Research On Machining Technology Of Nanostructures Over Microsphere Surface Using The Force Control Approach

Inertial confinement fusion(ICF)experiment is one of the most important ways to realize controlled thermonuclear fusion on earth.It is similar to the evolution process of astrophysical supernova with external propagation of internal energy.Previous studies suggest that the surface quality of ICF targets directly affects the implosion performance.The defects on target ball surface will lead to hydrodynamic instability in the process of centripetal compression,where makes implosion of energy towards the weak parts and eventually brings the failure of ICF experiments.To this end,scholars propose to fabricate three-dimensional nanostructures on target ball surface for obtaining controllable modulation defects making use of simulating different sizes and shapes.At present,the preparation of various nanostructures on target surfaces are mainly realized by the methods of laser processing,micro turning and nano machining based on atomic force microscope.However,these existing processing technologies have definitely insufficiencies,such as undeterministic machining,simple nanostructures and small machining range.Therefore,the research on machining technology of three-dimensional nanostructures over microsphere surface using the force control approach was investigated from the aspects of theoretical modeling,machining mechanism and processing technology.The specific research contents include the following aspects:The study on nano machining mechanism based on micro force control between tool and workpiece was carried out.The theoretical models of relationship between normal forces and machined depths for different cutting tools were established.The experiments of machining nanostructures on the plane under constant normal forces control were implemented for verifying the feasibility of micro force control and accuracy of theoretical models.And then the influence of normal forces and other cutting parameters on machined depths was analyzed.A novel experimental setup for nanostructures machining based on the principle of microforce control was set up to realize the control of normal forces applied by cutting tools on the samples to be constant or periodic change during machining process.Under constant force control,the effect of normal forces,cutting depths and tool shapes on the surface formation of machined nanostructures was studied.TEM was used to analyze the difference of subsurface damage of grooves with different machined depths under micro force control.A control algorithm based on model predictive control framework was employed,and validated through numerical simulation that the machining system composed of piezoelectric tube and force sensor can track given periodic force signals fast and accurately.The effect of FIB processing parameters on the accuracy of machined nanostructures on diamond substrate was investigated.The optimal parameters for machining diamond material by FIB was obtained through experimental analysis,and the sinusoidal array structures with different periods and amplitudes were designed to realize the high-precision and high-efficiency manufacturing of three-dimensional nanostructures at the tip of diamond cutting tool.The simulation model of nanomachining with diamond structured tool under microforce control was established by molecular dynamics simulation method.The influence of the amplitude of normal force,cutting speed,workpiece material characteristics and tool shapes on the material removal form,subsurface damage and surface formation in nano scale was analyzed and verified by TEM experimental results.Under variable forces,the effect of processing parameters,such as normal forces,loading rate and machining speed,on the surface quality of three-dimensional nanostructures was explored for realizing high precision machining of three-dimensional periodic sinusoidal nanogrooves array structure.Taking the hollow thin-walled target ball used in ICF experiments as research object,the approach of microforces control for machining nanostructures on the surface of target ball was proposed.The key technical problems affecting nanostructure machining,such as target ball centering and cutting tool alignment,had been solved.Under constant force,the effect of applied forces,sample material characteristics and tool shapes on machined nanogrooves morphology was systematically studied.The three-dimensional sinusoidal nanostructures on different microsphere annuli were obtained by nanogrooves superposition,or by structured diamond cutting tool through single machining.Under variable force control,the influence of normal loads and target ball speed on the morphology of pits was investigated.Depending on the change of target ball speed and cutting tool trajectory,the fabrication of pits array with controllable adjacent distance on same annulus and controllable vertical distance between different annuli was finally realized over the global surface of target ball.