Particle size effect on the magneto-rheological behavior of powder injection molding feedstock

• A magneto-rheology of 3 different particle size feedstocks is investigated for PIM.
• There is an upper limit to the increase of feedstock viscosity with magnetic field.
• Smaller particle size shows higher viscosity under the magnetic field (B=0~0.6T).
• The magneto-rheological behavior is characterized by a phenomenological model.
• This model can well represent the experimental shear viscosity data.

Powder injection molding is one of the important manufacturing technologies for the net-shape production of metallic and ceramic components. This technology can also be a promising process for mass production of magnetic parts with complex geometries. In the magnetic powder injection molding process, powder characteristics and magneto-rheological behavior of the feedstock are significant factors affecting the final product quality. In the present study, we've investigated the magnetorheological behaviors of 17-4 PH feedstock by using a rotational rheometer. Particularly, the effects of particle size and magnetic flux density on the magneto-rheology of the feedstock were studied in detail. An upper limit on viscosity increase with the external magnetic field was found, which depended on the shear rate and the size of magnetic particles. Higher shear rate reduced the viscosity of feedstock, while larger particles with a wider distribution in size showed relatively lower viscosity. These magneto-rheological behaviors were characterized with our empirical models, which can be directly applied to the process optimization of powder injection molding for magnetic components.

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