Optimization Design And Experimental Study Of Large Length Diameter Ratio Of Vibration Boring Bar

There are many parts need deep hole processing in aerospace,military,automobile and other fields,and the precision requirements for deep hole machining are also very high.The tool used for deep hole processing is easy to produce vibration during the cutting process because of the high suspension and low rigidity,which causes the quality of the workpiece surface to decline,and cannot meet the processing requirements,and even shorten the service life of the tool and machine tool.The structure of parts in aerospace,military and automobile is very complex,which leads to the dynamic characteristics of the workpiece system in the process of deep hole processing,which will have a great influence on the vibration of the whole cutting system.A constrained damping boring bar is put forward in this paper.The constrained damping structure can effectively improve the stiffness,natural frequency and damping characteristics of the tool,and analyze the influence of the designed tool and the stiffness of the workpiece on the stability of the whole cutting system.The main contents of this article as follows:Firstly,in order to solve the problems of deep hole processing,the design scheme of damping and boring bar based on laminated composite damping structure is put forward.Based on the complex stiffness method,the calculation model and its parameter expressions of the loss factor are established.Secondly,the dynamic model of the restraint damping boring bar is established.It can be seen from the expression of the maximum amplitude of modal vibration of each order that increasing the structural loss factor or increasing the natural frequency can effectively improve the vibration damping performance of boring bar.The influence of the shear parameters and stiffness parameters on the loss factor of the structure is analyzed.The theoretical optimization scheme of the loss factor parameter is put forward.On this basis,the theoretical optimization formula of the shear parameters and stiffness parameters is established,and the optimum thickness of the damping layer and the constraint layer is obtained.At the same time,the influence of the damping structure parameters on the first natural frequency of the boring bar is analyzed,and the thickness of the damping layer and the restraint layer when the natural frequency is maximum is obtained,which provides the theoretical basis for the design of the constrained damping and damping boring bar.Thirdly,on the basis of the designed cutting tools,the influence of cutting tools and workpiece on the cutting stability of the system is considered,and the dynamic model of the cutting process is established.The influence of the stiffness of the workpiece system and the stiffness of the tool subsystem on the cutting stability is analyzed.It is found that there is an optimal stiffness ratio between the tool and the workpiece that make the cutting chatter tends to be stable.Finally,the finite element simulation results show that the static stiffness of the constrained damping damper is improved obviously,the natural frequency is about 50 Hz higher than that of the ordinary boring bar,and the maximum vibration amplitude of the constraint damping damper is reduced by 65.1%.From the modal experiment results,the inherent frequency of the restrained damping damper is increased by about 41 Hz compared with that of the ordinary boring bar,and the damping ratio is raised nearly one times.Under the same cutting parameters and elongation(the ratio of length to diameter is 7.5),the stability of vibration-reducing boring bar is better than that of ordinary boring bar,and the surface roughness of workpiece is reduced by 61.4%.When the workpiece stiffness is fixed,the tool has an optimum stiffness value,which tends to stabilize the amplitude of the cutting vibration acceleration.