Adiabatic shearing and performances of milling 304 stainless steel based on cooling strategies of flood, LN2 and LN2+LCO2

During high-speed milling, stainless steel is prone to generating adiabatic shear bands in the cutting zone, which affects the cutting quality. The main factors causing adiabatic shear are high temperature and elastoplastic instability. An energy dissipation model for stainless steel milling was established and analyzed based on adiabatic shear. A series of flood and cryogenic cooling milling experiments with liquid nitrogen (LN 2 ) and LN 2 +liquid carbon dioxide (LCO 2 ) cooling were carried out. Simultaneously, an innovative research about the effect of LN 2 +LCO 2 on adiabatic shear was executed. The results show that the energy dissipation is mainly determined by the influence factors such as milling force and shear strength at the same milling parameters. Compared with flood cooling, the influence factors are all increased at LN 2 cryogenic temperature conditions, and the energy dissipation result is also enhanced. At 200 m /min, the temperature in the cutting zone of LN 2 +LCO 2 is below 60 °C compared with 400 °C of flood cooling. The formation of serrated chips is related to the brittle cutting characteristic at lower temperature. Meanwhile, the tool wear is obviously inhibited, and the machined surface is improved with a roughness of less than Ra 0.3 μm at v c = 150 m/min, which is lower than Ra 0.7 μm of flood cooling. Conclusion: due to the instantaneous cold brittleness of LN 2 and lubricating effect of LCO 2 , there is difficult to obtain the conditions at the shear zone for generating adiabatic shear bands, and the milling performances are improved at the same time.