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Additive Manufacturing Technologies:
Technology Introduction and
Business Implications
Brent Stucker
University of Louisville
INTRODUCTION
Additive manufacturing (AM) technologies have finally hit the mainstream.
After 25 years of development as “rapid-prototyping” techniques, the industry
is transforming into a manufacturing-focused enterprise. Today, when you walk
the trade show floors and attend industry conferences, there are more than just
engineers and manufacturers walking around. You also bump shoulders with
investment bankers, venture capitalists, and do-it-yourself enthusiasts. A recent
National Geographic video has gone viral on the Internet, showing the potential
for 3D printing of a crescent wrench. So many people have seen the video and for-
warded its link via email that some recipients assumed it must be a viral hoax, and
snopes.com (the email hoax-tracking website) had to confirm the reality of “3D
printing.” Within the past year the Economist, the New York Times, Standard &
Poor’s, Wired magazine, and others have all written about 3D printing techniques.
So what is the hype all about? Many believe additive manufacturing is revo-
lutionary and has the potential to transform manufacturing in the same way that
Web 2.0 transformed cyberspace (the transition of the Internet to user-driven
content, such as Facebook, Twitter, LinkedIn, etc.). As consumers begin to see the
potential for creating their own manufactured goods using additive manufactur-
ing, Factory 1.0 (production of physical goods by companies and manufacturing
experts) will transform to Factory 2.0 (production of physical goods by con-
sumers), thus permanently transforming the manufacturing landscape.
5
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6 FRONTIERS OF ENGINEERING
ADDITIVE MANUFACTURING
Additive manufacturing techniques are a collection of manufacturing pro -
cesses that join materials to make physical 3D objects directly from virtual
3D computer data. These processes typically build up parts layer by layer, as
opposed to subtractive manufacturing methodologies, which create 3D geometry
by removing material in a sequential manner. In 2009, after more than 20 years
of confusing terminology, the ASTM International F42 Committee on Additive
Manufacturing Technologies defined additive manufacturing as the “process of
joining materials to make objects from 3D model data, usually layer upon layer,
as opposed to subtractive manufacturing methodologies.” These technologies
were also called rapid prototyping, direct digital manufacturing, solid freeform
fabrication, additive fabrication, additive layer manufacturing, and other similar
technology names over the years. In the technical community, an international
consensus has coalesced around the use of “additive manufacturing,” whereas in
the popular press the technologies are known as “3D printing.”
Every existing commercial AM machine works in a similar way. First a 3D
computer-aided design (CAD) file is sliced into a stack of two-dimensional planar
layers. These layers are built by the AM machine and stacked one after the other
to build up the part (Figure 1). Today, there are seven different approaches to AM,
and dozens of variants of these approaches. As most of these approaches were first
patented in the late 1980s and early 1990s, in many cases the fundamental process
patents have expired or are expiring soon—thus opening up the marketplace for
significant competition in a way that was impossible over the past 20 years due
to intellectual property exclusivity.
The remainder of this paper provides an overview on the seven differ-
ent approaches to AM, followed by a discussion of the business trends and
opportunities afforded by AM techniques. The breakdown of AM processes
into the following seven categories is based upon the work of the Terminol -
ogy Subcommittee of the ASTM F42 committee. At the time of the writing
of this paper this categorization is being balloted, and thus the final names of
these categories are subject to change as the standards-development consensus
process proceeds.
Material Jetting
Material jetting is the use of inkjet printers or other similar techniques to
deposit droplets of build material that are selectively dispensed through a nozzle
or orifice to build up a three-dimensional structure. In most cases these droplets
are made up of photopolymers or wax-like materials to form parts or investment
casting patterns, respectively. These processes are truly 3D-printing machines,
as they use inkjet and other “printing” techniques to build up three-dimensional
structures.
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ADDITIVE MANUFACTURING TECHNOLOGIES
Desired Shape Actual Shape from Additive
Manufacturing Machine
FIGURE 1 Layered approach to AM.
Photopolymers are useful materials for material jetting because they trans -
form from a liquid to a solid in the presence of light. Photopolymers can be tuned
to cross-link and harden in response to different wavelengths of light, and for AM
they typically transform in the visible or ultraviolet wavelength ranges.
Material-jetting techniques often use multiple arrays of printheads to print
different materials. The most common reason for printing two materials is for
one of the materials to be used as the “build” material, while the second material
is used as a “support” material. For 3D geometry that includes channels, voids,
or overhanging structures, a support must be built below any overhanging sur-
faces (as droplets have to land on something to keep them in a fixed location; see
Figure 2). When a secondary support material is used, a water-soluble material
is commonly used so that the supports can be removed by immersing the part in
a water-based liquid.
Material jetting is capable of printing multimaterial and gradient-material
structures. Applications of multimaterial parts range from parts with controlled
hardness and flexibility to parts with differing electrical properties in various
regions to tissue-engineered structures with different biological properties in dif -
ferent regions of the part.
Binder Jetting
Binder-jetting techniques also use nozzles to print material, but instead of
printing with the build material, the printed material is “glue,” which holds powder
together in the desired shape. A binder-jetting process starts by first depositing
a thin layer of powder. A printhead is then used to print a glue pattern onto the
powder, thus forming the first layer. A new layer of powder is deposited and glue
is printed again. This pattern is repeated until the part is completed.
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8 FRONTIERS OF ENGINEERING
FIGURE 2 Thermojet wax manifold. Note the supports.
Two benefits of binder jetting are its speed and its lack of need for secondary
support materials. Since the majority of the volume of the part is made up of the
powder material, only a small fraction of the volume of the part needs to be depos-
ited from the printheads. As a result, a layer can be formed very quickly (using
arrays of printheads)—often in a matter of seconds. The powder that surrounds the
part being formed will naturally act as a support for any subsequent overhanging
geometries, and no secondary support materials are necessary.
The only commercially available full-color 3D printing machines are binder-
jetting machines. A binder-jetting machine can be set up in such a way that a
complete color spectrum can be printed layer-by-layer. This enables assembled
parts to be produced in the intended colors (for marketing purposes) and for
graphics, labels, and other visual features to be directly printed onto a part as it
is being produced (Figure 3).
Photopolymer Vat
Photopolymer vat processes involve selective curing of predeposited photo-
polymers using some type of light source. Stereolithography, the first patented
and commercialized AM process, works by scanning a laser across the surface of
a vat of photopolymer. A platform is raised to just one layer thickness below the
surface of the liquid. The laser scans the first cross-sectional layer, attaching the
layer to the platform. The platform is lowered within the vat one layer thickness
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ADDITIVE MANUFACTURING TECHNOLOGIES
FIGURE 3 ZCorp 3D printed layer. Glue is printed inside the blue contours of the part layer.
Color figure available online at http://www.nap.edu/catalog.php?record_id=13274.
(and material flows over top of the previously formed layer, or is formed over the
previous layers using a blade or deposition device), and the process repeats until
the part is completed. Photopolymer vat techniques give some of the best accura -
cies and surface finishes of any AM process.
Some photopolymer vat technologies have been developed to use digital light
processing projectors to project an image of the layer on the surface of the vat,
thus cross-linking the photopolymer and converting the entire layer from a liquid
to a solid simultaneously.
Photopolymer vat technologies require a support network to be built for over-
hanging structures, otherwise these structures are subject to breaking or deform -
ing. These supports are made from the same material that the part is made from,
so these supports must be cut away after the part is completed.
Material Extrusion
The largest installed base of AM techniques is based upon material extru -
sion. Material-extrusion machines work by forcing material through a nozzle in a
controlled manner to build up a structure. The build material is usually a polymer
filament that is extruded through a heated nozzle—an automated version of the
hot-glue gun used for arts and crafts. After a layer of material is deposited by
the nozzle onto a platform, the platform either moves down or the nozzle moves
up, and then a new layer of material is deposited.
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10 FRONTIERS OF ENGINEERING
In instances where two nozzles are installed in a machine, one of the nozzles
is typically used to deposit a water-soluble support material. Three or more
nozzles are sometimes used in machines designed for tissue-engineering research,
so that scaffolds and other biologically compatible materials can be deposited in
specific regions of the implant.
The simplicity of material-extrusion machines makes them suitable for
in-office and home environments. Today, thousands of inexpensive extrusion
machines, ranging in price from $700 to $3,000, are sold each year to do-it-
yourself enthusiasts, small companies, educational institutions, and hobbyists.
This proliferation of low-cost AM machines is a major reason for the current
mainstream interest in 3D printing.
Powder Bed Fusion
Powder-bed-fusion machines work in a manner similar to binder jetting;
however, instead of printing glue onto a layer of powder, thermal energy is used
to melt the powder into the desired pattern. In most machines a laser is used to
melt polymer or metal powders to build up three-dimensional objects. Another
common variant is the use of an electron beam to melt metal powders.
In the case of polymer powders, the powder surrounding the part being built
makes possible the creation of complex three-dimensional objects without sup -
ports. However, for metal powders, the thermal shrinkage of metal parts during
solidification causes the parts to warp; supports are used to attach the part to a
thick metal baseplate to maintain the accuracy of the parts and restrain them from
warping. These metal supports are machined off after the part is completed.
Powder-bed-fusion machines are the most commonly used AM machines
for the creation of end-use parts for highly engineered products. Polymer and
metal parts made using these techniques are becoming widely used in aerospace,
defense, and other highly engineered systems.
Directed Energy Deposition
Directed-energy-deposition machines melt material with a laser or other
energy source as material is being deposited. These machines work similarly to
material-extrusion machines except that, instead of melting the material with a
nozzle, the wire or powder feed material is melted as it is being deposited onto
a part (Figure 4).
In order to make parts with overhangs, directed-energy-deposition systems
need to use either a five-axis deposition system (so that material can be deposited
from any orientation) or a secondary support material. Because these systems are
typically used to make metal parts or metal-ceramic composite structures, any
supports that are used require machining to remove them.
Directed-energy-deposition processes are used primarily to add features
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ADDITIVE MANUFACTURING TECHNOLOGIES
FIGURE 4 Trumpf machine depositing metal from powder (across a curved surface).
to an existing structure (such as adding strengthening ribs onto a plate) or for
repair of damaged or worn parts. In most cases these processes are used to build
up metal structures, and thus they are commonly referred to as metal-deposition
AM machines.
Sheet Lamination
Sheet lamination techniques work by cutting and stacking sheets of material
to form an object. This approach has been used with paper, plastic, and metal
sheets to build up wood-like, plastic, and metal parts, respectively. A binder is
typically used to bond paper and plastic sheets, whereas welding (either thermal
brazing or welding, or ultrasonic welding) or bolting of sheets together is typi -
cally used for metals. Additionally, sheet lamination has been used with ceramic
and metal green tapes (e.g., powder held together by a polymer binder in the form
of a sheet of material) to build up structures that are later fired in a furnace to
achieve a dense part.
Hybrid and Direct-write AM
In some instances multiple AM techniques are combined within the same
machine or AM is combined with subtractive techniques such as computer
numerical control milling or laser cutting. For instance, by combining a simple
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12 FRONTIERS OF ENGINEERING
horizontal milling head into a material-jetting machine, Solidscape has created a
popular line of high-precision wax printing machines with layer thicknesses of
0.0005 in. that are heavily used in the jewelry industry to create wax patterns for
custom jewelry.
Several AM techniques have been modified to work at a small scale to deposit
passive electronic structures (conductors, insulators, resistors, antennas, etc.).
These techniques are often known as direct-write techniques and, for instance,
use electronic “inks” that contain nanoparticles or other additives that result in
electronic properties after drying, thermal decomposition, or other post-treatment.
By combining direct-write techniques with other AM techniques it becomes pos -
sible to create multifunctional 3D-embedded electronic structures on a layer-by-
layer basis that combine structural, thermal, electronic, and other functions into
a single component.
BUSINESS IMPLICATIONS OF AM
AM has made a significant impact on manufacturing design over the past
25 years as rapid-prototyping techniques. The ability to create three-dimensional
objects directly from CAD data allows designers to print out 3D representations
of their designs for form, fit, and functional testing during the design process. This
reduces the time needed to prototype new designs and enables more optimized
designs to propagate through to manufacturing, catching errors before committing
to costly mass-production tooling and assembly lines.
The layer-by-layer approach of AM is particularly well suited for highly com-
plex geometries, including geometries with internal passageways, undercuts, and
features that are difficult or impossible to make using traditional manufacturing
techniques. For small, highly complex objects, AM powder-bed-fusion processes
are sometimes cheaper than injection molding for volumes of parts approaching
100,000 components. However, the larger the part or the simpler its geometry, the
more cost-effective traditional manufacturing processes become, compared to AM.
AM is well suited for parts with complex geometries that are made in low
volumes or for personally customized geometries. For instance, AM is used today
in many aerospace systems, including the Space Station, microsatellites, F-18
fighter jets, Boeing 787 aircraft, and more, and for custom dental aligners and
hearing aids. AM techniques are commonly used as assembly jigs and fixtures
by BMW and others to enable more ergonomic, accurate, and quick assembly of
automobiles.
One of the key benefits of AM techniques is that there is no tooling or spe -
cialized hardware needed for any individual component. Each and every part can
be unique from the part created just before or after it. A manufacturer can thus
distribute AM machines near to the point of assembly or to the end customer,
dramatically changing the logistics and distribution models for manufacturing
rather than concentrating manufacturing where tooling is located. Since AM
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ADDITIVE MANUFACTURING TECHNOLOGIES
involves little human involvement to create a part, there is no longer an incentive
to offshore manufacturing to a region of low-cost labor. As a result, onshoring is
the standard for AM.
One particularly good opportunity for AM techniques is in the area of spare
part production. If an out-of-production component is needed, a scanning tech -
nique can be used to capture the geometry of a broken part, modifications can be
made to the CAD file, and a replacement part can be printed out. This is increas-
ingly being used by people who restore automobiles, aircraft, defense systems,
and other machines that were designed and built decades ago for which there are
no CAD drawings or tooling available to make a replacement part and/or where
the original manufacturer is no longer in business.
PERSONAL MANUFACTURING
AM is today where personal computing was in the late 1970s and early
1980s. AM is starting to move from the “mainframe” manufacturing arena into
the “personal” manufacturing arena. In 2010, more than 5,978 “personal” AM
machines were sold (all material-extrusion machines, most of which are sold for
between $700 and $1,500), as compared to an estimated 6,164 other AM systems.
In 2007, when personal AM machines first became available, only 66 personal
AM machines were sold compared to 4,938 other AM systems (Wohlers, 2011).
Thus, even though mainframe AM systems are growing at a respectable rate, the
personal AM market has grown explosively. From an economic standpoint, as
personal AM machines are sold at a cost of between 0.1 and 10 percent of the cost
of other AM machines (with a commensurate lack of speed, accuracy, materials
flexibility, etc.), the personal market is still a small portion of the overall AM
market. However, explosive growth has caught the eye of many investors and
companies, who are starting to make plans to enter the market.
ENTREPRENEURSHIP
A comparison of 3D printing to 2D printing is commonly used to under-
stand the potential for AM. For 2D printing, there is a relatively stable mix
of high-volume printers (e.g., newspapers, magazines, advertisements, etc.),
medium-volume printers (e.g., digital photocopiers), and low-volume printers
(e.g., laser and inkjet printers). In the same way that a consumer can purchase a
mass-produced poster, print their own photos at Walmart, or use their own inkjet
printer at home, 3D printing will likely be used by major manufacturers in facto -
ries, local suppliers in neighborhood 3D print shops, and within peoples’ homes
in the near future.
For AM, entrepreneurial opportunities include the development of new AM
machines, supplying AM-produced components to major manufacturers, printing
designs for consumers, selling unique designs for people to print at home, and more.
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14 FRONTIERS OF ENGINEERING
Thus, AM offers entrepreneurs the opportunity to develop new hardware, software,
and services that either supplant existing products or introduce completely new
products. For instance, entrepreneurs have started companies that develop and sell
personal AM machines (www.makerbot.com), provide web portals for designers
and consumers to sell and buy parts (www.shapeways.com; i.materialise.com),
provide customized dental aligners (www.aligntech.com), sell unique artistic (www.
bathsheba.com) and consumer products (www.freedomofcreation.com), and more.
AM enables designers and entrepreneurs to start selling products without their
own brick-and-mortar infrastructure. This is a new paradigm in manufacturing.
Instead of requiring investors to provide startup capital, a creative person can cre -
ate and sell unique goods without ever buying a manufacturing machine or paying
for the development of a mold or tool. This means that the barrier to market for
entrepreneurial activity in AM is very low and the distinguishing factor between
successful and unsuccessful entrepreneurs may often have more to do with their
ability to create marketing momentum through social media than their ability to
secure venture capital or other financing. This means that entrepreneurs who are
creative and understand the capabilities, benefits, and limitations of AM will have
an edge over others.
CONCLUSIONS
AM technologies have the potential to create a new type of industrial revo -
lution. AM is moving far beyond rapid prototyping in many industries. In the
same way that the Internet has democratized the creation and distribution of
information, AM has the potential to democratize the creation and distribution
of physical goods. The ability to create customized, geometrically complex
parts without tooling lowers the barriers for entrepreneurial activity and gives
designers never-before-available opportunities for optimized design. Today AM
is crossing the barrier from a specialized set of manufacturing and design tools
into the regime of “personal” manufacturing. Those who are able to capitalize
upon new business models involving physical goods might very well be the
“Internet billionaires” of the future.
SUGGESTED SOURCES FOR FURTHER INFORMATION
Gibson, I, D.W. Rosen, and B. Stucker. 2010. Additive Manufacturing Technologies: Rapid Proto-
typing to Direct Digital Manufacturing. New York: Springer (an engineering textbook).
Rapid Prototyping Journal, Emerald Publishing (the leading AM-related journal, in its 16th year of
publication).
Solid Freeform Fabrication Symposium proceedings (the premiere academic conference on AM
since 1990). All papers are available for download at http://utwired.utexas.edu/lff/symposium/.
Wohlers Report 2011: Additive Manufacturing and 3D Printing State of the Industry. 2011. Fort
Collins, Colo.: Wohlers Associates (a detailed industry analysis, updated annually).
www.additive3d.com (the well-known “Castle Island” website. Its terminology is a bit dated, but it
has a lot of information for people who are new to the industry.)
