基于伺服电流与切削力关系的间接测量技术研究

分析了切削加工过程,依据三相永磁同步交流伺服电机矢量控制原理,提出伺服电流间接监测切削力的测量方法,并提取了反映切削力变化的电机电流信号特征参数.基于转矩模拟平台、霍尔元件,设计并搭建电磁转矩-进给伺服电流实验平台,进行伺服电流与转矩关系测量实验,研究实时监测进给伺服驱动单元的电流信号.     

Feed Cutting Force Estimation from the Current Measurement with Hybrid Learning

It is very important to use reliable and inexpensive sensors to obtain useful information about manufacturing processing, such as cutting force, for monitoring automated machining. In this paper, the feed cutting force is measured using an inexpensive current sensor installed on the a.c servo motor of a CNC turning centre. The factors that affect a feed drive system are analysed in detail, and a model of the feed drive system for estimating feed cuttinng force is presented. The feed cutting force is estimated using feed motor current measurement and neuro-fuzzy techniques. Experimental results demonstrate that this medthod can accurately estimate feed cutting force within an error of 5%.     

基于铣削力/力矩模型的铣削表面几何误差模型

在端铣加工过程中 ,影响铣削表面的因素包括铣削力 /铣削扭矩、机床和工件的性质等等。通过研究这些因素 ,基于铣削力 /铣削扭矩和瞬时未变形切屑厚度的关系 ,建立了一个考虑了铣削力 /铣削扭矩的解析模型 ,用来预报在端铣情况下工件的表面几何误差。与数值模型相比 ,解析模型能够更好地来研究工艺参数和工件质量、产品设计、工艺规划和控制之间的关系。并且可以对铣削工艺的设计和优化提供帮助。一系列的试验验证了模型的有效性 ,并且通过仿真结果得到一些有用的结论     

Cutting torque and tangential cutting force coefficient identification from spindle motor current

This article presents an enhanced methodology for cutting torque prediction from the spindle motor current, readily available in modern machine tool controllers. This methodology includes the development of the spindle power model which takes into account all mechanical and electrical power losses in a spindle motor for high-speed milling. The predicted cutting torque is further used to identify tangential cutting force coefficients in order to predict accurately the cutting forces and chatter-free regions for milling process planning purposes. The developed model is compared with other studies available in the literature, and it demonstrates significant improvements in terms of the completeness and accuracy achieved. The developed model is also validated experimentally, and the obtained results show good compliance between the predicted and the measured cutting torque. The developed enhanced procedure is very appealing for industrial implementation for cutting torque/force monitoring and tangential cutting force coefficient identification.     

基于数控高速铣齿机切削力模型的切削用量优化

依据常规金属切削加工的特点和原理,对数控高速铣齿加工的铣削力大小进行监测.采用统计分析软件STATISTICA建立高速铣齿的切削力模型,分析铣削速度和进给速度对铣削力的影响,并以最大生产效率为目标,使用MATLAB对铣削用量进行优化分析,从而提高铣齿加工效率.     

基于主轴电流的铣削力间接监测方法

实时准确地监测铣削状态对于提高加工质量与加工效率具有重要意义,切削力作为重要的加工状态监测对象,因其监测设备昂贵且安装不便而受到限制,为此提出一种考虑刀具磨损的基于主轴电流的铣削力监测方法.首先基于切削微元理论建立了考虑后刀面磨损的铣削力模型,并通过铣削实验进行铣削力模型系数标定;然后对主轴电流与铣削力的关系进行理论建...     

An investigation of the characteristics of the stationary feed motor current in NC machines

The cross-feed directional cutting force acts normal to the machined surface of a workpiece. It is important to estimate and control this force, since it directly affects the machined surface. However, using the current supplied to a stationary motor to predict the cutting state poses difficulties, because of the current's somewhat undesired behaviour. In this paper, a largely empirical approach was used to help resolve this problem. We show that the current's undesired behaviour is related to infinitesimal rotations of the motor. Subsequently, the relationship between the current and the cutting force was identified with an error of less than 15%. The predictions obtained using two machine tools with different characteristics were compared to confirm the validity of the method when investigating the characteristics of the stationary feed motor current.     

螺纹铣削切削力有限元分析及试验

为了研究螺纹铣削法加工钛合金螺纹时切削力随切削参数的变化规律,通过对材料本构关系、刀—屑接触及切屑分离准则进行分析,建立了能反映刀具自转、公转及轴向进给运动的三维螺纹铣削模型。利用该模型对每齿进给量和切削速度对切削力的影响进行分析,结果表明:切削力随每齿进给量的增大而增大,随切削速度增加而减小,且每齿进给量对切削力的影响较为显著。通过螺纹铣削试验对所建立的三维铣削模型进行验证,表明所建立模型的误差最大为14%,可满足实际加工需要。     

ENHANCEMENT OF PRODUCTIVITY BY INTELLIGENT PROGRAMMING OF FEED RATE IN 3-AXIS MILLING

An optimized feed scheduling strategy (OFSS) is proposed in this paper to maximize the metal removal rate in 3-axis milling while guaranteeing the machining accuracy. This strategy integrates the feed drive dynamics, described by the acceleration/deceleration (Acc/Dec) profile, with the minimum-time trajectory planning in order to achieve the desired feed rate at the appropriate position. An optimum use of the feed drive capabilities is considered to track the changes in the cutting geometry along the tool path. Therefore, this strategy combines different constraints and various criteria in modifying the feed rate to maintain near-constant cutting force resulting in highly non-linear problem. The constraints include the cutting force, the feed rate boundaries, the contour error and the characteristics of the (Acc/Dec) profile. The criteria are the maximum production rate, the machining accuracy and safety. The performance of the OFSS in terms of these criteria, is compared to two end milling operations where the trajectory planning disregards the feed drive dynamics. The first is based on a feed scheduling strategy using control points (FSCP). The second is a milling operation with nominal feed rate. By increasing the feed rates, the OFSS improves the machining accuracy, reduces the machining time, and allows a better regulation of the cutting force.     

ENHANCEMENT OF PRODUCTIVITY BY INTELLIGENT PROGRAMMING OF FEED RATE IN 3-AXIS MILLING

An optimized feed scheduling strategy (OFSS) is proposed in this paper to maximize the metal removal rate in 3-axis milling while guaranteeing the machining accuracy. This strategy integrates the feed drive dynamics, described by the acceleration/deceleration (Acc/Dec) profile, with the minimum-time trajectory planning in order to achieve the desired feed rate at the appropriate position. An optimum use of the feed drive capabilities is considered to track the changes in the cutting geometry along the tool path. Therefore, this strategy combines different constraints and various criteria in modifying the feed rate to maintain near-constant cutting force resulting in highly non-linear problem. The constraints include the cutting force, the feed rate boundaries, the contour error and the characteristics of the (Acc/Dec) profile. The criteria are the maximum production rate, the machining accuracy and safety. The performance of the OFSS in terms of these criteria, is compared to two end milling operations where the trajectory planning disregards the feed drive dynamics. The first is based on a feed scheduling strategy using control points (FSCP). The second is a milling operation with nominal feed rate. By increasing the feed rates, the OFSS improves the machining accuracy, reduces the machining time, and allows a better regulation of the cutting force.     

Estimation of the cutting torque without a speed sensor during CNC turning

In this paper, the cutting torque of a CNC machine tool during machining is monitored through the internet. To estimate the cutting torque precisely, the spindle driving system is divided into two parts: electrical induction motor part and mechanical part. A magnetized current is calculated from the measured three-phase stator currents and used for the total torque estimation generated by a spindle motor. Slip angular velocity is calculated from the magnetized current directly, which gets rid of the necessity of a spindle speed sensor. Since the frictional torque changes according to the cutting torque and the spindle rotational speed, an experiment is adopted to obtain the frictional torque as a function of the cutting torque and the spindle rotation speed. Then the cutting torque can be calculated by solving a 2^nd order difference equation at a given cutting condition. A graphical programming method is used to implement the torque monitoring system developed in this study to the computer and at the same time monitor the torque of the spindle motor in real time through the internet. The cutting torque of the CNC lathe is estimated well within an about 3% error range in average in various cutting conditions.     

Real-Time Prediction of Workpiece Errors for a CNC Turning Centre, Part 3. Cutting Force Estimation Using Current Sensors

This paper presents a new method for measurement of cutting force using reliable and inexpensive current sensors. The relationship between the various factors which affect the performance of the spindle and feed drive systems are analysed, together with models of the spindle and feed drive system. The tangential (Ft) and axial cutting forces (Fa) are measured, using a neuro-fuzzy technique, with inexpensive current sensors installed on the a.c. servomotors of a CNC turning centre. The normal cutting pressure (Kn) and effective friction coefficient (Kf ) are calculated using the model of the cutting force and the two cutting forces measured by motor current, then the radial cutting force (Fr) can be calculated based on the model of cutting force. Experimental results show that the method can measure tangential, axial and radial cutting forces within errors of 10%, 5% and 25%, respectively, so the need for controlling or monitoring the cutting processes can be met in practice.     

GH4169插铣参数对切削力的影响规律研究

为了优化高温合金GH4169插铣加工过程中的切削参数,采用正交试验法进行高温合金GH4169的铣削试验。基于试验法建立了切削力与切削参数之间的经验公式,分析了各切削参数对切削力的影响规律。运用方差分析法检验了经验公式的显著性。结果表明:F_x、F_y、F_z都随着切削速度V_c、每齿进给量f_z、径向切深a_e的增大而增大;三个方向的切削力受径向切深a_e的影响最大,其次是切削速度V_c,每齿进给量f_z的影响最小,且Z方向切削力F_z大于X、Y方向切削力F_x、F_y。     

高速铣削铝合金时切削力和表面质量影响因素的试验研究

对高速铣削典型铝合金框架结构工件时的切削力和加工表面质量进行了试验研究。在高速进给铣削时 ,当进给方向发生改变 ,机床的加减速特性将导致在拐角处进给量减小、铣刀切入角增大 ,从而引起切削力增大和加工振动。在恒切削效率条件下高速铣削铝合金的试验结果表明 ,高速铣削时宜采用较小的轴向切深和较大的径向切深 ,以减小铣削力、提高加工表面质量 ;刀具动平衡偏心量是高速铣削时引起轴向振纹的主要原因     

硬质合金刀具高速切削高强度钢切削力非线性规律研究

利用2k因子试验设计和均匀试验设计方案,进行了硬质合金刀具高速铣削高强度钢的切削力试验,找出r埘切削力有重要影响的主效应及交互效应,建立了切削用量与动态切削力之间的非线性数学模型.试验结果表明,切削深度和每齿进给量之间的交互作用对切削力有显著影响,切削力与切削用量间存在非线性特征规律,切削用量对切削力的影响效应随切削用...     

THE GEOMETRY, SPECIFICATION AND PREDICTIVE FORCE MODELS FOR PLANE FACED BALL-END MILLING CUTTERS AND OPERATIONS

In this paper the geometry and specification of ball-end milling cutters are studied and discussed followed by an outline of the development of computer-aided predictive models for the three force components, torque and power in plane faced ball-end milling operations, based on the 'Unified-Generalised Mechanics of Cutting Approach'. The models allow for six milling modes, namely; slotting, 'on-centre' end-milling and 'off-centre' end-milling, each machining at the cutter ball-end cutting edge only or at the cutter ball-end and cylindrical periphery cutting edges for two or more flute cutters. The models include all the tool and cut geometrical variables and the cutting speed as well as the tool-workpiece material combination (via the database of basic cutting quantities). The models are verified through extensive numerical simulation studies and a comprehensive experimental testing programme. Good qualitative and quantitative correlation has been found between predicted and measured fluctuating and average force components and torque.     

In-Process Tool Fracture monitoring in Face Milling Using Spindle Motor Current and Tool Fracture Index

A new algorithm for tool fracture detection using spindle motor current is suggested for face milling. A tool fracture index (TFI) is suggested to represent the magnitude of tool fracture. Dynamic cutting force variation in the face milling process is measured indirectly using spindle motor current. Even though the dynamic sensitivity of the spindle motor current is low, the cutting force can be correctly represented by the spindle r.m.s current in rough face milling. In rough milling, tool fracture is distinguished well from cutter run-out and transient cutting. The magnitude of tool fracture can be predicted by the proposed tool fracture index using the spindle motor current.     

微细铣削氧化锆陶瓷铣削力特征分析

针对硬态氧化锆陶瓷的微细精密加工问题,采用金刚石涂层微铣刀进行了微细铣削试验。介绍了微细铣削陶瓷材料时加工区的几何特征,分析了可能产生单齿铣削的原因。通过测力仪记录了铣削力信号,对特征力信号进行了描述和分析,研究了铣削参数以及刀具磨损对铣削力大小的影响。结果表明,微细铣削陶瓷材料时,由于每齿进给量非常小,故铣削过程易产生单齿铣削现象;铣削力轴向分量Fz的值最大,随着每齿进给量的增大,Fz呈明显上升趋势;随铣削路程的增加,刀具磨损加剧,铣削力也随之增大,受刀具磨损影响产生一定波动,特别是Fz,其增加幅度明显大于Fx和Fy的增加幅度。     

钻削GH4169高温合金薄壁件钻削力仿真研究

GH4169高温合金的薄壁钻孔与厚壁钻孔相比有特殊性,运用ABAQUS软件进行钻削GH4169高温合金薄壁件的仿真,研究钻削加工过程中钻削参数和工件厚度对钻削力的影响规律及变化特征,分析应力的分布规律。结果表明:钻削初期,横刃的挤压和主切削刃切削长度的增加使钻削力和扭矩增大;稳定钻削阶段,横刃切出后,主切削刃切削长度不变切削直径增加,钻削力和扭矩稳定增加;钻削后期,副切削刃参与切削,主切削刃切削长度减小,轴向钻削力和扭矩减小,但副刃与孔壁的挤压摩擦,曲线波动较大;钻削速度、进给量及工件厚度的增加都会导致轴向钻削力和扭矩的增加;钻削时的最大应力分布在横刃和主切削刃与工件的接触部位。     

Extracting cutting constants via harmonic force components for a general helical end mill

Mechanistic cutting constants serve well in predicting milling forces, monitoring the milling process as well as in helping to understand the mechanistic phenomena of a machining process for a unique pair of workpiece and cutter materials under various types of cutting edge geometry. This paper presents a unified approach in identifying the six shearing and ploughing cutting constants for a general helical end mill from the dynamic components of the measured milling forces in a single cutting test. The identification model is first presented assuming the milling force is measured with a known phase angle of the cutter spindle. When the phase angle of the cutter rotation is not available, as is the case for most milling machines, it is shown that the true phase angle can be identified through the theoretical phase relationship between the different harmonic components of the milling forces measured with an arbitrary phase angle. The numerical simulation and the experimental results for ball and cylindrical end mills are presented to demonstrate and validate the identification methods.