【作者】 胡创国；

【导师】 张定华；

【作者基本信息】 西北工业大学 ， 航空宇航制造工程， 2007， 博士

【摘要】 为了实现减重和增效的目的，在航空发动机结构的设计中，广泛采用了钛合金等高强度-重量比材料制成的薄壁零件，如机匣和叶片等。从数控铣削加工角度看，此类零件具有薄壁、刚性差、切削力大的特点。在精密切削过程中，切削力作用下的刀具-工件弹性变形、切削表层残余应力引起的工件扭曲变形以及刀具-工件系统加工振动现象是影响加工精度和型面质量的三个最为突出的因素。为此，围绕薄壁零件高效精密切削加工亟待解决的关键技术问题，遵循误差源识别、加工过程仿真、误差控制补偿、工艺方案优化和实验验证的总体思路，本文主要开展了以下几个方面的研究工作：一、切削过程数值模拟。在阐述切屑-工件分离准则、刀具-切屑界面接触摩擦行为、自适应网格划分技术和切削条件下材料屈服流动本构模型的基础之上，建立切削加工过程的有限元仿真模型，模拟钛合金TC11连续状和锯齿状切屑的形成过程，同时给出切削区域应力场、应变场以及温度场的分布状态信息。实验和模拟结果表明，就切削力的大小而言，锯齿状切屑的情形小于连续状切屑的情形。二、薄壁零件加工弹性变形误差预测与补偿方法。提出加工表面静态误差预测、补偿总体方案，利用有限元模拟技术结合切削力模型，迭代求解各个刀位点处的弹性让刀变形量，据此修正原始的数控刀具轨迹代码，达到消除加工变形误差的目的。文中基于单位切削力系数法，分别建立平底刀侧铣、球头刀点铣时的切削力预报模型，并讨论了将切削力大小向刀齿和工件单元节点的等效离散方法。对薄壁平板的切削试验证实，运用多层次循环误差补偿方式，可以获得很高的加工精度。三、薄壁零件切削扭曲变形控制方法。利用钻孔法测量钛合金材料铣削加工表层残余应力的分布规律，经过离散后输入至有限元模型，模拟单面行切法和双面环切法这两种不同走刀方式下的零件扭曲变形行为。仿真结果表明，采用双面环切工艺有利于保持铣削表层残余应力始终处于平衡状态，能够较好的解决加工过程中薄壁零件的扭曲变形问题，显著提高型面的加工精度。通过采用双面铣削工艺，薄壁叶片叶尖区域沿厚度方向的最大数控加工误差比采用单面铣削工艺平均降低了一个数量级。四、薄壁零件加工颤振抑制方法。基于切削动力学模型，利用模态分析方法识别系统结构的动态特性参数，建立加工稳定性极限判定准则，以指导选取主轴转速和切削深度等工艺参数，从而将切削过程控制在稳定区域之内。此外，针对薄壁自由曲面叶片而言，通过合理设计叶身半精加工余量的分布规律，在减少前后缘和叶尖部位精加工切除量的同时减小切削力的大小，改善叶片在精加工过程中的刚性状态，能够有效抑制加工颤振现象的发生。本文的部分研究结果，已经成功应用于薄壁叶片等复杂结构件的高效精密数控加工实践中，取得了令人满意的效果。更多还原

【Abstract】 Thin-walled complex parts, namely casing and blade made of difficult-to-machine materials, are widely used in the structure design of high performance aeroengine, which results in weight savings of up to 30% with consequent improvements in thrust-to-weight ratios. However, due to factors such as cutting force induced part/tool static deflection and dynamic vibration, precision machining of these low-rigidity complex parts has been providing a serious challenge for engineers. As a result, there is usually a significant deviation between the planned and machined part profiles while providing a poor surface quality. Hence, the main objectives of this research are to predict and compensate the tool-workpiece machining deformation errors, and to develop strategies to suppress chatter phenomenon and residual stresses induced thin-walled parts distortion.Firstly, an FE model is presented using ABAQUS/Explicit^TM to simulate continuous and saw-tooth chip formation when machining titanium alloy TCll. Modelling details, including the chip separation criterion, the sticking and sliding tool-chip frictional behavior, the adaptive meshing technique and the constitutive equation for the workpiece material, are discussed carefully. The model is also used to predict the cutting forces, stress, strain and temperature contours near the cutting zone. For the saw-tool chip, the magnitude of the cutting force is lower than with the continuous chip.Secondly, a general quasi-static error compensation methodology is proposed, which focuses on force-induced errors in machining thin-walled structures. The methodology is based on modelling and prediction of milling forces, finite element simulation of deflection of the part during machining and analysis of the resultant surface errors. An iterative procedure is used to determine the local equilibrium conditions between the cutting force and deflection at each cutter location. The results show that high machining accuracy could be achieved efficiently using multi-level error compensation scheme.Thirdly, a spiral milling process technique is presented to finishing thin-walled workpiece taking into account the residual stresses induced distortion. The residual stress variation in titanium alloy TC11 has been determined by a strain-gauge technique involving blind-hole drilling. The measured residual stresses are fed into an FEA model for simulation of the distortion behaviour of the part under two different tool path strategies. With the spiral tool paths, the allowances on both sides of parts are removed concurrently, therefore the residual stresses in the machined layers will be approximately maintained symmetrical balance status. As a result, the residual stresses induced distortion during finishing thin-walled workpiece is controlled successfully. The machining accuracy near blade tip region has been significantly improved by one order of magnitude.Finally, Based on dynamic cutting force model, a method for obtaining the instability or stability lobes is developed. In order to identify the modal parameters, the frequency response function of the machine-tool structure is determined by a standard impact test procedure. The predicted stability boundary has been used to determine the optimal cutting conditions to suppress chatter phenomenon while maximizing material removal rates. Furthermore, with respect to finishing sculptured surface blade, it is verified that the chatter vibration could be suppressed successfully through optimizing the allowances distribution during the semi-finishing process.更多还原