January_AMP_Digital

4 8 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 | J A N U A R Y 2 0 1 8 3D PRINTSHOP SOFTWARE UPGRADE DOUBLES PRINT SPEED Engineers at the University of Michigan (U-M), Ann Arbor, are work- ing on advanced forms of control with the potential to benefit 3D printing and expand its use. Today’s long, slow print cycles are one of the biggest annoyanc- es with 3D printing and a major impedi- ment to wider application. The problem is especially prevalent with lightweight desktop models made from low-cost components slung on relatively springy frames. Such systems are prone to vibration and a variety of errors that worsen as operating speeds increase. The two most common pathways over which vibrations can impact print qual- ity are ringing —resulting in what the U-M engineering team describes as “surface waviness”—and registration error observed as “build layer offset.” Both types of error are related to the use of stepping motors, according to the researchers. To demonstrate the magnitude of the errors as well as the effect of their new software, U-M engineers by- passed the controller on a commer- cial 3D printer and proceeded to run it LLNL researchers examine a sample of 3D-printed stainless steel, verifying successful production of one of the most common forms of marine grade stainless that breaks the strength-ductility barrier. at progressively faster rates. Under ordinary open-loop control, as ex- pected, the printer per- forms noticeably worse with each increase in speed. But with the new software—a type of feed-forward control— the same printer can produce the same part in less than half the time without a hint of regis- tration error and only a trace of ringing. U-M intends to extend this work to time-varying lin- ear systems, which in the case of 3D printing would account for changes in dynamics as a function of build height. www.news. engin.umich.edu. RESEARCHERS PRINT MARINE GRADE STAINLESS STEEL “Marine grade” stainless steel is valued for its performance in corro- sive environments and its high duc- tility, making it a preferred choice for oil pipelines, welding, chemical equipment, medical implants, en- gine parts, and nuclear waste storage. However, conventional techniques for strengthening this class of materials typically must compromise on duc- tility. Lawrence Livermore National Laboratory (LLNL) researchers, along with collaborators at Ames Na- tional Laboratory, Georgia Tech, and Oregon State University, recently achieved a breakthrough in 3D printing one of the most common forms of ma- rine grade stainless steel. The steel, low carbon 316L, promises an unparalleled combination of strength and ductility for critical applications. To meet performance require- ments for 316L stainless set by tradi- tional manufacturing processes, the team first had to overcome a major 3D printing impediment—porosity and the associated propensity for cracking, distortion, and fracture. Researchers addressed this through a combination of experiments and computer model- ing, and by manipulating the materi- al’s microstructure. In doing so, they not only solved the porosity problem, but also shattered the long-standing strength-ductility tradeoff and the com- promise it imposes on steel and other alloys. The new process is based on la- ser powder bed fusion and a melting technique that produces a hierarchical cell-like microstructure reminiscent of stained glass. In the course of their work, the team discovered that the cellular structure acts as a filter, letting some defects move free- ly (and thus provide duc- tility), while blocking others to help preserve strength. Researchers be- lieve their work will lead to new insights on the structure-property rela- tionship of additively manufactured metals. llnl.gov. A 3D-printed scale model of the U.S. Capitol highlights the effect of vibration-induced registration error. Part distortion (bottom) is the result of excessive vibration; the part shown above printed successfully with the aid of the new software.