Abstract:
A pipe shaping method forms a narrow neck at one end of a workpiece in the form of an elliptical pipe having a cross sectional shape elongated in a predetermined elongating direction, with a roller. The pipe shaping method includes the following steps of: cutting the end of the workpiece into a shape having first and second projections and first and second recesses which are arranged alternately along a circumference of the end of the workpiece, the first and second recesses of the end of the workpiece being spaced apart from each other in the elongating direction, each of the first and second projections projecting in a longitudinal direction of the workpiece between the first and second recesses each recessed in the longitudinal direction; mounting the workpiece (W) to a pipe holder; disposing the roller around the workpiece; and reducing a cross sectional size of the end of the workpiece by applying a compressive force on the circumference of the end of the workpiece by making such a relative movement between the roller and the workpiece as to revolve the roller relatively around the workpiece, to move the roller relatively in the longitudinal direction of the workpiece, and to vary a distance between the roller and a revolution axis of relative revolution of the roller around the workpiece.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Conventionally, a method of reducing an end portion of a pipe and the like in diameter is referred to as a spinning work.  
           [0002]    Japanese Patent Unexamined Publication No. 11(1999)-147138 discloses a method (spinning work) of forming a pipe  4  (workpiece) having a circular cross sectional shape. In this first related art, a roller  28  of a forming apparatus is compressed against a circumferential end portion of a fixed pipe  4 . Simultaneously with this, the roller  28  is revolved and put into the spinning work so as to form a narrow neck  4   c  at the end portion of the pipe  4 . During the spinning work, a revolution axis X 5  of the roller  28  is eccentric from a longitudinal center line X 4  of the pipe  4 , to thereby form the narrow neck  4   c  that is eccentric with respect to the longitudinal center line X 4  of the pipe  4 .  
           [0003]    For carrying out the spinning work, the forming apparatus having the roller  28  is needed to be so constructed that the roller  28  is also movable radially with respect to the revolution axis X 5  during its revolution. In the first related art, the forming apparatus has a bracket  27  for supporting the roller  28 . The bracket  27  is provided with a first taper surface  27   a . Moreover, the forming apparatus has a ring plate  26  which is provided with a second taper surface  26   a . The first and second taper surfaces  27   a  and  26   a  abut against each other. The ring plate  26  is moved forward and backward relative to the pipe  4 , to thereby allow the roller  28  to move radially with respect to the revolution axis X 5 .  
           [0004]    Similarly to the above first related art, Japanese Patent Unexamined Publication No. 11(1999)-179455 discloses a method of forming a narrow neck  44  (reduced diameter portion) of a pipe  42  which is fixed. In this second related art, a roller  27  of a forming apparatus  10  is compressed against an external circumference at an end portion of the pipe  42 , and is revolved during the spinning work for forming the narrow neck  44  with a reduced diameter.  
           [0005]    In the forming apparatus  10  according to the second related art, a support shaft  28  for supporting a roller  27  is mounted on a spinning portion  24  via a slide lock plate  26 . A plate cam  29  rotating with the slide lock plate  26  during the spinning work allows the support shaft  28  to move in a radial direction of the spinning portion  24 .  
           [0006]    A rod member  19  of a main shaft  18  penetrates through an axial center of the spinning portion  24 . A pivot converting portion  19 A converts an axial displacement of the rod member  19  into a rotation relative to the spinning portion  24 . The plate cam  29  is driven by the pivot converting portion  19 A.  
           [0007]    A rotation axis  48  of the spinning portion  24  is deviated from a longitudinal center line  47  of the pipe  42 , to thereby form the narrow neck  44  that is eccentric with respect to the longitudinal center line  47  of the pipe  42 .  
           [0008]    The above first and second related arts make it possible to produce casings such as those for catalytic converters for vehicles with a small number of component parts in a short time.  
           [0009]    Each of the above first and second related arts requires the pipe (workpiece) that has a “circular” cross sectional shape. However, the casing for the catalytic converter for the vehicle has an overall configuration preferably as flat as possible so that the casing can be mounted below a floor of the vehicle. Therefore, a workpiece shaped into an “elliptical” pipe is needed for the casing, instead of the circular pipe.  
           [0010]    However, according to the first and second related arts, spinning an elliptical pipe (workpiece), instead of the circular pipe (workpiece), cannot always produce an elliptical pipe (product) having a desired narrow neck.  
           [0011]    More specifically, FIG. 9 shows an elliptical pipe  70  (workpiece) made of steel having the following dimensions: a wide diameter of 150 mm, a narrow diameter of 105 mm, and a plate thickness of 1.5 mm, with an end portion thereof cut perpendicular to an axial direction. The elliptical pipe  70  (workpiece) is fixed and then put into a spinning work by means of a roller in order to reduce the end portion in diameter to 70 mm. As a result, a gradual reduction in diameter is seen with a pair of slopes  71  (taper) having an intersection angle of 60 degrees (not shown). However, the slope  71  and the narrow neck have an abnormal deformation  72 , that is, a wall surface partly rolled inward. As a result, the thus obtained narrow neck (reduced diameter portion) does not have a cross section shaped into a complete round.  
         SUMMARY OF THE INVENTION  
         [0012]    It is therefore an object of the present invention to provide a method of shaping an elliptical pipe (product) through a spinning work.  
           [0013]    It is another object of the present invention to make an elliptical pipe (workpiece) usable for shaping the elliptical pipe (product) having a narrow neck which has a cross section shaped into a complete round.  
           [0014]    There is provided a pipe shaping method, according the present invention. The pipe shaping method shapes a workpiece in the form of an elliptical pipe having a cross sectional shape elongated in a predetermined elongating direction and extending longitudinally from a first end to a second end, into a form having a narrow neck at least at the first end of the workpiece. The pipe shaping method comprises the following steps of: cutting the first end of the workpiece into a shape having a projection located at a subsidiary vertex portion and a recess located at a principal vertex portion, the projection projecting in a longitudinal direction of the workpiece, the recess being recessed in the longitudinal direction of the workpiece; mounting the workpiece to a pipe holder; disposing a roller around the workpiece; and reducing a cross sectional size of the first end of the workpiece by applying a compressive force on the circumference of the first end of the workpiece by a relative revolving movement between the roller and the workpiece. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a longitudinal sectional view of a forming apparatus  10 , according to first, second and third preferred embodiments of the present invention;  
         [0016]    [0016]FIG. 2 is a front view of a spinning portion  24  of the forming apparatus  10 ;  
         [0017]    [0017]FIG. 3 shows an orbit of a roller  27  compressed against an elliptical pipe W;  
         [0018]    [0018]FIG. 4 ( 4 A,  4 B and  4 C) shows an end shape of a first workpiece material WA (elliptical pipe), with a center Q of a narrow neck  52 A coinciding with a longitudinal center line N of the first workpiece material WA;  
         [0019]    [0019]FIG. 5 ( 5 A,  5 B and  5 C) is similar to FIG. 4, but showing the first workpiece material WA after forming;  
         [0020]    [0020]FIG. 6 ( 6 A,  6 B and  6 C) shows an end shape of a second workpiece material WB (elliptical pipe), with a center Q of a narrow neck  52 B deviated by an eccentricity H from a longitudinal center line N of the second workpiece material WB;  
         [0021]    [0021]FIG. 7 ( 7 A,  7 B and  7 C) is similar to FIG. 6, but showing the second workpiece material WB after forming;  
         [0022]    [0022]FIG. 8 ( 8 A and  8 B) is an essential part of the other forming apparatus with a workpiece W turnable; and  
         [0023]    [0023]FIG. 9 shows a workpiece  70  after a spinning work, according to a related art. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0024]    A first preferred embodiment is concerning a structure of a forming apparatus  10 , a second preferred embodiment is concerning a first shaping method by means of the forming apparatus  10 , and a third preferred embodiment is concerning a second shaping method by means of the forming apparatus  10 .  
         [0025]    First of all, in the following preferred embodiments of the present invention, the term “revolution” as well as those in relation thereto are defined as a motion of a body around a closed orbit (like the earth revolves around the sun); contrary to this, the term “rotation” as well as those in relation thereto distinctively defined as a motion of a body in which all the points on a central straight line of the body are fixed (like the earth rotates about its axis).  
         [0026]    As is seen in FIG. 1, there is provided the forming apparatus  10 , according to the first preferred embodiment of the present invention. Description of the forming apparatus  10  according to the first preferred embodiment is based on a forming apparatus  10  according to Japanese Patent Unexamined Publication No. 11(1999)-179455 recited in the BACK GROUND OF THE INVENTION above.  
         [0027]    The forming apparatus  10  has a forming unit  11  and a pipe holder  33  disposed, respectively, on left and right sides of a base plate  12  in FIG. 1. The forming unit  11  is equipped with a roller  27 , and is used for shaping an elliptical pipe W (workpiece W) so that the elliptical pipe W can have a diameter thereof reduced. The pipe holder  33  is used for fixedly holding the elliptical pipe W. The forming unit  11  has a spinning portion  24  which is provided with a plurality of rollers  27 . The forming unit  11  further has various driving mechanisms (to be mentioned afterwards) for drivingly holding the spinning portion  24 , and is placed on a slide table  13 .  
         [0028]    The slide table  13  is provided with a first ball screw  15 . The forming unit  11  is movable in the longitudinal direction (in other words, a direction toward and away from the pipe holder  33 ) in FIG. 1 on the base plate  12  via the slide table  13 .  
         [0029]    More specifically, the first ball screw  15  is rotatably driven via a first pulley belt  17  by means of a first servo motor  16  which is mounted to the base plate  12 . Thereby, the slide table  13  is movable in the longitudinal direction in FIG. 1 on the base plate  12 .  
         [0030]    The forming unit  11  rotatably supports a main shaft  18  to a support member  14  which is fixed to the slide table  13 . The main shaft  18  is driven via a second pulley belt  32  by means of a motor  30  which is disposed on the support member  14 . The main shaft  18  is provided with the spinning portion  24  on a first side facing the pipe holder  33 . The spinning portion  24  has a plate cam  29  which is circular and is rotatably mounted on the spinning portion  24 . The plate cam  29  is connected to a rod member  19  via a pivot converting portion  19 A. The rod member  19  penetrates through an axial center portion of the main shaft  18 . Furthermore, the rod member  19  extends from the pivot converting portion  19 A toward a second side opposite to the first side facing the pipe holder  33 , and is connected to a converter  20 A which is provided with a second ball screw  20 . The converter  20 A is used for converting a rotational movement into a linear movement, and the linear movement into the rotational movement. The rod member  19  and the converter  20 A are rotatable relative to each other.  
         [0031]    A cover  21  is fixed to the support member  14  in such a manner as to cover the converter  20 A. The second ball screw  20  is driven by means of a second servo motor  22  via a second pulley belt  23 . The second servo motor  22  is disposed on the cover  21 . Operating the second servo motor  22  allows the rod member  19  to be displaced in its axial direction (transverse direction in FIG. 1). Then, the axial displacement of the rod member  19  allows the plate cam  29  to rotate relative to the spinning portion  24 .  
         [0032]    As is seen in FIG. 2, the spinning portion  24  is provided with a plurality of slide grooves  24 A extending radially at predetermined angular intervals on the circular spinning portion  24  which is circular in shape. Each of the slide grooves  24 A is provided with a slide block  25  which is movable and has a slide lock plate  26  secured to the slide block  25 . A support shaft  28  is mounted on each of the slide blocks  25 .  
         [0033]    As is seen in FIG. 2, there are provided a plurality of cam grooves  29 A at predetermined angular intervals on the circular spinning portion  24 . Progressing in a clockwise direction in FIG. 2, each of the cam grooves  29 A becomes more spaced apart from a center of the spinning portion  24  (spiral). Each support shaft  28  of the slide block  25  projects in an area defined within one of the cam grooves  29 A, and is movable along one of the cam grooves  29 A.  
         [0034]    Each slide lock plate  26  is provided with one of the rollers  27 . The plurality of rollers  27  are used for forming, and are disposed at regular angular intervals around a rotation axis M of the main shaft  18 . Rotation of the plate cam  29  allows each of the rollers  27  to move radially along one of the slide groove  24 A on the spinning portion  24 . Moreover, each of the rollers  27  makes a revolution around the rotation axis M of the main shaft  18  in the same circular orbit.  
         [0035]    On the other hand, the pipe holder  33  is movable, via a slide table  35 , in a direction perpendicular to the movement of the forming unit  11  (also perpendicular to a flat surface of FIG. 1). The slide table  35  is driven by a hydraulic cylinder (not shown). The pipe holder  33  is equipped with an immovable holder  38  on the slide table  35 , and a movable holder  39  which is movable upward and downward by means of a hydraulic cylinder  40 . Each of the immovable holder  38  and the movable holder  39  has an inside wall portion corresponding to a cross section of the elliptical pipe W. The elliptical pipe W is preferably mounted on the pipe holder  33  in such a manner that the narrow diameters of the elliptical pipe W face upward and downward. According to the first preferred embodiment of the present invention, the narrow diameters of the elliptical material W face upward and downward.  
         [0036]    With the elliptical pipe W fixedly held between the immovable holder  38  and the movable holder  39 , a longitudinal center line N of the elliptical pipe W and the rotation axis M of the main shaft  18  are, basically, positioned on the same line in the vertical position in FIG. 1. In addition to the basic positioning stated above, the longitudinal center line N and the rotation axis M can be so adjusted as to make a required offset in the vertical position in FIG. 1 by means of an adjuster (not shown).  
         [0037]    The first and second servo motors  16  and  22  are controlled by means of a control device (not shown).  
         [0038]    The forming apparatus  10  according to the first preferred embodiment of the present invention differs from the forming apparatus  10  according to Japanese Patent Unexamined Publication No. 11(1999)-179455 in that the former puts the workpiece W that is an “elliptical” pipe (instead of a “circular” pipe) between the immovable holder  38  and the movable holder  39 . For more details in terms of the structure of the forming apparatus  10 , refer to Japanese Patent Unexamined Publication No. 11(1999)-179455.  
         [0039]    Hereinafter, there are provided the first and second shaping methods, according to, respectively, the second and third preferred embodiments of the present invention. Each of the first and second shaping methods uses the forming apparatus  10  so as to form, respectively, narrow necks  52 A and  52 B. Each end on both sides of the elliptical pipe W (workpiece W) is formed with the narrow neck  52 A through the first shaping method, while formed with the narrow neck  52 B through the second shaping method.  
         [0040]    Each of the first and second shaping method is a spinning work by means of the forming apparatus  10 . As is seen in FIG. 1, the main shaft  18  of the forming unit  11  is rotated, with the elliptical pipe W fixedly held to the pipe holder  33 . Then, the first servo motor  16  drives the forming unit  11  into a movement in the longitudinal direction along the base plate  12 , and simultaneously with this, the second servo motor  22  rotates the plate cam  29  so as to change a distance between the roller  27  and the rotation axis M of the spinning portion  24 .  
         [0041]    In other words, the control device (not shown) controls the first and second servo motors  16  and  22 . Thereby, the roller  27  is compressed against a side surface of the elliptical pipe W in FIG. 1, and makes a movement indicated by a zigzag arrow as is seen in FIG. 3. More specifically, the roller  27  carries out three types of movement; one is a revolution around the elliptical pipe W, another is a round trip in an axial direction of the elliptical pipe W, and the other is a radial movement so as to change the distance between the roller  27  and a revolution axis M of the roller  27 . With this, the elliptical pipe W is deformed stepwise by a predetermined dimension so as to reduce the elliptical pipe W in diameter until the predetermined narrow neck  52 A or  52 B is formed.  
         [0042]    For each of the spinning works in the first and second shaping methods, the workpiece W has the end that is to be shaped for the reduced diameter. As is best seen in FIG. 4B and FIG. 6B, the end of the workpiece W is so profiled (gently curved like an undulating edge) as to correspond to a wide diameter portion (recess EL) and a narrow diameter portion (projection ES, ES 1 , ES 2 ) of the ellipse. In other words, the end of the workpiece W is not cut merely vertical nor diagonal with respect to the longitudinal center line N.  
         [0043]    [0043]FIG. 4 shows a first workpiece material WA viewed from three different directions, in the first shaping method according to the second preferred embodiment of the present invention. FIG. 4A is a plan view, FIG. 4B is a front view, and FIG. 4C is a side view of the first workpiece material WA. A longitudinal center line of the end of the narrow neck  52 A which is cylindrical in shape coincides with the longitudinal center line N of the elliptical pipe WA.  
         [0044]    The first workpiece material WA is an elliptical pipe having a narrow diameter of 105 mm and a wide diameter of 150 mm. There are defined a projection ES, a recess EL, and a starting point P for the roller  27  of the spinning portion  24  to start compressing against the wide diameter portion EL. As is best seen in FIG. 4A, the projection ES is set at 75 mm from the starting point P, and the recess EL is set at 62 mm from the starting point P. As is best seen in FIG. 4B, the elliptical pipe is cut along a smooth curve between the projection ES and the recess EL, so as to form the first workpiece material WA. In other words, each of the narrow diameter portions ES (projection ES) on upper and lower sides in FIG. 4B is so positioned as to project from the wide diameter portion (recess EL). The upper and lower sides are symmetrical to each other with respect to a reference line of a workpiece axis N (longitudinal center line N). A length T of 13 mm (75 mm minus 62 mm) is a projection of the narrow diameter portion ES relative to the wide diameter portion EL.  
         [0045]    Then, the thus obtained first workpiece material WA is put into the spinning work, to thereby form a casing having a wide diameter slope  51 A of 63 mm measured longitudinally, the narrow neck  52 A having a diameter of 70 mm, and an intersection angle of 60 degrees between two wide diameter slopes  51 A, as is seen in FIG. 5.  
         [0046]    After the spinning work in the first shaping method, no failure (such as an abnormal deformation  72  seen in FIG. 9) is found in slopes or in the narrow neck  52 A.  
         [0047]    [0047]FIG. 6 shows a second workpiece material WB viewed from three different directions, in the second shaping method according to the third preferred embodiment of the present invention. FIG. 6A is a plan view, FIG. 6B is a front view, and FIG. 6C is a side view of the second workpiece material WB. A center axis of the end of the narrow neck  52 B is deviated from the longitudinal center line N of the elliptical pipe WB.  
         [0048]    In the second shaping method, a center Q of the narrow neck  52 B is eccentric in the transverse direction as is seen in FIG. 6C. The direction of deviation is divided into the following first and second cases:  
         [0049]    In the first case, the pipe holder  33  holds the elliptical pipe (second workpiece material WB) with narrow diameters of the second workpiece material WB facing upward and downward. The second workpiece material WB is put between the immovable holder  38  and the movable holder  39  in such a manner that the longitudinal center line N of the second workpiece material WB makes an offset (upward in FIG. 1) by an eccentricity H from the rotation axis M of the main shaft  18 . Such adjustment is carried out by means of the adjuster (not shown). In other words, the center Q of the narrow neck  52 B is deviated lower than the longitudinal center line N in FIG. 6B.  
         [0050]    Contrary to this, in the second case, the pipe holder  33  holds the second workpiece material WB with wide diameters of the second workpiece material WB facing upward and downward. The slide table  35  is so moved that the longitudinal center line N of the second workpiece material WB makes an offset by the eccentricity H from the rotation axis M of the main shaft  18  in a direction perpendicular to the flat surface of FIG. 1.  
         [0051]    As is seen in FIG. 6, the second workpiece material WB is an elliptical pipe having a narrow diameter of 105 mm and a wide diameter of 150 mm. There are defined a first projection ES 1 , a second projection ES 2 , a recess EL, and a starting point P for the roller  27  of the spinning portion  24  to start compressing against the wide diameter portion EL. As is best seen in FIG. 6A, the first projection ES 1  is set at 65 mm from the starting point P, the second projection ES 2  is set at 80 mm from the starting point P, and the recess EL is set at 60 mm from the starting point P. As is best seen in FIG. 6B, the elliptical pipe is cut along a smooth curve between the first projection ES 1 , the recess EL, and the second projection ES 2 , so as to form an end of the second workpiece material WB. A length T 1  of 5 mm (65 mm minus 60 mm) is a projection of a first narrow diameter portion ES 1  relative to the wide diameter portion EL, and a length T 2  of 20 mm (80 mm minus 60 mm) is a projection of a second narrow diameter portion ES 2  relative to the wide diameter portion EL. In other words, as is seen in FIG. 6B, the second projection ES 2  projects longer than the first projection ES 1  by 15 mm (80 mm minus 65 mm) in the direction of the longitudinal center line N.  
         [0052]    Then, the thus obtained second workpiece material WB is put into the spinning work, to thereby form a casing having a wide diameter slope  51 B of 61 mm measured longitudinally, a narrow neck  52 B having a diameter of 70 mm, an intersection angle of 60 degrees between two wide diameter slopes  51 B, and the eccentricity H of 9 mm of the narrow neck  52 B, as is seen in FIG. 7.  
         [0053]    After the spinning work in the second shaping method, no failure (such as the abnormal deformation  72  seen in FIG. 9) is found in the slopes or in the narrow neck  52 B.  
         [0054]    Each of the narrow necks  52 A and  52 B, respectively, in the first and second shaping methods has an end surface thereof shaped through a cutting work or a sanding work for a desired configuration.  
         [0055]    In the first shaping method, the projection ES has a projection longer than the recess EL, as is seen in FIG. 4B. Likewise, in the second shaping method, each of the first and second projections ES 1  and ES 2  has a projection longer than the recess EL, as is seen in FIG. 6B. As a result, this allows even the elliptical pipe to be shaped into the casing having the narrow neck  52 A or  52 B each shaped into a cylinder with a desired reduced diameter, causing no failures of the material such as the abnormal deformation  72  shown in FIG. 9.  
         [0056]    In the first shaping method, it is preferable that the more elliptical the pipe WA is, the more projecting the length T of the projection ES is, relative to the recess EL. Likewise, in the second shaping method, it is preferable that the more elliptical the pipe WB is, the more projecting each of the first and second lengths T 1  and T 2  (respectively of the first and second projections ES 1  and ES 2 ) is, relative to the recess EL.  
         [0057]    In the first shaping method, the center Q of the narrow neck  52 A coincides with the longitudinal center line N of the elliptical pipe WA. In this case, the length T of the upper projection ES is equal to the length T of the lower projection ES, as is seen in FIGS. 4A and 4B.  
         [0058]    Contrary to this, in the second shaping method, the center Q of the narrow neck  52 B is deviated from the longitudinal center line N of the elliptical pipe WB. In this case, the second length T 2  of the second projection ES 2  (lower) is relatively more projecting than the first length T 1  of the first projection ES 1  (upper), as is seen in FIGS. 6A and 6B. In this case, the narrow neck  52 B is closer to the second projection ES 2  than the first projection ES 1 . In other words, for forming a narrow neck ( 52 B) through the spinning work, it is preferable to allow a projection (ES 2 , T 2 ) of an edge (ES 2 ) to become relatively more projecting than its counterpart (ES 1 , T 1 ) of the opposite edge (ES 1 ), when the narrow neck ( 52 B) is closer to the edge (ES 2 ) than the opposite edge (ES 1 ). With this, products can be produced with high accuracy, causing no failures (such as the abnormal deformation  72  seen in FIG. 9).  
         [0059]    According to the first, second and third preferred embodiments of the present invention, the forming apparatus  10  has the pipe holder  33  for holding the elliptical pipe W (workpiece W) so as to revolve the roller  27  around the main shaft  18 . However, the forming apparatus  10  is not limited to the one for “turning (revolution) the roller” in terms of the spinning work.  
         [0060]    For example, as is seen in FIGS. 8A and 8B, the “workpiece W can be turned.” FIG. 8A is a side view showing an essential part of a pipe holder  62  of the other forming apparatus. FIG. 8B is a front view of the pipe holder  62  of the other forming apparatus. The pipe holder  62  is mounted to a rotation shaft  60  which is driven by a motor (not shown). The pipe holder  62  has first and second movable holders  67  and  68  that are held on a holding base plate  64 . The holding base plate  64  is fixed to the rotation shaft  60 . Each of the first and second movable holders  67  and  68  is mounted on one of support walls  65 . One support wall  65  is disposed at an upper end of the holding base plate  64 , while the other support wall  65  is disposed at a lower end of the holding base plate  64 . The two support walls  65  extend in parallel with the rotation shaft  60 . A hydraulic cylinder  69  allows the opposing first and second movable holders  67  and  68  to move toward and away from each other.  
         [0061]    [0061]FIG. 8A shows that the elliptical pipe W is clamped between the first and second movable holders  67  and  68  of the other forming apparatus. FIG. 8B shows that the first and second movable holders  67  and  68  are spaced apart from each other.  
         [0062]    Although not shown in FIGS. 8A and 8B, a mechanism of the other forming apparatus having the following conditions is preferred: A center of a narrow neck of the elliptical pipe W to be formed is defined as an imaginary axis. The roller is not revolved. The elliptical pipe W is so moved as to vary the distance between the roller and the imaginary axis.  
         [0063]    As stated above, the forming apparatus has no particular limitations in terms of structure. However, of the two alternatives; one allowing the roller  27  to revolve, the other allowing the pipe holder  62  to turn (with the workpiece W being held), the former is more cost effective than the latter, because the former has a simpler and smaller overall structure than the latter.  
         [0064]    Moreover, the second and third preferred embodiments (respectively, first and second shaping methods) show, respectively, the narrow necks  52 A and  52 B, each of which has a cylindrical shape and is formed adjacent to the tapering slopes. However, the present invention is not limited to this. Alternatively, a narrow neck having no cylindrical shape (in other words; being conical, or having only tapering slopes with gradual reduction in diameter up to an end opening of the workpiece W) is allowed under the present invention.  
         [0065]    Furthermore, the second and third preferred embodiments show, respectively, the narrow necks  52 A and  52 B each having a cross section of a complete round. However, the present invention is not limited to this. Alternatively, a desired shape such as ellipse is applicable to a cross section of a narrow neck. In this case, however, it is necessary to control the roller  27  so that the roller  27  traces its revolution orbit in accordance with the desired shape of the cross section of the narrow neck.  
         [0066]    Still furthermore, the second and third embodiments show, respectively, the narrow necks  52 A and  52 B, each of which disposed at one end of the workpiece W has its counterpart with the same diametral dimension at the other end. However, the present invention is not limited to this. Alternatively, a pair of narrow necks can have different diameters from each other. In this case, however, it is necessary to control the roller  27  in accordance with the corresponding diameter at each end.