Fundamental Study On Laser-assisted Diamond Cutting Of Hard And Brittle Materials

Reducing diamond tool wear and improving machined surface integrity are the important issues to be resolved in the field of diamond turning.Based on the thermal softening characteristics,the laser assisted diamond turning(LADT)method can effectively reduce the hardness and improve the machinability of hard and brittle materials.Optic surface finishing requires material removal at nanoscale.However,the study of temperature field prediction and material removal mechanism in laser assisted nanometric cutting have not been thoroughly carried out.The negative rake angle tool can promote the highpressure phase transformation of hard and brittle materials,thereby improving the surface quality.However,the corresponding tool path generation and interference check methods have not been studied.Focusing on the above issues,the systematic study is performed on the typical hard and brittle material,binderless tungsten carbide(WC).Through theoretical analysis,the temperature field and the material removal mechanism during LADT process is successfully presented and deeply understood.Furthermore,newly proposed methods would enhance the controllability in the high-effective and high-quality finishing of hard and brittle materials.Main research contents in this thesis include:(1)Based on the Fourier-law,the workpiece cumulative temperature field during laser spiral scanning process is studied.The nanoscale constitutive model of binderless WC is obtained based on the high temperature nanoindentation tests.The finite element model of in-process-heat laser assisted cutting(In-LAC)is established with the Abaqus/Explicit.And the temperature field of workpiece and diamond tool are calculated and analyzed,thereby facilitating the selection of laser power and other machining parameters.(2)The binderless WC materials’ machinability improvement under laser heating is studied through taper cutting experiments.The In-LAC molecular dynamics(MD)model is established by considering the accumulated thermal effect and the laser in-process-heat thermal boundary condition simultaneously.And the influence of laser power density on polycrystalline WC material removal mechanism is revealed by numerical simulation.Results of MD analysis are remarkably consistent with the experimental results qualitatively,verifying the reliability of simulation model and analysis results.(3)Based on the self-developed laser assisted diamond turning system(LADT-α),orthogonal experiments are conducted to optimize the machining parameters of in-processheat laser assisted turning.Aiming at the inherent defects of the existing methods,the high effective laser assisted turning method is proposed,which could effectively prolong diamond tool life and achieve ideal surface quality on the binderless WC mould.(4)A universal tool path generation method,which caters to arbitrary rake angle tools and the steady X movement,and the corresponding universal tool interference check method are proposed.Based on the theoretical analysis,the tool path design software,named Nanopath is developed.And the machining experiment results indicate that the proposed methods can realize typical aspherical and freeform workpiece machining with roughness on the nanometric scale and a form accuracy of submicron level.Finally,the glass molding mould with ideal finish quality and form accuracy can be achieved based on the LADT-α system.