Traditional Machining Processes presentation

Chapter Two
Traditional Machining
Processes
2/29/2024 Manufacturing Engineering I 1

2. Traditional machining processes
2.1. Mechanics of machining
What is machining?
Machining is a general term describing a group of processes that
consist of the removal of material and modification of the
surfaces of a workpiece after it has been produced
™
Machining involves both in traditional and nontraditional
machining operations such as turning, boring, drilling, milling,
planing, shaping, broaching, and grinding, ultrasonic machining;
chemical, electrical electrochemical machining; and high-energy-
beam machining.

• Workpieces are brought to its required shape and size by
removing unwanted material from workpiece material in the
form of chips.

Machining processes involves
 Cutting
 Abrasive processes
 Advance machining processes
Cutting processes remove material from the surface of workpiece
by producing chips
• Turning: a tool remove a layer of material from a rotating
workpiece
• Cutting-off operation, where the cutting tool moves radially
inward and separates the right piece

• Slab-milling: rotating cutting tool removes a layer of material
from the surface of workpiece
• End-milling: a rotating cutter travels along a certain depth in
the workpiece and produces a cavity

Working Principle of machine tools
Machining operation takes place by the relative movement of tool
and work piece. Either tool move (milling, drilling, shaping) or
workpiece move (lathe, planing)
Machine tool produces geometrical surfaces
• Flat surfaces
• Cylindrical surfaces
• Contour surfaces
Milling operation Lathe operation

Cont.
The tool will cut 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 pressure but keen
enough to severe the metal
• Movement of tool relative to workpiece

Depth of cut, feed and cutting velocity
• The basic elements of machining operations:
1. Workpiece
2. Tool
3. Chip
Depth of cut(d): the amount of diameter to be reduced
Feed (f): amount of length reduced per revolution
Cutting speed(v): the measure of cutting tool how it rotates.

2.2. Mechanism of chip formation
The fig. shows shaping operation
 Metal gets compressed severely
as tool reciprocates results in
shear stress
 Stress is maximum along the
plane called shear plane
If job is ductile, the material flows
plastically along the shear plane
forming chip, which flows upwards
along the face of the tool

• A cutting tool moves to the left along the workpiece at a
constant velocity V, and a depth of cut t
• A chip is produced a head of the tool by plastically deforming
and shearing the material continuously along the shear plane.

Types of chips
a) Continuous chips
b) Discontinuous or segmental chips
c) Continuous chips with built-up edge

Cont.
a) Continuous chips
 It is continuous plastic deformation of metal ahead of the tool, the
chip moving smoothly up the tool face
 These type of chip is produce while
machining ductile material like mild
steel under favorable condition
 Bigger rake angle, finer feed and
keen cutting edge

Cont.
b) Discontinuous chip
 These chips are produced in the form of small segment during
machining of brittle material like cast iron
 These also produced in machining of
ductile material when low cutting
Speed without adequate lubrication
 These results wear of tool and poor
surface finish

Cont.
c) Continuous chips with built up edge
 While machining ductile material when high friction exists at tool –
chip interface results a continuous chip with built up edge
 Reaction of the chip on tool rises an
extensively high temperature and
compressed metal adjacent to tool
nose gets welded to it
 The extra metal welded to the tool is called built up edge

Orthogonal and oblique cutting
Orthogonal cutting: in which the cutting edge is normal to workpiece
(angle = 90°)
Oblique cutting: in which the cutting action is inclined with the job by
a certain angle called inclination angle

2.3. Tool geometry
• Tool geometry is basically referred to some specific angles or slope
of the salient faces and edges of the tools at their cutting point.
Both material and geometry of the cutting tools play a big roles on the
effectiveness, efficiency and economics of machining
• Tool geometry affects mechanics of chip formation, cutting
temperature, wear and product accuracy and finish.
Cutting tools classified based on number of major cutting edges
1. Single point cutting tools : Examples: turning tools, shaping,
planning and slotting tools and boring tools

Cont.
1. Double or Two point cutting tools : Example : drills
2. Multipoint (more than two) cutting tool: Example: Milling cutters,
Broaching tools, Hobs, Gear shaping cutters etc.
Single point Double point cutting tool multi point cutting
tool

Geometry of Single point cutting tool (SPCT)
Angles
i) Back rake angle
It is the angle between the face of the tool and a line parallel with
base of the tool measured in a perpendicular plane through the
side cutting edge.
ii) Side rake angle
It is the angle by which the
face of tool is inclined side
ways.

iii) End relief angle
It is the angle that allows the tool to cut without rubbing on the
workpiece
iv) Side relief angle
It is the angle between the portion of the side flank immediately
below the side edge and a line perpendicular to the base of the
tool measured at right angles to the side.

Geometry of Single point cutting tool (SPCT)
v) End cutting edge angle
It is the angle between the end cutting edge and a line
perpendicular to the shank of the tool. It provides clearance
between tool cutting edge and work piece.
vi) Side cutting edge angle
It is the angle between straight cutting edge on the side of tool
and the side of the shank. It is also known as lead angle. It is
responsible for turning the chip away from the finished surface
vii) Nose radius
It is the nose point connecting the side cutting edge and end
cutting edge

Geometry of single point cutting tool
Face or rake surface, which is the surface of cutting tool along which
the chips move
Flank surface that face the workpiece. There are two flank surfaces,
namely principal and auxiliary flank surfaces.
Cutting edge that remove material from the workpiece.
Corner or cutting point, which is meeting point of the principal and
auxiliary cutting edges. Often a nose
radius is provided to avoid a sharp
corner

2.3.1 Concept of rake and clearance angle
• Rake and clearance angle of a cutting tool are the most important
feature of cutting tool
Rake angle (𝜸): inclination of rake surface from reference plane
Clearance angle (α): Angle of inclination of clearance or flank surface
from the finished surface
Rake and clearance angles of cutting tools

Cont.
Function of rake angle
• It allows the chip to flow in convenient direction
• Reduce cutting force and hence reduce power consumption
• Increase tool life and Improve surface finish
Rake angle may be positive, or negative or even zero as shown in Figure

Relative advantage of rake angle
 Positive rake – helps reduce cutting force and thus cutting power
requirement
 Negative rake – to increase edge-strength and life of the tool
 Zero rake – to simplify design and manufacture of the form tools
Clearance angle is essentially provided to avoid rubbing of the tool
(flank) with the machined surface which causes loss of energy and
damages of both the tool and the job surface. Hence, clearance
angle is must be positive (3 ~ 15° depending upon tool-work
materials and type of the machining operations)

Geometry of double point cutting tool

Description system of single point cutting tool
1. Tool - in - hand system
2. Machine reference system – ASA system
3. Tool reference system
Orthogonal rake system (ORS)
Normal rake system (NRS)
4. Work reference system (WRS)

1. Tool-in-hand system
This system of description is where only the salient features of the
cutting tool point are identified or visualized as shown in Fig. There is
no quantitative information, i.e., value of the angles.

Cont.
2. Machine reference system (ASA system)
Geometry of a cutting tool refers mainly its salient working surfaces
and cutting edges. Those angles are expressed with respect to some
planes of reference
In Machine Reference System (ASA), the three planes of reference and
the coordinates are chosen based on the configuration and axes of the
machine tool concerned

Cont.
Planes and axes of references in ASA system are as shown below.
 𝜋𝑅 −Reference plane – plane perpendicular to velocity vector
 𝜋𝑋 −Machine longitudinal plane – plane perpendicular to 𝜋𝑅 and in
the direction of longitudinal feed

Cont.
 𝜋𝑌 − Machine transverse plane – Plane Perpendicular to
both 𝜋𝑅 𝑎𝑛𝑑 𝜋𝑋
• The axes 𝑋𝑚, 𝑌𝑚 and 𝑍𝑚 are in the direction of longitudinal feed,
cross feed and cutting velocity respectively.

Cont.
Definition of angles in ASA system
• 𝛾𝑦 = back rake: angle of inclination of the rake surface from the
reference plane and measured on Machine Transverse plane, 𝜋𝑦
• γx = side/axial rake: angle of inclination of the rake surface from the
reference plane (πR) and measured on Machine Ref. Plane, πX
• αx = side clearance: angle of inclination of the principal flank from
the machined surface (or Vc) and measured on πX plane.
• αy = back clearance: same as αx but measured on πy plane

Cont.
• ∅𝑒 = end cutting edge angle: angle between the end cutting edge
(its projection on 𝜋𝑅) from 𝜋𝑥 and measured on 𝜋𝑅
• ∅𝑠 = approach angle: angle between the principal cutting edge (its
projection on 𝜋𝑅) and 𝜋𝑦 and measured on 𝜋𝑅
• Nose radius, r (in inch) curvature of the tool tip
The order of angles in machine reference system (ASA) is
𝛾𝑦, 𝛾𝑥, 𝛼𝑦, 𝛼𝑥, ∅𝑒, ∅𝑠, 𝑟(𝑖𝑛𝑐ℎ)

3. Tool geometry in tool reference system
Orthogonal rake system (ORS) [also called ISO - old]
In ORS system configuration of tool geometry is taken as a reference
The planes of reference and the co-ordinate axes used for expressing
the tool angles in ORS are: 𝜋𝑅 − 𝜋𝑐 − 𝜋𝑜 𝑎𝑛𝑑 𝑋𝑂 − 𝑌𝑂 − 𝑍𝑂

Cont.
• where,
𝜋𝑅 = Reference plane perpendicular to the cutting velocity vector, 𝑉
𝑐
𝜋𝑐 = cutting plane; plane perpendicular to 𝜋𝑅 and taken along the
principal cutting edge
𝜋𝑂 = Orthogonal plane; plane perpendicular to both 𝜋𝑅 and 𝜋𝑐
and the axes;
Xo = along the line of intersection of 𝜋𝑅 and 𝜋𝑜
Yo = along the line of intersection of 𝜋𝑅 and 𝜋𝑐
Zo = along the velocity vector, i.e., normal to both Xo and Yo axes

Cont.
• The main geometrical angles used to express tool geometry in
Orthogonal Rake System (ORS) and their definitions will be clear
from figure below

Cont.
Definition of angles:
 𝜸𝒐 = orthogonal rake: angle of inclination of the rake surface from
Reference plane, 𝜋𝑅 and measured on the orthogonal plane, 𝜋𝑜
 λ = inclination angle; angle between 𝜋𝑐 from the direction of assumed
longitudinal feed [𝜋𝑋] and measured on 𝜋𝑐
 𝛼𝑜= orthogonal clearance of the principal flank: angle of inclination of the
principal flank from 𝜋𝑐 and measured on 𝜋𝑜

Cont.
• 𝛼𝑜′ = auxiliary orthogonal clearance: angle of inclination of the
auxiliary flank from auxiliary cutting plane, 𝜋𝑐′ and measured on
auxiliary orthogonal plane, 𝜋𝑐′ as indicated in Fig. below

Cont.
• φ = principal cutting edge angle: angle between 𝜋𝑐 and the
direction of assumed longitudinal feed or 𝜋𝑋 and measured
on 𝜋𝑅
• φ1 = auxiliary cutting angle: angle between 𝜋𝑐′ and 𝜋𝑋 and
measured on 𝜋𝑅
• Nose radius, r (mm) r = radius of curvature of tool tip
ORS System – λ, 𝛾𝑜, 𝛼𝑜, 𝛼𝑜’, φ1, φ, r (mm)

2.4. Forces analysis using merchants’ circle diagram
Knowing the cutting forces are required for :
• Estimation of cutting power consumption, for proper selection of
the power source(s)
• Structural design of the machine – fixture – tool system
• Evaluation of role of the various machining parameters ( process –
cutting velocity 𝑉
𝑐, feed(𝑠𝑜), depth of cut(𝑡), tool – material and
geometry, environment – cutting fluid) on cutting forces
• Study of machinability characterization of the work materials
• Condition monitoring of the cutting tools and machine tools

Cont.
The relationship among cutting forces were established
by Merchant with the following assumptions:
• The cutting velocity remains always constant
• Cutting edge of the tool remains sharp throughout the cutting
• There is no side ways of flow of chip
• Only continuous chip is produced
• There is no built up edge
• No consideration is made of the inertia force of the chip

Cutting force components
The single point cutting tools characterized by having one cutting force
during machining. But that force is resolved into three components for
ease of analysis
• 𝑭𝒁: main or major component as it is the largest in magnitude
• 𝑭𝒀: not large in magnitude but is
responsible for causing dimensional
inaccuracy and vibration.
• 𝑭𝑿: larger than 𝐹𝑌, and least
significant.

Cont.
Vector sum of force component, where R is resultant force
• 𝑅 = 𝐹𝑋 + 𝐹𝑌 +𝐹𝑍
• 𝐹𝑋𝑌 = 𝐹𝑋 + 𝐹𝑌
• 𝑅 = 𝐹𝑋𝑌 + 𝐹𝑍

Cont.
Relation between various forces and angle
𝐹𝑐 −Horizontal cutting force exerted by tool on the workpiece
𝐹𝑡 −vertical or tangential force which helps in holding the
tool in position and acts on the tool nose
𝐹 −Shear force due to tool-chip interface
𝑁 −normal to the chip force
𝐹𝑠 −shear force along shear plane
𝑁𝑠 −force acting normal to shear
plane

Cont.
Fz is cutting force also
denoted by Fc
𝐹𝑥𝑦 =Ft
𝐹𝑠 = 𝐹𝑐 cos ∅ − 𝐹𝑡 sin ∅
𝑁𝑠 = 𝐹𝑐 sin ∅ + 𝐹𝑡 cos ∅
𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 𝑜𝑓 𝑓𝑟𝑖𝑐𝑡𝑖𝑜𝑛
𝜇 = 𝑡𝑎𝑛𝛽 =
𝐹
𝑁
𝐹 = 𝐹𝑡 cos 𝛾 + 𝐹𝑐 sin 𝛾
𝑁 = 𝐹𝑐 cos 𝛾 − 𝐹𝑡 sin 𝛾

2.5. Tool wear and tool life
Tool failure
A properly designed cutting tool is expected to perform the metal
cutting operation
If it is not giving a satisfactory performance it is indicator of the tool
failure and these are observed by the following effect during operation:
• Poor surface finish
• Higher consumption of power
• Overheating of cutting tool
• Appearance of burnishing band on the work surface

Cont.
• During the operation, a cutting tool may fail due to one or more of
the following reasons:
1. Thermal cracking and softening
2. Mechanical chipping
3. Gradual wear

Tool failure due to Thermal cracking and softening
• Although the cutting tool is quit hard to withstand high
temperature, still every tool material has a certain limit to which it
can withstand the elevated temperature without losing its hardness
• If that limit crossed, the tool material starts deforming plastically at
the tip and at the cutting edge under the action of cutting pressure
and the high temperature
• The main factors responsible for creating such condition of tool
failure are cutting speed, high feed rate, excessive depth of cut,
smaller nose radius and improper selection of tool material

Cont.
Source of heat generation
Heat is generated in three main region
o Around shear plane
o Tool chip interface
o Tool work piece interface

Cont.
• The temperature ranges within which the common tool materials
can successfully operate without losing their hardness are:
𝐶𝑎𝑟𝑏𝑜𝑛 𝑡𝑜𝑜𝑙 𝑆𝑡𝑒𝑒𝑙𝑠 200℃ − 250℃
𝐻𝑖𝑔ℎ 𝑠𝑝𝑒𝑒𝑑 𝑠𝑡𝑒𝑒𝑙𝑠 560℃ − 600℃
𝐶𝑒𝑚𝑒𝑛𝑡𝑒𝑑 𝐶𝑎𝑟𝑏𝑖𝑑𝑒 800℃ − 1000℃
Fluctuation of temperature on the cutting tool subjected to local
expansion and contraction leads to thermal cracking

Tool failure due to mechanical chipping
• Mechanical chipping of the nose and/or the cutting edge fail due to
high cutting pressure, mechanical impact, excessive wear, too high
vibration and chatter, weak tip and cutting edge, etc.

Tool failure due to gradual wear
• When a tool is in use for sometime it is found to have lost some
weight or mass, implying that it has lost some material from it, which
is due to wear
Types of wears −crater wear
−Flank wear

Cont.
Crater wear
Crater wear is created due to pressure of hot chip sliding up the
face of the tool
The metal from the tool is supposed to transferred sliding chip in
the form of diffusion
Higher feed and lack of cutting fluids increase the rate of crate
wear

Cont.
Flank wear
• It occurs due to abrasion between tool flank and work piece and
excessive heat generation
• The magnitude of these wear is depend on tool material hardness
when a tool is subjected to such type of wear:
 Work piece loses its dimensional accuracy
 Energy consumption/power requirement is increased
 Poor surface finish of work piece

Mechanism of wear
1. Abrasion
2. Adhesion
3. Diffusion
4. Chemical wear

Abrasion
The material of the tool face is softened due to high temperature; and
hard particles present on the underside of the chip may be:
• Fragments of hard tool material
• Broken pieces of built-up edge which are strain hardened
• Extremely hard constituents
fragment of hard tool material plough into relatively softer
material of tool face and remove metal particles by mechanical
action

Adhesion
• Due to excessive pressure high friction occurs between the sliding
surface of the chip and the tool face
• This gives rise in temperature, causing metallic bond between the
material of tool face and the chip
• When the chip slides, these small
small welds are broken. But this
separation is not along the line of
contact

Diffusion
Solid sate diffusion, which consists of transfer of atoms in metal crystal
lattice, at elevated temperature
The amount of diffusion depends on
o Temperature at the contact between the tool face and chip
o Period of contact between the tool face and chip
o The bonding affinity between the material of the tool and the
chip

Chemical wear
 These occurs when cutting fluid is chemically active to the material
of the tool
 Chemical reaction taking places between the cutting fluid and the
tool material, leading to a change in chemical composition of
material of tool

Tool Life
• Tool life is a time interval for which tool works satisfactorily
Tool life is expressed in
 Time period in minutes between two successive grindings
 Number of components machined between two successive grindings
 Volume of material removed between two successive grindings

Cont.
Volume of material removed per unit time
𝜋. 𝐷. 𝑡. 𝑓. 𝑁𝑚𝑚3
𝑚𝑖𝑛
Where, D diameter of work piece in mm
t depth of cut in mm
f feed rate in mm/rev
N number of revolution of workpiece per minute
The total volume of metal removed to tool failure
𝜋. 𝐷. 𝑡. 𝑓. 𝑁. 𝑇 𝑚𝑚3
T time in minute to tool failure

Cont.
Cutting speed
𝑉 =
𝜋𝐷𝑁
1000
𝑚 𝑚𝑖𝑛
Total volume of metal removed to tool failure
𝑉. 1000. 𝑡. 𝑓. 𝑇 𝑚𝑚3

Taylor’s tool life equation
• Taylor’s tool life equation
𝑉𝑇𝑛 = 𝐶
Where, V – cutting speed
T – tool life in min
C – constant
n – taylor exponent: depends on tool and workpiece material and
cutting workpiece

Cont.
Values of n in different materials
Tool life curves for variety cutting tool
material

Example1
1. Using Taylor equation for tool life and letting n=0.5 and C=120,
calculate the percentage increase in tool life when the cutting speed is
reduced by 50%

Example2
If in turning of a steel rod by a given cutting tool (material and geometry)
at a given machining condition (𝑠𝑜 𝑎𝑛𝑑 𝑡) under a given environment
(cutting fluid application), the tool life decreases from 80 min to 20 min.
due to increase in cutting velocity, 𝑉
𝑐 from 60 m/min to 120 m/min., then
at what cutting velocity the life of that tool under the same condition and
environment will be 40 min.?

Economics of Machining
 In manufacturing activity the cost of manufacturing is great
importance.
 The parameters to be considered in the evaluation of cost
production.
 Low production cost
 high production rate
 large quantity of production

2/29/2024 Economics of Machining 67
• To maximize the rate of production , high speed and feed can be
used. But higher speed and feed reduces tool life
 results in frequent tool change.
• Even though tool life is longer with low speed and feed , the rate of
production will be too small.
• There exists optimum cutting condition for minimum production
time and minimum production cost.

Cutting speed
Cost
Total cost
Material
handling
Raw Material
Machining Tool
Tool
changing
.
opt
V

Cost of a single pass turning
1) Cost of labour
 salaries of workers
2) Cost of operating a machine
Interest
depreciation cost
 cost for power consumption
cost of maintenance

3) Overhead Cost
 Cost of establishment which includes: building , land , office
equipment and staff salaries.
4) Job handling cost
Cost due to loading and unloading
5) Cost of a tool
6) Cost of resetting of Tool
Included cost of resetting and regrind
Cont.

Cont.
 Cost of cutting action
Machining time per piece
N
f
l
Tm
.

V
N
f
L Length of work piece
Feed
Number of rotation (rpm)
Cutting speed
min
1000
m
DN
V


V
f
Dl
Tm
.
1000


u
C Cost of operating a machine(including cost of labour) per unit time
Cost of cutting action m
uT
C



Cost of a single pass turning
 Job handling cost
Let be time of loading and unloading
h
T
 Cost of tool per job
Let denote the cost per cutting edge of the tool
e
C
 For throw-away carbide bits
Number of cutting edges/bit

e
C
Cost of a bit
 For regrind able tools
Number of times the tool can be reground

e
C
Cost of the tool
+ Cost of regrinding
h
uT
C

Job handling cost


Cont.

T
T
C m
e

Cost of tool per job is tool life
T
 Tool setting cost
Let be time required for setting the tool
s
T
s
m
u T
T
T
C

Cost of tool per job

2/29/2024
74
Cont.
Total machining cost
Let the total cost of turning per piece
p
C
T
T
C
T
T
T
C
T
C
T
C
C m
e
s
m
u
h
u
m
u
p 




Cont.
The total machining time per piece is given by:
0
T
T
T
T
T
T
T s
m
h
m 


0
Let denote the rate of production. it is
expressed by the reciprocal of machining time
per piece
p
R
T
T
T
T
T
T
T
T
T
T
T
R
s
m
h
m
s
m
h
m
o
p














1
1
1

Optimum cutting speed for minimum cost in
turning
2/29/2024
76
T
T
C
T
T
T
C
T
C
T
C
C m
e
s
m
u
h
u
m
u
p 



T
T
C
T
T
T
T
T
C
C m
e
s
m
h
m
u
p 









V
f
Dl
Tm
.
1000


Keeping constant to analyze the effect of cutting speed
f
Constant(B)
V
B
Tm  f
DL
B
1000


C
VT n

n
V
C
T
/
1








Cont.
T
T
C
T
T
T
T
T
C
C m
e
s
m
h
m
u
p 









Optimum cutting speed for minimum cost opc
V
0



V
C p
 
n
u
e
s
opc
C
C
T
n
C
V















/
1
1
 
 
n
n
e
n
n
s
h
u
p
C
BV
C
V
C
BT
T
V
B
C
C /
1
1
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Tool life for optimum cutting speed for minimum cost opc
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Traditional Machining Processes presentation

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