Gear Hobbing – Parts, Working, Types, Advantages, and Disadvantages

Gear Hobbing is a multipoint machining process used for cutting gears from raw material, typically metal. In this process, a hob, a cutting tool with helical teeth, is used to cut gear teeth.
The result is a precisely shaped gear with smooth, accurate teeth.

A hob cutter is used to cut teeth in gear Blank that is why this process is called gear hobbing.

Gear Hobbing is often used for high-volume gear production, as it is a fast and efficient method for producing high-quality gear.
Gear Hobbing is most commonly used for machining spur and helical gears.

Gear Hobbing is used in various industries, including automotive, aerospace, and power transmission.

The process can create gears of various sizes, shapes, and tooth counts, and is suitable for cutting a range of materials, including steel, aluminum, and bronze. The precision and repeatability of the gear hobbing process make it a popular choice for manufacturing high-quality gears.

Gear Hobbing
Gear Hobbing

Parts of gear Hobbing-:

1) Hob: A cutting tool used to create gear teeth by cutting into a rotating workpiece. The hob has a large number of cutting teeth on its circumference, which are shaped to match the desired gear profile.

Gear Hob
Gear Hob

In the hob, there are straight flutes that are parallel to the axis of the hob and after every straight flute, there is a line of cutting teeth. These straight flutes are also called gashes.

Gear Hob (Side and Front View)
Gear Hob (Side and Front View)

2) Workpiece: A blank piece of material, such as steel or cast iron, that will be machined into a gear.
3) Gear blank: Gear blank is produced by machining the workpiece into a desired shape. The semi-finished part produced by machining the workpiece into the desired shape is called gear blank. This gear blank is machined by a hob to cut gear teeth.
4) Chuck: A clamping device used to hold the workpiece in place during the hobbing process is called a chuck.
5) Spindle: The hobbing machine has two spindles. One is mounted with a blank workpiece and the other holds the hob.
5) Hobbing machine: A specialized machine tool used to perform the hobbing process. It consists of a rotating spindle that holds the hob, a workpiece holder or chuck, and a cutting feed mechanism.
6) Cutting fluid: A lubricant used during the hobbing process to reduce friction and heat, as well as to flush away chips and debris.

Working Of Gear Hobbing:

1) At first, the gear hob and workpiece are mounted and clamped in the hobbing machine.
2) The cutting speed is set based on the material of the gear and hob, and the desired surface finish.
3) The feed rate is set based on the desired depth of cut and the size of the gear. Feed rate is the distance traveled by the tool during its single spindle revolution.
4) The hob is rotated at a constant speed, typically by an electric motor.
5) Both the hob and blank are rotated as they are in mesh with each other.
6) The speed of the hob and the blank are adjusted in such a way that for each rotation of the hob, the blank rotates through one pitch distance.
5) Then, The hob is moved into the workpiece, cutting material from the gear blank and creating gear teeth. The materials are removed from the gear blank in the form of chips.
Four to five gear teeth can be cut at a time using the hob cutter.

Gear Hobbing Working
Gear Hobbing Working

6) The hob is withdrawn from the workpiece and repositioned for the next pass.
7) Steps 5 and 6 are repeated until the desired depth of cut is reached.
8) The gear is inspected to ensure it meets the desired specifications and tolerances.
9) The gear may undergo additional finishing operations, such as shaving or grinding, to improve surface finish and accuracy.
10) The finished gear is removed from the hobbing machine.

Types OF Feed On Gear Hob:

The feed provided to the hob should be properly maintained. According to the type of gear to be cut, different types of feed are provided to the Gear Hob. The most used feed provided to the gear cutters is given below:-

Axial feed:
When axial feed is provided, the gear hob is fed against the gear blank along the face of the gear blank and parallel to the face of the axis of the gear blank.

Radial feed:
When radial feed is provided, the hob and the gear blank are set in such a way that their axis becomes normal to each other.

Tangential feed:
When tangential feed is provided in hobbing, the hob is held with its axis horizontal and at a right angle to the axis of the blank. Tangential feeds are mainly used for manufacturing worm gears.

Diagonal feed:
The most commonly used combined feed is called diagonal hobbing in which tangential and axial feed are used simultaneously. In radial and axial hobbing about 1.5 to 3 teeth are in operation but in diagonal hobbling, more teeth are required.

Advantages of gear hobbing:

1) High precision and accuracy of gear teeth.
2) Fast and efficient production of high-volume gears.
3) No repositioning of the hob and gear blank is required.
4) Suitable for cutting a range of materials, including steel, aluminum, and bronze.
5) Ability to create gears of various sizes, shapes and tooth counts.
6) High repeatability and consistency of the machining process.
7) Ability to produce gears with smooth and accurate teeth.
8) More than one blank workpiece can be processed simultaneously by mounting them on the same arbor.
9) Suitable for various industries, including automotive, aerospace, and power transmission.

Disadvantages Of Gear Hobbing:

1) High initial investment in specialized hobbing equipment.
2) Limited to hobbing straight teeth and simple gear profiles.
3) Internal gear cannot be cut using gear hobbing.
4) Not suitable for cutting more complex or irregular shapes.
5) Higher tool wear and replacement costs due to the high cutting forces involved.
6) Not as flexible as other gear-cutting methods, such as shaping or broaching.
7) Limited ability to produce small or fine gears, due to the nature of the hobbing process.

Application Of Gear Hobbing:

Gear Hobbing is used to produce the following:
1) Spur Gear.
2) Helical Gear
3) Sprockets
4) Cycloid Gear
5) Splines
6) Worn Gears
7) Involute Gears
8) Ratchets

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