CNC three-axis gear hobbing machine can feed in axial, tangential and radial directions at the same time. The axial feed of hob is the same whether it is straight or oblique. The cutting process of hob is the same as that of worm gear meshing. Gear hob cuts the cylindrical surface of parts along the program path until the whole machining process of gear is completed. In order to reduce the feeding time of hobbing, radial and axial feeding are usually carried out at the same time. This section focuses on axial feed, and tangential and radial feed are not described temporarily.
Axial feed the feed direction of gear hob is consistent with the axial direction of gear parts. The inclined installation angle of gear hob for parts is relatively small. According to the rotation direction of gear hob, the cutting direction is usually from bottom to top. For helical gear parts, the inclined installation angle of gear hob is large, and the selection of feed is determined by the rotation direction of gear hob and the rotation direction of parts.
When the inclined installation angle of the gear hob is small, the feed is along the tangential direction of the rotation of the gear hob. Although the size and shape of the gear hob are different, the gear hob cuts continuously according to the feed direction until the tooth profile of the part is processed, which is usually called back milling.
For parts with large helix angle, the direction of tool feed is usually opposite to the tangential direction of rotation. As the helix angle of the part increases, the installation angle of the gear hob increases, and the hob axis is parallel to the axis of the part. This common cutting method is regarded as forward milling.
Gear hob cutting does not require which feed mode must be adopted, mainly considering the required roughness of tooth surface and the size of burr. If conditions permit, it is best to use gear hob for trial cutting to see which method is more satisfactory. In most cases, gear hob back milling is more suitable for the time when the cutting load is large and the burr requirement is small.