| Turbine blades are the core components, whose major function is energy conversion, and the safe operation of the turbine blade has a decisive role of the safety of turbine. With the introduction of large-scale nuclear power generator, the large hollow static blade of nuclear steam turbine was utilized step by step. Among the manufacturing technology of turbine, the steel hot stamping technology combined with welding assembly process has advantages, such as short production cycle, low cost, light weight and so on, which made the process interested by major global manufacturer. At present, the domestic large hollow static blade of nuclear steam turbine mainly depended on mature technology overseas. To change the situation, this paper studied the large hollow static blade of nuclear steam turbine formed with hot stamping process that developed by Chongqing university and a steam turbine factory. Finite element simulation software was used to analysis the forming quality defects of the positive comber in hot stamping, such as springback, uneven thickness and thinning. The parameters of hot stamping were designed and optimized, and finally got the qualified blades through die surface compensation. Based on the above, this paper carried out the research as following aspects:(1) Firstly, the current status at home and abroad of turbine blade forming technology are introduced, subsequently, the characteristics of parts and deformation behavior are analyzed, and carry out the sheet size optimization and addendum surface design. Finally, the forming process scheme of blade black is designed.(2) The hot stamping finite element model blade is established based on factory empirical parameters and according to the simulation results, the forming limit diagram, the sheet thickness changes, temperature distribution during forming and springback changes of blade are emphatically analyzed. For the poor quality of forming, the law of blade thermoforming process parameters, which include heating temperature, friction coefficient, blank holder force and pressure-holding time, impact on the minimum thickness and the maximum amount of springback after sheet forming is studied by using control variables method. Finally, the appropriate ranges of each forming process parameters is obtained.(3) The new objective function was constructed by weighting the average amount of springback and the average amount of thickness reduction. Firstly, the second order response surface model is built between the new objective function and heating temperature, friction coefficient, blank holder force and pressure-holding time based on response surface method by using central composite design of experiments and experimental data processing normalization, and then analyzed the significance and accuracy of the model. Secondly, the model was solved to obtain a set of optimal blade thermoforming process parameters by using particle swarm optimization algorithm toolbox of MATLAB, which heating temperature x1 is 872.44℃、friction coefficient x2 is 0.30、blank holder force x3 is 577.92 KN and pressure-holding time x4 is 7.75 min. At last the optimize results obtained by simulation was verified by the finite element simulation.(4) The springback compensation of mold surface was simulated by Autoform and SINOVATION after optimization process parameters. Firstly, according to the simulation results of the optimized process parameters, the module of springback compensation in Autoform was used and then actual tryout, the size deviation of blade was got by seizure and blu-ray scan method. Subsequently, the scan results was import to SINOVATION to go on the second surface compensation, and then adjusted mold surface based on compensation results. Finally, the production trial of blade shows that the obtained blu-ray scan data and seizure of all the measured data verify the surface springback compensation is feasible and reliable.The results of this study offers an effective method to optimize thermoforming process parameters of blade combining finite element simulation and mathematical analysis method. Using blue-ray scanning technology and mold surface springback compensation technology, the size deviation of forming blade is solved, which provides a feasible method for producing good quality and stability parts of hot stamping turbine static blade. So it provides a good theoretical guidance significance to use hot stamping forming to manufacture similar nuclear steam turbine hollow blades and provides technical support to realize large nuclear power steam turbine lightweight strategy. |
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