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 | N O V E M B E R / D E C E M B E R 2 0 2 2 6 4 3D PRINTSHOP 3D PRINTED CUSTOM MEMS Researchers at KTH Royal Institute of Technology in Stockholm, developed a technique to cost-effectively print custom electronic “machines” the size of insects that enable advanced applications in robotics and medical devices. The researchers built on a process called two-photon polymerization, which can produce high-resolution objects as small as a few hundreds of nanometers in size, but not capable of sensing functionality. To form the transducing elements, the method uses a technique called shadow-masking, which works something like a stencil. They fabricate features with a T-shaped cross-section on the 3D-printed structure, which work like umbrellas. They then deposit metal from above, and as a result, the sides of the T-shaped features are not coated with the metal. This means the metal on the top of the T is electrically isolated from the rest of the structure. Frank Niklaus, who led the research, says with this method it takes only few hours to manufacture a dozen or so custom designed microelectromechanical systems (MEMS) accelerometers using relatively inexpensive commercial manufacturing tools. The method can be used for prototyping MEMS devices and manufacturing small- and medium-sized batches of tens of thousands to a few thousand MEMS sensors per year in an economically viable way, he says. “This is something that has not been possible until now, because the start-up costs for manufacturing a MEMS product using conventional semiconductor technology are on the order of hundreds of thousands of dollars and the lead times are several months or more,” he says. “The new capabilities offered by 3D-printed MEMS could result in a new paradigm in MEMS and sensor manufacturing. “Scalability isn’t just an advantage in MEMS production, it’s a necessity. This method would enable fabrication of many kinds of new, customized devices.” www.kth.se. CONSISTENT PRINTING OF 17-4 PH STAINLESS STEEL A study from the National Institute of Standards and Technology (NIST), the University of Wisconsin-Madison, and Argonne National Laboratory, describes how researchers used x-ray diffraction (XRD) to study how the crystal structure of 17-4 PH stainless steel changed over the course of a 3D print, letting them finetune the composition of the alloy for more consistent parts. The research could help producers of 17-4 PH parts use 3D printing to cut costs and increase their manufacturing flexibility. The approach used to examine the material in this study may also set the table for a better understanding of how to print other types of materials and predict their properties and performance. “Additive manufacturing me- tals is essentially welding millions of tiny, powdered parti- cles into one piece with a high- powered source such as a laser, melting them into a liquid and cooling them into a solid,” says NIST physicist Fan Zhang, a study co-author. “But the cooling rate is high, sometimes higher than one million degrees Celsius per second, and this extreme nonequilibrium condition creates a set of extraordinary measurement challenges.” Because the material heats and cools so hastily, the crystal structure of the atoms within thematerial shifts rapidly and is difficult to pin down, Zhang says. Without understanding what is happening to the crystal structure of steel as it is printed, researchers have struggled for years to 3D-print 17-4 PH, in which the crystal structure must be just right for the material to exhibit its highly sought-after properties. “Composition control is truly the key to 3D-printing alloys. By controlling the composition, we are able to control how it solidifies. We also showed that over a wide range of cooling rates, say between 1000 and 10 million degrees Celsius per second, our compositions consistently result in fully martensitic 17-4 PH steel,” Zhang says. Mechanical testing showed that the 3D-printed steel, with its martensite structure and strength-inducing nanoparticles, matched the strength of steel produced through conventional means. nist.gov. A microscopic image of 3D-printed 17-4 stainless steel. The colors in the left-side version of the image represent the differing orientations of crystals within the alloy. Courtesy of NIST. A 3D-printed MEMS device is seen beside a two-cent Euro coin. Courtesy of Simone Pagliano.
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