Metal injection molding

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MIM is based on a combination of two routinely used procedures, technology of injection of thermoplastic materials and conventional powder metallurgy. In case of the conventional powder metallurgy, fine metal powder is pressed into moulds under high pressure and sintered at high temperatures (approx. 1300°C). Material is bonded just during sintering when grid diffusion occurs. The technology MIM uses injection of mixtures of metal powders and binders on injection presses that are almost the same as presses used for injection of thermoplastic materials. The input raw material for MIM consists of a mixture of binders and fine metal powders, called feedstock. Metal powder is produced by atomization of a metal and sizes of metal particles is from 5 to 20 µm. Binder amounts to 10 to 20% of the mixture weight. The binding component consists of a polymer and the stage of removal of the binder depends just on the binder type. Binder is connected with powder by pugging and mixing and the resulting product is granulated. Feedstock is mostly a commercially available product that is suitable for direct processing because it is delivered in form of granules. Now there is a wide range of metals on the market that can be processed using the technology MIM, such as ferrous alloys, nickel, alloyed steels, titanium, tungsten, etc. The most frequently used binders include polyethylenglycol (PEG) that shall be leached in water and then subject to thermal decomposition. Other binders include paraffines, also used after thermal decomposition and polyoxymethylen (POM) that shall be decomposed using a catalyst.
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