Fabrication Of Nanotwinned Diamond Cutting Tool Through Femtosecond Laser And Mechanical Chemical Polishing

Single crystal diamond is widely applied in ultra-precision machining non-ferrous metals and nonmetals to acquire nano-scale surface roughness and ultra-precision surface.However,rapid wear,short tool life and bad surface quality for machining Si C/Al composite,single crystal silicon,spinel,et al.with single crystal diamond tool seriously restrict the development of ultra-precision manufacturing.Therefore,developing novel ultra-precision cutting tool of nanotwinned diamond(nt-D)with superior performance has very important scientific significance and application prospect.Aiming at providing theoretical and technical supports for developing ultra-precision cutting tool with high wear resistance and stable machining surface quality,this paper studied on the machining methods of femtosecond laser ablation and mechanical chemical polishing to fabricate ultra-precision nt-D cutting tool with nano-scale edge sharpness.The main research contents include the study on mechanism and technology of processing nt-D material,fabricating method of high-precision nt-D tool with femtosecond laser,the study on mechanism and technology of polishing nt-D tool by mechanical and mechanical chemical polishing and the cutting performance testing of nt-D tool.In terms of femtosecond laser processing nt-D surface,material removal mechanism and surface generation processed by femtosecond laser were studied.The ablation threshold of nt-D was calculated.Focused on beam wavelength,pulse repetition rate and pulse-shoot repetition rate,ablation parameters influenced on processing depth and width of micro-groove and roughness of plane surface was revealed.The influence of beam incident direction on processed surface morphology and quality was investigated.The formating scheme for precisely fabricating nt-D tool was finally comfirmed.Main factors influencing surface roughness,edge sharpness and material removal efficiency for fabricating nt-D tool were analyzed based on the tool formating scheme.The theoretical model of trochoidal trajectory was established,and the regularity of distribution of laser energy density was analyzed.Based on the optimal galvanometer-assist beam scanning trajectory and control of energy density distribution on machining surface,this study proposed process controllable scheme of femtosecond laser machining nt-D tool,which provided theoretical support for optimizing parameters to fabricate nt-D tool.The influence of femtosecond laser processing parameters on surface quality and material removal efficiency was studied based on laser machining experiments.The parameters for forming nt-D tool was optimized.A rounded-nose nt-D tool with micro-scale tip roundness,submicro-scale edge radius and surface roughness of tens of nanometers was finally well-fabricated.The fabricated nt-D tool with femtosecond laser needed to be processed to nano-scale surface roughness and high sharpness.Mechanical lapping was an important method for fabricating diamond tool.Therefore,the surface microstructure,chemical component and material removal mechanism after mechanical lapping were investigated.The influence of processing parameters on surface roughness and thickness of damage layer was analyzed.The mechanism of cutting edge generation for mechanical lapping nt-D tool was revealed.The main factor that restricted the edge sharpness was the falling off of nt-D grain.Therefore,to aquire the edge sharpness that suitable for ultra-precision cutting,the nt-D tool needed to be further polished by mechanical chemical polishing method.Mechanical lapping was suitable for semifinishing nt-D tool.Moreover,the equipment for lapping relief face of rounded-nose nt-D tool was designed in this paper.Regularity of rotary speed and swing frequency of tool tip influencing on the surface roughness of tool relief face was studied.Equipment of mechanical chemical polishing was established in this paper,based on the mechanical polished nt-D tool.The oxidant was choosen and optimized.The chemical mechanism of material removal for mechanical chemical polishing nt-D was analyzed.The influence of polishing parameter on surface roughness,material removal efficiency,thickness of damage layer and edge sharpness were investigated.Finally,the ultra-precision nt-D cutting tool with subnano-scale surface roughness,nano-scale thickness of damage layer and edge radius of 64 nm was successfully fabricated by mechanical chemical polishing.By cutting Si C/Al composite and spinel,the well-prepared nt-D tool was found to possess better wear resistance,impact resistance and cutting performance than single crystal diamond tool.