This slide is all about Metal cutting and Machining tools insights. It covers Mechanics of metal cutting, orthogonal and oblique machining, Tools geometry, Types of Chips, and Tools Signature.

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MANUFACTURING SCIENCE
METTAL CUTTING AND MACHINING TOOLS

2. Table of Contents:
• Mechanics of Metal Cutting
• Mechanics of basic Machining Operation
• Orthogonal and Oblique Machining
• Tools Geometry
• Parts and angles of Single Point Cutting Tool
• Types of Chips
• Orthogonal Rake System
• Tool Signature
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3. MECHANICS OF METAL CUTTING:
Metal Cutting and Machine Tools:
Introduction:
• Metal cutting and machining is the process of
producing a work piece by removing unwanted
material from the block of metal, in the form of
chip.
• The body which removes the material through
direct mechanical contact is called cutting tool
and the machine which provides the necessary
relative motion between the work and the tool
is known as the machine tool.
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4. • The relative motion (between the tool and
work piece) responsible for cutting action is
known as “THE PRIMARY OR CUTTING
MOTION” and that responsible for gradually
feeding the uncut portion is termed as the
‘SECONDARY OR THE FEED MOTION”.
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MECHANICS OF METAL CUTTING:

5. MACHANICS OF BASIC MACHINING
OPERATION:
• The mechanics of the machining can be
understood easily, if we understand that the
basic similarity in the nature of material
removal during the different types of
machining operations
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6. In this view, it is clear that basic nature of material removal in each case
i.e. shaping, turning, drilling etc is similar and therefore can be
represented in the common form.
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7. Therefore the operations can be
represented as in the following figure.
The important parameters involved in the basic machining operation are the following.
1.The thickness of uncut layer (t1).
2.The thickness of chip produced (t2).
3.The inclination of the chip-tool i.e. Rake Face.
(The value of Rake Angle).
4.The clearance angle between the work and the flank surface.
5.The relative velocity of tool and work piece.
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8. ORTHOGONAL MACHINING & OBLIQUE MACHINING
 Figure (a) shows machining operation “Two- Dimensional” because when all the
work and chip material particles move in the planes parallel to the plane of the
paper. There is no component of velocity or motion in the direction
perpendicular to the plane of paper. In this case the cutting edge is straight and
the relative velocity of the work and the tool is perpendicular to the cutting edge.
Note, this type of machining is known as “ORTHOGONAL MACHINING.”
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9.  When the relative velocity of the work and the tool is not perpendicular
to the cutting edge (refer figure (b) i.e. “OBLIQUE”), all the work and chip
material particles do not move in parallel planes, and thus two
dimensional representation of operation is not possible. Such machining
is termed as “AN OBLIQUE MACHINING”.
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11. ORTHOGONAL
CUTTING
OBLIQUE
CUTTING
1. The cutting edge of the tool is
perpendicular to the direction of
tool travel.
2. The cutting edge clears the width of
work piece on either ends.
3 .The chip flows over the tool face and
the direction of chip flow velocity is
normal to the cutting edge.
4. Only two components of the cutting
force are acting on the tool. These two
components are perpendicular to each
other and can be represented in a
plane.
5. Maximum chip thickness occurs at its
middle.
6. For the same feed and depth of cut, the
force which acts or shear the metal acts
on a smaller area. So the tool life is less.
1. The cutting edge is inclined at an angle
(known as inclination angle) with the
normal to the direction of tool travel.
2. The cutting edge may or may not clear
the width of the work piece.
3. The chip flow on the tool face making
an angle with the normal on the cutting
edge. The chip flows the side ways in a
long curl.
4. Three component of forces mutually
perpendicular act at the cutting edge.
5. The maximum chip thickness may not
occur at the middle.
6. It acts on longer area and thus the tool
life is more.
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12. TOOL ANGLES: TOOL GEOMETRY
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13. PARTS AND ANGLES OF SINGLE CUTTING POINT TOOL
 Shank: is the main body of the tool at one end of which the cutting
portion is formed. The portion which is reduced in a section to form
necessary cutting edge and the angle is called the neck. The face of
the tool is the surface across which the chips travel as they are
formed.
 Base: is the surface on which on which the tool rests.
 Heel: (known as lower face) is the horizontal surface at the end of
the base in the neck portion which does not participate in the
cutting process.
 Side Rack Angle: is the angle by which the face of the tool is inclined
sideways where the back rack angle is the angle by which the face
of the tool is inclined towards the back. If the inclination of the face
backwards is downwards, the back rack angle is positive and if the
slope is upwards then the angle is negative.
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14.  Back Rack Angle: is the angle between the face of the
tool and line parallel to the base of the shank.
 Increasing the rake angle facilitates easy flow of chip
and its easy removal increases tool life, improves the
surface finish and reduces cutting forces.
 Increasing the rack angle also minimizes size and effect
of built up edges, cutting temperature, cutting forces
and power consumption. It must be noted that
increasing the rack angle too much makes the point
weak which may induce tool chattering.
 End Relief Angle: is provided on the tool to provide
clearance between the work piece and the tool so as to
prevent the rubbing of work piece with end flank of the
tool. Excessive relief angle reduces the strength of tool,
therefore, it should not be too large.
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15.  Side Relief Angle: is provided on the tool to provide the clearance between its
flank and the work piece surface. It is angle between the surface of the flank
immediately below the point and a plane at the right angles to the centre line
of the point of the tool. This angle must be large enough for turning
operations.
 End Cutting Edge Angle: provides clearance between the tool cutting edge and
the work piece and the side cutting edge angle is responsible for turning the
chip away from the finished surface. It provides the major cutting action and
should, therefore be kept as sharp as possible. Too much of this angle causes
chatter.
 Nose Radius: is provided to remove the fragile corner of the tool, it increases
the tool life and improves the surface finish.
 Clearance Angle: is angle between the portion of the flank adjacent to the
base and plane perpendicular to the base. This angle provides free cutting
action, minimizes tool forces and decreases cutting temperature.
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The rake angle may be Positive, Zero, Negative.
•Cutting angle and the angle of shear are affected by the value for rake
angle Negative.
• Larger the rake angle the smaller the cutting angle (and larger the shear
angle) and lower the forces and power.
•Since increasing the rake angle decreasing the cutting angle, this leaves
less metal at the point of the tool to support the cutting edge.
•In general, rake angle is small for cutting hard materials and large for
cutting ductile materials.
•An exception is brass which is machined with a small or negative rake
angle to prevent the tool digging in to work.
•The negative rake angle is employed on carbide cutting tools.
•When we use positive rake angle, the force is directed towards the
cutting edge, tending to chip or break it.

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•Carbide being brittle lacks shock resistance and will fail if
positive rack angle is used with it.
•Using negative rack angle directs the force back in to the
body of the tool away from the cutting edge.
•The use of negative rack angle increases the cutting force.
• But at higher cutting speed at which the carbide cutting tool
can be used, this increase in force is less than at normal
cutting speed.
•High speed is always used with negative rake, which requires
high power of machine tool.

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The use of positive rake angle is recommended under the following
conditions.
•When machining low strength ferrous and non-ferrous materials.
•When using low power machines.
•When machining long shafts of small diameters.
•When the set up lacks strength and rigidity.
•When cutting at low cutting speeds.
The use of negative rake angles is recommended under the
following conditions:
•When machining high strength alloys.
•When there are heavy impact loads such as in interrupted machining.
•For rigid set ups and when cutting at high speed.

19.  Negative – Rake angle:
 In brittle materials like brass, ZERO rake angle is provided
 In tougher materials like cooper, NEGATIVE RAKE angle is used, this is because of
tougher characteristics of the material. This type of material has a tendency to
cause the cutting edge of the tool to dig into the material and spoil the job
surface.
 POSITIVE AND NEGATIVE RAKE ANGLE TOOLS:
 With the carbide tools with the negative back rake are being used quite often.
Cutting at high speed has been developed with negative rake tools. The geometry
of negative rake followed by positive rake is prepared by grinding and lapping.
Certain advantages are being found with the use of negative rake angle.
 Negative rake tools are often more strength to the cutting edge since the cutting
edge is always under pure compression. Where as in positive rake conditions the
cutting edge is under the conditions of shearing and bending, refer fig.
 Since the carbide possesses a very high value of compressive strength, negative
rake tools thus proves to be more useful and the cutting action is improved.
 To decrease the temperature at the tool tip because more heat flows to the chip
from tool,
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NEGATIVE RAKE ANGLEPOSITIVE RAKE ANGLE

21. TYPES OF CHIPS:
When ever the cutting action takes place the
chips produced may be of following types.
• Discontinuous Chips.
• Continuous Chips
• Continuous Chips with build-up-edge (BUE).

22. • The plastic flow takes place in the localized
region called the SHEAR PLANE. This shear plane
extend from cutting edge obliquely up to the
uncut surface ahead of the tool.
•The grains of the metal ahead of the cutting edge of the tool start
elongating along the line AB and continue to do so until they are
completely deformed along the line CD. The region between the line AB
and CD is called SHEAR ZONE

24. •After passing out the shear zone the deformed metal
slides along the tool face due to the velocity of the
cutting tool. Shear zone is treated as shear plane.
•The angle made by plane of shear with the direction of
the TOOL TRAVEL IS KNOWN AS SHEAR ANGLE (Φ).
•If the shear angle (Φ) is small the path of shear will be
long, the slip will be thick, the force required to remove
the layer of the metal of given thickness will be high or
vice- versa.

25. DISCONTINUOUS CHIPS:
• These types of chips are produced when cutting more brittle
materials like grey cast iron, bronze and hard brass.
•These materials lack the ductility necessary for appreciable plastic
chip formation.
•Material ahead of the tool edge fails in a brittle fracture manner
along the shear zone.
•This produces small fragments of discontinuous chips.
•Since the chips break up into small segments, the friction between
the tool and the chips reduces, resulting in better surface finish.
•These chips are convenient to collect, handle and dispose off.

26. CONTINUOUS CHIPS:
These types of chips are produced when
cutting more ductile materials under
the following conditions.
Large chip thickness.
Low cutting speed.
Small rake angle of the tool.
Cutting with the use of cutting fluid.

27. CONTINUOUS CHIPS:
•These types of chips are produced when, machine more DUCTILE
MATERIALS due to large plastic deformations possible with ductile
materials long continuous chips are produced.
•This type of chip is the most desirable, since it is stable cutting,
resulting in generally good surface finish on the other hand these
chips are difficult to handle and dispose off.
•Sometime, the chips coil in a helix (chip curl) and curl around the
work and the tool and may injure the operator when break lose.
•These chips formation may result in more frictional heat.

28. Under the following conditions continuous
chip formation may table place.
• Ductile Material
• High cutting speed
• Large rake angle
• Suitable cutting fluid

29. •In order to avoid long coil in a helix (chip curl), we have
to provide “CHIP BREAKE”
•Chip breaker is small step fixed into the face of the tool
or some time separate piece is also fastened to the tool.
•The function of chip breaker is to reduce the radius of
curvature of the chip and thus break it.
CHIP BREAKE

30. CONTINUOUS CHIPS WITH BUILT UP EDGE (BUE)
When machining ductile materials, the condition are
•High local temperature
•High pressure in the cutting zone
•High friction in the tool chip interface
•These conditions may cause the work material to adhere or weld to the
cutting edge of the tool, forming the built-up-edge.
•Similarly, the successive layer of work materials is then added to the built up
edge.
•When built up edge becomes larger and instable, it breaks up and part of it is
carried up the face of the tool along with the chip while the remaining is left
over the surface being machined, which make the surface rough
The following are condition when continuous chips are produced with built-up-edge
Strength adhesion between chips and tool face.
Low rake angle

31. “ORTHOGONAL RAKE SYSTEM” (ORS).
This system defines the principle parameter of tool i. .e. side
cutting edge(also termed as principal cutting edge); end cutting
edge(also termed as auxiliary edge); and nose with no reference to
their location, inclination or orientation.

32. TOOL SIGNATURE OR TOOL DESIGNATION:
• This is used to denote a standardized system
of specifying the principle tool angles of a
single point cutting tool. It is numerical
method of identification of the tool angles.
• In ASA system of tool angles, are specified
independently of the position of cutting edge.
It, therefore, does not give any indication of
the behavior of the tool in practice.

33. According to ASA system seven elements
comparing signature of single point tool are
always stated in the following manner
• Back Rake Angle (άy)
• Side Rake Angle (άx)
• End clearance (Relief Angle) (βy)
• Side clearance (βx)
• End Cutting Edge Angle (Φe)
• Side cutting Edge Angle (Φs)
• Nose Radius

34. TOOL SIGNATURE

35.  According to ASA system seven elements comparing signature of single point
tool are always stated in the following manner
• Back Rake Angle (άy)
• Side Rake Angle (άx)
• End clearance (Relief Angle) (βy)
• Side clearance (βx)
• End Cutting Edge Angle (Φe)
• Side cutting Edge Angle (Φs)
• Nose Radius
 In ORS system, only the main parameters of a single point cutting tool are
designated in the following order:
• Inclination angle (λ),
• Orthogonal rake angle (ά),
• Side relief angle (γ),
• End relief angle (γ1),
• Auxiliary cutting edge angle (Φ1),
• Approach angle (Φ0),
• and Nose radius ( R ).
• Generally, symbols for degree and millimeters are not indicated. Each
parameter is indicated by number only.

36. TOOL SIGNATURE