Accuracy is Everything in Precision Engineering
The ability of modern engineering techniques to manufacture components to an
astounding degree of accuracy has led to the development of products that
enhance every aspect of life. It is now possible with the use of computer
technology to set machines to microscopic tolerances, and this has allowed the
range of manufactured products to be limited only by human imagination. However,
in so doing, industry recognises that the margins for error are also greatly
reduced. What may have been an acceptable degree of tolerance twenty years ago
is now considered to be an error that must be corrected and is the basis of the
continuous improvement philosophy.
5 Axis Machining is a technique that provides intricate and precise cutting
abilities. The complexity involved in operating around five different axes of
movement requires a computer program, but of necessity to get the required level
of accuracy, 5-axis deviations must be taken into account and the measurement
process needed is complex and time-consuming.
To counter this, some companies are using a measurement system called the
“R-test” which accurately locates a rotary axis using a measuring head in
conjunction with a precision ball. The deviations measured in this way show the
location errors of the rotary axes, and the machine coordinate system can
compensate for these errors, thus producing microscopic degrees of accuracy.
There are two purposes for this test:
1. To identify axis location errors - the test finds the centre point of
rotation and the parallelism of a rotary axis with respect to the machine’s
other axes. The machine’s controller manages the centre-point location error,
while the parallelism deviation is usually done by manually adjusting the table.
When machine tool users know the axis location error they can improve machine
accuracy by compensation and/or adjustment to reduce those errors.
2. As a total acceptance test - When the machine is programmed to move all axes
around the precision ball when placed in an eccentric position on a table, it
records all error parameters, including geometric errors and dynamic, controller
errors eg. following or reversal errors.
To set up the test, a probe is fixed to the non-rotating part of the machine. A
master ball mounted on a rotary table fixed to the machine’s trunnion, makes
contact with three planar elements of the probe. Three measuring systems in the
probe monitor the displacements of contacting elements during this motion,
allowing the centre point coordinates to be pinpointed with sub-micron accuracy.
The R-test is just one method in engineering designed to produce the quality and
accuracy required by aerospace, mining, medical, energy production and other
industries. CNC Townsville clients can be confident that the best technology is
available here to produce the accurate results they require.