Manufacturing Processes-2SUBJECT CODE :4ME04

DEPARTMENT OF MECHANICAL ENGINEERING

SEM 4

BY MR.K.P.PAWAR

LECTURER

ANURADHA COLLEGE OF ENGINEERING

*

LECTURE -4

Objectives of Lecture

To understand merchant cutting force diagram

To learn various sources of heat in metal cutting

Merchant cutting force diagram

Assumptions:1.The cutting velocity always remains constant

2. Cutting edge of the tool remain sharp throughout the cutting

3. There is no side ways of flow of the chip

4. Only continuous chip is produced

5.There is no built-up edge

6. No consideration is made of the inertia force of the chip

7. The behavior of the chip is like that of a free body which is in

the state of stable equilibrium under the action of two resultant

forces which are equal, opposite & collinear

Fs = Shear force, which acts along the

shear plane, is the resistance to shear of

the metal in forming the chip

Fn = Force acting normal to the shear

plane ,is the backing up force on the

chip provided by the work piece

F = Frictional resistance of the tool

acting against the motion of the chip as

it moves upward along the tool

N = Normal to the chip force, is

provided by the tool

Fc = Horizontal cutting force exerted by

the tool on the work piece

Ft = Vertical force which helps in

holding the tool in position and acts on

the tool nose

1. Merchant circle is useful to determine the relation between the

various forces & angles.

2. In the diagram two force triangles have been combined & R &

R’ together have been replaced by R

3. The force R can be resolved into two components Fc & Ft

4. Fc & Ft can be determined by force dynamometers

5. The rack angle (α ) can be measured from the tool & forces F &

N can then be determined

6. The shear angle (Ф) can be obtained from it’s relation with chip

reduction coefficient

7. Now Fs & Fn can also be determine

Relationship of various forces

F=OA=CB=CG+GB

=ED+GB

=Fc sin 𝛼 + Ft cos 𝛼

N=AB=OD-CD

=OD-GE

=Fc cos 𝛼 + Ft sinα

Frictional force diagram

Shear Force System

Fs = OA=OB-AB

=OB-CD

= Fc cosФ – Ft sinФ

Fn = AE= AD+DE

=BC + DE

= Fc sinФ + Ft cosФ

Ф

Sources of Heat in Metal Cutting

Around shear Plane

Region in which actual plastic deformation of the metal occurs

during machining.

Due to this deformation heat is generated.

Portion of this heat is carried away by the chip, due to which

it’s temperature is raised.

The rest of the heat is retained by the work piece.

Region is known as primary deformation zone.

Tool- chip interface

As the chip slides upwards along face of the tool friction occurs

between their surfaces, due to which heat is generated.

A part of this heat carried by the chip, which further raises the

temperature of the chip and the rest transferred to the tool & the

coolant.

This area is known as secondary deformation zone.

The amount of heat generated due to friction increases with the

increase in cutting speed.

It is not appreciably effected with the increase in depth of cut.

When the feed rate is increased the amount of frictional heat

generated is relatively low. But, in that case,the surface finish

obtained is inferior

Tool- work piece interface

That portion of tool flank which rubs against the work surface

is another source of heat generation due to friction.

This heat is also shared by the tool, work piece and the coolant

used.

It is more pronounced when the tool is not sufficiently sharp.

Question & Answer Session

Q.1 .What are various assumptions assume by merchant for

cutting force analysis ?

Q.3.What are various sources of heat in metal cutting ?