A team of researchers from the University of Twente, The Netherlands, has established a process to Additively Manufacture structures of copper and gold by stacking microscopically small metal droplets. The droplets are made by melting a thin metal film using a pulsed laser.
In this method, a pulsed laser is focused on a thin metal film that locally melts and deforms into a flying drop. The researchers then carefully position thie drop onto a substrate. By repeating the process, a 3D structure is made. As an example, the researchers stacked thousands of drops to form micro-pillars with a height of 2 mm and a diameter of 5 µm. They also printed vertical electrodes in a cavity, as well as lines of copper. In effect, virtually any shape can be printed by smartly choosing the location of the drop impact.
In this study, the researchers used a surprisingly high laser energy in comparison to earlier work, to increase the impact velocity of the metal droplets. When these fast droplets impact onto the substrate, they deform into a disk shape and solidify in that form. The disk shape is essential for a sturdy 3D print: it allows the researchers to firmly stack the droplets on top of each other. In previous attempts, physicists used low laser energies. This allowed them to print smaller drops, but the drops stayed spherical, which meant that a stack of solidified droplets was less stable.
In their article, the researchers explain which speed is required to achieve the desired drop shape. They had previously predicted this speed for different laser energies and materials. This means that the results can be readily translated to other metals as well.
One remaining problem is that the high laser energy also results in droplets landing on the substrate next to the desired location. At present this cannot be prevented. In future work the team will investigate this effect, to enable clean printing with metals, gels, pastas or extremely thick fluids.
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