Tae Gon Kang

Rheological behavior of magnetic powder mixtures for magnetic PIM

Powder injection molding (PIM) is a promising manufacturing technology for the net-shape production of small, complex, and precise metal or ceramic components. In order to manufacture high quality magnets using PIM, the magneto-rheological (MR) properties of the PIM feedstock, i.e. magnetic powder-binder mixture, should be investigated experimentally and theoretically. The current research aims at comprehensive understanding of the rheological characteristics of the PIM feedstock. The feedstock used in the experiment consists of strontium ferrite powder and paraffin wax. Steady and oscillatory shear tests have been carried out using a plate-and-plate rheometer, under the influence of a uniform magnetic field applied externally. Rheological properties of the PIM feedstock have been measured and characterized for various conditions by changing the temperature, the powder fraction and the magnetic flux density.

Modeling and simulation of metal injection molding (MIM)

Abstract: Powder injection molding (PIM) is a means of mass-producing various metal or ceramic three-dimensional components in large production quantities at low costs. Computer simulations used for plastic injection molding and powder metallurgy have been applied to PIM, but the high solid content in the powder–binder feedstock makes for differences in density, conductivity, shear rate sensitivity, and other factors. Thus, simulations for the PIM process build on the success demonstrated in plastics and powder metallurgy, but rely on modifications to properly handle mixing, molding, debinding, and sintering. In this chapter the basic models and numerical simulations are introduced in sequence to treat mixing, molding, debinding, and sintering to make predictions relevant to defect-free, high-quality production. The simulations are applied to optimization for a few applications.

Numerical study on the mixing in a barrier-embedded partitioned pipe mixer (BPPM) for non-creeping flow conditions

In this paper we investigated numerically the flow and mixing characteristics of the barrier-embedded partitioned pipe mixer (BPPM) in non-creeping flow conditions. Numerical simulations are conducted for three mixing protocols of the BPPM, co-rotational, mirrored co-rotational, and counter-rotational protocols in the range of the Reynolds number (Re), 0.1≤Re≤300, focusing on the effect of the Reynolds number, the barrier height, and the mixing protocols on the mixing in the BPPM. Each mixing protocol creates two crosssectional flow portraits with crossing streamlines. Poincaré sections were plotted to investigate the flow system affected by the Reynolds number and the barrier height. Mixing in a specific BPPM is characterized using the intensity of segregation in terms of the compactness and the energy consumption. The dependency of the barrier height and the Reynolds number on the final mixing state of the BPPMs was identified by mixing analyses. The co-rotational protocol results in an efficient mixing in the creeping flow regime. Meanwhile, mirrored co-rotational and counter-rotational protocols, which lead to poor mixing in the creeping flow regime, turned out to be efficient protocols in the higher Reynolds number regime.

Powder Injection Molding of Ti-6Al-4V Alloy for Defect-Free High Performance Titanium Parts with Low Carbon/Oxygen Contents

In this work, powder injection molding (PIM) of Ti-6Al-4V alloy powder has been studied. Defect-free high performance Ti-6Al-4V parts with low carbon/oxygen contents have been successfully prepared by PIM. A pre-alloyed Ti-6Al-4V alloy powder and wax-polymer binder system have been mixed together to prepare the feedstock. In mixing stage, the solid loading percentage and mixing conditions have been optimized. Rheological and thermal debinding behaviors of prepared feedstock have been characterized and numerically expressed based on rheometry and thermal gravity experimental results. In addition, the injection molding process of Ti-6Al-4V parts has been numerically analyzed to optimize the injection molding conditions. Consequently, the defect-free Ti-6Al-4V parts with low carbon and oxygen contents have been successfully fabricated by PIM, which exhibits excellent physical and mechanical properties.

Numerical investigation of the dynamics of Janus magnetic particles in a rotating magnetic field

We investigated the rotational dynamics of Janus magnetic particles suspended in a viscous liquid, in the presence of an externally applied rotating magnetic field. A previously developed two-dimensional direct simulation method, based on the finite element method and a fictitious domain method, is employed to solve the magnetic particulate flow. As for the magnetic problem, the two Maxwell equations are converted to a differential equation using the magnetic potential. The magnetic forces acting on the particles are treated by a Maxwell stress tensor formulation, enabling us to consider the magnetic interactions among the particles without any approximation. The dynamics of a single particle in the rotating field is studied to elucidate the effect of the Mason number and the magnetic susceptibility on the particle motions. Then, we extended our interest to a two-particle problem, focusing on the effect of the initial configuration of the particles on the particle motions. In three-particle interaction problems, the particle dynamics and the fluid flow induced by the particle motions are significantly affected by the particle configuration and the orientation of each particle.