Compared to conventional manufacturing methods, additive manufacturing (also known as 3D printing) is far better at producing metal parts with very complex geometries, and this ability makes 3D printing attractive for applications in the aerospace and biomedical industries, among many others.
But there’s a big downside. Metal parts created with additive manufacturing have defects, such as pores and cracks in the material, that significantly compromise the finished part’s strength and durability.
Lianyi Chen
“Using metal 3D printing, we haven’t been able to consistently produce parts with the same high quality and reliability as those made by conventional methods, which means we have big concerns about using 3D-printed parts for critical or load-bearing applications where failure isn’t an option,” says Lianyi Chen, a University of Wisconsin-Madison assistant professor of mechanical engineering. “This quality problem is the biggest barrier for using metal 3D printing in various applications.”
Now, Chen and his students have discovered a way to enable a prominent additive manufacturing technique called laser powder bed fusion to produce metal parts that have significantly fewer defects. They detailed their findings in a paper published Feb. 28, 2022, in the journal Nature Communications.
“In this paper, we demonstrate a potential way to solve the quality problem by making metal 3D printing technology much more reliable, enabling it to produce consistent, defect-lean parts,” Chen says. “Using our unique method, we were able to 3D print a metal part that has very few defects and a comparable quality to that of a commercially manufactured part that you could buy off the shelf.”
It’s a promising solution to a longstanding problem in metal additive manufacturing, and it opens a door to widespread industry adoption of this manufacturing technology.
The researchers’ technique involves using ceramic nanoparticles to control instabilities in the laser powder bed fusion additive manufacturing process that cause defects.
Laser powder bed fusion uses a high-energy laser beam to melt thin layers of metallic powder in select locations. The material then cools, forming the finished metal part.
However, as the laser interacts with the powdered material, the powder surface heats to boiling temperature and creates hot vapor. This vaporization creates pressure that pushes down on the melt pool—the melted powder bed—causing droplets to splash out of the pool. These droplets can cause unpredictable defects in the printed part.
Droplets also can collide during flying and merge to form a larger droplet, or “large spatter,” creating even more problems in the additive manufacturing process and leading to subpar printed parts.
By coating the metal powder with ceramic nanoparticles, the researchers could control these instabilities. Using both high-speed synchrotron x-ray imaging and theoretical analysis, they found that the nanoparticle coating stabilized the melt pool, preventing liquid droplets from spraying out and forming the larger spatters.
“When we introduced the nanoparticles, we found that they made the liquid droplets almost have an ‘armor’ on the surface, so that when they collided, they didn’t merge together,” says PhD student Minglei Qu, the lead author of the paper. “For the first time, we were able to get rid of the problematic large spatter.”
In addition to the possibilities it holds for 3D manufacturing, Chen says the advance could lead to improvements in a broad range of applications, including laser polishing, laser cladding, welding, casting, and fluid stability control, among others.
Chen is the Charles Ringrose Assistant Professor in mechanical engineering at UW-Madison.
Additional authors on the Nature Communications paper include Qilin Guo, Luis I. Escano, Ali Nabaa, S. Mohammad H. Hojjatzadeh, and Zachary A. Young, all are PhD students in Chen’s group.
This work was supported by grants from the National Science Foundation (Award No. 2002840) and the University of Wisconsin-Madison Startup Fund.