Enhancing the machinability of Cf/SiC composite with the assistance of laser-induced oxidation during milling

Abstract

Carbon fiber-reinforced silicon carbide matrix (Cf/SiC) composites have been widely used in aerospace for its superior properties. However, due to high hardness, heterogeneity, and anisotropy, many problems such as machining damage, low process efficiency, and rapid tool wear are encountered in machining Cf/SiC composite. In this study, laser-induced oxidation-assisted milling (LOAM), as novel hybrid machining process, was proposed to enhance machinability of Cf/SiC composites. Pulsed laser was used to induce reaction between Cf/SiC composites and oxygen. Easily removable loose and porous oxides were produced, which were simultaneously removed with milling tool, leading to improved material removal rate and tool life. Oxidation mechanisms and influences of laser parameters on oxidation behavior of Cf/SiC composite were studied. Conventional milling (CONV) without the assistance of laser was also performed on Cf/SiC composite for comparative analysis. Milling force, tool wear, and surface quality were studied in detail. Under laser irradiation, Cf/SiC composite was modified into metamorphic-layer that consisted of oxide layer and transition layer. Material irradiated with laser got melted, vaporized, and then reacted with oxygen, producing oxide. Oxide layer was formed due to the accumulation of oxide. Increasing laser energy density boosted oxidation reaction and increased the thickness of oxide layer. In contrast, increase in laser scanning speed decreased thickness of oxide layer. Results show that cutting force was extremely low and no tool wear occurred during milling oxide layer, indicating significant enhancement in machinability. Abrasive wear mainly occurred on flank face when milling transition layer. Surface damages, for instance fiber fracture and matrix fragmentation, were significantly contained by LOAM. Surface roughness Sa obtained via LOAM was 9.5 μm, which was lower than that obtained by CONV (35 μm). This study indicates that LOAM can achieve high-efficiency processing, low-defect surface, and prolonged tool life when machining Cf/SiC composite.