Preform Optimization For Die Forging Process Of Turbine Wheel By Rigid Visco-Plastic FEM Simulation

As one of the important parts of the middle or small type gas turbine, the big turbine wheel was endured with the tremendous tangential stress, radial stress and vibration stress when used in high temperature and at high gas pressure and high rotatory speed, so that the whole section has to need large strength, high toughness and low resident stress.At present, the forging method is always applied to manufacture the big turbine wheel practically. So far, the conventional free forging process is still adopted in most countries but Russian and US, where die forging process was used for the reason of the possession of large forging facilities. The free forging process has many drawbacks which mainly includes:(1)oversize turbine wheel consumes much more materials(steel ingot) with only availability of 15% about and spends more time for machining, (2)some of the finish products with certain defects could be detected by ultrasonic inspection because of underforging. The main reason was the processing design relying on experience, such as the unreasonable preform design for die forging large gas turbine wheel leads over-hammered, reducing the using life of dies and facilities. Therefore, it was very meaningful to optimize the die forging processing of large gas turbine wheel by applying the advanced metal forming theories and methods.So, aiming at the preform optimization for die forging process of a turbine wheel, the isothermal die forging process of the turbine wheel is simulated by using the rigid visco-plastic finite element method(RVPFEM), and the affects of the billet height to diameter ratio on forming load, plastic strain energy and flow diversion face are analyzed. the developed research works are as following.1)The theory of rigid visco-plastic finite element method is illustrated systematically. The practice processing technology and methods is developed for simulating the isothermal die forging process of the turbine wheel by RVPFEM, and some corresponding solution procedures and algorithms are proposed.2)By analyzing plastic forming processing for the large turbine wheel, a preform optimization scheme for the turbine wheel die forging process is established based on RVPFEM. Namely the optimal object function is to minimize the plastic strain energy and the forming load, the constraint condition is to make full filling and the billet height to diameter ratio is regarded as. the optimal variable.3)By using of MSC.Marc software, a RVPFEM simulation is built for the die forging process of large gas turbine wheel. The value of the billet height to diameter ratio is optimized by analyzing the metal flowing rule during filling process. The result of RVPFEM simulation shows that the preform with optimized H/D dimension can significantly reduce hammering times and die wear. The proposed FEM preform optimization method is very effective and overcomes abuse of experience design. Consequently, a scientific gist is provided for performing process optimization of die forging large gas turbine wheel.In a word, the proposed perform optimization scheme for gas turbine wheel based on RVPFEM in this paper can make up the lacks of conventional performing process. which also establishes the foundation for realizing large turbine wheel die forging with high quality, high efficiency and low costs.