| With the development of aviation,aerospace,energy and other manufacturing industries,the surface quality requirements for milling thin-walled parts and complex curved parts are increasing gradually.The low stiffness of the workpiece and the low mechanical impedance of the slender tool are the fundamental reasons for inducing chatter when machining such parts.Chatter will affect the life of tool and machine tool,reduce the efficiency of processing,is restricted high performance milling jam problem.At present,the research on flutter is carried out from two aspects: on the one hand,the rapid and accurate analysis of milling stability;on the other hand,the research on how to better suppress flutter,and as soon as possible for engineering applications.This paper revolves around the problem of suppressing regenerative chatter generated during milling of parenchyma,which poses difficulties for kinetic modeling as well as suppression chatter due to its lower stiffness.This paper discusses and studies from building a kinetic model of milling,developing a stability analysis,and suppressing chatter by means of the spindle variable speed:(1)In terms of milling machining kinetic models.Previous studies have mostly focused on a two degree of freedom milling kinetic model,but during actual machining,the conventional milling kinetic model did not meet the requirements when performing stability analysis.The study of the milling system of three degrees of freedom is not perfect at present,and in this paper,a three degree of freedom kinetic model of the milling system was constructed by introducing an axial angle.(2)In terms of stability analysis.This paper uses a modified semi discrete method to predict the size of the milling process to stabilize the domain,and after solving the transfer matrices of the two adjacent milling processes by numerical integration into a finite time interval,the size of the characteristic values is predicted to stabilize the domain based on Floquet theory.The improved semi discrete method takes into account both the stability of the predicted trails tangential depths and also greatly improves the computational efficiency over traditional discrete methods.(3)In terms of suppression of regenerative chatter.In this paper,a spindle variable speed based method is used to suppress the regenerative chatter phenomenon during milling.The method of varying speeds of triangular wave and sine wave is proposed to compare the stable region size with that under constant speed working condition.And in combination with the acceleration of the machine spindle in real machining,the test protocol is optimized.The timevarying time lag is used to accurately obtain and optimize the discrete step size to improve the stability of machining with variable spindle speeds.Milled and machined thin pieces using five axis numerical control linkage machine.Real time monitoring of the milling force under two operating conditions of constant / variable speed by a spike dynamometer shank,the experimental results show that the milling force obtained under the variable speed working condition of the main axis is smaller than that under the constant speed working condition.Shows that the spindle variable speed is effective for suppressing regenerative chatter at the partial rotation interval and is able to improve the surface quality of the part.In this paper,the parenchyma structure is used as an experimental object,and the problems such as kinetic modeling,stability analysis and suppressed chatter are intensively studied through theoretical research,simulation as well as experimental strategies to optimize the mutual combination,so as to enrich the basic theory of milling kinetics. |
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