【作者】 董万鹏；

【导师】 陈军；

【作者基本信息】 上海交通大学 ， 材料加工工程， 2009， 博士

【摘要】 转轮叶片是水力发电机组中的核心部件,形状复杂,尺寸厚薄不均,制造难度大。从产品设计、工艺规划到生产试制等多个环节中都存在着技术瓶颈,传统的工艺设计方法具有盲目性和试验周期长等缺点。本文基于数值模拟的方法,系统研究了转轮叶片热模压成形过程,提出了新的设计思路和方法,完成了水轮机转轮叶片的预成形工艺设计,建立了成形过程的有限元分析模型与多目标优化模型,并将计算结果、优化结果与工厂试制结果进行了对比分析与验证。本文取得的主要研究成果如下:针对X型转轮叶片的参数化CAD模型,基于合模状态下的共同坐标,提出了新的水平基准的定位方式:以叶片工作面的进水边与下环交点为原点,出水边与上冠交点为X轴线点作为参考定位。针对热模压模具,建立了模具向冷却水传递热流的数学模型,求解了冷却水流速度。为使整个成形过程中的模具温度不低于300℃,冷却水流速应不低于970 mm/s。将基于理想变形理论的一步模拟法和基于相似原理的类等势场法相结合,提出了一种复合的预成形设计新方法。以一步模拟法反向计算外形轮廓尺寸,以类等势场法正向计算特征截面厚度分布,建立了不等厚度变截面的叶片展开坯料模型。中面模型展开计算采用可以表征弯曲作用的薄膜/板壳混合单元,摒弃了传统木模图中关于特征截面的展开计算方法,提高了叶片预成形设计的精度与效率。为确保实际生产中压力中心的波动始终处于设定的公差范围之内,提出了一种基于刚塑性有限元法,通过计算实时节点力获取不等厚度板坯模压成形过程中动态压力中心的新算法。在DEFORM 3D软件上二次开发实现了该算法,给出了用户坐标系下压力中心的变化规律,为压力中心的优化提供了必要的信息。基于金属材料热压缩试验结果,以分段函数的形式,建立了0Cr13Ni5Mo材料的高温流动应力模型。针对流动应力-应变曲线上升阶段和稳态阶段,分别采用了影响系数法和Arrhenius方程建立了应力关于变形温度、应变和应变速率的数学表达式。利用统计学的方法分析并验证了新材料模型的可靠性。考虑温度对磨损模型中参数的影响,采用修正的Archard模型,分析了0Cr13Ni5Mo材料热模压模具的磨损情况,发现模具磨损最严重处都位于模具同叶片出水边与下环相交的端部对应处。分析发现:成形温度对模具磨损的影响最为显著。为了降低成形抗力与能耗成本,建立了叶片热塑性加工多目标优化问题的数学模型,选取了变形温度、应变速率以及摩擦因子作为优化变量,构建了新的成形载荷子函数、能耗子函数、生产效率子函数。针对成形载荷子函数,设计了析因试验,采用回归分析等统计学方法,拟合其为包含交互效应的完全二次多项式。针对能耗子函数与生产效率子函数,通过分析其计算方法,将能耗函数、效率函数分别归纳为各自对应分量的和函数。利用线性加权和法,建立了评价函数,将多目标优化问题转化为单目标非线性规划问题。优化后的最大成形载荷为6.21 MN,小于设备额定载荷10 MN;成形能耗值由原设计的23 MJ降为18.63 MJ,降幅达19%;生产效率为39.67 min/件,较原工艺提高了17%。将工艺优化前、后的转轮叶片与初始设计原型在各测量点的厚度值进行了对比分析,工艺优化后的叶片厚度的相对误差由优化前的25%降至了15%,充分表明优化技术对现有工艺的改进作用。更多还原

【Abstract】 Francis turbine blade is one of the key components of hydraulic generator, and it has complicated configurations and varied thickness. It is a difficult and time-consuming task to manufacture such products,there are also lots of technical bottlenecks in the whole manufacturing process. Traditional design, so called trial-and-error method, inherits disadvantages such as immature process plan, high investment risk and repeated trials. In the dissertation, the research was carried out about the blade hot forging process based on finite element analysis, and new ideas such as hybrid method of blade preform design were brought forward. Process design and multiple-objective optimization were also studied, the results by theory analysis, optimization calculating and trial manufacture were compared and verified. The research achievements are listed as follows:Using the CAD model of X shape Francis turbine blade, a new horizontal positioning method was put forward under the common coordinate of the upper die closure. The new original point was the intersection point between the inlet edge and the lower ring, and the X anchor point as reference positioning point was the intersection point between the outlet edge and the upper ring. In order to ensure effective cooling effects, a mathematical model of heat transfer from die to water was set up. Calculation results show that the flow velocity should be larger than 970 mm/s so as to keep the die temperature around 300℃during forming process.A hybrid method for turbine blade perform design integrating One-step FEA and Equi-potential Lines Method was proposed, while One-step FEA was used to predict the profile of the unfold billet and Equi-potential Lines Method provided the thickness distribution of featured sections. The hybrid membrane/shell element was used by integrating CST3 and DKT6 elements to consider bending effect. Configuration calculations of the unfold blade billet were improved with a higher design efficiency.To keep the variation of forming load center within predefined tolerance scope during the whole forging process, a new algorithm to dynamically calculate the forming load center for the whole process of non-uniform thickness metal thermal forming was put forward based on rigid plastic FEA simulation, The formulations were developed and coded into a user routine on software DEFORM 3D V 6.1. The history of forming load center could be calculated, which is helpful for the unbalanced load control and optimization.Based on thermal compression test, a new two-segment function was put forward to characterize the flow stress behavior of 0Cr13Ni5Mo during ascend and steady stage. A sub-function utilized the influence coefficient method and the other sub-function adopted the Arrhenius equation, statistic analysis proves the reliability of the new model clearly.The modified Archard model was introduced to evaluate the effects of process parameters on die wear, the effect of temperature to the parameters in Archard model was considered. It concluded that the most severe die wear is located at the corresponding area where the outlet and lower ring intersect, and the forming temperature has most sensitive effect to the die wear.To minimize forming load and energy consumption, multi-objective optimization method was proposed, and new sub-functions were established with constraint conditions. By linear weighing-sum method, the multi-objective optimization was converted into a linear programming problem with the evaluation equation. Process parameters were optimized with SQP algorithm. The optimized load was 6.21 MN, much lower than the limit value of the press (10 MN); the optimized energy consumption was 18.63 MJ, reduced by 19% compared with the original one (23 MJ); and the optimized product efficiency was 39.67 min per piece, increased by 17%. The optimization design was evaluated by comparing the thickness distribution error between the optimized result and original design with that between plant try-out result and original design, and the relative thickness error was reduced down to 15% from 25%, which demonstrated the effective optimization advantage.更多还原