弱刚度环类零件装夹变形的研究

弱刚度环类零件车削加工易变形,在装夹过程中产生的弹性形变是造成加工后形状误差的一个重要原因。将普通卧式车床上所使用的三爪自定心卡盘改良为扇形卡盘,分别计算了2种装夹方式产生的理论变形量,建立了影响装夹变形的各个因素与变形量之间的函数关系,根据计算结果得到了扇形卡盘的最优结构参数,并通过有限元仿真实验,针对齿圈这类典型的弱刚度件的2种装夹方式进行了对比验证,为减小弱刚度环类零件的装夹变形提供了理论基础。     

异型薄壁铝合金腔体的精密加工技术

异型薄壁铝合金腔体由于形状复杂、外形协调性高、零件外廓尺寸相对截面较大、侧壁厚薄不匀、相对刚度低、材料去除量大和加工工艺性差等特点,导致零件变形尺寸超差,精度误差严重,生产加工效率低下。通过对异型薄壁铝合金腔体的结构工艺性进行分析,分析了影响零件产生变形的各种因素,研究了金属材料特性的机理,制订了一套完整的精密加工方案,解决了传统的工艺方法加工的零件变形的难题。该方案通过采用防变形装夹工装解决了由于夹紧力、重力、惯性力的作用而导致切削力、切削热、摩擦热、切削颤振等影响变形的因素产生;并采用合理选用刀具、切削参数、冷却液及多次走刀、反淬火处理等工艺方法,有效地解决了异型薄壁零件的加工变形难题,保证了质量稳定可靠。     

薄壁件加工变形控制快速仿真平台开发

为控制薄壁件装夹变形和加工变形,建立了集装夹优化、加工变形预测、切削参数优化及误差补偿功能为一体的快速仿真平台.在平台实现中,装夹方案的优化采用基于形位公差控制的方法,通过多种装夹方案的比较,确定优化方案.加工变形预测时考虑了前-层变形对后-层切削深度的影响,并使切削力和加工变形达到动态平衡.为获得优化切削参数,建立了以变形控制为目标的优化模型.采用有限元法计算加工变形,采用遗传算法求解优化模型.为解得优化补偿量,仿真时考虑了变形与力的耦合效应.完成了基于ABAQUS的快速仿真平台开发.以镜座零件为例进行仿真,求得了优化的装夹方案和切削参数,验证了平台的可行性.     

低刚度零件切削辅助支撑技术研究综述

由于低刚度零件的低刚度特性,在切削加工中很容易受到切削力、切削热及切削振动等作用而产生加工变形,因此被认为是机械加工中的难题,而采用辅助支撑可以有效减小低刚度零件的变形。本文总结了几种辅助支撑技术在低刚度零件中的应用,很好地保证了零件的加工精度和表面质量。     

某铝合金薄壁件装夹方法的工艺改进

对铝合金薄壁件装夹方式进行受力分析,建立了切削加工的力学模型及有限元分析模型,设计了一种轴向夹紧的车床夹具,夹具结构简单、夹紧可靠、操作迅速方便,并与试验数据进行对比,结果显示采用轴向夹紧可以明显减小零件的装夹变形。     

薄壁类零件加工装夹技术研究

薄壁零件刚性差,在加工过程中因受到切削力、夹紧以及切削热和残余应力影响极易产生变形,装夹是保证薄壁零件数控加工质量和效率的关键因素。本文介绍了常用的几种装夹形式及工装发展趋势。     

平口虎钳装夹下零件受力分析和变形控制

平口虎钳装夹是机械铣削加工中最常用的一种装夹方式.这种装夹方式简便、通用性强,但是在夹紧过程中容易导致零件弯曲变形,特别是厚度薄、宽度大的零件.文中主要分析平口虎钳装夹下钳口和铣刀对零件的作用力,以及这两种力的相互关系,探讨了在平口虎钳装夹下影响零件变形的因素和控制零件变形的措施.     

薄壁焊接结构的中央传动壳体工艺方法研究

研究了某新型航空发动机中央传动壳体加工过程中由焊接应力、装夹应力及切削应力引起的变形原因;阐述了零件加工过程中因基准质量不高、装夹变形、应力释放变形及累计误差而引起的高精度孔位置度加工不合格的问题,并找到了解决这些难题的加工方法。通过对零件加工边界条件分析来确立零件的加工关键要素控制点。通过调整零件的加工工艺路线来控制零件的焊接应力、切削应力。在能满足零件质量要求的范围内,同时采用精密磨削的方法来保证零件的基准质量。通过设计制造专用工装解决零件装夹变形和误差累计的问题,通过钻孔、铣孔、镗孔的孔加工方式来保证被加工孔的位置度及圆度。本方法在零件的实际加工验证中取得良好的效果,保证了零件的加工质量。实践证明,这种方法对其他壳体类零件的加工具有触类旁通的效果。     

航天薄壁框架类零件数控加工的变形抑制方法

针对航天薄壁框架类零件数控加工过程中的变形抑制问题,对加工工艺、装夹方式与切削路径进行分析,获得产品数控加工变形的影响因素并提出相关优化方向,改进总体加工工艺,量化夹持点、夹紧力等装夹要素,提出切削路径优化方法。通过产品加工验证试验,证明上述优化要素的有效性,为航天薄壁框架类零件的数控加工变形抑制提供技术支撑。     

基于铝质薄壁筒件切削加工的自动装夹技术研究

铝罐零件的刚性差,在切削过程中,容易受到切削力和夹紧力的作用而发生变形,从而影响产品的质量。合理的装夹方法可以有效地减小加工变形。因此设计了一种新的装夹方法,提高了加工精度,保证了加工质量,同时实现一次装夹完成切口与翻边的一体化加工。     

Effect of fixture compliance and cutting conditions on workpiece stability

This paper computes and investigates the effect of fixture compliance and cutting conditions on workpiece stability and uses it as a basis for selecting a suitable fixture among several alternatives. We use two criteria, the minimum eigenvalue of the fixture stiffness matrix and the largest displacement of the workpiece due to the cutting forces to assess the stability of the workpiece. First, the minimum eigenvalues of the fixture stiffness matrices, for the fixtures being considered, are computed. Second, since the eigenvalues are not dependant on the cutting forces, a displacement measure, the largest displacement of the workpiece due to the cutting force, is computed for each fixture. This displacement is a function of the cutting force and the fixture compliance. The choice of fixture is often a compromise between the two criteria. We also consider the combined influence of fixture compliance and cutting conditions on workpiece stability. The results from the simple study used for illustration show that the eigenvalues remain constant under different cutting conditions whilst the largest displacement reduces by 68%, a significant reduction.     

Modeling and compensation technology for the comprehensive errors of fixture system

Error modelling and compensating technology is an effective method to improve the processing precision.The position and orientation deviation of workpiece is caused by the fixing and manufacturing erro...     

轮毂加工过程分析与设计

轮毂是需要大批量生产的特殊中空类零件,为了提高工件生产效率,设计了一种专用夹具,可以对工件实现可靠的夹紧定位。通过 Pro/ E 软件对专用夹具和工件进行三维建模、Pro/ Mechanica 有限元分析,计算工件由于切削力产生的位移变形,证明了轮毂加工方案的可行性。     

Design and optimization of machining fixture layout using ANN and DOE

In machining fixtures, minimizing workpiece deformation due to clamping and cutting forces is essential to maintain the machining accuracy. This can be achieved by selecting the optimal location of fixturing elements such as locators and clamps. Many researches in the past decades described more efficient algorithms for fixture layout optimization. In this paper, artificial neural networks (ANN)-based algorithm with design of experiments (DOE) is proposed to design an optimum fixture layout in order to reduce the maximum elastic deformation of the workpiece caused by the clamping and machining forces acting on the workpiece while machining. Finite element method (FEM) is used to find out the maximum deformation of the workpiece for various fixture layouts. ANN is used as an optimization tool to find the optimal location of the locators and clamps. To train the ANN, sufficient sets of input and output are fed to the ANN system. The input includes the position of the locators and clamps. The output includes the maximum deformation of the workpiece for the corresponding fixture layout under the machining condition. In the testing phase, the ANN results are compared with the FEM results. After the testing process, the trained ANN is used to predict the maximum deformation for the possible fixture layouts. DOE is introduced as another optimization tool to find the solution region for all design variables to minimum deformation of the work piece. The maximum deformations of all possible fixture layouts within the solution region are predicted by ANN. Finally, the layout which shows the minimum deformation is selected as optimal fixture layout.     

Development of a finite element analysis tool for fixture design integrity verification and optimisation

Machining fixtures are used to locate and constrain a workpiece during a machining operation. To ensure that the workpiece is manufactured according to specified dimensions and tolerances, it must be appropriately located and clamped. Minimising workpiece and fixture tooling deflections due to clamping and cutting forces in machining is critical to machining accuracy. An ideal fixture design maximises locating accuracy and workpiece stability, while minimising displacements.The purpose of this research is to develop a method for modelling workpiece boundary conditions and applied loads during a machining process, analyse modular fixture tool contact area deformation and optimise support locations, using finite element analysis (FEA). The workpiece boundary conditions are defined by locators and clamps. The locators are placed in a 3-2-1 fixture configuration, constraining all degrees of freedom of the workpiece and are modelled using linear spring-gap elements. The clamps are modelled as point loads. The workpiece is loaded to model cutting forces during drilling and milling machining operations. Fixture design integrity is verified. ANSYS parametric design language code is used to develop an algorithm to automatically optimise fixture support and clamp locations, and clamping forces, to minimise workpiece deformation, subsequently increasing machining accuracy. By implementing FEA in a computer-aided-fixture-design environment, unnecessary and uneconomical “trial and error” experimentation on the shop floor is eliminated.     

EROWA电极定位夹头专用夹具设计

结合被加工零件的结构及加工工艺特点,设计制造了一款专用铣床气动多功能夹具。为保证夹具具有良好的强度,运用ANSYS Workbench软件对夹具工件系统进行了平面铣削和钻孔过程受力仿真分析。结果表明:装配件在钻削力和切削力作用下,产生的最大应力远小于材料的屈服强度,且最大位移值在加工公差范围内。经样品试制、现场实验检验,使用专用夹具生产出来的产品,其工件尺寸和几何误差均满足精度要求,达到预期目标。因此,该夹具结构设计合理,具有一定的推广应用价值。     

Machining fixture layout design using ant colony algorithm based continuous optimization method

In any machining fixture, the workpiece elastic deformation caused during machining influences the dimensional and form errors of the workpiece. Placing each locator and clamp in an optimal place can minimize the elastic deformation of the workpiece, which in turn minimizes the dimensional and form errors of the workpiece. Design of fixture configuration (layout) is a procedure to establish the workpiece–fixture contact through optimal positioning of clamping and locating elements. In this paper, an ant colony algorithm (ACA) based discrete and continuous optimization methods are applied for optimizing the machining fixture layout so that the workpiece elastic deformation is minimized. The finite element method (FEM) is used for determining the dynamic response of the workpiece caused due to machining and clamping forces. The dynamic response of the workpiece is simulated for all ACA runs. This paper proves that the ACA-based continuous fixture layout optimization method exhibits the better results than that of ACA-based discrete fixture layout optimization method.     

数控车削轮毂的夹爪改进与工艺优化

阐述在轮毂的数控车削加工过程中,由于受到夹具的夹紧力和切削力的作用,致使工件在加工时产生变形,尺寸精度大大超差,严重时甚至工件会脱落于夹具,导致工件报废。经过本人认真研究,通过改进夹爪、调整工件夹紧位置,适当改变夹头夹紧力及优化加工工艺等,从而大大提高了加工精度和生产效率,降低了劳动强度,节约生产成本。希望以上的方法能对从事相关工作的人员有一定的借鉴作用。     

机械式恒力夹紧装置

设计了一种机械式的可提供恒定夹紧力的夹紧结构,采用这种设计时,作用在工件上的夹紧力不随外加载荷的改变而变化,且在工作过程中即使工件产生微小变形,夹紧力也基本保持不变。此种夹紧结构适合对易碎、刚度差等工件的夹紧。     

Fundamental modeling for oblique cutting by thermo-elastic-plastic FEM

In this paper, the finite deformation theory and updated Lagrangian formulation were used to describe the oblique cutting process. Either the tool geometrical location condition or the strain energy density constant was combined with the twin node processing method to act as the chip separation criterion. An equation of three-dimensional tool face geometrical limitation was first established to inspect and correct the relation between the chip node and the tool face. And, a three-dimensional finite-difference heat transfer equation was derived. Based on this approach, tool advancement was achieved in displacement increment step by step from the initial tool contact with the workpiece till the formation of steady cutting force. In this case, a large deformation thermo-elastic–plastic finite element model for oblique cutting was established. The mild steel was used as the workpiece, the tool was P20 and the cutting speed was 274.8 mm/s in this article. The chip deformation process and temperature effect on the strain energy density, chip flow angle, cutting force and specific cutting energy were studied first. Finally, the integrity on machined workpiece surface was explored from the variation of residual stresses and temperature distribution on it after cutting. During the chip deformation process, the chip flow angle obtained by this simulation result was approximately equal to the tool inclination angle, which confirmed with the geometrical requirement of Stabler’s criterion. Besides, the simulated specific cutting energy was compared with the experimental specific cutting energy value, the result of which was within acceptable range. It is obvious from the above findings that the model presented in this paper is consistent with the geometrical and mechanical requirements, which verifies the proposed model is acceptable.