Advanced monitoring of machining operations

CIRP has had a long history of research and publication on the development and implementation of sensor monitoring of machining operations including tool condition monitoring, unmanned machining, process control and, more recently, advanced topics in machining monitoring, innovative signal processing, sensor fusion and related applications. This keynote follows a recent update of the literature on tool condition monitoring and documents the work of the cutting scientific technical committee in CIRP. The paper reviews the past contributions of CIRP in these areas and provides an up-to-date comprehensive survey of sensor technologies, signal processing, and decision making strategies for process monitoring. Application examples to industrial processes including reconfigurable sensor systems are reported. Future challenges and trends in sensor based machining operation monitoring are presented.     

虚拟加工环境建模关键技术

提出一个虚拟制造系统的体系结构.针对实际加工设备的特点,将虚拟设备模型分为几何模型和仿真模型.重点研究了零部件几何模型的获取和实现方法,采用面向对象技术建立了虚拟加工环境.应用表明,该方法可根据实际加工情况快速构建虚拟加工环境.     

Fuzzy adaptive networks in machining process modeling: surface roughness prediction for turning operations

Due to the complexity of the machine tool structure and the cutting process, the dynamics of machining processes are still not completely understood. This is especially true due to the demand of high-speed machining to increase productivity. In order to model and control these complex processes, new approaches, which can represent complex phenomenon combined with learning ability, are needed. The combined neural–fuzzy approach appears to be ideally suited for this purpose. In this paper, the recently developed fuzzy adaptive network (FAN) is used to model surface roughness in turning operations. The FAN network has both the learning ability of neural network and linguistic representation of complex, not well-understood, vague phenomenon. Furthermore, it can continuously improve the initially obtained rough model based on the daily operating data. To illustrate this approach, a model representing the influences of machining parameters on surface roughness is established and then the model is verified by the use of the results of pilot experiments. Finally, a comparison with the results based on statistical regression is provided.     

Development of a thermomechanical cutting process model for machining process simulations

A thermomechanical model for cutting processes is presented. The deformation in the shear zone is represented using Johnson-Cook material model. The rake contact is modeled using sticking and sliding zones, and their lengths are also predicted. The parameters of the material model and the friction coefficient on the rake are directly identified from a few number of orthogonal cutting tests. The model can predict cutting forces, shear angle and stress, pressure distribution and contact lengths on the rake face and temperature distribution. The application of the model to common operations such as turning and multi-axis milling is also presented with experimental verification, and satisfactory results are obtained.     

Delayed-reference control (DRC) applied to machining operations

This paper deals with a non-time based control for machining operations. Such a control can be implemented in most of the CNC centers in a practical way. Basically, in this control, which belongs to the category of non-time based controllers, the desired input reference is a function of the time and of a variable which plays the role of a time delay: x_d(t−T). Indeed, the proposed controller is called delayed-reference control (DRC). It is recalled that in a time-based control, the desired input reference is described as a function of time only, which is referred to as reference time: x_d(t). The calculation of this function is usually implemented off-line by means of the so called path-planning process. According to this traditional approach, during the task execution, at each instant, the control module is required to track an input reference. What is relevant is that such a reference can never be modified by any event or circumstance. The DRC control differs from time-based controllers in the sense that time delay is properly calculated on-line according to the measured force signals in such a way to improve the interaction during the cutting process. In fact, the DRC consists in an outer force feedback loop around an inner position feedback loop. The effectiveness of the controller has been proven by means of its implementation on a three axes CNC center for wood machining. Eventually, experimental results are presented.     

薄壁类零件加工变形的解决工艺方法

介绍薄壁类零件的加工,通过对筒体段节的特点以及加工进行分析,总结了薄壁类零件加工工艺方法。指出只有根据零件的具体结构特点,设计合理的加工工艺路线、选择合适的刀具、确定合理的切削速度才能真正解决薄壁零件的加工变形。     

Calculation of optimum cutting conditions for turning operations using a machining theory

A method is described for calculating the optimum cutting conditions in turning for objective criteria such as minimum cost or maximum production rate. The method uses a variable flow stress machining theory to predict cutting forces, stresses, etc. which are then used to check process constraints such as machine power, tool plastic deformation and built-up edge formation. A modified form of Taylor tool life equation where the constants are determined using the machining theory has been employed in predicting tool life for the optimisation procedure. The obtained results indicate that the described method is capable of selecting the appropriate cutting conditions.     

Computer simulation applied to an orthogonal three-rod machine tool for machining a complicated three-dimensional surface

A computer simulation approach to machine a complicated three-dimensional surface by using a virtual orthogonal three-rod machine tool is presented. First, based on a Hunt’s parallel mechanism of three degrees of freedom, a three-dimensional virtual orthogonal three-rod machine tool with three degrees of freedom is created with advanced C software. Secondly, a tool spiral path base on the three-dimensional surface of workpiece is constituted. Thirdly, the tool spiral path base of the three-dimensional surface is assembled into a virtual orthogonal three-rod machine tool with some auxiliary links and a new virtual one-degree of freedom mechanism is created. Finally, by analyzing reversing motion, a reasonable input rotation function is determined, and the kinematic curves of the three rods and the feeding process are simulated and analyzed.     

Improvement of a delayed velocity reference control (DVRC) for machining operations

This paper deals with a non-time-based controller for machining operations, suitable to control the interaction force between the tool and the workpiece.In the traditional approach usually the tool feed velocity (on which the force depends) is predetermined: it is chosen on the basis of some important parameters, such as tool dimensions, shape and material, the depth of cut, the workpiece material, etc. In this traditional approach, the reference function is calculated off-line, and during the task execution, at each instant, the control module is required to track the input reference; the drawback of this approach is that the system is not able to modify its velocity if unpredictable events occur or if side conditions change; this could produce high forces that could damage the tool or the workpiece.This paper presents a non-time-based controller for machining operations. Basically, in this control, the desired input reference is calculated on-line according to the measured force signal in such a way to improve the interaction. The controller allows to set the optimum interaction force F_max. In addition to this the same control is able to move the tool, during free motion paths, with a constant customizable velocity V_max, thus implementing a velocity control. As a third feature, it is possible to set the maximum allowed acceleration A_max of the end effector during the motion. This control scheme, called delayed velocity reference control (DVRC) belongs to the category of non-time-based controllers, since the reference signal is not directly related to time.The effectiveness of the controller has been proven by means of its implementation on a three-axes CNC center for EPS foam cutting.     

Guide curve based interpolation scheme of parametric curves for precision CNC machining

Real-time parametric interpolation has played a key role in the computer control of machine tools. To achieve highest quality parts, generated trajectories not only describe the desired toolpath accurately, but also have smooth dynamics profiles. This paper presents a novel parametric interpolator based on guide curve. The relationships between geometric properties and kinematic properties are firstly discussed. Then, with a consideration of the important effect of the curvature of curvilinear path on the machining dynamics, a corresponding formula, which describes the relation of the maximum allowed feed acceleration/deceleration and the maximum allowed rate of change of curvature radius of paths, is built. Thus, based on a near arc parameterization and through modifying the curvature radius curve to deal with corners, key regions and other cases, adaptive feedrate schedule is completed according to the reconstructed smooth curvature radius curve. Consequently, confined chord errors, corners on the path and the acceleration/deceleration capabilities of the machine tool are simultaneously considered and incorporated into the guide curve based parametric interpolation system without using look-ahead scheme. Simulation results indicate the feasibility and precision of the proposed interpolation method.     

Ultra-precision machining by the cylindrical polishing process

A process planning method for removing an arbitrary and axially symmetric error profile by the cylindrical polishing process (abbreviated as the CPP process) is proposed in this study. This method is to plan the dwelling-time of the polishing tool so that the error profile can be accurately removed. The tool dwelling-time distribution is solved by a non-negative least square method. By using this method, the residual error between actual and desired removal depths may be induced. It is shown that the residual error is related to the width of the machining zone, the wavelength of the error profile, and the tool’s resolution. The computer simulations indicate that the residual error is always negligible when the wavelength of the error profile is larger than the width of the machining zone. If the wavelength of the error profile is large, a small size of the tool’s resolution is found effectively to reduce the residual error. The experimental study confirms that an arbitrary error profile can be accurately removed on the basis of the proposed method.     

The influence of cryogenic cooling on process stability in turning operations

This paper presents results of the influence of cryogenic machining on the process stability. The stability diagrams are obtained experimentally using the coarse-grained entropy rate estimator for chatter detection from measured cutting forces. In comparison with conventional machining, enlarged stability windows are observed for the case of cryogenic machining. Based on the defined specific force models in turning operations, it is shown that a higher machining stability is achievable in cryogenic machining due to the reduction of specific cutting force components, in comparison with dry machining.     

Analytical stability lobes including nonlinear process damping effect on machining chatter

Indentation of the tool edge and flank face into workpiece surface undulations has been recognized in the literature as the main source of process damping. This damping affects the process stability at low cutting speed greatly. Numerical simulations have allowed integrating the nonlinear indentation force into machining chatter models. It is shown in this paper that the indentation force requires very high discretization resolution for accurate numerical simulation. The objective of the current work is to develop the stability lobes analytically taking into account the effect of nonlinear process damping. The developed lobes could be established for different amplitudes of vibration. This is a departure from the traditional notion that the stability lobes represent a single boundary between fully stable and fully unstable cutting conditions. Plunge turning is utilized in the current work to illustrate the procedure of establishing the lobes analytically. Experimental cutting tests were conducted at three feedrates for sharp and worn tools and the results agreed well with the analytically established lobes.     

基于Master CAM叶片零件的四联动数控加工

随着加工技术日益普及,CAD／CAM软件也在不断更新,而多轴数控加工一直是航空发动机加工的关键技术。以叶片零件为例,通过对其工艺分析、数学分析、三维建模以及后续的数控加工,证明了MasterCAM在四联动数控加工中具有广泛的应用。     

A computer simulation approach to machining complicated shapes, on an orthogonal 6-rod machine tool

A computer simulation approach to machining a gear and cam by using a virtual orthogonal 6-rod machine tool is presented. First, based on Stewart's parallel mechanism, a virtual 3D orthogonal 6-rod machine tool with 6 degrees of freedom is created with advanced CAD software. Secondly, a 3D spur gear base and cam base are constituted. Thirdly, the gear base and cam base are assembled into a virtual orthogonal 6-rod machine tool with some auxiliary links and a new virtual 1-degree of freedom mechanism is created. Finally, using reversing motion analysis, the kinematic curves of the 6 rods and the feeding process are simulated and analyzed.     

基于神经网络的加工过程模型辨识

介绍了神经网络动态建模方法,以车削加工过程为例,用一个带单隐层的反向传播网络对非线性的加工过程进行了辨识研究,并将神经网络模型的跟踪响应与参数模型的跟踪响应作了对比分析。仿真结果表明,神经网络是建立非线性加工过程模型的一种有效方法。     

Compensation for machining defects due to spindle dilatation

Defects are a common occurrence in industry when it comes to prolonged machining tasks (machining moulds, series of work-pieces, etc.). The relatively long machining time is generally what gives significant value added to the work-piece. We therefore need to avoid having to produce test work-pieces as much as possible [NC Machines, Hermès Paris (1997)]. This article considers dispersions introduced by dilatation of the spindle during machining on NC machine tools. Such dispersions are obviously prejudicial to obtaining accurate dimensions along the Z-axis of the machine. Firstly, we introduce the context of the study and the problem we had to confront. Secondly, the experimental study enabled us to highlight those parameters having an influence and quantify defects. By expressing dilatation and relaxation in the form of an equation, we were then able to calculate defects at a given instant. This enabled us to generate an algorithm for processing of the N.C. program so we could correct errors by compensating for defects during machining. We completed the study by machining a series of work-pieces using the programme integrating compensation for dilatation so as to validate the approach.     

虚拟制造技术与机床CAD／CAM

虚拟制造为制造业迎接新的挑战提供了一种新的制造策略和方法，本文阐述了企业实施虚拟制造技术(Virtual manufacturing technology，VMT)的意义与可行性，分析了虚拟制造技术的核心技术群，并对机床CAD／CAM技术的发展方向和实施VMT的具体步骤进行了讨论。     

虚拟制造技术与模具CAD/CAE/CAM

简要介绍了虚拟制造的概念、特点及其核心内容与关键技术,并论述了虚拟制造技术的研究与应用现状以及在模具工业中应用的可行性,同时对模具CAD／CAE／CAM在此技术中的应用前景进行了探讨与展望。     

A method of tool path compensation for repeated machining process

This paper proposes a software method to compensate for the contour error in repeated machining process. In the proposed method, the profile of the first machined part is measured by a coordinate measuring machine. Based on the measured data, the tool path is modified by a compensation algorithm, and then, is represented by a series of linear segments. Finally, the compensated tool path is fed to the CNC machine tool for the machining of subsequent parts. Mathematical analysis and experimental evaluation are presented in this paper.