The additive manufacturing industry is continually evolving, as new ways to make things arrive frequently.

Types of additive manufacturing technology that have been around the longest, though, are stereolithography, PolyJet, Fused Deposition Modeling, laser sintering in various forms, Digital Light Processing, and Electron Beam Melting.

Here’s a look at the key aspects of each of these additive manufacturing technologies.

Stereolithography (SL) works with an ultraviolet laser that cures resins known as photopolymers. Two key attributes of parts made in this process are good resolution and feature detail. A drawback is that the resin continues to be photosensitive long after a build and lose its resolution, feature detail, become yellow or brittle. SL companies are continually working on new materials that overcome these drawbacks.

PolyJet technology uses a number of nozzles to jet liquid polymers that are hardened with ultraviolet light. The polymers can simulate a range of thermoplastic materials. For rigorous applications, however, another additive technology may be better. As with SL materials, the materials used in PolyJet can be subject to brittleness and lose their shape.

In Fused Deposition Modeling (FDM), thermoplastic filaments are heated in the deposition nozzle for layer-by-layer deposit. A number of materials are available to suit specific functions or applications. Fixturing is one of the more dominant uses of this technology.

The Selective Laser Sintering (SLS) process works with powdered materials that are sintered with a laser beam. This layer-by-layer process works with either plastics or metals, depending on the system. Laser Sintering handles complex geometries well, especially designs based on topology optimization programs.

Digital Light Processing (DLP) uses a projector to focus light onto photosensitive resin material. One variation of this process from the company Carbon injects oxygen at a specific point in the build to slow the curing time, which delivers parts without the typical stair-step finish of other photopolymer methods.

Direct Metal Laser Sintering (DMLS) is a specific additive process now owned by EOS. Like laser sintering, this process works with metal powders cured by a laser in a layer-by-layer build process. The powder material can range from aluminums, steels, titanium, Inconel, and more. In most cases, the final part will undergo a heat treatment to reduce porosity and defects and increase part density.

Electron Beam Melting uses an electron beam to melt predominantly metal powders together to create parts layer-by-layer. Materials include titanium, cobalt-chrome alloys, and some steels. EBM is a hot bed process, which helps reduce possible residual stresses in parts. In most cases, the final part will undergo a heat treatment to reduce porosity and defects and increase part density.

A new but popular additive process is Multi Jet Fusion (MJF). This process uses multiple nozzles to jet a fusing agent onto a layer of powder that is then cured with an infrared energy source. MJF handles small intricate parts. This process is reportedly faster than many other additive processes, with a good finish. A key feature of parts made through MJF is that they are nearly isotropic.