STUDY ON TITANIUM ALUMINIDE TURBINE WHEEL BLADE MACHINING FOR TURBOCHARGERS BY ELECTROCHEMICAL MACHINING (ECM)

A turbocharger is the device of a car that is used to add extra air into the combustion chambers of an engine. Recently, researches have been conducted on the use of TiAl materials in turbine wheels to replace traditional Ni-based alloys. Since TiAl material has good heat resistance and is lightweight, it is effective in reducing the moment of inertia of the turbine wheel. However, the TiAl material has a problem that it has high viscosity when it is melted and that it is not suitable for precision casting. Even when the thickness of the turbine wheel blades is increased to about 1 mm, the molten TiAl does not always flow to the tip of the mold, and the problem of chipped tip often occurs. In this study, authors investigated the method of manufacturing blades with thickness of more than 1 mm by precision casting in a yield of almost 100%, and then machining them into thin shape of about half thickness by electrochemical machining (ECM). In ECM, it is well known that the flow of the electrolyte affects the machined shape. It was difficult to finish the blade in the desired shape at first and unmachined area remained. Then authors examined the flow of electrolyte using computational fluid dynamics (CFD) analysis and tried to make it appropriate. As a result, a technology was established to machine turbine wheel blades that meet the requirements for shape accuracy and surface roughness in a short time of about 100 seconds.