ANNEX G: SUNDRIES PAGE 61
THE CONTACT POINT (CP) OR PINCH POINT
Definition:
The contact point is the position of the beam which corresponds to the mo-
ment when the point of the punch makes contact with the sheet metal placed
in the die.
This point is not programmable, but is calculated by the DNC using the
REF Y value and the sheet thickness.
The position is determined by the following calculation:
PCT = REF Y + Th (sheet thickness).
The CP is used by the DNC cycle to maintain the sheet when an X back-
gauge retraction is programmed.
As we have seen at the beginning of this chapter, the CP is closely linked to
the Y reference and the sheet thickness.
The following cases may occur:
a) the sheet is not pinched during X backgauge retraction
b) the sheet is bent too much during X backgauge retraction
To remedy these problems you must:
verify the sheet thickness and if necessary correct it
verify the reference and if necessary correct it
add a CP correction in parameter 37.
A simple way of verifying the position of the CP is to program a sequence
with a very large retraction (approx. 400 mm) and make a descent of the
beam.
During the execution of the retraction, the beam stops on the sheet, it is thus
easy to control if the sheet is pinched sufficiently or too much.
Simply interrupt the descent command before the end of retraction to prevent
the beam from bending the sheet. An ascent command frees it immediately
for another try.
For software with the "CP correction" parameter, if the reference, the tooling
dimensions and material thickness are correct you can modify this parameter
in order to correct the CP (adjustment of the material clamping) without in-
terfering with the other points.
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