Metal Additive Manufacturing. Ehsan Toyserkani

the end of this chapter, you will be able to:

       Understand the standard definition of additive manufacturing (AM) and seven standard classes of AM processes

       Gain basic knowledge on AM market size

       Gain basic knowledge of opportunities, threats, and trends in the AM industry

       Gain insight into applications of metal AM

1.1 Additive Manufacturing: A Long‐Term Game Changer

Additive manufacturing (AM), also known as 3D printing, is a layer‐by‐layer fabrication technology “poised to be one of the most valued forms of manufacturing in history” [1]. AM is becoming a major research target for industrialized countries as they seek to regain leadership in manufacturing through innovation. The global economy is on the verge of the next industrial revolution, known as “Industry 4.0”, i.e. the fourth industrial revolution. Sector after sector is pulling away from traditional/conventional methods of production in order to engage in and utilize AM. This fresh manufacturing method has garnered a great deal of public curiosity and international publicity. Every week brings news of novel and astounding AM innovations. This technology, which builds up objects by layers, has piqued the industrialized world's curiosity and imagination. This public interest was triggered around 2013–2014, as shown in Figure 1.1, in which the Google Trend suggests that a public interest in “3D Printing” has been increased more than 50‐fold from 2012 to 2016. The trend stays very much the same from 2017 to 2020, but it is the highest in Google Trend compared with counterpart advanced manufacturing technologies. This figure also sheds some light on the geographical distribution of the public interest. North America, Europe, and Australia are among the regions with the highest number of news and interests related to “3D printing” technologies.

Figure 1.1 Global public interest trends for “3D Printing”.

      Source: Extracted from “Google Trends” on 25 November 2020.

      In November 2015, the United Nations encouraged countries to invest in AM technology, forecasting major expansions in business and explosive economic growth and comparing 3D printing to the most influential technologies of the past, such as airplanes, antibiotics, and semiconductors [2]. AM technology has been recommended for substantial research investment [3]. Major initiatives have been announced in Singapore, Australia, the United States, Canada, and Europe [4]. McKinsey estimates that by 2030, the global economic impact approaches $550 billion per year [5].

      As worldwide interest in AM escalates, numerous industries are taking steps to integrate AM technologies into their applications and offerings. Many industries, including aerospace, medical, automotive, tooling, energy, natural resources, consumer, defense, etc. have started to embrace the benefits of AM processes.

      For years, AM has been identified as a technology addressing “economies of scope” through customization, prototyping, and low‐volume manufacturing. However, in recent years, AM has been deployed for “economies of scale,” i.e. mass production, without compromising the economies of scope. This advancement from prototyping to serial production has created many research and development opportunities, especially for quality management and certification. Richard D'Aveni writes: Today, additive manufacturing is achieving economies of scale in a variety of ways– and doing so without sacrificing economies of scope … No longer limited to product prototypes, customized one‐offs, or specialized items made in small quantities, AM is now beginning to take over the kinds of mass manufacturing that have long dominated the industrial economy [6].

AM has been considered a platform to convert digital models to physical parts in a short chain of processes, a platform facilitating a rapid move from “Art” to “Part” in a fancy analogy. The process starts with a digital model that reflects the desired design. Preprocessing is needed on the file depending on materials, applications, and AM processes. A proper AM process must be chosen that fulfills the material and application of interest. After the layered manufacturing is completed, post‐processing may be needed to arrive at the physical part eventually. Figure 1.2 shows the AM process chain schematically.

Figure 1.2 AM chain, enabling physical parts from digital design.

      The history of AM is very well connected to human civilization. The idea of “layered manufacturing” has been around as the activities of human kind have been recorded. More than five million blocks of limestone were put together “stone‐by‐stone” by ancient Egyptians to build the pyramids using human‐made stones. Layered cakes were formally introduced in Maria Parloa's Appledore Cook Book, published in Boston in 1872, which contained one of the first layer‐by‐layer made cake recipes. Francois Willeme developed a method called “photographic sculpture” in 1859. In this method, 3D models of human subjects could be extracted using 24 cameras placed at different angles. Joseph E. Blanther patented an apparatus in 1892, where the apparatus uses a layering idea to create 3D topographical maps. The film industry also fancied the idea of AM processes through science fiction that speculated on “replicating” technology. The term “replicator” was used in the series “Star Trek: The Next Generation.” In the animated series in 1974 and in the episode entitled “The Practical Joker”!, there were scenes where food could be requested to be replicated.

      However, modern AM history starts in 1980s when computer features provided unique opportunities for people to think out of the box and introduce the first AM processes. AM first emerged in 1987 with the idea of Charles Hull, who successfully acquired a patent for his Stereolithography Apparatus, a process that solidifies thin layers of photopolymer using a laser beam. This patent opened venues for a few more 3D printing technologies in the late 1980s. Selective Laser Sintering (SLS), a method that uses a laser beam to sinter metal powder particle to form a solid object, was developed by Carl Deckard at the University of Texas in Austin.

      S. Scott Crump and Lisa Crump developed another 3D printing technology based on material extrusion in the 1980s in which a material is heated and extruded through a nozzle to create an object layer by layer. The technology was called Fused Deposition Modeling (FDM), and it is now known as material extrusion. FDM is the most commonly used AM technology as of 2020.

In the 1990s, many new technologies, including Direct Metal Laser Sintering or so‐called Selective Laser Melting (SLM) and Binder Jetting (BJ), were developed. The binder jetting was developed in 1993 in the Massachusetts Institute of Technology (MIT) based on an inkjet process to create 3D objects by gluing metal or ceramic powder particles.

      Cost of AM machines was starting to decrease in 2000s, helping the technology to be more accessible and adopted. New AM technologies such as material jetting have been emerging and innovation in this field is at high. The internet has continued to increase accessibility to AM when open‐source online libraries for AM digital models are growing rapidly. The 2020 pandemic has proved that such accessibility to digital files and the availability of inexpensive 3D printers can help the community to fill the gap in the medical supplies. There have been many stories over the internet indicating that regular people printed parts of face shields in the period that the supply chain was interrupted due to the pandemic. This feature is now encouraging industry to pay more attention to localized manufacturing to be able to address on‐demand manufacturing with minimum dependencies to foreign countries.

      When the skill gap is one of the major issues in the adoption of AM