MIM Process Overview
Metal injection molding is a powder metallurgy (PM) technique in which metal powder is plasticized with the help of a thermoplastic additive. The latter is usually referred to as binder,and is a mixture of waxes, polymers and additives. The mixture of metal powder and binder is called feedstock, and it can be injected into intricate molds to create complex components in high quantities.
While the concept of molding metal like plastic is very simple, due to several factors the process needs more attention to detail and expertise. The idea to plasticize powdered rawmaterials with the help of thermoplastic additives and subsequently use injection molding to form complex components was first developed for ceramic components. In the 1970’s the process was adapted for metal powders by Raymond Wiech in the USA. Since then, MIM has developed into a well-established manufacturing technology producing complex metal
components in all industrial sectors.Historically, injection molding was mainly used for plastic materials. The main breakthrough,however, was using a high volume fraction of metal powder so that instead of a plastic part a metal part bonded by plastic can be produced. After removing the binder, a fragile metal part remains, which can be sintered, and further achieve densities of over 98%. This high density gives the finished parts similar properties to parts made out of wrought material. Therefore,the mechanical properties of parts produced via MIM are comparable if not superior to traditional PM parts. A very important feature of MIM manufacturing is that intricate parts can be manufactured quite cheaply; another is that a multitude of materials can be used. The process is can be highly automized and MIM parts can have extremely thin walls, small holes, and other intricate details. Since the material cost is relatively high, most MIM parts are rather small to reduce the relative share of material cost per part. Compared to other metal manufacturing technologies, MIM is most efficient if two prerequisites are met: the manufactured metal parts are of high complexity, and the yearly production volume is high. Usually, MIM parts are produced in quantities greater than 10000 per year, with the highest production volumes ranging in the millions
A big advantage of MIM compared to other technologies is the possibility to produce parts to near-net-shape, since the freedom in mold design allows for very precise parts. MIM is not restricted to a few select materials; almost any metal or alloy can be produced in suitable metal form. Example materials are nickel-iron, copper, titanium or advanced super alloys. Infact only PM/ MIM can produce several new novel alloys, which are not possible in conventional cast technologies.While it is possible to buy metal powders and manufacture feedstock on-site, many MIM factories buy premade feedstock. Therefore, several large chemical companies have developed an assortment of MIM feedstock’s encompassing various materials.