Rapid Prototyping and manufacturing
Introduction
The term “rapid prototyping” (RP) is a relatively new expression for the generation of three-dimensional models manufactured without the need for machining or products designed on a computer aided design system, the first rapid prototyping system was introduced on to the US market in 1988 and gave the engineer the opportunity to produce 3 dimensional objects directly from Computer Aided Design (CAD) date and succeed in the cost-effective production of patterns and moulds with complex surfaces. The principle advantages of using this technology are: High speed at which the solid model is generated. The complexity of the model does not form any limitation to its production. The early use of these models was to assist the designer in determining fitnes s and form. It also provided the sales team with a 3 dimensional object to show to a prospective customer, this being far better than the traditional orthographic drawing which many people find difficult to interpret.
The benefits of RP:

  1.Converts 3D CAD images into accurate physical models at a fraction of the cost of traditional methods.
  2.Improves design communication and helps eliminate design mistakes.
  3.Reduces “time to market” for a new product.
  4.Can be used as a powerful marketing tool since the prototype can be seen rather than the drawing.
  5..The development of this technology has reached into many of the traditional fields, attracting the interest of artisans whose skill any knowledge has led to 3-D objects being used directly and indirectly as patterns and model for soft tooling.
  6.Production of models by machining has a number of limitations.
  7. Material removed during forming is difficult to reclaim.
  8.Machining in the form of drilling turning milling spark erosion etc., is limited by the shapes it can produce.
  9.In the event of design change, conventional tooling such as patterns ,core boxes, dies, jigs etc. ,become expensive to alter ,and in many cases, may require complete re-manufacture. What RP&M CAN DO? To substantially shorten the time for developing patterns, moulds, and prototypes, some manufacturing enterprises have started to use rapid prototyping methods for complex patterns making and component prototyping. Over the past few years, a variety of new rapid manufacturing technologies, generally called Rapid Prototyping and Manufacturing(RP&M),have emerged ;the technologies developed include Stereo lithography (SL), selected laser sintering(SLS),fused deposition modeling(FDM),laminated object manufacturing(LOM),and three dimensional printing (3D Print).They have a common important feature ;the prototype part is produced by adding materials rather than removing materials. This simplifies the 3D part producing processes to 2D layer adding processes so that a part can be produced directly from its computer model. rapid prototyping differs with conventional manufacturing methods by adding material layer
by layer until the desired sharp is achieved, immediately reducing or avoiding the loss of material. THE BASIC PROCESS IN RP RP machines process CAD data by slicing the computer model into layers ,each layer being typically
  0.1-
  0.25mm thick the machine then uses this data to construct the model layer by layer ,each layer being bonded to the previous until a solid object is formed. Due to this laminated method of construction a stepped surface is developed on curved faces, the removal of which is essential if maximum advantage of the process is to be realized. Schematic representation of the stepped construction, which requires post processing, is on the above Figure
  8.
  1. DEVELOPMENT More recent developments have been prompted by problems caused by the expansion of the model where it is used as a disposable pattern (like the wax pattern in the lost wax process), Where the resin model is produced to form solid walls, expansion during the “burning-out” stage weakens the ceramic shell, and can cause failure in the firing and/or casting stages. The company, 3D System GmbH, has developed a machine and software, which together allow for the model to be constructed in the form of a honeycomb. The honeycomb structure collapses in on itself during “burning-out” thus avoiding the problems of expansion. Each pocket of the honeycomb structure is connected to its neighbor by a small hole that allows for the uncured resin to be drained prior using. Other methods of producing tooling directly from the rapid prototype -such as metal spraying ?are also being developed, and this seems to have potential in the production of less complex parts, although it is inevitable that some detail will be lost. Prototyping Company ARRK EUROPE LTD, London, has developed a thin layer technology, which removes many of the inaccuracies inherent in mechanical finishing. It claims to be the first company in the world to achieve
  0.05mm layer build accuracy. ARRK’s development team used a combination of subtle mechanical alterations to setting up of its four stereo lithography (SL) rapid prototyping machines and proprietary techniques to over come de-wetting. It also called upon its knowle dge of resins. THE BASIC PROCESS IN RP RP machines process CAD data by slicing the computer model into layers ,each layer being typically
  0.1-
  0.25mm thick the machine then uses this data to construct the model layer by layer ,each layer being bonded to the previous until a solid object is formed. Due to this laminated method of construction a stepped surface is developed on curved faces, the removal of which is essential if maximum advantage of the process is to be realized. Schematic representation of the stepped construction, which requires post processing, is on the above Figure
  8.
  1. Using this new technology, the company is now able to produce extremely accurate high-quality master parts and tooling. With
  0.05mm layer, the build is more precise and all but eliminates the stair-stepping effect. In addition, the need for finishing is dramatically reduced. As a result, the process is ideal for switches, electronic components or any finely details part. Current Application Areas of RP&M Design Engineering (
  1) Visualization With RP&M, the prototype of a complex part can be built in short time, therefore engineers can
evaluate a design very quickly, for it isn’t difficult to visualize exactly what the actual complex product will look like. (
  2) Verification and optimization Improving product quality is always an important issue of manufacturing. An RP&M prototype can be produced quickly without substantial tooling and labor cost. As a result, the product quality can be improved within the limited time frame and with affordable cost. (
  3) Iteration With RP&M technology, it is possible to go through multiple design iterations within a short time and substantially reduce the model development time. Manufacturing We can use the RP&M prototype for productively studies. By providing a physical product at an earlier design stage, we can speed up process planning and tooling design. In addition, by accurately describing complex geometry, the prototype can help reduce problems in interpreting the blue prints on the shop floor. It can also be used in tooling development for mould and master pattern for castings. Marketing To assist product sales, a prototype can be used to demonstrate the concept, design ideas, as well as the company’s ability to produce it. The reality of the physical model illustrates the feasibility of the design. Also, the prototype can be used to gain customs’ feedback for design modification so that the final product will meet customs’ requirement.
快速成型和生产
介绍 快速成型这个术语是对于不通过机器和工具的三维造型生产而产生的一种新的相关的 表示.通过快速生产的准确能力,用电脑设计系统帮助切实的造型的设计生产,第一个快速成 型的系统于 1988 年在美国的市场内被引进并且给工程师一个通过 CAD 来设计三维实物的 机会且成功的生产出复杂表面的模型. 使用这项技术的操作优势如下: 固态模型的高速产生. 这个模型的复杂性对于生产不能形成任何的限制. 最早使用这些模型是用来帮助设计者决定形状和适当性.它也能提供给预期的顾客展示 三维实物的销售群,这将远远优于那些很多人发现很难去解释的传统直角作图. 快速成型的好处:
  1.一小部分传统方法的价值是把准确的物理模型转化成三维影象.
  2.改进设计的讯息帮助删除设计的错误.
  3.对于新的产品减短上市的时间.
  4.自从原形相比做图更能被理解后它就能作为一种强有力的工具.
  5.这技术的发展到达了入许多传统领域, 吸引技巧和知识导致了直接地和间接地使用作 为样式和模型的三维对象为软的工具模型。
  6.模型的生产是通过用机器制造有一定数量的限制。
  7.在成形期间被除去的材料是难回收的。
  8.用机器制造以钻井转动的碾碎的火花电蚀等的形式。 由它可能导致的形状限制。
  9.在设计变动情形下,常规凿出的装饰例如样式,核心装箱,模子,夹具等。 变得昂 贵而难变更,并且在许多情况下,可以要求完全再制造。快速成型法是不同于以通过增加物
质层数的常规制造方法,直到达到所期望的锐利程度,立刻减少或避免材料的损失层数。 RP&M 能做什么? 为开发的样式、 模子和原型去极大地缩短时间。 一些制造业企业开始对于一些复杂部件 的制造和成型的成分使用快速成型的方法。在过去几年,各种各样新的迅速制造业技术,通 常称为快速成型和制造(RP&M) ,已经涌现了;被开发的技术包括立体声石版印刷(SL),所 选择的激光焊接(SLS),合并的证言塑造(FDM),薄片叠成物体的制造业(LOM),和 3D 打印(3D Print)。 他们有一个共同的重要特点; 原型零件是通过增加材料而不是除去材料导致的。 这简 化 3D 部分生产过程到增加过程的第 2 层数,以便零件可以直接地由它的计算机模型生产。 快速成型的基本过程 快速成型的机器是通过切计算机模型来制造处理 CAD 数据入层数,每层数是典型地
  0.1-
  0.25 毫米厚的机器然后使用这数据一层一层去修建,每一层都将被拈合成以前的样子直 到一个坚实对象被形成。 由于这个建筑被碾压的方法一个有台阶的表面在弯曲的表面上被开 发,如果过程的最大好处被了解,那么其中是根本的将被撤除,有台阶建筑的图示,是要求 分步处理的. 发展 更多的发展由与模型的扩展而引起的问题已经提示了,使用它就像一个一次性部件(象 蜡本身在失去蜡过程中),那里的合成树脂模型导致了形成坚实的墙壁,扩展在“燃烧的” 阶段期间来减弱陶瓷的外壳,并且在生火和铸件阶段都能导致失败。 3D 系统 GmbH 公司,开发了机器和软件,一起允许模型以蜂窝的形式被修建。 蜂窝结 构在本身崩溃在“燃烧的”因而避免扩展的问题。 蜂窝结构的每个口袋通过一个小孔连接 到它的旁边从而考虑到未固化的树脂在使用之前被排泄出去。 其它快速成型的工具直接加工的方法-比如金属喷镀-也被开发,并且看上去这在较不复杂零 件的生产似乎有潜力,但不可避免的一些细节将丢失。 ARRK 有限公司是快速成型的欧洲公司,伦敦,已经开发了薄片技术,这除去了很多在机械 加工中固有的不准确性。 他们宣称他们是世界上第一家能够达到
  0.05 毫米厚度的准确制造。 ARRK 的开发小组使用了微妙的机械改变的组合到它的四个立体声石版印刷(SL), 快速成型的 机器安装,并且私有的技术去克服湿度。 它也要求了对于树脂的知识. 使用这种新技术,公司现在能生产极端准确优质主要零件和工具。 以
  0.05mm 层数, 所有的修造是精确的,除了消灭台阶跨步的作用。 另外,显著减少对精整的需要。 结果, 过程作为理想的开关,电子元件是理想的或其中任一微小的详细的部件。 快速成型和制造的当前应用的区域 设计工程 (
  1) 形象 运用快速成型和制造技术, 一个复杂部分的原型在短期可以被制作,因此工程师能非常迅 速的评估设计,因为这很难确切的使实际复杂的产品看上去形象化。 (
  2) 证明和优化 改进产品质量总是制造业的一个重要问题。 快速成型和制造能够快速的生产不用坚固的工具 和人工成本。结果,产品质量可以改进在有限的时间表之内和以付得起的费用。 (
  3) 叠代 运用快速成型和制造技术, 在短时间内审阅多样的设计叠代和极大地减少式样研制时间是可 能的。 制造 我们可以为有生产力地使用快速成型和制造原型学习。 通过提供一个物理产品在更加 初期的设计,我们可以加速处理计划和凿出的装饰设计。 另外,通过准确描述复杂几何,
原型在解释方案可能帮助减少问题在车间上。 可能也用于工具的发展为模子和主模浇铸。 营销 要协助产品销售,原型可以用于展示概念,设计想法,是由
 

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