The Aachen research campus DPP offers its partners from science and industry a place for joint, interdisciplinary research. The seventeen current research projects, known as sprints, focus on using light as a tool for industrial production and digitalizing process chains. Their vision is to manufacture virtually any component from digital data using laser radiation – in other words, digital photonic production. With this goal in mind, the partners are developing solutions for the entire production chain. And since all activities literally take place under one roof, the DPP produces results suitable for industrial use within a short period of time. The Fraunhofer IPT is currently working on four of the seventeen research projects.
Structured films are nowadays produced in so-called roll-to-roll processes: The desired structure is embossed into a continuous plastic belt via a negative roll. This roll is usually heated during the process with continuous, large-area heat sources. However, the infrared heaters frequently used have some disadvantages. For one thing, energy efficiency is very low because the energy is emitted in a wide spectral range. Secondly, the temporal and spatial resolution is sluggish and cannot be controlled selectively.
Vertical Cavity Surface Emitting Laser (VCSEL) beam sources allow process heat to be precisely introduced spatially and temporally and controlled as needed. VCSELs are small lasers that are assembled in arrays and can be controlled individually, like the pixels of a screen. The small lasers are very energy-efficient because they have a narrow wavelength spectrum and the arrangement as an array enables spatially and temporally individualized heating.
The goal of the subproject is to use VCSEL lasers as a heat source in continuous roll-to-roll processes to significantly expand the range of materials that can be processed and geometries that can be molded.
Non-destructive, non-contact quality control of laser structured components poses a major challenge, especially for small structure sizes. Common processes for surface characterization either require long measurement times (e.g., for point-measuring processes or tactile measurements), or the resolution is insufficient to detect small structural changes in both lateral and axial directions.
As a non-destructive, interferometry-based measurement method, optical coherence tomography (OCT) combines fast data acquisition with high spatial resolution. However, there is still potential for optimization here as well.
This sprint aims to optimize the resolution of OCT, which, within so-called ultrahigh-resolution OCT (UHR-OCT), improve the imaging of structured components with structure sizes from 1µm up.
In laser structuring, the structures to be created are usually read into the CAM system as grayscale images. This generates large amounts of data since high-resolution images are necessary to enable clean processing. In addition, when the structures are transferred to three-dimensional objects, they are always distorted and require extensive processing.
In contrast, in the analytical description, the surface structure is represented as a formula. Here, the size of the data set does not depend directly on the resolution, but only on the size of the mathematical formula and the number of variables of the structure to be described. The method allows users to construct a resolution-independent, distortion-free model of the structures and enables them to calculate the processing data in near real-time.
Sprint Team 14 is researching how to convert the analytical description models into so-called procedural structures for laser beam structuring. Small programs are required so that the manufacturing systems can process these procedural structures. These so-called real-time services require a technical environment for monitoring and controlling the laser structuring processes. Thanks to communication technologies at the RWTH Aachen Campus, these real-time services can be executed on a high-performance cloud computer and sent wirelessly to the manufacturing plant through 5G infrastructure.
The goal of the subproject is to use procedural structures to make the laser scribing process more efficient and to demonstrate the necessary infrastructure.
Additive manufacturing can incorporate sensor technology during the building process, a distinct advantage. One such option is hair-thin, movable fiber-optic sensors that use interferometry to detect even the finest changes in length in the component. This method can be used to measure component temperature, strain and stress.
Sprint Team 18 is developing a manufacturing strategy for the laser powder bed fusion (LPBF) process to directly integrate the fiber sensors while components are fabricated. To do this, the team is identifying appropriate fiber types, processing strategies, and geometry elements to position the fibers in the component. The researchers then validate the manufacturing success by measuring the fibers in unloaded and loaded real-world use.
The aim of the sprint is to develop how to monitor components using sensor technology over a long-term. Integrated into components, the sensors can determine the static or dynamic load live to indicate cracks and local stresses.
The joint project "DPP-Open - Research Campus Digital Photonic Production Open-Know-how-Pool" is funded by the BMBF in accordance with the German government's high-tech strategy. Funding program: Research Campus - Public-Private Partnership for Innovation
Project Management Jülich (PTJ)
Funding phase 1: 10/2014 to 9/2019
Funding phase 2: 4/2020 to 3/2025