They call it rapid manufacturing, and its progress has been slow, though steady, in gaining the acceptance of industry.
by Harry Hutchinson, Executive Editor
The Museum of Modern Art in New York currently has one of its periodic exhibits showcasing artifacts that make use of industrial and commercial technology. It's called Design and the Elastic Mind. Objects and installations involve video, computers, nanotechnology, and various forms of manufacturing.
One curious object is a handbag made of interlocking links that weave among each other, much like the endless knots that decorate old manuscripts.
The bag, produced for a Dutch design house called Freedom of Creation, does not consist of loops that were pieced together, though.
The object, called Punch-bag, was made of polyamide resin on a sintering machine from EOS GmbH (http://www.eos.info/) of Munich.
EOS is one of several companies trying to push the boundaries of additive manufacturing—the building of parts by curing or melting layer on layer of material.
They say there is a role for their machines in turning out finished products in plastic or metal. EOS markets equipment designed to sinter polymers and also is one of the leading suppliers of metal sintering equipment, but it is not alone. A competitor, for instance, MCP Group in Germany, recently formed a partnership with 3D Systems Corp. in the United States to market metal sintering machines.
 A custom surgical plate for the hip was built on a 3D Systems' Sinterstation Pro SLM System.
Photo courtesy of the Walter Reed Army Medical Center
The companies are positioning their equipment to make far more than novel handbags. They say their technology is uniquely suited to producing medical and dental prostheses, and even has advantages in turning out working parts for use in aircraft, automobiles, and factories.
The Punch-bag was conceived by two designers, Janne Kyttanen and Jiri Evenhuis. The design was created in a 3-D CAD file. FKM Sintertechnik (http://www.fkm-sintertechnik.de) of Wallau, Germany, converted the file to drive an automated machine that sintered the bag from the polymer powder. When it came out of the bed of powder, the bag was a complete network of articulated parts, ready for the handle, which was made in the same bed of polyamide resin. (You can go Freedom of Creation's Web site and see a recap of how the bag was made, at http://www.freedomofcreation.com/video.html.)
Freedom of Creation produces a collection of unusual and complex objects, including lamps that mimic intricate patterns found in nature. You can see examples on the company's Web site, or in person at the museum show. (The Museum of Modern Art, (www.MoMA.org) is on 53rd Street between Fifth and Sixth Avenues in Manhattan. Design and the Elastic Mind runs through May 12.)
CREDIBILITY ISSUES
Sintering and other build-by-layer processes are not new. But they are not universally accepted, either, as bona fide manufacturing options. Part of the reason is that additive manufacturing began as a means of making rough protoypes quickly and cheaply, and many manufacturers don't trust the ability of the process to make production-quality parts.
There are legitimate concerns. Terry Wohlers runs a consulting firm, Wohlers Associates (http://wohlersassociates.com) in Fort Collins, Colo., that follows developments in product design, prototyping, and manufacturing. Currently, there are no universally defined standards specifically for testing sintered parts, he said. Although there are specifications of hardness, tensile strength, and other properties made for materials, it is not always certain how the properties of pieces made by sintering or other additive processes were measured.
"It takes time to qualify and certify materials and processes," he said. It may not be critical in some consumer goods, but in aircraft and automobiles, lives may rely on the quality of parts. "Currently, customers bear that burden," Wohlers said. They must test often at each stage of manufacture.
Wohlers also has a word of caution. "System manufacturers would love to have their equipment used more widely for manufactured parts, because they will sell more machines." Indeed, there will be more finished products made than prototypes. But not all rapid processes lend themselves to making durable parts. The mechanical properties of photopolymers, the resins that harden under light, unlike thermoplastics, change in time under exposure to humidity or light, Wohlers said.
Wohlers sees a number of practical roles in industry for additive manufacturing, including production of short runs of products and replacement parts. What's more, he also sees the process as a solution to fill the time gap between a finished design and manufacturing.
A company, he said, may face a long wait for the tooling to make a key part. Rather than wait weeks for delivery of tools, the manufacturer can get an early start on production and turn to sintering, which requires no tooling. According to Wohlers, a manufacturer of heavy machinery was in such a situation, waiting for tooling to make an assembly for a wire harness. The manufacturer was able to sinter several hundred copies of the part and get its equipment into limited production and on the market before the tooling arrived.
Among the additive fabrication processes, sintering has an advantage in that it can build parts of metal as well as of plastic. Because it requires no tooling, sintering is a practical method for manufacturing one-of-a-kind objects, such as dental prostheses, which have to be tailored to each patient. Sintered metal can form the substrate of a dental crown, for instance. Implants for bone and joint reconstructions can also be manufactured for each patient's unique needs and build. What's more, the machine can produce several dissimilar objects simultaneously—as many as the designer can fit onto the build platform.
Geometry is one of the key selling points for additive manufacturing. It can produce objects of more complex shapes than any machining process can. An assembly of eight or a dozen parts, including moving parts, can be built as a single piece, without tooling. That, its advocates say, gives additive manufacturing a clear advantage over CNC machining for short runs of complex metal parts. Machining would require a design of several discrete parts that would have to be assembled.
PUSHING THE BUILD ENVELOPE
Researchers also say that additive, or rapid, manufacturing— at least for certain jobs—promises advantages over the injection molding of plastics.
Neil Hopkinson is a member of the academic staff of the Rapid Manufacturing Research Group (http://www.lboro.ac.uk/departments/mm/research/rapid-manufacturing/) at the University of Loughborough in England. One of his research projects is called "Proving Commercial Viability of High Speed Sintering Through a Large Build." His work suggests a way to make additive manufacturing more economical in high-volume production.
Hopkinson is working with polymers in a two-step process. The machine deposits a layer of polymer as in a conventional sintering operation. Then, a radiation-absorbing layer is placed on the polymer powder bed. The second layer absorbs energy from an infrared lamp and heats to the point where it can melt and sinter the polymer.
Printing the energy-absorbing layer and using a lamp for heat instead of a laser allows scaling to bigger beds, Hopkinson said. A one-meter-square bed for certain geometries—such as small, complicated parts—could produce a few thousand pieces over 24 hours. That would avoid the cost of tooling for injection molding and could prove practical for products needed in runs into the tens of thousands of units, he said.
The project is funded by the university's Innovative Manufacturing and Construction Research Centre and by a British government agency, the Engineering and Physical Sciences Research Council.
Hopkinson also pointed out that a manufacturer can take advantage of sintering's ability to build very complex shapes. "It will allow geometries that are impossible by injection molding or machining," he said. At least, impossible without a good deal of assembly.
As an example, Hopkinson said he had worked a few years ago with an automobile manufacturer on a design to simplify the manufacture of a door handle. The original design consisted of an assembly of 11 components in eight materials. They were able to manufacture a prototype as a proof of concept by selective laser sintering, as if it were a single piece, including the spring mechanism, he said.
SEPARATE TO BE EQUAL
One of the advocates for metal laser sintering in the United States is Greg Morris. He and two partners, Wendell Morris and Bill Noack, operates Morris Technologies in Cincinnati, which offers services ranging from engineering and design to rapid prototyping and CNC machining.
The three partners of Morris Technologies along with a fourth associate, Curt Taylor, last year formed a company, Rapid Quality Manufacturing (http://www.rqmfg.com) in Hamilton, Ohio. The company operates three metal laser sintering machines built by EOS. Taylor is the new company's president.
Between the two companies, Morris and his partners own eight sintering machines from EOS. Morris Technologies has five—one an older model called M250Xtended, and four of EOS's latest, the M270. Rapid Quality Manufacturing has three of the M270 machines. The companies run four metals, including stainless 17-4 and cobalt chromium.
The new company distances itself from the prototyping image and instead focuses on manufacturing using additive fabrication technologies such as direct metal laser sintering.
 The eight parts of a lockbox were manufactured simultaneously by Morris Technologies in a production run that took 53 hours of automated, unattended operation using EOSINT M 270 direct metal laser-sintering equipment.
Photo courtesy of Morris Technologies and SentriLock
According to Morris, a company historically producing prototypes—which usually serve to fit a test or as a visual aid—faces significant obstacles in establishing itself as a supplier of finished, production parts. "It is difficult for many industries to see traditional rapid prototyping companies as manufacturing sources," he said.
Although Rapid Quality Manufacturing has been in business for less than a year, it is making finished parts using direct metal laser sintering for customers in the aerospace, medical, and dental fields.
"It is essential to pick the right kind of geometry," Greg Morris said. If a part can be produced by machining, then it should be machined. Sintering is outstanding for the production of smaller parts with highly complex geometry. It also allows for the combination of parts into one, and thus can eliminate labor-intensive assembly steps.
Speed of building and layer thickness depend on the material used. According to EOS, the machine can build 2 to 20 cubic millimeters per second in layers 20 to 100 micrometers thick. Effective build envelope is 250 x 250 x 215 mm.
EOS’s metal laser sintering machine, the Eosint M270, carries a price of about $500,000. The company’s machines for sintering plastics range from $190,000 to $750,000.
Morris said the thinnest practical wall thickness of a part is 0.010 inch across short distances.
Applications can range from runs of one or two to hundreds of pieces, but even for some cases sintering has applications for thousands and tens of thousands of pieces.
FAST TRACK
Another company, Quickparts.com, as its name implies, has founded its business on supplying prototypes and short runs of finished products with a fast turnaround. The company uses a variety of manufacturing processes, including laser sintering, stereolithography, CNC machining, and metal stamping. The company has automated its online ordering process to make that faster, as well.
According to Patrick Hunter, vice president of sales and marketing at Quickparts, "The big brake on acceptance of additive manufacturing has been the reliability of materials."
Today, however, rapid manufacturing is "growing into the education stage," he said. The job at hand is "to convince customers that the process can meet their needs."
Quickparts' president, Ronald Hollis, wrote a book as an introduction to rapid manufacturing technology for engineers and manufacturers. It is called Better Be Running. (The title comes from a brief discussion of the realities of life for the lion and the gazelle. One must run to eat. The other has to run to escape.)
In the book, he discusses various rapid manufacturing processes, including CNC machining, laser sintering, and a patented process developed by Stratasys (http://www.stratasys.com/), which it calls fused deposition modeling.
The process uses two materials, which are laid down layer by layer in a heated chamber. One material is the polymer that will harden into the finished part. The other provides support and is removed when the part is complete.
 Stratasys's FDM 900 MC manufacturing center contains 32 parts made by the company's rapid manufacturing process, fused deposition modeling.
Photo courtesy of Stratasys
Stratasys has several build materials with the names of conventional polymers. It has an ABS, for instance, and although the material has properties like those of the generic polymer, the Stratasys version is a proprietary chemical formulation designed specifically for the FDM process. According to Stratasys, its ABS has a tensile strength of 3,200 psi or 22 megapascals, and a tensile modulus of 236,000 psi or 1,627 MPa, when tested under ASTM D638. It lists a Rockwell hardness for the material of R105.
The company has published a number of case studies about the uses of its process to meet manufacturing challenges. Digital Mechanics AB in Sweden used the process to build a redesigned robot gripper to be used by an injection molder.
The gripper holds and transfers conical parts with diameters ranging from 400 to 500 mm, but vacuum hoses of the original design interfered with the movement of the robot. Digital Mechanics was able to use additive fabrication to remake the gripper arms with internal vacuum channels and so eliminated the vacuum hoses.
According to Digital Mechanics' managing director, Fredrik Finnberg, the company has recently filled another order for a customer that ran to 6,000 pieces. Finnberg said the order came in stages. The parts measure approximately 15 x 10 x 5 mm, to fit a lock for interior use, as on a cabinet. The manufacturer of the locks ordered 3,000 parts initially, which it would use to assemble the finished product while it waited for conventional tooling to arrive. Then the customer ordered 1,000 more to cover the period when it installed the tooling. A third order, for 2,000 units, came when the manufacturer retooled to alter the part.
Finnberg said it takes about four weeks to build 3,000 of the parts.
Above: Components for the robotic gripper were first prototyped, then manufactured, using FDM (fused deposition modeling). Below: The robot is used by an injection molder to hold and transfer large, conical parts.
BMW, meanwhile, has used fused deposition modeling to make hand-held assembly tools that it uses on its assembly line.
What's more, practicing what it promotes, Stratasys has taken a new approach to manufacturing one of its own machines. The company's FDM 900 MC manufacturing center contains 32 production parts that are made by fused deposition modeling. According to a spokesman for Stratasys, no tooling has been made for those parts.
TESTING ONE'S METAL
Materials Solutions (http://www.materialssolutions.co.uk) is the name of a manufacturer based at the University of Birmingham campus in England. It works in additive manufacturing, and plans eventually to offer net shape manufacturing and coatings. It added a third EOS M270 metal sintering machine earlier this year.
Responding to questions by e-mail, Carl Brancher, CEO of Materials Solutions wrote: "The latest metal machines have lasers that are well absorbed by metal powders and in principle a broad range of recognizable engineering alloys can be processed. The materials properties of e.g. 17-4 stainless steel are not exactly the same as a forged or cast part, but thus far materials properties are as good as cast, and in some cases more like forged."
Resistance to new manufacturing technology is to be expected, Brancher said.
"There has to be a compelling reason to adopt a new manufacturing route," he wrote. "Being cheaper is never enough, as any change comes at a cost (risk/money). Being able to make otherwise unmakable parts requires an investment in the new technology—because if the materials properties are not good enough or the parts not reliable over time, then there is no fallback position."
As he sees it, "Our job is to prove out the materials."
He said that rapid manufacturing technology belongs in a supply chain along with wire EDM, and other processes, and that one problem it faces may be that it has been oversold— "as a 'magic bullet' where you simply throw CAD files and powder at a machine and watch parts drop out the back end." The consequence has been disappointment when expectations have been raised too high.
He added that sintering and other additive processes lack the history that other manufacturing technologies have developed. People may raise questions, for instance, about voids in a sintered piece. The same questions could be asked of a casting, but castings have had time to prove themselves, whereas rapid manufacturing has not.
There are a variety of metal powders available for sintering from various suppliers. Options include alloys of steel, titanium, and aluminum.
 One direct metal laser-sintering system can produce as many as 500 dental copings directly from CAD data within 24 hours. The sintering technology eliminates process steps such as casting of the copings and can increase the efficiency of dental laboratories.
Photo courtesy of EOS GmbH
Materials from EOS, for example, include a maraging steel, a bronze-based powder called DirectMetal 20, 17-4 and PH1 stainless, two types of cobalt-chrome, and a titanium alloy.
As more of their customers embrace direct manufacturing, more companies have added metal-based processing to their offerings.
Earlier this year, for example, 3D Systems Corp. (http://www.3dsystems.com) added two models to its Sinterstation line that are designed specifically for metal parts. They are made by a German company, MCP Group (http://www.mcp-group.de), and will be marketed worldwide by 3D Systems under a private label arrangement, according to Simon van de Crommert, 3D's product manager for direct metal products. The two machines from MCP will be marketed along with 3D Systems' current line of equipment under the brand name Sinterstation.
The smaller of the two, called DM100, has a 5-inch-diameter build area and a 3-inch build height. Its price is about $500,000, van de Crommet said. The other, DM250, is 10 x 10 x 9 inches and carries a price of $1 million.
Initial materials offerings consist of two grades of aluminum and two of titanium, a toll steel, a stainless, and cobalt-chrome, which is especially desirable for dental and other medical uses.
SMALL AS A BIG IDEA
At one point in Better Be Running, Ronald Hollis considers the new manufacturing landscape. Plentiful, cheap labor has given China an edge in mass production. A manufacturer in the developed world has to find a niche to survive. It could be custom, short runs, high-precision machining, or something else that can't be done as well from the far side of the globe.
"China's strengths provide a strong competitive edge to continue to grow and maintain their status as a leading manufacturer of the world," Hollis wrote. "However, the U.S. manufacturer has an opportunity to continue to transform into a segment that can profitably operate in the new economy, most likely through low-volume manufacturing. … Low-volume manufacturing allows the manufacturer to specialize in an area, such as tight tolerances or fast lead times."
If Hollis sees rapid manufacturing as a wave of the future, he doesn't think it's the only wave. But it's one that his company and several others intend to ride.
Technology that allows for limited volume production and very short runs lends itself to mass customization. According to EOS, industry and consumers increasingly request individually manufactured products. Automated laser sintering, which is EOS's interest, and other rapid manufacturing processes are designed to do that kind of work.
Representatives of EOS last year polled visitors to two manufacturing trade fairs in Germany, 2007 K in Düsseldorf and Euromold in Frankfurt, for their opinions concerning the manufacture of functional parts and tools directly from CAD data. Some 70 percent of the people who responded said they believe the mass market is ready for digital manufacturing—or e-manufacturing, as EOS called it.
According to Greg Morris at Rapid Quality Manufacturing, it may take 10 or 20 years for the technology to become fully accepted, but he is convinced it will become mainstream. As he put it, "Rapid manufacturing will change the way many parts are produced."
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