弱刚度结构件切削加工残余应力的研究

弱刚度结构件具有刚度差和材料去除量大等特点,加工过程中产生的残余应力容易导致其加工变形,尤其对于精度要求高且厚度不均匀的弱刚度结构件,更有必要研究切削加工残余应力的影响因素,从而为控制弱刚度结构件的加工变形提供基础。根据正交切削理论和热弹塑性有限元理论建立了切削加工的三维有限元模型,对材料为40CrNiMo的变厚度弱刚度结构件进行了切削加工模拟,对切削过程中的残余应力进行了有限元计算。通过对比不同切削参数情况下残余应力的分布,得到了残余应力随切削参数的变化规律;将变厚度弱刚度结构件的加工分为二次等厚度的切削加工,通过与一次加工得到的残余应力进行对比,得到了2种不同加工工序对变厚度弱刚度结构件的残余应力影响规律。     

一种逐层切削法的残余应力动态测量实验研究

在航空整体结构件加工中,残余应力影响着零件尺寸的稳定性。为提高航空整体结构件加工质量,减少残余应力对加工变形的影响,需要准确分析板材内残余应力的分布规律。提出一种采用逐层切削法去除毛坯材料,利用动态应变测量技术测量残余应力释放引起的应变,从而获得材料内部残余应力大小和分布规律的方法。设计了测量实验方案,完成了数据采集和数据分析,得到残余应力的三维分布规律,同时获得残余应力释放的速度变化规律。     

航空结构件数控加工变形及其控制策略

航空结构件加工变形直接影响了结构件的高效、高精加工,这也是航空结构件加工制造所面临的挑战。在对航空结构件分类的基础上分析了航空结构件数控加工变形的机理,指出残余应力、切削力与切削热、工件装夹条件、切削走刀路径等直接影响了数控加工变形。对航空结构件数控加工变形实施控制,具体措施为控制残余应力、优化加工参数、优化走刀路径和优化装夹布局等,为航空结构件数控加工变形控制提供参考。     

飞机整体框类结构件铣削加工的模拟研究

针对航空整体结构件铣削加工变形的复杂制造问题，建立了三维铣削加工有限元模型。深入研究了材料模型、残余应力施加、动态切削载荷、材料去除等铣削加工模拟所涉及的关键技术．并详细论述了铣削加工模拟过程。应用该模型对某框类结构件进行了不同铣削顺序的加工模拟，通过零件变形模拟值与实验加工所得零件变形值的比较，证明该有限元模型可以实现对零件铣削加工变形规律的预测。     

残余应力对航空整体结构件加工变形的影响分析

基于理论计算和有限元模拟,研究了毛坯的初始残余应力对大型整体结构件数控加工变形的影响,对单向 应力作用的矩形截面梁在剥层过程中的变形挠度值进行了求解。结果表明,理论解与有限元计算值是一致的。面 向工程应用,采用ABAQUS有限元软件模拟了残余应力对隔框类整体结构件加工变形的影响,并进行了试验验证。 有限元仿真结果与试验数值非常吻合。最后,根据工件加工变形的有限元模拟结果,提出了提高整体结构件制造 精度的工艺措施。     

2124铝合金薄壁结构件整体加工变形仿真分析

薄壁结构件的整体轮廓变形主要是由其毛坯内部残余应力重新分布而引起的,根据双面槽腔薄壁结构件的结构特点建立了薄壁件铣削加工的有限元模型,系统地研究了残余应力的施加,材料去除加工过程所涉及的关键技术,并通过优化薄壁整体结构件的装夹方案以及多个特征结构的加工顺序,控制了薄壁整体结构件的加工变形。     

残余应力作用下的航空整体结构件加工变形仿真

铝合金预拉伸板在成型过程中会产生较大的残余应力,在切削过程中毛坯的初始残余应力的释放对整体结构件的宏观变形有重要的影响。在弹塑性力学的基础上,综合运用Hypermesh和ABAQUS建立残余应力单因素作用下的三维铣削仿真加工变形场的有限元模型,利用生死单元技术模拟了材料的去除,分析了铝合金板材材料去除过程中残余应力释放引起的加工变形规律。并且运用Hypermesh提高了有限元前处理的速度,解决了复杂模型的残余应力加载困难与单元去除困难的问题。     

面向加工变形控制的航空整体结构件拓扑优化设计方法

在毛坯制造过程中,材料力学性能的非均匀性导致铝合金厚板内产生残余应力,以致在后续的高速切削加工过程中,随着材料的大量去除,残余应力的释放使得整体结构件发生变形,严重影响着整体结构件的尺寸稳定性。当初始残余应力水平及状态一定时,随着从毛坯上去除材料切削成形为不同的零件结构,零件变形会表现出不同的形式。因此,研究零件变形与零件结构形式之间的关系对于实现加工过程的高效化和精密化至关重要。首先,通过铝厚板的材料去除等效为残余应力的释放,利用弯曲变形理论建立铝厚板厚度方向上加工变形的解析分析模型及有限元分析模型。通过航空企业现场加工、测试零件后可知：加工变形的解析值、仿真值与测量值相比,无论是幅值水平还是变形曲线,解析值与仿真值完全吻合,而两者与实验值之间仅存在不到10%的幅值误差。其次,为了使得加工变形达到最小,构建以结构体积为约束的拓扑优化设计模型,通过利用一系列凸显式子问题逼近目标和约束函数,构建拓扑优化模型的MMA求解技术。最后利用所提出的优化方法计算出C919直梁件的结构,优化前、后的加工变形分别为22.02 mm与0.7414 mm,在相同的材料去除量情况下,通过优化结构可以使得加工变形减小96.63%。     

基于SIGINI子程序的零件残余应力变形数值模拟研究

为提高飞机性能,整体结构件成为飞机广泛采用的主要承力构件,而整体结构件毛坯由于残余应力的存在往往导致加工后出现较大变形影响零件精度。根据模锻毛坯件的残余应力测试试验数据,逆向构建了初始应力仿真模型,采用用户子程序SIGINI施加初始应力场,运用生死单元法对分层材料进行去除。结果表明,通过表层残余应力试验数据逆向构建初始残余应力分布场计算变形的可行性,同时可以直观分析生死单元法逐层杀死单元过程中,初始残余应力的释放过程,与零件加工后的变形测量结果对比,有较高的吻合性。     

航空整体结构件高效高精度加工关键技术研究（下）

（2）薄壁结构件加工变形的预测与控制针对薄壁型结构件产生的局部加工变形问题,武凯等人采用有限元仿真技术研究了薄壁腹板、侧壁加工变形规律及其变形控制方案,指出大切深法以及分步环切法可以充分利用薄壁件自身刚性,减小加工变形,提高加工精度;王志刚等人基于材料始终处于弹性范围的假设,分析了薄壁零件的加工变形,数值模拟时考虑了切削力作用下侧壁的弹性变形,但没有考虑初始残余应力和切削热对变形影响;     

高速铣削加工汽车覆盖件模具表面残余应力研究

汽车覆盖件模具的高速加工具有特征型面形状复杂、材料硬度大、结构尺寸大、表面精度要求高等特点,在高速切削加工过程中,属于难加工产品。残余应力的存在促使疲劳裂纹形成与扩展、促进腐蚀、促进模具的关键型面变形,因此汽车覆盖件尺寸的稳定性和加工质量与其密切相关。本文在数值模拟思想的指导下,利用有限元解法,研究了高速铣削加工表面的残余应力对加工变形的影响,给出了预测残余应力数值的解析模型,具有重要的理论及现实意义。     

Machining distortion minimization for the manufacturing of aeronautical structure

The distortion of machined parts is a major concern in the manufacture of aeronautical monolithic structures. We investigated the influence of material removal partition on residual stress in high-strength aluminum alloy parts to minimize machining distortion. In the present study, a methodology of minimizing machining distortion based on an accurate cross-sectional residual stress determination is presented, which can be applied to avoid or minimize part distortions in advance by adapting machining strategies or process conditions. A powerful contour method was used first to measure bulk residual stress within the blank. Next, a finite element model was applied to predict machining distortion based on measured residual stress for analyzing part distortion. Finally, experimental verification was provided by comparing measured distortion and predicted distortion by the finite element analysis. This simulation showed that part distortion is mainly affected by the partition of material removal in T-shaped components. Our results also indicate that distortion can be minimized by optimizing the partition of material removal to ensure a symmetrical distribution of residual stress in the part so that the residual stress-induced bending moment could reach self equilibrium.     

高速铣削加工汽车覆盖件模具表面残余应力研究

汽车覆盖件模具的高速加工具有特征型面形状复杂、材料硬度大、结构尺寸大、表面精度要求高等特点,在高速切削加工过程中,属于难加工产品。一些学者对其高速铣削加工进行了研究,但对其表面残余应力的研究较少。残余应力的存在促使疲劳裂纹的形成与扩展、促进腐蚀、促进模具的关键型面变形,因此汽车覆盖件尺寸的稳定性和加工质量与其密切相关。本文在数值模拟思想的指导下,利用有限元解法,研究了高速铣削加工表面的残余应力对加工变形的影响,给出了预测残余应力数值的解析模型。     

Influence of the machining sequence on the residual stress redistribution and machining quality: analysis and improvement using numerical simulations

The manufacturing of aluminium alloy structural aerospace parts involves multiple steps, the principal ones being the forming (rolling, forging etc.), the heat treatments and the machining. During this last step, the final geometry of the part is obtained. Before machining, the workpiece has therefore undergone several manufacturing steps resulting in unequal plastic deformation and metallurgical changes which are both sources of residual stresses. On large and complex aluminium alloy aeronautical parts, up to 90 % of the initial workpiece volume can be removed by machining. During machining, the mechanical equilibrium of the part is in constant evolution due to the redistribution of the initial residual stresses.The residual stress redistribution is the main cause of workpiece deflections during machining as well as of post-machining distortion (after unclamping). Both can lead to the non-conformity of the part with the geometrical and dimensional tolerance specifications and therefore to a rejection of the part or to additional conforming steps. In order to improve the machining accuracy and the robustness of the process, the effect of the residual stresses has to be considered for the definition of the machining process plan. In this paper, a specific numerical tool [2] allowing to predict workpiece deflections during machining and post-machining distortion is used to study the influence of the machining sequence on the machining quality in taking into consideration the initial residual stresses. A first machining process plan defined as the reference case is simulated. Simulation results are then compared with experimental ones showing the feasibility to use the developed tool to predict the machining quality depending on the initial residual stresses, the fixture layout and the machining sequence. Using the computational tool, a method to optimise the machining quality depending on the initial workpiece and on the machining sequence is presented. A machining process plan allowing to respect the tolerance specifications is then defined. This demonstrates the feasibility to adapt and to optimise the machining process plan to ensure conformity of the part with the tolerance specifications.     

Modeling of machined surface characteristics in cryogenic orthogonal turning of inconel 718

The determination of the optimal machining conditions for assuring desired machined surface characteristics of a part is one of the main goals in a machining process. In this article, the impact of a cooling lubrication fluid, its delivery phase and location, as well as machining parameters, on residual stresses have been investigated. The workpiece material under observation is Inconel 718. For measuring residual stress profiles, X-ray diffraction technique has been used. Additionally, besides the experimental work, modeling with the finite element method model was implemented and correlated with experimental results. The results show that residual stresses are influenced by the cooling lubrication scenario, even though the machining parameters are kept constant. However, flood and cryogenic machining show more compressive residual stresses than a dry machining case. On the other hand, the results have shown also that machining parameters influence residual stresses, where stresses increase with their increase (v_c and f).     

Study on Cutting Force,Cutting Temperature and Machining Residual Stress in Precision Turning of Pure Iron with Different Grain Sizes

Pure iron is one of the di cult-to-machine materials due to its large chip deformation, adhesion, work-hardening, and built-up edges formation during machining. This leads to a large workpiece deformation and challenge to meet the required technical indicators. Therefore, under varying the grain size of pure iron, the influence of cutting speed, feed, and depth of cut on the cutting force, heat generation, and machining residual stresses were explored in the turning process to improve the machinability without compromising the mechanical properties of the material. The experimental findings have depicted that the influence of grain size on cutting force in the precision turning process is not apparent. However, the cutting temperature and residual stress of machining fine-grain iron were much smaller than the coarse grain at all levels of cutting parameters.     

Prediction of welding residual distortions of large structures using a local/global approach

Prediction of welding residual distortions is more difficult than that of the microstructure and residual stresses. On the one hand, a fine mesh (often 3D) has to be used in the heat affected zone for the sake of the sharp variations of thermal, metallurgical and mechanical fields in this region. On the other hand, the whole structure is required to be meshed for the calculation of residual distortions. But for large structures, a 3D mesh is inconceivable caused by the costs of the calculation. Numerous methods have been developed to reduce the size of models. A local/global approach has been proposed to determine the welding residual distortions of large structures. The plastic strains and the microstructure due to welding are supposed can be determined from a local 3D model which concerns only the weld and its vicinity. They are projected as initial strains into a global 3D model which consists of the whole structure and obviously much less fine in the welded zone than the local model. The residual distortions are then calculated using a simple elastic analysis, which makes this method particularly effective in an industrial context. The aim of this article is to present the principle of the local/global approach then show the capacity of this method in an industrial context and finally study the definition of the local model.     

长钢管的大变形量镦粗工艺及模具设计

针对长钢管大变形量镦压加工难等问题,开展了镦压工艺计算与设计,建立了钢管的高径比、镦压变形量与镦压质量之间的关系。在镦压工艺和模具设计上对坯料可能产生的失稳和制品内、外径保证问题进行了评价,并进行了镦压试验,提出了解决因长钢管大变形量镦压而导致失稳倾向和制品易折叠的镦压加工方法,规定了模具工作过程及注意事项。研究结果表明,长钢管接受镦压加工时,若其高径比和镦压总变形量大大超过镦压加工规范时,采取两次镦压、在毛坯内径中加装芯棒和在外径外部设计模圈及对坯料进行酸洗、磷化、浸涂固体润滑剂等技术,可以有效地解决长钢管大变形量镦压加工难的问题。     

Comparison and analysis of main effect elements of machining distortion for aluminum alloy and titanium alloy aircraft monolithic component

Main effect elements of machining distortion for aluminum alloy and titanium alloy aircraft monolithic component are investigated by finite element simulation and experiment. Based on an analysis of milling process characters, finite element models of machining distortion are developed. Considering the action of initial residual stress, finite element simulation and analysis of machining distortion for aluminum alloy aircraft monolithic component are performed. Initial residual stress, cutting loads, and coupling action of these two effect factors are taken into account, respectively, to perform finite element simulations of machining distortion for titanium alloy aircraft monolithic component. The finite element simulation results are compared with experiment results and found to be in good agreement, indicating the validation of the proposed finite element models. The research results show that the initial residual stress in the blank is the main effect element of machining distortion for aluminum alloy aircraft monolithic component, while cutting loads (including cutting force and temperature) are the main effect element of machining distortion for titanium alloy aircraft monolithic component. To decrease machining distortion of aluminum alloy aircraft monolithic component, the initial residual stress in the blank must be controlled first. Similarly, to decrease machining distortion of titanium alloy aircraft monolithic component, the cutting loads must be controlled first.