Mechanism Of High Speed Cutting Based On Split Hopkinson Bars

With the requirement of lightweight aerospace products,thin-walled structural parts have been widely used in aerospace field due to their light weight and high strength.The hollow cutting process is mostly used in the processing technology High-speed cutting has the characteristics of high processing efficiency,and has been wildly used in aerospace and other manufacturing industries.Ti-6Al-4V is typical difficult cutting material with excellent application characteristics.Therefore,the study of high-speed cutting mechanism of titanium alloy is key for the further development of high-speed cutting technology.In this paper,high-speed cutting experiments are carried out on a self-designed high-speed cutting platform.The mechanism of high-speed cutting of Ti-6Al-4V is studied by combining experiment and finite element simulation technology.The formation mechanism of sawtooth chips and the variety of cutting force in high-speed cutting are studied.The removal mechanism of chips from workpiece surface is studied.The influence of JC constitutive model parameters on sawtooth chips is also studied.Firstly,a high-speed cutting platform is designed based on the Split Hopkinson Pressure Bar(SHPB)device.The platform mainly includes support part,direction control part,tool holder part and acquisition part.Quick drop tool experiment is carried on the high speed cutting platform with synchronous pressure device by adjusting the position of incident bar and transmitted bar.Secondly,high-speed cutting experiments and quick tool drop experiments are carried out with high-speed cutting device.The experimental results show that the cutting forces increase with the increase of cutting thickness,and decrease sharply with the increase of cutting speed.When the chip speed is greater than 15m/s,the cutting force remains unchanged.The chips obtained by high-speed cutting are sawtooth chips.There are obvious shear bands in the chips,and the sawtooth degree becomes more serious with the increase of cutting speed.The increase of cutting thickness induces the distance between the shear bands increases obviously,but the sawtooth degree has no obvious change trend.There is grain elongation in the shear band of sawtooth chips,and no cracks and voids in shear band.Under SEM,the free surface of toothed chips is lamellar,and the increase of cutting speed and thickness will lead to the increase of lamellar spacing.There are dimples on the lamellae.With the increase of cutting speed,the dimples increase obviously.Therefore,the generation mechanism of sawtooth chips is more inclined to adiabatic shear mechanism.The hardness of adiabatic shear band is obviously higher than its vicinity.The hardness of adiabatic shear band increases with the increase of cutting thickness.Measurements of surface and subsurface hardness show that the surface and subsurface hardness increase with the increase of cutting speed and thickness.By observing metallographic structure on machined surface,the grain size of machined surface decreases obviously with the existence of plastic deformation.Finally,the accuracy of finite element simulation is verified by experiments,and it is found that the simulation results of chip shape and cutting force are very close to the experimental results.The variation of equivalent plastic strain and temperature in high speed cutting sawtooth chips is studied by finite element simulation.The influence of JC constitutive model parameters on sawtooth chips is studied by finite element simulation,and the influence of material properties on sawtooth chips is revealed.