Research On The Hole-making Quality Of CFRP/Ti Alloy Laminated Materials During A New Method Of Gyro Milling Process

Carbon fiber reinforced plastic(CFRP)and titanium alloy are widely used in aircraft manufacturing because of their excellent properties.Because its laminated form is a good combination of the excellent properties of the two materials,the two materials often appear in the laminated form in aircraft manufacturing,which is connected by bolts or rivets.In order to ensure assembly accuracy,two materials are usually pre-clamped together and drilled once.At present,helical milling is the most commonly used hole-making method.However,during the helical milling process,the defects such as dilacerations,delamination and fiber pull-out usually occur at the entrance of the hole and burrs usually occur at the outlet.Therefore,a new process of gyro milling is proposed in this paper.In which the milling cutter is tilted at a certain angle,and the milling cutter makes a conical pendulum motion around the central axis of the hole while turn on its axis,and feeds downward in the direction of the central axis of the hole,thus the required hole are processed.In this paper,the gyro milling and helical milling process are compared by theoretical calculation,and the material removal rate equations of each time period in the two kinds of hole making processes.The axial force trend of the two hole making processes and the hole exit and entrance quality were predicted by the material removal rate equation,and verified by test on CFRP and titanium alloy single layer plates.The results show that the gyro milling process can effectively reduce the axial force of the hole making,and the axial force of the hole is more gentle,which avoids the abrupt change of the axial force in the helical milling hole,therefore the hole exit and entrance quality has been improved.The kinematics of the gyro milling hole were analyzed and calculated.The equation of the end face of the tool and the velocity equation are obtained.The velocity zero point position of the tool end face is calculated by the velocity equation,and the parameter conditions for avoiding the velocity zero point of the tool end face are given.The milling ratio equations of the side and bottom edges of the gyro milling tool are obtained.It is found that the cutting ratio of the tool side and bottom edge is related to the hole diameter,the tool diameter and the tool tilt angle,and has nothing to do with the feed speed,revolution speed and rotation speed.On CFRP/Titanium alloy laminates,the hole temperature and hole wall roughness of gyro milling and spiral milling were compared by experiments.It is found that compared with spiral milling,gyroscopic milling can reduce the temperature of CFRP partial hole-making by 13.33%~40%,the axial force of hole-making by 75%~85%,and the roughness of hole wall by 15.88%~49.32%.Gyroscopic milling can reduce the temperature of part of titanium alloy by 14.29%~28.57% and the axial force of hole-making by 71.43%~82%,but the roughness of hole wall increases by about 1~6 times.On the CFRP/titanium alloy stacks,a single factor test was carried out to study the influence of processing parameters on the temperature,axial force and wall roughness of the gyro milling hole.It is found that the axial force,temperature and wall roughness of the hole increase first and then decrease with the increase of the tool revolution speed,and increase with the increase of the feed speed.With the increase of the rotation speed,the axial force increases,the CFRP part hole temperature increases,but the titanium alloy part decreases.The variation rule between the hole wall roughness and the tool rotation speed is not obvious in this test.