First, hobbing knife cutting teeth:

Cutting conditions:

For the relationship between cutting speed, feed amount (travel speed) and hob wear, generally:

(1) In order to reduce the friction of the hob, it is better to reduce the cutting speed. But the cutting feed is too small to be good;

(2) In order to increase the durability of the hob, instead of using a high cutting speed, it is better to use a high cutting feed, but the tooth surface will be bad;

(3) The cutting speed is increased (the number of revolutions is increased), the feed amount is decreased, and the tooth surface is improved;

(4) The rigidity of the hobbing machine itself has a great impact on the hob life.

(5) Hob material points: (1) tool steel (titanium plating); (high-speed steel, helium) (2) super hard (tungsten steel);

(6) Check whether the idle gear is installed according to the spiral direction of the hob.

Second, hob and its application:

The hob's accuracy grade can be divided into AAA, A, B, and C grades, and correspondingly processes grades 6 and above, 7, 8, 9, and 10 gears.

3. Cutting teeth of HOB:

Hob is to add several longitudinal grooves to the screw teeth, and there are many cutting tools for cutting teeth on the screw lead;

(1) Integrated hobbing cutter (Hobbing cutter used by our factory)

(2) Combined hobbing cutter

关系 Relation between hob and workpiece: (hobbing process, forming method).

When the hob is installed, the blade lead will be aligned with the tooth direction of the gear. At this time, the blade lead of the hob is equivalent to the imaginary rack. In the case of involute gears, the shape of the blade is straight. There are turning, one after another blades cut into the workpiece, cut out the teeth. Because the cutting edge is distributed along the thread, the cutting edge that cuts in with the rotation moves to the left, and the workpiece also moves to the left with this action. As long as the gear is turned, the tooth shape is gradually cut from the tooth top to the tooth. In the case of one hob (single port, both in our factory), the hob 1 turns, which is equivalent to the imaginary rack advance one pitch. The gear workpiece only needs to run at one pitch. That is to say, when cutting the gear with the number of teeth, the hob must be rotated with respect to 1 rotation of the gear workpiece.

4. The influence of hob precision error on its production:

齿 Tooth profile error caused by hob regrind

(1) Hob segmentation error: When there is a segmentation error, it will be reflected in the tooth shape error, which has a great impact. When a hob with a pressure angle of 20º has a segmentation error of 0.1mm on the periphery, it will cause a 6um tooth shape error.

(2) Inclination angle error: The inclination angle error of the hob will become the pressure angle error of the gear. When the inclination angle error of the hob is 1º, the pressure angle error is about 3´, which is not a big influence.

(3) Error of cutting edge surface: When the cutting edge surface of the hob is not straight, but is uneven, it will cause tooth shape error.

(4) Spiral error of the edge groove: Usually the axis of the hob and the cutting edge groove are parallel. If there is such an error, an asymmetric pressure angle error of the left and right tooth surfaces will occur, and an error of 1º is about 10´. Tooth profile error caused by hob deflection.

(5) If the hob has a deflection, the gear will produce a large bending error. The tooth shape error at a deflection of 0.03mm and a pressure angle of 20º is about 10um (this error is very large).

(6) The eccentricity of the hob has the following phenomena:

a) Eccentricity of cutting edge and hole (produced during hob production)

b) Eccentricity during hob installation.

间隙 There is a gap between the hob inner hole and the hob shaft;

Eccentricity of the reel nut when tightened: The parallelism of the end faces of the nut, washer, and reel is bad; iron slag adhesion during cutting causes the reel shaft to bend, or improper tightening causes the reel shaft to bend; hob The eccentricity of the shaft itself.

多 Polygonal error caused by cutting edge groove of hob:

(7) The polygon error can be reduced due to the large number of cutting edges;

(8) The more the number of hobs, the greater the error;

(9) When the number of teeth cannot be divided evenly by the number of hobs, the error becomes small;

(10) When the number of teeth can be evenly divided by the number of hobs, the error becomes large.

Other causes of tooth profile error:

(1) The hob pressure angle error directly becomes the gear pressure angle error;

(2) The pressure angle error will occur when the hob pitch is the same.

(3) Tooth error of hob will cause gear tooth shape error. The above all exist in the accuracy of hob production.

(4) If both ends of the hob are used, incomplete creation may occur and tooth shape errors may occur;

(5) The tooth surface is out of edge-the trimming is unequal;

(6) Asymmetric tooth shape-misalignment of hob installation;

(7) Tooth shape angle error-the repair fails

(8) Tooth profile period error—the radial and axial runout is large after the tool is installed;

(9) Pitch error, cumulative pitch error—the axial movement of the hob spindle is large, and the hob radial runout is large (the tool accuracy is not enough);

(10) After re-grinding the hob, remove the edge of the cutting edge with a brass brush.

5. Selection of hob:

The hob can be selected according to the accuracy requirements of the machined parts. Generally, gears with grade 5 accuracy (GB) should be processed with "AAA" grade hobs, and gears with grade 6-7 accuracy should be processed with "AA" grade hobs. Gears with 8-9 grade accuracy can use "A" grade or ordinary hob.

六 、 Hob installation:

The installation of the hob should select the corresponding hob according to the pressure angle, modulus, accuracy and tool bar diameter. After the hob is installed and clamped, a dial indicator should be used to check the radial runout of the two bosses on the hob. (Some hobs have only one boss.) The runout direction and value of the two bosses should be the same as much as possible to avoid the skew of hob installation. According to the different accuracy grades of processed parts, the allowable radial runout value of hob installation is: (according to GB accuracy)

Roll cut 5-level precision gear, the allowable radial runout value at A and B is 0.005-0.007mm;

Roll cut 6-level precision gear, the allowable radial runout value at A and B is 0.007-0.009mm;

Roll cutting 7-level precision gear, the allowable radial runout value at A and B is 0.01mm.

When the radial runout of the hob is not larger than the allowable value, you can loosen the hob to tighten the screw, turn the hob or washer, and then re-clamp for inspection. Repeat several times until the accuracy requirement of the hob is reached.