CM- polishing process for free-form surfaces and targeted minimisation of SSD structures

• Applicant: Professor Dr. Jens Bliedtner
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 518666024

With the availability of the large-scale equipment "Intelligent free-form polishing center with at-line SSD measuring technology" in March 2022, the technical equipment prerequisite for the project was created. A key objective is the development of new types of polishing tools, which are to be used in particular as sub-aperture tools. In a first development step, the additive manufacturing of graduated tools is planned, in which the hardness gradient changes continuously from the center of the tool to the outside. Starting from the surface to be polished (arrow height profile and lens diameter), tool designs are created and the resulting hardness profile is simulated. In a second development step, the development of polishing tools with bonded grit is planned. The material design envisages a plastic matrix of thermoplastic (PU) in which an abrasive component with cerium oxide and a fine-grained support structure of zirconium oxide particles are admixed. The new polishing tool designs enable scientific research into a novel bonded-grain chemical-mechanical (CM) polishing process. The testing of CM polishing with bonded polishing tools, will initially be carried out in a deterministic polishing process on flat and weakly curved optical surfaces and will be specifically transferred to free-form surfaces in the course of the project. A further goal is to determine the achievable removal rates and micro-roughnesses with special consideration of the Mid-spatial frequency error. For the selected free-form surfaces, an optimization step is to be carried out with the aim of minimizing the Mid-spatial frequency defects. In the planned project, the direct coupling of the Optical Coherence Tomography (OCT) system with the polishing center is also planned. If the topological assignment of the optical surface to the measured and analyzed SubSurfaceDamage (SSD) structures is successful, it will be possible to draw conclusions about the origin of the crack-damaged zones. Furthermore, the development of an extended mathematical image evaluation analysis is planned, in order to be able to display SSD up to a depth of 3 to 100 µm on free-form surfaces and to classify these SSD structures.

• DFG Programme: Research Grants