Research And Simulation On Mechanical Properties Of The Camshaft Milling Process

As a critical component of the internal combustion engine,the manufacturing precision of intake and exhaust cam profilet has an important influence on the characteristics of the valve mechanism.Because of the large length-diameter ratio,flexible bending deformation under cutting force is still a problem for integral camshafts machining.For the new type of camshaft outer cylindrical milling machine,intermittent milling force will also stimulate the vibration of workpiece,cutter and the machine tool,the cam surface processing quality couldn't be guaranteed.For solving the problem,this paper studied the cam lift table data processing method,static and dynamic characteristics of the camshaft during milling process,and explored the effect of the auxiliary support number on the cam machining precision.Firstly,noise analysis and smoothing about original data of the intake cam in the discrete lift data processing were carried out by using Johnson difference method and cubical smoothing algorithm with five-point approximation.Then cam profile curve fitting was executed using different methods including artificial neural networks,cubic spline interpolation,generalized extended approximation and N-order harmonic approximation with the processed data.It is concluded that the N-order harmonic approximation was the most suitable method by comparing the fitting error and the smoothness of the fitting curve acceleration.And then,the three-dimensional entity model of camshaft was established with the method aforementioned.Secondly,based on the analysis about milling force model of a single cam,the influence of milling force on the X-C axis position error of milling machine was analyzed.The deflection equations of canshaft rules under different support conditions were solved by diagrammatic multiplication method,transfer matrix method and singular function method.The results showed that the camshaft deformation at the same milling position reduced gradually by finite element model research with the increasing of support number,which was consistent with the theoretical data.Thirdly,the models of free bending vibration and forced vibration under excitation milling force of camshaft were established using the Euler-Bernoulli beam theory.Natural frequencies of the camshaft without support were worked out,mode shapes and the dynamic response of first-order in forced vibration were also graphed.According to the simultaneous segmentation method and Krylov function method,natural frequency equation of camshaft with support were established and then solved.Modal analysis,harmonic analysis and transient dynamic analysis of camshaft under different supporting conditions were investigated by using the finite element analysis,the results showed that the natural frequency of camshaft increased gradually and vibration response amplitude of camshaft reduced at the same position as the support number increased.It was concluded that the most appropriate auxiliary support number was 3 after comprehensive static and dynamic analysis.Finally,conclusions could be made that alternating milling force caused by current cutter speed would not stimulate itself sympathetic vibration with the results of modal analysis.The aforementioned research provided bases for improving the performance of milling machine and manufacturing precision of camshaft.