Tool engineering

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 Metal cutting
 Metal cutting process consist in removing
unwanted layers of metal from blank, to obtain
a machined part of required shape and
dimensions and with the specified quality of
surface finish.
 Metal cutting
 In chip removal processes the desired shape
and dimensions are obtained by separating
layers of unwanted material from the work-
piece in form of chip.
 Chip Forming Processes
 Turning
 Shaping
 Boring
 Drilling
 Milling
 Honing
 Grinding
 During the metal cutting process there is
relative motion between the work and
cutting tool.

Such relative motions are produced by
combination of rotary and translatory
movements of either work or cutting tool or of
both.
 Metal Cutting Principle
If wedge shaped tool is made to move relatively to
work-piece, as the tool makes contact with the metal,
cutting tool exerts a compressive force on work-
piece. Under this compressive force the material of
work-piece is stressed beyond its yield point causing
the material to deform plastically and shear off.
 Metal Cutting Principle
The plastic flow takes place in localised region
called shear plane.
 Metal Cutting Principle

The sheared material begins to flow

along the cutting tool face in the form of
small pieces or thin ribbon called chip.
The compressive force applied to form
the chips is called cutting force.
 Metal Cutting Principle
The flowing chip causes wear of cutting tool. The
heat generated during shearing action, this
generated heat rises the temperature of work,
cutting tool and chips.
As temperature rises in the cutting tool, it tends to
soften cutting edge of cutting tool which may
lead to fail your of cutting-edge.
 Metal Cutting Processes
There are two basics methods of metal cutting
depending on the arrangement of cutting tool
edge with respect to direction of relative work-
tool motion.
A. Orthogonal cutting or two dimensional cutting
B. Oblique cutting or three dimensional cutting
 Metal Cutting Processes
Orthogonal cutting
In orthogonal cutting the major cutting edge of
cutting tool is arranged perpendicular to the
direction of feed motion, that is perpendicular
to the cutting velocity vector.
 Metal Cutting Processes
This type of cutting is also known as two
dimensional cutting because force developed
during cutting can be plot in one plane or can be
represented by two dimensional coordinates.
 Metal Cutting Processes
Oblique cutting
In oblique cutting the major edge of cutting tool is
is presented to work at an angle which is not
perpendicular to the direction of feed.
 Metal Cutting Processes
Type of cutting is also known as three
dimensional cutting because the cutting force
develop during cutting need to be represent in
three dimensional coordinates.
 Metal Cutting Processes
In oblique cutting the force which cut or share
the material acts on a large area, the tool have
longer life as heat developed per unit area due
to friction is smaller than orthogonal cutting.
The oblique cutting tool remove more material in
same life then orthogonal cutting tool.
 Types of chip

Chips are materials removed from a
workpiece with the aid of cutting tools.

The knowledge of chip type and when they
are produced are very essential because it
tells about the condition of machining.
 Factors that determine the types of chips to be
produced
1) Material used as workpiece.
2) Material used in cutting tool.
3) Dimension of Tool.
4) Speed of cutting.
5) Feed Rate.
6) Cutting environment like temperature.
7) Friction between tool and workpiece.
8) Forces involved in metal cutting.
 Types of chip
Three different type of chips are formed during
metal cutting
A. Continuous chip
B. Discontinuous chip
C. Continuous chip with built up edge (BUE)
A. Continuous chip
A. Continuous chip
 This type of chip producer when machining ductile
material such as steel, aluminium and copper.
 Due to large plastic deformation continuous longe ribbon
of metal are produced.
 This type of chip is most desirable, which results
1. good surface finish
2. low friction at tool-chip interface
3. low power consumption
4. long tool life
A. Continuous chip
 These chips are difficult to handle and
dispose off.
 The chip coil in helix (chip curl) and may be
curl around the work and tool, it may be injure
the operator.
 This problem of continuous chip forming can
be avoided by attaching chip breakers.
A. Continuous chip
Following considerations are help to generate
continuous chips
1 small chip thickness
2 high cutting speed
3 large rake angle
4 high surface finish on tool
B. Dis-continuous chip
B. Dis-continuous chip
 The discontinuous chips are small individual segments
regularly formed due to the rupture of metal takes place,
when
a) the metal directly above the cutting edge has
compressed to such an extent that the material deforms.
b) when the magnitude of compression force reached to the
fracture limit of metal, the material starts sliding along
surface of tool.
 This type of chip obtained in machining mostly brittle
material such as cast iron and bronze.
B. Dis-continuous chip

These materials rupture during plastic
deformation and forms chips as separate small
pieces.

As the cutting edge passes over the irregularities
of workpiece surface, chips are produced and
fairly good surface finish is obtained.

In brittle material tool life is good and required
low power.
B. Dis-continuous chip

In brittle material tool life is good and required
low power.
 The discontinuous chips are also produced
when cutting ductile material under following
conditions.
1. High depth of cut
2. Low cutting speed
3. Small rake angle
C. continuous chip with BUE
C. continuous chip with BUE

In machining ductile material due to high
local temperature and extreme pressure
and also high friction in tool-chip interface
the small lump of metal welded to chip-
tool contact area. This lamp of metal is
known as built up edge BUE.
C. continuous chip with BUE
 The built up edge grows gradually and when
its growth becomes sufficiently larger, it
collapse.
 Some part of it escapes with chips in the
form of very thin flake's welded to chip.
 Some part of it is left over the machined
surface of workpiece, which produce
roughness on the surface of workpiece.
C. continuous chip with BUE

The built-up edge changes its size during cutting to
higher, then decreases, then again increases.
 Built up edge protect cutting edge, it changes

geometry of tool.
 Factors responsible for built up edge

1. Ductile material
2. Small rake angle
3. Cutting speed
4. Dull cutting edge
5. High friction at chip-tool interface.
Classification of cutting tools
1. Single point cutting tool
-one cutting tip
- lathe machine tool, shaping machine tool,
planing machine tool
2. Multi point cutting tool
- more than one cutting tip
- milling cutter, drill, grinding wheel
Single point cutting tool
Types of single point cutting
A. Ground type - in it cutting edge is formed by grinding
B. Forged type - the rough cutting edge is formed by
forging before hardening and grinding

A. Ground type B. Forged type

Single point cutting tool
Types of single point cutting
C. Tipped type - the cutting edge is formed of small tips made up of
high grade material, which is welded to shank of low grade material.
D. Bit type - in it the high grade material of square, rectangular or
some other shape is held mechanically into the tool holder.

C. Tipped type D. Bit type

Single point cutting tool
The single point cutting tool can also classified as Right hand and left hand
A) Right hand single point cutting tool - In right hand cutting tool the side
cutting edge is on the side of thumb when right hand placed on the tool with
palm downward and finger pointed towards tool nose. In it cutting tool cuts
material when feed is given from right hand to left hand in the lathe i.e. from
tailstock to headstock.
B) Left hand single point cutting tool - Left hand single point cutting tool is
mirror to the right hand.
Tool Geometry ( Single point cutting tool)
Both material and geometry of the cutting tools play very
important roles on their performances in achieving
effectiveness, efficiency and overall economy of
machining.
The shape and angle of tool face and cutting edge is known
as tool geometry.
Tool geometry depends on
- Tool and work material
- Cutting conditions – feed depth, and speed of cut.
- Type of cutting
- Required quality of cutting
Tool Geometry ( Single point cutting tool)
Tool Geometry ( Single point cutting tool)
1. Shank 2. Face
3. Flank 4. Nose
5. Nose radius 6. Cutting Edges
Angle:
1. Side Cutting edge angle 2. End cutting edge angle
3. Side relief angle 4. End relief angle
5. Back Rack angle 6. Side rack angle
Tool Geometry
1. Shank: This is the main body of the tool. The shank is used to
hold the tool (i.e tool holder).
2. Face:The surface on which the chips flows/slide is called the face
of the tool.
3. Cutting edge: it the edge on the face of tool which removes
material from the work piece.
The total cutting edges consists of side cutting edge (major cutting
edge) and end cutting edge ( minor cutting edge and nose)
4. Flank: The surface below and adjacent to the cutting edge is
called flank of the tool. Sometime flank is also known as cutting
face. It is the vertical surface adjacent to cutting edge. According to
cutting edge, there are two flank side flank and end flank.
Tool Geometry
Tool Geometry
5. Nose: It is the point where the side cutting edge and
end cutting edge ( Major and Minor cutting edges) are
intersects.
6. Noise radius: The nose radius provides long life and
also good surface finish with its a sharp point on the
nose.
6. Noise radius: It does not have a sharp profile. Sharp
profile may cause scratches on work piece which gives
poor surface finish. To avoid this some radius known
as nose radius is provided.
By giving curve to the nose it will impart strength to the
single-point cutting tool. Nose radius plays an
important role in the surface finish of the final product.
 Tool Angles
The various angles influence tool performance to
considerable extent and therefore value of angle should
be selected with great care and consideration.
Angle:
Rack angle - 1. Back Rack angle
2. Side rack angle
Cutting edge angle- 1. Side Cutting edge angle
2. End cutting edge angle
Relief angle - 1. Side relief angle
2. End relief angle
Tool Angles
Tool Angles
 Tool Angles
Rack – 1. It is slop on top surface of tool on which chip flows. It allow chip to flow in
desired direction.
2. It gives sharpness to the cutting edge
3. It increases tool life
4. It improve surface finish
Back Rack angle – It is angle between downward slop of top surface of tool from nose
to the rear along the longitudinal axis. Its purpose is to guide direction of chip flow.
It also protect cutting point of tool.
Back Rack angle
Back Rack angle
The back rack angle can be positive, neutral or
negative.
A) Positive rake angle

It is generally used in the cutting of soft material.

It requires less cutting force.

However, the higher positive value of rake angle
weakens the cutting edge.

The force acting on tool tends to shear off the
cutting edge of the tool.
A) Positive rake angle

Positive rake angle makes the tool sharp and
pointed, but reduce the strength of cutting edge.

It helps the formation of continues chip in ductile
material and contributes to avoiding the
formation of build-up edge chip.

HSS tools are typically given a positive rake
angle. They used in machining of low-strength
ferrous and non-ferrous metal.

Positive rake angle is not preferred to high-
speed operation.
B) Negative rake angle

Cutting tool with negative rake angle is stronger
and used to cut high-strength material.

The force directed to the strongest part of the
tool.

Negative rake angle provides greater the
strength to cutting edge.

Cemented carbide tools are normally given
negative rake angle.
B) Negative rake angle


It can be used in the high-speed cutting
operation.

Higher cutting force during machining, this also
increases the power consumption.

Increase vibration, friction and temperature at
cutting edge.
C) Neutral rake angle

A neutral rake angle tool is simplest and
easiest to manufacture, but it causes a high
wear when compared to other types.

Neutral rake angle obstructs the movement of
chip flow and causes build-up chip formation.

Such tools also provide advantage while
re-sharpening the tools.

Thread cutting tools are usually provided with
zero rake angle.
 Side rake angle

It is slop of top of tool to the side in direction
perpendicular to longitudinal axis.

It also guide direction of chip away from the job.
 Tool Angles
End cutting edge angle: The angle between end
flank and a plane perpendicular to the side of
the shank.
At smaller values of the angle, larger forces
normal to the machine surfaces are produced
and the tool may chatter.
Side cutting edge angle: Angle between side
cutting edge and the line extending from the
shank (or a line parallel to the tool axis).
 Tool Angles
Side relief angle - It is the angle between the
side flank and the line passing through the tip
perpendicular to the base and the angle is
measured in a plane perpendicular to the tool
axis.
End relief angle: The angle between the end
flank and plane normal to the base.
Extra edge clearance is provided; it is also called
clearance angle.
 Systems of description of tool
geometry
A. Tool-in-Hand System – where only the important features
of the cutting tool point are identified or visualized. There is
no quantitative information, i.e., value of the angles.
B. Machine Reference System – ASA system
C. Tool Reference Systems
∗ Orthogonal Rake System – ORS
∗ Normal Rake System – NRS
D. Work Reference System – WRS
Machine Reference System (ASA System)
 This system is also called ASA system (American
Standards Association)
 In it three mutually perpendicular planes are taken
for reference purpose
a. Reference plane ‘πR’
b. Longitudinal Plane ‘πX’
c. Machine Transverse plane ‘πY’
Machine Reference System (ASA System)
 Machine Reference System (ASA System)

where,
π R = Reference plane; plane perpendicular to the velocity
vector
π X = Machine longitudinal plane; plane perpendicular to πR
and taken in the direction of longitudinal feed
π Y = Machine Transverse plane; plane perpendicular to both
πR and πX
Machine Reference System (ASA System)
 Machine Reference System (ASA System)

Where,
Xm = direction of longitudinal feed
Ym= direction of cross feed
Zm = direction of cutting velocity (vector)
 Tool signature in ASA system
Tool signature in ASA system consists of two rack angle,
two clearance angle, two cutting edge angle, one nose
radius.
Designation (signature) of tool geometry in ASA System –
Rack - Clearance - Cutting edge - Nose radius
γy, γx, - αy, αx, - φe, φs, - r (inch)
 Tool signature in ASA system

Rack - Clearance - Cutting edge - Nose radius

γy, γx,- αy, αx, - φe, φs, - r (inch)
Back, side Back, side end, approch
Definitions
Rake angles:
γy = back rake angle = angle of inclination of the rake surface
from the reference plane (πR) and measured on Machine
Transverse plane (πY).
γx = side rack angle = angle of inclination of the rake surface
from the reference plane (πR) and measured on Machine
longitudinal Plane (πX)
Tool angles in ASA system
Definitions
• Clearance angles:
αy = back clearance angle= angle of principal
flank from machine surface and machine
transverse plane.
αx = side clearance angle = inclination of the
principal flank from the machined surface and
machine longitudinal plane.
Tool angles in ASA system
Definitions
• Cutting angles:
φe = end cutting edge angle= angle between the
end cutting edge (its projection on πR) from πX
and measured on πR
φs = approach angle = angle between the
principal cutting edge (its projection on πR) and
πY and measured on πR
Definitions
• Cutting angles:
Nose radius, r (in inch)
r = nose radius : curvature of the tool tip. It
provides strengthening of the tool nose and
better surface finish. Measured in Inch
 • Tool Reference Systems
Orthogonal Rake System – ORS

The planes of reference and the co-ordinate axes

used for expressing the tool angles in ORS are:
πR - πC - πO and Xo - Yo - Zo
which are taken in respect
of the tool configuration as
indicated in Fig.
 • Tool Reference Systems
Orthogonal Rake System – ORS
where,
πR = Refernce plane perpendicular to the cutting velocity vector,
VC
πC = cutting plane; plane perpendicular to πR and taken along the
principal cutting edge
πO = Orthogonal plane; plane perpendicular to both πR and πC
and the axes;
Xo = along the line of intersection of πR and πO
Yo = along the line of intersection of πR and πC
Zo = along the velocity vector, i.e., normal to both Xo and Yo axes
Definition of –
• Rake angles in ORS
γo = orthogonal rake: angle of inclination of the
rake surface from Reference plane, πR and
measured on the orthogonal plane, πo
λ = inclination angle; angle between πC from the
direction of assumed longitudinal feed [πX] and
measured on πC
Definition of –
• Clearance angles
αo = orthogonal clearance of the principal flank:
angle of inclination of the principal flank from
πC and measured on πo
αo’ = auxiliary orthogonal clearance: angle of
inclination of the auxiliary flank from
auxiliary cutting plane, πC’ and measured
on auxiliary orthogonal plane, πo’
Definition of –
• Clearance angles
αo = orthogonal clearance of the principal flank:
angle of inclination of the principal flank from
πC and measured on πo
αo’ = auxiliary orthogonal clearance: angle of
inclination of the auxiliary flank from
auxiliary cutting plane, πC’ and measured
on auxiliary orthogonal plane, πo’
 • Tool Reference Systems
Orthogonal Rake System – ORS

The planes of reference and the co-ordinate axes

used for expressing the tool angles in ORS are:
πR - πC - πO and Xo - Yo - Zo
which are taken in respect
of the tool configuration as
indicated in Fig.
 • Tool Reference Systems
Orthogonal Rake System – ORS

The planes of reference and the co-ordinate axes

used for expressing the tool angles in ORS are:
πR - πC - πO and Xo - Yo - Zo
which are taken in respect
of the tool configuration as
indicated in Fig.
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