Suppression of Boring Bar Vibrations
Ahmed Abd El Monem Barakat Mosaad;
Abstract
Boring bars are considered the most
exible element in the Machine-
Fixture-Tool-Workpiece (MFTW) system in the boring process. Their
exibility originates from their nature of being long enough for deep
holes and thin enough to enter the hole to be enlarged. The boring
bars
exibility causes lower accuracy, worse surface nish and the
occurrence of chatter at small width of cut.
Several authors have investigated factors a ecting the boring bar
tendency to chatter occurrence that include cutting conditions and
system parameters. The increase of system inherent damping was not
applicable due to size limitations, while the increase of system sti ness
or the use of vibration absorbers had more signi cant e ects. The
variation of cutting conditions can be bene cial if they are available
for the required process.
The present work was conducted to propose a newly developed boring
bar design that is concerned with increasing the system sti ness.
The proposed design concept depends on adding an extra support for
the boring bar inside the workpiece itself during the cutting process.
As the cutting tool proceeds in the cutting process, the added support
lies behind the cutting tool to support the boring bar with respect to
the workpiece. This is applied through pressing circumferentially distributed
balls between the boring bar body and the workpiece inner
surface using a hydraulic piston-cylinder assembly.
The proposed design was modeled mathematically to determine its
static properties, and modeled numerically using the Finite Element
Method to obtain both static and dynamic properties. The improvement
of static and dynamic properties while applying the hydraulic
pressure was clearly observed theoretically.
ix
x THESIS SUMMARY
Experimental investigation was carried out to determine the improvement
of static and dynamic performance of the proposed design
and compare it to the theoretical calculations. Then, the chatter tendency
was measured through the limiting width of cut- cutting speed
(blimv) relation and compared to the chip compression ratio- cutting
speed ( c v) relation in the case of no added support.
At the cutting speed having the minimum limiting width of cut (the
worst condition) the proposed design concept is applied by pressing
the supporting balls between the boring bar and the workpiece using
the hydraulic mechanism. Furthermore, two other cutting speeds
are investigated for the improvement caused by the proposed design,
thus, the improvement in chatter tendency is investigated at 3 cutting
speeds and 4 pressure levels.
To study the e ect of the added support on the vibration level in
stable cutting process, the vibration level at 3 di erent cutting speeds
and 5 pressure levels were investigated.
The proposed design concept was found to increase the system
sti ness to values that are in a good accordance with the theoretical
values. Considering the dynamic properties, the receptance of the
system was found to decrease signi cantly while using the hydraulic
pressed support, but also other natural frequencies for the system were
found to be not matching the theoretical values.
The proposed design was found to increase the limiting width of
cut signi cantly at all speeds but with a variation of improvement
percentage due to the e ect of damping factors other than the e ect
of increased sti ness. At the contrary, the vibration level was found
to give unsatisfactory results and have higher values as the value of
hydraulic pressure increases.
From the results obtained through the study, it can be concluded
that the proposed design had a positive e ect in the resistance of
chatter phenomenon, and therefore increase the allowable depth of
cut and material removal rate. Furthermore, it is recommended to
use the proposed design concept at the least e ective pressure level to
decrease its e ect on the system vibration level.
Further future work should be carried out to study the e ect of
THESIS SUMMARY xi
the balls-workpiece contact on the system vibration level, and also to
study the change of the proposed design parameters for the sake of
obtaining higher practicality.
Keywords: Boring Bar, Chatter, Sti ness, Limiting width
of cut, Vibrations
exible element in the Machine-
Fixture-Tool-Workpiece (MFTW) system in the boring process. Their
exibility originates from their nature of being long enough for deep
holes and thin enough to enter the hole to be enlarged. The boring
bars
exibility causes lower accuracy, worse surface nish and the
occurrence of chatter at small width of cut.
Several authors have investigated factors a ecting the boring bar
tendency to chatter occurrence that include cutting conditions and
system parameters. The increase of system inherent damping was not
applicable due to size limitations, while the increase of system sti ness
or the use of vibration absorbers had more signi cant e ects. The
variation of cutting conditions can be bene cial if they are available
for the required process.
The present work was conducted to propose a newly developed boring
bar design that is concerned with increasing the system sti ness.
The proposed design concept depends on adding an extra support for
the boring bar inside the workpiece itself during the cutting process.
As the cutting tool proceeds in the cutting process, the added support
lies behind the cutting tool to support the boring bar with respect to
the workpiece. This is applied through pressing circumferentially distributed
balls between the boring bar body and the workpiece inner
surface using a hydraulic piston-cylinder assembly.
The proposed design was modeled mathematically to determine its
static properties, and modeled numerically using the Finite Element
Method to obtain both static and dynamic properties. The improvement
of static and dynamic properties while applying the hydraulic
pressure was clearly observed theoretically.
ix
x THESIS SUMMARY
Experimental investigation was carried out to determine the improvement
of static and dynamic performance of the proposed design
and compare it to the theoretical calculations. Then, the chatter tendency
was measured through the limiting width of cut- cutting speed
(blimv) relation and compared to the chip compression ratio- cutting
speed ( c v) relation in the case of no added support.
At the cutting speed having the minimum limiting width of cut (the
worst condition) the proposed design concept is applied by pressing
the supporting balls between the boring bar and the workpiece using
the hydraulic mechanism. Furthermore, two other cutting speeds
are investigated for the improvement caused by the proposed design,
thus, the improvement in chatter tendency is investigated at 3 cutting
speeds and 4 pressure levels.
To study the e ect of the added support on the vibration level in
stable cutting process, the vibration level at 3 di erent cutting speeds
and 5 pressure levels were investigated.
The proposed design concept was found to increase the system
sti ness to values that are in a good accordance with the theoretical
values. Considering the dynamic properties, the receptance of the
system was found to decrease signi cantly while using the hydraulic
pressed support, but also other natural frequencies for the system were
found to be not matching the theoretical values.
The proposed design was found to increase the limiting width of
cut signi cantly at all speeds but with a variation of improvement
percentage due to the e ect of damping factors other than the e ect
of increased sti ness. At the contrary, the vibration level was found
to give unsatisfactory results and have higher values as the value of
hydraulic pressure increases.
From the results obtained through the study, it can be concluded
that the proposed design had a positive e ect in the resistance of
chatter phenomenon, and therefore increase the allowable depth of
cut and material removal rate. Furthermore, it is recommended to
use the proposed design concept at the least e ective pressure level to
decrease its e ect on the system vibration level.
Further future work should be carried out to study the e ect of
THESIS SUMMARY xi
the balls-workpiece contact on the system vibration level, and also to
study the change of the proposed design parameters for the sake of
obtaining higher practicality.
Keywords: Boring Bar, Chatter, Sti ness, Limiting width
of cut, Vibrations
Other data
| Title | Suppression of Boring Bar Vibrations | Other Titles | كبح إهتزازات عمود الخراطة الداخلي | Authors | Ahmed Abd El Monem Barakat Mosaad | Issue Date | 2015 |
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