Modeling and Analysis
of High Speed Spindles
In modern machine tool systems, high speed spindles are frequently used to provide high
speed machining capabilities. High speed spindles are the most critical element of high
speed machining systems and usually very expensive. The focus of this work is to develop
comprehensive dynamic and thermal models for high speed spindles with mechanical roller
bearings. Current development includes dynamic models of high speed spindles with angular
contact and tapered roller bearings. The computer program developed based on these models
can predict comprehensive thermal and dynamic behavior of spindle-bearing systems,
including contact angle, contact load, and stiffness of bearings, and stiffness, natural
frequencies and deflection of an entire spindle as a function of bearing configuration,
preload, external load and rotational speed. The program can also predict bearing
temperatures and corresponding thermal growth as a function of bearing design, operating
conditions and external loading.
The Intelligent Spindle Bearing Analysis Program (ISBAP) is modular such that tools and
attachments can be easily added to the spindle model with a minimum modeling effort.
Experimental validations performed with various spindles indicate that the program
is capable of predicting dynamic and thermal characteristics of spindle bearing systems.
Potential benefits of ceramic bearings for high speed spindles are also being investigated
and experimental facilities for testing high speed spindles and high speed machining
have been developed in the High Speed Machining Laboratory at Purdue University. The
developed computer program can be used for spindle design, trouble shooting of existing
spindles, selecting optimal operating conditions of spindles and machining process design.
Some features of the program are described below.
For the detailed descriptions of the software, please see the documents.
Bearing stiffness depends on a number of parameters. The following shows a sample
calculation from the program, illustrating how the bearing stiffness, contact angle and
deflection change in terms of rotational speed and radial load.
|
|
| Radial Stiffness of an Angular Contact Bearingvs. Speed
and Radial Load |
Outer contact angle vs. axial load
and speed, NSK 7014c bearing |
 |
 |
| Bearing deflection vs. speed under three levels of preload
|
Comparison between predicted and measured bearing temperatures |
- Modeling of a spindle
The spindle shaft is
modeled using a discretization technique as shown below. This technique allows to
capture the complexity of spindle geometry without intensive modeling efforts. A
typical spindle can be modeled by discretizing it into 15 to 25 elements. External force
can be applied to any element in the spindle model as shown and bearings can be located in
any configuration. Different tool models can be easily assembled with the
spindle model with little effort.
 |
 |
Discretization of a spindle shaft
|
A thermal model of a motorized spindle |
- Prediction of spindle behavior
Spindle natural
frequencies vary depending on the tool holders and cutting tools amounted. The
program calculates these changes with minimal modeling efforts. The following shows
the comparison between calculated and measured natural frequencies of a spindle with three
different cutting tool holders.
|
|
| Comparison between predicted and calculated natural
frequencies for a spindle with three different cutters. (Green:
Predicted, Yellow: Experimental) |
Spindle natural frequency change vs. RPM (solid:
predicted, dots: measured) |
For
further information, see the list of publication related to high
speed spindles.
This project has been funded by National Science Foundation under grant
DMI-0000089 and The Precise Corporation.
[ Welcome ] [ Research
] [ Education ] [ Laboratories ] [ Collaboration
]
© 2000 Purdue ME Manufacturing Laboratories
Last modified on 26 February 2001.
