April 2008
The Art of the Quick and Complex
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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