| Along with the development of modern industry, hot die forging has been playing an important role. The inactivation and lifespan of hot-working die are still problems difficult to solve because of uncompleted analysis in quantity and quality for many factors. In this thesis, analysis of hot open-die forging for cylinder is achieved in finite element method (FEM).This thesis comprises five parts. In introduction part, the failure mode and mechanism are analyzed basing on experimentation research, manufacture experience and investigation. Furthermore, we conclude the status quo and deficiencies in hot-working die lifespan research worldwide.In the second part, the theory of numerical simulation is introduced, including description of body configuration, elastic-plastic large deformation constitutive equation and finite element formula. It is followed by the derivation of equation from the basic theory of elastic-plastic deformation. The solution to temperature field, thermal stress, thermal strain, equivalent effective stress and equivalent strain is achieved then. In addition, we exposit the relation between machine load and thermal load in coupling analysis. The character of the Mare AutoForge software is introduced at last.In the third section, by using the professional software Marc AutoForge, the hot forging process is simulated considering the difference in initial temperature and heater exchange among moving die, cover half, workpiece, moving die push and environment. Analyzed the working strok in dynamic method, we obtain satisfying result which is consistent with that of practice, that's an innovation. After simulation, we get temperature field, equivalent total strain field and equivalent thermal strain field at any time of the process. The rule of change to them and how these factors affect the die lifespan is analyzed then. It is concluded that the thermal strain and the temperature field play important roles in reducing life of die, this is in accord with the practice.We have accomplished the numerical simulation twenty times to hot die forging process consecutively and every process consists of two periods, namely the forging and the cooling procedure. In the cooling period, with the help of heat exchange equilibrium method, we computed the cooling time. This heat exchange equilibrium method isthe other innovation in this thesis. Based on a serial of successful simulations, we get temperature field, equivalent total strain field and equivalent thermal strain field at any time of the process under the condition of heat exchange equilibrium. Comparing their variation in each process and every step, we have analyzed the effect brought by these factors on die lifespan.According to the simulation above-mentioned and combining with the manufacture experience, we bring forward the standpoint of dividing Ideal Hot Die Material structure into three zones, namely basal body zone, working zone and transition zone. They are different in component and performance and do their job respectively. This is anther creativity. The feasibility study of manufacture method for "Ideal Material Structure Hot Forging Die" is expressed. After analyzing all the exiting manufacturing method, we bring forward a new project, that is, firstly, we spray plasma arc coating onto the hot die steel surface whose material must be wear resistant and thickness must be appropriate; Secondly, we fuse the coating with electron bundle so that the coat and the steel can be combined roundly, which result in the emergency of transition layer which become the intermediate zone of Ideal Hot Die Structure Material. At the same time, the original die steel turns into the basal body zone and the coating become the working zone. In addition, the other high performance will be achieved.Most of the simulation results are in good accordance with the practice. It is proved that FEM simulation is a good way to develop the die failure mechanism and can turn traditional way of empirical analysis into effective way of qualitative ana...
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