Comparison between plasticizing extrusion molding and injection molding of metal powder


Until today, powder metallurgy technology has developed many branches and various processes, in which two kinds of most representative processes must be plasticizing extrusion molding and injection molding. Although they both belong to powder metallurgy, they also have many differences. Below, will introduce some differences between plasticizing extrusion molding and injection molding in the following points.

Metal powder plasticizingMetal powder plasticizing extrusion molding technology was developed on the basis of metal powder sheath extrusion and other technologies, which is a kind of new technology that will have extrusion molding for copper, tungsten, cemented carbide, high-melting intermetallic compound and ceramic material that have high mobility under low temperature. Currently, this technology has been equipped with specified continuous extrusion equipment. Metal powders that have high mobility and have been added with certain amount of accelerative reagents will be used in this technology. Blanks that produced by this technology can be made into final products after drying and sintering process.

Metal injection molding technology is a kind of near net forming process that combines traditional powder metallurgy technology with modern plastic injection molding technology and relies on binder formula development and feeding production technology. It is a kind of molding technology that has developed for a long time at slow speed. In this technology, the mixture of metal powder and binder will be injected into specific cavity under certain temperature and pressure conditions, thus the blanks that are close to the size and shape of final products will be generated; after debonding and sintering, the final product that has certain mechanical property can be obtained.

It can be seen from the above descriptions that powder plasticizing extrusion molding has many similar advantages with injection molding. Therefore, these two kinds of technologies have developed rapidly in recent years. The common advantages will be summarized in the following four points: a. near net forming, in which they can both form blanks that are close to the final shape of products only with one step; b. they can both produce metal products that have complex shape by using traditional casting and machining, especially that they will have large advantages in producing small complex parts as well as slender parts; c. they can both be used in a wide range of materials, which can be used in processing materials into products that are difficult to produce by conventional processes; d. they can both be used as the new methods in developing new materials and related final products.

Besides, binder will be used in both of the two kinds of technologies. According to the selection and formula, binders can be classified into three systems, which are ceryl, methyl cellulose and plastic base. The dosages of all of them will not vary a lot, which are all in the mass ratio range of 8-20 percents. In addition, binders will be removed thoroughly after the forming of blanks.

However, they also have some obvious differences. Regarding raw materials, metal powder particles that used in plasticizing extrusion molding will have wide range, which can be ranged from several microns to several hundred microns; while metal injection molding will have high requirement on metal powders, in which the powder particle size is usually in the range of 0.5-20 microns, besides, it will have higher requirements on preparation method and powder shape. Therefore, after forming, the products will become more compact, the shrink rate will be smaller in the sintering process and the dimensional precision will be higher.

In addition, different molding equipments and material stress will be used in these two technologies. Plasticizing extrusion molding technology uses screw extrusion molding machine, in which the materials will be compressed in two dimensions as well as will be extruded and stretched in one dimension as well as the extrusion force usually will not exceed 300Mpa; while the injection molding will use injection molding machine, in which the materials will bear three-dimensional compressive press in the forming process.

After comparing the common points and different points of the two kinds of technologies, we have come to know that they both will become the new development trend of powder metallurgy technology and will both be able to form products that have small complex shape. Plasticizing extrusion molding can be used in producing products that require low precision and can reduce production cost; while injection molding that has strict requirement on powder particle size can be used in forming products that require high precision.