Research Aim

To investigate the effects of asymmetric tooth profile and polymer mating gear on the bending fatigue behavior and tooth deflection characteristics of injection-molded polymer spur gears, and evaluate the influence of selective laser sintering and build configuration on the bending fatigue behavior.

Methods

·         Fabrication of polymer gears – Injection-molding (IM) and Selective laser sintering (SLS)

·         Evaluation of bending fatigue life – Bending fatigue tests using in-house developed test rig

·         Study of thermal behavior – Infrared thermography

·         Study of failure morphology – Optical and Field-emission scanning electron microscopy

·         Evaluation of gear mesh deflection – static deflection tests using in-house developed test setup

·         Prediction of stress and deflection – Non-linear, viscoelastic, contact analysis in Abaqus/CAE

Figure 1. (a) Injection-molded gears, (b) Selective laser sintered gears, (c) Bending fatigue test rig, (d) Deflection test rig, (e) Sample infrared thermal image of asymmetric gear (20°/34°), and (f) Finite element model of asymmetric gear (34°/20°).

Principal findings

·         Asymmetric configuration with greater drive side pressure angle causes maximum bending stress reduction. Asymmetric configuration with lower drive side pressure angle minimizes the hysteresis heat generation.

·         Bending fatigue strength of metal-polymer pairs (M-P) of asymmetric gears depends on the bending stress. In polymer-polymer pairs (P-P), operating temperature determines the fatigue life.

·         Metal mating gear enhances the mesh stiffness of the gear pair. Polymer mating gear balances the mesh stiffness in the addendum and dedendum region.

·         Selective laser sintered gears built in ‘flat’ configuration confers greater crack propagation resistance. ‘On-edge’ build configuration varies the tooth layer orientation, inducing significant anisotropy in bending fatigue strength.

Figure 2. (a) Bending fatigue life of Injection-molded gears, (b) Typical von Mises stress distribution in polymer-polymer pair of symmetric gear (inner: flat contact surface owing to similar material stiffness), (c) Mesh deflection variation in a cycle, (d) Tooth deflection variation in metal-polymer pair of asymmetric gear (34°/20°), (e) Bending fatigue crack in injection-molded gear, and (f) Bending fatigue crack in selective laser sintered gear built in ‘flat’ configuration.