1Definitions and correlations of 3D volumetric positioning
errors of CNC
machining centers Ondrej Svoboda and Pavel Bach
Research Center of
Manufacturing Technology Czech Technical University in Prague, Czech Republic
And
Gianmarco Liotto and
Charles Wang Optodyne, Inc., Compton, CA 90220 Email: optodyne@aol.com Abstract The
worldwide competition and quality standards
such as ISO 9000 and QS 9000,
demanded tighter tolerance
and regular maintenance of all machine
tools. To generate
good quality or accurate parts, the
measurement of true 3 dimensional
volumetric positioning accuracy
of a machine tool is critical.
However, the 3D volumetric accuracy has not been defined in the standards.
Currently, both the ASME B5(TC52)
and ISO 230(TC39) are working on a
new definition of volumetric
accuracy. There are many possible definitions, such as the
root mean square of the 3 axes displacement
errors, the root mean square of the total errors in the 3-axis directions,
the maximum 4 body diagonal displacement
errors without squareness
and the maximum 4 body diagonal
displacement errors with squareness errors.Reported here
are some definitions of 3D volumetric
positioning errors and their correlations. We have measured
the positioning errors of 10 CNC
machine tools, representing a
selection of modern mid-size CNC machining centers. Based on these
measurement results, the
3D volumetric errors using various
definitions can be calculated. It is concluded that
the 4 body diagonal displacement errors
with squareness errors correlate with
the true 3D volumetric errors very well. It may be used as a quick check of 3D volumetric accuracy of CNC machine
tools. Keywords 3D positioning error, Laser calibration, CNC machines, ISO
standards, Manufacturing.
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Presented in the IMTS 2004 Manufacturing
Conference, Chicago, Il, September 8-10, 2004. .
