The processing of powder metallurgy is divided into four steps. First, the preparation of powder involves the preparation of materials. According to the requirements of materials, the ingredients are prepared according to the formula, and then the mixture is mixed. The method mainly considers the particle size and flowability of the powder and the bulk density. The particle size of the powder determines the gaps to fill in the particles, use the mixed materials immediately, do not leave them for too long, it will cause moisture and oxidation.
Secondly, the powder is pressed. There are two main pressing methods commonly used in the powder metallurgy process, namely unidirectional pressing and bidirectional pressing. Due to the different pressing methods, the internal density distribution of the product is also different. In simple terms, for unidirectional pressing, as the distance from the punch increases, the friction of the inner wall of the die reduces the pressure, and the density changes with the pressure.
A lubricant is then usually added to the powder to facilitate pressing and demolding. The lubricant reduces the friction between the powders in the low pressure stage and increases the density rapidly; but in the high pressure stage, because the lubricant fills the gaps between the powder particles, it will hinder the density of the product instead. Controlling the release force of the product avoids surface defects caused by the demolding process.
During the pressing process of powder metallurgy, it is necessary to confirm the weight of the product, which is very critical, because the unstable pressure in many factories will cause the weight difference to be too large, which directly affects the performance of the product. The pressed product must be blown off the powder and impurities remaining on the product surface, neatly placed in the appliance, and protected from impurities.