To introduce machining process
To understand mechanics of chip formation
To study important parameters of metal machining
To understand methods of machining
2. Unit-1 ( Theory of Metal Cutting)
BY MR.K.P.PAWAR
LECTURER
ANURADHA COLLEGE OF ENGINEERING
3. UNIT I
( SYLLABUS)
Theory of Metal cutting:
Mechanics of Metal cutting
Tool material
Tool Geometry
Tool life &Tool wear
Cutting forces and power consumption
Machinability
Metal cutting economy
Cutting fluid
Machine Tool classification.
4. LECTURE-2
Objectives of lecture
To introduce machining process
To understand mechanics of chip formation
To study important parameters of metal machining
To understand methods of machining
5. Introduction to machining process
Metal cutting or “ Machining” is
the process of producing a work
piece by removing unwanted
material from a block of metal, in
the form of chips.
All the products get their final
shape & size by metal removal,
either directly or indirectly.
Major drawback of the process is
loss of material in the form of
chips.
6. Characteristics of Machining Process
1. Improve the dimensional accuracy & tolerance of the
components produced
2. Internal & external surface features can easily produced
3. Specified surface characteristics or texture can be achieved on
a part
4. May be economical to produce a component
7. Basic objectives of the economical and efficient
machining practice :
Quick metal removal
High class surface finish
Economy in tool cost
Less power consumption
Economy in the cost of replacement &
sharpening of tools
8. Introduction to metal cutting
* Metals are shaped in to usable forms through various
processes
1. No cutting shaping
Ex. Forging,Drawing,Spinning,Rolling,Extruding
etc.
2. Cutting shaping
Ex.Turning,Boring,Milling,Drilling,Shaping,Planning,
Broaching
11. Mechanics of Chip Formation
1. A typical metal cutting process can be schematically shown in
fig.
2. A wedge shaped tool is made to move relative to work piece
3. Tool exerts a pressure on work piece resulting in the of metal
near the tool tip.
12. 4.This introduce shear type deformation within the metal & it starts
moving up-word along the top face of the tool
5.Metal is shared continuously along a plane called the “shear plane”
6.Shear plane is a narrow zone (about 0.025 mm)
7.Surface along which the chip moves up-words is called as Rack
surface.
Rack surface
13. 8. Surface which is relieved to avoid rubbing with machined surface
is called Flank surface.
9. Angle between rack surface & normal is known as Rack angle(α)
( Which may be + or -)
10. Angle between the flank & the horizontal machined surface is
known as “ relief or clearance angle”(γ)
Flank surface
15. Mechanics of Chip Formation
Chip Thickness Ratio (r) :
푟 =
푡표
푡푐
∴ 푡표 ≠ 푡푐
푟 =
푡표
푡푐
=
퐴퐵.sin ∅
퐴퐵 cos(∅−훼)
∴ tan ∅ =
푟 cos 훼
1 − 푟 sin 훼
………..Hence proved
16. Rake Angle (α)
• Positive α
– sharper cutting
– reduces shear plane size
– lower strain than negative rake
– lower cutting force
– lower power consumption
Negative Rake Angle (α)
• Stronger edge
• Increases shear plane size
– more deformation
• Can be turned over, α
yielding twice as many
edges
– negative - 8 edges
– positive - 4 edges
17. Influence of Parameters on Machining
1. Chemical composition & physical properties of the metal
2. Tool material & Tool geometry
3. Method of cutting
4. Chemical composition & rate of flow of the cutting fluid
18. Important Parameters of Metal Machining
1. Cutting Speed :( mpm)
Definition : The relative surface speed between the tool & the job.
It is relative term, since either the tool or the job or both may be
moving during cutting.
2. Feed : ( mm/rev)
Definition: The relatively small movement per cycle of the cutting
tool, relative to the work piece in a direction which is usually
perpendicular to the cutting speed direction .
It is more complex element as compared to cutting speed.
3. Depth of cut:( mm)
Definition: The thickness of the layer of metal removed in one cut.
It is always perpendicular to the direction of feed motion.
19. Methods of Machining
In the metal cutting operation, the tool is wedge –shaped & 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:
1. Orthogonal cutting (Two dimensional cutting)
2. Oblique cutting ( Three dimensional cutting)
21. Orthogonal Cutting Oblique Cutting
1. Cutting edge of tool normal to the
direction of tool feed or work feed
1. Cutting edge of tool incline at an
acute angle to the direction of tool feed
or work feed
2. Direction of chip velocity is normal to
the cutting edge of tool ( Chip flow
angle)
2. Direction of chip velocity is at angle β
with the normal to the cutting edge of
tool ( Chip flow angle)
3.Angle of inclination (i) of cutting edge
of the tool with normal to cutting
velocity (Vc) is zero
3. Cutting edge of the tool is inclined at
an angle (i) with normal to direction of
work feed or cutting velocity(Vc)
4. Angle between direction of chip flow
& normal to cutting edge of
tool,measured in the plane of tool face is
zero
4. Three mutually perpendicular
components of cutting forces act at
cutting edge of tool
5. Cutting edge is longer than width of
the cut
Cutting edge may or may not be longer
than width of the cut
22. Question & Answer Session
1.What are basic element of machining process ?
2.What are method of machining processes ?
3.What are different types of parameters to be considered
for machining ?
