequent manipulation of a solid CAD model as a substitute for a physical prototype for the purposes of simulation and analysis, and is not inclusive of the construction of the solid 3D model. VP includes the following functions: 1. Finite element analysis. 2. Mechanical form, fit and interference checking. 3. Mechanical simulation. 4. Virtual reality applications. 5. Cosmetic modelling. 6. Assemblability. The relationships between RP and VP are shown in Fig. 1. Fig. 1. Classification of RP and VP 3. Prototyping in Singapore Two selected multi-national companies (one American and one French) based in Singapore with significant product development activities showed differing approaches to both RP and VP. Both use RP in their prototyping activities. The first company, B, placed more emphasis on virtual prototyping. It manufactures telecommunications equipment such as pagers and handphones. It is moving all prototyping applications upstream, which is to move prototyping from RP to VP. At present, their RP models are used only for proof of concept and marketing purposes. Other prototyping activities are being carried out with VP. The second company, C, manufactures consumer electronics products such as television sets, video cassette recorders and telephones. It uses VP only as a tool to create a solid 3D model. From the solid 3D model, C generates the STL file needed to produce the RP prototype. Company C then uses the RP part as a master for silicone rubber moulds to produce a limited number of physical ABS (polyacrylonitrite butadienestyrene) prototypes for the various prototyping tests and simulation. Company B intends to move more prototyping to VP, rather than using physical models. Virtual prototyping allows for improvements in reliability and quality as well as reducing costs. Manipulation of virtual prototypes makes it easier for B to implement design improvements compared to an iterative cycle using physical prototypes. Company B drafts the CAD models in Pro/ENGINEER, then uses Patran to pre-process the models. Static finite-element analysis (FEA) is carried out with ABAQUS Standard whereas dynamic scenarios are analysed with ABAQUS Explicit. ALIAS/Wavefront is used for cosmetic modelling when presenting different conceptual and actual designs. The bulk of the VP carried out by B uses FEA, which typically takes 4–6 weeks for a pager design. Of all the FEA carried out, the majority are concentrated on structural strength (static) analysis and drop test (dynamic) analysis. Vibration tests are occasionally carried out. Some cosmetic modelling is carried out, but usually only for presentation purposes. Finite-element analysis is used to investigate the following problems: Relative comparison of different design options; to see how one design compares to another. Possible failure modes are: 1. To evaluate a design change or design correction. 2. To assess the possibility of failure, based on past experience. 3. To make some educated-guess correlation with physical testing. 4. To try to identify what initiated a failure. According to B, the drawback of VP is that it cannot simulate process problems efficiently and effectively. The accuracy of FEA is also limited because of the inconsistent behaviour of material. The amount of computing power also determines the accuracy of FEA. The application of RP is rather limited in B. The in-house laminated object manufacturing (LOM) RP system is used to produce design prototypes for proof of concept only, and not geometrical prototypes. Company C uses RP heavily, but has very little VP. The parts produced using RP range from audio products to 29-in. television casings. Typically, it takes 1 year from the conception of the product to the sale of the product. Company C aims to prototype all (mostly plastic) parts by RP. A comparison between numerically controlled (NC) machining of prototypes from ABS against RP is shown in Table 1. Company C projected 50% savings using an in-house RP system versus an NC machining system. CAD models are created using I-DEAS. The .STL format is then created for production of the RP part. The main purpose of the RP parts is to verify the design. Rapid prototyping parts are used for the following functions: 1. Form fitting. 2. Ergonomics check. 3. Proof of concept (to confirm design with industrial designers). 4. Manufacturability (design for tooling, design for assemblability). 5. Reliability check (whether part dislodges or breaks when force applied, especially snap-on covers). 6. Kinematic check. Company C offers some insight into the limitations of VP, in that VP is unable to model: 1. Tactile feeling (for buttons) not quantified; may be able to VP if able to quantify “pressing” force. 2. Assemblability (e.g. PCBs inserted at an angle, difficult to visualise). 4. Case Study 1: Prototyping of a Telephone Handset This case study investigates the design verification, assembly, interference check and form fitting aspects of both the RP and VP model. The production ABS, RP and VP parts or models were evaluated in the above aspects. The RP system used here is the stereolithography apparatus (SLA). Both the ABS and RP parts are shown in Fig. 2. Inspection of the RP parts reveal that: 1. The surface finish was much poorer than in the ABS part. 2. Warpage was clearly evident (see Fig. 3). 4.1 Design Verification As a true dimensional physical part, the RP model is able to give the designer a sense of size estimation. The judgement of a VP part can be erroneous because parts are often automatically sized to fit the viewing window. Another advantage of a physical part is that it allows for ergonomic checks, ranging from the fit of a telecommunications device in a user’s palm to the inspection of potentially dangerous corners and edges. Also, it offers tactile inspection which is crucial in products for which ergonomics is important, such as touch buttons on audio or video products, which is not possible on VP systems. Rounded edges which appear innocuous on a VP model may prove to be unsafe upon scrutiny of the RP part. Above all, most RP parts are produced for aesthetic evaluation purposes. Aesthetic evaluation is also possible on VP models. All CAD software allows the model to be viewed in any spatial orientation, along with at least rudimentary rendering capabilities. It is then possible to view the part under the desired simulated lighting conditions with millions of shading and colour combinations. RP parts cannot be coloured, thus surface preparation and painting introduce additional finishing processes. Any visibly apparent design discrepancies could be immediately rectified without having to invest in a physical part. It also allows designers to evaluate the aesthetics of the design and make corrections, if necessary. In the case of most multi-national companies, the design and manufacturing facilities are often a considerable distance apart and in different countries and continents. The ease with which CAD files can be sent and received via electronic means greatly helps the design process, be it iterative or concurrent. With identical or compatible CAD software, the prototyping process can be swift and cheap. Any design change of the virtual prototype can bemade almost instantly available to all parties involved in the design process. 4.2 Assembly Assembly of RP parts must be carried out quickly, as warpage and shrinkage increases with time. Warpage is a function of both part geometry design and shrinkage. All but the bestdesigned parts suffer from varying degrees of warpage and shrinkage. Some RP material such as the SLA inherently shrinks and the part is actually built slightly larger to allow it to shrink to its proper dimensions. With such arrangements, assembly is possible but is often hampered by warpage and/or shrinkage. Some parts can be mated only with the application of some force. Assembly of RP parts allows the user not only to attempt different assembly sequences, but also if a part cannot be positioned in a linear movement, to insert the part, say, at an angle before being set into its proper location. The drawback in assembling RP parts is that for some RP parts such as SLA, the material is weak and brittle, and fails when attached using fasteners or under low to moderate loading (see Figs 4 and 5). CAD software allows for the assembly of parts and subassemblies in the form of 3D solid or surface models. Assembly in the virtual realm is very often used to check for interference and form fitting which will be discussed later. The ability of CAD software to assemble parts and/or subassemblies allows a product designer to quickly check to see if he or she has designed the part or parts correctly, i.e. whether a boss is tall enough to accept a screw inserted through another part or if two slots are aligned to form a larger slot. The advantage of assembling in a virtual environment is that no physical parts need be produced and thus this reduces cost. The absence of physical parts also means that tooling time is eliminated. The assembly in a virtual environment can be done in a matter of minutes or up to a few days, but is much faster than producing the physical parts and then assembling them. The user can also build or change a part, or modify its attributes when all instances of the part will be changed accordingly. Assembly relationships can be written in engineering parameters, part dimensions and orientation dimensions. The equations are solved variationally to allow for flexibility while working with the assembly. Evaluation of the tolerance specifications of the design to optimise the engineering performance at the lowest possible cost can be carried out. This allows the user to measure the sensitivity of a critical dimension in an assembly to changes in individual constraints. Manufacturing cost can then be reduced by tightening the tolerances which contribute most to the overall variation of a critical dimension, and loosening tolerances that have little impact. 4.3 Interference Check and Form Fitting Again, interference checking and form fitting is hampered by warpage and shrinkage of the RP part. Therefore, the problem of parts which interfere or fit poorly may be due to one or more of: warpage; shrinkage; or design error. Even when RP parts fit well, there is no assurance that the parts are dimensionally correct, as shrinkage of two or more parts in the same direction or directions could still produce a good fit. When such situations arise, CAD models are often used to determine whether the interference or poor fit is due to design flaws. The ability to check for interference as well as form fitting is very widely used in CAD systems. It gives the user the ability to fit two parts together and check for interference without having to produce a part or parts which are potentially dimensionally incorrect, thereby increasing cost. The interactive nature of the process in a CAD system also frees the user or designer from the need to manually interpret engineering drawings to detect interference. This process also allows the user to establish tolerances which are crucial in the manufacturing process. The advantage of interference checking on a CAD system is not evident when an assembly consists of a small number of parts. For complex assemblies with a large number of parts, there are often many features on a particular part that must be mated or aligned with features on one or more other parts. CAD systems allow not only the detection of any misalignment or interference but also immediate rectification of the problem. Interference checking is performed by the CAD system on an assembly when required by the user, and is relatively faster and more accurate and precise than other methods. The CAD system would also identify and list the features which interfere. The user can then view the entities to rectify the situation. 5. Case Study 2: Prototyping of a Knee Prosthesis 5.1 Background Rapid prototyping has applications in the field of medicine. However, in this application the STL file is no longer obtainable from a CAD model. There is a need to generate the necessary STL files from data acquired by medical equipment. Swaelens and Kruth [4] proposed three approaches to producing an RP part from computer assisted tomography (CT) scanner data (see Fig. 6). In most cases, STL-interfacing was used. In STL-interfacing, a CT scanner maps the contour of a 3D surface. This data is then converted into triangular file format which is then converted into the STL format required by RP machines. There is a direct conversion of data from the CT scanner to the RP machines. In effect, the scanned surface is faithfully reproduced by the RP machine. When used in this fashion, VP plays an almost negligible role, in RP-assisted surgery prototyping, as a viewer to verify the contour of the surface. Jacob et al. [5] constructed 3D models from CT scanner data using CTrans from Proform. They reported that the decisive advantage lies in the clearness and manual “getting in touch” as the surgery proper is elaborate manual craftsmanship. The model can be viewed and palpated from any angle and could even be operated upon. In that way, surgeons could literally grasp the problem. This study shows VP as a viewer for a 3D model. While the study did not state whether the 3D model was a solid model, it opened the possibility of integrating CAD software into the process, data exchange problems notwithstanding. This contrasts with the CAD system route shown above. Researchers in the University of Leuven, Belgium identified contours from CT scanner data and introduced them into CAD software to generate surface models. The physical model of a hip was produced with much effort, and the whole procedure took several working weeks. The procedure of converting CT scanner data to a solid 3D model is tedious and prone to error. Given the triangulation points from the CT scanner, they must be joined to the appropriate adjacent points to form curves. Confusion sometimes occurs when a surface folds back; while a point “below”is the nearest point, it may not be an adjacent point. These curves must then be individually and manually selected to define surfaces. Again, care must be taken to ensure that the appropriate surfaces which approximate the original surfaces are formed. After the surfaces are formed, they are connected to form patches or quilts. These quilts are then combined to form a surface model. If the surface model is fully enclosed, the CAD system may then convert it into a shell or solid 3D model. The complexity and shape of the human body also presents problems. Most of the extracted outlines are represented as complicated Bezier curves. A mapping algorithm sometimes fails to combine these Bezier outlines to form 3D data. So, it is necessary that this process be supported by hand [6]. Human supervision is also required where software i