Tool wear detection and fault diagnosis based on cutting force monitoring

In metal cutting processes, an effective monitoring system, which depends on a suitably developed scheme or set of algorithms can maintain machine tools in good condition and delay the occurrence of tool wear. In this paper, an approach is developed for fault detection and diagnosis based on an observer model of an uncertain linear system. A robust observer is designed, using the derived uncertain linear model, to yield the necessary and key information from the system. Subsequently, it is used as a state (tool wear) estimator, and fault detection is carried out by using the observed variables and cutting force. The developed approach is applied to milling machine center. Several linear models are identified based on different working conditions. A dominant model plus uncertain terms is derived from these model set and used as an observer. Threshold values are proposed for detecting the fault of the milling machine. Examples taken from experimental tests shown that the developed approach is effective for the fault detection. The approach can be used for fault detection of failures arising from sensor or actuator malfunction.     

Influence of machining cycle of horizontal milling on the quality of cutting force measurement for the cutting tool wear monitoring

The cutting tools are today used a lot by industry and they are expensive, so it was interesting to optimize their use, by developing a predictive method of their wear, particularly, the flank wear V _b . For this task, the flank tool wear was measured in off-line using a binocular microscope, whereas, the cutting forces are recorded by means of a dynamometer (Kistler 9255B). The acquired signatures are analyzed during the milling operation throughout the tool life. In this paper, we are interested in the extraction of the appropriate indicators which characterize the tool wear by temporal and frequential analyses of the cutting force signals; and highlighting the influence of the clamp holes and the machining cycle to the quality of the measurements.     

Adaptive cutting force control for a machining center by using indirect cutting force measurements

This paper presents an adaptive cutting force controller for the milling process, which can be attached to most commercial CNC machining centers in a practical way. The cutting forces of x, y and z axes are measured indirectly from the use of currents drawn by a.c. feed-drive servo motors. A typical model for the feed-drive control system of a horizontal machining center is developed to analyze cutting force measurement from the drive motor. The pulsating milling forces can be measured indirectly within the bandwidth of the current feedback control loop of the feed-drive system. It is shown that indirectly measured cutting force signals can be used in the adaptive controller for cutting force regulation. The robust controller structure is adopted in the whole adaptive control scheme. The conditions under which the whole scheme is globally convergent and stable are presented. The suggested control scheme has been implemented into a commercial machining center, and a cutting experiment on face milling process is performed.     

曲面精加工过程切削负载自适应新策略研究

分析了曲面积、精加工过程的不同特点,指出传统的切削负载自适应方法应用到曲面精加工过程时的缺陷,提出新的简单、易行的曲面精加工负载自适应策略－等切削力余量模型方法,论述了模型的构造算法及其关键技术。     

Prediction of chatter in NC machining based on a dynamic cutting force model for ball end milling

Ball end milling is one of the most widely used cutting processes in the automotive, aerospace, die/mold, and machine parts industries, and the chatter generated under unsuitable cutting conditions is an extremely serious problem as it causes excessive tool wear, noise, tool breakage, and deterioration of the surface quality. Due to the critical nature of detecting and preventing chatter, we propose a dynamic cutting force model for ball end milling that can precisely predict the cutting force for both stable and unstable cutting states because our uncut chip thickness model considers the back-side cutting effect in unstable cutting states. Furthermore, the dynamic cutting force model considers both tool runout and the penetration effect to improve the accuracy of its predictions. We developed software for calculating the cutting configuration and predicting the dynamic cutting force in general NC machining as well as single-path cutting. The chatter in ball end milling can be detected from the calculated cutting forces and their frequency spectra. A comparison of the predicted and measured cutting forces demonstrated that the proposed method provides accurate results.     

Multi-grooved cutting tool to reduce cutting force and temperature during bone machining

The cutting temperature of a cutting tool are required to be low during bone machining for preventing damage to bone cells. However, conventional tools are practically the same as those used for metal cutting, and many operational limitations have been reported. In this study, a dedicated cutting tool was designed for reducing cutting force and temperature. A short contact between the workpiece and the cutting edge leads to a reduction in the cutting force. Furthermore, a straight-line edge improves surface roughness. The effectiveness was evaluated using bovine bone, and the cutting force was found to be decreased by about 40%.     

A new procedure to determine instantaneous cutting force coefficients for machining force prediction

This paper presents a new procedure to determine instantaneous cutting force coefficients which are required for process simulation by mechanistic modeling. This new procedure drastically reduces the number of experiments for calibration and improves the accuracy of dynamic cutting forces and force signatures by considering the size effects. Comparisons are shown to illustrate the effectiveness of the proposed method in determining the chip flow angle and those predicted by various existing analytical models. The importance of using instantaneous cutting force coefficients instead of conventional average coefficients is demonstrated through simulation based on the mechanistic models.     

TWEM, a method based on cutting forces—monitoring tool wear in face milling

One of the most important objectives in manufacturing is the intelligent machining system. To come to such a solution, the tool wear has to be determined on-line during the cutting process on unmanned machining systems. This contribution discusses the results experimentally obtained in face milling with a new rotating dynamometer. The paper introduces the concept of tool wear indicators which can be determined by simple analysis of the feature parameters of cutting force signals. The disturbance of the cutting force signals obtained by using the rotating dynamometer can be solved by applying tool wear indicators such as Normalized Cutting Force indicator (NCF) and Torque-Force Distance indicator (TFD). The Method for Tool Wear Estimation—TWEM is proposed.     

Optimization of machining parameters in magnetic force assisted EDM based on Taguchi method

A versatile process of electrical discharge machining (EDM) using magnetic force assisted standard EDM machine has been developed. The effects of magnetic force on EDM machining characteristics were explored. Moreover, this work adopted an L18 orthogonal array based on Taguchi method to conduct a series of experiments, and statistically evaluated the experimental data by analysis of variance (ANOVA). The main machining parameters such as machining polarity (P), peak current (I_p), pulse duration (τ_p), high-voltage auxiliary current (I_H), no-load voltage (V) and servo reference voltage (S_v) were chosen to determine the EDM machining characteristics such as material removal rate (MRR) and surface roughness (SR). The benefits of magnetic force assisted EDM were confirmed from the analysis of discharge waveforms and from the micrograph observation of surface integrity. The experimental results show that the magnetic force assisted EDM has a higher MRR, a lower relative electrode wear ratio (REWR), and a smaller SR as compared with standard EDM. In addition, the significant machining parameters, and the optimal combination levels of machining parameters associated with MRR as well as SR were also drawn. Moreover, the contribution for expelling machining debris using the magnetic force assisted EDM would be proven to attain a high efficiency and high quality of surface integrity to meet the demand of modern industrial applications.     

Tool wear monitoring and breakage detection based on “intelligent filtering”

Several physical quantities can be used for indirect tool wear monitoring and breakage detection. Cutting forces are appropriate, since they determine the suitability of a tool for cutting. However, disturbances make the accurate and fast tool condition monitoring based upon force analysis difficult. To eliminate disturbances averaging or filtering within a predetermined bandwidth has often been applied. A new method of decomposing the force signal into components having close relationships with physical phenomena taking place during cutting is presented. The term “intelligent filtering” denotes decomposition based on on-line identification of model(s) of the cutting process. Application of “intelligent filtering” for the milling process with two cutting insert tools is discussed.     

A cutting power model for tool wear monitoring in milling

This paper describes a cutting power model in face milling operation, where cutting conditions and average tool flank wear are taken into account. The cutting power model is verified with experiments. It is shown with the simulations and experiments that the simulated power signals predict the mean cutting power better than the instantaneous cutting power. Finally, the cutting power model is used in a cutting power threshold updating strategy for tool wear monitoring which has been carried out successfully in milling operations under variable cutting conditions.     

基于PROFIBUS的加工中心控制系统

结合淮阴工学院的实际情况和专业特点，介绍了一种基于PROFIBUS的集教学、科研和生产为一体的轴类零件柔性加工系统的结构，重点介绍了加工中心控制单元的硬件结构、功能，同时对系统控制软件的编制作了分析和研究。     

Evaluation of a spindle-based force sensor for monitoring and fault diagnosis of machining operations

This paper presents an evaluation of a spindle-based force sensor, the force ring, which is a strong candidate for in-process monitoring and fault diagnosis of machining operations. The evaluation criteria include the effect of integration of the force ring on the dynamics of the spindle, the drift behavior due to temperature change inside the spindle, the cross-talk between the channels, and the existence and compensation of the spindle-internal forces. The application of the force ring to process model-based monitoring and fault diagnosis has been demonstrated by the determination of force calibration coefficients using the force ring and their comparison with results obtained with a platform dynamometer. It has been concluded that the force ring provides dynamometer quality force measurements.     

加工中心刀具选配及切削参数生成系统

介绍了一种加工中心刀具选配及切削参数生成系统。该系统通用性强、使用灵活，具有良好的开放性，可大大提高刀具选配及确定切削参数的效率。     

Practical implementation of cutting force model for step drill using 3D CAD data

As an extension of the cutting force model, which was developed by analyzing the forces on rake and relief face, a practical method of cutting force model is suggested. By a calibration test, cutting coefficients are determined, including the information on tool geometry, work material and cutting conditions such as cutting speed and feed rate. As inputs for the force model, normal rake angle and normal relief angle were obtained by a new method from the measured angles using a 3D CAD machine. This practical force model can be applied for machining CFRP successfully, which was proved from the experiments.     

Real-time tool wear monitoring in milling using a cutting condition independent method

This paper describes a new method to monitor end milling tool wear in real-time by tracking force model coefficients during the cutting process. The behavior of these coefficients are shown to be independent from the cutting conditions and correlated with the wear state of the cutting tool. The tangential and radial force model coefficients are normalized and combined into a single parameter for wear monitoring. A number of experiments with different workpiece materials are run to investigate the feasibility of tool wear monitoring using this method. We show that this method can be used in real-time to track tool wear and detect the transition point from the gradual wear region to the failure region in which the rate of wear accelerates.     

On cutting parameters selection for plunge milling of heat-resistant-super-alloys based on precise cutting geometry

In plunge milling operation the tool is fed in the direction of the spindle axis which has the highest structural rigidity, leading to the excess high cutting efficiency. Plunge milling operation is one of the most effective methods and widely used for mass material removal in rough/semi-rough process while machining high strength steel and heat-resistant-super-alloys. Cutting parameters selection plays great role in plunge milling process since the cutting force as well as the milling stability lobe is sensitive to the machining parameters. However, the intensive studies of this issue are insufficient by researchers and engineers. In this paper a new cutting model is developed to predict the plunge milling force based on the more precise plunge milling geometry. In this model, the step of cut as well as radial cutting width is taken into account for chip thickness calculation. Frequency domain method is employed to estimate the stability of the machining process. Based on the prediction of the cutting force and milling stability, we present a strategy to optimize the cutting parameters of plunge milling process. Cutting tests of heat-resistant-super-alloys with double inserts are conducted to validate the developed cutting force and cutting parameters optimization models.     

基于切削技术的金刚石刀具磨损特征分析

金刚石刀具的磨损情况决定其使用寿命。用金刚石PCD刀具切削6061-T6镁铝合金工件,通过不同切削速度、切削深度、振动频率、刀具后角时的切削力及切削温度变化,研究不同刀具前后角、进给量、切削转速时的工件表面粗糙度及刀具磨损面积。结果表明:金刚石刀具的切削力和切削温度随切削速度、切削深度的增加而增大,随振动频率的增加而减小;刀具后角增大,金刚石刀具的切削力呈先下降而后缓缓上升趋势,但对切削温度的影响很小。当刀具前角为10°,刀具后角为8°,切削速度为0.46?m/s,切削深度为28?μm,进给量为0.10?mm/r,切削转速为4100?r/min,振动频率为22?kHz,切削振幅为9?μm时,金刚石刀具的磨损面积最小,磨损程度最低,使用寿命最长,但工件的表面粗糙度稍高。      

Effect of machining parameters and coating on wear mechanisms in dry drilling of aluminium alloys

The temperature generated by friction and plastic deformation in the secondary shear zone strongly controls tool wear. At lower cutting speeds tool wear is not severe insofar as the temperature is not significant. When the cutting speed is increased, there is a transition in wear mechanisms from abrasion and/or adhesion to diffusion. In the present paper, the change in wear mechanisms as a function of cutting speed and coating material is discussed. The cutting tests were performed on a rigid instrumented drilling bench without the use of cutting fluids. AA2024 aluminium alloy was used to investigate the wear mechanisms of cemented tungsten carbide and HSS tools. Three cutting speeds (25, 65 and 165 m/min) and a constant feed rate of 0.04 mm/rev were selected for the experiments. The best results in terms of maximum and minimum hole diameter deviations and surface roughness are obtained for the uncoated and coated tungsten carbide drills. The results also show that HSS tool is not suitable for dry machining of AA2024 aluminium alloy.     

Identification of cutting force characteristics based on chatter experiments

Cutting force coefficients exhibit strong nonlinearity as a function of chip loads, cutting speeds and material imperfections. This paper presents the connection between the sensitivity of the dynamics of regenerative cutting and the cutting force characteristic nonlinearity. The nonlinear milling process is mathematically modelled. The transitions of dynamic cutting process between the stable and unstable zones are considered and experimentally illustrated by applying wavelet transformations on the measurement data.