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.