Technical Article
Investment Castings with Unique Levitation Melting Technology FastCast
by Sergejs Spitans, Christian Bauer, Henrik Franz, Björn Sehring, ALD Vacuum Technologies GmbH & Egbert Baake, Institute of Electrotechnology at Leibniz University Hannover
Abstract
simulation has been used to verify the new method and to design ALD’s pilot investment casting furnace – called FastCast. It allows levitation melting of various reactive metals and alloys up to 500 g with high purity, short cycle times and large adjustable superheating up to 250ºC followed by single-batch defect- free casting with >98% of material landing in the mould. This report gives an update on features and recent technical achievements of the FastCast demonstrator which is in operation at ALD.
A Introduction
Crucible-less levitation melting and single-batch casting of Ti- or Ni-based alloys (e. g. for turbocharger impellers or turbine blades up to 500 g) has many advantages over multi-batch castings obtained with ceramic- or cold-crucible induction furnaces. First of all, electromagnetic (EM) levitation prevents contamination of the melt with the crucible material and results in a superior and predefined quality of alloy. Heat losses from the liquid metal are reduced and limited to radiation and evaporation that permits fast melting and much higher overheating. Due to the small melt-cast cycle time the process retains productivity comparable with conventional multi-batch investment castings, while simpler design of the crucible-less furnace and utilization of smaller single-batch molds have economic benefits. Apart from that, single-batch casting breaks down the statistical nature of a single product quality in case of a multi-piece casting, advances production to the “one-piece- flow” concept and meets requirements
44 ❘ May 2022 ®
novel method for the large-scale crucible-less levitation melting of metals is developed. Numerical
(a)
(b)
Figure 1. Classical levitation melting of Aluminum sample (20 g) in experiment (a) and simulation illustrating the lack of Lorentz forces at the axis of the sample (b) [4]
(a)
(b)
Figure 2. Optimized design of the novel two-frequency levitation melting unit (side view) based on modelling of the free surface shape of molten TiAl (500 g) levitating in the gap between coil pairs (a). Enhanced Lorentz force confinement and turbulent flow on the vertical cross-section of the melt (b)
for process digitalization. However,
in conventional
axisymmetric levitation melting (Figure 1, a), already known since 1920’s [1], [2] the Lorentz force vanishes on the symmetry axis (Figure 1, b) and the melt leakage is counteracted only by the melt surface tension. Therefore, only small molten metal samples up to 50 g can be levitated in conventional way and industrial needs for the scale-up remain unsatisfied [3].
A novel method for the levitation melting of metals is developed to transfer the advantages of levitation melting from laboratory/R&D applications into industrial field. Numerical simulation has been used to verify the new method and to design a pilot investment casting furnace – called FastCast – capable of contact-less melting and single-batch casting of Ti- and Ni-based alloys up to 500 g. This report gives an update on features
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