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Aluminum

Modeling the future

By Corinna Petry

Above: Arconic (formerly Alcoa) is a participant in several research projects at LIFT Detroit. Shown: Aerospace engine blades made with aluminum.

Lightweight Innovations for Tomorrow is at the forefront of metals processing R&D

February 2017 - If some held out scant hope for real progress within a public-private partnership that fosters the seemingly impossible fast-track transition from pie-in-the-sky ideas to practical applications, they might be astounded by the fact that revolutions do occur in materials and manufacturing technologies.

Alan Taub, chief technology officer for the Detroit center of Lightweight Innovations for Tomorrow (LIFT), can name five projects just focused on aluminum. “The institute covers all versions of metal processing. In the melt area, we have a thin-wall die casting project led by Boeing Co. and Alcoa.”

The goal, says Taub, is to reduce wall thickness by 40 percent. In doing so, “you can clearly lightweight a component. The key is to use super-high vacuum die casting, where you pull air out of the die to create a 50 millibar vacuum. That allows for easier filling of the mold but, more importantly, it reduces trapped air and porosity in the alloy.” Because there is less air and porosity in the thin wall casting, alloys that could not previously be heat-treated now can, “which improves material properties.”

FFJ 0217 aluminum image1

Danieli is installing an extrusion press at LIFT that will start up by the end of the first quarter.

Taub says the super-high vacuum die-casting equipment has started to become available primarily in Europe but what’s new in the American arsenal is computer modeling.

What LIFT is developing, with the aid of software companies as well as material producers and OEMs, “is the modeling that lets you optimize the alloy and the mold, controlled first in the computer simulation. The term is Integrated Computational Materials Engineering (ICME),” Taub says, which “allows us to go after the next revolution in materials processes—not just the ability to process but by modeling from atomistic calculations and be able to predict the properties you’ll get locally through various processing methods.” That ability, Taub says, “changes the game for the designer.”

Generally, when a mechanical or materials engineer designs a part, he or she must design to the lower end of any achievable property. With ICME, however, the engineer can develop models locally and achieve different properties in different sections of the same part. “These tools talk to each other, so that you can fine tune the manufacturing process and deliver the properties you want locally,” says Taub. To date, these models are most mature in castings.

“ICME launched a mere five years ago and LIFT is playing a major part. We bring in software suppliers to develop models into commercial code.” The models—proprietary to LIFT member companies participating in and paying for the research—“are revolutionary for being able to develop new manufacturing properties in aluminum alloys,” Taub says.

Defense and aerospace companies like United Technologies and Lockheed Martin are especially involved in manufacturing simulations. One program “is exploring how to model the forging of aluminum-lithium alloys. There have been some implementations before: Ford used it on its new engine block,” says Taub.

Blacksmithing, updated

In castings, he says, the engineer must “know the thermal history and how the microstructure develops. The latest extension of [this exploration] is thermomechanical processing, which is what the blacksmith used to do with the furnace, anvil and hammer.”

When melting metal, producers must control both heating and cooling. “With thermomechanical processing, you’re also dealing with the forming of the material while it’s hot.” That process requires more complex modeling and “the program for aluminum-lithium alloys is on the forefront of doing that.”

Once the desired properties are achieved in perfect proportions throughout a part, it can be applied to landing gear, a frame or a chassis, says Taub. 

“The smaller the motors you need to accelerate, the smaller battery you need to provide adequate range.” He adds that any time a structure that moves people and goods is lighter, “you win on performance and fuel economy.”

FFJ 0217 aluminum image2

Defense companies like Lockheed Martin, which builds the F-35 (shown), are especially involved in manufacturing simulations.

The matrix

A third LIFT project is seeking better ways to consolidate aluminum metal matrix composites. “If you can put in second phases of processing into aluminum alloys, you can dramatically improve properties,” Taub says. But for processes requiring high temperatures to form a component, “the obstacle has been cost.”

The LIFT project is going after cost of the consolidation step of making aluminum metal matrix composites. The industry leader in this area—and the project leader—is Materion Corp.

Metal matrices start with powder mixed with other material. Simple enough. However, “when making a final component, two thirds of cost is the consolidation step—pressing into the shape you want at high temperature.” The process used today is called hot isostatic pressing, which is expensive compared with other methods, all followed by machining.

Says Taub, “We are going after alternate routes for consolidation. In particular, we are looking at ways to produce components in one step, in bulk form. That includes taking the powder, putting it in billet form and extruding it. Compacted powder extrusion and compacted powder rolling.”

After pressing, the material would enter an extrusion press or roll forming machine “to get the shape you want—whether it’s sheet, an extrusion or bar—and compact it to a greater yield strength.”

Work is being performed at partner companies, which are collaborating with a research network and national laboratories. LIFT is installing a large extrusion press and hopes to start it up by the end of the first quarter, according to Taub.

Local sheet deformation

The fourth project in aluminum, called incremental sheet forming (ISF), “is a novel breakthrough process,” LIFT’s Taub claims. Normally, parts are made by putting sheet metal into a large stamping press or deep drawing press, which forms a whole sheet at once within a die.

With ISF, the idea is to take a small, hardened steel tool, up to 1⁄2 inch in diameter, featuring a spherical tip. “You put the tool in a milling machine, spiral it around the sheet so you form it locally. You push it down into the material and form the same sheet by local deformation, so you don’t need big dies or stamping presses.”

Of course, says Taub, an automotive stamping plant making 100,000 parts a year will still need that large press. “But if you’re going to make parts up to maybe several thousand units, the ISF can reduce a metalformer’s capital investment. One possible drawback is speed—“a longer forming time might be necessary.”

However, like 3D printing, ISF “can make extremely complex parts. Because this starts in sheet, I can source material that has much higher structural performance. It’s an agile process,” adds Taub.

He acknowledges that automotive and aerospace OEMs have been exploring ISF at the laboratory experimentation phase for a decade but what LIFT’s teams are trying to demonstrate is the prediction of springback, a common obstacle in metalforming processes. 

“The first pass yields die geometry in modeling. That modeling needs to be developed for this process. So the tool pass takes into account springback, understands the mechanical properties of the finished part, and helps to improve surface finish,” says Taub, adding, “This could be a game changer in terms of agile sheet metal forming.”

Battling corrosion

Lastly, Taub credits LIFT with developing an ICME model he calls “quite clever.” Galvanic corrosion occurs when two different metals are in contact—such as steel and aluminum. “With electrolytes between them, differing electronic potential drives corrosion. Our team is approaching the problem at the microstructure level.”

Each metal features different microstructure phases, and each phase possesses different elements within. Researchers are using equipment to study the materials at the microscopic level and modeling at that level. 

“So, for the first time, researchers will provide a tool to design alloys and surface coatings to prevent corrosion.” This means that engineers can design with a multimaterial strategy in mind—AHSS, titanium, magnesium, etc. 

“There is a synergy with the materials at the modeling level and—combined with new manufacturing processes—leveraging that synergy enables the revolution in lightweighting,” Taub concludes. MM

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