Three factors affecting the flowability of MIM stainless steel

Metal Powder Injection Molding (MIM) is a process in which metal powder and an organic binder are mixed and granulated into feedstock pellets, which are then shaped into specific products via injection molding. This process is particularly suitable for manufacturing small, precision, and complex parts, and plays a significant role in fields such as powder metallurgy micro gears, automotive parts, and mobile phone components.

The MIM process imposes strict requirements on the rheological properties of the feedstock. The two most commonly used metal powder injection feedstocks are iron-based feedstocks (e.g., Fe2Ni, Fe8Ni) and stainless steel feedstocks (e.g., SUS316L, SUS630 also known as 17-4, SUS304, etc.). With the increasing demand for stainless steel products, research on stainless steel feedstocks has rapidly intensified.

Three main factors affecting the flowability of stainless steel feedstock:

First, powder loading. Powder loading is the volume percentage of metal powder relative to the total feedstock volume. The higher the powder loading, the greater the viscosity of the feedstock and the poorer the rheological behavior. When the powder loading decreases, the binder proportion increases, the viscosity decreases, and the flowability improves. It is important to note that more binder is not always better, as its impact on subsequent processes must also be considered.

Second, shear rate. When the feedstock flows at a high shear rate, it generates heat, reducing its viscosity and enhancing flowability. When flowing at a low shear rate, the heat generation is slower, the viscosity does not decrease significantly, and the flowability is poorer.

Third, temperature. Temperature affects flowability by influencing the viscosity of the feedstock. As the temperature rises, the feedstock viscosity decreases, and flowability improves. As the temperature drops, the feedstock viscosity increases, and flowability deteriorates.