Influence of rake angle and nose radius on optical silicon nanomachining feed rate and surface quality: a modelling, prediction and optimisation study

Silicon is widely used in infrared (IR) optics due to its high transmissive ability at wavelength (λ) ranging from 1.2 μm to 6.0 μm. However, optical components of high quality require surface roughness (Ra) below or equal to 8 nm. Ultra-high precision single-point diamond turning of optical silicon has filled this gap due to enhanced chip removal, well-defined grain structure and low coefficient of friction of diamond tool. This study aimed at reducing optical silicon Ra value by manipulating both cutting parameters and tool geometry. The recommended Ra value of less than 8 nm was achieved with standard runs 5, 6, 8, 9, and 10 respectively. Also, high surface roughness due to high feed rate was noted to be greatly reduced at high tool negative rake angle and nose radius. Additionally, with increase in tool nose radius at 0° rake angle, poor surface quality resulting from high feed rate reduced.