Morphology of Cu and CuNi microlattices. a–c,e–g, SEM image of Cu(a–c) and CuNi(e–g) octet lattices, showing multiple unit cells from the top (a, e), a single node (b, f) ) and a FIB Milled Cross-section showing the internal structure of the node from an inclination angle of 52° (c,g). d, h, EDS elemental mapping, show a uniform distribution of Cu(d) and a uniform distribution of Cu and Ni(h). Scale bar: a, e, 100 Phase; b, f, 50 Phase; c, g, 20 Phase; d, h, 50 Phase. Credit: Nature (2022). DOI: 10.1038/s41586-022-05433-2
Engineers at Caltech have developed a method of 3D printing pure metal and multi-component, at a resolution that is, in some cases, smaller than previously possible. The process, which uses water-based chemistry and 3D printing, has been described in a paper published in Nature on October 20.
The new process can be used on a wide variety of metals—even many in the same manufactured part—with only minor adjustments. It has the potential to pave the way for the fabrication of microscopic components for microelectromechanical systems (MEMS)—precision parts for space vehicles and applications, heat exchangersor biomedical devices.
In 3D printing (also known as additive manufacturing), an object is built layer by layer, allowing for the creation of structures that cannot be manufactured by conventional methods. metal-forming methods such as forging and injection molding, or through subtractive methods such as engraving or milling. Current metal 3D printing processes use a laser to ignite metal powder, which melts the metal and then solidifies it into specific shapes. That way, manufacturers can create structures with a resolution of about 100 microns, equivalent to the thickness of two sheets of paper. (Resolution is the scale of the smallest detail a process is capable of producing.)
The problem is that metals, especially those with high thermal conductivity such as copper, transmits heat so well that even with a well-focused laser, heat is radiated and melted the powder outside the desired area, reducing the possible resolution of the print.
A team led by then graduate student Max Saccone (Ph.D. ’22), now a postdoctoral researcher at Stanford University, was; Rebecca Gallivan (MS ’22), currently a postdoctoral researcher at ETH Zurich; Daryl Yee (MS ’16, Ph.D. ’20), Upcoming Assistant Professor at EPFL, Switzerland; and Kai Narita (Ph.D. ’21) working in the lab of Julia R. Greer at Caltech, took a different approach to the problem: Instead of writing metal directly, they 3D printed a hydrogel and use it as a metal holder for liquid money. Narita founded a startup called 3D Architech that is licensing new technology from Caltech.
“We had to develop a new way of doing things, and we couldn’t rely on heat to build our structures,” says Saccone.
Hydrogels are materials made of flexible polymer chains that are insoluble in water and are used for products such as soft contact lenses. Light from a low-power ultraviolet lamp is capable of triggering a chemical reaction in liquid polymers, causing them to harden by creating cross-linking of polymer chains. If you repeat this process over and over in a specific pattern, you can form the desired micro-shapes.
Caltech researchers then infuse 3D-printed hydrogel scaffolds with metal salts dissolved in water (think saltwater), causing the metal ions to permeate the hydrogel—not just coat its surface. Then, in the “reaction” part of the process, the researchers ignited the hydrogel portion of the structure in a furnace between 700 and 1100 degrees Celsius, depending on the material. Since the melting point of all metals is higher than the combustion temperature of the hydrogel, the metal remains intact.
The heat not only removes the hydrogel, but also causes the overall structure to shrink as the hydrogel burns out, resulting in an even smaller metallic structure. With this process, in addition to pure metal, the team can 3D print metal alloys and multi-component metal systems, with a feature size of about 40 microns, or less than half the width of a human hair. .
“One of the exciting things is that it works with a wide range of metals just by slightly tweaking the ‘reaction’ phase of the process, and creates new opportunities for materials engineering at scale,” says Gallivan. micro. While developing the process, the team created 3D printed structures made of copper, nickel, silver, and various metal alloys.
“The hydrogel infusion additive manufacturing Greer, Ruben F. Professor of Materials Science, Mechanics and Materials Science, and Donna Mettler for Medical Engineering; Director of the Fletcher Jones Foundation of the Kavli Institute of Nanoscience; and is a pioneer in the field of structural materials at the nano and micro level.
The paper is titled “Additive production of microarchitecture metals through hydrogel transmission.”
Max A. Saccone et al, Microarchitecture metal additive manufacturing through hydrogel infusion, Nature (2022). DOI: 10.1038/s41586-022-05433-2
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California Institute of Technology
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