Error Modeling And Prediction Method For Shaft Hole Precision Machining Of Thin-walled Box Part

High power density transmission box system has the advantages of compact structure,precise and efficient transmission,and is widely used in the transmission equipment of vehicles,ships,aviation,etc.It is easy to deform or vibrate in processing due to the box-shaped part structure with lower stiffness.Thus,the machining accuracy of transmission box shaft hole is difficult to control.At present,the research on the shaft hole machining mainly considers the lower stiffness of cantilevered slender toolbar and focuses on the hole cutting chatter behavior and its suppression technology.However,ignoring the coupling effect of the fixturing state and dynamic cutting force,as well as the influence of the uneven radial stiffness of the shaft hole on the shape and position errors of the box shaft hole precision machining will result in the shaft hole machining error being great and the qualified rate of finished products being low.Therefore,it is important in the theory and engineering to explore the generation mechanism of shape and position errors of the shaft hole machining and establish an accurate prediction model for the shaft hole fine machining,so as to improve the qualified rate and quality stability of the shaft hole precision machining.This paper focuses on error modelling and intelligent error prediction method for the thin-walled box shaft hole precision machining.It starts with the characterization of asperities random contact at the interface between the box workpiece and the fixture.An accurate prediction model of the box shaft hole position deviation in fixturing state is constructed.The formation mechanism of the box shaft hole machining error under the coupling effect of the box fixturing state and dynamic cutting force is analyzed.A dual-time-delay dynamic model of the thin-walled box shaft hole fine boring is established.And methods of intelligent error prediction and accuracy control for the precision machining error of the thin-walled box shaft hole based on a data-simulation drive model is proposed.The main research contents are as follows:(1)For the position error accurate prediction of the thin-walled box shaft hole caused by clamping deformation in thefixture with one plane and two pins locators,effects of the contact surface contour error and unequal clamping force action on the locating deviaton and clamping deformation of box workpiece are considered comprehensively.The two-parameter W-M fractal function is used to characterize random asperities contact at the clamping contact interface,then the equivalent normal stiffness of the clamping contact interface is calculated.And an accurate prediction model of the box shaft hole position error in fixturing state is constructed.It solves the problem that traditional elastic half-space model cannot exactly calculate the contact micro-deformation between two large planes.Simulation results have show that the proposed model prediction accuracy is more accurate.It lays a foundation for the shape and position error prediction of box shaft hole machining.(2)Aiming at the problem of the generating principle of box hole form and position error in process,the formating mechanism of box shaft hole machining error under the coupling effect of fixturing state and dynamic cutting force is deeply analyzed.A prediction model for the shape and position error of the box shaft hole machining considering the influence of the hole position deviation in fixturing state and the box wall and tool rod deformation caused by cutting force on the cutting depth is established.It has been to reveal the reason that the thin-walled box shaft hole machining position out of tolerance in theory,and lays a foundation for the research on the box shaft hole machining error control based on fixturing process optimization.(3)In order to solve the problem of surface topography prediction in finishing machining of the box shaft hole,a dual-time-delay dynamic model of the box shaft hole fine boring topography is established to simulate the cutting dynamic behavior of the hole fine boring,which has been considering the effects of uneven radial stiffness of the hole and periodic rotary cutting motion on the undeformed chip load area.It has explored the influence law of the toolbar deflection and box-wall deformation on the instantaneous undeformed chip thickness.Based on that,the relationship between the cutting parameters and the shaft hole forming surface is clarified,and the accurate prediction of the surface topography of hole finish boring is realized.The accuracy of the proposed dynamic model and surface topography prediction algorithm is verified by the box shaft hole fine boring tests.It provides a research basis for error control strategy and process parameter optimization of thin walled box shaft-hole.(4)For the problem of the error prediction and accuracy control of the thin-walled box shaft hole boring,an intelligent method is proposed to predict and control the machining error of thin-walled box shaft holes through a data-simulation driven model jointly trained with model-simulated “priori” data and the experimentally measured“posterior” data.The proposed method not only overcomes the structural defect that inaccurate prediction results of the box shaft hole machining error model constructed by several major factors,but also solves the problem that the training of intelligent prediction model is not sufficient due to a few “posterior” real data samples.The prediction accuracy tests of several machining error prediction models trained by different training modes,respectively,on the same measured “posterior” samples that did not participate in the training process are investigated.Test results have proved that the proposed error prediction model for the box hole boringing is effective and more accurate.Based on the presented data-simulation driven model,a more economical method for optimizing machining parameters and controlling boring precision for the shaft hole is developed.It provides technical support for quality stability control of precision machining of the thin-walled box shaft hole.