Sintering method of metal powder metallurgy products and factors that can influence sintering quality

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Metal powder metallurgy is a kind of metal parts forming technology that uses metal powder or the mixture of metal powder and other nonmetal powders as raw materials, in which sintering is an indispensable process no matter in powder pressing or in powder injection molding. As different powder metallurgy process and different powder metallurgy material will use different sintering methods, different factors will influence metal powder metallurgy products. Below, we will introduce different sintering methods of powder metallurgy products and different factors that can influence sintering quality.

metal powder for powder metallurgyFirst of all, as different kinds of metal powder metallurgy products will have different performances, the sintering methods will vary a lot. According to different raw material compositions, sintering methods can be divided into single component system sintering, multicomponent system solid phase sintering and multicomponent liquid phase sintering. Single component system sintering refers to the solid phase sintering of pure metals or compounds under the temperature lower than the melting point; multicomponent system solid phase sintering refers to the solid phase sintering of materials that have two kinds or more than two kinds compositions under the temperature lower than the melting point of low melting point compositions; multicomponent liquid phase sintering refers to the sintering of materials that have two kinds or more than two kinds of compositions under the temperature higher than the melting point of low melting point compositions.

Secondly, according to different charging methods and sintering equipments, metal powder metallurgy products sintering methods can also be divided into continuous sintering and batch sintering. In the continuous sintering, continuous sintering furnace will be used and the commonly used charging methods mainly include pusher feed method, roller feed method and wire belt transmission feed method. By using continuous sintering method, as dewaxing, presintering, sintering, refrigeration and other various steps can be finished in a same device, the sintering efficiency will be very high and can be used in mass production. In the batch sintering, the multifunctional sintering furnace will be used for preheating, heating and cooling cycle. Besides, it also can accurately formulate the sintering temperature of some special sintering parts in the furnace. However, as it has very low production efficiency, it can only be used in small scale production.

Thirdly, according to different sintering temperatures, it also can be divided into medium temperature sintering and high temperature sintering. According to different sintering atmospheres, it can be divided into air sintering, hydrogen protection sintering and vacuum sintering. In conclusion, the sintering methods will vary a lot according to different classification standards.

Fourthly, there are many kinds of factors that can influence the sintering quality of metal powder metallurgy products, such as metal powder shape, forming conditions, forming technology and the selection of sintering methods. Besides, heating rate, sintering temperature, sintering time, cooling velocity, sintering atmosphere, sintering pressurization condition and other factors can influence the sintering process.

Among them, the sintering temperature and sintering time are the two key factors that can influence sintering quality, as they can influence the porosity, compactness, strength and hardness of sintering body. If the sintering temperature is too high or the sintering time is too long, it may reduce product performance and will even lead to oversintering of products; if the sintering temperature is too low or the sintering is too short, the products performance will be reduced due to the undersintering.

No matter in traditional metal powder metallurgy technology or metal injection molding technology, sintering atmosphere is an important factor that can influence sintering quality. In powder metallurgy, the commonly used sintering atmosphere mainly includes reducing atmosphere, vacuum and hydrogen atmosphere. Regarding some kinds of materials that are easy to have composition segregation or are easy to pollute in the forming process, sintering atmosphere will directly influence the performance of powder metallurgy products.

For example, by sintering under reducing sintering atmosphere, it can prevent the burning loss of compact and can reduce surface oxide. Iron base and copper base often use producer gas or decomposed ammonia atmosphere, while cemented carbide and stainless steel often use pure hydrogen atmosphere. Vacuum sintering can be used in reactive metals or refractory metals (such as beryllium, titanium, zirconium and tantalum), cemented carbide that contains TiC and stainless steel, which can not only avoid the adverse effect that caused by the harmful ingredients (H2O, O2 and H2), but also can reduce sintering temperature (usually it can reduce 100-150 degree Celsius).

In conclusion, it can be seen that the sintering process of metal powder metallurgy will have important effect on the whole technology process; there are many factors that can influence sintering quality; sintering methods will vary a lot according to different influence factors. Besides, when choosing the sintering methods, enterprises should also pay attention to the characteristics of various powder materials, products performance and other factors.