Cutting Stability Analysis And Vibration Control Of A Damping Boring Bar

The boring bar is an important processing tool for hole machining.When performing deep hole machining,the cutting vibration often occurs due to the poor rigidity caused by a large length to diameter ratio.In addition to causing vibration waves on the machined surface,causing the roughness to fall short of requirements,severe vibrations can also cause a sharp increase in cutting force,increasing the risk of tool chipping,which will endanger the personal safety of the workers.In order to suppressing the vibration of the bar,active or passive vibration damping technologies can be used.Among them,the active vibration damping technology is well targeted but has good low robustness due to the addition of electrical components such as sensors and actuators.In contrast,although the passive vibration damping technology is not as effective as the active vibration damping technology,but it is more applicable in the application due to its high robustness.Through reasonable parameter design,the passive boring bar can suppress the vibration significantly in a wide range of excitation frequencies,which makes it become a hot issue for a large number of scholars.This paper also focuses on the stability and vibration control of passive damping boring bar with a vibration absorber,in the hope of obtaining a better vibration suppression performance and providing theoretical basis and guidance for the industrial production and application of the damping boring bar.At present,linear system modeling is often used for the research of damping boring bar,but in order to facilitate the calculation,the model has been greatly simplified in most studies,which makes the theoretical model and the real model have a large gap.In addition,the research on the dynamic vibration absorber?DVA?is mainly focused on the proposal of the new structure.Few scholars have clearly pointed out the specific implementation method of the optimal parameters of the dynamic vibration absorber and analyzed the influence of the structural parameters,which makes the existing research difficult to guide real processing.Based on the Jiangsu Provincial Graduate Student Innovation Program?KYLX16₀186?,this paper conducted the study on cutting stability and vibration control for a damping boring bar with a dynamic vibration absorber and obtained some meaningful conclusions.The research results have important theoretical significance and practical value for the vibration control of the damping boring bar.The main research contents and innovations of this paper are as follows:?1?A linear model of the damping boring bar was established,and the comparison research of the vibration characteristics between the boring bar with and without DVA was conducted.The vibration amplitude ratios of the boring bar under specific frequency ratio conditions are studied.The influence of the stiffness and damping of the DVA on the vibration amplitude ratios of the boring bar are studied in different frequency ratio ranges.The stability analysis of the boring bar flutter is carried out,and the closed-loop system with time-delay characteristics is established.The influence of the negative real part of the transfer function on the limit cutting width is studied.According to the flutter stability,the parameters of the boring system are optimized,and a comparison study between the bimodal equal optimization method and the flutter stability optimization method is carried out.?2?A nonlinear model of the body of the bar was established.The relationship between the amplitude-frequency characteristics and the nonlinear parameters is studied.The forward and reverse frequency sweep analysis of the nonlinear model is conducted to simulate the start up and shut down phases of the machine.The calculation results of the nonlinear model can more fully reflect the vibration characteristics of the bar.The double nonlinear system modeling of the damping boring bar is carried out by considering both the stiffnessnonlinearity of the bar and the DVA.The vibration damping principle of the boring bar with nonlinear stiffness is studied.The influence of the damping and stiffness parameters of the nonlinear DVA on the vibration of the bar is studied.The selection criteria of the damping coefficient,the primary stiffness coefficient and the cubic stiffness coefficient of the DVA were found.?3?The stiffness characteristics of the DVA are studied.Three kinds of rubber bush connecting ways are proposed.Among them,the fixed condition and contact condition are studied in detail.For the fixed condition,according to the constitutive relationship of the rubber material,the calculation formula of the dimensionless radial stiffness coefficient of the rubber bush was obtained.The finite element analysis of the radial stiffness of a special case was conducted to find the relationship between the radial stiffness and the length,inner diameter and outer diameter of the rubber bush.For the contact condition,the radial stiffness of the rubber bush with and without pre-compression was conducted.The loading process of the rubber bush during the installation of the DVA was studied,and the changing law of the radial stiffness of the rubber bush under different chamfers and the different pre-compression conditions were obtained.The experimental study on the radial stiffness of the DVA is carried out.The influence of various structural parameters of the rubber bush on its radial stiffness is obtained.The radial stiffness of the DVA is predicted by the neural network.?4?The damping characteristics of the DVA are studied.The damping recovery force model is established and the relationship between the damping oil viscosity and the equivalent damping is derived by using the relationship between the damping coefficient of the damping oil and the Reynolds number.The fluid simulation of the damping oil was carried out,and the force-displacement hysteresis curve of the damping oil was obtained.Several typical states of the oil flow were observed and the experimental study of a special case was carried out on the test platform.The simulation model is used to conduct a series of studies of the structural parameters,and the influence of the length,inner diameter,outer diameter,oil pressure and excitation frequency of the damping oil on its damping value is obtained.Three kinds of nonlinear damping grooves with spiral arrangement,in-line arrangement and staggered arrangement are designed to increase the damping effect.The effects of these three structures on the damping value of the DVA are studied.?5?The dynamic response experimental study of the damping boring bar is carried out and the time domain attenuation curve is obtained under different stiffness of the DVA.On the vibration platform,the frequency sweep experiments were carried out under three different axial compressions of the DVA.At the same time,the parameters obtained by using the bimodal equal optimization method and the flutter stability optimization method were selected for the frequency sweep experiment,and the experimental results were compared with the theoretical calculation results.The cutting experiment of the damping boring bar was carried out on the machine,and the experimental cutting force was compared with the theoretical analysis.In the experiment,the cutting force and moment corresponding to the stable and unstable cutting states were observed.The stable and unstable cutting profile of the damping boring bar was obtained by changing the axial compression of the DVA and the frequency ratio,which can provide a basis for selecting parameters of the damping boring bar in engineering processing.