Metal Injection Moulding is a manufacturing process in which fine metal powder is mixed with a special binder and injected into a die to form the required shape. The binder is then removed and the part is finally sintered, to produce a high-density metal component. The design principles are similar to those for plastic injection mouldings and pressure die-castings, but the MIM process offers far superior mechanical properties to either of these.
The first stage involves mixing fine powdered metal with a wax/polymer binder. The powder-metal particles used for the metal Injection moulding process are much finer and more spherical than those used for the conventional sintered metal process.
After further mixing the MIM material is made into pellets which can be stored as feedstock batches, ready for use in an injection moulding machine.
The feedstock pellets are loaded into an injection moulding machine and the material is injected under pressure into a die. This part of the MIM process uses similar equipment and techniques to those used in plastic injection moulding. The MIM parts are produced oversize to allow for contraction in the next stages.
The injection sprues are removed from the moulded parts, which are then placed on trays ready for the debinding stage.
The injected MIM parts in their ‘green state’ are placed in an oven to remove the binder, leaving the parts in the ‘brown state’.
The final stage is a high temperature sintering treatment in a vacuum, which releases surface energy stored in the fine powder and fuses the metal particles together. This results in high density, high strength MIM parts.
After sintering the metal Injection mouldings are completed, unless additional operations are required such as straightening or setting and inspection. Additional operations such as machining, polishing, plating, heat-treatment may be carried out depending on the finished part required.
