Shape Distortion and Tooth Root Bending Fatigue Strength Obtainable with Various Hardening Process Routes of Ring Gears made of PM Material
Ring gears are used in a planetary gear system to transfer torque from one axis to another. During this transfer the resulting gear forces cause tensile, compressive and contact stresses, which must not exceed permitted values and fatigue stress limits of the material used. To reach necessary fatigue stress levels on gears, i.e., on flank and root, and also to improve tribological performance during gear contact, a number of wellknown processes such as heat treatments can be selected. However, this selection can be limited by the impact on possible distortion of the gear geometry. It is therefore important that both the strength and the geometry, such as dimensions, shape and runout can meet the given specifications. Today, ring gears are in general made from steel forged preforms and undergo a substantial number of expensive machining processes prior to heat treatment. The ring gear design and its critical tolerances, such as runout, are set in order to also minimize gear noise. Ring gears made from PM can be made near to net shape and help to substantially reduce the machining and total cost per unit. In this investigation, different hardening processes have been applied on gears and the influence on shape distortions and fatigue stress limits were determined.