Multifunctional spindle for machining film cooling holes in EDM

The rotary accuracy, the feed compensation of the tool electrodes, and rapid chip removal are all important in electrical discharge machining (EDM) of film cooling holes. A spindle was designed to give accurate rotations and inchworm feed of the tool electrodes while spraying high-pressure dielectric liquid from the tubular tool electrode. The spindle design is based on the inchworm feed principle using double clamps with the spindle rotary mechanism overlaid on the axial feed mechanism. The spindle gives better clamping force, better drive mode of the normally closed-and-rotating clamp, a better seal for the high-pressure dielectric liquid, and the current supply between the tool electrode and the pulsed power supply. In addition, the interference between the sealing mechanism and the tool-electrode movements is avoided. Performance tests on the spindle show that the runout error is less than 8 μm during electrode rotation. The inchworm stroke is 150 mm, the inchworm speed is greater than 4 mm/s, the dielectric liquid pressure can range up to 4.2 MPa, and the resistance between the tool electrode and the pulse power supply is less than 1.3 Ω. Machining tests with deep, small holes verified the spindle design.