Optimized tool path generation for fast tool servo diamond turning of micro-structured surfaces

Fast tool servo (FTS) diamond turning is a promising machining process for fabricating ultra-precision micro-structured surfaces which have already gained wide application especially in the optics industry. However, most research focused on designing different types of FTSs for better performance, including bandwidth, stroke, stiffness, acceleration, accuracy, etc. There is a lack of systematical tool path generation (TPG) for FTS diamond turning, especially from the influence of TPG on surface quality point of view. This paper presents an optimized tool path generation for FTS diamond turning of micro-structured surfaces with either analytical description or non-uniform rational B-spline description. The tool path is optimized from three aspects to ensure high precision form and nanometric surface finish. Firstly, the tool path is optimized by a stable tool nose radius compensation method, which is different from the conventional one, to reduce the form error caused by the tool nose radius. Secondly, the ideal machined surface profiles are simulated to predict the ideal surface quality, with which the cutting conditions and tool geometry can be optimized to ensure nanometric surface finish and avoid tool interference. Thirdly, the influence of the control dynamics of the machine axes on machined surface quality, which is ignored in conventional machining, was considered. As the FTS dynamics dominate the influence, it is controlled to be a desired dynamics which was then used to modify the tool path to minimize the form error in machined surface. Experiments were carried out to prove the effect of TPG on surface quality and the effectiveness of the optimized TPG method.