Thermal stress crack initiation method of surface annular groove root of bar blanking

Abstract

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.

Description

technical field [0001] The invention belongs to the technical field of precision blanking of metal rods, and in particular relates to a method for initiating thermal stress cracking at the root of an annular groove on the surface of blanked rods. Background technique [0002] Metal bar blanking widely exists in various shafts, metal standard parts, internal combustion engine accessories (such as piston pins, tappets), cold extrusion, precision die forging and other material preparation processes, and its cutting efficiency and section quality will directly affect Manufacturing accuracy, production efficiency and economic cost of parts. The traditional blanking process mainly adopts lathe cutting and sawing machine sawing methods. The section of the blank bar is flat, but the blanking efficiency is too low. The shearing blanking method is widely used in industrial production, but the section of the bar stock produced by ordinary shearing blanking presents an obvious horsesho...

AI Technical Summary

Problems solved by technology

The shearing blanking method is widely used in industrial production, but the section of the bar stock produced by ordinary shearing blanking is obviously horseshoe-shaped, and the quality of the section is poor. It is necessary to increase the process of turning and flattening the section, which reduces the production efficiency and increases the production cost. waste material

[0003] In recent years, the low-stress bar precision blanking technology developed by using the prefabricated notch stress concentration effect and dynamic crack propagation method has made new breakthroughs in the metal bar blanking process. The circumferential direction proposed by Chinese patents 201320338632. Low-stress bending fatigue fracture precision blanking machines have achieved chip-free and material-saving production, but due to the long life of dynamic crack growth, the blanking efficiency still cannot meet mass production

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