Non-uniformly variable errors inherent in the turning operation

Variations of the depth of cut during the turning operation result in the generation of dynamic cutting forces which act upon the processing system to introduce non-uniformly variable errors. These are in turn transferred to the turned workpiece. Equations were derived to describe the dynamic forces generated owing to initial errors in the blank. Evaluation of the dynamic forces generated and the corresponding transferred error is presented.     

Repetitive Measurement and Compensation to Improve Workpiece Machining Accuracy

Achieving workpiece high accuracy at low cost is one of the greatest challenges in the manufacturing industry. A repetitive error measurement and compensation scheme to improve the workpiece diameter accuracy for machining centres is des-cribed. The scheme entails an on-machine measurement and error compensation technology between machining processes. The workpiece diameters are measured along the workpiece length by using a fine touch sensor. The workpiece diameters in the compensation program are modified for implementation of next pass error correction. The technology is realised on a CNC turning centre. This method works well in hard machining and turned workpieces with large length–diameter ratios where the machining process induced errors are significantly greater than errors from other sources. It demonstrates that the work-piece can obtain maximum possible machining accuracy by this repetitive measurement and compensation technique.     

虚拟加工物理仿真中的误差分析研究

基于虚拟制造的理论与方法,模拟真实加工条件,建立了面向虚拟数控车削加工环境的加工精度分析系统。该系统基于有限元方法,用有限元法计算刀具-工件在切削要素（切削力、夹紧力、切削温度等）作用下的变形,通过求工件-刀具的布尔差集获取切削后的工件轮廓;利用MATLAB优化工具箱,分析工件轮廓,预测零件加工误差。     

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...     

用于加工中心的在线工件自动测量系统

介绍一种可用于加工中心的在线工件自动测量系统的构成及功能。该系统采用新型触发式传感器 ,可使刀具刀尖自身作为测头测试工件加工尺寸。该系统可用于工件的装夹找正 ,也可对工件进行自动在线测量 ,并能根据测量结果对加工误差进行补偿以提高加工精度     

Application of projection pursuit regression to thermal error modeling of a CNC 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, a thermal error model was proposed by using projection pursuit regression (PPR). The PPR method improves the prediction accuracy of thermal errors in the computer numerical control (CNC) turning center. A thermal error compensation system was developed based on the PPR model, and which has been applied to the CNC turning center in daily production. The results show that the thermal drift in workpiece diameter has been reduced from 34 to 5???m.     

Chucking compliance compensation with a linear motor-driven tool system

This paper describes a system that compensates for machining errors resulting from chucking with separated jaws. In machining a chucked cylindrical workpiece, degradation in machining accuracy, such as out-of-roundness, is inevitable due to variation in the radial compliance of the chuck workpiece system caused by the position of jaws with respect to the direction of the applied force. To compensate for the machining error induced by chucking compliance, the roundness profile of the workpiece due to chucking compliance after machining should be predicted first. Then, using this prediction profile, a compensating tool feed trajectory can be generated. By synchronizing the cutting tool drive system with the rotation of the workpiece, machining errors induced by chucking compliance can be reduced. To satisfy the condition that the cutting tool feed system must provide both high speed and high position accuracy, a brushless linear DC motor is used. In this study, first, the variation in the radial compliance of the chuck workpiece system is obtained through a force-deflection experiment with a workpiece-chucked lathe. Next, using mathematical equations and the results of the cutting experiment, a workpiece profile prediction and its compensating tool trajectory are generated. Then, the configuration of the compensation system based on a linear motor is described, and a proportional integral derivative (PID) controller is designed to improve the system performance. Finally, the tracking performance of the system is confirmed by experiment. A real cutting experiment shows significant improvement in roundness.     

Thermal error compensation of a 5-axis machine tool using indigenous temperature sensors and CNC integrated Python code validated with a machined test piece

Achieving high workpiece accuracy is the long-term goal of machine tool designers. There are many causes for workpiece inaccuracy, with thermal errors being the most common. Indirect compensation (using prediction models for thermal errors) is a promising strategy to reduce thermal errors without increasing machine tool costs. The modelling approach uses transfer functions to deal with this issue; it is an established dynamic method with a physical basis, and its modelling and calculation speed are suitable for real-time applications. This research presents compensation for the main internal and external heat sources affecting the 5-axis machine tool structure including spindle rotation, three linear axes movements, rotary C axis and time-varying environmental temperature influence, save for the cutting process. A mathematical model using transfer functions is implemented directly into the control system of a milling centre to compensate for thermal errors in real time using Python programming language. The inputs of the compensation algorithm are indigenous temperature sensors used primarily for diagnostic purposes in the machine. Therefore, no additional temperature sensors are necessary. This achieved a significant reduction in thermal errors in three machine directions X, Y and Z during verification testing lasting over 60 h. Moreover, a thermal test piece was machined to verify the industrial applicability of the introduced approach. The results of the transfer function model compared with the machine tool's multiple linear regression compensation model are discussed.     

Modelling of dimensional and geometric error prediction in turning of thin-walled components

In die-mold manufacturing and aircraft industry, many components that have thin-walled features are produced by turning operation. The major problem encountered during internal or external turning is cutting force induced deflection of workpiece along the periphery as well as axial length of a component. The present research work aims to develop a mathematical model for estimating dimensional and geometric errors during turning of thin-walled hollow cylinder qualitatively and quantitatively. In the proposed model, a mechanistic approach which is semi-analytical in nature is followed to achieve accuracy of the predicting results. First of all, process geometry model for thin-wall turning is developed based on process geometry variables such as uncut chip thickness, actual feed per revolution, actual depth of cut, peripheral cutting speed, effective cutting area etc. Using these process geometry variables and mechanistic cutting constants, a force model of turning is developed to estimate the tangential and radial force components. Later on, based on the predicted forces, tool-workpiece combined deflection model is developed to estimate radial, diametric and various geometric errors of the turned surface. The developed models are able to predict radial, diametric and various geometric errors such as straightness, circularly and cylindricity errors without conducting expensive actual machining operation. Hence, the present study will be helpful to take care of precautionary measures for controlling of dimensional and geometric errors more efficiently and reliably. Therefore, an attempt has been made to provide a basic platform to machining practitioners and process planners for in-depth comprehension and characterization of dimensional and geometric errors of the entire turned surface for varying machining conditions.     

Prioritization analysis and compensation of geometric errors for ultra-precision lathe based on the random forest methodology

Geometric errors remarkably affect the dimensional accuracy of parts manufactured by ultra-precision machining. It is vital to consider the workpiece shape for the identification of crucial error types. This research investigates the prioritization analysis of geometric errors for arbitrary curved surfaces by using random forest. By utilizing multi-body system (MBS) theory, a volumetric error model is initially established to calculate tool position errors. An error dataset, which contains information of 21 geometric errors, workpiece shape, and dimensional errors, is then constructed by discretizing the workpiece surface along the tool path. The problem of identifying crucial geometric errors is translated into another problem of feature selection by applying random forest on the error dataset. Moreover, the influence extent of each geometric error on the dimensional accuracy of four typical curved surfaces is analyzed through numerical simulation, and crucial geometric errors are identified based on the proposed method. Then, an iterative method of error compensation is proposed to verify the reasonability of the determined crucial geometric errors by specifically compensating them. Finally, under compensated and uncompensated conditions, two sinusoidal grid surfaces are machined on an ultra-precision lathe to validate the prioritization analysis method. Findings show that the machining accuracy of the sinusoidal grid surface with crucial geometric error compensation is better than that without compensation.     

细长轴磨削变形的变速优化智能预测控制研究

在建立细长轴磨削过程中工件弹性变形数学模型的基础上，打破了传统的恒速控制方法，提出了一种控制细长轴磨削弹性变形的变速优化适应控制策略：根据磨削系统沿工件轴向各点刚度的不同，通过不断改变工件转速和纵向进给速度，控制法向磨削力的变化，进而控制工件的弹性变形；同时，由一个神经网络预测系统和一个模糊控制系统实时控制加工过程中的磨削深度，进一步控制加工中由于砂轮磨损而引起的细长轴形状误差。仿真和实验结果表明：变速优化适应控制策略和模糊神经网络预测控制方法是可行的，可极大地提高磨削生产率，减小细长轴的形状误差。     

变工况下基于迁移学习融合域内对齐的机床主轴热误差模型

热误差建模和补偿是提高机床加工精度的重要手段。 将得到的热误差模型应用到类似或相近任务中,对减少模型构建 和数据收集的成本具有重要意义。 本文提出了一种简易迁移学习(EasyTL)融合域内对齐的主轴热误差建模方法,以实现不同 工况下误差模型的迁移复用。 建立基于域内对齐和距离矩阵全组合择优的热误差迁移模型参数选取方法,获得最优组合。 进 一步分析不同类型的域内对齐和距离矩阵各自对模型迁移性能的影响。 最后,将迁移模型与 kNN 典型机器学习模型和卷积神 经网络深度模型进行比较验证,分别预测不同工况下主轴 Z 向和 Y 向的热误差。 此外,根据预测的主轴热误差进行工件补偿 加工实验。 该方法为热误差建模及补偿提供了一种新思路。     

Real-Time Prediction of Workpiece Errors for a CNC Turning Centre, Part 1. Measurement and Identification

This paper analyses the error sources of the workpiece in bar turning, which mainly derive from the geometric error of machine tools, i.e. the thermally induced error, the error arising from machine–workpiece–tool system deflection induced by the cutting forces. A simple and low-cost compact measuring system combining a fine touch sensor and Q-setter of machine tools (FTS FQ) is developed, and applied to measure the workpiece dimensions. An identification method for workpiece errors is also presented. The workpiece errors which are composed of the geometric error, thermal error, and cutting force error can be identified according to the measurement results of each step. The model of the geometric error of a two-axis CNC turning centre is established rapidly based on the measurement results by using an FTSFQ setter and coordinate measuring machine (CMM). Experimental results show that the geometric error can be compensated by modified NC commands in bar turning.     

矩形花键滚刀法向齿形的圆弧参数优化

根据平面啮合原理 ,由已知的滚刀圆弧齿形 ,推导出与其共轭的工件齿形方程。通过对工件齿形误差的分析 ,根据最大误差最小法的基本原理 ,对矩形花键滚刀法向齿形的圆弧参数进行优化 ,使滚刀加工出的工件齿形误差最小     

基于GSK980TA数控系统工件坐标系的建立与刀具补偿

介绍了两种基于GSK980TA数控系统建立工件坐标系的方法和对刀具进行补偿的方法。建立坐标系方法之一是用试切法建立工件坐标系,方法二是使用回机械零点对刀的方法建立工件坐标系。此外还介绍了日常使用中解决磨损等造成的误差的方法即刀具补偿的方法。介绍的坐标系建立方法和刀具补偿量的设定方法可直接用于GSK980TA系统控制的车床,对其它数控机床工件坐标系得建立和刀具补偿也有一定的参考意义。     

Determination of key workpiece product characteristics in a machining fixture using uncertainty analysis and loss cost function implementation

The study of fixture related errors is playing an increasingly important role in the improvement of machined part quality. In this work, the locator variability of machining fixtures is analyzed following an uncertainty approach, allowing us to estimate the effect of fixture related geometrical errors on key product characteristics of machined workpieces. Monte Carlo simulation was implemented to generate sufficient variability to determine the expected value of the measuring points of the machined workpiece surface and its related key product characteristic. The results from the Monte Carlo simulation allow sufficient range of values to construct a mathematical relationship between fixture related errors and machined workpiece key product characteristics. Furthermore, the Taguchi loss function is used to investigate the loss cost incurred by a given fixturing uncertainty scheme. An example problem of a prismatic workpiece is presented, where the locating error due to the fixturing system is evaluated in order to know its influence on the workpiece flatness and its associated uncertainty.     

基于导磁粉末的夹持系统研究

针对整体结构件在加工时装夹精度不高的问题,提出了一种基于导磁粉末的夹持系统。介绍了该夹持系统夹持工件的基本原理,并将其与磁力吸盘相比较,从夹持原理上分析了该夹持系统的优越性。利用有限元软件对这两种夹持方法进行了二维建模,定性地分析了工件周围的磁场分布。从理论上分析了不同磁性的工件在基于导磁粉末的夹持系统中的夹持力产生机理,通过实验测定了在相同激磁装置下这两种夹持系统对磁性工件的水平和垂直夹持力,并利用有限元分析软件分析了工件在这两种夹持系统下的最大变形量。研究结果表明,基于导磁粉末的夹持系统对于不同磁性的工件均能可靠地夹持,磁力线经过导磁粉末形成回路,使得工件的变形量更小;基于导磁粉末的夹持系统比磁力吸盘更加优越,更易于实现工业自动化。     

Self-calibration and compensation of setting errors for surface profile measurement of a microstructured roll workpiece

Microstructured roll workpieces have been widely used as functional components in the precision industries. Current researches on quality control have focused on surface profile measurement of microstructured roll workpieces, and types of measurement systems and measurement methods have been developed. However, low measurement efficiency and low measurement accuracy caused by setting errors are the common disadvantages for surface profile measurement of microstructured roll workpieces. In order to shorten the measurement time and enhance the measurement accuracy, a method for self-calibration and compensation of setting errors is proposed for surface profile measurement of microstructured roll workpieces. A measurement system is constructed for the measurement, in which a precision spindle is employed to rotate the roll workpiece and an air-bearing displacement sensor with a micro-stylus probe is employed to scan the microstructured surface of the roll workpiece. The resolution of the displacement sensor is 0.14 nm and that of the rotary encoder of the spindle was 0.15r~. Geometrical and mathematical models are established for analyzing the influences of the setting errors of the roll workpiece and the displacement sensor with respect to the axis of the spindle, including the eccentric error of the roll workpiece, the offset error of the sensor axis and the zero point error of the sensor output. Measurement experiments are carded out on a roll workpiece on which periodic microstructures are a period of 133 i~m along the circumferential direction. Experimental results demonstrate the feasibility of the self-compensation method. The proposed method can be used to detect and compensate the setting errors without using any additional accurate artifact.     

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.     

高频响大行程微位移机构的研究

介绍了高频响大行程微位移机构研究的背影,结构特点,闭环系统的设计,以及在非圆截面零件数控车削中的应用。解决高频响与大行程之间的矛盾是设计微进给装置的关键。笔者采用永磁动圈式直线电机的方式成功地解决了这一矛盾,并在此基础上采用先进的控制策略构成闭环系统,解决了高精度跟踪正弦信号的问题。