The presentation content deals about metal cutting theory, types of chips, chip formation, chip mechanism, Merchant Circle Theory, Cutting force calculation, Properties and characteristics of cutting fluids, evolution of cutting tools

1. Secondary Manufacturing Processes
Presented by
S.Maharajan, Assistant Professor,
Department of Mechanical Engineering
Ramco Institute of Technology, Rajapalayam

2. Topics to be covered
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▸ Tool Geometry
▸ Mechanics of Chip Formation
▸ Merchants Circle Diagram
▸ Thermal Aspects of Machining
▸ Tool Wear & Tool Life

3. Tool Geometry
▸ Rake Angle
▸ Clearance Angle
▸ Shear Angle
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4. Tool Geometry
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5. Orthogonal Rake System
▸ Orthogonal rake angle: angle of inclination of the rake surface from the
reference plane and measured on orthogonal plane.
▸ Orthogonal clearance of the principal flank: Angle of inclination of the principal
flank from cutting plane measured on orthogonal plane.
▸ Principal Cutting Edge Angle: Angle between cutting plane and the direction of
machine longitudinal feed and measured on reference plane.
▸ Auxiliary cutting Edge Angle:
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6. Tool Designation ORS
▸ Orthogonal Clearance angle = Side Relief Angle
▸ Auxiliary Clearance angle = End Relief Angle
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7. Mechanism of Chip Formation
▸ Mechanism of Chip formation in
Machining Ductile Material
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▸ Lameller Chip Formation by Shear

8. Forms and Colors of chip depends upon
▸ Work Material
▸ Cutting Tool – Material and Geometry
▸ Levels of Process Parameters
▸ Applications of cutting fluid
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9. Chip formation in Machining Brittle
Materials
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10. Geometrical Characteristics of
Continuous Chip
▸ Chip Reduction coefficient = a2/a1
▸ Chip Thickness Ratio = a1/a2
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t = Depth of cut (mm) – perpendicular penetration of
the cutting tool tip in work surface .
so = feed (mm/rev) – axial travel of the tool per
revolution of the job
b1 = width (mm) of chip before cut
b2 = width (mm) of chip after cut
a1 = thickness (mm) of uncut layer (or chip before
cut)
a2 = chip thickness (mm) – thickness of chip after
cut

11. Geometrical Characteristics of
Continuous Chip
Inferences From Graph
ζ (Chip Reduction Coefficient)can be
desirably reduced by
▸ Using tool having larger positive
rake
▸ Reducing friction by using lubricant
▸ Larger value of ζ means more
thickening i.e., more effort in terms
of forces or energy required to
accomplish the machining work.
Therefore it is always desirable to
reduce a2 or ζ without sacrificing
productivity, i.e. metal removal rate
(MRR).
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12. Geometrical Characteristics of
Continuous Chip formation
Inferences from the Equations
▸ with the increase in ζ, shear angle
decreases.
▸ shear angle increases both directly and
indirectly with the increase in tool rake
angle.
▸ Increase in shear angle means more
favourable machining condition
requiring lesser specific energy.
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13. Build Up Edge 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.
▸ Characteristics of BUE Built-up-edges are characterized
by its shape, size and bond strength, which depend upon:
▸ Work tool materials
▸ Stress and temperature, i.e., cutting velocity and feed
▸ Cutting fluid application governing cooling and
lubrication.
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14. Formation of Build up Edge
Harmful effect of BUE formation
▸ Increases the cutting force, vibration.
▸ Deteriorated the surface quality.
▸ May reduce tool life by accelerating tool-wear at its rake surface by adhesion and flaking
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15. Types of Cutting Chips
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Continuous Chip With
Build up Edge
03
✔ Low cutting speed. High Depth of cut
✔ Decrease rake angle, Use a blended tool.
✔ Higher chemical affinity of tool and workpiece
material
Discontinuous Chip
02
✔ Low Rake angle, High Depth of cut
✔ Low cuting speed
✔ Lake of cutting fluid
✔ Brittle materials
Continuous Chip
01
✔ Ductile materials that are machined at high cutting
speeds and/or high rake angles

16. Types of cutting Chips
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17. Cutting Forces and its components in
machining by single point cutting tools
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18. Merchants Circle Diagram
(Ref: Kalpakjian)
Force Analysis: Merchants Eqn:
Fs = Fc CosΦ – FcN sin Φ
FsN = Fc Sin Φ + FcN Cos Φ
F = Fc Sin ∞ + FcN Cos ∞
N = Fc Cos ∞ - FcN Sin ∞
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2
2
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19. Merchants Circle Diagram
(Ref.IIT Kharagpur)
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20. Use of Merchant Circle Diagram
▸ Determination of several other relevant forces from a few
known forces (Machining) without much calculations.
▸ Easy and quick evaluation of coefficient of friction and
dynamic yield shear strength of material of work material.
▸ Development of equations relating the various forces in
machining.
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21. Problems – Merchant circle
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22. Problems in Merchant Circle
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23. Velocity Relations
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24. Problem
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25. Sources of Heat Generation
▸ Primary shear zone (1) where the major
part of the energy is converted into
heat.
▸ Secondary deformation zone (2) at the
chip – tool interface where further heat
is generated due to rubbing and / or
shear.
▸ At the worn out flanks (3) due to
rubbing between the tool and the
finished surfaces.
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26. Cutting Temperature
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27. Temperature distribution
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28. Steps to reduce the cutting temperature
▸ Temperature can be reduced by lowering the principal cutting
edge angle, φ and increasing nose radius, r.
▸ Increase in rake angle will reduce temperature by reducing the
cutting forces but too much increase in rake will raise the
temperature again due to reduction in the wedge angle of the
cutting edge.
▸ Proper selection and application of cutting fluid help reduce
cutting temperature substantially through cooling as well as
lubrication.
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29. Cutting Tool Material Hardness and
Effect of coating Material
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30. Multiphase Coatings
▸ Multiphase coatings on a tungsten-
carbide substrate. Three alternating
layers of aluminum oxide are separated
by very thin layers of titanium nitride.
Inserts with as many as thirteen layers
of coatings have been made. Coating
thicknesses are typically in the range of
2 to 10 μm.
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31. Ranges of properties for
various groups of tool materials
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32. Operating Characteristics of Cutting-
Tool Materials
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33. Favourable Properties of Tool Material
▸ Mechanical properties:
▹ High hardness at elevated temperature.
▹ High deformation resistance to prevent plastic deformation at cutting edge.
▹ High stiffness to maintain accuracy.
▹ High fatigue resistance to resist maximum mechanical load.
▹ High fracture toughness.
▸ Thermal properties:
▹ High thermal conductivity to transfer the temperature away from the cutting edge.
▹ High thermal shock resistance.
▸ Chemical composition being stable.
▸ Tribological properties:
▹ Wear resistance.
▹ Adequate lubricity to prevent build-up on the cutting edge.
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34. Evaluation of Cutting Tool Material
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1960
1986
1900
HSS(W: 18%; Cr: 4%; V: 1%; C: 0.7%)
1930
1910 1920
1940 1950
1970 1980
1990 2000
Automobile WWI Aircraft WWII
Chemical &
Petrochemical
& Polymer
Industries
Jet Engines&
Space
Programs
Reductionof
Cost of
Manufacturing
Defense
SuperAlloys
Just In Time
Stellite
HSS(V: 2~4%, Co: 5 – 12% in W & Cr)
Sintered Carbide for C.I
Carbide for steels
HSS with high V, Mo, Co & C Plain ceramics, Syn. Diamond
Ceramics and Cermets
Coated carbides, PM – HSS, PCD
CBN, coated HSS, SIALON
High performance ceramics
Diamond coated carbides
Diamond and CBN

35. Tool Wear
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During Machining, tool wear takes place due to friction of the chip on the rake
face and of the flanks on the workpiece, and involves abrasion and the removal of
micro particles, as well as microscopic chipping of the cutting edge.
Types of tool wear
Abrasion wear (The removal of micro particles of the tool material by the hard
constituents of the work material)
Adhesion wear (Due to forces of molecular adhesion pick up or sticking
between tool and chip, with the sliding chip tearing away minute particles from the
tool surface)
Diffusion wear (Wear due to mutual dissolution of the reacting materials or
elements at high surface temperature)
Corrosive wear
Fatigue wear

36. Variation of tool wear rate with cutting
time
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37. Geometry and Major Features of wear of
Turning Tools
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38. Tool Life
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39. Growth of Flank wear and assessment of
tool life
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40. References
1. Serope Kalpakjian, ‘Manufacturing Engineering and
Technology’, Pearosn, Prentice Hall, latest Edition.
2. Prof.A.P.Chattopadhyay, IIT Kharagpur, NPTEL Study
Materials.
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