Dynamics And Stability Of High-speed Composite Boring Bars Considering The Internal Damping Of Materials

With the rapid development of precision manufacturing and continuous advancement of technology,high-speed boring technology with high precision and high efficiency has been widely used in the field of machining.High-speed rotating composite boring bars have emerged.The superiority of using a composite boring bar to replace the metal manufacturing boring bar is reflected in:it has high static stiffness,high damping and a very high specific stiffness,which can simultaneously improve the dynamic stiffness and basic natural frequency of the machine structure including the boring bar,and can be used for deep-hole high-speed machining.However,due to the high damping of the composite boring bars,it is imperative to study the influence of the internal resistance of the material on the dynamics and stability of the rotating composite material boring bars.Therefore,this article takes the composite boring bars considering the internal resistance of the material as the research object,and it has important theoretical and practical significance to model and analyze the stability of the composite boring bar cutting system.Based on the Hamilton principle and the Bernoulli-Euler beam theory,this thesis proposed a continuous distribution parameter dynamics analysis model for a composite boring bar with one end fixed and another end free.And the damping properties of the composite were introduced into the model.The Galerkin method was used to solve the complex bending vibration equation,and the characteristic equation of the composite boring bar was derived.The variation curves of the natural frequency,damping,and dynamic stiffness with the ply angle were obtained by numerical calculation,and the effects of the ply angle,layup configuration,and length-diameter ratio were analyzed.At the same time,the natural frequency-rotating speed curve and damping-rotating speed curve of the composite boring bars were obtained,and the effects of the ply angle and aspect ratio were analyzed.The taper parameter was introduced to establish the dynamic model of composite conical boring bars.Based on the resulting characteristic equation of the conical composite boring bars,the natural frequency and damping were obtained by numerical calculation.The effects of the fiber angle,length-diameter ratio,and taper ratio were studied.At the same time,the critical speed-taper ratio curve and the instability threshold-taper ratio curve of the composite boring bar are obtained to study the effect of the fiber angle and length-diameter ratio.The effect of the fiber ply angle,length-diameter ratio,and taper ratio on the critical speed and instability threshold was revealed.On the basis of the chatter model of Altintas et al.,the regeneration chatter analysis model of the composite boring bar with linear time-delay was established by introducing the rotating gyro effect of a composite boring bar.According to the cutting parameters and the dynamic parameters of the structure dynamic system of the machine,the transfer functions of the cutting system with the gyro effect were obtained,and then the formula for calculating the limit cutting depth was established.The variation curve of the limit cutting depth with the rotation speed was calculated by Matlab numerical simulation,and the effect of material,ply angle,length-diameter ratio and taper ratio on the limit cutting depth was analyzed.