MONITORING OF THE MACHINE ELEMENTS IN DRILLING MACHINE USING VIBRATION SIGNALS BY FEM

摘要

Deterioration in the machine running conditions always produces a corresponding increase in the vibration level. By monitoring vibration level it is possible to obtain information about the machine condition. Here, drilling machine was considered for the analysis. Spindle bearings and gearbox are found to be the critical elements of the machine tools on which condition monitoring has to be concentrated. To analyze the condition of the existing machine elements, finite element method has been used. An attempt has been made by modeling drilling machine to find out the response of the structure for various defects in machine elements. The finite element model of the machine tool was developed by using finite element package ANSYS. Modal analysis has been carried out to determine the natural frequencies and mode shapes of the structure. Frequency response analysis was used to determine the response of the structure due to the unbalance forces. Transient response analysis was used to study the effect of assumed defects on the machine tool structure. A defect was assumed on the outer race of the spindle bearing and on the gear and responses were observed at the spindle bearings location. From the analysis for the assumed defect in the outer race of the bearing, it was observed that the vibration velocity increases with the increase in depth of defect and depends on location of the defect. From the vibration signature resulting due to assumed destructive pitting defect in all teeth of the driven gear, it was observed that the vibration velocity level decreases with increase in spindle speed. This is because, at lower speeds time taken by each tooth to mesh with its counterpart is more, and hence persistence of disturbing force due to defect in meshing gear is more at lower speeds. Experimentation was carried out on the drilling machine by using the instrument Machine Condition Tester T-30. The experimental data obtained were used to analyze the condition of the machine elements. The vibration velocity was measured on the spindle bearings location for different spindle speed. From the Experimental analysis it was observed that with the increase in spindle speed, the vibration velocity also increases. Finally, theoretical results were judged against the experimental results. Thus the present work shows that the FEM is a valuable tool in finding sources of undesirable vibrations from various defects present in the machine elements of the machine tool structure.