Issue link: https://wardsworld.wardsci.com/i/1507671
5 3D Printing (continued) + ward ' s science the printhead does not know how pre- cise its action was or whether its action was successful. For example, when an inkjet printhead is instructed to deposit a droplet with a diameter of 50 μm at (x0, y0, z0), it does not know the exact size and location of the droplet it deposited or even whether a droplet was depos- ited. This creates challenges in the quality control of 3D-printed parts. The 3D printing industry Since its birth three decades ago, the global 3D printing industry has grown into a multibillion-dollar industry and is experiencing a second boom (after the first boom in the 1990s) with an average annual growth rate of more than 20%. The industry consists of six major parties as described below. Machine suppliers 3D Systems and Stratasys have become the two dominant suppliers of nearly ev- ery major type of 3D printer, especially in plastic printing, after a series of mergers and acquisitions. HP joined the competi- tion with their unique Multi Jet Fusion process, claiming to be more than 10 times faster than its competitors. Gen- eral Electric (GE) became a major player in metal printing after its acquisition of Arcam AB and Concept Laser, in forming GE Additive. EOS and Optomec are also major suppliers in the metal-printing field. Two notable start-ups are Carbon and Desktop Metal. Carbon's unique CLIP process speeds up the printing by about 100 times and shows promise for using 3D printing for mass customization. Desktop Metal aims to bring 3D printing to mass production with its production system, claiming to increase the print- ing speed by about 100 times for metal printing. In addition, there are hundreds of small machine suppliers worldwide, mostly focused on consumer 3D printers, such as Ultimaker and XYZprinting. Content providers 3D printing requires 3D digital models, which can be acquired in three different ways: • CAD [or virtual reality (VR)/augment- ed reality (AR)] modeling: Popular CAD software includes and has in- cluded Tinkercad, Blender, Autodesk, SolidWorks, NX, CATIA, and others. VR/AR tools can also help create great 3D content with ease. Some notable VR modeling tools include Blocks, Gravity Sketch, and MakeVR. • 3D scanning: Common 3D scanner suppliers include FARO, NextEngine, Trimble, and Makerbot. • Online repositories: Thingiverse and GrabCAD are two popular online repositories to download 3D models. Yeggi provides a search engine for 3D models. NIH is also running a 3D Print Exchange for 3D models. Software providers To ensure good print quality, software packages are needed to edit and slice the model and to manage the 3D printing process. Two prominent professional software packages are Netfabb from Autodesk and Magics from Materialise. For prosumers, Simplify3D offers more sophisticated functionalities than open- source software at a relatively low price. For consumer 3D printing, open-source software, such as Cura and Slic3r, are commonly used. The marketplace The marketplace is where different parties exchange 3D printing-related resources (such as design or use of 3D printers), which includes B2C (business to customer), C2C, and B2B. On B2C, United Parcel Service (UPS) has rolled out 3D printing services nationwide (United States) in selected stores, where custom- ers can come in to use their 3D printers. Examples of popular sites that provide or have provided online 3D printing services to order are ShapeWays and Fig. 3: Components of a typical 3D printer