Experimental Research On CFRP Holemaking With Ultrasonic Vibration Assisted Helical Milling

Carbon Fiber Reinforced Plastic(CFRP)composites are widely used in aerospace industry because of high specific strength,corrosion resistance,fatigue resistance and other excellent properties.As structural parts,CFRP composites are usually connected by holes,but as typical anisotropic difficult-to-cut material,cutting force and cutting heat have great influence on the quality of hole-making,which often leads to burr,tear,delamination and damage of machined surface.Therefore,it is of great significance to improve the quality of hole-making of CFRP composites for its further application in aerospace industry.In this paper,ultrasonic vibration assisted helical milling(UVHM)technology for CFRP composites hole-making is proposed,and the kinematics of the cutting edge in UVHM is studied.The cutting mechanism and hole quality of the UVHM are analyzed by the theoretical model and comparative test,and the influence of process parameters on the CFRP composites hole quality of the UVHM is studied.Firstly,based on the kinematics model of traditional helical milling(HM),the kinematics models of axial ultrasonic vibration assisted helical milling(A-UVHM),longitudinal and torsional ultrasonic vibration assisted helical milling(LT-UVHM)are established,including the trajectory of cutting edge,the speed,acceleration and effective rake angle of side edge,which can provide theoretical basis for the analysis of the hole quality of UVHM and the removal mechanism of materials.Secondly,the comparison tests of UVHM and HM for CFRP composites holemaking were carried out.The results show that the axial force of UVHM is reduced by9.0%-35.7% compared with HM.Because of the decrease of axial force,when machining a small number of holes,the delamination damage of UVHM is obviously lower than that of HM.The periodic trajectory,cutting speed and acceleration change the cutting angle between cutting edge and fiber and bring impact.The burr damage of UVHM is slight.When the fiber cutting angle is in 0°?45°,the phenomena of fiber pullout and debonding have been observed on the machined surface of HM.Due to the shear effect brought by vibration,the fracture of the fiber is promoted.The machined surface of the UVHM is relatively flat and smooth.In addition,the maximum effective rake angles of the A-UVHM and LT-UVHM are 112.1% and 192.6% higher than that of HM,respectively,and larger effective rake angle is helpful for material removal in cutting.Finally,the effects of processing parameters(spindle speed,pitch,tangential feed per tooth)on the cutting force and cutting temperature in the UVHM for CFRP composites hole-making are studied.The morphology,delamination,hole diameter and roundness of the hole entrance and exit were measured.Considering variation of cutting force and cutting heat,the influence of process parameters on the quality of CFRP composites hole-making in UVHM was analyzed.