Study on the influence of temperature uniformity on subsurface damage in laser-assisted turning of monocrystalline silicon

Monocrystalline silicon is a critical material for optical components and semiconductor devices. Low-damage ultra-precision machining of monocrystalline silicon is essential for ensuring the performance of optical systems and micro-electromechanical systems devices. Laser-assisted turning (LAT) is an energy-field-assisted machining method that enhances the machinability of hard and brittle materials. The thermal effect of the laser improves turning quality and extends tool life. However, due to the temperature gradient in the heating zone, traditional LAT processes cannot meet the machining requirements for complex-shaped monocrystalline silicon workpieces. In this study, we investigated the influence of cutting-edge temperature uniformity on sub-surface damage (SSD) in LAT and reduced SSD by homogenising the laser-energy distribution. Molecular dynamics (MD) simulations reveal that temperature gradients exacerbate SSD during material removal. Insufficient laser energy in low-temperature regions leads to cold cutting. Simultaneously, the flow of a large number of atoms from low-to high-temperature regions causes atom accumulation in high-temperature zones, resulting in stress concentration and more severe SSD. Under uniform temperature-distribution conditions, SSD is effectively suppressed. Transmission electron microscopy characterisation demonstrates that homogenising the laser-energy distribution reduces the SSD depth from 470 nm to 194 nm. Thus, the quality of LAT for complex-shaped monocrystalline silicon workpieces is enhanced. The SSD depth, reduced to less than half of that caused by traditional processes, significantly minimises the amount of material to be removed for the subsequent ultra-precision polishing. Therefore, the findings of this research can significantly improve the manufacturing efficiency of high-precision silicon components.