Research On Vibration And Wear Coupling Mechanism Of Large-pitch Turning Tool And Cutting Stability

Large-pitch threaded parts are used as the key components of CNC gantry mobile vertical turning and milling machines and CNC large-scale multi-station presses.It has the characteristics of large feed,deep cut and low speed in turning,which leads to unreasonable matching of cutting speed and feed speed,multiplication of cutting force,and serious vibration of process system.Under the coupling action of nonlinear multi-strong field,the chatter between the tool and the workpiece changes the contact relationship between the tool-workpiece friction pair,resulting in a dynamic change in its tribological system,which in turn causes the tool wear pattern to change.As a result,it is difficult to guarantee the stability of the large-pitch screw in the turning process and to finish the high-quality machining of the large-pitch screw surface,which has become the bottleneck of greatly improving the cutting efficiency of the large-pitch screw.In this paper,the coupling mechanism of vibration and wear and the cutting stability of the tool were studied.Based on the study of the dynamic characteristics of the large-pitch screw turning process system,the interaction law and coupling mechanism of the cutting tool vibration and wear were revealed.Through the prediction of the machining accuracy and surface quality of the workpiece,the cutting stability control method was proposed.It has important theoretical significance and engineering application value to ensure the high-quality machining of large-pitch threaded parts,perfect the design theory of turning large-pitch threaded tools,and promote the development of efficient cutting technology.The main contents include:Based on the concept of "generalized dynamic space" and expanding the spatial scale of dynamics research,the entire cutting system was studied as a whole.Considering the change in the actual working angle of the tool caused by vibration and the change in the thickness of the instantaneous cutting layer caused by the "quasi-regenerative effect",the instantaneous cutting force model of the large-pitch screw was constructed.The dynamic model of the large-pitch screw turning process system was constructed to characterize the dynamic behavior of the process system under the excitation of unbalanced operating loads such as cutting forces and machine tool spindles.Considering the influence of tool space position on the dynamic changes of the process system,simulation models of the stiffness field and modal field of the large-pitch screw turning process system were constructed.Based on the established frequency response functions of machine tool-tool and machine tool-workpiece,superimposing the influence of machine tool excitation and cutting force on large-pitch thread turning machining system,a comprehensive frequency response model of large-pitch thread turning technology system based on generalized dynamic space was constructed.The tribological behavior of the tool for turning large-pitch thread is closely related to its dynamic behavior.Based on the cross-correlation analysis of the tool vibration signal and the tool wear curve under the time history,the nonlinear relationship equation between them was established.Through the simulation model of large-pitch thread turning under the action of vibration,the causes of vibration frequency,amplitude affecting temperature field,stress field and tool wear were analyzed.The effects of vibration and wear patterns and wear evolution on the turning surface of large-pitch thread cutting tools and the interaction between cutting force and tool vibration were studied.A large-pitch thread turning tool wear model under the influence of vibration was constructed,and the coupling mechanism of tool vibration and wear was clarified.By optimizing the cutting edge structure and cutting parameters and suppressing the influence of vibration on wear,a method for controlling the cutting edge shape retention was proposed.Thereby,the wear of the cutting edge is uniform,and the life of the tool is improved.The machining accuracy and surface quality of the large-pitch thread surface directly affect the operational performance of the large-pitch screw.The large-pitch screw vibration mechanical model under the three-dimensional moving force in the workpiece coordinate system was established.The workpiece machining accuracy prediction model under workpiece self-excited and tool-workpiece coupled vibration was established,and the degree of influence of vibration on the accuracy of the screw's large and small diameters and half-angles of the left-and right-side threads were analyzed.A model for predicting the surface morphology under tool-workpiece coupled vibration was established,and the influence of vibration on the contour of the workpiece surface was analyzed.The relationship equation between the surface roughness and the characteristic value of the vibration acceleration signal was constructed,and the mechanism of the influence of vibration on the surface morphology during the cutting process was characterized.Through the special follow-up tool holder for large-pitch threaded parts,the overall rigidity of the workpiece was improved and the vibration of the workpiece was suppressed,thereby effectively improving the machining accuracy and surface quality of the workpiece.The cutting stability can ensure the high-quality creation of large-pitch screws.Through the reasonable planning of the turning process of large-pitch screw,the process of turning large-pitch screw was proposed.The artificial bee colony algorithm was used to optimize the multi-objective cutting parameters,and the cutting parameters were optimized based on the dynamic stability domain and the instantaneous cutting force model.Taking machining process(machining process,machining machine,machining tool and feed direction),cutting parameters,machining accuracy and machining surface consistency as optimization variables and turning stability as optimization objective,the turning stability control model of large-pitch screw was established.The reliability of the control method of the large-pitch thread turning process system was verified by the stability experiment of turning large-pitch thread.