【作者】 白万金；

【导师】 柯映林； 董辉跃；

【作者基本信息】 浙江大学 ， 机械制造及其自动化， 2009， 博士

【摘要】 为了实现减重和提高比强度的目的,航空工业中广泛采用了航空铝合金等材料制成的薄壁零件。从切削加工的角度看,航空薄壁零件壁厚薄、相对刚度低、外形协调要求高、加工工艺性差。在精密切削加工过程中,切削力作用下薄壁工件的局部弹性变形、残余应力不均匀分布引起的整体加工变形以及加工系统的振动现象是影响薄壁件加工质量和精度的三个突出问题。本文采用理论分析、力学建模、有限元模拟和实验验证等手段,对航空薄壁件精密铣削加工变形的预测理论和方法进行了深入、系统的研究。主要研究工作包括以下几方面:针对铝合金材料7050-T7451的高速铣削加工,基于大变形理论和虚功原理,建立了切削加工过程的三维热-弹塑性有限元模型。分析、研究了有限元网格模型、材料本构关系、刀-屑间摩擦模型、切屑分离标准以及热传导控制方程等涉及切削加工模拟的关键技术。利用该模型对铝合金材料的高速切削加工过程进行了有限元模拟,分析了高速切削加工过程中切屑的形成过程及其形貌,三维铣削力的变化情况,以及应力、应变、切削温度及已加工表面残余应力的分布规律。针对航空铝合金材料7050-T7451的周铣加工过程,进行了铣削力理论建模研究,在不同切削情况下分别采用“刚性法”和“柔性法”对各自情况下的铣削力进行了预测分析,并进行了铣削力实验及模型验证。随后,对铣削温度进行了预测分析及实验研究。搭建了适合测量铣削温度的实验系统,并通过正交实验及回归分析获得了铣削温度的经验公式模型。对薄壁件铣削加工过程中的振动及其稳定性进行了研究。基于薄壁件铣削加工动力学模型,利用有限元模态分析方法识别薄壁件动态特性参数,建立加工稳定性极限判定准则,并绘制了以机床主轴转速为横坐标,临界切削深度为纵坐标的稳定极限图,以指导选取主轴转速和切削深度等工艺参数,提高加工质量和加工效率。最后对薄壁件铣削加工整体变形及局部加工变形进行了研究。在研究了薄壁件铣削加工有限元模拟所涉及相关关键技术的基础上,建立了适合分析薄壁件整体加工变形的有限元模型及分析流程,并重点分析了加工过程中的应力场和温度场分布规律、加工后工件残余应力分布规律以及加工路径和切削载荷对残余应力的大小及其分布的影响。薄壁件局部加工变形预测的研究主要针对走刀方式和切削力这两个因素进行。结合铣削力预测的有关研究,建立了适合研究薄壁件局部加工变形误差的“刚性预测法”和“柔性预测法”流程。关于走刀方式主要研究了分层对称走刀和阶梯对称走刀对薄壁件局部加工变形的影响。更多还原

【Abstract】 At present,airframes are widely made of monolithic thin-walled components for the sake of weight reducing and strength ratio improvement.However,due to factors such as cutting force induced flexible deflection,dynamic vibration and non-uniform residual stress distribution induced distortion,precision machining of these low-rigidity thin-walled parts has been providing a serious challenge for engineers.In this article,the models and methods for predicting the precision milling deformation errors are systematically invested by means of theoretic analysis,mechanics modeling,finite element simulation and experiments verification.Firstly,based on large deformation theory and virtual work principle,a three-dimensional(3-D) thermo-elastic-plastic coupled finite element analysis(FEA) model is constructed to investigate the high-speed milling(HSM) processes of 7050-T7451 aluminum alloy.Several key FEA techniques,such as finite element mesh model,material constitutive model,chip separation criteria,frictions on the tool-chip interface and 3-D heat conduction governing equations,are analyzed and implemented to improve the accuracy and efficiency of the FEA simulation.A HSM case is simulated with the 3-D FEA model.The detailed calculated results are presented and analyzed,including the chip’s geometric shape and its evolution processes,the stress,strain,cutting forces, and temperature distributions in the workpiece,tool and chip,as well as the residual stresses distributions on the machined surface.Secondly,based on two typical cutting force predicting models,namely the rigid model and the flexible model,a numerical simulation procedure is developed to evaluate cutting forces under different cutting conditions.The precision and validity of the prediction models are verified by the milling force experimental measurements.Then,a semi-artificial thermocouple device is developed to explore the dynamic cutting temperature variation rules in high-speed milling of A17050-T7451 aluminum alloy.Also, a cutting temperature empirical formula is constructed by means of orthogonal experimental design and multivariate linear regression analyses.Thirdly,based on the dynamic cutting force model,a method for obtaining the stability lobes is developed.The modal parameters are identified by the finite element modal analyzing.The predicted stability lobes are used to determine the optimal cutting conditions to suppress chatter phenomenon during the high speed milling process.Finally,the thin-walled workpiece distortion prediction model is systematically invested. Several key influencing factors,such as initial residual stress,cutting loads,fixture, cutting path and sequence are considered.The fields of the stress and temperature distribution rules during the thin-walled parts machining process,as well as the residual stress distribution laws,are detailed analyzed.The thin-walled workpiece local flexible deflection prediction research is mainly focused on two factors:cutting path and force. Based on two typical cutting force predicting models,a numerical simulation procedure is developed to evaluate the flexible deflections in both symmetry and step-symmetry milling process.更多还原