Takashi Iwai

Thermal and mechanical coupling in granular modeling for metal injection molding

Abstract Metal injection molding (MIM) employs viscous thermoplastic polymer materials (binders)_ with metallic powders to improve flowability and formability. It is essential to be able to describe the behavior of such mixed materials, for this purpose a new granular model being proposed to deal with the powder characteristics and mechanics. The composite element is designed to consider both elasticity and viscosity for powder particles and binders. A thermal and mechanical coupling effect is introduced directly to describe the cooling process. Numerical results demonstrate the effectiveness and validity of the presently-developed granular modeling in dealing with the various phenomena appearing in the MIM process.

Granular Modeling Approach to Electro-Packaging Materials.

Abstract The particulate material to be used for electro-packaging of LSI-chip is a compound of polymer matrix and silica particles. In its materials design, a volume fraction of silica must be designed to reduce the difference of thermal expansion coefficients between the compound and the semiconductive device. Since the loading ratio of silica particles in the polymer matrix reaches to 60 vol.% in actual situation, the viscous flow of the compound can be identified as a non-Newtonian fluid; since nonlinear viscosity changes itself even in local with the process time, various defects or porosities have to be left in the final product. In other words, new materials processing design is necessary to rationally determine the geometry and dimensions of a die-set system and to adequately optimize the process parameters. In the present paper, a granular modeling is proposed to describe the rheological behavior of this high-loaded particulate compound. Use of this modeling enables us to make direct process simulations for investigation of the formation of defects and understanding of mechanism to be free from defects. Simulated results indicate a rational possibility for the present granular modeling to be used for the related materials processing design to the particulate electro-packaging materials.

GRANULAR FLOW SIMULATION FOR METAL INJECTION MOLDING PROCESS

Metal Injection Molding treats the complex fluid which consists of thermoplastic tic polymer medium and dense metallic powder suspensions to improve flowability and formability. To understand its fundamental mechanical behavior, it is important to consider powder structures and mechanics precisely. For the analysis of this process, a new granular model is proposed, which is based on the Distinct. Element Method. Each element in this method is constituted by combining a metal powder with a binder (polymer) shell surrounding it. Both elasticity and viscosity for powder particles and binders are only considered in this mixture model as the constitutive relations. Several numerical results have demonstrated the effectiveness and validity of our developed granular modeling to deal with the various phenomena appearing in MIM process.

Modeling for Powder Compaction and Flow in the Thermal or Magnetic Fields

Various characteristic behaviors [1] are often seen in powder materials. Due to bridging and arching behaviors, where powder particles are locally stacked, the applied external stresses cannot be transferred to every spot of medium. At the presence of a binder material, powder-binder compound with high loading ratio of particles shows its intrinsic non-newtonian behaviors with locally varying viscosity coefficient.