Numerical Simulation & Parameters Optimization Of The Hot Forming Process For A Large-Scale Thick-Walled Semi-Spherical Head

Head is an important component of boiler and pressure vessel which is used to bear great pressure. It is widely used in electric power stations, chemical factories, petroleum industries, nuclear stations and other fields. Along with economic development, particularly in the energy field, electricity demand is growing tremendously. The capacity of generator has developed from 100 MW to 1000MW. Boiler pressure has increased from 3.82MPa to 27.56MPa. The thickness and size of head tend to be large. At present, large-size thick-walled semi-spherical head was produced by hot forming in domestic and abroad. The processing enterprises have formed theoretical calculation method on the head forming process from long-term production practice, but these methods often has big error, and was not a good guide in practice. In this paper, numerical method was used to simulate the hot forming process and optimize the process parameters.First, this paper introduced the research progress of sheet metal forming process, and then introduced the hot forming process of thick-walled semi-spherical head in domestic and abroad, pointed out the significance of simulating the forming process of thick-walled semi-spherical head.This paper did compression experiment about DIWA353 steel above the crystallization temperature, under the conditions of different strain rate. Get the true stress-true strain data. The activation energy was calculated according to the data obtained by the thermal deformation tests, and then a constitutive equation about the steady stress under high temperature was established. The equation was established considering the effect of temperature and strain rate on the flow stress.The constitutive equation was then used in the finite element simulation. Based on the elastic-viscoplastic finite element method, Make use of material data under high temperature, the hot forming process of head was simulated using ABAQUS6.6-3. The head has a diameter of 2000 mm and 130 mm in thickness. Then the stress, strain, contact forces, thickness, temperature distribution during the hot forming process were analyzed. The forming quality was evaluated from defects, diameter deviation and spring-back. Compared to the real data obtained in practice, they are in good agreement.In the last, based on the orthogonal design principle, the main parameters that affect the forming quality were simulated. Thinning effect of different parameters were analyzed using variance methods, and then the significance of each factor was evaluated. Friction is the most significant one in the selected factors.