April_AMP_Digital

7 2 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 | A P R I L 2 0 1 8 3D PRINTSHOP NYU TEAM CREATES PRINT-READY SYNTACTIC FOAM Materials scientists at the NYUTan- don School of Engineering are working to bring syntactic foam technology to 3D printing. Syntactic foams are among a special class of composites that in- corporate hollow or low-density micro- spheres in a metal, ceramic, or polymer matrix. They find wide use in aerospace and undersea applications due to their extraordinary buoyancy and strength. One of the motivations for NYU’s work is that today’s syntactic-foam structures leave significant room for improvement through the elimination of joints and seams and the risks and constraints they impose. Before NYU researchers could be- gin assessing the potential of print- ed foam parts, they had to develop a suitable filament that would work on ordinary fused-filament printers. The team investigated several formulations, ultimately settling on a high-density polyethylene matrix filled with micro- spheres extracted from recycled fly ash. Getting the proportions right proved to be a challenge because the microspheres are easily crushed during the mixing process and have a ten- dency to clog printer nozzles. Through trial and error, the team found that a blend of approximately 40 wt% fly-ash Left, a commercial 3D printer operates with syntactic foam filament developed at the NYU Tandon School of Engineering. Right, syntactic foam composite under high magnification reveals uniformly distributed hollow spheres in a high-density polyethylene matrix. particles provides the best combina- tion of material properties and printer performance. As may be expected, part quality is sensitive to process variables such as printer speed, layer thickness, nozzle temperature, and cooling conditions. However, the team proved that once a machine is dialed in, it can print syntac- tic foam components that compare fa- vorably to their injection molded coun- terparts in terms of tensile strength, elastic modulus, and other properties. engineering.nyu.edu . X-RAY SHEDS NEW LIGHT ON AM PROCESS Researchers at the Department of Energy’s SLAC National Accelerator Laboratory are using one of the most powerful instruments in the world to better understand how metal powders respond to the intense heating and cooling cycles associated with additive manufacturing. Working in collabora- tion with scientists from Lawrence Liv- ermore and Ames labs, the SLAC team is investigating the selective laser melting (SLM) process, using x-ray microscopy to capture melt, flow, and resolidifica- tion dynamics and whatever insights they provide on how to control micro- structure and prevent formation of pits and other flaws. Prior attempts to correlate SLM dynamics with part quality have been limited by an inability to see below the surface of the powder, making it impos- sible to precisely determine melt depth as each new layer is added. Thermal imaging once offered hope, but it does not capture enough information to identify how and why flaws originate. In contrast, the high flux, penetrating beam from SLAC’s hard x-ray, synchro- tron light source illuminates the en- tire depth of the metal powder, giving scientists a detailed, real-time view of melt dynamics. SLAC researchers are leveraging this x-ray power in two ways—to gen- erate high-resolution images showing what happens as build layers accu- mulate, and to analyze changes in the atomic structure of the metal during melting and cooling intervals. Fol- lowing their initial studies on SLM, re- searchers plan to investigate directed energy deposition (DED) processes, in which metal powder or wire is melted as it is being laid down. DED printers excel at producing complex geometries and are especially useful for making re- pairs. slac.stanford.edu . X-ray characterization chamber contains a build platformwhere SLAC researchers conduct selective laser melting experi- ments on metal powder while capturing detailed images using x-ray light.