Abstract
Laser-based directed energy deposition (L-DED) is an additive manufacturing (AM) technique that is fundamentally different from powder bed fusion processes such as laser powder bed fusion (LPBF) and electron beam melting (EBM). L-DED, also commonly known as laser metal deposition (LMD) or laser engineered net shaping (LENS), possesses a unique capability of repairing metal parts. This chapter presents the history, fundamentals, processing characteristics, powder materials, and equipment of L-DED, and it discusses the microstructures and properties of parts printed by L-DED. L-DED originated from a wire welding technology and was previously known as welding AM (Kratky 1937; Isaac 1942) . A patent with early concepts of L-DED was filed in the 1980s, describing a layerwise additive deposition process via laser powder metallurgy (Brown et al. 1982) . Subsequently, a method for repairing metal parts through the continuous deposition and melting of powder on their surface was patented (Mehta et al. 1988) . In 1988, Hammeke patented a laser spray nozzle, while Buongiorno patented a metal cladding nozzle in 1995 (Hammeke 1988; Buongiorno 1995) . Directed light fabrication was proposed as a form of single-nozzle, powder-based L-DED combining computer-aided design (CAD), computer numerical control (CNC), and laser-based powder deposition for the rapid freeform fabrication of stainless steel parts. In 1995, researchers from Sandia National Laboratories developed a multi-nozzle L-DED system with high powder delivery efficiency, which was commercialized and trademarked as Laser Engineered Net Shaping. In 1997, the Optomec Company also began to promote commercialization of the technology. Different L-DED techniques have emerged in the past 20 years with varying degrees of success in terms of commercialization and market/research adoption. A wide range of terminologies has been proposed for L-DED, including LMD, LENS, direct metal deposition (DMD), and laser rapid forming. A new generation of the L-DED technology is currently being developed by several companies under the generic name of laser metal deposition.
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