Surface finishing method for tooth flank of heat-treated surface-hardened small gears using a gear-shaped tool composed of alumina-fiber-reinforced plastic

High-accuracy gears are necessary to ensure the strength and silence of compact geared motors. Heat-treated surface-hardened small gears are employed in the reducer of a compact geared motor. The heat treatment causes distortion, which deteriorates the gear accuracy. To remove this distortion, surface-hardened small gears are rehobbed with a carbide hob. The rehobbing makes a tool mark on the gear tooth surface. This tool mark leads not only to strength deterioration of the tooth surface, but also vibration and noise. Therefore, a surface finishing method that eliminates the tool mark is required. However, it is difficult to finish surface-hardened small gears. This study proposes a tooth surface finishing method for a surface-hardened small gear. The method employs a gear-shaped tool composed of alumina-fiber-reinforced plastic (ALFRP) and a surface finishing device with an oscillation/traverse system. The proposed method was used in an experiment to remove the tool mark on the gear tooth flank of a surface-hardened small gear rehobbed by the carbide hob. The effectiveness of this method was verified. In addition, the processing mechanism of the ALFRP gearshaped tool was analyzed by observing the tool and the chips.