Research On Milling Stability Of Thin-walled Parts Based On Multi-Frequency Solution And Its Parameter Optimization

Thin-walled parts are a kind of commonly used material in the field of mechanical manufacturing for its light weight and small size.However,the problems of deformation and chatter in the processing of thin-walled parts have been difficult to solve.Therefore,it is of great significance to study the milling force,dynamic characteristics,and surface quality in the processing of thin-walled parts.Meanwhile,how to improve the structure,processing methods and processing parameters of thin-walled parts to achieve ideal processing efficiency and effectiveness is of great value to the study.Aiming at the above problems,this paper establishes the milling force model for the milling of thin-walled parts.Basing on the mechanical model,the dynamics model of thin-walled parts milling is established by using multi-frequency method through the introducing of process system dynamics parameters.As for the problem of milling chatter of thin-walled parts,the suppression mechanism of the existing chatter suppression technology is studied through theoretical analysis and simulation.Afterwards,a peripheral milling surface integrity model was established according to whether considering chatter or not.Finally,each parameter is optimized by genetic algorithm.The main research topics in the paper including the following parts:(1)By analyzing the geometric of milling of thin-walled parts,a mechanical model of thin-walled part milling is established by using discrete-differential-integral method.The linear milling force coefficient model and the polynomial milling force coefficient model are used for specific tool and workpieces.Then compare two kinds of model with experiments to decide which model is better,and analyze the effect of various processing parameters on the milling forces in different directions.(2)The modal parameters of the milling process system are obtained through modal experiments and the introduction of relative transfer functions of the machine tool-workpiece system.Based on the above analysis,the multi-frequency method is used to analyze the stability of the milling system and is compared with the zero-order frequency method.Using time-domain simulation methods and experimental methods to verify the accuracy of frequency methods of chatter stability.According to the result of simulation and experiment of milling force and milling surface,it is proved that muti-frequency method is more precise than zero-order frequency.(3)For the chatter stability of thin-walled parts,various chatter suppression techniques have been analyzed and compared.Through modal analysis and stability analysis,the influence of the dynamic characteristics of the milling system on the stability is discussed.After that,the chatter suppression of the workpiece-fixture and tool-machine chatter suppression technology were analyzed.For chatter suppression of a variable-pitch cutter,the skew condition is changed due to different pitches,and vibration suppressed by changing the time-lag to suppress the regenerative effect.Simulations and experiments were then used to illustrate the suppression effect of a variable pitch cutter.(4)Z-map surface milling model based on coordinate transformation was established,and the surface morphology and surface roughness of different parameters were analyzed and compared.Then,basing on time domain simulation,the surface topography of chatter was established.Selecting the chatter processing parameters and the no-chatter processing parameters to establish simulation and experiment.The empirical formula of maximum milling force and surface roughness is then established according to experimental data and the maximum material removal rate and the optimal processing quality were targeted.Finally,the genetic algorithm was used to optimize the design variables.