| The product of aeroengine blade which mainly formed by hot forging process usually possesses the characters of complicated shape, high dimensional accuracy, required mechanical properties. As difficultes in blade forging technology, a multi-stage hot forging process is necessary to make the forging part formed gruadually and achieve sufficient diefilling. Preforming stage relates the for mer and latter forming stages and appropriate preform shape is the key issue to assure the forging quality. So, in-depth investigations on preform design are significant meanings for saving the materials, enhancing the forging qualities, simplifying the latter forging technique, reducing the die wear and energy consumption of forging process.Preform optimal design of aeroengine blade with complicated shape has been investigated systematically based on the topology optimization method in this study. The central issue of optimizing a model with complicated shape is how to appropriately deal with the form of variables to simplify the mathematics modeling for improveing the system feasibility and efficiency. However, the coordinates of control points or data points have been universally adopted as the design varabiles for characterizing the preform shape in the majority of optimization methods. Based on the different optimization algorithms, iterative optimization to design varabiles will continue until the objective function value converges to a predetermined threshold or the termination condition has been fulfilled. While, complicated model shape generally needs enough design variables for supporting the structural details, which benefits to obtain the more satisfactory result. But, with the increase of dimensions and numbers of design variable, it would be extremely time-consumption for solving such an optimization problem under the computing power of current hardware even if feasible optimization model existed.In the area of continuum structure optimization, the methods of topology optimization have been developed rapidly recently. The designing idea of topology optimiza toin is to subdivide the solid model into uniform grids in design domain. The topological structure may be changed gradually by dynamic element addition and removal operation to fulfill the objevtive function requirements during each iterative process. Compared to the form of design variable with free point coordinates, discrete elements are stationary in design space, which definitely reduces the difficulty of optimization modelling and makes the algorithm realization more easily.Based on the principle of topological optimization algorithm and combined with bulk metal forming characteristics, multi-objective constrained optimization method for preform design with complicated shape has been put forward on the condition of large deformation in this study. An optimial design platform which includes topologized solid model, surface approximation and geometry reconstruction, forming simulation by FEM, data tracking, dynamic element addition and removal, update of topological model, etc has been developed. The optimal preforms of different 2D forging models including planar strain model with aerofoil section, axially symmetric model with disk and 3D forging blade with complicated shape have been achieved successfully. The major research achievements and conclusions are as follow:(1) a variety of element addition and removal criteria which satisfy different optimization objectives have been investigated to be suitable for optimizing the preform in large deformation situation; The relationships on how dependence between individual grid and grid disposal velocity affect the optimized preform shape have been explored to construct dynamic treatment of element for improving optimization accuracy and efficiency overall.(2) Addition or removal operation for each topological element during topology optimization process should be decided by corresponding forming result from FE simulation. So, considering possible remesh or mesh refinement process during FE calculation, high precision mapping algorithm has been developed for data interpolation computatin between elements of numerical simulation and topological elements.(3) In order to deal with the conversion from uneven topological model s to CAD geometric models used for FE simulation, surface approximation and smoothing alg orithm for 3D complicated shape has been developed.(4) By integrating all algorithms, modules and FE simulation process, an optimization platform for preform design with complicated shape programmed using C# code has been developed to optimize the preform form of typical blade and ensure the optimization process with systematization, reliability and high efficiency.(5) Blade forging experiment had been carried out to validate the designed preform. The result indicated that the preform with complicated shape can be successfully optimized based on the topology optimization method in large deformation situation. A satisfactory design of optimized preform had been achieved on the whole.Compared with other optimization methods for preform design, the topology optimization algorithm has shown some characteristics as follow: no quantity limits for design variables, the details in shape evolution appear clearly durging each iterative process; dynamic quantity change of addition or removal elements can effectively control the optimization speed and degree accompanied by evolution process; initial blank shape has little effect on final optimization result, whether the blank volume is larger than final forging or not; the developed platform has shown satisfactory optimization accuracy and efficiency with validation of plane strain case, axisymmetric case, 3D complicated case. The forged preforms with optimization have universally achieved sufficient diefilling and dramaticly reduced flash. The preform optimized based on the criterion of strain uniformity has shown better performance in enhancing the uniformity of material flow, reducing the deformation resistance and forming load, improving the microstructure and me chanical properties of forged part. Meanwhile, blade forging experiment has also proved the reliability of optimization result for preform design. |
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