Dynamic Model And Reconstruction Method Of Magnetorheological Damping Support Fixture-Workpiece System

Aeroengine blisks and blades are the key and important workpieces with the features of complicated structure,thin-wall thickness,difficult-to-machine materials and so on.These workpieces are easy to deform and vibrate in machining,which cause strong time-varying characteristics in machining,low machining efficiency,workpiece accuracy and surface quality difficult to control.Therefore,How to control the strong time-varying response of the process system and ensure stable and efficient machining is the urgent problem to be solved in the field of thin-walled parts processing.In the view of those problems mentioned above,a dynamic modeling and reconfiguration method of magnetorheological damper supported fixture-workpiece system are proposed in this paper.The controllable damping support device design,fixture-workpiece system dynamics modeling,system configuration and damping support layout optimization,system dynamics characteristic reconstruction method are investigated in-depth,and experiments were carried out with the blades as the research object.The main research work and innovative contribution are as follows:(1)In controllable damping support device design,for obtaining the small displacement and high frequency response vibration suppression in milling of thin wall workpieces,a design method of squeeze magnetorheological damping support device used in machining is proposed,and the device has the characteristics of small displacement sensitivity,large output damping force,high frequency response performance and simple structure.Based on the analysis of dynamic characteristics of the thin-walled workpieces cutting process,the magnetorheological damping material is reasonably chosen and the device structure is optimized by magnetic field simulation.On this foundation,the dynamic model of the device is established.Then,the model parameters are identified by testing device performance of the device,and the model is evaluated.Test results show that the developed magnetorheological damping support device can realize the vibration response 0.01 mm and the high frequency response 1000 Hz,which meet the machining requirements.(2)In damping support fixture-workpiece system dynamic model,in order to investigate the system dynamics and interaction under strong time-varying conditions,the system of the thin-wall workpiece,clamping and locating element and adjustable damping support device is constructed by analyzing the geometric structure and machining characteristics of thin-walled workpieces,the natural frequencies and modal shapes of the system are calculated.Then,based on that,a fixture-workpiece system dynamic modeling method considering complex damping characteristics is proposed.Subsequently,the modal test method is used to identify the dynamic model parameters,and the system dynamic response is solved.Finally,cutting force mechanical model and stability prediction model considering complex damping characteristics of fixture workpiece system are presented.The models proposed provide a basis model for the process stiffness enhancement and dynamic characteristics reconstruction of fixture workpiece system.(3)In magnetorheological damping support layout optimization,considering the effect of fixture layout on workpiece dynamic response characteristic distribution,the static equilibrium condition of the fixture-workpiece system is analyzed,and the clamping constraint model of the thin-walled workpiece with damping support is given on the basis of considering the initial clamping configuration of the workpiece clamping and locating elements.Subsequently,the stiffness model of fixture-workpiece system under the action of damping support device is established.Then,the damping support layout optimization algorithm based on the stiffness distribution characteristics of thin-walled workpiece is proposed,and fixture system configuration is determined and verified by simulation.Results show that the damping support layout optimization method proposed in this paper can improve the system process stiffness,which can provide stable fixture configuration for the dynamic characteristics reconstruction of fixture-workpiece system.(4)In fixture-workpiece system dynamic characteristics reconstruction,due to fixture-workpiece system dynamic evolution caused by material removal,firstly,the modal evolution process of thin-walled workpiece in machining is analyzed and the initial modal parameters are obtained.Then,structural dynamic modification method is adopted to calculate the evolutionary process of the system stability diagram under different machining conditions.Subsequently,on this foundation,a novel method of fixture-workpiece system dynamic characteristics reconstruction for machining stability control is proposed,which can be used to calculate the control current magnitude of magnetorheological damping controllable support device for satisfying cutting requirement.By the control current,dynamic output characteristic of the device is adjusted,which realizes the system dynamics reconstruction to ensure machining stability.Finally,sheet experiments show that the method can increase the stability region obviously,and control the machining vibration response effectively.(5)According to the theory and methodology proposed in this paper,the experimental verification platform of magnetorheological damping controllable support fixture-workpiece system is established.Taking the testing blade sample as the object,the dynamic characteristics reconstruction method of the fixture workpiece system proposed is comprehensively validated.Based on the stability diagram,the dynamic properties of the fixture-workpiece system are reconstructed with the magnetorheological damping controllable support device by adjusting the current.Experimental results show that under the constant spindle speed and feed rate,stability region increases and the stable cutting depth is improved,which not only guarantee the surface quality,but also enhance machining efficiency.