Tech Briefs

New technique is a game-changer in 3D metal printing.

Researchers at Arizona State University have made potentially game-changing progress in the emerging realms of 3D printing and additive manufacturing — an advance that could have a dramatic impact on how things are made from metals.

Fig. 1 – The arch was formed by first printing a stainless steel arch supported in the center by carbon steel. After printing, the carbon steel was electrochemically removed in a mixture of nitric acid with bubbling oxygen. Since carbon steel is easily dissolved while stainless steel isn’t, this simple process leaves behind a free-standing stainless steel arch that didn’t require any of the expensive machining operations that typically plague 3D metals printing. (Credit: Owen Hildreth)

Owen Hildreth, an assistant professor of mechanical and aerospace engineering in ASU’s Ira A. Fulton Schools of Engineering, has collaborated with several colleagues to develop a technique that promises to make manufacturing of metal components, devices, and structures less expensive, less technically complex, and less labor intensive. Significantly, the process overcomes what has been a nagging difficulty for the 3D printing of metal objects.

As an alternative to laborious machining processes, 3D printing has been a major driver of additive manufacturing. Conventional manufacturing is essentially a subtractive process. Manufacturers start with a mass of material and remove — or subtract — parts of the mass to produce a desired object.

“It’s like sculptors working with blocks of marble,” Hildreth explained. “They remove parts of the marble blocks until they get the shape of whatever kind of sculpture they wanted to create.”

Additive manufacturing, particularly with the use of 3D printing technology, is the opposite, he said: “You just add layers of material until you get what you want. You extrude products. The printer just pushes things out in one piece.” The process works great with lightweight and flexible plastics and polymers. But with weighty metals, it’s much more of a challenge. That’s because when objects made of plastics and similarly soft materials emerge from a 3D printer with extraneous material, the unneeded material can usually be easily cut away to give the object its intended form.

How it Works

The researchers employed a printing method — called directed energy deposition — that enables the printing of an object using two kinds of metal at the same time in combination, and then electively dissolving the “sacrificial” material with a simple electrochemical etching technique.

To demonstrate their new approach, they printed a stainless steel arch supported by carbon steel (see Figure 1). “The stainless steel is very chemically resistant. The carbon steel is not very chemically resistant,” Hildreth said. The printed metal structure was immersed in a “chemical bath” of nitric oxide and bubbling oxygen capable of dissolving metals that are not chemically stable — in this case, the carbon steel supporting the top of the arch.

“We took advantage of the differences in the chemical and electrochemical stability between the two metals,” Hildreth said. “The carbon steel was etched away without any machining. The stainless steel wasn’t affected. So what we have is the world’s first 3D-printed metal arch made with directed energy deposition.”

What that makes possible is a big reduction in the amount of post-processing required to remove support structures from 3D-printed metal components. “We’re fairly certain our method is going to be applicable to a broad range of metals used in manufacturing,” Hildreth said.

To achieve the advance, Hildreth teamed up with Timothy Simpson, a professor of mechanical and nuclear engineering as well as industrial and manufacturing engineering at Pennsylvania State University, and a leading expert in both 3D printing of metals and additive manufacturing. They were joined by Pennsylvania State University engineering research associate Abdalla Nassar and Kevin Chasse, a corrosion engineer with the Naval Surface Warfare Center.

Together they authored the report “Dissolvable Metal Supports for 3D Direct Metal Printing,” published in a recent edition of the research journal 3-D Printing and Additive Manufacturing. Hildreth’s recent research in these areas has been funded in large part through a Bisgrove Scholars Program award he received in 2015 from Science Foundation Arizona.

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