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Rapid prototyping takes on manufacturing
Stereolithography techniques are now creating models of such high quality and reasonable cost that they are entering the sphere of real production processes
By Anna Kochan, UK, Global Design News -- Design News, July 22, 2002
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| Objet's Quadra machine uses an array of 1,536 ink-jet nozzles to selectively deposit a specially developed resin material and ultra-violet lamps to solidify it. |
London — London—With new materials being developed, and machines becoming more reliable, faster, and lower-cost, an increasing number of companies are taking up the idea of using rapid prototyping technology for manufacturing finished series production parts. So says Terry Wohlers, specialist consultant for rapid prototyping (twohlers@compuserve.com). "Not all companies are in the business of making hundreds of thousands of parts," he comments. "Many need just a few hundred or a few thousand. And if the parts are small enough, rapid prototyping can be less costly than tooling, molding, or casting."
The best rapid manufacturing applications are those where the surface requirements are not too strict, and the parts are hidden from view and do not have high mechanical demands, Wohlers says.
Targeting medical technology. For applications such as dental devices where the products have to be tailored to each individual's needs, rapid manufacturing techniques are particularly well adapted. Align Technology, an orthodontics specialist based in Sunnyvale, CA, has developed a method of producing its Invisalign teeth-straightening devices that is based on stereolithography. The company uses 3D Systems' SLA 7000 machine to build up parts from a CAD model layer-by-layer, using laser technology to selectively harden a liquid resin.
For Montreal-based Cynovad, a specialist in digital dentistry, rapid prototyping is the process of the future for manufacturing prosthetics such as copings, crowns, and bridges. It has entered into an agreement with 3D Systems that relates to the manufacture and supply of several hundred solid-object printers by the end of 2004. Cynovad's plan is to sell the machine, rebranded as WaxPro, to dental laboratories worldwide to make the master patterns for subsequent investment casting in metals or ceramics. "The WaxPro system responds to dental laboratories' needs to increase their throughput and reduce their operating costs, while keeping consistent and reliable prostheses quality," according to Naoum Araj, Cynovad president.
Also in the medical field, Interpore Cross International has developed a rapid manufacturing technique to make spinal implants. These are devices with a latticed structure that come in a variety of shapes and sizes. At the heart of the process is the Solidscape ModelMaker II rapid prototyping machine that builds the investment casting patterns for the spinal implants out of a thermoplastic material.
Car parts also. Automotive applications of rapid manufacturing are also starting to appear. The Jordan-Honda Formula 1 Team, for example, incorporated a number of parts made by SLS (selective laser sintering) on its cars. They were built for Jordan by 3T RPD, a UK service bureau.
For example, the boxes for electrical connections that are needed to hold the cars' complex wire harnesses together were made by SLS because they are constantly revised during the racing season. These boxes are conventionally made of carbon fiber-reinforced plastic, a solution that is strong and light. However, the tooling and hand lay-up process is time-consuming. By making the boxes from glass-filled Nylon materials, by SLS, considerable savings resulted. "A carbon box takes a long time to tool up, so it requires a few days to turn one around," says Mike Stevens, senior CAM engineer at Jordan. "The SLS process can do a dozen boxes in that time." Success with this application has led Jordan to apply SLS to aerodynamic body parts and cooling ducts as well.
Luxury car manufacturers are also taking on rapid manufacturing, according to Michael Turner, product manager at Laser Lines, the company that distributes Stratasys FDM (Fusion Deposition Modeling) machines in the UK. "One company that makes just one or two cars at a time is using actual FDM parts on its products, particularly for ducting assemblies. To make tooling on a one- or two-off basis would be prohibitively expensive," he explains.
The newest FDM material from Stratasys is polyphenylsulfone, which withstands temperatures above 200C and is also very strong. Turner suggests it has great potential for under-hood applications, as well as for plastic parts in the aerospace industry and for sterilized medical devices.
Costs down, innovation up. One factor that is helping rapid prototyping processes take on real production applications is the falling cost of the machines. According to industry consultant Wohlers, a recent price war has already led to a number of products becoming cheaper. The latest Stratasys machine at $30,000 (the Dimension 3D Printer, see box) is reportedly less than half the price of the product it replaces.
Alongside the arrival of rapid manufacturing, the rapid prototyping techniques themselves are evolving. The latest innovation is from Generis, a newcomer to the market, whose GS1500 machine is designed for producing large sand molds and cores. The German company is delivering the first two production machines to BMW and DaimlerChrysler, who will use them to produce the sand cores necessary for casting prototype cylinder heads and engine blocks.
The GS1500 builds models in common foundry sand, with common foundry resin, and is capable of making 12 water core jackets in 12 to 15 hours, which is much faster than the 2 to 3 weeks conventional techniques would need for just one water core jacket, according to Rainer Hochsmann, Generis managing director. Other systems generate models from sand, too, but they are slower, more expensive, and do not offer such a big envelope, he claims.
The Generis GS1500 is capable of producing parts measuring 1.5 × 0.75 × 0.75m with a build speed of 8 l/hr. Ink jet technology is the key to this machine: 512 nozzles dispense first a binder onto each layer of sand (non-selectively), followed by a reactant, which they dispense selectively. When the last layer has been completed, the model is automatically transferred to an unload area by roller conveyor. It is ready to use immediately.
At $679,000, the machine is a significant investment, but running costs are only $9.70 per hour, which Hochsmann claims is lower than those of competitors by a factor of more than seven.
An innovative Israeli rapid prototyping machine from Objet Technologies is now into its second generation. The Quadra Tempo is 20 to 25% faster than the original Quadra and has the capacity for longer unattended operation, according to Dror Danai. The machine uses an array of 1,536 ink-jet nozzles to selectively deposit a specially developed resin material (see figure). Ultra-violet lamps at the front and rear of the nozzle array solidify the resin as it is deposited.
Danai reports a high level of interest from manufacturers of consumer goods, particularly shoes and mobile phones. "With a 20µ layer thickness, the Quadra excels at generating curved surfaces, achieving a smooth contour with a fine level of detail," he claims.
Material improvements. New materials for rapid prototyping are being developed continuously. One recent development of interest: an optically clear stereolithography resin from DSM. Known as DSM Somos 10120 WaterClear, the material can be applied to housings where it is useful to see through to the inside of a device. It can also be used to make models of optically clear parts such as lenses for lamps. This is just one example from many.
For more information about
SLA 7000 from
3D Systems,
www.3dsystems.com:
Enter 533
ModelMaker II from
Solidscape,
www.solid-scape.com:
Enter 534
FDM and Dimension from
Stratasys,
www.stratasys.com:
Enter 535
GS1500 from
Generis,
www.generis-systems.com:
Enter 536
Quadra Tempo from
Objet,
www.objet.co.il:
Enter 537
10120 WaterClear from
DSM Somos,
www.dsmsomos.com:
Enter 538
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