Additive manufacturing techniques are a collection of manufacturing processes that join materials to make physical 3D objects directly from virtual 3D computer data. These processes typically build up parts layer by layer, as opposed to subtractive manufacturing methodologies, which create 3D geometry by removing material in a sequential manner. In 2009, after more than 20 years of confusing terminology, the ASTM International F42 Committee on Additive Manufacturing Technologies defined additive manufacturing as the “process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing methodologies.” These technologies were also called rapid prototyping, direct digital manufacturing, solid freeform fabrication, additive fabrication, additive layer manufacturing, and other similar technology names over the years. In the technical community, an international consensus has coalesced around the use of “additive manufacturing,” whereas in the popular press the technologies are known as “3D printing.”
Every existing commercial AM machine works in a similar way. First a 3D computer-aided design (CAD) file is sliced into a stack of two-dimensional planar layers. These layers are built by the AM machine and stacked one after the other to build up the part (Figure 1). Today, there are seven different approaches to AM, and dozens of variants of these approaches. As most of these approaches were first patented in the late 1980s and early 1990s, in many cases the fundamental process patents have expired or are expiring soon—thus opening up the marketplace for significant competition in a way that was impossible over the past 20 years due to intellectual property exclusivity.
The remainder of this paper provides an overview on the seven different approaches to AM, followed by a discussion of the business trends and opportunities afforded by AM techniques. The breakdown of AM processes into the following seven categories is based upon the work of the Terminology Subcommittee of the ASTM F42 committee. At the time of the writing of this paper this categorization is being balloted, and thus the final names of these categories are subject to change as the standards-development consensus process proceeds.
Material jetting is the use of inkjet printers or other similar techniques to deposit droplets of build material that are selectively dispensed through a nozzle or orifice to build up a three-dimensional structure. In most cases these droplets are made up of photopolymers or wax-like materials to form parts or investment casting patterns, respectively. These processes are truly 3D-printing machines, as they use inkjet and other “printing” techniques to build up three-dimensional structures.