A study of the laser milling process for polycrystalline diamonds

摘要

A comprehensive literature review into the current status of the technologies for processing difficult-to-machine materials has been conducted. It has revealed that very limited research has been carried out to investigate the pulsed laser milling process for difficult-to-machine materials like polycrystalline diamonds (PCD), and to understand the physics behind this process.An experimental investigation has been undertaken to study the feasibility of nanosecond-pulsed laser milling process for PCDs and to understand the process characteristics. Plausible trends for the various milling performance measures, such as material removal rate, surface roughness and subsurface thermal damage, with respect to the process parameters have been revealed.A computational model for single-pulse laser ablation process has been developed and solved using the finite element method to understand the heating/cooling and material removal process in laser ablation of PCD. A comparison between the model predicted and the measured ablation depths has been carried out and shown that the model predictions agree well with the corresponding experimental data. The simulation results have shown that surface evaporation dominates the material removal process when laser pulse fluence exceeds the ablation threshold for PCD. Diamond graphitization results in heat accumulation, which leads to higher evaporation rates; melting and ejection of cobalt takes place at smaller pulse energies, which increases the heat loss.The single-pulse laser ablation model has then been extended to the study of laser milling process incorporating multiple traverse scans. The model predicted depths and profiles of the milled pockets show a good agreement with the corresponding experimental data. A simulation study has been carried out to investigate the temperature evolution and the material removal process involving different milling conditions, which has provided an in-depth understanding of the effects of process parameters on the laser milling process.This study has demonstrated the capability of laser milling process for PCDs. The analysis of the material removal mechanisms in both single pulse ablation and laser milling process has provided an in-depth understanding of the physical phenomena involved. The work has formed a solid basis for further research in this avenue to bring laser milling of PCDs into practical applications.