Abstract: The microstructure of chips in high-speed milling is analyzed, and the relationship between the cutting factors, chip formation, cutting force and surface roughness is established. It is found that the higher cutting speed is the less time heat spreads, the more heat in the shear zone gathers, the higher the possibility of occurrence of dynamic recrystallization in shear zone gets. A large amount of heat promotes the thermoplastic instability within the shear zone, the frequencies of the adiabatic shear band and the degree of serrated chip increase. The temperature and the cooling rate in adiabatic shear band are calculated, and it is found that deformation time is much lower than the cooling time. It is proved that dynamic recrystallization phenomenon occurs in high speed milling. The modeling of new developed J-C constitutive model which considers recrystallization softening effect is built; it has two expressions according to the different characteristics of material constitutive during critical strain values. Theoretical calculations proved that the developed J-C constitutive is more suitable than J-C constitutive.

Key words: chip morphology, dynamic recrystallization, high speed milling, the constitutive model, Ti-6Al-4V alloy