As additive manufacturing technologies become more popular and more important to traditional manufacturers looking to cut costs and lead times during production runs, understanding the different capabilities becomes key to applying these techniques appropriately.
At Inside 3D Printing Conference & Expo at the Javits Center in New York City, Scott McGowan, vice president of marketing for Solid Concepts Inc, led a talk discussing the different types of additive manufacturing (AM) techniques currently employed for industrial-scale rapid prototyping and production purposes.
Additive manufacturing relies on CAD part designs in order to form a three dimensional image of the desired component, which software then slices into cross-section layers. The software can calculate fusion or laser paths required to build each layer from the bottom up.
The mechanism of polyjet 3D printing most resembles a standard desktop 2D printer, as a nozzle sprays a liquid photopolymer on a surface, controlled by a hanging rail. When the material covers a layer in designated outline, it is rapidly cured by a UV lamp in the build area, allowing the nozzle to rise and begin producing the next layer, and so on.
Polyjet printing is so-named because it can deposit multiple materials with its nozzle, often two or three. One example of this is Connex printing system from Stratasys, which deposits one structural material and one modeling material, each of a different color and rigidity.
As McGowan noted, polyjet techniques are ideal for small parts with fine resolution, as it is capable of processing layers as thin as 16 microns. The rapid capabilities of polyjet printing have lead to its use producing medical, entertainment, and automotive components.
Stereolithography (SLA) uses a laser to trace patterns on a photopolymer resin, which causes it to solidify. The elevated build area is lowered the width of a layer, and more resin is added, to be traced and solidified by the layer, and so on. You can see a video of the process here. Mr. McGowan noted that SLA requires finishing, which many manufacturers new to AM might not expect. SLA-produced parts must go through hand sanding and painting after production to remove extra particles and achieve a finished look.
SLA is typically used to produce concept models and master patterns in the aerospace, medical, and architecture industries. Hollywood has also taken advantage of SLA to produce various film props.
Selective laser sintering (SLS)
As the name suggests, manufacturers use a laser in selective laser sintering (SLS), this time to melt heated materials into a CAD shape. The material can be a polymer or metal, but also ceramic or glass, but it is used in the build box as a powder. The laser heats the powders until they melt and adhere to produce a solid shape. The laser scans each layer, then targets areas where the previous layer needs to be fused with the next layer of material. Most commonly, SLS uses a carbon dioxide laser, though other lasers can be incorporated into the process.
Because SLS can manufacture parts out of various types of materials, it has been used to produce production parts or molds for traditional manufacturing. Solid Concepts has used nylon to make automotive fuel tanks. SLS-produced parts can be combined with different materials to make robust components, as you can see in this video from 3D Systems.
Fused Deposition Modeling (FDM)
The most commonly-seen form of additive manufacturing is fused deposition modeling (FDM), because it is the guiding technology behind many of the small, maker-oriented desktop 3D printers available from companies like Solidoodle or MakerBot. However, many industrial printers also employ FDM for production needs. These printers wind a coiled wire of polymer into a heated nozzle, which melts the wire and deposits it in the build area per CAD layering design. The build surface remains flat in the build area, while the nozzle rises layer by layer to produce the final part.
FDM is often used for prototyping and modeling, but it can also make smaller production parts. Aerospace companies have used FDM to produce models. Mr. McGowan said that when NASA revealed their launch of the IRIS telescope, they presented an FDM-printed model of the space scope during media functions.