February 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 | F E B R U A R Y / M A R C H 2 0 1 9 8 0 3D PRINTSHOP MOVE OVER TRUSSES, PLATE LATTICES ARE HERE A research team from ETH Zurich and MIT has developed and fabricated material architectures that are equally strong in all three dimensions and si- multaneously extremely stiff. It is pos- sible to determine mathematically just how stiff materials with internal voids can theoretically become. Structures created by lead researcher Dirk Mohr of ETH have been shown to come ex- tremely close to this theoretical maxi- mum stiffness. A characteristic feature of the design is that the stiffness in the material’s interior is achieved through plate lattices rather than trusses. “The truss principle is very old; it has long been used for steel bridges and steel towers, such as the Eiffel Tow- er. We can see through truss lattices, so they are often perceived as ideal light- weight structures,” says Mohr. “Howev- er, using computer calculations, theory, and experimental measurements, we have now established a new family of plate-lattice structures that are up to three times stiffer than truss lattices of the same weight and volume.” It is not just the stiffness of these structures that approaches theoretical maximum values—their strength does too. ETH researchers initially develop- ed these lattices on the computer, cal- culating their properties in the process. Then they produced them at the micrometer scale from plastic through 3D print- ing. Mohr sees advantages in other applications as well, such as medical implants, lap- top casings, and ultralight ve- hicle structures. www.ethz.ch/ en, mit.edu . OPTOMEC ACQUIRES HUFFMAN Optomec, Albuquerque, N.M., a supplier of additive manufactur- ing systems, acquired Huffman, Clover, S.C., a provider of 3Dmetal printing sys- tems for additive repair of gas turbine components in the energy and aviation markets. Huffman’s equipment and softwareare inproductionat virtuallyall major manufacturers of aircraft engines and industrial gas turbines, who use the company’s metal deposition capabili- ties to restore damaged components. optomec.com . 3D PRINTING GIVES NEW LIFE TO LIGNIN Scientists at the DOE’s Oak Ridge National Laboratory (ORNL), Tenn., dis- covered a renewable 3D printing feed- stock that could spur a profitable new use for an intractable biorefinery by- product: lignin. The discovery expands ORNL’s achievements in lowering the cost of bioproducts by cre- ating novel uses for lignin— the material left over from processing biomass. Lignin gives plants rigidity and also makes biomass resistant to being broken down into use- ful products. Researchers combined a melt-stable hardwood lig- nin with conventional plas- tic, a low-melting nylon, and carbon fiber to create a composite with just the right charac- teristics for extrusion and weld strength between layers during the printing process, as well as excellent mechan- ical properties. However, the work is tricky. Lignin chars easily and unlike workhorse composites such as acry- lonitrile-butadiene-styrene (ABS) that are made of petroleum-based thermo- plastics, lignin can only be heated to a certain temperature for softening and extrusion from a 3D-printing nozzle. Prolonged exposure to heat dramatical- ly increases its viscosity—so it becomes too thick to be extruded easily. When researchers combined lig- nin with nylon, they found a surprising result: The composite’s room tempera- ture stiffness increased while its melt viscosity decreased. The lignin-nylon material had tensile strength similar to nylon alone and lower viscosity than conventional ABS or high impact poly- styrene. Scientists were also able to mix in a higher percentage of lignin—40 to 50 percent by weight—a new achieve- ment in the quest for a lignin-based printing material. ORNL scientists then added 4 to 16 percent carbon fiber into the mix. The new composite heats up more easily, flows faster for speedi- er printing, and results in a stronger product. The lignin-nylon composite is patent-pending and work is ongoing to refine the material and find other ways to process it. ornl.gov. ORNL scientists make use of lignin—a biofuels byproduct—to create a new composite material for additive manufacturing. Plate lattices hold promise for advanced lightweight porous materials. Courtesy of ETH Zurich/Marc Day.

RkJQdWJsaXNoZXIy MjA4MTAy