It’s hard enough to remove supports from many plastic 3D printed parts, but more than one company has been working on developing ways to make plastic support removal easier, to the delight of many. Metal supports are a different story. The laborious machining required to remove metal support structures can take days – often longer than it took to 3D print the part itself. But thanks to the research of Arizona State University professor Owen J. Hildreth, Pennsylvania State University professor Timothy W. Simpson, and colleagues, there’s finally an easier way.
Last year, we wrote about the development of a dissolvable support material, which the research team created for multi-material direct energy deposition (DED) 3D printing. Now, in a new paper entitled “Dissolvable Supports in Powder Bed Fusion-Printed Stainless Steel,” the team details how they have continued their research to create – yes – dissolvable supports for powder bed fusion 3D printing.
In last year’s experiment, the team took advantage of the multi-material 3D printing capabilities of direct energy deposition to 3D print a stainless steel part with carbon steel supports, which were dissolved in a nitric acid solution while the stainless steel remained untouched. But that technique isn’t possible with powder bed fusion 3D printers, which are limited to a single material, so a new method was needed for the more frequently used powder bed process.
The team tried two approaches to removing supports from a 3D printed stainless steel cylinder, which was printed with a single row of 100-micron-diameter needle-like supports. In the first, called direct dissolution, the part was heat-treated, or annealed, while packed with sodium ferrocyanide. The process successfully removed the supports, but the part suffered significant chemical etching because the sodium ferrocyanide removed the steel’s protective chromium carbide. The etching increased the longer the part sat in the solution.
“More importantly, it is not a self-terminating process, and controlling key process outputs (etch rate, etch depth, and pitting) could vary significantly with even minor changes in component geometry, counter electrode geometry, relative positions/orientations, electrolyte viscosity, and more,” the researchers state.
The second approach tried a self-terminating process by introducing sodium hexacyanoferrate, a sensitizing agent, during the annealing stage. Sodium hexacyanoferrate decomposes at high temperatures, giving off carbon and nitrogen that diffuse into the stainless steel part and turn the very top layer, about 100 or 200 microns, into carbon steel, which easily corrodes or dissolves. Since the supports were only about 125 microns thick, they were completely transformed, while the part itself was barely affected.
“The ‘sensitized’ region is designed to be highly susceptible to corrosion/dissolution, and selecting the correct etchant and applied potential ensures that the etching reaction self-terminates once the sensitized region is dissolved. As a result, the component separates from the support in a highly controllable manner with only minor dimensional changes and little pitting,” the researchers explain. “Relative to the direct dissolution approach,the self-terminating sensitization approach requires only minor additions to the postprint annealing step and has less sensitivity to component shape, working electrode shape, or their relative orientations. Design allowances of 100–200 μm can be added to the component surface to accommodate the small change in dimensions.”
The team then tested the process by 3D printing a complex part, made from interlocking stainless steel rings, on an EOS M280 PBF 3D printer. The part included multiple densely packed supports, which broke off after about seven hours in the solution – as opposed to the three or four days that traditional machining would likely have taken for such a complicated, support-heavy part.
The researchers’ findings could potentially save manufacturers thousands of dollars, not to mention hours and days of work. Hildreth and his team are currently working to refine the process and apply it to other metals with different chemical solutions. Additional authors on the research paper, which you can access here, include Simpson, Christopher S. Lefky, Brian Zucker, David Wright, and Abdalla R. Nasser. Discuss in the Dissolvable Supports forum at 3DPB.com.
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