Abstract: Fiber reinforced ceramic matrix composites have excellent strength, stiffness, corrosion resistance, high temperature resistance and low density, and can maintain stable performance in a variety of harsh environments. Helical milling process also faces problems such as unclear removal mechanism and poor hole quality. In order to investigate the removal mechanism, damage mechanism and surface quality influence law of 2.5D-C_f/SiC composite during helical hole milling, the removal mechanism of 2.5D-C_f/SiC composite fiber at different angles is analyzed by smooth particle fluid dynamics (SPH) simulation and helical hole milling test. Then the damage mechanism of 2.5D-C_f/SiC composite is revealed through experiments. Finally, the influence of helical milling parameters on the surface quality of hole wall is analyzed by single factor test. The results show that in the helical milling process of 2.5D-C_f/SiC composites, the SIC matrix is mainly brittle and cracked, which is removed by debris. Fiber breakage, fiber wear, fiber pulling damage occurred in fibers at 0° direction, fiber breakage and fiber outcrop occurred in fibers at 45° direction, fiber breakage and fiber pulling out occurred in fibers at 90° direction, fiber pulling out, fiber breakage and fiber outcrop occurred in fibers at 135° direction, and fiber damage at acupuncture direction was similar to fiber damage at 0° direction. The interface phase region produces interface debonding failure. Burr damage and edge collapse damage are the main damage at the entrance and exit of the hole. The surface quality improves with the increase of spindle speed, and deteriorates with the increase of pitch and revolution speed. When the spindle speed is increased from 1 000 r/min to 4 000 r/min, the surface roughness of the hole wall is reduced by 23.76%; when the pitch is increased from 0.1 mm to 0.4 mm, the surface roughness of the hole wall is increased by 38.69%; when the revolution speed is increased from 5 r/min to 20 r/min, the surface roughness of the hole wall increased by 8.1%. This study provides an important reference for helical milling of 2.5D-C_f/SiC composites with high quality hole making.

Key words: helical milling, material removal mechanism, hole surface quality, SPH simulation, 2.5D-C_f/SiC