The advantages of powder metallurgy process: 1, the vast majority of refractory metals and their compounds, false alloy, porous materials can only be made from powder metallurgy method. 2, due to the powder metallurgical method can be compressed into the final size of the compact, and don't need or rarely need subsequent mechanical processing, so can greatly save metal, reduce product cost. With products manufactured by the powder metallurgy, metal loss is only 1-5%, and with the general casting method production, metal loss could reach 80%. 3, due to powder metallurgy technology in material does not melt during production, are not afraid with impurities from crucible and deoxidizer, and sintering in a vacuum and restore general atmosphere, is not afraid of oxidation, also did not give any material pollution, therefore, likely to preparing high purity materials. 4, powder metallurgy method can guarantee the correctness of the material composition ratio and uniformity. 5, powder metallurgy, suitable for the production of the same shape and quantity of the products, especially the gear etc. The high cost of processing products, manufactured by powder metallurgy method can greatly reduce the production cost. Is the basic process of powder metallurgy industry: 1, the preparation of raw material powder. Existing pulverizing method in general can be divided into two categories: mechanical and physical chemistry method. And mechanical method can be divided into: mechanical crushing and atomization method; Physical and chemical method is divided into: the electrochemical corrosion method, reduction method, legal, reduction - legal, vapor deposition method, liquid phase deposition method and electrolysis method. One of the most widely used is the reduction method, atomization method and electrolysis method. 2, powder molding for shape of briquette. Obtained is the purpose of forming a certain shape and size of compact, and make it has a certain density and strength. Forming method is basically divided into extrusion forming and non pressure molding. Most used in extrusion forming is moulded. 3, compact sintering. Sintering is a crucial process in the powder metallurgy process. After forming compact required is obtained by sintering the final physical and mechanical properties. Sintering is divided into units of sintering and sintering. For unit system and multiple system of solid phase sintering, the sintering temperature than the low melting point of metal and alloy; For multicomponent system of liquid phase sintering, the sintering temperature is usually low melting point of the refractory compounds, and higher than the melting point fusible components. In addition to the ordinary sintering, there are apparent sintering, infiltration method, hot pressing method, and other special sintering process. 4, products after order processing. After sintering processing, can be different according to product requirements, adopt a variety of ways. Such as finishing, oiled, machining, heat treatment and plating. In addition, in recent years, some new technology such as rolling, forging is used in sintering of powder metallurgy materials after processing, obtain ideal effect. Powder metallurgy materials and products in the future development direction: 1, the representative of the iron base alloy, precision products to the large volume, high quality of the structural components. 2, manufacture with homogeneous microstructure structure, processing difficulties and fully dense high performance alloys. 3, made generally enhance the densification process to special alloys containing mixed phase composition. 4, manufacturing inhomogeneous materials, amorphous and microcrystalline or metastable alloys. 5, processing unique and unusual shape or composition of composite parts.

Disadvantages:

1: in the absence of mass to consider the size of the parts.

2: the mold cost is relatively higher casting mold.

Powder metallurgy (P/M) technique is an important material preparation and shaping technology, referred to as the key to solve the problem of high-tech, new materials... . High performance, low cost, net forming has been close to is one of the important research topic of powder metallurgical workers. Powder metallurgy method can realize workpiece less cutting and no cutting, is a highly efficient, high quality, precision, low consumption, energy-saving advanced technology of manufacturing parts. Entering the 1980 s many industries, especially in automobile industry more than any time before rely on powder metallurgical technology, using powder metallurgy of high performance components as much as possible is to improve the car, especially the car a powerful means in the market competition ability. High density P/M products is to guarantee its excellent mechanics performance of the key factors. Therefore, in order to enlarge the range of powder metallurgy (P/M parts, must increase its density in order to obtain excellent mechanical properties of powder metallurgy parts. At present, the commonly used approach is to improve the density of P/M parts mainly include: application of iron powder compressibility, after pressure after burn, leaching of copper, high temperature sintering, powder hot forging and so on.

Because the process there are different levels of costs and the workpiece dimensional accuracy guarantee difficult technical problems, such as make the competitive potential of powder metallurgical parts are hard to get into full play. Flow compaction, powder molding technology development has become an effective way to improve the density of P/M parts.

1. The flow of pressing powder forming technology development

1.1 warm pressing technology development

In the late 1980 s, the human density increase parts, such as Musella Hoeganaes company in diffusion bonding of iron powder preparation technology research, on the basis of the powder and the mould heating to a certain temperature to suppress, developed a kind of new craft of temperature, pressure, namely ANCORDENSE process. Compaction process is to use special powder heating, powder conveying and mould heating system, mixed metal powder with special polymer lubricant and mould heating to 130 ~ 150 ℃, then pressing and sintering according to traditional powder compacting process in order to improve the new method of compacting density according to the data analysis, although a suppression of temperature, pressure process than conventional sintering process of the relative costs increased by 20%, but better than copper infiltration process, sintering process, powder hot forging process was reduced by 20%, 30% and 20% respectively, the cost of development potential of the application of powder metallurgy. Therefore is known as "start a new application of a new era of powder metallurgy parts manufacturing technology", between performance and cost for the parts to find an ideal combining site, is also thought to be in powder metallurgy parts production technology since the 90 s the most important a technological progress ". At present, the powder preparation, process optimization, the densification mechanism, warm pressing and sintering behavior and so on have carried out extensive research, and realize the industrial production.

1.2 the development of metal injection molding technology

Metal Injection Molding MIM (Metal Injection Molding) is the traditional powder metallurgy technology combined with modern plastic Injection forming process and forming a new net shaping technology. Dates back in the 1930 s of the ceramic plug preparation of powder injection molding, subsequent decades focused on ceramic powder injection molding injection molding. Until 1979, organized by Wiech et al Parmatech company won two awards, metal injection molding products and the time of the Wiech and Rivers has been patented, began to turn to the metal powder injection molding injection molding is dominant.

1.3 flow of pressing powder forming technology

Metal powder injection molding technology is suitable for mass production parts with complex geometry, high performance, high precision, is also a breakthrough in terms of industrialization. But the process need to add one more binder in powder, ultrafine powder with 10 um or less nearly spherical powder, from mixed expect debinding, sintering, process more complex, the craft is strict, especially need longer debinding and sintering time, manufacturing costs are often on the high side. Flow pressure forming (WFC: Warm Flow Compaction) is on the basis of the metal powder Compaction, combines the advantages of metal powder injection molding technology, by adding appropriate amount of coarse powder and fine powder, and increase the content of thermoplastic lubricant and greatly improving the liquidity of mixed powder, filling and forming ¨. Because when suppressing mixed powder into a viscous fluid with good liquidity, has both the advantages of liquid, and has high viscosity, and reduce the friction, the suppression of pressure in the powder distribution even, also got good delivery. So powder can flow to every corner in the pressing process and not crack, so that the density has been greatly improved. The technology by the German Fraunhofer institute for advanced materials and manufacturing (IFAM) was first reported in 2001.

Flow pressure can in temperatures of 80 ~ 130 ℃, in conventional tabletting machine precision very complex shape workpiece, such as with pressing direction vertical groove, hole and threaded hole complex artifacts, without the need for subsequent secondary machining. WFC technology overcomes the traditional cold pressing both in forming complex geometric shapes, and avoid the high cost of the injection molding technology, is a potential new technology, has a broad application prospect.

Flow compaction process is suitable for almost all the powder system, but the most suitable for forming low alloy steel, Ti, WC and Co hard alloy powders.

2. The flow characteristics of temperature, pressure powder molding technology

Flow process is based on the compaction process combines the advantages of metal injection molding and developed, it is a new net shaping technology of powder metallurgy parts. In the study of temperature pressure, people found thermobaric forming in radial produced large radial pressure, and injection feeding in the injection molding technology of liquidity and good formability gave inspiration, combined the advantages of both and the mixed powder optimizes flow compaction creates powder molding technology. Flow pressure process is to have good liquidity of mixed powder into the mold cavity, and then under certain temperature to suppress forming has the complex geometric shape of the workpiece, without special degreasing process and direct sintering was new technology of powder metallurgy parts. Its main features can be summarized as follows.

2.1 can be forming parts with complex geometries

With the direction of flow pressure can direct forming and suppression of the vertical groove, hole and threaded hole workpiece. Cold press method is used in manufacturing this kind of the shape of the workpiece is very difficult or even impossible, generally need to pass through subsequent machining to finish. Using nc tablet machine to realize the complex and precise action can only produce such artifacts is relatively simple.

Fraunhofer researchers also use with a slight taper forming punch successfully directly the deep blind hole workpiece, blind hole wall is high and the ratio of wall thickness can reach 3 ~ 7, wall thickness range can be in 1 ~ 3 mm. Flow pressure process in order to systematically study the flow behavior of powder, Fraunhofer researchers used a special mould ¨ led as shown in figure 1. The mould in two bolted connection, horizontal hole and vertical hole diameter is 16 mm. Researchers on T hole hole, hole, L shaped cavity mould is studied, and the pressing direction perpendicular to the length of the side hole can be through the bolt to adjust. With flowing temperature pressure process was successfully out of the T shape workpiece. The experimental results show that the mixed powder of the liquidity is good enough to avoid cracks around the corner.

Flow process can also be formed parts using more complex geometrical shape. Mixed powder of good liquidity can flow compaction makes craft precision forming workpiece fine outline. Therefore, flow pressure forming process can be used for thread. With external thread core mould after compacting, the core screw out from the semi-finished products, and then sintering thread can be obtained. According to choose a suitable shrinkage of core diameter can be pressed out the screw without the need for secondary machining required. This is perhaps the most significant technological processing flow applications.

Flow pressure is studied, to create a special device, flow pressure flow study trends and implement cross parts forming.

2.2 compact density is high, the density is relatively uniform

Flow pressure due to the filling density is higher, so the temperature and pressure of the density of semi-finished products can achieve very high value. Good besides density increase, due to the powder flow, forming parts density are more homogeneous. Or a simple die (does not need auxiliary floating die multiaxial) can be more steps of powder metallurgy workpiece.

For pure Ti powder difficult forming, flow compaction applied and achieved obvious results. If use Ti powder density distribution of T type workpiece (marked on the part drawing in 1 ~ 6 Numbers) as shown in the figure below. Can be seen from the diagram, flow pressure can be obtained using high density, artifact in addition to good sintering performance, density distribution is more uniform. "5" place distance parts in figure central axis with 14 mm, density is low when cold, this is mainly female die mold wall caused by uneven friction and stress transfer.

Ti semi-finished product and finished product density distribution in different locations (ri no space density of 4.5 g/cm3)

2.3 good adaptability of materials

Flow technique can be applied to all kinds of metal powder, powder including low alloy steel, stainless steel powder, pure Ti powder and tungsten carbide powder, etc. Fraunhofer research personnel flow compaction was carried out on all kinds of metal powder technology research, has achieved remarkable results, including the low alloy steel powder (DistolayAE), 316 l stainless steel powder, pure Ti powder and WC - Co hard metal powder. Flow process in principle can be applied to all the powder series, the only requirement is that the powder must have enough good sintering performance, in order to eventually reach the required density and performance.

2.4 process simple, low cost

With the traditional method of powder metallurgy forming parts in the direction perpendicular to the suppression of grooves, cross hole shape, need to design complicated mould or through sintering after secondary machining to finish. Although the injection forming technology in the aspect of forming parts of complex shape almost is not subject to any restrictions, but because of the large number of adhesive added, in heating process can make the workpiece deformation occurred because of gravity, therefore often require additional a more complex and more expensive special degreasing process, compared to the conventional powder metallurgy technology makes the injection forming technology cost is high, so the parts of injection molding will not be able to replace can meet the conventional powder metallurgy parts of its design function, which makes the application of the injection molding technology is limited by a certain range.

Flow compaction, powder molding technology can not only direct forming complex geometrical shape without the need for subsequent secondary machining; Flow compaction, on the other hand, in the forming process, using special adhesive and lubricant content is moderate, the configured mixed powder has high viscosity and the critical shear strength, will not happen deformation in the heating process, thus get rid of adhesive can be directly in the sintering process. Therefore, compared with traditional powder forming process and the injection molding process, flow temperature pressing powder forming technology for forming complex geometrical shape of parts, it simplifies the production process, and greatly reduces the manufacturing cost.

3. The mobile application prospect of temperature, pressure powder molding technology

Flow pressure forming technology combines the traditional advantages of repression and metal injection molding mim parts when both shorten the process, and reduced the cost, at the same time, the density and complexity of the parts is improved, and good application prospect. Flow pressure can be artifacts in the traditional powder metallurgy machine press forming, so you need to make before machining to forming of complex shape parts can be easily realized. Therefore, flow pressure forming technology will greatly expand the application range of the technology of powder metallurgy forming, has wide application potential and prospects.

4. The flow pressure technology research significance

WFC as a new type of powder metallurgy metal parts near net shaping technology, can produce high performance at a relatively low cost short process complex shapes (such as sockets, cross hole and threaded hole, etc.) of parts, and adopts the traditional powder pressing mechanism to build this kind of powder metallurgy parts in the past was thought to be very difficult, even impossible.

Flow pressure in forming the three-dimensional complex parts cannot replace injection molding technology, but the use of flow forming unique characteristics can produce the parts shape complexity between cold press and injection molding of moderately complex parts, it can make the traditional powder metallurgy complicated components of the machine are low cost short process manufacturing technology, the breakthrough progress is on track to automobile, electronics, medical equipment, daily necessities, office machinery, instruments, machinery manufacturing industry such as application, the application will also further expand application range of temperature, pressure forming and traditional field. Flow compaction of metal powder forming technology for high performance complex precision parts of low cost, short process of advanced manufacturing open up new development direction, forming of powder metallurgy materials processing technology is expected to expand and deepen.