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OEM Report: Aerospace

Operation warfighter

By Gretchen Salois

Above: Military aircraft like the V-22 Osprey are being flown beyond intended flight hours and as a result, parts are failing that are difficult to supply. Photo: Joshua Hammond, U.S. Navy

The latest in metal additive manufacturing, fabrication and forming keeps troops well equipped and prepared

October 2016 - From the engineering of an aircraft to the strategic planning behind the location of a landing zone, many decisions go into the planning of a transport aircraft mission. For MV-22B Osprey helicopter pilot Major Travis Stephenson, who has served multiple deployments in the Middle East, safely ushering troops onto the battlefield demands a smooth flight from start to finish. “If [we fly] in a way that makes our passengers disoriented or sick, we’ve already done the enemy’s job for them,” Stephenson says. 

Months of work by experts and engineers prepared the equipment that Maj. Stephenson manned during the inaugural flight of a flight-critical 3D-printed titanium nacelle link and fitting assembly on July 29, 2016. This crucial link and fitting assembly is one of four that secure the V-22’s engine nacelle to the primary wing structure. Engineers monitored the link using stress-strain gauges to track it mid-air in real time. 

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Creating the 3D-printed link and fitting assembly for the engine nacelle required virgin titanium powder that was hard to find. It was necessary to avoid any contaminants that could negatively affect performance.

“This level of attention gives our air crew the best possible awareness of what the aircraft is experiencing in flight, allowing us to proceed along our plan with confidence, or come home to reevaluate when we see something unexpected,” Stephenson says.

Additive manufacturing is quickly shifting aerospace industry attitudes as it advances beyond prototyping into a full-fledged solution to extend the life of existing fleets and develop new war fighting tools.

Printed replacements

Navy airplanes are being flown beyond their initial design life and parts not designed for this extended service life are failing. “These parts were not expected to fail and, therefore, aren’t in the supply chain,” says Dr. William Frazier, NAVAIR chief scientist, Air Vehicle Engineering Department. “The time and cost of procuring an out-of-production part can be a huge obstacle. A contract must be issued, the contractor qualified, the part manufactured and the component tested prior to its use.”

In 2014, NAVAIR established a roadmap and team to look at whether additive manufacturing could be a solution, says Elizabeth McMichael, director of innovation at NAVAIR’s Readiness at Naval Air Systems Command. 

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Aviation Mechanic Cody Schwarz installs a 3D-printed titanium link and fitting on an MV-22B Osprey engine nacelle in July 2016, at Patuxent River Naval Air Station, Maryland. Photo: U.S. Navy

New processes involve prototyping and testing. “In the case of additive manufacturing, prototyping hasn’t always let us use this technology for end-use parts as it’s still maturing; our intention was to accelerate our processes,” McMichael says. “How can we push progress faster and achieve customized parts that are more cost effective to print where you don’t need a complete production line for each part?”

Having worked on several projects with NAVAIR, researchers at Penn State University’s CIMP-3D (Center for Innovative Materials Processing through Direct Digital Deposition) started on the V-22 titanium link in autumn 2015. The project took nine months to complete—an expedited approach to government work. 

“We did our homework” to determine which 3D printing process would work best, says Frazier. The powder bed printing method was viewed as the most mature and came closest to producing a net shape part. “The directed energy printing methods [powder blown and wire fed] work much better for larger parts but produce parts with greater surface roughness and require a lot more machining,” he says.

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Test pilot Major Travis Stephenson manned the test flight on July 29, 2016, of a flight-critical 3D-printed titanium link and assembly fitting. Photo: U.S. Navy

One challenge engineers faced during the pursuit of the V-22 link was acquiring enough powder, which “wasn’t always available,” Frazier says. “Only virgin titanium powder was used because potentially deleterious particles and oxygen pickup could adversely affect part performance—but we’re hopeful we won’t need virgin material for future projects, which will be more cost effective.”

Other challenges when working with a net-shaped 3D-printed part included what would otherwise be a relatively simple process, like boring a hole. NAVAIR found machining easier when it left some material within the area of the planned hole, Frazier says. “In order to eliminate surface-connected porosity, which would negatively impact fatigue performance, we machined off a few millimeters of surface material.”

Establishing the inspection process proved helpful for future projects, but came at a hefty cost. “Based on the initial plans and number of builds and parts, we were going to spend nearly $500,000 on powder alone to qualify one part. So we obviously scaled back the number of samples and test specimens,” says Professor Timothy Simpson, co-director at CIMP-3D. Working through the Defense Advanced Research Projects Agency (DARPA), public resources made the process a reality. “A private company isn’t in a position to spend that kind of money on a single part, but it is critical that the information is available for other companies to use,” he adds.

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Pratt & Whitney installed an isothermal press at its Columbus Forge facility in Georgia to handle engine parts made from nickel superalloys and titanium. Photo: Pratt & Whitney

As a result, aerospace engineers now understand the variables better and the 3D metal printing process can be expedited because the material and the machine have already been qualified. Manufacturing additional builds using new materials can be leveraged from what was learned from this first build, Simpson says.

Change the game

For additive manufacturing, “there’s an incredible amount of creativity and revolution going on that will continue for years to come,” says Eric Roegner, COO, Investment Castings, Forgings & Extrusions and Defense at Alcoa Inc., Pittsburgh. For example, Alcoa’s recent contract with Airbus to develop metallic structural parts for a fuselage and engine pylon will employ powder bed printing using titanium. 

Hybrid approaches that combine traditional and additive manufacturing are “where you can change the game,” says Roegner. “With additive manufacturing in general, you can print shapes you couldn’t machine before and make organic bionic structures,” as well as hybrid structures.

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Alcoa developed the Ampliforge process, which uses additive manufacturing techniques to enhance traditionally manufactured parts. “We are able to print up preforms that go into the final forging process that uses all the benefits of additive manufacturing in terms of material optimization and we can then forge it once instead of five to seven times. Instead of a four-week process with seven to eight separate heat cycles with 50 percent material loss, it’s an eight-hour cycle with 95 percent material recovery,” Roegner says. “It’ll change the game of forgings.” 

Beyond additive

Other metals innovations have engineers at Lockheed Martin looking at new ways to make the F-35 Lightning II more efficient and lightweight. One method includes using large forgings from Alcoa closer to shape to reduce final machining, helping pare weight as well as reduce residual stress. “We’re getting closer to shape titanium forgings as well,” says Dr. Don Kinard, senior fellow at Lockheed Martin, Fort Worth, Texas. 

Cryogenic machining, qualified for use on the F-35, would be particularly useful for titanium machining, which prolongs tool life. “But our supply base in the industry has to be convinced of the benefits and willing to invest in the technology so that we can find the right vendors to do that work for our projects,” Kinard says. “Instead of using lubrication and water emulsion—which produces a lot of waste—cryogenic titanium machining forces liquid nitrogen at the cutting edge allowing greater speeds [and clean chips].

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Linear friction welding machine at Pratt & Whitney Middletown, Connecticut facility. Photo: Pratt & Whitney

“We are looking to replace traditional CMM [coordinate measurement machine] inspection with either laser scanning or structured light, which produces 3D images of parts and inspects them by comparing them to the engineering models,” Kinard says. “It’s faster, lower cost and accurate. Using this non-contact metrology has been very useful over the last two years and we’re looking to move forward in that area.”

Meanwhile, Alcoa is in a race to assemble its massive plate stretching machine by mid-2017. Each of its two largest components weigh more than 700,000 pounds. The parts that will make up Alcoa’s new thick plate stretcher are arriving from all over the world, making their way from Korea, the U.K. and Germany, and then by barge up the Mississippi River to Riverdale, Iowa.

“The bigger the stretched plate, the bigger the parts that can be made without residual stress buildup,” says Alcoa Vice President of Global Aerospace and Defense Mark Stuckey. “And the more parts that can be made from thick plate, the more time and weight savings can be captured by aerospace parts suppliers.”

 Several factors are driving demand for thick plate, such as “composite structure airplanes that use aluminum for many applications, including wing ribs and center wing boxes,” says Stuckey. “Machining thick plate speeds up manufacturing, and the new thicker and wider applications that couldn’t be made from plate before are now possible. This opens a whole new area for aerospace designers and parts suppliers.”

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An MV-22B Osprey, equipped with 3D printed titanium link and fitting inside an engine nacelle, hovers during a successful test flight. Photo: U.S. Navy

Pratt & Whitney is working on several closely guarded innovations. The company installed a 200-ton linear friction welder machine late last year. Besides lowering both costs and lead times, linear friction welding yields material properties that are nearly equal to parent material, resulting in a high-strength weld suitable for aerospace applications and other applications where weld and weight is a consideration, says Maya Raichelson, general manager of P&W’s Compression Systems Module Center.   

“With our unprecedented production ramp, and to ensure we are best positioned to meet our customer commitments, we are investing heavily in our facilities and manufacturing technologies,” she says.

The company installed a new isothermal forging press at its Columbus Forge in Georgia, too. It is useful for engine parts composed of nickel superalloys and titanium. Once a part is taken from a mult, it is flattened, followed by forging at a high temperature under a vacuum. All heat is contained within the machine, according to Pratt & Whitney’s Ricky Cummings, a working leader.

“Other considerations to use the isothermal process are the need for material uniformity, high raw material cost and the cost of machining the raw forging to its finished state,” Pratt & Whitney General Manager Keith Bagley says.

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Large forgings from Alcoa allow engineers at Lockheed Martin to get pieces closer to shape for the F-35 Lightning II, allowing for less final machining, helping pare weight as well as reduce residual stress. Photo: Lockheed Martin

New paradigm

The metals sector is embracing every development. One major takeaway from printing the titanium link is rethinking the current engineering and manufacturing paradigm, NAVAIR’s Frazier says. 

“When you can manufacture something in a day or two, whereas lead time for some of these critical parts can be up to two years—it changes your thinking on what can and cannot be done,” Frazier says. “Our conventional process qualification and part certification methodology is a linear building approach. This latest breakthrough shows us that we can concomitantly develop material and process allowables while pursuing component certification testing.” 

The single link for the V-22 test flight in July was only the first step. “The next step is a fully integrated life part that will be available for manufacturing,” McMichael says. “Implementing a configuration change that allows it to be a regular part available for regular production is key.” FFJ

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