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

Monday 1:20 PM
September 19, 2022
Room: Grand Ballroom
Location: Bellevue Hotel

Session Chair: Harald Holzgruber, INTECO Special Melting Tech GmbH

1:20 PM Introductory Comments

1:25 PM  
Characterization of Vacuum Arc Remelting with a High-density Magnetic Sensor Array: Matthew Cibula1; Daniel McCulley1; Nathan Pettinger1; Joshua Motley1; Paul King1; 1Ampere Scientific
    Magnetic measurements coupled with traditional VAR process measurements has enabled the characterization of the spatial distribution of electrical current through the furnace; a process variable that today’s VAR furnaces do not measure. This work presents data acquired by VARmetric, a high density magnetic sensor array, on an industrial VAR furnace processing Fe- and Ni- based alloys. VARmetric is used to identify events which would go undetected through traditional process signal analysis, and importantly, can be used to distinguish between distinct arc modes, e.g. diffuse arcs, constricted arcs, and glows. This information facilitates a new method to assess the quality of an ingot in terms of the probability of segregation defects along the ingot axis.

1:50 PM  
Effect of Transient Heat Flux on the Predictions of Pool Characteristics During Vacuum Arc Remelting of Nitinol: Kyle Fezi1; Alex Archambault1; 1Fort Wayne Metals
    Vacuum arc remelting (VAR) is commonly utilized to produce reactive alloys like Nitinol, which has chemistry sensitive shape memory and super-elastic properties that are desirable for many applications. The thermal characteristics and ensuing molten pool characteristics (e.g. flow field, sump shape, temperature gradients, etc.) of the VAR process directly influence the ingot structure and downstream material performance. Recent experimental measurements of the temperatures within the water-cooled copper mold allowed for inverse heat conduction models to predict the transient heat flux of the VAR process. In this study, a quasi-steady state VAR model developed in OpenFOAM was employed to examine the effect of the sidewall cooling conditions in different regimes of the VAR process on the molten pool and solidification behavior of Nitinol. The sensitivity of the sump depth, strength of the flow field, and local solidification time (LST) to the sidewall cooling conditions were analyzed.

2:15 PM  
A Numerical Study on the Impact of a Time-varying Axial Magnetic Field On An Industrial Vacuum Arc Remelting (VAR) Process: Ebrahim Karimi Sibaki1; Abdellah Kharicha1; 1Univ of Leoben
    Nowadays, the Vacuum Arc Remelting (VAR) process is effectively utilized to manufacture Titanium-based alloys. Most often, an external axial magnetic field (AMF) is deliberately introduced to stabilize the arc. The AMF also impacts the magnetohydrodynamics (MHD) in the melt pool, and consequently the solidification (macrosegregation and grain structure) of the ingot. To study the aforementioned phenomena, we propose a 2D axisymmetric swirl model that includes calculation of electromagnetic and thermal fields in the entire system (electrode, vacuum plasma, ingot, and mold) as well as MHD in the melt pool. Both sinusoidal and rectangular variations of AMF are examined. Additionally, the effect of reversal time of the direction of AMF (5 to 30 sec) on MHD in the melt pool, and consequently solidification of the ingot is analyzed. Eventually, the model is validated against an experiment.

2:40 PM  
Effects of Controllable Transverse Magnetic Fields During the VAR Melt Process: Joshua Motley1; John Henjum2; Matthew Cibula1; Daniel McCulley1; Nathan Pettinger1; Paul King1; Gordon Alanko2; 1Ampere Scientific; 2ATI Specialty Alloys and Products
    This work describes the utilization of applied transverse magnetic fields to influence the arc dynamics during laboratory and industrial VAR melting. The arc motion was monitored with VARmetricTM as an external sensing platform to inform the system on the resultant direction and magnitude of the arcs due to the applied transverse magnetic field. Electromagnetic coils were mounted outside of the VAR in order to produce the near-uniform transverse magnetic field inside the furnace. These fields interact with the arc in a precise and measurable way, providing a control mechanism for arc motions and distributions. Results are provided for conditions where the applied fields were chosen such that the resultant force forces the arcs into non-ideal distributions, replicating potential deleterious operating conditions that could lead to defects. Results at both laboratory and industrial scale are provided and, wherever possible, ingots were sectioned and the resulting grain structures were analyzed for defects.

3:05 PM Break