1. UNIT – 4
ABRASIVE PROCESSES
AND
GEAR CUTTING

2. SYLLABI
Abrasive processes: grinding wheel -
specifications and selection, types of
grinding process - cylindrical grinding,
surface grinding, centreless grinding - Gear
Finishing Process-honing, lapping, super
finishing, polishing and buffing, abrasive jet
machining, Gear cutting, forming, generation,
shaping, hobbing

3. Abrasive Process
• Abrasive machining Process is one of the
oldest forms of metal removal. It is also one
of the most important. Abrasive machining
can produce surface finishes ranging from
rough to extremely fine.
• Abrasive machining is a process where chips
are formed by small cutting edges on abrasive

4. CLASSIFICATION OF MACHINING BY
ABRASION

5. INTRODUCTION
• Grinding is a material removal process in which
abrasive particles arc contained in a bonded
grinding
• The metal is removed with the help of rotating
grinding wheel.
• The grinding wheel is usually disk shaped and is
precisely balanced for high rotational speeds.

6. Grinding Machine

7. Grinding wheel

8. Grinding Wheel Parameters
• Abrasive material
• Grain size
• Bonding material
• Wheel grade
• Wheel structure

9. Abrasive Material Properties
• High hardness
• Wear resistance
• Toughness
• Friability - capacity to fracture when cutting
edge dulls, so a new sharp edge is exposed

10. Abrasives
• Grinding wheel is made up of small abrasive
particles held together by bonding material.
Thus it forms a multi edge cutter.
CLASSIFICATION
1. Natural Abrasives
2. Artificial Abrasives

11. 1. Natural Abrasives
These are obtained from mines
a) Sandstone or solid quartz
b) Emery (50 – 60 % crystalline Al2O3 + iron oxide)
c) Corundum (75-90 % crystalline Al2O3 + iron oxide)
d) Diamond

12. 2. Artificial Abrasives
• To achieve the require property we go for
artificial abrasives than natural.
• These are manufactured under some pressure
and temperature in a furnace
• Aluminium oxide
• Silicon carbide
• Artificial Diamond
• Boron Carbide
• Cubic boron nitride

13. Traditional Abrasive Materials
• Aluminum oxide (Al2O3) - most common abrasive
– Used to grind steel and other ferrous high strength alloys
• Silicon carbide (SiC) - harder than Al2O3 but not as
tough
– Used on aluminum, brass, stainless steel, some cast irons and
certain ceramics

14. Newer Abrasive Materials
• Cubic boron nitride (CBN) – very hard, very expensive
– Suitable for steels
– Used for hard materials such as hardened tool steels and
aerospace alloys
• Diamond – Even harder, very expensive
– Occur naturally and also made synthetically
– Not suitable for grinding steels
– Used on hard, abrasive materials such as ceramics, cemented
carbides, and glass

15. Grain Size
• Coarse grained (small grit number)wheels are
produce rough grinding.
• Fine grained (larger grit number) wheels are
produce finish grinding.
• Soft grade wheels are used for grinding hard
materials.
• Hard grade wheels are used for grinding soft
materials.

16. Bonding Material Properties
• Must withstand centrifugal forces and high temperatures
• Must resist shattering during shock loading of wheel
• Must hold abrasive grains rigidly in place for cutting yet allow
worn grains to be dislodged to expose new sharp grains

17. Wheel Structure
Refers to the relative spacing of abrasive grains
in wheel
• In addition to abrasive grains and bond
material, grinding wheels contain air gaps or
pores
• Volumetric proportions of grains, bond
material, and pores can be expressed as:
0
1.


 p
b
g P
P
P

18. Typical structure of a grinding wheel.
Wheel Structure

19. Wheel Structure
• Measured on a scale that ranges
between "open" and "dense."
– Open structure means Pp is relatively large
and Pg is relatively small - recommended
when clearance for chips must be provided
– Dense structure means Pp is relatively small
and Pg is larger - recommended to obtain
better surface finish and dimensional
control

20. Grinding wheel marking

21. Grinding wheel marking
Wheel grade (Hardness)
Very soft: A,B,C,D, E, F, and G
Soft: H, I, J, K
Medium: L, M, N, O
Hard: P, Q, R, S
Very hard: T, U, V, X, Y, Z
Soft grades are, generally, used for machining hard materials
Hard wheels are used for soft materials
Wheel bond
Vitrified (V)
Resinoid (B)
Silicate (S)
Rubber (R)
Shellac (E)
Oxychloride (O)
Metal

22. GRINDING WHEEL Markings
Wheel structure
Open structure wheels are used for high material
removal rates and consequently produce a rough
surface finish.
Dense structures are used for precision form grinding
operations.
Very compact: 1, 2
Compact: 3, 4
Semi-compact: 5, 6
Porous: 7, 8
Very porous: 9, 10
Extra porous: 11 to 15

23. TYPES OF BOND
• Various types of bonds used in their choice depends on
operating conditions of abrasive tool such as
grinding speed
pressure on the tool
heat formation in the grinding zone
S.NO BOND TYPE BOND
1 Organic Resinoid , rubber , oxy-Chloride
2 Non - Organic Metallic, Vitrified and silicate bond

24. 1. Vitrified Bond
• This is made of the mixture of clay and water.
• This mix is placed in mould to get require shape in
wheel
• Then the dried wheel is fed in to furnace few days at
a temperature of 1260 deg.celcius.
• This fusing gives the uniformity in the bond.
• Then the wheel is trimmed to
required shape & size.

25. 2.Silicate Bond
• The abrasive particles are mixed with silicate of soda.
• Then the mixture is moulded to get a required shape and
dried for few hours
• Then its kept in a furnace at about 260’c for 20 – 80 hours
• This wheel having moderate tensile strength
• Its used more rapidly
than vitrified bond

26. 3. Resinoid Bond
• The abrasive particles are mixed with synthetic resins.
• This mixture is rolled to get a required shape & size
• Then its kept in a furnace at about 210 – 250 ‘c for few
hours
• At this temp. the resins hold the abrasive particles firmly.
• This wheel is strong and elastic
• Operating speeds at 300m/min.
• Used to machine cast iron ,
malleable cast iron.

27. 4. Rubber Bond
• The abrasive particles are mixed with liquid rubber and
sulphur.
• This mixture is rolled in to sheet for require thickness and
then vulcanized.
• These are strong bonds having closed grains in thin sections
also.
• Its mainly used for very close surface finish. And also used in
centreless grinding

28. 5. Shellac Bond
• The abrasive particles are mixed with shellac.
• Then the mixture is rolled and pressed to require shape
and size.
• Then its kept in furnace at about 160’c for few hours
• These are strong and posses some elasticity like rubber
bond
• Used in the finishing of cam shaft and mill rolls

29. 6.Oxy-Chloride Bond
• The abrasives are mixed with oxide and chloride of
magnesium.
• Then its is moulded to required shape and size
• Then its kept in a furnace for few hours
• These wheels are less brittle and less sensitive to side loads
as compared to vitrified bond.
• No coolant required in operation

30. FACTORS IN SELECTION OF GRINDING
WHEEL
COSTANT FACTORS
1. Material to be machined
2. Material removal rate
3. Area of contact
4. Type of grinding machine
VARIABLE FACTORS
1. Work speed
2. Wheel speed
3. Condition of grinding machine
4. Personal factors ---- (labour ability)

31. Truing & Dressing of grinding wheel
• Dressing is the term used
to describe the process of
cleaning the periphery of
grinding wheels. This
cleaning breaks away dull
abrasive grains and
smoothes the surface so
that there are no grooves.
• Truing is the term used to
describe the removal of
material from the cutting
face of the wheel
(Trimming)
• so that the resultant
surface runs absolutely
true to some other surface
such as the grinding wheel
shaft.

32. Types of dressing tools
1. Star wheel dressing tool
2. Round abrasive stick
3. Diamond dressing tool

36. Shapes of grinding wheel

37. Mounting wheels and points
• These are small grinding wheels of different
shapes.
• This is attached to the shank of the portable
grinding machine

38. Types of grinding
machine

39. Types grinding machines
1. Rough grinders
(a) Floor stand grinders (b) Bench grinders (c) Portable grinders
(d) Abrasive belt grinders (e) Swing frame grinders
2. Precision grinders
(a) Cylindrical grinders
(i) Plain centre type grinders (ii) Universal centre type grinders
(iii) Centreless grinders
(b) Internal grinders
(i) Chucking type grinders (ii) Planetary type grinders
(iii) Centreless grinders
(c) Surface grinders
(i) Horizontal spindle – reciprocating table
(ii) Horizontal spindle – rotary table
(iii) Vertical spindle – reciprocating table
(iv) Vertical spindle – rotary table
(v) Tool and cutter grinders
(vi) Special grinders

40. Floor stand grinder

41. Bench grinder

42. Portable Grinder

43. Abrasive belt Grinder

44. Swing Frame Grinder

45. Precision Grinder
- Cylinderical Grinder

46. TYPES OF OPERATIONS IN
CYLINDRICAL GRINDING
(i). Traverse grinding.
(ii). Plunge grinding.

47. Traverse Grinder

48. Plunge cut Grinder

49. CYLINDERICAL GRINDING

50. PLAIN CENTRE TYPE
CYLINDERICAL GRINDING MACHINE

52. USES
• Used for machining cylindrical parts and also for
tapers , fillets, contoured cylinders etc.
• It has base
head stock
tail stock
wheel head

53. UNIVERSAL GRINDING MACHINE

54. Universal grinding Machine
• These grinders are used in tool room for grinding tools.
• It has same operation as like of plain type grinding M/C
• The wheel head can be swiveled into any shape
• The head stock can be swiveled in to any angle in
horizontal plane.

55. Surface grinder
• To machine flat plane surface
• The various machine parts such as machine guide ways,
piston rings, dies, surface plates, valves are finished by
surface grinding.
• Small work pieces are held by magnetic chuck and heavy
work pieces are clamped on the table by means of pads,
strap clamps and other devices or fixtures.
Types
1. Horizontal spindle reciprocating table surface grinder
2. Horizontal spindle Rotary table surface grinder
3. Vertical Spindle reciprocating table surface grinder
4. Vertical Spindle Rotary table surface grinder

56. Horizontal spindle reciprocating table
surface grinder

57. Horizontal spindle Rotary table surface
grinder

58. Vertical Spindle reciprocating table
surface grinder

59. Vertical Spindle Rotary table surface
grinder

60. CENTRELESS GRINDING MACHINE

61. CENTRELESS GRINDING
• Its performed on the work pieces which do not
having centers such as pistons, valves, rings, tubes,
balls, wrist pins, drills , bushings, shafts etc
• It can be done on both external and internal
cylindrical surfaces.
• It has two wheels – larger grinding wheel
small regulating wheel

62. CENTRELESS GRINDING
The regulating wheel make the work piece to rotate.
So the work piece is pressed between the wheel
Grinding wheel only remove the material

63. METHODS OF CENTRELESS GRINDING
• Through feed -
This is used for machining lengthy work piece. Regulating wheel
tilted to some angle.
• In Feed –
Its similar to plunge grinding. The end stop limit the axial
movement of the work piece
• End Feed –
Here both grinding and regulating wheels are tapered. So it can
machine tapered surfaces

64. INTERNAL GRINDERS
• They are used to finish straight , tapered or formed
holes to the correct size, shape and finish.
1. Chucking type
2. Planetary Type
3. Center less Type

65. Chucking type Internal Grinder
• The work is held in the
chuck and rotated.
• The rotating grinding
wheel is moved from
left to right for making
hole

66. Planetary Type Internal Grinder
• Here the work is
stationary and the
rotation of the wheel
spindle gives an eccentric
motion according to the
diameter of the hole to
be ground

67. Center less Type Internal Grinder
• It has the same working
like external centre less
grinding. The work is
supported by three
rollers.
• It has one regulating
wheel and supporting
wheel and one pressure
roll to hold the work
piece on the other two
wheels
The grinding wheel directly contact the inside diameter of the
work piece and reciprocates about its axis for the given feed.

68. SPECIAL PURPOSE GRINDING
MACHINE

69. USES
• Its designed to do specific works
• like forming , gear teeth grinding, thread grinding,
cam grinding , tool and cutter grinding etc.

70. FORM GRINDING
• To produce complex
shapes.
• EXAMPLE.
DOVE TAIL WAY

71. Gear Teeth Grinding
• Two methods
Gear generating Process – using 2 saucer type wheel
Gear Forming Process – Using Form tool with fixtures

72. Thread Grinding
• Its same like forming process.
• The grinding wheel itself having the contours
of the thread to be machined on the work
piece

73. Cam Grinder
• From the rotation of cam
shaft , the grinding wheel
having the up and down
movement in radial
direction.
• A hardened steel roller in
conjunction with the
template actuates the
movement of whole unit to
produce the desired shape

74. Tool post grinder
• This grinder is mounted on the tool post of
the lathe for doing small operations.

75. Disc Grinder
• This is for removing material rapidly.
• Used for small polishing work
• Operated by hand wheel.

76. Tool and Cutter Grinder

77. Tool and Cutter Grinder
• To reconditioning various tools like milling, drilling,
tapping, hobs and single point tools
• By using special attachment this machine perform
various operations
• Single purpose and cutter grinder – to grind drills , tool bits
• Universal tool and cutter grinder – to sharpening milling tool ,
reamer, special driller etc.

78. HONING
• Honing is a low abrading process using
bonded abrasive sticks for removing stock
from metallic and non-metallic surfaces.
However, it can also be used for external
cylindrical surfaces as well as flat surfaces, for
which it is rarely used. Commonly it is used for
internal surfaces.

79. Honing Conditions
All materials can be honed. However, the
material removal rate is affected by the
hardness of the work material. The typical rates
are:
• Soft material 1.15 mm/min on diameter
• Hard materials 0.30 mm/min on diameter

80. LAPPING
Lapping is generally the final finishing operation
done with loose abrasive grains. The process is
employed to get
• Extreme accuracy of dimension
• Correction of minor imperfection of shape
• Refinement of surface finish
• Close fit between mating surfaces

81. SUPER FINISHING

82. SUPER FINISHING

83. POLISHING AND BUFFING
• Both these processes are used for making the surfaces
smoother along with a glossy finish. Polishing and buffing
wheels are made of cloth, felt or such material, which is soft
and have a cushioning effect. Polishing is done with a very fine
abrasive in loose form smeared on the polishing wheel with
the work rubbing against the flexible wheel. A very small
amount of material is removed in polishing. In buffing the
abrasive grains in a suitable carrying medium such as grease
are applied at suitable intervals to the buffing wheel.

84. ABRASIVE BELT GRINDING
This method is most suitable for flat surfaces.
However, cylindrical surfaces can also be belt
ground by using a suitable contact wheel.
Abrasive belt with a very fine grit may be used
for polishing application.

85. ABRASIVE JET MACHINING
• 10 % MATERIAL REMOVAL BY ABRASIVE JET
• 90% MATERIAL REMOVAL BY WHEEL
Abrasive jet machining is the
process of impinging the high-
speed stream of abrasive particles
by high-pressure gas or air on the
work surface through a nozzle and
metal removal occurs due to
erosion caused by high-speed
abrasive particles.
Because of repeated impacts small
bits of material get loosened which
is carried away by jet and exposing
the fresh surface to the jet.

86. Applications
• Cutting slots and thin sections.
• Contouring and drilling operation.
• Producing shallow crevices and deburring.
• Producing intricate hole shapes in a hard and
brittle material.
• Cleaning and polishing the plastic, nylon and
Teflon component.
• Frosting of the interior surface of glass tubes.
• Etching of marking of glass cylinders.
• Machining super-alloys and refractory material.

87. GEAR CUTTING

88. GEAR CUTTING METHODS
• By single point form tool
• By shear speed shaping process
• Gear milling using a formed end mill
• Gear broaching
• Template method

89. Gear cutting - single point form tool
• Using the single point cutting tool in planner and
shaper we can produce spur and bevel gears.
• Here form tool is used to make gear on the blank.
• The work is held between the centers and the cutter
reciprocates along the length of the work piece.

91. Gear cutting - speed shaping process
• Here the form tools are arranged radially in the cutter
head.
• The number of form tools are equal to the number of
teeth to be cut on the gear blank
• All the tooth spaces are cut at the same time by feeding
along with tools towards the centre of the blank during
cutting stroke
• The depth of cut can be adjusted by radial movement.

93. Gear milling using a formed end mill
• The cutting edges are formed to
the shape of the gear tooth
space.
• The formed end mill cutter is
held on the spindle of a vertical
milling machine
• The blank is held in the dividing
head and fed against the cutter.
• The axis of cutter and blank is
perpendicular to each other

95. GEAR GENERATION PRINCIPLE

96. Principle
• This is based on the fact that any two involutes gears
of same module will mesh together.
• One of the meshing gear as cutter and the other will
reciprocate and rotate along the width
• For producing high accurate gears the following
process are used
Gear Shaping Process
Gear Planning Process
Gear Hobbing process

97. Gear Shaping Process
• A pinion type of cutter is used.
• Proper angles are given to the
cutter initially
• A hole is made on the cutter for
mounting on a stub arbor or
spindle of the machine.
• The cutter axis and work axis
are parallel to each other.
• The cutter reciprocates
vertically and parallel to the
axis of the blank.
• During this both cutter and
work rotated slowly.
• So the rotation of the cutter
generates the gear profile.

99. Gear Hobbing
• The gear blank is
mounted on a rotating
vertical arbor
• The rotating hobber is in
horizontal position
• The intersection of these
two makes a gear profile
on the blank.

103. FINISHING OF GEAR

104. GEAR SHAVING

106. ROLL FINISHING OF GEAR TOOTH

107. GEAR BURNISHING

108. GEAR LAPPING (Polishing machine)
• It’s a fine polishing process carried out by hand or machine.
• The fine abrasive particles are mixed with oil like vegetable
oil, mineral oil, kerosene, olive oil and machine oil.
• This oil is fed between the two surfaces .
• Then the surfaces are rubbed or rotated one over other for
getting fine finishing.

109. Types of lapping
• Hand lapping – for doing ordinary
operations.
example : moulding die , press die

110. Types of lapping – machine lapping
• Machine lapping - for getting highly finished jobs.
ex – crank shaft , piston, gauges, bearing etc.

111. Lapping media
• Metal laps and abrasive powder
• Bonded abrasive
• Abrasive paper or cloth

112. OTHER PROCESS
• POLISHING - This is Similar to grinding
process .using abrasive belt or coated wheel
we polish the work surface. The wheel is made
up of abrasive paper, cloth etc
BUFFING ----- Using the binding solution the
fine abrasive particles are added to rotating
wheel. Then this wheel is rotated on work for
fine finishing

113. GEAR HONING PROCESS
• It’s a process carried out for finishing
previously machined surfaces.
• Its mostly used for finishing internal
cylindrical surfaces such as drilled or
bored holes

114. Horizontal honing machine
• There is no reciprocating motion to the work in the
machining process.
• But the honing tool rotated and reciprocated for
machining lengthy work piece.

115. Vertical honing machine
• The work is stationary
• But the honing tool in the vertical spindle rotated
and reciprocated to machine the work piece.

116. Advantages
– Favourable surface texture reduces the noise
emission in the transmission.
– Induced residual stresses in tooth flanks increase
the bearing capacity.
– Low cutting speed prevents structure damages
(burning).
– It needs low cost and the process is economical process.
– It reduces or corrects the geometrical errors induced by
previous manufacturing or finishing processes.

117. Disadvantages of gear honing
• It has limited life of honing gear tool.
• Honing time is increased as error in tool shape
increases.

118. Applications of gear honing
• It can be used for finishing hardened external
and internal gears.
• Honing can do crowning of gears
• Applied to improve the geometric accuracy
and surface conditions and to remove nicks
and burrs.
• It is used for minor corrections in tooth shape
which increases wear resistanceand reduces
noise generation.