Methods of Electrical Discharge Machining (EDM) ceramic components are provided. In one aspect, a method includes electrical discharge machining a ceramic component, such as a Ceramic Matrix Composite (CMC) component. The ceramic component is electrical discharge machined while a contact matrix is positioned so that electrically conductive compliant and pressurized contacts of the contact matrix engage the ceramic component and so that an electrically conductive member of the contact matrix is in electrical conduction to a grounding structure.

Provided is a zinc-nickel-alloy-electroplated steel sheet comprising a base steel sheet, and a zinc-nickel-plated layer which is located on at least one surface of the base steel sheet and which has a hairline pattern formed thereon, wherein the surface roughness of the surface of the base steel sheet, which forms an interface with the zinc-nickel-plated layer, is 0.7-1.0 um on the basis of the center line average roughness (R.sub.a). According to the present invention, provided are: a zinc-nickel-electroplated steel sheet, which has a beautiful surface appearance after hairline processing, has better price competitiveness than a conventional stainless steel or a vinyl-coated steel, and can ensure high productivity in a coil polishing line; and a manufacturing method therefor.

Provided is a zinc-nickel-alloy-electroplated steel sheet comprising a base steel sheet, and a zinc-nickel-plated layer which is located on at least one surface of the base steel sheet and which has a hairline pattern formed thereon, wherein the surface roughness of the surface of the base steel sheet, which forms an interface with the zinc-nickel-plated layer, is 0.7-1.0 um on the basis of the center line average roughness (R.sub.a). According to the present invention, provided are: a zinc-nickel-electroplated steel sheet, which has a beautiful surface appearance after hairline processing, has better price competitiveness than a conventional stainless steel or a vinyl-coated steel, and can ensure high productivity in a coil polishing line; and a manufacturing method therefor.

EDM assemblies mount on a machining surface and discharge rotating sub-electrodes against the surface. The sub-electrodes can also revolve about another shared axis while discharging. Rotation and revolution may be achieved with planetary gears fixed with the sub-electrodes and meshing with a stationary sun gear. Several sub-electrodes can be used in a single assembly. Downward movement of the sub-electrodes from a central shaft on the mount allows several inches of the surface to be machined. Assemblies are usable in a nuclear reactor during a maintenance period to machine a hole for a replacement manway cover underwater in the flooded reactor. The differing rotational movements and vertical movement can be independently controlled with separate motors in the assembly. Power and controls may be provided remotely through an underwater connection.

EDM assemblies mount on a machining surface and discharge rotating sub-electrodes against the surface. The sub-electrodes can also revolve about another shared axis while discharging. Rotation and revolution may be achieved with planetary gears fixed with the sub-electrodes and meshing with a stationary sun gear. Several sub-electrodes can be used in a single assembly. Downward movement of the sub-electrodes from a central shaft on the mount allows several inches of the surface to be machined. Assemblies are usable in a nuclear reactor during a maintenance period to machine a hole for a replacement manway cover underwater in the flooded reactor. The differing rotational movements and vertical movement can be independently controlled with separate motors in the assembly. Power and controls may be provided remotely through an underwater connection.

An electrical discharge machining (EDM) electrodes and associated methods are provided. An EDM electrode includes a holder rotatable about a rotation axis and a plurality of electrode elements attached to the holder and circumferentially arranged around the rotation axis. Respective positions of the electrode elements are radially adjustable relative to the rotation axis.

An electrical discharge machining (EDM) electrodes and associated methods are provided. An EDM electrode includes a holder rotatable about a rotation axis and a plurality of electrode elements attached to the holder and circumferentially arranged around the rotation axis. Respective positions of the electrode elements are radially adjustable relative to the rotation axis.

A wire electrical discharge machine includes a first voltage applying circuit, a second voltage applying circuit, and a switch controller. The first voltage applying circuit includes a first DC power source for applying a positive polarity voltage across an electrode gap, and a first switch for on/off-switching of application of the positive polarity voltage. The second voltage applying circuit includes a second DC power source for applying a reverse polarity voltage to the electrode gap, and a second switch for on/off-switching of application of the reverse polarity voltage. The switch controller controls the first switch and the second switch so that the first switch and the second switch are not turned on simultaneously. The first DC power source and the second DC power source are set up so that the absolute value of the reverse polarity voltage is lower than the absolute value of the positive polarity voltage.

A wire electrical discharge machine includes a first voltage applying circuit, a second voltage applying circuit, and a switch controller. The first voltage applying circuit includes a first DC power source for applying a positive polarity voltage across an electrode gap, and a first switch for on/off-switching of application of the positive polarity voltage. The second voltage applying circuit includes a second DC power source for applying a reverse polarity voltage to the electrode gap, and a second switch for on/off-switching of application of the reverse polarity voltage. The switch controller controls the first switch and the second switch so that the first switch and the second switch are not turned on simultaneously. The first DC power source and the second DC power source are set up so that the absolute value of the reverse polarity voltage is lower than the absolute value of the positive polarity voltage.

A method of manufacturing an integrated impeller has a first shroud forming a bottom portion, a second shroud forming a lid portion, a hub formed at the center portion of the first shroud, and blades that section a flow path which is formed between the first shroud and the second shroud and through which a fluid flows. This method includes forming a flow path on the inner circumferential side of the impeller; and forming a flow path on the outer circumferential side of the impeller. The step of forming the flow path on the outer circumferential side of the impeller has the steps of: while rotating the linear electrode having a tip-end part and a base-end part about a longitudinal direction axis thereof, applying electric discharge machining to the first shroud; applying electric discharge machining to the second shroud; and applying electric discharge machining to the blade.