Tool path generation for ultra-precision machining of free-form surfaces

The generation of tool paths for ultra-precision machining is still a limiting factor in the manufacturing of parts with complex optical surfaces. In conventional machining as well as in complex five axes machining the application of CAD- and CAM-software for the generation of tool paths is state of the art. But these software solutions are not able to generate tool paths according to the high requirements of ultra-precision machining. This paper describes possible ways to generate tool paths for ultra-precision machining when the optical surface can be analytically described or when the surface data is derived from optical design software. Ultra-precision milling experiments with different tool paths have been carried out and the quality of the machined geometry has been evaluated concerning the achievable form accuracy.     

Tool path generation and error control method for multi-axis NC machining of spatial cam

In this paper, based on the homogeneous coordinate transformation and conjugate surface theory, a tool path generation method is developed for generating spatial cam in order to establish the interface between the design and manufacture of this class of product. The mathematical error (chordal deviation) between the design and manufacture surface has been analysed and used as a basis for selecting the tool path control point. Moreover, the developed tool path generation method is verified through a cutting simulation software with solid model. It is also verified through the trial cut with model materials on a five-axis numerical controlled machine. The results show that the mathematical error of the cam surface can be controlled within given tolerance by the proposed method.     

模具型腔电火花创成加工无干涉运动轨迹生成研究

针对电火花创成加工具有复杂自由曲面的模具型腔,提出利用简单圆柱形电极在五坐标联动电火花机床上加工自由曲面无干涉电极运动轨迹的生成算法,并对电火花加工过程中的电极损耗进行了补偿,提高了曲面的加工质量和加工精度。     

混粉电火花加工技术在粗加工中的应用研究

在对混粉电火花加工机理进行系统研究的基础上，对混粉电火花粗加工中的加工效率和加工表面粗糙度进行了实验研究。结果表明，通过合理选择放电参数，混粉电火花加工在相近加工表面粗糙度时，能显著提高加工效率，从而为混粉电火花加工技术在粗加工中应用提供依据。     

Tool path generation for NC grinding

A new method for tool path generation for grinding is proposed. This method for tool path generation is based on a conceptually simple yet fundamental representation of the manufactured surface. Such representations of the manufactured surface, which are derived analytically, were traditionally derived by measurement based methods. The representation of the manufactured surface is also advantageous in developing analytical estimates of surface roughness. These analytical estimates provide a starting point for the measurement or inspection operations which are usually data intensive and often times expensive for free-form surfaces. This paper thus presents an integrated approach to tool path generation which takes into account the manufacturing and measurement activities.     

Real-time generation and control of cutter path for 5-axis CNC machining

This paper presents a new approach to real-time generation and control of the cutter path for 5-axis machining applications. The cutter path generation method comprises real-time algorithms for cutter-contact path interpolation, cutter offsetting, and coordinate conversion. In addition, a global feedback loop is closed by the CNC interpolator so as to augment the controlled accuracy in practical cutter path generation. An error compensation algorithm and a feedrate adaptation algorithm for the control loop are developed, respectively.     

直接基于点云数据的刀具轨迹生成

直接基于测量数据来获得刀具轨迹的方法操作简单、计算稳定、加工效率高,适应快速制造的发展趋势。论文利用ATOSII光学扫描系统获取模型点云数据,并对点云数据处理,采取直接对点云数据分层,研究了轮廓数据提取,加工区域识别以及刀具轨迹规划等关键问题。     

Tool path generation and tolerance analysis for free-form surfaces

This paper focuses on developing algorithms that generate tool paths for free-form surfaces based on the accuracy of a desired manufactured part. A manufacturing part is represented by mathematical curves and surfaces. Using the mathematical representation of the manufacturing part, we generate reliable and near-optimal tool paths as well as cutter location data file for post-processing. This algorithm includes two components. First is the forward-step function that determines the maximum distance, called forward step, between two cutter contact (CC) points with a given tolerance. This function is independent of the surface type and is applicable to all continuous parametric surfaces that are twice differentiable. The second component is the side step function which determines the maximum distance, called side step, between two adjacent tool paths with a given scallop height. This algorithm reduces manufacturing and computing time as well as the CC points while keeping the given tolerance and scallop height in the tool paths. Several parts, for which the CC points are generated using the proposed algorithm, are machined using a three-axes milling machine. As part of the validation process, the tool paths generated during machining are analyzed to compare the machined part and the desired part.     

自由曲面平头立铣刀五轴数控加工轨迹的计算方法

提出了一种在参数坐标系下自适应步长和行距的计算方法 ,该算法考虑了不同刀具接触点处的曲率差异 ,在满足加工精度和粗糙度的前提下 ,又能有效地提高加工效率。该算法适合加工汽车车身模具等曲率变化大的曲面。文中还给出了刀位计算公式。     

自由曲面数控三坐标投影加工误差及补偿对策

分析了自由曲面三坐标投影法数控加工的步长误差和行距误差。提出了自由曲面三坐标投影加工误差补偿对策。引入控制参数Δz,根据曲面加工精度要求设定限值Δzmax,当Δz>Δzmax时,进行插入刀位处理,以保证曲面加工精度。     

A method of tool path compensation for repeated machining process

This paper proposes a software method to compensate for the contour error in repeated machining process. In the proposed method, the profile of the first machined part is measured by a coordinate measuring machine. Based on the measured data, the tool path is modified by a compensation algorithm, and then, is represented by a series of linear segments. Finally, the compensated tool path is fed to the CNC machine tool for the machining of subsequent parts. Mathematical analysis and experimental evaluation are presented in this paper.     

Autonomous form measurement on machining centers for free-form surfaces

This research aims at developing a measurement technique on machining centers for 3D free-form contours. An autonomous measuring principle is proposed and a prototype measuring device applicable to a machining center has been produced. In the measuring device, a laser displacement detector in a narrow range, which directly detects the distance from a point on the measured surface to the reference position of the detector output, is put together with the movable part of a linear encoder on the nut of a ball screw. A stepping motor controls the laser detector position to keep the output at the central value of the detector measuring range by driving the ball screw. Both the motor and the fixed part of the linear encoder are placed on the device base. The linear encoder detects the moving displacement of the screw nut, i.e. the position change of the laser detector. By installing the base on the spindle of a machining center and moving the table along a plane perpendicular to the spindle, the laser detector can automatically follow the contour of a work piece set on the table and measure its form along a scanning line, simultaneously. The displacement of a measured point relative to the reference position of the linear encoder output on the spindle side is just equal to the sum of the outputs of the two sensors, i.e. the laser detector and the linear encoder. Moreover, a simple experimental approach to identifying the sensing direction errors for an assembled measuring device is developed. The results of some experiments are also shown, which sufficiently demonstrate the effectiveness of the proposed inspection method and error identification approach.     

四轴联动加工中心几何误差软件补偿技术研究

以多体系统理论为基础,通过分析位移变换矩阵和位置变换矩阵,建立了四轴联动加工中心的几何误差模型.基于Windows平台开发了误差补偿软件,可以对测量数据进行机床几何误差的软件补偿,有效地提高了在线检测精度.软件系统在MAKINO立式加工中心上进行了实验验证,补偿效果明显.     

玻壳屏凸模型面数控加工刀具运动轨迹研究

数控加工刀具运动轨迹是确定数控加工工艺的重要环节,刀具运动轨迹设计质量的好坏,直接影响零件的加工质量及加工成本。为此,进行了基于切削力波动控制的球头刀铣削刀具路径优选实验研究,提出了针对玻壳屏凸模表面及其相似形状特征的模具型面编程策略。     

复杂直纹面加工中电极丝中心轨迹的求取算法研究

针对电火花线切割加工复杂直纹面的问题，以直纹面理论为基础，从实际加工要求出发，提出了求取电极丝中心轨迹的“广义电极丝”模型。分析了直导线直纹面电极丝中心轨迹的变化趋势，计算结果表明直接用电极丝中心轨迹两端点的连线近似表示该中心轨迹是欠妥的，为提高代码精度应对求取的电极丝中心轨迹进行同步线性化处理。     

Influence of the pulse shape on the EDM performance of Si3N4-TiN ceramic composite

This paper describes the influence of the EDM discharge pulse shape on the machining performances and material removal mechanisms of Si₃N₄-TiN. Dramatic differences of material removal, ranging from classical melting to chemical decomposition, are observed by applying different pulse shapes such as the iso-energetic or relaxation type discharge pulses. It not just leads to the change of surface texture and machining performances, but also has influences on the ceramic properties. An EDM strategy is developed for the production of ceramic components in Si₃N₄-TiN and validated through the fabrication of a high temperature mesoscopic gas turbine.