Effect of gear tooth fillet radius on the performance of injection molded Nylon 6/6 gears

In metal gears the gear manufacturing process and cutting tool dimensions decide the gear tooth geometry and affect the gear performance. In polymer base gears, injection molding process permits development of gears with any tooth geometry economically. In this paper, the effect of gear tooth fillet radius on the performance of injection molded Nylon 6/6 gear made with different tooth fillet radius 0.25 and 0.75 mm is reported. Finite element analysis carried out indicates high fillet root stresses and gear tooth deflection in gears with low fillet radius. Gear performance was evaluated using a power absorption type gear test rig. Repeated gear tooth loading during service causes a rise in the gear temperature which is due to hysteresis effects and friction. The temperature rise depends on the fillet radius. At low applied loads, gears with less fillet radius fail by crack initiation at the root region due to increased stress concentration whereas gears with large fillet radius fail by micro cracking at the pitch region.