COMPARISON OF TIME-DOMAIN VIBRATION SIGNATURES OF A MINI CNC SPINDLE UNDER DIFFERENT WOOD CARVING TOOL PATHS
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Abstract
This study aimed to compare the time-domain vibration signatures of a mini-CNC spindle under different wood-carving tool paths and to investigate the effect of signal smoothing on preserving the characteristics of the original vibration signal. Hopea wood was used as a workpiece, and a 3 mm two-flute HSS cutter was employed. The cutting parameters were fixed at a spindle speed of 10,000 rpm, a feed rate of 150 mm/min, and a cutting depth of 5 mm. Three carving tool paths were investigated: straight line, circle, and triangle. Acceleration vibration signals were measured at the spindle separately in the axial, horizontal, and vertical directions. Each experimental condition consisted of 2,048 data points acquired over 0.080 s. The signals were analyzed using RMS, Peak, Peak-to-Peak, and coefficient of variation (CV). Signal smoothing was performed using Moving Average (MA) and Simple Exponential Smoothing (SES), while MAE, RMSE, and NRMSE were used to quantify the differences between the raw and smoothed signals. The results showed that the straight-line tool path produced the highest RMS values in all three measurement directions, with values of 7.875, 8.120, and 8.644 g in the axial, horizontal, and vertical directions, respectively. Its CV values were relatively low, ranging from 3.701% to 11.532%, indicating a high but comparatively stable response to vibration. In contrast, the circular tool path exhibited greater signal variability, with CV values ranging from 46.778% to 72.974%. The triangular tool path showed relatively stable vibration in the axial and horizontal directions but high variability in the vertical direction, with a CV of 58.617%. The smoothing-error metrics reflected the degree of deviation introduced by signal smoothing and were therefore interpreted as measures of signal distortion rather than as sole criteria for selecting an optimal smoothing method. The results demonstrate that different tool paths and measurement directions produce distinguishable time-domain vibration characteristics in the mini-CNC spindle.
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