| The optical domes made of hard and brittle materials such as spinel,magnesium fluoride,and sapphire have excellent mechanical and optical properties.The characteristics of high hardness,high temperature resistance,high strength and high transmittance make them widely used in national defense,aerospace and other fields.However,the production of optical ball dome is highly challenging due to the difficulties in processing brittle materials,low efficiency,and the complex structure of thin-walled parts,as well as the challenges in clamping.Therefore,it is crucial to improve the processing quality and efficiency of domes to meet the demands of optical dome production and applications.This paper focuses on the challenges encountered during the processing of optical ball dome.It presented a comprehensive design of a surface polishing equipment specifically tailored for ball dome,utilizing the spherical unfolding polishing method.To address the issue of complex clamping,a vacuum adsorption fixture structure was designed,and its stability in holding the dome was verified.The finite element method was used to analyze the dynamic and static characteristics of the machine tool structure,and to identify and optimize the structure of weak components.A machine tool error model was established based on the multibody theory,and compensation method was proposed to address errors caused by static deformation of each guide rail.The main content of the paper are outlined below:(1)In order to take into account both the processing efficiency and processing quality of the surface of the optical dome,the generating processing method of "two rotations + one swing+ micro-feeding" was proposed.Based on the required motion for processing,an overall structure plan for the machine tool was designed,and the overall design and three-dimensional modeling of the polishing machine for the surface of the domes were completed.The polishing workflow and main technical parameters for the polishing machine were established.(2)According to the structural characteristics of the domes,the clamping structure of the vacuum adsorption and the circuit of the vacuum adsorption system were designed,and the components of the system were selected and designed.Through theoretical calculation,the force state of the dome under the coarse grinding condition and the minimum vacuum negative pressure required were 0.01 MPa.It was verified that the dome will not slip under this negative pressure and the maximum working state.Workbench software was used to simulate the deformation of the clamping head model of the ball cover during the processing process.The simulation results showed that the deformation of the internal clamping head model was larger than that of the external clamping head model under the same parameters.It was simulated under the internal clamping head model that selecting 45 steel as the clamping head material resulted in smaller deformation,the deformation of the model increased with the increase of grinding pressure,and the vacuum negative pressure and wheel size had little effect on the model deformation.(3)A simplified finite element model of the polishing machine for the dome was established,and the dynamic and static characteristics of the machine tool structure under different processing conditions were analyzed.The maximum deformation of the machine tool structure under the maximum processing condition was found to be 15.92 μm,and the maximum stress at this time was 4.51 MPa,which met the accuracy and strength requirements of the machine tool.The natural frequencies and mode characteristics of each order of the whole machine were obtained through modal analysis,and the rib distribution of the column structure was optimized to improve the first-order natural frequency of the whole machine.After considering factors such as overall mass,first-order natural frequency,and deformation,Wshaped ribs were selected to reinforce the column structure.The optimized first-order frequency was increased to 89.8 Hz.(4)Based on the multi-body theory,the error source of the ball cover polishing machine was modeled and analyzed,and the error model of the kinematic chain from the workpiece to the polishing head of the ball cover polishing machine was established.According to the established error model,the influence of the static deformation error of each guide rail mounting surface on the precision of the end processing point was deduced,and the static deformation error generated was compensated by calculating the scraping curve and scraping amount of each guide rail mounting surface.It was proved that the compensation scheme can effectively improve the machining accuracy of the machine tool. |
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