Failure Analysis And Numerical Simulation Of Cold Ring Rolling Mandrel

Cold ring rolling is an advanced metal plastic forming technology for manufacturing seamless ring parts, which is employed in many industrial fields, such as machinery, automobile, metallurgy, chemical engineering, energy sources, and aeronautics.Cold ring-rolling mandrel is one of the important and damageable parts of ring-rolling equipment. And the life of cold ring-rolling mandrel has a direct influence on the efficiency and the cost of products. Except that, cold ring-rolling play a crucial role on the quality and the accuracy of the products. Because of the complex stress and bad work environment, the mandrel which is used to product bearing ring is easy to fracture. In order to solve these problems, the law of mandrel in the cold ring rolling process has been studied by some research methods, such as failure analysis and numerical simulation.In this thesis, the fractures of the W6Mo5Cr4V2 cold ring rolling mandrels with different life were analyzed. The mandrel is used to product GCrl5 bearing ring. We found the regularity in life distribution of the broken mandrels that the majority of mandrels concentrated in two zones, high life zone (>8000) and low life zone (1000-3000). The macro/micrograph, fatigue sources and surface defects of the mandrels with different life were analyzed and compared. The characters of mandrel with different operating life were found and the factors which affect the operating life were analyzed.Utilized the correlative knowledge of mathematics and theoretical mechanics, the stress distribution of mandrel has been studied that based on the cold ring rolling theory. And the corresponding mechanics model has been established. It was revealed the law of friction force and pressure in the contact area. The requirement of microscopic structure and mechanical property that suited to the work environment has been gained. It can be used as a theoretical foundation for the improvement of heat treatment.The dynamic explicit finite elements analysis code ANSYS/LS-DYNA is used to simulate the law of mandrel in cold ring rolling process based on the results of stress distribution analysis. The calculation model of mandrel in cold ring rolling has been established. The laws of the stress distribution of mandrel and its effects on fatigue in cold ring rolling have been studied based on the simulation of the model. The researches can be used as a theoretical foundation for the prediction of the life of mandrel. The laws of the roll force and stress distribution of mandrel in the cold ring rolling in different feed velocities have been gained. According to the results of the static analysis, the easier areas in the surface of mandrel have been found.