CAD/CAM, CA Engineering

At first a seemingly indecipherable collection of symbols, these acronyms are fairly easy to understand once one realizes that each "CA" stands for Computer-Aided (or Assisted). Thus, CAD is Computer-Aided Design; CAM stands for Computer-Aided Manufacturing; and the last acronym denotes Computer-Aided Engineering. Although presently interrelated technologies, they evolved separately.

The earliest to develop was CAD, originally termed Computer-Aided Drafting, a terminology still in use by approximately half the users of this technology mainly in the architectural, consulting, construction, mapping, and public utility fields. In many instances, the acronym is presented as CADD, signifying both applications. Invented by American engineer Ivan Sutherland, CAD was outlined in his seminal 1961 Ph.D. dissertation. Sutherland described a computerized sketchpad in which he used a CRT display and light pen to construct basic geometric entities such as points, lines, and arcs. Sutherland's initial concept resulted in the first commercially available CAD systems in the mid 1970s—systems which have evolved, over the following decades, developing into the CAD software in use today.

In computer-aided drafting, the mouse, or "puck," on a digitizing tablet attached to the computer is used to trace or draw lines that are stored in the computer as graphic primitives. Combined with a digitizing tablet, which is basically an electronic drafting board, CAD represents the primary means for entering paper map documents into the computer. It should be noted that an alternative means is a scanner—basically a large, spatially accurate fax machine. However, the digital data produced by these two techniques is quite different. Digitizing (or drafting) with CAD produces vector (points and lines) digital data while a scanner provides raster data, which is essentially an accurate digital picture.

The basic drafting capabilities of CAD were supplemented through the addition of software tools allowing for the production of precise engineering drawings of intricate designs, such as complex machine parts or electronic circuit boards. A key development in CAD was the introduction of the graphic display terminal, which not only offered dramatically real displays of objects but also allowed the designer to interact graphically rather than through the keyboard or digitizer. In such a manner, designers could concentrate on decisions concerning the objects represented on the screen rather than focusing on the drawings. Indeed, the development of computer graphics is closely linked to that of CAD. Thus, in the manufacturing arena, CAD became an integral part of the design process, offering efficient and accurate creation, modification, analysis, and optimization of designs.

Computer-aided design applications enabling precise two-dimensional and three-dimensional designs to be implemented and graphically displayed are now routine parts of the manufacturing process for a wide variety of products in many fields, such as aerospace and automotive engineering. They are employed by such companies as Boeing, Ford, Toyota, and Volvo. AutoCAD and Microstation software are two of the standard products for industrial strength CAD for both two-dimensional and three-dimensional drafting and design.

If a design exists in the computer, then the next logical step would be to have the computer drive machine tools to produce the object indicated by the design. This is how CAM, or computer-aided manufacturing, was created. Since the mid-1980s, CAM has been closely linked with CAD, and the union is represented by the single acronym CAD/CAM. Although CAM actually includes various applications in the manufacturing process, such as production scheduling and inventory control, it is best illustrated by the integrated CAD/CAM systems within which a design can be developed and the manufacturing process controlled. In such a union, CAD software creates CNC/NC (computer numeric control/numeric control) codes, which are coded numerical instructions for automated control of machine tools such as lathes and mills, and are similar to the programming codes that drive plotters. Originally, paper tapes were produced to drive the machine tools, but newer tools are connected directly to the computer, so that the design and manufacturing process is seamless and computer-aided. This has resulted in faster, more efficient, and more accurate procedures.

A good illustration of the versatility offered by an integrated CAD/CAM approach is the design and development of printed circuit boards. A schematic is created, using interactive graphics, to recall symbols from a database and place them in the appropriate locations. Once the design is completed, a circuit analysis program is used to test and verify the performance of the circuit board. The final step is to produce a photographic transparency directly from the CAD/CAM system, which is then used to manufacture the circuit board.

This basic feat of engineering, integrating computer capabilities with manual design, has recently been perfected by the integration of complex mathematical functions or analyses, such as finite element modeling and analysis, computational fluid dynamics , boundary element analysis, and rigid body analysis, into the engineering design process, thereby establishing the field of computer-aided engineering.

CA engineering can basically be considered a set of numerical tools and processes to conduct numeric simulations. A good example is the analytic simulation of the aerodynamics of a body in a wind tunnel. Such an approach is used, for example, to make sure that a designed part is strong enough, or to simulate the operation of a designed feature before its manufacture. By providing analytic prototypes in the manufacturing process, CAE has reduced the need for physical prototypes, thereby speeding up the production process. Expert systems are also being added to extend the capabilities of the process. One such system presently under development is intelligent CAD, or IntCAD.

A practical application of these technologies occurred when the U.S. Civil War submarine H. L. Hunley was raised off the coast of Charleston, South Carolina, in October 2000. CAD and CAE techniques were used in this historic project to assess the submarine's structural weaknesses and to test and simulate various methods for raising the vessel. The final and successful method, fully tested in the system before application, was to place thirty-two nylon slings under the submarine, support it with a steel structure from above, and squirt foam along the side of the vessel to replace the sand that had supported it for more than a century.

see also Display Devices; Graphic Devices; Process Control.

Robert D. Regan