2. Several types of classification has
been defined
A. Primary process (foundry)
B. Secondary processes: (metal cutting,
metal forming & metal joining processes).
Metal Cutting
Why machining needed:
Many products manufactured by primary
manufacturing methods needs maching to get
their final shape, accurate size and surface
finish.
3. TYPES OF MACHINING
A. Conventional ( e.g. boring, milling..
etc)
Cutting Abrasive
Axisymmetric (drilling) Bonded cutting (grinding)
Prismatic (milling..) Loose cutting (lapping..)
B. Non Conventional (e.g. WJM, EDM,
AJM, AWJM.. etc)
4. MECHANICS OF METAL CUTTING
Mechanics of metal cutting consists of study of
machining process and accurate estimation of
dynamic and cutting forces.
Different scientist have given their different models
and their own theories.
A wedge shaped tool with straight cutting edges is
made to move relative to the workpiece and a layer
of metal called chip is removed. The chip is formed
by continuous shearing action of workpiece.
5. CLASSIFICATION
Orthogonal cutting : It is a
special case in which
cutting edge of tool is
kept perpendicular to
direction of work-tool
movement
Oblique cutting : If the
cutting edge of tool is
not perpendicular to
direction of work-tool
movement
7. SYSTEMS OF DESCRIPTION OF
TOOL GEOMETRY
Tool-in-Hand System – where only the salient
features of the cutting tool point are identified or
visualized. There is no quantitative information,
i.e., value of the angles. e.g. Carpenter
Machine Reference System – i.e. ASA system
(as defined on the basis of reference planes x-x, y-
y, z-z or πR - πX - πY)
Tool Reference Systems (defined w.r.t. Tool)
Orthogonal Rake System – ORS
Normal Rake System – NRS (ISO – new)
Work Reference System – WRS
8. # ASA system has limited advantage
and use like convenience of inspection.
But ORS is advantageously used for
analysis and research in machining
and tool performance. But ORS does
not reveal the true picture of the tool
geometry when the cutting edges are
inclined from the reference plane.
9. GEOMETRY: SINGLE POINT CUTTING TOOL
(ASA)
End cutting edge
Side cutting edge
End
flank
Side
11. TERMINOLOGIES
Rake angle
Back rake angle
Side rake angle
Rake :-- 1. Make the tool more sharp and pointed.
This reduces the strength of tool, as the small
included angle in the tip may cause it to chip away.
2. Reduce cutting forces and power requirements.
3. Helps in the formation of continuous chips
in ductile materials.
4. Avoid the formation of a BUE
12. Relief (clearance)
End relief angle
Side relies angle
Relief:-- 1. To provide a clearance between
machined surface and surface going to be
machined.
2. To keep tool safe during machining and
avoid contact which might disturb its
positioning.
13. Cutting edge angle
End Cutting edge angle
Side Cutting edge angle
Cutting edge angle :-- Increasing the
side cutting edge angle increases the chip contact
length and tool life improves.
Nose radius : To increase the strength of edge.
14. TOOL SIGNATURE
Orthogonal rake
system (ORS)
Inclination angle(і)
Normal rake angle (α)
Side relief angle (γs)
End relief angle (γe)
End cutting edge angle
(ce)
Approach angle(λ)
Nose radius(rn)
American standard
association (ASA)
Back rake angle (αb)
Side rake angle (αs)
End relief angle (γe)
Side relief angle (γs)
End cutting edge angle
(ψe)/(Φe)
Side cutting edge angle
(ψs)/(Φs)
Nose radius(rn)
15. DEFINITION’S (ASA)
Back rake angle (αb) :
Angle between line
parallel to tool axis
passing through the tip
and the rake face where
angle is measured in a
plane perpendicular to
the base.
Side rake angle (αs) (5-
15) : Angle between the
rake face & line passing
through the tip
perpendicular to the tool
axis, where angle is
measured in a plane
perpendicular to the
base.
(αb) = 0 brass
> 0 soft &
ductile materials
< 0 brittle
materials
(αs) = Large
Less Fc, less chip
formation, good
surface finish
Tool
life
Back
rake
15
16. End relief angle (γe ) (5-15) : Angle
between end flank & the line passing
through the tip perpendicular to the
base, where angle is measured in a
plane parallel to the tool axis.
Side relief angle(γs) (5-15) : Angle
between side flank & the line
parallel to tool axis passing through
the tip, perpendicular to the base
where angle is measured in a plane
perpendicular to the tool axis.
End
flank
side
17. End cutting edge
angle (ψe))/(Φe) (ECEA)
: Angle between end
cutting edge & the line
passing through the tip
perpendicular to the tool
axis, where angle is
measured in a plane
parallel to the base.
Side cutting edge
angle (ψs))/(Φs) (SCEA)
: Angle between side
cutting edge & the line
extending the shank
where angle is measured
in a plane parallel to the
base.
18. Cos ψs =
d = depth of cut
w = width of cut
Again = cosψs
Where
f t = true feed
= f(cos ψs)
= uncut chip
thickness = t1/tu
f
f t
s
s
s
s
w
20. TOOL LIFE
Smooth, safe and economic machining:
Prevention of premature and catastrophic
failure of the cutting tools
Reduction of rate of wear of tool to prolong
its life
Cutting tools generally fail by :
Mechanical breakage due to excessive forces
and shocks.
Quick dulling by plastic deformation
Gradual wear of the cutting tool at its flanks
and rake surface.
21. ESSENTIAL PROPERTIES FOR
CUTTING TOOL MATERIALS
High mechanical strength; compressive, tensile, and TRA
Facture toughness – high or at least adequate
High hardness for abrasion resistance
High hot hardness to resist plastic deformation and reduce
wear rate at elevated temperature
Chemical stability or inertness against work material,
atmospheric gases and cutting fluids
Resistance to adhesion and diffusion
Thermal conductivity – low at the surface to resist
incoming of heat and high at the core to quickly dissipate the
heat entered
High heat resistance and stiffness
Manufacturability, availability and low cost.
22. MECHANICS OF CHIP FORMATION
Machining is a process of gradual removal of excess
material from the preformed blanks in the form of
chips.
The form of the chips is an important index of
machining because it directly or indirectly
indicates:
Nature and behavior of the work material
under machining condition
Specific energy requirement (amount of
energy required to remove unit volume of work
material) in machining work
Nature and degree of interaction at the chip-
tool interfaces.
23. Machined chips depend mainly upon:
Work material
Material and geometry of the cutting tool
Levels of cutting velocity and feed and also
to some extent on depth of cut
Machining environment or cutting fluid
that affects temperature and friction at the
chip-tool and work-tool interfaces.
24. MECHANISM OF CHIP FORMATION IN
MACHINING DUCTILE MATERIALS
During
continuous
machining the
uncut layer of
the work
material just
ahead of the
cutting tool
(edge) is
subjected to
almost all
sided
compression as
indicated
Normal
force
Friction
force
25. Due to such compression, shear stress develops, within that
compressed region, in different magnitude, in different
directions and rapidly increases in magnitude. Whenever and
wherever the value of the shear stress reaches or exceeds the
shear strength of that work material in the deformation
region, yielding or slip takes place resulting shear
deformation in that region and the plane of maximum
shear stress. But the forces causing the shear stresses in
the region of the chip quickly diminishes and finally
disappears while that region moves along the tool rake
surface towards and then goes beyond the point of chip-tool
engagement. As a result the slip or shear stops
propagating long before total separation takes place. In the
mean time the succeeding portion of the chip starts undergoing
compression followed by yielding and shear. This phenomenon
repeats rapidly resulting in formation and removal of chips in
thin layer by layer. This phenomenon has been explained in a
simple way by Piispannen using a card analogy
28. The basic two mechanisms involved in chip formation
are
Yielding – generally for ductile materials
Brittle fracture – generally for brittle materials
During machining, first a small crack develops at the
tool tip, due to wedging action of the cutting edge. At
the sharp crack-tip stress concentration takes place.
In case of ductile materials immediately yielding
takes place at the crack-tip and reduces the effect of
stress concentration and prevents its propagation as
crack. But in case of brittle materials the initiated
crack quickly propagates, under stressing action,
and total separation takes place from the parent
workpiece through the minimum resistance path as
indicated
29. The basic major types of chips and the conditions generally
under which such types of chips form are given below:
(Built up Edges)
30. Built-up-Edge (BUE):
Causes of formation: In machining ductile metals like
steels with long chip-tool contact length, lot of
stress and temperature develops in the secondary
deformation zone at the chip-tool interface. Under
such high stress and temperature in between two clean
surfaces of metals, strong bonding may locally take
place due to adhesion similar to welding. Such bonding
will be encouraged and accelerated if the chip tool
materials have mutual affinity or solubility.
The weldment starts forming at
the most favorable location and
thus gradually grows resulting the
formation of Built-up-Edges.
31.
32. Surface roughness
measurement
1. Center Line Average (CLA) method
2. Maximum Peak to valley height, Rt
or Rmax
3. RMS Value, Rq
f = feed
ECEA = ψe SCEA = ψS
R = Nose radius
Peak to valley height formula =
Hmax =
Centre line
avg. value (Ra) = Hmax
34. ζ = chip production coefficient > 1
= 1/r where r is chip reduction coefficient
where, r < 1
AP = t1 = OP sin Φ
PB = t2 = OP sin (90 - (Φ – α)) = cos (Φ – α)
chip reduction coefficient (r) = t2 / t1 = 1/ζ
r
Where Φ is
shear angle
35. VELOCITY TRIANGLE
Relief angle
rake angle
α
Shear plane
Shear angle
Vs
V
Velocity of
Un-cut chip
Vc, chip
velocity
α
Φ
90-Φ
90 + α - Φ
Equation can be reduced to
Where,
Vc = chip velocity
Vs = shear velocity
V = un-cut chip velocity
According to sine rule..
36. NUMERICAL
During a orthogonal metal cutting
operation the limit of shear angle
provided was 8 degree, and the shear
velocity limit was 10 m/s, find the
maximum value of chip velocity
obtained during machining.
37. Cutting force Pz/ Fc
Feed
forceNormal
thrust
force Resultant force
Resultant
force
1 2
3
Friction
Force
N
Normal Friction
force F
Resultant
force
Fc
Cutting
force
Pxy/ FT
Thrust
force
Shear
Force Fs
Normal
Shear
Force FN
4
39. MERCHANT CIRCLE DIAGRAM
α
90- β
Assumptions
Cutting edge straight
& sharp
Homogeneous
material
Orthogonal cutting
β
40. NOMENCLATURE MCD
The conclusion of MCD consists of relation between
different forces.
F (Friction force) = R sin β
N (Normal friction force) = R cos β
Fc (Cutting force) = R cos (β - α)
FT ( Thrust force) = R sin (β - α)
Fs (Shear force) = R cos (Φ + β - α)
Fn (Normal shear force) = R sin (Φ + β - α)
tan β = => β = tan-1µ
µ = friction co-efficient
41. INTER-RELATIONSHIP BETWEEN FORCES
Fs = Fc cos Φ - FT sin Φ
Fn = Fc sin Φ + FT cos Φ
Fc = Fs cos Φ + Fn sin Φ
FT = Fs sin Φ - Fn cos Φ
F = Fc sin α + FT cos α
N = Fc cos α - FT sin α
µ = tan β =
=
42. RELATION BETWEEN FORCES
From the diagram
Fs = AE - BE
= AE – CG
AE = Fc cos Φ
CG = FT sin Φ
Fs = Fc cos Φ - FT sin Φ
Φ = shear angle
Fn = DG + GB
DG = FT COS Φ
CE = FT SIN Φ
Fn = Fc sin Φ + FT cos Φ
AB ║ CG
ACZ ~ ABZ
B & G A & C
Z
Fn
43. SIMILARLY
CG = CH + HG
= CH + BE
CH = FT cos α
BE = Fc sin α
F = Fc sin α + FT cos α
N = AG = AE – EG
= AE – BH
AE = Fc cos α
BH = FT sin α
N = Fc cos α - FT sin α
44. CUTTING FORCE & POWER
Cutting Power = FCV
Friction Power = FVC
Shear Power = FSVS
Cutting Power = Friction Power + Shear Power
FCV = FVC + FSVS
Specific cutting Power =
=
Where, MRR = wt1V
Specific cutting power =
45. ERNEST AND MERCHANT THEORY
&
LEE AND SHAFFER THEORY
Relation between α , β & Φ for minimum power
consumption during machining.
Minimum cutting power PC = FCV
Fs = R cos(Φ + β - α) =
Fc = R cos(β - α)
Fc =
Power req Pc =
For Pc min. (sin Φ cos (Φ + β – α))
should be max.
46. i.e.
let X = sin Φ cos (Φ + β – α) &
Cos (2Φ + β – α) = 0
i.e. 2Φ + β – α =
[Ernest and Merchant theory]
Φ + β – α =
[Lee and Shaffer theory]
47. HEAT GENERATION
Effects of the
high cutting
temperature
on tool and job.
• Rapid tool
wear, which
reduces tool life
• Plastic deformation of the cutting edge
enough hot-hard and hot-strong thermal
flaking.
• Fracturing of cutting edge.
• Built-up-edge formation
10
10
80
33
33
33
48. EFFECTS
Dimensional inaccuracy
Surface damage by oxidation, rapid
corrosion, burning
Induction of tensile residual
stresses and microcracks at the
surface / subsurface
49. DETERMINING OF TEMPERATURE
Some of the methods used for measurement of
temperature at the different interface are are:
Tool work piece thermocouple
Inserted thermocouple
Infrared measurement
Calorimetric method
50. CUTTING FLUIDS/LUBRICANTS
Purpose
Cooling of the job
Lubrication at the chip–tool interface
Cleaning the machining zone
Essential properties of cutting fluids
High specific heat
Friction reducing
Spreading and wetting ability
Easily available and low cost.
51. TYPES OF CUTTING FLUIDS
Air blast or compressed air: Materials like grey cast
iron become inconvenient or difficult if any cutting fluid
is employed in liquid form.
Water: Good wetting and spreading properties and very
high specific heat, water is considered as the best
coolant
Soluble oil: Emulsifying agent and additive mixed with
water
Cutting oils: To reduce friction, adhesion and BUE
formation in heavy cuts.
Chemical fluids: Organic and or inorganic materials
are dissolved in water.
Solid or semi-solid lubricant : applied directly to the
workpiece
Cryogenic cutting fluid : Extremely cold (cryogenic)
fluids like liquid CO2 or N2
55. TOOL WEAR
Flank Wear
Crater Wear (rake face wear): Dominates at high
temperature in ductile materials at high speed
Chipping off of the cutting edge: (brittle, Weak design,
or shock loading).
57. FLANK WEAR
Reason
Abrasion by hard particles and inclusion.
Shearing of the micro welds between tool and work
material.
At low speed flank wear predominates.
If MRR increased flank wear increased.
Effect
Flank wear directly affect the component dimensions
being produced.
Flank wear is usually the most common determinant of tool
life.
58. FLANK WEAR: (WEAR LAND)
Stages
Flank Wear occurs in three
stages of varying wear rates
Primary wear: The region
where the sharp cutting
edge is quickly broken
down and a finite wear land
is established.
Secondary wear: The
region where the wear
progresses at a uniform
rate.
Tertiary wear:
The region where
wear progresses at a
gradually increasing
rate due to increased
tool temperature
59. TAYLOR’S TOOL LIFE EXPERIMENT
Wear and hence tool
life of any tool for any
work material is
governed mainly by
the level of the
machining
parameters i.e.,
cutting velocity, (Vc),
feed, (so/f) and depth
of cut (t/d). Cutting
velocity affects
maximum and
depth of cut
minimum.
60. The tool life obviously
decreases with the increase
in cutting velocity keeping
other conditions unaltered.
If the tool lives, T1, T2, T3,
T4 etc are plotted against
the corresponding cutting
velocities, V1, V2, V3, V4
etc a smooth curve like a
rectangular hyperbola is
found to appear. When
both V and T in log-scale, a
linear relationship
appears….
61. With the slope, n and intercept, c Taylor derived the
simple equation as
VTn = C
where, n is called, Taylor’s tool life exponent. The values of
both ‘n’ and ‘c’ depend mainly upon the tool-work
materials and the cutting environment (cutting fluid
application).
Problem: 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, VC 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.?
62. n = 0.08 to 0.2 for HSS tool
= 0.1 to 0.15 for Cast Alloys
= 0.2 to 0.4 for carbide tool
[IAS‐1999; IES‐2006]
Cutting speed used for different tool
materials
HSS (min) 30 m/min < Cast alloy < Carbide <Cemented carbide
150 m/min < Cermets < Ceramics or sintered oxide (max) 600
m/min
63. MACHINABILITY.
For defining grading of work materials w.r.t.
machining characteristics
Effectively
Machining Efficiently
Economically
Better
dimensional accuracy
&
surface finish
Lower
power consumption,
tool wear
&
surface deterioration
64. The machinability characteristics and their
criteria, i.e., the magnitude of cutting forces
and temperature, tool life and surface
finish are governed or influenced more or less
by all the variables and factors involved in
machining such as,
Properties of the work material
Cutting tool; material and geometry
Levels of the process parameters
Machining environments (cutting fluid
application etc)
And becomes complex to explain as a
whole
65. POSSIBLE WAYS OF IMPROVING MACHINABILITY
OF WORK MATERIALS
Proper tool material.
Optimum selection of Vc.
Selection and method of
application of cutting
fluid.
66. DYNAMOMETER,
Dynamometers are devices used to
measure cutting forces in machining
operation. The cutting force cannot be
detected or quantified directly but their
effect can be sensed using Transducer, for
determining the machine requirement
for the cutting operation. Output consists
of
Elastic deflection
Deformation, pressure
Strain etc
67. Surface Finish.
A machined surface can have two type of
irregularities roughness (small
wavelength) (wrong cutting fluid selection)
& waviness (large wavelength) (due to m/c
vibration) & is defined in terms of surface
roughness, and waviness.
DYNAMOMETER,
68. SURFACE FINISH
Flaws -irregularities
that occur occasionally on
the surface texture
(Includes cracks,
scratches, inclusions in &
on surface)
Lay - Predominant direction
or pattern of the surface
texture
flaw
72. ECONOMICS OF METAL CUTTING
Implementation of economics in machining to optimize
profit.
Tool Wear (regrinding)
Variables Production Rate Tool Life
Vc [ d, f ] MRR Tool changing cost
Production Cost
Calculation cases :
•Total minimum cost.
•For maximum
production rate
•For maximum profit
rate.
(VOpt)Production rate >
(VOpt)Profit rate > (VOpt)
minimum unit cost
73. Previous year papers
Name the two system of designating tool
Discuss variables affecting tool life
Describe cutting tool temperature
Discuss the condition for discontinuous chips.
Difference orthogonal cutting & oblique cutting.
What is continuous chip with build up edges.
What do you understand by tool life
Various types of chips & condition of formation.
Explain merchants circle diagram & derive 2Φ + β – α =
π/2
What are cutting fluids. Explain some.
What is machinability, explain factor affecting
machinability.
How does cutting process parameter affects the cutting
tool wear in a single point tool.
Discuss various types of Chips during metal cutting
