Introduction to IEEE STANDARDS and its different types.pptx
Merchant circle.ppt
1.
2. Brief introduction to Merchant’s Circle.
Assumptions for Merchant’s Circle Diagram.
Construction of Merchant’s Circle.
Solutions of Merchant’s Circle.
Advantages of Merchant’s Circle.
Need for the analysis of cutting forces.
Limitations of Merchant’s Circle.
Conclusion
3. Merchant’s Circle Diagram is
constructed to ease the analysis of
cutting forces acting during
orthogonal (Two Dimensional)
cutting of work piece.
Ernst and Merchant do this
scientific analysis for the first time
in 1941 and gives the following
relation in 1944
It is convenient to determine
various force and angles.
4. Cutting Edge is normal to tool feed.
Here only two force components are
considered i.e. cutting force and thrust
force. Hence known as two dimensional
cutting.
Shear force acts on smaller area.
Cutting Edge is inclined at an acute
angle to tool feed.
Here only three force components are
considered i.e. cutting force, radial force
and thrust force. Hence known as three
dimensional cutting.
Shear force acts on larger area.
Metal Cutting is the process of removing unwanted material from the workpiece
in the form of chips
5. α : Rack angle
λ : Frictional angle
ϕ : Shear angle
Ft : Thrust Force
Fn: Normal Shear Force
Fc: Cutting Force
Fs: Shear Force
F: Frictional Force
N: Normal Frictional Force
V: Feed velocity
RAKE ANGLE
Back Rake Angle: It is the angle
between the face of the tool and
measured in a plane perpendicular
to the side cutting edge
Side Rake Angle: It is the angle
between the face of the tool and
measured in a plane perpendicular
to the base
Front View
Back Rake Angle
Side Rake Angle
Frictional Angle
It is the angle between the
resultant ,of the Frictional Force &
Normal Force, and Normal
Reaction.
λ = tan
-1
μ
μ: coefficient of friction
P
F
R
N
λ
Shear Angle
It is the angle made by the shear
plane with the direction of the tool
travel.
Fs
Ft
Fc
Fn
F
N
V
φ
Shear Force
Resistance to shear of the metal in
forming the chip. It acts along the
shear plane.
Normal Shear Force
Force on the chip provided by the
workpiece. Acts normal to the shear
plane.
Friction Force
Resisting force acted at the tool
workpiece interface to resist the
motion of tool.
Thrust Force
This force acts normal to the
cutting force or the velocity of the
tool.
Normal Friction Force
It act at the tool chip interface
normal to the cutting face of the tool
and is provided by the tool.
Cutting Force
Force acted along the velocity of
tool
Cutting force increases as speed
increases and decreases as rake
angle decreases
6. Tool edge is sharp.
The work material undergoes deformation across a
thin shear plane.
There is uniform distribution of normal and shear
stress on shear plane.
The work material is rigid and perfectly plastic.
The shear angle ϕ adjusts itself to minimum work.
The friction angle λ remains constant and is
independent of ϕ.
The chip width remains constant.
The chip does not flow to side, or there is no side
spread.
8. Fs , Resistance to shear of the metal in forming the chip. It
acts along the shear plane.
Fn , ‘Backing up’ force on the chip provided by the
workpiece. Acts normal to the shear plane.
N, It at the tool chip interface normal to the cutting face of
the tool and is provided by the tool.
F, It is the frictional resistance of the tool acting on the chip.
It acts downward against the motion of the chip as it glides
upwards along the tool face.
9. Knowing Fc , Ft , α and ϕ, all other component forces
can be calculated as:
The coefficient of friction will be then given as :
On Shear plane,
α
α
φ
λ-α
λ
φ
Fs
Ft
Fc
Fn
F
N
R
V
Now,
10. Now shear plane angle
The average stresses on the
shear plane area are:
α
α
φ
λ-α
λ
φ
Fs
Ft
Fc
Fn
F
N
R
V
Let ϕ be the shear angle
Where,
11. Assuming that λ is independent of ϕ ,
for max. shear stress
α
α
φ
λ-α
λ
φ
Fs
Ft
Fc
Fn
F
N
R
V
Now the shear force can be written as:
and
12. Analysis of cutting forces is helpful as:-
Design of stiffness etc. for the machine tolerance.
Whether work piece can withstand the cutting force
can be predicted.
In study of behavior and machinability
characterization of the work piece.
Estimation of cutting power consumption, which
also enables selection of the power source(s) during
design of the machine tool.
Condition monitoring of the cutting tools and
machine tool.
13. Proper use of MCD enables the followings :-
Easy, quick and reasonably accurate determination
of several other forces from a few forces involved in
machining.
Friction at chip-tool interface and dynamic yield
shear strength can be easily determined.
Equations relating the different forces are easily
developed.
14. Some limitations of use of MCD are :-
Merchant’s Circle Diagram (MCD) is valid only for
orthogonal cutting.
By the ratio, F/N, the MCD gives apparent (not
actual) coefficient of friction.
It is based on single shear plane theory.
15. Following conclusions/results are drawn from MCD :-
Shear angle is given by
For practical purpose, the following values of ϕ has
been suggested:
ϕ = α for α>15o
ϕ = 15o for α<15o