Gear generating process
This
method of gear manufacturing is based on the fact that any two involute
gears of the same module will mesh together. In this one of the meshing
gears is made as the cutter. The other gear rotates and also
reciprocates along the width of the gear blank. Because of the relative
rolling motion of the cutter and the blank, gear teeth are generated on
the gear blank.
The gears may be generated by a
rack cutter, pinion cutter, or a hob. Using the generating method,
profile of the gear teeth can be very accurately produced.
The following methods are generally used to produce gear
Gear shaping
Gear shaping is done on a special type of machine called as gear shaper.
In
gear shaping, a pinion type cutter is used. The cutter teeth are ground
with a top rake and clearance. The cutter is mounted on a vertical
spindle. The axes of a cutter and blank are parallel. The cutter and the
blank are made to rotate together as two gears which are in mesh. The
apparent speeds of the cutter and the blank are the same. The cutter
reciprocates in vertical direction along the width of the blank.
The
pinion cutter is fed radially into the gear blank to give the depth of
cut. The cutter and blank slowly rotate together till all the teeth are
generated on the blank. During each return stroke of the cutter, the
blank is withdrawn. This is done to prevent rubbing of the cutting edges
and damage to gear teeth being cut.
The different movements are given below:
1. Rotary motion of the cutter and the blank.
2. Vertical reciprocating motion of the cutter.
3. Radial feed of the cutter towards the blank.
4. Withdrawal motion of the blank away from the cutter during return stroke.
Gear Planing
Here
the cutter is in the form of an involute rack. The rake and clearance
angles are cut on it. The cutter is mounted on a reciprocating slide.
The blank is mounted a vertical arbor. The cutter is fed radially into
the gear to give the depth of cut. The rack cutter reciprocates across
the face of the blank.
The
blank rotates. While reciprocating, the cutter also moves in a
longitudinal direction, i.e. the cutter and the blank roll together as
rack and pinion.
Gear hobbing
Hobbing
is a process of generating a gear by means of a rotating cutter called
hob. The hob has helical threads. Grooves are cut in the threads
parallel to the axis. This will provide the cutting edges. Proper rake
and clearance angles are ground on these cutting edges. The rotating hob
acts like a continuously moving rack as it cuts.
The
gear blank is mounted on a vertical arbor. The hob is mounted in a
rotating arbor. The hob axis is tilted through the hob lead angle so
that its teeth are parallel to the axis of the gear blank.
The
hob is rotated at a suitable cutting speed. It is fed towards the gear
blank. The hob and the gear blank are made to rotate in a correct
relationship with each other. for one rotation of the hob the gear is
moved by one tooth.
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