Additive manufacturing or 3D printing^[1] is a process of making a three-dimensional solid object of virtually any shape from a digital model. 3D printing is achieved using an additive process, where successive layers of material are laid down in different shapes.^[2] 3D printing is considered distinct from traditional machining techniques, which mostly rely on the removal of material by methods such as cutting or drilling (subtractive processes).

A materials printer usually performs 3D printing processes using digital technology. Since the start of the twenty-first century there has been a large growth in the sales of these machines, and their price has dropped substantially.^[3]

The technology is used for both prototyping and distributed manufacturing in jewelry, footwear, industrial design, architecture, engineering and construction (AEC), automotive, aerospace, dental and medical industries, education, geographic information systems, civil engineering, and many other fields.

Contents 1 Terminology 2 General principles 2.1 Modeling 2.2 Printing 2.3 Finishing 3 Additive processes 3.1 Extrusion deposition 3.2 Granular materials binding 3.3 Lamination 3.4 Photopolymerization 4 Printers 4.1 Printers for domestic use 4.2 Printers for commercial and domestic use 5 Applications 5.1 Industrial uses 5.1.1 Rapid prototyping 5.1.2 Rapid manufacturing 5.1.3 Mass customization 5.1.4 Mass production 5.2 Domestic and hobbyist uses 5.3 3D printing services 5.4 Research into new applications 6 Intellectual property 7 Effects of 3D printing 8 See also 9 References 10 Bibliography 11 Further reading 12 External links

Terminology

The term additive manufacturing refers to technologies that create objects through a sequential layering process. Objects that are manufactured additively can be used anywhere throughout the product life cycle, from pre-production (i.e. rapid prototyping) to full-scale production (i.e. rapid manufacturing), in addition to tooling applications and post-production customization.

In manufacturing, and machining in particular, subtractive methods are typically coined as traditional methods. The very term subtractive manufacturing is a retronym developed in recent years to distinguish it from newer additive manufacturing techniques. Although fabrication has included methods that are essentially "additive" for centuries (such as joining plates, sheets, forgings, and rolled work via riveting, screwing, forge welding, or newer kinds of welding), it did not include the information technology component of model-based definition. Machining (generating exact shapes with high precision) has typically been subtractive, from filing and turning to milling and grinding.

General principles

Modeling

Additive manufacturing takes virtual blueprints from computer aided design (CAD) or animation modeling software and "slices" them into digital cross-sections for the machine to successively use as a guideline for printing. Depending on the machine used, material or a binding material is deposited on the build bed or platform until material/binder layering is complete and the final 3D model has been "printed." It is a WYSIWYG process where the virtual model and the physical model are almost identical.

A standard data interface between CAD software and the machines is the STL file format. An STL file approximates the shape of a part or assembly using triangular facets. Smaller facets produce a higher quality surface. PLY is a scanner generated input file format, and VRML (or WRL) files are often used as input for 3D printing technologies that are able to print in full color.

Printing

To perform a print, the machine reads the design from an .stl file and lays down successive layers of liquid, powder, paper or sheet material to build the model from a series of cross sections. These layers, which correspond to the virtual cross sections from the CAD model, are joined together or automatically fused to create the final shape. The primary advantage of this technique is its ability to create almost any shape or geometric feature.

Printer resolution describes layer thickness and X-Y resolution in dpi (dots per inch),^{[citation needed]} or micrometres. Typical layer thickness is around 100 micrometres (0.1 mm), although some machines such as the Objet Connex series and 3D Systems' ProJet series can print layers as thin as 16 micrometres.^[4] X-Y resolution is comparable to that of laser printers. The particles (3D dots) are around 50 to 100 micrometres (0.05–0.1 mm) in diameter.

Construction of a model with contemporary methods can take anywhere from several hours to several days, depending on the method used and the size and complexity of the model. Additive systems can typically reduce this time to a few hours, although it varies widely depending on the type of machine used and the size and number of models being produced simultaneously.

Traditional techniques like injection molding can be less expensive for manufacturing polymer products in high quantities, but additive manufacturing can be faster, more flexible and less expensive when producing relatively small quantities of parts. 3D printers give designers and concept development teams the ability to produce parts and concept models using a desktop size printer.

Finishing

Though the printer-produced resolution is sufficient for many applications, printing a slightly oversized version of the desired object in standard resolution, and then removing material with a higher-resolution subtractive process can achieve greater precision.

Some additive manufacturing techniques are capable of using multiple materials in the course of constructing parts. Some are able to print in multiple colors and color combinations simultaneously. Some also utilize supports when building. Supports are removable or dissolvable upon completion of the print, and are used to support overhanging features during construction.

Additive processes

Several different 3D printing processes have been invented since the late 1970s. The printers were originally large, expensive, and highly limited in what they could produce.^[6]

A number of additive processes are now available. They differ in the way layers are deposited to create parts and in the materials that can be used. Some methods melt or soften material to produce the layers, e.g. selective laser sintering (SLS) and fused deposition modeling (FDM), while others cure liquid materials using different sophisticated technologies, e.g. stereolithography (SLA). With laminated object manufacturing (LOM), thin layers are cut to shape and joined together (e.g. paper, polymer, metal). Each method has its own advantages and drawbacks, and some companies consequently offer a choice between powder and polymer for the material from which the object is built.^[7] Some companies use standard, off-the-shelf business paper as the build material to produce a durable prototype. The main considerations in choosing a machine are generally speed, cost of the 3D printer, cost of the printed prototype, and cost and choice of materials and color capabilities.^[8]

Printers that work directly with metals are expensive. In some cases, however, less expensive printers can be used to make a mould, which is then used to make metal parts.^[9]

Type	Technologies	Materials
Extrusion	Fused deposition modeling (FDM)	Thermoplastics (e.g. PLA, ABS), HDPE, eutectic metals, edible materials
Wire	Electron Beam Freeform Fabrication (EBF3)	Almost any metal alloy
Granular	Direct metal laser sintering (DMLS)	Almost any metal alloy
	Electron beam melting (EBM)	Titanium alloys
	Selective heat sintering (SHS)[citation needed]	Thermoplastic powder
	Selective laser sintering (SLS)	Thermoplastics, metal powders, ceramic powders
	Powder bed and inkjet head 3d printing, Plaster-based 3D printing (PP)	Plaster
Laminated	Laminated object manufacturing (LOM)	Paper, metal foil, plastic film
Light polymerised	Stereolithography (SLA)	photopolymer
	Digital Light Processing (DLP)	photopolymer

Extrusion deposition

Fused deposition modeling (FDM) was developed by S. Scott Crump in the late 1980s and was commercialized in 1990 by Stratasys.^[10] With the expiration of patent on this technology there is now a large open-source development community this type of 3-D printer (e.g. RepRaps) and many commercial and DIY variants, which have dropped the cost by two orders of magnitude.

Fused deposition modeling uses a plastic filament or metal wire that is wound on a coil and unreeled to supply material to an extrusion nozzle, which turns the flow on and off. The nozzle heats to melt the material and can be moved in both horizontal and vertical directions by a numerically controlled mechanism that is directly controlled by a computer-aided manufacturing (CAM) software package. The model or part is produced by extruding small beads of thermoplastic material to form layers as the material hardens immediately after extrusion from the nozzle. Stepper motors or servo motors are typically employed to move the extrusion head.

Various polymers are used, including acrylonitrile butadiene styrene (ABS), polycarbonate (PC), polylactic acid (PLA), high density polyethylene (HDPE), PC/ABS, and polyphenylsulfone (PPSU). In general the polymer is in the form of a filament, which can be fabricated from virgin resins or from post-consumer waste by recyclebots.

FDM has some restrictions on the shapes that may be fabricated. For example, FDM usually cannot produce stalactite-like structures, since they would be unsupported during the build. These have to be avoided or a thin support may be designed into the structure which can be broken away during finishing processes.

Granular materials binding

Another 3D printing approach is the selective fusing of materials in a granular bed. The technique fuses parts of the layer, and then moves the working area downwards, adding another layer of granules and repeating the process until the piece has built up. This process uses the unfused media to support overhangs and thin walls in the part being produced, which reduces the need for temporary auxiliary supports for the piece. A laser is typically used to sinter the media into a solid. Examples include selective laser sintering (SLS), with both metals and polymers (e.g. PA, PA-GF, Rigid GF, PEEK, PS, Alumide, Carbonmide, elastomers), and direct metal laser sintering (DMLS).

Selective Laser Sintering (SLS) was developed and patented by Dr. Carl Deckard and Dr. Joseph Beaman at the University of Texas at Austin in the mid-1980s, under sponsorship of DARPA.^[11] A similar process was patented without being commercialized by R. F. Housholder in 1979.^[12]

Electron beam melting (EBM) is a similar type of additive manufacturing technology for metal parts (e.g. titanium alloys). EBM manufactures parts by melting metal powder layer by layer with an electron beam in a high vacuum. Unlike metal sintering techniques that operate below melting point, EBM parts are fully dense, void-free, and very strong.^[13][14]

Another method consists of an inkjet 3D printing system. The printer creates the model one layer at a time by spreading a layer of powder (plaster, or resins) and printing a binder in the cross-section of the part using an inkjet-like process. This is repeated until every layer has been printed. This technology allows the printing of full color prototypes, overhangs, and elastomer parts. The strength of bonded powder prints can be enhanced with wax or thermoset polymer impregnation.

Lamination

In some printers, paper can be used as the build material, resulting in a lower cost to print. During the 1990s some companies marketed printers that cut cross sections out of special adhesive coated paper using a carbon dioxide laser, and then laminated them together.

In 2005, Mcor Technologies Ltd developed a different process using ordinary sheets of office paper, a Tungsten carbide blade to cut the shape, and selective deposition of adhesive and pressure to bond the prototype.^[15]

There are also a number of companies selling printers that print laminated objects using thin plastic and metal sheets.

Photopolymerization

Stereolithography was patented in 1987 by Chuck Hull. Photopolymerization is primarily used in stereolithography (STL) to produce a solid part from a liquid.

In digital light processing (DLP), a vat of liquid polymer is exposed to light from a DLP projector under safelight conditions. The exposed liquid polymer hardens. The build plate then moves down in small increments and the liquid polymer is again exposed to light. The process repeats until the model has been built. The liquid polymer is then drained from the vat, leaving the solid model. The EnvisionTec Ultra^[16] is an example of a DLP rapid prototyping system.

Inkjet printer systems like the Objet PolyJet system spray photopolymer materials onto a build tray in ultra-thin layers (between 16 and 30 microns) until the part is completed. Each photopolymer layer is cured with UV light after it is jetted, producing fully cured models that can be handled and used immediately, without post-curing. The gel-like support material, which is designed to support complicated geometries, is removed by hand and water jetting. It is also suitable for elastomers.

Ultra-small features can be made with the 3D microfabrication technique used in multiphoton photopolymerization. This approach traces the desired 3D object in a block of gel using a focused laser. Due to the nonlinear nature of photoexcitation, the gel is cured to a solid only in the places where the laser was focused and the remaining gel is then washed away. Feature sizes of under 100 nm are easily produced, as well as complex structures with moving and interlocked parts.^[17]

Yet another approach uses a synthetic resin that is solidified using LEDs.^[18]

Printers

Printers for domestic use

There are several projects and companies making efforts to develop affordable 3D printers for home desktop use. Much of this work has been driven by and targeted at DIY/enthusiast/early adopter communities, with additional ties to the academic and hacker communities.^[19]

RepRap is one of the longest running projects in the desktop category. The RepRap project aims to produce a free and open source software (FOSS) 3D printer, whose full specifications are released under the GNU General Public License, and which is capable of replicating itself by printing many of its own (plastic) parts to create more machines.^[20] Research is under way to enable the device to print circuit boards, as well as metal parts.

Because of the FOSS aims of RepRap, many related projects have used their design for inspiration, creating an ecosystem of related or derivative 3D printers, most of which are also open source designs. The availability of these open source designs means that variants of 3D printers are easy to invent. The quality and complexity of printer designs, however, as well as the quality of kit or finished products, varies greatly from project to project. This rapid development of open source 3D printers is gaining interest in many spheres as it enables hyper-customization and the use of public domain designs to fabricate open source appropriate technology through conduits such as Thingiverse and Cubify. This technology can also assist initiatives in sustainable development since technologies are easily and economically made from resources available to local communities.^[21]

The cost of 3-D printers has decreased dramatically since about 2010, with machines that used to cost $20,000 costing less than $1,000.^[22] For instance, as of 2013, several companies and individuals are selling parts to build various RepRap designs, with prices starting at about €400 / US$500.^[23] The price of printer kits vary from US$400 for the Printrbot Jr. (derived from the previous RepRap models), to over US$2000 for the Fab@Home 2.0 two-syringe system.^[23] The Shark 3D printer comes fully assembled for less than US$2000. The open source Fab@Home project^[24] has developed printers for general use with anything that can be squirted through a nozzle, from chocolate to silicone sealant and chemical reactants. Printers following the project's designs have been available from suppliers in kits or in pre-assembled form since 2012 at prices in the US$2000 range.^[23]

Printers for commercial and domestic use

The development and hyper-customization of the RepRap-based 3D printers has produced a new category of printers suitable for both domestic and commercial use. The least expensive assembled machine available is the Solidoodle 2, while the RepRapPro's Huxley DIY kit is reputedly^{[weasel words]} one of the more reliable of the lower-priced machines, at around US$680. There are other RepRap-based high-end kits and fully assembled machines that have been enhanced to print at high speed and high definition. Depending on the application, the print resolution and speed of manufacturing lies somewhere between a personal printer and an industrial printer. A list of printers with pricing and other information is maintained.^[23] Most recently delta robots have been utilized for 3D printing to increase fabrication speed further.^[25]

Applications

Three-dimensional printing makes it as cheap to create single items as it is to produce thousands and thus undermines economies of scale. It may have as profound an impact on the world as the coming of the factory did....Just as nobody could have predicted the impact of the steam engine in 1750—or the printing press in 1450, or the transistor in 1950—it is impossible to foresee the long-term impact of 3D printing. But the technology is coming, and it is likely to disrupt every field it touches.

— The Economist, in a February 10, 2011 leader^[26]

Additive manufacturing's earliest applications have been on the toolroom end of the manufacturing spectrum. For example, rapid prototyping was one of the earliest additive variants, and its mission was to reduce the lead time and cost of developing prototypes of new parts and devices, which was earlier only done with subtractive toolroom methods (typically slowly and expensively).^[27] With technological advances in additive manufacturing, however, and the dissemination of those advances into the business world, additive methods are moving ever further into the production end of manufacturing in creative and sometimes unexpected ways.^[27] Parts that were formerly the sole province of subtractive methods can now in some cases be made more profitably via additive ones.

Standard applications include design visualization, prototyping/CAD, metal casting, architecture, education, geospatial, healthcare, and entertainment/retail.

Industrial uses

Rapid prototyping

Industrial 3D printers have existed since the early 1980s and have been used extensively for rapid prototyping and research purposes. These are generally larger machines that use proprietary powdered metals, casting media (e.g. sand), plastics, paper or cartridges, and are used for rapid prototyping by universities and commercial companies. Industrial 3D printers are made by companies including Mcor Technologies Ltd, 3D Systems, Objet Geometries, and Stratasys.

Rapid manufacturing

Advances in RP technology have introduced materials that are appropriate for final manufacture, which has in turn introduced the possibility of directly manufacturing finished components. One advantage of 3D printing for rapid manufacturing lies in the relatively inexpensive production of small numbers of parts.

Rapid manufacturing is a new method of manufacturing and many of its processes remain unproven. 3D printing is now entering the field of rapid manufacturing and was identified as a "next level" technology by many experts in a 2009 report.^[28] One of the most promising processes looks to be the adaptation of laser sintering (LS), one of the better-established rapid prototyping methods. As of 2006, however, these techniques were still very much in their infancy, with many obstacles to be overcome before RM could be considered a realistic manufacturing method.^[29]

Mass customization

Companies have created services where consumers can customize objects using simplified web based customization software, and order the resulting items as 3D printed unique objects.^[30][31] This now allows consumers to create custom cases for their mobile phones.^[32] Nokia has released the 3D designs for its case so that owners can customize their own case and have it 3D printed.^[33]

Mass production

This section requires expansion. (November 2012)

The current slow print speed of 3D printers limits their use for mass production. To reduce this overhead, several fused filament machines now offer multiple extruder heads. These can be used to print in multiple colors, with different polymers, or to make multiple prints simultaneously. This increases their overall print speed during multiple instance production, while requiring less capital cost than duplicate machines since they can share a single controller. Distinct from the use of multiple machines, multi-material machines are restricted to making identical copies of the same part, but can offer multi-color and multi-material features when needed. The print speed increases proportionately to the number of heads. Furthermore, the energy cost is reduced due to the fact that they share the same heated print volume. Together, these two features reduce overhead costs, yet the main cost continues to be the raw filament, which is unchanged.

Many printers now offer twin print heads. However, these are used to manufacture single (sets of) parts in multiple colors/materials.

Few studies have yet been done in this field to see if conventional subtractive methods are comparable to additive methods.

Domestic and hobbyist uses

This section requires expansion. (May 2012)

As of 2012, domestic 3D printing has mainly captivated hobbyists and enthusiasts and has not quite gained recognition for practical household applications. A working clock has been made^[34] and gears have been printed for home woodworking machines^[35] among other purposes.^[36] 3D printing is also used for ornamental objects. One printer (the Fab@Home) includes chocolate in the materials that can be printed. Web sites associated with home 3D printing tend to include backscratchers, coathooks, etc. among their offered prints. The Fab@Home gallery includes many objects that lack practical application, but includes examples of practical possibilities, including a flashlight/torch using conductive ink for the electrical circuit, a battery-powered motor, an iPod case, a silicone watch band, and somewhat miscellaneously, a translucent cylinder completely enclosing a brown box, a construct difficult to fabricate any other way.^[37]

The open source Fab@Home project^[24] has developed printers for general use. They have been used in research environments to produce chemical compounds with 3D printing technology, including new ones, initially without immediate application as proof of principle.^[38] The printer can print with anything that can be dispensed from a syringe as liquid or paste. The developers of the chemical application envisage that this technology could be used for both in industrial and domestic use. Including, for example, enabling users in remote locations to be able to produce their own medicine or household chemicals.^[39][40]

3D printing services

Some companies offer on-line 3D printing services open to both consumers and industries.^[41] Such services require people to upload their 3D designs to the company website. Designs are then 3D printed using industrial 3D printers and either shipped to the customer or in some cases, the consumer can pick the object up at the store.^[42] Some examples of 3D printing services companies are Staples Inc.,^[43] Shapeways,^[44] and Freedom of Creation.^[45]

Research into new applications

Future applications for 3D printing might include creating open-source scientific equipment^[46] or other science-based applications like reconstructing fossils in paleontology, replicating ancient and priceless artifacts in archaeology, reconstructing bones and body parts in forensic pathology, and reconstructing heavily damaged evidence acquired from crime scene investigations. The technology is even being explored for building construction.

In 2005, academic journals had begun to report on the possible artistic applications of 3D printing technology.^[47] By 2007 the mass media followed with an article in the Wall Street Journal^[48] and Time Magazine, listing a 3D printed design among their 100 most influential designs of the year.^[49] During the 2011 London Design Festival, an installation, curated by Murray Moss and focused on 3D Printing, was held in the Victoria and Albert Museum (the V&A). The installation was called Industrial Revolution 2.0: How the Material World will Newly Materialise.^[50]

As of 2012, 3D printing technology has been studied by biotechnology firms and academia for possible use in tissue engineering applications in which organs and body parts are built using inkjet techniques. In this process, layers of living cells are deposited onto a gel medium or sugar matrix and slowly built up to form three-dimensional structures including vascular systems.^[51] Several terms have been used to refer to this field of research: organ printing, bio-printing, body part printing,^[52] and computer-aided tissue engineering, among others.^[53] 3D printing can produce a personalized hip replacement in one pass, with the ball permanently inside the socket and is available in printing resolutions that don't require polishing.^{[citation needed]}

A proof-of-principle project at the University of Glasgow, UK, in 2012 showed that it is possible to use 3D printing techniques to create chemical compounds, including new ones. They first concept printed chemical reaction vessels, then use the printer to squirt reactants into them as "chemical inks" which would then react.^[38] They have produced new compounds to verify the validity of the process, but have not pursued anything with a particular application.^[38] They used the Fab@Home open source printer, at a reported cost of US$2,000. Cornell Creative Machines Lab has confirmed that it is possible to produce customized food with 3D Hydrocolloid Printing.^[54]

The use of 3D scanning technologies allows the replication of real objects without the use of moulding techniques that in many cases can be more expensive, more difficult, or too invasive to be performed, particularly for precious or delicate cultural heritage artifacts^[55] where direct contact with the molding substances could harm the original object's surface. Objects as ubiquitous as smartphones can be used as 3D scanners: Sculpteo unveiled a mobile app at the 2012 Consumer Electronics Show that allows a 3D file to be generated directly via smartphone.^[56]

As an example of possible future applications, an open source group emerged in the US in 2012 that was attempting to design a firearm that was downloadable and printable from the Internet.^[57] The weapon would still require bullets produced by traditional methods. Calling itself Defense Distributed, the group wants to facilitate "a working plastic gun that could be downloaded and reproduced by anybody with a 3D printer".^[58] Soon after Defense Distributed succeeded in designing the first working blueprint to produce a plastic gun with a 3D printer in May 2013, the United States State Department demanded that they remove the instructions from their website^[59].

An additional use being developed is building printing, or using 3d printing to build buildings. This could allow faster construction for lower costs, and has been investigated for construction of off-Earth habitats.^[60][61]

Intellectual property

Three different sorts of intellectual property are commonly defined, patent, copyright and trademark. Patents are to do with protecting how something works, and lasts up to about 25 years, depending on the jurisdiction. Copyrights protect artistic works, and generally last the artists life plus 70 years.^[62]

Usually, purely functional items, and plans and documents for these items, older than 25 years are usually no longer patented and can be freely copied, scanned and 3D printed.^[62]

However, if an item has artistic features, those artistic features are generally considered copyrighted.^[62][63] When a feature has both artistic and functional merits, when the question has appeared in US court, the courts have often held the feature is not copyrightable unless it can be separated from the functional aspects of the item.^[62]

Effects of 3D printing

Predive manufacturing, starting with today's infancy period, require manufacturing firms to be flexible, ever-improving users of all available technologies in order to remain competitive. Advocates of additive manufacturing also predict that this arc of technological development will counter globalisation, as end users will do much of their own manufacturing rather than engage in trade to buy products from other people and corporations.^[6] The real integration of the newer additive technologies into commercial production, however, is more a matter of complementing traditional subtractive methods rather than displacing them entirely.^[64]

See also

• 3D modeling
• 3D scanner
• Additive Manufacturing File Format
• Cladding (metalworking)
• Mcor Technologies Ltd
• RepRap Project
• Fab lab
• Fab@Home
• List of common 3D test models
• List of emerging technologies
• Self-replicating machine
• Tissue engineering
• Milling (machining) -computer controlled machine production
• Numerical control - DIY machine production

References

Bibliography

• Vincent; Earls, Alan R. (February 2011). "Origins: A 3D Vision Spawns Stratasys, Inc. Today's Machining World's new feature "Origins" tells us the stories of how successful technologies, companies and people got their start. This month we interview a pioneer of rapid prototyping technology, Scott Crump, the founder and CEO of Stratasys Inc". Today's Machining World (Oak Forest, Illinois, USA: Screw Machine World Inc) 7 (1): 24–25.
• Albert, Mark [Editor in Chief] (2011-01-17). "Subtractive plus additive equals more than ( − + + = > ): subtractive and additive processes can be combined to develop innovative manufacturing methods that are superior to conventional methods ['Mark: My Word' column—Editor's Commentary]". Modern Machine Shop (Cincinnati, Ohio, USA: Gardner Publications Inc) 83 (9): 14.

Further reading

• Easton, Thomas A. (November 2008). "The 3D Trainwreck: How 3D Printing Will Shake Up Manufacturing". Analog 128 (11): 50–63.
• Wright, Paul K. (2001). 21st Century Manufacturing. New Jersey: Prentice-Hall Inc.

External links

Wikimedia Commons has media related to: 3D printing

• Rapid prototyping websites at the Open Directory Project
• Fabbers
• 3-D printing at MIT
• 3D Printing: The Printed World from The Economist
• Comparison chart of 3D printers
• How to Fabricate a Toy Model from Scratch
• Jay Leno's 3D Printer Replaces Rusty Old Parts
• Rapid Manufacturing for the production of Ceramic Components
• How does 3D printing work? (from physics.org)