UNIT-1

1. UNIT 1
Theory of metal cutting
Mechanics of chip formation, single point cutting tool,
forces in machining, Types of chip, cutting tools –
nomenclature, orthogonal metal cutting, thermal aspects,
cutting tool materials, tool wear, tool life, surface finish,
cutting fluids and Machinability.

2. INTRODUCTION
 Components are made into various shapes and sizes by using metals.
 Depending the types of tools and operations.
 During the metal removal process, various forces act on the cutting
tool and work piece.

3. Metal Removing Process
 Non-cutting process (or) Chipless process
Forging, Drawing, Spinning, Rolling, Extruding
 Cutting process (or) Chip process
Turning, Drilling, Milling, Planer, Shaping

4. Mechanism of metal cutting

6. Mechanism of Chip Formation
 The type of chip formed during metal cutting depends upon the
machining condition and material to be cut.
 The following variables are influencing in producing the type of
chip such as
 Mechanical properties of material to be cut in particular ductility and
brittleness.
 Depth of cut
 Various angles of tool especially rake angle
 Cutting speed
 Feed rate
 Type of cutting fluid
 Surface finish required on work piece

7. SINGLE POINT CUTTING TOOL

8. Nomenclature of Single Point Cutting Tool
 Parts of a single point cutting tool
 Angles of single point cutting tool
 Effects of Back rake angle
 Effects of Side rake angle

9. Parts of a single point cutting tool
 Shank
 Face
 Flank
 Base
 Nose
 Cutting Edge

10.  Shank: Main body of tool, it is part of tool which is gripped in tool
holder
 Face: Top surface of tool b/w shank and point of tool. Chips flow
along this surface.
 Flank: Portion tool which faces the work. It is surface adjacent to &
below the cutting edge when tool lies in a horizontal position.
 Base: Bearing surface of tool on which it is held in a tool holder.
 Nose radius: Cutting tip, which carries a sharp cutting point. Nose
provided with radius to enable greater strength, increase tool life &
surface life.
 Cutting edge: It is the junction of face and flank.

11. Angles of single point cutting tool
 Rake angle
Back rake angle
Side rake angle
 Relief angle (or) clearance angle
End relief angle
Side relief angle
 Cutting edge angle
End cutting edge
Side cutting edge
 Nose radius

12. Effects of Back rake angle

13.  When will be the positive rake angle used?
To machine the work hardened materials
To machine low strength ferrous and non-ferrous metals
To turn the long shaft of smaller diameters
To machine the metal having lesser recommended cutting speeds
 When will be the negative rake angle used?
To machine high strength alloys
The feed rates are high
To give heavy and interrupted cuts

14. Effects of side rake angle
 During the cutting process, the amount of chip bend depends on side
rake angle.

15. Tool Signature
 Tool angles given in a definite pattern is called tool signature. The tool
angle have been standardized by the American Standards Association
(ASA).
 Back rake angle
 Side rake angle
 End relief angle
 Side relief angle
 End cutting edge angle
 Side cutting edge angle
 Nose radius

16. Types of chip formation
 Continuous chip
 Discontinuous chip
 Continuous chip with built-up edge

17. Continuous chip
 During cutting of ductile material, a continuous ribbon such as chip is
produced due to pressure of the tool cutting edge in compression and
shear.
 It gives the advantage of,
 Good surface finish
 Improving tool life
 Less power consumption
 However, the chip disposal is not easy and the surface finish of the
finished work get affected.

19. The following condition favors the formation
of continuous chips
 Ductile material such as low carbon steel, aluminum, copper etc.
 Smaller depth of cut
 High cutting speed
 Large rake angle
 Sharp cutting edge
 Proper cutting fluid
 Low friction between tool face and chip interface.

20. Discontinuous chip
 Discontinuous chip produced while machining brittle materials such as
grey cast iron, bronze, high carbon steel at low cutting speeds without
fluids.
 During machining the brittle material lacks its ductility which results
for plastic chip formation.

22. The following condition favors the formation
of discontinuous chips
 Machining of brittle material
 Small rake angle
 Higher depth of cut
 Low cutting speeds
 Excess cutting fluid
 Cutting ductile material at very low feeds with small rake angle of the
tool.

23. Continuous chip with built-up edge
 During the cutting process, the interface temperature and pressure are
quite high and also high fiction between tool-chip interface.
 It causes the chip material to weld itself to the tool face near the nose is
called “built-up edge”.
 This process gives the poor surface finish on the machined surface and
accelerated wears on the tool face.

25. The following condition favors the formation
of discontinuous chips with built-up edge.
 Low cutting speed
 Small rake angle
 Coarse feed
 Strong adhesion between chips and tool interface
 Insufficient cutting fluid
 Large uncut thickness

26. Types of metal cutting process
 Orthogonal cutting process (Two – dimensional cutting)
Cutting edge of the tool is perpendicular to the cutting velocity
vector.
 Oblique cutting process (Three dimensional cutting)
Cutting edge is inclined at an acute angle with the normal to the
cutting velocity vector.

28. Sl
No
Orthogonal cutting process Oblique cutting process
1 The chip flows over the tool face and
the direction of chip flow velocity is
normal to the cutting edge.
The chip flows on the tool face
making an angle with the normal
on the cutting edge.
2 The maximum chip thickness occurs
at its middle.
The maximum chip thickness may
not occur at the middle.
3 Tool is perfectly sharp and it contacts
the chip on rake face only.
Frequently, more than one cutting
edges are in action.
4 Tool life is less Tool life is more

29. Thermal aspects
The heat is generated in three region such as shear zone, chip tool
interface region and tool work interface region.
 Shear zone
 The zone which is affected by the energy required to shear the chip or to
separate the chip and work is called shear zone. The heat generation range
is 80-85%
 Chip - tool interface region
 The energy used to overcome the friction completely is the source of the
heat. The heat generation range is 15-20%
 Tool - work interface region
 The energy is supplied to overcome the rubbing friction between flank
face of the tool and work piece is the source of the heat. The heat
generation range is 1-3%

31.  The tool temperature increases due to the following factors such as
Cutting speed
Feed
Properties of tool materials etc.

32. TOOL WEAR
Attrition

33. Diffusion

34. Classification of tool wear
 Flank wear
 Feed < 0.15 mm/revolution
 Crater wear
 Nose wear

36. TOOL LIFE
 Tool life is defined as the cutting time required for reaching a tool life
criterion or time elapsed between two consecutive tool resharpening.
 The following are some of ways of expressing tool life.
Volume of metal removed per grind
Number of work pieces machined per grind
Time unit

37. Factors affecting tool life
 Cutting speed
 Feed and depth of cut
 Tool geometry
 Tool material
 Cutting fluid
 Work material
 Rigidity of work, tool and machine

38. Cutting speed

39. Feed and depth of cut

40. Tool geometry

41. SURFACE FINISH
 Generally, the surface finish of any product depends on the following
factors.
 Cutting speed
 Feed
 Depth of cut

42. CUTTING FLUIDS
 Cutting fluids are used to carry away the heat produced during the
machining. At the same time, it reduces the friction between tool and chip.

43. Functions of cutting fluids
 It prevents the work piece from excessive thermal distortion
 It improves the surface finish
 It causes the chips to break up into small parts. It protects the finished
surface from corrosion.
 It washes away the chip from the tool.
 It prevents the corrosion of work and machine.

44. Properties of cutting fluids
 It should have the high heat absorbing capacity
 It should be odourless
 It should be non-corrosive to work and tool
 It should have high flash point
 It should have low viscosity
 It should be economical to use

45. Types of cutting fluids
 Basically two main type of cutting fluids
 Water based cutting fluids
 Straight (or) heat oil based cutting fluids

46. Water based cutting fluids
 To improve the cooling and lubricating properties of water, the soft soap
or mineral oils are added to it. These oils are known as soluble oils.

47. Straight (or) heat oil based cutting fluids
 Straight oil based cutting fluids means pure oil based fluids. Most of the
oils are not directly used but it is mixed with other oils.
 It is classified into the following subgroups
 Mineral oils
 Straight fatty oils
 Mixed oils
 Sulphurised oils
 Chlorinated oils

48. Methods of applying cutting fluids
 Cutting fluids are used in many ways such as
 Drop by drop under gravity
 Flood under gravity
 Form of liquid jet
 Atomised form with compressed air
 Through centrifugal action

49. MACHINABILITY
 Machinability is defined as the ease with which a material can be
satisfactorily machined. It can also be defined as follows
 The life of tool before tool failure
 The quantity of the machined surface
 The power consumption per unit volume of material removed.

50. Variables affecting machinability
 Work variables
 Tool variables
 Machine variables
 Cutting conditions

51. Evaluation of machinability
 Tool life per grind
 Rate of metal removal per tool grind
 Surface finish
 Dimensional stability of the finished work
 Chip hardness
 Shape and size of chips

52. Advantages of high machinability
 Good surface finish can be produced
 Higher cutting speed can be used
 Less power consumption
 Metal removal rate is high
 Less tool wear

53. Machinability index
 Machinability index
I =
𝐶𝑢𝑡𝑡𝑖𝑛𝑔 𝑠𝑝𝑒𝑒𝑑 𝑜𝑓 𝑚𝑒𝑡𝑎𝑙 𝑖𝑛𝑣𝑒𝑠𝑡𝑖𝑔𝑎𝑡𝑒𝑑 𝑓𝑜𝑟 20 𝑚𝑖𝑛𝑢𝑡𝑒𝑠 𝑡𝑜𝑜𝑙 𝑙𝑖𝑓𝑒
𝐶𝑢𝑡𝑡𝑖𝑛𝑔 𝑠𝑝𝑒𝑒𝑑 𝑜𝑓 𝑠𝑡𝑎𝑛𝑑𝑎𝑟𝑑 𝑠𝑡𝑒𝑒𝑙 𝑓𝑜𝑟 20 𝑚𝑖𝑛𝑢𝑡𝑒𝑠 𝑡𝑜𝑜𝑙 𝑙𝑖𝑓𝑒
I =
𝑉𝑖
𝑉𝑠
 The machinability index for some common materials is given by
 Low carbon steel - 55 - 60%
 Stainless steel - 25%
 Aluminium alloy - 390 - 1500%

54. SHEAR STRAIN