20 Feb 2019
Fraunhofer ILT-led HoPro-3D project intended to produce finer polymer structures faster, with diverse applications.
But now scientists at the Fraunhofer Institute for Laser Technology (ILT), Aachen, Germany, say that their successful combination of stereolithography and multiphoton polymerization should enable rapid, high-quality 3D printing by laser.
They are developing a machine for high-precision, cost-effective 3D construction technologies using both methods. In November, 2018, Fraunhofer ILT and partners launched the project High Productivity and Detail in Additive Manufacturing through the Combination of UV Polymerization and Multi-Photon Polymerization, "HoPro-3D”.
Together with companies LightFab, Aachen, Bartels Mikrotechnik, Dortmund and Miltenyi Biotec, Bergisch Gladbach, the Fraunhofer ILT is developing a new machine for producing macroscopic polymer structures with a resolution down into the submicrometer range. So far, various separate processes have been available for this purpose: UV polymerization based on lasers, such as stereolithography or micromirror arrays, and multiphoton polymerization on a microscopic scale.
In the SLA process, a UV laser writes a two-dimensional structure in a resin bath, causing the photosensitive material to polymerize. The component is lowered step by step and a 3D structure is built up in layers. The build-up rate is well above 1 mm3 per second. Newer 3D printer use UV LED light engines and a Digital Light Processor chip instead of the scanner. This allows the exposure to be parallelized, thus increasing the build rate. Both methods achieve a maximum resolution above 10μm.
The multiphoton polymerization is suitable for constructing even finer structures. In this process, the necessary photon energy is generated by intense laser pulses with wavelengths in the visible or infrared range, with several low-energy photons virtually adding up to a UV photon. The advantage is the extremely high precision of up to 100 nm in all three spatial directions; however, the build rate here is only about 10 ?m? per second.
The project partners are now combining the DLP-based process with the MPP process and developing a machine with two selectable exposure systems for either high build rates or high precision. They use high-performance LEDs emitting at 365 nm wavelength and a DLP chip with HD resolution for lithography. The MPP module uses a femtosecond laser with a fast scanner and microscope optics.
“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,” commented 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, control software is being developed, which shall independently decide – on the basis of CAD data – when a change between the two sources makes sense. The bottom line is that this transition works smoothly and the structures can be built in a resin vat without having to change the photo resin. The project team is examining different materials and optimizing the process combination in detail.
Many components have a body that can be assembled quickly, but also certain structures that require high precision. The combination of processes allows, for example, optical function elements such as lenses or prisms to be integrated directly into a larger component with great precision. By this approach, complete collimating optics for reading optical information in analysis technology can conceivably be built.
Fields of application are manifold, but ILT says that "this machine should prove most interesting for the production of components used in biomedical analysis technology." Support scaffolds for 3D tissue models, micromechanical components or complete microfluidic systems are typical application examples for this process.
The HoPro-3D project is scheduled to run for three years and is coordinated by Fraunhofer ILT. The project is supported by the European Fund for Regional Development 2014-2020 (EFRE).