OVERVIEW
Today’s industries cannot survive worldwide competition unless they introduce new products with better quality（quality，Q），at lower cost（cost，C），and with shorter lead time（delivery，D）．Accordingly，they have tried to use the computer’s huge memory capacity，fast processing speed，and user-friendly interactive graphics capabilities to automate and tie together otherwise cumbersome and separate engineering or production tasks，thus reducing the time and cost of product development and production[1]．Computer-aided design（CAD），computer-aided manufacturing（CAM），and computer-aided engineering（CAE）are the technologies used for this purpose during the product cycle．Thus，to understand the role of CAD，CAM，and CAE，we need to examine the various activities and functions that must be accomplished in the design and manufacture of a product．These activities and functions are referred to as the product cycle．The product cycle described by Zeid（1991）is presented here with minor modifications，as shown in Fig. 10-1．
As indicated by the boxes bounded by solid lines in Fig. 10-1，the product cycle is composed of two main processes：the design process and the manufacturing process．The design process starts from customers’demands that are identified by marketing personnel and ends with a complete description of the product，usually in the form of a drawing．The manufacturing process starts from the design specifications and ends with shipping of the actual products．
The activities involved in the design process can be classified largely as two types：synthesis and analysis．As illustrated in Fig. 10-1，the initial design activities（such as identification of the design need，formulation of design specifications，feasibility study with collecting relevant design information，and design conceptualization）are part of the synthesis subprocess．That is，the result of the synthesis subprocess is a conceptual design of the prospective product in the form of a sketch or a layout drawing that shows the relationships among the various product components[2]．The major financial commitments needed to realize the product idea are made and the functionality of the product is determined during this phase of the cycle．Most of the information generated and handled in the synthesis subprocess is qualitative and consequently is hard to capture in a computer system．
Once the conceptual design has been developed，the analysis subprocess begins with analysis and optimization of the design．An analysis model is derived first because the analysis subprocess is applied to the model rather than the design itself．Despite the rapid growth in the power and availability of computers in engineering，the abstraction of analysis model will still be with us for the foreseeable future．The analysis model is obtained by removing from the design unnecessary details，reducing dimensions，and recognizing and employing symmetry．Dimensional reduction，for example，implies that a thin sheet of material is represented by an equivalent surface with a thickness attribute or that a long slender region is represented by a line having cross-sectional properties．Bodies with symmetries in their geometry and loading are usually analyzed by considering a portion of the model．In fact，you have already practiced this abstraction process naturally when you analyzed a structure in an elementary mechanics class．
Once a design has been completed，after optimization or some tradeoff decisions，the design evaluation phase begins．Prototypes may be built for this purpose．The new technology called rapid prototyping is becoming popular for constructing prototypes．This technology enables the construction of a prototype by deposition layers from the bottom to the top．Thus it enables the construction of the prototype directly from its design because it requires basically the cross-sectional data of the product．If the design evaluation on the prototype indicates that the design is unsatisfactory，the process described is repeated with a new design．
When the outcome of the design evaluation is satisfactory，the design documentation is prepared．This includes the preparation of drawings，reports，and bills of materials．Conventionally，blueprints are made from the drawings and passed on to manufacturing．
As illustrated in Fig. 10-1，the manufacturing process begins with process planning，using the drawings from the design process，and it ends with the actual products．The outcome of process planning is a production plan，a materials order，and machine programming．Other special requirements，such as design of jigs and fixtures，are also handled at this stage．The relationship of process planning to the manufacturing process is analogous to that of synthesis to the design process：It involves considerable human experience and qualitative decisions．This description implies that it would be difficult to computerize process planning．Once process planning has been completed，the actual product is produced and inspected against quality requirements．Parts that
pass the quality control inspection are assembled，functionally tested，packaged，labeled，and shipped to customers．
NOTES：
[1]本句主要结构是They have tried to use... to automate... and tie...，其中to use有3个并列宾语；separate此处为形容词，义“分开的”、“独立的”等。
[2]in the form of a sketch or a layout drawing以草图或布局图的形式；that shows...定语从句，修饰 sketch or a layout drawing。
KEYWORDS
CAD（computer-aided design） 计算机辅助设计
CAM（computer-aided manufacturing） 计算机辅助制造
CAE（computer-aided engineering） 计算机辅助工程
product cycle 产品周期
prototype 原型
feasibility 可行性
qualitative 定性的
symmetry 对称，匀称
cross-sectional property 截面性质
翻译：
除非能以较低的价格提供更好的质量及更短的交货时间提供新产品，否则任何企业都无法在当今的国际竞争中立足。因此，他们都试图用计算机的巨大存储能力、快速处理速度及用户友好的交互图形能力，来自动完成并紧密联系其他繁重的和单独的工程或生产任务，从而减少产品开发和生产的时间和成本。计算机辅助设计（CAD）、计算机辅助制造（CAM）和计算机辅助工程（CAE）正是生产周期中为此目的而采用的技术。因此，为了了解CAD、CAM和CAE所扮演的角色，需要了解在一个产品设计和生产过程中必须完成的各项活动和功能。这些活动和功能被称之为产品周期。对Zeid（1991）所描述的产品周期稍加改动后如图10-l所示。
正如图10-1的实线框所示，产品周期由两个主要过程组成：设计过程和制造过程。设计过程始于由市场人员认定的用户需求，止于对产品的完整描述，通常用图形来表现。制造过程则始于设计的规格说明，止于产品发运。
设计过程所涉及的活动大体上分为两类综合和分析。如图10-1所示，原始设计活动，如设计需求的认定，设计规格说明的规划，根据收集的相关设计信息进行可行性研究以及设计概念化等，都属综合子过程部分；即综合子过程的结果是各个产品部件间的关系以草图或布局图的形式来表示的所期望产品的概念设计。用于实现该产品理念的主要财政承诺和产品功能都在产品周期的这一阶段确定。在综合子过程中产生和处理的大多数信息是定性的，因此在计算机系统中很难得到。
一旦概念设计形成，分析子过程就开始对设计进行分析和优化。首先要导出一个分析模型，因为分析子过程适用于该模型而非设计本身。尽管在工程上，计算机的能力和可用性迅速提高，但对分析模型的抽象依然会在可预见的未来仍有待人去完成。分析模型可从设计中去除不必要的细节，缩小尺寸和识别并使用对称性。例如：尺寸缩小表示一张薄的材料由具有厚度属性的等效曲面来代表，或一个细长区域由具有截面特性的线段来表示。在几何和负荷上具有对称性的物体通常用模型的某一部分进行分析。实际上，在初等机械课程上对一个结构进行分析时，早就实践过这种自然的抽象过程。
一旦设计完成，在经过优化或一些权衡制定之后，就开始了设计评价阶段。为此目的可进行原型制作。一种用于构建原型称之为原型速成的新技术现已非常普及。这种技术可通过从底到顶层层地构建原型，由于它可以根据设计直接构建原型，因此它只需要产品的截面数据即可。如果在原型上的设计评价表明这种设计不尽人意，那么，就以新的设计重复进行上述过程。
当设计评价结果令人满意时，就准备设计文档。设计文档包括图纸、报告和材料清单的准备。按常规，应将设计图纸制成蓝图交送制造部门。
如图10-1所示，制造过程根据设计过程的图纸始于工艺计划，止于实际的产品。工艺计划的结果就是生产计划、材料订单和加工程序。其他诸如设计钻模和夹具这样的特殊要求都在这一阶段进行处理。工艺计划与制造过程的关系就如同综合与设计过程的关系：它涉及到许多经验和定性的判断，这表示很难对工艺计划进行计算机化。一旦工艺计划结束，便开始生产实际产品并根据质量要求进行检查。对通过质量检查的零件进行组装、功能测试、包装、贴标签并发运给客户。
追问有 长点 的么 感觉译成中文 太少了