重庆科创职业学院Unit04CADandApplications

1、Unit 4 CAD and Applications1Unit 4 CAD and ApplicationsBefore we present the basics of CAD, it is appropriate to give a brief history. CAD is a product of the computer era. It originated from early computer graphic systems to the development of interactive computer graphics. Such two systems include

2、 the Sage Project at the Massachusetts Institute of Technology (MIT) and Sketchpad. The Sage Project was aimed at developing CRT displays and operating systems. Sketchpad was developed under the Sage Project. A CRT display and light pen input were used to interact with the system. This coincidentall

3、y happened at about the same time that NC and APT (Automatically Programmed Tool) first appeared1. Later, X-Y plotters were used as the standard hard-copy output device for computer graphics. An interesting note is that an X-Y plotter has the same basic structure as a NC drilling machine except that

4、 a pen is substituted for the tool on NC spindle2.2Unit 4 CAD and Applications In the beginning, CAD systems were no more than graphics editor with some built-in design symbols. The geometry available to the user was limited to lines, circular arcs, and the combination of the two. The development of

5、 free-form curves and surfaces, such as Coons patch, Beziers patch, and B-spline, enables a CAD system to be used for sophisticated curves and surface design. Three-dimensional CAD systems allow a designer to move into the third dimension. Because a three-dimensional model contains enough informatio

6、n for NC cutter-path programming, the linkage between CAD and NC can be developed. So called turnkey CAD/CAM systems were developed based on this concept and became popular in the 1970s and 1980s.3Unit 4 CAD and ApplicationsThe 1970s marked the beginning of a new era in CADthe invention of three-dim

7、ensional solid modeling. In the past, three-dimensional, wire-frame models represented an object only by its bounding edges. They are ambiguous in the sense that several interpretations might be possible for a single model. There is also no way to find the volumetric information of a model. Solid mo

8、dels contain complete information; therefore, not only can they be used to produce engineering drawing, but also engineering analysis can be performed on the same model as well. Later, many commercial systems and research systems were developed. Quite a few of these systems were based on the PADL an

9、d BUILD systems. Although they are powerful in representation, many deficiencies still exist. For example, such systems have extreme compute the mid-1980s that solid modelers made their way into the design environment. Today, their use is as common as drafting and wire-frame model applications.4Unit

10、 4 CAD and ApplicationsCAD implementations on personal computers (PCs) have brought CAD to the masses. This development has made CAD available and affordable. CAD originally was a tool used only by aerospace and other major industrial corporation. The introduction of PC CAD packages, such as, AutoCA

11、D, VersaCAD, CADKEY, and so on, has made it possible for small companies and even individuals to own and use CAD systems. By 1988, more than 100 000 PC CAD Packages had been sold. Today, PC-based solid modelers are available and are becoming increasingly popular. Because rapid developments in microc

12、omputers have enabled PCs to carry the heavy computational load necessary for solid modeling, many solid modelers now run on PCs and the platform has become less of an issue. With the standard graphics user interface (GUI), CAD systems can be ported easily from one computer to another. Most major CA

13、D systems are able to run on a variety of platforms. There is little difference between mainframe, workstation, and PC-based CAD systems.5Words and Expressionsappropriate 5pruprit adj. 适当的适当的graphic 5grAfik adj. 绘画似的，图解的绘画似的，图解的interactive intr5Aktiv adj. 交互式的交互式的Massachusetts mAsE5tFu:sits n.马萨诸塞马萨

14、诸塞(美国州名美国州名)coincidentalkuinsi5dentl adj. 一致的，符合的，巧合的一致的，符合的，巧合的plotterplCt n.阴谋者，计划者阴谋者，计划者drilling 5driliNn. 演练演练spindle5spindl n. 轴，杆，心轴轴，杆，心轴geometrydVi5Cmitrin. 几何学几何学arc a:kn. 弧，弓形，拱弧，弓形，拱curvek:v n.曲线，弯曲，曲线图表曲线，弯曲，曲线图表vt.弯，使弯曲弯，使弯曲vi.成曲形成曲形6Words and Expressionssophisticates5fistikeitn.久经世故的人

15、久经世故的人vi. 诡辩诡辩dimension di5menFnn. 尺寸，维尺寸，维(数数)cutter-path5kQtpB:W n.刀具路径，切割轨道刀具路径，切割轨道linkage5liNkidVn. 连接连接concept5kCnsept n. 观念，概念观念，概念ambiguousAm5bigjusadj. 暧昧的，不明确的暧昧的，不明确的representationreprizen5teiFn n. 表示法，表现表示法，表现deficiency di5fiFnsin.缺乏，不足缺乏，不足extremeiks5tri:madj. 尽头的，极端的尽头的，极端的n. 极端，极端的事物极

16、端，极端的事物APT(Automatically Programmed Tool) 自动编程语言自动编程语言7NOTES1. This coincidentally happened at about the same time that NC and APT (Automatically Programmed Tool) first appeared.CAD与初次出现的与初次出现的NC和和APT(自动编程工具自动编程工具)碰巧同时问世。碰巧同时问世。(coincidentally为插入语，为插入语，at about the same time 为介词短语，可译为为介词短语，可译为“几乎几乎”

17、，“同时同时”)2. An interesting note is that an X-Y plotter has the same basic structure as a NC drilling machine except that a pen is substituted for the tool on NC spindle.一个有趣的现象是一个有趣的现象是X-Y绘图仪与绘图仪与NC钻床具有相同的基本机构，除了绘图笔被钻床具有相同的基本机构，除了绘图笔被NC机床上的主机床上的主轴刀具替代之外。轴刀具替代之外。(the sameas可译为可译为“与与相同相同”，as为介词，引导短语为介词

18、，引导短语)8CAM and Applications When a design has frozen, manufacturing can begin. Computers have an important role to play in many aspects of production. Numerically controlled (NC) machine tools need a part program to define the components being made; computer techniques exist to assist, and in some c

19、ases virtually automate the generation of part programs. Modern shipbuilding fabricates structures from welded steel plates that are cut from a large steel sheet. Computer-controlled flame cutters are often used for this task and the computer is used to calculate the optimum layout of the components

20、 to minimize waste metal. Numerically controlled pipe-bending machines are able to operate directly from part programs generated by pipe-routing software. Printed circuit board assembly can also be improved by computer methods. Quality is maintained by computer-controlled automatic test equipment th

21、at diagnoses faults in a particular board and rejects defective boards from the assembly line. Computers are used extensively to plot the artwork used to etch printed circuit boards and also to produce part programs for NC drilling machines.9CAM and Applications One of the most important manufacturi

22、ng function is stock and production control. If the original design is done on a computer, obtaining lists of material requirements is straightforward. Standard computer data processing methods are employed to organize the work flow and order components when required (Figure 4-1).Figure 4-1 The bloc

23、k diagram of a CAD/CAM system10CAM and Applications Part geometry requires calculation of a large number of tool positions. Part programming software is usually incorporated into a family of CAM (Computer Aided Manufacturing) software. Some CAM software is associated with CAD (Computer Aided Design)

24、 software into CAD/CAM stations. Then the CAM software can use the CAD files as a source of data, which speeds up the programming process. Part programming software is user-friendly, meaning the programmer does not have to know the computer programming language or its operating system. It uses scree

25、n menus to lead the user through the programming process. Data can be entered via the keyboard, the mouse, or the function keys. Experienced programmers can use built-in macro capabilities and advanced techniques such as a family of parts to become even more productive. Programming software has a dy

26、namic graphics database to hold the actual machining sequences. These sequences can be viewed, edited, chained, or deleted. The programming can be accomplished whether single cuts or CNC machine canned cycle will be used. The software will also automatically calculate the proper feeds and speeds to

27、be used during the machining, create a tooling list, and define the tool path.11CAM and Applications Programmers can use different layers to associate with each profile being created or to construct clamps and fixtures to get a complete picture of the part setup. The tool motion can be seen as it wi

28、ll occur at the machine. Using part programming software, the programmer can easily solve trigonometry problems to define an accurate tool path. When the program is done, the programmer can send it from the PC to the machine via a communication channel using built-in software with communications cap

29、ability. Good part programming software is capable of:(1) Establishing the machining parameters and tooling for a particular machine or job. (2) Defining the geometry and tool path.(3) Code generation, enabling the programmer to define what code is to be generated and how it is output to the machines.(4) Communication enabling the programmer to use standard communications protocols or create his or her own.12Words and Expressionsnumerically 5nju:5merikli adv. 用数字，在数字上用数字，在数字上 define di5fain n. 定义，详细说明定义，详细说明fabricate 5fAbrikeit vt.制作，构成，捏造，伪造制作，构成，捏造，伪造