Milling-Induced Surface Roughness in Carbon Fiber Reinforced Polymer: A Diagnostic Study between Ra and Sa
DOI:
https://doi.org/10.15282/Keywords:
CFRP, Milling, surface roughness, surface damage, chilled airAbstract
Carbon Fiber Reinforced Polymer or CFRP is among the composite with high utilisation especially in the high-end industrial sectors such as automotive, aviation and architecture. This is due to its superior characteristics such as excellent strength-to-weight ratio, high stiffness and corrosion, and can be manufactured near its end shape. However, the abrasive nature originated from the carbon fiber impregnated in the epoxy resin creates an anisotropic and inhomogeneous material. It is a challenge to machine the CFRP as the carbon fiber abraded the cutting edges. This implicated in the tool wear progression, thus affecting the surface quality of the CFRP. Since the CFRP is impregnated in the epoxy resin, machining must be conducted below the glass transitional temperature (Tg), to avoid degradation of the polymer to occur. This study investigates the influence of different cutting environments (dry, coolant and chilled air) on the surface evaluation of the CFRP during the milling process with a constant Vc = 150 m/min and Vf = 2100 mm/min. The surface roughness was evaluated by both Ra and Sa. There is a minimal contrast in the Ra values along the milling process, whereas the Sa value shows significant increases across the machining process for all the conditions of dry, coolant, and chilled air. It is indicated that milling in dry conditions produced Sa values that were 28.23 % and 14.48 % higher compared to coolant and chilled air, respectively. These values highlight the efficiency of coolant and chilled air in reducing the heat generation. This reduction minimizes the thermal effects thus improving the surface quality. Flooding the cutting zone with coolant prominently helps in reducing the heat produced from the friction between the CFRP and the mill tool. It is evidently supported and visualised by the pseudo-color depth maps of the areal surface roughness analysis. The areal surface roughness, Sa proven to be beneficial in understanding the surface topography and condition for inhomogeneous materials like CFRP. It justifies the occurrences of surface damages such as delamination, matrix smearing, and fiber pull out when observed under the scanning electron microscope. This study emphasizes the importance of suitable cooling method to maintain the integrity of the CFRP surfaces.
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