More About 3D Printing
A 3D printer based on the Vat Photopolymerization method has a container filled with photopolymer resin which is then hardened with UV light source.
Vat photopolymerization schematics. Image source: lboro.ac.uk
The most commonly used technology in this processes is Stereolithography (SLA). This technology employs a vat of liquid ultraviolet curable photopolymer resin and an ultraviolet laser to build the object’s layers one at a time. For each layer, the laser beam traces a cross-section of the part pattern on the surface of the liquid resin. Exposure to the ultraviolet laser light cures and solidifies the pattern traced on the resin and joins it to the layer below.
After the pattern has been traced, the SLA’s elevator platform descends by a distance equal to the thickness of a single layer, typically 0.05 mm to 0.15 mm (0.002″ to 0.006″). Then, a resin-filled blade sweeps across the cross-section of the part, re-coating it with fresh material. On this new liquid surface, the subsequent layer pattern is traced, joining the previous layer. The complete three-dimensional object is formed by this project. Stereolithography requires the use of supporting structures which serve to attach the part to the elevator platform and to hold the object because it floats in the basin filled with liquid resin. These are removed manually after the object is finished.
This technique was invented in 1986 by Charles Hull, who also at the time founded the company, 3D Systems.
Animation of the SLA process
Other technologies using Vat Photopolymerization are the new ultrafast Continuous Liquid Interface Production or CLIP and marginally used older Film Transfer Imaging and Solid Ground Curing.
In this process, the material is applied in droplets through a small diameter nozzle, similar to the way a common inkjet paper printer works, but it is applied layer-by-layer to a build platform making a 3D object and then hardened by UV light.
Material Jetting schematics. Image source: custompartnet.com
Here you can see presentation of Stratasys’ Objet500 Connex 3D printers that use their proprietary Triple-Jetting technology where you can clearly see the print heads and UV light:
With binder jetting two materials are used: powder base material and a liquid binder. In the build chamber, the powder is spread in equal layers and binder is applied through jet nozzles that “glue” the powder particles in the shape of a programmed 3D object. The finished object is “glued together” by binder remains in the container with the powder base material. After the print is finished, the remaining powder is cleaned off and used for 3D printing the next object. This technology was first developed at the Massachusetts Institute of Technology in 1993 and in 1995 Z Corporation obtained an exclusive license.
The following video shows a high-end binder jetting based 3D printer, the ExOne M-Flex. This 3D printer uses metal powder and curing after the binding material is applied.
The most commonly used technology in this process is Fused deposition modeling (FDM)
Fused deposition modeling (FDM), a method of rapid prototyping: 1 – nozzle ejecting molten material (plastic), 2 – deposited material (modeled part), 3 – controlled movable table. Image source: Wikipedia, made by user Zurek’s under CC Attribution-Share Alike 4.0 International license.
The FDM technology works using a plastic filament or metal wire which is unwound from a coil and supplying material to an extrusion nozzle which can turn the flow on and off. The nozzle is heated to melt the material and can be moved in both horizontal and vertical directions by a numerically controlled mechanism, directly controlled by a computer-aided manufacturing (CAM) software package. The object is produced by extruding melted material to form layers as the material hardens immediately after extrusion from the nozzle. This technology is most widely used with two plastic filament material types: ABS (Acrylonitrile Butadiene Styrene) and PLA (Polylactic acid) but many other materials are available ranging in properties from wood filed, conductive, flexible etc.
FDM was invented by Scott Crump in the late 80’s. After patenting this technology he started the company Stratasys in 1988. The software that comes with this technology automatically generates support structures if required. The machine dispenses two materials, one for the model and one for a disposable support structure.
The term fused deposition modeling and its abbreviation to FDM are trademarked by Stratasys Inc. The exactly equivalent term, fused filament fabrication (FFF), was coined by the members of the RepRap project to give a phrase that would be legally unconstrained in its use.
Animation of the FDM process
Powder Bed Fusion
The most commonly used technology in this processes is Selective laser sintering (SLS)
SLS system schematic. Image source: Wikipedia from user Materialgeeza under Creative Commons Attribution-Share Alike 3.0 Unported license
This technology uses a high power laser to fuse small particles of plastic, metal, ceramic or glass powders into a mass that has the desired three-dimensional shape. 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. After each cross-section is scanned, the powder bed is lowered by one layer thickness. Then a new layer of material is applied on top and the process is repeated until the object is completed.
All untouched powder remains as it is and becomes a support structure for the object. Therefore there is no need for any support structure which is an advantage over SLS and SLA. All unused powder can be used for the next print. SLS was developed and patented by Dr. Carl Deckard at the University of Texas in the mid-1980s, under the sponsorship of DARPA.
Animation of the SLS process
Sheet lamination involves material in sheets which are bound together with external force. Sheets can be metal, paper or a form of a polymer. Metal sheets are welded together by ultrasonic welding in layers and then CNC milled into a proper shape. Paper sheets can be used also, but they are glued by adhesive glue and cut in shape by precise blades. A leading company in this field is Mcor Technologies.
A simplified model of ultrasonic sheet metal 3D printing. Image source: Wikipedia from user Mmrjf3 shared under Creative Commons Attribution 3.0 Unported license.
Here is a video with a metal sheet 3D printer by Fabrisonic that uses additive manufacturing paired with CNC milling:
… and here is an overview of Mcor 3D printers that use standard A4 paper sheets:
Directed Energy Deposition
This process is mostly used in the high-tech metal industry and in rapid manufacturing applications. The 3D printing apparatus is usually attached to a multi-axis robotic arm and consists of a nozzle that deposits metal powder or wire on a surface and an energy source (laser, electron beam or plasma arc) that melts it, forming a solid object.
Direct Energy Deposition with metal powder and laser melting. Image source: Merlin project
Sciaky is a major tech company in this area and here is their video presentation showing electron beam additive manufacturing:
Examples & applications of 3D printing
Applications include rapid prototyping, architectural scale models & maquettes, healthcare (3D printed prosthetics and 3D printing with human tissue) and entertainment (e.g. film props).
Other examples of 3D printing would include reconstructing fossils in paleontology, replicating ancient artifacts in archaeology, reconstructing bones and body parts in forensic pathology and reconstructing heavily damaged evidence acquired from crime scene investigations.
3D printing industry
The worldwide 3D printing industry is expected to grow from $3.07B in revenue in 2013 to $12.8B by 2018 and exceed $21B in worldwide revenue by 2020. As it evolves, 3D printing technology is destined to transform almost every major industry and change the way we live, work, and play in the future.
Source: Wohlers Report 2015
The outlook for the medical use of 3D printing is evolving at an extremely rapid pace as specialists are beginning to utilize 3D printing in more advanced ways. Patients around the world are experiencing improved quality of care through 3D printed implants and prosthetics never before seen.
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