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Introduction to the Pressing Step in Powder Metallurgy

2022-01-14

　　The powder metallurgy processing procedure consists of four main steps. First, powder preparation involves the preparation of raw materials: based on material requirements, ingredients are formulated according to a specified recipe and then thoroughly mixed. This method places particular emphasis on the particle size, flowability, and packing density of the powder. The particle size of the powder determines the gaps between the filled particles; therefore, the mixed materials should be used immediately and not left standing for too long, as prolonged storage can lead to moisture absorption and oxidation.

　　Second, the powder is compacted. In powder metallurgy, the two most commonly used compaction methods are unidirectional compaction and bidirectional compaction. Due to the differences in compaction methods, the internal density distribution of the resulting products also varies. Simply put, in unidirectional compaction, as the distance from the punch increases, the frictional force on the mold wall decreases, and the density changes accordingly with the applied pressure.

　　Next, a lubricant is typically added to the powder to facilitate pressing and demolding. During the pressing process, the lubricant reduces friction between powder particles in the low-pressure stage and rapidly increases density. However, in the high-pressure stage, since the lubricant fills the gaps between powder particles, it conversely hinders the densification of the product. Controlling the release force of the product helps prevent surface defects caused by the demolding process.

　　During the pressing process in powder metallurgy, it is essential to verify the weight of the products—this is critically important, as unstable pressure at many factories can lead to excessive weight variations, directly affecting product performance. It is necessary to blow off any residual powder and impurities from the surface of the pressed parts, neatly place them into appropriate containers, and take measures to prevent contamination.

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Factors Affecting the Sintering Quality in Powder Metallurgy and Sintering Methods

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