S. C. M. Yu

Simulation of Particle Migration of Powder-Resin System in Injection Molding

Powder injection molding is an important processing method for producing precision metallic or ceramic parts. Experience, intuition and trial-and-error have been the practice for the design and process optimization of such molding operations. However, this practice is becoming increasingly inefficient and impractical for the molding of larger, more complicated and more costly parts. In this investigation, a numerical method for simulating the mold-filling phase of powder injection molding was developed. The flow was modelled using the Hele-Shaw approach coupled with particle diffusion transport equation for the calculation of powder concentration distribution. The viscosity of the feedstock was evaluated using a power-law type rheological model to account for the viscosity dependency on shear rate and powder concentration. A numerical example is presented and discussed to demonstrate the capabilities and limitations of the simulation algorithm, which has the potential as an analytical tool for the mold designer. The variation of powder density distribution can be predicted, which is ignored by the existing simulation packages. Preliminary simulation indicated that powder concentration variation could be significant. Non-isothermal analysis indicated that most of the key parameters for filling process would change due to a change in powder concentration distribution.

Shear-induced particle migration modelling in a concentrated suspension flow

Shear-induced particle migration was investigated by using a continuum diffusive-flux model for the creep flow of nickel-powder-filled polymers, which is viscous with shear-thinning characteristics. The model, together with flow equations, was employed for solving the generalized-Newtonian flow patterns and non-uniform particle concentration distribution of mono-modal suspensions in a pressure-driven tube flow. Particle volume fraction and velocity fields for the non-homogeneous shear flow field were predicted with different particle concentrations. Effects of different viscosity models of the binder system on particle migration during non-homogeneous shear fluid flow were investigated.

Numerical and experimental investigation of thermal debinding

Abstract Numerical simulation and experimental verification were carried out on polymer removal from a PIM compact by thermal debinding. An integrated model, considering the interactive effects of various mechanisms, is proposed. It avoided the necessity of making the unrealistic assumption of a receding liquid/gas interface front, which is commonly employed by other models. From the numerical and experimental investigations, it is revealed that the distribution of polymer residue is a smooth continuous function of distance. The phenomenon observed experimentally by other researchers, namely enrichment with liquid polymer in the outer surface region of the compact, was predicted numerically and observed experimentally. The results of numerical simulation are in good agreement with experimental observations.

Numerical Simulation of Thermal and Flow Characteristics Inside a Rod Type Cathode (RTC) Plasma Torch

A mathematical modeling of argon thermal plasma flows inside a rod type cathode (RTC) plasma torch based on electromagnetic principle is presented. Numerical investigations on the model are carried out for a better understanding of its output characteristics in terms of the plasma velocity, temperature, mass fraction and electro-magnetic field calculations. A direct comparison of the present numerical results with a reported experimental data is made and found to be in fair agreement.Copyright