The factors that affect the forming process mainly include the properties of the powder, the characteristics and effectiveness of additives, and the pressure, pressurization method, and pressurization speed during the pressing process. The properties of the powder mainly include the particle size, particle size distribution, particle shape, and moisture content of the powder.

First. The influence of powder properties on the pressing process

(1) The influence of the hardness and plasticity of metal powder itself. The hardness and plasticity of metal powder have a significant impact on the pressing process. Soft metal powder is easier to press than hard metal powder, which means that in order to obtain a certain density of compact, the pressing pressure required for soft metal powder is much smaller than that for hard metal powder. Soft metal powder deforms greatly during compression, increases the contact area between powders, and is easier to increase the compact density. Hard metal powders with poor plasticity must use forming agents during compression, otherwise they are prone to compression defects such as cracks.
(2) The influence of metal powder friction performance. Metal powder has a significant impact on the wear of molds, and the lifespan of molds is short when compressing hard metal powder.
(3) The influence of powder purity. The purity (chemical composition) of the powder has a certain impact on the pressing process. The higher the purity of the powder, the easier it is to press. When manufacturing high-density parts, the chemical composition of the powder has a significant impact on its formability, as impurities mostly exist in the form of oxides, and metal oxide powders are mostly hard and brittle and exist on the surface of the metal powder. During compression, the compression resistance of the powder increases, the compression performance deteriorates, and the elastic aftereffect of the billet increases. If lubricants or forming agents are not used to improve its compression performance, the resulting density and strength of the compression will inevitably decrease.
The oxygen content in metal powders exists in the form of compounds or surface adsorption, and sometimes also exists in the form of irreducible impurities. When the powder is not fully reduced or left for too long after reduction, the oxygen content will increase and the compression performance will deteriorate.
(4) The influence of powder particle size and particle size composition. When the particle size and particle size composition of the powder are different, the behavior during the pressing process is inconsistent. Generally speaking, the finer the powder, the poorer its flowability, and the more difficult it is to fill narrow and deep mold cavities, making it easier to form bridges. Due to the fine powder, its loose density is low, and the filling volume in the mold is large, requiring a larger mold cavity size. In this way, the movement distance of the die and the internal friction between the powders will increase during the pressing process, resulting in an increase in pressure loss and affecting the uniform distribution of the compact density. Compared with coarse powders of the same shape, fine powders have poorer compressibility and better formability, due to the increased contact area between the particles of the fine powder. For spherical powders, the particle size of the powder has almost no effect on the density within a medium or large pressure range.
(5) The influence of powder shape. The shape of the powder has the greatest impact on the filling of the mold cavity. Powder with a smooth and regular surface, close to a spherical shape, has good flowability and is easy to fill the mold cavity, resulting in a uniform density distribution of the compact; However, filling powders with complex shapes is difficult and prone to bridging phenomena, resulting in uneven density of the compact due to uneven powder loading. This is particularly important for automatic pressing, as the powders used in production are often irregularly shaped. In order to improve the flowability of the mixture, granulation treatment is often required.
(6) The influence of loose packing density of powder. When the loose density is small, the height of the mold and the length of the punch must be large. When pressing high-density blanks, if the size of the blank is long, the density distribution is prone to unevenness. However, when the loose packing density is low, the contact area of the powder increases during the pressing process, and the strength of the compact is high, which is its advantage.

Second. The influence of lubricants and forming agents on the pressing process

1) The influence of lubricants and forming agents on the pressing process
Different metal powders must use different lubricants or forming agents.
Has appropriate viscosity and good lubricity, and is easy to mix evenly with powder materials.
No chemical reaction occurs with powder materials, making it easy to eliminate and leaving no harmful impurities during pre firing or sintering.
The loose density and flowability of the mixed powder are not significantly affected. Except for special circumstances, its softening point should be high to prevent melting due to temperature rise during the mixing process.
There is no adverse effect on product performance and appearance after sintering.

(2) The dosage and effect of lubricants and forming agents
The amount of lubricant and forming agent added is related to the type and particle size of the powder, the pressing pressure, and the friction surface area, as well as their own materials. The amount of lubricant added is approximately proportional to the shape factor.

Third. The influence of suppression methods on the suppression process

During the compression process, two parameters need to be selected, one is the pressurization speed and the other is the holding time. (1) The impact of pressurization methods. Due to pressure loss during the pressing process, uneven density of the billet may occur. To reduce this phenomenon, bidirectional pressing, multi-directional pressing, or changing the die structure can be used. For parts with complex shapes, composite die punching can be used during forming.
(2) The impact of pressure holding time. During the pressing process, if the powder is maintained at a specific pressure for a certain period of time, it can often achieve very good results.

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