COMPUTER-AIDED DESIGN (CAD)
AND COMPUTER-AIDED MANUFACTURING
(CAM)

Photo by: higyou
Computer-aided design (CAD) and computer-aided manufacturing (CAM) are a pair of often interdependent industrial computer applications that have greatly influenced the chain of processes between the initial design and the final realization of a product. Many would add to this duo a third technology, computer-aided engineering (CAE). Ongoing refinements in CAD/CAM systems continue to save manufacturers tens of millions of dollars in time and resources over non-computerized methods. As a consequence, CAD and CAM technologies are responsible for massive gains in both productivity and quality, particularly since the 1980s. For some purposes CAD and CAM methods can be used exclusively of one another, and in general, CAD is used more commonly than CAM.
CAD involves creating computer models defined by geometrical parameters. These models typically appear on a computer monitor as a three-dimensional representation of a part or a system of parts, which can be readily altered by changing relevant parameters. CAD systems enable designers to view objects under a wide variety of representations and to test these objects by simulating real-world conditions.
CAM picks up where CAD leaves off by using geometrical design data to control automated machinery. CAM systems are associated with computer numerical control (CNC) or direct numerical control (DNC) systems. These systems differ from older forms of numerical control (NC) in that geometrical data is encoded mechanically. Since both CAD and CAM use computer-based methods for encoding geometrical data, it is possible for the processes of design and manufacture to be highly integrated.
THE ORIGINS OF CAD/CAM
CAD had its origins in three separate sources, which also serve to highlight the basic operations that CAD systems provide. The first of these sources resulted from attempts to automate the drafting process. These developments were pioneered by the General Motors Research Laboratories in the early 1960s. One of the important time-saving advantages of computer modeling over traditional drafting methods is that the former can be quickly corrected or manipulated by changing a model's parameters. The second source of CAD's origins was in the testing of designs by simulation. The use of computer modeling to test products was pioneered by high-tech industries like aerospace and semiconductors. The third influence on CAD's development came from efforts to facilitate the flow from the design process to the manufacturing process using numerical control (NC) technologies, the use of which was widespread in many applications by the mid-1960s. It was this source that resulted in the linkage between CAD and CAM. One of the most important trends in CAD/CAM technologies is the ever tighter integration between the design and manufacturing stages of CAD/CAM-based production processes.
Numerical control (NC) of automated machinery was developed in the early 1950s and thus preceded the use of computerized control by several years. Like CAM, NC technologies made use of codified geometrical data to control the operations of a machine. The data was encoded by punch holes on a paper tape that was fed through a reader, essentially the same mechanism as that on a player piano. Once the control tape was produced, it offered a reliable means to replace the skilled machinists that had previously operated such machines. From the firm's point of view, the drawback of the old NC technologies was the difficulty in converting the design for a three-dimensional object into holes on a tape. This required the services of a tape encoding specialist. Since this specialist was required to work without any significant visual feedback, work was essentially trial and error and could only be tested in the actual production process. The tape encoder had to account for a large number of variables, including optimal feed rates and cutting speeds, the angle at which the tool should contact the part, and so on. Given the considerable time and expense involved in NC technologies, it was only economically viable when a large number of parts were to be produced.
The development of CAD and CAM and particularly the linkage between the two overcame these problems by enabling the design and manufacture of a part to be undertaken using the same system of encoding geometrical data. This eliminated the need for a tape encoding specialist and greatly shortened the time between design and manufacture. CAD/CAM thus greatly expanded the scope of production processes with which automated machinery could be economically used. Just as important, CAD/CAM gave the designer much more direct control over the production process, creating the possibility of completely integrated design and manufacturing processes.
The rapid growth in the use of CAD/CAM technologies after the early 1970s was made possible by the development of mass-produced silicon chips and the microprocessor, resulting in more affordable computers. As the price of computers declined and their processing power improved, the use of CAD/CAM broadened from large firms using large-scale mass production techniques (the automobile industry, for instance) to firms of all sizes. The scope of operations to which CAD/CAM was applied broadened as well. In addition to parts-shaping by traditional machine tool processes such as stamping, drilling, milling, and grinding, CAD/CAM has come to be used by firms involved in producing consumer electronics, electronic components, and molded plastics. Computers are also used to control a number of manufacturing processes that are not defined as CAM because the control data are not based on geometrical parameters. An example of this would be at a chemical processing plant.
Using CAD it is possible to simulate in three dimensions the movement of a part through a production process. This process can simulate feed rates, angles and speeds of machine tools, the position of part-holding clamps, as well as range and other constraints limiting the operations of a machine. The continuing development of the simulation of various manufacturing processes is one of the key means by which CAD and CAM systems are becoming more tightly integrated. CAD/CAM systems also facilitate communication among those involved in design, manufacturing, and other processes. This is of particular importance when one firm contracts another to either design or produce a component.
ADVANTAGES AND DISADVANTAGES
Modeling with CAD systems offers a number of advantages over traditional drafting methods that use rulers, squares, and compasses. Designs can be altered without erasing and redrawing. CAD systems offer "zoom" features analogous to a camera lens whereby a designer can magnify certain elements of a model to facilitate inspection. Computer models are typically three-dimensional and can be rotated on any axis, much as one could rotate an actual three dimensional model in one's hand, enabling the designer to gain a fuller sense of the object. CAD systems also lend themselves to modeling cutaway drawings, in which the internal shape of a part is revealed, and to illustrating the spatial relationships among a system of parts.
To understand CAD it is useful to understand what it can't do. CAD systems have no means of comprehending real-world concepts, such as the nature of the object being designed or the function that object will serve. CAD systems function by their capacity to codify geometrical concepts. Thus the design process using CAD involves transferring a designer's idea into a formal geometrical model. In this sense, existing CAD systems can't actually design anything, but can provide tools, shortcuts, and a flexible environment for a designer to work with.
Other limitations to CAD are being addressed by research and development in the field of expert systems. This field derived from research done on artificial intelligence. One example of an expert system involves incorporating information about the nature of materials—their weight, tensile strength, flexibility and so on—into CAD software. By including this and other information, the CAD system could then "know" what an expert engineer knows when that engineer creates a design. The system could then mimic the engineer's thought pattern and actually "create" a design. Expert systems might involve the implementation of more abstract principles, such as the nature of gravity and friction or the function and relation of commonly used parts, such as levers or nuts and bolts. Expert systems might also come to change the way data is stored and retrieved in CAD/CAM systems, supplanting the hierarchical system with one that offers greater flexibility.
One of the key areas of development in CAD technologies is the simulation of performance. Among the most common types of simulation are testing for response to stress and modeling the process by which a part might be manufactured or the dynamic relationships among a system of parts. In stress tests, model surfaces are shown by a grid or mesh that distorts as the part comes under simulated physical or thermal stress. Dynamics tests function as a complement or substitute for building working prototypes. The ease with which a part's specifications can be changed facilitates the development of optimal dynamic efficiencies both as regards the functioning of a system of parts and the manufacture of any given part. Simulation is also used in electronic design automation, in which simulated flow of current through a circuit enables the rapid testing of various component configurations.
The processes of design and manufacture are, in some sense, conceptually separable. Yet the design process must be undertaken with an understanding of the nature of the production process. It is necessary, for example, for a designer to know the properties of the materials with which the part might be built, the various techniques by which the part might be shaped, and the scale of production that is economically viable. The conceptual overlap between design and manufacture is suggestive of the potential benefits of CAD and CAM and the reason they are generally considered together as a system.
AN EXAMPLE OF THE USE OF CAD/CAM
The Boeing Company's development of the 757 airplane illustrates the benefits of CAD/CAM technologies. The 757 was the first plane Boeing produced that was completely designed by CAD systems. Designing the 757 took longer than the 747, its predecessor. This occurred in part because the use of CAD incorporated a broader scope of considerations into the design process. The benefits of CAD/CAM were seen most clearly in the post-design phases of production. The 757 was made from parts produced by over 50 different firms. CAD/CAM enabled the more precise fit of parts, the result being that the first 757 required only six shims, compared to several hundred for the first 747. Additionally, Boeing engineers had scheduled ten days for the assembly of the fuselage and wing spars of the first 757, but actual assembly took only two days. Boeing estimated that the use of CAD throughout the design process lowered overall person hours for assembly by one-third. Last, the analysis functions of CAD enabled the number of working prototypes to be reduced to 3, down from 12 for the 747.
Many CAD/CAM software tools are highly specialized, and thus a multi stage manufacturing process, such as is used for complex products like motor vehicles, airplanes, and ships, requires more than one CAD program to design and integrate the various parts. For example, in ship design manufacturers may use one CAD application for designing the vessel's steel structure and another for designing the propeller assembly. Such specialization ensures that designers have adequate layout and specification tools in the software to work with; however, the drawbacks are the need to learn multiple software packages and the need to eventually integrate pieces of the design that are coming from unlike systems.
The integration of CAD and CAM systems with the broader aspects of a firm's operations is referred to as simultaneous or concurrent engineering. Concurrent engineering was adopted by the Ford Motor Co.'s Engine Division, B.F. Goodrich, and Cannondale in the early 1990s. Ford's Engine Division was moving to integrate all production and design systems into a single database that could be accessed from workstations, Macintoshes and IBM-compatible personal computers alike, permitting a large number of groups to comment on engine designs. This enabled not only engineers and designers but also buying agents to make comments. In its production of wheels and carbon braking systems for Boeing's new 777, B.F. Goodrich developed a system that linked all relevant departments, including planning, purchasing, design, manufacturing, quality control and marketing. Cannondale claimed that CAD/CAM technologies enabled it to produce five times as many bicycles per year with the same floor space. CAD/CAM also enabled the firm to redesign 90-95 percent of its 37 models each year.
CAD/CAM EMPLOYMENT TRENDS
CAD/CAM technologies continue to provide growing opportunities for employment as companies seek out cost-efficient methods to develop new products. There are a number of professions associated with CAD/CAM, but the most common is probably that of industrial designers. Industrial design generally requires at least a four-year degree that includes computer based design course work. Designers are typically employed either at specialized design and engineering services firms or at large end-user corporations that require regular design work, such as car manufacturers. As of 1998 the average salary for CAD users was around $44,000. Starting designers made only $28,000, but senior designers typically earned upwards of $60,000 and design managers made $80,000-$ 140,000.
THE FUTURE OF CAD/CAM
Recent technical developments have addressed all aspects of CAD/CAM systems. The use of personal computers and Microsoft Corp.'s Windows software emerged as an alternative to older mainframe- and workstation based systems. The greater viability of personal computers for CAD/CAM applications results from their ever-increasing processing power and comparatively low costs. Faster and more elaborate systems may be run on Unix and other platforms, but these tend to be more expensive and less widely supported. An important trend is toward the standardization of software, so that different packages can readily share data. Standards have been established for some time regarding data exchange and graphics, and the X Windows System and Microsoft's Windows are becoming established as industry standards for user interfaces.
Other improvements in software include greater sophistication of visual representation, such as the replacement of three dimensional by solid modeling, in which objects are represented in a more fully defined manner. Improvements have also been made in the greater integration of modeling and testing applications. Another area under active exploration has been the use of CAD voice control (CVC) software, based on voice-recognition technology. This software can be faster, more accurate, and less tiring than typing or using a mouse—important considerations for designers who spend all day at their computers.
SEE ALSO : Flexible Manufacturing
[ David Kucera ]
FURTHER READING:
Beard, Thomas L. "It's Not Just the Technology That Matters." Modern Machine Shop, July 1998.
"The CAD/CAM Hall of Fame." Machine Design, 22 October 1998.
Hars, Adele, and Mark Halpem. "In Japan It's CAM/CAD, Not CAD/CAM." Design News, 20 July 1998.
Hoffman, Thomas. "Visual Tools Key to Chrysler Cost-Cutting." Computerworld, 18 August 1997.
Machover, Carl. The CAD/CAM Handbook. New York: McGraw Hill, 1996.
Sunderland, John. "Voice Actuation: New Tool for CAD." Appliance Manufacturer, January 1999

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