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What Methods Are Used in 3-D Printing?
January 10, 2015
Next in our series about 3-D printers and printing, today we examine the common methods that create the object from the various filaments. To learn more about filaments, please read this article which explains the three main types, ABS, PLA, and PVA. According to 3DPrinting.com, there are three main types of 3D printing which include selective laser sintering (SLS), fused deposition modeling (FDM), and stereolithography (SLA). Below, we will take each in turn to explain about the technology.
Selective Laser Sintering (SLS)
As the name implies, with SLS a high-powered laser is used to fuse particles of plastic, metal, ceramic, or glass powders into a solid form that matches the chosen three dimensional shape. The powdered material is fused layer by layer based on the encoding of the 3D modeling program used to design the object. When a layer is finished, the powder bed is lowered down by one layer thickness. Then each successive layer is added on top of the previous one until the model is complete.
As far as the unused powder goes, it remains unchanged and acts as a support structure for the finished design. Because of this, there is no need for any additional support, providing an advantage with the method over SLS and SLA. Further, unused powder can be used for the next printing project as well. SLS traces its roots back to Dr. Carl Deckard who invented and patented the technology at the University of Texas in the mid-1980s and was sponsored by Defense Advanced Research Projects Agency (DARPA).
Here’s a video demonstrating SLS:
Fused Deposition Modeling (FDM)
With FDM, plastic filament or metal wires unwinds from a coil and is advanced through an extrusion nozzle which can control the flow. The nozzle is heated in order to melt the material and can be manipulated to move side to side or up and down. This is accomplished with the aid of a mechanism operated through a computer-aided manufacturing (CAM) software package. Objects are produced when the melted material is pushed through or extruded from the nozzles. The material re-hardens once it is out of the nozzle.
The inventor of FDM technology is Scott Crump who did so in the latter part of the 1980s. After obtaining a patent for the technology, he founded a company called Stratasys in 1988. To support the structures as they form, as the build material comes out, the machine simultaneously extrudes additional material which can be disposed of after the object is complete.
Because fused deposition modeling and FDM are trademarked by Stratasys, the technology is also referred to as fused filament fabrication (FFF). This term was first used by people involved with the RepRap project so the technology could be referred to without running into legal trouble.
Here’s a video demonstrating FDM/FFF:
The last technique we are going to discuss is stereolithography, or SLA. With this method, photopolymerization is used to create the solid object out of liquid ultraviolet resin. A beam from an ultraviolet laser is turned onto a vat of the resin and traces a cross-section of the part pattern on the surface of the resin. The exposure to the light turns the resin from a liquid state into a solid one molds it to the layer below.
Once the pattern has been fully traced, the platform is lowered by the thickness of one layer, generally between 0.05mm and 0.15mm. Once it is done, a blade that is filled with resin is sent across the shape, resulting in a new top coat of fresh material. From the new material, the next pattern is traced and then molded to the previous layer. These set of steps continues until the object is fully finished. As it is being built, support structures are needed to attach the part to the elevator platform.
SLA was developed by Charles Hull in 1986 around the same time he founded his company, 3D Systems.
Here’s a video demonstrating this technique: