Cutting Orthogonal cutting Cutting tools

1. 1
Machining processes

2. BOOKS
1.Manufacturing Technology, Volume 2, P.N. Rao, McGraw
Hill Education (India) Private Limited.
2.Manufacturing Processes for Engineering Materials, S.
Kalpakjain, Addision-Weseley Publishing Company.
3.Fundamentals of Metal Cutting and Machine Tools, B.L.
Juneja, G.S. Sekhon, New Age International Private Limited.
4.Engineering Metrology, Jain, Khanna Publishers
5.CAD/CAM: Computer-Aided Design and Manufacturing by
M.P. Groover & E.W. Zimmers, Jr.
6.CNC Machines by B.S. Pabla & M. Adithan
2

3. Machine Tools
A power-driven machine that performs a
machining operation, including grinding
• Functions in machining:
– Holds workpart
– Positions tool relative to work
– Provides power at speed, feed, and depth
that have been set
• The term is also applied to machines that
perform metal forming operations
3

4. Mechanics of machining
4

5. Important parameters of machining
1. Thickness of uncut layer
2. Thickness of chip
3. Inclination of the chip-tool interface with respect to the face of
the tool (rake angle)
4. The relative velocity of the work piece and the cutting tool
A clearance angle between the work and the flank surface
make the cutting possible.
5

6. 6
Mechanism of chip formation

7. 7
Cutting ratio

8. 8
Shear angle

9. 9
Shear angle
 





sinr1
cosr
tan
cos
sin
r
t
t
rRatio_Cutting
c






10. 10
Shear strain
 
 








cossin
cos
,or
)tan(cot
BD
DCAD
BD
AC
strain_Shear

11. 11
Shear Strain
Shear strain in machining can be computed
from the following equation, based on the
preceding parallel plate model:
 = tan( - ) + cot 
where  = shear strain,  = shear plane angle,
and  = rake angle of cutting tool

12. Chip velocity, Vc
• Maintaining mass continuity
12
)cos(
sinV
V
rVV
velocity_cuttingV
tVtV
c
f
cf
cwhere
2f1c








13. 13

14. Velocity diagram
14
 
 
 
  Y
V
cos
cos
Y
V
,,
tY
S
ratestrain
sinV
V
cossin
cos
,or
)tan(cotstrainShear
sin
V
cos
Vs
cos
V
s
s
f





















(90o-Φ+α)
α
Φ
(90o-α)
Vs
V
Vf
Where, ∆Y = thickness of the deformation zone
∆t = time taken

15. 15
Types of chips
• Continuous chip without built-
up edge (BUE)
• Continuous chip with built-up
edge (BUE)
• Serrated chip
• Discontinuous chip

16. Continuous chip without built-up edge (BUE)
•Ductile material
•Small uncut thickness
•High cutting speed
•Large rake angle
•Suitable cutting fluid
16

17. Continuous chip with built-up edge (BUE)
•Stronger adhesion between chips and
tool face
•Large uncut thickness
•Low rake angle
17

18. 18
Continuous chip with BUE

19. Serrated chip
•Appears as saw teeth
•Low conductivity metal
•Strength of the metal decreases
sharply with temperature
•E.g. titanium
19

20. Discontinuous chip
•Brittle material
•Large uncut thickness
•Low cutting speed
•Small rake angle
20

21. 21
Problem
The following data are available from an orthogonal cutting
operation:
Determine the (a) cutting ratio (b) shear angle (c) shear strain and strain rate on
shear plane(d) chip velocity and (e)shear velocity.
Work material Aluminium Steel
Uncut chip thickness (t1), mm 0.13 0.23
Width of cut, mm 2.5 2.5
Rake angle 5o -5o
Cutting speed, m/s 2 2
Chip thickness (t2), mm 0.23 0.58

22. Orthogonal cutting
22

23. 23
Orthogonal cutting
• Can be represented by a 2-dimensional figure
• The work move in the plane parallel to the
plane of the paper
• The chip material particles also move in the
plane parallel to the plane of the paper
• No component of velocity in the direction
perpendicular to the plane of the paper

24. 24
Orthogonal Cutting Model
A simplified 2-D model of machining that describes
the mechanics of machining fairly accurately
Figure - Orthogonal cutting: (a) as a three-dimensional process

25. 25

26. 26
Orthogonal cutting

27. 27

28. 28
Oblique cutting

29. 29

30. 30

31. 31

32. 32
Cutting forces

33. 33
• First proposed by Ernst and Merchant
– Trans. ASME, 29, 299,1941.
– Considered idealized case of a single plane
– An approximate is predicted
– Forces on chip from rake face = Forces on work
surface along shear plane
• Forces on tool
– FC -along the direction of cutting velocity v
– FT-normal to the direction of cutting velocity v

34. 34
Forces in orthogonal cutting

35. 35

36. 36
Merchant’s circle diagram

37. 37

38. 38
Forces in Metal Cutting
For orthogonal cutting the forces can be
derived as:
F = Fc sin + Ft cos
N = Fc cos - Ft sin
Fs = Fc cos - Ft sin
Fn = Fc sin + Ft cos
Fc = Fs cos + FN sin
FT = FN cos - Fs sin

39. 39
Forces in Metal Cutting


cos(
F
R s



cos(
cos(F
F s
c

40. 40
Shear Stress
Shear stress acting along the shear plane:
sin
wt
A o
s 
where As = area of the shear plane
Shear stress = shear strength of work material during cutting
s
s
A
F
S 

41. 41
The Merchant Equation



cos(sin
v)cos(wt
vF)(W
c
c
s1
C
Whereas, t1, w, and vc are constants.
For minimum power, differentiating work, W w.r.t Ø, we get:
0sin(sin)cos(cos  
s
,Hence
)2/cos(0)2cos(  
2/2  

42. Shear angle relations
42
Source Results
Ernst and Merchant 2Ø + λ - α = π / 2 Ø = π/4 + α/2 – λ/2
Merchant’s second solution 2Ø + λ - α = Cm 2Ø =Cm+α/2 – λ/2
Lee and Shaffer Ø + λ - α = π / 4 Ø = π/4+ α - λ
Stabler Ø + λ - α / 2 = π / 4 Ø = π / 4+ α / 2 - λ

43. 43
Specific energy
Total specific energy
• vc = cutting velocity
• w = width of cut
Specific energy for friction
ovf = chip velocity
orc = cutting ratio
o
c
o
c
t
wt
F
vwt
vF
u
c
c

o
ctc
o
c
o
f
f
wt
rFF
wt
Fr
vwt
Fv
u
c
)cossin( 


44. 44
Specific energy for shearing
cvwt
vF
u
o
ss
s 
Thus, the total specific energy
ut = uf + us
# vs = shear velocity

45. Problem 1
• Assume that in orthogonal cutting the rake angle is 15o and the
coefficient of friction is 0.2. using Merchant’s first solution, determine
the percentage increase in chip thickness when friction is doubled.
Solution: Hint
Ø = π/4 + α/2 – λ/2; r = ? tc = ?
Ø’ = π/4 + α/2 – λ’/2; r = ? t’c = ?
45

46. 46
Problem 2
The following data are available from an orthogonal turning
operation:
Determine the (a) shear angle (b) friction coefficient (c) shear stress and shear strain
on shear plane(d) chip velocity and shear velocity and (e) energies uf, us and ut.
Work material Aluminium Steel
Feed (t1), mm/revolution 0.33 0.13
Width of cut, mm 2.5 2.5
Rake angle 5o -5o
Cutting speed, m/s 2 2
Chip thickness (t2), mm 0.53 0.58
Cutting force, Fc, N 430 890
Thrust force, Ft, N 280 800

47. 47
Heat generation and temperature
profile
• During cutting
– Plastic deformation
• Primary shear zone
• Secondary shear zone
– 99% of energy converted into heat
• Heat taken away
– Chip
» Major portion
– Work
– Tool
– Faster wear
– Failure of tool

48. 48
Heat calculation
• W = total power consumed
= FCvc “vc = cutting velocity
• Wp & Ws are heat generated in primary and
secondary deformation zones
• W = Wp + Ws
• Ws = Fvf = Frc vc “vf = chip velocity
• Wp = W – Frc vc

49. 49
• Temperature at primary shear zone Tp is
Where
• x = fraction of primary heat goes to work
• ρ = density of the work material
• s = specific heat of the work material
• t1, = uncut chip thickness
• w = width of cut
1
p
p
svwt
W)x1(
T




50. 50
• Ts = temperature rise at secondary shear zone
• To = initial temperature of the work piece
• Total temperature, T is given by
T = To + Ts + Tp
The maximum temperature is along the rake
face of the tool.

51. 51
Temperature profile when cutting
with a single cutting tool

52. 52

53. 53

54. 54

55. 55

56. 56

57. 57

58. 58

59. 59

60. 60

61. 61

62. 62

63. 63

64. 64
CNC Shaper Machine

65. 65

66. 66

67. 67

68. 68

69. 69

70. 70

71. 71

72. 72

73. 73

74. 74

75. 75

76. 76

77. 77

78. Classification of Cutting Tool
1. Single-Point Tools
– One cutting edge
– Turning uses single point tools
– Point is usually rounded to form a nose radius
2. Multiple Cutting Edge Tools
– Also called multipoint cutting tools
– More than one cutting edge
– Motion relative to work usually achieved by
rotating
– Drilling and milling use rotating multiple cutting
edge tools.
78

79. Single Point Cutting Tools
79

80. 80

81. 81

82. 82

83. Nomenclature of single point cutting tool
83

84. 84

85. 85

86. 86
Signature of right hand single point
cutting tool
( American Standard System)
10-20-7-6-8-5-0.8

87. Multipoint cutting tools
87

88. 88

89. 89

90. 90

91. 91
Broaching tools

92. 92
Broaching tools

93. 93
BORING TOOL TYPES AND NOMENCLATURE

94. Problem
The following data are available from a turning operation:
* s stands for (second digit of serial number)
Determine the (a) shear angle (b) friction coefficient (c) shear stress and shear strain
on shear plane(d) chip velocity and shear velocity and (e) energies uf, us and ut.
94
Work material Aluminium Steel
Tool signature 0,s*,6,7,10,0,9 0,-s* ,6,7,15,0,9
Feed, mm/revolution 0.15 0.15
Depth of cut, mm 2.5 2.5
Cutting speed, m/s 2 2
Chip thickness, mm 0.23 0.58
Cutting force, Fc, N 430 890
Thrust force, Ft, N 280 800

95. Oblique cutting
95

96. 96

97. 97

98. 98

99. 99

100. 100

101. 101

102. 102

103. 103

104. 104
Orthogonal cutting
1- Cutting tool travel in the
direction perpendicular to the
cutting edge.
2-The cutting edge clear either
end of work piece.
3- Chip flows in the direction
perpendicular to the cutting
edge.
4-Two mutually perpendicular
cutting forces act on the work
piece.
Oblique cutting
1-cutting edge travels,
making an angle with the
normal of cutting edge.
2-The cutting edge may or
may not clear either end of
work piece.
3- chip flows, making an
angle with normal of cutting
edge.
4-Three mutually
perpendicular forces are
involved.

105. 105
Ff
Fr
Ft
Z
X
Y
Fc
Orthogonal plane
R
Turning tool
Cylindrical job
Rake face
Forces acting during oblique turning


106. 106
Cutting forces acting during oblique
turning operation
• Feed force, Ff - along z-axis
• Radial force, Fr - along x-axis, radial direction
• Cutting force, Fc- along y-axis perpendicular to
x-z plane
• Merchant circle diagram is drawn for the forces
acting in orthogonal plane, i.e. the plane containing
cutting force Fc and Ft ( resultant of Ff and Fr)

107. 107
Normal rake angle (αn)
Where αb and αs = back and side rake angles
Ψ =side cutting edge angle
Shear angle (φn)
nc
nc
n
sinr1
cosr
tan




108. 108
Z
X
Y
Turning tool
Cylindrical job
Rake face
Forces acting during oblique turning
Depth
ofcut=
d
Feed = f
Chip
ψ
ψ

109. 109
Depthofcut=d
Feed = f
ψ

110. 110
cos
d
wcut.of.Width 
cosftthickness.chip.Uncut 1 
cc1 fdvvwtmrrrate.removal.Metal 
Where,
Cutting velocity = vc = πDN
D = Average diameter of the
work
N = RPM
ψ = side cutting edge angle
d, f = depth of cut, feed/
revolution

111. 111
volume.unit/consumed.Energy..........
)U(energy.Specific c

fd
F
mrr
vF
U
ccc
c 
ccvFW
Wnconsumptio.Power



112. 112
Machining time (tc)
(for a single cut)
fN
t
L
c 
Where,
L = Length of the work along the axis
F = feed/ revolution
N = rpm of the work

113. 113
Problem
The following data are available from a turning operation:
* s stands for (second digit of serial number)
Determine the (a) shear angle (b) friction coefficient (c) shear stress and shear strain on
shear plane(d) chip velocity and shear velocity and (e) energies uf, us and ut.
Work material Aluminium Steel
Tool signature 9,s*,6,7,10,15,9 mm 9,s*,6,7,10,15,9 mm
Depth of cut, mm 2.5 2.5
Cutting speed, m/s 2 2
Chip thickness, mm 0.23 0.58
Cutting force, Fc, N 430 890
Thrust force, Ft, N 280 800

114. Thanks
114