The present pace of technological advancement is fast and furious. It is becoming harder than ever to predict what will come next. When Stratasys announced1 that it had produced world’s first color multi-material 3D printer, the race for faster new product design began. It has the ability to produce anything regardless of the complexity of the shape and color. Call it hype or not, the 3D printing technology is already in the spotlight and is undoubtedly an important fabrication technology (Figure: Gear wheel; Courtsey of Anubis3D). The incredible range of potential consumer applications that this game changing technology is starting to provide has caught the eye of the general press, for example Stuart Dredge2 wrote an article for the Guardian newspaper that starts “from jet parts to unborn babies, icebergs to crime scenes, dolls to houses: how new technology is shaking up making things.”
This review article provides answers to the general questions that might occur to users of 3D printing technology, it points the reader to some of the excellent articles about various aspects of the topic, provides a glimpse of the current trends and discusses the limitations of the technology and their impact on its future prospects.
How did it all begin?The idea of printing 3D objects was born in the ‘80s, when Chuck Hull of 3D Systems conceptualized and patented the idea which he used to found 3D Systems in 19863. 3D technology is based on stereolithography (STL). Mr. Hull recognised how uv light might be used to solidify layers of molten plastic into whatever shape he liked and then combine these layers to make a 3D product. The New York Times article4 “Who made that 3D printer” gives a lucid picture of how 3D printer evolved. Early research at MIT was focused on rapid tooling using metals and ceramics5,6. It took another decade to commercialise rapid prototyping.
Are there different ways to print 3D objects?
In an attempt to classify 3D printing processes, ASTM International (ormerly known as American Society for Testing and Materials) identified seven distinct additive manufacturing processes7. These are all based on the same principles as ink jet printing, which creates a digital image by shooting ink droplets onto a sheet of paper, a plastic object a textile or other more exotic substrates. 3D printing provides complex shapes by replacing the ink with droplets of plastics or metal those are used to construct 3-dimensional objects by adding layer upon layer of material. This allows the construction of customized objects without making expensive moulds.
In a manufacturing context this technique is called Additive Manufacturing. To print a 3D object, virtual models from CAD or other modeling software are taken and layered into digital cross-sections, which the 3D printer uses as a guideline for printing successive layers. This approach uses materials more efficiently than traditional manufacturing techniques (such as cutting or drilling) since excess material is not needed. The quality of the final print and the object and print speed depend on the printer type and model. 3D printing can be used in applications such as industrial design, automotive, aerospace, medical, fashion, footwear, eyewear, food and others. Cheaper machines can be used to produce prototypes, while machines that make production grade products tend to be much more expensive.
There are several ways that a printer can create the individual 2D layers from a design and combine them to produce the final 3D object. In the first approach to 3D printing (Stereolithography as patented by Chuck Hull of 3D Systems in 19848), liquid materials (photopolymer resins) are cured on an elevator platform with a UV laser shone onto it. Stereo lithography needs a supporting structure to attach the part to the elevator platform. Supports have to be removed after the build is complete.
Stereolithography is a versatile process where different materials can be combined in one product. An example of multi-material stereolithography is shown in the picture rook. The rook displayed here was fabricated using the stereolithography additive manufacturing process with three photopolymers and four build phases8a: 1) construction of outer structure using Somos®WaterShedTM11120, 2) construction of staircase using Somos®ProtoThermTM12120 in red, 3) construction of white double spiral using Somos®14120 White, and 4) construction of top structure using Somos®WaterShedTM11120.
Selective laser-sintering (SLS) is a widely used method for making plastic parts, in which layers of powdered plastic or metal are selectively hardened (sintered) with a moving laser or electron beam and the remaining, material removed. The SLS process typically uses a carbon dioxide laser which traces the required shape directly in a compacted powder bed of material from a 3D CAD model via an STL computer file. As each layer of powder is fused (sintered) by the laser to form the necessary shape, next layer of powder is introduced to the laser and gets sintered and adhered to the previous layer. SLS makes little waste and unused raw material could be recycled. The method is known for the quality, reproducibility and the strong plastic parts that result. SLS is the most accurate additive manufacturing process and is used to build prototypes and for small batch production. Aerospace industries such as Boeing have exploited this method extensively to make various non-structural parts. The method can also be used to repair worn parts, such a turbine blades9.
Fused deposition modeling (FDM)10 is another commonly used process, commercialized by Stratasys in 1990. Virgin resin, filament wound on a coil, is unreeled to feed material to an extrusion nozzle head. Objects are built by melting these plastic filaments and extruding them along computer-controlled paths. FDM is used to make product development prototype parts because of its robustness. It is often used in small 3D printers for hobbyists. However, the surface finish looks porous.
In a recently published report, Gridlogics Technologies categorized and graphically analyzed trends, processes, and applications of 3D printing technologies11. Inquisitive readers can also read more about practical advantages and drawbacks of all the layering processes at the anubis3d website12. More background and historical references are available in Wikipedia13.
Which Plastic can be used for 3D printing?
Plastics engineers can make objects of their choice polymers that range from thermoplastics to thermosets to TPEs. Photopolymers and epoxy resins can also be used for stereolithogrphy. For SLS, nylon powders (PA11 and PA 12) predominate. Nylons can be filled with glass, aluminum or carbon fiber. They can also be impact-modified or modified with flame retardants.
Late last year Solvay unveiled new materials (Sinterline PA6 powders) which expanded the capability of 3D printing to make end-use nylon parts for automotive injection moulding14. Highly engineered PEEK and PEI are also available for SLS. For thin walled parts, Stratasys has developed a new ABS material (ABS2) for its Polyjet 3D printer. Styrolution provides styrenic polymers for 3D printing industries. Bayer Materials Science now has Desmosint X 92A-1, a TPU with high elasticity, tear strength and abrasion resistance. Microfol Compounding GmbH is offering PP (SinterPlast PP) for laser sintering. These and other plastic materials designed for use in 3D printing are reviewed in a recent article15.
What can 3D printing do?
The technology empowers entrepreneurs to design innovative products and test concepts without the investment of a great deal of time and money since a good knowledge of machinery or skills are not required to convert ideas into a concrete product with 3D printer. For example the Stratasys Objet500 Connex3 Color Multi-material 3D Printer is claimed to enable designers, engineers, and manufacturers to develop models, molds, and parts which match the characteristics of production parts meeting mechanical property requirements such as tensile strength, elongation at break and hardness16.
Ford engineers use industrial-grade 3-D printing machines that cost as much as $1-million to produce prototypes of cylinder heads, brake rotors, and rear axles for test vehicles. These are produced in less time than that required with traditional manufacturing methods. These engineers reduced the production time by about a month for the EcoBoost family of engines by using 3D printing to create a casting for a prototype cylinder head. This complex part included numerous ports, ducts, passages and valves to manage fuel and air flow. The traditional casting method can take four to five months since it involves designing a sand mold as well as the tool to cut the mold. With 3-D printing, engineers can design and print the sand mold and pour the metal in three months17.
A Stratasys case study18 describes how KOR EcoLogic used Fused deposition modeling (FDM) to build a car body (see Figure below on the right). How did FDM compare to traditional prototyping methods? A comparative analysis showed that cost and lead time for the FDM process was lower than the traditional method using FRP or fiberglass.
Magnetometer is known to measure the strength and/or the direction of the magnetic field at a point of space. It has numerous applications from measuring earth's magnetic field to tactical military technology. The magnetometer displayed in the figure (photo below: left) contains a microprocessor and three Hall effect sensors placed in orthogonal planes to detect magnitude and direction of a magnetic field. The circuit interconnects were direct printed onto a stereolithography manufactured outer shell18a.
At the W.M. Keck Center for 3D Innovation,University of Texas at El Paso, Professor Ryan Wicker's group is actively pushing the boundaries of Additive Manufacturing technologies. The group recently built a novelty six-sided gaming die via stereolithography and direct write of conductive ink traces with manual placement of electronic components (photo below: right). A microprocessor and accelerometer work in unison so that upon halting, the top surface is identified and light-emitting diodes (LEDs) are illuminated. A USB port allows recharging of a lithium polymer battery, enhancing user interface18b.
In bio-medical field, when 3D printing technology is used to fabricate scaffolds, the additive process must be chosen with care, since each method has its own merits and drawbacks. Given the fact that interconnected pores can be created with controlled structures, rapid prototyping for bone scaffold fabrication is an active area of research. Scaffold fabrication, however depends on the types of additive process used. This application is well summarized in a recent review19.
Microfluidic chips are used for applications such as point-of-care diagnostics and environmental monitoring. Shallan et al recently reported that microfluidic chips could be made quickly and at low cost. Fabricated chips that are transparent and which have smaller channel sizes can be made using a consumer level 3D printer19a. These are examples of the numerous application areas where 3D printing can have huge impact on new products manufacturing.
What are the limits to 3D printing today?
It is debatable whether or not 3D printing can replace high volume manufacturing techniques such as moulding, which easily spit out products by the minute.
Constraints currently include manufacturing speed and cost.
3D printers are slow especially for large products. The process can be further slowed because models don’t always scan well.
At present the costs for the printers, the software and the materials means that the cost to make 3D printed products is much higher than the price for which these goods are sold. Laseter and Hutchison-Krupat20 wrote, “It’s a stretch to envision a near term future in which 3D printer at home to make a fork or a chess piece”.
Raw material costs are high because material volume dictates the price. An injection molding grade of ABS in bulk costs anything between $2 and $3 per kilo whereas a bespoke powder or filament of ABS for 3D printing could cost as much as $70 - $80 per kilo.
The range of materials currently available for 3D printing compared to traditional molding process is limited. There is a question as whether a 3D printer can be made to work with the range of grades used in traditional manufacturing. There are millions of molded and extruded plastics products in the market and these are made from thousands of different plastics including amorphous, semi-crystalline, and crystalline materials. Whereas plastics used for 3D printing need to have certain properties such as melt index or viscosity which allows them to be pass through an ink-jet nozzle and set quickly.
Metal-plastic hybrid is another area of commercial interest. Current 3D printers do not have the ability to print metal-plastic hybrid objects. Ability to print only to a few types of metal alloys limits the technology.
The size of objects that can be printed provides a further limitation, although the Dutch government is supporting an interesting project, the goal of which is to use 3D printing to build a house21.
Concerns have been expressed about limitations in mechanical strength and whether the plastics layers have sufficient adhesion so that they do not delaminate in the z- direction21a. There are also issues with certain angles of printer head, surface finish, post-processing, and availability of appropriate 3D model libraries.
As a result of the current limitations, the notion of 3D printing technology bringing any kind of industrial revolution is arguable. The answer to the question 'Can 3D printing be labeled as a disruptive manufacturing technology?' depends on who you ask! Nevertheless, certain application areas will see a major shift towards 3D printing as manufacturing cost becomes lower and where more complex parts can be made than with traditional methods.
Are there any commercial applications yet?
Despite the current limitations, 3D printing has a tremendous future. The examples such as those we describe below in areas as diverse as aerospace and healthcare those have created huge expectations in this technology.
Companies such as Stratasys (SYS), 3D Systems (DDD), Voxeljet AG (VJET), Hewlett-Packard (HPQ), Hitachi Chem Co. Ltd. (HCHMY), IBM Corporation (IBM), are publicly traded and are at the forefront of the 3D printing business. Reference 11 provided a current list of 20 major companies in the world who are actively pursuing the technology. Recently, first of its kind a mutual fund has been touted that consists of 3D printing businesses only. The name of the fund is 3D printing and Technology Fund. Articles22, 22a in Bloomberg Business Week and CNN Money are for those who are interested in knowing more about these companies.
BAE Systems engineers are using 3D printed metal components in its Tornado GR4 aircraft. Use of 3D printed component could save the Royal Air Force £1.2 million in maintenance and service cost over the next 4 years22b. Morris Technologies (now part of GE) was well known for its additive manufacturing services to industries including lightweight parts for unmanned aerial vehicles. GE plans to 3D print tens of thousands of parts for its jet engines alone. NASA has announced that that it has successfully tested a 3D printed rocket engine part. It is also preparing to launch a 3D printer into space so that the printer could make spare parts on the fly to avoid carrying large loads of spares with them. A typical F-18 fighter jet likely to contain 90 3D printed parts although has been in service for 2 decades. On a less romantic note, aircraft such as MD-80 jets, which ceased its production long ago, have leaking toilets for which it is difficult to find spare parts. Its new plumbing is now being 3D printed in an aerospace grade plastic23.
Robots are part of automation in the plastics industry. Often mechanical grippers are used to pick-up, transport, and lay down machine parts on a production line. Wittman Robot Systeme had a gripper consisting of 21 different components made of aluminum, rubber and plastics. Kuhn-Stoff Gmbh & Co, a German designer founded in 2005 simplified the gripper design by using EOS’s FORMIGA P 100 3D printer with only 2 different plastic components weighing 86% lighter than the original gripper24.
The health-care industry is an early adopter of the 3D printing technology despite stringent bio-compatibility standards . Millions of hearing-aid shells from scans of patients’ ear canals to straightening teeth using transparent plastic “aligners” are in use25. Oxford Performance Materials in Connecticut (USA) has developed FDA approved OsteoFabTM from PEEK polymer. OsteoFabTM can be used to replace bone damaged by disease or trauma. In one case it has been reported that a man has had 75% of his skull replaced with a custom made 3D printed implant26. 3D printed low cost prosthetic limbs for amputees are another exciting area. Not Impossible Labs27 is tackling the healthcare challenges in poorer countries with low cost low cost prosthetic limbs, made with consumer grade 3D printers operating with open-source software.
Synthetic organ technology could help to remove an important medical need by reducing the long transplant waiting list for vital organs. The main problem is to make thicker and more complex tissues having blood vessels. Harvard university researchers created a tissue containing skin cells and biological structural material interwoven with blood-vessel like structures. The tissue is touted as the first 3D printed material that includes potentially functional blood vessels28.
Different colour products for consumers' use can be manufactured and Stratasys has shown by printing numerous product items such as cyan glasses, multi-colour bi-cycle helmet etc.
There are also more whimsical applications created by hobbyists and entrepreneurs. In one example a full body scanner takes an image of the customer’s body, transfers the file to a printer, which is used to produce statues for display. Twinkind, a German startup has used SLS process to create figurines29. In another, enthusiasts are developing techniques to use 3D print technology to automate tattooing30.
Which applications can we expect soon?
The following recent advancements promise applications in the near future.:
- The Technology Partnership (TTP) claims to have developed multi-material jetting head (Vista 3D) that could print multiple materials including metals, plastics, ceramics, enzymes, and biological cells31.
- Arburg, an injection moulding machinery maker unveiled at K2013 “freeformer”, a new 3D printing system that work with the same resin as those used in conventional injection moulding machine. The novelty is not only that standard polymer resin can be used but also the system allows parts to be moulded in two materials or colours.
- EnvisionTEC’s commercialized 3SP (scan, spin and selectively photocure) process that touts high speed without losing accuracy or resolution regardless of the geometric complexity.
- EOS GmbH’s PrimePartPLUS can use more recycled materials. It needs only 35% virgin powder.
- A collaborative team (Marcelo Coelho and Skylar Tibbits) at MIT is developing Hyperform which can make large part irrespective of a printer’s bed size in small volumes. The concept stems from when Skylar Tibbits of MIT unveiled in his TED2013 talk how chunks of 3D printed parts intelligently arrange themselves into any object32. This development gave birth to the concept of 4D printing. University of Colorado, Boulder researchers showed a 4D printing process where shape memory polymer fibers could fold, stretch, curl or twist when allowed the environmental exposure changes33 (water, heat or pressure).
- Harvard researchers reported in a recently concluded American Chemical Society (ACS 2014) meeting that they have created a printed tissue that mimics natural heart muscles.
How fast is the industry expected to grow?
According to the Freedonia Group study34, world demand for 3D printing is projected to rise to US $5 billion by 2017. Although plastics will continue to be important, the use of metals for 3D is expected to grow faster. Fastest growth is also expected for medical and dental applications. Specific opportunities are expected in dental applications for braces, crowns, bridges, aligners and models for dental restorations. The aerospace markets expected to see above average growth.
The USA will account for 42% of the global sales in 2017. It has been reported34a that China has committed almost $500 million to establish 10 national 3D printing development institutes and this is expected to result in rapid growth.
Wohlers Associates Inc. has predicted that the global revenues from 3D printers would reach US $3.7 billion by 2015, $6 billion by 2017, and $10.8 billion by 2021. It also reports that the growth in the low cost (under $5000) “personal” 3D printer market segment is slowing down. This segment consists of hobbyists, do-it-yourselfers, engineering students, and educational institutions. Wohlers Report 201335 provides an overview and analysis of additive manufacturing and 3D printing worldwide.
A recently published report by IDTechEx36 gave a detailed account of pricing, properties and projections for materials including photopolymers, thermoplastics and powders. According to the report, the market for photopolymers will retain the largest single segment of the market until 2025. An earlier report by IDTechEx discussed several 3D printing technologies and on-going technological advances along with current and future markets for 3D printing.
What technological advancement is needed to unlock the potential?
The market for prototypes produced with 3D printing is expected to grow tremendously. Larger printers will be built to address the need of making bigger parts.
3D printing promises to help people develop design gift ideas and print these. These same printers might be used to print spare parts and other useful household items (see figure of hand held blender). However the question as to whether a 3D printer will become an indispensable household tool is debatable. The cost of 3D printers will have to drop and more open sourced 3D modeling software must becomes freely available. In addition Killer Applications will have to be developed to catch the imagination of consumers.
Both hardware and software will see improvements. 3D Printers will continue to become more sophisticated. Multiple types of polymers such as ABS, PLA, nylons will be used to make the different products with the same printer. Printers might even be developed that will print with either metals or plastics. Further improvement is required in many areas including speed, resolution and tolerances, surface finish and dimensional stability (warpage and shrinkage).
Techniques to recycle 3D printed objects will be needed before 3D printer can be considered for commodity items. This will require work to maintain the quality of 3D printed parts containing regrind.
Printing a large object faster will become a hot area. Collaborations between research institute and industry will increase. Joint work has already begun with Oak Ridge National Laboratory (ORNL) and the Cincinnati Incorporated, a machine tool manufacturer37.
There is a need to print 3D ‘on demand’ spare parts for automotive and medical applications, to avoid the need for wait time and to maintain inventory.
Manufacturing cells for use in patients or to try new drugs in different types of tissues for screening application will see major interest. Already University of Toronto researchers in collaboration with Sunnybrook Hospital are exploring the possibility of printing soft tissues such as skin to treat burned patients. The challenges that exist in using 3D printing for bone tissue engineering will be the next frontier of research in this area as researchers start to find ways to deal with the post- processing shrinkage, such as the non-uniform shrinkage that can occur during the sintering of porous scaffolds, which can cause parts to crack. Techniques are also needed to keep minimum distance between pores in a highly porous scaffold with a sintered pore size below 300 microns.
As the reader will appreciate, 3D printing provides a lot of promise. Barriers have been identified, but ways around these obstacles are being found at a rapid rate. At this point no one can predict the results of this game changing approach to manufacturing. Even if economics prevents its application to commodity manufacturing, it will serve an extremely important niche in this competitive market environment.
The authors would like to thank Professor Ryan Wicker, and companies Stratasys, Anubis3D, and Sculpteo for their assistance in providing the photographs for use in this article.
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