Mid-spatial Frequency Control for Automated Functional Surface Processing

Functional surfaces interact with surrounding substances, such as another solid, a liquid, gas, acoustic or electromagnetic waves etc., in order to achieve a required effect. Surfaces are increasingly required with complex forms and ever-increasing precision, can be very challenging to make. In particular, mid-spatial frequency (MSF) ripples are difficult to avoid for various reasons, but especially the changing misfit between a polishing tool as it moves across a complex workpiece surface.

Current surface processing techniques are limited in their ability effectively to control or remove MSF errors for the reasons: i) lack of the ability to conform to the complex working surfaces, including grinding and lapping; ii) low material removal rate, such as Magnetorheological finishing and fluid jet polishing; iii) high cost (typically for ion beam figuring); iv) constrains for the size of the workpiece, such as stressed lap polishing and stressed mirror polishing.

This thesis reports on the development of enhanced techniques, both to understand the formation of MSF errors on aspherical surfaces, and to mitigate them, increasing overall production efficiency. This has been achieved by:

1) Development of a novel stressed mirror technique providing a universal platform for aspheric experiments.

2) Results and analysis of kinetic simulations to understand the working mechanism of the non-Newtonian material under different stress conditions.

3) Developing a non-Newtonian tool, used in a novel way, to manage misfit between an aspherical workpiece and the tool surface. Peak-to-valley MSF error on an off-axis aspheric part better than 10 nm has been achieved.

4) Using bonded diamond pads, with various diamond sizes in a ‘grolishing’ (hybrid between grinding and polishing) procedure to achieve extremely high material removal rates (up to 267 mm3 /min), and control MSF errors 10 nm peak-to-valley, on flat and spherical surfaces.

5) Providing an aspherical surface after grolishing by a 3-microns diamond pad, with texture of sufficiently quality to be measured directly by an interferometer, which usually be achieved only after polishing.