薄壁腹板加工变形规律及其变形控制方案的研究

针对薄壁结构框体零件切削加工中腹板变形问题进行了分析研究。通过建立薄壁腹板铣削加工受力模型、有限元变形分析模型，结合切削试验，得到了薄壁腹板加工变形的基本规律，并据此提出了相应的变形控制工艺措施。结果表明，薄壁腹板加工变形模式与腹板结构尺寸、走刀路径、切削用量等因素的组合有关；大切深法以及分步环切法可以充分利用薄壁零件自身刚性，减小加工变形，提高加工精度，是两种控制薄壁腹板加工变形的有效工艺措施。     

薄壁零件数控铣削加工工艺技术研究

针对薄壁类零件加工的困境,在分析了加工变形的主要因素,即工艺系统刚度、零件结构、工艺路线、走刀策略及工件装夹等的基础上,提出了控制零件加工变形,提高工件精度的工艺技术方案,对此类零件的数控加工有一定的参考作用。     

基于尺度效应的介观尺度零件多工位制造误差建模与分析

针对介观尺度零件制造过程中的加工精度控制问题,提出包括尺寸误差传递模型、多元统计过程控制和误差源诊断的加工精度控制体系,为精密微小零件多工序数字化制造提供了技术基础。通过研究介观尺度零件的特点及其在切削加工中的特性,提出基于微细切削尺度效应的工件变形和刀具变形引起的加工误差模型,构建了介观尺度零件尺寸误差传递的状态空间模型;在此基础上提出集成尺寸误差模型和多元统计过程控制的质量监控策略以及基于协方差分析的误差源诊断方法,实现了对介观尺度零件加工误差的诊断与加工精度的控制。以不锈钢工件微细槽铣削加工为例,验证了模型的有效性和可行性。     

装夹大长径比薄壁工件的自定心装置

<正>1引言起落架生产中常遇到一些长径比≥6、壁厚≤1的薄壁工件,在切削力、夹紧力及切削热和残余应力作用下易产生弯曲变形,因此控制加工变形是大长径比薄壁工件加工质量的关键。目前,控制加工变形的主要措施有合理选择刀具材料、刀具几何角度、切削用量和改进装夹方式等,其中装夹方式的作用较为重要。薄壁工件在机床上的装夹精度是影响加工质量的重要因素,20%-60%的加工误差由定位、夹紧方式引起,因此通过优化定位、夹紧方案来减小     

数控机床定位精度研究进展

数控机床定位精度及重复定位精度是零件加工精度的决定因素,是提高机床加工精度和运行稳定性的关键。数控机床定位精度影响因素多、非线性程度高,受到持续的、广泛的关注。本文基于精度提高过程,从定位精度误差源、定位精度检测、误差补偿等方面进行评述。当前研究在系统性、普遍性、实用性等方面存在不足,建立普遍适用的定位精度综合模型、控制方法和实现高精度、低成本、易操作的补偿方法是发展趋势。     

基于Rayleigh-Ritz法的钛合金薄壁件非均匀余量加工变形控制研究

为减小钛合金薄壁件切削加工过程中的变形，提出了一种新型的非均匀余量设计策略。建立了基于Rayleigh-Ritz法的薄壁件铣削加工变形预测数学模型，提出了离散化的余量体积单元设计思路并完成了工件的非均匀余量设计，最后对比分析了不同余量设计策略对薄壁悬臂结构件加工变形的影响。研究结果表明：所提出的基于Rayleigh-Ritz法的离散余量体积单元非均匀余量设计策略对工件自身刚度利用率高，表面加工误差分布一致性好，且对控制最大表面加工误差具有更优的效果。     

薄壁矩形深腔体数控加工防变形工艺研究

薄壁矩形深腔体零件在加工、装配及物流过程中极易产生变形，由于工件材料、壁厚、刚性、装夹等多种原因，导致零件加工工艺编制的难度增加。通过实例从零件的变形理论分析、防变形工艺方法等角度出发研究了薄壁矩形深腔体零件的数控加工工艺。     

机床传动链传动误差采集及滚珠丝杠副导程误差分析

在齿轮、螺纹、丝杠等零件的加工中,影响加工精度的主要因素之一是加工机床传动链中传动件的加工制造及装配误差。这些误差通过一定的传动环节。按一定的比例关系反映到被加工零件上。寻找误差源的途径大致可以分为两种t一种是直接检测机床传动链两端间的相对运动关系来分析误差源;另一种是通过对被加工零件的检测来间接地分析机床传动链中的误差。无论采用哪种方法都是把形成工件表面的两个相对运动(或运动轨迹)间的误差计算出来。 本文将以滚珠丝杠副导程测量分析为例,说明加工零件的检测和分析寻找误差源的微型机数字比相、误差回归分析…     

不锈钢薄壁零件的车削加工工艺研究

针对薄壁不锈钢薄壁零件的材料强度高和加工难度大的问题,以数控加工技术平台为基础,研究了辅助衬胎具、油泥填充、切削用量及车削加工工艺。铝由于其具有高强度低硬度的特点,因此选取该材料作为加工不锈钢薄壁零件外形用的辅助衬胎具;为减少零件和胎具间由于机械加工产生的摩擦和热量,采用自主设计的油泥,主要成分为工业润滑脂与汽车使用的5W-30机油,通过将几种物质混合进行搅拌成糊状,在加工时均匀涂抹在胎具表面,填充胎具与零件间的微小间隙;切削加工问题上,根据材料性能、机床误差、操作误差和测量误差等确定合理的切削余量,降低了薄壁零件废品率,降低加工成本,从而提高质量。目前,该操作法在某发动机外壳零部件、某弹药壳体部件精车加工工序上应用,基于当前加工技术平台,利用我单位现有的国内自产数控车床上使用得到的验证。通过探索该零部件的工艺方案及加工过程,有效地解决了工件装夹、加工变形等难题,极大地提升了工件表面粗糙度和尺寸精度,对推动同类薄壁筒类零件加工起到了指导作用。     

铝合金航空薄壁框铣削变形预测研究

铝合金航空薄壁框刚性差,铣削加工过程中极易产生加工变形,影响工件加工精度和生产成本。本文利用有限元方法,模拟分析了铣削力对航空薄壁框类零件加工变形的影响,从控制航空薄壁框铣削加工变形的角度出发,分析了不同框体尺寸航空薄壁框的铣削应力与加工变形情况,得到了加工变形规律。本研究可为预测和控制航空薄壁框类零件的加工变形提供方法和依据,对航空薄壁框类零件的结构设计、缩短研制周期和进一步提高生产率等都具有重要意义。     

考虑热误差的双转台机床工艺误差谱预测方法

五轴数控机床的几何误差和热误差是影响工件加工精度的两个重要因素,对这些误差因素进行分析可以有效提高薄壁件工件的加工精度。本文首先基于齐次坐标变换法,建立了双转台五轴数控机床的旋转轴几何误差模型;然后基于对标准球进行在机接触测量,辩识得出两旋转轴的12项几何误差,这些误差考虑了两旋转轴之间的相互影响和其热误差的影响;最后分析五轴数控机床加工空间的几何误差场,在该加工空间内几何误差从中心到外侧逐渐增加,当A轴旋转角度增加时,误差的最大值也随之增加。与其它位置误差辨识方法相比,本方法的测量精度符合加工要求,测量时间只需要30 min。     

Redesigned Surface Based Machining Strategy and Method in Peripheral Milling of Thin-walled Parts

Currently, simultaneously ensuring the machining accuracy and efficiency of thin-walled structures especially high performance parts still remains a challenge. Existing compensating methods are mainly focusing on 3-aixs machining, which sometimes only take one given point as the compensative point at each given cutter location. This paper presents a redesigned surface based machining strategy for peripheral milling of thin-walled parts. Based on an improved cutting force/heat model and finite element method(FEM) simulation environment, a deflection error prediction model, which takes sequence of cutter contact lines as compensation targets, is established. And an iterative algorithm is presented to determine feasible cutter axis positions. The final redesigned surface is subsequently generated by skinning all discrete cutter axis vectors after compensating by using the proposed algorithm. The proposed machining strategy incorporates the thermo-mechanical coupled effect in deflection prediction, and is also validated with flank milling experiment by using five-axis machine tool. At the same time, the deformation error is detected by using three-coordinate measuring machine. Error prediction values and experimental results indicate that they have a good consistency and the proposed approach is able to significantly reduce the dimension error under the same machining conditions compared with conventional methods. The proposed machining strategy has potential in high-efficiency precision machining of thin-walled parts.     

An integrated error compensation method based on on-machine measurement for thin web parts machining

Thin webs are widely used in the aerospace industry for the advantages of compact structure, light weight and high strength-to-weight ratio. Due to its low rigidity, serious machining error may occur, therefore, Finite Element method and mechanism analysis are usually utilized to modeling its deformation. However, they are very time-consuming and only suitable for elastic deformation error. In this study, an integrated error compensation method is proposed based on on-machine measurement (OMM) inspection and error compensation. The OMM inspection is firstly applied to measure the comprehensive machining errors. The Hampel filtering is then used to eliminate outliers, followed by the triangulation-based cubic interpolation as well as a machine learning algorithm which are used to establish the compensation model. At last, the real time compensation of high-density cutting points is realized by developing the compensation system based on External Machine Zero Point Shift (EMZPS) function of machine tool. Three sets of machining experiment of a typical thin web part are conducted to validate the feasibility and efficiency of the proposed method. Experiment results revealed that after compensation, the comprehensive machining errors were controlled under different machining conditions and 58.1%, 68.4% and 62.6% of the machining error ranges were decreased, respectively. This method demonstrates immense potential for further applications in efficiency and accuracy improvement of thin-walled surface parts.     

钛合金薄壁微铣削精度研究现状与发展趋势

随着航空、航天、船舶等工程领域对具有薄壁结构的钛合金零件需求的不断提高,加工效率相对较高且适用于曲面等复杂几何形状制造的微铣削加工方法在钛合金薄壁加工中获得了广泛的应用。然而由于其刚度较低,在微铣削加工钛合金薄壁时极易产生工件变形、失稳和振动等问题,并导致加工精度的下降。为此从理论建模、有限元仿真和试验测量三个方面分析了国内外弱刚度金属薄壁微铣削技术研究的现状。相关研究表明,在加工过程中对薄壁变形进行准确预测对于薄壁微铣削加工误差补偿模型的建立与薄壁加工精度的提高具有重要意义。并指出,在获得数学规律的基础上对薄壁微铣削加工变形和该变形对加工精度造成的影响之间蕴含的物理关系仍有待进一步的研究。     

Effects of tool diameters on the residual stress and distortion induced by milling of thin-walled part

Residual stress has a sustained impact on the deformation of thin-walled parts after processing, raising the strict restrictions required in their using procedure. In general, with regard to thin-walled parts, different processing parameters will affect the distortion and residual stress generation of the workpiece, which play the key role in the machining. However, controlling the material removal rate is also quite critical to machining of thin-walled parts. In order to reach these goals, based on the relation between residual stress and uncut chip thickness (UCT), a method is proposed by optimizing the milling tool diameters. The research finding reveals that, by improving the tool diameter, at the same circular position, smaller UCT can be achieved. In addition, take 6 and 12 mm tool diameter as analysis cases; larger tool diameter can reduce the residual tensile stress distribution significantly (the ratio ranges from 13.9 to 34.7 %) and improve the material removal rate. Moreover, a typical thin-walled part is evaluated using different tool diameters (6 and 12 mm) by experiments, as the final distortion can be decreased by 60 % with 12-mm tool diameter. The distribution of machined surface and subsurface residual stress is turning to be more uniform. Hence, it proves that, under the goals of maintaining machining accuracy and material removal rate, also improving the distribution of residual stress, it is possible to achieve by controlling the UCT (tool diameters) in the processing of thin-walled. All these findings can help to enhance the milling precision of thin-walled parts, as well as control and optimize the residual stress distribution.     

Error Compensation of Thin Plate-shape Part with Prebending Method in Face Milling

Low weight and good toughness thin plate parts are widely used in modern industry, but its flexibility seriously impacts the machinability. Plenty of studies focus on the influence of machine tool and cutting tool on the machining errors. However, few researches focus on compensating machining errors through the fixture. In order to improve the machining accuracy of thin plate-shape part in face milling, this paper presents a novel method for compensating the surface errors by prebending the workpiece during the milling process. First, a machining error prediction model using finite element method is formulated, which simplifies the contacts between the workpiece and fixture with spring constraints. Milling forces calculated by the micro-unit cutting force model are loaded on the error prediction model to predict the machining error. The error prediction results are substituted into the given formulas to obtain the prebending clamping forces and clamping positions. Consequently, the workpiece is prebent in terms of the calculated clamping forces and positions during the face milling operation to reduce the machining error. Finally, simulation and experimental tests are carried out to validate the correctness and efficiency of the proposed error compensation method. The experimental measured flatness results show that the flatness improves by approximately 30 percent through this error compensation method. The proposed method not only predicts the machining errors in face milling thin plate-shape parts but also reduces the machining errors by taking full advantage of the workpiece prebending caused by fixture, meanwhile, it provides a novel idea and theoretical basis for reducing milling errors and improving the milling accuracy.     

Study on the influence of geometric errors in rotary axes on cubic-machining test considering the workpiece coordinate system

Evaluating the influence of geometric errors in rotary axes is a common method used by a five-axis machine tool for improving the machining accuracy. In conventional geometric error models, the table coordinate system is considered as the final workpiece coordinate system. In this study, an additional workpiece coordinate transformation was proposed to identify the influence of geometric error. First, a cubic machining test was conducted. Second, the necessity of workpiece coordinate transformation was analyzed, and a method for coordinate transformation was proposed. In addition, both machining simulation and an actual machining experiment of the cubic machining test were conducted to verify the efficiency of the proposed method. The results indicate that the workpiece coordinate transformation is an essential part of the geometric error model for accurately simulating the geometric error influence. The method for identifying the geometric error influence considering the workpiece coordinate transformation is applicable in manufacturing.     

工件分特征下的五轴数控机床关键几何误差分析与补偿方法

提出了工件分特征下的五轴数控机床关键几何误差分析与补偿方法,将复杂工件进行特征分解,通过灵敏度分析辨识工件分特征下的关键几何误差并补偿,从而提高工件整体加工精度。以某一复杂工件为例,首先,将其分解为平面、斜面、圆柱和圆锥台四个典型特征;然后,基于灵敏度分析分别辨识出各典型特征对应的关键几何误差;最后,分特征地进行误差补偿。在AC双转台五轴数控机床上进行了实验验证,实验结果表明,辨识得到的关键几何误差灵敏度系数之和占比均大于90%,补偿后工件四个典型特征的加工精度提高了20%~30%。研究结果表明,所提方法能有效辨识不同工件分特征下的关键几何误差,从而提高复杂工件的加工精度。     

基于有限元数值模型和进给速度优化的薄壁件侧铣变形在线控制

为实现在加工过程中对薄壁件侧铣产生的较大切削变形进行在线控制,提出基于有限元数值模型和进给速度优化的在线控制策略。根据薄壁件切削过程的有限元仿真结果,建立数控机床进给速度、切削力、工件切削变形间的数值模型,进而确定用于控制变形的最优目标切削力。在具有开放式模块化的数控系统平台上开发了切削力信号实时采集、滤波功能和基于Brent-Dekker算法的进给速度在线优化策略,并根据滤波后的切削力及相应算法在加工过程中实时调整机床进给速度,保证切削力逐渐接近最优控制目标而实现切削变形的在线控制。试验结果表明,经过进给速度在线优化后的切削过程可将薄壁件侧铣变形控制在规定范围内,同时提高了切削效率。     

Application of ACO-BPN to thermal error modeling of NC machine tool

Thermal errors are the major contributor to the dimensional errors of a workpiece in precision machining. Error compensation technique is a cost-effective way to reduce thermal errors. Accurate modeling of errors is a prerequisite of error compensation. In this paper, four key temperature points of a NC machine tool were obtained based on clustering method. A thermal error model based on the four key temperature points was proposed by using ant colony algorithm-based back propagation neural network (ACO-BPN). The ACO-BPN method improves the prediction accuracy of thermal deformation in the NC machine tool. A thermal error compensation system was developed based on the proposed model, and which has been applied to the NC machine tool in daily production. The results show that the thermal drift in workpiece diameter has been reduced from 33 to 8 μm from its center of tolerance.