Introduction to metal powder metallurgy

Introduction to powder metallurgy products

Powder metallurgy products are process technologies that use forming and sintering processes to make metal powders (or mixtures of metal powders and non-metallic powders) into materials and products.It is a branch of metallurgy and materials science.
The application range of powder metallurgy products is very wide, from ordinary machinery manufacturing to precision instruments; from hardware tools to large machinery

Cemented carbide mechanical forming machine

; From the electronics industry to motor manufacturing; from the civil industry to the military industry; from general technology to cutting-edge high technology, powder metallurgy technology can be seen.
History of powder metallurgy development：
The powder metallurgy method originated in more than three thousand BC.The first method of manufacturing iron essentially uses powder metallurgy.

2 signs

There are three important signs in the development of modern powder metallurgy technology：

1. Overcome the difficulties generated in the casting process of refractory metals.The manufacture of tungsten wire for electric lamps in 1909 promoted the development of powder metallurgy; the emergence of powder metallurgy cemented carbide in 1923 was hailed as a revolution in machining.
2. In the 1930s, porous oil-containing bearings were successfully prepared; then the development of iron-based mechanical parts of powder metallurgy gave full play to the advantages of powder metallurgy with less cutting or even no cutting.
3. Develop towards more advanced new materials and processes.In the 1940s, materials such as cermet and diffuse reinforcement appeared. From the late 1960s to the early 1970s, powder high-speed steel and powder high-temperature alloys appeared one after another; the use of powder metallurgy forging and hot isostatic pressing has been able to manufacture high-strength parts.

Advantages of powder metallurgy process：

1. Most refractory metals and their compounds, fake alloys, and porous materials can only be manufactured by powder metallurgy.
2. Since the powder metallurgy method can be pressed into the final size of the blank, without the need or little subsequent machining, it can greatly save metal and reduce product costs.When manufacturing products by powder metallurgy method, the loss of metal is only 1-5%, while when producing by general casting method, the loss of metal may reach 80%.
3. Since the powder metallurgy process does not melt the material in the material production process, it is not afraid of mixing with impurities caused by crucibles and deoxidizers, and sintering is generally carried out in a vacuum and reducing atmosphere. It is not afraid of oxidation and will not cause any pollution to the material, so it is possible to prepare high-purity materials.
4. The powder metallurgy method can ensure the correctness and uniformity of the material composition ratio.
5. Powder metallurgy is suitable for the production of products of the same shape and in large quantities, especially products with high processing costs such as gears. Manufacturing by powder metallurgy method can greatly reduce production costs.
Disadvantages of powder metallurgy process: Overall disadvantages: 1) There are always pores inside the product; 2) The strength of ordinary powder metallurgy products is lower than that of corresponding forgings or castings (about 20%~30% lower); 3) Because the fluidity of the powder during the forming process is far inferior to that of liquid metals, there are certain restrictions on the shape of the product structure; 4) The pressure required for pressing and forming is high, so the product is limited by the ability of pressing equipment; 5) The stamping cost is high, and it is generally only suitable for batch or mass production.In terms of metal powder: the quality of the final product is difficult to control freely; metal powder is expensive; the powder does not obey the laws of hydraulics, which restricts the shape of the product structure.Manufacturing equipment and methods: 1) Press: expensive powerful presses are often used 2) Press: it is a consumable product and the cost is higher 3) Sintering furnace 4) The powder is easy to oxidize and it takes a long time to mix 5) The size and shape of the product are limited.

3 Process steps

The basic process of powder metallurgy process is：

1. Preparation of raw material powder.The existing milling methods can be roughly divided into two categories: mechanical methods and physical and chemical methods.The mechanical method can be divided into: mechanical crushing and atomization method; the physical and chemical method can be divided into: electrochemical corrosion method, reduction method, chemical synthesis method, reduction-chemical synthesis method, vapor deposition method, liquid deposition method and electrolysis method.Among them, the most widely used are reduction method, atomization method and electrolysis method.
2. The powder is formed into a blank of the desired shape.The purpose of molding is to prepare a blank of a certain shape and size, and to make it have a certain density and strength.The molding method is basically divided into compression molding and non-compression molding.The most used in pressurized molding is molding.
3. Sintering of blanks.Sintering is a key process in the powder metallurgy process.The molded billet is sintered to obtain the required final physical and mechanical properties.Sintering is divided into unit system sintering and multi-system sintering.For solid-phase sintering of unit systems and multivariate systems, the sintering temperature is lower than the melting point of the metals and alloys used; for liquid-phase sintering of multivariate systems, the sintering temperature is generally lower than the melting point of the refractory components, but higher than the melting point of the fusible components.In addition to ordinary sintering, there are special sintering processes such as loose sintering, melt immersion method, and hot pressing method.
4. Post-processing of the product.The treatment after sintering can be carried out in a variety of ways according to different product requirements.Such as finishing, oil immersion, machining, heat treatment and electroplating.In addition, in recent years, some new processes such as rolling and forging have also been applied to the processing of powder metallurgy materials after sintering, which has achieved better results.

4 Development direction

The future development direction of powder metallurgy materials and products：

1. Representative iron-based alloys will develop into large-volume precision products and high-quality structural parts.
2. Manufacture high-performance alloys with uniform microstructure, difficult to process and completely dense.
3. Use the enhanced densification process to manufacture special alloys that generally contain mixed phases.
4. Manufacture of non-uniform materials, amorphous, microcrystalline or metastable alloys.
5. Process composite parts with unique and non-ordinary forms or components.

---------------Shenzhen Yujiaxin Hardware Products Co., Ltd.