LINK Systems System 1100 Tonnage Monitor - Manual (Page 103)

USING SYSTEM 1100 TONNAGE MONITORS
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9-12
Snapthrough forces associated with blanking or piercing action can
be displayed on the System 1100 by pressing the TONNAGE
FORWARD/REVERSE key to select reverse tonnage. Reverse tonnage is
indicated by a minus sign on the tonnage displays.
Snapthrough tonnages greater than 20% of rated machine tonnage (10%
for some machines) can cause more rapid machine structural fatigue
than overloading the machine substantially in the forward
direction. System 1100 Tonnage Monitors provide reverse tonnage
setpoint limits to stop the production process in the event of an
above limit reverse tonnage reading. If too much snapthrough is
indicated by the System 1100, dies can often be reworked to reduce
snapthrough. Placing shear on cutting edges or "catching"
snapthrough on subsequent "bottoming" die action can significantly
reduce snapthrough.
9.4.3 Stop Block Forces
Dies constructed with stop blocks to control depth of action can
often present setup problems. If too much force is applied to stop
blocks in faster operations, the stop blocks can heat and expand,
changing penetration depth and tonnage required. Also, wear can
change the die action relative to stop blocks, requiring more force
on stop blocks to achieve the same depth of action.
The System 1100 can be used in setup to determine standards for
stop block tonnage by cycling the machine when no material is in
the die and observing the tonnage due to stop blocks alone. Also,
when stop block tonnage must be increased to make a good part, as
indicated by the System 1100, grinding the stop blocks can often
reduce required tonnage.
9.4.4 Scrap Choppers
When separate crankshaft driven scrap choppers operate in the
machine upstroke, scrap chopper tonnage may replace primary tooling
tonnage readings on the System 1100 tonnage displays. This can be
avoided by using the zeroing by position (cam zero) option with the
System 1100. The cam should be set to open before die action
occurs and to close again after the scrap chopper has operated.