Electroforming mandrel and method of fabricating and using same

A process for fabricating a plated cylindrical electroforming mandrel comprising providing a cylindrical mandrel core having substantially parallel sides and at least one tapered end having curved sides which converge toward an apex, the profile of an axial cross section of said tapered end from the intersection between said curved sides and said parallel sides to about said apex having the shape of half an ellipse defined by the formula:

• ##EQU15## where:
• a=1/2 the length of the major axis of the ellipse and has a value between about 2.3b and about 1.7b,
• b=1/2 the height of the minor axis of the ellipse and has a value at least about 1,000 times greater than the thickness of said plated metal coating on said parallel sides, and
• x and y define a point lying along the outer surface of the ellipse measured from the center of the ellipse and
• electroplating a metal coating onto said parallel sides and said tapered end of said mandrel core.

An electroforming process comprising providing a cylindrical electroforming mandrel comprising a substantially cylindrical mandrel core having substantially parallel sides and at least one tapered end having curved sides which converge toward an apex and a plated metal coating on said parallel sides and said tapered end, the profile of an axial cross section of said tapered end from the intersection between said curved sides and said parallel sides to about said apex having the shape of half an ellipse defined by the formula:

• ##EQU17## where:
• a=1/2 the length of the major axis of said ellipse and has a value between about 2.3b and about 1.7b,
• b=1/2 the height of the minor axis of said ellipse and has a value at least about 1,000 times greater than the thickness of said platd metal coating on said parallel sides, and
• x and y define a point lying along the outer surface of said ellipse measured from the center of said ellipse,
• immersing said electrode in a plating bath, electroforming an electroformed layer on said plated metal coating to form an electroformed article, and removing said electroformed article from said mandrel by sliding said electroformed artcle over said tapered end of said mandrel.