1. Definitions:

Undershoot hold-on, cavity float up and down by the support of  spring, cylinder or oil cylinder. Put pressure on uprush in pressing, with the pressing of powders, the friction between the cavity die wall and different powders increases gradually. When the friction force is greater than the support force

(such as the floating force) of the spring, the cavity die decreases with the uprush, which is equivalent to the action of the bidirectional pressing of the undershoot and the reverse compression ( called synchronous compaction). In the floating pressing, the core rod can also float when the cavity die is floating, and the density distribution is in the same direction as the double action pressing. If the cavity die is floating and the core rod hold-on, the lock block where near to the cavity die is approximately pressed in double action pressing. The central density is the lowest, the lock block where close to the  cavity is similar to the single action pressing, and the bottom density is the lowest. Floating pressing is for the parts of H/T = 6 or H/D = 2.

 

2. Classification:

1) Spring floating die

2) Hydraulic floating die

3) Air pressure floating die

 

3. Characteristics:

1) Pressing effect and double action pressing type.

2) The density of lock block is better than single action pressing and double action pressing.

3) The cavity block floats so that it is easy to load powder;

4) Pressing force and knockout force requirement is smaller.

 

4. Pressing force analysis:

Cavity block under stress: Fs, Fx, Pf, W, see diagram.

There are: Fs+W=Fx+Pf,

    ∵Fs=Fx，Ps=Px

∴Pf=W

Only the floating pressure Pf is equal to W, can up and down pressure be equivalence. The floating pressure Pf is too large, the neutral axis moves downward, and increase the density difference. In actual production, because the need for automatic reset of the cavity block, the Pf needs to be slightly larger than W (using a reset cylinder or mechanical reset)