Study On The Mechanism Of Ultrasonic Cavitation And Ultrasonic Vibration Combined Micro Drilling

Micro-hole parts are widely used in aerospace,shipbuilding,power,microelectronics and other important industries,such as aerospace inertial gyroscope instrument components,cooling holes of turbine engine blades and printed circuit boards.These microporous parts are usually made of corrosion-resistant,high-strength stainless steel and other materials.In traditional drilling process,it is very easy to have the problem of chip clog,tool premature break and poor quality of hole.Therefore,this paper proposes a combination of ultrasonic cavitation and ultrasonic vibration micro drilling method to optimize the micro drilling performance of difficult to machine materials.Through the combination of theory,simulation and experiment,the micro drilling process of 304 stainless steel is studied.The mechanism of the compound drilling is analyzed from the aspects of chip morphology,micro-hole quality and tool wear,and the mechanism of material removal and chip cutting is clarified.The main contents are as follows:(1)The ultrasonic vibration drilling process of 304 stainless steel is studied.the kinematics characteristics of ultrasonic vibration drilling are analyzed.The finite element simulation model of drilling is established.It is found that the chip curling of ultrasonic vibration drilling is large,and chip breaking is easier to achieve.Ultrasonic vibration drilling improves the cutting condition of tool edge and significantly reduces drilling force.Drilling experiments show that the chip of ultrasonic vibration drilling is small and easy to discharge micro-hole.The extrusion deformation of ultrasonic vibration drilling is small,and chip removal is smooth.The transverse edge of micro holes in ultrasonic vibration drilling is approximately circular and the hole burrs are small.Compared with conventional drilling,the ultrasonic vibration drilling force has decreased by 5.2%.(2)The ultrasonic cavitation micro drilling process for 304 stainless steel is studied.The conditions and influencing factors of ultrasonic cavitation field are analyzed.The calculation results show that the velocity of the cavitation micro jet is 380m/s,the water hammer pressure is 570 MPa,and the shock wave intensity is 424 MPa.The cone cavity structure of the ultrasonic radiation end is observed by high-speed camera,and its range can reach more than 10 mm.There is a cavitation bubble cluster at the bottom of the hole.In addition,the experimental results show that ultrasonic cavitation drilling significantly reduces tool sticking.Compared with the conventional drilling,the ultrasonic cavitation drilling reduces the aperture error by 8.5%?15.6%,the roundness error is reduced by20.0%?37.8%,and the pore wall roughness is reduced by 12.7%?18.6%.(3)The ultrasonic cavitation and ultrasonic vibration micro drilling process for 304 stainless steel is studied.Through the experiments of ordinary drilling,ultrasonic vibration drilling,ultrasonic cavitation drilling and compound drilling,it is found that the length of the common drilling chip is more than 10 mm,the ultrasonic vibration drilling chip is about6 mm,the ultrasonic cavitation drilling and the compound drilling are fragmented chips,and the chip length is from tens to hundreds of ?m.Common drilling force > ultrasonic vibration drilling force > ultrasonic cavitation drilling > compound drilling force,compound drilling reduces drilling force and improves tool life.The roundness error of composite drilling hole is the smallest and the burr is small.