is usually installed far from the machining centre, which cannot
induce noise disturbances for operators close to the machining
area.
A data acquisition system was installed to collect milling
process sound through two ½00 condenser microphones. One was
placed inside the machine-tool enclosure (Fig. 2, micro 1 at 40 cm
away from the cutting zone) and the other where operators are
commonly installed to check cutting operations in front of the CNC
system (Fig. 2, micro 2). Sounds were analyzed by sampling the
signal of the microphones with a frequency up to 48 kHz. The
signals were post-processed with a A-weighted filter in order to
estimate the noise level in dBA within the range of the response to
sound of the human ears. Finally, a spectral analysis was performed
using the Fast Fourier Transform (FFT) algorithm to identify
dominant frequencies.