Unit - IMETAL CUTTING MACHINING PROCESS.ppt

METAL CUTTING

1. COURSE: MACHINING PROCESSS
CODE: A40315
V Semester
Regulation: R-23
G. Pullaiah College of Engineering and Technology
(Autonomous)
Pasupula, Kurnool- 518002
Dr G Praveen Kumar
Assistant Professor
Mechanical Engineering
Prepared by

2. Course objectives:
 
Gain knowledge on working principle of different metal cutting
processes and familiarize with cutting forces, machining calculations
and cutting fluids.
Make the student learn about principles of lathe and Drilling
machines.
Make the student learn about principles of Grinding and Milling
machines.
To acquire knowledge in the elementary mechanism and
machinability of materials with different Mechanical and Electrical
energy-based Machining Processes.
To make student familiar with various advanced machining
operations.
 

3. Course Outcomes (COs)
After the completion of the course, the student will be able to:
A40315.1 - Operation of various machines like lathe, drilling, grinding,
slotting, shaping, milling etc.
A40315.2 - Practical exposure on flat surface machining, milling and
grinding operations.
A40315.3 - Illustrate advanced machining processes, cutting tools and
cutting fluids for a specific material and part features.
A40315.4 - Differentiate Electrical Energy Based machining processes,
mechanism of metal removal, machine tool selection.
A40315.5 - Interpret Electro Chemical machining process, economic
aspects of ECM

4. Course Syllabus
UNIT I
Elementary treatment of metal cutting theory – Elements of cutting
process – Geometry of single point tool and angles, chip formation and
types of chips – built up edge and its effects, chip breakers. Mechanics
of orthogonal cutting –Merchant‘s Force diagram, cutting forces –
cutting speeds, feed, depth of cut, heat generation, tool life, coolants,
machinability –economics of machining. cutting Tool materials and
cutting fluids –types and characteristics.
 
UNIT II
Engine lathe – Principle of working- specification of lathe – types of
lathes – work holders and tool holders –Taper turning, thread cutting
operations and attachments for Lathes.
Drilling, Boring Machines, Shaping, Slotting and planning machines -
Principles of working, specifications, types, Tools and tool holding
devices – operations performed, machining time calculation.
 

5. UNIT III
Milling machine – Principles of working – specifications – classifications
of milling machines – methods of indexing, milling cutters - machining
operation, Accessories to milling machines.
Grinding machine –Theory of grinding – classification– cylindrical and
surface grinding machine – Tool and cutter grinding machine –
Grinding wheel specification - types of abrasives – bonds, Truing and
Dressing of wheels. Lapping, Honing and Broaching machines –
comparison of grinding, lapping and honing. Principles of design of Jigs
and fixtures and uses, Classification of Jigs & Fixtures – Principles of
location and clamping –types.

UNIT IV
Mechanical Energy Based Processes: Abrasive Jet Machining, Water
Jet Machining, Abrasive Water Jet Machining, Ultra Sonic Machining –
Working Principle, Description of Equipment, Process Parameters,
Metal Removal Rate, Applications, Advantages and Limitations.
Electrical Energy Based Processes: Electric Discharge Machining – Wire
cut EDM - Working Principles, Process Parameters, Applications
Advantages and Limitations.

 

6. UNIT V
Chemical and Electro Chemical Energy Based Processes: Chemical
Machining and Electro Chemical Machining – Working Principle,
Etchants, Maskants, Techniques of Applying - Process Parameters,
Electro Chemical Grinding, Electro Chemical Honing, Applications,
Advantages and Limitations.
Thermal Energy Based Processes: Laser Beam Machining and Drilling,
Plasma Arc Machining, Electron Beam Machining – Working Principle,
Process Parameters, Applications, Advantages and Limitations.

7. . Books and References
 
Text Books:
1. Manufacturing Technology-Kalpakzian- Pearson Seventh edition. (2018)
2. Production Technology by R.K. Jain and S.C. Gupta, Khanna Publishers, 17th
edition.
3. Jain V.K., Advanced Machining Processes, 1st Edition, Allied Publishers Pvt.
Ltd., New Delhi, 2007.
4. Jain V.K., Advanced Machining Processes, 1st Edition, published by CRC Press
(Taylor & Francis), September 7, 2022
 
Reference Books:
1. Pandey P.C and Shan H.S., Modern Machining Processes, 1/e, McGraw Hill,
New Delhi, 2007.
2. Modern Machining Processes by Anand Pandey, published by Ane Books Pvt. Ltd,
2019
3. Production Technology by H.M.T. (Hindustan Machine Tools),TMH, 1st edition,
2001
4. Manufacturing Technology Vol II by P.N. Rao, Tata McGraw Hill, 4th edition,
2013
5. Machine Technology Machine tools and operations by Halmi A Yousuf &
Harson, CRC Press Taylor and Francies.
6. Workshop Technology – Vol II, B.S.Raghu Vamshi, Dhanpat Rai & Co, 10th
edition, 2013

8. Chapter :1
Mechanics of
Metal Cutting
M. Eugene Merchant

9. Machining is
 
a manufacturing process where the desired shape is created
by removing material from a larger piece. It is used for making finished
products and for raw material processing. Machining processes are also
known as subtractive manufacturing processes.
 Machining – Produces finished products with high degree of accuracy.
Tradition Machining Processes (like turning, drilling ,milling) use a sharp cutting
tool to remove the from work piece by shear deformation
Machining Process

11. Introduction - Metal Cutting
Metals are shaped in to usable forms through various
processes.
No-cutting shaping:
No chip formation takes place, and the metal is shaped
under the action of heat, pressure or both.
Ex: Forging, drawing , Spinning, Rolling, Extruding, etc.
Cutting shaping:
The components are brought to the desired shape and
size by removing the unwanted material from the
parent metal in the form of chips through machining.
Ex: Turning, Boring, Milling, Drilling, Shaping, Planning,
Broaching, etc.

12. Examples of cutting process

13. Basic Elements of Machining
The basic elements of machining operations are:
1.Work piece
2.Tool
3.Chip

14. Basic Elements of Machining
For providing cutting action, a relative motion between the
tool and work piece is necessary.
This relative motion can be provided by:
•Either keeping theworkpiece
stationaryand moving the tool.Or
•By keeping the tool stationary and moving the
work.
Or
•By moving both in relation to one another.

15. Influence of Parameters on Machining
The work piece provides the parent metal, from which the
unwanted metal is removed by the cutting action of the
tool to obtain the predetermined shape and size of the
component.
The chemical composition and physical properties of the
metal of the workpiece have a significant effect on the
machining operation.
The tool material and its geometry are equally significant
for successful machining.
The type and geometry of the chip formed are greatly
effected by the metal of the work piece, geometry of the
cutting tool and the method of cutting.
The chemical composition and the rate of flow of the
cutting fluid also provide considerable influence over the
machining operation.

16. ORTHOGONAL AND OBLIQUE CUTTING
The process of metal cutting is divided into the following
two main classes:
Orthogonal Cutting

17. ORTHOGONAL AND OBLIQUE CUTTING
Oblique Cutting

18. ORTHOGONAL AND OBLIQUE CUTTING

19. ORTHOGONAL AND OBLIQUE CUTTING
ORTHOGONAL
OBLIQUE

20. Orthogonal Vs Oblique
Orthogonal Cutting
The
cuttingremains normal to the direction
of tool feed or work feed.
The
direction
ofchipflow
velocity is normal to the cutting
edge ofthetool.(chip
flow angle)
The angle of inclination ‘i’ of
the cutting edge of the tool with
the normal to the velocity V
c is
zero.
Only two components of cutting
forces act on tool.These two
components are perpendicular
to each other.
The cutting edge is longer than
the width of the cut.
Examples are jack
plane ,broaching,slotting,sawing
etc.
edgeofthetool
Oblique Cutting
The cutting edge of the tool always
remains inclined at an acute angle
to the direction of tool feed or work
feed.
The direction of chip flow velocity
is at an angle β with the normal to
the cutting edge of the tool. (chip
flow angle)
The
cutting
edgeofthetoolis
inclined at an ‘i’with the normal to
thedirectionofworkfeed or tool
cfeed V.
Three
mutually
perpendicular
components of cutting forces act at
the cutting edge of the tool.
The cutting edge may or may not be is
longer than the width of the cut.
Examples are lathe turning, Milling and
drilling etc.
.

22. Classification of Cutting Tools
The cutting tools used in metal cutting can be broadly classified
as:
•Single point tools :
Those having only one cutting edge.
Ex: Lathe tools, shaper tools, planer tools, boring tools, etc.
•Multi-point tools:
Those having more than one cutting edge.
Ex: milling cutters, drills, broaches, grinding wheels, etc.
The cutting tools can be classified according to the motion as:
•Linear motion tools:
Ex: Lathe, boring, broaching, planing, shaping tools, etc.
•Rotary Motion tools:
Ex: milling cutters, grinding wheels, etc.
•Linear and Rotary Motion tools:
Ex: drills, honing tools, boring heads, etc.

24. Principal Angles of Single Point Tools
Side rake angle
(α
s)
End relief angle
(ERA)
End cutting edge angle (ECEA)
Side View
Front View
Top View
Lip angle
Nose Radius (NR)
Side cutting edge angle (SCEA)
Back rake angle (α
b)
Side relief angle (SRA)

26. Principal Angles of Single Point Tools
Rake Angle
i)Positive Rake
ii)Zero Rake
iii)Negative Rake
Side rake angle
(α
s)
End relief angle
(ERA)
Nose Radius (NR)
End cutting edge angle (ECEA)
Lip Angle
Clearance Angle
Relief Angle
Cutting Angle
Side cutting edge angle (SCEA)
Side View
Front View
Top View
Lip angle
Back rake angle (α
b)
Side relief angle (SRA)

27. Geometry of Single Point Cutting Tool (Turning)
27
TOOL ELEMENTS

Fig. 1.14 Elements of Single Point Cutting Tool
Shank 
– It is main body of tool. It is the backward
part of tool which is hold by tool post. The shank
is gripped by tool holder.
Flank 
– Sometime flank is also known as cutting
face. It is the vertical surface adjacent to cutting
edge. According to cutting edge, there are two
flank side flank and end flank.
Face 
– It is top surface of the tool along which
the chips slides. It is the horizontal surface
adjacent of cutting edges
Base 
–The bottom surface of tool is known as base. It is
just opposite surface of face.
Heel 
– It is the intersection of the flank & base of the tool. It
is curved portion at the bottom of the tool.
Nose or cutting point 
– It is the front point where side
cutting edge & end cutting edge intersect.
Cutting edge 
– It is the edge on face of the tool which
removes the material from workpiece. The cutting edges
are side cutting edge (major cutting edge) & end cutting
edge ( minor cutting edge)
Noise radius 
–It is radius of the nose. Nose radius
increases the life of the tool and provides better surface
finish. Too large a nose radius will induce chatter.

28. Geometry of Single Point Cutting Tool (Turning)
28
TOOL ANGLES

End Cutting Edge Angle: 
The angle formed in
between the end cutting edge and a line
perpendicular to the shank is called end cutting
edge angle. It provides clearance between tool
cutting edge and workpiece.
Side Cutting Edge Angle: 
The angle formed in
between the side cutting edge and a line parallel
to the shank. It is responsible for turning the chip
away from the finished surface.
Fig. 1.15 Figure explaining end cutting edge angle and side
cutting edge angle

29. Geometry of Single Point Cutting Tool (Turning)
29
TOOL ANGLES

3. Back Rack Angle:
 The angle formed between the tool
face and line parallel to the base is called back rake
angle. Positive back rake angle takes the chips away from
the machined surface, whereas negative back rake angle
directs the chips on to the machined surface.
4.
 End Relief Angle:
 
The angle formed between the
minor flank and a line normal to the base of the tool is
called end relief angle. It is also known as front clearance
angle. It avoids the rubbing of the workpiece against tool.
5. Lip Angle/ Wedge Angle: 
It is defined as the angle
between face and minor flank of the single point cutting
tool.
Fig. 1.16 Figure explaining Back rake angle, End relief angle
and Wedge or lip angle

30. Geometry of Single Point Cutting Tool (Turning)
30
TOOL ANGLES

6.
 Side Rake Angle:
 
the angle formed between
the tool face and a line perpendicular to the
shank is called side rake angle.
7. Side Relief Angle: 
the angle formed between
the major flank surface and plane normal to the
base of the tool is called side relief angle. This
angle avoids the rubbing between workpiece and
flank when the tool is fed longitudinally.
Fig. 1.17 Figure explaining Side rake angle & Side relief angle

32. American System
For example a tool may
designated in the following
sequence:
8-14-6-6-6-15-1
•Bake rake angle is 8
•Side rake angle is 14
•End relief angle is 6
•Side relief angle is 6
•End cutting Edge angle is 6
•Side cutting Edge angle is 15
•Nose radius is 1 mm
Tool Signature

33. Chip Formation
The fig.representsthe
shapingoperation,wherethework
stationaryremains
advancesintothework
piece
andthetool
piece
towards left.
Thusthe metalgets
compressed very severely, causing
shear stress.
Thisstressis maximum
alongthe plane is called
shear plane.
Ifthe material ofthe workpiece
isductile,flows plastically along the shear
plane, forming chip, which flows upwards
along the face of the tool.
.

34. Chip Formation
The complete plastic deformation of the
metal does not take place entirely along
the shear plane only.
It actually occurs over a definite area
PQRS.
The metal structure starts getting
elongated along the line PQ below the
shear plane and continues above the
shear plane and continues up to the line
RS where its deformation is completed.
The complete area PQRS is known as
shear zone.
The shape of the shear zone is a wedge
shape, with its thicker portion near the
tool and the thinner one opposite to it.
This shape of shear zone is one of the
reasons to curl the chip.
The produced chip is very hot and its
safe disposal is very necessary.

35. Chip Formation
The tool will cut or shear off the metal, provided by
•The tool is harder than the work metal,
•The tool is properly shaped so that its edge can be
effective in cutting the metal,
•The tool is strong enough to resist cutting pressures
but keen enough to sever the metal, and
•Provided there is movement of tool relative to the
material or vice versa, so as to make cutting action
possible.

36. Chip formation in metal cutting is the process where material is
removed from a workpiece in the form of chips due to plastic
deformation and shear when a cutting tool interacts with the
material. The type of chip formed (continuous, discontinuous, or
serrated) depends on factors like the workpiece material, tool geometry,
cutting speed, and feed rate. Understanding chip formation is crucial for
optimizing machining processes and achieving desired surface finishes
Chip Formation

37. Types of Chips
The chipsproducedduringmachining
can be broadly classified as three types.
•Continuous Chips
•Discontinuous or segmented chips
•Continuous Chips with built-up edge

38. Types of Chips
1. Continuous Chips
The basis of the production of the
continuous chip is the continuous plastic
deformation of the metal ahead of the tool,
the chip moving smoothly up the tool face.
This typechipis
producedmachiningaductilematerial,like
while
mild
steel, under favorable conditions, such as
high cutting speeds and minimum friction
between the chip and the tool face.
The friction between the chip-tool
interface can be minimized by polishing
the tool face and adequate use of coolant.
Other factors responsible : bigger rake
angle, finer feed and keen cutting edge.

39. Types of Chips
2. Discontinuous or Segmental Chips
This type of chips produced during machining of brittle materials
like cast iron and bronze.
These chips are produced in the form of small segments.
As the tool advances forward, the shear plane angle gradually decreases
until the compressive stresses acting on the shear plane become too low
to prevent rupture.
At this stage, any further advancement of the tool results in the fracture
of the metal ahead of it, thus producing a segment of the chip.
With further advancement of the tool, the processes of metal fracture
and production of chips segments go on being repeated, and this is how
the discontinuous chips are produced.

40. Types of Chips
2. Discontinuous or Segmental Chips
These are also produced in machining of
brittle materials when low cutting speeds
are used adequate lubricant is not
provided.
This causes excessive friction between the
chip and tool face, leading to the fracture of
the chip in to small segments.
This will also result in excessive wear on
the tool and the poor surface finish on the
work piece.
Other factors responsible: smaller rake
angle, too much depth of cut.

41. Types of Chips
3. Continuous Chips with built-up edge
While machining ductile material when
high friction exists at the chip-tool
interface results the continuous chips with
built-up edge.
The normal reaction of the chip on the
tool face is quite high.
It is maximum at the cutting edge or nose
of the tool.
This givesrisetoan
extensively
high
temperatureandcompressed metal
adjacent to the tool nose gets welded to it.
The chip is also sufficiently hot and gets
oxidized as it comes off the tool and turns
blue in colour.
The extra metal welded to the nose of the
tool is called built-up edge.

42. Types of Chips
3. Continuous Chips with built-up edge
Metal in built-up edge is highly strain
hardened and brittle.
During the chip flow up the tool, the built-
up edge is broken and carried away with
chip, rest of it bonded to the work piece
and make it rough.
Due to the built-up edge the rake
angle also altered and so is the cutting
force.
Other factors responsible : low cutting
speed, excessive feed, small rake angle,
lack of lubricant.

43. Types of Chips
3. Continuous Chips with built-up edge
Adverse effectsof built-upedge
formation:
•Rough surface finish.
•Fluctuating cutting force, causing,
vibrations in cutting tool.
•Chances of carrying away some
material from the tool by the built-up
surface, producing crater on the tool
face and causing tool wear.
Precautionsto avoidbuilt-upedge
formation:
•The coefficient of friction at the chip-
tool interface should be minimized by
means of polishing the tool face.
•Adequate supply of coolant.
•Large rake angle.
•High cutting speeds and low feeds.

44. Chip Control and Chip Breakers
The chips produced during machining, specially while employing
higher speeds in machining of high tensile strength materials,
need to be effectively controlled.
Higher speeds causing to higher temperatures resulting chip will be
continuous, of blue colour and take the shape of coil.
Adverse effect of coiled chips on machining:
•Effects the tool life by spoiling the cutting edge, creating
crater and rising the temperature.
•Lead to poor surface finish on the work piece.
•If the chip gets curled around the rotating w/p or tool, it may be
hazardous the machine operator.
•If a large and continuous coil is allowed to be formed, it may
engage the entire machine and even the work piece, its quite
dangerous.
•Very large coils offer a lot of difficulty in their removal.
Such difficulties are not encountered while machining materials like
brass and cast iron.

45. Chip Control and Chip Breakers
The chip breaker break the produced chips
into small pieces.
The work hardening of the chip makes the
work of the chip breakers easy.
If the job requirements do not call for very
strict chip control the common methods
used for chip breaking are :
•By control of tool geometry :
By grinding proper back rake and side rake
according to the speeds and feeds.
•By obstruction method :
by interposing a metallic obstruction in the
path of the coil.

46. Chip Control and Chip Breakers
When a strict chip control is desired, some sort of chip
breaker has to be employed.
The following types of chip breakers are commonly used.
•Groove type
•Step type
•Secondary Rake type
•Clamp type

47. t2 is cut chip thickness
r is chip thickness ratio
r = t1/t2 < 1 ( t1 < t2)
k = 1/r = chip reduction coefficient
α is rake angle
φ is shear angle
Vc is cutting velocity
Vf is chip flow velocity
Vs is shear velocity
t1 is un-cut chip thickness
. Mechanics of orthogonal cutting
Assumptions made in the analysis of
orthogonal machining
1. The tool is perfectly sharp and has no contact along the clearance face
2. Width of chip remains constant.
3. Uniform cutting velocity.
4. A continues chip is produced without BUE
5. Volumetric changes of material during machining is zero.
That is
Volume before cutting = volume after
cutting
t1 *b*l1 = t2*b*l2 t1/t2 = l2/l1 = r
Also we can say that volumetric flow rate is also equal
t1*b*Vc = t2*b*Vf t1/t2 = Vf / Vc

48. Chip Thickness Ratio
Thickness of the upward flowing chip is more than the actual depth
of cut.
t
2>t
1
Chip thickness ratio,
Chip reduction coefficient,
t
r 
1
t
2
k 
1

t
2
r t
1
It is an index of the amount of plastic deformation which the metal
in to the chip has undergone. So the chip thickness ratio is the ratio
of uncut chip thickness to the chip thickness.
Higher the value of r better is supposed to be the cutting action.

49. Shear angle
tan  
r cos
1 r sin 
t
1
sin

OP

From triangle OAP,
From triangle OBP,
t
2
OP

cos( 
 )
Hence,
Shear angle : The shear plane angle is
 the angle between the shear plane
and the direction of tool travel during metal cutting.
 It's a crucial parameter
in machining as it influences cutting forces, tool wear, and surface
finish.
 Essentially, it determines how the material deforms and breaks
away from the work piece.

50. V
c
V
f
Analyticall
y,

v
s
v
fv
c
cos
sin(90  (   ))sinsin(90  )
v
s
v
fv
c


cos(   )sin
f
v
c sin
cos(    )
v

v
f v
c 
r

 cos(  -  )

 sin
r 
s
v
c cos
cos(   )
v

c
f c
t
 v v  rAs, r 
t
0
Volume of material per unit time  Volume of material flowing up the chip
 v
c  t
0  w  v
f  t
c  w
Velocity Relationships

51. Force relationship in Orthogonal cutting
The relationshipsamongthecuttingforces
were withthefollowingestablishedbyMerchant
assumptions.
M. Eugene Merchant
1.The cuttingvelocityalways
remains constant.
2.Cuttingedge of the tool
remainssharp throughout the cutting.
3.There is no side ways of flow of the chip.
4.Only continuous chip is produced.
5.There is no built-up edge.
6.No consideration is made of the inertia force
of the chip.
7. The behavior of the chip is like that of a free
body which is in the state of stable
equilibrium under the action of two resultant
forces which are equal, opposite and
collinear.

52. F
s = Shear Force, which acts along the shear
plane, is the resistance to shear of the metal in
forming the chip.
F
n = Force acting normal to the shear plane, is
the backing up force on the chip provided by
the work piece.
F = Frictional resistance of the tool acting
against the motion of the chip as it moves
upward along the tool.
N = Normal to the chip force, is provided by
the tool.
F
c = Horizontal cutting force exerted by the
tool on the work piece.
F
t = Vertical or Tangential force which helps in
holding the tool in position and acts on the
tool nose
Force relationship in Orthogonal cutting

53. It is useful to determine the relation
between the various forces and angles.
In the diagram three force
triangleshavebeencombinedandRandR’
together have been replaced by R.
The force R can be resolved into two
components F
c and F
t.
F
c and F
t can be determined by force
dynamometers.
The rake angle (α) can be
measuredfrom the tool, and forces F and N can
then be determined.
The shear angle () can be obtained
from it’s relation with chip reduction
coefficient.
Now Fs & Fn can also be determined. tc
→→
→

F
R 
F
Work
Tool
Chip
F
t
F
c
F
N
F
n
α
α
β
F
s
∅
(
β

- )
α
R
Merchant’s circle

54. The procedure to construct a Merchant’s circle diagram
Clearance Angle
Work
Tool
Chip
F
t
F
c
F
F
n
F
s
α
α
β
N
∅
R

55. Relationship of various forces acting on the chip with the horizontal
and vertical cutting force diagram
Chip
Tool
Clearance
Angle
Work
F
t
F
c
F
N
F
n
α
α
β
F
s
∅
(
β

-
)
α
R F
S  F
C cos  F
t sin
F
N  F
C sin  F
t cos
F
N  F
S tan(     )
F F
C sin  F
t cos
N F
C cos  F
t sin

56. Forces in a single point tool in Turning
It is a case of oblique cutting in which three component
forces act simultaneously on the tool point.
 F
t = The feed force or thrust force acting in
horizontal plane parallel to the axis of
the work.
 F
r = The radial force, also acting in the horizontal
plane but along a radius of the work piece. (along the
axis of the tool)
 F
c = The cutting force acting in vertical plane and is
tangential to the work
surface. (also called as tangential force)
Incase of orthogonal cutting,only
two component forces come in to play (F
r = 0)
c
c r
F
2
F
2
R

 F
2
 F
2
t r
R

 F
2
For orthogonal cutting.

57. Work Done in Cutting

59. CUTTING SPEED, FEED AND DEPTH OF CUT
Cutting speed :(m/min)
Cutting speed of a cutting tool can be defined as the rate at which its
cutting edge passes over the surface of the work piece in unit time.
It is normally expressed in terms of surface speed in meters per
minute (m/min).
It considerably effects the tool life and efficiency of machining.
If it is too high, the tool gets overheated and its cutting edge may fail,
needing regrinding.
If it is too low, too much time is consumed in machining and full
cutting capacities of the tool and machine are not utilized, which
results in lowering of productivity and increasing the production cost.

60. CUTTING SPEED, FEED AND DEPTH OF CUT
Feed Rate: (mm/rev)
Feed of the cutting tool can be defined as
the distance it travels along or into the work
piece for each pass of its point through a
particular position in unit time.
For example, in turning operation on a
lathe it is equal to the advancement of the
tool corresponding to each revolution of
the work.
However, it is computed and mentioned in
different machine tools and different
operations.
For example, in planning it is the work
which is fed and not the tool.
Similarly, in milling work involving the
use of a multi-point cutter, the feed is
basically considered per tooth of the
cutter.

61. CUTTING SPEED, FEED AND DEPTH OF CUT
The cutting speed and feed of a cutting
tool is largely influenced by the
following factors.
Materials being machined.
Material of the cutting tool.
Geometry of the cutting tool.
Required degree of surface finish.
Rigidityof the machine
toolbeing used.
Type of coolant being used.

62. CUTTING SPEED, FEED AND DEPTH OF CUT
Depth of Cut : (mm)
It is indicative of the penetration of the
cutting edge of the tool into the work
piece material in each pass, measured
perpendicular to the machined surface.
It determines the thickness of the metal
layer removed by the cutting tool in one
pass.
For example, in turning operation on a
lathe it is given by:
Depth of cut = (D-d)/2
Where,
D=Original diameter of the stock in mm
d=Diameter obtained after turning, in mm.

64. SOURCES OF HEAT IN METAL CUTTING
When material deformed plastically, most of the energy used in
converted in heat energy.
During metal cutting, heat is generated in three region as shown in
Fig.
1.Primary heat zone
(Around share plane)
2. Secondary heat zone
(Tool-chip interface)
3. Tertiary heat zone
(Tool-work piece interface)

65. SOURCES OF HEAT IN METAL CUTTING
It is the region in which actual plastic
deformation of the metal occurs
during machining.
Due tothis
deformation
heatis
generated.
A portion of this heat is carried away
by the chip, due to which its
temperature is raised.
The rest of the heat is retained by the
work piece.
It is known as Primary Deformation
Zone.
1. Primary heat zone (Around share plane)

66. SOURCES OF HEAT IN METAL CUTTING
As the chip slides upwards along face of the
tool friction occurs between their surfaces,
due to which heat is generated.
A part of this heat carried by the chip,
which further raises the temperature of the
chip. And the rest transferred to the tool
and the coolant.This areaisknown
as
Secondary
deformation zone.
The amount
of
heat
frictionincreaseswiththeincrease
generateddueto
in
cutting speed.
Itisnotappreciably
effected
withthe
increase in depth of cut.
When the feed rate is increased the amount
of frictional heat generated is relatively low.
But, in that case, The surface finish
obtained is inferior.
2. Secondary heat zone (Tool-chip interface)

67. SOURCES OF HEAT IN METAL CUTTING
3. Tertiary heat zone
(Tool-work piece interface)
That portion of tool flank which rubs
against the work surface is another
source of heat generation due to
friction.
This heat is also shared by the tool, work
piece and the coolant used.
It is more pronounced when the tool is
not sufficiently sharp.

68. SOURCES OF HEAT IN METAL CUTTING
Fig.
shows
thedistributionoftheheat
generated during metal cutting, neglecting
the heat flowing to the atmosphere.
On an average, about 70% of the total heat
is carried away by the chip, about 15% is
transferred to the tool and the remaining
15% to the work piece.
With an increase in the cutting speed a
higher amount of heat is absorbed by the
chip and lesser amount is transferred to the
tool and the work piece.
It is an obvious advantage in high speed
machining.
Some of the heat generated is also shared
and carried away by the flowing cutting
fluid, when used.
The shear angle also effects the heat
generation.
A larger share angle leads to a smaller heat
generation in the primary deformation zone.

69. TOOL LIFE
Tool life can be defined as the time interval for which the tool works
satisfactorily between two successive grindings (sharpening).
When the tool wear is increased considerably, the tool loses its ability
to cut efficiency and must be reground.
The tool life can be effectively used as the basis to evaluate the
performance of the tool material, assess machinability of the work
piece material and know the cutting conditions.
There are three common ways of expressing tool life:
•As time period in minutes between two successive grindings.
•In terms of number of components machined between two
successive grindings. This mode is commonly used when the tool
operates continuously, as in case of automatic machines.
•In terms volume of material removed between two successive
grindings. This mode of expression is commonly used when the tool
is primarily used for heavy stock removal.

70. TOOL LIFE
The method of assessing the tool life in terms of the volume of
material removed per unit of time is a practical one and can be easily
applied as follows:
Volume of material removed per unit time
Volumeof material removed per unit time
  .D.t. f .Nmm
3
/ min
Where,
D= dia. Of work piece in mm t=depth of cut in mm
f=feed rate in mm/rev
N=No. of revolutions of work per minute
If ‘T’ be the time in minutes to tool failure, then:
Total volume of metal removed to tool failure:
 .D.t. f .N.Tmm
3

71. TOOL LIFE
We also know that the cutting speed,
V 
 DN
m / min1000
 Total Volumeof metal removed totool
failure :
V 1000  t  f Tmm
3
 Tool life , T V .1000.t. f .Tmm
3
L

72. TOOL LIFE
Tool life equation : Taylor’s tool equation
Tool life of a cutting tool may be expressed as:
VT
n
 C
Where,
V= cutting speed in m/min T=Tool life in min
C=A constant
(numerically eqaul to cutting speed that gives the tool life in one min)
n=A constant
(depends on finish, workpiece material and tool material)

73. FACTORS AFFECTING TOOL LIFE
1.Cutting speed
2.Feed and depth of cut
3.Tool Geometry
4.Tool material
5.Work material
6.Nature of cutting
7.Rigidity of machine tool and work
8.Use of cutting fluids.

74. EFFECT OF CUTTING SPEED

75. FEED AND DEPTH OF CUT
Tool life can be defined as the time interval for which the tool works
257
m /
min
V
T
0.19
 f
0.36
 t
0.80
where,
V  cutting speed inm / min
T Tool life in min
f  Feed rateinmm / min
t  Depthof cut inmm
For a give Tool life,
C
m /
min
V

f
a
 t
b
where,
C  Acons tan

76. TOOL MATERIAL
The main characteristics of a good cutting tool material are its hot
hardness, wear resistance, impact resistance, abrasion
resistance, heat conductivity, strength, etc.
What is important to tool life is the likely changes in these
characteristics at high temperature because the metal cutting
process is always associated with generation of high amount of heat
and, hence, high temperatures.
The cutting speed has the maximum effect on tool life, followed by
feed rate and depth of cut.
All these factors contribute to the rise of temperature. That is why it
is always said that an ideal tool material is the one which will remove
the largest volume of work material at all speeds.
The tool material which can withstand maximum cutting
temperature without losing its principal mechanical properties
(specially hardness) and geometry will ensure maximum tool life,
and, hence, will answer the most efficient cutting of metal.
We, therefore, conclude that the higher the hot hardness and
toughness in the tool material the longer the tool life.

77. CHARACTERRISTICS OF CUTTING TOOL MATERIALS
cuttingtoolsshouldThe materialusedforthemanufacture
of posses the following characteristics:
1. Ability to retain its hardness at elevated temperatures, called
hot hardness.
2. Ability to resist shock, called toughness.
3. High resistance to wear, to ensure longer tool life.
4. Low coefficient of friction, at the chip-tool interface, so that the
surface finish is good and wear is minimum.
•Should be cheap.
•Should be able to be fabricated and shaped easily.
•If it is to be used in the form of brazed tips, its other physical
properties like tensile strength, thermal conductivity,
coefficient of thermal expansion and modulus of elasticity,
etc., should be as close to the shank material as possible to
avoid cracking.

78. TYPES OF CUTTING TOOL MATERIALS
The following materials are commonly used for manufacturing the
cutting tools.
Selection of a particular material willdepend on the type of
service it is expected to perform.
•High Carbon Steel
•High speed Steel
•Cemented Carbides
•Stellite
•Cemented Oxides or Ceramics
•Diamond

79. High Carbon Steel
Plain carbon steels having a carbon percentage as high as 1.5% are in
common use as tool materials for general class of work.
However, they are not considered suitable for tools used in
production work on account of the fact that they are not able to
withstand very high temperature.
With the result, they cannot be employed at high speeds.
Usually the requiredhardness is lost by the as soonas the
temperature rises to bout 200
0
C – 250
0
C.
They are also not highly wear resistant.
They are used mainly for hand tools.
They are, however less costly, easily forgeable and easy heat treat.
High carbon medium alloy steels are found to be more effective than
plain high carbon steels.
These steels, are provided better hot hardness, higher impact
resistance, higher wear resistance etc., by adding small amounts of
tungsten chromium, molybdenum, vanadium, etc., which
improves their performance considerably and they are able to
successfully operate up to cutting temperatures of 350
0C.

80. High Speed Steel (HSS)
It is a special alloy-steel which may contain the alloying elements like
tungsten, chromium, vanadium, cobalt and molybdenum, etc., up to
25 percent.
These alloying elements increase its strength, toughness, wear
resistance, cutting ability to retain its hardness at elevated
temperatures in the range of 550
0C to 600
0C.
On account of these added properties the high speed steel tools are
capable of operating safely at 2 to 3 times higher cutting
speeds than those of high carbon steel tools.
The most commonly used high speed steel is better known by its
i.e,theone
that
composition ofalloyingelementsas18-4-2
contains 18%W ,4% Cr and 1% V.
Another class ofH.S.S. contains high proportions of cobalt
(2 to 15%) and is known as cobalt H.S.S.
It is highly wear resistance and carries high hot hardness.
AhighlytoughvarietyofH.S.S.,knownasVanadium
H.S.S., carries 2%V, 6%W, 6% Mo and 4% Cr.
It is widely favored for tools which have to bear impact loading and
perform intermittent cutting.

81. Cemented Carbides
The Everyday growing demand of higher productivity has given rise
to the production of cemented or sintered carbides.
These carbides are formed by the mixture of tungsten, titanium or
tantalum with carbon.
The carbides, in powered form, are mixed with cobalt which acts as a
binder.
Then a powder metallurgy process isapplied and the mixture,
sintered at high pressures of 1500kf per sq. cm to 4000 kg per sq Cm
and temperatures of over 1500
0C, is shaped in to desired forms of
tips.
These carbide tips are then brazed or fastened mechanically
(clamped) to the shank made of medium carbon steel.
This provides an excellent combination ofan extra-hard cutting
edge with a tough shank of the tool.

82. Cemented Carbides
These cemented carbides posses a very high degree of hardness and
wear resistance.
Probably diamond is the only material which is harder than these
carbides.
They are able to retain this hardness at elevated temperatures up to
1000
0C.
With the result, the tools tipped with cemented carbide tips are
capable of operating at speeds 5 to 6 times (or more) higher than
those with the high speed steels.
It will be interesting to note at this stage that the best results with
these tools can be obtained only when the machines, on which they
are to be used, are of rigid construction and carry high powered
motor so that higher cutting speeds can be employed.

83. Stellite
It is a non-ferrous alloy consisting mainly of cobalt, tungsten and
chromium.
Other elements added in varying proportions are tantalum,
molybdenum and Boron.
It has good shock and wear resistance and retains its hardness at red
heat up to about 920
0
C.
On account of this property, it is advantageously used for
machining materials like hard bronzes, and cast and malleable
iron, etc.
Tools made of stellite are capable of operating at speeds up to 2
times more than those of common high speed steel tools.
Stellite does not respond to the usual heat treatment process.
Also, it can be easily machined by conventional methods.
Only girding can be used for machining it effectively.
A stellite may contain 40-50%Co, 15-35%Cr, 12-25%W and 1-4%
carbon.

84. Cemented Oxides or Ceramics
The introduction of ceramic material as a useful cutting tool
material is rather, a latest development in the field of tool
metallurgy.
It mainly consists of aluminum oxide (Al
2O
3), which is
comparatively much cheaper than any of the chief constituents of
cemented carbides.
Boron nitrides in powdered form are added and mixed will
aluminum oxide powder and sintered together at a temperature of
about 1700
0C.
They are then compacted into different tip shapes.
Tool made of ceramic material are capable of withstanding high
temperature, without losing their hardness, up to 1200
0C.
They are much more wear resistant as compared to the cemented
carbide tools.

85. Cemented Oxides or Ceramics
But at the same time, they are more brittle and possess low
resistance to bending.
With the result, they cannot be safely employed for rough
machining work and in operations where the cut is intermittent.
However, their application for finishing operations yields very
satisfactory results.
It is reckoned that, under similar conditions, the ceramic tool are
capable of removing (MRR) 4 times material than the tungsten
carbide tools with a consumption of 20 percent less power than the
latter.
They can safely operate at 2-3 times the cutting speeds of tungsten
carbide tools.
Ceramic tool material is used in the form of tips which are either
brazed to the tool shank or held mechanically on them as the
cemented carbide tips specially designed tool holders are also
used for holding these tips.
Usually no coolant is needed while machining with ceramic tools.

86. Diamond
Diamond is the hardest material known and used as cutting tool
material.
It is brittle and offers a low resistance to shock, but is highly wear
resistant.
On account of the above factors diamonds are employed for only
light cuts on material like Bakelite, carbon, plastics, aluminum and
brass, etc.
Because of their low coefficient of friction they produce a high
grade of surface finish.
However, on account of their excessively high cost and the
demerits narrated above, they find only a confined use in tool
industry.
They are used in the form of bits inserted of held in a suitably
designed wheel or bar.
Diamond particles are used in diamond wheels and laps.

87. MACHINABILITY
Def: Machinability of a material gives the idea of the ease with
which it can be machined.
The parameters generally influencing the machinability ofa
material are:
–Physical properties of the material
–Mechanical properties of the material
–Chemical composition of the material
–Micro-structure of the material
–Cutting conditions

88. MACHINABILITY
Since this property (machinability) of the material depends on
various variable factors, it is not possible to evaluate the same in
terms of precise numerical values, but as a relative quantity. The
criteria of determining the same may be as follows:
•Tool life - The longer the tool life it enables at a given cutting
speed the better is the machinability.
•Surface finish – It is also directly proportional i.e., the better the
surface finish the higher is the machinability.
•Power consumption – Lower power consumption per unit of metal
removed indicates better machinability.
•Cutting forces – The lesser the amount of cutting force required for
the removal of a certain volume of metal or the higher the volume
of metal removed under standard cutting forces the higher
will be the machinability.
•Shear angle – Larger shear angle denotes better machinability.
•MRR - Rate of metal removal under standard cutting conditions.

89. MACHINABILITY INDEX
The machinability for different materials are compared in terms of
their machinability indexes.
For thispurposethemachinabilityindex
of
freecuttingsteel
serves as datum, with reference to which all other machinability
indexes are compared.
The machinability index of this steel is taken as 100.
For computing the machinability index of any other material the
following relationship used.
Cutting speed of material for20min.tool life
Machinability Index (%)= ×100
Cutting speed of standard free-cutting steell for20min.tool life
The machinability index for free cutting steel is 70% the relative
machinability indexes for some materials are given as:
Material Machinability
Index (%)
Material Machinability index
(%)
Stainless steel
Low carbon steel
Copper
25
55-65
70
Red brass
Aluminum alloys
Magnesium alloys
180
300-1500
500-2000

90. USE OF CUTTING FLUIDS
Cutting fluids are used in machining work for helping the efficient
performance of the tool operation.
They are used either in liquid or gaseous form.
They assist in the operation in many ways, such as by cooling the tool
and work, reducing friction, improving surface finish, helping in
breaking of chips and washing them away, etc.
These factors help in improving tool life, permitting higher metal
removal rate and improving the quality of surface finish.

91. Cutting Fluids
The use of the metal working fluids is essential in all metal working
operations.
Inmetal machining, a lot of heatenergyis generated
proves harmful to the tool or work or both.
These fluids help in minimizing these adverse effects and, thus,
help to increase the tool life and surface finish.
Afew prominent metal working processesinvolving the use of
these fluids are:
Metal Machining,
Grinding,
Lapping,
Honing,
Stamping,
Drawing,
Spinning,
Blanking,
Molding,
Forging,
Rolling,
Extrusion,
Galvanizing,
Thinning.

92. Sources of heat generation during metal cutting
Friction :
A lot of friction is always takes place between the cutting tool and
the work piece and between tool face and chips passing over it.
The total amount of heat generated depends on many factors
like, cutting speed, feed, tool material, depth of cut and metal
being cut.
The heat is also called heat of friction.
Plastic deformation of Metal:
As the cutting is started, the cutting tool exerts significantly high
pressure on the adjacent metal grains.
This cause deformation or slipping of these grains over
adjacent grains in contact causes friction between them.
This friction leading to heat generation is known as heat of
deformation.
The total amount of heat generated depends on many factors
like, cutting speed, feed, tool material, depth of cut and metal
being cut.

93. Sources of heat generation during metal cutting
The sources of heat generation during metal cutting are :
Chip Distortion :
In metal machining, as the cutting proceeds and the chips curl
out, the inside and out side grains of the chip metal are
subjected to compression and tension respectively.
This causes distortion of the chip grains leading to internal
friction among them results the generation of heat.
The heat is also called heat of chip distortion.
The amount of heat generated depends largely on feeds and
depth of cut.

94. Functions of a Cutting Fluid
1.To cool the tool and work piece.
2.To provide adequate lubrication between the tool and the work
piece and the tool and chips.
3.To prevent the adhesion of chips to the tool or work or both.

95. Functions of a Cutting Fluid
To cool the tool and work piece.
The cutting fluid employed at low temperature, as
compared to the temperatures of the tool, work and chips.
The heat generated flows from them outwards the fluid, which
absorbs and drives it away along with it.
The fluid is thus heated up and needs a constant
replacement, by a fresh amount of cooler fluid.
For this reason only a steady flow of the cutting fluid, in ample
quantity is always needed during machining.

96. Functions of a Cutting Fluid
To provide adequate lubrication between the tool and the work
piece and the tool and chips.
It implies the reduction of friction between the tool and work piece
and tool and chips.
This helps in preventing a direct metal contact amongst the work
piece, tool and the chip at the point where the three meet and also
at the tool face.
Which results in appreciable reduction in friction amongst
these.
A lesser amount of heat is generated and less power is consumed
in the machine in metal cutting operation.

97. Functions of a Cutting Fluid
To prevent the adhesion of chips to the tool or work or both
To prevent this, the addition of chemically active agents, like
compounds of sulfur or chlorine are made to the cutting
fluids.
The compounds produce soapy films between the work and
tool and chip and tool face.
Which prevents the direct metal to metal contact, and hence,
the chances of welding or adhesion.
This film also provides lubrication, called metal
lubrication between the mating surface.

98. Qualities of a good Cutting Fluid
1.It must carry away the heat generated during the process and
thus, cool the tool and work piece both in order to minimize the
tool wear and prevent distortion of the work piece.
2.It must provide sufficient lubrication between the tool and work
and the tool and chips.
3.It should be capable of importing anti-welding properties to the
tool and work.
4.It must carry such constituents which will prevent the finished
work surface and the tool from the being rusted or corroded.
5.It should not discolor the finished work surface.
6.It should carry a fairly a mild smell.
7.It should not produce fog and smoke during use.
8.It should be non-poisonous and should not cause skin irritations.
9.Its flash point should be high enough.

99. ECONOMICS OF METAL MACHINING
The basic Endeavour in any production process is to produce an
acceptable component at the minimum possible cost.
In order to achieve this objective in metal cutting or metal
machining, many attempts have been made in several different
ways: such as optimizing the tool life in order to minimize the
production cost, etc.
If cutting speed is reduced in order to enhance the tool life the
metal removal rate is also reduced and, therefore, the production
cost is increased.
A similar effect is observed if effort is made to increase tool life by
reducing the feed rate and depth of cut.
Against this, if effort is made to increase the metal removal rate by
substantially increasing the cutting speed, feed and depth of cut, the
tool life shortens and, therefore, tooling cost increase and so the
total production cost also increase.
A balance is, therefore, required to be struck and a reasonable
(optimum) cutting speed determined, corresponding to which an
economical tool life will be ensured and an economical production
will result.

100. ECONOMICS OF METAL MACHINING
In order to determine the optimum cutting
speed a batch of manufactured components
is considered and its total cost and other cost
components calculated and plotted as shown
in fig.
It will be observed that the tooling cost
increase while the machining cost decrease
with increase in cutting speed.
Also, there is a point (lowest point) ‘P’ on the
total cost curve which indicates the
minimum cost of production.
The cutting speed (V
0) corresponding to this
point gives the optimum cutting speed for
economical tool life.
Similarly, the production cost per piece (K
m)
corresponding to this point is the minimum
cost per piece.
Now, the total production cost of a product
comprises several components as follows:
•Cutting cost or machining cost
•Tool changing cost.
•Tool grinding cost
•Idle cost.

101. RELATIONSHIPS AMONG CUTTING SPEED, PRODUCTION RATE AND COST
The relationship between cutting speed and production rate
(number of pieces produced per unit of time) is shown in
fig.
When thecuttingspeed
is
lowthe
production rate is also low because of
lesser amount of metal removal per unit of
time.
But, as the cutting speed increase the
production also increase and continues to
increase up to a point (P
m) where the rate of
production is maximum.
The corresponding
cutting
speed(V
mp)
represents the optimum value of cutting
speed at which the rate of production will be
highest.
Any Further increase in the cutting speed
will lead to a quicker wearing of tool, more
frequent changing of tool, more down time
and, therefore, a reduced rate of
production.

102. RELATIONSHIPS AMONG CUTTING SPEED, PRODUCTION RATE AND COST
To obtain the diagram, different time
curvesformachiningtime,non-
productivetime,toolchanging
time,tool regrinding time and total time per
piece are drawn.
The lowest point on the total time
curve gives the minimum time taken
for production of each piece.
The corresponding cutting speed (V
mp)
represents the optimum value of
cutting speed at which the total time
taken in production of the component
will be minimum.

103. RELATIONSHIPS AMONG CUTTING SPEED, PRODUCTION RATE AND COST
Our
main
interestisinproducingthe
components atmaximum rateandat
minimum cost.
For this, we replot the minimum cost and
maximum production curves, as shown in

fig.
While observing this diagram we find that the
cutting speed (V
0), at which the total
production cost is minimum, is not the same
as that at which the production rate is
maximum
.The area lying in between these two values
ofcuttingspeedsis
EfficiencyRange(Hi-E
knownashigh
Range) andthe

cutting speeds lying in this range are either
economical or more productive.
For efficient and economical production of
a work piece the cutting speed should
always be selected form with in this range
only.

104. CUTTING SPEED,RELATIONSHIPS AMONG
PRODUCTION RATE AND COST
From the Fig. we can easily draw the
following conclusions:
•Non-productive time : It remains constant
and is not effected by variations in cutting
speed.
•Machining time : It reduce with increase
in cutting speed
•Tool changing time : It increase with
increase in cutting speed.
•Tool regrinding time : It also increase with
increase in cutting speed.
•Total time : It reduce till the cutting speed
reaches the value V
mp and beyond that it
increase with increase in cutting speed.
•Production rate : It increase with increase
with increase in cutting speed till the
latter attains the optimum values (V
mp).
Beyond this, it decrease with increase in
cutting speed.

105. CUTTING SPEED,RELATIONSHIPS AMONG
PRODUCTION RATE AND COST
The effects of cutting speed on various costs
can also be summarized, with respect to
Fig. as follows:
•Non-productive cost : It is not effected by
variations in cutting speed and, therefore,
remains unchanged.
•Machining cost : It reduces with increase
in cutting speed.
•Tool changing cost : It increases with
increase in cutting speed.
•Tool regrinding time : It also increases
with increase in cutting speed
•Total cost : It reduces with increases in
cutting speed until the latter attains its
optimum value (V
0) and beyond that it
increases with in cutting speed.

106. SOME IMPORTANT CONSIDERATIONS FOR
INCRESESING THE PRODUCTION RATE
By increase the cutting speed and feed rate the cutting time (machining
time) can be reduced.
When this reduction in machining time is obtained by increasing the
cutting speed it is known as High Velocity Cutting.
When it is obtained by increasing the feed rate it is known as High power
cutting.
But, the tool life is less adversely effected by increasing the feed rate as
compared to increasing the cutting speed.
However, it is not possible to increase the feed rate indefinitely because it
will call for a higher rigidity of machine tool and an increase in the cutting
forces.
This may ultimately result in the failure of cutting tool, poor surface finish
and a distorted shape of the work piece.
Also, in some cases the work surface may be work-hardened to an
unacceptable extent.
As such, once the higher permissible feed rate has been applied any
further reduction in machining time can be safely obtained by increasing the
cutting speed instead of feed rate.
Moreover, by increasing the cutting speed the cutting forces are reduced,
resulting in better surfaces finish on the work piece and lesser work
hardening of the work surface.

107. SOME IMPORTANT CONSIDERATIONS FOR
INCRESESING THE PRODUCTION RATE
Against this, with higher speeds the amount of heat generated at
the chip tool and work-tool interfaces is higher and so is the
friction.
Consequently, the tool hardness reduces and wear increases
sharply.
These factors reduce the tool life.
Therefore, a very careful consideration has to be made while
deciding about the method to be used to reduce the machining time.
For longer tool life, it is better to increase the feed rate for this
purpose because its effect on tool life is not as detrimental as of
increasing the cutting speed, especially for H.S.S tools.

108. SOME IMPORTANT CONSIDERATIONS FOR
INCRESESING THE PRODUCTION RATE
But, if higher cutting speeds are to be employed the use of
cemented carbides or ceramic tools should be made since they
possess more hot hardness and higher wear resistance.
However, the problem with these tool materials is their brittleness,
Due to which they may fail under high shear, bending or impact
load.
That is why these materials are normally used in the form of bits
instead of making the complete tools out of them.
A vital requirement for high-velocity cutting or high-speed
machining is that the machine tool used should be highly rigid,
strong and free of vibrations.
Also, the cutting tool to be used should be strong and should be
carefully ground to carry correct geometry and high class finish on its
all faces and flanks.
To obtain maximum efficiency, it is also necessary that the fixtures
and attachments used in high-velocity cutting should be strong, rigid,
quick acting and accurate.
This will help in reducing handling time considerably and,
therefore, increasing the production rate.

109. Mechanics of Metal cutting
References :
1.A course on Work shop Technology, Volume –II by
B.S. Raghuwanshi.
2.Elements of Work shop Technology, Volume –II
Machine tools by S.K. Hajra choudary, A.K. Hajra
choudary, Nirjhar Roy.
3.A Text Book of Manufacturing Technology by
R.K. Rajput.
4. A Text Book of Production Engineering by K.C.Jain,
A.K. Chitale.

111. Set up x-y axis labeled with forces, and the origin in the
centre of the page. The cutting force (Fc) is drawn
horizontally, and the tangential force (Ft) is drawn
vertically. (Draw in the resultant (R) of Fc and Ft.
Locate the centre of R, and draw a circle that encloses
vector R. If done correctly, the heads and tails of all 3
vectors will lie on this circle.
Draw in the cutting tool in the upper right hand
quadrant, taking care to draw the correct rake angle (α) from
the vertical axis.
Extend the line that is the cutting face of the tool (at
the same rake angle) through the circle. This now gives the
friction vector (F).
A line can now be drawn from the head of the friction
vector, to the head of the resultant vector (R). This gives the
normal vector (N). Also add a friction angle (β) between
vectors R and N. Therefore, mathematically, R = Fc + Ft = F +
N.
Draw a feed thickness line parallel to the horizontal axis.
Next draw a chip thickness line parallel to the tool cutting
face.
WORK
TOOL
α
CHIP
α

β
F
N
F
c
F
t
F
s
R
F
n
The procedure to construct a Merchant’s circle diagram
Draw a vector from the origin (tool point) towards the
intersection of the two chip lines, stopping at the circle. The result will
be a shear force vector (Fs). Also measure the shear force angle
between Fs and Fc.
Finally add the shear force normal (Fn) from the head of Fs to
the head of R.
Use a scale and protractor to measure off all distances
(forces) and angles.

112. F
t
F
c
F
N
α
α
β
R
α
(
β
-
)
α
α
(90- )
α
α
(90- )
α
O
A
C
B
G
E
D
Chip
Tool
Clearance
Angle
Work
F
t
F
c
F
N
F
n
α
α
β
F
s
∅
(
β

-
)
α
R
F  OA  CB  CG  GB  ED 
GB
 F  F
C sin  F
t cos
N  AB  OD  CD  OD  GE
 N  F
C cos  F
t sin
The coefficient of
friction
  tan 
F
N
Where   Friction angle
Relationship of various forces acting on the chip with the
horizontal and vertical cutting force diagram
Frictional Force System

113. F
t
F
c
A
O
F
n
F
s
∅
α
α
(
β
-
)
α
R
C
D
E
∅
∅
(90-
∅)
(90-
∅)
Chip
Tool
Clearance
Angle
Work
F
t
F
c
F
N
F
n
B
α
α
β
F
s
∅
(
β

-
)
α
R
F
S  OA  OB  AB  OB  CD
 F
S  F
C cos  F
t sin
F
N  AE  AD  DE  BC  DE
 F
N  F
C sin  F
t cos
Also:
F
N  F
S tan(     )
Shear Force System
Relationship of various forces acting on the chip with the
horizontal and vertical cutting force diagram

114. s s
s
s n
s
A
A
Mean shear stress  
F
s
(kgf / mm
2
) F  shear force in kgs
Mean normal stress  
F
n
(kgf / mm
2
) F normal force in kgs
0
0 0
0
s
c
c c
s
F
sF
s
A
v
s
But
sin 
A
s  Area of the shear plane
The shear strain be  .
Considering no loss of work during
shearing
We Know,
Work done in shearing unit volume of
the metal  shear stress  shear strain
F
s  v
s
  

t  w 
v
F
s  v
s F
s  v
s F
s  v
s
    

v
s

1
v
c
sin 

s  t
0  w 
v
c
 t  w 
v
 t  w 
v
t 
w

cos 
, therefore
v
ccos(   )
cos 
  
cos(   ) sin 
Stress and Strain acting on the chip

115. α
Φ
D
D
/
B A
C
Too
l
Wor
k
(Φ-α)
A
/
E
Φ
(90-Φ)
Shearing of
chip
Chi
p
Stress and Strain acting on the chip

116. The magnitude of shear strain 
BE BE
AE A
/
E/
 tan ABE  tan A BE 
BE BE
AEA
/
E
  
cos
sin cos(   )
sin cos(   )
cos(     )
  
  
cos cos(   )  sin sin(    )
sin cos(   )
sincos(    )
   cot   tan(    )
  
cos

sin(    )
A
/
BE  90  ( 90   )      
  
α
Φ
D
D
/
B A
C
Too
l
Chi
p
Wor
k
(Φ-α)
A
/
E
Φ
(90-Φ)
Shearing of
chip
Stress and Strain acting on the chip (contd..)

117. SOURCES OF HEAT IN METAL CUTTING
427
Kcal / min.
In metal cutting, the amount of heat generated per unit of
time is given by the thermal equivalent of the mechanical work done.
Now, the mechanical work done(W.D) is given by :
WD = Cutting force (kgf) X Cutting velocity (m/min
= F
c x V
C kgf m/min.
Now, if Q be the amount of total heat generated in cutting the metal,
then,
Q 
WD (in kgf m / min)
427

F
C V
C

118. Types of Cutting Fluids
1.Cutting oils – which are used neat.
1.Active cutting oils are as shown in fig.
2.Inactive cutting oils :straight minerals or straight mineral oils
mixed with neat fatty oils.
2.Water soluble oils or compounds – which are mixed with water to
form emulsions for use in the machines.

119. Selection of Cutting Fluids

120. Selection of Cutting Fluids

121. Selection of Cutting Fluids