Dawn Roberta White

In situ Temperature Measurement During Spray Forming of A2-tool Steel and Axisymmetric Two-dimensional Analysis

An in situ temperature measurement was performed during spraying of A2-tool steel, and the results were used to verify an axisymmetric two-dimensional computer simulation program, which was developed for the prediction of shape and temperature variation in a spray-forming process. A thin thermocouple was placed inside of the chamber in advance and brought to the surface of the deposit during spraying. The temperature was then recorded. The surface temperature of the deposit was also measured by an infrared video camera. The emissivity of the surface of A2-tool steel during spraying was determined to be 0.23 through comparison of the temperatures measured by the thermocouple with the ones measured by the infrared video camera. The heat transfer coefficient at the top surface was estimated by comparing the calculated results with the experimental data. The cooling curve predicted on the basis of the numerical simulation showed good agreement with the experimental data.

Modeling of spray-formed materials: Geometrical considerations

In this article, a mathematical model is formulated to predict the evolution and final geometry of an axisymmetric billet (i.e., round) obtained using an off-axis spray arrangement. The model is formulated by calculating the shape change of a profile curve of a billet surface, based on an axisymmetric surface. On the basis of this model, a methodology to determine the “shadowing effect” coefficient is presented. The modeling results suggest that there are three distinct regions in a spray-formed billet: a base transition region, a uniform diameter region, and an upper transition region. The effects of several important processing parameters, such as the withdrawal velocity of substrate, maximum deposition rate, spray distribution coefficient, initial eccentric distance, and rotational velocity of substrate, on the shape factors (e.g., the diameter size of the uniform region and the geometry of the transition regions) are investigated. The mechanisms responsible for the formation of the three distinct regions are discussed. Finally, the model is then implemented and a methodology is formulated to establish optimal processing parameters during spray forming, paying particular attention to deposition efficiency.