What exactly happens in the hobbing process?

What exactly happens in the hobbing process?

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Maybe you have a large demand for gears, so do you know the specific manufacturing process of gear hobbing? If you are interested in this topic, this article will explain to you exactly what happens during gear hobbing.

The process of hobbing tooth profile formation

Starting from the contact cutting between the hob and the workpiece, the number of teeth involved in cutting gradually increases, and no longer increases after reaching a certain level. When the cutting is about to end, the cutter teeth participating in the cutting gradually decrease until the processing ends.

In order to objectively reflect the cutting conditions of all the cutting teeth in the cutting area, it is assumed that the gear has formed a complete tooth profile on the end face to analyze the cutting state of the hob when it continues to feed axially. According to this assumption, the initial position of the hob is at 0 position, the workpiece rotates one circle, and the hob feeds along the axis of the workpiece. At this time, part of the metal of ABC is cut in the tooth groove, and the complete tooth profile is formed on the end face of the gear. The workpiece turns around again, the center of the hob reaches position 2, and the metal in the same section as ABC is cut off in the tooth groove, so that the hob gradually cuts off all the metal in the tooth groove in the downward feed .

Alveolar cutting and tooth profile forming process

In the actual hobbing process, the processing of the tooth space to be processed does not start from the No. 0 cutter tooth, but starts from the bN No. cutter tooth. The position where the hob rotates counterclockwise around the gear blank by ϕ angle is the initial state where the bN number cutter tooth starts cutting the tooth groove to be processed.

The process of gear hobbing is actually the process of meshing (creating) the helical surface of the hob with the tooth surface of the gear.

Gear hobbing belongs to multi-edge intermittent non-free bevel cutting. Compared with ordinary turning, the relative position and relative motion relationship between the cutter teeth and the workpiece are more complicated during the machining process. During the hobbing process, each cutter tooth enters the cutting The shape of the formed alveolar corresponding to the state is different, the shape of the removed material is different, and the new alveolar entity formed is also different.

During the gear hobbing process, the gear workpiece rotates around the gear axis, and at the same time the hob rotates around its own axis and moves linearly along the gear axis. Therefore, each tooth on the hob corresponds to the tooth slot it cuts. spatial position and movement relationship.

Cutting process of a single tooth

The hob is formed by a series of teeth of the same shape distributed in a helical array on its basic worm surface. During the hobbing process, each knife tooth successively removes material from the gear blank according to the hobbing principle, and finally envelopes the gear tooth surface.

When the hob is fed to a certain position along the axial direction of the workpiece, as the hob and the gear workpiece rotate relative to each other, the teeth distributed on the basic worm thread of the hob envelop the gear tooth profile and form a tooth groove. According to the feeding position of the hob, the formation process of the cogging can be divided into three stages:

The first stage is the cutting process, which means that the hob contacts the tooth blank and starts cutting until the top of the tooth blank is cut out of the complete tooth groove profile (A in the figure);

The second stage is the complete cutting process, which refers to the end of the first stage until the hobbing forms the full tooth width of the gear;

The third stage is the cutting process, which refers to the end of the second stage until the hob is out of contact with the tooth blank.

Since the cutting edge trajectory and the contact length of the workpiece remain unchanged only in the complete cutting state of the second stage, and generally the processing time in this stage of the cutting process is much longer than the processing time of the first and second stages.

Alveolar formation in three stages

In the hobbing process of the second stage of gear hobbing, every time the gear workpiece rotates once, each tooth groove on the gear must undergo a cutting process, and a tooth groove on the gear to be machined will contact the hob from entering the cutting state (the tooth groove m enters During the process from the contact point a) to the separation from the cutting state and the hob (tooth m’ leaving the contact point b), a certain number of hob teeth will participate in cutting in turn. The cutting experienced is defined as a hobbing cycle.

Since the relative positions of the cutting teeth and the tooth grooves on the hob constantly change during the hobbing process, when each tooth enters the cutting, the parts cut by the teeth are different, and the amount of material removed by each tooth is different. The shapes are different, and the shape of the formed alveolus corresponding to the next cutter tooth when it enters the cutting is also different from the shape of the corresponding alveolus of the previous cutter tooth.

The material of the gear workpiece to be cut is sequentially removed through the cutter tooth trajectory. The material removed by each trajectory is the chip obtained by the corresponding cutter tooth hobbing, which is actually the undeformed state of the chip obtained from the actual workshop processing and simulation experiments.

Hope the above content is helpful to you!

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