大型薄壁零件装配误差有限元分析
摘要
在机械、船舶、航空航天等领域中有许多薄壁零件，它们主要由各种薄型板、腔体和加强筋条构成，结构复杂，一般认为零件最大尺寸大于2m，且零件厚度与零件最大尺寸比小于5％即属于大型薄壁零件。600MW超临界汽轮机组低压缸体由各种薄型板、加强筋、支承梁和叶片等构成。缸体尺寸较大，直径约为6m。上下爿缸体装配后，高约为7m。而缸体壁厚较薄，约为32mm。因此，600MW超临界汽轮机组低压缸体属于典型大型薄壁零件。由于体积大、总体刚性较差，薄壁零件在装配过程中极易在重力、夹紧力的作用下产生变形，采用传统的装配工艺方法已难以保证其装配精度要求。
针对超临界600MW机组低压缸体在装配过程中出现的垂直中分面间隙过大、裙座接触不良和通流间隙超差等装配问题，文章首先在理论上分析零件定位方式和各种装配工艺对薄壁零件装配精度的影响，并利用提出的装配工艺评价原则对缸体总装配工艺进行了设计和评价。
接触问题由于其边界非线性，即使是弹性光滑接触问题，采用数值方法分析求解也有很大的难度。缸体装配过程主要通过多体接触分析模拟，文章中详细介绍了接触问题，研究了接触分析的边界条件、接触参数及单元尺寸、形状、网格划分方法，以确立适合缸体零件全装配的三维接触分析有限元模型，从而得到更为精确的计算分析结果。
最后，基于有限元分析软件ANSYS/LS-dyna，模拟了低压缸体总装配过程。根据不同装配误差问题，分别建立了相应的有限元分析模型。分析了缸体零件装配变形及其在装配体中的传递情况，确定了缸体变形部位以及变形趋势并量化了具体的变形量，为装配工艺的改进提供了依据。
关键词：汽轮机缸体，接触问题，装配变形，误差传递　
THE FINITE ELEMENT ANALYSIS OF ASSEMBLY ERROR FOR LARGE THIN-WALL PART
ABSTRACT
Large-scale thin-wall part is used wildly in mechanical, ship, aviation
& aeronautic industries.Many parts have thin-wall (shell)、cavity and rib enforcement,complex structure. Generally speaking, large-scale part refers to those structure the largest size of part is more than 2m and the ratio of wall thick and largest part’s size is less than 5%. 600MW stream turbine cylinder is mainly constructed by all kinds of thin-wall、rib enforcement 、bearing bar and lamina. The cylinder’s diameter is almost 6m. The height of cylinder assembled is almost 7m. To some extent, 600MW stream turbine cylinder is some kind of large-scale thin-wall part. Because this kind of part has large volume and bad stiffness, there is serious deformation during processes of assemblying.It’s difficulty to satisfay the assembly error requirements using the old means.机械论文
Aim at the large middle plane flatness error ,plane contact gap and flow clearance error occurred in the process of 600MW stream turbine cylinder’s assemblage, the article analyzed the parts fixture ways and diversified assembly technics in principle, then designed and evaluated the turbine cylinder assemblage technics by using the assemblage thecnics priciple provided preciously.
Because of boundary non-linearity, even it’s the elastic smooth contact question ,it’s very difficulty to analysize with numerical method. The analysis of turbine assembly is mainly involved with polysome contact, so the article particularly introduced contact problem, research on the boundary condition of the contact analysis、contact parameter and element dimension、shape and meshing way to construct the 3D contact analysis FE model suitable for the turbine assembly, and work out more accurate results.
Finally,based on the software of ANSYS/LS-dyna，the finite element simulation of the turbine overall assembly is provided. According to the different assembly error problem, the FEA models were constructed with ANSYS. Through the computing of assembly deformation and it’s transfer
in the assembly parts, the location and deformation trend is verified, the guidance is offered for improvement of assembly thchnics.
KEY WORDS: stream turbine cylinder, contact problem, assembly analysis, error propagation
上海交通大学
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学位论文作者签名：孙稳
日期：２００９　年　２　月２日