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CSME 2021/12
Volume 42 No.6
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561-569
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Investigation of Modal Characteristics and Milling Dynamics for a Machine-Tool System
Shen-Yung Lina and Meng-Ru Song b
aDepartment of Mechanical and Computer-Aided Engineering, National Formosa University, Yunlin, Taiwan, ROC.
bDepartment of Mechanical and ComputerAided Engineering, National Formosa University, Yunlin, Taiwan, ROC.
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Abstract:
The vibrations easily deduce the resonance or fatigue for a structure system and resulting in structure damage. Therefore, the modal characteristics of the structure itself should be investigated in detail, and make efforts to avoid the occurrence of resonance and unnecessary dissipation of loss. In addition to structure modal characteristics, process dynamics is another important factor that strongly related to cutting stability for machining accuracies of the machine-tool.An integrated execution methodology is proposed in this study for this purpose, in which the modal test, dynamic stiffness test and cutting experiments are performed step-by-step in a sequential manner. To this end, hammer, spectrum analyzer, accelerometer,ME’scope software and dynamometer are utilized together to conduct the tests and experiments on a CNC milling machine-tool, and the modal-related parameters and cutting process dynamics can systematically be investigated. From the synthesized results and investigations, it shows that the mode shapes, Mode 1 to Mode 3, mainly regarded to the deformation in head-stock and column structure components of a machine tool. While the main deformation parts corresponding to mode shapes of Mode 4 and Mode 5 are worktable and saddle, and these two modes exhibit a bending deformation behavior which will possibly make the joint interface to separate. The results from dynamic stiffness testshow that when the head-stock moved along z-axis from -100mm height position down to -300mmlocation, the dynamic stiffness of the structure in xaxis direction may be changed from 217N/μm to 106N/μm, which have some impact on milling stability. The results from the milling experiment show that vibration marks left on the machined surface obviously under the conditions of cutting speed of 143.3m/min, feed rate of 400mm/ min and axial depth of cut of 0.5mm during up-milling process, and this phenomenon is judged as the chatter occurrence when comparing with those cases of stable milling state. The results obtained in this study can be utilized as a reference for milling parameter planning in industry.
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Keywords: Modal characteristics, Dynamic stiffness, Cutting stability, Spectrum analysis
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©
2021
CSME , ISSN 0257-9731
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