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Materials in flight

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In the commercial aircraft business, the competition that often grabs attention is the race to supply the largest jets. But while variants of the Boeing 747 and the Airbus A-380 for long-haul flights get headlines, many smaller aircraft are manufactured – single-aisle medium- and short-haul planes. According to the 2017-2036 market forecast by Bombardier Commercial Aircraft, the intra-regional segment accounts for 80% of global traffic.

For example, Bombardier, based in Canada, makes a range of smaller aircraft, as does rival Brazilian manufacturer Embraer. Both of those aircraft businesses compete at the smaller end of the mainline jet market, where Boeing and Airbus offer their B-737 and A-320 families.
According to a Bombardier report: “Mature markets use large regional aircraft to optimize profits on high-yield routes. Turboprop productivity and fleet utilization has increased over the past decade.” Bombardier also asserts that the single-aisle segment will facilitate airline network optimization: “This segment will increase point-to-point flying on short- to medium-haul routes. Of the current fleet in this segment, 86% will be retired by 2036.”

All of that bodes well for demand for aerospace metals, particularly aluminium. Established models of aircraft, especially turboprops and regional jets, are generally not markets demanding the most advanced metals or materials. Those segments are well served by aluminium. Larger, newer commercial aircraft designs are often the ones driving growth for the latest high-tech lightweight metals and composites, but aluminium still serves close to half the market.

According to the latest data from ICF International and AeroDynamics Advisory, the overall aerospace materials sector will grow by about 6% from 1.7 billion pounds in 2016 to 1.8 billion pounds in 2021. Composites are forecast to be the fastest growing at a 5.4% compound annual growth rate, but by 2021 they will still represent a relatively small market share by weight: 80 million pounds, or about 4% of the market.
The aluminium segment is ten times larger by weight, or about 40% of the market, but in the forecast its total shrinks slightly from 740 million pounds to 730 million pounds. Titanium usage shows a healthy growth rate of about 4% over the 2016-2021 period.

“Over the last five years we have invested heavily in aluminium-lithium casting technology,” says Rafael Carbonell, vice-president of sales for aerospace, Constellium. “As the Airbus A-350 program has advanced, along with other programs in civil aviation, space, and defense. Aluminium-lithium is aluminium’s response to the challenge from composites in the aerospace industry. We are an aluminium company in our heritage, and aerospace is a strategic segment for us.” 

Constellium is a major global supplier of aero plate and fuselage sheet, as well as holding a leading position in aluminium-lithium flat-rolled products. The company operates 24 manufacturing sites in Europe, North and Central America, and China. It has a technology center in Voreppe, France, and a new technical hub in Plymouth, Michigan.

Late in 2017 Arconic announced plans to install a new $137 million horizontal heat-treat furnace at its Davenport Works in Iowa. It is to be in service in 2019. “This investment will help meet both existing and future customer demand,” said Tim Myers, president of global rolled products, transportation, and construction, in announcing the new furnace. “With this new capability, we will meet increasing demand for plate used for aircraft wing ribs, skins, and other structural components, particularly in single-aisle [aircraft]. It also opens the door to growth in other markets, such as semi-conductors for consumer electronics and injection molding for automotive applications.” 

According to Mark Stuckey, vice president of global aerospace and defense sales: “While we have other heat-treat furnaces, this new one will enable Arconic to heat treat longer and thicker plate than ever before. So in combination with our new very-thick plate stretcher, it does differentiate Arconic among competitors in the aerospace segment.”

Also at the end of last year privately held Aleris signed a multi-year contract with Embraer to supply aluminium flat-rolled metal for use in all types of aircraft. The renewed contract included technically advanced alloys and extends the portfolio of materials that Aleris is supplying to Embraer. The contract includes the supply of material from the company’s facilities in Koblenz, Germany and Zhenjiang, China, the latter of which represents a greenfield project for Aleris which opened in 2013. Aleris also has production in North America and Europe. 

“Fundamentally aluminium is well established in aerospace,” states Carbonell. “Clearly the material is in competition with composites. Even for those aircraft with primarily composite fuselages and wings, there is still a lot of aluminium in the airframe. In the Bombardier C-Series [single-aisle jet] we see the fuselage of the future using aluminium-lithium alloys, along with advanced aluminium joining components.” The company is working with fabricators on demonstrator components.

Carbonell adds that “with the aluminium wings of the future we are seeing the same performance, or at least close to, as composite wings at a cost close to current metal wings.” In this context performance is primarily weight, but importantly also length between inspection intervals, as well as fatigue and damage resistance.The primary aluminium-lithium alloy is 2050, but Constellium has a total of seven alloys flying. “They have lower density, about 4% to 6% lower than legacy alloys,” says Carbonell. “They also have better corrosion resistance. Overall they contribute as much as 15% to 20% mass reduction. That is significant.”

To put an even finer point on metallurgical development, Carbonell states: “We are not in other aerospace metals. We still see many more opportunities in aluminium than in other aerospace metals. Our industry continues to develop alloys with higher strength and improved toughness and corrosion resistance. It is remarkable that after 100 years there can still be advances in basic metal.”

It is interesting that Arconic’s discussions of the Davenport plan specifically cite aluminium components that work with composite wings. So the increasing use of composites seems to be driving growth in at least some aspects of aerospace aluminium applications.

“We have a very strong value proposition on both metallic and composite-intensive aircraft,” says Jeremy Halford, president of Arconic Engineered Structures. “In some cases, our content is higher on carbon-fiber reinforced polymer (CFRP) [components] as a result of our multi-material offerings, such as titanium fasteners and Ti and nickel engine castings.” 

He adds for titanium: “it is the fastest growing metal in aerospace, driven in part by the trend towards increasing adoption of CFRP, given its compatible properties. In addition to incorporating titanium into the aircraft bodies – for fastening systems and seat tracks, for example – the new engines for aircraft such as the Boeing 737 MAX and the Airbus A320neo are bigger and hotter, and so we’re seeing more lightweight titanium in the engines on those aircraft.”

In 2016, Arconic invested in new titanium-aluminide alloy melting technology at its facility in Niles, Ohio. “That alloy significantly improves material properties and substantially reduces the weight of low-pressure turbine blades compared to traditional nickel-based alloy materials,” says Halford. “It is being used for the first time on single-aisle commercial jets as part of the new CFM International LEAP engines.”

Arconic has also developed advanced aluminium-lithium alloys used to lightweight aerospace applications. “When alloyed with aluminium and other metals, lithium provides an outstanding combination of strength, toughness, stiffness, corrosion resistance, and high-temperature performance, and at a lower cost than titanium or composites,” says Halford.

New manufacturing techniques
Aluminium makers have responded to the composite challenge in several ways. New alloys are one approach but new manufacturing techniques are also being advanced. “Aero plate and high-speed machining are very efficient ways to make aerospace structures,” says Carbonell. “We are shifting from assembled structures to monolithic ones.”

That trend is also a response to cost pressures from aircraft makers. “The big manufacturers don’t want to lose a single sale,” says Carbonell, “so there is significant pressure of the supply chain.”

An important method of lowering cost and improving efficiency is recycling clean scrap. Of every tonne of plate that is delivered, only about 10% on average ends up flying. The ratios for sheet or extrusion are different, but it is not unusual for a 400 kg part to be milled from a three-to five-tonne plate.
The scrap generated sometimes has a circuitous route back to liquid metal from the workshops making components, but now suppliers like Constellium are doing more “rough machining” in advance of delivery. That is especially important for high-purity alloys so that clean scrap is kept in-house.

3D printing
Another avenue of growth and expansion is 3D printing. In February a consortium of Constellium, Stelia Aerospace, and Ecole Centrale de Nantes announced that they had developed a 3D-printed demonstrator for fuselage panels. As part of the project, the consortium developed a method for producing self-reinforced fuselage panels by applying aluminium wire to said panels via additive manufacturing. The idea was to demonstrate how 3D printing can be used on a large scale to make functional aerospace components.

“3D is interesting and exciting,” says Carbonell. “It makes the most sense in aluminium for complex parts that cannot be made with current technology.” He also notes that “in contrast to other materials, wrought aluminium shows improvement in mechanical properties after being worked. That is not so with titanium or nickel.”

Arconic also sees significant opportunity for 3D printing in aerospace. “With 3D printing we can start with nothing and put material only where we need it – and we can make it stronger, lighter and better performing in the process, with less material,” says Halford. “We already have three agreements with Airbus for 3D printed parts made using powder-bed technologies. And we recently announced a multi-year cooperative research agreement with Airbus to produce large, structural 3D printed components using high deposition-rate technologies. We’re also working with hybrid technologies. Our proprietary Ampliforge process combines traditional and additive manufacturing to enhance the properties of 3D printed parts and reduce material input and production lead times.” In the Ampliforge™ process, Arconic designs and 3D prints a near complete part or preform, then treats it using a traditional manufacturing process, such as forging.

In 2016 Arconic opened a metal powder facility at its technology center outside Pittsburgh. “We are developing proprietary titanium and other metal powders with the specific properties needed for 3D printing high-performance components” Halford said.

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