Review of hybrid methods and advanced technologies for in-process metrology in ultra-high-precision single-point diamond turning

Single-point diamond turning (SPDT) is a leading machining technology for advanced manufacturing of high-accuracy optical components characterized by their nanometric surface characteristics. By employing SPDT, optical surfaces with roughness down to 1 nm could be machined. However, in a purely mechanical ordinary SPDT procedure, different factors may influence the outcome of the process and significantly affect the quality of the diamond-turned optical surface. In the last few years, non-conventional machining technologies have been successfully implemented on the basis of traditional mechanical SPDT for optical surface generation. These non-conventional methods assist the purely mechanical SPDT process to improve the diamond machining performance and machinability of various optical materials. They attempt to eliminate the process disturbances that occur during mechanical interactions between the tool and workpiece in order to further reduce the surface roughness indicator. Recently, the application of hybrid SPDT methods in optical surface generation has emerged, in which more than one non-conventional machining technique impact the workpiece surface during the mechanical interaction with the diamond tool cutting edge. Compared with conventional SPDT solutions, in a hybrid SPDT method, superior results in terms of optical surface quality could be obtained. In addition, development of intelligent SPDT solutions for achieving the best possible results in optical surface generation is a novel approach. In an intelligent SPDT solution, in addition to the hybrid machining methods, automatic control systems and advanced on-machine metrology systems need to be implemented on the diamond turning machine platform. This may help further improve the quality of optical surface by continuously performing in-process error diagnosing and consequently conducting in-process tuning of the diamond cutting parameters and optimizing the machining conditions. In this review paper, recent advances in ultra-precision SPDT based on hybrid methods, associated metrology systems, and their process control systems are surveyed. In addition, the effect of developed various hybrid SPDT methods and influencing factors that may affect optical surface generation have been discussed. At the end, guidelines for further developments of intelligent SPDT platforms by using hybrid SPDT methods, automatic process control, and in-process metrology solutions are proposed.