The task of removing support structures for metal 3D printed / additively manufactured parts has always been a challenge. So much so, that it’s often better to design the part so that it doesn’t need support. But when the design must have an overhang that requires support, or support to reduce thermally induced distortion, you know finishing will be required.
Now, new research indicates that metal additive designs can still include support without all the hassle of post processing. The research out of Arizona State University suggests that dissolvable metal material may work as a support material for metal additively made parts. The benefit is reduced post-processing. Co-authors Owen Hildreth, Arizona State University (Tempe), Abdalla Nassar and Timothy Simpson, Pennsylvania State University (State College, PA), and Kevin Chasse, Naval Surface Warfare Center (W. Bethesda, MD), wrote a paper on this technique,” first published in the journal 3D Printing and Additive Manufacturing.
The researchers discovered that if they took advantage of the different chemical and electrochemical properties of different metals, they could develop metal supports that are more easily removed.
One example given in their research paper was a stainless steel bridge that had a 90-degree overhang. The sacrificial metal support was Metco 91 carbon steel. Electrochemical etching in a 41 wt.% nitric acid with bubbling O2 solution was used to dissolve the support.
Stainless steel tends to resist nitric acid, but it can still have small amounts etched away. Carbon steel, on the other hand, dissolves in the nitric acid, although quite slowly. In initial trials, the researchers noted that it took ten hours to remove 1.4 mm of the carbon. That’s why they experimented with speeding up the process with a bubbling O2 solution. With this approach, they were able to remove 7 mm of carbon in six hours.
Their research indicates that other metals may be suitable for this purpose, but the material must meet the following criteria.
The sacrificial material must be metallurgically compatible with the main material used for the part. Thus, sacrificial material characteristics include similar crystal structure, thermal characteristics, and similar coefficient of thermal expansion. But the sacrificial material should not be too similar to the part material to avoid unwanted intermetallics. The sacrificial material must be strong enough to handle the additive build and the part, but not so strong as to be hard to remove.
Dissolvable metals are an exciting development in metal additive manufacturing. Other research has shown that post-processing tasks can be time-consuming and costly, and are often not accounted for in the overall decision to work with additive machines. But the additive industry is in a dynamic phase. Other methods of speeding post-processing are just on the horizon.