Thesis-2008-Karthikeyan.pdf (11.09 MB)
Tribo-dynamics of high speed precision spindle bearings
thesis
posted on 2013-08-13, 14:14 authored by B.K. KarthikeyanThe demand for higher productivity and improved quality of the machined surfaces
requires spindle designers to aim for higher spindle speeds and feed rates. For
instance, in routing of non-ferrous metals, wood and plastics, spindle speeds of the
order of 60,000 rpm have been achieved with the help of better assembly aiming for
higher operational accuracy, and increased component quality. The limitations on
attainable speeds and quality of surface finish are partly governed by rolling element
bearing vibrations. Dynamic performance of a rolling bearing has been of
considerable interest. Although fatigue life is sometimes a significant parameter, it has
been fairly well established that in the case of many practical applications, bearing
failure is caused by dynamic instability in the motion of the rolling elements. Ball
bearings are widely used for high speed spindles, where high speeds, high
temperatures, and heavy load/forces are encountered, because they offer low friction,
appropriate stiffness characteristics and minimum starting torque.
Dynamic stiffness of a bearing is very important characteristic in bearing design for
achieving precise tolerances, which has been the concern of industry, especially wood
machining industry. Due to poor machining the energy consumed in manufacturing
better quality product is very high. Higher energy consumption and the time to carry
out extra finishing processes is a major concern.
This thesis provides a numerical model incorporating inertial dynamics of vertical
routing spindle with five degrees of freedom simulating an existing routing spindle,
which can run at speeds up to 60,000 rpm (Le. 2.4 million DN).
An experimental rig is also devised to investigate the vibration spectra the high speed
precision 7.5 kW power routing spindle. The vibrations generated in the high speed
precision spindles have amplitudes in the order of microns. Fine measurement of
spindle vibration characteristics are carried out using laser vibrometry. Use of this
technique is quite novel for high speed applications, with precise resolution of rigid
body motions with fine alignment of a single laser beam with respect to an optically
smooth surface of a specially designed tool held in the spindle collet. The
experimental spectra are compared with the numerical model predictions with very
good agreement. .
Numerical model for grease lubrication· capable of solving thermal
elastohydrodynamic lubrication of rough surfaces with combined entraining and
squeeze motions is developed. For this a modified Reynolds equation is derived from
basic principles considering grease as a Bingham solid using the Herschel Bulkley
flow model. Heat generation and the power loss in contact conjunction due to viscous
shear and compressive action is quantified by solving the energy equation. Boundary
interactions due to adhesive and ploughing friction are taken into account. The power
lost due to friction and viscous shear was found to account for 16% of the total input
power at the speed of20,000 rpm.
History
School
- Mechanical, Electrical and Manufacturing Engineering
Publisher
© Bindu Kumar KarthikeyanPublication date
2008Notes
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough UniversityLanguage
- en