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

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

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

Slaughter also commented on Boeing's interest in the new approach at a meeting held bythe Edison Welding Institute in Ohio to kick off a consortium where OEMs arejoining forces to share testing and other data. Participants at the meetingincluded representatives from GE Aviation, Lockheed Martin, the Air ForceResearch 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 themanufacturing readiness levels of additive processes.

"Manyi ndustries, researchers, technology providers and government agencies areindependently working to develop and implement additive processes," says ChrisConrardy, vice president of technology and innovation at EWI. "The consortiumwill create a forum for these groups to prioritize needs and coordinateprograms to advance key technologies through to implementation," he says.

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

Expandingthe Concept

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

Onecandidate part at Lockheed Martin is a flaperon spar on the F-35 stealthfighter. A flaperon controls the roll or bank of an aircraft. Analysis showedconsiderable cost and lead time savings with the electron beam process comparedto forging. Most of the savings come in reduced materials costs, one of thehuge payoffs for the aircraft industry. Pieces produced by additive processesare close to net shape, and only require minimal machining.

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

TheDMLS 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 ahigh-powered, tightly focused laser to create dense three-dimensional parts.The platform then lowers by 20 microns, and a fresh layer of powder is sweptover the previously sintered layer. Several high-performance metal alloys(including nickel and titanium) created with this method are available now andmore are under development.

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

Otheradditive manufacturing processes are better suited for other types of aerospaceparts, particular larger parts - such as aircraft frames - and parts that don'trequire complex features.

EngineeringConcerns

Some engineers fear that commercially available additive manufacturing technologiesmay not be sufficiently productive, reliable, cost-effective or capable ofproducing components of the sizes, alloys or properties needed by the aircraftindustry.

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

He posed this question to the EWI meeting: "Can we compensate for the surfacefinish with increased component bulk? Sure. Can we develop reliable inspectionmethods? Possibly. Does the increased component weight make sense over the lifeof the platform?"

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

ASTM Committee F42 on AdditiveManufacturing Technologies has been established to set standards. Subcommitteesare in place for test methods, processes, materials, design and terminology.