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Metal additive manufacturing
CHAPTER 1
Metal additive manufacturing Abbreviations AM ASTM BJ CAD 3D DED DMD DMLS EBM GE ISO LENS ME MJ NIST PBF SL
additive manufacturing American Society for Testing of Materials binder jetting computer-aided design three-dimensional direct energy deposition direct metal deposition direct metal laser sintering electron beam melting General Electric Corporation International Organization for Standardization laser energy net shaping material extrusion material jetting National Institute of Standards and Technology powder bed fusion stereo lithography
1.1 Introduction Three-dimensional (3D) printing and additive manufacturing (AM) have been dubbed the third industrial revolution [1]. While the second industrial revolution in the early 20th century began with the assembly line and ushered in the era of mass production, the third industrial revolution is thought to make things economically in much smaller numbers, more flexibly, and with greater customization. That was the thought in 2012. Six years later, the technology has advanced further and production parts manufactured using 3D printing have made their way into jet engines and aircraft, in medical and dental industry, in the oil and gas industry, and general industrial markets. CFM International (a joint venture between General Electric Corporation (GE) Aviation and Safran) has successfully introduced a 3D printed fuel nozzle in the LEAP jet engine [2]. Avio Aero is printing TiAl blades for the GE9X engine [3]. 3D printing of Science, Technology and Applications of Metals in Additive Manufacturing DOI: https://doi.org/10.1016/B978-0-12-816634-5.00001-7
© 2019 Elsevier Inc. All rights reserved.
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Science, Technology and Applications of Metals in Additive Manufacturing
Figure 1.1 3D printed parts: (A) LEAP engine fuel nozzle [2], (B) 3D printed TiAl blades for the GE9X engine [3], and (C) orthopedic implants [4]. Photo courtesy of GE Additive, Mike Cloran.
titanium orthopedic implants is gaining popularity [4]. Airbus is also using 3D printed titanium brackets in the A350 XWB. Despite the speed of 3D printing being far too slow to produce millions of parts for the automotive industry, its throughput is steadily increasing while manufacturing costs are decreasing and “Such skepticism looks less and less credible.” [5]. 3D printing is a disruptive technology that affects the complete value chain of a product, from design to production (Fig. 1.1).
1.1.1 What is additive manufacturing and why additive manufacturing? AM is defined as a process whereby parts or components are directly built from a solid model using a heat source and filler material. The process involves slicing a solid model of the part into multiple layers, creating a toolpath to trace the individual layers, and then building the part layer by layer using the filler material in a computer-controlled automated machine. Since the process relies on material addition in each layer leading to the final part geometry, it is called an additive process. In contrast, a conventional machining process starts with a block of material and follows a material removal technique to create the final part geometry and therefore is called a subtractive process. Although the terms 3D printing and AM are often used interchangeably, 3D printing is actually a subset of AM that builds up parts from scratch using the above-mentioned technique. AM, however, includes techniques such as 3D printing, but also material addition to existing parts or components for the purpose of repair, remanufacturing, or property enhancement. Major benefits of AM over conventional manufacturing roots from its ability to build parts directly from CAD data. This
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eliminates the need for a tool or die and allows significant reduction in design-to-manufacturing time as well as significant cost reduction for low volume part production. In addition to this, AM offers a greater degree of design freedom and allows manufacturing of geometries that are not feasible by conventional manufacturing at all. Other benefits of AM include reduction of scrap through efficient material usage and its ability to remanufacture damaged parts. While AM is not a direct replacement for conventional manufacturing, especially for high volume production, as the parts are becoming more and more engineered and complex, AM offers a great solution to manufacturing industry and facilitates innovation by reducing lead time to market for new products.
1.1.2 History of additive manufacturing The history of metal AM dates back to at least 1920 by Baker (US patent, 1,533,300) who used an electric arc and metal electrode to form walled structures and decorative articles (Fig. 1.2) [6]. Today direct energy deposition (DED) techniques such as direct metal deposition (DMD), laser energy net shaping (LENS), or direct manufacturing (DM) are based on similar ideas, but integrate the layered manufacturing concepts to create parts directly from computer-aided design (CAD) data. However, the concept of layered manufacturing finds its roots from two different technologies that started in the 19th century: topography and photosculpture. As early as 1892 Blanther patented a technique for making a mold for topographical relief maps using impressions of topographical contour lines
Figure 1.2 A typical decorative article as described by Baker’s 1920 patent [6].
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Science, Technology and Applications of Metals in Additive Manufacturing
on a series of wax plates, cutting these wax plates on these lines and stacking them to create a raised relief map of paper. In 1972 Matsubara proposed a process using photopolymer resin coated onto graphite powder/ sand, spread into a layer, select areas of the layer heated and hardened using a mercury vapor lamp and the remaining area dissolved to create sheets with defined geometry, which were then stacked together to form a casting mold. In 1974 utilizing a similar stacking technique, DiMatteo [7] produced three dimensional shapes from contour milled metallic sheets that were then joined in layered fashion by adhesion, bolts, or tapered rods (Fig. 1.3a). In 1968 Swainson proposed a process to directly fabricate a plastic pattern by selective, three-dimensional polymerization of a photosensitive polymer at the intersection of two laser beams. This followed work by Ciraud (1972), Householder (1979) (Fig. 1.3b) [8], Kodama (1981), Herbert (1982), Hull (1984), and Deckerd (1986) paving the way for modern 3D printing technologies that are based on powder bed fusion (PBF) technologies (Fig. 1.4). Patents by Ciraud (1972), Arcella and Lessmann (1989), Jeantette et al. (1996), and Koch and Mazumder (1998) form the basis of modern DED technologies. More details about the
Figure 1.3 (A) Laminated mold from DiMatteo’s 1974 patent [7] and (B) schematic drawing showing Householder’s invention [8].
Figure 1.4 Apparatus for laser sintering from Chuck Hull's invention [11].
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history of AM and 3D printing, as well as the commercialization of this industry, can be found elsewhere [9,10]. Commercial efforts at AM started with the introduction of stereo lithography (SL) and the formation of 3D Systems Corp. in 1987. This was followed by the formation of EOS GmbH in 1990, Stratasys in 1991, DTM Corp. in 1992, Fockele & Schwarze (F&S) in 1994, Z Corp in 1996, and subsequently many other companies jumped in. While most of this effort was on polymeric materials, commercialization of metal AM started with DTM. DTM launched a metal sintering system, by laser sintering polymer-coated metal powders in the sinter station to form a green part, followed by a furnace process to remove the polymer, bonding the metal matrix, and infiltrating it with a secondary metal to remove the porosity. In contrast, EOS developed a direct metal laser sintering (DMLS) process where metal powders were directly sintered using a moving laser beam [12]. In 1997 Swedish company Arcam AB was formed that used its patented electron beam melting (EBM) technology to produce titanium medical components. Arcam’s continued work with Adler Ortho Group resulted in Conformité Européene, meaning “European Conformity” (CE-certification) of EBM-manufactured titanium hip implants in 2007, marking a significant step in metal AM. The first commercial effort in DED started with the formation of Aeromet Corporation in 1997, which focused on a laser-based DED technology for large aerospace components made of titanium [13]. In 1998 commercialization of Sandia National Laboratory developed laser engineered net shaping (LENS) by Optomec Inc. and University of Michigan developed DMD by POM Group (now DM3D Technology) which brought further impetus to metal AM. For economic reasons, early efforts on metal AM were focused on expensive parts and components, and the aerospace and medical industries were a natural fit. This resulted in a major focus on titanium and its alloys, besides other expensive alloys. The other application area of early metal AM was the tooling industry. The use of 3D printing allowed building of complex cooling channels in injection molding inserts that resulted in a substantial reduction in the cycle time and hence significant cost savings. The huge cost savings justified use of AM techniques that were slower and more expensive as compared to traditional manufacturing techniques. Solidica (now Fabrisonic), founded in 1999, invented a new AM technology based on sheet lamination using ultrasonic energy. Sciaky, in 2009, began an electron beam- and wire-based EBAM technique to print large parts.
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Science, Technology and Applications of Metals in Additive Manufacturing
As 3D printing has gained significant market attention in the past few years, the bulk of this has been due to metal AM. While polymer printing techniques have advanced over the years, the maturity of metal AM techniques has pushed AM technology to a whole new level by allowing the fabrication of functional parts in a wide range of engineering and industrial applications that offer comparable properties and enhanced performances with conventionally manufactured components. Naturally, this has led to major changes in the marketplace and several consolidations and mergers took place, starting with Renishaw’s acquisition of MTT, General Electric’s acquisition of AM job shop Morris Technology (2012), and eventually machine OEMs ARCAM (2016) and Concept Lasers (2017), RTI International’s acquisition of NORSK titanium (2015), and ALOCOA acquisition of RTI International (2015). The two largest 3D printing companies, 3D Systems and Stratasys, have also grown organically through a series of acquisitions over the years. While the industry is growing at a compound growth rate of 35%, more and more interest is focusing on metal AM.
1.1.3 Brief introduction to various additive manufacturing technologies with a focus on metal additive manufacturing All AM technologies are based on the common principle of slicing a solid model in multiple layers, creating a toolpath for each layer, uploading these data into the machine, and building the part up layer by layer following the sliced model data using a heat source (laser, electron beam, electric arc, or ultrasonic energy, etc.) and feedstock (metal powder, wire, or thin metal sheet, etc.). ASTM (american society for testing of materials) F2792-12a categorizes all AM technologies into a broad group of seven categories, namely binder jetting (BJ), DED, material extrusion (ME), material jetting (MJ), PBF, sheet lamination, and vat polymerization [14]. BJ involves laying a layer of metal powder and then applying a binder following the part CAD geometry. Successive layers build up the part and when finished the part is put into an oven to bake-off the binders and infiltrate porosities with a liquid metal, such as bronze. DED involves using a heat source such as a laser or electron beam or a gas-tungsten arc to create a melt pool and adding filler metals in powder or wire form into the melt pool. The process follows a toolpath created from the CAD geometry and builds up parts in successive layers. ME is similar to the DED process. It involves using a resin filament, heating it up and extruding it through the process nozzle, and depositing it on a substrate layer by layer. MJ dispenses droplets of a photosensitive material that solidifies
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under ultraviolet (UV) light, building a part layer by layer. The materials used in MJ are thermoset photopolymers (acrylics) that come in a liquid form. PBF uses layers of powder, either polymer or metal, that are fused together using a heat source such as a laser or electron beam following a toolpath created from CAD data. Sheet lamination uses thin sheets of metal laid on layer-by-layer one on top of another and fused together using an ultrasonic process following the CAD data. Vat polymerization uses a vat of liquid photopolymer resin, out of which the model is constructed layer by layer. A UV light is used to cure or harden the resin where required, while a platform moves the object being made downward after each new layer is cured. Of these seven categories, only four involve metal processing; DED, PBF, sheet lamination, and BJ. Recently, companies such as, Markforged are using material extrusion technology to print metals with the help of a filament comprised of metal powder and plastic binder. After printing, the binder is dissolved away and metal powder sintered to form a full metal part. Each of these techniques varies significantly in their approach and capability. The details of working principles of various AM techniques are discussed in Chapter 2, capabilities, merits, and demerits of these techniques are discussed in Chapter 3, microstructure and properties of additive manufacturing builds are discussed in Chapter 5, modeling and simulation of AM processes are discussed in Chapter 6, design for AM is discussed in Chapter 7 and qualification of AM materials is discussed in Chapter 8. Among the various metal AM applications, medical and aerospace applications are at the forefront. Beginning with medical and aerospace applications, metal AM appears to have found the right fit of small volume of parts with high cost [10,15,16]. Applications in tool and die industry and general industrial are also gaining popularity. Besides machines and their capabilities, future of metal AM and its success depends very much on properties of AM built materials as well as its ability to build novel deigns. Markets, cost structures and applications for metal AM is discussed in Chapter 9.
1.1.4 Relevance to existing manufacturing processes While for some applications AM is deemed as a replacement for traditional manufacturing processes, such as forging, casting, and machining, for a vast number of applications, AM is not a replacement. In fact, the best way to consider AM is as an additional tool in the toolbox for design engineers; a tool that lends a significant amount of design freedom to engineers while reducing the design-to-market time drastically and thus aiding innovation in the marketplace.
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Science, Technology and Applications of Metals in Additive Manufacturing
Conventional metal-forming processes such as forging or casting are much more economic for large production runs and provides very high throughput [17]. These traits make these processes suitable for industries, such as automotive and agriculture, where cost and throughput are primary concerns. Size limitations of AM technologies also hinder their application in large-part manufacturing and limit their uses in industries including oil and gas, construction, etc. In contrast, AM offers significant cost benefit for short-run productions, prototypes, and one-off parts [18]. AM excels in making small intricate parts with very complex geometries. The low throughput and high cost of raw materials make AM a better fit for the aerospace, space, and medical industries. For complex geometries AM also saves materials when compared to traditional manufacturing such as forging and machining. As AM technologies are maturing, technologists and engineers are exploring hybrid manufacturing processes that can draw benefits of traditional manufacturing as well as AM [19]. Another way that AM is changing the manufacturing world is by impacting the supply chain. With AM, the final product can be manufactured in closer proximity to the end user and thus shorten the length of the supply chain, reduce transportation cost, save time and conserve energy [20]. In addition, AM’s ability to produce parts on-demand allows inventory reduction, eliminates the need for spare parts inventory [21], and reduces maintenance costs. Finally, in today’s world where global warming and energy scarcity are looming as major future threats, AM is unlocking the potential for designing newer parts that demand less energy through their life cycle from the cradle to the grave. Examples include lighter aerospace parts that reduce fuel consumption, or material saving during manufacturing of high buy-to-fly ratio parts that causes significant energy savings during raw material production. These are some of the ways that AM is impacting the manufacturing world and challenging traditional manufacturers to think differently and find more energy-efficient ways of manufacturing for betterment of the environment and the way of living in general. Impacts of metal AM on our society as a whole is discussed in more detail in Chapter 9.
1.1.5 Challenges to additive manufacturing for qualification One of the barriers to the adoption of AM technologies in mainstream manufacturing has been lack of established standards and difficulty of qualifying AM parts for production [22]. Qualification depends on the
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following steps: (i) establishing process capabilities, (ii) creating standards for these processes, (iii) monitoring and validating process adherence to accepted and approved capabilities and (iv) developing inspection techniques for certifying final products. As is the case for any new technology there are no established standards for AM. While the engineers, technologists, and scientists have been working diligently to create new standards, the process has been slow and cumbersome due to the following facts: (1) there are seven major AM technology categories and multiple subcategories and each of these has their own unique ways of material processing and therefore has their own unique challenges and issues. (2) It also poses additional challenges in terms of resource allocation from standards committees [such as ASTM, International Organization for Standardization (ISO), National Institute of Standards and Technology (NIST)] to so many technologies that may be similar in concept, but very different in approach. (3) AM processes are quite different from traditional manufacturing processes and therefore a lot of standard inspection techniques need major modifications for successful application on AM parts. The ASTM F42 Committee has been created with the goal of producing standards for all AM processes. These standards address material specifications for AM, feedstock handling, storing and disposal, machine monitoring and control, as well as testing of the parts produced using AM. On the plus side, since AM is a digital technology it allows for digital traceability through monitoring and acquisition of real-time data during part processing. Also, the layer-by-layer nature of AM processes allows for inspection of each layer by various non-destructive evaluation (NDE) techniques. While some of the current inspection techniques are inappropriate for AM parts and new inspection methods are needed, many of the standard testing techniques are still applicable for AM parts [23,24]. In conclusion, while AM technologies are facing adoption challenges due to the lack of standards, in the long run these techniques offer better monitoring and quality control opportunities. Details of AM part qualifications, inspection techniques, and standards are discussed in Chapter 8.
References [1] A third industrial revolution. Economist, April 21, 2012. Paul Markillie. [2] The FAA Cleared the First 3D Printed Part to Fly in a Commercial Jet Engine from GE. ,https://www.ge.com/reports/post/116402870270/the-faa-cleared-thefirst-3d-printed-part-to-fly-2/. (accessed 22.08.18).
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Science, Technology and Applications of Metals in Additive Manufacturing
[3] The Blade Runners: This Factory Is 3D Printing Turbine Parts For The World’s Largest Jet Engine. ,https://www.ge.com/reports/future-manufacturing-take-lookinside-factory-3d-printing-jet-engine-parts/. (accessed 15.02.19). [4] EBMs for Orthopedic Implants quality of life built with Additive Manufacturing. ,http://www.arcam.com/solutions/orthopedic-implants/. (accessed 15.02.19). [5] The Economist Takes a Look at 3D Printing. Economist, July 4, 2017. Michael Petch. [6] Method of making decorative articles. R. Baker, US Patent 1,533,300, 1925. [7] Method of generating and constructing three-dimensional bodies. P. DiMtteo, US Patent 3,932,923, 1976. [8] Molding Process. R.F. Householder, US Patent 4,247,508,1981. [9] J.J. Beaman, J.W. Barlow, D.L. Bourell, R.H. Crawford, H.L. Marcus, K.P. McAlea, Solid Freeform Fabrication: A New Direction in Manufacturing, Springer, New York, 1997, pp. 1 21. [10] Wohlers Report. 3D Printing and Additive Manufacturing State of the Industry. Terry Wohlers, Wohlers Report 2014. [11] Apparatus for production of three-dimensional objects by stereolithography. Charles W. Hull, US Patent 4,575,330, 1986. [12] DMLS Development History and State of the Art. M. Shellabear, O. Nyrhilä, Presented at LANE 2004 Conference, Erlangen, Germany, September 21 24, 2004. [13] G. Lutjering, J.C. Williams, Titanium, Springer, Berlin, 2003, p. 95. [14] ASTM F2792-12a, Standard Terminology for Additive Manufacturing Technologies, ASTM International, West Conshohocken, PA, 2012. [15] B. Dutta, F.H. Froes, Additive manufacturing of titanium alloys, Adv. Mater. Process. 172 (2) (2014) 18 23. [16] B. Dutta, F.H. Froes, Additive Manufacturing of Titanium Alloys, Elsevier, 2016. [17] Die Casting vs 3D Printed Metals. ,http://www.diecastingdesign.org/3d-printedmetals.. Accessed Dec 20, 2018. [18] NIST Special Publication 1176, Costs and Cost Effectiveness of Additive Manufacturing, Douglas S. Thomas Stanley W. Gilbert. [19] M.D. Bambacha, M. Bambachb, A. Sviridovb, S. Weissa, New process chains involving additive manufacturing and metal forming a chance for saving energy? Proc. Eng. 207 (2017) 1176 1181. [20] A. Verhoefa, B.W. Buddeb, C. Chockalingamb, B.G. Nodarb, J.M. van Wijkc, The effect of additive manufacturing on global energy demand: an assessment using a bottom-up approach Leendert, Energy Policy 112 (2018) 349 360. [21] The Defense Industry Is Expanding the Use of 3D Printing. https://www.defenseone.com/ technology/2014/09/defense-industry-expanding-use-3d-printing/95396/. Accessed April 16th, 2019. [22] W.E. Frazier, D. Polakovics, W. Koegel, Qualifying of metallic materials and structures for aerospace applications, JOM 53 (2001) 16 18. [23] J. Slotwinski, S. Moylan, Applicability of existing materials testing standards for additive manufacturing materials, Ref NIST. IR. 8005. Available from: ,https:// doi.org/10.6028/NIST.IR.8005., 2014. [24] Measurement science roadmap for metal-based additive manufacturing. Prepared by Energetics Incorporated, Columbia, Maryland for NIST, Deparment of Commerce from presentations made in the Roadmap Workshop on Measurement Science for Metal-Based Additive Manufacturing held on December 45, 2012 at the NIST campus in Gaithersburg, MD.
Metal additive manufacturing Abbreviations AM ASTM BJ CAD 3D DED DMD DMLS EBM GE ISO LENS ME MJ NIST PBF SL
additive manufacturing American Society for Testing of Materials binder jetting computer-aided design three-dimensional direct energy deposition direct metal deposition direct metal laser sintering electron beam melting General Electric Corporation International Organization for Standardization laser energy net shaping material extrusion material jetting National Institute of Standards and Technology powder bed fusion stereo lithography
1.1 Introduction Three-dimensional (3D) printing and additive manufacturing (AM) have been dubbed the third industrial revolution [1]. While the second industrial revolution in the early 20th century began with the assembly line and ushered in the era of mass production, the third industrial revolution is thought to make things economically in much smaller numbers, more flexibly, and with greater customization. That was the thought in 2012. Six years later, the technology has advanced further and production parts manufactured using 3D printing have made their way into jet engines and aircraft, in medical and dental industry, in the oil and gas industry, and general industrial markets. CFM International (a joint venture between General Electric Corporation (GE) Aviation and Safran) has successfully introduced a 3D printed fuel nozzle in the LEAP jet engine [2]. Avio Aero is printing TiAl blades for the GE9X engine [3]. 3D printing of Science, Technology and Applications of Metals in Additive Manufacturing DOI: https://doi.org/10.1016/B978-0-12-816634-5.00001-7
© 2019 Elsevier Inc. All rights reserved.
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Science, Technology and Applications of Metals in Additive Manufacturing
Figure 1.1 3D printed parts: (A) LEAP engine fuel nozzle [2], (B) 3D printed TiAl blades for the GE9X engine [3], and (C) orthopedic implants [4]. Photo courtesy of GE Additive, Mike Cloran.
titanium orthopedic implants is gaining popularity [4]. Airbus is also using 3D printed titanium brackets in the A350 XWB. Despite the speed of 3D printing being far too slow to produce millions of parts for the automotive industry, its throughput is steadily increasing while manufacturing costs are decreasing and “Such skepticism looks less and less credible.” [5]. 3D printing is a disruptive technology that affects the complete value chain of a product, from design to production (Fig. 1.1).
1.1.1 What is additive manufacturing and why additive manufacturing? AM is defined as a process whereby parts or components are directly built from a solid model using a heat source and filler material. The process involves slicing a solid model of the part into multiple layers, creating a toolpath to trace the individual layers, and then building the part layer by layer using the filler material in a computer-controlled automated machine. Since the process relies on material addition in each layer leading to the final part geometry, it is called an additive process. In contrast, a conventional machining process starts with a block of material and follows a material removal technique to create the final part geometry and therefore is called a subtractive process. Although the terms 3D printing and AM are often used interchangeably, 3D printing is actually a subset of AM that builds up parts from scratch using the above-mentioned technique. AM, however, includes techniques such as 3D printing, but also material addition to existing parts or components for the purpose of repair, remanufacturing, or property enhancement. Major benefits of AM over conventional manufacturing roots from its ability to build parts directly from CAD data. This
Metal additive manufacturing
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eliminates the need for a tool or die and allows significant reduction in design-to-manufacturing time as well as significant cost reduction for low volume part production. In addition to this, AM offers a greater degree of design freedom and allows manufacturing of geometries that are not feasible by conventional manufacturing at all. Other benefits of AM include reduction of scrap through efficient material usage and its ability to remanufacture damaged parts. While AM is not a direct replacement for conventional manufacturing, especially for high volume production, as the parts are becoming more and more engineered and complex, AM offers a great solution to manufacturing industry and facilitates innovation by reducing lead time to market for new products.
1.1.2 History of additive manufacturing The history of metal AM dates back to at least 1920 by Baker (US patent, 1,533,300) who used an electric arc and metal electrode to form walled structures and decorative articles (Fig. 1.2) [6]. Today direct energy deposition (DED) techniques such as direct metal deposition (DMD), laser energy net shaping (LENS), or direct manufacturing (DM) are based on similar ideas, but integrate the layered manufacturing concepts to create parts directly from computer-aided design (CAD) data. However, the concept of layered manufacturing finds its roots from two different technologies that started in the 19th century: topography and photosculpture. As early as 1892 Blanther patented a technique for making a mold for topographical relief maps using impressions of topographical contour lines
Figure 1.2 A typical decorative article as described by Baker’s 1920 patent [6].
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Science, Technology and Applications of Metals in Additive Manufacturing
on a series of wax plates, cutting these wax plates on these lines and stacking them to create a raised relief map of paper. In 1972 Matsubara proposed a process using photopolymer resin coated onto graphite powder/ sand, spread into a layer, select areas of the layer heated and hardened using a mercury vapor lamp and the remaining area dissolved to create sheets with defined geometry, which were then stacked together to form a casting mold. In 1974 utilizing a similar stacking technique, DiMatteo [7] produced three dimensional shapes from contour milled metallic sheets that were then joined in layered fashion by adhesion, bolts, or tapered rods (Fig. 1.3a). In 1968 Swainson proposed a process to directly fabricate a plastic pattern by selective, three-dimensional polymerization of a photosensitive polymer at the intersection of two laser beams. This followed work by Ciraud (1972), Householder (1979) (Fig. 1.3b) [8], Kodama (1981), Herbert (1982), Hull (1984), and Deckerd (1986) paving the way for modern 3D printing technologies that are based on powder bed fusion (PBF) technologies (Fig. 1.4). Patents by Ciraud (1972), Arcella and Lessmann (1989), Jeantette et al. (1996), and Koch and Mazumder (1998) form the basis of modern DED technologies. More details about the
Figure 1.3 (A) Laminated mold from DiMatteo’s 1974 patent [7] and (B) schematic drawing showing Householder’s invention [8].
Figure 1.4 Apparatus for laser sintering from Chuck Hull's invention [11].
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history of AM and 3D printing, as well as the commercialization of this industry, can be found elsewhere [9,10]. Commercial efforts at AM started with the introduction of stereo lithography (SL) and the formation of 3D Systems Corp. in 1987. This was followed by the formation of EOS GmbH in 1990, Stratasys in 1991, DTM Corp. in 1992, Fockele & Schwarze (F&S) in 1994, Z Corp in 1996, and subsequently many other companies jumped in. While most of this effort was on polymeric materials, commercialization of metal AM started with DTM. DTM launched a metal sintering system, by laser sintering polymer-coated metal powders in the sinter station to form a green part, followed by a furnace process to remove the polymer, bonding the metal matrix, and infiltrating it with a secondary metal to remove the porosity. In contrast, EOS developed a direct metal laser sintering (DMLS) process where metal powders were directly sintered using a moving laser beam [12]. In 1997 Swedish company Arcam AB was formed that used its patented electron beam melting (EBM) technology to produce titanium medical components. Arcam’s continued work with Adler Ortho Group resulted in Conformité Européene, meaning “European Conformity” (CE-certification) of EBM-manufactured titanium hip implants in 2007, marking a significant step in metal AM. The first commercial effort in DED started with the formation of Aeromet Corporation in 1997, which focused on a laser-based DED technology for large aerospace components made of titanium [13]. In 1998 commercialization of Sandia National Laboratory developed laser engineered net shaping (LENS) by Optomec Inc. and University of Michigan developed DMD by POM Group (now DM3D Technology) which brought further impetus to metal AM. For economic reasons, early efforts on metal AM were focused on expensive parts and components, and the aerospace and medical industries were a natural fit. This resulted in a major focus on titanium and its alloys, besides other expensive alloys. The other application area of early metal AM was the tooling industry. The use of 3D printing allowed building of complex cooling channels in injection molding inserts that resulted in a substantial reduction in the cycle time and hence significant cost savings. The huge cost savings justified use of AM techniques that were slower and more expensive as compared to traditional manufacturing techniques. Solidica (now Fabrisonic), founded in 1999, invented a new AM technology based on sheet lamination using ultrasonic energy. Sciaky, in 2009, began an electron beam- and wire-based EBAM technique to print large parts.
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Science, Technology and Applications of Metals in Additive Manufacturing
As 3D printing has gained significant market attention in the past few years, the bulk of this has been due to metal AM. While polymer printing techniques have advanced over the years, the maturity of metal AM techniques has pushed AM technology to a whole new level by allowing the fabrication of functional parts in a wide range of engineering and industrial applications that offer comparable properties and enhanced performances with conventionally manufactured components. Naturally, this has led to major changes in the marketplace and several consolidations and mergers took place, starting with Renishaw’s acquisition of MTT, General Electric’s acquisition of AM job shop Morris Technology (2012), and eventually machine OEMs ARCAM (2016) and Concept Lasers (2017), RTI International’s acquisition of NORSK titanium (2015), and ALOCOA acquisition of RTI International (2015). The two largest 3D printing companies, 3D Systems and Stratasys, have also grown organically through a series of acquisitions over the years. While the industry is growing at a compound growth rate of 35%, more and more interest is focusing on metal AM.
1.1.3 Brief introduction to various additive manufacturing technologies with a focus on metal additive manufacturing All AM technologies are based on the common principle of slicing a solid model in multiple layers, creating a toolpath for each layer, uploading these data into the machine, and building the part up layer by layer following the sliced model data using a heat source (laser, electron beam, electric arc, or ultrasonic energy, etc.) and feedstock (metal powder, wire, or thin metal sheet, etc.). ASTM (american society for testing of materials) F2792-12a categorizes all AM technologies into a broad group of seven categories, namely binder jetting (BJ), DED, material extrusion (ME), material jetting (MJ), PBF, sheet lamination, and vat polymerization [14]. BJ involves laying a layer of metal powder and then applying a binder following the part CAD geometry. Successive layers build up the part and when finished the part is put into an oven to bake-off the binders and infiltrate porosities with a liquid metal, such as bronze. DED involves using a heat source such as a laser or electron beam or a gas-tungsten arc to create a melt pool and adding filler metals in powder or wire form into the melt pool. The process follows a toolpath created from the CAD geometry and builds up parts in successive layers. ME is similar to the DED process. It involves using a resin filament, heating it up and extruding it through the process nozzle, and depositing it on a substrate layer by layer. MJ dispenses droplets of a photosensitive material that solidifies
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under ultraviolet (UV) light, building a part layer by layer. The materials used in MJ are thermoset photopolymers (acrylics) that come in a liquid form. PBF uses layers of powder, either polymer or metal, that are fused together using a heat source such as a laser or electron beam following a toolpath created from CAD data. Sheet lamination uses thin sheets of metal laid on layer-by-layer one on top of another and fused together using an ultrasonic process following the CAD data. Vat polymerization uses a vat of liquid photopolymer resin, out of which the model is constructed layer by layer. A UV light is used to cure or harden the resin where required, while a platform moves the object being made downward after each new layer is cured. Of these seven categories, only four involve metal processing; DED, PBF, sheet lamination, and BJ. Recently, companies such as, Markforged are using material extrusion technology to print metals with the help of a filament comprised of metal powder and plastic binder. After printing, the binder is dissolved away and metal powder sintered to form a full metal part. Each of these techniques varies significantly in their approach and capability. The details of working principles of various AM techniques are discussed in Chapter 2, capabilities, merits, and demerits of these techniques are discussed in Chapter 3, microstructure and properties of additive manufacturing builds are discussed in Chapter 5, modeling and simulation of AM processes are discussed in Chapter 6, design for AM is discussed in Chapter 7 and qualification of AM materials is discussed in Chapter 8. Among the various metal AM applications, medical and aerospace applications are at the forefront. Beginning with medical and aerospace applications, metal AM appears to have found the right fit of small volume of parts with high cost [10,15,16]. Applications in tool and die industry and general industrial are also gaining popularity. Besides machines and their capabilities, future of metal AM and its success depends very much on properties of AM built materials as well as its ability to build novel deigns. Markets, cost structures and applications for metal AM is discussed in Chapter 9.
1.1.4 Relevance to existing manufacturing processes While for some applications AM is deemed as a replacement for traditional manufacturing processes, such as forging, casting, and machining, for a vast number of applications, AM is not a replacement. In fact, the best way to consider AM is as an additional tool in the toolbox for design engineers; a tool that lends a significant amount of design freedom to engineers while reducing the design-to-market time drastically and thus aiding innovation in the marketplace.
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Conventional metal-forming processes such as forging or casting are much more economic for large production runs and provides very high throughput [17]. These traits make these processes suitable for industries, such as automotive and agriculture, where cost and throughput are primary concerns. Size limitations of AM technologies also hinder their application in large-part manufacturing and limit their uses in industries including oil and gas, construction, etc. In contrast, AM offers significant cost benefit for short-run productions, prototypes, and one-off parts [18]. AM excels in making small intricate parts with very complex geometries. The low throughput and high cost of raw materials make AM a better fit for the aerospace, space, and medical industries. For complex geometries AM also saves materials when compared to traditional manufacturing such as forging and machining. As AM technologies are maturing, technologists and engineers are exploring hybrid manufacturing processes that can draw benefits of traditional manufacturing as well as AM [19]. Another way that AM is changing the manufacturing world is by impacting the supply chain. With AM, the final product can be manufactured in closer proximity to the end user and thus shorten the length of the supply chain, reduce transportation cost, save time and conserve energy [20]. In addition, AM’s ability to produce parts on-demand allows inventory reduction, eliminates the need for spare parts inventory [21], and reduces maintenance costs. Finally, in today’s world where global warming and energy scarcity are looming as major future threats, AM is unlocking the potential for designing newer parts that demand less energy through their life cycle from the cradle to the grave. Examples include lighter aerospace parts that reduce fuel consumption, or material saving during manufacturing of high buy-to-fly ratio parts that causes significant energy savings during raw material production. These are some of the ways that AM is impacting the manufacturing world and challenging traditional manufacturers to think differently and find more energy-efficient ways of manufacturing for betterment of the environment and the way of living in general. Impacts of metal AM on our society as a whole is discussed in more detail in Chapter 9.
1.1.5 Challenges to additive manufacturing for qualification One of the barriers to the adoption of AM technologies in mainstream manufacturing has been lack of established standards and difficulty of qualifying AM parts for production [22]. Qualification depends on the
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following steps: (i) establishing process capabilities, (ii) creating standards for these processes, (iii) monitoring and validating process adherence to accepted and approved capabilities and (iv) developing inspection techniques for certifying final products. As is the case for any new technology there are no established standards for AM. While the engineers, technologists, and scientists have been working diligently to create new standards, the process has been slow and cumbersome due to the following facts: (1) there are seven major AM technology categories and multiple subcategories and each of these has their own unique ways of material processing and therefore has their own unique challenges and issues. (2) It also poses additional challenges in terms of resource allocation from standards committees [such as ASTM, International Organization for Standardization (ISO), National Institute of Standards and Technology (NIST)] to so many technologies that may be similar in concept, but very different in approach. (3) AM processes are quite different from traditional manufacturing processes and therefore a lot of standard inspection techniques need major modifications for successful application on AM parts. The ASTM F42 Committee has been created with the goal of producing standards for all AM processes. These standards address material specifications for AM, feedstock handling, storing and disposal, machine monitoring and control, as well as testing of the parts produced using AM. On the plus side, since AM is a digital technology it allows for digital traceability through monitoring and acquisition of real-time data during part processing. Also, the layer-by-layer nature of AM processes allows for inspection of each layer by various non-destructive evaluation (NDE) techniques. While some of the current inspection techniques are inappropriate for AM parts and new inspection methods are needed, many of the standard testing techniques are still applicable for AM parts [23,24]. In conclusion, while AM technologies are facing adoption challenges due to the lack of standards, in the long run these techniques offer better monitoring and quality control opportunities. Details of AM part qualifications, inspection techniques, and standards are discussed in Chapter 8.
References [1] A third industrial revolution. Economist, April 21, 2012. Paul Markillie. [2] The FAA Cleared the First 3D Printed Part to Fly in a Commercial Jet Engine from GE. ,https://www.ge.com/reports/post/116402870270/the-faa-cleared-thefirst-3d-printed-part-to-fly-2/. (accessed 22.08.18).
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[3] The Blade Runners: This Factory Is 3D Printing Turbine Parts For The World’s Largest Jet Engine. ,https://www.ge.com/reports/future-manufacturing-take-lookinside-factory-3d-printing-jet-engine-parts/. (accessed 15.02.19). [4] EBMs for Orthopedic Implants quality of life built with Additive Manufacturing. ,http://www.arcam.com/solutions/orthopedic-implants/. (accessed 15.02.19). [5] The Economist Takes a Look at 3D Printing. Economist, July 4, 2017. Michael Petch. [6] Method of making decorative articles. R. Baker, US Patent 1,533,300, 1925. [7] Method of generating and constructing three-dimensional bodies. P. DiMtteo, US Patent 3,932,923, 1976. [8] Molding Process. R.F. Householder, US Patent 4,247,508,1981. [9] J.J. Beaman, J.W. Barlow, D.L. Bourell, R.H. Crawford, H.L. Marcus, K.P. McAlea, Solid Freeform Fabrication: A New Direction in Manufacturing, Springer, New York, 1997, pp. 1 21. [10] Wohlers Report. 3D Printing and Additive Manufacturing State of the Industry. Terry Wohlers, Wohlers Report 2014. [11] Apparatus for production of three-dimensional objects by stereolithography. Charles W. Hull, US Patent 4,575,330, 1986. [12] DMLS Development History and State of the Art. M. Shellabear, O. Nyrhilä, Presented at LANE 2004 Conference, Erlangen, Germany, September 21 24, 2004. [13] G. Lutjering, J.C. Williams, Titanium, Springer, Berlin, 2003, p. 95. [14] ASTM F2792-12a, Standard Terminology for Additive Manufacturing Technologies, ASTM International, West Conshohocken, PA, 2012. [15] B. Dutta, F.H. Froes, Additive manufacturing of titanium alloys, Adv. Mater. Process. 172 (2) (2014) 18 23. [16] B. Dutta, F.H. Froes, Additive Manufacturing of Titanium Alloys, Elsevier, 2016. [17] Die Casting vs 3D Printed Metals. ,http://www.diecastingdesign.org/3d-printedmetals.. Accessed Dec 20, 2018. [18] NIST Special Publication 1176, Costs and Cost Effectiveness of Additive Manufacturing, Douglas S. Thomas Stanley W. Gilbert. [19] M.D. Bambacha, M. Bambachb, A. Sviridovb, S. Weissa, New process chains involving additive manufacturing and metal forming a chance for saving energy? Proc. Eng. 207 (2017) 1176 1181. [20] A. Verhoefa, B.W. Buddeb, C. Chockalingamb, B.G. Nodarb, J.M. van Wijkc, The effect of additive manufacturing on global energy demand: an assessment using a bottom-up approach Leendert, Energy Policy 112 (2018) 349 360. [21] The Defense Industry Is Expanding the Use of 3D Printing. https://www.defenseone.com/ technology/2014/09/defense-industry-expanding-use-3d-printing/95396/. Accessed April 16th, 2019. [22] W.E. Frazier, D. Polakovics, W. Koegel, Qualifying of metallic materials and structures for aerospace applications, JOM 53 (2001) 16 18. [23] J. Slotwinski, S. Moylan, Applicability of existing materials testing standards for additive manufacturing materials, Ref NIST. IR. 8005. Available from: ,https:// doi.org/10.6028/NIST.IR.8005., 2014. [24] Measurement science roadmap for metal-based additive manufacturing. Prepared by Energetics Incorporated, Columbia, Maryland for NIST, Deparment of Commerce from presentations made in the Roadmap Workshop on Measurement Science for Metal-Based Additive Manufacturing held on December 45, 2012 at the NIST campus in Gaithersburg, MD.