Cycle Stress Analysis And Fatigue Life Prediction Of Hot Forging Die

Because of the working environment of hot working die is very bad, the diesurface subjects to high temperature and thermal stress produced by the rapid changeof temperature, the die life is generally low. As a kind of hot working die, hot forgingdie need to bear the double effects of mechanical and thermal loads while working, itssurface is extremely easy to damage resulting in failure. At present, in order toimprove die life, the surface hardening technology is chosen to coat a material withheat-resistant, wear-resistant and high temperature strength on the hot forging diesurface. Surfacing is an effective method for preparing a multi-metal hot forging die.Currently hot forging die life prediction is mainly based on wear and plasticdeformation, there are little research about fatigue life. This paper adopts theStress-life approach to predict the fatigue life of hot forging die through cyclic stressand material S-N curve. In the working process of hot forging die, the temperaturechanges constantly, and the material S-N curve changes with the temperature, sotraditional approaches can’t accurately calculate the fatigue life of hot forging die.According to the correlation study at home and abroad, a new damage model ischosen to predict the fatigue life of hot forging die, this model fully considers theeffects of temperature, and the required parameters can be obtained by the finiteelement analysis and nsoft, it’s simple to use.As a fatigue life analysis software, nsoft integrates a variety of fatigue lifeanalysis approaches, therefore the approach of combining CAE technology with nsoftsoftware is chosen to predict fatigue life.Deform is used to numerical simulate the process of gear billet hot forging,analyze the temperature and stress, get the temperature and cyclic stress data of thedangerous point, find that the temperature and stress of bottom die gradually stabilizesafter10cycles. The temperature of the dangerous point gradually increases in the tencycles, and the stress decreases as the change of temperature.The temperature of multilayer metal forging die slightly decreases compared tothe homogeneous die, but the stress greatly increases. After ten working cycles, themaximum stress of the dangerous point is370MPa higher than homogeneous die, thisis because that although the thermal conductivity of the layer is higher than the matrixmaterial, but the thermal expansion coefficient and elastic modulus are larger.Finally, through the nsoft software and damage model, we complete the thermo-mechanical fatigue life prediction of hot forging die, find that the fatigue lifeincreases2530times afer surface coated.