Gear Cutting :
A gear is a rotating machine part having cut teeth, which mesh with another toothed part to transmit torque. Gear is cut from round blank carrying teeth along its periphery. Gear cutting is a specialized job. Gear cutting is any machining process for creating a gear. The most common gear-cutting processes include hobbing, broaching, milling, and grinding. Such cutting operations may occur either after or instead of forming processes such as forging, extruding, investment casting, or sand casting.
Gear Hobbing Process – Introduction
Hobbing is a continuous gear generation process widely used in the industry for high or low volume production of external cylindrical
gears. Gear hobbing is one of the major manufacturing processes in the industry. Modern engineering practice is continually increasing its demands for more gearing of old and new types with a higher and higher degree of accuracy.
Construction Of Gear Hobbing Machine
- Hob– In this process, the gear blank is rolled with a rotating cutter called a hob. Gear hobbing is done by using a multipoint cutting tool called gear hob. It looks like a worm gear having a number of straight flutes all around its periphery parallel to its axis. These flutes are so shaped by giving proper angles to them so that these work as cutting edges.
- In gear hobbing operation, the hob is rotated at a suitable rpm and simultaneously fed to the gear blank.
- The gear blank is also kept as revolving. Rpm of both, gear blank and gear hob are so synchronized that for each revolution of gear bob the gear blank rotates by a distance equal to one pitch distance of the gear to be cut.
- The motion of both gear blank and hob is maintained continuously and steady. A gear hob is shown in Figure and the process of gear hobbing is illustrated in Figure
- The hob teeth behave like screw threads, having a definite helix angle. During operation the hob is tilted to helix angle so that its cutting edges remain square with the gear blank.
- Gear hobbing is used for making a wide variety of gears like spur gear, helical, hearing-bone, splines and gear sprockets, etc.
Working Of Gear Hobbing :
- Gear hobbing is a process in which gear is cut by a generating process by rotating the gear blank and the cutter called a hob at the same time with a fixed gearing ratio between hob and gear blank. In this process the gear blank is fed towards the rotating hob until the required depth is reached. The hob is fed across the face of the blank until all the teeth are complete.
- In hobbing spur gear the hob teeth are set parallel to the axis of rotation of the blank. For helical teeth bobbing, the axis of the hob is set over an angle to produce the proper helix. While worm gears are produced with the axis of the hob set the right angle to the gear blank.
- Generally two techniques are used in the hobbing process.
i) Conventional hobbing
ii) Climb hobbing.
- The rate of production is quite high as compared to the other gear generating processes. The process can be used for the production of spur, helical, worm gears, sprockets, splines, etc. But due to the rotary cutter cutting up to the shoulder is not possible.
Gear Hobbing Parameters :
Three important parameters are to be controlled in the process of gear hobbing indexing movement, feed rate, and the angle between the axis of gear blank and gear hobbing tool (gear hob).
Read More :
- Gear Cutting- Gear Manufacturing | Interview Question and Answers
- 19 Methods Of Manufacturing Of all types of Gears
Types Of Hobbing Process :
Advantages and Limitations of Gear Hobbing Process
Disadvantages of Gear Hobbing machine :
2. Restricted adjacent shoulders larger than the root diameter of the gear.
3. Splines and serrations are not suitable for hobbing.
Applications of Gear hobbing :
2. It can also be used for producing internal gears for which the machine should have a facility for fitting a special head.
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