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隔振系统实验台总体方案设计【9张CAD图纸+毕业论文】【答辩通过】

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目录
前言..................3

摘要..................4

第一章隔振理论.................................................................6
1.1 振动.......6
1.2 隔振概念.6
1.3 隔振原理.6
1.4 隔振装置性能的影响因素................................................7
1.5 隔振理论在工程上的应用................................................8
第二章实验台总体方案设计..............................................10
2.1 设计任务与目的...........................................................10
2.2 激振方案的选择...........................................................10
第三章激振系统的设计.....................................................13
3.1 推杆的设计与校核............................................................13
3.2 滑动轴承的设计与校核......................................................13
3.3 滑块与滑槽的设计与校核....................................................14
3.4 滚动轴承,曲轴,滚针轴承的设计与校核.................................14
3.5 箱体的设计.................................................................17
第四章激振系统附件的设计....................................................19
4.1 油塞.................................................................19
4.2 轴承盖.................................................................19
4.3 视孔盖.................................................................19
第五章振动系统的动力选择....................................................20
5.1 选择电动机.................................................................20
5.2 选择电动机的调速方法........................................................21
第六章激振系统用于汽车部件振动的分析............................22
6.1 汽车座椅振动分析.............................................................22
6.2 汽车减振器振动分析......................................................23
第七章隔振系统测试与信号分析..........................25
7.1 传感器.................................................................25
7.2 电荷放大器.................................................................26
7.3 示波器，采集器与电子计算机........................................26
第八章设计小结.................................................................27
参考文献.........28
致谢..................29
英文资料..............
英文翻译..........
附录..................

前言
机械设备在运转时将不可避免地产生振动，振动是造成工程结构损坏及寿命降低的原因，同时，振动会导致机器和仪器仪表的工作效率、工作质量和工作精度的降低；此外，机械结构的振动是产生结构振动辐射噪声的主要原因，如建筑机械、交通运输机械等产生的噪声是构成城市噪声的主要来源；振动对人体也会产生很大的危害，振动会引起人体内部器官的振动或共振，从而导致疾病的发生，对人体造成危害，严重时会影响人们的生命安全，因此振动是一种不可忽略的公害.
随着经济的发展，高等级公路里程的增加，长途客流已成为我国公路运输的主要特征.在这一背景下，长距离(2000 km以上)、长时间(20 h以上)的驾驶作业已是平常.隔振装置在汽车上发挥着越来越重要的作用，如轮胎、弹簧钢板、减振器、座椅、气囊等等.这些装置缓和了路面不平传给人体的冲击和衰减了由此引起的振动，也给驾驶员和乘员提供舒适、安全的乘座条件及工作条件.所以检测汽车的座椅和减振器是必要和必行的.本文考虑仅对于汽车座椅和减振器的隔振性能进行检测，通过改变其阻尼或刚度，或同时改变其阻尼和刚度，而使其舒适性得以改善.

摘要
振动在日常生活中是到处可见的.隔振是阻止振源向隔振物体的传递.汽车座椅或减振器的功能都是在人体的敏感频率范围内(2Hz～8Hz)阻止振源向人体的传递.
本设计任务要设计出一套激振装置，给予座椅或减振器以宽频范围的正弦激励，通过检测汽车座椅或减振器的输出振幅，观察其是否在人体敏感频率范围内处于减振状态.如果没有达到理想的减振效果，则通过改变座椅或减振器的刚度或阻尼，或同时改变其刚度及阻尼，以期达到预定的减振要求.
推而广之，本文所设计的激振装置也可用于检验其它种类的隔振装置.

关键词：振动，隔振，座椅，减振器

Abstract:
It is normal that there is the vibration in our daily lives everywhere. The vibration is prevented from vibration source to vibrated object by technology of vibration insulation.
The Automobile seat and anti-vibration device are all belonged to a kinds of anti-vibration. The paper aims at designing a set of vibration exciting device, getting output amplitude while giving sinusoid excitation to the seat or vibration isolator. Through experimenting, the output amplitude was observed whether it is reduce in the frequency domain of 2Hz~8Hz which is sensitivity to human body. If the result of experiment isn’t met the ideal purpose, we can change either the spring stiffness or damp of seat or anti-vibration device, or change spring stiffness and damp of seat or anti-vibration device with the output amplitude was observed again, until the ideal purpose is attained.
This set of vibration exciting device may also be used for the other anti-vibration devices.

Keywords: vibration，anti-vibration，seat，anti-vibration device

第一章隔振理论
1.1 振动
振动是自然界以及工程技术中普遍存在的自然现象.一方面，振动常常破坏机器的正常工作，加速机器的损坏，造成事故，也危害人体的健康；另一方面我们可以利用隔振的原理，使消极的振动一面转变为积极的，有利于人身健康的一面.引起振动的原因很多.在长期的生活实践中，人们积累了丰富的宝贵经验，掌握了不少行之有效的减少和控制振动的方法.如减少扰动、采取有效的隔振措施等.本文将从隔振的角度出发，设计一种激振器，从而检验汽车驾驶座椅和减振器的隔振效果.
1.2 隔振概念
隔振是在振源和被隔振的物体之间的传递途径中插入适当量值的弹簧和阻尼，切断或阻止振动由振源向隔振物体传递.车辆振动是影响车辆性能的重要因数,这种振动不仅大大降低了车辆行使平顺性,也影响其操纵稳定性.车辆振动严重时,还影响其行使速度;同时车辆振动也是车内噪声的主要来源.研究隔振的原理,将大大的提高汽车的舒适性和平稳性.

内容简介：: 南通大学毕业设计附录（英文资料翻译）实体自由成型制造与快速原型制造11实体自由成形制造方法可以用几种制造方法将CAD信息转换为原型物体。自1987年以来，又出现了几种新的技术来完成这一转换。就在1987年，3D系统公司(3D Systems Inc)推出了立体光刻(SLA)这一技术。在随后的5年里，又出现了几种与之相竞争的技术。这一组新技术一般通称为实体自由成形制造(solid freeform fabrication，SFF)。正如大多数新技术都要经历第2章所描述的市场接纳S形曲线一样，实体自由成形制造领域经历了相当长的广告宣传阶段。其他用来描述实体自由成形制造这一技术的词汇还包括：需求中的零件(part on demand)；从艺术到零件(from art to part)；桌面上制造(desktop manufacturing)；快速成形(rapid prototyping)。在撰写本书时，专门从事原型制造的公司已将立体光刻(SLA)、选择性激光烧结(SI。S)、熔融沉积制造(FDM)和分层实体制造(LOM)用于日常商业活动中。以玉米淀粉、塑料和陶瓷为材料的三维印刷(3DP)也正进入商业应用。还有几种原型制造方法虽具有潜力，但并没有以盈利目的被第三方普遍采用。铸造是一个特例，它仍然被用于单件原型制造。另外，当用立体光刻做好模具后，采用铸造进行10500批量范围的生产仍然非常经济。机加工也用于单件或几件批量的原型制造。111 实体自由成形制造与快速成形技术总结用于日常商业性活动的包括：立体光刻；选择性激光烧结；分层实体制造；熔融沉积制造。处于研究与开发阶段的包括：以玉米淀粉、塑料和陶瓷为材料的三维印刷；以塑料为材料并由机加工来铣平的三维印刷；实体磨削固化(SGC，与SLA类似)；形状沉积制造(SDM，分层叠加与分层递减的结合)。非实体自由成形制造(传统方法)包括：机加工；铸造。克莱斯勒汽车公司于20世纪90年代初所作的比较研究表明，SLA技术比与其竞争的非传统原型制造方法，在成本上和精度上要领先(此项研究没有包括对机加工和铸造工艺的评价)。本章对有关技术进行描述后，将附加图表来对它们的成本与精度进行比较。近10年来，SLA已进一步证明了它是应用最多的实体自由成形制造技术，特别是在铸造和注塑成形时用它来制作模具。在撰写本书时，SLS、FDM和LOM是继SLA后最常见的技术。112 实体自由成形制造的发展历史 20世纪70年代末，米得(Mead)和康韦(20nway)奠定了超大规模集成电路(VLSI)的快速成形基础口“。于是，电路的设计者们开始采用5种二维模式进行设计。这些模式定义了金属氧化物半导体(MOS)晶片上的三层叠式互连及各层之间通过孔隙的互连。当俯视电路芯片时(无论用来制作这些芯片的具体工艺和掩膜层数如何)，这些模式均可用来描述各种线路走势与通孔的实际几何图形(见文献36)。受以上分层电路成功的设计方法的激励，20世纪70年代以来，数家公司对分层制造机械零件进行了尝试。另外，到80年代中叶，几项美国政府的研究也对成立“机械领域的金属氧化物半导体执行服务机构(MOSIS)”的可能性进行了分析。于是，一提到机械领域的M()SIS的前景，人们就往往将它与上文列出的制造工艺联系起来。第一种商用SFF技术SLA是伴随着将CAD物体表示成STL。(STereoLithography)文档格式“STL。”的出现而产生的。“STL”文档是CAD格式的种变形，它适用于造型时的分层操作和后续的实际SLA、FDM或SLS机器上的激光扫描轨迹。足球是圆的吗?回答取决于你测量的准确程度。名义上，它是一个完美的圆球体，但仔细观察起来，它是由大约20多块六边形块和一些五边形块缝合而组成的曲面体。所以它实际上是对数学上圆球体的一种近似。类似地，“STL”文件用来对CAD模型中的边界曲面进行近似，将原曲面分割成相互连接的小三角形，通常称为分割镶嵌(tessellation)。每一块三角形由三个顶点的x、y、z坐标来表示，三个顶点的先后顺序符合右手法则，即从物体外部看，以逆时针方向定出这些顶点。同时，对每个三角块的法向也做了规定。这些分割镶嵌的小表面储存在一个“STL”文件中。这样形成的可能包含多至20万个三角块的文件通过Internet送往快速成形车间的机器。图4.1 一个“.STL”文件表示的是一个分割镶嵌后的物体。（a）图显示由许多表面面片表示的隐形眼镜盒。该“.STL”文件所表示的物体随后被分层，接着用激光扫描来硬化零件（由Lee Weiss教授提供）。如图41所示，这种分割镶嵌的CAD模型随后被分割成类似于一叠扑克牌的层次。对于3D系统公司的机器而言，这种文件被称为SLI文件或分层文件。尽管其他快速成形方法使用相似的技术，但它们的细节和命名却各有不同。如果对于一个假想的足球来说，这样的每一层都应该是一个圆形。但是由于使用这种分割镶嵌的方法，每一层都不是一个完美的圆形。由于这种分层技术沿三角块边界分割，因此，每一层圆实际是由一个多边形近似形成的，边的多少则取决于分割镶嵌所要求的精确程度。对于SLA机器而言，首先用激光器固化每层的边界，然后再填充边界内部。每层的厚度和填充方式则通常随机器生产商的不同和用户的选择而有所不同。特别是对于SLA和SLS机器而言，通常要进行一些逐步尝试才能探索出最令人满意的结果。这个问题将在稍后几节进一步探讨。目前，“STI。”格式已成为SFF的标准文件交换格式。但在很多情况下，此格式也存在一些不足。首先，由于采用分割镶嵌，文件所占容量很大。其次，它存在着一些冗余度。例如，一方面每块小三角形都按逆时针方向给出其三个顶点的坐标，以便用右手法则判断其法向。但同时，习惯上每块小三角形的法向矢量也同时由STI，另外保存。有时这两者会出现一些不一致性，而且目前还没有较好的方法来解决这一问题。正如文献32所述，“STI。”没有表达模型的拓扑结构和连接性，给修补文件中的一些常见错误带来困难，例如，间隙、渗透和额外面片，以及法向不一致。此时，人们不能不去设法猜测设计人员的原意。于是，一些更通常的数据交换格式有时也用于SFF中，包括ACIS和IGES。然而，正如文献38所述，在SFF中采用这些格式也存在某些问题。因此，目前对文件交换语言进行改善的研究正在进行。12可供快速成形选用的铸造方法121 简介一些经典的制造工艺教科书，如文献11、17、24及43，对各种铸造工艺有较详细地介绍，例如：失蜡铸造；陶瓷模铸造；壳型铸造；传统翻砂铸造；压模铸造。为避免重复以上教科书中的内容，本节着重介绍快速成形服务厂商所应用的铸造方法。应用这种方法制造原型的批量以50500较为典型。最主要的市场考虑是铸造经济且周期短。然而，如果公差要求较严，铸造出的样件也许不能成为最终产品。视具体铸造方法而言，其公差范围可以达到从失蜡铸造的士75pm至普通砂模铸造的375pm(另参见第2章)。122普通失蜡铸造正如第1章所述，基本的铸造方法是许多世纪以前朝鲜和埃及的艺术家所发明的。失蜡铸造由以下工序构成(如图416所示)：(ac)用于工程或艺术品的蜡模型；(df)将蜡模不断浸于陶瓷浆中以获得一定厚度的包壳；(g)将此陶瓷材料包裹的蜡模加热，将蜡熔化并从底部的孔流出形成空壳；(h)把空壳的孔堵住，将金属熔液从空壳上部浇入；(i)待金属固化后，打碎外壳，取出铸件；(j)清理、去毛刺、抛光及其他后置处理。失蜡铸造这一工艺在第二次世界大战中用来制造飞机零部件时得到了很大的改进。今天，此方法已广泛用于制造各种产品，如喷气涡轮发动机叶片及高尔夫球杆的杆头。图416的(af)示意了由注塑成形制作蜡模，再将许多蜡模粘接成树状结构，然后将此树状模浸入陶瓷溶液中而形成模具的过程。蜡模被交替沉浸于粗细不同的耐火材料粉浆里，先浸的细锆砂粉筛号细至250号，而后浸的粗硅线石砂粉筛号粗至30号。带有涂层的蜡模再浸到乙丙基硅酸盐与酸固化液中。烘干是在氨气容器中完成的。下一步则是将涂层烘干固化后的蜡模置于150的密封式蒸汽炉中让蜡熔化并流出，然后将空壳模具在950：的火炉里烧烤2h，最后将液态金属如钢或铝浇注入模具内。图4.16 失蜡铸造工艺。上图（a）至（c）形成模型阵列。（d）至（f）图显示沙浆和沙粉形成铸模外壳。（g）至（j）图表示铸造过程（引自美国钢铸造者学会的文献）总之，现代失蜡铸造是铸造工艺中精度最高的一种，这是因为作为母模的蜡模是通过精密机加工完成的。现在，失蜡铸造很容易达到75um的公差。同时，由于铸造表面已经很光滑，不经后置处理即可使用。这种工艺的其他优点包括：如果蜡模表面已经过手工抛光处理，则最后零件不存在分模线；具有表面刻纹的蜡模可以直接产生零件所需的表面特征，如高尔夫球杆头表面的凹痕；很容易用机器人使蜡模重复沉浸于粉浆这一过程自动化，从而降低成本；有些零件，如涡轮发动机的叶片，可以实现单向凝固，于是可在需要的方向获得好的机械性能。123陶瓷模铸造前面介绍的失蜡铸造的不足之处是每次要将蜡模熔化。陶瓷模铸造的优点为利用可重用的副母模来取代每次要被熔化的蜡模。这种新型铸造方法的精度和成本很大程度取决于第1步中的母模制作。具体的五个步骤如下：第1步，阳模：用SI。A或机加工制作最原始的母模。第2步，阴模：在阳模的周围用高度稳定的树脂产生一层壳体。这层壳可以分开以提供一条分模线。第3步，阳模：用以上生成的阴模壳和橡胶来制作可重用的副母模。第4步，阴模：在以上阳模的基础上生成可破坏性的陶瓷模具。第5步，零件：浇注金属溶液于以上制作的陶瓷模具内，待金属固化后打破陶瓷模具，取出铸件并去掉浇注口及毛刺。SLA可用来制作第1步中的原始母模，也可用数控加工来铣削青铜、黄铜或钢材制作原始母模。虽然陶瓷模铸造可从以上过程的第3步开始，但这样有可能损坏原始母模，特别是在用SLA来制作原始母模的情况下。另外，从提高生产率的角度来讲，通常在第3步制作许多橡胶母模，所有这些橡胶模都可以从第2步的树脂阴模获得。快速成形服务商喜欢用硬树脂来制作第2步中的阴模，这是因为这种树脂有较好的尺寸稳定性。要注意的是，一般要准备两个半边的树脂模，以便将该壳状阴模沿分模线分开。一旦这种硬的树脂模固化后，再在第3步中用胶糊状橡胶填充其中，硬化后生成橡胶阳模。该橡胶阳模可在它还是软化状时从树脂模里拔出，因此设计时不需要考虑拔模斜度的问题。这种橡胶材料对较简陋铸造车间而言较为理想。第4步中的阴模是由特定等级的氧化铝砂粉与粘合剂(乙基硅酸盐)和异丙基酒精溶液混合而形成的。这种砂粉液浆不断浇到第3步的橡胶模上。一旦这层砂浆干固后，将两个半干固的阴模(陶瓷模)合拢，然后将它们置入950炉火中烧烤以增加其强度。接着即可将金属铝溶液浇注于其中，开始铸造零件。待金属熔液固化后，打破陶瓷模，清理和去除毛刺。尽管开模线会造成一些问题，但一般可获得高至125375um的精度。124 壳模铸造另一种高精度铸造就是壳模铸造(shell molding)。金属母模先被加热到200240C，然后将大约51 5mm的一层砂粉喷涂于该热金属模表面。此砂浆拌有树脂浆，以保证它紧贴在金属型上。另外，以酚醛树脂与六甲撑四胺添加剂混合加入硅砂中，以确保喷涂砂粉的热固性。接下来是让壳模固化、拔开并烧烤壳模，这一过程通常能保证非常好的精度。一旦去除壳模铸造完成，精度能达到75um。125传统翻砂铸造较原始和便宜的一种铸造则是以木头和石膏为母模的翻砂铸造。先将母模周围分别埋满并充实砂土，并加入浇口与冒口。此方法通常可达到375pm的精度。这种方法的最新进展包括：(1)高压振压法。在该方法中，机械活塞给砂土施加振挤400psi(276MPa)的压力，以产生更结实与逼近的砂一模界面，从而获得较高的精度。(2)二氧化碳吹模法。在这种工艺中，砂与模之间的界面是由一层约12mm厚的特别材料制成的。该材料是由难熔的锆石或非常细的二氧化硅与以6 9，6的硅酸钠为粘接剂混合而成。该层材料再通过吹入二氧化碳来固化。126 压模铸造压模铸造主要是通过高压将热锌溶液注入永久性的钢模具而完成的。该工艺发展至今天，其模具几乎全由3或5轴加工中心数控加工而成。尽管压模铸造的模具成本较高，但可获得光滑的铸造表面，其精度通常能达到土75um。然而，由于模具成本较高，压模铸造严格而言并不属于快速原型制造的范围。因此，该工艺大多用于大批生产的汽车或其他消费品中的较小零部件。由于低熔点金属如锌合金的使用，铸件的强度只能算中等。现在，人们一般喜欢用注塑成形(见第8章)来代替压模铸造。13快速成形中的机加工方法131 简介第7章将详细讨论一般的机加工过程及其原理。本节着重介绍将CNC加工用于快速原型制造的CADCAM软件的进展。这种软件的一个目的是要实现CAD与制造之间的完全自动化，另一个目的则是尽量减少很有经验的机械工人的手工操作，如工艺规划和工夹具设计与制造。CyberCut是一种基于Internet的CNC机加工尝试性制造试验平台。它提供的服务允许Internet客户端的设计者在对机械零部件造型后，将相关文件传送到远程服务器上，以便在开放结构CNC机床上进行工艺规划及制造。快速刀具轨迹生成、新型夹具装置以及基于传感器的高精度加工技术，可以让原始设计人员很快获得高强度和高精度的零部件。132 WebCAD：位于Internet客户端的面向机加工的设计在这里，一个关键的概念就是用“通晓工艺”的CAD工具来进行零件设计，这种原型生成系统称为WebCAD。SUN公司的JavaTM是一种可移植、面向对象的稳健编程语言(类似C+)，将它用于该试验平台以服务小型应用场合。该平台的图形用户界面是采用第3章介绍的析构实体几何(DSG)的基于25维特征的设计系统。在这种实体几何建模过程中，用户通常开始于一块长方体，然后逐步去除一块一块的材料。与之相反，传统的构造实体几何(CSG)则由零开始逐步往上添加一块一块的形体。在析构实体几何方法中，用户不能随意去除不同形状的材料，而是必须一个特征一个特征地去除。这些特征一般为槽、盲孔及通孔。 WebCAD还包括一个能确认可加工性的专家系统。正如图417所示，该图上面部分表示用户由这些专家系统内的规则所引导。例如，在一个通孔周围设置一个“禁区”以避免通孔太靠近边缘。当设计人员违反了这一规则时，自动弹出窗口会提示适当的补救办法，例如，将通孔往形体里面移近一点一般可通过减少其直径来完成。webCAD还采用了WYSlWYG环境(“你所看到的即是你所得到的”英语缩写译者注)，并提供明确的切削刀具及拐角半径以供选择。值本书写作之时，研究者们还在对这个系统进行改进，包括添加自由表面编辑造型以及根据零件最终加工位置进行刀具选择。之所以采用DSG来引导用户进行设计是因为所选用的那些特征可以与标准的CNC铣削工艺相对应。这一情形正类似于考虑到文件的“可打印性”时，文字处理软件与打印机之间的关系。虽然人们很容易批评由于使用DSG而带来的给用户设计零件时的一些限制，但DSG设计环境的主要优点是保证和改善设计的可加工性。与传统设计方法相比，这种设计的可加工性要更确定些，因为传统设计方法主要依靠无约束的设计，同时，设计、工艺规划与制造三者之间联系较松散。经验证明，虽然设计人员最初感到有些约束，但能加工出“正确”的零件这一点很快证明这个方法具有足够的吸引力。133位于Internet服务端的工艺规划一旦用户设计完成后，零件造型的电子文件可通过Internet送给远程服务端的工艺规划模块。自动化软件将该设计读入，并确定加工顺序、刀具轨迹、切削参数等。宏规划将各特征进行排序并针对给定夹具生成机加工准备工序。cyberCut目前的宏规划模块具有特征识别能力，它能从25维的实体几何中提取体积特征。该模块的输出不仅仅是一组加工特征，它还提供其他一些很丰富的数据结构，如特征与特征之间的联系。宏规划模块的一个最新进展是它能识别并处理自由表面。微规划与刀具轨迹规划模块将DSG形体分解成具体的刀具运动。打个比方来讲，这就像庭院里用割草机割草的过程一样：每一块草皮由某一直径的刀具将其割去，每次行程之间的覆盖量则由想获得的偏差与表面光滑度来决定。槽的边角也许会用到特别的刀具(正如草坪的边角一样)。自由表面必须分割成一块一块的平面和斜面。其中的平面由投影看上去像螺旋的刀具轨迹产生，而斜面则由切片状的刀具轨迹生成。这样不仅能产生较均匀一致的刀具轨迹，同时也只需中等复杂的计算难度。以上分割目的在于，在给定的公差、光滑度及机床安全性的条件下，优化加工时间。同时，每道工序的加工时间也可估算出来，这些数据反馈给设计人员后，可使他们进行早期机加工成本估计。134位于Internet服务端的铣削加工制造最后，一组数控指令在开放式结构的数控加工中心上实现加工(与之相比，如果服务平台感觉到SFF会更好地服务用户，CyberCut就接通FDM机器)。这里采用的机床是由开放式结构控制的可实现复杂刀具轨迹的加工中心。一个具体的实例则是该机器的插补器可执行由NURBS(非均匀有理B样条)表示的自由轨迹。这种复杂刀具轨迹的加工能力，可使传统的机加工制造出更为复杂的表面，因此，它使得数控加工能与SFF技术在复杂曲面快速成形方面继续竞争。关于开放式结构机床的详细情况则留在第7章介绍机加工时再讨论。图4.17 CyberCut 课题：设计、规划与制造集成- 10 -南通大学毕业设计附录（英文资料翻译）SOUD FREEFORM FABRICATION ISFF) AND RAPID PROTOTYPING11 SOUD FREEFORM FABRICATION ISFF)METHODSSeveral manufacturing processes are available to make the important transition from computer aided design(CAD)to a prototype partSeveral new technologies began to make their appearance after 1987In that year，stereolithography (SLA) was first introduced bv 3D Systems Inc，and over the next five years several rival methods also appearedTllS created the family of processes known as solid freeform fabrication fSFFlAs with most new technologies at the beginning of the“market adoption Sshaped curves”in Chapter 2the SFF domain iS accompanied by a relative amount of advertising“hype”SFF processes are sometimes described as： Parts on demand From arttopart Desktop manufacturing Rapid prototyping At the time of this writing，stereolithography (SLA)，selective laser sintering (SLS)，fused deposition modeling(FDM)，and layered object modeling(LOM) are being used on a day-to-day basis by commercial prototyping companiesThe three-dimensional(3一D)printing process in cornstarch，plastic，and ceramics is also being used commerciallyThe methods lower on the list show promise but do not seem to be in great use by third party prototyping houses to make their daily incomeCasting is a special caseIt is still used to make oneof-akind prototypesFurthermore，for batch runs in the 10 to 500 category it is a very cost effective method to use once an original mold has been made by a process such as stereolithographyMachining isalso used to make oneof a kind or several prototypes111 Summary of SFF and Rapid Prototyping ProcessesIn daily commercial use：Stereolithography (SLA)Selective laser sintering (SI S)Laminated object modeling (LOM)Fused deposition modeling (FDM)More at the research and development(R&D)stage：3-D printing in cornstarch，plastic，or ceramic3-D printing with plastics followed by planarization using machiningSolid ground curing(similar to SLA)Shape deposition modeling ra combination of addition and subtraction) Non-SFF(traditional)：MachiningCasting Comparisons done in the early 1990s by the Chrysler Corporation revealed that the SLA process was ahead of its rival nontraditional prototyping methods in terms of cost and accuracy(these studies excluded an evaluation of machining and casting)Following the technical descriptions in this chapteradditional figures and tables are thus included to compare these costs and accuraciesOver the last decade， SLA has further emerged as the most used SFF process,especially for the generation of the master patterns for casting and injection moldingAt the time of this writing，SLS，FDMand LOM have the most visibility after SLA112 The History of SFF MethodsDuring the late 1970s,Mead and Conway(1980)created the groundwork for the fast prototyping of very large scale integrated(VLSll circuitsDesigners were encouraged to think in terms of five two-dimensional(2D)patternsThese patterns defined three stacked interconnection layers on a metaloxidesemiconductor fMOSl wafer and their mutual connections through holesThe patterns descry bed the actual geometrv of the connection runs and via holes that one would see when looking down onto the circuit chip，regardless of the exact process and number of masking steps that were used to implement the chip(see MOSIS,2000) Inspired by this success，beginning in the 1970s,several companies tried to create layered manufacturing for mechanical partsAISO by the mid1980s,severa U.Sgovernment studies analyzed the possibilities of a“mechanical MOSIS”(Manufacturing Studies Board，1990；Bouldin，1994；NSF workshop I，1994，and II，1995) The prospects for a mechanical MOSIS were thus frequently linked to the fabrication processes in the lists mentioned(Ashley,1991，1998；Heller，1991；Kruth，1991；Woo，1992，1993；Au and Wright，1993；Kochan，1993；Kai，1994；UCLA，1994；Wleiss and Prinz，1995；Cohen et a1，1995；Dutta，1995；Jacobs，1992，1996；Beaman et a1，1997；Kumar et a1，1998；Sachs et a1，2000) The introduction of the first commercial SFF technology-stereolithography-was accompanied by the advent of the STereoLithography (STL)representation of a CAD obiect“STUis a modified CAD format that suits a subsequent slicing operaction and the“downstream”laserscanning paths on a physical SLAFDMor SLS machine Is a soccer ball round? The answer depends on how carefully the balIis measuredNominally,it is a perfect sphereHoweveron closer inspectionthe leather is sewn together from about 20 little hexagonal patches and a few pentagonal patches to create the curvatureIn reality it is an approximation to a sphere Likewisethe“STLformat approximates the boundary surfaces of a CAD model by breaking it down into interconnected small triangles-a process called tessellationEach triangle is represented by the xyz coordinates of each of its three vertices,enumerated by the righthand rulethat isCounterclockwise (ccw) order as viewed from the outside of the bodv The vector normal to the surfaee of each triangle is also specified1his tessellated surface is stored as an“STL file”this filePerhaps containing up to 200，000 triangles，is sent over the Internet to a prototyping shop As shown in Figure 41this tessellated CAD model is then sliced like a stack of playing cardsFor 3D Systemsmachines this is known as the SLI or sliced fileOther rapid prototyping machines use the slicing technique but have their own file creation details and namesEach slice for the imaginary soccer ball will thus be a circleHoweverbecause of the tessellation procedure it will not be a perfect circleThe slicing action cuts through the triangles on the boundaryThus，each circular slice (or disc will actually be a multisided polygon running inside the“bounding circle”The number of sides on this inner polygon is of course related to how finely divided the original tessellation was made Inside the SLA machinethe laser first creates the outer boundary of each slice and then“weaves”across each slice in a hatching pattern to create the layerThe number of slices and the style of the weaving pattern are chosen by each rapid proTotyping shopEspecially for SLA and SLS a certain amount of trial and errorOr craftspersonship，begins to play a role at this stageThis is reviewed in more detailover the next few pages “STL，is now the standard exchange format for SFF processesHoweverit is inadequate for many reasonsFirst，the files are large due to the tessellation methodSecondthere are redundancies in the“STLformat0ne example of redundancy is as follows：the triangles are represented by the“counterclockwise rule”so that it is clear in which direction the outer-surface normal actsHoweverit has also become customary to specify the surface vector as wellInconsistency can be introduced as a result of this redundancy, and no rules exist for resolving it McMains (1996)describes how“STLdoes not capture topology or connectivity, making it difficult to fix some of the common errors found in filessuch as cracks，penetrating or extraneous faces，and inconsistent surface normals without resorting to guessing the designers original intentMore general digital interchange formats have also been used with SFlF These include ACIS(1993)and IGES (Heller，1991)However，as described in NSF(1995)，problems arise with these formats，too One aspect of ongoing research is thus to improve this representation language (McMains et a1，1998)12 CASTING METHODS FOR RAPID PROTOTYPING121 IntroductionThe classic manufacturing texts by DeGarmo and associates(1997)，Kalpakjian (1997)，Schey (1999)，and Groover (1999)are remarkably comprehensive in their coverage of the casting processThe several methods of casting include：Lost-wax investment castingCeramic-mold investment castingShell molding Conventional sand molding Die casting Rather than duplicate the material found in other books, this section focuses on casting as it is done by rapid prototyping companiesBatch sizes from 50 to 500 are typicalThe key market strategy is that casting is cheap and fastHowever，it may not be the choice for the final product because of its tolerancesDepending on the type of casting chosen，the tolerances vary from+/一75 microns(0003 inch)for lost-wax processes to+一375 microns(0015 inch)for standard sand castings(also see Chapter 2)122 LostWax Investment CastingAs mentioned in Chapter 1the fundamentals of casting were invented by Korean and Egyptian artists many centuries agoThe following steps are known as the lost-wax investment cas“ng process(Figure 416)：(ac)a master pattern of an engineering or art object is first carved from wax；(d-f)it is surrounded by a ceramic slurry that soon sets into solid around the wax；(g)the wax is melted out through a hole in the bottom，leaving a hollow cavity；(h)this hole is plugged，and liquid metal is poured into the open cavity from the top；(i)after a while，the metal solidifies and the ceramic shell can be broken away to get the part；(j)some cleaning，deburring ，and polishing are needed before the object is finished The process was greatly improved and made more accurate during World Warn II for aeroengine componentsToday it is used for products such as jet engine turbine blades and golf club headsOn the top line of Figure 416wax patterns are formed from injection molds，assembled on treelike forms，and then treated with the slurry Alternate layers of fine refractory slip (zircon flour at 250 sieve or mesh size) are applied，followed by a thicker stucco layer( sillimanite at 30 sieve or mesh size)The coated components are dipped in fluidized beds that contain isopropyl silicate and liquid acid hardenerDrying takes place in ammonia gasThe next step is to eliminate the wax in a steam autoclave at 150。C，fire the mold for 2 hours at 950。C，then pour in the liquid steel or aluminum In summary, the modern lost-wax method has one of the best tolerances in the casting family because the original wax patterns are made in nicely machined molds Today, tolerances of+-75 microns r0003 inch)are readily obtainableAlso the ascast surface is relatively smooth and usable for the same reason0ther advantages include：Figure 416 The lostWax investment casting processUpper diagrams (a) through(C) lead to the tree of Wax master patterns . Middle diagrams show the slurry and stucco being appliedLower diagram shows the casting (adapted from literature of the Steel Founders Society ofAmerica) No parting lines if the wax original is hand finished Waxes with surface texture can give direct features such as the dimples on a Golf club Automation of the slurry dipping is possible using robots，thereby reducing costs Products such as turbine blades can be unidirectionally solidified，giving good mechanical properties in the growing direction123 Ceramic-Mold Investment Casting ProceduresThe snag about the previous method is that the wax pattern is destroyedThe ceramic-mold investment casting technique therefore employs reusable submaster patterns in place of the expendable wax patternsThis version of investment casting ideally involves five steps to make it efficient and to retain，as much as possible，the fine care and expense that go into creating the original master positive in Step 1The steps are as follows：Step 1Positive：make an original master pattern with stereolithography or machining Step 2Negative：create a shell around the master with highly stable resinA negative space is created around the original positive master patternThis shell can be pulled apart to give a parting lineStep 3Positive：create reusable submaster rubbery molds from the shellsStep 4Negative：create the destroyable slurryceramic moldsStep 5Positive：pour metal into the ceramic molds，which are then broken apart to get the components ,which must then be degated and deburred SLA can be used to make the original master pattern，or a CNC machine can be used to mill the master from brass，bronze，or steelOf course，the process can start at Step 3，but this might damage the original master，especially if it is SLAAlsoto get high productivity in the factory ,it is preferable to have many molds at Step 3All of which can be made from the stable resin negative in Step 2 Prototyping companies like to use the hard resin to fabricate the negative in Step 2，because the resin has good dimensional stabilityNote that it is typical to have two resin molds，one for each side of the casting，separable by a parting line Once the hard resin shells have set，they can be filled with a slurry gel that solidifies to a hard“rubbery positive”for Step 3111is intermediate submaster mold can be stripped away from the resin shells while it is still“rubbery”the material is ideal for the rather rough handling environments of a foundry and the rubbery properties mean that no draft angles are needed for stripping these submasters off the resin shells The Step 4 negative mold is made from a graded aluminosilicate with a liquid binder(ethyl silicate)and isopropyl alcoh01This is poured around the submasters from Step 3Once the slurry has set，the two ceramic halves are joined to create the inner cavity ,the slurry is fired at 950。C to give it strength，and the casting processsay with molten aluminum，can begin After solidification，the component is broken out of the ceramic，cleaned up，and deburred The parting line can cause problems，but in general，good accuracy is obtained：+-125 to 375 microns(+-0005 to 0015 inch)124 Shell MoldingAn alternative form of highaccuracy casting is shell moldingMetal pattern plates are first heated to 200。C to 240。CA thin wall of sand，5 to 15 millimeters f025 to 075 inch)thick，is then sprayed over the platesThe sand is resincoated to ensure adhesion to the metal platePhenolic resins, with hexamethylene -tetramine additives，are combined with the silica to ensure rigid thermosetting of the sprayed sandthe next steps are to cure，strip，and dry the sand molds ,which are comparably very accurate for castingOnes the excess sand is removed and casting is finished，accuracies can be as low as+一75 microns f0003 inch)125 Conventional Sand MoldingThe cruder，cheaper version of casting called sand castingA sand impression starting with wooden or plaster patterns is made around the pattern with gates and risers for the poured metalThis gives tolerances of+一375 microns(0015 inch) Newer developments include：1A highpressure ioltand-squeeze method：Here mechanical plungers push the sand against the mold at a jolt of 400 psi This gives a tighter fit of the sand against the pattern and hence better tolerances after casting2Carbon dioxide block molding：Here the interfacing between the sand and the pattern is made up of a special material about 12 millimeters(05 inch)thickIt is a refractory mix of zircon or very fine silicabonded with 6sodium silicate，which is then hardened by the passage of carbon dioxide126 Die CastingDie casting is predominantly done by the highpressure injection of hot zinc into a permanent steel dieToday ,the die or mold for this type of casting is almost certain to be milled on a threeor fiveaxis machine t001 Die costs are relatively highbut smooth components are produced with accuracies in the range of+-75 microns(0003 inch)However，these high costs for the permanent molds mean that die casting does not really fit into the rapid prototyping familyIt is mostly used for large-batch runs of small parts for automobiles or consumer productsSince low melting point materials such as zinc alloys are used in the process，component strengths are relatively modest Today , the injection molding of plastics(Chapter 8)is often preferred over zinc die casting13 MACHINING METHODS FOR RAPID PROTOTYPlNG131 OverviewChapter 7 deals with the generalized machining operation including the mechanics of the processThis chapter focuses on advances in CAD，CAM software that allow CNC machining to be more of a“turnkey rapid prototyping”processOne goal is to fully automate the links between CAD and fabricationAnother goal is to minimize the intensely hands-on craft operations(eg，process planning and fixturing )that demand the services of a skilled machinist CyberCut0M is an Internetbased experimental fabrication test bed for CNC machiningThe service allows client designers on the Internet to create mechanical components and submit appropriate files to a remote server for process planning and fabrication on an openarchitecture CNC machine t001Rapid tool-path planningNovel fixturing devices ,and sensor-based precision machining techniques allow the original designer to quickly obtain a high-strength，goodtolerance component (Smith and Wright，1996)132 WebCAD ：Design for Machining on the Internet”On the Client SideA key idea is to use a“process aware”CAD tool during the design of the partThis prototype system is called WebCAD (Kim et a1，1999)Sun MicrosystemsJava a portable，objectoriented，robust programming language similar to C+is being used as a framework for serving miniapplicationsThe GUI is a 25D featurebased。design system that uses the destructive solid geometry(DSG)idea introduced in the last chapter ( Cutkosky and Tenenbaum ，1990；Sarma and Wright，1996)Recall that the user starts out with a prismatic stock and removes primitives or “chunks” of materialBy contrast，conventional constructive solid geometry(CSG)means building up a part incrementally from“nothingnessIn the “destructive” paradigminstead of allowing arbitrary removal，the user is also constrained to removing certain shapes of material，referred to as featuresThese features take the form of pockets，blind holes，and throughholes WebCAD also contains an expert system capturing rules for machinabilityAt the top of Figure 417the designer is shown being guided by these rulesFor exampleA forbidden zone” is imposed around a through-hole feature to prevent it from being designed too close to an edgeIn the event that the designer violates a rule，a “popUp” window advises on an appropriate remedy by moving the hole further into the block-typically bv its radius dimensionWebCAD also uses ar、，SI、VYG what you see is what you get”)environment，with explicit cutting tool selection and visible comer radii on pocketsAt the time of this writing，further improvements also include freeform is face editing and selection of different cutting tool sets depending on final fabrication location(Kim，2000) The rationale for imposing destructive features upon the designer is that each of these features can readily be mapped to a standard CNC milling processThe scheme thus resembles the interaction between a word processor and a printer regarding the“printability”of the documentIt is easy to criticize that the restriction to DSG limits the set of parts that can be designedHoweverthe key advantage of this design environment is that the design-to-manufacture process is more deterministic than conventional methods，which rely on unconstrained design and on looser links between design，planning，and fabricationExperience shows that designers are

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