2. BROACHING PROCESS
It is a process of machining a surface with a special multipoint cutting
tool called BROACH which has successively higher cutting edges in a
fixed path
3. Specification of a broaching machine
1.Maximum length of stroke
2.Maximum force developed by the slide
3.Type of drive for straight line motion
4.Power rating of the electrical motor
5.Speed and feed range
6.Weight of the machine
7.Floor space rquired
5. Types of broaching machines
a) According to the nature and direction of primary cutting
motion
1. Horizontal broaching machine
2. Vertical broaching machine
3. Continous broaching machine
b)According to the purpose
1. Internal broaching machine
2. External or surface broaching machine
c) According to the method of operation
1. Pull broaching machine
2. Push broaching machine
6. d) According to the function
i. Keyway broaching machine
ii. Burnishing broaching machine
iii. Spline broaching machine
iv. Round hole broaching machine
v. Surface broaching machine
e) According to the motion of the broach tool relative
to the work
i. Straight line motion broaching machine
ii. Stationary broach tool broaching machine
14. Construction and Working :
In this type of machine the work pieces are carried by an endless
chain
Work pieces are loaded by means of fixtures.
Fixtures are mounted on the continuously moving chain or
conveyor.
Broach head does not move. It is the fixed member of the
machine.
Conveyor is made to rotate continuously by the two drums.
Out of these two drums, one drum is given power, the other drum
rotates freely. Chain connects these drums.
Toothed wheel is mounted on each drum to drive the chain.
Power driven drum rotates at constant speed by the electrical
motor and gear drive.
As the drum rotate, the work pieces pass under the broach tool
and the broach tool removes the material.
17. Types of broaching tools
1. According to the method of operation
i. Push broach
ii. Pull broach
2. According to the kind of operation
i. Internal broach
ii. External broach
3. According to their construction
i. Solid broach
ii. Built up of replaceable section
iii. Inserted tooth broach
iv. Overlapping teeth broach
v. Progressive cut broach
18. Broaching tool materials
i. High speed tool steels such as alloy
steel and stainless steel
ii. TiN coated carbides
iii. Aluminium
iv. Brass
v. 12L14
25. Like any other machining, broaching is also
accomplished through a series of following
sequential steps :
• Selection of broach and broaching machine
• Mounting and clamping the broach in the broaching
machine
• Fixing workpiece in the machine
• Planning tool - work motions
• Selection of the levels of the process parameters and
their setting
• Conducting machining by the broach.
27. Different Types Of Broaches And Their
Applications
Broaches can be broadly classified in several aspects
such as,
• Internal broaching or External broaching
• Pull type or Push type
• Ordinary cut or Progressive type
• Solid, Sectional or Modular type
• Profile sharpened or form relieved type
28. Internal broaching and broaches
•Internal broaching tools are used to enlarge and finish various
contours in through holes preformed by casting, forging,
rolling, drilling, punching etc.
•Internal broaching tools are mostly pull type but may be push
type also for lighter work.
•Pull type internal broaching tools are generally provided with
a
•set of roughing teeth followed by few semi-finishing teeth
and then some finishing teeth which may also include a few
burnishing teeth at the end.
32. External broaching
•External surface broaching competes with
milling, shaping and planing and, wherever
feasible, outperforms those processes in
respect of productivity and product quality.
•External broaching tools may be both pull and
push type.
34. Pull type and push type broaches
•During operation a pull type broach is subjected to tensile
force, which helps in maintaining alignment and prevents
buckling.
•Pull type broaches are generally made as a long single piece
and are more widely used, for internal broaching in particular.
•Push type broaches are essentially shorter in length (to avoid
buckling) and may be made in segments.
•Push type broaches are generally used for external broaching,
•preferably, requiring light cuts and small depth of material
removal.
35. Ordinary – cut and Progressive type broach
•Most of the broaches fall under the category of Ordinary – cut
type where the teeth increase in height or protrusion gradually
from tooth to tooth along the length of the broach.
•By such broaches, work material is removed in thin layers
over the complete form.
•Progressive – cut type broaches have their teeth increasing in
width instead of height.
36. Progressive – cut type
broaches;
(a) single bar and
(b) double bar type
38. ADVANTAGES AND LIMITATIONS OF BROACHING
Major advantages
• Very high production rate (much higher than milling,
planing, boring etc.)
• High dimensional and form accuracy and surface finish of
the product
• Roughing and finishing in single stroke of the same cutter
• Needs only one motion (cutting), so design, construction,
operation and control are simpler
• Extremely suitable and economic for mass production
39. Limitations
• Only through holes and surfaces can be machined
• Usable only for light cuts, i.e. low chip load and unhard
materials
• Cutting speed cannot be high
• Defects or damages in the broach (cutting edges) severely
affect product quality
• Design, manufacture and restoration of the broaches are
difficult and expensive
• Separate broach has to be procured and used whenever size,
shape and geometry of the job changes
• Economic only when the production volume is large.
41. Basic Purpose of Use of Gears
Gears are widely used in various mechanisms and
devices to transmit power and motion positively
(without slip) between parallel, intersecting ( axis) or
non-intersecting non parallel shafts,
• without change in the direction of rotation
• with change in the direction of rotation
• without change of speed (of rotation)
• with change in speed at any desired ratio
43. Gears are broadly classified
(a) According to configuration
• External gear
• Internal gear
Configuration of (a) external and (b) internal gears
44. (b) According to axes of transmission
Spur gears – transmitting rotation between parallel shafts
o Straight toothed
o Helical toothed
⎯ Single helical
⎯ double helical
(herringbone)
45. Bevel gears – transmitting motion between
intersecting shafts (axes)
o Straight toothed
o Helical toothed
⎯ Spiral bevel gear
Helical toothed bevel gears are used for smoother and larger
torque transmission.
46. Gears transmitting motion and power between non-
parallel non-intersecting shafts
o Worm and worm wheel
o Spiral gears
o Skewed or hypoid bevel
gears
47. (c) According to pattern of motion
• Rotation to rotation : wheel type gears
• Rotation to translation or vice versa – e.g. rack and pinion
o Straight toothed
48. Materials generally used for making gears are :
Δ Ferrous metals – for high loads
• Grey cast iron – preferred for reasonable strength and wear
resistance, ease of casting and machining and low cost
• Forged or rolled high carbon steels and alloy steels (Ni-Cr, Mo etc.)
which are either fully hardened or surface hardened for use under
high stresses and speed.
Δ Non ferrous metals – for light load
• Aluminium, bronze and brass are used for making gears having fine
teeth and working at very light load – e.g., in equipments, toys etc. or
against hard steel mating gears
• Aluminium alloys like aluminium bronze, Zinc – Al. alloy etc.
Δ Non-metals – widely used for light load, non-precision and noiseless
operation. Polymers (plastics) : both themoplastic and thermosetting type
and various composites (metals, graphite,
49. Size or major dimensions
Dimensional features that are used to express or
specify the gears are ;
Δ For spur gears and worm wheels
⎯ number of teeth, z
⎯ module, m
⎯ helix angle, if any (θ)
⎯ width (b)
Pitch Circle Diameter (PCD) = mZ/cosθ
50. • Gear geometry
Some geometrical features also need to be
mentioned while specifying gears, such as,
Δ Pressure angle
Δ Addendum and dedendum
51. • Special features
If there be any special feature, that also has to be included
with gear specification, such as
⎯ Tooth bevelling for safe handling
⎯ Tooth crowning for uniform wear and long service life
⎯ Tooth rounding for easy engagement
52.
53.
54. SAND CASTING
Characteristics :
• Cheaper low quality gear in small numbers
• The tooling costs are reasonable
• Poor Surface finish and dimensional accuracy
• Due to low precision and high backlash, they are noisy.
• They are suited for non- critical applications
Applications: (without finishing operation)
Toys , small appliances, cement-mixer barrels, Hoist
gearbox of dam gate lifting mechanism, Hand operated
crane etc.,
Materials:
C I, cast steel, bronzes, brass, ceramics
55. DIE-CASTING
Characteristics :
• Better surface finish and accuracy (tooth spacing and
concentricity)
• High tooling costs
• Suited for large scale production Applications:
Applications: Instruments, cameras, business machines,
washing machines, gear pumps, small speed reducers, and
lawn movers.
Materials:
Zinc, aluminium and brass
The gears made from this process are not used for high speeds
and heavy tooth loading. Normally applied for small size gears.
56. INVESTMENT CASTING OR LOST WAX PROCESS
Characteristics:
• Reasonably accurate gears
• Applicable for a variety of materials
• Refractory mould material
• Allows high melt-temperature materials
• Accuracy depends on the original master pattern used for
the mold.
Materials:
• Tool steel, Nitriding steel, Monel, Beryllium copper.
• The process is used only if no other process is suitable
since production cost is high.
69. Manufacture of Gears
Stages generally are :
⎯ Preforming the blank without or with teeth
⎯ Annealing of the blank, if required, as in case of forged or
cast steels
⎯ Preparation of the gear blank to the required dimensions by
machining
⎯ Producing teeth or finishing the preformed teeth by
machining
⎯ Full or surface hardening of the machined gear (teeth), if
required
⎯ Finishing teeth, if required, by shaving, grinding etc.
⎯ Inspection of the finished gears.
70. Preforming Gear Blanks
Casting
• Sand casting
• Metal mould casting
• Die casting
• Investment casting
• Shell mould casting
• Centrifugal casting
Manufacture of gears by rolling
Powder metallurgy
Blanking in Press tool
Plastic moulding
Extrusion process
Wire EDM
71.
72.
73. Production of Gear Teeth by Machining
• Preformed blanks of approximate shape and irregular surface
are machined to desired dimensions and finish and then the
teeth are produced generally by machining and occasionally
by rolling.
• Full gears with teeth are made by different processes and
then finished by further machining and / or grinding
• Accurate gears in finished form are directly produced by near
– net – shape process like rolling, plastic moulding, powder
metallurgy etc., requiring slight or no further finishing.
74. Gear teeth are produced by machining based
on
ο Forming – where the profile of the teeth are obtained as the
replica of the form of the cutting tool (edge); e.g., milling,
broaching etc.
ο Generation – where the complicated tooth profile are
provided by much simpler form cutting tool (edges) through
rolling type, tool – work motions, e.g., hobbing, gear shaping
etc.
75. Methods of production of gear teeth by
machining on Forming principle
Shaping, planing
and slotting
Milling
Parallel multiple
teeth shaping
Broaching
76. Gear teeth can be produced by both disc and end mill type
form milling cutter
78. Production of gear teeth by machining on Generation
principle
Generation method is characterised by automatic indexing
and ability of a single cutter to cover the entire range of
number of teeth for a given combination of module and
pressure angle and hence provides high productivity and
economy.
79. Sunderland method using rack type cutter
Rack type HSS cutter (having rake and clearance angles)
reciprocates to accomplish the machining (cutting) action
while rolling type interaction with the gear blank like a pair
of rack and pinion.
80. Gear shaping
Gear shaping is similar to the rack type cutting process,
excepting that, the linear type rack cutter is replaced by a
circular cutter
81. Gear Hobbing
HSS or carbide cutter having teeth like gear milling cutter and the gear
blank apparently interact like a pair of worm and worm wheel.
82. Having lesser number (only three) of tool – work
motions, hobbing machines are much more rigid,
strong and productive than gear shaping machine.
But hobbing provides lesser accuracy and finish and
is used only for cutting straight or helical teeth
(single) of external spur gears and worm wheels.
Gear Hobbing
83. Hob teeth are shaped to match the tooth space and are interrupted with
grooves to provide cutting surfaces
It rotates about an axis normal to that of the gear blank, cutting into the
rotating blank to generate the teeth
Most accyrate of the roughing processes since no repositioning of tool
or blank is required and each tooth is cut by multiple hob-teeth,
averaging out any tool errors
Excellent surface finish is achieved by this method and it is widely
used for production of gears
Gear Hobbing
85. Manufacture of bevel gears
In manufacture of bevel gears, first the blanks are
preformed by casting or forging followed by
machining to desired dimensions in lathes or special
purpose machine.
Then the teeth are produced in the blank by
machining.
86. Straight toothed bevel gear
o Forming by milling cutter – low productivity and quality
hence employed for production requiring less volume and
precision
o Generation – high accuracy and finish, hence applied for
batch to mass production.
In generation process, the inner flanks of two adjacent teeth
are developed with involute profile by the straight teeth of the
cutters under rolling action.
91. Manufacture of Spiral gears
Two common production methods of spiral bevel gears in
gear industry are face-milling and face-hobbing
92. During the tooth generation process, in the face-milling
technique, the cutting wheel interacts with one tooth
space and is then indexed to the next location.
The process continues until all tooth spaces are finish
cut to the required depth.
In the face-hobbing technique individual cutting blades
interact with different tooth spaces.
Face-hobbing is a continuously indexing tooth
generation process, where all the teeth are cut a little at a
time, until all the teeth are finished to the final desired
depth.
With the face hobbing process, the curve in the
lengthwise direction of the tooth is an extended epicycloid
and is a function of the relative roll between the workpiece
and the cutter.
93.
94. Spiral bevel gears are cut with a generating
machine that uses a series of cutting blades
mounted on a circular tool holder. The tooth
profiling between the cutter and the generating
tooth does not require any rotation of the
generating gear
95. Manufacture of worm
Screw like single or multi-start worms (gears) made of
steel are generally made by machining like long thread
milling or by cold rolling like thread rolling followed
by heat treatment for surface hardening and finishing
by grinding.
96.
97. Gear Errors
Forming principle – Gear errors due to
(i) Incorrect profile of the cutting
(ii) Incorrect positioning of the tool with respect
to the tool
(iii) Incorrect indexing of the blank
Generation principle – Gear errors due to
(i) Errors in the manufacture of the cutting tool
(ii) Errors in the positioning of the tool with
respect to the work
(iii) Error in the relative motion during the
generating
99. Methods of gear teeth finishing
Gear teeth, after preforming and machining, are finished
generally by;
For soft and unhardened gears
• gear shaving
• gear rolling or burnishing
For hard and hardened gears
• grinding
• lapping
For soft but precision gears
• shaving followed by surface hardening and then lapping
100. Gear shaving
Teeth of straight or helical toothed external spur gears and worm
wheels of moderate size and made of soft materials like aluminium alloy,
brass, bronze, cast iron etc. and unhardened steels are mostly finished by
shaving process.
Finishing action of shaving cutters work apparently as a spur gear, rack
or worm in mesh with the conjugate gears to be finished.
All those gear, rack or worm type shaving cutters are of hard steel or
HSS and their teeth are uniformly serrated to generate sharp cutting
edges.
While interacting with the gears, the cutting teeth of the shaving cutter
keep on smoothening the mating gear flanks by fine machining to high
accuracy and surface finish.
101. Shaving is similar to gear shaping, but uses accurate
shaving tools to remove small amounts of material from a
roughed gear to correct profile errors improve surface
finish
Gear
Shaving
102. For such minute cutting action, the shaving teeth need an actual or
apparent movement relative to the mating teeth along their length.
105. Gear rolling or burnishing
In this method the machined gear is rolled under
pressure with three hardened master gears of high
accuracy and finish.
Minute irregularities of the machined gear teeth are
smeared off by cold plastic flow, which also helps in
improving the surface integrity of the desired teeth.
106. Gear teeth grinding
• Grinding is a very accurate method and is, though relatively
expensive, more widely used for finishing teeth of different
type and size of gears of hard material or hardened surfaces.
• Properly formed and dressed wheel finishes the gear teeth
flanks by fine machining or abrading action of the fine
abrasives.
Like gear milling, gear grinding is also done on two principles
Forming
Generation, which is more productive and accurate
107.
108. Gear Lapping
Principle:-
It is the process of refining the gear element after the heat
treatment.
Process is done by rotating the gear and the lap tool as inter
meshing gears, with abrasive compound forced between the
teeth.
• It is the process used for improving surface finish by
reducing roughness, waviness & other irregularities on the
surface.
• Material for lapping tool can be natural or artificial abrasives
depending on work piece material.
• Lubricant is used to hold or retain the abrasive grains during
operation.
109. Lapping operation is done two methods
1. Hand lapping:- Work piece is held in hand & the
motion of the other enables the rubbing of two
surfaces in contact, this method is used for press dies,
valve seats etc.
2. Machine lapping:- It is done to obtain highly
finished surfaces on work piece, like ball and roller
bearings , engine parts.
111. Gear Honing
Principle
• It is a super finishing operation used for previously
machined surfaces.
• It is used for finishing internal cylindrical surfaces,
drilled or bored holes the tool is called as Hone which
is made out of bonded abrasive stone made in the form
of stick.
• The tool moves back & fourth while rotating about
its axis.
