Manufacturing Processes-2SUBJECT CODE :4ME04

DEPARTMENT OF MECHANICAL ENGINEERING

SEM 4

BY MR.K.P.PAWAR

LECTURER

ANURADHA COLLEGE OF ENGINEERING

Unit-1 ( Theory of Metal Cutting)

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.

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

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.

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

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

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

Examples of Machining Processes

Principle of Machining

1. Work-piece

2. Tool

3. Chip

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.

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

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

Mechanics of Chip Formation

Geometric Definitions

𝑡0 = Depth of cut (d)= Undeformed chip thickness

𝑡𝑐 = Chip thickness

α = Rake angle

φ = Shear angle

ζ = Clearance angle

Mechanics of Chip Formation

Chip Thickness Ratio (r) :

𝑟 =𝑡𝑜

𝑡𝑐

∴ 𝑡𝑜 ≠ 𝑡𝑐

𝑟 =𝑡𝑜

𝑡𝑐=

𝐴𝐵.sin ∅

𝐴𝐵 cos(∅−𝛼)

∴ tan∅ =𝑟 cos 𝛼

1 − 𝑟 sin 𝛼

………..Hence proved

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

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

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.

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)

Orthogonal & Oblique cutting

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

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 ?