# Correction of installation angle λ of hob for super large modified gear hobbing

The practice shows that using standard hob to gear hobbing this kind of gear with incorrect method may cause abnormal phenomena such as tool jacking and tool clamping. Hobbing gear with hob is based on envelope principle. In the process of hobbing super large modified gear, standard extended hob or non-standard hob can be used for gear hobbing, but special customized hob is required, which is suitable for mass processing. However, heavy machinery equipment is often single piece, special hob is not economical and long supply cycle; on the other hand, it is not easy to design and manufacture new hob. This paper introduces a method of hob axial displacement, that is, hob axial movement segmented gear hobbing, you can use standard hob correctly, smoothly and efficiently gear hobbing.

Because the hob is actually a helical gear, it is equivalent to the meshing of the helical gear with staggered axis during gear hobbing. In theory, the installation angle can be calculated according to this. However, the back angle of the hob during manufacturing is a certain value, and the back angle of the top edge during manufacturing is generally about 10 degrees, so the interference and extrusion phenomenon of the back of the top edge will not occur; Because of the combination of main motion and generative motion, the flank flank’s cutting plane and base plane incline. As a result, the flank’s flank’s flank angle changes during working, and the flank squeezes and makes abnormal sound. If you don’t pay attention to it, you will be in danger of hitting or damaging the gear hobbing machine.

Where: λ is the modified installation angle; m is the module of the gear to be hobbed; DDC is the outer diameter of the hob; DF is the root circle diameter of the gear to be hobbed; DZ is the calculated mean diameter of the gear to be hobbed, DZ = da-2m or DZ = 0.5 (DA DF), whichever is smaller; Da is the straight diameter of the addendum circle of the gear to be hobbed; DF is the root circle diameter of the gear to be hobbed; λ 0 is the helix rise angle of the indexing cylinder of the hob; Z0 is the head number of the hob; λ Z is the helix rising angle on the calculated pitch diameter of hob, λ z = arctan [M / (DDC + DF DZ) cos λ 0]

The “±” sign in the formula should be selected according to the following principles: when DZ < D, take “+” sign; when DZ > D, take “-” sign. By using the modified installation angle of the formula, not only the extrusion of the blade is avoided, but also the gear with the required tooth profile can be cut out.

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