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April 27, 2004 Manual Version 1.01
3.3
Figure 3.4: Tonnages from Example Die 2
tons distributed to the right side of the machine frame and 40 tons distributed to the left. This process
would result in the tonnage monitor displaying that the maximum tonnage measured on the left side of
the machine frame was 60 tons, that the maximum tonnage measured on the right side of the machine
frame was 60 tons, and that the maximum total tonnage exerted on the machine frame was 100 tons.
Section 3.1.3 Reverse Tonnage
In addition to monitoring the “forward” tonnages for a press, the tonnage monitor also measures and
monitors the “reverse” tonnage. A press frame acts as a kind of stiff spring. When exerting tonnage in
the down part of the cycle, portions of the press frame stretch proportionally to the tonnage exerted. In
the case of a punch, for example, the tooling comes down and contacts the material. The press frame
starts stretching, and this generates tonnage exerted on the material. Finally the tonnage exerted is
sufficient for the punch to “break through” the material, and when it does the press frame tries to “spring
back” to its original shape. Just like a regular spring, the press will overshoot its original resting position
due to inertia and will actually compress instead of stretch. The tonnage registered on the frame during
this “rebound” is the reverse tonnage. Reverse tonnages are typically much harder on the press than
forward tonnages. As a result, press manufactures typically allow much less reverse tonnage on a
machine than forward tonnage. For instance, a 500 ton machine may only be rated for 50 tons of reverse
load.