Additive Manufacturing

NOV 2017

ADDITIVE MANUFACTURING is the magazine devoted to industrial applications of 3D printing and digital layering technology. We cover the promise and the challenges of this technology for making functional tooling and end-use production parts.

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NOVEMBER 2017 Additive Manufacturing 50 TAKING SHAPE An Aerospace Perspective on Additive Manufacturing By Brent Donaldson Fig. 2: Here the laser power was increased to 520 W while beam size and exposure rate remained the same. Researchers found that the laser-metal interaction was more violent, with molten metal spreading outward from the surface. "The quantitative sample structure information we can obtain from these experiments is helping us better understand the physics underpinning the formation of different defects," he says, "and also helping build high-fidelity models to guide the process optimization for manufacturing parts with different geometries and dimensions." Figures 1 and 2 show the dramatic differences that resulted from adjustments to the laser power conditions during Argonne's experiments. Both image series were taken with the same frame rate, as well as the same exposure time: 350 nanoseconds per individual image. In Figure 1, the laser power was set at 340 watts, while in Figure 2 the power was increased to 520 watts. As outlined in the research, the differences are immediate and drastic. Using 520 watts of power, "the laser-met- al interaction is much more violent than the previous case. The Ti-6Al-4V powders and base are quickly melted locally. The continuous laser heating causes large cavity depth and strong oscillation behavior, and the molten metal spreads outward from the surface with a portion getting ejected away." For the first time ever, the team was able to directly observe and experimentally measure pore formation at the bottom of a melt pool, deep inside the base. Other direct observations from the research include "strong metal vapor evapora- tion around the laser beam," which result in melt ejections greater than when the laser power is set to 340 watts. The team believes that its findings and the processes behind them—which they plan to share with other researchers interested in building predic- tion models for 3D-printed materials—open the door not only to new dimensions of research and development in additive manufacturing, but also other laser processing and traditional manufacturing techniques, such as welding. Only through a precise ability to measure and control the mechanical properties of additively manufactured products will the technology truly flourish, Sun says. "Given that the precise control of the microstructure and dimension of parts is the major barrier that hinders laser AM techniques from reaching their full potential, the experiment tool we developed and its utilization by other scientists could potentially accelerate the coming of the AM age." While some lofty goals emerged at a recent additive manufacturing forum hosted by the Ohio Aerospace Institute (OAI) near Cleveland, Ohio, it was the real-time challenges facing additive manufacturers in the aerospace sector that kept attendees' feet planted firmly on the ground. Indeed, while success stories had their place at the forum, what became clear was that the hurdles—as well as the opportunities—for AM-produced parts in aerospace are high and numerous. The aerospace sector— which boasts more than $144 billion in export sales alone—is often cited as the most successful in the U.S. economy. But given the fact that the average commercial jet is a $70 million asset responsible for safely transporting untold numbers of human beings, it should not be unexpected that hurdles exist for creating certifiable parts. Rich Lonardo, a consultant for the Youngstown Business Incubator, reminded the group that castings made for the Air Force and Navy can take up to 700 days. "We

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