What is the development of powder metallurgy now?

Development of powder metallurgy technology in China in recent ten years;

Powder metallurgy is an advanced manufacturing technology integrating material preparation and part forming, which has the advantages of energy saving, material saving, high efficiency, one-step molding and less pollution. It plays an irreplaceable role in the manufacture of materials and parts, and has entered the forefront of the development of contemporary materials science. At present, powder metallurgy technology is developing towards high density, high performance and low cost.

New forming technology of powder metallurgy parts in recent ten years: 1. Warm compaction technology is a new technology developed in the field of powder metallurgy in recent years, which can produce high-density and high-strength powder and has a very broad application prospect. The so-called warm compaction technology is to use special

Powder heating, powder conveying and mold heating system is a technology that pre-alloyed powder and mold with special lubricant are heated to 130 ~ 150℃, and the temperature fluctuation is controlled within 2.5℃, and then pressed and sintered like traditional powder metallurgy process. Its technical points are: first, the preparation of warm compaction powder, and second, the warm compaction system. Compared with the traditional process, the density of green compact formed by warm compaction is increased by about 0. 15 ~ 0.30 g/cm3, and its density can reach 7.45 g/cm3. Under the same pressing pressure, the average yield strength, ultimate tensile strength and impact toughness of warm compaction materials are 1 1% higher than those of traditional technology, and 13.5% higher than those of traditional technology. In addition, the green strength of warm pressed parts is high, which can reach 20 ~ 30 MPa, which is 50- 100% higher than that of traditional methods. It not only reduces the breakage rate of green parts during handling, but also can be used to process green parts with good surface finish. In addition, the warm compaction process has the advantages of low pressing pressure, small demoulding force, uniform parts performance, high product precision and high material utilization rate. Another feature of warm compaction process is its simple process and low cost. The research shows that powder forging is successful if the cost of ordinary powder metallurgy process of one-time pressing sintering is 1.0.

Cost 2.0, relative cost of recompression and reburning 1.5, relative cost of copper infiltration 1.4, relative cost of warm compaction technology 1.25. At present, there are more than 200 kinds of powder metallurgy parts produced by warm compaction technology, and the weight of parts is 5- 1200 g. For example, SinterstahlGmbH of Germany produces complex synchronous gear rings with friction transmission by warm compaction technology, and won the prize at the international conference of PM2TEC200 1 held in New Oran, USA. The tooth density and ring density of this part are over 7.3g/cm and 7. 1g/cm, respectively, and the green strength reaches 28MPa. The minimum tensile strength of sintered hard pressed powder with diffusion alloying is 850MPa Due to the warm compaction technology and powder metallurgy parts, the comprehensive cost is reduced by 38%.

Second, the flow temperature and pressure technology

WFC is a new near-net-shape technology for powder metallurgy parts, which is based on powder pressing and warm compaction, and combines the advantages of metal powder injection molding. The key technology is to improve the fluidity of mixed powder. By improving the fluidity, filling ability and formability of the mixed powder, parts with complex geometric shapes, such as those with grooves, holes and threaded holes perpendicular to the pressing direction, can be accurately formed on the traditional press at the temperature of 8O ~ 130 ~ C without subsequent secondary processing. WFC technology not only overcomes the shortcomings of traditional powder metallurgy forming with complex geometry, but also avoids the high cost of metal injection molding technology. This is a new technology with great potential and has a very broad application prospect. As a new type of near-net-shape forming technology for powder metallurgy parts, WFC technology has the following main characteristics: (1) It can form parts with complex geometries; (2) the compact density is high and uniform; (3) Good adaptability to materials; (4) simple process and low cost. At present, the research on WFC technology abroad is still in its infancy, and its key manufacturing technology and densification mechanism have not been reported. In the traditional forming of powder parts, in order to reduce the friction between powder particles and the die wall, a certain amount of lubricant needs to be added to the powder mixture, but the mixed lubricant is not conducive to obtaining high-density powder metallurgical parts because of its low density; Moreover, the sintering of lubricant will pollute the environment and even reduce the life of sintering furnace and the performance of products. The application of die wall lubrication technology solves this problem well. In recent years, replacing powder lubrication technology with die wall lubrication has become another hot spot in powder forming research and development.

At present, there are two main ways to realize die wall lubrication: one is to bring liquid lubricant to the surfaces of the die and mandrel by using the capillary action generated by the gap between the punch and the die and mandrel under reset. The second is to spray the electrostatic solid lubricant powder onto the surface of the mold cavity with a spray gun, that is, an additional lubricant shoe device is installed at the front end of the powder shoe. At the beginning of molding, the lubricant shoe pushes away the green body, and compressed air sprays the lubricant with static electricity from the lubricant shoe into the mold cavity. Because the polarity of lubricant powder is opposite to that of female die, the powder collides and adheres to the mold wall under the traction of electric field, and then the powder is filled into the shoe powder for conventional compression molding. Using die wall lubrication technology can obviously improve the green density of powder materials, and compared with inter-powder lubrication, the green strength of iron powder can be increased by128-217%. Researchers at Toyota Motor Center in Japan use warm compaction, die wall lubrication and high pressing pressure to make iron-based green compact almost completely.

Fourth, high-speed pressing technology.

Hjgh high-speed compaction (HVC) is a new technology introduced by Hoaganas Company of Sweden in June 2006. The process of producing parts by high-speed pressing is the same as that by traditional pressing. The mixed powder is added into the hopper, and the powder is automatically filled into the mold cavity by the powder feeding shoes for pressing and molding, and then the parts are ejected and transferred to the sintering process. The difference is that the pressing speed of high-speed pressing is 500- 1000 times higher than that of traditional pressing, the hammer speed of the press is as high as 2-30m/s, the weight of the hammer driven by hydraulic pressure is 5- 1200kg, and the powder is subjected to high-energy impact pressing within 0.02s, resulting in strong shock wave during pressing. Higher density can be achieved by additional multiple impacts with an interval of 0.3s HVC technology has the characteristics of high density, high performance, low cost, high productivity and formability of large parts.

This technology is suitable for producing valves, simple gears, valve guides, main bearing covers, hubs, gears, flanges, shaft sleeve bearing rings, cam lobe mechanisms and other products. At present, the research and production of more complex multi-level components are still continuing.

V. Dynamic magnetic pressing technology

Dynamic magnetic compression (DMC) is a new type of high-performance powder final forming and pressing technology, which was studied in the United States from 65438 to 0995. DMC uses the pressure exerted by pulse modulated electromagnetic field to consolidate powder. Like the traditional powder metallurgy pressing process, dynamic magnetic pressing is also a two-dimensional pressing process, but it is radial pressing rather than axial pressing. When the powder is put into a conductive container (sheath) and placed in a central cavity with high field strength, a high current pulse is introduced into the coil, a magnetic field is formed in the coil, and an induced current is generated in the sheath. The interaction between the induced current and the external magnetic field produces a magnetic force that compresses the sheath from the outside to the inside, so that the powder is pressed. The whole pressing process is less than 1 ms. DMC has the following characteristics: (1) Because no mold is used, higher pressing force and lower maintenance and production costs can be realized; (2) It can be pressurized at any temperature and atmosphere, which is suitable for all materials and has more flexible working conditions; (3) Lubricants and binders are not used, which is beneficial to environmental protection. At present, many applications of dynamic magnetic compaction are close to the stage of industrialization. DMC is suitable for manufacturing cylindrical symmetrical final parts, thin-walled tubes, high aspect ratio parts and parts with complex internal shapes. Now we can produce parts with diameter× length: 12.7mm×76.2mm to 127.0mm×25.4mm, the first industrialized SPS device. This technology has really attracted the attention of the world. This technology integrates powder forming and sintering, and does not need pre-forming or any additives and binders. The electric field formed by external pulsed strong current is mainly used to remove oxides and adsorbed gases on the surface of powder particles, purify materials, activate the surface of powder, improve the diffusion ability of powder surface, and then heat the powder with strong current for a short time under low mechanical pressure to make it compact. Relevant research shows that this technology greatly reduces the sintering temperature of powder, shortens the sintering time, and makes full use of the self-heating function of powder, with high thermal efficiency and uniform heating, and can obtain high precision, uniformity, compactness, low oxygen content and.

Parts with fine grain structure.

At present, the research objects of SPS mainly focus on ceramics, cermets, intermetallic compounds, composite materials, nano-materials and functional materials. Many attempts have been made to prepare and shape amorphous alloys, shape memory alloys, diamonds and other materials, and good results have been achieved.

Seven, explosion suppression technology references:

Explosive compaction, also known as shock wave compaction, is a high-energy forming method using chemical energy. Usually, the metal powder material is placed in a mold with a certain structure, and the explosive pressure is applied. In a very short time, the chemical energy of the explosive substance is converted into a high-pressure shock wave in the surrounding medium, which acts on the powder in the form of pulse wave to obtain high density. The action time is only 1O- 100us, and the powder forming is about1ms. Explosive compaction is a unique processing method, which can make loose materials reach theoretical density. Materials that are not suitable for traditional pressure processing can be made into parts, and traditional incompressible cermet materials and low ductility metals can be pressed into composite materials. The typical application is to use super alloys powder to form high temperature resistant parts of aircraft engines.

Concluding remarks

Powder metallurgy is an important part forming technology. The continuous emergence of new technologies and processes of powder metallurgy will certainly promote the rapid development of high-tech industries and bring bright prospects to material engineering and manufacturing technology. At present, the overall technical level of China's powder metallurgy industry is low, and the technology and equipment are backward, which is far from the advanced foreign technical level. Therefore, it is of great significance to vigorously develop the research of new powder metallurgy technology to improve the grade and technical level of powder metallurgy products in China and shorten the gap with foreign advanced levels.