The Metal Injection Molding process was born from the meeting of two different technologies: the injection molding of thermoplastic polymeric materials and the sintering of metal powders. The peculiarities of injection molding – freedom of geometry, high productivity, minimum scrap – are extended to different metal alloys: low alloy steels, stainless steels, titanium alloys, bronzes and many other metal alloys.
THE PRODUCTS
Thanks to the metal injection molding technique, Mimest is able to create many different objects characterized by excellent mechanical properties, impeccable surface finish and high precision, with applications in the medical, sports, automotive, mechanical and micromechanical sectors in general, defense, fashion, aeronautics.
THE STAGES OF THE PROCESS
The Metal Injection Moulding process can be summarized in 4 main phases
1 - MIXING
The MIM process begins with the mixing of very fine metal powders with a binder (usually, a plastic material). This mixture is then extruded to form the so-called feedstock, our raw material.
2 - MOLDING
After carefully making the mold of the necessary shape, the feedstock is injected into its cavity thanks to a press similar to those used for plastic materials. This results in the molded parts, which at this stage of the process are called "green".
3 - DEBINDING
After injection, the organic part that acts as a binder to give shape to the metal particles is dissolved (usually in water), leaving a fragile and porous complonent (its volume is formed for about 40% by air). The components, after this step, are called "brown".
4 - SINTERING
At this point the pieces are brought inside furnaces at a temperature close to the melting point to allow the sintering of metal powders and the obtaining of compact objects. At this stage the volume is reduced by about 20%, the pores close and the desired density is obtained.
POST TREATMENTS
If required, the pieces can be finished with mechanical processing, calibration, heat treatments (such as cementing, carbonitriding, hardening) and surface treatments (such as PVD, galvanic, electropolishing).
ADVANTAGES
Freedom of design: injection molding gives the MIM the possibility to think of complex and newly designed geometries compared to traditional technologies while using high-performance materials such as steel or titanium.
Savings: is possible to make objects with materials that are difficult to process and of high cost with zero waste; it is also possible to achieve weight savings by working on the design of the parts.
Physical properties: many alloys can be used with excellent properties with results comparable to tilling both in terms of mechanical properties and chemical properties such as corrosion resistance.
Productivity: MIM allows to make metal objects with complex geometries with high productivity, comparable to other injection techniques (e.g. plastics or zamak).
APPLICATIONS
When the number and complexity of the parts justify the investment in a mold, then MIM becomes competitive.
Any type of mechanical reprocessing is possible on the parts obtained through MIM. The obtainable tolerances are a function of the size of the parts: indicatively 0.5% of the nominal measurement. Typically most applications range from a few grams to two/three ect in weight.
The main reasons for choosing MIM, in short, are: complex geometries, high number, use of expensive or difficult-to-process metal materials, excellent surface properties.