Metal injection molding ⎮ Powder Metallurgy ⎮ About Us 

• Powder forming is the second stage of powder metallurgy. It is a process in which loose powder is made into billets with a certain shape, size, density and strength.

• Powder through the forming process to obtain a given shape and strength of the powder body, called compact.

There are many methods of powder forming, in addition to the ordinary molding method, the others are classified as special forming methods. Die forming is the most basic method.

lacking press forming – pulp casting – loose sintering

The following processes are used to shape materials: pressure, die, hot, isostatic, rolling, centrifugal, extrusion, and explosion.

• Special forming techniques;

•ordinary molding;

•powder pretreatment;

•suppression theory

Powder pretreatment involves annealing, screening, mixing, granulating, and adding lubricants, among other things.

Ordinary powder die forming

Die forming is the most widely used powder forming technique. It refers to the method of loading evenly mixed powder into a closed mold in a certain amount at room temperature, and then pressing it into a billet with a certain unit pressure by a press.

This forming process usually consists of the following steps: weighing powder, filling powder, pressing, holding pressure and stripping.

Principle of molding

(1) Use a mold to give the powder the desired form.

(2) Provide the body at its precise size.

(3) Specify the billet’s necessary porosity and type of porosity.

(4) Provide the body with the right amount of strength and density for handling.

Pressing method

Unidirectional pressing: the concave die and the lower punch do not move, and the upper punch is unidirectional pressurized.

Two-way pressing: the concave die is fixed, and the upper and lower punch are pressed at the same time with equal and opposite pressures.

Floating pressing: the lower punch is fixed, the concave die is supported by springs, cylinders, cylinders, etc., and can float after being stressed。

Pressing process

The pressing process can be divided into four stages:

(1) The powder particles move, the pores decrease, and the particles squeeze each other;

(2) The powder is squeezed tightly, and the small particles are filled into the gap between the large particles, and the particles begin to deform;

（3） The concave and convex part of the surface of the powder particle is pressed and meshed into a firm contact state;

（4）The work hardening of the powder particles to the limit state, further increasing the pressure, the powder particles are destroyed and the crystallization is refined.

The relationship between hardness of metal powder and pressing pressure

Effect of powder purity

Due to the different process of powder making, the purity of the powder is not the same, and the powder contains a certain amount of impurities. The impurities in the powder are mostly in the form of metal oxides.

The metal oxide powder is mostly hard and brittle, and is mainly distributed on the surface of the metal powder, which increases the pressing resistance and deteriorates the pressing performance.

The manufacturability of powder forming  parts structure

1. To make mold-making and compaction easier, try to select a straightforward, symmetrical design that avoids extreme variations in section and narrow grooving, spherical surfaces, etc.

2. Avoid local thin walls to facilitate powder compaction and prevent cracks.

3. Avoid grooves and holes in the side walls to facilitate compaction or reduce residual blocks.

4. Avoid increasing the cross-sectional area along the pressing direction to facilitate compaction. Corners should be rounded at the junction of each wall to facilitate compaction and avoid stress concentration.

Powder Forming Component

The first type of parts: unidirectional pressing, thin wall, arbitrary shape, a table part (wall thickness is generally up to 6.35mm)

The second type of part: a table part, any height and shape, must be bidirectional pressing parts.

Part III: A part of two tables, of any height and shape, that must be pressed in both directions

The fourth type of parts: multi-table, any height and shape, must use multi-die stamping bidirectional pressing parts