The focus in the study of metal cutting process and the core is the chip formation process. Hard cutting process of serrated chip. Dr k.f.koch and Dr p.fallbochmer thinks, influence of chip shape inhard cutting by the maximum chip thickness, when the chip thickness is less than 20 m is easy to produce chip, or the formation of serrated chip. Cause of formation of serrated chip is the main toolworkpiece material near the surface of the knife is squeezed and accumulation on the rake face,and continue to move forward in the chip cutting tool material break suddenly.

On the serrated chip formation mechanism has many famous assertion. In 1964 Recht proposedcutting shear failure model of the classical mutation stability, when the nominal stress true straincurve slope is zero, the positive effects of strain hardening rate of the local temperature changes in the negative influence on strength is equal to or greater than the strength of the material, the plastic deformation zone inside the cut produced mutation. Houzhen-bin of Oklahoma State University and rangako, 1and proposed the serrated chip formation in the process ofthermodynamic model, show that their experiments, the cutting speed and feed rate instability plays an important role in shear. Samiatin and Rab found that when the normal flow softening rate ofstrain rate sensitivity value ratio is equal to or greater than 5, the metal cutting process of non-uniform flow occurs immediately. Thermoplastic process instability (strain hardening and thermal softening) to cut the area, even in the absence of thermal softening effect, other mechanisms also can make the shear zone shear strength decreases obviously.