数控机床动态轨迹误差仿真与优化研究

在介绍数控机床加工轨迹运动控制原理的基础上,对数控机床动态轨迹误差进行了仿真研究,得出数控机床动态轨迹误差与拟加工曲线的曲率和机床进给速度相关的结论。在待加工的工件几何曲线曲率已定情况下,提出了变进给速度的数控机床动态轨迹误差优化策略,仿真结果表明:该控制策略能够有效地减少机床动态轨迹误差量,提高相关轨迹曲线的加工精度。     

三轴数控机床加工精度可靠性分析

机床作为机械制造业的基础,几何误差、热误差、装配误差等都会影响数控机床的加工精度,数控机床加工精度的高低直接决定产品的生产质量。为保证数控机床对产品的加工质量,需要对数控机床的加工误差数据处理,求得数控机床加工精度可靠性,而一次二阶矩法和蒙特卡罗法是常用的可靠性分析方法。以三轴数控机床为研究对象,针对给定的误差数据,运用一次二阶矩法和蒙特卡罗法分析出数控机床加工精度可靠性。此分析对提高数控机床加工精度及保证使用寿命具有重要指导意义和参考价值。     

五轴联动加工中进给速度的控制算法

目的研究刀具进给速度平稳性对五轴联动加工中复杂自由曲面表面粗糙度、轮廓精度的影响。方法首先对五轴联动机床运动过程中的空间线性插补原理进行了分析,推导出插补周期内各轴的分解速度数学模型。根据数控系统中不同的速度指令方式以及刀具在空间的实际运动距离,分端铣和侧铣两种情况,分别建立了刀具空间运动的实际速度计算模型,然后根据机床各轴的最高速度及加速度约束条件,对各轴分速度、分加速度进行校核处理,最终求得刀具实际的合成速度。最后,基于后置处理技术,用开发的专用后置处理软件进行刀位源代码后置处理,采用某叶轮试件进行了验证,并对实验结果进行了分析。结果在复杂曲面加工中,稳定的表面进给速度会获得较高的表面质量及轮廓精度,曲面曲率变化越大,速度变化对加工质量的影响越大。在同等条件下切削,刀具采用恒表面速度与采用恒进给速度相比,获得的叶片进出汽边轮廓误差值由0.1 mm减小为0.04 mm。结论在五轴联动加工中,越稳定的表面进给速度,越能获得较高的表面质量和轮廓精度,对于曲率变化较大的复杂曲面,需要严格控制刀具的进给速度,尽量获得稳定的表面速度以减少过切值,从而提高零件表面质量。     

基于多体系统理论的车铣中心空间误差模型分析

数控机床的误差建模是进行机床运动设计、精度分析和误差补偿的关键技术,也是保证机床加工精度的重要环节.本文利用多体系统理论来构建超精密数控机床的几何误差模型,该模型简便、明确,不受机床结构和运动复杂程度的限制,为计算机床误差、实现误差补偿和修正控制指令提供了理论依据.在机床实际应用中,可以利用由精密机床误差建模所推导出的几何位置误差来修正理想加工指令,控制机床的实际运动,从而实现几何误差补偿,提高机床加工精度.     

Total differential methods based universal post processing algorithm considering geometric error for multi-axis NC machine tool

Multi-axis numerical control machining for free-form surfaces needs CAD/CAM system for the cutter location and orientation data. Since these data are defined with respect to the coordinate of workpiece, they need converting for machine control commands in machine coordinate system, through a processing procedure called post processing. In this work, a new universal post processing algorithm considering geometric error for multi-axis machine tool with arbitrary configuration. Firstly, ideal kinematic model and real kinematic model of the multi-axis NC machine tool are built respectively. Difference between the two kinematic models is only whether to consider the machine tool's geometric error or not. Secondly, a universal generalized post processing algorithm containing forward and inverse kinematics solution is designed to solve kinematic models of multi-axis machine tool. Specially, the inverse kinematics solution is used for the ideal kinematic model, while the forward kinematics solution is used for the real kinematic model. Then, a total differential algorithm is applied to improve the calculation speed and reduce the difficulty of inverse kinematics solution. Realization principle of the total differential algorithm is to transform the inverse kinematics solution problem into that one of solving linear equations based on spatial relationship of adjacent cutter locations. Thirdly, to reduce the complexity of geometric error calibration experiment, effect weight of geometric error components is determined by the sensitivity analysis based on orthogonal method, and then the real kinematic model considering geometric error is established. Finally, the universal post processing algorithm based on total differential methods is implemented and demonstrated experimentally in a five-axis machine tool. The results show that the maximum error value can be decreased to one-fifth using the proposed method in this paper.     

Virtual High Performance Milling

The goal of future manufacturing is to design, test and manufacture parts in a virtual environment before they are manufactured on the shop floor. This paper presents a generalized process simulation and optimization strategy for 2 1/2 axis milling operations to increase Material Removal Rate (MRR) while avoiding machining errors. The process is optimized at two stages. Optimal spindle speed, radial and axial depth of cut are recommended to process planner by considering the chatter, and spindle's torque/power limits. The cutter-part engagement conditions are extracted from CAD system by geometrically processing the NC program and part geometry. Long tool path segments are broken into smaller segments whenever the geometry varies. The spindle speed and feed fields of the NC program are automatically optimized by constraining maximum torque, power, tool deflection and chip load set by the user. The acceleration and speed limits of the machine tool feed drives are considered to prevent frequent variations of the feed unnecessarily. The optimization is experimentally verified by milling a helicopter gear box cover on a high speed, horizontal machining centre.     

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.     

基于进给优化的五轴机床高精度加工研究

介绍五轴机床最佳进给率和高性能精密控制算法加工方式,并进行实验验证。通过引入进给率调度算法,以最大限度地减少五轴弯曲刀具路径的循环加工时间。在寻找沿刀具路径的最佳进给时,考虑了五轴驱动器的速度、加速度和加加速度限制,以确保伺服驱动器以最小的跟踪误差平稳和线性运行。为设计一个精确的轮廓控制器,开发分析模型来估计五轴加工实时过程中的轮廓误差,通过考虑刀尖与参考路径的法向偏差和刀轴方向与参考方向轨迹的法向偏差来定义两种类型的轮廓误差。     

基于内置传感器的数控机床动态加工误差测量方法

以HJ044双转台型五轴联动数控机床为例,以机床内置传感器信息和多体系统理论为基础,建立了刀具相对工件的运动学模型,提出了一种基于内置传感器信息的动态加工误差测量方法。该方法利用机床编码器或光栅尺等机床内置传感器信息获取机床各轴运动位移,并结合机床运动学模型,测量由机床的动态特性引起的加工误差。并通过实验表明该方法是一种简单有效的数控机床动态加工误差测量方法。     

图形化三轴数控加工系统设计

针对数控系统中,低成本以及操作简易的需求,研发了一种基于HMI+机器控制器的数控加工系统。该加工系统通过在机器控制器内预编常见零件加工程序,并调用在人机界面上组态的零件图形结合输入相关的加工参数,实现对特定类型零件或者零件的特定部位数控加工。另外,该系统可以根据实际需要设置不同的零件加工参数,只需一次编程,就能加工出多个结构相似的零件,解决了传统的数控系统加工前必须进行G代码生成或者手工编程的问题。表明该系统具有较强可操作性和较高的实用价值。     

基于ADAMS的数控机床进给系统动力学仿真

为了分析机床进给系统在零件加工时对其精度影响,利用三维造型软件Solid Works建立数控机床进给系统的动力学模型;利用Ansys分别建立丝杠和工作台的有限元模型,将模型导入Adams,对数控机床进给系统进行振动仿真。结果表明:固定转速下,工作台在不同位置的振幅不同,改变转速其规律相近;在不同转速下,速度越大,工作台振幅越大,并呈线性关系。     

大型壳体零件的数控加工工艺分析及研究

合理地规划工艺可有效地提高加工质量和数控机床利用率。以某采煤机摇臂壳体C0N00301为例,通过分析摇臂壳体的结构特征及加工技术要求,确定了机床设备,设计了在KCR160加工中心上的定位装夹方案、数控加工工艺路线、加工刀具、切削参数以及不同加工特征的走刀路线等,并在VERICUT数控加工仿真系统中进行了虚拟加工仿真验证,证明设计的数控工艺能够满足零件的加工要求。     

空心滚珠丝杠在数控机床伺服进给系统中的应用

针对数控机床主轴和伺服传动系统的热误差阻碍进一步提高机床定位精度的问题,对数控机床伺服进给系统的热变形作了深入研究。结果表明:螺母摩擦和轴承摩擦是滚珠丝杠伺服进给系统的主要热源,其摩擦热量与滚珠丝杠转速及轴向载荷几乎成正比;采用空心丝杠和空心螺母有效抑制了滚珠丝杠在高速进给时的热变形量,减小伺服进给系统的稳态误差。     

Evaluation of servo,geometric and dynamic error sources on five-axis high-speed machine tool

Many sources of errors exist in the manufacturing process of complex shapes. Some approximations occur at each step from the design geometry to the machined part.The aim of the paper is to present a method to evaluate the effect of high-speed and high dynamic load on volumetric errors at the tool center point.The interpolator output signals and the machine encoder signals are recorded and compared to evaluate the contouring errors resulting from each axis follow-up error. The machine encoder signals are also compared to the actual tool center point position as recorded with a non-contact measuring instrument called CapBall to evaluate the total geometric errors. The novelty of the work lies in the method that is proposed to decompose the geometric errors into two categories: the quasi-static geometric errors independent from the speed of the trajectory and the dynamic geometric errors, dependent on the programmed feed rate and resulting from the machine structure deflection during the acceleration of its axes.The evolution of the respective contributions for contouring errors, quasi-static geometric errors and dynamic geometric errors is experimentally evaluated and a relation between programmed feed rate and dynamic errors is highlighted.     

再制造双圆弧齿轮单齿切削机床设计

目前抽油机减速器双圆弧齿轮使用一段时间后会出现单个齿破损或多个齿间隔破损的情况,现有的修复方法效率低。针对这种情况,提出设计一种对修复后的再制造双圆弧齿轮进行再加工的切削机床,验证再制造双圆弧齿轮单齿加工的可行性。结合再制造双圆弧齿轮单齿展成加工理论,对单齿加工机床的刀具运动部件、齿向螺旋进给部件、齿形展成进给部件以及工件运动部件进行设计,最终得到满足加工要求的再制造双圆弧齿轮单齿切削机床。分析再制造双圆弧齿轮单齿加工的误差后,提出一种减小再制造双圆弧齿轮轴向齿距误差的方法。     

Identification and compensation of geometric errors of rotary axes on five-axis machine by on-machine measurement

The geometric errors of rotary axes are the fundamental errors of a five-axis machine tool. They directly affect the machining accuracy, and require periodical measurement, identification and compensation. In this paper, a precise calibration and compensation method for the geometric errors of rotary axes on a five-axis machine tool is proposed. The automated measurement is realized by using an on-the-machine touch-trigger technology and an artifact. A calibration algorithm is proposed to calibrate geometric errors of rotary axes based on the relative displacement of the measured reference point. The geometric errors are individually separated and the coupling effect of the geometric errors of two rotary axes can be avoided. The geometry error of the artifact as well as its setup error has little influence on geometric error calibration results. Then a geometric error compensation algorithm is developed by modifying the numeric control (NC) source file. All the geometric errors of the rotary errors are compensated to improve the machining accuracy. The algorithm can be conveniently integrated into the post process. At last, an experiment on a five-axis machine tool with table A-axis and head B-axis structure validates the feasibility of the proposed method.     

螺旋锥齿轮端铣加工刀位计算方法

针对螺旋锥齿轮在数控加工中心上加工效率低的问题,提出利用盘状铣刀对螺旋锥齿轮进行端铣的加工方法.由螺旋锥齿轮齿面及刀具的几何特征,调整铣刀与被加工齿面的相对位置,使齿面与刀具包络面的法截面相对法曲率最小,增大切削带宽,同时控制刀轴矢量调整切削深度避免加工干涉.最后将规划的加工刀位转化到数控机床轴上,利用VERICUT进行加工仿真验证该方法的可行性与正确性.     

瑕疵刀位点几何特征分析及其对插补指令的影响

由于CAD曲线建模的误差以及CAM算法的精度问题，刀位点中存在着瑕疵。通过对典型加工零件的刀位数据点进行分析，归纳瑕疵的类型，分析瑕疵的几何特征，研究瑕疵对数控插补指令的影响。结果表明：瑕疵类型包括密集、突起、折返、重复加工和相邻不一致；密集瑕疵造成线段长度的减小，突起瑕疵造成转角的增大，折返瑕疵在开始和结束位置造成曲率变化率的增大，重复加工在零件同一位置多次加工，相邻轨迹不一致造成点的分布不均匀；密集、突起、折返瑕疵刀位点造成指令速度的降低，以及重复加工对同一位置的多次加工，影响加工效率，突起、折返瑕疵造成指令加速度和加加速度的波动增大，引起机床振动，相邻轨迹不一致在加工同一特征时速度和加速度不同，影响加工表面质量。     

BF-850B立式高速数控机床精度检测及误差补偿研究

机床在加工的过程中会因为物理变形和热变形,使得加工零件的精度难以保证,因此必须对运动中的影响机床精度的误差源进行误差分析及实时补偿。利用激光干涉仪和球杆仪对数控机床定位精度进行检测,并建立了关于机床变形的检测数据的数学模型,确定了定位误差补偿方法,同时以具体的数控机床为例进行了定位精度检测与误差补偿,最后对补偿效果进行了分析。结果表明：该定位误差检测及补偿方法具有可行性与实用性,使数控机床的定位精度得到了显著的提高。     

基于动力学的机床加工运动分析

数控定梁龙门机床的加工精度受多种因素影响,包括零部件的制造、装配误差、材料的刚度阻尼、振动、材料切削厚度等。从提高机床加工精度出发,根据拉格朗日动力学原理建立了机床的动力学模型;分析横梁、床身等部件的自由度关系,建立了机床运动学模型;采用ADAMS软件仿真机床的瞬态动力和运动关系,对比研究了不同的瞬态切削力变化对机床切削位移、速度的影响。结果表明:当机床切削厚度增大时,切削力、切削速度和切削加速度会随之增大,同时切削速度和加速度的变化滞后切削厚度和切削力的变化;在切削受力突变处切削速度有波动,移动加速度有突变,波动时间滞后切削力突变时间。仿真结果与实际机床加工情况吻合,为机床加工的运动分析提供参考。