A team of researchers from the University of Twente in the Netherlands have developed a method for 3D printing metal microstructures made of pure gold. The technique being pioneered by the team uses a laser-based technology to deposit tiny droplets of metal to build up complex shapes.
The method is described in a recently published article in the journal Additive Manufacturing and is known as “laser-induced forward transfer” or LIFT. In slightly more detail, the process works by emitting an ultra-short laser pulse onto a metal film (we’re talking just a nanometer in width) which melts a tiny droplet of the metal in question. This droplet is then “ejected” onto its target and solidifies when it lands.
At this stage in the project, the team is using the LIFT technique to build structures out of copper and gold microdroplets. The copper droplets reportedly act as a “mechanical support” for the gold material. The process is capable of not only piling the tiny droplets on top of each other but also of making incredibly complex shapes, including overhangs.
For instance, the University of Twente researchers have 3D printed a helix measuring just a few microns in size out of pure gold. This structure has the potential to function as a mechanical spring and as an electric inductor at the same time.
“This helix is printed with copper around it: together with the helix, a copper ‘box’ is printed,” the University of Twente reports. “In this way, a droplet that is meant for the new winding that is printed, is prevented from landing on the previous winding. After building the helix, drop by drop and layer by layer, the copper support box is etched away chemically. What remains is a helix of pure gold, no more than a few tens of microns in size.”
In terms of applications for the LIFT additive manufacturing technique, the research team believes it could be used to 3D print micro components for electronics or photonics as well as for micromechanic devices and sensors for biomedical applications.
There were some challenges in developing the LIFT process. For instance, the researchers worried that the two metal types would mix at their interface after being ejected, which could compromise the end quality of the 3D printed structure. Fortunately, the process was devised so that mixing would not occur. As the team specifies, the way the structure it built results in a surface roughness of between 0.3 to 0.7 microns because the metal droplets are only a few femtoliters in volume each (roughly 10-15 liters).
Though the team is currently focused on printing with copper and gold, it says there is the potential to expand LIFT for other metal combinations as well.