机械工程英语第二版-part2-第11单元翻译(共7页).docx

精选优质文档-倾情为你奉上Unit11 Rapid Prototyping and Manufacturing Technologies 快速成型与制造技术Introduction 导言Manufacturing community is facing two important challenging tasks: Substantial reducition of product development time; and Improvement on flexibility for manufacturing multi-variety and small batch-size products. Computer-aided design and manufacturing(CAD and CAM) have significantly improved the traditional production design and manufacturing. However, there are a number of obstacles in true integration of computer-aided design with computer-aided manufacturing for rapid development of new prodcts.制造社会面临两个重要的富有挑战性的任务：大幅度减少产品开发时间，提高多种产品，小批量大小产品的制造灵活性。计算机辅助设计与制造(CAD 和 CAM)有着显著改善了传统的产品设计及制造。然而，在新产品快速开发方面有一些障碍，这些障碍阻碍着计算机辅助设计与计算机辅助制造的真正集成。To substantially shorten the time for developing patterns, moulds, and prototypes, some manufacturing enterprise have started to use rapid prototyping(RP) methods for complex partterns 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),selective laser sintering(SLS), fused deposition modeling(FDM), laminated object manufacturing(LOM), and three dimensional printing(3D Printing). These technologies are capable of directly generating physical objects from CAD databases. They have a common important feature: the prototype part is produced by adding materials rather than removing materials, that is , a part is first modeled by a geometric modeler such as a solid modeler, and then is mathematically sectioned(sliced) into a series of parallel cross-section pieces. For each piece, the curing or binding paths are generated. These curing or binding paths are directly used to instruct the machine for producing the part by solidifying or binding a line of material. After a layer is built, a new layer is built on the previous one in the same way. Thus, the model is built layer by layer from the bottom to top.为了大大缩短母模，模具和样件的制作时间，一些制造厂开始利用快速原型制造技术(RP)来制作复杂的母模和零部件的原型。在过去的几年，各种新型的快速制造技术，通常称为快速成型制造(RP&M)已经出现.已开发的技术包括立体光刻(SL), 选择性激光烧结(SLS)，熔融沉积制造(FDM)，分层实体制造(LOM)和三维打印(3D Printing)。这些技术都是直接从CAD数据库生成物体的能力。它们都有一些共同的重要特征：原型件都是通过增材制造，而不是材料去除工艺制作的，也就是说，零件首先通过几何建模软件，如一个零件建模模块来建模，然后用数学的方法进行切层处理，使其成为一连串平行的横截面片，每一平行的横截面片固化的或者具有约束力的路径便生成了。这些固化的或具有约束力的路径就直接用于指导机器通过固化的或者具有约束力的线性层材料生产零部件。每建完一层材料实体，新一层材料实体就会以相同的形式建立在前一层材料实体上。因此，模型是从下到上一层一层建立起来的。RP Processes 快速成型过程As mentioned earlier, there are several technologies available for model production based on the principle of "growing" or "additive" manufacturing. The major differences among these technologies are in two aspects: (1) Materials used, and (2) Part building techniques. The following sections will explain in detail these rapid prototyping technologies with respect to the above two aspects.如前所述，有几种技术的模型制作上载于“成长“或“添加剂“的制造原则为基础。在这些技术的主要区别是在两个方面：(1)所用材料，以及(2)零件创建技术。下面几节将详细说明就上述这些快速原型技术的两个方面。1.Stereolithography 1.光固化成型机Stereolithography apparatus (SLA) was invented by Charle Hull of 3D Systems Inc. It is the first commerically available rapid prototyper and is considered as the most widely used prototyping machine. The material used is liquid photo-curable resin. acrylate. Under the initialtion of photons, small molecules(monomers) are polymerized into large molecules. Based on this principle, the part is built in a vat of liquid resin as shown in Fig1.1.光固化成型机是由3D System公司的Charle Hull发明。 它是世界第一台使用最广的商业快速成型机。使用的材料为丙烯酸光敏树脂。 在光子的引发下，小分子(单体)聚合成大分子。 原型零件就是根据这一原理从树脂槽中制作出来的。如图1.1所示。The SLA machine creates the prototype by tracing layer cross-section on the surface of the liquid photopolymer pool with a laser beam. Unlike the contouring or zigzag cutter movement used in CNC machining, the beam traces in parallel lines. The laser beam is deflected horizontally in X and Y axes by galvanometer-driven mirrors so that it move across the surface of the resin to produce a solid pattern. After a layer is built, the elevator drops a user-specified distance and a new coating of liquid resin covers the solidified layer. A wiper helps spread the viscous polymer over for building the next layer. The laser draw a new layer on the top of the previous one. In this way, the model is built layer from bottom to top.光固化成型机通过激光光束对液体感光树脂池面层的横截面进行跟踪的方式创建原型。同数控机床加工时刀具的轮廓走刀和循环走刀方式不一样，激光束是以平行方式扫描的。激光束通过振镜驱动水平在XY轴偏转，这样它跨越了树脂表面产生固体模型，创建好一层横截面片后，升降机下降一个用户指定的距离，新的液态树脂固化涂料就覆盖了上一个固化层，刮板用来将粘稠的树脂均匀涂覆在零件上表面以便于下一层的制作。 激光在前一层的顶部进行新一层的扫描。这样原型就自下而上地逐层制作而成。There are several features worthy of mentioning of SLA.(1)Material.There are five commercially available photopolymers. All of them are a kind of acrylate.(2)Support.Because a model is created in liquid, the overhanging regions of the part (unsupported below) may sag or float away during the building process. The prototye thus needs some predesigned support until it is cured or solidified. These additional features are built on the model parts and have to be trimmed after the model building is completed.(3)Model accuracy and performance.The accuracy achieved is about 0.1% of the overall dimension and deteriorates with larger sizes but no more than 0.5%. The layer thickness is between 0.004¨ and 0.03¨. Presently, the SLA machines made by 3D Systems Inc. are the most accurate machines among the RP& M systems.有很多值得一提的SLA几个特点。(1)材质。有五个商用光聚合物。他们都是一类的丙烯酸酯。(2)支持。由于模型是建立在液体之上的，零件的悬垂区域在创建过程中可能下垂或者漂浮。因此快速成型在零件凝固化或者固结家有时需要一些预先设计的支持。这些额外的特征是建立在模型零件之上的，所以必须在模型创建完成后对其进行必要的修剪。(3)模型精度与性能。整体模型大小精度达到0.1%左右，当精度超过0.1%但不超过0.5%时就会恶化。每一截面层的厚度在0.004¨与0.03¨之间。目前，由3D System公司开发的SLA机械是RP&M系统中精度最高的机械。2.Selective laser sintering(SLS) 选择性激光烧结(SLS)SLS uses a carbon dioxide laser to sinter successive layers of powder instead of liquid.In SLS processes, a thin layer of powder is applied by a rotating roller mechanism onto the work place. The powder material is preheated to a temperature slightly below its melting point. The laser beam traces the cross-section on the powder surface to heat up the powder to the sintering temperature so that the powder scanned by the laser is bonded. The powder that is not scanned by the laser will remain in place to serve as the support to the next layer of powder, which aids in reducing distortion. When a layer of the cross-section is completed, the roller levels another layer of powder over the sintered one for the next pass. Fig.11.2 shows the working principle of SLS.选择性激光烧结采用二氧化碳激光代替液体激光烧结粉末，在选择性激光烧结过程中，一层薄薄的的粉末采用一种旋转滚轴机制实用分布到工件上。该粉末材料预热到稍低于其熔点的温度。激光光速追踪粉末表面横截面的加热温度使表面温度达到烧结温度，这样就可以使得激光扫描的粉末结合。而对于未经过激光扫描的粉末将保留在原地以为支撑下一粉末层服务。这些粉末可辅助减少截面层的扭曲。当一个横截面层完成后，为了方便下一次通过已烧结的横截面层滚轴将新一层的粉末层与烧结层上一层对齐。图11.2显示了SLS的工作原理。3.Fused deposition modeling(FDM) 熔融沉积制造(FDM)In an FDM process as shown in Fig.11.3, a spool of thermoplastic filament feeds into a heated FDM extrusion head. The movement of the FDM head is controlled by computer. Inside the flying extrusion head, the filament is melted into liquid(1 above the melting temperature) by a resistance heater. The head traces an exact outline of each cross-section layer of the part. As the head moves horizontally in X and Y axes, the thermoplastic material is extruded out of a nozzle by a precision pump. The material solidifies in 1/10 second as it is directed onto the workplace. After one layer is finished. the extrusion head moves up a programmed distance in Z direction for building the next layer. Each layer is bonded to the previous layer through thermal heating.图11.3中显示了熔融沉积制造的过程。一卷热塑性长丝进给挤压进一个加热的FDM挤压头。FDM的头部运动由电脑控制，在高速运动的挤压头里，丝材被电阻加热到融化成液态(高于熔点1).挤压头精确按零件截面轮廓形状移动(从而逐层将原型零件制作出来)。随着挤压头小平地在XY轴上移动，热塑性材料通过一个精密泵挤压出一个喷嘴。随着材料接触到工件，热塑性材料将在1/10内凝结。当一层完成后，为创建下一层挤压头在Z轴方向移动一个已编程好的距离。通过热电阻加热，每一层材料都与上一层材料很好的结合。4.Laminated object manufacturing(LOM) 分层实体制造(LOM)The LOM processes produce parts from bonded paper plastic, metal or composite sheet stock. LOM machines bond a layer of sheet material to a stack of previously formed laminations, and then a laser beam follows the contour of the part cross-section generated by CAD to cut it to the required shape. The layers can be glued or welded together and the excess material of every sheet is either removed by vacuum suction or remains as next layer's support. Fig.11.4 shows the working principle of LOM.在分层实体制造过程中，通过将纸质塑料，金属或者复合薄板材料进行结合生产零件。分层实体制造机将一层薄板材料与先前生成的叠片结构结合，然后采用激光光束沿着由CAD产生的零件横截面轮廓切出所需的形状。叠片层可以通过粘合或者焊接在一起，每片多余的材料可以采用真空抽取的方法去除也可以保留作为下一层的支撑。图11.4显示了分层实体制造(LOM)的工作原理。5.Three-dimensional printing(3D Printing) 三维打印Three-dimensional printing was developed at Massachusetts Institute of Technology. In the 3D printing process, a 3D model is sliced into2D cross-section layers in a computer. A layer of powder is spread on the top of the pistom, the powder bed, in a cylinder, and then an ink-jet printing head projects droplets of binder material onto the powder at the place where the solidification is required according to the information from the computer model. After one layer is completed, the piston drops a predefined distance and a new layer of powder is spread out and selectively glued. When the whole part completed, heat treatment is required to enhance the bonding of the glued powder, and then the unbounded powder is removed. FIg.11.5 showns the working process of 3D Printing.三维打印技术是由美国麻省理工学院开发出来的。在三维打印过程中，计算机中的三维模型被切成二维横截面层，首先在气缸的活塞(粉料床)顶部铺上一层粉末，然后一个喷墨打印头根据计算机模型信息在要求固化的粉末部分表面喷上粘结材料。一层完成后，活塞下降预定距离，新层粉末分散开并进行选择性的粘合。当整个零件完成后，为增加粘合粉末的粘合需要对零件进行热处理，热处理后无粘性的粉末也被移除。图11.5显示了三维打印的工作原理。Current Applications of RP&M 快速成型技术的应用现状A large number of industrial companies such as Texas Instruments, Inc., Chrysler Corporation, Amp Inc. and Ford Motor Co. have benefited from applying the technologies to improve their product development in the following three aspects.许许多多的公司如得克萨斯仪器公司，克莱斯勒公司，AMP公司和福特汽车公司工业公司得益于应用技术以提高其在以下三个方面的产品开发。1.Design engineering 设计工程(1)Visualization. Conceptual models are very important in product design. The touch of the physical objects can reveal unanticipated problems and sometimes spark a better design. With RP&P, the prototype of a complex part can be built in a short time, therefore engineers can evaluate a design very quickly.(1)可视化。在产品设计过程中概念模型是非常重要的。触摸真实的物理实体可以暴露某些无法预料的问题，有时还会引发出更好的设计。随着快速成型技术的发展，一个复杂的零件原型可以在短时间内完成，因此工程师们可以很快的对设计进行评估。(2)Verification and optimization 验证和优化Improving product quality is always an important issue of manufacturing. With the traditional method, developing of prototypes to validate or optimize a design is often time-consuming and costly. In contrast, an RP&M prototype can be produced quickly without substantial tooling and labour cost. Consequently, the verification of design concepts becomes simple: the product quality can be improved within the limited time and with affordable cost.提高产品质量始终是制造业的重要问题。采用传统的方法来验证原型开发或优化设计往往是费时又费钱。与此相反，快速原型制造原型可以快速的生产，没有大量的工具和劳动成本的消耗。因此，设计概念验证变得简单：产品质量可以在有限的时间和可承受的成本范围内得到提高。(3)Iteration 迭代Just like the automotive industry manufacturers often put new product models into market. With RP& M technology, it is possible to go through multiple design iterations within a short time and substantially reduce the model development time. 就像一些汽车行业的制造商经常将新产品投入到市场中。有了快速原型与制造技术，就有可能在较短时间里通过多次设计迭代，从而大大减少模型的开发周期。2.Manufacturing 制造We can use the RP&M prototype for producibility studies. By providing a physical product at an earlier design stage, we can speed up process planning and tooling design. In addtion, by accurately describing complex geometry, the prototype can help reduce problems in interpreting the blue prints on the shop floor. Another application is tooling development for moulds.The prototypes can also be used as master patterns for castings.我们可以利用RP&M原型进行生产研究。在早期设计阶段通过提供一个实体产品，我们就可以加速过程规划与工具的设计。此外，在工厂内原型可以帮助减少工程图翻译问题。另一个应用是工装模具的开发。该原型也可以用作铸件主模式。3.Marketing 市场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. Also, the prototype can be used to gain customers' feedback for design modifications so that the final product will meet customers' requirements. Meeting customers' demands in a timely manner is the key to penetrating the market in today's economy.为了帮助产品销售，原型可用来验证设计概念，设计思路以及公司的生产能力。此外，原型可以用来获得客户对设计的修改意见，使最终产品满足客户的需求。在今天的经济市场情况下，及时地迎合顾客的需求是打入市场的关键。专心-专注-专业