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Beam Deposition Processes (BD): Beam deposition (BD) processes enable the creation of parts by melting and deposition of material from powder or wire feedstock. Although this basic approach can work for polymers, ceramics, and metal matrix composities, it is predominantly used for metal powders. Thus, this technology is often referred to as "metal deposition" technology. To avoid limiting the readers' understanding to just metal built materials, however, we will refer to this category of processes as beam deposition processes.
Most commercialized BD processes enable complete melting of powders using a focused high-power laser beam as the heat source. Research variants include using an electron beam or plasma source in place of laser beam or the use of a thin meatl wire instead of powder as the build material. In many ways, BD techniques can be in an identical manner to laser cladding and plasma welding machines. However, BD machines are considered as those which are designed to create depositions of complex 3D shapes directly from CAD files, rather than the traditional welding and cladding technologies, which where designed for repair, joining, or to apply coatings and do not typically use 3D CAD data as an input format. ( Additive Manufacturing Technologies - Ian Gibson, David W. Rosen, Brent Stucker - page 237 )

Powder Bed Fusion Processes (PBF) : Powder bed fusion (PBF) processes were among the first commercialized AM processes. Developed at the University of Texas at Austin, USA, Selective Laser Sintering (SLS) was the first commercialized powder bed fusion process. Its basic method of operation is schematically shown in Fig 5.1, and all other PBF processes modify this basic approach in one or more ways to enhance machine productivity, enable different materials to be processed, and/or to avoid specific patented features.
All PBF processes share a basic set of characteristics. These include one or more thermal sources for inducing fusion between powder particles, a method for controlling powder fusion to a prescribed region of each layer, and mechanisms for adding and smoothing powder layers.
The SLS process was orginally developed for produsing plastic prototypes using a point-wise laser scanning technique. This approach has been extended to metal and ceramic powders; additional thermal sources have been utilized; and variants for layer-wise fusion of powdered materials now exist. As a result, PBF processes are widely used world-wide, have a broad range of materials (including polymers, metals, ceramics and composites) which can be utilized, and are increasingly being used for direct digital manufacturing of end-used products, as the material properties are comparable to many engineering-grade polymers, metals and ceramics. ( Additive Manufacturing Technologies - Ian Gibson, David W. Rosen, Brent Stucker - page 103)

Photoiniator System: The role of the photoinitiator is to convert the physical energy of the incident light into chemical energy in the form of reactive intermediates. The photoinitiator must exhibit a strong absorption at the laser emission wavelenght, and undergo a fast photolysis to generate the initiating species with a great quantum yield. The reactive intermediates are either radicals capable of adding to vinylic or acrylic double bonds, thereby initiating radical polymerization, or reactive cationic species which can initiate polymerization reactions among epoxy molecules. The free-radical polymerization process was outline in Fig4.4, with the formation of free radicals as the firs step. In typical case in SL, radical photoinitiator systems include compounds that undergo unimoleculer bond cleavage upon irradiation. This class includes aromatic carbonly compounds that are known to undergo a homolytic C-C bond scission upon UV exposure. The benzoyl radical is the major initiating species, while the other fragment may, in some cases, also contribute to the initiation. The most efficient photoinitiators include benzoin ether derivatives, benzyl ketals, hydroxyalkylphenones, (alfa)- amino ketones, and acylphosphine oxides. The Irgacure family or radical photoinitiators from Ciba Specialty Chemicals is commonly used in SL. ( Additive Manufacturing Technologies - Ian Gibson, David W. Rosen, Brent Stucker - page 68)

Automated Fabrication (Autofab): This term was popularized by Marshall Burns in his book of the same name, which was one of the first texts to cover this technology in the early 1990s. The emphasis here is on the use of automation to manufacture products, thus implying the simplification or removal of manual tasks from the process. Computers and microcontrollers are used to control the actuators and to monitor the system variables. This term can also be describe other forms of Computer Numerical Controlled (CNC) machinig centers since there is no direct reference as to how parts are built or the number of stages it would take to built them, although Burns does primarily focus on the technologies also covered by this book. ( Additive Manufacturing Technologies - Ian Gibson, David W. Rosen, Brent Stucker - page 6)