The footprint of the Fluid Jet Polishing process is determined by the shape of the nozzle as well as by the orientation of the slurry beam with respect to the local surface normal. Besides, no tool wear occurs and the footprint remains constant during the manufacturing process allowing shape corrections in a deterministic way. To that aim, FJP has been implemented on a CNC machine and applied for both shaping of previously polished aspheres and polishing of fine ground a-spheres. In this paper, results will be presented showing the application of FJP as a sub-aperture shape correction method. Besides, experimental data will be reported demonstrating FJP's capability of polishing previously fine ground surfaces. The wear rate depends on the sharpness of the abrasives and their kinetic energy. It can thus be adjusted by various parameters, among others the applied pressure, slurry concentration and abrasive sizes. In this paper, an additional process parameter is identified allowing the application of the same polishing compound for wear rates ranging from nanometers to micrometers. This large wear range is achieved by mixing a well controlled amount of gas into the slurry flow allowing the abrasives to travel at higher speeds.
This article presents the recent achievements with Jules Verne, a sub-aperture polishing technique closely related to Fluid Jet Polishing . Whereas FJP typically applies a nozzle stand-off distance of millimeters to centimeters, JV uses a stand-off distance down to 50 μm. The objective is to generate a non-directional fluid flow parallel to the surface, which is specifically suited to reduce the surface roughness [2, 3]. Different characteristic Jules Verne nozzle geometries have been designed and numerically simulated using Computational Fluid Dynamics (CFD). To verify these simulations, the flow of fluid and particles of these nozzles has been visualized in a measurement setup developed specifically for this purpose. A simplified JV nozzle geometry is positioned in a measurement setup and the gap between tool and surface has been observed by an ICCD camera. In order to be able to visualize the motion of the abrasives, the particles have been coated with fluorescence. Furthermore, these nozzles have been manufactured and tested in a practical environment using a modified polishing machine. The results of these laboratory and practical tests are presented and discussed, demonstrating that the CFD simulations are in good agreement with the experiments. It was possible to qualitatively predict the material removal on the processed glass surface, due to the implementation of appropriate erosion models [4, 5] in the CFD software.
Through single scratch experiments on glass, the transition from ductile to brittle mode grinding is analysed and the ductile regime dependent on load and coolant type is determined. The influence of different coolants on the grinding mode is discussed and certain manufacturing "tricks" used in the optical shop are explained. The results are verified by loose abrasive grinding experiments.
A variation on the fluid jet polishing (FJP) technique, arbitrarily named Jules Verne (JV), will be described in this article. Jules Verne is a glass processing technique that removes material due to the fact that the tool and the surface are in close contact, and a slurry moves in between the tool and the surface. This approach has both advantages and disadvantages with respect to the original FJP modus: it enables a feed-controlled machining process, but deeper lying areas are harder to reach. A simulation model will be presented that predicts the flow of the slurry in the Jules Verne setup, which is followed by the computation of the trajectories of the particles in the flow. Furthermore, experimental data will be reported demonstrating the feasibility of the JV idea. A model will also be presented simulating the interaction between the surface and the impinging abrasives at a microscopic level, enabling the prediction of the final surface roughness.
The possibilities of iTIRM, an in-process surface measurement tool, are explored in this research. Experiments are done to test the applicability for qualifying and optimizing finishing processes for optical surfaces. Several optical glasses, different polishing agents and ductile grinding are included in these experiments. It is concluded that iTIRM can be used for both mentioned applications but that it is, at least for now, an R&D tool only and not applicable in production.
UV curing plays an important role in the optical shop for cementing optics or for the fabrication of replicated optics. Material shrinkage is a common but unwanted effect during UV curing, because it causes stress and form modifications. In order to minimize these effects it is useful to measure shrinkage and surface changes that occur during the UV curing process. For replicated optics, shrinkage and form modifications are usually measured by comparing the replica to the mould geometry after the curing process has finished. In this paper, a measuring method is presented, which enables the observation of shrinkage and changes of the surface shape in situ. The surface of UV hardening material, in this case a commercially available optical adhesive, is monitored interferometrically during UV curing. This enables observing the material effects that cause stress and form modifications in real time.