| 摘要 |
There is disclosed an insert of cylindrical shape and of substantially uniform predetermined diameter and length. This insert has a greater hardness than the tube to be employed. Thus, generally, the tube is an aluminum alloy tube and the insert is stainless steel to provide the desired comparative hardnesses. For convenience in handling of the insert during the process, a cylindrical, coaxial recess is drilled in the insert. A conventional thread-rolling device is provided with dies of a hardness greater than the insert and the pattern on the contacting surfaces of said dies is a plurality of annular, spaced, alternate crests and grooves. The crests and grooves are disposed in two longitudinally spaced sections and with the grooves and crests in the first section each having a common diameter and with the diameters of the crests and grooves in the second section each having gradually decreasing diameters. Such dies are used to form a pattern of annularly spaced grooves and crests on the surface of the insert. The crests in the first section of the dies imprint grooves in a first section on the insert and which grooves have a common diameter. The material displaced in the insert, in the imprinting and forming of such grooves, migrates laterally from the grooves or in a direction longitudinally of the insert and forms the crests of uniform diameter in the first section on said insert. The crests in the second section of the dies imprint grooves in a longitudinally spaced second section on the insert and which grooves have gradually increasing diameters. The material displaced in forming said grooves in said second section of said insert forms crests which are not fully formed and which gradually decrease in diameter. Next, and prior to swaging of a tube upon said insert, the insert is provided with a plurality of longitudinally extending grooves by imprinting the said insert with an appropriate tool thus causing said grooves and causing a raise of stock elsewhere of the insert by the same amount as the extent of the said grooves.
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