Mechanics of chip formation, single point cutting tool, forces in machining - Types of chip - cutting tools- nomenclature, orthogonal metal cutting, Thermal aspects, Cutting tool materials, tool wear, tool life, surface finish, cutting fluids and Machinability.

1. UNIT - 1
THEORY OF METAL CUTTING

2. SYLL
Mechanics of chip formation, single point
cutting tool, forces in machining, Types of
chip, cutting tools– nomenclature, orthogonal
metal cutting, thermal aspects, cutting tool
materials, tool wear, tool life, surface finish,
cutting fluids and Machinability.

3. FOLLOWING OBJECTIVES OF ECONOMICS
AND EFFICIENT MACHINING PROCESSES
Quick metal removal.
High-class surface finish.
Economy in tool cost.
Less power consumption.
The minimum idle of machine tools.

4. METAL REMOVING PROCESSES
• Non-cutting process (or) Chipless process
• Cutting process (or) Chip process

5. What is a Cutting Tool
• A cutting tool is any tool that is used to
remove metal from the work piece by means
of shear deformation.
• It is one of most important components in
machining process
• It must be made of a material harder than
the material which is to be cut, and the tool
must be able to withstand the heat
generated in the metal cutting process.
• Two basic types
– Single point
– Multiple point 5

6. Single Point Cutting Tool

7. Multi Point Cutting Tool

8. 8
Single Point Cutting
Tool

9. Single point cutting tool

10. Know the Single Point Cutting
Tool
• Shank: Main body of tool, it is part of
tool which is gripped in tool holder
• Face: Top surface of tool b/w shank
and point of tool. Chips flow along this
surface
• Flank: Portion tool which faces the work. It is surface adjacent to &
below the cutting edge when tool lies in a horizontal position.
• Point: Wedge shaped portion where face & flank of tool meet.
• Base: Bearing surface of tool on which it is held in a tool holder.
• Nose radius: Cutting tip, which carries a sharp cutting point. Nose
provided with radius to enable greater strength, increase tool life
& surface life.
Typical Value : 0.4 mm – 1.6 mm

11. SPC Tool
Geometry
11

12. Angle of Single Point Tool
The most significant terms in the geometry of a
cutting tool angles are:
–Relief or clearance angle
» Side relief
» End relief
–Rake angle
» Back Rake angle
» Side Rake angle
–Cutting edge angle
» Side Cutting edge angle
» End Cutting edge angle
» Nose Radius
12

13. Cutting-Tool Terms
Rake angle:
Ground on a tool to provide a smooth flow of the chip over
the tool so as to move it away from the work piece
13
Back Rake angle
• Ground on the face of the
tool
• Influences the angle at
which chip leaves the nose
of the tool
• Generally 8 - 100
Side Rake angle
• Ground on the tool face
away from the cutting edge
• Influences the angle at
which the chip leaves the
work piece
• A lathe tool has 140 side
rake.

14. Side Rake Angle
• Large as possible to allow
chips to escape
• Amount determined
– Type and grade of cutting tool
– Type of material being cut
– Feed per revolution
• Angle of keenness
– Formed by side rake and side
clearance
14

15. Back Rake Angle
• Angle formed between top face of tool and top
of tool shank
– Positive
• Top face slopes downward
away from point
– Negative
• Top face slopes upward
away from point
– Neutral
15

16. Rake Angles
• Small to medium rake angles cause:
– high compression
– high tool forces
– high friction
– result = Thick—highly deformed—hot chips

17. Cutting-Tool Terms
17
Functions:
• Strengthens finishing
point of tool
• Improves surface
finish on work
• Should be twice
amount of feed per
revolution
• Too large – chatter; too
small – weakens point
Nose Radius:
• Rounded tip on the point of the tool

18. Tool Angle Application
• Factors to consider for tool angles
– The hardness of the metal
– Type of cutting operation
– Material and shape of the cutting tool
– The strength of the cutting edge

19. Cutting Tool Geometry
• Cutting tool is device with which a material could be cut to the desired size, shape or finish.
So a cutting tool must have at least a sharp edge. There are two types of cutting tool. The
tool having only one cutting edge is called single point cutting tools. For example shaper
tools, lathe tools, planer tools, etc. The tool having more than one cutting edge is called
multipoint cutting tools. For example drills, milling cutters, broaches, grinding wheel honing
tool etc.
• A single point cutting tool may be either right or left hand cut tool depending on the
direction of feed.
25/19
Primary Cutting Edge
Right hand cutting
tool
Left hand cutting
tool

20. Tool-in-hand Nomenclature
• The geometry of a cutting tool consists of the following elements: face or rake surface, flank,
cutting edges and the corner. Face or rake is the surface of the cutting tool along which the
chips flow out. Flank surfaces are those facing the work piece. There are two flank surfaces,
principal and auxiliary flank surfaces. Principal cutting edge performs the major portion of
cutting and is formed by the intersecting line of the face with the principal flank surface.
Auxiliary cutting edge (often called end cutting edge) is formed by the intersection of the rake
surface with the auxiliary flank surface. Corner or cutting point is the meeting point of the
principal cutting edge with the auxiliary cutting edge.
25/20
Auxiliary flank surface
Corner
Principal cutting edge
Rake or Face
Shank of tool
Tool axis
Principal flank surface
Auxiliary
cutting edge

21. Single Point Cutting Tool
25/21
Side clearance
angle (αx)
Nose radius (r)
Side cutting edge
angle (φs)
Back rake
angle (γy)
End
clearance
angle (αy)
End cutting edge
angle (φe)
Side rake angle (γx)
Note: All the rake and clearance
angles are measured in normal
direction

22. • Side Cutting Edge Angle (φs): The side cutting-edge angle (SCEA) is usually referred to as the lead angle. It
is the angle enclosed between the side cutting edge and the longitudinal direction of the tool. The value
of this angle varies between 0° and 90°, depending upon the machinability, rigidity, and, sometimes, the
shape of the workpiece. As this angle increases from 0° to 15°, the power consumption during cutting
decreases. However, there is a limit for increasing the SCEA, beyond which excessive vibrations take place
because of the large tool-workpiece interface. On the other hand, if the angle were taken as 0°, the full
cutting edge would start to cut the workpiece at once, causing an initial shock. Usually, the recommended
value for the lead angle should range between 15° and 30°.
25/22

23. • Auxiliary or End Cutting Edge Angle (φe): The end cutting-edge angle (ECEA) serves to
eliminate rubbing between the end cutting edge and the perpendicular to the tool shank.
the machined surface of the work piece. Although this angle takes values in the range of 5°
to 30°, commonly recommended values are 8° to 15°.
• Side Clearance Angle (αx) and End Clearance Angle (αy): Side and end clearance (relief)
angles serve to eliminate rubbing between the workpiece and the side and end flank,
respectively. Usually, the value of each of these angles ranges between 5° and 15°.
25/23

24. • Back Rake Angle (γy) and Side Rake Angle (γX): Back and side rake angles determine the direction of flow
of the chips onto the face of the tool. Rake angles can be positive, negative, or zero. It is the side rake angle
that has the dominant influence on cutting. Its value usually varies between 0° and 15°, whereas the back
rake angle is usually taken as 0°.
• Nose radius (r): Nose radius is favorable to long tool life and good surface finish. A sharp point on the end
of a tool is highly stressed, short lived and leaves a groove in the path of cut. There is an improvement in
surface finish and permissible cutting speed as nose radius is increased from zero value. Too large a nose
radius will induce chatter.
25/24

25. Designation of Cutting Tools
• By designation or nomenclature of a cutting
tool is meant the designation of the shape of
the cutting part of the tool. The following
systems to designate the cutting tool shape
which are widely used are:
– Tool in Hand System
– Machine Reference System or American Standard
Association (ASA) System
– Tool Reference System
• Orthogonal Rake System (ORS)
• Normal Rake System (NRS)
– Maximum Rake System (MRS)
– Work Reference System (WRS)
25/25

26. Classification of Metal cutting Process
• Orthogonal cutting (2 Dimensional cutting)
• Oblique cutting (3 Dimensional cutting)

27. Orthogonal cutting
• The cutting edge of the tool
perpendicular to the cutting
velocity.
• Chip flow over the tool face and
direction of chip-flow velocity is
normal to the cutting edge.
• The Max. chip thickness occurs
at its middle
• This cutting involves two forces
only
• Its also called 2-dimensional
cutting

28. Oblique cutting
• When the cutting edge is
inclined at an acute angle with
the normal cutting velocity
vector is called oblique cutting.
• Chip flow on the tool face
making an angle with the normal
to the cutting edge.
• The Max. chip thickness occurs
at its middle
• This cutting involves three
forces
• Its also called 3 –dimensional
cutting

29. .

30. CHIP FORMATION
The type of chip formed mainly based on
• Mechanical properties of metal to be cut
• Depth of cut
• Tool angles in process
• Cutting speed
• Feed , type of cutting fluid
• Surface finish required
• Co-efficient of friction between tool and work piece
• Machining temperature in cutting region

31. TYPES OF CHIPS
• Continuous chips
• Dis-continuous Chips
• Continuous chips with built-up edge

32. continuous chips
• A long ribbon like chips are
produced in the cutting operation
• advantage
• This kind of chip formation results
good surface finish, tool life and less
power consumption.
• Dis-advantage
• The coil type of chip will affect the
surface of the machined part and
also the worker to work
continuously.
• The disposal of this kind of chip also
tough

33. Required conditions of
continuous chips formation
• Ductile material
• Smaller depth of cut
• High cutting speed
• Large rake angle
• Sharp cutting edge
• Proper cutting fluid
• Low friction b/w tool face and chip

34. Dis-continuous chips
The rupture of tool on the
work piece will result the
discontinuous chip formation.
Advantage
• The disposal of chip from the
w/p is easier.
Dis-advantage
• Suitable only for selected work
materials

35. Required conditions of
Dis -continuous chips formation
• Suitable for brittle material
• Small rake angle
• High depth of cut
• Low cutting speed
• Excess cutting fluid
• Low feed

36. Continuous chip with built up edge
.
• This is a chip to be avoided
and is caused by small
particles from the work piece
becoming welded to the tool
face under high pressure and
heat.
• The phenomenon results in a
poor finish and damage to the
tool.
• It can be minimized or
prevented by using light cuts
at higher speeds with an
appropriate cutting lubricant.

37. Reasons for this type of chips
• Low cutting speed
• Poor cutting fluid
• Small rake angle
• Large under cut thickness
• Strong adhesion between chips and tool face

38. CHIP BREAKER
 During machining, long and
continuous chips formed at high
cutting speed.
 It will affect the machining
process.
 It will spoil the tool, workpiece
and machine.
 The chips are hard, sharp, and
hot. It will be difficult to remove
the metal and also dangerous to
safety.
 The chip breakers are used to
break the chips into small pieces
for easy removal, safety and to
prevent damaging the machine
and work.
 The simplest form of chip
breaker is made by grinding a
groove on the tool face a few
millimeters behind the cutting
edge.
TYPES
1. Step type - A step is ground on the tool
face behind the cutting edge. This step will
break the chip.
2. Groove type – A groove on the tool face
behind the cutting edge will break the chip
3. Clamp type – A thin breaker is clamped or
screwed on the face of the tool

39. CUTTING FORCES IN ORTHOGONAL CUTTING
• During the design of cutting tool,
we have to consider all the
forces acting on the tool. There
are three components of cutting
forces are acting mutually right
angles.
• Fx - Feed force – acts in a
horizontal plane but in the
direction opposite to the feed.
• Fy - Thrust Force – acts in the
direction perpendicular to the
generated surface
• Fz - Cutting Force – acts in the
direction of the main cutting
motion

40. The various cutting forces acting on the tool and
the work piece
• Fs – Shear force -- acts along the shear
plane and it gives the resistance to the
shear of the metal in forming the chip.
• Fn – Normal force --- acts normal to the
shear plane
• Resultant Force F = Fs + Fn
• ß = Shear angle
• In the figure
• Force P is the frictional resistance of
the tool acting down ward against the
motion of the chip as it moves along the
tool face.
• Force N is the normal force on the
tool face provided by the tool.
• There force the Resultant force by
the tool on the work piece F’ = P + N

41. GEOMETRY OF CHIP FORMATION

44. Merchant’s circle diagram
ASSUMPTIONS
• The tool has sharp cutting edge,
• The chip formation will be continuous type
• The chip may be considered as a separate body
• The cutting velocity remains constant

45. In merchant circle
• The two force triangles have been combined, F
and F’ are combined as F. The tool has a diameter
equal to F or F’ passing through tool point.
• The cutting force Fx and Fz can be determined by
using dynamometer.
• The resultant of these forces is the diameter of
the circle.
• The rake angle ά is measured from the tool, and
forces P and N can be determined.

47. SHEAR STRESS IN SHEAR PLANE
As
A1
β

48. SHEAR STRAIN
• The chip consist of series of plate
elements of thickness Δt.
• It’s displaced through a
distance Δs to each other.
• Therefore shear strain,
e = Δs / Δt
e = (K2 – 2k sin α + 1) / k cos α

49. CUTTING TOOL MATERIAL

50. Material selection Factors
• The various tool materials used to removed the metal from the
work piece.
• The tool should be harder than the material which is to be cut
The selection of cutting tool material will
depend on the factors
• Volume of production
• Tool design
• Type of machining process
• Physical and chemical properties of a work material
• Rigidity and conditions of machine

51. PROPERTIES OF CUTTING TOOL MATERIAL
• A cutting tool must have the following characteristics in order to
produce good quality and economical parts:
• Hardness — harness and strength of the cutting tool must be
maintained at elevated temperatures, also called hot hardness
• Toughness — toughness of cutting tools is needed so that
tools don’t chip or fracture, especially during interrupted cutting
operations.
• Wear Resistance — wear resistance means the attainment of
acceptable tool life before tools need to be replaced.
• Low friction - The co-efficient of friction between tool and
work piece must be low.
• Cost of the tool – The material should be economical in
production. And it should be easy to manufacture.

52. ADDITIONAL PROPERTIES - Required
• It should have high thermal conductivity
• Resistant to thermal shock
• Easy to manufacture

53. Classification of tool material
• Carbon tool steel
• High speed steel
• Cemented Carbides
• Ceramics
• Diamonds

54. Carbon Tool Steel
Composition
• Carbon – 0.8 – 1.3 %
• Silicon - 0.1 – 0.4 %
• Manganese – 0.1 – 0.4 %
Suitable for low cutting speeds and
below 200 ‘ c appllication places
It has good hardness, strength and
toughness.
Its cheap
Easy to forge
Easy to harden
With this chromium and
molybdenum are added to increase
hardness
Tungsten is added for improving
wear resistance

55. Example : Carbon tool steel
Tap – Dies , Reamer, Punches

56. High Speed steels (H.S.S)
• These metal cuts the metal effectively at high speeds.
• The speed is 2 to 3 times greater than the carbon tool steel
• These tool maintain the hardness up to 900’c
• Various alloying elements improve the hardness and wear
resistance.
• Those are tungsten , chromium, vanadium, cobalt and
molybdenum
• TYPES
18 – 4 -1 High speed steel
Molybdenum high speed steel
Cobalt High speed steel

57. High speed steel - Types - Composition
• .
Types
18- 4-1 High
speed steel
18 % tungsten 4 % chromium 1 % Vanadium
Molybdenum
high speed steel
6 % Molybdenum
5 % Tungsten
4 % chromium 2 % Vanadium
Cobalt high
speed steel
Cobalt 12 %
Tungsten 20 %
4 % chromium 2 % Vanadium

58. Examples for High speed steel –
Milling cutter , Broaches, turning tools

59. Cemented Carbides
• .its a mix of tungsten powder and carbon at high temperature
Tungsten
powder
+ Carbon
at high temperature
=
Its also combined with 82 % tungsten Carbide , 10 % titanium ,
8 % Cobalt
It can with stand at 1000’c , can operate at high speed – 6
times greater than high speed steel ..
Used in the form of insert in the tool.

60. Example – Cemented Carbides
– Inserts

61. Ceramics
• It’s a mixture of aluminium oxide and boron
nitrate powder at 1700 ‘c
• This has good hard and compressive strength
• It’s a high brittle material. So can not be used for
shock load operations
• Its also has a mixture of 90% aluminium oxide
10 % chromium oxide, magnesium oxide and
nitrogen oxide

62. Having
• Good cutting speed
• Rigidity of tool and w/p
• Highly finished surface on cutting tool
• Use of effective chip removal and chip guards

63. Examples :

64. Diamond
• It’s a hardest cutting tool
• Poly crystalline diamond is manufactured by sintering
under high pressure and temperature.
• It has low co-efficient of friction, high compressive
strength and wear resistance.
• Deformation is less in process
• These tools are produced good surface finished object
at high speed with good dimensional accuracy
• It’s a small and best suited for good surface finish tool
• Having high thermal conductivity

65. Example:

66. TOOL WEAR

67. TOOL WEAR
• Tool wear is still a significant problem in
cutting.
• Typical types of tool wear include,
• - Flank wear
• - Crater wear

68. .

69. FLANK WEAR
• Tool wear resulting in
the gradual wearing
away of the cutting edge.
Flank wear is mostly
caused by abrasion, is
predictable, and is the
most desired form of
tool wear.

70. FLANK WEAR
• Flank wear - the point of the tool degrades

71. CRATER WEAR
• The chip coming out wills slide over the tool
face with some pressure, this causes wear in
the face is called face wear.
• The cavity formed on the tool surface is called
crater wear.
• Crater wear is commonly occurred while
machining a ductile material which produces
continuous chips

72. .

73. CRATER WEAR
• Crater wear also decreases tool life

74. NOSE WEAR
• The tip of the tool having more contact with
work piece during the machining operation.
• Due to this type of wear, more heat will be
generated.
• More cutting force will act on the tool.
• Due to this abrasion force, a small portion of
metal comes out is called nose wear.

75. Parameters influence tool wear

76. TOOL LIFE
• The tool life is an important factor in a cutting
tool performance since a considerable time is
lost whenever the tool is ground and reset.
• The length of time that a cutting tool can
function properly before it begins to fail.
• During this period, the tool serves effectively
and efficiently.
THE FOLLOWING SOME EXPRESSING TOOL LIFE:
Volume of metal removed per grind.
No. of work pieces machined per grind.
Time unit.

77. .
MRR = Feed Rate X Width of Cut X Depth of Cut.
Speeds, feeds and DOC influence many aspects of
machining performance:
• Tool life
• Surface finish
• Dimensional accuracy of the manufactured part
• Power required by the machine tool

78. FACTORS AFFECTING TOOL LIFE
• Cutting speed
• Feed
• Depth of cut
• Tool geometry
• Tool material
• Work material
• Cutting fluid
• Rigidity of work, tool and machine

79. 1.Cutting speed -(FACTORS AFFECTING TOOL LIFE)
• When cutting speed increases, the cutting
temperature will increases. So hardness of the
tool decreases.
• This lead to flank wear and crater wear in the
tool. Finally will fail in a short time period
• So the tool life depend on cutting speed.

80. Taylor tool life equation
• where n and C are constants, whose values
depend on cutting conditions, work and tool
material properties, and tool geometry.

81. Feed & Depth of cut -(FACTORS AFFECTING TOOL LIFE)
• The life of the cutting tool influenced by the amount
of metal removed by the tool per minute.
• Fine feed – having continuous metal removal by the
tool. This result wear in the tool face.
• Coarse or depth of cut feed – having thicker chip
removal of dis-continuous chips. But this also affect
the tool geometry and lead it to wear.
• So optimum feed only minimize this problem
regarding tool life

82. Formula
• For low carbon steel material and cemented carbide tool , the
following relation applied
• V – cutting speed
• F – feed
• t – depth of cut
• T – tool life

83. TOOL GEOMETRY -(FACTORS AFFECTING TOOL LIFE)
Name of
the Angle description Required angle
Rake angle
If the rake angle is more the heat
distribution come to low – so tool life is
reduced
- 5 to + 10 degree
for turning austenitic
steel by carbide tool
So we need a optimum rake angle
Relief angle
Relief angle related to friction between tool
and work piece
More relief angle – results weakens the tool
strength – this lead to tool failure 12 to 15 degree
So we need optimum relief angle
Cutting angle
Nose radius
This angle should be optimum for having
good surface finish.
Increasing nose radius improve the life of the
tool
30 to 25 degree

84. Tool material -(FACTORS AFFECTING TOOL LIFE)
• The physical and chemical properties of tool
material affect the life of the tool.
• Example:
• For the given cutting speed H.S.S tool is more
durable than carbon steel tool.
• But carbide tool having more life than H.S.S tool

85. Cutting fluid -(FACTORS AFFECTING TOOL LIFE)
• The cutting fluid plays major role in reducing friction between
tool and work piece and also reduce the heat produced in the
process.
• Like wise it increase the tool life
• The cutting fluid directly controls the amount of heat at the chip
tool interface is given by
• T = tool life
• θ = temperature of chip tool interface
• n = An index which depend on shape and material of the cutting tool

86. Work piece material
-(FACTORS AFFECTING TOOL LIFE)
• Tool life also depend on the microstructure of
the work piece material.
• Tool life will be more when machining soft
materials than hard material like cast iron and
alloy steel

87. Rigidity of work, tool and machine
- (FACTORS AFFECTING TOOL LIFE)
• A strongly supported tool on a rigid machine
will have more life than tool machining under
vibrating machine.
• Loose work piece will reduce the life of the
tool.

88. SURFACE FINISH

89. FACTORS - (for surface finish)
• Cutting speed
• Better surface finish takes place at higher
cutting speed
• Rough cutting takes place at lower cutting
speed

90. Feed - (for surface finish)
• Fine feed result good surface finish
• Coarse feed results poor surface finish

91. Depth of cut - (for surface finish)
• Lighter depth of cut gives good surface finish
• Higher depth of cut gives poor surface finish

92. CUTTING
FLUIDS
.

93. INTRODUCTION
• In the metal cutting process the heat is produced due
to plastic deformation of metal.
• This heat weakens the strength of the tool and also
work piece.
• Also the friction between tool and work piece affect
the life of the tool.
• These all are avoided by using of cutting fluid in the
machining process

94. FUNCTIONS OF CUTTING FLUID
To avoid thermal distortion –
The cutting fluid minimize the temperature produced
in the cutting zone and avoid the metallurgical changes
in the work piece.
To avoid friction –
The cutting fluid also act as a lubricant and it minimize
the friction between tool and work piece , so that we
increase tool life and surface finish
• It also carried away the chip from the machining
area.
• It prevents the corrosion of work and machine

95. PROPERTIES OF CUTTING FLUID
• should act as a lubricant
• Low viscosity
• High specific heat, high heat conductivity
• High film coefficient
• should be economical
• should be odorless
• non – corrosive
• high flash point
• high heat absorbing capacity
• should be stable in all conditions
• It should not get oxidized or decomposed when left in air
• Economical to use

96. TYPES OF CUTTING FLUIDS
Depend on material and machining process
1. water based cutting fluids
2. Straight or heat oil based cutting fluids

97. 1. water based cutting fluids
• Water 80 % + remaining soft soap Or Mineral oil
Is called soluble oil
• These soap oil increase the adhering property with
the work piece and minimize heat and
temperature.
• Emulsifiers break oil into minute particles and keep
them separated in water
• These kind of oils reduce corrosion , heat , friction and
tool wear in the process.
• Its available in less cost

98. 2. Straight or heat oil based cutting fluids
• It’s a un-diluted or pure oil based fluids.
• Mostly it mixed with sulphur and chlorine.
• CLASSIFICATION
• Mineral oil
• Straight fatty oil
• Mixed oil
• Sulphurised oil
• Chlorinated oil

99. Mineral oil
• These are the different composition of hydro
carbons
• This oil used light machining operations.
• Example
• Petroleum, kerosene , paraffin and some high
viscous oils
• Used in ordinary operations in turret and
capstan lathe

100. Straight fatty oil
• These are straight exact oil
example :
• vegetable oil,
• fish oil , animal oil
• Olive oil
• Cotton seed oil
• Whale oil
• These are not stable in operation . They are
used in thread cutting operation

101. Mixed oil
• It’s the mixture of straight fatty and 75% mineral
oil
• So it has excellent properties like cooling, lubricating
in all operation
• And its very cheaper than fatty oil
Uses
• In heavy duty machining , thread milling , all
lathe works

102. Sulphurised oil
• This is one type chemical additive oil
• Sulphur 5 % + Lard oil (animal oil)
• It act as a good lubricant and coolant
• Used in heavy duty lathe work, gear cutting
and thread grinding

103. Chlorinated oil
• Its also a chemical additive oil
• Chlorine 3% + mineral oil
• If we add sulphur and chlorine with mineral oil
it give very good properties.
• So we can use it in all severe cutting
operations on strong and tough materials such
as stainless steels and nickel alloys.

104. FACTORS CONSIDERED FOR
SELECTION OF CUTTING FLUID
• Cutting speed
• Feed rate
• Depth of cut
• Tool and work piece material
• Velocity of cutting fluid
• Life of the cutting fluid
• Tool life to be expected
• Economical aspects

105. Methods Of Applying Cutting Fluids
♦ Drop by drop under gravity
♦ Flood under gravity
♦ Form of liquid jet
♦ Atomized form with compressed air
♦ Through centrifugal action

106. MACHINABILITY
The term machinability refers to the ease with which a
metal can be cut permitting the removal of the
material with a satisfactory finish at low cost.
It can be defined as follows:
 Tool life before tool failure or resharpening.
 Quality of the machined surface.
 The power consumption per unit volume of materials
removed

107. VARIABLES AFFECTING
MACHINABILITY
Work Variables
Tool Variables
Machine Variables
Cutting Conditions

108. WORK VARIABLES:
 Chemical composition of work materials.
 Microstructure composition of work materials.
 Mechanical properties such as ductility, toughness,
brittleness.
 Physical properties.
 Method of production.

109. TOOL VARIABLES:
 The geometry and tool materials.
 Nature of engagement of tool with the work.
 Rigidity of tool.
MACHINE VARIABLES:
 Rigidity of the machine.
 Power and accuracy of the machine tool.
CUTTING CONDITIONS:
 High cutting speed.
 Correct dimensions of cut.

110. EVALUATION OF MACHINABILITY
Tool life/grind.
Rate of metal removal/grind.
Cutting force and power consumption.
Surface finish.
Dimensional stability of the finished work.
Heat generated during cutting.
Ease of chip disposal.
Chip hardness
Shape & size of chips.

111. ADVANTAGES OF HIGH
MACHINABILITY
 Good surface finish.
 High cutting speed.
 Less power consumption.
 High metal removal rate.
 Tool wear reduced.
 Tool life increased.

112. MACHINEABILITY INDEX
It is a quantitative measure of machinability. It is used to compare the
machinability of different metals and acts as a quick and reliable checking
method.
Machinability index, I
= (cutting speed of material for 20 min tool life) / (cutting speed of free
cutting steel for 20 min tool life)
I = Vi / Vs
Some common materials is:
 Low carbon steel - 55 – 60%
 Stainless steel - 25%
 Red brass - 180%
 Aluminium alloy - 390 – 1500%
 Magnesium alloy - 500 – 2000%

113. THERMALASPECTS OF
METAL MACHINING

114. THERMAL ASPECT OF
MACHINING
The power consumed in machining is largely
converted into heat near the cutting edge of the
tool.
This causes the temperature of the tool, chip and
work piece to rise.
This can influence the properties of the work
material being machined, as well as the effective
life of the cutting tool.

115.  Plastic deformation by shearing in the primary
shear zone
 Plastic deformation by shearing and friction on
the cutting face
 Friction between chip and tool on the tool flank
Distribution of Heat

116. • Also known as shear zone.
• Maximum heat is generated due to plastic deformaion of metal.
• Since the process is continuous and rapid process,80-85% heat
is generated from this zone.
PRIMARYZONE

117. • It is also called a friction zone.
• As the chip moves along the tool face under great pressure
being resisted by the friction
• Heat is generated due to friction between moving chip on
• rake face of tool.
• 15-20% heat is generated in this zone.
SECONDARYZONE

118. • It is the work tool contact zone.
• Burnishing action is the cause of heat generation.
• Rarely present , if present then 1-3% of heat generation occurs
and occurs due to built up edge formations.
T E RT I A R Y ZONE

119. Disadvantages of Heat
Generation
• Affects the wear of the cutting tool.
• Can induce thermal damage to the machined
surface
• Causes dimensional errors in the machined
surface

120. Heat dissipation
The temperature in metal cutting can be
reduced by:
Application of cutting fluids .
Change in the cutting conditions by
reduction of cutting speed and/or feed;
Selection of proper cutting tool geometry
(positive tool orthogonal rake angle).

121. MEASUREMENT OF CUTTING TOOL
TEMPERATURE
NEEDS OF CUTTING TOOL TEMPERATURE
MEASUREMENTS:
Assessment of machinability in terms of cutting
forces, temperature and tool life.
Design and selection of cutting tools.
Evaluation of various machining parameters on
cutting temperature.
Proper selection and application of cutting fluid.
Analysis of temperature distribution in the chip, tool
and job.

122. Methods of Measuring Cutting Tool
Temperature
CALORIMETRIC METHOD
It is simple and low cost. But it is inaccurate
and its gives only the grand average value.
DECOLORISING AGENT
Some paint and tape is pasted on the cutting
tool to show the variation in temperature.
According to the cutting tool temperature, the
colour change is show for the indication.

123. TOOL-WORK THERMOCOUPLE