工业设计专业英语(第三版)

Lesson33 Just in Time Design

A dizzying array of choices is available to designers needing to output their CAD designs as physical prototypes. The question of which is best requires some careful consideration. Much depends on what the designer is trying to achieve with the prototype,whether it is a study of form--requiring some degree of high finish and detail-or function, requiring a more robust technique or a particular type of material.

The accuracy of many of the techniques listed below is within a margin of around 0.1 to 0.2 mm, but this tends to vary relative to the direction of the slicing and size of models. (Designers should check with the vendor first if this is a major concern.) All rapid prototyping techniques are limited by the size of parts they can produce in one piece, but vendors can be asked to divide and conquer. They are very savvy at splitting a CAD model and rejoining the pieces to create very large parts.

The Web is a useful resource for keeping an eye on all of these continually changing techniques. Rapid prototyping is such a competitive industry that vendors are always improving materials and processes. Models now take a third of the cost and time that they did five years ago. As a consequence, design teams can now, in theory, make three times as many models, creating a more sophisticated and mature end product.

It is worth remembering that while it is easy to be romanced by all of this computer-aided design and virtual prototyping, the tried and tested foam model, generated in an afternoon from simple 2-D drawings, will often beat out its hi-tech sister in both schedule and cost Here' s an overview of the latest modeling techniques.

Rapid prototyping: the choices.

Selective Laser Sintering(SLS) DTM Corp. Austin, TX; 512-339-2922

Method: Uses laser energy to melt layers of powdered nylon, polycarbonate or elastomer 5,000th of an inch (mils) thick to build up parts with 75 percent the properties of the normal polymer.

Uses: The parts have a slightly granular look making them best suited to models needing strength rather than looks. Good for medical applications.

Laminated Object Modeling(LOM)Helisys Inc., Torrance, CA; 310-891-0600

Method: Build up low-cost sheet materials, such as paper and plastic, into models.

Uses: The main advantage is model size(up to 22'' x32 " x20" )and slightly lower cost. Parts are less accurate and have a thicker,stepped look.

Fused Deposition Modeling(FDM)Stratasys Inc., Eden Prairie, MN; 612-937-3000

Method: Weaves models from a thermoplastic thread ofABS or elastomer.

Uses: Atechnique still in its infancy, FDM produces a coarse 3-D fabric look unsuitable for anything aesthetic.

Ballistic Particle Manufacturing(BPM)BPM Technology, Greenville, SC; 803-297-7700

Method: uses a nozzle to spray tiny molten particles of thermoplastic into 3-D models. The nozzle can deliver the material from any angle, which reduces the stepping effect.

Uses: Holds promise for curvy shapes.

Laser Cutting Lasrcam, Menlo Park, CA, 650-324-2525

Method: Used extensively for architectural models of plastic, paper and wood (not always considered a rapid prototyping technique)

Uses: Any design that can be built up, kitlike, from 2-D CAD profiles can be lasercut. A wide