Simulation analysis of the effect of tool geometry in diamond turning of KDP crystal

Potassium dihydrogen phosphate (KDP) crystal is one of the most difficult-to-machine optical materials owing to its inherent characteristics of low hardness, high brittleness and easy deliquescence. This paper presents an approach using numerical simulation combined with machining experiment to investigate the effect of tool rake angle on the machining mechanism of KDP crystal. A 3D model with the use of smoothed particle hydrodynamics (SPH) is employed to simulate the diamond turning process of KDP crystal. Simulation results including the stress distribution state and the interface pressure between diamond tool and workpiece are analysed to reveal the underlying mechanism of different tool geometries in machining. Moreover, machining experiments corresponding to the simulation parameters are performed on the tripler plane of KDP crystal. The experiment and simulation results show that the tool with large negative rake angle is conducive to obtaining a crack-free machined surface and suggested for the diamond turning of KDP crystal. It is also proved that the SPH method is a reliable method to investigate the machining mechanism of brittle materials because of the good consistency between experiment and simulation results.