In the "3D Matter Made to Order" cluster of excellence, researchers from the Karlsruhe Institute of Technology (KIT) and the University of Heidelberg are working across disciplines on innovative solutions and materials for digitally scalable additive manufacturing to optimize the precision, speed and performance of 3D printing. The goal of the research is to fully digitize 3D manufacturing and materials processing from the molecule to the microstructure. In addition to being funded as a cluster of excellence under the Excellence Strategy competition of the German federal and state governments, "3D Matter Made to Order" is funded by the Carl Zeiss Foundation.

Squaring 3D printing

The goal of most 3D printing processes is to print objects from plastic precisely, quickly, reliably and as inexpensively as possible. However, achieving fine resolution or good quality while maintaining high speed and reliability remains a technological challenge. A research association of three renowned institutes - the Karlsruhe Institute of Technology (KIT), the University of Heidelberg, and the Queensland University of Technology (QUT) - has recently come a great deal closer to squaring this challenge of 3D printing. He developed a laser printing process that can print micrometer-sized parts in a fraction of a second. The international team has now published the results of its work in Nature Photonics.

A new process is establishing itself

Because of its advantages, stereolithography 3D printing has recently established itself as one of the most popular additive manufacturing processes for plastics, both in the private sector and for industrial applications. Unlike the more familiar fused deposition modeling (FDM) process, in which printed pieces are created layer by layer from a meltable plastic, stereolithography involves projecting layers of a 3D object one at a time into a resin-filled container and curing them with UV light. However, conventional stereolithography processes are still too slow for high industrial requirements, and there is still room for improvement in terms of resolution. And this is where the light-sheet 3D printing used by KIT researchers comes into play. As a fast and high-resolution alternative, it is expected to meet even industrial requirements in the future.

3D Printing with Two Colors in Two Stages

In light-sheet 3D printing, blue light is first projected into a container, which pre-activates the liquid resin inside. In a second pass, a red laser beam then provides the additional energy needed to actually cure the resin. However, 3D printing can only print really fast resins that quickly return from their pre-activated state to their original state, because only then can the next layer be printed. Consequently, this return time dictates the waiting time between two successive layers and thus the printing speed. "For the resin we used, the return time was less than 100 microseconds, which allows high printing speeds," said first author Vincent Hahn of KIT's Institute of Applied Physics (APH).

Micrometer-sized structures in just the blink of an eye

In order to make optimal use of the speed advantage of the new resin, the researchers have also designed a matching 3D printer. In this printer, blue laser diodes first project the layers into the liquid resin at high frequency using a high-resolution display. A red laser, in turn, is formed into a thin "light sheet" beam and crosses the blue beam vertically in the resin. With this arrangement, the team was able to 3D print micrometer-sized parts in a few hundred milliseconds, the blink of an eye. But that's just the beginning, they say: "With more sensitive resins, we could even use LEDs instead of lasers in our 3D printer," says Professor Martin Wegener of APH. "Ultimately, we want to print 3D structures that are centimeters in size, while maintaining micrometer resolution and high printing speeds."

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