复杂曲面零件在线检测与误差补偿方法

复杂曲面零件的高精度加工与精密检测一直是数字化制造领域的研究热点。为提高复杂曲面零件的加工精度、检测精度,提出一种集数控机床在线检测、加工误差分解与补偿加工为一体的集成化方法。介绍集成化在线检测方法及补偿系统的基本原理,分析数控加工后曲面零件测点数据的误差组成,提出一种基于空间统计分析的加工误差分解方法,在建立基于B样条曲面的确定性曲面回归模型的基础上,对回归模型残差进行空间独立性分析,分解出系统误差和随机误差,进而通过数控代码的修改,实现零件加工过程的系统误差补偿。列举一个曲面零件的加工与检测实例,进行方法有效性验证。通过加工工件的在线检测、误差分解、代码修改及补偿加工等环节,实例零件的加工精度有了大幅提高,而该系统的检测精度也通过与三坐标测量机(Coordinate measuring machine, CMM)检验结果的对比,得到了有效验证。     

精密复杂零件数控加工在线检测与误差补偿技术研究

针对精密复杂零件数控加工离线检测误差大、效率低,在线检测尺寸、形状受限制等问题,建立了基于B样条曲面的确定性曲面回归模型,通过对回归模型残差空间独立性分析,将复杂零件的数控加工误差分解为系统误差和随机误差,通过修改数控代码,实现了精密复杂零件数控加工在线检测及误差补偿。为验证有效性,进行了大量试验,将试验结果与CMM检测结果对比,结果显示提出的在线检测及误差补偿方法行之有效,实现了精密复杂零件数控加工"加工-测量-补偿加工"的闭环制造。     

运用点涉法原理确定平头立铣刀三轴联动数控加工轨迹

针对现有的空间自由曲面数控编程系统和ＣＡＤ／ＣＡＭ软件只能生成球面刀三轴联动数控加工轨进的局限性，以及实际切削加工中较少采用球面刀，多用小直径平头立铣刀等非球面刀来替代球面刀在三轴联动数控机床上完成空间自由曲面的切削加工这一现状，本文根据点涉法原理推导出在空间自由曲面上生成平头立铣刀三轴联动数控加工轨迹的算法。只要给出被加工曲面的参数表达式，就可以利用该算法在被加工曲面上确定平头立铣刀的三轴联动数控加工轨迹。     

运用点涉法原理确定平头立铣刀三轴联动数控加工轨迹

针对现有的空间自由曲面数控编程系统和ＣＡＤ／ＣＡＭ软件只能生成球面刀三轴联动数控加工轨迹的局限性，以及实际切削加工中少采用球面刀，多用小直径平头立铣刀等非球面刀来替代球面刀在三轴联动数控机床上完成空间自由曲面的切削加工这一现状，本文根据点涉法原理推导出在空间自由贡面上生成平头立铣刀三轴联动数控加工轨迹的算法。只要给出被加工曲面的参数表达式，就可以利用该算法在被加工曲面上确定平立铣刀的三轴联动数控加     

适应数控加工的空间曲面的建立

在数控加工中,对复杂形体表面加工的一个难点就是曲面方程的建立,如何对空间自由曲面建立数学模型已成热点。文中论述了适应数控加工B样条曲面建立的方法,指出了B样条曲面具有一、二阶连续的特性,可以用多个曲面片的拼接而组成任意形状的自由曲面,从而解决了数控加工中空间曲面建模的难题,为建立空间自由曲面提供了确凿的理论依据。     

数控线切割加工空间曲面CAD/CAM技术研究

目前国内加工空间曲面零件通过采用锥度切割装置使电极丝倾斜一定角度来实现锥度切割,这种方法易产生的加工误差较大.论文在五轴联动数控线切割加工系统的运动分析的基础上,建立了直角坐标下空间曲面零件线切割加工成型的数控模型,阐述了利用G代码合成空间曲面的方法,提出了运用模块化技术设计空间曲面线切割五轴联动数控系统上位机软件设计方案,为空间曲面线切割CAD/CAM系统的研究提供了依据.     

空间曲面电火花线切割CAD/CAM系统

为解决高速走丝电火花线切割机床加工空间曲面的难题,实现大锥度空间复杂曲面零件的加工,以空间曲面数学模型和数控模型为基础,开发了一种计算机辅助设计/计算机辅助制造(Computer aided design/computer aided manufacturing,CAD/CAM)系统.其硬件系统以研制的数控转摆摆工作台为核心装置,并与现有高速走丝电火花线切割机床结合,组成空间曲面线切割加工系统.其软件系统可以根据上下导线的参数方程进行分析计算,建立空间曲面的三维模型,自动生成NC加工代码,进行加工仿真和空间曲面零件的加工.利用本系统进行典型空间复杂曲面零件的加工试验,结果表明加工结果与仿真结果基本相似.此外,还分析数控模型以及回摆间隙角对加工误差的影响.这些工作为解决高速走丝电火花线切割加工空间曲面的难题打下基础.     

空间自由曲面三坐标平头立铣刀数控加工系统

一、前言 自由型曲面的CAM技术一直是机械CAD/CAM研究的一个重要课题。国内外有关空间自由曲面的CAM技术的研究多集中在球头刀加工的方法上。采用球头刀具加工自由曲面虽然具有编程计算及干涉处理简单的特点,然而球头刀又因其在切削加工中存在一些不足,非球面形状刀具(平头立铣刀、锥状刀、成形刀等)在曲面加工中的重要性正逐渐为人们所认识。特别是平头刀,其作用更加显得突出。我国三坐标以上的数控机床数量尚少,所以研究使用平头立铣刀数控加工空间自由曲面,就更有实际意义。     

自由曲面五轴加工刀具轨迹规划技术的研究进展

利用五坐标设备进行自由曲面的数控加工是提高加工质量和加工效率的有效途径,自由曲面形状和五坐标机床运动的复杂性导致其刀具轨迹规划技术十分困难。针对自由曲面五坐标端铣加工、侧铣加工以及碰撞干涉分析中的关键技术,综述了近年来自由曲面五坐标数控加工领域刀具轨迹规划技术的研究进展和现状。结合自由曲面数控加工的工程实用性要求,分析了当前研究中存在的不足,指出目前的研究成果在通用性、稳定性和有效性方面尚不能完全满足工程应用,认为自由曲面五坐标数控加工刀具轨迹规划技术的研究应从三维的角度出发,在更为广域的刀具影响空间研究刀具同自由曲面之间的几何啮合关系,同时需要考虑机床的运动学和动力学特性以实现五坐标机床的高速和高效运行。     

数控仿形测量的密集散乱数据的曲面重建方法研究

数字化仿形技术是加工自由曲面的一种有效方法，而快速准确地重建数控仿形测量得到的散乱数据是实现数控仿形加工的关键步骤之一。分析了数控仿形测量数据的特点，确定重建曲面采用规则四边形网格几何结构，并提出了一种基于距离加权模型的节点插值方法，实现了散乱数据群的曲面重建。最后提供的曲面重建实例和加工实例证实了该方法是可行的。     

Deviation model based method of planning accuracy inspection of free-form surfaces using CMMs

Measurements of free-form surfaces are performed with the use of numerically controlled CMMs on the basis of a CAD model, which results in obtaining coordinates of discrete measurement points. The local geometric deviation, i.e. the distance of a particular measurement point from the CAD model of the nominal surface, is established for each point. The measurement aims at evaluating the form deviation and thus the greatest deviation of the actual surface from the CAD model. An effective measurement is one in which the probability of locating the greatest deviation is highest with the smallest possible number of measurement points. The present article suggests a method of planning a measurement strategy for objects with free-form surfaces. Repeatability of deterministic deviations on surfaces processed under the same conditions was applied. A CAD model of the product, built on the measurement points, and including the deterministic component of these deviations, was constructed. Effective surface measurements were planned locating the measurement points in the critical areas. The devised model was used for performing the measurement.     

Modelling of tolerances and manufacturing dimensions

To obtain imposed dimensional and geometrical specifications for any mechanical piece, production tolerances must be calculated. So a simulation of workpiece behavior when it is machined, has permitted calculations of deviations on machined surfaces.The method of deviation calculation is based on a comparison between imposed functional tolerance and the tolerance calculated in relation to deviations on two machined surfaces or between a machined surface and the operational datum.The one direction modelling of deviations inquires practical inputs such as the planning process, the operational datum, the deviations on rough surfaces, and deviations on surface datum for any stage of machining. The developed method allows determining the deviations on machined surfaces. Then, tolerances on production dimensions were calculated in three directions. These results have permitted to define average production dimensions, which may be used for NC machine programming and to prepare an optimal rough piece configuration.The developed method has been applied for the machining of a fixing screw.     

自由曲面磁流变抛光最佳压力场获取方法

针对自由曲面光学元件面形较复杂的特点,文中提出了一种磁流变抛光最佳的压力场获取方法.首先通过对磁流变抛光自由曲面光学元件抛光区域的压力场进行分析,得到压力场影响因素;其次,结合压力场影响因素,基于几何相贯理论建立压力场量化形态学评价方法;然后,基于自由曲面的几何模型,将该方法分别用于平面、不同曲率的球面和自由曲面,进行...     

A model-based approach for monitoring of shape deviations in peripheral milling

This paper presents a model-based approach for monitoring of shape deviations for milling operations. In order to detect occurring shape deviations of the machined workpiece during the milling process, different kinds of process models are presented and discussed for their application on manufacturing quality monitoring. Thereby, a model-based system was presented for the monitoring of shape deviations based on measured cutting forces. For the transformation of cutting forces into shape deviations, a tool deflection model and material removal model were designed and applied to a monitoring system. The presented model-based monitoring approach delivers accurate quality information, like geometric shape deviations, which can be monitored against geometric tolerances, providing a quality monitoring of manufacturing processes. The reconstruction of shape deviations from measured cutting forces is verified experimentally by comparing measured and reconstructed shape contours.     

The effect of characteristics of free<Emphasis Type="Bold">-</Emphasis>form surface on the machined surface topography in milling of panel mold

In the milling process of automobile panel mold of hardened steel, the characteristic of free-form surface is one of the dominant factors for surface topography. In this paper, the trajectory of cutting edge is firstly modeled to analyze the residual height of the free-form surface in ball-end milling of hardened steel. Furthermore, the non-uniform rational B-splines (NURBS) surface reconstruction is utilized to generate the surface topography. Subsequently, the influences of surface curvature, lead angle, milling vibrations on the machined surface topography, and residual height are investigated, respectively. Finally, the accuracy of the surface topography and the roughness prediction model are validated by the milling experiments of free-form surface, where two-dimensional contour maps could be obtained. The simulation and experimental results demonstrate that the machined surface topography of hardened steel is fitted by means of NURBS surface reconstruction. In that manner, the effects of surface characteristics on the machined surface topography can be accurately predicted.     

Prediction and compensation of machining geometric errors of five-axis machining centers with kinematic errors

Kinematic errors due to geometric inaccuracies in five-axis machining centers cause deviations in tool positions and orientation from commanded values, which consequently affect geometric accuracy of the machined surface. As is well known in the machine tool industry, machining of a cone frustum as specified in NAS979 standard is a widely accepted final performance test for five-axis machining centers. A critical issue with this machining test is, however, that the influence of the machine's error sources on the geometric accuracy of the machined cone frustum is not fully understood by machine tool builders and thus it is difficult to find causes of machining errors. To address this issue, this paper presents a simulator of machining geometric errors in five-axis machining by considering the effect of kinematic errors on the three-dimensional interference of the tool and the workpiece. Kinematic errors of a five-axis machining center with tilting rotary table type are first identified by a DBB method. Using an error model of the machining center with identified kinematic errors and considering location and geometry of the workpiece, machining geometric error with respect to the nominal geometry of the workpiece is predicted and evaluated. In an aim to improve geometric accuracy of the machined surface, an error compensation for tool position and orientation is also presented. Finally, as an example, the machining of a cone frustum by using a straight end mill, as described in the standard NAS979, is considered in case studies to experimentally verify the prediction and the compensation of machining geometric errors in five-axis machining.     

Frequency domain error analysis in turning

In spite of the large body of work on error analysis in turning, there are very few references that directly address the relationship between the original frequency content of the different dynamic errors of the machine tool and of the machining process and the resulting spatial frequency content of the machined surface. In this paper, the dynamic errors of a machine tool are classified into two categories: (a) kinematics-induced and (b) vibration-induced dynamic errors. Through a theoretical analysis, it will be shown that the spatial frequency content of the turned surface is not directly influenced by the original frequency factors of the machine dynamic error components, but by the aliased frequency factors which will be explained in this paper. On the basis of the establishment of the deterministic mathematical relationship between the frequency contents of the machine dynamic errors in the volumetric error model and the spatial frequency content of the turned surface in radial directions, a method for obtaining the frequency spectrum of the machined surface error in radial directions is given. In addition, a method to influence the number of spatial frequency components of the surface error in radial directions and to predict and control their magnitude is put forward. A case study of a flat surface turning is presented to highlight the effectiveness of the theoretical analysis and of the proposed methods. This study has potential applications in predicting and controlling the spatial content of machined surfaces, in selecting proper machining conditions, as well as in designing machine tools for applications in which strict spatial frequency requirements are placed on the workpiece surface.     

随机参数结构振动控制闭环特征值的标准差

用随机模型讨论参数不确定性系统的振动控制问题．把随机系统的振动控制问题转化为近似的确定性问题来处理，然后讨论随机参数对闭环特征值的影响，提出闭环系统特征值实部和虚部标准差的计算方法，并用数值例子说明文中方法的实际应用。     

A study on the five-axis end milling for sculptured surfaces

The direction vector of milling cutter for CL-data of five-axis milling is obtained by the fact that the bottom part of the milling cutter rides on free-form surfaces using the z-map method. Since the direction vector is known, CL-data can be transformed to the NC-code with regard to the geometry of the five-axis machine and post-processing. For uniform surfaces, the tool path is created from the prediction of cusp heights. After generating the NC-code, a sculptured surface was machined by five-axis end milling and cusp heights on the machined surface were measured by a three-dimensional CMM with laser scanner. From this machining test, it was found that this machining method is effective.