The Emerging Role of Electrodeposition in Additive Manufacturing

R apid prototyping has been used for creating threedimensional objects from computer-aided design (CAD) files since the 1980s. There are a suite of technologies that underpin rapid prototyping, but a key advantage of many is their use of additive manufacturing (AM) processes; objects are created by placing material just where it is needed. AM processes use materials efficiently, reduce waste, and sometimes eliminate any post-processing steps. In recent years, the dropping costs and increasing availability of 3D-printing technologies (one class of AM methods) have driven widespread use and creative user communities. The easy-to-use, integrated software and hardware provides users with freedom in design that has created vast doit-yourself/hobbyist markets. Software reconfigurable additive manufacturing technologies are empowering users by simplifying the way objects and devices are fabricated today. Additive manufacturing has evolved over the past three decades to the point where current methods encompass lateral and vertical resolutions ranging from nanometers to centimeters, as shown in Fig. 1.1-3 The first of these technologies commercialized was stereolithography (SL), which uses a photosensitive liquid polymer that hardens when an ultraviolet laser impinges on the resin.4 The partially cured object is then lowered into the liquid to allow for curing of each subsequent additive layer. Stereolithographic resolutions are typically in the millimeter range, but the development of microstereolithography (MSL) has enabled additive manufacturing at sub-micron level resolution.5,6 However, SL and MSL have limited material capabilities as they require photosensitive polymers. Selective laser sintering (SLS) is similar to SL, except a solid powder is sintered (fused) by the application of a high-energy carbon dioxide laser beam.7 The primary advantage of SLS is increased material capabilities (polymers, metals, and composites), but the vertical and lateral resolutions are typically in the millimeter range due to laser focus diameter, powder granule size limitations, and thermal conduction beyond the laser focus. Similar technologies to SLS include electron beam melting (EBM) which uses an electron beam instead of a carbon dioxide laser to melt the powder and laser engineered net shaping (LENS) which injects the powder into a specific location before then heating it with a high powered laser.2 The 3DP process (developed at MIT) also uses powder as the material stock but instead applied inkjet nozzle technology to deliver liquid binder.8 3DP eliminates the need for high powered lasers or electron beams and achieves better resolution than SLS, but was originally limited to powdered polymer materials. Later, Prometal developed a steel powder and liquid binder to form metal features in a manner similar to 3DP.2 However, Prometal-fabricated steel objects typically required high temperature sintering as a postprocessing step to fuse the metals. Fused deposition modeling (FDM) processes have recently become the most commercially available additive manufacturing technology because of the inexpensive machinery and low materials cost. Ubiquitous machines like “Makerbot” rely on low melting point polymer filaments to transfer liquid polymer to the object, followed by solidification. Despite the low cost, commercial FDM systems are limited to printing thermopolymers and often have millimeter scale XY resolution as set by the diameter of the extrusion nozzle. Stereolithography, selective laser sintering, 3DP, and fused metal deposition represent some of the Fig. 1. The lateral and vertical resolutions for various additive manufacturing techniques govern the kinds of objects that can be fabricated. Shown here is the approximate design space for seven different additive manufacturing methods. Abbreviations for each method are given in the text.