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. RAMCO INSTITUTE OF TECHNOLOGY
Mr.M.LAKSHMANAN
Assistant Professor (Senior Grade)
Department of Mechanical Engineering

2. Manufacturing Vs Production
Manufacturing is a process of converting raw
material in to finished product by using
various processes, machines and energy. it is
a narrow term.
Production is a process of converting inputs in
to outputs. it is a broder term.
Every type of manufacturing can be a part of
production, but every production is not a
manufacturing.

3. Value addition by Manufacturing

4. Possibility of Manufacturing in number of
routes

5. Classification of Manufacturing Processes
1. Forming Processes – Casting , Powder metallurgy
Techniques, etc.,
2. Deforming Processes – Forging, Sheet metal
operations, Rolling, Extrusion, etc.,
3. Machining/Removing Processes – Turning, Milling,
Drilling, Advanced Machining (AWJM,
USM,LBM,PAM), etc.,
4. Joining Processes – Welding, soldering, Brazing, etc.,
5. Surface finishing Processes – Grinding, Broaching,
Surface coating, etc.,
6. Material property Modification Processes-
Annealing, Surface Heat Treatment, etc.,

6. UNIT I THEORY OF METAL CUTTING
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.

7. UNITII TURNING MACHINES
Centre lathe, constructional features,
specification, operations – taper turning
methods, thread cutting methods, special
attachments, machining time and power
estimation. Capstan and turret lathes- tool
layout – automatic lathes: semi-automatic –
single spindle: Swiss type, automatic screw
type – multi spindle:

8. Shaper – Types of operations. Drilling,
reaming, boring, Tapping. Milling
operations-types of milling cutter. Gear
cutting – forming and generation principle
and construction of gear milling ,Hobbing
and gear shaping processes –finishing of
gears.
UNIT III SHAPER, MILLING AND GEAR
CUTTING MACHINES

9. Abrasive processes: grinding wheel –
specifications and selection, types of
grinding process– cylindrical grinding,
surface grinding, centre less grinding and
internal grinding- Typical applications –
concepts of surface integrity, broaching
machines: broach construction – push, pull
surface and continuous broaching machines
UNIT IV ABRASIVE PROCESS AND
BROACHING

10. UNIT V CNC MACHINING
Numerical Control (NC) machine tools – CNC
types, constructional details, special
features, machining centre, and part
programming fundamentals CNC – manual
part programming – micromachining –
wafer machining

11. UNIT I
THEORY OF METAL CUTTING

12. Machining
Machining is any of various processes in which a
piece of raw material is cut into a desired final
shape and size by a controlled material-removal
process.
The removal of extra material from a metal surface
by shearing or cutting action is know as
machining.
Process such as cutting, drilling, forming, grinding,
and/or shaping of a piece of metal or other
material performed by machine tools such as
lathes, power saws, and presses.

13. History of Machine Tools
• 1775 - John Wilkinson - Horizontal Boring Machine
• 1794 - Henry Maudsley - Engine Lathe
• 1817 – Roberts Planer - Planer
• 1818 - Eli Whitney - Milling Machine
• 1840 - John Nasmyth - Drill Press
• 1845 - Stephen Fitch - Turret Lathe
• 1869 - Christopher Spencer - Automatic TurretLathe
• 1880 - Surface Grinder - P. V. Miller
• 1952 – Numerical Control - John T. Parsons

16. Machine Tools
• In US, more than $ 100 billions were spent
annually on the machining and related
operations.
• Typically a large majority (above 80%) of all the
machine tools used in the manufacturing
industry are metal cutting in nature.
• An estimate in 1957 showed that about 10 to
15% of all the metal produced in U.S.A. is
converted into chips.

17. Objectives of Machining
• Quick metal removal
• High class surface finish
• Economy in tool cost
• Less power consumption
• Economy in the cost of replacement and
sharpening of tools
• Minimum idle time of machine tools

18. Variety of Machine Tools
• Turning machines (Lathes)
• Drilling machines
• Boring machines
• Milling machines
• Grinding machines
• Shaping and Planning machines
• Gear cutting machines
• Sawing machines
• Unconventional machining machines

19. Classification of Material Removal Process

20. Metal Removing Processes
• Non cutting process or Chipless Process
• Cutting process or Chip forming process
Types of Metal cutting Process
• Orthogonal cutting process (2Dimensional Cutting)
• Oblique cutting process (3Dimensional cutting)

21. Types of Metal cutting Process
1. Orthogonal Cutting:
It is a machining process in which the
cutting edge of the tool is kept perpendicular
to the direction of the tool travel.

22. 2. Oblique Metal Cutting
The cutting edge of the tool is inclined at
some acute angle to the direction of the tool
travel.

24. Orthogonal cutting Oblique metal cutting
The cutting edge of the tool is
perpendicular to the direction of the tool
travel
The cutting edge of the tool is inclined at some
acute angle to the direction of the tool travel
The cutting edge clears the width of the
work piece on either end
The cutting edge may or may not clear the width
of the work piece on either end
The chip flows over the rake surface of
the cutting tool in the direction
perpendicular to the cutting edge
The chip flows on the rake surface of the tool
making an angle with the normal on the cutting
edge
The shape of the chip coil is tight flat
spiral
The shape of the chip coil is long curl
Only two components of the cutting force
act on the cutting edge
Three components of the forces mutually
perpendicular act at the cutting edge
Maximum chip thickness occurs at the
middle
The maximum chip thickness may not occur at
the middle
Tool interface is more Tool interface is less
Tool life is less Tool life more

26. Mechanism of Metal Cutting
(Chip formation)
• The removal of extra material from a metal surface
by shearing or cutting action is know as machining
or metal cutting.
• The cutting takes place along a plane, known as
shear plane. There is a cutting zone.
• The extra material due to this deformation flows
over the tool surface, known as chip, and this
shearing zone is known as primary shear zone.

27. • At high speeds, this zone can be assumed to be
restricted to a plane called shear plane inclined
at an angle shear angles (ф)

28. Important Influence on Metal Cutting
• Work material
• Cutting tool material
• Cutting tool geometry
• Cutting speed
• Feed rate
• Depth of cut
• Cutting fluid used

29. Factors influencing cutting process

30. Influence of Tool Angles
• Rake angle:
Rake angle is a parameter used in various cutting
and machining processes, describing the angle of the
cutting face relative to the work.
There are three types of rake angles:
• Positive rake angle
• Negative rake angle
• Zero rake angle

32. 1. Positive rake angle:
The slope given to tool face in such a way that it
should be away from the cutting edges and slant
towards the back or side of the tool.
• Makes the tool more sharp and pointed
• Reduces cutting forces and power requirements
• Helps in the formation of continuous chips in
ductile materials
• Can helps avoid the formation of a built up edge

33. 2. Zero rake angle:
No slope is provided on the tool face. So tool face is
parallel to the shank. Tools made of brass materials. It
increases the strength of the tool and avoid welding the
chip over work surfaces.
3. Negative rake angle:
The slope should be away from the cutting edge but
upwards towards the back or side of the tool. The
negative rake angle increases the tool force to some
extent. Its provided on cemented carbide tools.
• Can improve surface finish.
• Increasing the strength of the cutting edge.
• To machine high strength alloy

35. • Clearance angle or Relief angle:
Both side and end clearance angles are given to
the tool to prevent the rubbing of the job on the
tool.

39. Tool Signature
• Back rake angle
• Side rake angle
• End relief angle
• Side relief angle
• End cutting edge angle
• Side cutting edge angle
• Nose radius
• A typical tool designation(Signature) is
0-10-6-6-8-90-1 mm

40. Cutting Tools

41. Cutting Tools
Cutting tool or cutter is used to remove material
from the workpiece by means of shear
deformation.

42. Types of Machine Tools
• Single point cutting tools:
These tools have only one cutting edge;
such as lathe tools, shaper tools, planer
tools, Boring tools,etc.
• Multi-point cutting tools:
These tools have more than one cutting
edges; such as milling cutters, drills,
broaches, grinding wheels, etc.

43. Cutting tools classified according to the motion :
• Linear motion tools (Lathe, shaping tools)
• Rotary motion tools (Milling, Grinding
wheels)
• Linear and rotary motion tools (Drilling,
honing tools)

44. Classification of single point cutting tools:
• According to the method of manufacturing the
tool
 Forged tool
 Tipped tool brazed to the carbon steel shank
 Tipped tool fastened mechanically to the carbon
steel shank
• According to the method of holding the tool
 Solid tool
 Tool bit inserted in the tool holder

45. • According to the method of using the tool
• Turning tool
• Chamfering tool
• Thread cutting tool
• Facing tool
• Boring tool
• Grooving tool
• Parting off tool
• According to the method of applying feed
• Right hand tool
• Left hand tool
• Round nose tool

47. Parts of Single point cutting tool

48. Nomenclature of single point cutting tool
• Shank:
The body of the tool which is not ground is called
shank.
• Face:
The surface over which the chip of the metal slides is
known as face.
• Flank:
The surface of the tool which is facing the workpiece is
known as flank.
• Base:
It is the bottom surface of the shank.

49. • Nose:
The junction of slides and end cutting edges are called
nose.
• Cutting edge:
It is the junction of face and flank. It is generally
denoted by two types of cutting edges.
– End or auxiliary cutting edge
– Side or main cutting edge

50. Types of Chips
Chip:
The cutting tool removes from the work piece
in the form of “chips”.
Types of Chips
• Continuous chip
• Discontinuous chip
• Continuous chip with
built-up-edge.

51. Types of Chips

52. 1. Continuous Chips
Continuous chips are formed by the continuous plastic
deformation of metal without fracture in front of the
cutting edge of the tool and is formed by the smooth
flow of the chip up the tool face.
Mild steel and copper are considered to be most
desirable materials for obtaining continuous chips.
The chips obtained have same thickness throughout.
This type of chip is the most desirable. Since it is
stable cutting, resulting in generally good surface
finish.

53. Continuous chips tend to be formed when the
following condition exist:
1. ductile material
2. high cutting speed
3. small chip thickness
4. large rack angle
Minimum friction of chip on tool face by :
• Polished tool face
• Use of efficient cutting lubricants.
• Use of tool material with low-coefficient of
friction.

54. 2.Discontinuous chips
• Discontinuous chips is formed by a series of
rupture occurring approximately perpendicular
to the tool place face each chip element passing
off along the tool face the chip element in the
form of small segment may adhere loosely to
each other and becomes slightly longer.
• Since the chips break up into small segments the
friction between the tool and the chips reduces
resulting in better surface finish. These chips are
convenient to collect handle and dispose off.

55. Discontinuous chips tends to be formed when one
or more or the following conditions exist:
1. Brittle material , such as cast iron and bronze.
2. large chip thickness
3. low cutting speed
4. small rack angle

56. 3. Continuous Chip with Built up Edge:
This type of chip is very similar to the continuous
chip. With the difference that it has a built up
edge adjacent to tool face and also it is not so
smooth. It is obtained by machining on ductile
material, in this condition of high local
temperature and extreme pressure in the cutting
and high friction in the tool chip interference,
may cause the work material to adhere or weld to
the cutting edge of the tool.

57. Successive layers of work material are then added to
the built up edge. When this edge becomes larger
and unstable , it breaks up and part of it is carried up
the face of the tool along with the chip while the
remaining is left over the surface being machined,
which contributes to the roughness of the surface.
The built up edge changes its size during the cutting
operation. It first increases , then decreases, then
again increases etc.

59. Chip Breakers
During machining, long and continuous chips formed
at high cutting speed will affect the machining
process.
Chip breakers are used to break the chips into small
pieces for easy removal, safety and to prevent
damaging the machine and work.

60. Types of Chip Breakers (Chip Control)
• Step type
• Groove type
• Clamp type

61. Mechanics of Orthogonal Cutting
• The current analysis is based on
Merchant's thin shear plane model
considering the minimum energy
principle.
• This model would be applicable at very
high cutting speeds, which are
generally practised in production.

62. Merchant's Assumptions
• Tool edge is sharp
• Chip acts as a rigid body
• Chip moves on the tool face with constant
velocity
• The surface where the shear occurs is a plane
• The chip does not flow to either side
• The stress on the shear plane are uniformly
distributed.

63. Merchant's Analysis
• FV-Force perpendicular to the primary tool
motion (thrust force)
• Fs-Force along the shear plane
• Ns-Force normal to the shear plane
• F -Frictional force along the rake face
• N -Normal force perpendicular to the rake
face
• R – Resultant

66. MERCHANT CIRCLE DIAGRAM OF FORCES
ɸ = π/4 – β/2 + α/2

70. LEE and SHAFFER’S THEORY
Its used to analyze the stresses and forces
involved in the major deformation of metals.
A line which generally(curved, tangential)
along its length to the maximum shear stress
is called slip line. A complete set of slip line
in a plastic region forms a slip line field(Slip
line field Theory).
ɸ + β- α = π/4

71. LEE and SHAFFER’S Theory Assumptions
• The work ahead of the tool behaves as ideal
plastic mass.
• There exists a shear plane which separates
the chip and workpiece.
• No hardening occurs in chip.

72. THERMAL ASPECTS
In metal cutting process the energy dissipated at
the cutting edge is converted into heat. This
heat influences a tool wear on cutting tools
and its develops friction between cutting edge
of the tool and chip interface. The continuous
heat accumulation takes place on tools and it
leads to plastic deformation on cutting edges.
The heat is generated in three regions:
1. Shear zone
2. Chip-Tool interface Region
3. Tool-work interface Region

74. 1.Shear zone(Primary zone):
The zone which is affected by the energy
required to shear the chip and work is called
shear zone. Nearly 80-85% of heat is
generated in the region.
2. Chip-Tool interface Region(Secondary zone):
In this region the energy required to overcome
the friction completely is the source of heat.
Some plastic deformation also takes place.
The heat generation is in the range of
15-20%.

75. 3.Tool-work interface Region (Tertiary zone):
In this region, the energy required to
overcome the rubbing friction between
flank face of the tool and workpiece is the
source of heat. The heat generation is in the
range of 1-3%.

76. Heat generation, Temperature distribution,
and Heat dissipation in Metal cutting
• Heat Generation:
In the metal cutting process, the tool
performs the cutting action by overcoming
the shear strength of the workpiece
material. This generates a large amount
of heat in the workpiece resulting in a
highly localized thermomechanically
coupled deformation in the shear zone.

78. • Temperature Distribution:
Determination of the temperature
distribution is needed in the machining
process because of its controlling influence
on tool performance, and the quality of the
machined part.
Elevated temperatures have a negative
impact on tool performance due to the
softening of tool materials, and increasing
diffusion, which also affect the quality of
the machined part.

79. • Temperature Distribution:

80. • Heat Dissipation in Metal cutting:
• There are three elements which receive the
heat and are known as heat sinks.
• As cutting speed increases, a large portion of
the heat generated is carried away by the chip
and little amount of the heat goes into the
work piece and the tool.

81. Method of measuring cutting Tool Temperature

82. IR Technique

83. CUTTING TOOL MATERIALS
Good Characteristics of cutting Tool Materials:
• Hot hardness
• Wear resistance
• Toughness
• Low friction
• Low Cost of Tool
• High thermal conductivity

84. Types of Cutting Tool Materials
• Carbon Tool Steel
• High Speed Steel (HSS)
• Cemented Carbide (CC)
• Ceramics
• Cubic Boron Nitride (CBN)
• Diamonds

85. Carbon Tool Steel
Carbon steels have been used since the 1880s
for cutting tools. However carbon steels start
to soften at a temperature of about 180oC.
This limitation means that such tools are rarely
used for metal cutting operations. Plain
carbon steel tools, containing about 0.9%
carbon and about 1% manganese, hardened
to about 62 RC, are widely used for
woodworking and they can be used in a
router to machine aluminium sheet up to
about 3mm thick.

86. High Speed Steel (HSS)
Developed around 1900 HSS are the most highly alloyed
tool steels. The tungsten (T series) were developed
first and typically contain 12 - 18% tungsten, plus
about 4% chromium and 1 - 5% vanadium. Most
grades contain about 0.5% molybdenum and most
grades contain 4 - 12% cobalt.
HSS tools are tough and suitable for interrupted cutting
and are used to manufacture tools of complex shape
such as drills, reamers, taps, dies and gear cutters.
Tools may also be coated to improve wear resistance.
HSS accounts for the largest tonnage of tool materials
currently used. Typical cutting speeds: 10 - 60 m/min.

87. Cemented Carbide
Also known as carbides or sintered carbides were introduced in
the 1930s and have high hardness over a wide range of
temperatures, high thermal conductivity, high Young's modulus
making them effective tool and die materials for a range of
applications.
The two groups used for machining are (both types may be
coated or uncoated):
Tungsten carbide
Titanium carbide
3 - 6% matrix of cobalt gives greater hardness while 6 - 15%
matrix of cobalt gives a greater toughness while decreasing the
hardness, wear resistance and strength.
Tungsten carbide tools are commonly used for machining steels,
cast irons and abrasive non-ferrous materials.

88. Ceramics
Introduced in the early 1950s, two classes are used for
cutting tools:
Aluminium oxide (Al2O3)
Silicon nitride (Si3N4)
These are pressed into insert tip shapes and sintered at
high temperatures.
Silicon carbide (SiC) whiskers may be added to give better
toughness and improved thermal shock resistance.
The tips have high abrasion resistance and hot hardness
and their superior chemical stability compared to HSS
and carbides means they are less likely to adhere to the
metals during cutting and consequently have a lower
tendency to form a built up edge.

89. Cubic Boron Nitride (CBN)
Introduced in the early 1960s, this is the second hardest
material available after diamond.
CBN tools may be used either in the form of small solid tips
or as a 0.5 to 1 mm thick layer of polycrystalline boron
nitride sintered onto a carbide substrate under pressure.
In the latter case the carbide provides shock resistance and
the CBN layer provides very high wear resistance and
cutting edge strength.
Cubic boron nitride is the standard choice for machining
alloy and tool steels with a hardness of 50 RC or higher.
Typical cutting speeds: 30 - 310 m/min.

90. Diamonds
The hardest known substance is diamond. This consists
of very small synthetic crystals fused by a high
temperature high pressure process to a thickness of
between 0.5 and 1mm and bonded to a carbide
substrate.
The result is similar to CBN tools. The random
orientation of the diamond crystals prevents the
propagation of cracks, improving toughness.
Typical cutting speeds: 200 - 2000 m/min.

91. Cutting Tool Materials

93. Tool Wear
During machining process, the tool is subjected to
three important factors such as forces,
temperature and sliding action due to relative
motion between tool and workpiece.
It is continuous removal of material from the
surface of the tool due to wearing action or
rubbing action of chip and work surface with tool.
Types of Tool wear:
• Flank wear
• Face wear or Crater wear
• Nose wear

94. Types of Tool wear

95. 1. Flank wear:
This is also called “Edge wear”. Friction,
abrasion and adhesion are the main causes
for this type of wear.
This wear takes place when machining the
brittle material such as cast iron. Its also
occurs when the feed is less than 0.15mm/rev.
Flank wear results in a rough machined
surface.

96. Flank wear

97. 2. Face wear or Crater wear
The face of the tool is always contact with the
chip. The chip slides over the face of the tool.
Due to the pressure of the sliding chip, the tool
face gradually wears out.
A cavity is formed on the tool face. The cavity is
called Crater. This type of wear is known as
crater wear.
Cratering is commonly occurred while machining
a ductile material which produces continuous
chips.

98. Face wear or Crater wear

99. 3. Nose wear:
The wear occurs on the nose radius of the tool.
When the nose of the tool is rough, abrasion and
friction between tool and workpiece will be high.
Due to this type of wear, more heat will be
generated. Also more cutting force acts on the
tool. This type of wear is more prominent than
flank wear.

101. Tool Life
Tool life can be defined as the time interval for
which the tool works satisfactorily between two
successive grinding of sharpening.
Factors affecting Tool life:
• Cutting speed
• Feed and depth of cut
• Tool geometry
• Tool material
• Cutting fluid
• Work material
• Rigidity of work, Tool and Machine

102. 1.Cutting speed:
Cutting speed has greater influence on the tool life. When
the cutting speed increases, the cutting temperature
will also increase. Due to this the hardness of the tool
decreases. There is a definite relationship between
cutting speed and tool life. This relation is given by
Taylor’s formula as given below:
VTn = C
V= cutting speed in m/min
T= Tool life in minutes
n= index which depends on the tool and work.
0.1 to 0.5 for High speed steel tools
0.2 to 0.4 for Tungsten Carbide tools
0.4 to 0.6 for Ceramic tools.
C= Constant

104. 2. Feed and Depth of cut:
The life of the cutting tool is influenced by the
amount of metal removed by the tool per
minute. When the fine feed is used, the area
of chip passing over the tool face is greater
than a course feed for a given volume of metal
removal.
The effect of feed and depth of cut on tool life is
given by :
V= 257 in m/min
T0.19 X f0.36 X t0.08

105. Where,
V = Cutting speed
T = Tool life
f = Feed in mm/min
t = Depth of cut in mm

106. 3. Tool geometry
Large rake angle reduces the tool cross section. Hence, the
amount of heat absorbed by the tool is also reduced. It
weakens the tool. The optimum rake angle for maximum
tool life lies between -5˚ to 10˚ for turning mild steel by
carbide tool.
If more relief angle, the friction will be less but more relief
angle decreases the tool life because of decreased
strength. The optimum relief angle is 12˚ to 15˚.
Similarly, a higher value of side cutting edge angle gives
longer life to the tool. The optimum side cutting edge
angle lies between 25˚ to 30˚.
The relationship between cutting speed (V), Tool life (T)
and Nose radius (r) is as follows
VT0.0927 = 331 r0.244

107. 4. Tool material:
An ideal tool material is one which removes the maximum
volume of material at all cutting speed. Both physical and
chemical properties of tool material will influence on tool
life.
5. Cutting fluid:
Heat produced during metal cutting is carried away by tool
and work by means of cutting fluid. It reduces the friction at
chip-tool interface and it increases the tool life.
TƟn = C
T = Tool life
Ɵ= Temperature of chip tool interface in ˚C
n = index which depends on shape and material of the
cutting tool.

108. 6. Work material:
Tool life does also depends on the microstructure of the
workpiece material. Tool life will be more when
machining soft metals than hard metals such as cast
iron and alloy steel.
7. Rigidity of work, Tool and Machine:
A strongly supported tool on a rigid machine will have
more life than tool machining under the vibrating
machine. Loose workpiece will decrease the tool life.

109. SURFACE FINISH
Surface finish is one of the important factors
that control friction and transfer layer
formation during sliding.
Surface finish of any product depends on the
following factors:
• Cutting speed
• Feed
• Depth of cut

110. CUTTING FLUIDS
• During metal cutting, heat is generated due to
plastic deformation of metal and friction at
the tool workpiece interface. it will increase
the temperature of both workpiece and tool.
• Hence, the hardness of the tool decreases. It
leads to tool failure.

111. Functions of cutting Fluids
• Cutting fluid cools the work piece and tool by carrying away
the heat generated during machining.
• It acts as lubricant at the friction zones, hence tool
life increases.
• As friction get reduced, the forces and electricity power
consumption decreases.
• Using cutting fluids produces better surface finish to the
work piece.
• It causes to break the chips into small pieces.
• It washes away the chips from the tool.
• It prevents the corrosion of chips and machine.
• Improves dimensional accuracy and control on the work
piece.
• It permits maximum cutting speed hence the time for
machining reduce and cost of manufacturing increases.

112. Properties of cutting Fluids
• Cutting fluids should have low viscosity to permit free
flow of the liquid.
• It should posses good lubricating properties.
• It should have high specific heat, high heat
conductivity and high heat transfer coefficient.
• It should be non-corrosive to work and machine.
• It should be non-toxic to operating person.
• It should stable in use and storage.
• It should be safe.
• It should permit clear view of the work operation.
• It should be economical to use.

114. Types of cutting Fluids
• Water based cutting fluid
• Straight or Neat oil based cutting fluid

115. Water based cutting fluids
To improve the cooling and lubricating
properties of water, the soft soap or mineral
oils are added to it. These oils are known as
Soluble oils.
Soluble oils are emulsions composed of around
80% of water remaining soap and mineral oils.
The soap acts as an emulsifying agent which
breaks the oil into minute particles to disperse
them throughout the water.

116. Straight or Neat oil based cutting fluids
Straight oil based cutting fluids refer undiluted
or pure oil based fluids. Most of the oils are
not directly used but it is mixed with other oils
or oils with chemicals such as sulphur and
chlorine. Its classified into the following
subgroups;
• Mineral oil
• Straight fatty oil
• Mixed oils or compound oil
• Sulphurised oil
• Chlorinated oil

117. • Mineral oil:
These oils are primarily composed of
hydrocarbons of different structures and
molecular weights.
Ex: Straight mineral(Petroleum) oils, Kerosene
and paraffin
Its used for light machining operations such as
turret and capstan lathes.

118. • Straight fatty oil or Fixed Oils:
These oils are consist of animal, fish and
vegetable oils. Some commonly used oils are
lard oil, olive oil, whale oil, cottonseed and
linseed oil.
These oils are not stable and rapidly lose their
lubricating properties.
Its used during thread cutting operations. These
oils are more expensive and less available than
mineral oil.

119. • Mixed oils or compound oil:
It is the mixture of straight fatty and mineral oils.
The film strength of fatty oils is retained even
when diluted with 75% mineral oil.
Its used for automatic screw machine work,
heavy duty operations such as Threading on
capstan and Turret lathes, thread Milling etc,.

120. • Sulphurised oil:
• It is one type of chemical additive oil. When
sulphur (about 5%) is mixed with lard oil, it
gives good lubricating and cooling qualities.
• It is used for heavy duty lathe work, gear
cutting and thread grinding.

121. • Chlorinated oil:
It is another type of chemical additive oil. The
chlorine of about 3% is added to mineral oils.
These oils are particularly effective in
promoting anti weld characteristics.
If both chlorine and sulphur are used with
mineral oil, they give the extreme pressure
property to oil and are suitable for severe
cutting operations on strong and tough
materials such as stainless steels and nickel
alloys.

122. Selection of cutting fluids depends on the
following factors:
• Cutting speed
• Feed rate
• Depth of cut
• Tool and workpiece material
• Velocity of cutting fluid
• Expected tool life
• Economical aspects
• Life of cutting fluid

123. 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

124. MACHINABILITY
• It is defined as the ease with which a given
material can be cut permitting the removal of
material with a satisfactory finish at lower
cost.
• Machinability is defined as the ease with which
a material can be satisfactorily machined.
• Machining may be easier in some materials
where it may be difficult in other.

125. MACHINABILITY

127. Variables affecting Machinability
• Work Variables
– Chemical composition of workpiece material
– Microstructure composition of workpiece
– Mechanical properties (Ductility, toughness, brittleness, etc.)
• Tool Variables
– The geometry and tool material
– Rigidity of tool
• Machine Variables
– Rigidity of machine
– Power and accuracy of machine tool
• Cutting conditions
– Cutting speed
– Surface finish
– Dimensions of cut

128. Evaluation of Machinability
• Tool life per grid
• Rate of Metal removal per tool grid
• Magnitude of cutting forces and power
consumption
• Surface finish
• Dimensional stability of the finished work
• Heat generated during cutting
• Ease of chip disposal
• Chip hardness
• Shape and size of chip

129. Machinability 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.
US National Standard for 100% Machinability is SAE
1112 Hot Rolled Steel. This steel is widely used as
standard steel for comparison.
• Machinability Index
I =
𝑐𝑢𝑡𝑡𝑖𝑛𝑔 𝑠𝑝𝑒𝑒𝑑 𝑜𝑓 𝑚𝑒𝑡𝑎𝑙 𝑖𝑛𝑣𝑒𝑠𝑡𝑖𝑔𝑎𝑡𝑒𝑑 𝑓𝑜𝑟 20𝑚𝑖𝑛.𝑡𝑜𝑜𝑙 𝑙𝑖𝑓𝑒
𝑐𝑢𝑡𝑡𝑖𝑛𝑔 𝑠𝑝𝑒𝑒𝑑 𝑜𝑓 𝑎 𝑠𝑡𝑎𝑛𝑑𝑎𝑟𝑑 𝑠𝑡𝑒𝑒𝑙 𝑓𝑜𝑟 20𝑚𝑖𝑛.𝑡𝑜𝑜𝑙 𝑙𝑖𝑓𝑒
I = Vi/Vs

130. The machinability index for some common
materials is given below;
• Low carbon steel = 55 – 60%
• Stainless Steel = 25%
• Red Brass = 180%
• Aluminum Alloy = 390 – 1500 %
• Magnesium Alloy = 500 – 2000%