Method of forming reinforced box-selection frame members

A method of forming a box-section frame member having a reinforced area and of which at least an elongate portion is of uniform cross-section having at least two generally opposed and planar sides, the method comprising:

• (a) providing a tube and a tubular sleeve within which the tube can be received, the tube and sleeve each having a continuously smooth, arcuate cross-section;
• (b) positioning the sleeve about the tube in an area of the tube to be reinforced;
• (c) deforming the tube and sleeve in a preliminary step in which the side walls of the tube and sleeve are deformed inwardly in opposed areas of an elongate portion thereof which generally corresponds in position to the planar sides of the product frame member to provide the tube and sleeve with a continuously smooth arcuate cross-section having generally opposed, inwardly deformed, side walls;
• (d) enclosing the deformed tube and sleeve within a sectional die having at least two co-operating die sections which define an elongate passage of approximately the same elongate shape as the tube and sleeve and which is throughout of smoothly continuous cross-sectional profile having an at least approximately linearly profiled portion adjacent and parallel to each concavely curved side wall portion of the tube and sleeve, all transverse dimensions of the passage being at least equal to or larqer than the deformed tube and sleeve;
• (e) expanding the blank circumferentially by application of an internal fluid pressure until all exterior surfaces of the tube and sleeve conform to the profile of the die passage and the sleeve is mechanically locked to the tube;
• and
• (f) separating the die sections and removing the product reinforced frame member from the die.