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Heavy metal impact: ASU engineer improving 3-D printing of metals

New technique by ASU prof, team is a game-changer in 3-D metal printing.
September 9, 2016

As an example of an engineering breakthrough, the tiny metal arch Owen Hildreth keeps in his office at Arizona State University isn’t anywhere close to visually impressive. But it is something special once you understand how it was made.

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

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, technically complex and labor intensive.

Significantly, the process overcomes what has been a nagging difficulty for the 3-D printing of metal objects.

Alternative to laborious machining processes

3-D 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 3-D 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 3-D printer with extraneous material, the unneeded material can usually be easily cut away to give the object its intended form.

With metals, however, the high temperatures required to print them cause objects to warp as they are being printed, and so the process requires metal supports strong enough to prevent this warping. After printing, the supports must be removed to produce an object with its intended shape.

The only way to remove such supports has been through heavy-duty, laborious and painstaking machining techniques, involving the use of computer numerical control milling machines and wire electrical discharge machining.

Electrochemical etching and chemical baths

Even when 3-D printing of plastic and polymer materials does require supports, “it’s easy to make them go away,” Hildreth said. “You just break them off, or you melt them off with a soldering iron.  Or better yet, you print supports made out of a water-soluble material. You can just dunk your object in water for an hour and the support material is gone.”

That doesn’t work in printing metal objects because they require metal supports during the printing process — and metals are not water-soluble.

But here is where the new technique demonstrated in the making of Hildreth’s tiny metal arch comes into play.

Combining his expertise with that of his collaborators, they 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 the stainless steel arch supported by carbon steel.

“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.

two people in ASU lab
Arizona State University engineer Owen Hildreth (right, with ASU engineering graduate student Avinash Mamidanna) is part of a team that has developed a technique to enable more efficient and less costly manufacturing of 3-D-printed metal materials. Photo by Jessica Hochreiter/ASU

 

Combining team's wide range of expertise

“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 3-D-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 3-D-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 3-D 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 that attracted immediate attention from manufacturing industry news outlets.

Mapping steps to further engineering advances

The team is already at work refining their techniques and mapping the next step forward. They hope to help develop methods that would apply the capabilities of 3-D printing to manufacturing metal products and structures to further eliminate the need for multiple parts and multiple assembly steps.

Along with private industry, they see the Department of Defense and NASA being particularly interested in supporting their endeavors.

They have also submitted a proposal to the National Science Foundation for support of research to look more deeply at the fundamental physics and chemistry involved in 3-D printing and additive manufacturing.

“We want to see what we can learn from mixing different materials together and printing them on top of each other,” Hildreth said. “We want to more closely study the diffusion and corrosion mechanisms involved in manipulating metals, with a focus on stainless steel, aluminum, titanium and an iron-nickel-chrome alloy.”

Local support put research on fast track

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.

Bisgrove Scholars awards are given to academics and researchers whose work is deemed to have “the potential to transform ideas into great value for society.”

Hildreth said the support “gave me the freedom to pursue this work, which so far has led to seven patent applications and the development of two startup companies.”

 

Top photo: The making of this small metal arch involved a novel technique that promises to make it easier to produce metal objects using 3-D printing. 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 3-D metals printing. This process is expected to dramatically simplify 3-D metals printing. Photo courtesy of Owen Hildreth

Joe Kullman

Science writer , Ira A. Fulton Schools of Engineering

480-965-8122

 
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September 12, 2016

Summer is often a time to take a break from academic studies. But many scholars at Arizona State University would rather trade their summer vacations for a chance to get ahead and make an impact in fields ranging from philosophy to chemistry.

More than 40 high-achieving undergraduate students in the College of Liberal Arts and Sciences spent the summer conducting research in their degree field, as recipients of the Undergraduate Summer Enrichment Awards.

"We're trying to solve problems no one knows the answer to," said Chloe Warpinski, an award recipient. "It's not often you get to work in something that has the opportunity to make meaningful change in your community."

Warpinski, a senior who studies global health in the School of Human Evolution and Social Change, saw an opportunity to solve problems without a set solution.

Warpinski’s research focuses on the homeless population in the Phoenix metro area, specifically the intersection of ecosystem services, homelessness and water insecurity. She is working on the project with her partner, Christine Demyers, a graduate anthropology student and previous teaching assistant in one of Warpinski’s classes.

“These are issues that affect not just one person or one community, but the entire world,” she said.

Through extensive interviews, mapping and other research tactics, Warpinski hopes to create a database of resources for the homeless in the area, many of whom are families and children. Warpinski was inspired after a semester abroad in Chile, where a lack of water affected not only her daily living situation, but her emotional health as well.

“It’s a chance to turn statistics into stories,” Warpinski said. “It’s been very interesting to listen to people tell their story from their point of view, and really empower them to be a person and not just a figure or a fact, which is awesome.”

Warpinski and Demyers hope to present at different anthropological conferences, with the goal of having similar research replicated in other urban cities or countries.

Economics and political science major Tyler Helms is taking a hard look at physical disability and accessibility concerns to solve another issue affecting major cities.

Helms, whose brother is physically disabled, has always been interested in disabilities and the policy activism that surrounds the issue.

For his project, Helms hopes to craft an “accessibility score” for cities, based on factors such as walkability or the average age of buildings. He is also looking at other socioeconomic factors that often affect disability, like employment and poverty rates.

Although the Americans with Disabilities Act has been in place since 1990, many public places like doctor’s offices or restaurants have been found violating the ADA laws. Alongside traditional research, Helms is interviewing lawmakers, policy advocates and disability lawyers to get a sense of why there is still noncompliance.

“As long as anything would help the disabled community, whether it’s awareness, or even just finding out what problems there might be systematically and offering a way of fixing it,” he said. “And even if it doesn't, it says 'hey' and gets some attention.”

Aaron Flegenheimer, a biological science major with an interest in psychology, is studying chronic stress to shed more light on post-traumatic stress disorder, which affects nearly eight million adults every year according to the U.S. Department of Veterans Affairs.

Partnered with graduate student J. Bryce Ortiz in professor Cheryl Conrad’s lab, Flegenheimer will induce the effects of chronic stress on rats and mice to determine how certain brain processes, specifically in the hippocampus, aid and assist in recovery.

Flegenheimer hopes this research will give scientists a better understanding of how chronic stress affects the human brain, offering more insight into the discovery, treatment and recovery from PTSD.

The Summer Enrichment Award winners are broadening their horizons and helping bring about positive change in the world. Their commitment to research, ranging from domestic violence and sexual trauma to climate change and cancer, will be instrumental in finding innovative solutions to pressing concerns across the globe.  

Students have the potential to earn $2,000 by completing three different phases of the program. Over the summer, they’ll partner with a faculty mentor to complete a unique research project of their choice. In the spring of 2017, students will present their research at a poster symposium and receive another portion of the award.

“The College of Liberal Arts and Sciences is providing a number of opportunities for students to enrich their experiences and one area we have been dedicating resources is to facilitate a research experience,” said Patrick Kenney, dean of the college.

The final goal for the students is to have their work published, speak at a regional or national-level conference or sponsor an activity submission connected to the college’s project. Many students who received the Summer Enrichment Award were also given assistance with summer housing, which allowed them to focus more on their research and undergraduate work.

“These opportunities allow students to receive a first-hand and up-close look at the process that leads to discovery and publications,” said Kenney. “These experiences improve their resumes for seeking admissions to professional schools and when searching for employment.”

Written by Sarah Edwards

Amanda Stoneman

Copywriter , College of Liberal Arts and Sciences