July 2013 6.12 Spindle 977
6.12.9 Rigid tapping
Cycle 17
Define the rigid tapping process in the NC program with Cycle 17.
While Cycle 17 is running, the iTNC automatically switches the tool axis to
velocity feedforward mode.
Define the dynamic response of the spindle and the machine tool axes in
machine parameters. See “The control loop" on page 810 and „Spindle" on
page 944.
With Cycle 17 the spindle can also be feedback-controlled. This results in a
better speed curve:
Set MP7160 bit 2 = 1 to drive the spindle under position feedback control
with Cycle 17.
The tool axis can track the spindle or it can be interpolated with the spindle.
Interpolation can result in higher speed stability of the tool axis. The path jerk
(spindle and tool axis) can be set via MP3415.3:
Whichever value is smaller from this formula and from MP1090.0 is valid.
In MP7160, set bit 4 = 1 to interpolate the tool axis with the spindle.
With small thread depths and excessive spindle speeds it is possible that the
programmed spindle speed may not be attained. The immediate transition
from the acceleration phase to the braking phase can diminish the quality of
the thread:
Set MP7160 bit 1 = 1 in order to limit the spindle speed so that the spindle
runs for about 1/3 of the tapping time at a constant speed.
During tapping, the position of the tool axis tracks the actual position of the
spindle.
Please note that the use of acceleration feedforward control for the tool axis
makes the tool axis sensitive to fluctuations in spindle speed caused, for
example, by gear transmission. If this happens, the tool axis starts to run
rough:
In MP7160, set bit 3 = 1 to switch off acceleration feedforward control for
Cycle 17.
Before tapping, the axes (e.g. Z and S) are synchronized through an oriented
spindle stop, i.e., every Z position is assigned to a certain spindle angle. The
NC orients the spindle. The NC sets M4017. The position control loop must be
closed (M4012). Also see „Oriented spindle stop" on page 968.
Synchronization makes it possible to cut the same thread more than once. The
assigned spindle angle depends on the thread pitch entered in the cycle. You
can deselect this function to save machining time:
Set MP7160 bit 0 = 1
In this case you cannot cut the thread more than once.
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MP3415.3
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