大型铝合金薄壁回转体零件切削力分析研究

根据大型薄壁回转体零件切削力测试试验要求,研制了外圆专用压电式测力仪和内孔专用压电式测力仪。通过单因素试验分析,得出切削力的变化规律曲线,并采用有限元分析方法对切削力和工件变形影响进行了分析研究。最终得出在切削过程中主切削力Fz数值最大且对工件的加工精度影响最大。     

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.     

Workpiece locating error prediction and compensation in fixtures

In machining process, fixture is used to keep the position and orientation of a workpiece with respect to machine tool frame. However, the workpiece always cannot be at its ideal position because of the setup error and geometric inaccuracy of the locators, clamping force, cutting force, and so on. It is necessary to predict and control the workpiece locating error which will result in machining error of parts. This paper presents a prediction model of a workpiece locating error caused by the setup error and geometric inaccuracy of locaters for the fixtures with one locating surface and two locating pins. Error parameters along 6 degrees of freedom can be calculated by the proposed model and then compensated by either using the “frame transformation” function of a numerical control (NC) system or modifying NC codes in post-processing. In addition, machining error caused by the workpiece locating error can be predicted based on a multi-body system and homogeneous transfer matrix. This is meaningful to fixture design and machining process planning. Finally, a cutting test has shown that the proposed method is practicable and effective.     

MACHINING RESIDUAL STRESSES IN AISI 316L STEEL AND THEIR CORRELATION WITH THE CUTTING PARAMETERS

It is well known that machining results in residual stresses in the workpiece. These stresses correlate very closely with the cutting tool geometrical parameters as well as with the machining regime. This paper studies the residual stress induced in turning of AISI 316L steel. Particular attention is paid to the influence of the cutting parameters, such as the cutting speed, feed and depth of cut. In the experiments, the residual stresses have been measured using the X-ray diffraction technique (at the surface of the workpiece and in depth). The effects of cutting conditions on residual stresses are analyzed in association with the experimentally determined cutting forces. The orthogonal components of the cutting force were measured using a piezoelectric dynamometer.     

STABILITY ANALYSIS OF BORING BARS WITH ASYMMETRY

Stability analysis in machining systems is often based on linearized models of the cutting forces, and it is common to assume that chatter is due primarily to relative tool/workpiece motion normal to the workpiece surface. Reasonable agreement between theory and experiment has been noted in previous studies using these types of cutting force models, combined with machine tool structural models. In Parker's work,[[1]] a boring bar was used which had dissimilar stiffnesses in the directions tangent and normal to the workpiece surface. While good agreement between theory and experiment was found for many spindle speeds, poor agreement was noted for certain speed ranges. In these speed ranges, the relative tool/workpiece motion was primarily tangential to the workpiece surface. It has been assumed by Parker, and others, that additional terms may be required in the cutting force model to account for the tangential motion effect and to accurately predict chatter in some boring operations. This paper presents an analysis of Parker's system, and shows that conventional cutting models can explain the tangential motion effect he encountered, without any additional terms.     

基于有限元数值模型和进给速度优化的薄壁件侧铣变形在线控制

为实现在加工过程中对薄壁件侧铣产生的较大切削变形进行在线控制,提出基于有限元数值模型和进给速度优化的在线控制策略。根据薄壁件切削过程的有限元仿真结果,建立数控机床进给速度、切削力、工件切削变形间的数值模型,进而确定用于控制变形的最优目标切削力。在具有开放式模块化的数控系统平台上开发了切削力信号实时采集、滤波功能和基于Brent-Dekker算法的进给速度在线优化策略,并根据滤波后的切削力及相应算法在加工过程中实时调整机床进给速度,保证切削力逐渐接近最优控制目标而实现切削变形的在线控制。试验结果表明,经过进给速度在线优化后的切削过程可将薄壁件侧铣变形控制在规定范围内,同时提高了切削效率。     

Stability analysis of turning process with tailstock-supported workpiece

This paper proposes an analytical scheme for stability analysis in turning process by considering the motion of tailstock-supported workpiece using a compliance model of tool and work. A dynamic cutting force model based on relative motion between the cutting tool and workpiece is developed to study the chatter stability. Linear stability analysis is carried out in the frequency domain and the stability charts are obtained with and without considering workpiece flexibility. Variations of stability limits with workpiece dimensions and cutter position as well as the effects of cutting tool dynamics are studied and wherever possible results are compared with existing models. Experimental analysis is conducted on tailstock-supported workpiece to examine the correctness of the proposed stability model.     

超声磁力复合研磨钛合金锥孔的试验研究

为了提高钛合金锥孔的研磨质量和研磨效率,提出了采用超声波振动辅助磁力研磨的复合加工方案。加工时,磨粒在磁场束缚下切削锥孔表面,并对其进行不断撞击,且因为磁场力、超声振动力和离心力等综合影响的原因,磨粒的切削轨迹呈现明显的多向性。针对钛合金锥孔,与传统磁力研磨法进行试验对比,并分析研磨后试件的材料去除量、表面粗糙度和表面形貌等来验证超声磁力复合研磨的效果。结果表明：超声磁力复合研磨加工效率得到提高;锥孔的材料去除量增加至1.6倍;研磨后锥孔平均表面粗糙度由原始的R_a1.23 μm降至R_a0.25 μm,下降率是传统工艺的1.3倍;试件表面的微波峰、凹坑和加工纹理均被去除,锥孔表面质量得到显著提高,且试件形状精度得到改善。     

Analyzing the drivers of end-of-life tire management using interpretive structural modeling (ISM)

A sensor module that incorporates a thin film polyvinylidene fluoride (PVDF) piezoelectric strain sensor rosette as well as data logging and wireless transmitting electronics has been designed and implemented for monitoring dynamic cutting torque in the end milling process—a material removal process widely used in the aerospace industry. The dynamic shear strain produced in the rotating tool during the cutting process is picked up by the PVDF sensor rosette attached to the tool shank and can be either logged into the onboard micro secure digital card or wirelessly transmitted to a nearby base station. The PVDF sensor rosette is largely insensitive to the pyroelectric effect of the PVDF sensor and the other strain components such as bending strain and thermal strain. A physics-based model is used to relate the measured PVDF sensor signal to the dynamic milling torque. The proposed method is experimentally validated using reference milling torque signals computed from cutting force signals measured using a platform-type piezoelectric force dynamometer.     

Real‐Time Monitoring of Tool Fracture in Turning Using Sensor Fusion

The sensor fusion method using both an acoustic emission (AE) sensor and a built-in force sensor is introduced for on-line tool condition monitoring during turning. The cutting force was measured by a built-in piezoelectric force sensor, which was inserted in the tool turret housing of an NC lathe. FEM analysis was carried out to locate the most sensitive position for the sensor. A burst of AE signal was used as a triggering signal to inspect the cutting force. A significant drop in cutting force indicated tool breakage. The algorithm was implemented in a DSP board and the monitoring system was installed on a CNC lathe in an FMS line for in-process tool-breakage detection. The proposed system showed an excellent monitoring capability.     

System identification and admittance model-based nanodynamic control of ultra-precision cutting process

The control of diamond turning is usually achieved through a laser-interferometer feedback of slide position. The limitation of this control scheme is that the feedback signal does not account for additional dynamics of the tool post and the material removal process. If the tool post is rigid and the material removal process is relatively statie, then such a non-collocated position feedback control scheme may suffice. However, as the accuracy requirement gets tighter and desired surface contours become more complex, the need for direct tool-tip sensing becomes inevitable. The physical constraints of the machining process prohibit any reasonable implementation of a tool-tip motion measurement. It is proposed that the measured force normal to the face of the workpiece can be filtered through an appropriate admittance transfer function, providing an estimated depth of cut. This can be compared to the desired depth of cut to generate the adjustment control action in addition to position feedback control. In this work, the design methodology on admittance model-based control with a conventional controller is presented. The recursive least-squares algorithm with forgetting factor is proposed to identify the parameters and update the cutting process in real time. The normal cutting forces are measured to identify the cutting dynamics in the real diamond turning process using a precision dynamometer. Based on the parameter estimation of cutting dynamies and the admittance model-based nanodynamic control scheme, simulation results are shown.     

CUTTING PROCESS DIAGNOSTICS UTILISING A SMART CUTTING TOOL

A new sensorised boring tool has been developed to enhance the flexibility and precision of line boring processes. A position sensor and tool tip actuator to control and its controller electronics were integrated into a cutting tool. To take further advantage of this highly sophisticated tool, a process diagnostic method based on cutting force measurement method was developed. An observer implemented in the tool controller estimates the disturbance to the actuator using the tool position sensing information. The estimated disturbance is the same as cutting force applied to the tool tip. The algorithm utilising the cutting force to detect cutting process faults, such as tool tip breakage and misalignment of workpiece has been designed and tested experimentally.     

固定式三向铣削测力仪的研究

由于铣刀在铣削过程中切削位置不同,固定型铣削测力仪将产生输出误差。为降低铣削位置变化对传感器输出的影响,研制了一种四竖直敏感梁结构的应变型固定式三维铣削测力仪。研究表明,当铣削位置范围限定时,该测力仪可以将输出信号误差维持在可用范围,并分别进行了静态力测量和动态铣削实验。在静态力测量实验中,在70mm×70mm×15mm工件上,传感器解耦偏差不大于5.58%;在动态切削实验中,使用相同加工参数在不同位置处铣削,传感器测得的铣削力峰峰值最大相差3.73%。对该铣削测力仪的研究为解决竖直方向高刚度的应变型固定式铣削力传感器的解耦问题提供了新的思路和参考。     

径向槽回转切削运动学及加工误差分析

提出采用无分度运动的回转切削方法加工径向槽,建立了刀尖相对于工件的运动轨迹方程和两种理论加工误差模型(轮廓倾斜误差模型和轮廓周向误差模型),结合实例分析了中心距、刀具半径等参数对理论加工误差的影响.结果表明,采用回转切削方法加工径向槽不仅可以提高自动化程度和生产效率,而且通过合理选择中心距和刀具半径等参数,可将理论加工误差控制在允许的范围内.     

虚拟数控车削物理仿真模型及实用系统的开发

建立了车削加工动态物理仿真模型及相关切削力、随机振动及干扰分析的子模型,同时应用该仿真系统进行了某典型零件的物理仿真,并提供了关于瞬时切削力、切削振动及各统计数据的输出结果。     

多线切割机过程张紧力控制的研究

多线切割机过程张紧力是影响切割线运动状态的重要因素之一,对加工件表面质量和加工精度及切割线寿命都有着重要影响。对过程张紧力的特点及其影响因素进行了分析,通过采用磁场力来合理的控制过程张紧力,是改善加工件加工质量及提高钢线寿命的有效途径。     

基于线性插补加工零刃带螺旋回转面刀具的精度研究

针对多轴线性插补方法加工零刃带回转面刀具建立了刃带宽度误差的分析模型,兼顾分析了两个几何体——砂轮大圆和锥面,在工件表面按一定规律运动时对刀刃宽度的精度影响,给出了减小误差的方法。同时提出了刀刃节点交错的刀位(CL)轨迹计算原理,可以大大改善刀具加工工件的表面质量,此方法简单可靠,具有通用性。     

Surface textural analysis using acousto optic emission- and vision-based 3D surface topography��a base for online tool condition monitoring in face turning

In metal cutting as a result of the cutting motion, the surface of workpiece will be influenced by cutting parameters, cutting force, and vibrations, etc. Thus, by monitoring the machined surface topography of the workpiece and extracting the relevant information the cutting process and tool wear state should be able to be monitored and quantified. But the effects of vibrations have been paid less attention. The work in the present paper is divided into two parts. First part consists of a data acquisition and signal processing using acousto optic emission sensor (i.e., laser Doppler vibrometer) for online tool condition monitoring and the second part of the work presents the surface topography analysis of machined surfaces during the progression of the tool wear. Most of the work presented is also a study where surface metrology is being used to measure all aspects of the machining in combination with an online metrology tool. The encouraging results of the work pave the way for the development of a real-time, low cost, and reliable tool?Ccondition?Cmonitoring system. A high degree of correlation is established between the results of the acousto optic emission signal- and vision-based surface textural analysis in identification of tool wear state.     

数控机床主轴径向运动误差在线高精度检测

数控机床加工工件时，在切削力的作用下，用“以被加工工件为测量基准”的测量方案，实时测量机床主轴的径向运动误差．为了提高信噪比，采用基于精确重构的小波变换算法去除加工时存在的噪声．这种新算法成功地应用于自行开发的在线检测装置中。为了掌握测量系统频域特征，还从谐波抑制和总体频域特性两方面做了分析。通过实验验证了该方法的正确性。     

CONDITION MONITORING FOR INDEXABLE CARBIDE END MILL USING ACCELERATION DATA

In order to automate machining operations, it is necessary to develop robust tool condition monitoring techniques. In this paper, a tool monitoring strategy for indexable tungsten carbide end milling tools is presented based on the Fourier transform and statistical analysis of the vibrations of the tool during the machining operations. Using a low-cost, tri-axial piezoelectric accelerometer, the presented algorithm demonstrates the ability to accurately monitor the condition of the tools as the wear increases during linear milling operations. One benefit of using accelerometer signals to monitor the cutting process is that the sensor does not limit the machine's capabilities, as a workpiece mounted dynamometer does. To demonstrate capabilities of the technique, four tool wear life tests were conducted under various conditions. The indirect method discussed herein successfully tracks the tool's wear and is shown to be sensitive enough to provide sufficient time to replace the insert prior to damage of the machine tool, cutter, and/or workpiece.