What is powder metallurgy?（2)

2. Forming

Before the powder is fed into the mold, the powder must be carefully selected so that the product can meet the economic requirements, and after compaction, the required performance can be obtained.

When only one type of powder is used, as long as the particle size and distribution are appropriate, it can be fed into the mold for pressure forming.

When powder particles (such as stearic acid, lithium stearate or powdered graphite) are often added to the powder powder to increase the powder fluidity or density, it is necessary to incorporate powder particles of different sizes to reduce the adhesion between Powder and reduce the frictional resistance of the mold wall, so the finished product is easy to demold; however, the addition of lubricant will make the product prone to holes after sintering.

sintering

The operation of pressing the component to an appropriate temperature to increase its mechanical strength and hardness is called sintering.

During the sintering process, the grain interface is formed first, which results in the recrystallization of the grain. High temperature will increase the plasticity of the metal surface and establish a layer of liquid network to improve the mechanical interlocking properties. Dissolved gases in metals can also be removed at high temperatures. For the sintering temperature, usually the main component metal below the melting point, the sintering time is about 20-40 minutes. In addition, during the sintering process, in order to avoid the oxidation of the powder and the atmosphere, reducing gas or nitrogen can be used to prevent the formation of harmful oxides at high temperatures .

In addition, for sintered parts, due to factors such as product shape, particle size and distribution, chemical composition, sintering operation, pressure, etc., their size increases or decreases slightly.

4. Complete the processing

Main methods: oil immersion, penetration, size and embossing, heat treatment, electroplating and processing.