Production process of powder metallurgy

Production process of powder metallurgy

Powder metallurgy is an industrial technology for making metal or using metal powder as raw material, forming and sintering metal materials, composite materials and various types of products. The powder metallurgy method is similar to the production of ceramics, so it is also called cermet method. So what is the production process of powder metallurgy? The following is the introduction of zhongwei precision editor.

1、 Pulverization

Pulverizing is the process of making raw materials into powder. The commonly used pulverizing methods include oxide reduction method, atomization method, electrolysis method, rotating electrode method, and mechanical crushing method.

1. Mechanical method: the method of using ball mill or power (such as air or liquid flow) to make metal material fragments collide and friction to obtain metal powder.

2. Oxide reduction method: It refers to the method of reducing metal oxide into powder with solid or liquid reducing agent.

3. Atomization method: a powder preparation method that breaks metal or alloy liquid into small droplets by impact of fast-moving fluid (gas or water) or by other means (such as centrifugation), and then condenses into solid powder.

4. Electrolytic method: direct current is applied to the electrolyte - water solution or molten metal salt, and the positive metal ions get electrons at the cathode to form loose metal powder

5. Rotating electrode method: The consumable electrode is made of metal or alloy, and its end surface is heated by electric arc and melted into liquid. The liquid is thrown out and crushed into small droplets by centrifugal force of high-speed rotation of the electrode, and then condensed into powder.

2、 Mixture

Mixing is the process of mixing various required powders in a certain proportion and homogenizing them into powder billets. The mixing method is divided into dry type, semi-dry type and wet type.

1. The dry type is used when the density of each component is close and the requirement of mixing uniformity is not high.

2. Semi-dry type is used in the case where the density difference of each component is large and the degree of uniformity is high. Add a small amount of liquid (such as engine oil) when mixing.

3. During wet mixing, a large amount of volatile liquid (such as alcohol) is added together with ball milling to improve the uniformity of mixing, increase the contact area between components and improve the sintering performance. In order to improve the formability of the mixture, plasticizer should be added to the mixture.

3、 Forming

Forming is the process of putting the uniformly mixed materials into the press mould and pressing them into a parison with a certain shape, size and density. There are two common methods for forming:

1. Normal temperature pressure forming. Under the mechanical pressure, the mechanical meshing force and atomic adsorption force between the powder particles will be generated to form the cold welding combination and make the parison, as shown in Figure 10-1. The advantages of this forming method are that it has no special requirements for equipment and die materials and is easy to operate; The disadvantage is that the binding force between powder particles is weak, and the parison is easy to be damaged. Since the parison is formed at normal temperature, it is necessary to exert greater pressure to overcome the work-hardening phenomenon caused by plastic deformation of powder particles. In addition, the density of the parison formed under pressure at normal temperature is low, so its porosity is large.

2. Heat and pressure forming. At high temperature, the powder particles become soft and the deformation resistance decreases. A compact parison can be obtained with less pressure.

4、 Sintering

Sintering is the process of diffusion, fusion welding, recrystallization and other processes between the parison particles through melting and sintering, so that the powder particles are firmly welded together, the porosity is reduced, the density is increased, and finally the "crystal combination" is obtained, so as to obtain the required physical and mechanical properties.

5、 Post-processing

Powder metallurgy products can be directly used after sintering; However, when the performance requirements of products are high, post-treatment is often required. Common post-processing methods include the following:

1. Shaping: put the sintered parts into the shaping mould with the same structure as the pressing mould, and then press them on the press for another time to improve the dimensional accuracy of the parts and reduce the surface roughness of the parts, which is used to eliminate the micro deformation caused during the sintering process.

2. Immersion: the process of placing parts in hot oil at 100~200 ℃ or making oil penetrate into the pores of powder parts under vacuum. Parts soaked in oil can improve wear resistance and prevent parts from rusting.

3. Steam treatment: iron-based parts are treated in 500~600 ℃ steam to form a hard and dense oxide film on the internal and external surfaces of the parts, so as to improve the wear resistance of the parts and prevent the parts from rusting.

4. Sulfuration treatment: place the parts in the molten sulfur bath at 120 ℃, take them out after more than ten minutes, and then heat them to 720 ℃ under the protection of hydrogen to form sulfide on the surface of the parts. Vulcanization treatment can greatly improve the friction reduction and processing performance of parts.

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