Estimation of Chatter Vibration Under End-Milling Process With a Wavelet Transform

In this study, a new analysis method using a wavelet transform was considered to evaluate the chatter vibration generated during end milling. End milling often generates vibrations between the tool and work material, called chatter vibration, which causes deterioration of the finished surface and breakage of the tool. Therefore, countermeasures to detect chatter vibration at an early stage have been attempted in the past by using fast Fourier transform (FFT) and short-time Fourier transform (STFT) methods and monitoring the dynamic stability of the cutting process. However, the FFT analysis method assumes steady-state vibration, and the STFT method does not have sufficient frequency resolution. In contrast, the wavelet transform is excellent for analyzing non-stationary vibrations and has a high noise separation capability. To fully validate the analysis method, a groove was added to the machined surface, so that the cutting condition changed with time, and the cutting vibration under the condition where the disturbance was involuntary was analyzed. As a result, it was possible to identify minute fluctuations in chatter vibration, which could not be obtained using the STFT method.

Cutting State Estimation via Chatter Mark on End Milled Surface and Analysis of Its Formation Mechanism Using Voxel Model Simulation

When chatter vibrations occur during cutting, a characteristic pattern called chatter mark appears on the machined surface. In our previous studies, it was estimated that this chatter mark is formed by the tool (or workpiece) vibration in the normal direction with respect to the machined surface. We thus proposed a method to inversely analyze the chatter vibration information during cutting through the chatter mark using two-dimensional discrete Fourier transform. Previous studies confirmed that the analysis results of this method are in good agreement with those of the information obtained via conventional sensing. However, the correctness of the pattern formation mechanism is yet to be directly verified, as it is difficult to measure the cutting phenomenon directly. In this study, the chatter vibration during cutting was measured by the displacement of the tool-shank. Then, based on the results obtained in the static stiffness test, the movement of the tool edge was estimated. A cutting simulation using a voxel model was executed based on this tool-edge movement. When the simulation using the chatter vibration in the normal direction was performed, a chatter mark appeared on the simulated surface. It could thus be confirmed more directly that the analytical model is correct compared with the previous methods.

Time Domain Simulation of Dynamic Corner Milling Process Considering Chatter Vibration With Finite Amplitude

A number of analysis methods for the process with chatter vibration have been proposed so far. These methods can be used to improve processes stability resulting in better production efficiency. However, the poor estimation accuracy of the phenomenon severely limits the performance of process optimization using the simulation-assisted approach. One of the causes of accuracy deterioration is the modeling error of the phenomenon accompanied by chatter vibration with finite amplitude. In this study, we developed a model that can consider the non-linear uncut chip thickness fluctuation caused by the influence of finite amplitude and the process damping due to the contact of the tool flank face against the finished workpiece surface. Furthermore, we developed a time domain simulator that implements the proposed model, and estimated the finished surface profile of the workpiece based on the results of the time domain simulation. To verify the proposed method, corner machining experiments with an end mill were conducted. Corner machining is frequently used in industrial, but it is known that chatter vibration is likely to occur. In corner machining, machine tools generate motions that accompany acceleration and deceleration. The motion of this feed drive system strongly depends on the dynamic characteristics of the machine tool and the trajectory generation algorithm, which greatly affects the emersion angle of the cutter. Therefore, we simulated the dynamic corner machining process considering the measured data of the motion trajectory of the feed drive system. The estimation result of chatter vibration in corner machining is in good agreement with the measurement result of the machining process. In addition, high-precision estimation of the machined surface profile with chatter mark has been realized.

Pendekatan alternatif dalam menghasilkan stability lobes diagram untuk memprediksi getaran chatter pada proses pemesinan berdinding tipis

Machining is widely used for finishing process of the entire manufacturing process chain. Machining process of thin plate, however, is not an easy task. This is because excessive vibration (chatter) can rise during operation. To predict the chatter vibration, a stability lobe diagram (SLD) is usually utilized which is strongly dependent on the frequency response function (FRF). This paper proposes an alternative approach for analyzing modal analysis by finite element method (FEM) to obtain FRF during machining thin-walled plate. The result showed that simulation result has good enough agreement to experimental result with slight differences caused by the assumed boundary conditions in the FEM process. This approach can be used to reduce the use of hammering tests and can be used to get FRF of multi stage working.

Analyzing chatter vibration during turning on computer numerical control lathe using ensemble local mean decomposition and probabilistic approach

Chatter vibration is an undesired and indispensable phenomenon in turning operation, which cannot be completely avoided. However, it can be suppressed by early identification and with the proper choice of input turning parameters. The key issue of chatter detection is to process the acquired signals and extract the features pertaining to it. In the present work, a methodology has been proposed for exploring tool chatter features in the incipient stage during turning on lathe. Chatter signals generated during the turning of Al 6061-T6 have been acquired using a microphone. A stability lobe diagram has been plotted to access the stability regime. Further, in order to study the effect of feed rate on stability, the recorded signals have been processed using a local mean decomposition signal processing technique, followed by the selection of dominating product functions using the Fourier transform. The decomposed signals have been used to evaluate the new output parameter, that is, chatter index. Further, the Nakagami probability distribution has been used to ascertain stability region (threshold). From the experimental validation, it has been inferred that cutting combinations obtained from the Nakagami probability distribution are significant and capable of limiting chatter vibrations. The present methodology will serve as guidelines to the researchers and machinist for the identification of tool chatter in the incipient stage, explore its severity, and finally suppress it with the proper selection of input turning parameters.