虚拟加工系统研制与加工误差分析

面向数控车削加工过程研制了一个虚拟数控加工系统。该系统以Windows2000为开发平台，以Visual C 6．0为开发工具，基于OpenGL技术实现了数控车削加工过程3维仿真。该系统能够有效地仿真数控车削过程，具有更接近实际车削加工过程的特点。同时在仿真研究中，分析了加工过程中由切削力导致的加工误差，实现了对虚拟车削工件加工误差的预测。     

基于VERICUT的虚拟数控加工刀具轨迹优化

虚拟物理数控加工仿真主要研究加工过程中切削力、切削热、机床运动误差、加工系统颤振以及负载变化引起加工结果变化的预测问题,目前已成为虚拟制造最具魅力的地方。通过在VERICUT下的电吹风外壳模盖的虚拟数控加工刀具轨迹优化研究,为复杂曲面零件的加工生产提供了有效参考。     

基于虚拟加工技术的数控程序优化

针对传统数控程序中进给速度固定限制加工效率的缺点,开发了面向粗铣加工的数控程序优化系统。系统基于虚拟加工技术,能完成数控程序驱动下的切削过程仿真、切削力预测、碰撞检测等。系统利用粒子群进化算法,在满足加工条件的下,实现了数控程序中进给速度和主轴转速的优化,数控程序加工效率得到显著提高。     

A real time machining error compensation method based on dynamic features for cutting force induced elastic deformation in flank milling

During the machining process, cutting forces cause deformation of thin-walled parts and cutting tools because of their low rigidity. Such deformation can lead to undercut and may result in defective parts. Since there are various unexpected factors that affect cutting forces during the machining process, the error compensation of cutting force induced deformation is deemed to be a very difficult issue. In order to address this challenge, this article proposes a novel real time deformation error compensation method based on dynamic features. A dynamic feature model is established for the evaluation of feature rigidity as well as the association between geometric information and real time cutting force information. Then the deformations are calculated based on the dynamic feature model. Eventually, the machining error compensation for elastic deformation is realized based on Function Blocks. A thin-walled feature is used as an example to validate the proposed approach. Machining experiment results show that the errors of calculated deformation with the monitored deformation is less than 10%, and the thickness errors were between ?0.05 mm and +0.06 mm, which can well satisfy the accuracy requirement of structural parts by NC (Numerical Control) machining.     

虚拟制造中基于刀具磨损的复杂曲面加工误差补偿

基于数控铣削加工仿真系统,研究了在虚拟制造环境下对球头铣刀磨损引起的曲面加工误差的预测与补偿。建立了与加工参数相关的球头铣刀磨损模型,用于预测球头铣刀切削刃的磨损量,提出了球头铣刀铣削加工误差的补偿方法,并通过实验验证了该方法的有效性。     

Cutting forces prediction in generalized pocket machining

Cutting force prediction is important for the planning and optimization of machining process. This paper presents an approach to predict the cutting forces for the whole finishing process of generalized pocket machining. The equivalent feedrate is introduced to quantify the actual speed of cutting cross-section in prediction of cutting force for curved surface milling. For convenience, to analyze the process with varying feed direction and cutter engagement, the milling process for generalized pocket is discretized into a series of small processes. Each of the small processes is transformed into a steady-state machining, using a new approximation method. The cutting geometries of each discrete process, i.e., feed direction, equivalent feedrate per tooth, entry angle, and exit angle are calculated based on the information refined from NC code. An improved cutting force model which involves the effect of feed direction on cutting forces prediction is also presented. A machining example of a freeform pocket is performed, and the measured cutting forces are compared with the predictions. The results show that the proposed approach can effectively predict the variation of cutting forces in generalized pocket machining.     

Geometric error compensation software system for CNC machine tools based on NC program reconstructing

It has been proved that error compensation is an effective approach to improve machining accuracy of a machine tool cost efficiently. In this paper, the framework of an error compensation software system, which can realize software error compensation via numerical control (NC) programs reconstructing, is investigated. And the algorithms relating to error prediction are discussed in detail, such as positioning movement error compensation, linear interpolation movement, and circular interpolation movement error compensation. To realize the error compensation, NC program is reconstructed according to the predicted errors during virtual machining before it is fed to the actual machining. Two controlled machining experiments were carried out. The results show that error compensation methods via reconstructing NC programs can improve the movement accuracy of a computer numerical control CNC machine tool obviously.     

基于VERICUT的五轴数控加工仿真与优化

虚拟加工平台的构建、数控加工程序的正确性验证及加工过程的仿真与优化及是五轴数控机床实现高效加工的重要基础技术。基于VERICUT数控加工仿真与优化平台,以非正交五轴数控机床DMC70ev为研究对象,构建了数控加工仿真平台;以曲面加工为例,建立了基于恒定体积去除率和恒定切屑厚度的优化设计数学模型,进行了刀位轨迹的优化。应用表明:研究成果实现了五轴数控加工过程仿真及数控加工程序的正确性验证,减少了刀具磨损,提高了加工效率与加工质量,可以较好地提升企业数控加工技术的应用水平、应用质量,推动现代制造技术的发展。     

球头铣刀刀具磨损建模与误差补偿

针对刀具磨损度量方式和模型建立的问题,以球头刀具为研究对象,提出球头铣刀刀具磨损的度量方式,建立球头刀具磨损模型.以复映磨损在硬度较软加工材料上的方式测量球头刀具磨损,确定刀具磨损模型系数,给出刀具磨损模型系数确定的具体实现方法.加工试验验证球头刀具磨损度量方式的合理性和所建立刀具磨损模型的正确性,同时针对数控铣削加工中球头铣刀刀具磨损引起的误差提出离线仿真误差补偿算法,给出离线仿真误差补偿算法的具体实现步骤,通过建立的刀具磨损引起的加工误差模型仿真获得加工走刀步的误差.对于误差超差的走刀步,预先修改数控加工(Numerical control,NC)程序,保证实际加工零件满足精度要求.误差补偿验证试验表明所提出的离线仿真误差补偿算法的正确性和有效性.     

薄壁件加工变形控制快速仿真平台开发

为控制薄壁件装夹变形和加工变形,建立了集装夹优化、加工变形预测、切削参数优化及误差补偿功能为一体的快速仿真平台.在平台实现中,装夹方案的优化采用基于形位公差控制的方法,通过多种装夹方案的比较,确定优化方案.加工变形预测时考虑了前-层变形对后-层切削深度的影响,并使切削力和加工变形达到动态平衡.为获得优化切削参数,建立了以变形控制为目标的优化模型.采用有限元法计算加工变形,采用遗传算法求解优化模型.为解得优化补偿量,仿真时考虑了变形与力的耦合效应.完成了基于ABAQUS的快速仿真平台开发.以镜座零件为例进行仿真,求得了优化的装夹方案和切削参数,验证了平台的可行性.     

In-situ process monitoring and adaptive control for precision micro-EDM cavity milling

The linear tool wear compensation method (LCM) is commonly applied in micro-EDM 3-D milling to compensate the tool length wear in order to achieve high machining accuracy. Traditional LCMs mainly rely on empirical models and off-line wear measurements, whereas the process dynamics are not taken into account. When machining complex 3D cavities, an increasing number of tool wear compensation cycles have usually to be performed in order to maintain the targeted machining accuracy. This negatively affects the duration of the overall machining cycle. To realize efficient precision micro-EDM cavity milling, without the necessity to predefine Z-axis tool feed in the NC trajectory before machining, an in-situ process control system is developed to adaptively control the tool wear compensation factor based on the discharge pulse behavior. Experiments have shown that the change of the compensation factor can be detected and also a continuous increase of the factor (over compensation) leads to the saturation of the mean effective pulse frequency. Pulse monitoring therefore provides valuable information for understanding the process dynamics and for selecting the machining parameters towards better machining efficiency. Furthermore, the information gathered in-situ can be utilized to predict the tool wear and perform in-situ tool wear prediction. To implement this on machine-level, a combined off-line and in-line adaptive control of the tool wear compensation factor is proposed and experimentally validated by milling different 3D cavities. The off-line adaptive control is only necessary when the predicted machining depth error exceeds a certain limit. In this way, more than 80% of the off-line adaptive control cycles can be eliminated, whereby a total save of cycle time up to 18% has been reached, while still maintaining the desired dimensional and form accuracy.     

虚拟制造中基于刀具变形的复杂曲面加工误差预报

复杂曲面加工过程中刀具的弹性变形是产生曲面加工误差的重要原始误差。着重研究了虚拟制造环境下基于球面铣刀弹性变形的曲面加工误差预报模型。研究并建立了球面铣刀加工复杂曲面的切削力模型和刀具弹性变形模型,在此基础上,分析了曲面生成机理,提出了利用曲面变形敏感系数建立刀具弹性变形对法向加工误差的影响关系。利用该模型可以在实际切削加工前对曲面加工误差进行预报,用以进行误差补偿或切削参数优化。最后,以二维半圆形拉伸曲面为例通过切削实验对本文提出的模型进行了验证。     

基于刀具沿进给方向蠕动式进给的数控加工技术研究

通过对数控加工中存在的问题分析,提出了一种在数控加工中,刀具在被加工工件曲面上沿进给方向蠕动式切削加工的方珐,通过刀具与工件时续分离和切削,改善了工艺系统的刚性,从而使工件的加工精度得到改善,并具体从被加工工件的几何形状、切削过程中刀具受力情况及切削区的切削热释放情况方面,分析了采用该方珐对加工精度的改善情况。     

Development of a virtual reality wire electrical discharge machining system for operation training

Wire electrical discharge machining (WEDM) uses a metallic thin wire to cut a programmed profile with high strength having sharp edges such as extrusion dies and blanking punches. However, the cost of purchasing and maintaining of WEDM equipment is very high for both the industry and general education institutions. Therefore, there are potential demands to reduce the expensive machine operation training cost, provide off-line collision-free simulation verification of the tool path, and examine the correctness of the programmed wire cutting NC codes. This paper presents the development of a virtual reality-based WEDM full machine simulation system which can emulate major functions of a real controller related to operation training and education. These functions include the tool path simulation, NC program interpretation and processing, kinematics of the machine mechanism, workpiece origin setting, etc. To demonstrate the developed system and illustrate the adopted method, the system capability is explained and shown in this paper. The research result can be used as a cost-effective interactive 3D digital tutoring system that has the benefits of improving on the inefficient, dangerous, and costly drawbacks in traditional learning and training for operating the real WEDM machine.     

Theoretical and experimental analysis of the effect of error motions on surface generation in fast tool servo machining

The fast tool servo (FTS) machining process provides an indispensable solution for machining optical microstructures with sub-micrometer form accuracy and a nanometric surface finish without the need for any subsequent post processing. The error motions in the FTS machining play an important role in the material removal process and surface generation. However, these issues have received relatively little attention. This paper presents a theoretical and experimental analysis of the effect of error motions on surface generation in FTS machining. This is accomplished by the establishment of a model-based simulation system for FTS machining, which is composed of a surface generation model, a tool path generator, and an error model. The major components of the error model include the stroke error of the FTS, the error motion of the machine slide in the feed direction, and the axial motion error of the main spindle. The form error due to the stroke error can be extracted empirically by regional analysis, the slide motion error and the axial motion error of the spindle are obtained by a kinematic model and the analysis of the profile in the circumferential direction in single point diamond turning (SPDT) of a flat surface, respectively. After incorporating the error model in the surface generation model, the model-based simulation system is capable of predicting the surface generation in FTS machining. A series of cutting tests were conducted. The predicted results were compared with the measured results, and hence the performance of the model-based simulation system was verified. The proposed research is helpful for the analysis and diagnosis of motion errors on the surface generation in the FTS machining process, and throws some light on the corresponding compensation and optimization solutions to improve the machining quality.     

An intelligent feedrate scheduling based on virtual machining

Off-line feedrate scheduling is an advanced methodology to automatically determine optimum feedrates for NC code modification. However, most existing feedrate scheduling systems have limitations in generating the optimised feedrates because they use the material removal rate or the cutting force model which is dependent on cutting conditions. This paper proposes a feedrate scheduling system based on an improved cutting force model that can predict cutting forces accurately in general end milling situations. Original blocks of NC code were divided into smaller ones with the optimised feedrates to adjust the peak value of cutting forces to a constant value. The acceleration and deceleration characteristics for a given machine tool were considered for realistic feedrate scheduling. Moreover, a modified type of Z-map model was developed to reduce the entry/exit angle calculation error in the cutting force prediction and named the moving edge node Z-map (ME Z-map). Pocket machining experiments show that the proposed method is accurate and efficient in maintaining the cutting force at a desired level.     

基于仿真的数控铣削加工参数优化研究

针对数控铣削加工参数优化问题,通过加工仿真,计算每一走刀步的切削深度和切削宽度并划分区间。在每一个由组合划分区间内所有刀步构成的一个加工特征组合段上建立了多目标优化模型,模型采用遗传算法对每一加工特征组合段的加工参数进行优化,自动修改NC程序中的加工参数并反映优化结果。应用实例证明,提出的多目标优化模型和优化求解算法正确、有效。     

弧齿锥齿轮成形三维虚拟仿真研究

通过分析弧齿锥齿轮加工原理及加工机床的结构和运动关系,并基于空间啮合理论,建立了刀刃锥面方程和啮合方程,应用图形变换原理,推导了弧齿锥齿轮NC机床运动参数的计算方法。基于VERICUT软件平台,建立了弧齿锥齿轮NC机床模型及弧齿锥齿轮三维虚拟仿真加工模型,对一对具体的弧齿锥齿轮进行了几何参数、刀具参数和NC机床运动参数的计算,并在VERICUT环境下进行了虚拟仿真加工,验证了弧齿锥齿轮NC机床模型及三维虚拟仿真加工模型的正确性。     

基于OpenGL的虚拟数控车床加工仿真系统研究

在分析虚拟数控机床系统结构的基础上,以Visual C++6.0为平台,研究开发了基于OpenGL交互控制的虚拟数控车床加工仿真系统,实现了在不同转速、进给速度、NC代码等条件下数控车床切削过程的动态仿真。系统具有良好的实时性、交互性、可扩展性以及三维图形显示能力,能够有效地验证程序的正确性,有助于减少试切法检查引起的低效高耗,提高数控设备的生产效率。利用计算机图形学和虚拟现实技术对数控车床的加工过程进行模拟,可以节约成本、避免制造风险、开展数控培训。     

A new high-efficiency error compensation system for CNC multi-axis machine tools

To enhance the accuracy of CNC machines for the request of modern industry, an effective static/quasi-static error compensation system composed of an element-free interpolation algorithm based on the Galerkin method for error prediction, a recursive software compensation procedure, and an NC-code converting software, is developed. Through automatically analyzing the machining path, the new error prediction method takes into consideration the fact that the machine structure is non-rigid, and can efficiently determine the position errors of the cutter for compensation without computing a complex error model on-line. The predicted errors are then compensated based on a recursive compensation algorithm. Finally, a compensated NC program will be automatically generated by the NC-code converting software for the precision machining process. Because of the advantage of the element-free theory, the error prediction method can flexibly and irregularly distribute nodal points for accurate error prediction for a machine with complex error distribution characteristics throughout the workspace. To verify the algorithm and the developed system, cutting experiments were conducted in this study, and the results have shown the success of the proposed error compensation system.