Additive manufacturing: A review, recent developments, and future possibilities
a Department of Industrial Engineering, International University of Sarajevo, Sarajevo, Bosnia and Herzegovina; [email protected]
In this paper an extensive review of various literature sources was made to see where the technology is now, and what will the future trends be. Additive manufacturing procedures use information from a computer-aided design (CAD) file as an input. That file is later transformed to a stereolithography (STL) file. Stereolithography is a way of 3D printing technology used for generatingmockups, prototypes, designs, and production of parts layer by layer using photopolymerization, a procedure by which light causes molecule chains to link together, creating polymers. In the mentioned process, the drawing made by CAD software where the information of each layer which is going to be printed is approximated using triangles and sliced encompassing. A discussion covering the appropriate additive manufacturing procedures and their applications currently exists. The aerospace industry values them greatly so they would be able to make lighter structures,so they could minimize weight. Additive manufacturing transformed the current medical practices and it also made architecture jobs lot easier. In 2004, the Society of Manufacturing Engineers organized different technologies, and sorted them into four different groups of additional technologies they categorized as relevant. Studies on strength of products completed in the area of additive manufacturing processes were reviewed. Though, a lot of work and research is to be made before additive manufacturing technologies can become a standard in the manufacturing industry because a lot of used materials in manufacturing cannot be handled. The precision needs improvement to eliminate the necessity of a finishing procedure. The growth that the technology witnessed since its beginnings up to now is tremendous. That is why we can expect additive manufacturing to be one of the significant technologies in future manufacturing.
Keywords: Additive manufacturing, Review, 3D printing, Manufacturing processes
Figure SEQ Figure * ARABIC 1In this timeline we can see the historical development of AM
left3105604A highly popular technique used for additive manufacturing is 3-dprinting. 3-D printing is nowadays used for constructionof a wide variety of structures, parts, or products from 3D model data. The process works by printing successive layers of materials which form on each other. This is what makes the difference between additive and subtractive manufacturing. AM is a technique for producing a wide range of different structures from three-dimensional (3D) model data. The process consists of printing consecutive layers of materials one over the other. The type of process differs additive manufacturing from subtractive manufacturing, in which material is added, as stated, unlike in the subtractive manufacturing where it is subtracted. Additive manufacturing was first introduced in the 1980s, back then it was quite limited as to what it could produce, and what materials it could use CITATION Hid81 l 5146 1. In 1984, Chuck Hull filed his own patent for stereolithography fabrication system, in which layers were added one on top of the other by curing photopolymers with ultraviolet light lasers CITATION Dav12 l 5146 2. His contributions were followed by developments suchas fused deposition modelling, inkjet printing, powder bed fusion and contour crafting CITATION Tua18 l 5146 3. In 1988 the technology mostly used by modern 3D printers is fused deposition modelingthat presents a special application of plastic extrusion CITATION Bau06 l 5146 4. Year 1993 saw many developments in this rapidly growing technology. The term 3D printing which was initially denoted as a powder bed process, using typicalinkjet print heads. This year also saw the start of a company called Solidscape, which introduced a high-precision polymer jet fabrication system, (branded as a “dot-on-dot” system).In year 1995 the Fraunhofer Institute established the selective laser melting process CITATION Pea10 l 5146 5.
3D-printing nowadays has much more capabilities than it used to have, now it includesnumerousapproaches, resources, and equipment, and can transform manufacturing and coordinationprocesses. Additive manufacturing has been widely applied in differentindustries, including construction, prototyping and biomechanical. The development of 3D printing in the construction industry, precisely, was quite slow and incomplete, although it was proven that the advantages exist, e.g. automation, less waste, and freedom of design CITATION Ber12 l 5146 6.
Picture SEQ Figure * ARABIC 2 CAD model used for 3D printing
Picture 1 A Jet Engine turbine that was 3Dprinted
Recent developments in this technology were to reduce the cost of 3D printers, so expanding its applications in homes, schools, universities, laboratories, etc.
Usage of 3D printing has minimized the additional costs incurred in the process of developing a product, that is in the process of making a model. Though, it is only inthe recent few years that 3D printing has been fully utilized in numerous businesses from prototypes to products. Product customization has beena great challenge for producers due to the high costs of producingcustom-tailored products for end-users. Instead, AM can 3D print small quantities of customized products with relatively lowcosts. Also, the general market growth and the future projection of the market growth of AM can be seen in the REF _Ref514141526 h Figure 3.
Figure 3 Market value in USD through time CITATION Jas15 l 5146 73D printing has numerous advantages, but on the other hand, there are disadvantages as well.The advantages of this technology will continue to arise through continuous research efforts, which should be undertaken to eradicate and recognize the constraints which inhibit the use of this technology and eliminate constraints that inhibit the use of this technology.Design tools used for AM are more user-friendly and progressive simulation abilities are the key aspects which should be grasped. A notablebenefit of 3D printing is the possibility of mass customization, since it is devoid of the additional costs which arise due to moldmaking and tooling for a customized product. Therefore, mass productionof several identical parts has the possibility of being as cost-effective as thesame number of different personalized goods CITATION Iva13 l 5146 8. The alterationamong different designs is simple alongside with negligible added cost and with no need for special preparation. AM also has the possibility for mass productionof complex geometries as well.
This paper aims to provide a review of 3D printing, it’s recent developments, techniques in terms of the main methods employed, materials used, it’s applications, as well as its future development possibilities. The paper will also focus on other existing secondary and primary research to focus on the current research gaps, as well as to explore the challenges encountered in adopting this relatively “young” technology.
Figure 4. AM application in scientific research CITATION Sco18 l 5146 9
The figure above describes the application of AM in scientific research, and how the research interest for this technology grew over time.
The newest AM application in certain scientific areas is shown in REF _Ref514141798 h Figure 5.
Figure 5. AM application per scientific area 82
AM as scientific method was most popular in scientific areas of Engineering, Material Science and ComputerScience. Its application in these areas counts about 50% compared to all other scientific areas.
In additive manufacturing (AM) we have methods which were developed so we could be able to print complex structures at fine resolutions.The factors which drove the development of AM technologies forward are the ability to print large structures, reducingprinting defects and enhancing mechanical properties are some of thekey factors that have driven the development of AM technologies CITATION Wei15 l 5146 10.3D printing uses mostly polymer filaments, and this is known as fused deposition modelling (FDM). Also, it uses the following,additive manufacturing of powders by selective laser sintering (SLS),selective laser melting (SLM) or liquid binding in three-dimensionalprinting (3DP), as well as inkjet printing, contour crafting, stereolithography,direct energy deposition (DED) and laminated objectmanufacturing (LOM) are the main methods of AM CITATION Tua18 l 5146 3. These methods arebriefly explained, their applications and suitable materials for eachmethod are introduced, and their benefits and drawbacks are discussed CITATION Moh15 l 5146 11.
AM Method Advantages Disadvantages
Fused deposition modeling Low cost
Simplicity Weak mechanical properties
Limited materials (only
Powder bed fusion Fine resolution
High quality Slow printing
High porosity in the binder
Inkjet printing and CC Ability to print large
Quick printing Maintaining workability
Lack of adhesion between
Stereolithography Fine resolution
High quality Very limited materials
Laminated object manufacturing Reduced tooling and
A vast range of materials
Excellent for manufacturing
of larger structures Inferior surface quality and
Limitation in manufacturing
of complex shapes
Table SEQ Table * ARABIC 1 provides a short overview of methods, their benefits, and drawbacks
2.1. Fused deposition modelling (FDM)
In this method, there is a continuous filament made of thermoplastic polymerused to print layers of materials. FDM works in a way that the filament is heated atthe nozzle, so it would reach a semi-liquid state, afterwards it is extruded on the base or on top of layers that were previously printed. An essential property for this method is the thermoplasticity of the polymer thread. This property allowsthe threads to fuse together during the printing itself and then afterwards to harden ata room temperature after printing. Properties of the layer, such as width, thickness,and orientationof filaments and air gap represent the main processing parameters whichmark the mechanical propertiesof printed parts CITATION Soo10 l 5146 12 CITATION Moh15 l 5146 11.
However, FDM does carry certain drawbacks such as weak mechanical properties, poor surface quality CITATION Cho17 l 5146 13, layer-by-layer appearance, and a scarce number of thermoplastic materials CITATION Soo10 l 5146 12. Additionally, the recent development of fiber-reinforcedcomposites which use FDM has strengthened the mechanicalproperties of parts printed using 3D CITATION Wan17 l 5146 14. On the other hand, orientation of the fibers, bondingbetween the matrix and fiber and void formation are the main encounters of 3D printed composite parts CITATION Cho17 l 5146 13 CITATION Wan17 l 5146 14.
2.2. Powder bed fusion
The process consists of very thin layers of finepowder. The layers are then spread and packed closely on a platform. Thepowder in each layer isthen bonded together with a laser beam or some sort of a different binder.Following layersof powder are placed on top of preceding layers andbonded together until the finalpart in 3D is built.Afterwards, the excesspowder is removed by a vacuum or if needed, additional processingand detailing is carriedout CITATION Ute08 l 5146 15. The laser can only be used for powders that possess a lowmelting temperature, otherwise a liquid binder should be used. The main advantages of powder bed fusion are fine resolution and high quality of printing, which is why it is appropriate for printing complex structures. This method isbroadly used in several industries for advanced applications such asscaffolds for tissue engineering, lattices, aerospace, and electronics. Also, one of the key advantages is the fact that the powder bed is used assupport, which can overcome problems in removing supporting material.On the other hand, the main drawbacks of powder bed fusion are that it is a slowprocess which includes high costs and high porosity when the powder is fusedwith a binder CITATION Yap15 l 5146 16.
2.3. Inkjet printing and contour crafting
Inkjet printing is a method mainly used for AM of ceramics, more specifically for printing complex and advancedceramic structures. This method works in a way that a stable ceramic suspension e.g. zirconiumoxide powder in water CITATION Dou11 l 5146 17 is pumped and deposited in the form ofdroplets via the injection nozzle onto the substrate. The droplets thenform a continuous pattern which solidifies to sufficient strength to hold subsequent layers of printed materials. Great advantage of the method is that it isfast and efficient, which adds flexibility for designing and printingcomplex structures. Two main types of ceramic inks are wax-based inksand liquid suspensions CITATION Tra14 l 5146 18.
A similar technology to inkjet printing, called contour crafting, is the main method of additive manufacturing of large building structures. This method is capable of extruding concrete paste or soil by using larger nozzles and high pressure. Contour crafting has been prototyped to be used for construction on the moon CITATION Kho04 l 5146 19.
2.4. Stereolithography (SLA)
Figure 4 Schematic diagrams of four main methods of additive manufacturing: (a) fused deposition modelling; (b) inkjet printing; (c) stereolithography; (d) powder bed fusion 13.
305797927430SLA is one of the initial methods used in additive manufacturing. The method was developed in 1986 CITATION Mel10 l 5146 20. The method works by using UV light tostart a chain reaction on a layer of resin. Theresinwhich is usually acrylic or epoxy-based is UV-active, meaning it instantly
converts to polymer chains after it has been activated. After the process of polymerization,a pattern inside the resin layer is solidified to holdthe subsequent layers, while the unreacted resin is removed afterwards. Advantage of SLA is that it can be efficiently used for the AM of complex nanocomposites CITATION Man17 l 5146 21. The biggest drawbacks of the method are that it is relatively slow, expensive and the range ofmaterials which could be used for printing islimited.
2.5. Laminated object manufacturing
This manufacturing (AM) methodwas one of the pioneers in commerciallyavailable additive
manufacturing methods based onlayer-by-layer cutting and lamination of sheets.It works by cutting successive layers precisely using a mechanical cutter or laser. Then they are bonded together. The excess materials are left as support after cutting and upon completion of the process, can be removed and recycled CITATION Gib44 l 5146 22.Advantage of LOM is that can be used for a wide range of materials i.e. polymercomposites, ceramics, paper, and metal-filled tapes.
3. Material overview
Materials used in 3D printingnowadays are:
Metals and alloys, Metal additive manufacturing is showing excellent perspectives of growth CITATION Woh17 l 5146 23 CITATION Cou04 l 5146 24.
Polymers and composites, which are the most commonly used materials in the 3Dprinting industry due to their diversity and ease of adoption to different3D printing processes CITATION Lig17 l 5146 25. Polymers used for AM can be found in the form of thermoplastic filaments, reactive monomers, resin, orpowder CITATION Tak17 l 5146 26.
Concrete: Additive manufacturing technology has expanded to the construction industry as well CITATION Kho041 l 5146 27.Presently, 3D printing technology for the building industry is in its beginning.
Ceramics: AM became a vital method for manufacturing of advanced ceramics for biomaterials and tissue engineering e.g. scaffolds for bones and teeth CITATION Wen17 l 5146 28. Although highly accurate printing, the main challenges for 3D printing of ceramics are layer-by-layer appearance and a limited selection of materials CITATION Tra141 l 5146 29.
Material Usage/ Industry Advantages Disadvantages
Metals and alloys Aerospace and Automotive
Biomedical Multifunctional optimization
Reduced material waste
Fewer assembly components Limited selection of alloys
Dimensional inaccuracy and poor surface finish
Polymers and composites Aerospace and Automotive
Biomedical Fast prototyping
Mass-customization Weak mechanical properties
Limited selection of polymers and reinforcements
Anisotropic mechanical properties
Concrete Construction Mass-customization
No need for formwork
Less labor required especially useful in harsh
environment and for space construction Layer-by-layer appearance
Anisotropic mechanical properties
Poor inter-layer adhesion
Difficulties in upscaling to larger buildings
Limited number of printing methods and tailored
concrete mixture design
Aerospace and Automotive
Chemical industries Controlling porosity of lattices
Printing complex structures and scaffolds for human body
Reduced fabrication time Limited selection of 3D-printable ceramics
Dimensional inaccuracy and poor surface finish
Table SEQ Table * ARABIC 2 presents materials used in AM, which industry they are used in, as well as advantages and disadvantages
3.1. Quick comparison of different materials for 3D printing
A wide range of materials can beprinted in 3Dbecause of fast development inadditive manufacturing technologies. Numerous materials in different forms of filaments,wire, powder, paste, sheets, and inks are used in 3D printing technology CITATION Vae13 l 5146 30.Polymers are most commonly used materials, and they have beendeveloped for aerospace, automotive, sports, medical, architectural andtoy industries.
Applications of 3D printers can be seen in various industries. They are industries like medical industry, aerospace industry, construction industry, etc. CITATION Gay14 l 5146 31.
AM is often used in biomedical industry has been already used in the biomedical industry and does have a bright future in the industry as well. Although it is very popular in the industry, there are some issues as well, such as:
– Regulatory issues. For example, many countries require the approval of it by the relevant institutions. Some devices can be approved faster, and some require time to be tested and then approved. CITATION DiP15 l 5146 32;
– Limited materials. This means that many of the traditional biomaterials cannot be 3Dprinted, while on the other hand the best performing materials are not biocompatible CITATION Zad17 l 5146 33. Therefore, the development of fresh techniques andmaterials is vital;
– Quality inconsistencies. The mechanical properties of materials havenot been properly categorized CITATION Cam11 l 5146 34, it is important because materials and the processparameters can greatly influence the final properties.
Future trends will focus on:
On-demand and patient-specific applications CITATION Ban13 l 5146 35;
Complex parts CITATION Wan16 l 5146 36;
Bio-printing and in-situ printing CITATION DiB17 l 5146 37.
4.2. Aerospace industry
Aerospace industry is quite specific. That is why they require a lot from AM techniques. They have the are following peculiar characteristics like complex geometry CITATION Lay17 l 5146 38, on-demand manufacturing CITATION Kha14 l 5146 39, high-performance to weight ratio CITATION Cap l 5146 40, customized production, etc.Many metallic and non-metallic CITATION Yin18 l 5146 41 CITATION Tur17 l 5146 42parts which can be used in aerospace industry can be produced or repaired using3D printing. Those parts include aero engine components, turbine blades and heat exchangers.Non-metal 3D printing methods such as stereolithography, multi-jetmodelling CITATION Chu10 l 5146 43and FDM are used for therapid prototyping of parts and for manufacturing fixtures and interiorsmade of plastics, ceramics, and composite materials.The aerospace industry can drivefurther development CITATION 3Do l 5146 44 while trying to overcome some restrictions such as size of parts, scalability, and so on. We will list these restrictions in more detail in Table 2.
Figure 5 A short overview of AM process and applications CITATION Wei15 l 5146 10center249
4.3 Construction industry
Wohler’s’ report 22 showed that the architectural applications representonly a small proportion of the entire AM industry, roughly 3 percent.Although this sector is in its beginnings, since it started to be used for housing structures from 2014CITATION 3DPse l 5146 45 and has shown great potential ever since. Automated buildingconstruction with 3D printing technology has gained popularity recently. It has the potential to revolutionize the constructionindustry CITATION NLa17 l 5146 46. It offers a great reduction in construction time and labor, meaning it offers huge savings CITATION WuP16 l 5146 47,when compared to traditional techniques used in construction. Its reliabilityis basically due to theability to construct with high accuracy and opens various design potentials.
Industry Limitations Requirements Future Possibilities
Biomaterials Regulatory issues
Quality inconsistencies. High complexity.
Customization and patient-specific necessities.
Small production quantities.
Easy public access. On-demand and patient-specific applications.
Bio-printing and in-situ printing.
Aerospace Industry Size of the parts.
Limited material and high cost.
Difficult-to-machine materials and high buy-to-fly ratio.
High-performance to weight ratio Multifunctional structures.
Functionally Graded Materials.
Automated repair processes.
Construction Industry Size Customized production.
The possibility of building infrastructure on the Moon with the useof lunar soil
Table SEQ Table * ARABIC 3 Industry specific limitations, opportunities, and requirements
5.Challenges and Opportunities
Although numerous benefits of 3D printing exist such as the customization CITATION Pal10 l 5146 48, freedom of design CITATION Des01 l 5146 49, and the ability to print complex structures, few drawbacks exist as well that require further research anddevelopment. The drawbacks comprise of high costs CITATION Hol05 l 5146 50, limited applicationsin large structures and mass production, and limitation of materials CITATION She18 l 5146 51 CITATION HuY18 l 5146 52. Researchand development of materials and methods has helped inavoidingsome of the abovementioned challenges CITATION Oro16 l 5146 53. Though, few residual challenges CITATION Iva131 l 5146 54 need tobe solved to expand AM to awidervariety of applications and industries. Some challenges exist in only a printing method or material, but only few of them arecommon in nearly all AM methods.
5.2 Future Prospects CITATION Pro12 l 5146 55We are now on the edge of ”a third industrial revolution” CITATION Ath12 l 5146 56when numerousdevelopingbusinesses are rethinking traditional manufacturing CITATION Kar12 l 5146 57, and how it can be transformed. The ways of these transformations are described in the text bellow.
5.2.1 Additive manufacturing for ”desktop fabrication”
Though AM devices are perceived as desktop merchandises by the public, such developments are currently restricted to certain demographics. These ”makers” CITATION And12 l 5146 58 are customers of various age groups that actively pay towards the design and creation of modified products CITATION Pra04 l 5146 59. AM technologies are now able to help in customization CITATION mat l 5146 60 of products by directly involving customers in the design part.But, these technologies are in an emerging stage due to various design and printing software issues CITATION Laz08 l 5146 61 CITATION Moo12 l 5146 62. Nowadays, the progress in this field is much more rapid because of the expiration of many patents (more information in the references CITATION Hul86 l 5146 63 CITATION Dec89 l 5146 64 CITATION Cru92 l 5146 65 CITATION Sac93 l 5146 66), registered in the 90-s. Education also became important in this technology, due to its growing popularity educated and knowledgeable workforce CITATION Nat l 5146 67 that will know how to apply it will also be needed.
Although additive manufacturing became very attractive for research CITATION Bri11 l 5146 68, specifically after recent popularity gain CITATION Tra142 l 5146 69 due to the expiration of the base patents ( full list is given here CITATION Gri12 l 5146 70 ), we can see many problems in organizing, participating, and having truthfulinfluence with the research CITATION Dri06 l 5146 71. The main reason is that the research is disjointed CITATION Ree95 l 5146 72, and integration mechanisms do not exist. Integration mechanisms CITATION Pal14 l 5146 73 don’t exist because of large variations in AM methods and representations, that is why it becomes hard to repeat or reuse research CITATION Pal13 l 5146 74. Though many people would like standards CITATION Gri10 l 5146 75 CITATION AST13 l 5146 76 to arise in the technology, many commercial entities with larger revenues resist that change. There are ways to overcome this problem, and it is by having an open academic research platform CITATION AWi02 l 5146 77, and with significant expertise and investments in organizing these topics. Additive manufacturing currently progresses in a way that researchers are investigating different printing techniques CITATION OeT12 l 5146 78 individually. We imagine that soon the integration of 3D shapes,electronics, and actuators will deliver affordance and allow a ”print-it-all” production process for building more functional products CITATION Bul09 l 5146 79.
In todays’ modern world there is a huge need for rethinking and reorganizing manufacturing CITATION NSF l 5146 80 CITATION Nat18 l 5146 81. Problems regarding the intellectual property, particularly with key patents which expired, have played an important role in the commercialization CITATION Chu00 l 5146 82 of AM. It made it more accessible to the masses and every day users CITATION War07 l 5146 83. If the future of manufacturing CITATION JMa10 l 5146 84 CITATION Rva12 l 5146 85 floors transfers to rows of 3D printers that sit amongst planers, mills and drilling machines, new operations and scheduling systems will be needed to support mass production CITATION TWo11 l 5146 86. These changes will inevitably result in a new production models in design and processes that will eventually infiltrate throughout the PLC CITATION Die10 l 5146 87 CITATION Mye09 l 5146 88 (Product life cycle). AM canback decentralized production at low to medium volumes allowing companies to drive important changes within the supply chain CITATION VPe11 l 5146 89 CITATION Bak03 l 5146 90 CITATION Hul861 l 5146 91. Changes mentioned above include, reduction of costs CITATION Mue99 l 5146 92, ability to produce products closer to customers, reduction in logistic costs as well as complexity, involving consumers in design processes, and reduction in capital disposition.
5.3 Educational view of AM
Given this need, a recent National Science Foundation workshop on AM Education was held, wherein attendees from industry, academia, and government met to discuss the educational needs and opportunities for the AM engineering workforce CITATION Bou09 l 5146 93. Following presentations from industrial attendees, it was determined that the future AM workforce need to have an understanding of (1) AM processes and process/material relationships, (2) engineering fundamentals with an emphasis on materials science and manufacturing, (3) professional skills for problem solving and critical thinking, (4) design practices and tools that leverage the design freedom enabled by AM, and (5) cross-functional teaming and ideation techniques to nurture creativity, CITATION Bøh97 l 5146 94 CITATION Wil12 l 5146 95 CITATION Fid12 l 5146 96 CITATION Tab12 l 5146 97. Typically characterized as unstructured, socially-based educational environments wherein students collaborate autonomously on a project, informal learning environments, these opportunities have been shown to positively contribute to students’ engineering education CITATION Vol04 l 5146 98. University-level informal learning environments. Inspired in part by the Maker movement, several universities have engaged their students in ”maker spaces” that feature several digital fabrication tools CITATION Gri18 l 5146 99 CITATION Inv l 5146 100 CITATION Mei13 l 5146 101 CITATION Vir l 5146 102.
The main benefits associated with 3D printing are freedom of design, mass-customization, and the ability to printcomplex structures with minimum waste. A comprehensive review of 3D printing methods, materials, the current state, and the future prospects was carried out. The main challenges attributed to the nature of 3Dprinting were also discussed.
When we speak about the methods FDM seems to be themost common one in 3D printing technologies because of low-cost, simplicityand speedy processing. FDMis mostly used for fast prototyping, but the mechanical properties andquality are lower in comparison to the powder-bedmethods such as selective laser sintering (SLS) and selective lasermelting (SLM). Directenergy deposition (DED) uses a source of energy (laser or electronbeam) to melt metal powders, it is like FDM, but it consumes more energy for melting metals. extremely higher Inkjet printing is also quick and is used forprinting of ceramics but requires post-processing heattreatments.
Although it is a revolutionary method for making customized and niche products, 3D printing needsfurther development so it would be able to compete with traditional methods in the mass production of commonplace goods because of its higher cost and lower speed. Nevertheless, the growth of AM in recent years has been remarkable, and it has made the technology more accessible. Increased R;D, and increased funding worldwide would result in a much quickershift from traditional manufacturing to 3D printing.
1 H. Kodama, “A Scheme for Three-Dimensional Display by Automatic Fabrication of Three-Dimensional Model,” IEICE Transactions on Electronics (Japanese Edition), Vols. J64-C, no. 4, p. 237–41, 1981.
2 D. H. Freedman, “Layer By Layer,” Technology Review, vol. 115, no. 1, pp. 50-53, 2012.
3 T. D. Ngoa, A. Kashani, G. Imbalzano, K. T. Nguyen and D. Hui, “Additive manufacturing (3D printing): A review of materials, methods,applications and challenges,” Elsevier, vol. 143, no. 1, pp. 172-196, 2018.
4 M. Bauser, G. Sauer and K. Siegert, Extrusion, ASM International, 2006, p. 270.
5 J. M. Pearce, C. Morris Blair, K. J. Laciak, R. Andrews, A. Nosrat and I. Zelenika-Zovko, “3-D Printing of Open Source Appropriate Technologies for Self-Directed Sustainable Development,” Journal of Sustainable Development, 2010.
6 B. B., “3-D printing: the new industrial revolution,” Bus Horiz, vol. 55, no. 2, pp. 155-62, 2012.
7 D. Jason and B. Robert, “Introduction to the Additive Manufacturing Powder Metallurgy Supply Chain,” Johnson Matthey Technol. Rev., vol. 59, no. 3, p. 243–256, 2015.
8 W. C. C. T. Ivanova O, “Additive manufacturing (AM) and nanotechnologypromises and challenges,” Rapid Prototyp J , vol. 19, no. 5, p. 353–64, 2013.
9 “Scopus,” 2018. Online. Available: www.scopus.com. Accessed May 2018.
10 W. Gao, Y. Zhang and D. Ramanujan, “The status, challenges, and future of additive manufacturing in engineering,” Elsevier, vol. 69, no. 1, pp. 65-89, 2015.
11 M. S. B. J. Mohamed OA, “Optimization of fused deposition modeling process parameters: a review of current research and future prospects,” Adv Manuf, vol. 3, no. 1, pp. 42-53, 2015.
12 O. R. M. S. Sood AK, “Parametric appraisal of mechanical property of fused deposition modelling processed parts,” Mater Des, vol. 31, no. 1, p. 287–95, 2010.
13 S. R. B. K. P. R. F. F. Chohan JS, “Dimensional accuracy analysis of coupled fused deposition modeling and vapour smoothing operations for biomedical applications,” Compos B Eng , vol. 117, no. 1, p. 138–49, 2017.
14 J. M. Z. Z. G. J. H. D. Wang X, “3D printing of polymer matrix composites: a review and prospective,” Compos B Eng , vol. 110, no. 2, p. 442–58, 2017.
15 S. D. A. R. G. M. Utela B, “A review of process development steps for new material systems in three dimensional printing,” Elsevier, vol. 10, no. 2, p. 96–104, 2008.
16 C. C. D. Z. L. Z. Z. D. L. L. S. S. Yap CY, “Review of selective laser melting: materials and applications,” Appl Phys Rev , vol. 2, no. 4, pp. 41-101, 2015.
17 W. T. G. Y. D. B. Dou R, “Ink-jet printing of Zirconia: Coffee staining and line stability,” J Am Ceram Soc , vol. 94, no. 11, p. 3787–92., 2011.
18 B. A. D. B. F. T. F.-D. I. S. L. S. T. G. P. Travitzky N, “Additive manufacturing of ceramic-based materials,” Adv Eng Mater, vol. 16, no. 6, p. 729–54., 2014.
19 K. B., “Automated construction by contour crafting – related robotics and information technologies,” Autom ConStruct , vol. 13, no. 1, p. 5–19, 2004.
20 F. J. G. D. Melchels FPW, “A review on stereolithography and its applications in biomedical engineering,” Biomaterials , vol. 31, no. 24, p. 6121–30, 2010.
21 C. Q. Y. P. A. R. Manapat JZ, “3D printing of polymer nanocomposites via stereolithography,” Macromol Mater Eng, vol. 302, no. 9, 2017.
22 R. D. S. B. Gibson I, “Sheet lamination processes. Additive manufacturing technologies: 3D printing, rapid prototyping, and direct digital manufacturing,” Springer New York, pp. 219-44, 2015. p. 219–44..
23 W. T., “3D printing and additive manufacturing state of the industry Annual Worldwide Progress Report Wohlers Report,” 2017.
24 Council NR, “. Accelerating technology transition: bridging the valley of death for materials and processes in defense systems,” National Academies Press, 2004.
25 L. R. S. J. G. M. M. R. Ligon SC, “Polymers for 3D printing and customized additive manufacturing,” Chem Rev , vol. 117, no. 15, p. 10212–90., 2017.
26 K. M. Takezawa A, “Design methodology for porous composites with tunable thermal expansion produced by multi-material topology optimization and additive manufacturing,” Compos B Eng , vol. 131, p. 21–9, 2017.
27 K. B., “Automated construction by contour crafting – related robotics and information technologies,” Autom ConStruct , vol. 13, no. 1, p. 5–19, 2004.
28 X. S. H. M. B. S. P. C. X. L. K. Z. X. Y. J. P. S. L. Wen Y, “3D printed porous ceramic scaffolds for bone tissue engineering: a review,” Biomaterials Science , vol. 9, no. 5, p. 1690–8, 2017.
29 B. A. D. B. F. T. F.-D. I. S. L. S. T. G. P. Travitzky N, “Additive manufacturing of ceramic-based materials,” Adv Eng Mater , vol. 16, no. 6, p. 729–54, 2014.
30 V. M, C. S, M. B and Y. S., “Multiple material additive manufacturing–Part 1: a review: this review paper covers a decade of research on multiple material additive manufacturing technologies which can produce complex geometry parts with different materials,” Virtual Phys Prototyp , vol. 8, no. 1, pp. 19-50, 2013.
31 G. AT, M. NA, W. CB and G. JK., “Gaynor AT, Meisel NA, Williams CB, Guest JK. Multiple-material topology optimization of compliant mechanisms created via PolyJet three-dimensional printing,” J Manuf Sci Eng , vol. 136, no. 6, pp. 610-15, 2014.
32 D. P. M, C. J, H. D, K. J, K. A and R. L., “Additively manufactured medical products–the FDA perspective,” 3D Print Med , vol. 2, no. 1, p. 1, 2015.
33 Z. AA and M. J., “Additive manufacturing of biomaterials, tissues, and organs,” Springer, 2017.
34 C. T, W. C, I. O and G. B., “Could 3D printing change the world Technologies, Potential, and Implications of Additive Manufacturing Washington,” DC: Atlantic Council, 2011.
35 B. J., “Adding value in additive manufacturing: researchers in the United Kingdom and Europe look to 3D printing for customization,” IEEE pulse, vol. 4, no. 6, p. 22–6, 2013.
36 W. X, X. S, Z. S, X. W, L. M, C. P, Q. M, B. M and X. YM., “Topological design and additive manufacturing of porous metals for bone scaffolds and orthopaedic implants: a review,” Biomaterials , vol. 83, no. 2, p. 127–41., 2016.
37 D. B. C, D. S, O. CD, B. R, A. C, Y. Z, T. F, R. C, B. S and O. C., “In-situ handheld 3D Bioprinting for cartilage regeneration,” J Tissue Eng Regen Med , 2017.
38 “Layer by Layer,” 13 10 2017. Online. Available: https://www.technologyreview.com/s/426391/layer-by-layer/..
39 K. SH, P. J and H. J, “Additive manufacturing in the spare parts supply chain,” Comput Ind , vol. 65, no. 1, p. 50–63, 2014.
40 “Capabilities & Services | SpaceX,” Online. Available: http://www.spacex.com/about/capabilities.
41 Y. L, D. J, T. X and L. D., “Design and characterization of radar absorbing structure based on gradient-refractive-index metamaterials,” Compos B Eng , vol. 132, p. 178–87, 2018.
42 T. E, G. M, G. I and D. F., “Pantographic lattices with nonorthogonal fibres: Experiments and their numerical simulations,” Compos B Eng , vol. 118, p. 1–14, 2017.
43 C. CK, L. KF and L. CS., “Rapid prototyping: principles and applications,” World Scientific, 2010.
44 “3D opportunity for aerospace and defense. Additive manufacturing takes flight.,” Online. Available: https://dupress.deloitte.com/dup-us-en/focus/3d-opportunity/additivemanufacturing- 3d-opportunity-in-aerospace.html.
45 “3D Print Canal House,” DUS Architects, 23 10 2017. Online. Available: http://houseofdus.com/project/3d-printcanal-house. Accessed 2018.
46 L.-M. N, S.-R. M, D.-Á. J and M.-F. J., “Additive manufacturing for a Moon village,” Procedia Manuf , vol. 13, p. 794–801, ;13:794–801. 2017.
47 W. P, W. J and W. X., “A critical review of the use of 3-D printing in the construction industry,” Autom ConStruct , vol. 68, p. 21–31, 2016.
48 D. K. W. J. Pallari JH, “Mass customization of foot orthoses for rheumatoid arthritis using selective laser sintering,” IEEE (Inst Electr Electron Eng) Trans Biomed Eng , vol. 57, no. 7, p. 1750–6, 2010.
49 F. N. Deshpande V, “Collapse of truss core sandwich beams in 3-point bending,” Int J Solid Struct, vol. 38, no. 36, p. 6275–305, 2001.
50 H. SJ., “Porous scaffold design for tissue engineering,” Nat Mater , vol. 4, no. 7, p. 518–24, 2005.
51 T. E. Sheydaeian E, “A new approach for fabrication of titanium-titanium boride periodic composite via additive manufacturing and pressure-less sintering,” Compos B Eng , vol. 138, p. 140–8, 2018.
52 C. W. W. X. L. Y. N. F. W. H. Hu Y, “Laser deposition-additive manufacturing of TiB-Ti composites with novel three-dimensional quasi-continuous network microstructure: effects on strengthening and toughening,” Compos, vol. 133, p. 91–100, 2018.
53 P. L. Oropallo W, “Ten challenges in 3D printing,” Eng Comput , vol. 32, no. 1, p. 135–48, 2016.
54 W. C. C. T. Ivanova O, “Additive manufacturing (AM) and nanotechnology: promises and challenges,” Rapid Prototyp J , vol. 19, no. 5, p. 353–64, 2013.
55 P. D. J. Gausemeier, Thinking ahead of Future of AM, Padeborn, 2012.
56 “A third industrial revolution,” The Economist, 2012.
57 B. A. S. S. D. L. T. G. R. Karunakaran K, “Rapid manufacturing of metallic objects,” Rapid Prototyp J , vol. 18, no. 4, p. 264–80, 2012.
58 A. C., “Makers: the new industrial revolution,” Crown Business, no. 1, 2012.
59 R. V. Prahalad C, “Co-creating unique value with customers,” Strategy Leadership, vol. 32, no. 3, p. 4–9, 2004.
60 “matterport,” Online. Available: http://matterport.com/.
61 S. G. G. A. Lazaros N, “Review of stereo vision algorithms: from software to hardware,” Int J Optomechatronics, vol. 2, no. 4, p. 435–62, ;2(4):435–62. 2008.
62 W. Moore J, “CB. Fatigue Characterization of 3D Printed Elastomer Material,” in International Solid Freeform Fabrication Symposium, 2012.
63 H. C., “Apparatus for production of three-dimensional objects by stereolithography”. USA Patent Patent 4,575,330, March 1986.
64 D. C., “Method and apparatus for producing parts by selective sintering”. USA Patent US Patent 4,863,538, September 1989.
65 C. S., “Apparatus and method for creating three-dimensional objects”. USA Patent US Patent 5,121,329, June 1992.
66 H. J. C. M. W. P. Sachs E, “Three-dimensional printing techniques”. USA Patent Patent 5,204,055 , April 1993.
67 “National science foundation workshop on additive manufacturing education.,” Online. Available: https://enge.vt.edu/nsfamed.
68 T. K. Brice CA, “Additive manufacturing workshop,” in Commonwealth Scientific and Industrial Research Organisation, Melbourne, 2011.
69 B. A. D. B. F. T. F.-D. I. S. L. Travitzky N, “Additive manufacturing of ceramic-based materials,” Adv Eng Mater , vol. 16, no. 6, p. 729–54, 2014.
70 Gridlogics technologies pvt ltd, “, 3D printing technology insight report—an analysis of patenting activity around 3D-printing from 1990—current,” 2012. Online. Available: http://www.patentinsightpro.com/. Accessed 2018.
71 P. J. Drizo A, “Environmental impacts of rapid prototyping: an overview of research to date,” Rapid Prototyp J , vol. 12, no. 2, p. 64–71, 2006.
72 S. L. Reece S, ” Laminated object manufacturing: process practice and research experience. In: Proceedings of the 1st national conference on rapid prototyping & tooling research, Vol. 101.,” in Buckinghamshire College, UK, 1995.
73 P. N. Z. K. S. B. Pal D, “An integrated approach to additive manufacturing simulations using physics based, coupled multiscale process modeling,” J Manuf Sci Eng, vol. 136, no. 6, 2014.
74 P. N. N. M. Z. K. K. K. S. B. Pal D, “An integrated approach to cyber-enabled additive manufacturing using physics based, coupled multi-scale process modeling,” in Solid freeform fabrication symposium proceedings, 2013.
75 G. T., “3D printer benchmark injection,” 2010.
76 ASTM, “Astm standard f2792, standard terminology for additive manufacturing technologies,” 2013. Online. Available: http://www.astm.org/Standards/F2792.htm. Accessed 2018.
77 A. Williams, “Architectural modelling as a form of research,” Architectural Research Quarterly, vol. 6, no. 4, p. 337–347, 2002.
78 S. B. T. J. Oe T, “Scan modeling: 3D modeling techniques using cross section of a shape,” in Proceedings of the 10th Asia Pacific conference on computer human interaction, 2012.
79 G. J. Bull G, “The democratization of production,” Learn Lead Technol, vol. 37, no. 3, p. 36–7, 2009.
80 “NSF research experience for teachers: Innovation-based manufacturing,” Online. Available: http://www.me.vt.edu/retibm.
81 “National science foundation workshop on additive manufacturing education,” Online. Available: http://www.enge.vt.edu/nsfamed. Accessed 2018.
82 F. C. F. T. Church KH, “Commercial applications and review for direct write technologies,” in MRS proceedings, Cambridge Univ Press, 2000.
83 W. L., “Fab at home, open-source 3D printer, lets users make anything,” 2007. Online. Available: http://www.popularmechanics.com/technology/gadgets/news/ 4224759.
84 J. Malik, “Are 3D-printed fabrics the future of sustainable textiles?,” Ecouterre, 2010. Online. Available: http://www.ecouterre.com/ are?3d?printed?fabrics?the?future?of?sustainabletextiles/. Accessed 2018.
85 R. v. Noort, “The future of dental devices is digital,” Dental Materials, vol. 28, no. 1, pp. 3-12, 2012.
86 T. Wohlers, “Making products by using additive manufacturing,” Manufacturing Engineering, vol. 146, no. 6, p. 70–74, 2011.
87 S. S. R. S. W. A. Diegel O, “Tools for sustainable product design: additive manufacturing,” J Sustain Dev , vol. 3, no. 3, p. 68–75, 2010.
88 M. D. A.-C. C. Myers RH, “Response surface methodology: process and product optimization using designed experiments,” John Wiley and Sons, vol. 705, 2009.
89 J. V. H. G. V. Petrovic, “Additive layered manufacturing: sectors of industrial application shown through case studies,” International Journal of Production Research, vol. 49, no. 4, p. 1061–1079, 2011.
90 B. D., “Rapid prototyping or rapid production? 3D printing processes move industry towards the latter,” Assem Autom, vol. 23, no. 4, p. 340–5, 2003.
91 H. C., “Apparatus for production of three-dimensional objects by stereolithography”. USA Patent US Patent 4,575,330, March 1986.
92 K. D. Mueller B, “Laminated object manufacturing for rapid tooling and patternmaking in foundry industry,” Comput Ind , vol. 39, no. 1, p. 47–53, 1999.
93 L. M. R. D. Bourell DL, “Roadmap for additive manufacturing: identifying the future of freeform processing,” The University of Texas, Austin, 2009.
94 B. JH., “Integrating rapid prototyping into the engineering curriculum—a case study,” Rapid Prototyp J, vol. 3, no. 1, pp. 32-7, 1997.
95 S. C. Williams CB, “Design for additive manufacturing curriculum: A problem-and project-based approach,” International solid freeform fabrication symposium, 2012.
96 F. I., “Remotely accessible rapid prototyping laboratory: design and implementation framework,” Rapid Prototyp J , vol. 18, no. 3, p. 344–52, 2012.
97 T. E, “Chandrasegaran SK, Ramani K. Me 444: Redesigning a toy design course,” in Proceedings of TMCE 2012, 2012.
98 L. L. T. P. S. L. S. J. Volkwein JF, “Engineering change: A study of the impact of EC2000,” Int J Eng Educ , vol. 20, no. 3, p. 318–28, 2004.
99 Gridlogics technologies pvt ltd., “3D printing technology insight report—an analysis of patenting activity around 3D-printing from 1990—current.,” Online. Available: http://www.patentinsightpro.com/. Accessed 2018.
100 I. studio. Online. Available: http://inventionstudio.gatech.edu/.
101 N. Meisel and C. Williams, “Design and assessment of an am vending machine for student use,” in Proceedings of the 24th annual international solid freeform fabrication symposium, Austin (TX), Austin, 2013.
102 “Virginia tech additive manufacturing vehicle design challenge,” Online. Available: http://vt-arcdc.org/.
103 L. D. Parandoush P, “A review on additive manufacturing of polymer-fiber composites,” Compos Struct , vol. 182, no. 2, p. 36–53., 2017.
104 I. Gibson and B. P. Jorge, “History of Stereolithography,” in Stereolithography: Materials, Processes, and Applications, 2011, pp. 41-43.