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 | M A R C H 2 0 2 3 6 8 3D PRINTSHOP SIMULATING LPBF PARAMETERS ResearchersatFraunhofer Institute for Mechanics of Materials IWM are combining several simulation methods to find the optimal process parameters for laser powder bed fusion (LPBF). They hope to identify direct correlations between the workpiece properties and the selected parameters. During LPBF a powder bed up to 50-mm thick is heated with pinpoint accuracy by a laser. The powder liquefies, the particles fuse, and the melt pool solidifies as soon as the laser moves on. It is important that the finished component has a density of 100%, no pores, and that each newly applied layer binds firmly to the layer below. This is achieved by adjusting the process parameters, such as the scan speed and power of the laser. Using the discrete element method, researchers first simulate how the individual powder particles are spread in the building chamber with the aid of a special tool, namely the doctor blade. Next, the way in which the powder particles melt is simulated using the smoothed particle hydro- dynamics method—both the laser interaction and heat conduction are calculated, as well as the surface tension that causes the melt to flow. The calculation also accounts for gravity and the recoil pressure that occurs when the material vaporizes. The simulation must also describe the microstructure of the material to predict mechanical material properties. The researchers use cellular automation to analyze the microstructure. This describes how the metallic grains grow as a function of the temperature gradient. The final step is the finite element simulation: The research team uses this to perform tensile tests in different directions on a representative volume element of the material to find out how the material reacts to these loads. www.fraunhofer.de/EN. HIGH-ASH BIOMASS MATERIAL SUITABLE FOR PRINTING Ash minerals found in naturally derived compound materials don’t affect its fitness for use as an additively printedmaterial, a team fromOak Ridge National Laboratory found (ORNL). Owing to its low cost and sustainable nature, lignocellulosic biomass has been used for reinforcing polymers, but it is crucial to understand the impact of high-ash concentrations in biomass on composite strength and processing. Biomass is not only desirable for biofuel production but could also have a strong market, if high-ash biomass is acceptable, for biocomposites. When mixed with polylactic acid, fibers sourced from corn stover and switchgrass yielded biocomposites with satisfactory properties for 3D printing. In fact, the presence of ash spheres appeared to improve the flow of material for extrusion printing, says ORNL’s Xianhui Zhao. “We went as high as 12% ash content on our corn stover biocomposite and found mechanical properties like stress and strain tolerance and tensile strength to be acceptable,” Zhao says. The research enables a use for high-ash biomass residue from bio-refining that could lower the overall cost of producing sustainable fuels and materials. Next steps include exploring more biomass materials and testing the composites in a large-volume printer at ORNL. ornl.gov. Researchers found that moderate levels of ash do not significantly affect the mechanical properties of biocomposites. Courtesy of Andy Sproles/ORNL, U.S. Dept. of Energy. Simulation of the formation of a columnar microstructure in the laser melt pool. Courtesy of Fraunhofer IWM.
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