Abstract An electrode for electrical discharge machining is made by providing a mould shaped to the desired shape wanted for the final article. The mould cavity is electroplated. Before the plating layer is removed from the mould cavity, it is backed up by a strong alloy having substantially the same coefficient of thermal expansion as the electroplate layer, the alloy being, for example, an alloy of bismuth and tin, poured into the mould cavity over the electroplated layer and around anchoring pins which depend into the cavity from a rigid locating bar mounted on the mould. When the alloy has solidified, the composite structure comprising the electroplate layer, the back-up strengthening alloy, the anchoring pins, and the locating bar, is removed as a unit from the mould, and is made ready for mounting on a conventional electrical discharge machine, to make duplicates of the original mould by the known electrical discharge machining process. The back-up alloy prevents the warping of the electroplate layer which frequently occurs when the electrode is made by prior methods.
The method as defined in claim 1, wherein the alloy applied to said electroplate layer is relatively thick and rigid as compared to the thickness and rigidity of the electroplate layer.
Claim 2
Dependent Claim
23 words
The method as defined in claim 1, wherein said alloy has a coefficient of thermal expansion close to that of said electroplate layer.
Claim 3
Dependent Claim
18 words
The method as defined in claim 1, wherein said alloy is an alloy mainly of bismuth and tin.
Claim 4
Dependent Claim
22 words
The method as defined in claim 4, wherein said alloy is composed essentially of substantially 58 percent bismuth and 42 percent tin.
Claim 5
Dependent Claim
91 words
An electrode for use in electrical discharge machining, comprising a layer of conducting material having a front face in the shape of a reverse duplicate of the shape to which a workpiece is to be machined, a strengthening back-up layer of alloy having a coefficient of thermal expansion similar to that of said conducting material and intimately engaged with a rear face of said conducting layer, a relatively rigid locating bar, and anchoring members projecting from the bar toward said conducting layer and embedded firmly in said back-up layer of alloy.
Claim 6
Dependent Claim
23 words
An electrode as defined in claim 6, in which said alloy is composed essentially of substantially 58 percent bismuth and 42 percent tin.