Metal deforming – Process – Tube making or reshaping
Reexamination Certificate
1999-12-14
2001-08-28
Larson, Lowell A. (Department: 3725)
Metal deforming
Process
Tube making or reshaping
C072S466200
Reexamination Certificate
active
06279369
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for bending a pipe formed by welding and to a mandrel assembly for use in being such a pipe.
2. Description of the Related Art
A hollow workpiece such as a pipe is typically bent with a mandrel inserted thereinto to provide the hollow workpiece with a bent portion free from such deformation as buckling and with a constant inner diameter throughout the length thereof. However, from time to time, the insertion of the mandrel does not provide sufficient effect upon bending of the hollow workpiece. As a result, the hollow workpiece undesirably includes wrinkly deformation at the bent portion thereof.
To overcome this problem, there has been proposed a hollow workpiece bending apparatus as disclosed in, for example, Japanese Patent Laid-Open Publication No. HEI-6-339731.
A hollow workpiece to be bent in such an apparatus is a seamless pipe of aluminum. A mandrel to be inserted into such a pipe is made of nylon and is sized to fit into the pipe. The mandrel inserted within the pipe extends forwardly through a workpiece-introducing aperture of a stationary die into a workpiece-introducing aperture of a movable die provided forwardly of the stationary die, such that a front end thereof is positioned at a central portion of the workpiece-introducing aperture. One supporting bar is connected to a rear end of the mandrel in support of the same.
Since the mandrel is an extruded product of nylon and extends into the workpiece-introducing aperture of the movable die, the hollow workpiece includes a portion to be bent which is supported by the mandrel inserted therewithin. Thus, it becomes possible for the bending apparatus to bend such a portion of the hollow workpiece without causing undesirable deformation such as buckle thereon. This bending apparatus is useful especially in providing a product including a bent portion of small radius or curvature.
However, the mandrel used in the aforementioned bending apparatus is designed to fit into the extruded hollow workpiece. Therefore, such a mandrel is less applicable to a weld tube having a bead including a projection or bulged portion protruding inwardly of the weld tube. If the mandrel is made thinner in correspondence to the bulged portion, the pipe inevitably includes very large gaps between a surface of the mandrel and inner surfaces thereof adjacent the surface of the bulged portion. This makes it difficult to precisely bend the pipe. Alternatively, one may propose provision of the mandrel with a recessed portion formed in conformation to the bulged portion, however, such a mandrel would become expensive.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a preferred method of bending a pipe having a weld seam.
A further object of the present invention is to provide a preferred mandrel assembly for use in bending the pipe having the weld seam.
According to a first aspect of the present invention, there is provided a method of bending a pipe with a mandrel inserted therewithin, the pipe having a weld seam extending longitudinally thereof, the weld seam including a bulged portion protruding inwardly of the pipe, the method comprising the steps of: providing plural resinous sheets for forming the mandrel having a thickness corresponding to an inside measurement of the pipe when the mandrel is inserted within the pipe; inserting a part of the resinous sheets into the pipe; inserting the rest of the resinous sheets into the pipe such that a surface of the part of the resinous sheets comes into intimate contact with the bulged portion; actuating a bender to apply pressure to the pipe to thereby bend the pipe with the part and the rest of the resinous sheets inserted therewithin; pulling the rest of the resinous sheets out of the bent pipe; and pulling the part of the resinous sheets out of the bent pipe after pulling the rest of the resinous sheets out of the bent pipe.
The part of the resinous sheets is initially inserted into a pipe having a weld seam extending longitudinally thereof. Since the part of the resinous sheets in small in thickness, the part of the resinous sheets can be inserted into the pipe without being caught by the bulged portion of the weld seam. Thus, these resinous sheets are not damaged by the bulged portion. Afterwards, the rest of resinous sheets is inserted into the pipe to thereby push the previously inserted resinous sheets against the bulged portion. Because the mandrel can be readily inserted into the pipe without being influenced by the bulged portion of the weld seam, the present invention is suitable for the bending of the pipe having the weld seam. More specifically, it is not necessary to provide the mandrel with any recessed portion formed in correspondence to the bulged portion of the weld seam. This makes it possible to reduce the cost of the mandrel. After bending the pipe, the above-mentioned resinous sheets are pulled out of the pipe in reverse sequence of insertion of the resinous sheets into the pipe. The pipe may be circular in cross-section.
According to a second aspect of the present invention, there is provided a method of bending a pipe of rectangular cross-section with a mandrel inserted therewithin, the pipe including top and bottom sheets either of which has a weld seam extending longitudinally thereof, the weld seam having a bulged portion protruding inwardly of the top or bottom sheet, the method comprising the steps of: providing plural resinous sheets for forming the mandrel having a thickness corresponding to an inside measurement between the top and bottom sheets when the mandrel is inserted within the pipe; inserting a part of the resinous sheets into the pipe; inserting the rest of the resinous sheets into the pipe such that a surface of the part of the resinous sheets comes into intimate contact with the bulged portion; actuating a bender to apply pressure to the top or bottom sheet of the pipe to thereby bend the top or bottom sheet with the part and the rest of the resinous sheets inserted therewithin; pulling the rest of the resinous sheets out of the bent pipe; and pulling the part of the resinous sheets out of the bent pipe after pulling the rest of the resinous sheets out of the bent pipe.
The pipe to be bent in accordance with the present invention is rectangular in cross-section. Such a pipe includes top and bottom sheets either of which has a weld seam. A part of plural resinous sheets for forming the mandrel is initially inserted into the pipe of rectangular cross-section. The thickness of the part of the resinous sheets is smaller than the inside measurement of the pipe. Accordingly, the part of the resinous sheets can be inserted into the pipe without being caught by the bulged portion of the weld seam protruding inwardly of the pipe. As a result, these resinous sheets are not damaged by the bulged portion. When pulling the resinous sheets out of the bent pipe after the bending of the pipe, the rest of the resinous sheets is first pulled out of the bent pipe.
According to a third aspect of the present invention, there is provided a mandrel assembly designed to be inserted into a pipe for bending the pipe, the pipe having a weld seam extending longitudinally thereof, the weld seam including a bulged portion protruding inwardly of the pipe, the mandrel assembly comprising: a first mandrel segment to be initially inserted into the pipe, the first mandrel segment being comprised of at least one resinous sheet; and a second mandrel segment comprised of one resinous sheet to be inserted into the pipe after the insertion of the first mandrel segment into the pipe such that the second mandrel segment brings a surface of the first mandrel segment into intimate contact with the bulged portion.
In a preferred form of the present invention, when the first and second mandrel segments are inserted into the pipe, thickness of the first and second mandrel segments are substantially equal to an inside measurement of the pipe.
In a further preferred form of the present in
Honda Giken Kogyo Kubushiki Kaisha
Larson Lowell A.
Merchant & Gould P.C.
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