Doctor of Philosophy, The Ohio State University, 2004, Industrial and Systems Engineering

There are usually two concerns for die casting designers, thermal characteristics and fill pattern because they are closely related to casting quality and die life. The traditional way to obtain the results is numerical simulation. However, due to the high computational cost, numerical simulation is not a perfect tool during the early stages of product development. In this study, a quick algorithm to compute the equilibrium temperature of the die and ejection temperature of the part is presented. The equilibrium temperature is defined as the time average temperature over a cycle after the process reaches the quasi steady state. This can help the cycle and die cooling/heating design. A few models to compute the heat released from part are tested and the combined asymptotic and surrogate model is applied. Special attention is paid to heat transfer calculation at the part-die interface and computational efficiency improvement. The algorithm also addresses the modeling of cooling/heat line, spray effects and techniques for die splitting at the parting line. The algorithm has been implemented in the software CastView based on the finite difference method. The previous algorithm used in CastView for fill pattern analysis based on geometric reasoning is redesigned. In this qualitative method, the flow behavior is calculated using the cavity geometric information. Many shortcomings in the old algorithm were fixed and improved. The new algorithm includes considerations which affect the flow behavior, such as flow resistance, more flow angle search and influence within neighborhood. Special attention is paid to computational efficiency improvement. The fill pattern algorithm for die casting process is adapted for slow fill processes including gravity casting and squeeze casting. The dominant term for flow behavior for different process is defined from dimensionless Navier-Stokes equations. Based on this analysis, the fill pattern algorithm for die casting is modified for slow (open full item for complete abstract)

Committee: R. Miller (Advisor) Subjects: Engineering, Industrial

Doctor of Philosophy, The Ohio State University, 2003, Chemical Engineering

Continuous production of microcellular foams, characterized by cell size smaller than 10 μm and cell density larger than 10 9 cells/cm 3 , was studied using supercritical carbon dioxide (CO 2 ) as the foaming agent. Microcellular foams of polystyrene and polystyrene nanocomposites were successfully produced on a two-stage single screw extruder. The contraction flow in the extrusion die was simulated with the FLUENT fluid dynamics computational code to predict profiles of pressure, temperature, viscosity, and velocity. The nucleation onset was determined based on the pressure profile and equilibrium solubility. It was shown that a high CO 2 concentration or a high foaming temperature induces an earlier nucleation near the die entrance. The pressure profile and the position of nucleation onset were correlated to cell nucleation and growth, which helps understand the effects of operating conditions on cell structure. To perform the simulation, viscosity and solubility of the CO 2 /polystyrene system were characterized. Sanchez-Lacombe equation of state was applied to represent the phase equilibrium. Effects of temperature, pressure, and CO 2 content on the shear viscosity were explained using the free volume theory. Systematic experiments were performed to verify effects of three key operating conditions: CO 2 content, pressure drop or pressure drop rate, and foaming temperature, on the foam cell structure. Experimental results were compared with simulations to gain insight into the foaming process. Studies exhibit that a higher pressure drop or pressure drop rate results in smaller cells and greater cell density. Below the CO 2 solubility, cell size decreases and cell density increases with an increase of CO 2 concentration. A high CO 2 concentration favors producing open cell foams. Die temperature affects both cell size and cell structure (open or closed). Combining nano-clay compounding with supercritical CO 2 foaming provides a new technique for the design and con (open full item for complete abstract)

Committee: Kurt Koelling (Advisor) Subjects: