The invention discloses a thermal stress
crack initiation method of a surface annular groove root of bar blanking. Before
crack initiation, an annular groove is prefabricated in the surface of a
metal bar, a deep cooling device is rapidly charged with
liquid nitrogen, and the temperature in the deep cooling device is kept between -196 DEG C and -130 DEG C. Then, the
metal bar is fed into the deep cooling device to be subjected to segmented rapid deep cooling. At the moment the cooling starts, due to the fact that the surface temperature is lower than the
core temperature, the surface of the
metal bar is sharply cooled and shrunk, large
stress concentration is generated at the bottom of the annular groove under the instant tensile stress and the notch effect, and a microcrack cluster is produced. After
crack initiation is ended, the metal bar is fed into a blanking
machine to be subjected to segmented blanking. The notch effect and the thermal stress function are utilized, dynamic cracks generated in the later blanking process can enter the expanding stage more rapidly, and the overall blanking efficiency is improved.