Application of low-cost dynamometer based on full octagonal ring for turning process monitoring

This article discusses a low-cost dynamometer based on a novel full octagonal ring-shaped transducer applied to measure the cutting forces and analyze them with the use of signal processing tools, in order determine their compatibility and the potential to monitoring machining conditions. The results showed that the performance of the developed dynamometer was in good agreement with cutting forces simulation. The cutting forces were about 30\;N in stable cutting and 80\;N in unstable cutting. In stable cutting, the spectrum showed the spindle frequency fs of 5.33 Hz, corresponding to 320 rpm of spindle speed, which was followed by its harmonic frequencies of 10.66, 16 and 21.33 Hz. Revealing of all characteristic frequencies during turning processes through the frequency spectrum showed the evidence that the developed dynamometer indeed functioned well measuring cutting forces in machining. Apart of the spindle frequency of 7.5 Hz and its harmonics, there also appeared the chatter frequency fc of 62 Hz in unstable cutting condition. By using the combination of signal processing tolls of the ensemble empirical mode decomposition with the short-time Fourier transform (EEMD-STFT), the chatter frequency was clearly captured. The combination of cutting forces measured by the developed dynamometer with EEMD-STFT makes it easier for the operator to reveal the machining conditions within a relatively short time.