Study On The Mechanism And Surface Quality Of KFRP Ultrasonic Vibration Assisted Hole Machining

Kevlar Fiber Reinforced Polymer(KFRP)has high specific strength and high specific modulus,and has broad application prospects in the fields of aerospace,armor protection,and automotive industry.Due to the anisotropy and low interlayer bonding strength of KFRP materials,machining damage such as burrs,delamination,and tears can easily occur during hole making,seriously affecting the service life of the workpiece.In view of this,ultrasonic assisted machining technology is used to conduct research on high quality hole making for KFRP.The main research contents are as follows:(1)The kinematic models of conventional drilling and ultrasonic assisted drilling are established to obtain their motion trajectories under specific parameters during machining;Establish a drilling axial force model for the cutting edge and cross edge,analyze the influencing factors of the axial force based on the established axial force model,predict the trend of the axial force,and compare it with the experimental drilling force results.The predicted trend is consistent with the experimental results.Secondly,a critical drilling axial force model is established based on the theory of composite thin plates.The calculated theoretical axial force resulting in delamination is compared with the critical axial force analyzed by experiments,with an error of 6.8%.(2)According to the Hashin failure criterion for FRP materials,a KFRP simulation model was created to dynamically simulate the hole processing process.Comparing the simulated drilling force curve obtained with the experimental drilling force curve under the same conditions,the error is 18.1%,and the simulation results are relatively reasonable;Compared with the simulation results of conventional machining and ultrasonic machining,the axial force of ultrasonic machining is reduced.At the same time,ultrasonic assisted machining can suppress the defects of delamination and burr in the process of twist-drill drilling KFRP,and improve the quality of hole making.(3)Carry out comparative experiments on the machining of cemented carbide drill bits and PCD drill bits,compare the drilling axial force,drilling temperature,and surface quality of the two drilling processes,and conduct ultrasonic machining tests on an optimal basis.For the drilling axial force,the PCD twist drill is generally lower than the cemented carbide twist drill,and the drilling axial force decreases by 7.9%;For drilling temperature,PCD twist drill drilling temperature decreases by 29.3%;In terms of hole making quality,PCD twist drill can obtain better quality at the inlet and outlet.There are fewer burrs at the outlet of the hole,which plays a significant role in controlling delamination and other damage.PCD drill can obtain better processing quality of KFRP holes.(4)Conduct KFRP ultrasonic assisted hole machining experiments to explore the impact of process parameters on hole manufacturing,and measure axial force,temperature,surface morphology,and outlet delamination ratio during hole machining.The experimental results show that ultrasonic machining can significantly reduce the drilling force and the exit delamination ratio by 4.8% and 17.0%,respectively.The axial force and delamination ratio decrease as the spindle rotation speed increases or the feed speed decreases.The drilling temperature of ultrasonic machining is higher than that of conventional machining.The drilling temperature gradually decreases with the increase of feed speed,and presents a trend of first increasing and then decreasing with the increase of spindle rotation speed.In terms of the micro aspect of the hole wall surface,ultrasonic machining can significantly improve the cutting ability of the tool to cut fibers,reducing the roughness by 32.1%,reducing resin adhesion,making the fiber fracture smooth,and improving the hole making quality.Through the above research,the kinematics characteristics and material removal mechanism of ultrasonic assisted machining are analyzed,the excellent process characteristics of ultrasonic machining are clarified,the influence of the change of processing parameters on the drilling axial force,drilling temperature and outlet delamination ratio is studied,and the processing parameters of KFRP high-quality hole processing are optimized,which provides technical reference for high-quality hole making and processing of difficult to machine materials such as KFRP,and has good engineering application value.