Study On Dynamic Behavior Of Geometrically Nonlinear Composite Boring Bar Considering The Effect Of Cutting Force Regeneration

High-speed boring technology characterized by high machining accuracy,quality and efficiency has been widely used in the field of mechanical processing.However,the chattering phenomenon of the boring bar is more likely to occur in the cutting process because the structure of the boring bar is a slender cantilever.In addition,the cutter rod structure in the cutting process also has the characteristics of geometric nonlinearity in essence.Composite materials exhibits a higher static stiffness capacity,a higher damping capacity and a higher specific stiffness capacity.The tool bar with high static stiffness,high damping and high inherent stiffness designed by composite material can eliminate the machine chatter.Therefore,this research work of dynamic behavior of geometrically nonlinear composite boring bar considering the effect of cutting force regeneration has very important theoretical and realistic meaning.In this thesis,the composite boring bar is taken as the research object.The main research issues are the cutting stability of composite tool bar cutting system and modeling theory and computing method of nonlinear dynamics.The main contents including:Based on regenerative flutter theory,flutter stabilities of single-degree-of-freedom and two-degree-of-freedom cutting systems were studied with frequency domain analyzing techniques.The general methods for calculating lobes of a single-degree-of-freedom and two-degree-of-freedom cutting system are established.Flutter frequency diagram,phase difference diagramand lobes diagram are obtained.A tool bar is assumed to be a plane bending cantilever beam.Nonlinearity of the tool bar originates from the non-elongation assumption.The material of the tool bar is assumed to be viscoelastic.It is described by the Kelvin-Voigt equation without considering the rotation of the tool bar.Nonlinear flutter equation of motion including regenerative cutting force of simple harmonic excitation is derived by the Hamilton principle.In order to obtain the closed-form solution of the vibration equation,the Galerkin method is used to discretize the partial differential equation of motion,and then the one-degree-of-freedom non-linear ordinary differential equation of motion expressed in the generalized coordinates is obtained.The numerical integration method is used to study the nonlinear flutter stability of the system.The multiple-scale approach is used to find the frequency response for the cutting process in primary resonances.A tool bar is considered to be Non-Planar bending cantilever beam.Considering the influence of higher-order bending deformation and external damping of the tool bar,it has two-dimensional regenerative cutting force with harmonic excitation.The nonlinear flutter motion equation of cutting system is derived by the Hamilton principle.The Galerkin method is used to simplify the flutter equation of motion,then the two-degree-of-freedom nonlinear ordinary differential equation of motion expressed in generalized coordinates is obtained.The numerical integration method is used to study the nonlinear flutter stability of the system.The multiple-scale approach is used to find the frequency response for the cutting process in primary and super harmonic resonances.Finally,the affection of parameters,such as the geometric dimensions(including length and diameter),damping,cutting coefficient,cutting depth,number of teeth,and cutting force amplitude and laying angle,on the non-linear lobes diagram,principal resonance response curve and super-harmonic response curve in boring process are analyzed by the numerical calculation.