Technical Article


(a)


(b)


Figure 4. Top view of the levitation melting of a single TiAl sample (500 g/1.1 lbs) in experiment (a) and the free surface shape of fully molten sample predicted by the 3D numerical model (b)


Continued from pg 45


contact with or contamination from other materials during heating up to the moment when the melt enters the mold. No crucible or other refractories are used.


New Investment Casting Furnace - FastCast The FastCast furnace consists of three chambers


for melting, casting


It is designed for demonstration of 10 consecutive casting cycles.


and


mould preheating (Figure 3). The melting chamber contains the “heart” of the plant - a levitation melting unit. The melting unit has two pairs of induction coils that generate horizontal and orthogonal EM fields of two different frequencies required for sample levitation in the gap between the coils. The EM field is enhanced by the water-cooled ferrite poles and looped through the outer ferrite ring. The casting chamber is located


right below the melting chamber and contains a mould manipulator arm, a mould table and a melt position sensor that synchronizes downward movement of the mould with the free-falling molten metal charge. And the mould preheating furnace,


in which up to 10 shell moulds can be stored and brought to temperature up to 1200ºC. The FastCast prototype has been


assembled at the ALD in the beginning of 2019 and has been used for research and optimization of the process parameters.


46 ❘ May 2022 ®


Levitation Melting And Casting Cycle The cycle starts as the mould manipulator arm takes an empty preheated mould from the mould preheating chamber and places it on the mould table. The table locks the mould and drives it up in the „ready for casting” position right below the melting unit.


Shortly after the melting starts as the lower end of the vertically oriented electrode (or a single sample) is immersed in the region of two-frequency horizontal and orthogonal EM fields by the electrode feeder. EM fields rapidly melt up to 500 g/1.1 lbs of material from the tip of the electrode and simultaneously confine the liquid metal in a levitation condition. Meanwhile, Lorentz forces contribute to intensive stirring and a great level of melt homogenization. The electrode is moved up and detached levitated melt is rapidly superheated (Figure 4). After that the EM field below the melt is reduced and the melt falls down under gravity in the awaiting preheated mould. Synchronized with the free-falling melt position, the mould is accelerated vertically down following the pre- programmed recipe to catch the melt and full-stop at the bottom of the casting chamber. Such mould movement reduces relative velocity between the falling melt and the mould at the


moment of the contact, avoids splashing and ensures smooth filling. On top of that, the mould table allows for the centrifugal casting at <800 rpm. As the filling process is accomplished, the manipulator arm stores the filled mould and takes the next preheated mould for repeating of the cycle. For instance,


TiAl investment


casting of different turbocharger wheels revealed good surface quality and defect-free filling of thin (0.5 mm) and detailed sections (Figure 5).


All degrees of freedom are fully


programmable to ensure the perfect tuning and optimization of the melting & casting cycle. On top of that, protection measures were thoroughly engineered to keep the production conditions safe and stable.


Melting and casting system design and process features are fully protected by 5 issued international patents.


The Fastcast Furnace Highlights • Levitation melting and casting process scaled-up for industrial applications → up to 500 g/1.1 lbs of Ti-alloys and up to 400 g/0.9 lbs of Ni-base alloys for mass production of turbocharger wheels, turbine blades and other castings


• Crucible-less contact-free melting → excellent purity and no material loss in the skull


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