Additive Manufacturing, also known as 3D printing, additive layer manufacturing or rapid prototyping, is defined as “the process of joining materials to make parts from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing and formative manufacturing methodologies” (ISO/ASTM 52900:2021).
The process is ‘additive’ in nature, with layers being successively added to build a part, as opposed to ‘subtractive’ technologies, where material is removed or shaped by machining, milling or forming. Importantly, in Additive Manufacturing the part geometry is always digitally defined and based on digital 3D model data from a computer-aided design (CAD) program.
Additive Manufacturing offers many advantages over more traditional manufacturing technologies. The ability to selectively deposit materials only where they are needed means that parts can be much more complex in design, and lighter weight, which can dramatically improve performance. The process is toolless, unlike processes such as casting and injection moulding that require significant up-front investment in tooling, and offers increased design freedom as well as one-off or personalised products.
Additive Manufacturing/3D printing is a relatively new form of manufacturing, being approximately thirty years old. In its early phases, Additive Manufacturing was used for rapid prototyping and was quickly adopted for use with polymer materials. The toolless nature of the process meant that prototypes could be fabricated easily and checked for form, fit and function, enabling rapid innovation in product development. The earliest AM machines, or 3D printers, were based on a process known as stereolithography, where thin layers of UV-sensitive resin were solidified with a laser. This process was commercialised in 1987 by 3D Systems, the first company to bring a commercial stereolithography machine to market.
Shortly thereafter, other polymer-based AM technologies entered the market, the most notable being fused deposition modelling (FDM), a Material Extrusion (MEX)-based process, introduced by Stratasys; and selective laser sintering, now known as Laser Beam Powder Bed Fusion (PBF-LB), a laser power-bed process commercialised by start-up company DTM.
In the early 1990s Additive Manufacturing processes were translated to metals processing, with the earliest attempts being laser powder bed approaches using a metal powder as a feedstock and a CO2 laser for consolidation. However, the laser power was not sufficient to fully densify and consolidate metal powder, and as such the products produced had to be sintered and had low density values, making them unsuitable for large-scale industrial use. Early pioneers of this process were the Fraunhofer Institute ILT in Aachen, whose technology became the basis of MTT Technologies (the forerunner of SLM Solutions and Renishaw AM). Another well-known pioneer is Hans Langer, the founder of Electro Optical Systems (now known as EOS), who was already active in polymeric-based systems, and brought a metal system to market in 1994.
In 1998, Optomec was formed to commercialise an Additive Manufacturing technology named Laser Engineered Net Shaping (LENS) that had been developed at Sandia National Labs. The process was based on laser cladding, where metal powder is sprayed into the path of a laser. In a similar vein, wire-based cladding systems were extended to additive technology; however, this has been slower to develop commercially, with wire-laser and wire-arc processes only more recently commercialised.
At a similar time, the Massachusetts Institute of Technology (MIT) had developed an AM technology involving the deposition of a binder onto a metal powder bed to produce a green part, followed by a debinding and infiltration process with an alternate metal of a lower melting point to produce a dense part. Extrude Hone secured a licence to this technology, known as Binder Jetting, and in 1998 released its first machine, the ProMetal RTS-300.
In 1997, Arcam AB was founded, and a system using an electron beam to melt metal powder in a powder bed (now known as Electron Beam Powder Bed Fusion [PBF-EB]) was developed in collaboration with researchers at the Chalmers University of Technology in Sweden. Patents were secured, importantly around the pre-sintering approach to reduce the static charge build-up on the powder bed. The company’s first machine, the S12 was released in 2002. Arcam was taken over by GE in 2016 and has enjoyed a monopoly of the Electron Beam Powder Bed Fusion market until relatively recently.
Many more variations of the above technologies have been developed and commercialised since the earlier days of Additive Manufacturing development. There is now a proliferation of companies offering metal AM machines, materials, and software. Research has uncovered many unknowns that existed around the various processes, which has assisted in making metal AM processes more reliable and repeatable. The quality of metal AM parts is now equivalent to, or exceeding, the quality of parts made via more traditional processes. Adoption by end-users, particularly in the aerospace and medical sectors, has been strong, with heavy investment in AM technology by these sectors enabling a rapid acceleration of industry growth from the 2010s onwards.