| The core devices in aerospace,optics,microelectronics and other fields have shown development trends such as structural complexity,miniaturization,and high processing requirements to enhance their functional characteristics and reduce their size.Most of these devices use hard and brittle materials that are difficult to process,which also increases processing difficulties.For example,hemispherical resonators are typical complex structural thin-walled components and are core components of hemispherical resonant gyroscopes.The hemispherical resonant gyroscope has attracted wide attention due to simple structure,small size,light weight,high accuracy,high reliability,long service life,and strong impact resistance.It is the first choice for high-value space missions,showing a trend to expand from space to navigation,land,and individual combat systems.The hemispherical resonator is composed of a central rod and a thinwalled spherical shell,and its material is fused silica.Ultra-precision grinding is currently an effective method,but it is easy to interfere with the grinding wheel and cause machining failure.The hemispherical resonator processing quality directly determines the working accuracy and service life of the hemispherical resonator gyroscope.Hence,high-quality processing of hemispheric resonators is a bottleneck problem that limits the navigation accuracy and service life of hemispheric gyroscopes.Here,the hemispheric resonator is taken as an example.Through the combination of theoretical analysis and experiments,the key technologies in the ultra-precision grinding process of complex thin-walled components are studied in depth from the aspects of grinding equipment,grinding wheels and grinding process,providing the theoretical and technical basis for its high-quality processing.To provide the equipment foundation for ultra-precision grinding of complex thinwalled components,an ultra-precision grinding machine was designed based on process driving,kinematic and error models were established,the influence of the machine tool static characteristics on processing accuracy was analyzed,and the error characteristics of the machine were studied.The machine tool structure of tilting grinding wheel spindle and four-axis linkage motion scheme were designed.The modal and harmonious response characteristics of the gantry configuration and the T-shape configuration were compared and analyzed through finite element analysis,and the gantry configuration was adopted.According to the machine function,the structure was divided into four modules: machine bed,X-Y axis,workpiece table,and Z-axis.An error model that comprehensively considers structural parameters,installation errors,and kinematic errors was established,and the influence and action mechanisms of each error parameter on the complex component processing accuracy were systematically analyzed.Based on the analysis of static characteristics,a mathematical analysis model was established to study the influence of static deformation on processing accuracy.Finally,the prototype of the machine tool was established,and its feasibility was verified.To investigate the influence of kinematic parameters and electrical parameters on small ball-end grinding wheel on-machine EDM dressing accuracy and surface quality,through theoretical modeling and experimental methods the numerical model was built to evaluate the relationship between the kinematic parameters and dressing accuracy and explore the effect electrical parameters on grinding wheel profile accuracy and surface topography.The mathematical model of the influence of the kinematic parameters on the dressing accuracy established based on the screw theory shows that the errors affecting the grinding wheel dimensional accuracy mainly come from the errors related to the tool electrode,and the errors make the same contribution to the dimensional accuracy;the factors affecting the profile accuracy are the grinding wheel spindle radial runout,electrode spindle radial runout,and non-coplanar error in order.Experimental research shows that electrical parameters will affect the dressing profile accuracy and surface quality of the ball-end grinding wheel.According to the fitting function and sensitivity analysis between electrical parameters and profile accuracy,the open voltage affects the profile accuracy most,followed by duty ratio,and finally peak current,and frequency.For the grinding wheel surface topography,when the discharge energy initially increases,the protrusion height of the grit increases;when high energy is adopted,the surface is severely burned,the recast layer covers the entire surface,and the graphitization of the diamond grits occurs,which damage the grinding ability.To theoretically study the formation mechanism of the grinding marks and comprehensively analyze the effect of grinding parameters on the grinding mark characteristics,a 3D simulation model was established to quantitatively analyze the influence of speed ratio,feed speed,radial runout amplitude,grinding depth,workpiece diameter,and grinding wheel diameter on inclination angle,spatial period and residual height of the grinding marks.The ball-end wheel radial runout causes single-point grinding,and grinding parameters affect the grinding points distribution and grinding pit shape and further affect the grinding marks.The results indicate that integer part of the speed ratio mainly affects the circumferential grinding pit density,which will increase the circumferential pitch,spatial period,and residual height.While the fractional part can affect the residual hight,spatial period,and inclination angle.As the feed speed increases,meridional pitch,spatial period and inclination angle increase.When grinding wheel speed is high,the influence of radial runout amplitude and grinding depth on the residual hight is limited.There is a negative correlation between the residual height and workpiece diameter and wheel diameter.The grinding marks modeling method was verified by the experiments,and the grinding marks suppressing method was explored.To explore the ultra-precision grinding technology of the complex component,a mathematical model for solving interference and analyzing grinding area distribution on a ball-end wheel surface was established,the grinding trajectory was planned,and the grinding characteristics were studied.Through the established model,the influence of the grinding wheel spindle inclination angle on rotatable range of the C axis was investigated to optimize the inclination angle.The quantitative relationship between Caxis angular displacement and grinding area distribution and grinding wheel wear was explored,and then the grinding trajectory was planned.Based on the study of grinding area distribution,the grinding speed and maximum undeformed chip thickness were studied,when a ball-end wheel grinds the complex component.Grinding experiments of the complex thin-walled component hemispherical resonator were conducted with the on-machine dressed ball-end grinding wheel on the developed grinding machine tool.No interference occurred during the grinding process.The surface roughness Ra was improved from 0.6158 μm to 0.0385 μm,and the profile accuracy PV was improved from 4.5904 μm to 0.3374 μm,which verified the validity and rationality of the ultraprecision grinding machine,ball-end grinding wheel on-machine dressing technology,grinding marks suppression and interference analysis method. |
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