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After insertion of a mandrel (23) into a blank tube (20) in the form of an electric welded tube, a parallel swaging operation is carried out by moving a cylindrical die (24) to cause the end of the blank tube (20) to contact tightly with a parallel forming portion (27) of the mandrel (23). After com

After insertion of a mandrel (23) into a blank tube (20) in the form of an electric welded tube, a parallel swaging operation is carried out by moving a cylindrical die (24) to cause the end of the blank tube (20) to contact tightly with a parallel forming portion (27) of the mandrel (23). After completion of parallel swaging operation, the die (24) is withdrawn out of the blank tube (20) and a push-die (33) is caused to move to the blank tube (20) from a radially outward position while leaving the mandrel (23) inside the blank tube (20) so that a weld bead on the blank tube (20) can be flattened by cooperation with the mandrel (23).

대표청구항 ▼

What is claimed is: 1. A method for working a tube comprising: inserting a mandrel into a blank tube in a form of a welded tube: applying a parallel swaging operation by translating a cylindrical die axially along and relative to the blank tube and the mandrel so as to cause the blank tube to conta

What is claimed is: 1. A method for working a tube comprising: inserting a mandrel into a blank tube in a form of a welded tube: applying a parallel swaging operation by translating a cylindrical die axially along and relative to the blank tube and the mandrel so as to cause the blank tube to contact tightly with the mandrel; subsequently withdrawing the cylindrical die from the blank tube, while keeping the mandrel in the blank tube; and moving a push-die to the blank tube from a radially outward position to flatten a weld portion on the blank tube in cooperation with the mandrel, wherein the push-die is moved to the blank tube after the cylindrical die is withdrawn from the blank tube and while the mandrel is in the blank tube. 2. A method for working a tube in accordance with claim 1, wherein a tapered surface is formed at an inner edge of a tip end of the blank tube through a cooperative action between the mandrel and the cylindrical die. 3. A method of working a tube in accordance with claim 2, wherein a reduced thickness portion is formed at the tip end of the blank tube through a cooperative action between the mandrel and the cylindrical die so that the reduced thickness portion can be used as a bent piece extending in a radially inward direction. 4. A method for working a tube in accordance with claim 3, wherein the cylindrical die comprises a tapered inlet portion and a relief portion formed in an inner surface of the cylindrical die, the relief portion being spaced from the tapered inlet portion of the cylindrical die to extend circumferentially, and the relief portion has a slightly enlarged inner diameter and is used as a reservoir for lubricating oil. 5. A method for working a tube in accordance with claim 2, wherein the cylindrical die comprises a tapered inlet portion and a relief portion formed in an inner surface of the cylindrical die, the relief portion being spaced from the tapered inlet portion of the cylindrical die to extend circumferentially, and the relief portion has a slightly enlarged inner diameter and is used as a reservoir for lubricating oil. 6. A method for working a tube in accordance with claim 1, wherein a reduced thickness portion is formed at a tip end of the blank tube through a cooperative action between the mandrel and the cylindrical die, so that the reduced thickness portion can be used as a bent piece extending in a radially inward direction. 7. A method for working a tube in accordance with claim 6, wherein the cylindrical die comprises a tapered inlet portion and a relief portion formed in an inner surface of the cylindrical die, the relief portion being spaced from the tapered inlet portion of the cylindrical die to extend circumferentially, and the relief portion has a slightly enlarged inner diameter and is used as a reservoir for lubricating oil. 8. A method for working a tube in accordance with claim 1, wherein the cylindrical die comprises a tapered inlet portion and a relief portion formed in an inner surface of the cylindrical die, the relief portion spaced from the tapered inlet portion of the cylindrical die to extend circumferentially, and the relief portion has a slightly enlarged inner diameter and is used as a reservoir for lubricating oil. 9. An apparatus for working a welded tube having a weld bead, said apparatus comprising: a parallel swaging machine and a push-die, said parallel swaging machine including a clamp for supporting the welded tube, a rotary mechanism associated with the said parallel swaging machine, means for controlling said rotary mechanism to orient the welded tube so that the weld bead is positioned in a stroke of said push-die, a mandrel insertable into the welded tube when supported on said clamp, and a cylindrical die that translates along the welded tube when supported on said clamp, said push-die being mounted on said parallel swaging machine so that it moves toward the welded tube from a radially outward position and away from the welded tube. 10. An apparatus for working a tube in accordance with claim 9, wherein a forming surface is provided on said mandrel for forming a tip end of the blank tube to have a thickness that is less than an adjacent wall portion of the blank tube. 11. A method for working a tube comprising: inserting a mandrel into a blank tube in a form of a welded tube having a weld bead; orienting the blank tube so that the weld bead is positioned in a stroke of a push-die; applying a parallel swaging operation by translating a cylindrical die axially along and relative to the blank tube and the mandrel so as to cause the blank tube to contact tightly with the mandrel; subsequently withdrawing the cylindrical die from the blank tube; and moving the push-die to the blank tube from a radially outward position to flatten a weld portion on the blank tube.