Wire Electric Discharge Machining of Curvilinear Swept Surfaces

Abstract

Fir tree root forms are one way to retain turbine blades in turbine disks. These features are ruled surfaces that span the entire thickness of the disk and are usually machined by broaching. With increasing use of new heat resistant and difficult-to-machine materials, mechanical machining methods exhibit severe problems with tool wear and surface integrity. To mitigate these problems, thermal material removal processes such as Wire Electrical Discharge Machining (WEDM) are being considered in the aerospace industry. Developments in turbine design have led to a root form geometry in the form of an arc across the thickness of the disk in order to decrease the contact stress by increasing the contact area between blade and disk. A curved surface such as this cannot be produced by conventional WEDM as it is not a ruled surface. A novel WEDM process is being developed where an arc shaped curve is formed from an axially moving wire to allow for the production of such curved surfaces.