This ppt covers the most about gear hobbing but the main contents.

1. GEAR
HOBBING
Nijerson Jeyaseelan, 2021507030

2. Introduction
01
CONSTRUCTION
02
WORKING
03
DIS/ADVANTAGES
04

3. INTRODUCTION
 What is a Gear?
Rotating machine part having cut teeth - Mesh with another toothed
part to transmit torque.
 Gear Cutting:
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.
 Gear Hobbing:
Continuous gear generation process widely used in the industry for
high or low volume production of external cylindrical gears.

4. CONSTRUCTION
 Hob:
Rotating cutter - Multipoint cutting tool.
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.
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.

6. WORKING OF THE MACHINE
“
In this process, 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.
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.

9. CONVENTIONAL HOBBING
TWO TECHNIQUES IN HOBBING
PROCESS
In Conventional Hobbing, the direction of feed matches the direction of the cutting
motion. In Climb Feeding, the feed is opposite to the direction of the cutting motion.
Generally, conventional hobbing produces a better finish, whereas climb hobbing yields
better tool life. For either method, the cutting forces of the hob should be directed towards
the work spindle and not the tailstock.
CLIMB HOBBING

11. PARAMETERS
Three important parameters:
 Indexing movement
 Feed rate
 The angle between the axis of gear blank and gear
hobbing tool (gear hob).

13. TYPES OF HOBBING PROCESS
The hob and gear blanks are set with their axis normal to
each other.
The rotating hob is fed against the gear blank in radial
direction or perpendicular to the axis of gear blank.
Used to make the worm wheels.
WITHRADIAL
FEED
The gear hob is fed against the gear blank along the
face of the blank and parallel to its axis.
Used to make spur and helical gears.
WITH AXIAL
FEED
Used for cutting teeth on the worm wheel.
Hob - axis horizontal but at the right angle to the axis of the blank -At full
depth of the tooth and then fed forward axially.
Then fed tangentially to the face of the gear blank..
WITH TANGENTIAL
FEED

14. Fast and continuous process - Economical
Lower production cycle time, i.e. faster production rate.
Capable to make a wide variety of gears like spur gear, helical gears, worms,
splines, sprockets, etc.
A special type of gear named herringbone gear cam be generated by gear hobbing
exclusively.
A wide variety of batch sizes (small to large volume) can be accommodated by this
process.
Several gear blanks, mounted on the same arbor, can be processed simultaneously.
Hob is a multipoint cutting tool having multi cutting teeth or edges at a time few
number of cutting edges work so lots of time is available to dissipate the generated
heat. There is no overheating and cutting tool.
ADVANTAGES OF GEAR HOBBING

15. Not adopted to generate internal gears
Restricted adjacent shoulders larger than the root diameter of the gear.
Splines and serrations are not suitable for hobbing.
DISADVANTAGESOF GEAR HOBBING

16. It is widely used to produce spur, helical gears, worms, and worm wheels.
It can also be used for producing internal gears for which the machine should have
a facility for fitting a special head.
APPLICATION OF GEAR HOBBING

17. THANK YOU