Cutter Runout Research Articles

Mechanistic cutting force model parameters evaluation in milling taking cutter radial runout into account

The simulation of the cutting process becomes a key aspect on production optimization. The search for optimal cutting parameters by simulation can be a very effective way of reducing the tuning time of the process and can demonstrate potential cost reduction. As the simulation of the microscopic behavior of the cut is still difficult to perform, most of the prediction techniques are based on mechanistic models of the cutting forces, whose parameters are deduced from experimental tests. The runout of the tool can be a parasite effect that lowers the precision of the identification of the cutting forces parameters. This paper shows the improvement of an identification algorithm given by the modeling of radial runout effect on the undeformed chip thickness. Two different models of cutter runout have been used and tested on experimental measurement performed on a static dynamometer. The adequacy between simulation and experiment is good and allows reliable prediction of cutting forces for different cutting conditions.

Estimation of Machined Surface Texture Being Based on Cutter Run-out Trajectory and Cutting Edge Profile of Small Diameter End-mill (1st Report)

This study deals with a development of analytical estimation system for machined surface texture based on tool run-out and cutting edge profile measurement for end-mills by optical method. In the article, geometrical cutting model is proposed with a consideration of tool deflection, tool run-out and cutting edge profile. In order to obtain those analytical parameter values, we constructed certain optical equipments for measuring spindle rotation trajectory and cutting edge profile in three dimensions. Through an analytical consideration of tool run-out trajectory, we revealed that the tool run-out components (both RRO and NRRO) are geometrically transferred to the machined surface as the corresponding wavelength components. From the experimental result, wavelength spectrum between surface roughness profile and tool run-out trajectory is closely conformed to the analytical simulation.

Systematic study on cutting force modelling methods for peripheral milling

This paper systematically studies the cutting force modelling methods in peripheral milling process in the presence of cutter runout. Emphasis is put on how to efficiently calibrate the cutting force coefficients and cutter runout. Mathematical derivations and implementation procedures are carried out based on the measured cutting force or its harmonics from Fourier transformation. Five methods are presented in detail. In the first three methods the cutting force coefficients are assumed to be constants whereas in the last two they are taken as functions of instantaneous uncut chip thickness. The first method and the fifth one are taken from literatures for comparison. The second, the third and the fourth methods are original contributions, which are carried out with optimization ideas. The second method proceeds using the first and Nkth harmonic forces as the source signal while the third and the fourth are derived based on the measured cutting forces and its first harmonics. The engagement of the cutter with the workpiece is considered in these three new calibration procedures without the requirement of a prior knowledge of the actual cutter runout. Comparisons among the calibrated results from different methods are made to study the limitations and consistency of the presented methods. Experiments are also conducted to show the prediction ability of all methods.

Consistency study on three cutting force modelling methods for peripheral milling

Three methods are presented for calibrating the instantaneous cutting force coefficient (ICFC) and the cutter runout parameters in peripheral milling. In the first method, ICFC and the runout parameters are calibrated separately. First, the nominal cutting force components extracted from the measured force data are used to calibrate the ICFC, and then the runout parameters are obtained by optimally selecting those producing the minimum squared difference between the measured and predicted cutting forces. The second method calibrates the cutting force coefficients and the runout parameters simultaneously by choosing those that best maintain the cutting force coefficients constant. The third method was previously proposed by the current authors. Comparisons between the calibrated results from different tests and different methods are made to validate the consistency of the presented methods. Experiments are also conducted for comparison purposes.

A New Algorithm for the Numerical Simulation of Machined Surface Topography in Multiaxis Ball-End Milling

In milling process, surface topography is a significant factor that affects directly the surface integrity and constitutes a supplement to the form error associated with the workpiece deformation. Based on the tool machining paths and the trajectory equation of the cutting edge relative to the workpiece, a new and general iterative algorithm is developed here for the numerical simulation of the machined surface topography in multiaxis ball-end milling. The influences of machining parameters such as the milling modes, cutter runout, cutter inclination direction, and inclination angle upon the topography and surface roughness values are studied in detail. Compared with existing methods, the basic advantages and novelties of the proposed method can be resumed below. First, it is unnecessary to discretize the cutting edge and tool feed motion and rotation motion. Second, influences of cutting modes and cutter inclinations are studied systematically and explicitly for the first time. The generality of the algorithm makes it possible to calculate the pointwise topography value on any sculptured surface of the workpiece. Besides, the proposed method is proved to be more efficient in saving computing time than the time step method that is commonly used. Finally, some examples are presented and simulation results are compared with experimental ones.

Complexity measure of motor current signals for tool flute breakage detection in end milling

Automated tool condition monitoring is an important issue in the advanced machining process. Permutation entropy of a time series is a simple, robust and extremely fast complexity measure method for distinguishing the different conditions of a physical system. In this study, the permutation entropy of feed-motor current signals in end milling was applied to detect tool breakage. The detection method is composed of the estimation of permutation entropy and wavelet-based de-noising. To confirm the effectiveness and robustness of the method, typical experiments have been performed from the cutter runout and entry/exit cuts to cutting parameters variation. Results showed that the new method could successfully extract significant signature from the feed-motor current signals to effectively detect tool flute breakage during end milling. Whilst, this detection method was based on current sensors, so it possesses excellent potential for practical and real-time application at a low cost by comparison with the alternative sensors.

New Cutting Force Modeling Approach for Flat End Mill

AbstractA new mechanistic cutting force model for flat end milling using the instantaneous cutting force coefficients is proposed. An in-depth analysis shows that the total cutting forces can be separated into two terms: a nominal component independent of the runout and a perturbation component induced by the runout. The instantaneous value of the nominal component is used to calibrate the cutting force coefficients. With the help of the perturbation component and the cutting force coefficients obtained above, the cutter runout is identified. Based on simulation and experimental results, the validity of the identification approach is demonstrated. The advantage of the proposed method lies in that the calibration performed with data of one cutting test under a specific regime can be applied for a great range of cutting conditions.

2301 振れ回りを考慮したエンドミルの加工モデル(OS2-3 加工システム)

A cutting force model for end mills with consideration of runout effects is introduced in this paper. The cutter runout caused by cutter setup can be expressed a location angle and a radical offset. An estimation method, which can accurately identify these two parameters from a surface geometry, is also proposed. The feasibilities of the cutting force model and the runout determination method are demonstrated by comparing estimated and measured cutting forces.

Efficient calibration of instantaneous cutting force coefficients and runout parameters for general end mills

This paper aims at developing a unified approach to identify the cutting force coefficients together with the cutter runout parameters for general end mills such as cylindrical, ball, bull nose ones, etc. The cutting forces that are modeled using the instantaneous cutting force coefficients are analyzed and separated into two terms: a nominal component independent of the runout and a perturbation component induced by the runout. The nominal component enables the calibration of the instantaneous cutting force coefficients whereas the runout parameters are determined from the perturbation component. The validity of the present method is demonstrated with simulation and experimented data.

Improved dynamic cutting force model in peripheral milling. Part II: experimental verification and prediction

Cutting trials reveal that a measure of cutter run-out is always unavoidable in peripheral milling. This paper improves and extends the dynamic cutting force model of peripheral milling based on the theoretical analytical model presented in Part I [1], by taking into account the influence of the cutter run-out on the undeformed chip thickness. A set of slot milling tests with a single-fluted helical end-mill was carried out at different feed rates, while the 3D cutting force coefficients were calibrated using the averaged cutting forces. The measured and predicted cutting forces were compared using the experimentally identified force coefficients. The results indicate that the model provides a good prediction when the feed rate is limited to a specified interval, and the recorded cutting force curves give a different trend compared to other published results [8]. Subsequently, a series of peripheral milling tests with different helical end-mill were performed at different cutting parameters to validate the proposed dynamic cutting force model, and the cutting conditions were simulated and compared with the experimental results. The result demonstrates that only when the vibration between the cutter and workpiece is faint, the predicted and measured cutting forces are in good agreement.

A force-model-based approach to estimating cutter axis offset in ball end milling

Cutter runout due to cutter axis offset is quite common in a milling process, yet it is difficult to directly measure the runout geometry of a ball end cutter during the cutting process. This paper presents an analytical method for the estimation of cutter radial offset via forces in ball end milling. Closed form expression for the total milling force in the presence of cutter offset is first obtained. Fourier series coefficients for the offset related force component are shown to be expressed explicitly in terms of the offset geometry and serve as the basis for the identification of the offset geometry from the measured cutting forces. The offset geometry including its magnitude and the phase angle are directly calculated from the measured force component at the spindle frequency through two algebraic expressions. The identification method is finally validated by milling experiments.

Theoretical modelling of cutting forces in helical end milling with cutter runout

A theoretical cutting force model for helical end milling with cutter runout is developed using a predictive machining theory, which predicts cutting forces from the input data of workpiece material properties, tool geometry and cutting conditions. In the model, a helical end milling cutter is discretized into a number of slices along the cutter axis to account for the helix angle effect. The cutting action for a tooth segment in the first slice is modelled as oblique cutting with end cutting edge effect and tool nose radius effect, whereas the cutting actions of other slices are modelled as oblique cutting without end cutting edge effect and tool nose radius effect. The influence of cutter runout on chip load is considered based on the true tooth trajectories. The total cutting force is the sum of the forces at all the cutting slices of the cutter. The model is verified with experimental milling tests.

A numerical study of the effects of cutter runout on milling process geometry based on true tooth trajectory

Cutter runout is a common phenomenon affecting the cutting performances in milling operations. To date, most of the milling process models considering cutter runout were established based on the circular tooth path approximation, which brought errors into the runout estimation. In this paper, a new approach is presented for modelling the milling process geometry with cutter runout based on the true tooth trajectory of cutter in milling. The mathematical relationship between the trajectories generated by successive cutter teeth with runout is analysed. The milling process geometrical parameters, including the instantaneous undeformed chip thickness, the entry and exit angles of a cutting tooth, and the ideal peripheral machined workpiece surface roughness, are modelled according to the true tooth trajectories. Numerical method is used to solve the derived transcendental equations. A simulation study of the effects of cutter runout on milling process geometry is conducted using the models. It was found that the change of cutter radius for a tooth relative to its preceding one is the most important factor in evaluating the effects of cutter runout.

Time-frequency-analysis-based minor cutting edge fracture detection during end milling

Successful application of tool condition detection during end milling can ensure high-quality parts and safeguard the machining system. This paper proposes an effective algorithm that consists of wavelet-based de-noising, discrete time-frequency analysis, FFT and second differencing for the detection of minor cutting edge fracture during end milling. The algorithm can be successfully applied to extract marked features from the feed-motor current signals to indicate the minor cutting edge fracture. Some typical experiments, the cutter run-out, entry/exit cuts and cutting parameters-variation, have been performed to confirm the robustness of the algorithm. The results show that the new approach has an excellent potential for practical and real-time application at low cost for the detection of minor cutting edge fracture during end milling.

Mechanistic modelling of the milling process using an adaptive depth buffer

A mechanistic model of the milling process based on an adaptive and local depth buffer is presented. This mechanistic model is needed for speedy computations of the cutting forces when machining surfaces on multi-axis milling machines. By adaptively orienting the depth buffer to match the current tool axis, the need for an extended Z-buffer is eliminated. This allows the mechanistic model to be implemented using standard graphics libraries, and gains the substantial benefit of hardware acceleration. Secondly, this method allows the depth buffer to be sized to the tool as opposed to the workpiece, and thus improves the depth buffer size to accuracy ratio drastically. The method calculates tangential and radial milling forces dependent on the in-process volume of material removed as determined by the rendering engine depth buffer. The method incorporates the effects of both cutting and edge forces and accounts for cutter runout. The simulated forces were verified with experimental data and found to agree closely. The error bounds of this process are also determined.

AN IMPROVED METHOD FOR CUTTER RUNOUT MODELING IN THE PERIPHERAL MILLING PROCESS

Cutter runout is an important problem in milling operations. Runout increases the maximum cutting force, degrades the surface finish, increases cutter wear, and affects the dynamic behavior of the cutting process. Unlike past research that has primarily centered on describing the effects of runout on the cutting forces and surface texture, the focus here is on a systematic modeling and measurement technique for cutter runout in peripheral milling. A three-step methodology for runout estimation is presented. The first step comprises of an enhanced runout model that includes the effects of cutter grind, parallel axis offset, and cutter tilt. The next step is to outline a simple procedure to measure the data to be used in the proposed model, and the final step is a technique for the estimation of the runout parameters from this model and the data collected. This runout estimation model is applied to three different types of carefully selected cutters. A designed set of experiments is performed to verify the adequacy of the proposed model and also to compare these predictions with the results obtained by past runout models.

In-Process Tool Fracture monitoring in Face Milling Using Spindle Motor Current and Tool Fracture Index

A new algorithm for tool fracture detection using spindle motor current is suggested for face milling. A tool fracture index (TFI) is suggested to represent the magnitude of tool fracture. Dynamic cutting force variation in the face milling process is measured indirectly using spindle motor current. Even though the dynamic sensitivity of the spindle motor current is low, the cutting force can be correctly represented by the spindle r.m.s. current in rough face milling. In rough milling, tool fracture is distinguished well from cutter run-out and transient cutting. The magnitude of tool fracture can be predicted by the proposed tool fracture index using the spindle motor current.

Detection of tool flute breakage in end milling using feed-motor current signatures

An effective algorithm based on improved time-domain averaging is proposed to detect tool flute breakage during end milling using feed-motor current signatures. The algorithm proposed is demonstrated to be effective in detecting tool flute breakage in real time through a series of milling experiments, and is also demonstrated to be insensitive to the effects for transients, such as cutter runout, entry/exit cuts, and noise in the feed-motor current signals. The results show that the approach has an excellent online application potential for tool flute breakage detection in end milling.

Prediction of the Amount of Tool Fracture in Face Milling Using Cutting Force Signal

Tool fracture index(TFI) was developed in order not only to detect tool fracture but also to predict the amount of tool fracture in face milling. TFI is calculated by using peak-to-valley values of cutting force acting on teeth and their ratio between the adjacent teeth. When the tool fractures, a large value of TFI proportional to the amount of tool fracture was obtained periodically and decreased gradually. It was found that TFI is independent of cutter runout and it almost does not vary during transient cutting such as cutting condition change during machining. The threshold of tool fracture can be analytically determined by TFI developed in this paper, because the magnitude of TFI was shown to be dependent on the ratio of the amount of tool fracture to feed per tooth and immersion ratio. It was possible to predict the amount of tool fracture in experiments by using the proposed TFI.

An Approach to Theoretical Modeling and Simulation of Face Milling Forces

A new approach to theoretical modeling and simulation of face milling forces is presented. The present approach is based on a predictive machining theory in which machining characteristic factors in continuous cutting with a single-point cutting tool can be predicted from the workpiece material properties, tool geometry, and cutting conditions. The action of a milling cutter is considered as the simultaneous work of a number of single-point cutting tools, and the milling forces are predicted from input data of workpiece material properties, cutter parameters and tooth geometry, cutting condition, cutter and workpiece vibration structure parameters, and types of milling. A predictive force model for face milling is developed using this approach. In the model, the workpiece material properties are considered as functions of strain, strain rate, and temperature. The ratio of cutter tooth engagement over milling is taken into account for the determination of temperature in the cutting region. Cutter runout is included in the modeling for the chip load. The relative displacement between the cutter and workpiece due to the cutter and workpiece vibration is also included in the modeling to consider the effect on the undeformed chip thickness. A milling force simulation system has been developed using the model, and face milling experimental tests have been conducted to verify the simulation system. It is shown that the simulation results agree well with experimental results.