Researchers Are Able to Dissolve Support Structures in Metal 3D Printing, Offering Great Potential for Future

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UntitledDissolvable supports in 3D printing. It’s music to the ears of anyone who works with this technology in any capacity, well aware of the headaches that using supports can involve—and the lengths that we will go to for eliminating their use—perhaps even skipping certain projects we might otherwise have endeavored to try. Sometimes though, supports are a necessary evil to get the desired result when making more intricate models with overhangs, offering sustainability during the printing process. And while soluble support materials have been created in some cases for polymers and some 3D printing systems, that has not been the case for metal, up until now.

In 3D printing with metal, just as in other materials, the need for supports can be prohibitive. Now that researchers have created dissolvable supports for this material however, 3D printing with metal may be about to expand even further. And in the realm of invention, it’s often all about refining the tools. Recently published in 3D Printing and Additive Manufacturing, and outlining their project in ‘Dissolvable Metal Supports for 3D Direct Metal Printing,’ researchers Owen J. Hildreth, Abdalla R. Nassar, Kevin R. Chasse, and Timothy W. Simpson expound on how they created dissolvable materials, and all the future potential that comes with this latest innovation.

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Overhang angle was measured from the vertical for this research.

After making carbon steel structures for temporary support of even larger structures, the researchers found they could dissolve them following the printing process through electrochemical etching in nitric acid with bubbling oxygen. To demonstrate how it works, the researchers chose to create a support for a stainless steel bridged structure with a 90 degree overhang. After successfully using their new technique, they reported that no “machining, grinding, or finishing operations” were required for removing the metal supports.

Upon success in dissolving the structures and working with this process further, the researchers contend that the potential is enormous in terms of eliminating post-processing work, as well as allowing that it will be useful in working with numerous metals, as well as oxides.

“The plastics extrusion 3D printing community has already solved the overhang problem by printing parts and supports out of polymers with different solubilities,” state the researchers in their paper.

In their project, they state that for the first time they’ve created a similar solution, allowing for supports to be made from ‘sacrificial metal’ that also displays low chemical resistance.

“We collected potentiodynamic polarization curves for the DED printed stainless steel, carbon steel, and mixed stainless/carbon steel part to select a driving potential, where stainless steel can be biased at a reducing electronegative potential, whereas the carbon steel will be at an oxidizing electropositive potential,” stated the researchers. “A free-standing stainless steel bridge was fabricated using a DED powder-fed AM process by printing the stainless steel bridge with a carbon steel support across the middle and then etching away the carbon steel in nitric acid with bias of 500–700 mV relative to saturated silver/silver chloride electrode.”

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(a) Optomec LENS MR-7 DED system with (b) dual powder feeder system

The researchers built the mixed steel structure using 60 layers with a predetermined layer spacing of 0.13mm, and hatched spacing of 0.61mm for the first 30 layers. In the middle third of the object being printed, mild carbon steel was surrounded by the deposited stainless steel. While in process, powder flow was switched from stainless steel to a mild carbon steel.

“For electrochemical dissolution of the sacrificial carbon steel, the working electrode was set between 400 and 900 mV so that the measured current was -100 mA for the initial half of the test to verify that the stainless steel was stable under a cathodic bias, then the applied potential was increased positive to reduce the measured current to between -20 and -10 mA,” stated the researchers. “Next, O2 gas was bubbled onto the carbon steel section of the working electrode to speed electrochemical dissolution of the sacrificial material.”

The researchers also “increased the etch rate significantly” through bubbling O2 into the area of the part composed of carbon steel in order to begin breaking it down. In the end, they found the removal process for the supports to be self-terminating, and offering strong potential for use in 3D printing applications.

“This innovative new approach using Directed Energy Deposition for 3D printing of dissolvable metallic components, without the need for machining operations to remove the sacrificial support materials, creates opportunities for new types of applications,” says Editor-in-Chief Skylar Tibbits, Director, Self-Assembly Lab, MIT, and Founder & Principal, SJET LLC. “I’m excited to see what effects this research has on the future of metal printing.”

Discuss this new approach over in the Dissolvable 3D Metal Printing Supports forum at 3DPB.com.

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From the research paper: (a) Before etching, the red square roughly outlines where the carbon steel support layer was printed. (b) After 10 h of etching 1.4 mm of carbon steel was removed from each side. (c) After etching showing that the carbon steel was completely etched from the sample.

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