Cutting Force Spectrum Research Articles

Compilation of drilling load spectrum based on the characteristics of drilling force

In order to overcome the problem that the existing methods of compiling load spectrum of spindle or machine tool mainly aim at the cutting force spectrum, torque spectrum and speed spectrum, respectively, which ignore the connection between each spectrum, in this paper, a method for compiling drilling load spectrum of motorized spindle in CNC machine tool based on the characteristics of drilling force is proposed. Firstly, drilling tests under different processing technologies are carried out to measure its load, and the correction coefficient in the empirical formula of drilling force is obtained through fitting the measured drilling force, which makes the calculation of the axial force and torque more reasonable. Secondly, compared with the extended factor method, the transcendental probability method is optimized to solve the ultimate load of the axial force. Then, after setting the axial force as the main load of drilling, an eight-stage load spectrum for the main load is compiled. Finally, according to the relationship between the axial force and other loads, the eight-stage loading spectrum is transformed into a multidimensional drilling load spectrum.

A frequency-based analysis of cutting force for depths of cut identification in peripheral end-milling

This paper presents a novel approach to identify both radial and axial depth of cut in 2.5-axis peripheral milling operations using cutting force signals analysed in the frequency domain (i.e., cutting force spectrum). In detail, the method exploits the normalized cutting force spectrum, which is directly obtained through dedicated analytical formulations, to estimate depths of cut. The proposed approach is promising and differs from previous works since it does require nor the cutting force coefficients or cutting force direction neither a dedicated instrumentation. The developed method was numerically and experimentally validated in different cutting conditions. The results obtained show that depths of cut are identifiable with a maximum absolute error less than 0.4 mm, proving that the proposed approach could be a solid foundation for a force based cutting condition monitoring system in peripheral milling.

DEPTHS OF CUT IDENTIFICATION IN 3-AXIS MILLING USING CUTTING FORCE SPECTRUM

Cutting forces analysis is one of the most important means of improving machining quality and productivity. In 3-axis milling, the frequency domain analysis of the cutting forces provides information which can be adopted for both predicting and monitoring the cutting process. However, the evaluation of the cutting forces spectra requires the application of specific tools (i.e., Fourier’s Transform) to the time domain representation of the same cutting forces. This paper presents analytical formulations to directly evaluate the cutting force spectra starting from the tool geometry and the cutting parameters. The proposed formulations start from the expression of the cutting forces as a Fourier series and enhance the predictions showed in previous works by reducing the overall number of calculations needed. Then, the proposed formulations are applied to identify both radial and axial depths of cut exploiting the normalized cutting force spectrum. Finally, the proposed formulations and their application were numerically and experimentally validated. This work represents a preliminary step in the development of a monitoring system to identify cutting conditions in 3-axis milling.

Compilation method of CNC lathe cutting force spectrum based on kernel density estimation of G-SCE

The cutting force spectrum of the CNC lathe is the basic data for the reliability design, reliability test, and reliability evaluation of the CNC lathe and its components. Due to the complex and changeable turning conditions and different cutting processes, the cutting load presents multi-peak characteristics. At the same time, grouping the counted load cycles when parameter modeling will produce certain errors. As a result, the parameter distribution model cannot meet the modeling requirements. Thus, a compilation method based on kernel density estimation (KDE) of goodness-smoothness comprehensive evaluation (G-SCE) is proposed. The KDE is used to establish the dynamic cutting force distribution of the CNC lathe in which grouping the counted load cycles is not needed. For the bandwidth-determining methods, the rule of thumb method (ROT) and the least-squares cross-validation method (LCV) do not take into account the influence of different bandwidths on the goodness estimation and the smoothness of the estimated curve, and the G-CSE for KDE is proposed to determining the optimal bandwidth. It includes the estimation accuracy test method based on multiple goodness-of-fit tests and the smoothness test method based on the envelope curve, and the entropy method is used to comprehensively weights the estimated goodness index and the smoothness index to determine the optimal bandwidth. The results of the case analysis indicate that the method proposed can solve the problem of too large estimation error of parameter distribution for multimodal distribution. At the same time, it can better comprehensively evaluate the KDE under different bandwidths. In short, a new method of optimal bandwidth selection is proposed in the original method.

Study on Multi-scale Time-frequency Analysis of Cutting Force Based on EMD Method

A method for establishing the multi-scale cutting force spectrum under complex random load history is presented according to the non-stationary random characteristics of the cutting force-time history. The IMF components of different time scales are obtained by EMD decomposition of complex random cutting force-time history data. The probability density distribution of cutting force in certain frequency band is obtained as the load spectrum on this time scale. This method avoids the disadvantage of the conventional method that the load or stress is regarded as a constant or variable amplitude load under one frequency to establish the load spectrum. The method for establishing the multi-scale load spectrum can provide a basis for fatigue life calculation and fatigue reliability analysis of mechanical components.

Time domain load extrapolation method for CNC machine tools based on GRA-POT model

The load extrapolation is to obtain load data that may occur during the whole life cycle of product based on the limited measured load data, especially extreme load. Aiming at the two problems of traditional time domain extrapolation: without considering the interval time between extreme adjacent values and the high sensitivity of the peak over threshold (POT) model to the extreme threshold, a time domain load extrapolation method for computerized numerical control (CNC) machine tools based on Gray relational analysis-peak over threshold model (GRA-POT) is proposed. Firstly, for the first problem, an improved Markov chain Monte Carlo (MCMC) time domain load reconstruction method is proposed and analysis of reconstructed time domain load; secondly, according to the mean excess function (MEF) method, the extreme threshold range of POT model is determined and divided into multiple sets. The generalized Pareto distribution (GPD) fitting is performed for multiple sets of candidate load extreme samples. Finally, the Gray relational degrees (GRD) between each group of GPD and the median rank distribution are calculated by the Gray relational analysis (GRA), and the extreme threshold corresponding to the maximum GRD is selected as the optimal threshold of the POT model. The dynamic cutting force signal of CNC machine tool under constant speed cutting condition was reconstructed and extrapolated using the proposed method, and the dynamic cutting force spectrum of CNC machine tool was compiled. Case analysis results show that the POT extrapolation model with high fitting precision can be obtained using the proposed method. Furthermore, the precision of load spectrum of CNC machine tool is improved.

Compilation of NC lathe dynamic cutting force spectrum based on two-dimensional mixture models

The load spectrum of numerical control machine tool (NCMT) is the basis data of reliability design, life prediction, and reliability bench test with simulated actual load conditions. Static cutting force spectrum, which can be compiled by empirical formula, cannot accurately reflect the real load conditions. Hence, a method for compiling the spectrum of dynamic turning force is proposed by using two-dimensional mixture models. Dynamic turning force is measured in the laboratory based on a large amount of cutting process data collected in the user field. Mean–frequency and amplitude–frequency matrices of dynamic turning force are obtained by the rainflow counting method. The probability distributions of mean and amplitude are established by using Weibull mixture models (WMM) according to the characteristics of the dynamic turning force, and the two main problems of this method are the determination of the number of mixture components and the estimation of parameters. Gray relation analysis is used to quantify the multi-objective evaluation matrix, and thus the number of mixture components is determined. Parameters are estimated using the improved expectation maximization (EM) algorithm, where the initial values of parameters are obtained by the K-means++ and Bayesian random classification. Finally, the joint probability distribution function between the mean and amplitude is established by the Copula function. Thus, the dynamic cutting force spectrum is compiled. Case analysis results show that the mean and amplitude distribution models with high fitting precision can be obtained using the proposed method. Furthermore, the precision of the load spectrum of NCMT is improved.

Investigation of cutting force oscillations when high productivity milling

The article analyzes cutting force oscillations of high-productivity milling. Based on end-milling experiments using a milling machine tool, characteristics of spatial oscillations of cutting forces were identified. The data analysis using software and oscillation theory methods showed that at high spindle rotation frequencies under certain milling conditions, interaction of the cutting edges and the workpiece is not uniform which deteriorates the machined surface. As the spindle rotation frequency increases due to resonances in the tool and spindle and mutual oscillations of the workpiece and the tool, the cutting force spectrum varies. Some extra harmonic components appear. They index the failure of interaction of the cutting edges and the workpiece.

Modeling and Emulation of 3d Dither Stability in Orthogonal Turn-Milling

Aiming at 4-axial orthogonal turn-milling by end mill, its theoretical 3d model for stable range of dither was put forward on the basis of its cutting principle by using analytical method. Based on modal trial, the stable range leaf figure of end mill’s dither in 4-axial turn-milling with eccentricity was simulated and analyzed. The results show that besides geometrical shape of mill, material of workpiece and frequency response function of machine-tool’s structure etc that can produce dither in 4-axial turn-milling, the rotating speed of mill and cutting depth are also related to dither. In trial of 4-axial turn-milling by end mill, the results of cutting force spectrum analysis show that: cutting is stable and un-dither when frequency of cutter tooth cutting-in plays leading role in force spectrum. Dither is produced when modal frequency of system plays leading role in force spectrum, the measured value of cutting force and surface roughness are also higher than those in the condition of un-dither. Thus the theoretical model and results of emulation can predict stability of end mill’s dither in 4-axial orthogonal turn-milling with eccentricity correctly and can provide theoretical guidance for surface quality and processing efficiency of workpiece.

Cutting Parameters Optimization Based on Cutting Force Spectrum when Ball Milling A880 Gas Turbine Blade Profiles

In this paper, experiment investigation is conducted on the machinability when ball milling A880 gas turbine blade profile. Cutting force spectrum acquired online is used to optimize the cutting parameters. The results indicate that cutting force signal in time domain and frequency domain can reveal the cutting stability, which provides an experimental guideline for gas turbine blades manufacturing.

Research on Cutting Force Spectrum Character and Tools Vibration Character under Titanium Alloy End-Surface Turning

titanium alloy cutting force testing experiment of end-surface turning is made, and spectrum character is analyzed by obtained data of cutting force experiment, and ten the influencing rule of cutting parameter on cutting force character is discovered; using the similarity between tools vibration character and cutting force spectrum character, and based on obtained data of machined surface roughness testing experiment, the two characteristic parameters of vibration frequency and amplitude value relative to work piece is calculated, and the relationship curve between cutting parameters and tools vibration character parameter is established is this paper.

Thin-Walled Part Machining Process Parameters Optimization based on Finite-Element Modeling of Workpiece Vibrations

Arising vibrations when milling thin-walled parts are the most essential factor that limits machining productivity and surface location accuracy. Such vibrations have large amplitude and often result in irreversible workpiece damage on finishing stage. Vibrations appear as a result of resonance of workpiece natural frequencies and cutting force spectrum harmonics from tooth- passing impacts.To eliminate resonance vibrations it is suggested to tune spindle speed in such a way, that workpiece natural frequencies differs from tooth-passing frequency harmonics. In practice changing of natural frequencies due to stock removal and changing of cutter position during machining process need to be considered.To estimate natural frequencies and mode shapes of workpiece mounted on NC machine worktable and its evolution during the process it is reasonable to apply widespread finite element modeling software. Using of FEM methods for vibration process modeling is considered. Also practical example of machining thin blade of compressor's aerodynamic model is considered.

On-line monitoring and suppression of self-excited vibration in end milling

A sensor system using the cutting force spectrum to monitor and suppress self-excited vibration in end milling is presented. Self-excited vibration is detected when the peak amplitude of the cutting force spectrum does not locate at the tooth frequency or cutter rotation frequency. A generalised spindle speed change method using the frequency of self-excited vibration to guide the modification of spindle speeds for suppression of self-excited vibration is then applied. Theoretical studies and experimental results show that self-excited vibration in end milling can be detected and suppressed by using this system.

An intelligent sensor for detection of milling chatter

In this paper, a new real-time sensor system has been developed to detect chatter in milling operations. In the developed sensor system, a pattern recognition technique based on an unsupervised neural network using the adaptive resonance theory (ART) is adopted for detection of milling chatter. The features on the cutting force spectrum are fed into the sensor system to classify the milling process with or without chatter. The experimental results indicate that the proposed sensor system can accurately detect milling chatter regardless of the variation in cutting conditions.

In-process monitoring of tool wear in milling using cutting force signature

This paper presents a new approach for on-line monitoring of flank wear in milling. This approach is based on the variations of the magnitude of cutting force harmonics with flank wear. It is shown first, using computer simulations, that the sensitivity of the magnitude of various harmonics in the cutting force spectrum to flank wear, varies depending on the immersion ratio and the number of teeth in the cutter. The results of the computer simulations were verified experimentally at various cutting conditions. An on-line monitoring strategy is then proposed which uses signature features selected from the harmonics of the cutting force signals. Incorporated in this strategy is a new method for the in-process identification of the immersion ratio.