Apr 20, 2017 | By Benedict

Owen Hildreth, an assistant professor of 3D nanofabrication at Arizona State University (ASU), has devised an electrochemical process that could be used to “eat away” the support structures used in metal 3D printing.

Thanks to the pioneering work of companies like Stratasys and the development of special soluble materials, getting rid of support structures is now easier than ever—if you happen to be 3D printing in plastic.

When you have a multi-material FDM 3D printer, you can simply load up an insoluble filament for printing the part and a soluble material for printing the support structures. Once printing is done, the soluble support material can be dissolved away using a chemical bath or other treatment method.

Unfortunately, 3D printing with metal isn’t so simple. For one, powder bed 3D printers generally aren’t as friendly to multi-material printing as extrusion-based 3D printers are. And secondly, it’s much easier to make a plastic dissolve than a metal.

Timothy Simpson, a research professor at Pennsylvania State University’s Center for Innovative Materials Processing through Direct Digital Deposition, had been interested in developing a new support structure solution for metal 3D printing, and happened to mention the topic at a lecture at ASU.

3D printed stainless steel part before (above) and after electrochemical treatment to remove supports

Owen Hildreth, ASU assistant professor of 3D nanofabrication, was in attendance at the lecture, and became intrigued by the challenge. His initial response was “Well, any metal could be dissolved if you control the local chemical environment,” and he imagined using sacrificial anodes—the kind used to prevent corrosion on steel ships—in 3D printing.

Simpson and Hildreth began working together on a electrochemical solution to the problem of metal supports in 3D printing. Their aim was to create a process that could “eat away” support material while leaving the printed part mostly intact.

Amazingly, the team actually came up with multiple solutions to the support problem, suitable for different methods of metal 3D printing. First, Simpson produced a one-inch stainless steel arch with carbon steel supports on a multi-material Optomec Direct Metal Deposition 3D printer. For this part, a nitric acid solution successfully dissolved away just the carbon steel supports, leaving the part intact. This, however, was the easy part, since metal deposition is actually a lot like FDM 3D printing.

But Hildreth also developed a more complex support removal process for parts made on a powder bed metal 3D printer, currently the most common kind of metal 3D printer—think SLM, DMLS, etc.

At first, he used sodium ferrocyanide while heat-treating a printed part, but found that the process “etched” away at the printed part too much. To improve the method, Hildreth introduced a sensitizing agent, sodium hexacyanoferrate, during the annealing stage. The addition of this chemical eventually made all the difference.

The stainless steel 3D printed part throughout the process

Sodium hexacyanoferrate decomposes at high temperatures and gives off carbon and nitrogen. So when the chemical was introduced to the annealing process, it effectively turned the top 100 to 200 microns of the 3D printed part into carbon steel. The supports, being just 125 microns thick, thus became completely “sensitized,” while only a thin shell of the actual part did.

Excitingly, this method proved effective for dissolving support structures created during the most common metal 3D printing processes. The main 3D printed part acts as a cathode, while the support structures become subject to anodic corrosion. A test part printed on an EOS powder bed 3D printer proved the efficacy of the technique, with the support parts etched away in around seven hours—much less than the 32 to 40 hours that machining would have required.

“This is a really big innovation for the additive manufacturing community because it removes a lot of the tedious, unneccesary costs associated with additive manufacturing,” Hildreth said. “It fits the ‘better, faster, cheaper’ approach that we’re always trying to push our technology towards.”

The 3D printing research has been published in 3D Printing and Additive Manufacturing.

 

 

Posted in 3D Printing Technology

 

 

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