This document discusses machine tools and machining processes. It covers topics such as cutting tools, tool selection factors, tool design and terminology, forces in metal cutting, tool life, cutting speeds and feeds, tool failure modes, machinability, cutting inserts, and cutting fluids. The document is presented by Vikrant Sharma of the Mechanical Engineering department and contains diagrams to illustrate machining concepts.

1. Machine Tools and
Machining
ME 210
Vikrant Sharma
Assistant Professor
Mechanical Engineering Department
FET, MITS

2. Cutting Tool
Cutting tool is a device used to remove the unwanted
material from the work. For carrying out the
machining process, cutting tool is fundamental and
essential requirement.
Single point cutting tool
Multi-point cutting tool
Vikrant Sharma FET, MITS
ME 210

3. Tool Selection Factors

Work material
 Type of cut
 Part geometry and size
 lot size
 Machinability data
 Quality needed
Vikrant Sharma FET, MITS
ME 210

4. Elements of an Effective Tool

High hardness
 Resistance to abrasion and wear
 Strength to resist bulk deformation
 Adequate thermal properties
 Consistent tool life
 Correct geometry
Vikrant Sharma FET, MITS
ME 210

5. Rake and Relief angle
Vikrant Sharma FET, MITS
ME 210

6. Variation of rake angle (positive to negative)
Positive rake angle:
positive rake angle have greater cutting efficiency
tool penetrates more easily into work
reduce cutting pressure
result in fragile cutting edge
limited to machining softer materials
Vikrant Sharma FET, MITS
ME 210

7. Negative rake angle:
provide stronger cutting edge
suitable for cutting high-strength alloys
Vikrant Sharma FET, MITS
ME 210

8. The rake angle for a tool depends on the following
factors

Type of material being cut: A harder material like cast iron
may be machined by smaller rake angle than that required by
soft material like mid steel or aluminum.

Type of tool material: Tool material like cemented carbide
permits turning at very high speed. At high speeds rake angle
has little influence on cutting pressure. Under such condition
the rake angle can minimum or even negative rake angle is
provided to increase the tool strength.

Depth of cut: In rough turning, high depth of cut is given to
remove maximum amount of material. This means that the
tool has to withstand severe cutting pressure. So the rake
angle should be decreased to increase the lip angle that
provides the strength to the cutting edge.

Rigidity of the tool holder and machine: An improperly
supported tool on old or worn out machine cannot take up
high cutting pressure. So while machining under the above
condition, the tool used should have larger rake angle.
Vikrant Sharma FET, MITS
ME 210

9. Effect of variation in relief angle
Vikrant Sharma FET, MITS
ME 210

10. Single Point Cutting Tool:
Shank : It is the main body of the tool.
Flank: Surfaces below and adjacent to the cutting edge is called flank of tool.
Face: The surface on which the chip slides is called the face of the tool.
Nose: It is the point where major and minor cutting edge intersect.
Cutting edge: It is the edge on the face of the tool which removes the material
from the work.
Tool axis
Shank of tool
Auxiliary
cutting edge
Rake or Face
Principal cutting edge
Principal flank surface
Nose
Auxiliary flank surface
Vikrant Sharma FET, MITS
ME 210

11. A single point cutting tool may be either right or left hand
cut tool depending on the direction of feed.
Primary Cutting Edge
Left hand cutting
tool
Right hand cutting
tool
Vikrant Sharma FET, MITS
ME 210

12. Tool Terminology:
Vikrant Sharma FET, MITS
ME 210

13. End cutting edge angle (ECEA)
Top View
Nose Radius (NR)
Side cutting edge angle (SCEA)
Back rake angle (αb)
Side rake angle
(αs)
Lip angle
Front View
Side View
Side relief angle (SRA) End relief angle (ERA)
Vikrant Sharma FET, MITS
ME 210

14. Side Cutting Edge Angle (SCEA): Side cutting edge angle is also
known as lead angle, is the angle between the side cutting edge and
the side of the tool shank. Usually, the recommended value for the
lead angle should range between 15° and 30°.
End Cutting Edge Angle (ECEA): this is the angle between the end
cutting edge and a line normal to the tool shank. The end cuttingedge angle serves to eliminate rubbing between the end cutting
edge and the machined surface of the work piece. Although this
angle takes values in the range of 5° to 30°, commonly
recommended values are 8° to 15°.
Vikrant Sharma FET, MITS
ME 210

15. Side Relief Angle (SRA) : It is the angle between the portion of the side
flank immediately below the side cutting edge and a line
perpendicular to the base of the tool, and measured at right angle to
the side flank. This angle serve to eliminate rubbing between the
work piece and the side flank. The value of this angle is between 5°
and 15°.
End Relief Angle (ERA): It is the angle between the portion of the end
flank immediately below the end cutting edge and a line
perpendicular to the base of the tool, and measured at right angle to
the end flank. This angle serve to eliminate rubbing between the
work piece and the side flank. The value of this angle is between 5°
and 15°.
Vikrant Sharma FET, MITS
ME 210

16. Back Rake Angle and Side Rake Angle: The back rake angle is the
angle between the face of the tool and a line parallel to the base of
the shank in a plane parallel to the side cutting edge. The side rake
angle is the angle by which the face of the tool is inclined side ways.
Both these angles determine the direction of flow of the chips onto
the face of the tool.
Nose Radius: Nose radius is favorable to long tool life and good
surface finish. The value of nose radius range between 0.4 mm to
1.6 mm.
Vikrant Sharma FET, MITS
ME 210

17. Tool Designation:
By designation or nomenclature of a cutting tool is meant the
designation of the shape of the cutting part of the tool. It is the
system of designating the principal angles of a single point
cutting tool.
The signature is the sequence of numbers listing the various
angles, in degrees, and the size of the nose radius.
There are several systems available like
American Standard Association system (ASA),
Orthogonal Rake System (ORS),
Normal Rake System (NRS), and
Maximum Rake System (MRS).
The system most commonly used is American Standard
Association (ASA)
Vikrant Sharma FET, MITS
ME 210

18. ASA System:
Bake rake angle, Side rake angle, End relief angle, Side relief
angle, End cutting Edge angle, Side cutting Edge angle and
Nose radius.
For example a tool may designated in the following sequence:
8-14-6-6-6-15-1
1. Bake rake angle is 8
2. Side rake angle is 14
3. End relief angle is 6
4. Side relief angle is 6
5. End cutting Edge angle is 6
6. Side cutting Edge angle is 15
7. Nose radius is 1 mm
Vikrant Sharma FET, MITS
ME 210

19. Methods of Machining:
In the metal cutting operation, the tool is wedge-shaped and has
a straight cutting edge. Basically, there are two methods of
metal cutting, depending upon the arrangement of the cutting
edge with respect to the direction of relative work-tool motion.
Orthogonal cutting or two dimensional cutting.
Oblique cutting or three dimensional cutting.
Vikrant Sharma FET, MITS
ME 210

20. Orthogonal Cutting
Oblique Cutting
Work
Work
Feed
Feed
Tool
Tool
Vikrant Sharma FET, MITS
ME 210

21. Chip Thickness Ratio (Cutting Ratio):
During cutting, the cutting edge of the tool is positioned a certain
distance below the original work surface. This corresponds to the
thickness of the chip prior to chip formation, to. As the chip is formed
along the shear plane, its thickness increases to tc. The ratio of to to
tc is called the chip thickness ratio (or simply the chip ratio) r
Vikrant Sharma FET, MITS
ME 210

22. Example:
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ME 210

23. Forces in Metal Cutting:
The friction force F is the frictional force resisting the flow of the chip
along the rake face of the tool. The normal force to friction N is
perpendicular to the friction force. These two components can be
used to define the coefficient of friction between the tool and the
chip:
The friction angle is related to the coefficient of friction as
Vikrant Sharma FET, MITS
ME 210

24. In addition to the tool forces acting on the chip, there are two force
components applied by the work piece on the chip: shear force and
normal force to shear. The shear force Fs is the force that causes
shear deformation to occur in the shear plane, and the normal force
to shear Fn is perpendicular to the shear force. Based on the shear
force, we can define the shear stress that acts along the shear plane
between the work and the chip:
Vikrant Sharma FET, MITS
ME 210

25. None of the four force components F, N, Fs, and Fn can be directly
measured in a machining operation, because the directions in which
they are applied vary with different tool geometries and cutting
conditions. However, it is possible for the cutting tool to be
instrumented using a force measuring device called a dynamometer,
so that two additional force components acting against the tool can
be directly measured: cutting force and thrust force. The cutting
force Fc is in the direction of cutting, the same direction as the
cutting speed v, and the thrust force Ft is perpendicular to the cutting
force and is associated with the chip thickness before the cut to.
Vikrant Sharma FET, MITS
ME 210

26. Merchant’s Analysis:
Merchant established relationship between various forces acting
on the chip during orthogonal metal cutting but with following
assumption.
Cutting velocity always remain constant.
Cutting edge of tool remains sharp always during cutting.
Chip does not flow sideways.
Only continuous chip is produced.
There is no built-up edge.
Width of tool is greater than width of cut.
Vikrant Sharma FET, MITS
ME 210

27. Vikrant Sharma FET, MITS
ME 210

28. Tool Life:
Tool life is defined as the time interval for which tool works
satisfactorily between two successive grindings or resharpenings
of the tool.
Tool life is expressed in the following ways.
Time period in minutes between two successive grinding of the
tool.
Number of components machined between two successive
grinding.
Volume of metal removed between two successive grinding.
In 1907 Taylor gave the following relationship between cutting
speed and tool life,
VTn = C
Where V is cutting speed, T is tool life, C is constant and n is an exponent.
n = 0.1 to 0.15 for HSS tool , 0.2 to 0.4 for carbide tool and 0.4 to 0.6 for
ceramic.
The tool life also depends upon the depth of cut and feed.
Vikrant Sharma FET, MITS
ME 210

29. Cutting Speed: Cutting speed is the distance traveled by the
work surface in unit time with reference to the cutting edge of
the tool. The cutting speed, v is simply referred to as speed
and usually expressed in m/min.
Where, D is Dia. Of work or cutter
N is rev / min. of work or cutter
Feed: The feed is the distance advanced by the tool into or
along the workpiece each time the tool point passes a certain
position in its travel over the surface. Feed f is usually
expressed in mm/rev. Sometimes it is also expressed in
mm/min and is called feed rate.
Depth of cut : It is the distance measured perpendicularly
between the machined surface and the unmachined (uncut)
surface or the previously machined surface of the workpiece.
The depth of cut d is expressed in mm.
Vikrant Sharma FET, MITS
ME 210

30. Tool Failure
A properly designed and ground cutting tool is expected to perform
metal cutting operation in an effective and smooth manner.
If, however, it is not giving a satisfactory performance it is indicative
of tool failure.
Following adverse effects observed during the operation.
1.
Extremely poor surface finish on the workpiece.
2.
Higher consumption of power.
3.
Overheating of cutting tool.
4.
Work dimensions not being produced as specified.
A cutting tool may fail due to one or more of the following reasons.
1.
Thermal cracking and softening
2.
Mechanical chipping
3.
Wear
Vikrant Sharma FET, MITS
ME 210

31. Thermal cracking and softening
A lot of heat is generated during the process of metal cutting. Due to
this heat the tool tip and the area closer to cutting edge become very
hot and tool material start deforming plastically at the tip and
adjacent to the cutting edge. Thus the tool loses its cutting ability
and is said to have failed due to softening.
Factors responsible:
1.
High cutting speed
2.
High feed rate
3.
Excessive depth of cut
Carbon tool steel
2000 – 2500
High speed steel
5600 – 6000
Cemented carbide
8000-10000
Vikrant Sharma FET, MITS
ME 210

32. Mechanical chipping
Mechanical chipping of the nose or the cutting edge of the tool are
commonly observed causes of tool failure.
Reasons:
1.
High cutting pressure
2.
Mechanical impact
3.
High vibration
4.
Weak tip and cutting edge
This type of failure is more common in carbide tipped and diamond
tools due to the high brittleness of the tool material.
Vikrant Sharma FET, MITS
ME 210

33. Tool Wear:
Loss of material due to rubbing of two sliding surfaces
accompanying friction is called wear. In case of machining
loss of cutting tool material is called tool wear.
The cutting tool is subjected to, a) high localised stresses b)
high temperature c) sliding of chip along the rake face d)
rubbing of flank surface with freshly machined surface e)
vibration and shock due to improper machining .
Due to above factors the loss of material from the tool body
accelerates and it loses sharp cutting edge.
Vikrant Sharma FET, MITS
ME 210

34. Vikrant Sharma FET, MITS
ME 210

35. Vikrant Sharma FET, MITS
ME 210

36. Vikrant Sharma FET, MITS
ME 210

37. Machinability:
Machinability of a material refers to the ease with which it can
be worked with a machine tool. Ease of metal removal
implies:
 that higher cutting speed and lower power consumption in
metal cutting.
 that the forces acting against the cutting tool will be relatively
low.
 that the chips will be broken easily.
 that a good finish will result.
 that the tool life will increase reducing its frequent resharpening or replacement.
Ease of machining is affected by metal properties such as
hardness,
tensile
strength,
chemical
composition,
microstructure and strain hardening. Machine variables such
as cutting speed, feed, depth of cut, tool material and its form,
cutting fluid etc. also affect machinability.
Vikrant Sharma FET, MITS
ME 210

38. Cutting tool insert:
Vikrant Sharma FET, MITS
ME 210

39. Cutting Fluids
The function of cutting fluids, which are often called coolants are,
1.
Cool the tool and the workpiece.
2.
Reduce the friction
3.
Protect the work against rusting
4.
Improve the surface finish
5.
To prevent the formation of built-up edge
6.
To wash away the chips from the cutting zone.
Vikrant Sharma FET, MITS
ME 210