Fraunhofer ILT researchers are looking beyond the current limitations of polymer 3D printing by developing a new AM process that combines stereolithography and multi-photon polymerization. The innovative technology could allow for fast 3D printing rates without sacrificing precision.
The project, called “High Productivity and Detail in Additive Manufacturing through the Combination of UV Polymerization and Multi-Photon Polymerization,” or HoPro-3D for short, launched in November 2018 in collaboration with LightFab GmbH, Bartels Mikrotechnik GmbH and Miltenyi Biotec GmbH. The three-year project is supported by EU and German funding.
The process being developed combines two disparate AM processes to produce macroscopic polymer structures with sub-micrometer resolution. Though a number of processes have been used to the same end—including SLA, DLP and MPP—existing systems have remained limited in terms of either print rates or precision.
For instance, in SLA and DLP processes, which use UV laser and UV LED lights, respectively, build rates are fairly high. In the case of SLA, print speeds exceed 1 mm³ per second, while DLP exposures can be even more rapid. The setback with these technologies, however, is resolution. Both processes can achieve a maximum resolution above 10 μm.
On the other hand, multi-photon polymerization is capable of printing finer structures, with precisions of up to 100 nm in all three spatial directions, but suffers from slower print speeds (only about 10 μm³ per second).
By combining DLP and MPP—which is undoubtedly less Frankensteinian than one might imagine—the researchers and their partners have come up with a machine that offers two exposure systems for high build rates or high precision. The hybrid process uses high-performance LEDs emitting a 365 nm wavelength and a DLP chip with HD resolution for lithography, as well as a femtosecond laser with a fast scanner and microscope optics for the MPP module.
“The advantage lies in the interplay between the two procedures: Depending on the need, we intend to switch between the exposure systems in the process,” said Dr. Martin Wehner, HoPro-3D project manager at Fraunhofer ILT. “The challenge we face is in process control. The concept has been developed, currently an appropriate machine is being built.”
In addition to the hardware, the team is also developing control software which will independently decide if and when a change between the two modules makes sense, depending on CAD data. The goal is to offer a single platform that allows for the seamless transition between both technologies, without the need to change the photo resin material. Presently, the researchers are investigating different materials and optimizing the combined process.
The combined AM technology could be used for various applications, most notable of which are in the field of biomedicine. For example, it could be used to produce support scaffolds for 3D tissue models, as well as to make micromechanical components and complete microfluidic systems.
Notably, the unique combination of technologies could enable optical elements, such as lenses or prisms, to be printed directed into larger components. In other words, it could allow for complete collimating optics for reading optical information in analysis technology to be built.