Reimagining 3D Metal Printing
3D printing is quickly catching fire in the world of manufacturing. Although the aerospace and medical-device industries were the first players to adopt the process, all industries that work with metals, including automotive, are now beginning to realize the promise of 3D printing, also known as additive manufacturing (AM).
If there is a company that hasn’t yet begun to explore the technology, they should. That’s the position of Jack Beuth, professor of mechanical engineering at Carnegie Mellon University (CMU).
“When it comes to additive manufacturing, the clock is ticking,” said Beuth, who specializes in process modeling and has been researching AM technology for over 20 years. “It is important to act quickly because those who understand and prepare for the coming changes in additive manufacturing will outcompete those who do not.”
AM has the potential to reduce waste (Fig. 1), decrease time to market, increase product performance and promote product innovation. The layer-by-layer manufacturing technique radically changes product-development procedures and can be used both for prototyping and as the final process for part fabrication. But as with any budding technology, AM faces challenges on the path to becoming a mainstream manufacturing process. Companies are concerned that the technology needs big improvements in areas such as the build rate of parts, fatigue resistance of materials and customization of the process.
Researchers like Beuth (Fig. 2) and Tony Rollett, a materials science and engineering professor at CMU, are confident that these hurdles will quickly be cleared, creating new opportunities for industry.
“Over the next five years, there will be a major shift in perspective when it comes to AM technology,” Rollett said. “Right now, there is excitement around reimagining shapes or manufactured parts because we now have the ability to build them up layer-by-layer. However, the real excitement will come when companies are able to manipulate part design, powder feedstocks, process variables and post-processing simultaneously.”
The NextManufacturing Center, which Beuth and Rollett (Fig. 3) lead, has focused its attention on making this goal a reality and increasing widespread adoption of the technology. NextManufacturing Center researchers are working on research projects to overcome the current challenges in the field. The center is developing an entirely new approach to metal AM, merging data from all parts of the process to create a fully integrated understanding of the technology that will allow the researchers to address some of the current metal AM challenges.
Currently, direct-metal AM processes do not offer much customization to the user. Users are only able to control a narrow range of process variables such as beam power, travel speed, layer thickness and part temperature. Beuth points out that machine users need more control of the process in order to better manipulate the outcome.
“Users need to be able to design the AM process as they design the geometry of the part,” Beuth said. “This customization would allow companies to optimize the specific process variables that they need based on characteristics of the part they are printing.”
To fill this need, Beuth has developed a patent-pending technology that has the potential to revolutionize metal 3D-printing processes. This technology, called process mapping, can map out actual process outcomes like surface finish, microstructure and porosity. Using process mapping, companies can differentiate themselves from their competitors by creating their own proprietary processing “recipes,” which include specialized process characteristics. In the next five years, this process-mapping technology will allow the user to further customize the process as they customize the design of their part.
Monitoring and Control
AM processes are currently not significantly monitored. For example, users are often only able to monitor the overall temperature in the build chambers of their machines. They are not able to monitor the consistency of other integral parts of the process, such as the precision with which the powder is spread or the size of the melt pool. This is problematic because it means that users are getting very little data about their build and are therefore unable to easily identify or correct problems, such as incomplete powder fusion.
The NextManufacturing Center is working to both improve sensors and add new ones. In five years, machine users will be able to monitor and control the AM process, which means adjusting the printing process as a part is being built (Fig. 4).
Mechanical properties such as strength are determined by the small-scale structure of metals known as microstructure. Currently, users are not able to vary the microstructure in different locations of an additively manufactured part. Beuth explains that this will soon change, giving engineers new tools to optimize part performance. It’s an advancement, in fact, that Beuth and his research team have begun to realize just this year. Beuth’s team recently demonstrated the ability to control key aspects of microstructure for two different types of additive processes and two different metals. Their techniques are advancing rapidly and are now being transferred to industrial members of the NextManufacturing Center.
Within five years, users will be able to vary the material microstructure and properties in different locations of a part by manipulating process variables as a part is being built.
Currently, most commercial 3D metal printers can only print with a few types of metal powders. These powders are made up of very specific particle sizes and can only be purchased from the companies that produce 3D-printing machines. The machine manufacturers require users to buy metal powder from them or risk losing the warranty of their printers. Because of the specialty nature of these metal powders, they are expensive to produce and drive up the cost of the final printed part.
Companies that hope to use AM to produce a large number of parts find the limitations on metal powders to be particularly challenging because of the cost it can add. Cost is often one of the most defining measures in a company’s decision to adopt AM technology.
“The question for companies becomes, ‘If we have a metal powder that is a different particle size than we’re supposed to use, can we successfully print a fully dense part?’” Rollett explained. “Our answer is ‘Yes, you actually can.’”
The NextManufacturing Center, in collaboration with North Carolina State University, has discovered how to 3D print with different metal powders, many that would normally be discarded because of their larger particle size and coarse texture. The center estimates that all 3D-printing machine users will be able to adopt these practices over the next five years in order to use a wide variety of metal powders in 3D-printing machines. This means that manufacturers will be able to purchase less-expensive metal powders from a wider range of distributors.
Materials science also plays a key role in improving the internal structure of AM metal parts. The biggest challenge is porosity, or tiny defects in the printed part, which makes the part susceptible to breakage (fatigue or fatigue failure) when it is exposed to repeated stress. Currently, some level of porosity is unavoidable if a manufacturer were to use a 3D metal printer’s suggested process parameters.
NextManufacturing (Fig. 5) researchers, however, have the knowledge required to control the porosity down to safe levels in AM metal parts. Rollett and his group use advanced characterization techniques to study metal printing powders and better understand how and why porosity forms in printed parts. Using this fundamental scientific approach, the group can determine how to eliminate the tiny defects. Using advanced characterization to visualize porosity with such high precision is a breakthrough capability in additive research.
Rollett and Beuth say that these results will be transferred to industry in the next five years, and users will be able to both eliminate and manipulate porosity in printed parts.
Looking Forward: Developing New Alloys, Using Machine Learning in 3D Printing
The NextManufacturing Center is not only focused on identifying and solving AM challenges over the next five years, it is already looking ahead to what industry will need within the next decade. One of these key areas is the development of new AM alloys.
“The metal powders that manufacturers are currently using for 3D printing were actually designed and optimized for conventional manufacturing processes,” Rollett explained. “There is a growing need for materials that are instead optimized for additive-manufacturing processes and their high cooling rates.”
Rollett and his colleagues are working on several projects in this space. Looking forward, users will have a wider range of materials to choose from when printing.
The second key area is the use of machine learning in additive manufacturing. By combining materials-science research and computer-science techniques, the NextManufacturing Center (in a project led by Elizabeth Holm, professor of materials science and engineering at CMU) is compiling a database of experimental and simulated metal-powder micrographs in order to better understand what types of raw materials are best suited for 3D-printing processes. Machine learning can potentially be used for better, more standard part qualification.
“3D printing is one of the best things to happen to the field of metallurgy in the past 100 years,” Rollett said. “The technology is challenging our engineers to think in completely new ways, and it is inspiring us to create interesting new collaborations across disciplines.”
For more information: Contact Hannah Diorio-Toth, communications manager, Carnegie Mellon University, College of Engineering, Pittsburgh, Pa.; tel: 412-268-1208; e-mail: email@example.com; web: www.engineering.cmu.edu