计算机辅助设计（CAD）及计算机辅助设计制造系统_中英文翻译.doc

附录:英文资料及翻译Computer-Aided Design CAD A CAD system is basically a design tool in which the computer is used to analyze various aspects of a designed product. The CAD system supports the design process at all levels?conceptual, preliminary, and final design. The design can then test the product in various environmental conditions, such as temperature changes, or under different mechanical stress. Although CAD systems do not necessarily involve computer graphics, the display of the designed object on a screen is one of the most valuable features of CAD systems. The picture of the object is usually displayed on the surface of cathode-ray tube CRTputer graphics enables the designer to study the object by rotating it on the computer screen, separating it into segments, enlarging a specific portion of the object in order to observe it in detail, and studying the motion of mechanisms with the aid of programs. Most CAD systems are using interactive graphics system. Interactive graphics allows the user to interact directly with the computer in order to generate manipulate, and modify graphic displays. Interactive graphics has become a valuable tool, if not a necessary prerequisite, of CAD system. The end products of many CAD systems are drawing generated on a plotter interfaced with the computer. One of the most difficult problems in CAD drawing is the elimination of hidden lines. The computer produces the drawing as wire frame diagram. Since the computer defines the object without regard to ones perspective, it will display all the objects surfaces, regardless of whether they are located on the side facing the viewer or on the back, which normally the eye cannot see. Various methods are used to generate the drawing of the part on the computer screen. One method is to use a geometric modeling approach, in which fundamental shapes and basic elements are used to build the drawing. The lengths and radii of the elements can be modified. For example, a cylinder is a basic element, the subtraction of a cylinder with a specific radius and length will create hole in the displayed part. Each variation, however, maintains the overall geometry of the part. Other CAD systems use group technology in the design of parts. Group technology is a method of coding and grouping parts on the basis of similarities in function or structure or in the ways they are produced. Application of group technology can enable a company to reduce the number of parts in use and to make the production of parts and their movement in the plant efficient. Recently CAD systems are using the finite-element method FEM of stress analysis. By this approach the object to be analyzed is represented by a model consisting of small elements, each of which has stress and deflection characteristics. The analysis requires the simultaneous solution of many equations; a task which is performed by the computer, the deflections of the object can be displayed on the computer screen by generating animation of the model. With any of these methods, or other which are used, the CAD system generates at the design stage a single geometric data base which can be used in all phases of the design and later in the manufacturing, assemble, and inspection processes.CAD/CAM Systems Computer-aided design CAD means the use of a computer to assist in the design of an individual part or a system, such as an aircraft. The design process usually involves computer graphics. Computer-aided manufacturing CAM means the use of a computer to assist in the manufacture of a part. CAM can be divided into two main classes: 1 On-line applications, namely, the use of the computer to control manufacturing systems in real time, such as CNC and AC systems of machine tools. 2 Off-line applications, namely the use of the computer in production planning and non-real-time assistance in the manufacturing of parts. CAD/CAM is a unified software system, in which the CAD portion is interfaced inside the computer with the CAM system. The end result of current CAD/CAM systems is usually a part program in the form of a list or punched tape. In advanced CAD/CAM systems part programs can be directly fed into the control computers of CNC machines and inspection stations. The main concept of CAD/CAM systems is the generating of a common database which is used for all the design and manufacturing activities. These include specifications of the product, conceptual design, final design, drafting, manufacturing, and inspection. At each stage of this process, data can be added, modified, used, and distributed over networks of terminals and computers. The single database provides a substantial reduction in human errors and a significant shortening of the time required form the introduction of a concept of a product to the manufacturing of the final physical product. The size and capability of the required computer system depend on the complexity of the product. In the aerospace and aeronautics industry, where a complete aircraft can be designed with a CAD/CAM processor, the system must accommodate new data and changes in data arriving from a variety of users. Therefore these systems must have a strong data management capability. By contrast, if a company designed simple products, the required CAD/CAM system would need only one computer terminal. Today the major users of CAD/CAM systems are the aero spaces and automotives, but the declining price of these systems enlarge the number of other users. Advanced CAD/CAM systems include solid geometry modeling capability, in addition to the wire frame mode diagrams. The solid description is important when NC verification programs are included in the CAM system, and the changing status of the work piece during machining simulation should be observed. In recent years CAD/CAM technology has improved industry productivity. It is a significant step toward the design of the factory of the future.Optimization for Finite Element Applications As engineers work with increasing complex structures, they need rational, reliable, fast, and economical design tools. Over the past two decades, finite element analysis has proven to be the most frequently used method of identifying and solving the problems associated with these complicated designs. Because most of the design tasks in engineering are quantifiable, computers have revolutionized the highly iterative design process, particularly the procedures for quickly finding alternative designs. But even now, many engineers still follow a manual trial-and-error approach. SuchAn approach makes designing-even for seemingly simple tasks more difficult because it usually takes longer, requires extensive human-machine interaction, and tends to be biased by the design groups experience. Design optimization, which is based on a rational mathematical approach to modifying designs too complex for the engineer to modify, automates the design cycle. If automated optimization can be done on a desktop platform, it can be save a lot time and money. The goal of optimization is to minimize or imize an objective, such as weight or fundamental frequency that is subject to constraints on response and design parameters. The size and/or shape of the design determine the optimization approach. Looking at optimization as part of the design process makes it easier to understand. The first step includes preprocessing, analysis, and post processing , just as in customary finite element analysis FEA and computer-aided design CAD program applications the difference in CAD lied in building the problems geometry in terms of the design parameters . In the step, the optimization objective and response constraints are defined. And in the last step, The repetitive task of design adjustment is automated. Optimization programs should allow engineers to monitor the progress of the design, stop it if necessary, change the design conditions, and restart. The power of an optimization program depends on the available preprocessing and analysis capabilities. Applications for 2-D and 3-D need both automatic and parametric meshing capabilities. Error estimate and adaptive control must be included because the problems geometry and mesh might change during the optimization loops. Revising, and reevaluating models to achieve specific design goals start with preliminary design data input. Next comes the specification of acceptable tolerances and posed constraints to achieve an optimum, or at least improve solution. To optimize products ranging from simple skeletal structures to complicated three-dimensional solid models, designers need access to a wide variety of design objectives and behavior constraints. Additional capabilities will also be needed for easy definition and use of the following: weights, volumes, displacements, stresses, strains, frequencies, buckling safety factors, temperatures, temperature gradients, and heat fluxes as constraints and objective functions. Moreover, engineers should be able to combine constraints from different types of analyses in multidisciplinaryoptimization. For example, designers can perform thermal analysis and transfer temperatures as thermal loads for stress analysis, put constraints over imum temperature, imumstress, and deflection, and then specify a range for thedesired fundamental frequency. The objective function can represent the whole model or only parts of it. Even more important, it should reflect the importance of the different portions of the model by specifying weight or cost factorsTWO-Dimensional Drawings CAD makes possible 2D drawings, with an endless possibility of views in a range of scales from microns to meters. It gives the mechanical designer the ability to magnify even the smallest of components to ascertain if the assembled components fit properly and even to design programs to identify automatically potential problems in CAD assembly. Parts with different characteristics, such as movable or stationary, can be assigned different colors on the display. Parts can be dimensioned with automatic dimensioning changes, allowing for expedient engineering design changes.Three-Dimensional Drawings Designers have even more freedom with the advent of 3D modeling. They can create 3D parts and manipulate them in endless variations to achieve the desired results. Through finite element analysis FEA, stresses can be applied to a computer model and the results graphically displayed, giving the designer quick feedback on any inherent problems in a design before the creation of a physical prototype. 3D models can be created in wire-frame, in surfaces or in solid form. In wire-frame, lines and arcs form edges that generate the model Fig.8-la. The result is a 3D form that can be viewed from any location but is still only a skeletal form. Creating a surface stretches a skin over the skeleton Fig.8-lb. Once this is done, the model can be rendered so that appears more tangible. Surface models are commonly used in the creation of sheet metal developments that can be unfolded for manufacture. Solid models are the most complex level of modeling and while the programs to create them have been available for some time on large mainframe computers, it is only recently that microcomputer have reached a level of power that allows the running of the sophisticated algorithms needed to create solid model Fid.8-2.The computer “thinks” the solid model is a solid mass so it can be “drilled,” machined, “welded” as if it were an actual physical part. It can be made out of any material and can take on that materials characteristics, thereby allowing calculations of mass to be made.CADs Benefits The benefits of computer use in drafting and design tasks are impressed speed, greater accuracy, reduction of hardcopy storage space as well as better recall, enhanced communication capabilities, improved quality and easier modification.Speed A personal computer used in industry can perform a task at an average rate of 33 million operations per second; newer computer are even faster. This is an important feat when using it to calculate the amount of deflection of a component, when theoretical physical forces are applied to it, through finite element analysis FEA or when displaying an entire city plan on a monitor, both of which are time-consuming and calculation-intensive tasks. AutoCAD software can duplicate any geometry as many times as required and can also perform crosshatching and dimensioning automatically and equally as fast.Accuracy The AutoCAD program has an accuracy of 14 significant digits of precision for each point, depending on the operating system and computer platform. This extremely important when the program must round off numbers during mathematical calculation such as segmenting a circle.Storage The computer can store thousands of drawings in the physical space that it would take to store hundreds of manual drawings. Also, the computer can search and find a drawing with ease, as long as the operator possesses the correct file name.Communication Because the computers data is stored in an electronic form, it can be sent to a variety of locations. The first obvious location is the monitor. The computer can display the data on the screen in different forms such as graphics, easily converting the data into readable drawings. The data can also be sent to a plotter to produce the familiar paper drawing, via a direct link to a computer-aided manufacturing CAM machine or via telephone to anywhere around the globe. You no longer have to mail drawings, risking damage and loss; they can now be at their destination instantly via the telecommunications network.Quality The computer always retains the data in the form in which it was first created. It can repeat the same output of data continuously without regard to fatigue. Lines will always be crisp and clear, with uniform line weight, and text will always be legible. The computer doesnt alter its output quality because of a wild weekend or a late night watching the game.Modification The computer data is stored in a format that allows easy modification to any facet of a drawing and gives instant feedback to the user. When something is drawn once, it never has to be drawn again because the object in question can be duplicated, stretched, sized, and changed in many ways without having to be redrawn. Except for the initial cost to purchase a CAD workstation, CADs only disadvantage is a small one because it can be so easily overcome. Because the drawing is stored in an electronic format and not a paper format, it is possible to erase a drawing file easily. Thats why it is essential to train yourself in good CAD practices to avoid an accidental erasure. And, although an ounce of prevention truly is worth a pound of cure, there are even ways of files that are usually successful if you follow the correct procedures. So relax! 计算机辅助设计(CAD) 计算机辅助设计系统基本上是一种设计工具,计算机是用来分析所设计的产品的各个方面。CAD系统支持各种阶段的设计过程?设计构想、初步设计及最终设计。设计者然后可在各种环境条件,比如温度的变化或不同机械压力下检验产品的状况。 尽管CAD系统并非一定要包含计算机绘图,但能将设计的产品显示在屏幕上是CAD系统的最有价值的特征之一。物体的图形通常显示在阴极线管屏幕上(CRT)。计算机图形功能使设计者可用多种办法研究物体:将物体在计算机屏幕上旋转、将其分成几段、将物体局部放大以仔细研究以及在运动程序的帮助下研究机构的运动。 大多数CAD系统使用互动式图形系统。互交式图形系统使用户可直接和计算机通过交互作用以对图形进行调整及修改。对CAD系统来说,交互式图形系统就算不是必要的,也已经是很有价值的工具。 许多CAD系统的最终产品是在与计算机连接的绘图仪中产生的图形。在CAD图形中,最难解决的问题之一是消去那些被挡住的线。计算机生成的图形是线框图线。由于计算机定义物体时没有考虑图的透视效果,它显示出物体的所有面,而不考虑这些面是在朝向观测者的一面还是位于通常人眼无法看到的背面。 可使用多种不同办法在计算机屏幕上生成图形。一种办法是采用几何模板形式,这种办法是用基本形状和基本的元素创建图形,元素的长度及半径可以修改。例如,圆柱是一个基本元素,在已显示的零件上去掉一个规定半径和长度的圆柱就可以生成一个孔。但是每次变化都保留零件所有的几何特征。 另外,CAD系统使用成组技术设计零件。成组技术是在功能、结构相同或加工方法相似的工件基础上采用分组编码的一种加工方法。采用成组技术可使工厂减少所用零件得数量,并使零件在工厂中的制造、运输效率更高。 最近的CAD系统使用了压力有限元分析法。在用这种方法时,待分析物体用很多有压力及弯曲特征的小元素组成的模型表示。这种分析办法要求同时分解许多方程,用计算机执行一项任务,物体的弯曲可以通过生成动画的方式显示在计算机屏幕上。 采用这些办法中的任一种或其它常用办法,CAD系统在设计段生成了单个的几何数据库,它可用于设计的各个阶段及其后的制造、装配和检验过程。 二维绘图 CAD使多视图的二维绘图成为可能,视图空间可以从微米到米的比例范围内无限变化。它提供给机械设计师放大的功能,即使在恰当配合的装配零件中最小的元件也能看清楚,设计程序甚至能自动辨认CAD装配图中的潜在问题。针对具有不同特征的零件,如运动的或静止的,在显示时可以被指定成不同的颜色。为了有利于工程设计的变化,可使用带有自动尺寸变化的系统对零件进行尺寸标注。 三维绘图 随着三维建模的出现,设计者具有了更多的自由度。他们可以生成三维零件图并且可以无限制地修改以获得所需的结果。