Blank Holder Plates and Ejector Plates in Blanking Dies

Blank holder plates are generally used in piercing dies, sequential piercing-blanking dies, combination piercing-blanking dies, bending dies, drawing dies, and similar dies. Blank holder plates are most commonly spring-loaded, rubber (hard rubber) loaded, or, in large dies, hydraulically or pneumatically loaded.

We can list the purposes of blank holder plates as follows;

1. In dies where the strip material needs to be held down and where the plate also needs to act as a stripper plate,
2. In inverted dies (with a moving bottom bolster),
3. In open dies where the process stages need to be visible,
4. In combination dies where the plate also serves as a guide plate for the holder and punch,
5. In dies where it needs to be used as an ejector (kicker) plate,
6. Used when the forming operation is precise and the sheet material is thin.

Blank holder plate thicknesses are generally selected based on the holding force. For this reason, we can list the benefits of thick blank holder plates as follows.

1. When the friction surface between the blank holder frame and the punch is large, the blank holder plate doesn’t warp.
2. A thick blank holder plate provides a bearing surface for the long springs that supply the holding force.
3. It’s resistant to variable forces.
4. It stays in constant contact with the blank holder frame.

The blank holder plate’s opening/closing height, or its range of motion, is designed to match the die’s stroke length.

The figure above shows the blank holder plate’s range of motion, or the spring compression height acting on the blank holder plate, based on the die’s closed and open positions.

X = A + B + T or X = H – H1

To prevent the spring acting on the blank holder plate from buckling, the depth of the hole in the upper die plate that guides the spring is made larger. (Above left.) When the blank holder plate stroke length is large, a guide pin prevents the spring from buckling. (Above right.)

A blank holder plate bolt is used to prevent the spring supplying the holding force from buckling, and to guide the blank holder plate. The bolt’s mounting on the blank holder plate and its operating position are shown in the figure above. When the blank holder plate thickness is small, a spring protector bushing is used so as not to weaken the blank holder plate and to prevent the spring from buckling.

The blank holder plate thickness should be no less than 25 mm. As seen in the figure above, when the die closes, the blank holder plate’s frame must not press onto the strip material.

To prevent the blank holder plate from warping, or to ensure it presses evenly, it’s recommended that the friction surface between the blank holder frame and the blank holder plate be large.

The figures above show correct and incorrect blank holder plate designs.

To reinforce blank holder plates that aren’t thick, an additional reinforcement bushing is used on the blank holder plate (above). Or, blank holder plates that are too thick are thinned down. (Image below)

As you’ll also see in the figure below, in some cases the blank holder plate frame is built with an additional plate.

Benefits of a Segmented Blank Holder Plate Frame

1. Mounting the blank holder plate frame to the upper die plate with pins and bolts is easy,
2. The additional plate can be mounted to the blank holder plate frame without a centering pin,
3. Removing the additional plate is enough to take the blank holder plate off the upper die plate,
4. A segmented blank holder plate frame reduces material consumption.

In dies requiring very high precision, blank holder plate guide pins, as shown in the figure above, or blank holder plate guide bushings, as shown in the figure below, are used.

In some dies, the formed part needs to be removed from inside the die. In such dies, the blank holder plate is also used as an ejector (kicker) plate. (Image below)

The figure above shows a die design with a spring-loaded ejector plate.

An ejector plate without spring loading operates via the press’s striker/knockout head. The figure above shows an ejector-plate die for low-tonnage dies.

The image above shows ejector-plate die designs and their main dimensions for high-tonnage dies.