The behavior of a metal vapor plasma arc in a vacuum arc remelting (VAR) furnace is believed to contribute to the formation of defects in reactive metal and super-alloy ingots. Industry standard instrumentation, which includes electric current and voltage measurements, can asses the stability of an arc but cannot predict the location of an arc. It is known that Maxwell's equations predict a magnetic flux density at a distance from an arc. It is shown that a single arc's location can be uniquely determined in a cross section by using an externally mounted 2-axis Hall Effect magnetic flux density sensor provided that the system's electric current is also measured and the geometry of the VAR furnace is known. The solution is based on the Biot-Savart Law with finite element modeling assisting the analysis. The methodology is validated using controlled, static experiments. The measurement system is deployed on a small scale, experimental VAR furnace to investigate arc behavior. Results from VAR operation show a time averaged arc distribution that does not significantly change over the course of a melt. By comparing the results from multiple sensors, observed arc motions are categorized as being either retrograde or sympathetic. The former is characterized by large periodic motions, and the latter either small random motions or motions associated with an event such as a liquid metal drip short. Significant alternating currents are found to exist in the DC VAR furnace. A magnetostatic single arc model is not sufficient to describe the current distribution in the VAR furnace at an instant but it may be an effective means to detect quasi static non-axisymmetry or slow time varying current profile changes during VAR operation.

Vacuum arc remelting (VAR) is a secondary melting process for exotic alloys. The main purpose of this process is to increase the input ingot’s physical and chemical homogeneity. This is accomplished through the application of a high current that melts the material through the emergence of electrical arcs that induce Joule heating. Arc behavior drives quality of the end product, but no methodology is currently used in VAR furnaces at large scale to track arcs in real time. An arc position sensing (APS) technology was recently developed as a way to predict arc locations using magnetic field values measured by sensors. This system couples finite element analysis of VAR furnace magnetostatics with direct magnetic field measurements to predict arc locations. Vertical position of the sensor relative to the electrode-ingot gap, a varying electrode-ingot gap size, ingot shrink-age, and the use of multiple sensors rather than a single sensor were studied to analyze potential changes of previous made assumptions and their effects on arc location prediction accuracy. Among the parameters studied, only vertical distance between arc and sensor locations causes large sources of error, and should be considered further when applying an APS system. However, averaging the predicted locations from four evenly spaced sensors helps reduce this error. In addition, the effects of the arc position on the solidification of the ingot was also studied. Where the arc is located alters the heat transfer and fluid dynamics of the liquid melt pool. Being able to both locate and conclude how exactly arc position effects the final product could aid in the development of arc position sensing technology and the industry as a whole.

Currently, the temporal arc distribution across the ingot during the vacuum arc remelting (VAR) process is not a known or monitored parameter. It is has previously been shown that arcs can spatially constrict during VAR, and this constriction can lead to undesired defects in the material. Additionally, correct accounting for the heat flux, electric current flux, and mass flux into the ingot are critical to achieving realistic solidification models of the VAR process. An arc position measurement system capable of locating slow moving arcs and determining the arc distribution within an industrial VAR furnace was developed. The system is based on non-invasive magnetic field measurements and VAR specific forms of the magnetostatic Biot-Savart Law. Electromagnetic finite element modeling assists the analysis. The measurement system was installed on an industrial VAR furnace at the ATI facility in Albany, OR. Data were taken during the commercial production of titanium alloy. Although more arcs were present than could be resolved with the number of sensors applied, overall arc distribution shifts were detected. Arc distribution and motion during the final production of Ti-6Al-4V were examined. It is shown that several characteristic arc distribution modes can develop. This behavior was not apparent in the existing signals used to control the furnace, indicating the measurement system provides new information. Finally, a solidification model was used to assess the potential impact of the different arc distribution modes. It is shown the magnetohydrodynamic stirring patterns in the molten pool are affected, which results in localized variations in solidification times in particular at the side wall.