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Gear Generation process
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Conventional Gear Genaration
Modern gear teeth have an involute profile.
These gear teeth are mostlymade by the
following processes:
Forming the gear teeth by using Milling.
Generating the gear teeth by Gear planing or
rack.
Generating the gear teeth by Gear shaping.
Generating the gear teeth by gear Hobbing.
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Gear Milling
A involute form-milling cutter, which has the theprofile of the
space between the gears, is used to
remove the material between the teeth from thegear blank on a
horizontal milling machine.
The depth of cut into the gear blank depends onthe cutter
strength, set-up rigidity and
machineability of the gear blank material.
Milling is a form-cutting process limited tomaking single gears
for prototype or very small
batches of gears as it is a very slow and
uneconomical method of production.
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Gear Milling
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Gear Milling
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Gear Planing or RackGeneration
This is used for mid volume production. A rack,
which may be considered to be a gear of infinite
radius, is used as the cutter.
It is constructed of hardened steel with cuttingedges round the
teeth boundaries.
The rack which is given a reciprocal laterial
motion equal to the pitch line velocity of the gear
is slowly fed to the slowly rotating gear blank. In this way,
the material between the teeth is
removed and the involute teeth are generated.
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RackGeneration
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Gear Generating
Fig : (a) Producing gear teeth on a blank by form cutting. (b)
Schematic illustration of geargenerating with a pinion-shaped gear
cutter. (c) Schematic illustration of gear generating in a
gear shaper using a pinion-shaped cutter. Note that the cutter
reciprocates vertically. (d) Geargenerating with rack-shaped
cutter.
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Gear Shaping
The cutter is a circular pinion-shaped cutter withthe necessary
rake angles to cut.
Both the gear blank and cutter are set in a vertical
plane and rotated such as that the two are like
gears in mesh. Gear shaping is faster than gear planing
because
the cutting process is continuous and the cutterdoes not have to
be stepped back.
This is the most versatile gearcutting processwhich could
produce internal and external gears,close-coupled cluster gears and
splines too.
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Gear Shaping
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GearHobbing
The hob is used to generate the involute teeth.
The hob is basically a straight cylindrical toolaround which a
thread with the same crosssection as the rack tooth has been
helicallywound.
This hob is then rotated with the gear blank fedonto the hob
according to the depth of cut. Thehelix pattern of hob as it
rotates is the same asthat of the rack moving
This is the most productive ofall the gearproduction
processes.
Itcannot beused to cut internal gears.
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GearHobbing
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Gear Cutting with a Hob
Fig : Schematic illustration ofthree views of gear cutting
with a hob.
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Gear Grinding
Fig : Finishing gears by grinding: (a) form grinding with shaped
grinding wheels; (b) grindingby generating with two wheels.
