The World of Rapid Prototyping

By Terry Wohlers

Published in the Proceedings of the Fourth International Conference On Desktop Manufacturing, September 24-25, 1992, San Jose, California
Copyright 1992 by Wohlers Associates

An estimated 436 rapid prototyping (RP) systems are running at customer sites around the world. As many as 12 RP system manufacturers have sold and shipped systems to customers. Six are U.S. manufacturers, three are Japanese, two are European and one is Israeli.

In addition, at least 32 universities, government laboratories and corporations around the globe are developing various forms RP technology. An estimated 19 of them (including the 12 mentioned above) have produced sample parts from their systems. The following is an overview of these organizations and their work.

StereoLithography Apparatus (SLA) by 3D Systems

The StereoLithography Apparatus from 3D Systems (Valencia, CA) is by far the most widely installed system, owning about 73 percent of the worldwide market based on unit sales. The SLA makes parts from thin layers of liquid photopolymer. You first create a 3D surface or solid model of a part with a CAD system, and then create a support structure and attach it to the bottom of the CAD model. Especially critical for parts which contain overhanging geometry, the support structure attaches the part to the SLA's elevator platform and supports the part as the machine builds it. It is removed after building the part.

The SLA-250, 3D Systems' most popular model, consists of several parts. The system includes a computer to run the company's proprietary slicing software and a DOS-based 386 PC to run the SLA control software. 3D Systems offers two options for the slice computer: a 386-based PC running the Unix 386 operating system, or a Unix-based Silicon Graphics Personal Iris workstation. The SLA-250 uses a galvanometer mirror x-y scanner, laser and an elevator mechanism housed inside a vat filled with ultraviolet sensitive liquid polymer.

3D Systems offers the SLA-190, SLA-250 and SLA-500 models. The primary differences between the three models are build chamber size, speed and cost. The SLA-500 uses a more powerful Argon-ion laser instead of a Helium Cadmium (HeCd) laser used in the SLA-250 and SLA-190. This permits the SLA-500 to process significantly faster. The SLA-500 laser moves at 100" (254 cm) per second, while the SLA-250 and SLA-190 laser moves at only 15" (38 cm) per second. The overall speed of SLA-190 parts is about one-half that of SLA-250 parts. This is mostly due to the lack of a wiper blade, which plays an important role in speeding the layer recoating in the SLA-250 and 500.

The SLA-500 is capable of producing parts of up to 20" x 20" x 24" (508 mm x 508 mm x 610 mm), compared to the SLA-250's maximum part size of 10" x 10" x 10" (254 mm x 254 mm x 254 mm) and the SLA-190's 7.5" x 7.5" x 9.8" (190 mm x 190 mm x 250 mm) maximum part size. The SLA-500 requires 67 gallons (254 liters) of polymer, while the SLA-250 uses 7.8 gallons (29.5 liters). The SLA-190 requires only 5.5 gallons (20.1 liters). The price of the SLA-190 is $95,000, compared to $210,000 for the SLA-250 and $420,000 for the SLA-500.

According to a statement issued jointly by 3D Systems and Quadrax in February of this year, the two companies settled the patent litigation that started in September 1990. Under the terms of the settlement, Quadrax transferred its laser modeling patent and related technology to 3D in exchange for 130,000 shares of 3D common stock. At the time, the stock was worth about $325,000. As part of the agreement, Quadrax has discontinued marketing its laser modeling equipment.

The Quadrax technology that 3D Systems now owns includes a special resin applicator which quickly deposits the material from the top. In comparison, the SLA lowers the part into the resin which requires considerable time for resin leveling and is why 3D Systems uses a wiper blade to help speed the process. As the Quadrax applicator spreads the new layer, the part remains stationary. As a result, the resin surrounding the part remains motionless. The SLA process, on the other hand, creates turbulence in the liquid when the part lowers into the liquid. This movement can create uneven tension in and around the part. Since the Quadrax applicator is about 10 times faster, expect to see it in a future version of the SLA.

Selective Laser Sintering (SLS) by DTM

DTM Corporation's (Austin, TX) announcement in 1988 was among the first after the 1987 introduction of the SLA. DTM (formally Nova Automation Corp.) has made their Sinterstation 2000 system available to five beta customers during the first half of this year.

Selective Laser Sintering operates on the same basic layer-by-layer principle as the SLA. However, it uses powder material instead of liquid. A leveling mechanism spreads an even layer of powder material on a platform and the machine sinters the powder. The sintering process uses a laser to raise the temperature of the powder to a point of fusing without actually melting it.

To reduce the laser energy needed to sinter the powder, the system preheats the powder in the build chamber. For example, the system raises the temperature to 365 degree Fahrenheit for nylon powder. This also helps to reduce thermal shrinkage of the layers, thus reducing part distortion. A half-ton air conditioning unit cools the system. Pre-heating can take 45 minutes.

For some applications, the SLS process may offer advantages over liquid-based system. For example, the surrounding powder material serves as a natural support, minimizing the need for support structures to support overhanging geometry. This saves time during the creation of the part, as well as after you remove it from the machine. Also, the SLS process can produce parts in several materials, including polycarbonate, polyvinyl chloride (PVC), investment casting wax and nylon. Polycarbonate parts approach a density of 85 percent. This means that 15 percent of the part is air. Parts of low density are usually weaker than solid parts.

The SLS process can produce parts at a rate of 0.5" (12.7 mm) to better than 1.0" (25.4 mm) per hour, depending on the size and layer thickness of the part. Therefore, you can build a four-inch tall part in 4-8 hours. If you buy a Sinterstation 2000 prepared for use with one material ($397,000), you can later add other materials. The cost for each additional material is $25,000. A Sinterstation 2000 prepared for use with four materials costs $427,000.

SOLIFORM by Teijin Seiki

DuPont Imaging Systems (Wilmington, DE) followed in 1989 with the announcement of their SOMOS 1000 Solid Imaging System, a technology similar to 3D Systems' SLA. Eight SOMOS systems are running at various DuPont facilities, including a DuPont service bureau in Delaware.

Late last year, DuPont licensed the SOMOS rapid prototyping technology to Teijin Seiki of Tokyo, Japan. Teijin Seiki is a global industrial company with annual sales exceeding $500 million. The Japanese company has gained exclusive rights to the technology for Asia, with an option to gain the remaining worldwide rights within one year. DuPont has chose not to manufacture SOMOS systems.

Teijin Seiki reports their RP system, called SOLIFORM, is now available in Asia. The system uses an Argon ion laser and a SPARCstation Unix workstation from Sun Microsystems. Matsushita Electric Industrial in Japan purchased a SOLIFORM system for 50,000,000 yen (about $385,000).

DuPont has retained the associated SOMOS materials technology and provides the materials to Teijin Seiki. DuPont also supplies SOMOS resins to users of 3D Systems' SLA products and Electro Optical Systems' Stereos 400.

Laminated Object Manufacturing (LOM) by Helisys

Formally named Hydronetics, Helisys, Inc. (Torrance, CA) first developed a powder-based system similar to DTM's SLS. Later, they abandoned it to concentrate on Laminated Object Manufacturing. Company president Michael Feygin of Russia invented LOM and began to discuss his invention publicly in 1988.

The LOM process is similar in concept to liquid and powder-based layering systems. However, the LOM machine builds parts using sheet material. The machine automatically positions a thin sheet of paper material from a roll on an elevator platform. It then uses a CO2 laser to cut the sheet using a computer-controlled Roland pen plotter to direct the laser beam. The cut corresponds precisely to the first cross section of the CAD model - in STL format.

The machine bonds fresh sheet material to the previous sheet using a heated roller that presses the two sheets together. The heat from the roller causes the polyethylene-coated paper to fuse together. The laser then cuts the next sheet and the process repeats until the part is complete. When the user of the LOM machine removes the part, the unwanted pieces fall from the part. This material supports the part during the building process; no additional support is necessary. LOM parts do not require post-curing.

LOM parts have the look and feel of wood. For certain parts, the LOM process promises to be faster than other layering processes because the laser outlines the periphery of the part instead of making contact with the entire surface of the part. The machine produces thick walls as fast as thin ones. Also, cutting the material, instead of solidifying it, preserves the original properties of the material. The LOM-1015 system is $85,000, while the larger LOM-2030 unit is available for $140,000.

Solid Ground Curing (SGC) by Cubital

Cubital America Inc. (Troy, Michigan) is a wholly-owned subsidiary of Cubital, Ltd. Two West German and two Israeli corporations jointly own Cubital, Ltd. of Herzlia, Israel. The Cubital unit, called the Solider 5600 Solid Ground Curing system weighs 4.5 tons and is complex. Yet the machine will simultaneously build as many parts as you can position in a 20" x 14" x 20" (508 mm x 356 mm x 508 mm) volume and maintains accuracy of 0.1 percent according to the company. The Solider system irradiates and solidifies a whole layer in a few seconds, regardless of size, complexity and number of parts. Therefore, processing speed may be an advantage of this system if you are making large or multiple parts.

The system charges a glass mask plate as it passes over an ion gun, which in turn shoots ions on the glass at a resolution of 300 dot per inch (118 dots per cm). This forms a pattern which is a negative image of the cross section. The system presents black electrostatic toner which adheres to the ion charged portions of the plate. The transparent areas reflect precisely the cross section of the part(s). The system positions the plate closely over the top of a thin layer of liquid polymer, and an intense flood of ultraviolet light shines through the plate, exposing the entire layer.

After being exposed to the light for a few seconds, the polymer solidifies and the system moves the partially finished part away from the exposing chamber. The solidified layer then undergoes several processes before the system produces a new layer. While these processes are underway, the system wipes the toner from the glass plate and processes the next cross section.

The system removes, by suction, the unhardened liquid surrounding the hardened layer. A thin layer of wax is then spread over the entire layer, filling the areas that before held liquid polymer. The wax, which goes through a cooling process, surrounds and supports the part. Finally, the partially finished part moves to a milling station. It mills the layer and produces a flat surface ready for the next layer. All of this repeats, automatically, until the part is complete. The surrounding wax must be melted away using hot tap water, a hot air gun, a microwave oven, or a conventional dish washer.

The system, priced at $490,000, constructs parts at a rate of about 1.5 cubic inches (28.1 cubic mm) per hour. Additionally, the process requires about 20 minutes of preprocessing time - from raw CAD file to the first layer built. The company has sold several systems in the U.S. and Europe.

Fused Deposition Modeling (FDM) by Stratasys

The 3D Modeler from Stratasys, Inc. (Minneapolis, MN) uses a spool of 0.050" (1.27 mm) diameter modeling filament resembling wire. The system feeds the filament through a heated head and nozzle. Just before deposition, the head heats the thermoplastic filament to a temperature slightly above its solidification state. As it deposits material, the material solidifies.

FDM is simple compared to most other RP processes. It consists of the main 3D Modeler unit, ProtoSlice slicing software and a Silicon Graphics workstation. The light weight FDM head operates at up to 15" (38.1 cm) per second. Successive laminations adhere to one another to form models up to 12" x 12" x 12" (30.5 cm x 30.5 cm x 30.5 cm) in size. The system does not waste material during or after producing the model, so the process requires little cleanup.

The system, priced at $182,000, uses thermoplastic materials, including a machinable wax, an investment casting wax, a nylon-like material called Plastic200 and a new tough plastic material called Plastic300. The investment wax material is appropriate for lost wax investment castings, leaving little residue in the cavity. You can achieve a glassy finish by applying a fluid to the surface of the part.

Stratasys has beta tested the 3D-Modeler at GM, 3M, Biomet, Pratt & Whitney and Texas Instruments. Since then, the company has sold production units to Pittsburg State University (Pittsburg, Kansas), Tri-Tech Precision (Anaheim, CA) and Marbeth Industries (Pico Rivera, CA). Tri-Tech and Marbeth are service bureaus. Recently, Stratasys secured Marubeni Hytech, a $1.5 billion corporation, to serve as an exclusive distributor of the 3D Modeler in Japan. Stratasys also reports they have sold at least one system in Japan.

In July of this year, Stratasys was issued a U.S. patent for the development of Fused Deposition Modeling techniques. The following month, 3M and Stratasys announced a joint development agreement. The partnership will accelerate the development of FDM materials and related technology, according to Stratasys. The company now employs 25 people.

Solid Object Ultraviolet Laser Plotter (SOUP) by CMET (Mitsubishi)

Solid Object Ultraviolet Laser Plotter (SOUP) is what Mitsubishi's CMET (Tokyo, Japan) calls their stereolithography system, which is similar to the SLA. CMET has sold 56 units to organizations such as Mercedes, Fujitsu, Matsushita Electric, two Japanese universities and Dornier Deutsche Aerospace in Germany. In addition to a customer, Dornier serves as a SOUP distributor in Europe.

CMET offers the SOUP 600 and 850 versions of the product. The 600 uses either a Helium Cadmium or Argon ion laser and produces parts up to 600 x 400 x 400 millimeters (24 x 16 x 16 inches) in epoxy resin. The 850 uses the more powerful Argon ion laser and produces parts up to 850 x 600 x 500 millimeters (33 x 16 x 20 inches). Rather than using a galvanometer mirror x-y scanner, the SOUP system uses an X,Y plotter mechanism to direct the laser light onto the surface of the liquid resin. The laser beam, therefore, stays perpendicular to the surface of the resin, which minimizes the undesirable spread light.

Solid Creation System (SCS) by DMEC (JSR/Sony)

Japan Synthetic Rubber (JSR) and Sony's D-MEC company of Tokyo, Japan, have sold 10 of their Solid Creation Systems, which uses stereolithography technology similar to the SLA. The system uses an Argon-ion laser similar to 3D Systems' SLA-500, but offers a larger build chamber. The company has announced an improved version, called the SCS-1000HD, featuring laser drawing speed that is twice as fast as 3D Systems' fastest model, the SLA-500. Toyota bought an SCS for about $500,000.

Stereos 400 by Electro Optical Systems (EOS)

Electro Optical Systems (EOS) of Munich, Germany, offers two versions of a stereolithography system, which are similar to the SLA. The smaller of the two has a build chamber of about 16" x 16 " x 10" (40.64 cm x 40.64 cm x 25.4 cm); the larger system has a build chamber of about 16" x 16" x 24" (40.64 cm x 40.64 cm x 60.96 cm). The smaller system uses a 25 mW HeCd laser, while the larger system uses a 300 mW Argon-ion laser. Both systems use a RISC-based workstation for slicing and a 386 personal computer for process control. The Stereos 400 allows you to quickly change vats of liquid resin without draining and rinsing the vat. EOS uses and distributes DuPont's SOMOS resin materials in Europe.

Three-Dimensional Printing by MIT

The Department of Mechanical Engineering at the Massachusetts Institute of Technology (Cambridge, MA), has developed a rapid prototyping device that uses a jetting mechanism -- the same technology used in ink jet printers. The system spreads a thin layer of ceramic powder on a flat bed, similar to the way DTM's SLS system spreads powder. Using the jetting mechanism, the system solidifies layers as it deposits a fine jet of ceramic binder onto the powder. Following a heat treatment, the unbound powder drops from the formed part as you remove it from the powder.

MIT's prototype system can produce 3D ceramic parts constructed of multiple layers, each 0.005" thick (0.127 mm). The process employs jetting head, a stepper motor and an X/Y positioning device controlled by a 386-based personal computer. Overall, the accuracy of the system is promising, but surface quality needs improvement.

Direct Shell Production Casting (DSPC) by Soligen

Soligen, Inc. (Northridge, CA) licensed MIT's ceramic 3D printing process several months ago. The company, which is focusing exclusively on the casting industry, has shipped three units to beta customers. With DSPC, you can produce expendable ceramic shells (molds) complete with cores, directly with the RP device. This eliminates the need for wax patterns and tooling for cast metal parts.

Several of the company's employees are former employees of 3D Systems. Soligen CEO Yehoram Uziel was vice president of engineering at 3D. Chick Lewis, also with Soligen, was 3D's first employee and helped engineer the SLA product line.

Printed Computer Tomography (PCT) by Texas Instruments

Texas Instruments (McKinney, TX) is developing an RP system using jetting technology called Printed Computer Tomography. They call their working prototype unit the ProtoJet 3D Printing System. It uses an inexpensive ink jet printing mechanism to deposit wax material, layer by layer.

The ProtoJet system produces wax parts up to 12" x 12 " x 12" in size. Resolution in the X,Y direction is 0.004 inch. Part accuracy in the Z direction depends on the layer thickness. The ProtoJet system software creates cross sections from an STL file as it prints them.

The system's design, according to Texas Instruments, reduces operation, maintenance and material costs, compared to other RP systems. The machine does not use toxic materials, so it can operate in an office environment. Support structures, for overhanging geometry, generate automatically in a water-soluble material. You can remove the support material by soaking the part in warm water.

Ballistic Particle Manufacturing (BPM) by BPM Technology

Formally, Perception Systems, BPM Technology, Inc. (Greenville, SC) is working on a rapid prototyping system similar to TI's ProtoJet ink jet system. Bill Masters, founder of the company, calls his technology Ballistic Particle Manufacturing. Initially, Automated Dynamics Corp. (Troy, NY) pursued the technology, but they abandoned the project due to a lack of funding.

The company is designing a new BPM prototype that will deposit a second material, an approach that Texas Instruments uses with their ProtoJet system. The BPM system will use polyethylene glycol, water-soluble synthetic wax, to physically support overhanging geometry. The cost of production should be relatively low because the system will use off-the-shelf parts.

BPM has secured Jon Leonard to serve as company president and CEO. Dr. Leonard was formally a chief scientist at Hughes Aircraft, with degrees in mathematics, engineering, physics and molecular biology/physiology. The company hopes to introduce one system in the $50,000 range and another in the $15,000 range. Product introduction may be 12-18 months away.

Visual Impact Corporation

Visual Impact (Windham, NH) has developed a second generation alpha machine that also uses jetting technology. Richard Helinski, a co-founder of the company, was recently awarded a patent that covers jetting of two materials. The primary material is a plastic that is supported by a secondary support material. Since the two materials differ in solubility and melting temperature, the support material can be removed leaving only the primary material. The company claims the materials are safe and do not require special environmental permits.

The company plans to ship beta units in the second quarter of next year. The beta system will enable you to build parts that fit inside a six inch cube. The company says the device is about the size of a standard office laser printer and operates as a desktop computer peripheral. It will sell for under $20,000 when it becomes available in early 1994.

Design-Controlled Automated Fabrication (DesCAF) by Light Sculpting

Dr. Efrem Fudim, president of Light Sculpting (Milwaukee, WI), has developed a process he calls Design-Controlled Automated Fabrication. Like the Cubital Solider system, Fudim's DesCAF process irradiates a whole layer based on cross section data. It uses a mask containing transparent and opaque areas similar to Cubital's Solider system; however, a person must create each of the DesCAF masks using a photoplotter. Also, a person must manually position each of the masks - one by one. The system irradiates each layer using conventional lamps.

Fudim says his smallest system, called the LSI-0609MA, creates parts up to 6" x 6" x 9" (152.4 mm x 152.4 mm x 229 mm) in size and costs $99,600. The company also offers two larger systems for $129,700 and $159,500. Fudim developed the DesCAF concept in 1986 and delivered the first DesCAF part to an aerospace company the same year. The company also operates as a service bureau for the automotive, aerospace, medical and casting industries.

Stereophotolithography (SPL) by Laser 3D

Laser 3D (Nancy, France) has developed a process called stereophotolithography. The product itself is called the SPL 1000/LSA. Claude Medard, managing director of Laser 3D, compares it to stereolithography technology from 3D Systems, but claims it is about 10 times faster. The SPL system uses a powerful >1 watt laser. By comparison, the SLA-250 uses a 16mW laser; the SLA-500 uses a 200mW laser. (1000 mW = 1 W)

The SPL 1000/LSA will be operational this summer or fall in France. Later this year, the company hopes to install systems in the U.S., operated by service bureaus. Companies in the U.S. that want to gain access to the SPL system will purchase and install a front-end to the system. The front-end reportedly permits you to prepare a CAD file for processing on the SPL system and enables you to send it to the service bureau by modem. A source close to the company (not an employee) claims the system software is about 50 times faster than software used by other RP manufacturers.

In addition to the liquid SPL system, Laser 3D is developing RP technologies that use solid films and powders. Laser 3D has access to research facilities at a university in France.

Shape Melting Technology (SMT) by Babcock & Wilcox

Babcock & Wilcox (Alliance, OH) has developed a process they call Shape Melting Technology. The SMT process uses robotics and arc welding to fabricate parts from weld metal. The process produces very strong parts from layers of material of controlled thickness. Much of their work consists of huge piping parts, such as elbows and flanges, for the U.S. Navy.

Hot Plot by Sparx AB

Sparx AB (Sweden) is selling a $12,900 rapid prototyping system. The unit, called Hot Plot, bonds 0.040 inch (1 mm) sheets of polystyrene. The machine cuts the material using a flat-bed plotter equipped with a heated cutting electrode. An operator must manually position the polystyrene sheets. The system uses AutoCAD and HPGL files as input.

Photochemical Machining (PCM) by Formigraphic Engine Company, Battelle and Osaka Prefecture

Photochemical machining is rapid prototyping technique that has been explored. It functions similarly to other liquid and laser-based systems. However, instead of solidifying the layers on the surface of the liquid, solidification occurs in the interior of the material. The technique uses two lasers of different wave lengths to initiate cross-linking. PCM chemically alters and solidifies polymer at the intersection point of the two beams.

Researchers are exploring several possibilities. One would involve a solid block, where the scanned areas would become cross-linked and insoluble. The final part would appear after soaking the block in a solvent. Another possibility would involve a block of soft gel, hardening where the laser beams meet. Yet another process would use a frozen solution. Only the unscanned material would liquefy when heated, leaving a free-standing part. Finally, the PCM process could degrade unwanted material from a solid block. This would be like machining the part with the two lasers.

Organizations that have researched PCM include Formigraphic Engine Company (Bolinas, CA), Battelle (Columbus, OH) and Osaka Prefecture (Japan). Formigraphic Engine holds patents on the process and had teamed up with Battelle. However, their work has been delayed due to a lack of funding. Osaka Prefecture has received a patent in Japan on a PCM-like technology.

Electrosetting by Electroset Synergistic Technology (EST)

Dr. Ronald Reitz of the U.S. Navy's David Taylor Research Center (Annapolis, MD) has worked on a process involving an electrosetting technique. Electrodes made from a standard pen plotter or laser printer are stacked, submerged in a container of liquid resin and subjected to an intense electrical charge. The process involves the Winslow Effect, the solidification of a fluid by imposition of a biasing electric field through the fluid, invented by Willis Winslow in 1939.

Experiments indicate the process would involve only standard office equipment. An early prototype unit produces parts in silicon, epoxy, polyurethane and polyester. Dr. Reitz has formed Electroset Synergistic Technologies Corporation to develop and eventually license or commercialize the electrosetting technology.

Incremental Fabrication by Incre, Inc.

David Gore of Incre (Corvallis, OR) is developing an RP system using a variation of ballistic particle manufacturing. Gore calls his invention Incremental Fabrication, a process that builds thin layers by ejecting small droplets of molten metal. Gore hopes to complete a prototype system by the end of this year.

Thermal Spray Metal Deposition by Carnegie Mellon

Carnegie Mellon University (Pittsburgh, PA) is developing an RP process that makes metal parts using a thermal spray metal deposition technique. The process creates thin layers by spraying metal through a paper mask. It uses a CO2 laser to cut the masks, similar to the way the Helisys LOM system cuts sheet material.

Colamm by Mitsui Ship Building

Mitsui Ship Building has developed a stereolithography system, called Colamm, but the company has not reported recent developmental or sales activity. Little is known about the system.

Laser Fare

Laser Fare (Smithfield, RI) is working on a second generation RP system that may be complete by the end of this year. The new system will employ thin film technology for mask generation and nonlinear optics, and will produce parts from a wide range of polymers. Rather than manufacturing systems, the company plans to license the technology.


Cybervid (Nashua, NH) is developing Macintosh software that cuts and scores sheet material. An individual then folds the material to create a three-dimensional object, similar to a sheet metal development.

Landfoam Topographics

Norman Kinzie of Landfoam Topographics (Needham, MA) has patented a LOM process that involves the coloration of each layer. This would permit the production of multi-colored parts from a desktop output device. Currently, RP systems can produce single color parts only. A working prototype is not yet available. Kinzie is discussing the process with companies interested in building a working prototype and bringing a system to market.


As new and attractive technologies become available, system prices may drop. For now, prices remain high, although the price/performance ratio continues to improve as existing technologies advance in speed, accuracy, material quality, surface finish, ease of use and safety.

As for desktop manufacturing, none of the systems on the market today sit on a desktop. Very thick concrete-top manufacturing is more accurate. Yet the industry wants a small and inexpensive device that can build models quickly using materials that are not hazardous or troublesome. Companies such as Visual Impact, Texas Instruments, BPM Technology and several others are working vigorously on solutions that meet this demand.

Copyright 1992 by Wohlers Associates