Patent ID: 7644601

Claim:
A method for manufacturing hollow shafts having first and second end portions of greater wall thickness and at least two intermediate portions of reduced wall thickness, from a tube having constant wall thickness, comprising: providing a mandrel having diameters stepped over its length, including at least a first longitudinal section having a smallest first diameter and, adjacent to said first longitudinal section, a second longitudinal section having a second diameter being greater than said first diameter of said first longitudinal section, and, adjacent to said second longitudinal section, a third longitudinal section having a third diameter being greater than said second diameter of said second longitudinal section, the mandrel comprising a first transition portion between said first longitudinal section and said second longitudinal section, the mandrel further comprising a second transition portion between said second longitudinal section and said third longitudinal section; inserting the mandrel into the tube; reducing the external diameter of a first portion of the tube over the first longitudinal section of the mandrel to produce the first end portion; reducing the external diameter of at least one first middle portion of the tube over said second longitudinal section of said mandrel to produce a first intermediate portion of said at least two intermediate portions of said hollow shaft, said first intermediate portion of said hollow shaft being arranged adjacent to said first end portion; reducing the external diameter of at least one second middle portion of the tube over said third longitudinal section of said mandrel to produce a second intermediate portion of said at least two intermediate portions of said hollow shaft, said second intermediate portion of said hollow shaft being arranged adjacent to said first intermediate portion of said hollow shaft; and reducing the external diameter of a further portion of the tube over the first, the second or another longitudinal section of the mandrel to produce the second end portion; wherein a wall thickness ratio between the first end portion of the hollow shaft and an intermediate portion having a smallest wall thickness is greater than 1.6.