Methods of Gear Manufacturing

1. METHODS OF GEAR MANUFACTURING
 Casting
 Hot Rolling
 Stamping
 Powder Metallurgy
 Powder Metallurgy
 Extruding
 Coining
 Machining :
 Form Tooth Process
 Template Process
 Cutter Generating Process

2. Gear manufacturing by CASTING
 Gears are CAST in sand moulds, parmanent moulds,
shell moulds, plastic mould dies, and lost–wax
moulds.
 The characteristics of Gears produced by CASING
 The characteristics of Gears produced by CASING
are same as those of other products made by these
processes.
 Sand casting is particularly used for making heavy
Gears of Cast Iron and Steel.

3. Gears manufacturing by Hot Rolling
 Gears are made by forcing a ‘Master Gear’ into a
Hot Blank and the two are then rolled together until
the teeth of the Master have penetrated far enough
to ‘form’ a complete Gear.
to ‘form’ a complete Gear.
 The Teeth are then Machined.
 Hot rolling is little used in present, but can be used
as a method of Gear manufacturing in future.

4. Gear manufacturing by STAMPING
 Stamped Gears are made from sheet metals.
 Materials upto 3 mm thickness are practically used
for this process.
 The Gears manufactured by ‘stamping process’
 The Gears manufactured by ‘stamping process’
may be Shaved to improve the accuracy and finish.
 Gears manufactured by ‘Stamping’ are used in
watches, clocks, toys and house – hold gadgets.

5. Gear manufacturing by POWDER METALLURGY
 In this process, a ‘Master Gear’ of ‘hard material’ is
rolled against a ‘heated Gear-Blank’, thereby
forming the teeth on the Hot Blank.
 Bakelite and other plastic materials are the most
commonly used materials for manufacturing of
Gears by this method.

6. Gear manufacturing by EXTRUDING
 In this process, the brass or aluminium bar is extended
through several block dies with the final die having the
shape of the desired tooth elements and thus the
material can finally be EXTRUDED to obtain gear form
on its surfaces, and the extruded bar is then hack-
on its surfaces, and the extruded bar is then hack-
sawed.
 At present only the Spur Gear is manufactured by this
process.
 As the material is displaced by pressure, the outside
surface of the material is quite hard and smooth.

7. Gear manufacturing by COINING
 Gears are coined from ‘blanks’ in a hydraulic press
or forging hammer.
 Gears manufactured by this process require a light
 Gears manufactured by this process require a light
machining.

8. Gear manufacturing by MACHINING
 Gears are machined from the blanks usually by a
roughing and a finishing operation.
Gear Machining Process:  In Milling machine
Gear Machining Process:
 Formed Tooth Process
 Templete Process
 Generating Process
 In Milling machine
 In Broaching machine
 In Shaper (Pinon and Rack)
 Shaving
 HOB Cutter process
 Rotary cutter process
 Reciprocating process

9. Gear manufacturing by : FORMED TOOTH PROCESS
FORMED TOOTH PROCESS :
 The theory of FORMED TOOTH process is based upon forming the cutter
tooth according to the shape of the tooth space to be removed.
 In Milling machine
 In Broaching machine
 In Shaper (Pinon and Rack type)
tooth according to the shape of the tooth space to be removed.
 Theoretically, there should be different shaped cutter for each size of gear
of given pitch, as there is a slight change in the curvature of the Involute.
 However, one cutter can be used for several gears having different
number of teeth without much sacrifice in their operating action.
 Commercially, each pitch cutter is made in slightly varying shapes to
compensate for this change.
 The forming operation can be performed in three ways i.e. MILLING,
BROACHING and SHAPPING.

10. Gear manufacturing by : MILLING
Gear manufacturing by MILLING
 The formed milling operations are usually employed for cutting Spur
Gear, but these can be employed for cutting every type of gear by using
a Universal Indexing mechanism.
 The cutter is mounted on the spindle in both horizontal and vertical
 The cutter is mounted on the spindle in both horizontal and vertical
milling machines and rotates while the work is mounted on the table and
reciprocated under the cutter.
 Once the cutter finishes tooth profile, the work is indexed to the next
position, and again the tooth profile is finished and so on.
 Gear MILLING process is employed for course pitch gears, racks of all
pitches, segment gears, worms and toothed parts as sprockets and
ratchets.

11. Gear manufacturing by MILLING
Gear manufacturing by MILLING

12. Gear manufacturing by MILLING
 All types of Gears i.e. Spur, Helical, Worm, Bevel etc can be
cut.
 It can be employed both for roughing and finishing
operations, and fine surface finish can be obtained.
Cutter
No.
No. of Teeth
1 135 teeth to a
rack
2 55 to 134
ADVANTAGES OF MILLING IN MANUFACTURING GEAR
operations, and fine surface finish can be obtained.
 The initial cost of the cutters is low compared to other types
of Gears.
 It can be used to machine almost any tooth form and usually
confined to producing replacement gears or small lot
production, roughing and finishing coarse pitch gears and
finish milling fine pitch gears having special tooth forms.
 It is necessary to have a tool with a special profile for milling
each gear with a different number and module as shown in
the table.
2 55 to 134
teeth
3 35 to 54 teeth
4 26 to 34 teeth
5 21 to 25 teeth
6 17 to 20 teeth
7 14 to 16 teeth
8 12 to 13 teeth

13. Gear manufacturing by BROACHING
Gear manufacturing by BROACHING
 The formed tooth principle can be utilized in a Broaching Machine
by making the broach tool, conforming to the Tooth space.
 In this process, full form finished gears are produced in one pass by
circular broach having inward facing teeth.
 The broaching tool consists of a series of full – form finishing rings
 The broaching tool consists of a series of full – form finishing rings
at the end of a series of generating ring.
 It is important that adequate chip space be provided and provision
be made of staggered chip breakers on successive broach teeth.
 This process has limited application, because of high initial cost of
tooling and is only used where mass production technique is to be
applied.
 It is usually used to produce only for Internal Spur and Helical
Gears, though broaching process can be used for external gears
also.

14. Gear manufacturing by MACHINING
SHEAR CUTTING OF GEARS
 It utilizes a cutter made from tool blades so shaped that the gap
between these blades forms the desired gear teeth shape.
 It is an operation very similar to Broaching.
 It cuts all teeth of external Spur forms simultaneously at a high rate of
 It cuts all teeth of external Spur forms simultaneously at a high rate of
production.
 It is possible to form-cut involute Spur Gear teeth with practically any
required tooth modification.
 Even unsymmetical or unequally spaced spur-tooth forms can be cut.
 The cutting tools are easily removed for sharpening and are sharpened
all at one time on a surface grinder.
 The process of Shear Cutting of Gears is limited to only coarse-pitch
gears having spur teeth.

15. Gear manufacturing by TEMPLATE PROCESS
Gear manufacturing by TEMPLETE PROCESS
 In this process, the form of the tooth is controlled by a template which
guides and reciprocates.
 The tool is similar to a side cutting tool and is given a reciprocating
motion in the process of cutting.
The machine used is called Gear Planner.
 The machine used is called Gear Planner.
 The frame of Gear Planner carries the reciprocating tool and is
guided at one end by a roller acting against the ‘template’, while the
other end is pivoted at a fixed point.
 Three sets of templete are used, one for roughing cut, and one for
finishing each side of tooth space.
 The ‘Gear blank’ is held stationary during the process and is moved
only when indexed.

16. Gear manufacturing by GENERATING
PROCESS
Gear manufacturing by
 In cutting Gears by using ‘generating’ type of machine, the gear teeth are
formed as a result of certain relative motions between ‘Gear blank’ and ‘cutter’,
instead of simply reproducing the shape of a formed cutter.
 A generating process is capable of enabling a cutter of a given pitch to cut
Gears having different numbers of teeth to the correct shape.
Gears having different numbers of teeth to the correct shape.
 ‘Gear cutter Generating’ process is based on the face that any two involute
gears of same pitch will mesh together.
 Hence, if one ‘Gear’ is made to act as a ‘Cutter’ and is given a reciprocating
motion, as in shaper, it will be capable of cutting of cutting into the Gear blank
and Generating conjugate teeth forms.
GEAR GENERATING principle is applied in three ways:
1. With PLANNING PROCESS using INVOLUTE RACK CUTTER
2. With HOB CUTTERS
3. In GEAR SHAPPERS in which both reciprocating as well as rotating cutting
principle are applied.

17. GEAR PLANING
 In GEAR PLANNING process, the cutter consists of true Involute rack which
‘reciprocates’ across the ‘face of the blank’ and the ‘blank’ ‘rotates’ in the
correct relationship to the longitudinal movement of the cutter as if both roll
together as ‘ rack and pinion’.
 Initially the cutter is fed into full tooth depth with ‘cutter’ reciprocating and
‘blank’ stationary.
‘blank’ stationary.
 ‘Involute shape’ is generated as the ‘blank’ rotates and involute ‘rack cutter’
feeds longitudinally.
 After completion of one or two teeth, the blank and cutter ‘stop feeding’ and
the cutter is withdrawn and indexed back to its starting position.
 Cutter is again 'fed back to depth’ and the cycle is repeated.
 Number of teeth is controlled by the machine gearing, and pitch and pressure
angle by the rack cutter.
 This method is used for the generation of ‘external spur gears’, being ideally
suited for cutting large, double helical gears.

18. GEAR PLANING

19. GEAR PLANING

20. GEAR HOBBING
 Hobbing is a process of generating a Gear by means of a ‘rotating cutter’ called a HOB.
 It is a continuous indexing process in which both the cutting tool and workpiece rotate in a
constant relationship, while the HOB is being fed into the WORK.
 A HOB resembles a ‘Worm’, with gashes made parallel to its axis to provide cutting
edges.
 For Involute gears, the hob has essentially straight sides at a given pressure angle.
 For Involute gears, the hob has essentially straight sides at a given pressure angle.
 The faces of the Hob teeth are relieved radially to form clearance behind the cutting
edge.
 The Hob is fed into the Gear blank to the proper depth and the two are rotated together
as if in ‘mesh’.
 The ‘teeth of Hob’ cut into the ‘workpiece’ in successive order and each in a slightly
different position.
 Each Hob tooth cuts its own profile depending on the shape of the cutter.
 One rotation of ‘cutter’ completes the cutting upto certain depth upto which the HOB is
fed.

21. GEAR CUTTERS : HOBS
HOBS

22. GEAR HOBBING
The Gear cutting with a HOB involves three basic motions, all of them
occurring at a time.
 The HOB and the BLANK have a rotating motion and the third one is the
radial advancement for the HOB , thus causing the cutting and indexing
simultaneously.
 HOB cutter may set with its teeth parallel to the axis of the ‘Gear Blank’ when
 HOB cutter may set with its teeth parallel to the axis of the ‘Gear Blank’ when
Spur Gear is cut. If Helical Gear are to be cut, the axis of the HOB can be set at
an angle to the helix.

23. GEAR HOBBING
(HOB)

24. GEAR HOBBING

25. GEAR HOBBING

26. Comparison of Gear HOBBING and Gear MILLING
 Gear Hobbing is faster than milling because several
teeth are cut at a time and because of the
continuous meshing process.
 Milling requires that the cutter and work disengage
before indexing can occur.
 The milling machine can cut only one tooth at a time,
while the Hob operates on several teeth at a time.

27. Characteristics, Merits and Limitations of HOBBING
 Any external tooth form which is uniformly spaced about the centre, so that all the
teeth are identical, can be hobbed using suitable hob.
 One hob of a particular module can be used to cut teeth of all involute Spur and
Helical Gears of any number of teeth of same module and pressure angle.
 It is thus a versatile process and can be used to cover a variety of work like Spur,
Helical, Worm, Splines and a variety of special forms.
Helical, Worm, Splines and a variety of special forms.
 Accuracy of Gears produced by Hobbing is dependent upon the accuracy of machine,
hob , and the blank, care in mounting work and Hob, and rigidity of the tooling.
 The indexing is continuous and there is no intermittent motion to give rise to errors. There
is no loss of time due to non-cutting on the return stroke.
 Finish is dependent on the amount of feed and upon the accuracy of Hob and rigidity
of Tooling also.
 It can’t be used to cut bevel and internal geras and for Gears having adjacent
shoulders larger than the root diameter of Gear and close enough to restrict the
approach or runout of the Hob.

28. Gear manufacturing by SHAPING
Gear manufacturing by SHAPING
In Gear Shapers, the above Generating Principle is applied in the following way:
 The Cutter is hardened disc shaped and slightly dished at the bottom (ground with top
rake and clearance) to facilitate cutting. The teeth have desired tooth profile and
pressure angle.
The cutter is reciprocated with the required cutting speed for stock removal along the
 The cutter is reciprocated with the required cutting speed for stock removal along the
face of the workpiece, and is gradually fed radially to plunge if for correct ‘teeth depth’
by means of a Cam. A relieving mechanism enables the cutter to clear the work on
noncutting or return stroke.
 The continuous generation motion is obtained by feeding ‘cutter’ to full depth and rotating
the cutter and the workpiece slowly in the exact ratio of their respective number of teeth.
 The ‘cutter’ is considered as the ‘driving gear’ and the ‘workpiece’ as the ‘driven member’.
 The workpiece gear is fully generated when the cutter has plunged to correct depth (set
previously) into the workpiece gear.
 The machine comes to rest automatically after the workpiece gear is fully cut.

29. Gear manufacturing by SHAPING
 In Gear manufacturing by SHAPING, the ‘generated ‘ surface, whether it is
curved or straight, is produced by continuous motion of a point, a line or a surface.
 The direction in which the generating point travels determine the shape
produced.
 The cutting point of the tool generates a circle when the work piece is rotated.
Cutting action of a pinion type cutter

30. Gear manufacturing by SHAPING
 The peripheral feeding of the
pinion type cutter takes place in
relation to the workpiece, when the
cutter has been feed to the full depth
of the tooth by the in fed cam.
Pinion type
cutter
 The bulk material is removed by the
tip and the fillet portion of the cutter.
 The involute portion of cutting tooth
profile removes very little material
during the fininshing stage , thus
producing supirion fininsh on the cut
gear.
cutter
Workpiece
or
GearBlank

31. Gear manufacturing by : SHAPING
Features of Gear Shaping:
 Ideally suited for mass production and
single piece production.
Gear manufacturing by SHAPING
single piece production.
 Gear SHAPING is a versatile process and
can cut Gears, Cams, Splines and special
shapes.
 Gear SHAPING has got automatic cycle
os operation and centralized control.
 High rate of production cuts.

32. Comparison of GEAR PLANNING,
GEAR HOBBING, GEAR SHAPPING
Relative Motions of Tool and Work for gear PLANNING, HOBBING, SHAPPING