Hob tooth thickness increment Sg hob tooth thickness increment Sg is equal to the gear's minimum tooth thickness reduction amount S, which is related to the gear accuracy level Q, backlash and number of teeth. To generate the minimum backlash jnmin, the sum of the two gear tooth thickness reductions Sj = jnmin / cos, in addition, should also consider the reduction of the backlash caused by the error of each element of the gear teeth, the error of each element makes the tooth thickness reduction of the gear Sf Calculated by the radial comprehensive tolerance Fi.
Jnmin=100023(006 003mn 00005Ai)(m) The standard center distance Ai=05(z1 z2)mn, which is taken into the above formula and reduced to Sj=(40 20mn)/cos mn(z1 z2)/(6cos) The former item is independent of the number of teeth z and is equally distributed to two wheels; the latter item is related to the number of teeth and is distributed to the two gears according to the gear ratio. The tooth thickness reduction is Sj1=(20 10mn)/cos mnz1/(6cos Sj2=(20 10mn)/cos mnz2/(6cos)Fi=(2)Q-5(32mn 101df 64)=(2)Q-5(32mn 101mnz1 64) where df is the index circle diameter; Sf= Fitan; S = Sf Sj1.
As seen from the above formula, S increases as the modulus and the number of teeth increase. The Sg value of the hob for the gear with the accuracy level Q=9 and the pressure angle of 20 is calculated. Theoretically, the number of teeth of the machined gear is different, and the Sg of the hob is also different, thereby greatly increasing the type of the hob. To reduce the type of the same modulus hob, S calculated as a smaller number of teeth z is used as the Sg of the hob. When machining a gear with a large number of teeth, the depth of the feed can be increased to achieve the minimum tooth thickness reduction S of the gear, which will reduce the outer diameter of the gear, and the reduction value should be in the GB10095.颔11 range. According to this principle, the recommended value of the Sg designation is listed in the middle. When the modulus mn<4, Sg is equal to S calculated as z=12; when mn=4 is processed, when z<40, Sg is equal to S, z40 calculated by z=12, and Sg is equal to z=40. S; processing gears with mn=56, when z<50, Sg is equal to S calculated by z=12, and Sg is equal to S=calculated by z=50. The number of teeth that can be machined by the median is 12127 Gears without special requirements.
The hob root radius coefficient k is divided by the root arc of the top hob, and its radius ri is different from that of the non-cutting hob. The gear tooth top height coefficient ha=1, the pressure angle is, the number of teeth is z, the top circle, the pitch circle, and the base circle radius are ra, rf, rb, respectively. According to the meshing principle, the gear tooth shape M (the conjugate point of the point is the intersection point of the tooth tip circle and the meshing line MN. M. The tool tooth root arc and the tooth side are cut at B, and the distance from B to the pitch line is BC. MPsin=(ra2-rb2-rfsin)sinBC=HC-HQ QKsin=mn-(1-sin)ri When BC=PA, the end circle that is rolled into an involute is the gear tooth tip circle. Ri=kmn(1) Let k=1-05sin((zsin)2 4z 4-zsin)1-sin(2) It is seen from equation (2) that the k value is only related to the pressure angle and the number of teeth z, the larger z The smaller k is.
Since the root arc ri of the tool manufacturing cannot be very small, when the actual ri value is larger than the value calculated by the formula (1) by ri=kmn (k value increases by k), the gear tooth tip is trimmed and involutes. The height of the line is reduced by h, the length of the meshing line is reduced by MG, the overlap factor is decreased, and AD is the decreasing value of BC: AD = BC = (1 - sin) ri. =MGmncos=1mncosADsin=2(1-sin)sin2k=12[z1(tana1-tan) z2(tana2-tan)]=z12(tana1-tan)- 2 where 2=z2(tana2-tan), which only Related to paired gears. The calculated value, the actual value, the overlap coefficient, and the involute height reduction value h of the partial gear k are (=20).
When the tooth thickness deviation of the gear machining is the same as the outer diameter deviation of the gear hobbing, the sum of the tooth thickness reduction (the product of the IT11 value and tan, = 20) and the hob tooth thickness increment Sg is The deviation of the tooth thickness of the gear is Esi. The Esi of each gear is indicated by a broken line; the minimum tooth thickness reduction amount S of each tooth is the deviation Ess of the tooth thickness of the gear, and is indicated by a straight line to make a tooth thickness deviation. The distance between the straight line and the broken line is the tooth thickness tolerance of the gear (taking mn=1 and mn=4 as an example). It can be seen from the above that the gear hob designed according to the number of teeth is used to machine the gear hob with the number of teeth of 12127, and the tooth thickness tolerances of different tooth numbers are small.
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