Additive Systems Slash Aircraft Materials Costs

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Titanium and high-performance alloys are in greater demand as OEMs strive to reduce weight in new aircraft, such as the Boeing Dreamliner 787. Content of titanium in the Dreamliner is 15 percent, by weight. But the high cost of mill products and machining are major obstacles in providing cost-effective planes. Many parts are machined from solid mill products, and many others are made from closed-die forgings or castings. As a result,long lead times needed for die design and fabrication create time-to-market problems.

"There is no doubt that additive manufacturing will replace some of the traditional manufacturing practices," says Greg Morris, CEO and chief operating officer of Morris Technologies, a Cincinnati-based company that was the first in North America to acquire Direct Metal Laser Sintering (DMLS) technology, one of several additive manufacturing processes. "There is tremendous opportunity for the aerospace industry to cut costs and to become more efficient."

Boeing engineering scientist Blake Slaughter has studied additive manufacturing systems and says that: "We have a huge task ahead of us, but we need to begin somewhere." Boeing's Commercial group has already used additive manufacturing to produce metallic, non-structural interior components.

Slaughter also commented on Boeing's interest in the new approach at a meeting held by the Edison Welding Institute in Ohio to kick off a consortium where OEMs are joining forces to share testing and other data. Participants at the meeting included representatives from GE Aviation, Lockheed Martin, the Air Force Research Lab., Boeing, Honeywell, Oak Ridge National Lab., NASA, Pratt & Whitney, Rolls-Royce (aircraft engines) and Northrup Grumman.

The goal of the consortium, the first of its kind in the U.S., is to advance the manufacturing readiness levels of additive processes.

"Many industries, researchers, technology providers and government agencies are independently working to develop and implement additive processes," says Chris Conrardy, vice president of technology and innovation at EWI. "The consortium will create a forum for these groups to prioritize needs and coordinate programs to advance key technologies through to implementation," he says.

Additive manufacturing is a term that emerged from the rapid prototyping business where CAD-driven lasers are used to create three-dimensional components from plastic and metal in multiple, tiny layers. Those systems are now being adapted for low-volume production, and are already widely used for dental applications and assembly fixtures. One example is DMLS, which works with some nickel materials and titanium as well as cobalt chrome alloys.

Expanding the Concept

The aircraft industry wants to take the concept a few steps farther and has brought in some additional manufacturing approaches. These include other bulk deposition systems, such as electron beam welding (which has a faster build time than DMLS) and cold spray. Also in play are feature deposition systems such as electron beam free-form fabrication (EBFFF or eBAM); laser-additive manufacturing (LAM), which would be best suited for small, intricate features; and plasma transferred arc solid free-form fabrication (PTA-SFFF).

One candidate part at Lockheed Martin is a flaperon spar on the F-35 stealth fighter. A flaperon controls the roll or bank of an aircraft. Analysis showed considerable cost and lead time savings with the electron beam process compared to forging. Most of the savings come in reduced materials costs, one of the huge payoffs for the aircraft industry. Pieces produced by additive processes are close to net shape, and only require minimal machining.

Eric Fodran, program manager at Northrup Grumman, estimates the "buy-to-fly" ratio for conventional manufacturing routes at a range of 10-20:1. The buy-to-fly ratio is the mass of material that is required to machine a part compared to the mass of material in the finished part. Northrup-Grumman analyses show that buy-to-fly ratios for additive systems offer a 35-45 percent cost reduction in comparison to alternative traditional manufacturing options.

The DMLS process developed by EOS begins by sintering a layer of 20 micron (0.0008-inch) powder onto a steel platform. They are then melted with a high-powered, tightly focused laser to create dense three-dimensional parts. The platform then lowers by 20 microns, and a fresh layer of powder is swept over the previously sintered layer. Several high-performance metal alloys (including nickel and titanium) created with this method are available now and more are under development.

"We have made parts with additive manufacturing that could not have been made with any other manufacturing technology," Morris says. The company expects to go into series production in the next year or two on parts that previously would have required multiple cast or machined components welded together to achieve the same functionality as a single part made with additive manufacturing. Details are confidential.

Other additive manufacturing processes are better suited for other types of aerospace parts, particular larger parts - such as aircraft frames - and parts that don't require complex features.

Engineering Concerns

Some engineers fear that commercially available additive manufacturing technologies may not be sufficiently productive, reliable, cost-effective or capable of producing components of the sizes, alloys or properties needed by the aircraft industry.

"Most of our understanding of fatigue performance is based on surface finishes of wrought or cast processing," says Boeing's Slaughter. "These processes inherently have better surfaces than most of the deposited technologies at their current maturation."

He posed this question to the EWI meeting: "Can we compensate for the surface finish with increased component bulk? Sure. Can we develop reliable inspection methods? Possibly. Does the increased component weight make sense over the life of the platform?"

Northrup Grumman's Fodran also says it's imperative to develop a materials properties' database that includes static and dynamic data. Another important issue is that deposited structures carry large amounts of residual stress or distortion, or both. Also, traditional modeling techniques are not applicable.

ASTM Committee F42 on Additive Manufacturing Technologies has been established to set standards. Subcommittees are in place for test methods, processes, materials, design and terminology.