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Gear Machining Method—Hobbing
Hobbing is one of the most widely used generating (gear-generating) processes in gear manufacturing. It involves the continuous cutting of gear tooth profiles on a hobbing machine through the meshing motion between a gear hob and the workpiece gear blank. Below is an introduction to hobbing from aspects including basic concepts and working principles, process characteristics, equipment and tools, and application scope.
1. Basic Concepts & Working Principles
Hobbing is a machining method that uses a gear hob (equivalent to a helical gear with very few teeth) on a hobbing machine. Through the forced meshing motion between the hob and the gear blank, the gear blank is continuously cut into the predetermined tooth profile. Essentially, it simulates the meshing process of a pair of helical gears: the hob acts as the driving gear, and the gear blank as the driven gear. The involute tooth profile is formed through the enveloping motion of the tool's cutting edges.
The core of hobbing lies in the combination of generating motion and cutting motion, which specifically consists of the following movements:
- Main Motion: The rotational motion of the hob, which provides cutting power for the cutting edges to remove metal from the surface of the gear blank.
- Generating Motion: The forced meshing rotational motion between the hob and the gear blank, ensuring that their transmission ratio strictly equals the theoretical transmission ratio of a gear pair. Let the number of hob heads be k (usually 1–2) and the number of teeth of the gear blank be z. The transmission relationship is designed such that the hob rotates z turns while the gear blank rotates k turns—this motion envelops the involute tooth profile.
- Feed Motion:
- Axial Feed: The linear movement of the hob along the axis of the gear blank (feed rate f, unit: mm/r), ensuring the entire tooth width is cut.
- Radial Feed: The movement of the hob along the radial direction of the gear blank, controlling the cutting depth (tooth height). This process usually involves two feeds: rough cutting and finish cutting.
2. Process Characteristics of Hobbing
1) Hob Clearance & Gear Structure Design
When designing gears for hobbing, several factors must be considered. The hob requires an "exit" clearance at the end of cutting. If the gear teeth are close to a shoulder or other obstacles, hobbing may not be completed. For herringbone gears, a clearance must be left between the two helical tooth sets to allow the hob to exit. The clearance of the relief groove for herringbone gears can refer to the recommended values in the table below (referenced from Mechanical Design Handbook).
| Module (m) | Relief Groove Width (e, mm) | Module (m) | Relief Groove Width (e, mm) | ||||
|---|---|---|---|---|---|---|---|
| (beta=15^circsim25^circ) | (beta>25^circsim35^circ) | (beta>35^circsim45^circ) | (beta=15^circsim25^circ) | (beta>25^circsim35^circ) | (beta>35^circsim45^circ) | ||
| 2 | 28 | 30 | 34 | 9 | 95 | 105 | 110 |
| 2.5 | 34 | 36 | 40 | 10 | 100 | 110 | 115 |
| 3 | 38 | 40 | 45 | 12 | 115 | 125 | 135 |
| 3.5 | 45 | 50 | 55 | 14 | 135 | 145 | 155 |
| 4 | 50 | 55 | 60 | 16 | 150 | 165 | 175 |
| 4.5 | 55 | 60 | 65 | 18 | 170 | 185 | 195 |
| 5 | 60 | 65 | 70 | 20 | 190 | 205 | 220 |
| 6 |
Pub Time : 2025-08-18 09:47:27
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