Additive Manufacturing

3D assembly by layer-by-layer manufacturing

The possibilities for 3D printing seemed trivial at first glance. There were the plastic toys, small metal gears, dental implants – hardly the next revolutionary technology. But a hip joint printed with a material stronger than bone with a printed coating that encourages cell growth added in the same operation - that begins to look revolutionary.

Pipeline Orthopedics, a seven-year-old start-up based in New Jersey, is making the personalized hip joint (i.e., the acetabular cup), which is targeted at younger patients who will require longer-lasting hip, knee, and shoulder replacements. The new parts are made using powder laser sintering, and they are expected to be approved shortly by the Food and Drug Administration, according to Robert Cohen, the company's senior vice president for research and development.

Cohen was speaking at the CIMP 3-D Technology Showcase at Penn State in January. The showcase, which was expected to attract around 75 attendees, swelled to nearly 300 by the time the first talk began, indicating the intense interest of industry and government agencies in the emerging technology. Another indication of the rise of 3D printing was President Obama's mention of additive manufacturing – the name given to 3D manufacturing when used for industrial purposes – in his State of the Union address this February. That reference was to a new public-private initiative for a proposed National Network for Manufacturing Innovation - advanced manufacturing hubs that will accelerate the growth of U.S. manufacturing. The pilot hub, called NAMII, short for the National Additive Manufacturing Innovation Institute, is located in Youngstown, Ohio, with a network of partner industries and universities in Eastern Ohio, Western Pennsylvania, and West Virginia. Penn State has been designated the metals node of NAMII.

At Penn State, the leader for additive manufacturing is the Center for Innovative Metal Processing through Direct Digital Deposition (CIMP 3-D) located in a 8,000 square-foot demonstration facility in the Innovation Park and operated by Penn State's Applied Research Laboratory, Sciaky Inc., and Battelle. The Center's purpose is to advance the technology of additive manufacturing and to pass the advances along to the Department of Defense and U.S. industry, while training students in the latest technology.

"When it comes to U.S. manufacturing, we've lost our swagger, but additive manufacturing will get it back. The Applied Research Lab has a long history of excellence in laser technology, and the region's powder metal industry is at the core of 3D manufacturing."
— Rich Martukanitz of the Applied Research Lab and co-director of CIMP 3-D told the showcase audience in January.

China has surpassed the United States in traditional manufacturing, and Europe is ahead in additive manufacturing, but he believes that the United States can leapfrog the competition and create a revolutionary manufacturing technology at home. That would be fitting, since most of the early technology was invented and commercialized in the United States in the 1980s and '90s.

Europe is ahead now, but it's still a young industry, Martukanitz elaborated during a tour of the CIMP 3-D facility in Innovation Park in early February. The necessary renovations were nearly complete, and cardboard taped to the floor marked the spots where equipment was scheduled to arrive and be installed in the coming weeks.

"I know of no place in the world that has this broad a spectrum from basic to applied technology," he continued as he pointed to the place where an x-ray tomography system for characterizing the interior of finished parts would stand. Nearby was a specially built storeroom in which the metal powders could be safely stored. Those powders will be fused by lasers controlled by CAD programs and built up layer by layer into a finished component. The 3D assembly by layer-by-layer manufacturing makes it possible to create complex shapes nearly impossible to fabricate by traditional milling or molding processes.

The CIMP 3-D co-director, professor of engineering Tim Simpson, leads the Center's educational and outreach program in partnership with Penn State's Digital Fabrication Network, DIGI-Net, and the Learning Factory, where teams of engineering students partner with industry to help solve real-world engineering problems. The Learning Factory already owns a number of 3D systems, including Makerbots and RepRap printers that can print the parts to replicate themselves.

"We will have senior engineering students, grad students, and technicians working on these machines," Simpson remarked. "We have projects from Penn State Hershey Medical Center and a variety of industries, and hope to have 20-25 students working on different projects with us. We also have summer internships planned for students and industry personnel, and ASM International (the Materials Information Society) is involved. Penn State will host the first teachers' camp for additive manufacturing next year."

Whereas NAMII, the national program, has a focus on applied research and development and the transition of that knowledge to industry, CIMP 3-D, the Penn State program, has a broader focus, and draws faculty from the College of Engineering, the College of Earth and Mineral Sciences, the Materials Research Institute, and the Applied Research Laboratory. Discussions are also underway with the Penn State College of Medicine and Hershey Medical Center. The expertise the Center can draw on ranges from laser processing of all types of materials, to powder processing to design to the very fundamental science of materials, phase transitions and thermodynamics.

The new science of additive manufacturing

Additive manufacturing is not just about cool designs and rapid prototyping of components. There is new science involved and the Center is engaging with materials scientists to go deep into the structureprocessing-property relations through computation, synthesis, and characterization.

Gary Messing, department head of Materials Science and Engineering at Penn State, is a part of the CIMP 3-D team. "These processes represent a new way of fabricating materials and products under different time and temperature conditions than conventionally used," he explained.

"What we have in additive manufacturing is a laserbased system and a melt solidification process. That sounds like the mainstay of metallurgy, in which we melt things and then cast them. But now, instead of trying to cast a bulk part into a mold, the part is built up layer by layer using a computer CAM-CAD file that directs the tool. The time-temperature conditions are radically different and thus can affect changes in the process-microstructure relationships and then the microstructure-property relationship in ways we have not explored. I think there is a lot of new materials science to be developed to enable production of parts with better properties."

Can we create composite materials that could not be created in any other way? Messing thinks so. "In my mind, that's one of the real strengths of the project. With metal-based composites you can add hard materials during the solidification process. It could be a carbide, a nitride, a boride, added in the powder stream and incorporated in the melt pool. Because it happens so fast, there isn't time for chemical reactions that you would normally have in a melt process. That could be a big advantage. We don't really know yet." This is where Zi-Kui Liu, a professor in the Materials Science and Engineering Department and director of the Center for Computational Materials Design, and

Long-Qing Chen, distinguished professor of Materials Science and Engineering, come in. Liu can look at the phase diagrams of the materials and predict what will happen when materials interact under different conditions with an alloy. His computational modeling of thermodynamic phase equilibria will be especially important for new composites. Chen's expertise in modeling microstructural evolution will accelerate process and materials development time. "We may still have to do 10 experiments," Messing predicted, "but we won't have to do 100."

What about ceramics?

"I'm an optimist. I think ceramics have a role to play in this," Messing, whose expertise is in ceramics science, cautiously responded. There are a lot of reasons why melting and then solidifying ceramic powders to make a dense part are problematic, he cautioned. In bulk ceramics, solidification is a slow process that allows the ceramic grains to grow larger. Large grains make for a weaker material. Another factor is the strain associated with solidification of the melt. As the temperature drops below the melting point, the dimensions change instantly, introducing stress inside the bulk material and causing it to crack. Stress is almost impossible to manage, and along with grain growth, the reason bulk ceramics are not melted and cast like steel.

"In class, I tell my students that we never try to melt and solidify ceramic materials for those reasons. Now I'm thinking, well, maybe there are ways to circumvent these problems. If you take the bulk and assemble it drop by drop, then there may be ways you can control the dimensional changes. You might be able to use composite particles to take up some of the stress."

"Materials faculty are a huge part of our plan," Martukanitz said, sitting at a conference table with Tim Simpson in a room full of computer monitors adjacent to the equipment lab. Simpson will use this room for instruction and student projects. "This is the first technology to come along in a long time that combines the three components of manufacturing, engineering, and materials science," Martukanitz continued. "Now you can vary all of the processes and materials on the fly. It's a new capability to be able to build components out of multiple materials. You could have a lightweight core surrounded by a high strength material and coated with a corrosion resistant coating. We will need to develop new design techniques to work with multiple materials." Simpson added, "For this generation of students, this is incredibly exciting. They've lived with computers all their lives. Now they can use their computers to make things with 3D printing. It changes the way we teach and allows us to take teaching to a new level. It is an exciting time to be an engineer, and 3D printing is playing a huge role in that."

By spring they will have two new machines. One is an electron beam direct manufacturing system from Sciaky. Another new machine uses an ink jettype printer to deposit a binder on a bed of powder material to form a shape one layer at a time. The excess powder can be removed and reused, and the part is then thermally treated to obtain structural integrity. The savings in expensive materials is a core benefit of additive manufacturing (AM) and is expected to make AM significantly cheaper than traditional subtractive manufacturing. "We have $500 open source printers that print in plastic, and $1 million-plus printers that can print with plastics, metals, even sand, and everything in between," Martukanitz remarked. "We want to be able to print with different materials, the next generation of aluminides, for instance, or ceramic-metal composites for high performance in a net shape."

"This technology, combined with a few other things, could revolutionize manufacturing."

Back at the technology showcase, Irene Petrick, a professor in the Penn State College of Information Science and Technology and a consultant to major companies on trends and roadmaps for manufacturing, gave the audience her view of the future of manufacturing.

"By creating a customized experience, and allowing the co-creation of products, 3D printing will change the relationship between consumer and producer. This technology, combined with a few other things, could revolutionize manufacturing," she said.

Those few other things are high performance computing applied to manufacturing, the use of multiple materials, and cloud-based computing solutions for small companies, which will eliminate the need to maintain expensive IT and accounting departments. These factors will level the cost of entry to people with new business ideas, giving internet-savvy do-it-yourself hobbyists easy entry to manufacturing. With no plants to build, and steadily falling prices for printers, 3D printing favors local manufacturing over global manufacturing, she said. Labor costs are essentially eliminated and the time and cost of shipping are reduced. In addition, Petrick believes 3D printing will make manufacturing sexy to a younger generation that has seen manufacturing jobs largely disappear.

Precision metal components could be an exception to the local manufacturing trend. Local artisans and garage-based entrepreneurs will not be making parts for the aerospace industry any time soon, she acknowledged. But she predicts that entrepreneurs and not established industry will be driving the changes in additive manufacturing and driving them in ways that are creative but difficult to predict.

After all, it was the changes in modern transportation and IT systems that outsourced U.S. manufacturing and distributed it around the globe to the places with the cheapest labor, she concluded. Now we are coming back to local artisans and crafters. It will be a renaissance in manufacturing in the U.S., but this is all still a decade away. Then Brian Rosenberger of Lockheed Martin showed examples of parts made by additive manufacturing for use in the new F-35 fighter plane, and Robert Cohen of Pipeline Orthopedics showed video of the customized hip joint that could only be made by 3D printing, and suddenly the renaissance seemed upon us.