Vibration in machine tools can be caused by various sources including workpiece inhomogeneities, tool wear, drive imbalances, intermittent cutting processes, and regenerative chatter from forces generated during cutting. Vibration affects surface finish, tool life, machine accuracy, and component wear. Methods for controlling vibration include reducing vibration sources, increasing machine stiffness and damping, optimizing cutting parameters and tool/workpiece design, and using vibration dampers.

1. Application
number:b68ad66be6a611e98c1259835bdf11f2
Name : S. Raam Kumar

2. VIBRATION-FORCED AND SELF
INDUCED
REGENERATIVE CHATTER
BY
S.Raam kumar

3. VIBRATION
Vibrations are oscillations of a system about an equilbrium position.
The vibration of machine cutting process affects
• surface finish of the work piece
• Life of the cutting tool
• Positioning accuracy of slides
• Life of machine tool parts, particularly transmission elements.

4. Types of vibration
Free or transient
vibration
Forced vibration
Self excited vibration or
Regenerative chatter

5. Forced vibrations
Dynamic behavior caused entirely by the load acting during the
action of the load.
Free vibrations
Dynamic behavior initiated by a load but persisting after load has
caused to act.
Self-excited vibrations
Dynamic behavior through an interaction between the structure and
the cutting process.

6. Effect of vibration on tool life
It has been shown that cutting variables are affected by vibration, as such it is expected that tool life will
also be affected by the tool vibration, because tool life is a function of the cutting variables only. It is
known:
Where Td= Tool life where vibration is present
To=Tool life in the absence of any vibration
A = Amplitude of vibration
v = Frequency of vibration in cycles/unit time
V0=Mean velocity between the job and the tool.
.
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00
11
2
V
Av
V
AvT
T
o
d

7. EFFECT OF VIBRATION
• ‘Peters’ has shown that there is a close correlation between vibration CLA values and
roughness CLA values.
• This conclusion has been derived from the results of experiments performed on five
different lathes which is indicated in Table below:
• Table: Vibration-Roughness Correlation
Test No. CLA vibration CLA roughness
1 1.13 1.29
2 0.36 0.40
3 0.52 0.50
4 1.25 1.36
5 0.59 0.43

8. SOURCES OF VIBRATION
• Inhomogenities in the work piece material.
• Built-up edges in cutting tools.
• Unbalance and disturbances in the drives.
• Intermittent cutting (like milling).
• Transmission of vibration from the ground which vibrates due to other
reasons.
• Generation of vibration from the cutting process itself.

9. Inhomogenities in the work piece material
 The varying nature of the cutting force is the result of the different
degrees of hardness in the material layer hardened by the deformation
process when acted upon by the cutting tool compared to the uncut depth
of layer.
 The cutting tool being deflected comes across every time relatively more
hardened layers of materials when moved from the machined surface.
Increase in force results in the deflection of the cutting tool in the same
direction.

10. Vibration due to Built-up Edges
 There are some cases of vibrations which are neither forced nor self-
excited.
 One such is due to built-up edges which change the instantaneous rake
angle γ by an amount Δγ. The energy input for such vibrations is
Where
 Py = radial component of cutting force,
 a = amplitude of vibration.







045.01
045.01
.4 aPW y

11. Unbalance and disturbances in the drives
Disturbance in the drives may be due to disturbance in rotating/driving
members of the machine tool.
This type of disturbances may be generated due to many reasons.
Some of the reasons are:
(i) Rotating unbalanced mass.
(ii) faulty arrangement of drive.
(iii) fault in the supporting bearings.

12. Vibration due to Intermittent Cutting
 When the cutting process itself is intermittent or periodically discontinuous then
cutting force becomes fluctuating with a definite period.
 Due to this fluctuating or dynamic cutting force which is transmitted to the
machine tool via the cutting tool and job, it is quite likely that a forced vibration
will be generated due to the elastic nature of the system.
 Most common types of intermittent cutting are:
(i) cutting with discontinuous chip formation.
(ii) milling.

13. MACHINE-TOOL CHATTER
• Chatter is a self-excited vibration
which is induced and maintained by
forces generated by the cutting process.
• It affects surface finish, tool life,
production rate and also produce noise.
• Chatter resistance of a machine tool is
usually characterized by a maximum
stable depth of cut .

14. Chatter Marks on Surface of Turned Part

15. Vibration control in machine tool
• A reduction of the Intensity of the sources of vibration.
• By enhancement of the effective static stiffness and damping.
• By appropriate choice of cutting regimes, tool design, and work-piece
design.
• application of vibration dampers and absorbers is an effective
technique for the solution of machine-vibration problems.

16. Damping
When the energy of a vibrating
system is gradually dissipated by
friction and other resistances,
the vibrations are said to
be damped.
The vibrations gradually reduce or
change in frequency or intensity or
cease and the system rests in its
equilibrium position.

17. Commonly used dampers

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