Two-step forging of polyimide powders into small-/medium-sized gears with and without carbon fiber reinforcement

A green polyimide cylindrical preform with short carbon fibers was prepared for two-step forging processes. Each preform was hot-forged at 623 K above the glass transition temperature of polyimide for near-net shaping of fifteen-teeth module-1.0 gear, and sinter-forged at 673 K below its melting point for densification. SEM and X-ray computer tomography were employed to make destructive and non-destructive diagnoses on the carbon fiber orientation during hot forging. Micro-hardness testing and gear-grade balancing were utilized to evaluate the engineering durability and dimensional accuracy of sinter-forged gears.