Patent ID: 6718860
Filing Date: 2004-04-13
Classification: B21D,F28F,Y10T

Abstract:
A method of making narrow and elongated slits to insert and fix core tubes thereto in a surface of a pipe having an elliptical section by press-work without using a die or a metal core, said surface having a large radius of curvature along the long diameter of the elliptical section of the pipe, the method comprising:a grooving step for forming a plurality of grooves in said pipe in the same direction as the length of each of said slits by operating a grooving punch having a predetermined shape in a direction along the length of the slit to be formed, and scraping off a part of said pipe to such a degree as not to cut through a wall of said pipe; and a hole-making step for making said slits in said groove formed in said grooving step in said pipe by operating a hole-making punch having a cutting edge comprising end portions thereof formed at an acute angle, cutting edge portions recessed from said end portions toward a central portion thereof and a depression formed between at least a part of said cutting edge portions to positively separate a cutting chip from the slit at the same time the slit is formed in a direction perpendicular to the length of each groove.