Study of sound signal for online monitoring in the micro-piercing process.

In this study, the feasibility of sound signal for monitoring the micro-piercing process is investigated. The effect of piercing parameters, i.e., sheet material, sheet thickness, and clearance to the power spectrum of emitted sound, is observed. The potential of sound in detecting the abnormal condition is also examined. The results show that the cutting process with different sheet material, sheet thickness, and clearance consistently shows a larger respond in similar frequency range, i.e., 3 to 4 kHz. In this region, the effect of variation of punch force history due to the different parameters is noticeable. A higher amplitude is noticed for piercing with a higher strength of sheet material, greater thickness, and greater clearance. During the experiments which are conducted until the breakage of punch, the fluctuation of signal power in this frequency range is the most salient. Before the punch breakage, the signal power of all the observed frequency ranges increases, but the increment in frequency 3 to 4 kHz is the most significant. The results show that the trend of signal power in this frequency range may reveal the trend of the process. The trend of the power in this frequency is in accordance with the trend of punch force and the growth of burr formation. These results evidence the correlation between the sound signal emitted by the piercing process and the tool condition. It can be concluded that the sound signal is potential for monitoring the micro-piercing process. [ABSTRACT FROM AUTHOR]