November 8, 2016
Additive Manufacturing Overview: What Innovation Has Brought Us
Mobile phones, Microsoft Word and Lotus Notes 123 were all introduced to the public in 1983. That same year, while we were awestruck by the first cell phone’s $3,995 price tag, Chuck Hull was formulating a concept that would eventually make a significant impact on the future of manufacturing.
Hull was using an ultraviolet (UV) light to harden tabletop coatings when he envisioned shooting a laser beam of that light into a vat of liquefied photopolymers. His concept eventually became the first patented Additive Manufacturing (AM) process, which he dubbed stereolithography (SLA). In the 33 years since the conception of SLA, new variants of the AM process have been developed to meet different manufacturing needs.
In addition to the advancements in processes, there have also been advancements in materials. It’s never a bad time to pause and do a little inventory on what innovation in Additive Manufacturing has handed to us over the years. Examining each AM process in depth here would make for a very lengthy article, so instead we will take the opportunity to summarize the various technologies that are being used today.
Stereolithography is the rapid process of directing a low-power, highly focused ultraviolet laser into a pool of photopolymer resin to cure layer upon layer of the resin into a model. Once the model is complete, it is raised from the vat, separated from the platform, given a chemical bath, and then cured in a UV oven. Because it is one of the most accurate AM technologies, SLA is used to make patterns for injection molding, thermoforming, and other casting processes. It’s ideal for concept models and form and fit studies.
Equipment providers: 3D Systems, DWS, EnvisionTEC
Fused Deposition Modeling (FDM)
In the Fused Deposition Modeling process, thin filaments of production-grade thermoplastic material and support material are melted and deposited by a heated nozzle into a two-dimensional pattern. The resulting products are both functional and durable. Additionally, parts can be post-processed as any plastic part. FDM is used in commercial, industrial, aerospace, automotive, and medical industries.
Equipment providers: 3D Systems, Afinia, Solidoodle, Stratasys
Multi-head Photopolymer Jetting
Liquid photopolymers are jetted onto a build platform by inkjet print heads in the Multi-head Photopolymer Jetting process. UV lamps are used to immediately cure and solidify the material. Because of the use of multiple print heads that can process several materials at the same time, multi-material and/or multi-color parts can be developed. Due to the use of UV-active photopolymers, however, parts are limited in durability and mechanical properties. Prototypes, casting patterns, and tools for injection molding can be produced with this technology.
Equipment providers: Stratasys/Objet
In the Binder Jetting process, a thin layer of powder is distributed onto a build platform. Inkjet print heads then apply a liquid bonding agent to the powder that glues the particles together. After each pass, the build platform lowers, the next powder layer is distributed, and the print heads go to work again. The part is built layer by layer in the powder bed and, because the parts are supported by the bed of non-bonded powder, no additional support structures are required. Thus the process is capable of producing multiple parts at the same time within the same bed of powder. Almost any material that is available in powder form can be used. Though it is a fast and cheap technology, the parts produced have are fragile and mechanically limited without further processing. Binder Jetting can be used for prototypes, green parts, casting patterns, and molds and cores.
Equipment providers: 3D Systems, ExOne, Voxeljet, Zcorp/3D Systems
Much like the Binder Jetting process, Laser Sintering starts with the distribution of a layer of plastic powder onto a build platform. One or more lasers then melt the powder, the platform is lowered, and the process repeats. Also like Binder Jetting, because the parts are supported by the surrounding non-melted powder, support structures are not needed. Multiple parts can be built at the same time in the same bed of powder. The parts produced have good mechanical properties, but will differ from injection molded counterparts, primarily in their surface finishes. Laser Sintering is used to produce prototypes, support parts and small series parts.
Equipment providers: 3D Systems, AFS, EOS, TPM
Laser Melting and Laser Sintering are very similar in process, but Laser Melting is used primarily with metal powder to produce metal parts. Other than the material used, the other main difference in the process is that Laser Melting requires support structures to anchor parts and overhanging structures to the build platform. Using structures keeps the heat transfer away from the areas where the laser is melting the powder and thus reduces thermal stress and prevents wrapping. As long as all parts are attached to the build platform, this technology can still produce multiple parts at the same time. Density is high—over 99%—and mechanical properties are good, but surface finishes are limited in this slow and expensive process. Post-processing can improve the tolerances and finishes of parts. Prototypes, support parts, tools for injection molds, and small series parts are created with Laser Melting.
Equipment providers: 3D Micro Print, 3D Systems, Concept Laser, EOS, SLM Solutions
Electron Beam Melting (EBM)
Used primarily with metal powders, Electron Beam Melting uses a computer controlled electron beam to bind the powder in layers on a build platform. It is similar to Laser Melting in process, but requires support structures to anchor parts and overhanging structures to the platform. The structures reduce thermal stresses and prevent wrapping by keeping the heat transfer away from the areas where the powder is melted. Several parts can be built in the same powder bed at the same time as long as each is attached to the build platform via a structure. Electron Beam Melting produces less thermal stress and requires less support structure than Laser Melting. It also builds faster, but is equally slow and expensive and materials for it are limited. While density and mechanical properties are good, surface finishes are not resulting in parts that usually require quite a bit of post-processing. Electron Beam Melting can be used for support parts, prototypes and small series parts.
Equipment providers: Arcam
In the Material Jetting process, inkjet print heads are used to jet melted wax-like materials onto a build platform where it cools and solidifies so the next layer can be added to it. The process continues until the part is built. This technology uses support structures built from a different material for overhangs. Good accuracy and surface finishes can be achieved, but wax-like materials are limited, parts are fragile, and the build process is slow. Material Jetting can be used for prototypes and casting patterns, especially in the medical, dental and jewelry industries.
Equipment providers: 3D Systems, Solidscape/Stratasys