The Metal Injection Molding Process
1. Feedstock Formation
Fine titanium powder and thermoplastic binders are combined at precise levels. The materials are mixed together and heated up to allow the metal powders to disperse within the melted binders. The mixture is then pelletized to form a feedstock suitable for injection molding.
Metal injection molding, like plastic injection molding, uses a conventional injection molding machine to form a molded part. In the case of MIM, feedstock is fed from a hopper into a heated barrel where the feedstock is melted however, only the binders are melted. Once the feedstock is molten, it is injected into a mold to form the desired geometry. Once the part is cool, the part is ejected and ready for debinding. At this point, the molded part is referred to as a “green part.”
The debinding process removes only a portion of the binder components. The remaining binder will stay to hold the part together during the first part of sintering. Debinding can be carried out in multiple ways, the most common routes are solvent extraction or catalytic decomposition.
4. Sintering / Thermal Processing
Debound parts are placed on ceramic setters and loaded into a furnace for high-temperature processing. During the early stage of sintering, the remaining binder is thermally decomposed. After this initial stage, the parts are heated to a high temperature where densification occurs, resulting in significant shrinkage of up to 20%.
5. HIP’ing / Secondary Operations
To achieve full density, the component may be hot isostatically pressed (HIP’d). Secondary finishing options such as CNC machining, anodizing, passivation, surface finishing, and laser marking are also possible.
6. Resulting Solid Component
The resulting solid component is completely dense and identical in chemistry to conventional titanium.