Vibration In Machining Process Research Articles

Chatter Investigation on Machining of Gray Cast Iron Considering the Damping Effect

In recent years, the study of chatter vibrations has been intensifying in the machining of materials. In this paper an investigation of this phenomena was conducted for gray cast iron (CGI). The chatter vibrations in machining process can considerably compromise the workpiece surface finish, tool wear and in some cases provide severe damage to the machine-tool. Thus there is an imminent need to expand the theory of chatter vibrations for the class of brittle materials. To analyze the vibrations of the process of machining and zones where the process is stable, and where it is unstable, the stability lobes diagram was used. This diagram is constructed at low speed cutting, where the phenomenon of damping arises. The damping is a crucial factor in the process, it increases system stability. This effect was considered in the formulation of chatter vibrations using the indentation model of Wu. For experimental validations the signals of cutting force were acquired and analysis was conducted in frequency domain to identify where the vibrations emerged allied with a roughness analysis of the workpiece. The results demonstrated perfectly the consequences of chatter vibrations in surface finish of grey cast iron and proved that the stability lobes diagram provides good results to detect these vibrations, determining the areas where the material removal should be avoid.

The effect of composite boring bars on vibration in machining process

One of the challenges of machining process is to improve the quality of machined surface by reducing the vibration of cutting tools. The research aims to suppress vibration using composite boring bars with an enhanced damping capacity. A new design of boring bars with different cross-sections is considered. Static and dynamic behavior of the proposed tools is investigated. A mathematical model for determining the eigenfrequency is proposed, and it is compared with computer simulation and experimental results. The validity of the proposed models is verified by conducting experimental machining tests in order to study the changes in vibro-acoustic signals depending on the cross-sections of the toolholder. The results show that the composite material significantly improves damping of boring bars, which leads to a reduction in the vibration compared to conventional boring bars.

Ultrasonic-assisted machining processes: a review

Ultrasonic-assisted machining process is one of the most recently explored hybrid machining processes. In ultrasonic assisted machining process, an oscillating motion (of small amplitude and high frequency) is superimposed on the conventional machining operation. The assistance of ultrasonic vibrations in machining process improves the performance of the process by reducing cutting forces and enhancing surface quality. The effect of ultrasonic vibration has been found very beneficial in different conventional and non-conventional machining processes. This paper reviews the analytical and experimental studies in the area of ultrasonic-assisted turning, milling and drilling. Additionally, the effect of ultrasonic vibration on non-conventional machining processes is also reviewed. The paper also explains the effect of ultrasonic vibration on the cutting mechanics. The research gaps present in the ultrasonic-assisted machining process domain have also been highlighted in order to drive on the path of future research in this area.

Effect of longitudinally intermittent movement of cutting tool in drilling of AISI 1045 steel: A three-dimensional numerical simulation

Applying ultrasonic vibrations in machining process is an effective method to improve desired machinability factors. In this study, a three-dimensional finite element model is developed to evaluate effect of added vibratory movement of cutting tool on output parameters in conventional drilling of AISI 1045 steel. Heat generation on drill faces, strain, and damage of deformed chip in addition to thrust force are taken into account to be analyzed. Besides, a dynamometer and a vision measuring microscope are used to investigate generated thrust force and built-up edge during conventional and ultrasonic-assisted drilling. As a result, it is shown that vibratory movement of drill bit results in lower temperature to be generated on tool faces resulting in almost elimination of built-up edge. Moreover, higher damage value resulted by additional chip bending is observed when ultrasonic vibration is added to the operation.

A novel approach for chatter online monitoring using coefficient of variation in machining process

Chatter is one form of severe self-excited vibration in machining process which leads to many machining problems. In this paper, a new method of chatter identification is proposed. During the machining process, the acceleration signal of vibration is obtained and the time domain root mean square value of the acceleration is calculated every proper segment, through which the real-time acceleration root mean square (RMS) sequence is obtained. Then, the coefficient of variation (i.e., the ratio of the standard deviation to the mean, CV) of the RMS sequence is defined as the indicator for chatter identification. The milling experiment shows that CV can well distinguish the state (stable or chatter) of the machining process. The proposed method has a quantitative and dimensionless indicator, which works for different machining materials and machining parameters, and even can be expected to work in a wider range condition, such as different machine tool and cutting method. This paper also designs a fast algorithm of CV, making it an ideal candidate for online monitoring system.

The Effect of Cutting Fluids and Cutting Speeds to The Vibrations of Milling CNC Machine

Vibration that occur in machining process is forced vibration. This vibration caused by external force excitation. External force that cause vibration in machining process is cutting force. This research was aims to determine the effect of cutting fluids and cutting speeds to vibration in milling process. The specimens were made using a cutting process type face milling, profile milling, pocket milling, and slot milling. Cutting speeds was variated at 62.83 m/min; 110 m/min; 157.14 m/min; 188.5 m/min. Vibration testing was done using the accelerometer sensor. Vibration response taken is the amplitude. The results show any type of cutting process has a different amplitude. Face milling has the smallest amplitude while slot milling has the biggest one. At cutting speeds parameter, the faster of cutting speeds the smaller of the amplitude. The use of cutting fluids can reduce the friction value between cutting tool and workpiece so that the cutting force will decrease. The use of cutting fluids causing the smaller the cutting force. The increase of the cutting force will cause greater vibration

Stability improvement and vibration suppression of the thin-walled workpiece in milling process via magnetorheological fluid flexible fixture

In aerospace industry, thin-walled workpiece milling is a critical task. Also, the machining vibration is a major issue for the accuracy of the final part. In this study, a new dynamic analytical model is proposed to determine the effect of damping factor on the dynamic response of thin-walled workpiece in machining. A complex structure workpiece is equivalent to a thin plate. The fixture constrains and the damping factor are crucial elements of this thin plate. Therefore, the magnetorheological fluid flexible fixture is designed to suppress the machining vibration in machining process. Then, the general dynamic cutting force model and the damping force model are proposed for the key dynamic equation for the prediction of dynamic response to evaluate the stability of the milling process with and without the damping control. Finally, the feasibility and effectiveness of the proposed model is validated by machining tests. The predicted values match on the experiment results.

Chatter stability prediction for CNC machine tool in operating condition through operational modal analysis

The stability of high-speed machining operations is crucial in machining process and presents a key issue for insuring better surface quality, increasing productivity and protecting both machines and safe workpiece. Stability prediction in milling is based on experimental modal analysis by the estimation of frequency response functions using a tap test. One limitation of accurately estimating the stability using such approach is the change in process and the dynamic characteristics of the machine tool under operation. This paper proposes a signal processing procedure applied to vibrations in machining process in order to obtain spindle’s modal variations in operation. The novelty of the proposed approach consists in removing “virtual modes”, caused by harmonic excitations, from the system response before performing operational modal analysis. Thus, the proposed procedure combines two existing techniques that are the Cepstral Editing Procedure and the Least Square Complex Exponential. The importance of the developed methodology is in adjusting the chatter stability criterion for material removal on a dynamic basis. The main work is given as follows: first of all, the Cepstral Editing Procedure (CEP) algorithm is applied on the acceleration signals for removing deterministic vibrations caused by harmonic excitations. The residue signal is the system response to white noise excitation. The frequency response functions (FRF) are then calculated from these signals at different cutting conditions. The outcome is compared to the result of impact test on the spindle under static condition. Similarities in the form of FRFs obtained in static and operational conditions validate the proposed approach while variations of modal properties under different cutting conditions are successfully captured. Secondly, the Least Square Complex Exponential (LSCE) method in operational modal analysis is invoked to find the natural frequencies and damping ratios of the system at different spindle speeds and cutting depths. Then, the dynamic chatter stability lobes diagrams (SLD) are established which account for spindle’s speed-dependent modal variations. A significant change in the stability border is observed which is interesting in machining fields. It will be shown that some depths of cut that are stable with static stability lobes become unstable with dynamic stability lobes and vice versa.

Principle and Experiment of Electric Hot Milling Superalloy

This paper introduces a kind of electric hot milling method for superalloy and analyses its feasibility. Fe-based superalloy GH2132 is selected as experimental object. An experiment platform is established. In the machining process, vibration signals are collected by a set of signal acquisition system. Afterward, these signals are processed by using wavelet transform, compared and analyzed in different machining parameters and working conditions. The results of the study indicate that compared with dry milling, electric hot milling can reduce vibration in machining process and machining superalloy more effectively. It also improves the cutting tool durablity.

Study on the Green Processing of Impeller

According to the characteristics and cutting requirements of the compressor impeller, such as low rigidity, easy to produce deformation and vibration in machining process, the high speed machining technology was adopted to reduce time, the virtual manufacturing technology was used to solve processing problems in computer before the trial machining and improved programming speed and other key supporting technologies were adopted. The study shows that this green processing of impeller had high machining efficiency, good surface roughness and product quality, low production cost and light environmental pollution. It accords with modern green machining development trend.

Analysis of kerf width in micro-WEDM

In micro-wire electrical discharge machining (micro-WEDM), the machined kerf width varies with different machining parameters, which greatly influences the machining precision. In order to study the kerf variations in micro-WEDM, the mathematical model of wire lateral vibration in machining process is established and its analytical solution is obtained in this paper. The model is practically verified on a self-developed micro-WEDM machine. Under this model, a 30.8 μm width slot is achieved on a stainless steel workpiece with ∅30 μm wire-tool.

Evaluation Tool Condition of Milling Wood on the Basis of Vibration Signal

The paper presents preliminary results of the research of tool condition monitoring based on both original and demodulated signals measurements of an vibration generated by a cutting process in milling. The experiments have been performed on the milling center (CNC). Because the dynamic characteristics of tool vibration in machining process will change with tool wear development, which is one of the important dynamic characteristics of tool vibration. The signals were analyzed through FFT analyzer and computer (realised in the environment of NI LabVIEW). Work supported by the Grant 3 P06L 025 24 from Committee of Scientific Research of Poland.

First report of System Identification in Wire Electrical Discharge Machining

In this paper, the behavior of wire vibration in machining process is studied by using a system modeled on the basis of experimental results. For the purpose of examining the behavior of wire vibration, dynamical changes in the material removal process must be taken into account. Therefore, a machining system set up is modeled where the interference between the vibration system of the wire electrode and the material removal system are considered. In this system, the material removal rate and the external force output from the material removal system are the input of the vibration system, whereas, the gap distance output from the vibration system is the input source of the material removal system. In order to analyze the modeled system, some simulations of the machining process are carried out. In the analysis of these simulations, a statistical method is applied to the wire displacement. Furthermore, the mean value and the magnitude of a simulated wire displacement are quantitatively compared with the measured results. Using the modeled system, the relation between wire vibration and state variables in the system are clarified.

An active method of monitoring tool wear states by impact diagnostic excitation

This paper presents an active method of monitoring tool wear states by using impact diagnostic excitation in the machining process. Because the dynamic characteristics of tool vibration in machining process will change with the tool wear development, the damping ratio, which is one of the important dynamic characteristics of tool vibration, will be used for monitoring the tool wear states in machining. In order to obtain the damping ratio, impact diagnostic excitation was applied to the tool in the feed direction and the signals of the tool vibration were measured for some flank wears under different cutting conditions. The signals were analyzed through FFT analyzer and computer, and then the damping ratio of the tool vibration in the feed direction was calculated. The experimental results have shown that the damping ratio measured by impact excitation increases linearly with tool wear development and the increment of the damping ratio is different for each cutting condition, but the damping ratio can be uniquely determined through the flank worn area. To explain the reason for increase with tool wear development, the damping mechanism on the flank worn land was also discussed. The results of the discussions and numerous cutting experiments have indicated that the presented active method could be used for effectively monitoring the tool wear states in machining.