October_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | O C T O B E R 2 0 2 0 5 6 3D PRINTSHOP 3D PRINTED LATEX RUBBER BREAKTHROUGH Virginia Tech researchers have dis- covered a novel process to 3D print la- tex rubber, unlocking the ability to print a variety of elastic materials with com- plex geometric shapes. The team chem- ically modified liquid latexes to make them printable and built a custom 3D printer with an embedded computer vi- sion system to print accurate, high-res- olution features of the high-perfor- mance material. 3D printed latex and elastomers could be used for a variety of applications including soft robotics, medical devices, or shock absorbers. Commercial liquid latex is ex- tremely fragile and difficult to alter, so the chemists built a scaffold around the latex particles to hold them in place. This way the latex could maintain its structure while photoinitiators and oth- er compounds were added to enable 3D printing using vat photopolymerization, which uses ultraviolet (UV) light to cure the material into a specific shape. The team also developed a print- er capable of printing high-resolution features across a large area. Even with the custom printer, the fluid latex par- ticles caused scattering outside of the projected UV light on the latex resin surface, which resulted in printing in- accurate parts. The researchers embed- ded a camera onto the printer to cap- ture an image of each vat of latex resin. With a custom algorithm, the machine is able to “see” the UV light’s interaction on the resin surface and then automat- ically adjust the printing parameters to correct for the resin scattering to cure just the intended shape. The final 3D printed latex parts ex- hibited strong mechanical properties in a matrix known as a semi-interpen- etrating polymer network, which had not been documented for elastomeric latexes in the prior literature. vt.edu . LASER INVERSION ENABLES MULTI-MATERIALS 3D PRINTING Researchers at Columbia Engi- neering, New York City, developed a new approach to selective laser sinter- ing (SLS) which allows creation of parts frommultiplematerials. Traditional SLS fuses together material particles using a laser pointing downward into a heated print bed. A solid object is built from the bottom up, with the printer placing down a uniform layer of powder and using the laser to selectively fuse some material in the layer. The printer then deposits a second layer of powder onto the first layer, the laser fuses new mate- rial to the material in the previous layer, and the process is repeated over and over until the part is completed. This process works well if there is just one material used in the printing process. But using multiple materials in a single print has been very challeng- ing, because after the powder layer is deposited onto the bed, it cannot be unplaced, or replaced with a different powder. “Also,” adds Ph.D. student John Whitehead, “in a standard printer, be- cause each of the successive layers placed down are homogeneous, the unfused material obscures your view of the object being printed, until you remove the finished part at the end of the cycle. This means that a print fail- ure won’t necessarily be found until the print is completed, wasting time and money.” The researchers found a way to eliminate the need for a powder bed en- tirely. They set up multiple transparent glass plates, each coated with a thin lay- er of a different plastic powder, lowered a print platform onto the upper surface of one of the powders, and directed a laser beam up from below the plate and through the plate’s bottom. This pro- cess selectively sinters some powder onto the print platform in a pre-pro- grammed pattern according to a virtual blueprint. The platform is then raised with the fused material, and moved to another plate, coated with a different powder, where the process is repeated. This allows multiple materials to either be incorporated into a single layer or stacked. Meanwhile, the old, used-up plate is replenished. Researchers are now experiment- ing with metallic powders and resins to directly generate parts with a wider range of mechanical, electrical, and chemical properties than is possible with conventional SLS systems today. www.engineering.columbia.edu . This impeller was 3D printed with latex rubber at 100-micron resolution and exhibits a unique combination of flexibility and toughness. Courtesy of Virginia Tech. Laser beam transmitting upward through glass. Courtesy of John Whitehead, Columbia Engineering.