H&Z summarizes ten terms related to powder metallurgy process, these are commonly used terms in our powder metallurgy process, let us learn together!
1. Sintering Process in Powder Metallurgy
Sintering is an important process in powder metallurgy production. It is a process in which powder compacts are heated at a certain temperature to cause physical and chemical changes between powder particles, thereby forming a whole with a certain strength and density. The sintering process is the key to the final shape and properties of powder metallurgy parts.
The sintering process mainly includes the following stages:
• Initial stage: At a temperature lower than the melting point of the powder, the surface oxides between the powder particles are reduced, the gas is expelled, and the contact points between the powder particles start to form.
• Sintering stage: As the temperature increases, the contact points between powder particles gradually expand, atom migration channels are formed between particles, and atoms begin to diffuse between particles.
• Crystallization stage: At the sintering temperature, the grains in the powder particles begin to grow and connect with the grains of adjacent particles.
• Solid state sintering stage: In the solid state sintering stage, the pores between the particles start to be filled, and the density of the powder compact gradually increases.
The process parameters such as temperature, time and atmosphere in the sintering process have an important impact on the performance of sintered parts. If the sintering temperature is too low and the sintering time is too long, the sintered parts will have low density and poor strength. If the sintering temperature is too high and the sintering time is too short, the sintered parts will have coarse grains and high brittleness.
2. Atomization Process in Powder Metallurgy
Powder metallurgy atomization refers to the process of forming powder particles with a certain shape and particle size under the action of high-speed airflow after melting metal or alloy. Atomization is an important process in the production process of powder metallurgy, which determines the particle size, shape, purity, etc. of the powder, and these factors have an important impact on the performance of powder metallurgy parts.
Powder metallurgy atomization methods are mainly divided into the following categories:
• Gas atomization: spray molten metal or alloy into high-speed airflow, so that the metal or alloy is broken into powder particles under the action of airflow. Gas atomization is the most commonly used atomization method in powder metallurgy, which has high production efficiency and good powder quality.
• Water mist atomization: Spray molten metal or alloy into water flow, so that the metal or alloy is broken into powder particles under the action of water flow. Water mist atomization can obtain powder with good wettability and dispersibility, which is suitable for the preparation of complex shaped parts.
• Arc atomization: placing the metal or alloy in the arc, so that the metal or alloy is broken into powder particles under the action of the arc. Arc atomization can obtain powders with high purity and high hardness, which are suitable for the preparation of high-performance parts.
3. Compacting Process in Powder Metallurgy
Powder metallurgy pressing refers to the process of compacting powder into a green body with a certain shape and size. Pressing is an important process in the production process of powder metallurgy, which determines the density, dimensional accuracy and surface quality of powder metallurgy parts.
Powder metallurgy pressing methods are mainly divided into the following types:
• Unidirectional pressing: The powder is compacted into a green body with a certain shape and size, and the pressing direction is consistent with the shape of the green body. Unidirectional pressing is the most commonly used pressing method in powder metallurgy, which has high production efficiency.
• Two-way pressing: The powder is compacted into a green body with a certain shape and size, and the pressing direction is perpendicular to the shape of the green body. Bi-directional pressing can obtain a green body with higher density and better dimensional accuracy.
• Isothermal pressing: The powder is compacted into a green body at a certain temperature. Isothermal pressing can obtain a powder with good fluidity, which is suitable for the preparation of complex shaped parts.
During the powder metallurgy pressing process, the following parameters need to be controlled:
• Pressure: If the pressure is too high, the powder is easily deformed, which will affect the dimensional accuracy; if the pressure is too low, the powder will be poorly compacted, which will affect the density and strength.
• Time: If the pressing time is too long, the powder will be easily deformed, which will affect the dimensional accuracy; if the pressing time is too short, the powder will be poorly compacted, which will affect the density and strength.
• Temperature: If the temperature is too high, the powder is easy to sinter, which affects the fluidity; if the temperature is too low, the powder fluidity is poor, which affects the density and strength.
Powder metallurgy impregnation is a post-treatment process in the production process of powder metallurgy parts. It infiltrates liquid into the pores of powder metallurgy parts to improve the strength, wear resistance and corrosion resistance of parts.
The powder metallurgy impregnation process is mainly divided into the following types:
• Hot dipping: heating the powder metallurgy part to a certain temperature, so that the liquid penetrates into the pores of the part.
• Cold impregnation: Infiltrating liquid into the pores of powder metallurgy parts at normal temperature.
• Vacuum impregnation: Infiltrating liquids into the pores of powder metallurgy parts in a vacuum environment.
The liquids in the powder metallurgy impregnation process mainly include the following types:
• Oil: Oil has good lubricity and rust resistance, which can improve the wear resistance and corrosion resistance of powder metallurgy parts.
• Resin: Resin has good adhesion and strength, which can improve the strength and heat resistance of powder metallurgy parts.
• Metal: Metal has good electrical and thermal conductivity, which can improve the electrical and thermal conductivity of powder metallurgy parts.
5. Sizing Process in Powder Metallurgy
Powder metallurgy size correction is a post-processing process in the production process of powder metallurgy parts. It is a process of placing the sintered parts in a mold with the same size and applying a certain pressure to make the sintered parts reach the required size and shape.
The size correction process is mainly divided into the following types:
• Cold size correction: size correction at room temperature.
• Thermal size correction: size correction is carried out at a certain temperature.
• Isothermal size correction: size correction is performed at a certain temperature and pressure.
There are mainly the following types of molds for size correction process:
• Metal molds: Metal molds have good strength and wear resistance and are suitable for mass production.
• Rubber mold: Rubber mold has good elasticity and is suitable for parts with complex shapes.
• Plastic molds: Plastic molds have good corrosion resistance and are suitable for parts with high corrosion resistance requirements.
6. Hot Isostatic Pressing in Powder Metallurgy
Hot isostatic pressing (HIP) is a post-processing process in the production process of powder metallurgy parts. It places sintered parts in a sealed container and pressurizes them under high temperature and high pressure to fill the pores in the sintered parts. , so as to improve the density, strength, toughness and fatigue life of parts.
The HIP process is mainly divided into the following steps:
Place the sintered part in a sealed container.
Place the container in a hot isostatic press.
Seal the container and fill the container with protective gas.
The vessel is heated to bring the sintered part to the desired temperature.
Apply pressure to bring the sintered part to the desired pressure.
Keep the pressure and temperature, and keep warm for a certain period of time.
Remove pressure and cool container.
The HIP process has the following advantages:
• It can improve the density, strength, toughness and fatigue life of powder metallurgy parts.
• It can improve the surface quality of powder metallurgy parts.
• Residual stresses in sintered parts can be eliminated.
• It can improve the machinability of powder metallurgy parts.
• The HIP process is widely used in aerospace, automotive, machinery, electronics, medical and other fields.
7. Injection Molding in Powder Metallurgy
Powder metallurgy injection molding (MIM) is a production process of powder metallurgy parts. It is to mix powder and binder, inject it into a metal mold, and sinter it at high temperature to obtain parts with high density, high precision and complex shape. Powder metallurgy parts.
The powder metallurgy injection molding process is mainly divided into the following steps:
1. Powder preparation: After melting the metal or alloy raw materials, it is prepared into a powder with a certain shape and particle size by atomization, spraying and other methods.
2. Binder addition: The powder is mixed with a binder to bind the powder particles together.
3. Injection molding: The mixed powder is injected into a metal mold.
4. Sintering: The injection molded powder body is sintered at high temperature to decompose the binder and combine the powder particles with each other.
5. Demoulding: The sintered part is released from the mold.
6. Post-processing: according to the performance requirements of parts, post-processing, such as heat treatment, size correction, surface treatment, etc.
The powder metallurgy injection molding process has the following advantages:
• Powder metallurgy parts with high density, high precision and complex shapes can be prepared.
• It can realize mass production and improve production efficiency.
• Production costs can be reduced.
8. Alloying in Powder Metallurgy
Powder metallurgy alloy refers to the alloy obtained by mixing two or more metal powders together and pressing and sintering. Powder metallurgy alloys have the following characteristics:
• Materials with various properties can be prepared, such as high strength, high toughness, high corrosion resistance, high wear resistance, high electrical conductivity, high thermal conductivity, etc.
• Parts with complex shapes can be prepared to meet the needs of various engineering applications.
• Mass production can be realized and production cost can be reduced.
Powder metallurgy alloys are widely used in aerospace, automobile, machinery, electronics, medical and other fields.
9. Surface Treatment in Powder Metallurgy
Powder metallurgy surface treatment refers to the treatment of the surface of powder metallurgy parts to improve the surface performance and service life of the parts. Powder metallurgy surface treatment technology mainly has the following types:
• Coating: Deposit a layer of metal or non-metallic materials on the surface of powder metallurgy parts to improve the corrosion resistance, wear resistance, electrical conductivity, thermal conductivity and other properties of the parts.
• Coating: Coating a layer of solid material on the surface of powder metallurgy parts to improve the performance of parts such as corrosion resistance, wear resistance and decoration.
• Chemical treatment: chemical treatment is carried out on the surface of powder metallurgy parts to improve the performance of parts such as corrosion resistance, wear resistance and surface strength.
• Heat treatment: Heat treatment on the surface of powder metallurgy parts to improve the strength, toughness, hardness and other properties of the parts.
10. Ball Milling in Powder Metallurgy
Ball milling is one of the important processes in the powder metallurgy process. It is a process of grinding, dispersing, mixing and forming powders by using high-speed rotating steel balls or other abrasives in a ball mill for metal or alloy raw materials.
The ball milling process is mainly divided into the following steps:
1. Powder preparation: After melting the metal or alloy raw material, it is prepared into a powder with a certain shape and particle size by atomization, spraying and other methods.
2. Ball milling: Put the powder and ball milling media (such as steel balls, copper balls, glass balls, etc.) into a ball mill, and grind, disperse, mix and shape under high-speed rotation.
3. Selection of ball milling media: The selection of ball milling media needs to be carried out according to the type, shape, particle size and performance requirements of the powder. For example, if the powder is easy to wear, you can use a ball milling medium with higher hardness; if the powder is easy to stick, you can use a ball milling medium with a rough surface.
4. Control of ball milling time: The control of ball milling time affects the particle size distribution, dispersibility and formability of powder. For example, if the ball milling time is too long, the powder particles will be too fine, which will affect the strength and toughness of the powder; if the ball milling time is too short, the powder dispersibility will be poor, which will affect the powder fluidity and formability.
5. Control of ball milling temperature: The control of ball milling temperature affects the chemical composition and properties of the powder. For example, if the milling temperature is too high, the powder will be oxidized or alloyed, which will affect the properties of the powder; if the milling temperature is too low, the chemical composition of the powder will be uneven, which will affect the properties of the powder.
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