Figure above: To ensure the suitability and efficiency of the system, common investment casting components such as turbocharger wheels have been casted using the plant.
castings such as medical or aerospace applications.
From Concept Work To Industrial-Scale Pilot Plant After an extensive series of simulation- aided design iterations, the optimized process was transferred into a functional plant including feeder, preheating furnace and casing. “The final scale-up configuration has a modular levitation assembly group that consists of four ferrite poles and four inductors, each is water- cooled and protected by heat shields,” describes Spitans. “The opposing inductors form a pair that operates at the same frequency and produces an instantaneous magnetic field in the same direction. The orthogonal orientation allows to compensate the regions of the zero Lorentz force that occurs if only one field is activated.” “Levitation melting is only slightly more efficient than the cold wall crucible, however, the advantages like predefined melt purity, absence of the skull scrap, fast melting speed and tremendous superheat up to 250ºC at the moment of mold filling makes the process extremely attractive for complex castings,” Spitans adds. To meet the demands of industrial production, the pilot plant offers a semi- automated process chain with up to 10 molds. The upper housing contains a vertical feeding unit of the pre-alloyed
®
metal electrode to be melted. The lift moves the mold to the upper position right below the melting zone. The melting starts as the lower end of the vertically oriented Ti-alloy electrode is immersed in the region of two-frequency horizontal and orthogonal electromagnetic (EM) fields. EM fields rapidly melt up to 500 g of material from the tip of the electrode and simultaneously confine the liquid metal in a levitation condition. The electrode is moved up and detached, the levitated melt can be superheated. After that the melt is released by retracting poles and it falls down under gravity in the awaiting preheated mold. Instantly the mold is accelerated vertically down to reduce the relative velocity and to catch the melt without splashing. Further mold deceleration to a full stop and consequent spinning completes the smooth and qualitative mold filling. After that, the form exits through the unloading chamber and the next cycle can start. All in all, the cycle times are rather short, with less than 60 seconds, making the process very economical.
Plant Can Be Used For Test Runs By Interested Companies
Up to this point, almost all relevant titanium- and aluminum-based alloys as well as super alloys were cast successfully using the pilot plant. To ensure the suitability and efficiency of
the system, common investment casting components such as turbocharger wheels were cast using the plant. Based on this design, ALD is going to develop a production FastCast system in cooperation with interested
users,
specifically for the needs of their own production. Feeding and mold number (adapted to the mold shell) in particular will be taken into account. Therefore, the demonstrator can be used for test runs. Although the actual plant is semi- automated, a special department at ALD is working on more features that meet the requirements of Industry 4.0. For example, a digital twin of each casting part can be generated to ensure highest quality control. Since they are individual casts, each part can be tracked down to defects that may show up before or after the casting. “The high purity, excellent reproducibility, and continuous and automated single batch production line favors a very high casting quality, making non-contact levitation melting particularly suitable for investment casting parts in demanding sectors such as aerospace and medical technology. We can’t wait to move this process to the next level together with industry partners,” Spitans sums up.
For further information, visit the ALD website at
www.ald-vt.com.
October 2021 ❘ 51
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