Tooth thickness is an important parameter for balancing the fatigue life of large and small wheels.Since the number of small wheel cycles is much greater than that of large wheel, the bending fatigue strength of small wheel is the weak point of gear pair, which balances the fatigue life of large and small wheel by increasing the thickness of small wheel teeth.Tooth thickness adjustment is achieved by large wheel cutter top pitch W2.The width of the small gear groove is shown in the formula:
Where: PN is the normal circumferential joint; hf1/hf2 is the tooth root height of small and large wheels; alphaf1/alphaf2 is the pressure angle of cone convex and concave surface of large wheel process pitch; jmin is the minimum normal side clearance.
According to the formula, increasing the top pitch of the large wheel cutter will decrease the width of the small gear groove and increase the thickness of the teeth, thus reducing the bending stress of the root of the teeth and increasing the bending stress of the large wheel.Since changing the tool tip distance only changes the tooth thickness and does not change the profile shape, it does not affect the size of overlap and contact stress.
The increment is calculated on the basis of theoretical cutter crest distance (equal thickness of large and small teeth at pitch line). The increment of large cutter crest distance increases from -0.5mm to 0.5mm. At this time, the thickness of small teeth increases by 1mm and the bending stress of small teeth root decreases by 55.2MPa.Corresponding to the increase of bending stress of large gear roots by 80.6MPa, it can be seen that changing the tooth thickness can adjust the bending stress of large and small gear roots more.