Patent Publication Number: US-7219527-B2

Title: Mandrel for bending

Description:
FIELD OF THE INVENTION 
   This invention relates to a mandrel for bending which inhibits formation of irregularities at a bending part of a pipe during the bending process. 
   BACKGROUND OF THE INVENTION 
   Unexamined Japanese Utility Model Publication No. 6-41921 and Unexamined Japanese Patent Publication No. 7-290156 disclose a known conventional mandrel for bending comprising a plurality of plugs coupled in series onto an end of a shank. As can be seen in  FIG. 4 , the outer peripheral surface of each plug  50  is formed to be spherical and a connection shaft  52  is inserted through the center of the plug  50 . The connection shaft  52  is provided with a spherical part  54  at one end and a spherical depression  56  at the other end. 
   The spherical part  54  of the connection shaft  52  is fitted into the spherical depression  56  of another connection shaft  52 , which thus constitutes an adjustable joint. In this manner, a plurality of plugs  50  are connected in series. Moreover, the shank  58  is provided with a spherical depression  60  which is identical to the spherical depression  56 . The spherical part  54  of the terminal connection shaft  52  is fitted into the depression  60  so that all the plugs  50  are connected to the shank  58 . 
   When bending is performed, the plugs  50  are inserted into a pipe  62  to be arranged at the bending part. While the bending is performed, the spherical parts  54  rotate within the spherical depressions  56 ,  60  and the plugs  50  are waggled along the bending direction. As a result, spaces between the respective plugs  50  are narrowed and the outer peripheral surfaces of the plugs  50  are abutted to the inner wall of the pipe  62  in a concentrated manner on the inside of the bend. 
   Thus, formation of irregularities, such as wrinkles, on the inside of the bend is inhibited. 
   SUMMARY OF THE INVENTION 
   However, as shown in  FIG. 4 , in the case of bending using the conventional mandrel as above, a small gap G is left between the neighboring plugs  50  on the inside of the bend, where the outer peripheral surfaces of the respective plugs  50  do not abut the inner wall of the pipe  62 . Therefore, during bending, especially during small radius bending, wrinkles are formed in this gap G. 
   There is a problem that the generation of irregularities cannot sufficiently be inhibited. 
   One object of the present invention is to provide a mandrel for bending which effectively inhibits formation of irregularities, such as wrinkles, in a pipe on the inside of the bend during the bending process. 
   To attain this and other objects, the present invention provides a mandrel for bending which inhibits generation of irregularities in a pipe by arranging plugs at a bending part within the pipe. Each plug is formed into a disc and a through-hole is created approximately in the center of the plug. A flexible member is inserted through the through-holes of a plurality of plugs. One end of the flexible member is fixed to a shank so that the plurality of plugs are connected to the shank in series. Each plug is provided with a slant surface which descends from about the center of the plug toward the outer periphery of the plug so that the peripheral side of the plug becomes thinner than the central side of the plug. 
   In the mandrel for bending of the present invention, the slant surface of the plug abuts a back surface of the adjoining plug and thus a plurality of plugs are closely abutted to each other without leaving a space. Therefore, formation of irregularities like wrinkles can be effectively inhibited while the pipe is being bent. 
   The slant surface may be a flat descending surface which extends from about the center of the plug toward the outer periphery of the plug. Also, the mandrel for bending may be provided with a turn lock mechanism which restricts rotation of the respective plugs within the pipe. The turn lock mechanism, for example, may comprise a flexible turn lock member. The turn lock member is passed through a lock hole provided in parallel to the previously described through-hole in each plug and is secured to the shank at one end. Moreover, the flexible member may be made of wire and a retaining member may be attached to the other end of the flexible member opposite to the shank. 

   
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     The invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
       FIG. 1  is a cross-sectional view of a mandrel for bending according to an embodiment of the present invention before bending; 
       FIG. 2  is a perspective view of plugs of the embodiment; 
       FIG. 3  is a cross-sectional view of the mandrel for bending according to the embodiment after bending; and 
       FIG. 4  is a cross-sectional view of a conventional mandrel for bending after bending. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   As shown in  FIG. 1 , a pipe  1  is arranged to be brought into contact with the outer periphery of a bend die  2  which is designed to bend the pipe  1  at a desired angle. Facing to the bend die  2 , a clamp die  4  is provided so that the pipe  1  is held between the bend die  2  and the clamp die  4 . While the bending is performed, the bend die  2  rotates and the clamp die  4  moves around the bend die  2 . A pressure die  6  is also provided in line with the clamp die  4 . The pressure die  6  receives bending reaction force induced while the pipe  1  is being bent. 
   A mandrel  10  for bending is inserted into the pipe  1 . The mandrel  10  is composed of a plurality of plugs  12  and a shank  14 . Each plug  12  is formed into a disc, as shown in  FIG. 2 . The outer peripheral surface of the plug  12  is formed to be spherical. The outer peripheral surface may be flat if the plug  12  is small in thickness. 
   A through-hole  16  is formed approximately in the center of each disc-like plug  12 . A flexible member  18  is passed through the through-holes  16  of a plurality of plugs  12  arranged in stacks. The flexible member  18  is made of material which is easy to yield. In the present embodiment, the flexible member  18  is made of metal or plastic wire. 
   The flexible member  18  is inserted through an insertion hole  20  formed in the shank  14 . The shank  14  is also provided with a large-diameter hole  22  which communicates with the insertion hole  20 . To the end of the flexible member  18  which projects from the insertion hole  20  into the large-diameter hole  22 , a retaining member  24  is attached. 
   Also to the other end of the flexible member  18  opposite to the shank  14 , a retaining member  26  is attached. Between the retaining member  26  and the shank  14 , a plurality of plugs  12  are held in a row. No tension is required to be applied to the flexible member  18 . The number of plugs  12  to be used can be determined at discretion according to the beading length of bending. 
   Each plug  12  is provided with a slant surface  28  on one side. The slant surface  28  descends from about the center of the plug  12  toward the outer periphery so that the plug  12  becomes partially thinner on the peripheral side than the central side. In the present embodiment, the slant surface  28  is not curved but flat. 
   As shown in  FIG. 3 , inclination of the slant surface  28  is so determined that a back surface  30  of the plug  12  abuts the slant surface  28  of the adjoining plug  12  and that a plurality of plugs  12  are brought into close contact with each other on the inside of the bend during the bending process. The back surface  30 , which is on the reverse side where there is the slant surface  28 , is formed entirely flat. Moreover, the front surface continuing into the slant surface  28 , which faces to the outside of the bend when bending is performed, is formed subtly inclined. The plug  50  can be a shape of a cone having the through-hole  16  provided along the axis of the cone. 
   In each plug  12 , a through lock hole  32  which opens to the slant surface  28  is provided in parallel to the through-hole  16 . A turn lock member  34  is inserted into the lock holes  32  of the respective plugs  12 . Similar to the flexible member  18 , the turn lock member  34  is made of a flexible material, such as metal wire and plastic wire, for example. One end of the turn lock member  34  is inserted into the shank  14  and secured. In the present embodiment, the lock holes  32  and the turn lock member  34  constitute a turn lock mechanism  36 . The turn lock mechanism  36  may be constituted in a manner other than the above-described constitution. For example, each plug  12  may be fixed to the flexible member  18  by caulking. Or, projections and depressions may be provided on the respective plugs  12  and the shank  14  so that the rotation of the plugs  12  can be avoided by engaging the projections and depressions. 
   Now, operation of the mandrel  10  for bending of the present invention will be explained. 
   Firstly, as shown in  FIG. 1 , a pipe  1  is held between the bend die  2  and the clamp die  4 . The pressure die  6  is abutted to the pipe  1 . Next, the mandrel  10  for bending comprising a plurality of plugs  12  is inserted into the pipe  1 . At the time of the insertion, each plug  12  is disposed in such a manner that the peripheral side with the slant surface  28  faces to the inside of the bend. 
   While the bend die  2  is rotated on its axis, the clamp die  4  is rotated around the bend die  2 . As a result, the pipe  1  is wound around the bend die  2 , resulting in that the outside of the bend is stretched and the inside of the bend is compressed at the bending part of the pipe  1 . 
   As shown in  FIG. 3 , in the mandrel  10  for bending, the spaces between the plugs  12  are expanded on the outside of the bend and are narrowed on the inside of the bend. Furthermore, the back surface  30  of the plug  12  abuts to the slant surface  28  of the adjoining plug  12 . As a result, on the inside of the bend, the neighboring plugs  12  are closely abutted, leaving no space therebetween. 
   Consequently, even if the pipe  1  is compressed on the inside of the bend while the bending is performed, formation of irregularities like wrinkles cannot be promoted. Accordingly, even if the bending radius is small, bending free of irregularities can be achieved. 
   The present invention is not limited to the above embodiment, and other modifications and variations are possible within the scope of the present invention.