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Process Description
The VAR process uses DC power to strike an arc between the electrode and the
ingot surfaces causing the electrode to melt. The molten metal droplets fall into a water-cooled mold. The electrode is continuously advanced as it melts to build up an ingot of improved
structure and composition.
Velocity and Temperature Fields, and Pool Region During a VAR Process Without Magnetic Stirring for
Ti-64 Alloy
Comprehensive Treatment of Process Physics
COMPACT-VAR performs a rigorous analysis of the process by considering all the
physical phenomena as listed below:
- Use of the two-equation k-e model for an accurate treatment of the turbulent flow in the molten pool
- Convective heat transfer in the molten pool, phase change in the mushy region,
and conduction heat transfer in the solidified ingot
- Heat loss from the ingot surface to the mold due to the combined effect of radiation and contact heat transfer
- Effect of ingot shrinkage on the loss of contact heat transfer and current
conduction between the ingot and the mold
- Distributions of the electric current, self-induced magnetic field, and Lorentz forces
- Analysis of all phenomena in the growing ingot including initial transients and hot topping
- Effect of magnetic stirring in creating an angular stirring force that produces an
angular velocity field and causes additional mixing in the pool due to the centrifugal force
- Macrosegregation of the alloying elements caused by the selective rejection or
absorption of the alloying elements by the solid and the redistribution of the elements within the molten metal pool
- Motion and dissolution of inclusions
- Treatment of temperature-dependent material properties of the alloy
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Velocity and Temperature Fields, and Pool Region During a VAR Process With Magnetic Stirring for
Ti-64 Alloy
Efficient Computational Solution
The control-volume method is used for performing the solution of the governing
equations in an axisymmetric domain. The computational method incorporates many algorithms that address specific aspects of the VAR process as described below:
- Unified treatment of the molten pool, semisolid, and solidified regions of the ingot
- Transient analysis with a special algorithm to address the growth of the ingot
- Automatic determination of the time step
- Robust treatment of nonlinear heat loss from the top, bottom, and side surfaces of the ingot
- Lagrangian method for the calculation of the trajectories of inclusions
- Thus, COMPACT-VAR provides a robust and efficient calculation of the transient
behavior of the ingot during the entire process.
Electromagnetic Fields in the Growing Ingot During a VAR Process With Magnetic Stirring for Ti-64 Alloy
Easy Model Setup and Visualization of Results
COMPACT-VAR allows easy creation of a process model by specifying ingot geometry,
temperature-dependent alloy properties, and melt schedule through a user-friendly graphical interface. Results of analysis are conveniently examined using powerful visualization software.
Concentrations of Alloying Elemnts in the Final Ingot Produced Using a VAR Process With Magnetic
Stirring for Ti-64 Alloy
Engineering Benefits
COMPACT-VAR has been shown to accurately predict the observed pool profiles and
alloy concentrations in practical processes for Titanium alloys. It is being actively used in the following manner by leading alloy producers to obtain substantial
cost-savings in process design:
- Optimization of Melt Schedule
- Investigation of Process Anomalies
- Processing of Titanium alloys, Superalloys and Steel
- Design of Process Variants
Behavior of Inclusions in the Growing Ingot During a VAR Process With Magnetic Stirring for Ti-64 Alloy
Technical Publication and Brochure
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