Metal Injection Molding

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  • Topic: Metal injection molding, Injection molding, Metalworking
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  • Published : April 8, 2013
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The Metal Injection Moulding process (MIM), considered as a development of the Powder Injection Moulding (PIM), became, over the years, a competitive manufacturing process for small components, offering an alternative to other processes, more expensive to create these parts. History of the technology

The PIM process was at first developed in the 1930s in the USA. This process was originally intended for ceramics. Then, during the Second World War, metal powders appeared. The process of Metal Injection Moulding was developed by Dr. Raymond E. Wich Jr. during the 1970s and became then an industrial process. Afterward, the MIM process spread in Japan and finally in Europe. (M. Martin, 1999) The context of its invention

Historical Context

In the 1940s, conventional powder metallurgy was developped in Germany before the Second World War. Later, in Sweden, the company Högänas developed pure iron powder that could be pressed and sintered to small mechanical components. But this material contained pores at this time. After the war, various alloys were used as powder metal which enhances the properties of the final part. In parallel, the "atomize" technique was developed : a jet of metal was crushed into a mold. But this technique results in part still with pores. Moreover, it cannot be used for high-alloy metal. In the 1950s, the automotive industry used a lot of powder metal, especially the US market, followed by Europe and Japan. In parallel, the atomization with pure gases (argon, helium or notrogen) was developed.

In the 1960s, a new process, using gas under pressure that presses the metal powder into a mold, was enhanced. It is the Hot Isostatic Pressing process (HIP). In the 1980s, the MIM process was invented and developed in California. Small components were made thanks to the MIM process while large components were made with the HIP process. (Metec, 2013) Economical context

In America, 330 industrial companies produce components made from the MIM process. There are 10 mixtures providers and 30 powders producers in the world. Stainless steel represents 50 % of the components made thanks to the MIM process (R.G. Cornwall, 2003). In 2008, all sales represent 600 million Euros (R.G. Cornwall, 2003). The annual production from the powder metal industry represents near a million tons a year (Y. Bienvenu, 2007). Half of the production is realized in Asia, mainly in China, in India and in South Korea. A quarter is produced by North America, 13 % by Europe and 10 % by Japan. The first world producer is the Swedish company Höganäs, with a production of 500 000 tons a year (R.M. German, 2008). Metal powders are used at 74 % by the automotive industry, 13 % by transport and space and 13 % by leisure activities (Y. Bienvenu, 2007). Publication and patents

The metal powder industry has been studied since 1970. Before this date, only 10 publications can be counted, 100 in 1980 and 1000 at the end of 1999 (R.M. German, 2000). In 8 years, the publications number has tripled.

In 20 years, the number of patents specific to the MIM process filed in the USA grew from 83 to 400 (R.M. German, 2007).

How does the MIM process work ?

The MIM process can be described as four different stages (German, 1997): The Mixing
A mixture of metal powder, binder and additives are put together in the form of granules : it is the feedback, also called Green Body. Some parameters have to be considered during this operation to obtain a good flow: the choice of the binder, the volume fraction of powder as well as the temperature of the mixture. The binder is a mixture of thermoplastic polymers (such as wax or polyethylene), processing aids and surfactant that helps all the granules to flow in the mold. The proportions between powders and binders vary according to the type of the chosen powder. Generally, the volume fraction of powder is around 60% to obtain a homogeneous mixture. Thus, cracks and distortions are avoided (T. Barrière,...
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