• many aspects of systems are completely computerized
• engineering and manufacturing functions are not co-located
• consumer products (with which we're most familiar) are easier and cheaper to replace than to repair -- young people are not as inclined to open devices and see how they work as they were perhaps a generation ago

But it that case, it's important to impress on the young engineer that "rapid prototyping" doesn't mean "building a prototype quickly." :-)

While both modeling and prototyping capture the functionality of some system, modeling does so without actually making the functions happen. Prototyping involves building a functional (if incomplete) version of the system.

If one picture is worth 1000 words, what's one working prototype of a conceptualized system worth? Here are some pros and cons for prototyping as a system development tool:

PROS

• makes the product real for (at least some) customers and investors; makes them feel that real progress is being made
• enables iteration and change, especially on required design features, early in the design process
• enables detection of errors, leading to better solutions, early in the design process
• proves that the system is manufacturable, or even feasible
• although users may find it difficult to describe what they want in a system, they usually recognize what they want/don't want when they see it

CONS

• could (theoretically) solve the wrong problem(s)
• could give the impression that documented specs are unnecessary
• skipping steps could lead to the first solution instead of the best solution
• might not address all design issues (it's by definition incomplete)
• might encourage premature commitment to a particular design; might give a false view of how long the system will take to complete; might encourage overcommitment to particular features
• a large number of design iterations could lead to maintenance and/or operational problems associated with previous versions; lessons learned can be more easily lost
• prototyping generally COSTS MORE than modeling and can also TAKE LONGER

If you recognize the risks, the rewards may win the day.

Rapid Prototyping

The term rapid prototyping is generally applied to processes which build a mechanical part from nothing, by applying and building up thin layers of material, usually via lasers or nozzles. These processes are driven by and depend heavily on CAD models.

Conventional processes, on the other hand, will generally generate a part by cutting material from a solid (e.g. by milling). Rapid prototyping may not be suitable for simple parts, if they can be created as simply and cheaply by conventional means. Some parts are most efficiently created by a combination of conventional and rapid means. Rapid prototyping processes may also be used to prepare tooling for actual production.

Rapid prototyping processes do not address software or electronic parts.

References

Rapid Prototyping Home Page
Whitten, J. L. and L. D. Bentley, Systems Analysis and Design Methods. Boston: McGraw-Hill, 1998. ISBN 0-256-19906-X

Ask yourself the following questions:

• Is the design mature? If it isn't, it may be a candidate for prototyping.
• Can you absorb the cost of the prototype? If you can't, either it may not be worth the gamble or you need to seek funding from an external source.
• Can a model tell you what you need to know? More complex designs may have effects that models alone can't reveal.

• Test CAM operations with reusable materials (e.g. wax) before formal machining. This can save a bundle of money on mistakes.
• Make sure you have a means of providing CAM operations with operator feedback. This can also save a bundle.