Process Chain Modelling and Analysis for Computer Controlled Ultra-precision Polishing of Optical Freeform Surfaces

Computer Controlled Ultra-precision Polishing (CCUP) provides an enabling technology for machining freeform components with optical surface quality (i.e., nanometer surface roughness and sub-micrometer or accuracy). It can be used to machine difficult-to-machine materials such as optical glass which are not amenable for diamond machining. Due to the complexity of material removal mechanism in the polishing process, a clear understanding of the material removal rate (MRR) or influence function are much needed to better control the polishing process precisely. It is interesting to note that the surface generation cannot be generally be achieved by a single polishing process step. In other words, it is usually realized by a series of polishing process steps. The surface generation in the current polishing process step is affected by that of the previous polishing process steps. However, most of the previous studies focus mainly on individual polishing process while the effect of the interaction of each of different processes and steps has received relatively little attention. As a result, this paper presents a study of process chain modelling for computer controlled ultra-precision polishing of optical freeform surfaces. This includes a study of the relationships between the surface error components of different wavelength and the optical performance of the optical freeform surfaces. Error decomposition of the optical freeform surfaces and corresponding polishing process steps will be analysed to control these surface error components. The surface error components will be controlled by using different polishing process steps. A prototype process chain modeling and analysis system will be established based on the previous work of authors to analyze the effect of various factors affecting the surface generation in computer controlled ultra-precision polishing. Preliminary experimental work will be undertaken to validate the system performance. The success of the development of the process chain modelling and analysis system not only provides a better understanding of theory and science of materials removal mechanisms but also their effect on surface generation due to design and planning of the polishing processes. This makes the computer controlled ultra-precision polishing technology to be more predictable which can minimize the cost and time in conducing expensive and costly trial polishing tests to build the polishing process.