Scientists from Binghamton University’s Watson School of Engineering have used 3D printing to produce a reconfigurable liquid metal lattice hand.
Created by combining liquid metal with a 3D printed shell skeleton, the metal appendage would not look out of place as part of the shape-shifting T-1000 terminator. The novel hybrid manufacturing approach integrates 3D printing, vacuum casting, and conformal coating to produce a shape memory effect, which holds the lattice material in place within any pre-designed shell.
The technique gives the metal lattice recoverable energy absorption, tunable rigidity, and reconfigurable behaviors, and this lends itself to maintenance and repair applications in the aerospace industry, according to the Binghamton scientists.
Applications of the liquid metal lattice
Previous studies used shape memory polymers due to their intrinsic flexibility and ease of fabrication, which led to applications in soft implants, tunable wave control, and deployable components. In April last year, engineers from Rutgers University-New Brunswick, New Jersey, used 3D printing to produce flexible, lightweight materials using shape memory polymers.
However, according to the Watson team, shape memory polymers exhibit limitations such as slow response speed, low thermal conductivity and less energy absorption due to a lack of stiffness compared to Field’s metal. Advances in 3D printing meanwhile, have allowed for the production of lattices with more complicated geometries, hierarchical structures, and gradient design. The Binghamton scientists combined these technologies to create their unique liquid metal material.
The scientists produced four prototype products, including the eye-catching Terminator-like hand, by coating the material with different specification elastomer shells. Other prototypes included honeycombs, soccer balls, a ‘spider web’ of antennas, and the letters BUME (for Binghamton University Mechanical Engineering).
Utilizing additive manufacturing to make the lattice
The production process begins with the 3D printing of a shell skeleton out of rubber and metal using a commercial Digital Light Projector (DLP) printer. The skeleton is then filled with hot liquid metal lattice which is produced using Field’s alloy, a metal used as a liquid coolant in nuclear engineering due to its low melting point of 62oC. As the lattice is allowed to cool, it becomes more malleable, allowing it to be fitted into any shape or design. When the metal is heated to melting point, it takes a liquid form, and is ready to be reused and reshaped.
The lattice hand was refigured into two temporary shapes during testing, and almost 100 percent of the liquid metal was recovered after re-melting, leading the Binghamton scientists to anticipate that it could take the form of any gesture possible with a human hand. Testing uncovered manufacturing accuracy and casting/coating defects, but the scientists suggest these inconsistencies could be resolved in the future by utilizing existing processes such as laser-based additive manufacturing.
The prototypes displayed enhanced characteristics such as recoverable energy absorption, tunable shape and rigidity, and reconfigurable behaviors. Using Field’s metal also gives the parts a greater stiffness than polymers, and therefore to dissipate a lot more energy. Compared to other shape memory alloys, the liquid metal lattice materials demonstrated a much larger reversible strain range, due to their hard to soft integrated design.
These attributes give liquid metal lattice materials the potential to be used as recoverable protection or cushion layers in engineering and aerospace applications. “A spacecraft may crash if it lands on the moon or Mars with some kind of impact. Normally, engineers use aluminum or steel to produce the cushion structures, but after you land on the moon, the metal absorbs the energy and deforms. It’s over, you can use it only once”, said assistant professor Pu Zhang who co-authored the paper. “Using this Field’s alloy, you can crash into it like other metals, but then heat it up later to recover its shape. You can use it over and over again,” added the professor.
The Watson team is already building on this metal lattice research, including different structure types and improved coating materials, with the goal of producing a full liquid lattice robot.
Electronics applications of liquid metal 3D printing
Liquid metals are already used in a range of applications within the 3D printing industry, most commonly in 3D printed electronics. In April 2018, researchers at Oregon State University (OSU), discovered that combining Galinstan, a liquid metal alloy, with nickel, created a paste that could be 3D printed into stretchy, electrically conductive components.
Researchers from Beijing announced in Match 2017 that they had used 3D printing and injected liquid metal as a novel way to create functional electrical components, and published a paper on using the process to enable the creation of PCB boards.
In March 2013, researchers at North Carolina State University developed a new method for printing conductive metals at room temperature. They identified potential applications of the technology ranging from soft, stretchable, and shape reconfigurable analogs to wires, electrical interconnects, electrodes and antennas.
The Watson School of Engineering researchers’ findings are detailed in their paper titled “Multifunctional Liquid Metal Lattice Materials with Recoverable and Reconfigurable Behaviors” which was published in the Science Direct journal, and was co-authored by Fanghang Deng, Quang-Kha Nguyen, and Pu Zhang.
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Featured image shows the liquid metal lattice hand produced by scientists from Binghamton University. Photo via Zhang/ Binghamton University.