Surface morphology characterization of unidirectional carbon fibre reinforced plastic machined by peripheral milling

This paper aims to characterise surface morphology and 3D roughness parameters of unidirectional carbon fibre reinforced plastic (UD-CFRP) milled at 0°, 45°, 90°, and 135° fibre orientation angles (FOAs). Side milling experiments are conducted on UD-CFRP laminates. Surface damage forms and texture direction of milled surface are analysed. Spatial frequency of defects on CFRP surface is quantitatively determined using radially averaged 2D PSD. The kinematic-dynamic surface topography is reconstructed considering feed, runout and vibration, then the ideal roughness parameters, S_a, S_q, S_sk, and S_ku are calculated and compared with the measured ones, finally the material factor-induced roughness components are quantified. Results show that CFRP surface has no regular feed marks. The frequency of fibre breakage or surface defects is greater than tooth passing frequency. FOAs sorted by their average S_a in descending order is 135°>90°>45°>0°, where surface defects contribute 93.9%, 77.1%, 73.2%, 72.2% of the total roughness respectively, which suggests that surface defects show a more important role than tool kinematics and vibration in formation of milled surface. The negative Skewness (S_sk < 0) and high Kurtosis (S_ku = 4.0–11.5) of milled surface signify porosity and the presence of many anomalous deep valleys in milled surface, respectively.