- Library Home /
- Search Collections /
- Open Collections /
- Browse Collections /
- UBC Theses and Dissertations /
- Dynamic modeling of single and multi point turning...
Open Collections
UBC Theses and Dissertations
UBC Theses and Dissertations
Dynamic modeling of single and multi point turning operations Suren, Muharrem Gokhan
Abstract
The thesis presents the dynamic modeling of single point cutting operations like turning and boring operations. Single point cutting operations such as turning and boring, are widely used in the industry. Turning operation is used to create axisymmetric surfaces whereas the boring is a machining operation used to enlarge the inner diameters of existing holes. A frequency domain stability solution for the oblique turning is introduced. The model takes all the flexibilities in three directions into account for the stability analysis. The vibrations are projected in the direction of chip thickness which is perpendicular to the cutting edge so that the system is oriented in one direction. By scanning the chatter frequencies around the dominant modes of the system, the stability lobes are created. Stability lobes are used to select stable cutting conditions for a particular machining operation, tool, workpiece and machine tool. Dynamics of boring operation are also investigated in the thesis. The vibrations in the process are shown to be in the radial direction which is different from other machining operations. The uncut chip area variation in the boring also brings complexity to the operation. This is caused by the corner radius of the insert used in the operation. The uncut chip area is a nonlinear function of tool geometry, feed rate and vibrations at the current and previous revolutions. A linear chip area formulation based on the least squares method is used for the linear stability solution. A recently developed method, Time Finite Element Analysis, is implemented to boring operation. The time in cut is divided into finite elements and with the help of boundary conditions, and a set of linear equations are obtained. The delay differential equation is transformed into a linear discrete dynamical system. The eigenvalues of the discrete dynamical equation determine the stability of the system. Turning of long shafts has been a problem for the manufacturers. Bearing supports have been used widely to increase the dynamic stiffness of the shafts during machining to prevent chatter. However, the supports should be placed to the most flexible regions of the shaft so that the dynamic stiffness is increased. The aim of increasing the dynamic stiffness is related to increasing the width of cut in turning of long shafts. The dynamic stiffness is proportional to the limiting width of cut in the chatter stability analysis. An algorithm is presented in the thesis which optimizes the bearing support locations according to the predicted Frequency Response Function (FRF) of the system in the cutting region. FRF of the system is calculated using Finite Element Method. The bearing support optimization is verified analytically. Multiple inserted boring operation is generally preferred instead of single inserted boring operation when high material removal rates are desired. The main advantage of using a multiple inserted boring bar is that the workpiece can be machined with a high feed rate, which is the number of inserts times the desirable feed rate per insert. An analytical three dimensional chatter stability approach is introduced for the multiple inserted boring heads which have regular pitch cutters. The simulation results are compared with the available experimental results. The method is further extended to variable pitch cutters. Variable pitch cutters are specially designed tools for preventing chatter vibrations for a desired spindle speed. The stability problem is solved analytically, and a method for selecting optimum pitch angles is presented. The method finds the optimum pitch angles in such a way that the depth of cut is maximized for a given spindle speed. The depth of cut is increased considerably against the regular pitch cutter for the desired spindle speed.
Item Metadata
Title |
Dynamic modeling of single and multi point turning operations
|
Creator | |
Publisher |
University of British Columbia
|
Date Issued |
2004
|
Description |
The thesis presents the dynamic modeling of single point cutting operations like turning and
boring operations.
Single point cutting operations such as turning and boring, are widely used in the industry.
Turning operation is used to create axisymmetric surfaces whereas the boring is a machining
operation used to enlarge the inner diameters of existing holes. A frequency domain stability solution
for the oblique turning is introduced. The model takes all the flexibilities in three directions
into account for the stability analysis. The vibrations are projected in the direction of chip thickness
which is perpendicular to the cutting edge so that the system is oriented in one direction. By
scanning the chatter frequencies around the dominant modes of the system, the stability lobes are
created. Stability lobes are used to select stable cutting conditions for a particular machining operation,
tool, workpiece and machine tool.
Dynamics of boring operation are also investigated in the thesis. The vibrations in the process
are shown to be in the radial direction which is different from other machining operations. The
uncut chip area variation in the boring also brings complexity to the operation. This is caused by
the corner radius of the insert used in the operation. The uncut chip area is a nonlinear function of
tool geometry, feed rate and vibrations at the current and previous revolutions. A linear chip area
formulation based on the least squares method is used for the linear stability solution. A recently
developed method, Time Finite Element Analysis, is implemented to boring operation. The time
in cut is divided into finite elements and with the help of boundary conditions, and a set of linear
equations are obtained. The delay differential equation is transformed into a linear discrete
dynamical system. The eigenvalues of the discrete dynamical equation determine the stability of
the system.
Turning of long shafts has been a problem for the manufacturers. Bearing supports have been
used widely to increase the dynamic stiffness of the shafts during machining to prevent chatter.
However, the supports should be placed to the most flexible regions of the shaft so that the
dynamic stiffness is increased. The aim of increasing the dynamic stiffness is related to increasing
the width of cut in turning of long shafts. The dynamic stiffness is proportional to the limiting
width of cut in the chatter stability analysis. An algorithm is presented in the thesis which optimizes
the bearing support locations according to the predicted Frequency Response Function
(FRF) of the system in the cutting region. FRF of the system is calculated using Finite Element
Method. The bearing support optimization is verified analytically.
Multiple inserted boring operation is generally preferred instead of single inserted boring
operation when high material removal rates are desired. The main advantage of using a multiple
inserted boring bar is that the workpiece can be machined with a high feed rate, which is the number
of inserts times the desirable feed rate per insert. An analytical three dimensional chatter stability
approach is introduced for the multiple inserted boring heads which have regular pitch
cutters. The simulation results are compared with the available experimental results. The method
is further extended to variable pitch cutters. Variable pitch cutters are specially designed tools for
preventing chatter vibrations for a desired spindle speed. The stability problem is solved analytically,
and a method for selecting optimum pitch angles is presented. The method finds the optimum
pitch angles in such a way that the depth of cut is maximized for a given spindle speed. The
depth of cut is increased considerably against the regular pitch cutter for the desired spindle
speed.
|
Extent |
13396468 bytes
|
Genre | |
Type | |
File Format |
application/pdf
|
Language |
eng
|
Date Available |
2009-12-02
|
Provider |
Vancouver : University of British Columbia Library
|
Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
|
DOI |
10.14288/1.0080710
|
URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
|
Graduation Date |
2005-05
|
Campus | |
Scholarly Level |
Graduate
|
Aggregated Source Repository |
DSpace
|
Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.