定心夹紧机构夹紧误差计算

机床夹具设计书和手册上都提到应考虑夹紧误差。但是 ,又认为“由于工件弹性变形的计算很复杂 ,而接触变形目前尚无可供实际应用的资料 ,所以在设计夹具时 ,对夹紧误差一般不作定量计算 ,而是采取各种措施来减少夹紧误差对加工精度的影响”。本文拟对常用的定心夹紧机构的夹紧误差分析计算方法进行探讨。因为讨论的是对心定中夹紧机构 ,在夹紧力的作用下 ,定位夹紧元件和工件的弹性变形和接触变形都是对称的 ,这样 ,对定位夹紧元件等速移动方式的定心夹紧机构的夹紧误差的计算就变为定位夹紧元件等速移动误差的计算。而对均匀弹性变形方式的…     

工件单面加工热变形误差计算分析

长尺寸重要零件单面加工过程中,因受热不均产生应力应变,容易出现热变形加工误差,为了准确计算这种误差,通过建立模型,应用数学和力学原理推导出单面加工热变形计算公式,并确定各项取值办法,进行了实例验证。本方法对一些高精度和典型重要工件加工误差的预测、修正、工艺结构设计改进和产品精度定位提供了重要依据。     

铝飞轮壳车削加工圆度超差分析与解决方案

针对某型号汽车发动机飞轮壳产品立车加工圆度超差问题,建立飞轮壳有限元模型,利用Altair Simlab与ANSYS Workbench等软件对工件在旋转状态下进行有限元仿真分析计算,得到工件的变形分布状况。结果表明:工件旋转产生的离心力引起的工件变形不是造成圆度误差的主要原因,而工件夹具系统偏心造成主轴轴承磨损产生间隙引起主轴的跳动才是最根本问题。根据最后的分析结果,针对夹具设计提出相应的改进方案。该结果可以为减少飞轮壳的加工圆度误差提供参考,提高产品的加工质量。     

自动线加工零件的精度(15)

4.工艺系统弹性变形对孔轴线偏移影响的确定 在自动线或流水线的加工工位上固定的工件孔轴线与刀具轴线不重合。偏移量取决于上道加工工序之后工件孔轴线相对于其工艺基准(平面和圆柱定位销孔轴线)的偏移△_(ΠP)、机床主轴轴线相对于工位定位基准(定位块平面和圆柱定位销轴线)的位置误差△_ρ以及工件在该工位的定位误差ε(参看图51)。     

零传动滚齿机热变形对加工精度的影响

根据零传动滚齿机YK3610的工件主轴和滚刀主轴的设计结构,分析了其热源及热变形机理,以此为基础,分析热变形对滚齿加工精度带来的影响,并建立了误差的数学模型;最后提出了对热变形进行误差补偿的简单方法.     

基于CAE和神经网络的切削参数优化

提出了一种以变形加工误差为约束的基于有限元分析和神经网络的切削参数优化方法.针对复杂工件夹具系统在切削过程中的变形问题进行有限元刚度计算,然后通过神经网络的方法拟合切削参数和工件夹具系统变形误差之间的关系.并以加工生产效率最大化为目标,在保证加工精度的前提下优化切削参数.从而实现以工艺成本最小化来提高零件的加工精度.     

基于C/S模式的数控车削物理仿真技术的研究

支持网络环境下数控加工仿真平台,当加工者和代码编制者不在同一物理地点或者相隔较远的情况,可以消除传统的数控加工仿真的局限性。目前的数控加工仿真大都是基于本地数控代码仿真,影响到仿真和加工的效率。文章提出建立基于C/S模式的数控车削仿真系统,重点分析了车削过程中工件受切削力作用产生的力变形,建立了力变形下工件直径误差的模型,并以此为基础对实际的阶梯轴车削加工进行分析。文章采用VC 编程实现了对加工刀具轨迹的仿真,并给出了考虑工件变形前后的真实加工轨迹对比。结果表明,可以采用误差补偿技术来消除因变形产生的误差。     

基于有限元分析的机床导轨热变形研究

高速高精度机床切削加工过程中,在多种热源的作用下导轨会产生热变形,影响工件与刀具间的相对位置,造成加工误差。找出导轨热位移较大的点,并分析其对加工精度的影响,对于减小加工误差提高加工精度至关重要。文章在对导轨热边界条件进行分析的基础上,应用有限元分析方法,建立了一类机床导轨的有限元热变形分析模型,并进行了热变形分析计算,为分析导轨的热变形对加工精度的影响提供了依据,并为机床综合热误差补偿提供参考。     

一面两销精确定位自动控制系统设计

针对传统的一面两销定位系统会产生较大的定位误差、影响零件的加工精度问题,设计一面两销精确定位自动控制系统。详细阐述了该系统的结构、工作原理和主要定位元件的设计计算方法,并通过箱体加工中使用一面两销定位的应用实例,对比分析了采用传统定位方式和采用精确定位系统时工件所产生的定位误差,得出使用一面两销精确定位自动控制系统可大大提高定位精度和能有效提高加工效率的结论。     

工艺系统综合变形对加工精度的影响

在实际加工中，工件的误差是工艺系统综合作用的结果。本文对机床-工件-刀具-夹具工艺系统综合变形对加工精度的影响展开讨论，并提出了减少工艺系统受力变形的措施。     

侧铣加工空间刀具半径补偿技术实现

通过对侧铣加工空间刀具半径补偿算法的研究,建立刀具和工件模型,并对其进行了求解和公式推导。对任意侧铣加工曲面进行偏置计算,生成带有刀具半径补偿的侧铣偏置曲面,从而解决了侧铣加工中曲面偏置位置的问题,实现了侧铣加工空间刀具半径补偿,该方法的应用为数控系统研究侧铣空间刀具半径补偿提供了参考。     

5-Axis adaptive flank milling of flexible thin-walled parts based on the on-machine measurement

Deformation of the part and cutter caused by cutting forces immediately affects the dimensional accuracy of manufactured parts. This paper presents an integrated machining deviation compensation strategy based on on-machine measurement (OMM) inspection system. Previous research attempts on this topic deal with deformation compensation in machining of geometries in 3-axis machine tools only. This paper is the first time that concerned with 5-axis flank milling of flexible thin-walled parts. To capture the machined surface precision dimensions, OMM with a touch-trigger probe installed on machine׳s spindle is utilized. Probe path is planned to obtain the coordinate of the sampling points on machined surface. The machined surface can then be reconstructed. Meanwhile, the cutter׳s envelope surface is calculated based on nominal cutter location source file (CLSF). Subsequently, the machining error caused by part and cutter deflection is calibrated by comparing the deviation between the machined surface and the envelope surface. An iteration toolpath compensation algorithm is designed to decrease machining errors and avoid unwanted interference by modifying the toolpath. Experiment of machining the impeller blade is carried out to validate the methodology developed in this paper. The results demonstrate the effectiveness of the proposed method in machining error compensation.     

A machining test to calibrate rotary axis error motions of five-axis machine tools and its application to thermal deformation test

This paper proposes a machining test to parameterize error motions, or position-dependent geometric errors, of rotary axes in a five-axis machine tool. At the given set of angular positions of rotary axes, a square-shaped step is machined by a straight end mill. By measuring geometric errors of the finished test piece, the position and the orientation of rotary axis average lines (location errors), as well as position-dependent geometric errors of rotary axes, can be numerically identified based on the machine׳s kinematic model. Furthermore, by consequently performing the proposed machining test, one can quantitatively observe how error motions of rotary axes change due to thermal deformation induced mainly by spindle rotation. Experimental demonstration is presented.     

Generation of engineered surfaces by the surface-shaping system

Engineering surfaces are generated by a variety of manufacturing processes, each of which produces a surface with its own characteristic topography. A method for the prediction of the topography of engineering surfaces has been developed based on models of machine tool kinematics and cutting tool geometry. The model termed the surface-shaping system accounts for not only the nominal or global cutting motions but also takes into account errors during machining such as tool runout, machine deformation and vibration, as well as higher order motions.     

基于UKF薄壁件加工变形预测技术研究

薄壁件加工中的零件变形和让刀是影响加工精度的主要原因,首先,根据零件加工路径构建UKF预测模型;之后,把数控机床误差和在机测量系统误差作为已知噪声输入到UKF算法中,在机检测系统对序中尺寸进行测量作为过程转移噪声,上次过程转移噪声输入到下次预测中;最后,使用MATLAB预测出零件变形量。上次状态转移噪声输入到UKF算法中以提高预测对真实加工环境的模拟,运用在机检测技术把零件加工数据传输到UKF算法中提高变形预测精度,为薄壁件数控加工序中补偿提供数据依据。     

Feasibility study of in-process compensation of deformations in flexible milling

During the machining of thin-walled parts, deformation can occur resulting in dimensional errors. These dimensional errors cause a variation on cutting forces. From the actual measured cutting forces and the estimated forces resultant from rigid machining, it is possible to determine the value of this deformation. Based on this, an on-line system for compensating workpiece errors, has been developed. The system is based on correcting the relative position of the tool-workpiece during machining by means of a piezoelectric actuator. The objective is achieved in real time to compensate for the part deformations from the measurement of the cutting forces, without the programming of the tool path trajectories in the machine tool being affected.     

Development of a virtual machining system, part 3: cutting process simulation in transient cuts

In Parts 1 and 2 of this three-part paper, a mechanistic cutting force model was developed and machined surface errors for steady cuts under fixed cutting conditions were predicted. The virtual machining system aims to simulate and analyze the machining and the machined states in a general flat end-milling process. This frequently involves transient as well as steady cuts. Therefore, a method for simulating the cutting process of transient cuts needs to be developed to realize the virtual machining system concept. For this purpose, this paper presents a moving edge-node (ME) Z-map model for the cutting configuration calculation. The simulation results of four representative transient cuts in two-dimensional pocket milling and an application of off-line feed-rate scheduling are also given.

In transient cuts, the cutting configurations that are used to predict the cutting force vary during the machining operation. The cutting force model (Part 1) and surface error prediction method (Part 2) were developed for steady cuts; these are extended to transient situations using the ME Z-map model to calculate the varying cutting configurations efficiently. The cutting force and surface errors are then predicted. To validate the feasibility of the proposed scheme, the measured and predicted cutting forces for transient test cuts were compared. The predicted surface error maps for transient cuts were constructed using a computer simulation. Also, off-line feed-rate scheduling is shown to be more accurately performed by applying the instantaneous cutting coefficients that were defined in Part I.     

The prediction of dimensional error for sculptured surface productions using the ball-end milling process. Part 2: Surface generation model and experimental verification

This paper presents a surface generation model for sculptured surface productions using the ball-end milling process. In this model, machining errors caused by tool deflections are studied. As shown in Part 1 of this paper, instantaneous horizontal cutting forces can be evaluated from the cutting geometries using mechanistic force models. In this paper, a tool deflection model is developed to calculate the corresponding horizontal tool deflection at the surface generation points on the cutter. The sensitivity of the machining errors to tool deflections, both in magnitude and direction, has been analyzed via the deflection sensitivity of the surface geometry. Machining errors are then determined from the tool deflection and the deflection sensitivity of the designed surface. The ability of this model in predicting dimensional errors for sculptured surfaces produced by the ball-end milling process has been verified by a machining experiment. In addition to providing a means to predict dimensional accuracy prior to actual cutting, this surface generation model can also be used as a tool for quality control and machining planning.     

Enhanced virtual machining for sculptured surfaces by integrating machine tool error models into NC machining simulation

Sculptured surface machining is a time-consuming and costly process. It requires simultaneously controlled motion of the machine axes. However, positioning inaccuracies or errors exist in machine tools. The combination of error motions of the machine axes will result in a complicated pattern of part geometry errors. In order to quantitatively predict these part geometry errors, a new application framework ‘enhanced virtual machining’ is developed. It integrates machine tool error models into NC machining simulation. The ideal cutter path in the NC program for surface machining is discretized into sub-paths. For each interpolated cutter location, the machine geometric errors are predicted from the machine tool error model. Both the solid modeling approach and the surface modeling approach are used to translate machine geometric errors into part geometry errors for sculptured surface machining. The solid modeling approach obtains the final part geometry by subtracting the tool swept volume from the stock geometric model. The surface modeling approach approximates the actual cutter contact points by calculating the cutting tool motion and geometry. The simulation results show that the machine tool error model can be effectively integrated into sculptured surface machining to predict part geometry errors before the real cutting begins.     

Particular behavior of spindle thermal deformation by thermal bending

Thermally induced errors reduce the accuracy in precision machining, and a great deal of research has been presented on compensation for these errors in machine tools. However, during the transition period after commencing or stopping spindle rotation, thermal deformation behavior is very complex. In particular, the y-directional movement of the vertical machining center cannot be explained by thermal expansion alone because of the relationship between deformation and temperature. Thermal bending that is generated from the thermal gradient in the structure causes this movement. In the research described in this paper, a theoretical explanation and an experimental verification is given for the particular behavior of spindle thermal deformation. As it is not easy to map the relationship of the compensation model, separation of the steady from the non-steady state in the mapping process is strongly recommended.