1. Definitions:

When friction core pressed, cavity block and undershoot hold-on, uprush move down with the force of the core rod, and the core rod down faster than the powder velocity, rely on the friction between core rod

and different powder particles can make the powders be driven down, thereby improving the density distribution along the height direction of the lock blank inhomogeneity. The method is suitable for pressing the slender thin-wall parts : H/T>6-10.

2. Characteristics

1) Cavity block and undershoot hold-on, core rod and uprush push together.

2) On the outer surface of the lock blank, the pressure decreases along the height, and the pressure decreases along the height at the inner diameter.

3) Density smaller than other Asian mode, strength of the lock block is higher.

4) Not suitable for thick lock blank: too large thickness will cause the uniformity of local density to fall, is suitable for pressing slender thin-walled products.

 

3. Force analysis

In theory, when pressed at a slower speed, F core + F uprush = F cavity block +F undershoot(for powder compact). 

In fact, there is no strict equality relation because the pressing process is an unbalanced state of force.

When F core= F cavity block, F uprush = F undershoot, namely the friction between cavity die wall and different powders is equal to the friction between the core rob and different powders, uprush is equal to the undershoot, the compaction density will be the best uniform.

The size of the core floating T is related to the powder loose height L, and the larger the L is, the greater the T will be. The empirical formula is as follows:

T=KL

K- empirical coefficients are different for different materials.

Loose height press down:

L= P / P'*H

ρ- compact density

ρ'- apparent density

H- lock blank height