Ultra-precision nano-structure fabrication by amplitude control sculpturing method in elliptical vibration cutting

This paper studies the nano-structure fabrication on hardened steel by means of elliptical vibration cutting equipped with the ultra-precision amplitude control sculpturing method. Machining performance of the amplitude control sculpturing method is investigated, and the limitation in nano-scale machining is explored. In this proposed method, machinable part geometry is essentially restricted by vibration conditions and tool geometry. In addition, a considerable error between the amplitude command and the envelope of the tool trajectory is generated when the slope of the machining part geometry becomes steep. To overcome this error, a compensation method for the amplitude control command is proposed. In order to clarify the machining performance of the proposed technology, a series of analytical and experimental investigations are conducted. Furthermore, by applying the proposed command compensation method, nano-structures with a large ratio of structure height to wave length are machined accurately. The proposed sculpturing method is subsequently applied to the machining of nano-textured grooves and a three-dimensional grid surface, which verifies the feasibility of the proposed amplitude control sculpturing method.     

基于误差模型的三轴联动加工轨迹预补偿方法

为了减小由于进给系统动态特性造成的多轴联动加工轮廓误差,提出了一种基于轮廓误差模型的三轴联动加工轨迹预补偿方法。首先建立了关于轨迹曲率、加工速率及进给系统动态特性参数的轮廓误差模型;然后根据读取的插补数据,利用轮廓误差模型实时预测三轴联动加工过程中的轮廓误差补偿向量并对加工轨迹指令进行补偿;最后通过对圆、变曲率和螺旋线轨迹的MATLAB仿真和机床加工实验,证明该补偿方法将轮廓误差减小了85%以上,可显著提高数控机床加工精度。     

Micro/nano sculpturing of hardened steel by controlling vibration amplitude in elliptical vibration cutting

A new ultra-precision sculpturing method in micro/nano scale for difficult-to-cut materials is proposed in the present research. Elliptical vibration cutting technology is well-known for its excellent performance in achieving ultra-precision machining of steel materials with single crystal diamond tools. Elliptical vibration locus is generally controlled and held to a constant in practice. On the contrary, the proposed method utilizes the variations of the elliptical vibration locus in a positive manner. Depth of cut can be actively controlled in elliptical vibration cutting by controlling vibration amplitude in the thrust direction. By utilizing this as a fast tool servo function in elliptical vibration cutting, high performance micro/nano sculpturing can be attained without using conventional fast tool servo technology. A high-speed amplitude control system is developed for elliptical vibration, with a bandwidth of more than 300 Hz, where the vibration amplitude can be controlled within 4 μm_p-p. The developed control system is applied to sculpturing ultra-precision nano textured grooves on hardened steel with single crystal diamond tools. It is confirmed that the textured grooves have the desired shapes, and their profiles agree well with the vibration amplitude commands input to the control system. Further, a high performance micro/nano sculpturing system for plane surfaces is developed, where the vibration amplitude is controlled in synchronization with the planing motion of an ultra-precision machine tool. Nano sculpturing experiments on hardened steel, carried out by the developed system, are reported, as well as consequent picture images and a variety of dimple patterns that were formed successfully on the hardened steel as nano-scale sculptures.     

蒙皮镜像加工误差实时补偿优化方法研究

针对传统的飞机蒙皮镜像加工误差补偿方法收敛速度慢,在大进给高速加工中很难完成较好的补偿效果的问题,提出了一种蒙皮镜像加工误差实时补偿优化方法。该方法基于双点弦截法,借助超声波测厚仪前两次获得的蒙皮壁厚与程序切削深度,计算下一点的补偿值,并通过控制镜像铣补偿轴运动实现加工误差补偿,有效的提升了飞机蒙皮镜像铣的补偿效果,减小了加工误差。最后通过有限元仿真和试验证明了该方法的优越性,最大加工误差降低了41.67%,总体加工误差降低了41.96%。     

考虑控制电信号中间量的机床运动控制误差数据驱动建模方法

现有数据驱动的机床运动控制误差建模方法通常使用端到端的模型,即通过机器学习算法直接构建参考轨迹信息(速度、加速度等)与伺服误差之间的模型,以降低建模复杂度。然而,该方法忽视了控制电信号对运动控制系统非线性扰动的反映,而导致建立的模型精度受限。为解决此问题,提出了一种使用控制电信号作为中间量的数据驱动运动控制误差建模方法。该方法采集参考轨迹信息(速度、加速度、急动度等)、控制电信号、跟踪误差以及构造的换向特征,构建并训练基于参考轨迹信息的控制电信号预测网络,以及基于电信号和参考轨迹信息的运动控制误差预测网络,利用控制电信号这一中间量有效反应系统所受非线性扰动的特点,实现了高精度的运动控制误差数据驱动建模。在实际验证测试时,将参考轨迹信息输入电信号预测网络,而后将得到的预测控制电信号和参考轨迹信息输入跟踪误差预测网络,即可实现运动控制误差的预测。通过实验对所提出的建模方法进行了验证,所提出方法相对于传统的端到端建模方法,运动控制误差的预测精度在X轴和Y轴分别提升16.33%和20.42%,误差补偿后运动控制轮廓精度相较于未补偿提升85.59%,验证了所提出方法的可行性。     

Self-tuned ultrasonic elliptical vibration cutting for high-efficient machining of micro-optics arrays on brittle materials

Ultrasonic elliptical vibration cutting is a very promising technique for the machining of brittle materials. However, its machining performance is currently limited by the ductile machining model and the machining strategy with a constant feed rate, leading to low machining efficiency. To overcome this defect, this paper presents a novel self-tuned ultrasonic elliptical vibration cutting (SUEVC) technique to achieve high-efficient ductile-regime machining of the micro-optics array on brittle materials. The proposed SUEVC includes a ductile-regime machining model and a tool path generation method. In SUEVC, the feed rate adaptively changes with respect to the local shape variation of the desired surface along the feeding direction to ensure both crack-free surface and high machining efficiency. Finally, two 1 × 3 spherical micro-optics arrays were successfully fabricated on single-crystal MgF₂ by SUEVC and the traditional machining strategy respectively. Results demonstrated that the SUEVC could enhance the machining efficiency by 30% relative to the traditional machining strategy, while maintaining similar surface roughness and a crack-free surface.     

Optimization of end mill tool geometry parameters for Al7075-T6 machining operations based on vibration amplitude by response surface methodology

This paper aims at developing a statistical model to envisage vibration amplitude in terms of geometrical parameters such as radial rake angle, nose radius of cutting tool and machining parameters such as cutting speed, cutting feed and axial depth of cut. Experiments were conducted through response surface methodology experimental design. The material chosen is Aluminum (Al 7075-T6) and the tool used was high speed steel end mill cutter with different tool geometry. Two channels piezoelectric accelerometers were used to measure the vibration amplitude. The second order mathematical model in terms of machining parameters was built up to predict the vibration amplitude and ANOVA was used to verify the competency of the model. Further investigation on the direct and interactive effect of the process parameter with vibration amplitude was carried out for the selection of process parameter so that the vibration amplitude was maintained at the minimum which ensures the stability of end milling process. The optimum values obtained from end milling process are Radial rake angle-12°, Nose radius-0.8 mm, Cutting speed-115 m/min, Cutting feed rate-0.04 mm/tooth, axial depth of cut-2.5 mm. The vibration amplitude exhibited negative relationship with radial rake angle and nose radius. The dominant factors on the vibration amplitude are feed rate and depth of cut. Thus it is envisaged that the predictive models in this study could produce values of the vibration amplitude close to the experimental readings with a 95% confidence interval.     

五轴数控机床加工误差动态修正方法研究

为修正五轴数控机床加工误差,提高五轴数控机床加工质量,提出一种新的五轴数控机床加工误差动态修正方法.构建五轴数控机床加工误差计算模型,获取五轴数控机床加工的刀心方位、刀轴方位轮廓误差;锁定误差方位后,通过五轴数控机床误差的动态实时补偿方法,实现五轴数控机床加工误差动态修正.研究结果表明:所提方法可实现全方位、高效率的五...     

In-process prediction of surface roughness in turning of Ti–6Al–4V alloy using cutting parameters and vibration signals

In this work, an attempt has been made to use vibration signals for in-process prediction of surface roughness during turning of Ti–6Al–4V alloy. The investigation was carried out in two stages. In the first stage, only acceleration amplitude of tool vibrations in axial, radial and tangential directions were used to develop multiple regression models for prediction of surface roughness. The first and second order regression models thus developed were not found accurate enough (maximum percentage error close to 24%). In the second stage, initially a correlation analysis was performed to determine the degree of association of cutting speed, feed rate, and depth of cut and the acceleration amplitude of vibrations in axial, radial, and tangential directions with surface roughness. Subsequently, based on this analysis, feed rate and depth of cut were included as input parameters aside from the acceleration amplitude of vibrations in radial and tangential directions to develop a refined first order multiple regression model for surface roughness prediction. This model provided good prediction accuracy (maximum percentage error 7.45%) of surface roughness. Finally, an artificial neural network model was developed as it can be readily integrated into a computer integrated manufacturing environment.     

数控随动磨床加工凸轮方法及其精度补偿策略

针对凸轮随动磨削中因工件轴转速差、伺服系统响应偏差、硬件制造误差等重复性误差影响因素造成的零件制造精度下降问题,将在线测量技术和Sinumerik 840D数控系统的插补表与电子齿轮功能应用到机床运动控制系统中,开展了随动磨削工艺的运动轨迹和控制方案分析,提出了由内嵌在系统PCU上的VB程序来处理在线测量获得的360个离散误差补偿数值,自动生成带插补表与电子齿轮功能的专用加工程序,利用同轴运动叠加控制方法,把补偿值叠加到进给轴上,使带误差补偿数据的凸轮加工NC程序不断根据实际加工状态更新,最后在工程样机上进行了磨削试验。试验结果表明,发动机凸轮轴的廓型最大加工误差降到了2.6μm以下,残余误差主要来源为机械振动、非线性摩擦扰动等随机性偏差。该运动控制和误差补偿方法能在实际加工中较好地补偿重复性误差因素对工件精度产生的影响。     

Contouring controller design for biaxial feed drive systems considering compliance of transmission mechanism

Contouring control is an effective method for computer numerical controlled machining, and various such designs have been proposed to date. However, the compliance of the transmission mechanism is not considered in most existent contouring controller designs. This paper presents a new contouring control system design considering the compliance of a transmission mechanism based on a fourth-order model of feed drive dynamics. First, we present a controller design that enables the controller gain assignment for reducing the error component orthogonal to the desired contour curve, independent of the tangential error component. Although this design provides better control performance with small control input variance, there exists an inherent contour error because of the difficulty in calculating the exact contour error for any contour curve in real time. To address this problem, a reference adjustment method is used to estimate the actual contour error. The effectiveness of the proposed design is experimentally verified by comparing the control performance with a design based on a plant model that neglects the compliance.     

车床振动的自动控制

车削时的振动,影响加工精度和生产率的提高,降低机床和刀具的寿命。因此,在现有机床和切削条件下,控制这种振动就成了十分重要的问题。在国内外,对车削时振动的控制的研究,一般均采用液压伺服系统或控制电机驱动系统,使刀具作补偿移动的方法。其控制方法复杂,控制装置的结构尺寸庞大,且对机床动态系统引入了附加系统的影响,对车床刀架的改装工作量也大。为此,我们提出了一种新的控制原理和方法,即外加上稳态控制力,同时利用车削时径向切削力的动态分量△P,来产生跟踪△P的变化,而相位与它相反的动态控制力△F,使切削力的波动的影响得到补偿,实现振动的自动控制。我们建立了控制系统,成功地进行了车削时振动的试验。试验结果表明,我们所建立的控制原理和方法,使车削时的振动显著减小,加工精度提高三倍,可大大提高生产率,不需要对车床的改装,方法简便。所以,它对于实际生产,和进一步扩展用于其它类型的切削加工,有重要的意义。     

无温度传感器的数控机床进给轴热误差补偿

分析了目前常见的进给轴热误差补偿方法的缺点,如需要多个温度传感器、模型的鲁棒性较差等。提出一种基于无温度传感器的、强鲁棒性的机床进给轴热误差补偿方法,在恒温环境下实现对运动生热导致的热误差的补偿。给出了热误差模型的推导过程以及应用ISIGHT平台进行参数优化的过程。热误差模型基于摩擦生热、热传导和散热机理实时预测滚珠丝杠的温度场,以实现预测并补偿丝杠热误差的目的。在一台立式加工中心VMC850上对x、y、z轴进行了热误差测试并给出了模型的仿真效果。在另一台立式加工中心VMC850上采用激光干涉仪进行了热误差补偿前后的对比试验和加工对比试验。试验结果表明,该热补偿方法具有很高的精度稳定性和强鲁棒性。     

圆弧刃刀具切削时理论粗糙度的计算

在圆弧刃刀具切削直线廓形时理论粗糙度计算的基础上，着重研究圆弧刃刀具切削圆弧廓形时理论粗糙度的计算方法。研究表明，工件已加工表面理论粗糙度取决于工件已加工表面的廓形、刀具切削刃形状和刀具切削运动方式，优化选取刀刃半径和刀具进给量后，可以有效地减小理论粗糙度值并提高切削效率。     

Prediction of vibration amplitude from machining parameters by response surface methodology in end milling

Decreasing vibration amplitude during end milling process reduces tool wear and improves surface finish. Mathematical model has been developed to predict the acceleration amplitude of vibration in terms of machining parameters such as helix angle of cutting tool, spindle speed, feed rate, and axial and radial depth of cut. Central composite rotatable second-order response surface methodology was employed to create a mathematical model, and the adequacy of the model was verified using analysis of variance. The experiments were conducted on aluminum Al 6063 by high-speed steel end mill cutter, and acceleration amplitude was measured using FFT analyzer. The direct and interaction effect of the machining parameter with vibration amplitude were analyzed, which helped to select process parameter in order to reduce vibration, which ensures quality of milling.     

Three-dimensional modeling for predicting the vibration modes of twin ball screw driving table

As a redundant drive mechanism, twin ball screw feed system has the advantage of high stiffness and little yaw vibration in the feeding process, while leads to increased difficulty with vibration characteristics analysis and structure optimization. Only low-dimensional structure and dynamics parameters are considered in the existing research, the complete and effective model for predicting the table＇s vibrations is lacked. A three-dimensional（3D） mechanical model of twin ball screw driving table is proposed. In order to predict the vibration modes of the table quantitatively, an analytical formulation following a comprehensive approach is developed, where the drive system is modeled as a lumped mass-spring system, and the Lagrangian method is used to obtain the table＇s independent and coupled axial, yaw, and pitch vibration modes. The frequency variation of each mode is studied for different heights of the center of gravity, nut positions and table masses by numerical simulations. Modal experiment is carried out on the Z-axis feed table of the horizontal machining center MCH63. The results show that for each mode, the error between the estimated and the measured frequencies is less than 13%. The independent and coupled vibration modes are in accordance with the experimental results, respectively The proposed work can serve a better understanding of the table＇s dynamics and be beneficial for optimizing the structure parameters of twin ball screw drive system in the design stage.     

HSM-ADAPTED TOOL PATH CALCULATION FOR POCKETING

High-speed milling imposes a precise choice of cutting conditions, because the feed rate and the radial depth of cut influence the maximum forces on cutting edges. But the control of these cutting conditions for pocket machining is very difficult due to the complex tool path shape. Our work is focused on the improvement of the geometrical definition of the tool path, in order to ensure a better respect of the cutting conditions required for HSM. Initially, we study variations in the radial depth of cut and the real feed rate, when the tool follows usual tool paths for pocketing. Numerical simulations and experimental measurements are used. Next, a new tool path computation method that increases the real feed rate and respects radial depth of cut requirements is proposed. The computation takes into account both the geometrical requirements and the HSM dynamic requirements. Such tool paths reduce machining time and respect initial cutting parameters which are favorable for process reliability and tool life.     

HSM-ADAPTED TOOL PATH CALCULATION FOR POCKETING

High-speed milling imposes a precise choice of cutting conditions, because the feed rate and the radial depth of cut influence the maximum forces on cutting edges. But the control of these cutting conditions for pocket machining is very difficult due to the complex tool path shape. Our work is focused on the improvement of the geometrical definition of the tool path, in order to ensure a better respect of the cutting conditions required for HSM. Initially, we study variations in the radial depth of cut and the real feed rate, when the tool follows usual tool paths for pocketing. Numerical simulations and experimental measurements are used. Next, a new tool path computation method that increases the real feed rate and respects radial depth of cut requirements is proposed. The computation takes into account both the geometrical requirements and the HSM dynamic requirements. Such tool paths reduce machining time and respect initial cutting parameters which are favorable for process reliability and tool life.     

车削精度主动控制系统与动态模型的研究

本文分析了以压电陶瓷作为驱动元件的振动切削刀具的振动特性和实现刀具谐振切削的电路匹配,分析了主轴误差补偿方法的特点,提出以振动切削和误差补偿为基础的提高车削加工精度的主动控制系统,并建立了该系统的动态模型,推导其频率响应函数,实验证实了该方法能全面地提高工件的加工质量。     

Robust iterative learning contouring controller with disturbance observer for machine tool feed drives

In feed drive systems, particularly machine tools, a contour error is more significant than the individual axial tracking errors from the view point of enhancing precision in manufacturing and production systems. The contour error must be within the permissible tolerance of given products. In machining complex or sharp-corner products, large contour errors occur mainly owing to discontinuous trajectories and the existence of nonlinear uncertainties. Therefore, it is indispensable to design robust controllers that can enhance the tracking ability of feed drive systems. In this study, an iterative learning contouring controller consisting of a classical Proportional-Derivative (PD) controller and disturbance observer is proposed. The proposed controller was evaluated experimentally by using a typical sharp-corner trajectory, and its performance was compared with that of conventional controllers. The results revealed that the maximum contour error can be reduced by about 37% on average.