Design And Cutting Performance Research Of The Ultrasonic Vibration Bi-directional Helical Milling Cutter For Machining CFRP

Carbon fiber reinforced plastics（CFRP）is an typically hard-to-machine material,which is prone to generate delamination,burrs and other defects during the helical milling of holes.The bi-directional helical milling method can restrain the damage of the outlet dispensing layer,reduce the dependence of hole wall quality on cutting parameters,and improve the surface quality at the exit of the hole.Ultrasonic auxiliary machining can change the movement trajectory of the milling cutter,so that the tool and the workpiece contact intermittently,which can reduce the net cutting time of the tool and extend the life of the tool.In order to improve the quality of holes,this thesis puts forward the processing strategy of bi-directional helical milling under ultrasonic auxiliary conditions and make deep research on the mechanism of production of helical milling damage and the mechanism of material removal under ultrasonic auxiliary conditions.Then the design and manufacture of CFRP bi-directional helical milling holes with gradual-removing reverse edge milling cutter under ultrasonic auxiliary conditions are carried out.According to the study has been done,this thesis carries out the finite element method comparison and experiment comparison of flat-bottomed reverse edge milling cutters and gradual-removing reverse edge milling cutter,and the specific contents are as followed:First of all,according to the cutting characteristics of CFRP materials,this thesis analyzes the mechanism of common damage caused by helical milling methods and puts forward the strategy of bi-directional helical milling under ultrasonic auxiliary conditions.Based on the motion model of cutting edges in the process of helical milling under ultrasonic auxiliary conditions established in this part,the influence mechanism that the axial vibration influences on the motion trajectory and cutting speed of the peripheral edge and end edge is indicated.Secondly,based on the mechanism of helical milling cutting,gradual-removing reverse edge milling cutter is designed,and by analyzing the shape of undeformed chips and the material removal mechanism under ultrasonic auxiliary conditions,the mechanism of material removal in the actual processing process of the tool is deeply studied.According to the research has been done,the grinding process of the gradualremoving reverse edge milling cutter is simulated and debugged by NUMROTO grinding simulation software,and the tool is grinded on the five-axis grinding machine.Then,the simulation model of 3D helical milling CFRP is established by FEM,and the simulation test of material with the gradual-removing reverse edge milling cutter and the flat-bottomed reverse edge milling cutter at reverse helical milling outlet is carried out under ultrasonic vibration conditions.Using this FEM model,the distribution law of cutting edge force,the dynamic change of material removal and the distribution of material stress near the hole wall are predicted and analyzed.Finally,the comparative test with the gradual-removing reverse edge milling cutter and the flat-bottomed reverse edge milling cutter of bi-directional helical milling CFRP under ultrasonic auxiliary conditions is carried out,and based on the experiment,the influence mechanisms such as cutting force,tool wear and hole quality in the reverse cutting process of the tool are analyzed.The results show that the wear of the peripheral edge on the gradual-removing reverse edge milling cutter is relatively light,the quality at the hole outlet is better and the tool life is longer.