The Rapid Guide

According to the Wohlers Report 2001, rapid prototyping (RP) has developed over the past decade into a $1 billion per year industry with around thirty manufacturers globally providing a variety of technologies.

Parts produced by RP systems are used for several purposes, including testing of form, fit and function. Form testing allows a designer to verify the CAD design, evaluate manufacturability, and get reactions from potential users.

Fit testing verifies that the designed part mates accurately with adjoining portions of the final assembly, and functional testing places the part in an operating assembly to see if it works.

While the limited range of RP materials has restricted functional testing, higher temperature and more durable materials are appearing.

RP parts are frequently used as the basis for rapid tooling. The system creates a positive or negative pattern, which is used to generate injection moulding, investment casting or other tooling for short to medium volume production runs.

Some methods of RP can produce metal parts directly, although still not with the complete size, accuracy and durability of subtractive metal fabrication techniques.

Selective laser sintering (SLS) produces parts that can be sintered and infiltrated to nearly full density. This is the approach taken by DTM in the US for its direct metal fabrication method. In contrast, German company EOS has a selective laser sintering process that fabricates fully dense metal parts directly.

While the choice of alloys is limited, it’s possible to use injection moulding tools fabricated this way to produce fairly high volumes of parts.

3-D Systems sold the first RP system in 1988, and Helisys, DTM, and Stratasys entered the market over the next four years with products based on different technologies. These first generation systems are, in general, expensive and relatively large.

The second generation of systems, based on inkjet techniques, appeared in 1995. Solidscape and Z Corporation offer products that are less expensive, easier to use, and smaller. 3D Systems also produces an inkjet product.

Stereolithography (SLA) still accounts for the largest share of systems. 3D Systems is today’s market leader and its SLA products use high-powered lasers to solidify successive layers of a liquid resin.

The company’s products are based on two different technologies. Stereolithography is sold as a solution for higher accuracy and resolution applications, while an inkjet based system is a lower cost concept modeller aimed at the office environment. 3D Systems has recently merged with DTM Corp.

DTM sold its first selective laser sintering (SLS) system in 1992. This system uses a high-powered laser to partially melt successive layers of powder.

The company offers a range of materials, including polyamide, glass-filled polyamide, steel, copper and polymer coated sand for casting applications. However, while improvements have been made, this SLS system still lags behind the market in terms of accuracy and surface finish.

Stratasys sold the first fused deposition modeling (FDM) system in 1991. Stratasys’ machines are mostly small, office-friendly and quiet although the company has recently introduced larger equipment. The systems extrude a narrow bead of plastic and can make small parts quickly, using an increasingly wide range of materials.

Helisys sold its first laminated object manufacturing (LOM) system in 1991 but ceased operations last year. This simple technology uses a laser to cut paper layers and then stacks and bonds them in a wood-like block.

The founder of Helisys has formed a successor organization, Cubic Technologies. This method is relatively fast, and materials are cheap, but accuracy and finish are not as good as competitive products. Also, laser cutting of paper generates heat, flames and smoke.

Solidscape, founded in 1993, produces an inkjet-based machine that can build small parts with excellent surface finish at a relatively slow rate. It uses a small milling head to trim each layer, allowing greater accuracy and the ability to correct mistakes resulting from a failure of the inkjet.

Z Corporation produces a concept modeller based on MIT’s three dimensional printing (3DP) technology. The system uses a wide inkjet head to bond a starch, cellulose or plaster-based powder with a binder into the form of an object. This system is significantly faster than other concept modellers although the accuracy and finish of the objects is poorer than the competition.

EOS GmbH of Germany manufactures both stereolithography and selective laser sintering systems. EOS sold its stereolithography business to 3-D Systems in1997, but remains the largest European producer.

Fockele & Schwarze produces stereolithography systems in Germany and offers the selective laser melting process developed at the Fraunhofer Institute.

Arcam of Sweden is developing electron beam melting technology. This process is similar to selective laser sintering, but replaces the laser with an electron beam and has the potential to form dense metal parts from a wide variety of metals and alloys.