Drilling process of Cf/SiC ceramic matrix composites: Cutting force modeling, machining quality and PCD tool wear analysis

Cf/SiC composites are continuous fiber-reinforced ceramic matrix composites with excellent properties, such as high-temperature resistance, high specific strength, and low coefficient of thermal expansion. However, Cf/SiC composites often cause severe tool wear and quality problems. In this paper, tool wear is studied during the machining of Cf/SiC materials. The cutting force model is applied to understand the correlation between cutting force and tool wear. Polycrystalline Diamond (PCD) tools with various point and clearance angles are designed to carry out drilling experiments on Cf/SiC composites with different machining parameters. During experimental investigations, force and acoustic emission signals are analyzed, and PCD tool wear and material machining quality are observed using scanning electron microscopy. Results indicate that PCD tools with a point angle of 140° and a clearance angle of 20° demonstrate the lowest tool wear during machining. Moreover, low-speed and feed machining parameters can effectively reduce tool wear and prolong its life. By observing fracture patterns of hole wall fibers and chip shapes at different stages of tool wear, and combined with the frequency domain distribution of AE signal, the effects of tool wear on the material removal mechanism are summarized. Before tool wear, fiber fracture is flatter, the matrix is mainly removed via crushing. After tool wear, although fiber fracture is more uneven, the matrix is changed from crushing to friction removal, leading to lower surface roughness of the hole wall.