Liquid Metal Processing & Casting Conference (LMPC 2022): Vacuum Arc Remelting I
Program Organizers: Matthew Krane, Purdue University; Mark Ward, University of Birmingham; Abdellah Kharicha, Montauniversitšt

Monday 8:55 AM
September 19, 2022
Room: Grand Ballroom
Location: Bellevue Hotel

Session Chair: Alec Mitchell, University of British Columbia

8:55 AM  
Transient Heat Flux Measurements in Vacuum Arc Remelting of Nitinol: Kyle Fezi1; Nils Hinniger1; 1Fort Wayne Metals
    The thermal behavior of the vacuum arc remelting (VAR) process strongly influences solidification phenomena that impact ingot defects, yields, and material performance. For chemistry sensitive alloys, like Nitinol, understanding the composition redistribution induced by the thermal conditions during the VAR process is of the utmost importance. To better understand the energy balance of the VAR process, a series of thermocouple arrays were installed in the sidewall of the copper crucible. The arrays were placed at four different heights in order to measure the temperature changes during the various VAR process regimes. Each array consisted of four thermocouples, equally spaced to allow for both a one- and two-dimensional inverse heat conduction calculation to estimate the heat flux through the copper mold. Comparisons between different inverse models and the uncertainty of the newly found thermal boundary conditions are discussed.

9:20 AM  
Use of Accommodation Coefficients in Modeling of Helium Heat Transfer in VAR: Examination of Their Uncertainty and Effect on Modeling: Richard Smith1; 1Carpenter Technology
    Application of helium cooling in VAR to supplement sidewall radiation cooling in the gap between the ingot and copper mold has seen widespread use. Published results on superalloys and tool steels have shown effects of the use of helium cooling on ingot and process characteristics such as pool depth, dendrite arm spacing and amounts of undesired second phases. Incorporation of helium cooling in process modeling of VAR has generally been through the sidewall heat transfer coefficient. A method has been presented to directly calculate helium heat conduction in the gap using the kinetic theory of gases. [1,2] At low pressures, the theory provides two methods for calculating heat transfer. One method corresponds to gas pressures sufficiently low that gas molecule interactions can be substantially reduced, which in turn causes a temperature discontinuity at the gas/metal interface. For this regime of behavior, a quantity referred to as the temperature-jump distance is calculated to account for the discontinuity. The other method corresponds to pressures low enough that gas molecules do not interact at all and move freely between two surfaces. This regime of behavior is referred to as free-molecule. For the range of gas pressures generally cited for use in VAR (several torr up to roughly 90 torr) conduction is generally considered to correspond to the temperature-jump regime. Both methods use a parameter referred to as the accommodation coefficient which accounts for the degree to which a gas molecule comes into thermal equilibrium with a surface on contact.

9:45 AM  
Experimental Setup for Mold Surface Temperature Measurement During Vacuum Arc Remelting Process: Application to Titanium Alloys: Julien Banos1; Julien Jourdan2; Thibault Quatravaux2; Alain Jardy2; 1TIMET Savoie; 2Institut Jean Lamour
    The heat transfer at the ingot/mold interface plays an important role in the control of the ingot final properties. All along the interface, this transfer is time dependent and influenced by many factors, including the formation of an interfacial gap. In order to deepen our understanding of the mechanisms at work and validate the numerical models of the process, in-situ measurements are required. As such, surface temperature was measured at the outer surface of the Cu crucible during the remelting of titanium alloys in an industrial VAR furnace. For this purpose, an embedded, non-intrusive experimental apparatus has been designed to meet the safety requirements involved with the process. The results of the first experimental campaign are presented and discussed.

10:10 AM Break

10:35 AM  
A Novel Technique to Measure the Arc Gap During Vacuum Arc Remelting Using Magnetic Fields: Daniel McCulley1; Matthew Cibula1; Nathan Pettinger1; Joshua Motley1; Paul King1; 1Ampere Scientific
    During vacuum arc remelting (VAR) the arc gap is a critical process control variable that is closely coupled to melt rate. These parameters are utilized to indicate deleterious conditions that could lead to product quality concerns. Modern industrial VAR furnaces typically employ drip-short analysis to infer the arc gap which is then provided as feedback back to control the melt rate. The successful implementation of drip-short analysis to control the arc gap requires a uniform electrode geometry and melt stability. However, these criteria are not always met during melting due to events such as constricted arcs, glows, and electrode tip geometry changes (e.g. cupping). A more reliable arc gap measurement can deliver higher quality control standards to the VAR industry. Here we present the development and characterization (including the spatial resolution) of an arc gap tracking and arc gap measurement technique utilizing magnetic field signatures produced during VAR.

11:00 AM  
Power Update During Vacuum Arc Remelting Using Vision Systems: Ashish Patel1; Nir Herscovici1; 1Timet
    In Vacuum Arc Remelting processes, the power setpoint changes as a melt progresses. During the initial stages of the melt, the power is gradually ramped up to a steady state level, and during the latter stages, the arc power is ramped down to complete the hot-topping process. These ramps can either be based on feedback from load cells, ram position, markers on the electrode, or a combination of these signals. In this work, feedback from a vision system is used to cutback the power using an open source convoluted neural network algorithm. The code is pre-trained using a combination of multiple image sources and is deployed during the melt to alert the control system.

11:25 AM Panel Discussion