Sign & Digital Graphics

November '15

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S I G N & D I G I T A L G R A P H I C S • November 2015 • 39 After a layer has been traced by the laser, an elevator platform to which the object is attached, descends by the dis- tance of the thickness of a single layer (0.002" to 0.006"). A resin-filled blade sweeps across the top-most layer and re-coats it with fresh material. On this new liquid surface, the subsequent layer pattern is traced joining it to the previous layer until the complete three-dimen- sional object is formed (see Figure 1). Material Jetting In this additive process, two nozzles supply the material in tiny droplets just like a desktop inkjet printer. One of the nozzles builds the 3D object and the other builds a support structure that stabilizes the object. The material is deposited layer-by-layer and leveled with a leveling blade. The material is hardened by an ultra-violet curing lamp that follows the printhead. Sometimes poly-jet technology (multiple jets) is used to print objects with multiple parts and colors (see Figure 2). Binder Jetting This technology uses two compo- nents: a gypsum based powder which is form of plaster, and a super-glue like binder. In the build chamber, a roller spreads a layer of powder over the build platform. A nozzle jets binder into the powder in the shape of the cross section of the object. It uses inkjet printer heads similar to an inkjet paper printer to jet the binder into the powder. Once a layer is printed, the build platform descends the thickness of a single layer and the roller distributes a new layer of powder. The process is repeated until the entire object is built. When completed, the object is removed from the build cham- ber and the excess powder is recycled. Figure 2: This material jetting schematic shows two nozzles on the printhead—one providing build material for the 3D object and the other providing material for the support structure. It also shows where the UV curing lamp goes that fuses the material. (See the video of the Connex 500 3D printer here: www.youtube.com/watch?v=ePhzUQ0IXFE) Figure 3: Binder Jetting employs two components - a gypsum based powder that is formed of plaster, and a super-glue like binder. (See the video here: www.youtube.com/ watch?v=TBU5DyPIr-w) By coloring the binder, multiple colored 3D prints can be created. Binder jetting machines make good solid objects, but because they are essentially composed of plaster and glue they are limited to the creation of rigid parts (see Figure 3). Powder Bed Fusion Selective Laser Sintering (SLS) SLS technology uses a high-powered laser to fuse small particles of plastic, metal, ceramic or glass powders into a 3D object. The laser selectively fuses the powdered material by scanning the cross-sections (or layers) generated by the 3D modeling program on the surface of a powder bed, similar to binder jetting. After each pass the powder bed is low- ered by the thickness of one layer, then a new layer of powder is deposited on top with a blade. The process is repeated until the object is completed. The surrounding untouched pow- der serves as a support structure for the object eliminating the need for an auxil- iary structure which is an advantage over technologies like material jetting that build support structures as the object is

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