The Improved Design Of Cutting Tool To Restrain Delamination Of Exit In Helical Milling On CFRP

Carbon fiber reinforced polymer(CFRP)has many advantages,such as high specific strength and specific modulus,high corrosion resistance and good fatigue resistance,which are widely used in the field of aviation.In the process of aircraft manufacturing,a large number of bolt holes or rivet holes need to be machined on CFRP for assembly,and the quality requirements of the hole are usually high.However,CFRP has a layered structure,which has the characteristics of low interlaminar binding force.Excessive axial force in the process of hole making will cause processing damage such as delamination and tear at the exit of the hole.The main reason for the delamination is that the axial force is greater than the critical delamination force of CFRP.In this paper,in order to effectively restrain the formation of the damage at the exit of the hole in the process of helical milling on CFRP,the structure of the end edge of the tool for helical milling is improved,so that the center area with low cutting edge speed is not involved in cutting,so as to avoid the extrusion effect of the tool center on the material,so as to reduce the axial force in the process of helical milling,and finally restrain the formation of CFRP exit damage effectively.The main research contents are as follows:Based on the kinematic principle of helical milling,the undeformed chip and the source of axial force in the process of helical milling are analyzed,the formation mechanism of delamination at the exit of CFRP is analyzed,the velocity distribution of the end cutting edge of the tool in the process of helical milling is calculated,and the position where the cutting speed is still 0 is analyzed.The simplified model of critical axial force for helical milling of CFRP is analyzed qualitatively.The contribution of the tool end edge to the axial force in helical milling on CFRP is studied by experiments.At the same time,a method to restrain the delamination at the exit in helical milling on CFRP is proposed.In this paper,the end backlash angle of end milling cutter is introduced and its function in the process of helical milling is analyzed,the influence of the end backlash angle on the cutting state of helical milling is analyzed,the condition that the center of the tool end edge does not participate in the cutting is deduced:E_t<1.Furthermore,under this condition,the undeformed chip is simulated,and the correctness of the critical condition E_t=1 is verified by simulation,The main geometric parameters of undeformed chip under this condition are analyzed.At the same time,the cutting in and cutting out process of the helical milling is simulated.The influence of E_t value on the shape of the undeformed chip is simulated.The variation of the diameter range of the tool center and the angle range of the end edge not involved in the cutting with the E_t value are obtained.At the same time,the shape of undeformed chips with different process parameters is simulated under the same E_t value,and the influence of different process parameters on the diameter range of the tool center and the angle range of the end edge not involved in cutting under the same E_t value is analyzed.The test of helical milling was carried out on CFRP,the correctness that the center of tool end edge does not participate in cutting when E_t<1 is verified by observing the wear range of tool end edge.The axial force and the exit damage are analyzed when E_t<1,and the axial force test of helical milling on CFRP was carried out under different process parameters.The test results show that under this condition,the axial force and its fluctuation is reduced obviously,the delamination damage on exit of the hole is restrained effectively,and the outlet quality of helical milling on CFRP is improved obviously.