Additive Manufacturing

NOV 2018

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 2018 Additive Manufacturing FEATURE / AM Qualification 16 By Brent Donaldson The F-35 Lightning II Joint Strike Fighter program is one of the most expensive and technologically ambitious engineering and manufacturing programs the world has ever known. When Lockheed Martin, the contractor for the F-35, initiated a pilot scale implementation of additive manufacturing in an effort to cut costs for the F-35 nearly a decade ago, the pilot program utilized large- scale electron beam additive manufacturing (AM) with the alloy Ti-6Al-4V. But while this alloy is the same material used in forged structures on the aircraft, the fabrication process—additive—was entirely different, and thus required a requalification of the mate- rial for the AM process. And that's where things got sticky. It's not unusual for performance demands in the defense sector to cause costs to skyrocket. This is especially true within aerospace, where critical structures often require a statistically validated qualification process that can entail thousands of tests in order to define and certify the mechanical properties and behavior of a new material. In 2011, Craig Brice, then a materials research engineer with NASA Langley Research Center, foresaw that aerospace qualification processes and additive manufacturing technologies were on a collision course. In a paper Brice produced that year for the 1st World Congress on Integrated Computational Materials Engineering, titled, "Unintended Consequences: How Qualification Constrains Innovation," he made his point clear: "The data generated under the qualification program effectively 'fixes' the materials and procedures in place and requires the process to become static. While this is desirable and necessary for a standardized and repeatable process, it also limits the ability to seek improvements in the process (and in the materials generated by the process). The additive manufacturing approach allows for more degrees of freedom in the fabrication process. Multiple process paths can yield the acceptable end product, both microstructurally and mechanically. Furthermore, the conditions and/or material chosen in the qualification study may turn out to not be the ideal path as the process evolves and matures. Unfortunately, any excursion from the standard depo- sition process, as established in the specification procedures, will not be allowed under the current methodology. The challenge for the additive manufacturing community is that the process segment of the process-microstructure-property relationship is not necessarily uniform or static. This implies the need for an outcome-based approach for material qualification." One of the central purposes of the ADAPT Center is to draw correlations between additive processes and material properties. Fundamentally, the ADAPT Center aims to decode the physics of energy input, mass flow and time, and allow these fundamentals to dictate how an additive process is occurring. A Public-Private Partnership Aims to Save Additive from Itself Overwhelming process variables for metal additive manufacturing processes are derailing AM's adoption for critical parts in aerospace. Colorado's ADAPT Center—and its growing cache of data—is seeking common ground.

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