Understanding Press and Die Shut Height
March 21, 2018Comments
Setting the press shut height correctly during the die-change process is critical for ensuring good part quality and also for preventing damage to the die and the press. Press shut height and die shut height are thought to be the same, but they are not. Confusing the two terms can produce disastrous results.
Press Shut Height
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| Fig. 1—Press shut height |
Shut height is defined as the distance from the bottom face of the ram (slide) to the top of the press bed, with the ram positioned at the very bottom of its stroke (Fig. 1) and ram adjustment set to the full-up position.
The press shut height can be found on a specification plate attached to the press frame (Fig. 2) and in the presses’ technical manuals. Shut height may be expressed in inches, metric units or both.
The press shut height listed on the specification plate is its maximum height. The ram has an adjustment screw that can be turned manually or by an electric motor to adjust the ram position downward to reduce the press shut height. The maximum amount of adjustment is determined by the adjustment-screw length. The maximum adjustment also is listed on the press-specification plate.
Die Height vs. Die Shut Height
A bolster plate attaches to the press bed in a manner that allows it to be removed, replaced or exchanged. Some presses have rolling bolsters that move in and out from under the ram to facilitate quick die change. Because bolsters are removable and exchangeable and also can vary in thickness, they directly affect the available die-height space under the ram.
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| Fig. 2—Press data specification plate |
Die height is defined as the distance from the bottom face of the ram to the top of the bolster, with the ram positioned at the very bottom of its stroke. Calculate maximum die height by subtracting the bolster thickness from the press shut height. To obtain minimum die height, subtract the ram-adjustment length from the maximum die-height distance.
Die shut height refers to the overall height of a die assembly in its fully closed (home) position. This includes any unsecured parallels or risers added above or below the die.
The die-shut-height dimension must fall within the minimum and maximum die-height space in the press. If the die-shut height is greater than the die-height space in the press, the die will close fully before the ram reaches the bottom of its stroke. This causes the press frame to stretch and the connections (pitman) and die assembly to compress, generating excessively high tonnage forces and potentially causing damage to the die and press.
