SLA/DLP can produce parts with very high dimensional accuracy, intricate details and a very smooth surface finish ideal that are ideal for visual prototypes. A large range of speciality materials, such as clear, flexible, castable and biocompatible resins, or materials taylored for specific industrial applications, are also available.

Generally, SLA/DLP parts are more brittle than FDM parts, so they are not best suited for functional prototypes. Also, SLA parts must not be used outdoors, as their mechanical properties and color degrades when they are exposed to UV radiation from the sun. Support structures are always required in SLA/DLP which may leave small blemishes in the surfaces they come in contact with that need extra post-processing to remove.
Merits
High accuracy & intricate details
Smooth surface ideal for visual prototypes
Large range of specialty materials

SLS parts have very good, almost-isotropic mechanical properties, so they are ideal for functional parts and prototypes. Since no support structures are required (the unsintered powder acts as support), designs with very complex geometries can be easily manufactured. SLS is also excellent for small-to-medium batch production (up to 100 parts), since the bin can be filled throughout its volume and multiple parts can be printed at a single production run.

SLS printers are usually high-end industrial systems. This limits the availability of the technology and increases its cost and turn-around times (compared to FDM or SLA, for example). SLS parts have a naturally grainy surface and some internal porosity. If a smooth surface or watertightness is required, additional post-processing steps are needed. Beware that large flat surfaces and small holes need special attention, as they are susceptible to thermal warping and oversintering.
Merits
Ideal for functional prototypes
Complex geometries – no support needed
Small batch production capabilities
Demerits
Higher cost than FDM or SLA
Slower turn-around due to batch production
Grainy surface & internal porosity

Directed Energy Deposition: Directed energy deposition (DED) technologies allow the fabrication of 3D object by utilizing focused energy source (plasma arc, laser beam, and electron beam) to melt the material deposited by a nozzle in the form of wire or powder. These techniques incorporate the characteristics of both power bed fusion and material extrusion techniques. However, different from the powder bed fusion techniques that melt the material predeposited on the substrate, these techniques melt the material as it is being deposited. Generally, a DED printer include a nozzle head that can move around a fixed object in multiple directions for depositing the material on the desired surfaces having geometry according to the CAD model and a high energy laser beam to direct the energy onto the desired surface to melt the material, that immediately gets hardened onto the platform. Once the first layer is deposited, the energy source and the nozzle are moved upwards to deposit the next layer and the process is repeated until the complete 3D object is being fabricated

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