Method of cold forming tubes with interior thicker wall sections

Abstract

A method for cold forming metal tubes with inwardly thickened wall sections including positioning a short, tubular blank in a die having an extrusion die throat, and pushing the blank through the die throat with a punch. The punch is formed with a co-axial mandrel-like extension which fits within the blank and die throat. The extension is formed of co-axial sections of successively smaller diameter. Thus, as the punch pushes the end of the blank to move the blank through the die throat, a narrower diameter extension section fits within the die throat to extrude a thickened end portion. Thereafter, continued punch movement positions a wider mandrel forming extension section within the die throat to extrude a thin wall tube section. At a point where a wall thickened section is to be formed interiorly of the tube, the punch is removed and replaced by a different punch having a mandrel forming extension of different diameter than that mentioned above, wherein movement of the second punch results in the extrusion of a thickened tube section in the annular space between the extension section and the die throat, with continued punch movement thereafter positioning a further punch extension within the die throat for forming additional thin wall sections on the tube. The trailing end of the blank may then be provided with a thickened end section similar to the leading end of the blank by utilizing the initial punch in place of the second punch.