Three-axis displacement sensor-integrated spindle system for carbon fiber-reinforced plastic (CFRP) machining process monitoring

Abstract

We present a carbon fiber-reinforced plastic (CFRP) milling process monitoring method based on the multi-axis displacement sensor integrated with the precision spindle system. Unlike conventional machining process monitoring methods by using accelerometers or dynamometers, in this study, 2-axis curved-edge sensor (CES) and single-axis capacitive sensor (CS) were integrated with the spindle and measured 3-axis spindle shaft motions along the radial and axial directions, respectively, while machining. Also, the CES showed a status of the spindle balancing while correcting the unbalanced mass on the spindle. The 3 × 3 stiffness matrix of the spindle shaft was multiplied by the 3-axis spindle shaft motions, and simultaneously estimates the cutting forces while cutting the unidirectional CFRP samples with 0o, 45o, and 90o fiber orientation. The conventional 3-axis force sensor installed under the workpiece was used for a baseline comparison with the cutting force results measured by the proposed method. To monitor and characterize the defects of CFRP, the time-frequency domain spectrogram images analyzed from the cutting force data were used. Unique features were extracted according to the fact of existence and nonexistence of the defects.