Die vorliegende Erfindung betrifft ein Herstellungsverfahren für eine Rohrstabilisatorhälfte (2), wobei ein Rohr (18) mit einem ursprünglichen Außendurchmesser (19) durch einen Knetvorgang verringert wird. Hierdurch ist es möglich, einstückige und werkstoffeinheitliche Rohrstabilisatorhälften (2) herzustellen.

A method for manufacturing a hollow engine valve, capable of simplifying the manufacturing process and reducing the manufacturing cost. A method for manufacturing a hollow engine valve is configured in such a manner that, in order to form the hollow shaft section of a half-finished product (1a) into a predetermined shape, the hollow shaft section is inserted in sequence into die holes (M1, M2, M(m-1), Mm, M(n-1), Mn'), which have different hole shapes, and subjected in sequence to drawing so as to reduce the outer diameter and the inner diameter of the hollow shaft section in stages and so as to stretch the length of the hollow shaft section in stages. In the method, the half-finished product (1a) is subjected to heat treatment so that the hardness thereof is lower than or equal to a predetermined level, a shaft end sealing section (15) is formed by increasing the wall thickness of the opening end of the hollow shaft section (12) toward the inside of the opening end by the die hole (Mn') of a die (Din'), the die hole (Mn') having an inner diameter adjusted to d2', and the gap in the shaft end sealing section (15) is welded.

When an outer circumference of a clamping portion 25 and an outer circumference of a circular outer circumference 26 are restrained by a die 6 while inserting a non-circular punch 5 into a circular hole 28, paddings 27, 27 are pressed by a semi-circular inner circumference of the die 6 to thereby be forced into interior of the circular hole 28. The volume of the paddings 27, 27 is set to be substantially the same as a volume obtained by subtracting the volume of a non-circular hole 23 in an extension shaft 2 from the volume of the circular hole 28. The circular hole 28 is deformed, and the paddings 27, 27 forced into the circular hole 28 abut with inclined planes 52, 52 of the punch 5, whereby the non-circular hole 23 is formed in the extension shaft 2.

By press-fitting a cylindrical blank (D) into a die (1) with one of a pair of punches (2, 3), and at the same time press-fitting small diameter end portions (2a, 3a) and tapered portions (2c, 3c) of the pair of punches (2, 3) into both ends of the cylindrical blank (D) while restraining both end surfaces of the blank (D) with cylindrical members (4, 5) movable on the outsides of the punches (2, 3), the external circumferential surface of the blank (D) is finish molded to the required diameter by the internal circumferential surface (1a) of the die (1) and, at the same time, tapered surfaces (E3, E4) are formed on the inner circumferential surface in both ends of the blank (D). The process produces a bushing (E) with its internal surfaces (E2, E3, E4) accurately coaxial, and with the external surface (E1) accurately formed to the required diameter.

Apparatus for thermal sizing elongated, tubular channels of a square cross section includes a die having plural elongated die elements and an elongated mandrel having a frame mounting plural pairs of rollers distributed along its length on all four sides. The die is inserted in the channel with its die elements disposed adjacent the channel corners. The mandrel is then inserted with its roller pairs peripherally engaging the die elements, pressing them against the channel corners. The channel, die and mandrel are then heated to a hot-forming temperature, thermally expanding the mandrel frame into pressing engagement with the die elements in lieu of the rollers to plastically reform the channel to a stable shape free of geometric irregularities.

A method of fabricating a tube (10') having enlarged ends (14',16') and made of material which can be strengthened by cold working comprises fabricating a pre-form having the overall configuration of the tube but with increased outside diameters and a decreased length. The pre-formed tube is cold forged or cold rolled over its entire length to reduce its outside diameter while maintaining its inside diameter substantially fixed. This elongates the tube and reduces its cross-sectional area. Cold working is continued until the final desired dimensions for the tube are reached. This produces a strengthening effect by cold working over the entire length of the tube.