What is metal injection molding (MIM)?


Metal injection molding (MIM) combines two well known technologies, plastic injection molding and powdered metallurgy. MIM provides perfect design flexibility than many other production processes by allowing designers to eliminate traditional constraints associated with trying to shape stainless steel, nickel iron, copper, titanium and other metals. APSX-PIM offers "injection molding" step to create the "green part". The rest of the MIM process is performed by using special equipment such as furnaces and chemical solvents.

1 - Feedstock

APSX suggests to obtain pre-packed feedstock rather than try to make it in-house since it requires extensive chemistry and metallurgy knowledge. Additionally the particle sizes are very fine about less than 15 microns to be mixed proportionally based on a special recipe. The "binder" can also contain multiple different material such as thermoplastic polymers and primary paraffin that help to achieve tight part tolerances on very small parts. Each fine metal powder particle is covered with a binder particle uniformly in a hot state to create a mixture so the feedstock pellets can be made through extrusion than granulation processes.

2 - Injection Molding - APSX-PIM

APSX-PIM can make the first stage "green part" through its standard injection molding process. However the key is the capability of custom settings that allows the user to perform this step properly. Custom settings involve injection pressure, holding pressure, holding time and fill rate to make a perfect green part. A standard-traditional large size injection molding machine may require extensive setting procedure or a small manual press can not offer the repeatibility and accuracy that APSX-PIM has. In that stage the part size is about 20% larger than the desired final part size due to shrinkage allowance. A secondary operation or a simple machining can be performed at this stage.

3 - Debinding

In this step the goal is to remove the most of the binder material out of the green part. It is a controlled step that may be a combination of chemical solvent bath and/or thermal burner process. The part is called "brown part" at the end of this step and has very little binder left in it so it very brittle.

4 - Sintering

This step completely eliminates the final binder material and gives the part its final geometry. The part gets exposed to heat in a furnace at temperatures close to its melting point. The temperature is precisely monitored based on the suggested temperature profile required. This final step is a long step that sometimes it takes 20 hours to complete. The part shrinks to its design dimensions. Final product properties are similar to those of one machined from bar stock. If necessary, post-sintering operations such as machining, heat treating, coating, and others, may be performed on the part to achieve tighter tolerances or enhanced properties.