鉄系焼結合金歯車の転造による高精度化・高強度化　−第３報− : 修整歯形工具による鉄系焼結合金歯車の歯元曲げ疲労強度向上

概要

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Surface finish rolling experiments were carried out using P/M spur gears of 0.6Mo-0.2Mn pre-alloyed sintered steel and of 0.8Mo-0.2Mn partially alloyed sintered steel with the density of 7.10 Mg/m3. A CNC form rolling machine of axis intersection type was employed, and a modified screw-shaped rolling tool was prepared: the modified concave tooth profile optimized by numerical tooth profile analysis for simultaneous rolling of tooth and fillet surface. Then, porosity distributions in the surface layer of rolled gear teeth were determined and the effects of the amount of tool radial feed R0 on the selective surface densification behaviors were evaluated. Besides, single tooth bending fatigue test was conducted. Gears with good tooth profiles were obtained by using the modified tools. As a result, the porosities in both the tooth flank and the fillet at the root were reduced to the target level at R0=600 μm in simultaneous rolling process. Furthermore, the single tooth bending fatigue durability was much improved to about 60 % of the case hardened wrought steel gears of SCM415.