Masters Theses

Date of Award

5-2001

Degree Type

Thesis

Degree Name

Master of Science

Major

Mechanical Engineering

Major Professor

Rao W. Arimilli

Committee Members

Masood Parang, Belle Upadhyaya

Abstract

Complex ceramic cores, which form the internal cooling passages of investment-cast turbine blades and used in the aircraft-engine and industrial-gas-turbine industries, are made by ceramic injection molding. The high injection pressure, the high viscosity of the ceramic/wax mixture, and the high injection velocity during the injection molding process result in high rate of erosion, or wear, of the internal surfaces of die. The resurfacing of eroded surfaces of core dies is very costly. In addition to that, inappropriate injection parameters introduce defects, such as weld line and mis-fill, into the quality of the final products. It is desirable to increase the productivity of the ceramic injection molding process and also cut back maintenance costs by evaluating the process performance with computer modeling and simulation to identify means to reduce these problems. In this study, a computer model and simulation of a three-dimensional transient ceramic/wax injection molding (CIM) process including filling and solidification, developed by the Advanced Casting Laboratory at the University of Tennessee for Howmet Research Corporation, was utilized and experimentally validated. The effect of variation of the interfacial heat transfer coefficients on the filling, solidification, and quality of the final products were carefully studied via the computer simulation of the ceramic injection molding process. Experiments were designed and conducted to measure the temperature of ceramic core material as a function of time for both filling and packing stages of the injection molding process. The experiments were conducted under production conditions at Howmet Casting Support in Morristown, Tennessee. The results from the experiments were used to validate the realism and accuracy of the ProCAST simulation of the ceramic core injection molding process. The results from the computer simulations indicated that the interfacial heat transfer coefficient modeled as a ramp function described in this work best represented the experimentally observed thermal characteristics of the filling and solidification process. The flow pattern from this computer simulation yielded a very desirable filling pattern that would avoid the introduction of weld line into the quality of the final product. Also, the computer model predicted the regions of high shear rate and the associated heating where excessive wear of the die was observed. In summary, the model developed was shown to predict successfully the thermal characteristics of the core filling process. The results of this research contributes to the formation of a database of process variables that can be used for control of the injection molding process and for predicting the final geometry as a result of the process.

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