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]本句主要結構是They have tried to use... to automate... and tie...，其中to use有3個並列賓語；separate此處為形容詞，義“分開的”、“獨立的”等。
[2]in the form of a sketch or a layout drawing以草圖或布局圖的形式；that shows...定語從句，修飾 sketch or a layout drawing。
KEYWORDS
CAD（computer-aided design） 計算機輔助設計
CAM（computer-aided manufacturing） 計算機輔助制造
CAE（computer-aided engineering） 計算機輔助工程
product cycle 產品周期
prototype 原型
feasibility 可行性
qualitative 定性的
symmetry 對稱，勻稱
cross-sectional property 截面性質
翻譯：
除非能以較低的價格提供更好的質量及更短的交貨時間提供新產品，否則任何企業都無法在當今的國際競爭中立足。因此，他們都試圖用計算機的巨大存儲能力、快速處理速度及用戶友好的交互圖形能力，來自動完成並緊密聯系其他繁重的和單獨的工程或生產任務，從而減少產品開發和生產的時間和成本。計算機輔助設計（CAD）、計算機輔助制造（CAM）和計算機輔助工程（CAE）正是生產周期中為此目的而采用的技術。因此，為了了解CAD、CAM和CAE所扮演的角色，需要了解在壹個產品設計和生產過程中必須完成的各項活動和功能。這些活動和功能被稱之為產品周期。對Zeid（1991）所描述的產品周期稍加改動後如圖10-l所示。
正如圖10-1的實線框所示，產品周期由兩個主要過程組成：設計過程和制造過程。設計過程始於由市場人員認定的用戶需求，止於對產品的完整描述，通常用圖形來表現。制造過程則始於設計的規格說明，止於產品發運。
設計過程所涉及的活動大體上分為兩類綜合和分析。如圖10-1所示，原始設計活動，如設計需求的認定，設計規格說明的規劃，根據收集的相關設計信息進行可行性研究以及設計概念化等，都屬綜合子過程部分；即綜合子過程的結果是各個產品部件間的關系以草圖或布局圖的形式來表示的所期望產品的概念設計。用於實現該產品理念的主要財政承諾和產品功能都在產品周期的這壹階段確定。在綜合子過程中產生和處理的大多數信息是定性的，因此在計算機系統中很難得到。
壹旦概念設計形成，分析子過程就開始對設計進行分析和優化。首先要導出壹個分析模型，因為分析子過程適用於該模型而非設計本身。盡管在工程上，計算機的能力和可用性迅速提高，但對分析模型的抽象依然會在可預見的未來仍有待人去完成。分析模型可從設計中去除不必要的細節，縮小尺寸和識別並使用對稱性。例如：尺寸縮小表示壹張薄的材料由具有厚度屬性的等效曲面來代表，或壹個細長區域由具有截面特性的線段來表示。在幾何和負荷上具有對稱性的物體通常用模型的某壹部分進行分析。實際上，在初等機械課程上對壹個結構進行分析時，早就實踐過這種自然的抽象過程。
壹旦設計完成，在經過優化或壹些權衡制定之後，就開始了設計評價階段。為此目的可進行原型制作。壹種用於構建原型稱之為原型速成的新技術現已非常普及。這種技術可通過從底到頂層層地構建原型，由於它可以根據設計直接構建原型，因此它只需要產品的截面數據即可。如果在原型上的設計評價表明這種設計不盡人意，那麽，就以新的設計重復進行上述過程。
當設計評價結果令人滿意時，就準備設計文檔。設計文檔包括圖紙、報告和材料清單的準備。按常規，應將設計圖紙制成藍圖交送制造部門。
如圖10-1所示，制造過程根據設計過程的圖紙始於工藝計劃，止於實際的產品。工藝計劃的結果就是生產計劃、材料訂單和加工程序。其他諸如設計鉆模和夾具這樣的特殊要求都在這壹階段進行處理。工藝計劃與制造過程的關系就如同綜合與設計過程的關系：它涉及到許多經驗和定性的判斷，這表示很難對工藝計劃進行計算機化。壹旦工藝計劃結束，便開始生產實際產品並根據質量要求進行檢查。對通過質量檢查的零件進行組裝、功能測試、包裝、貼標簽並發運給客戶。