Abstract:
A method for manufacturing an eccentrically expanded pipe in which the plate thickness of the peripheral surface on the large expanding side that tends to easily produce cracks and necking is suppressed from becoming thin is provided. The problem is solved with a method for manufacturing an eccentrically expanded pipe plastically deforming an end of a pipe to an eccentrically expanded pipe part through an eccentrically expanding step; said eccentrically expanding step includes a first eccentrically expanding step, expanding an peripheral surface of the end of the pipe opposing to a peripheral surface finally expanded to be a final product, and a second eccentrically expanding step, expanding the peripheral surface finally expanded to be the final product.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a method for manufacturing an eccentrically expanded pipe. The expanded pipe functions as a part for connecting an fuel supply pipe body of a fuel supply pipe and a filler neck for example. 
         [0003]    The terms used in this specification are defined below. A concentric expanded pipe refers to a pipe in which an axis of an expanded pipe part is concentric to an axis of a pipe, and is fabricated through a concentrically expanding step. The concentrically expanding step is a step expanding an end of pipe with an axis of the end of the pipe concentric to the axis of the pipe (hereinafter refer to as “concentric expansion”). The concentrically expanding step uses a concentric die and a concentric punch, which form a pair. The concentric die has an inner surface copying the end of the pipe undergone the concentric expanding step, that is, an outer shape of the expanded pipe part having a shape of final product. The concentric punch is fitted with pressure to the end, with the end of the pipe projecting to a range of said inner surface. 
         [0004]    An eccentrically expanded pipe refers to a pipe body having an expanded pipe part in which an axis of the expanded pipe part is eccentric to the axis of the pipe, and is fabricated through an eccentrically expanding step. The eccentrically expanding step is a step expanding the end of a pipe (hereinafter referred to as “eccentric expansion”) or the end of a pipe subjected to the concentric expansion in advance so that the axis of the expanded pipe part becomes eccentric to the axis of the pipe. In the eccentrically expanding step, a specific eccentric die (a second eccentric die of the present invention) and an eccentric punch, which form a pair, are used. The eccentric die has an inner surface copying the end of the pipe undergone the eccentrically expanding step, that is, an outer surface of the expanded pipe part having a shape of a final product. The eccentric punch is fitted with pressure, with the end of the pipe or the end of the pipe subjected to the concentric expansion in advance projecting so as to be within a range of said inner surface. 
         [0005]    The expanded pipe part undergone the eccentric expansion is eccentric to the pipe. In the present specification, the side in which the peripheral surface of the expanded pipe part is greatly spaced in a radial direction from the peripheral surface of the pipe is defined as a large expanding side. Similarly, the side in which the peripheral surface of the expanded pipe part is barely spaced apart or the side not spaced apart at all in the radial direction from the peripheral surface of the pipe is defined as a small expanding side. Therefore, the end of the pipe at a stage after the concentrically expanding step has an identical outer diameter for the peripheral surface on the large expanding side and the peripheral surface on the small expanding side. The expanded pipe part at the stage after the eccentrically expanding step has the outer diameter of the peripheral surface on the large expanding side larger than the outer diameter of the peripheral surface on the small expanding side. The “small expanding side” and the “large expanding side” use the expanded pipe part, which is the final product, as a reference, and does not use the extent of the expanded pipe in the first eccentrically expanding step as a reference. 
         [0006]    The first eccentrically expanding step of the present invention is the step of stretching the end of the pipe to the small expanding side, whereas the second eccentrically expanding step is the step of stretching the end of the pipe to the large expanding side. 
         [0007]    2. Description of the Related Art 
         [0008]    An eccentrically expanded pipe in which an axis of an expanded pipe part is eccentric to an axis of a pipe is used for a fuel supply pipe having a filler neck. Specifically, the pipe is the fuel supply pipe body connecting to a fuel tank, and the expanded pipe part is the filler neck. For instance, in a case of the eccentrically expanded pipe (expanding rate=outer diameter of expanded pipe part/outer diameter of pipe=100) in which the expanding rate is small (around 120 percent), the pipe is set to an eccentric die with the end of the pipe projecting so as to be within the range of an inner surface of the eccentric die having an inner surface copying the outer surface of the expanded pipe part having a shape of final product, and the eccentric punch is fitted with pressure to the eccentric die to process the end to the eccentrically expanded pipe in a relatively easy manner (hereinafter referred to as “eccentrically expanding step”). In recent years, the fuel supply pipe tends to be narrow from the necessity of lighter weight and suppression of the generation of vaporized fuel, but the expanded pipe part of the pipe cannot be made small since the size of the filler neck (corresponds to the expanded pipe part) that engages with a fuel cap is standardized. Therefore, the expanding rate of the eccentrically expanded pipe becomes larger in recent years in order to satisfy above-said conflicting demands. If the expanding rate is increased, cracks and necking is produced at the expanded pipe part. Therefore, the eccentrically expanded pipe having a large expanding rate (expanding rate of around 150%) is manufactured by combining the concentrically expanding step and the eccentrically expanding step, or repeating the concentrically expanding step or the eccentrically expanding step over plural times. 
         [0009]    JP2002-102959A1 discloses a method for manufacturing an eccentrically expanded pipe comprising a concentrically expanding step and an eccentrically expanding step. According to JP2002-102959A, the concentrically expanding step (coaxially expanding step) is a step forming an end of a coaxially expanded pipe (coaxially expanded open end) where a length in an axial direction (length in a pipe axis direction) of the peripheral surface on the large expanding side (axial wall length L 2 ) is longer than the peripheral surface on the small expanding side (axial wall length L 1 ). The eccentrically expanding step is a step forming an expanded pipe part (eccentrically expanded pipe end) by forcibly inserting an eccentric punch that contacts the peripheral surface on the large expanding side earlier than the peripheral surface on the small expanding side. The manufacturing method disclosed in JP2002-102959A has a feature in that a concentric punch where a boundary between a conical tip and its punch body (cylindrical body) is inclined such that the axial length of the peripheral surface small expanding side is longer than the axial length of the peripheral surface on the large expanding side, and an eccentric punch including a conical tip and the punch body with a boundary inclined in the direction opposite to the boundary of the concentric punch are used. It is explained in the paragraph 17 of JP2002-102959 that the flow of material (metal flow) of the peripheral surface large expanding side is suppressed in the eccentrically expanding step, and the flow of material from the peripheral surface on the small expanding side to the peripheral surface on the large expanding side is promoted, so that partial reduction in wall thickness is suppressed along a circumferential direction. 
       SUMMARY OF THE INVENTION 
       [0010]    The eccentrically expanding step mainly pulls and plastically deforms the peripheral surface on the large expanding side and forms the expanded pipe part by fitting with pressure the eccentric punch to the end of the pipe or to the end already subjected to concentric expansion projecting to the range of the eccentric inner surface of the eccentric die. The plate thickness of the peripheral surface on the large expanding side tends to become thin. This becomes the cause of cracks and necking at the peripheral surface on the large expanding side of the expanded pipe part. In order to solve this problem, the manufacturing method disclosed in JP2002-102959A adopts the eccentrically expanding step of compensating for the plate thickness of the peripheral surface on the large expanding side thinned by being pulled in a bias towards the peripheral surface on the large expanding side. Specifically, the flow of material of the peripheral surface on the large expanding side is suppressed, and the flow of material from the peripheral surface on the small expanding side to the peripheral surface on the large expanding side is promoted, so that partial reduction in wall thickness is suppressed along a circumferential direction. However, what phenomenon “flow of material” specifically means is unknown, and how the plate thickness of the peripheral surface on the large expanding side is suppressed from becoming thin is unknown, and thus to what extent the cracks and the necking are suppressed is unknown. In this context, a new eccentrically expanding step is developed to prevent thinning of the plate thickness of the peripheral surface on the large expanding side that becomes the cause of cracks and necking. 
         [0011]    In the present invention, the above-said problem is solved with a method for manufacturing an eccentrically expanded pipe plastically deforming an end of a pipe to an eccentrically expanded pipe part through an eccentrically expanding step; said eccentrically expanding step includes a first eccentrically expanding step, expanding an peripheral surface of the end of the pipe opposing to a peripheral surface finally expanded to be a final product, and a second eccentrically expanding step, expanding the peripheral surface finally expanded to be the final product; in the first eccentrically expanding step, a first eccentric punch whose axis of a cylindrical body is eccentric to a small expanding side with respect to an axis of tapered portion of the first eccentric punch and whose bus on the small expanding side of the tapered portion is longer than a bus on a large expanding side, is fitted with pressure to the end, of the pipe to expand the small expanding side; and 
         [0000]    in the second eccentrically expanding step, a second eccentric punch whose axis of a cylindrical body is eccentric to the large expanding side with respect to an axis of tapered portion of the second punch and whose bus on the large expanding side of the tapered portion is longer than a bus on the small expanding side, is fitted with pressure to the end of the pipe to expand the large expanding side. 
         [0012]    Preferably, in the first eccentrically expanding step, the first eccentric punch is fitted with pressure to the end of the pipe fixed to a first eccentric die having a space defined by an inner surface on the large expanded side, an inclined inner surface on the large expanding side, an inner surface on the small expanding side, and an inclined inner surface on the small expanding side, said space copying an outer shape of the first eccentric punch; and the second eccentric punch is fitted with pressure to the end of the pipe fixed to a second eccentric die having an inner surface on the small expanding side one size larger than the outer shape of the expanded pipe part in the following second eccentrically expanding step (this manufacturing method is hereinafter referred to as “present example”). The space copying the outer shape of the first eccentric punch means that the space defined by the inner surface on the large expanded side, the inclined inner surface on the large expanding side, the inner surface on the small expanding side, and the inclined inner surface on the small expanding side is similar to the outer shape of the first eccentric punch excluding the distal end portion of the tapered portion. Actually, this space is made to a space slightly larger than the first eccentric punch to obtain a size for accommodating the first eccentric punch. The inner surface on the small expanding side one size larger than the outer shape of the expanded pipe part means that a gap is formed between the expanded pipe part of the final product after the second eccentrically expanding step and the inner surface of the small expanding side (see  FIG. 4 ). 
         [0013]    As another example (hereinafter referred to as “another example”), the eccentrically expanded pipe may be manufactured as follows. In the first eccentrically expanding step, the first eccentric punch is fitted with pressure to the end of the pipe fixed to an eccentric die having a space defined by an inner surface on the large expanding side, an inclined inner surface on the large expanding side, an inner surface on the small expanding side, and an inclined inner surface on the small expanding side, said space being one size larger than an outer shape of the expanded pipe part, which is a final product; and the second eccentric punch is fitted with pressure to the end of the pipe fixed to above-said eccentric die right after the first eccentrically expanding step in the second eccentrically expanding step. In other words, the same die, namely the eccentric die, is used in both of the two steps. The space one size larger than the outer shape of the expanded pipe part means substantially similar to the outer shape of the expanded pipe part, which is the final product, after the second eccentrically expanding step, and formed with a slight gap between the inner surface on the large expanding side of the die and the peripheral surface on the large expanding side of the pipe, as well as the inner surface on the small expanding side and the peripheral surface on the small expanding side (see  FIG. 8 ). 
         [0014]    The first eccentrically expanding step and the second eccentrically expanding step are basically performed one time each, but may be performed over plural times. In this case, it is preferable to execute the second eccentrically expanding step over plural times after a completion of the first eccentrically expanding step over plural times. It is also preferable to combine one first eccentrically expanding step and one second eccentrically expanding step, and alternately execute the first eccentrically expanding step and the second eccentrically expanding step one time each. In the first eccentrically expanding step, the end of the pipe may be directly subjected to the eccentric expansion, or the end of the pipe may be preliminary subjected to the concentric expansion before performing the first eccentrically expanding step. The former is suitable when reducing the number of steps, and the latter is suitable when increasing the expanding rate. 
         [0015]    The manufacturing method for the eccentrically expanded pipe of the present invention has features in performing the first eccentrically expanding step of bulging out the peripheral surface of the peripheral surface of the small expanding side in the radial direction before performing the second eccentrically expanding step, which corresponds to the conventional eccentrically expanding step. Similar to the prior art, the second eccentrically expanding step bulges out the large expanding side of the end of the pipe in the radial direction, and pulls the peripheral surface on large expanding side to form the expanded pipe part, and thus the peripheral surface on the large expanding side is pulled and the plate thickness is thinned. In the first eccentrically expanding step, the peripheral surface of the small expanding side of the end of the pipe is bulged out in the radial direction to pull the small expanding side peripheral surface at an expanding rate lower than in the second eccentrically expanding step, to thereby form the end of the pipe made eccentric in the opposite direction as the product. This suppresses only the plate thickness of the peripheral surface on the large expanding side from becoming thin, and has a function of earning the expanding rate by pulling the peripheral surface on the small expanding side. Therefore, the peripheral surface on the large expanding side pulled in the second eccentrically expanding step is suppressed from becoming too thin, whereby production of cracks and necking are prevented. 
         [0016]    In the manufacturing method (present example), the first eccentric die and the first eccentric punch are used in the first eccentrically expanding step to bulge out the peripheral surface on the small expanding side and to once make the axis of the end of the pipe eccentric to the small expanding side. In this case, the plate is pulled on the small expanding side, and the peripheral surface on the small expanding side is stretched thin. In the following second eccentrically expanding step, the second eccentric die and the second eccentric punch are used to bulge out the peripheral surface on the large expanding side and to make the axis of the end of the pipe eccentric to the large expanding side. In other words, the axis once shifted to the small expanding side shifts to the large expanding side over the axis of the pipe through the second eccentrically expanding step. By the second eccentrically expanding step, the plate thickness of the large expanding side is also stretched, as a result, the plate thickness of the peripheral surface on the small expanding side and the peripheral surface of the large expanding side become even. When the first eccentric die is used in the first eccentrically expanding step, the large expanding side of the pipe is set in contact with the inner surface on the large expanding side of the second eccentric die, and thus the shift of the axis of the pipe to the large expanding side is restricted by such contact (see  FIG. 1 ). 
         [0017]    As another example, in the first eccentrically expanding step, an eccentric die having a space defined by an inner surface on the large expanding side, an inclined inner surface on the large expanding side, an inner surface on the small expanding side and an inclined inner surface on the small expanding side, the space being one size larger than the outer shape of the expanded pipe part, which is a final product, may be used. In other words, the same eccentric die is used in both steps, the first eccentrically expanding step and the second eccentrically expanding step. With the end of the pipe projected so as to be in the range of the inner surface on the small expanding side of the eccentric die in the first eccentrically expanding step preceding the second eccentrically expanding step, the first eccentric punch made eccentric to the small expanding side than the large expanding side is fitted with pressure to the end of the pipe to perform eccentric expansion on the small expanding side. In the first eccentrically expanding step, a gap is formed between the peripheral surface on the large expanding side of the pipe and the inner surface on the large expanding side of the die (see  FIG. 5 ), and thus the axis of the end of the pipe fitted with pressure with the first eccentric punch is made eccentric to the large expanding side. When the first eccentric punch is fitted deeper into the pipe with pressure, the plate of the peripheral surface on the small expanding side is gradually stretched, and the plate thickness of the peripheral surface on the small expanding side is processed thin. In this case, the plate thickness of the peripheral surface on the large expanding side is barely changed. In the following second eccentrically expanding step, the second eccentric punch is fitted with pressure to stretch and thin the plate of the peripheral surface on the large expanding side and obtain the evenly expanded pipe part. In the second eccentrically expanding step, the plate thickness of the small expanding side peripheral surface is barely changed. Therefore, according to the manufacturing method of another example, the expanded pipe part in which the plates of the peripheral surface on the large expanding side and the peripheral surface on the small expanding side are evenly stretched is formed through two steps, namely the first eccentrically expanding step and the second eccentrically expanding step. The axis of the end of the pipe moves to large expanding side in both steps. 
         [0018]    The manufacturing method for the eccentrically expanded pipe according to the present invention is advantageous in that the method can increase the expanding rate of the eccentrically expanded pipe without producing cracks and necking of the eccentrically expanded pipe. This is the effect of the procedure of dividing the eccentrically expanded pipe step into the first eccentrically expanding step and the second eccentrically expanding step, earning the expanding rate by pulling the peripheral surface on the small expanding side while suppressing the plate thickness of the peripheral surface on the large expanding side from becoming thin in the first eccentrically expanding step, and then finally eccentrically expanding the pipe by pulling peripheral surface on the large expanding side in the second eccentrically expanding step. 
         [0019]    If the pulling of the peripheral surface on the small expanding side in the first eccentrically expanding step and the pulling of the peripheral surface on large expanding side in the second eccentrically expanding step are the same extent, the plate thickness of the expanded pipe part of the eccentrically expanded pipe according to the present invention becomes substantially even in the circumferential direction. This means that the amount of plastic deformation with respect to the circumferential direction of the small expanding side and the large expanding side at the end of the pipe is substantially equal and the end face of the pipe become straight (see  FIGS. 4 and 8 ). According to a conventional eccentric expansion, the end of the pipe undergone the conventional eccentrically expansion inevitably became inclined. Therefore, wasted materials derived from cut pipes were produced since the end of the pipe were cut and made straight. Contrast to this, the present invention is advantageous in that such wasted materials are not produced since the end of the pipe is manufactured to be straight without cutting it, as explained above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a cross-sectional view illustrating an end of a pipe in a first eccentric die before starting a first eccentrically expanding step of the present example; 
           [0021]      FIG. 2  is a cross-sectional view illustrating the end of the pipe in the first eccentric die after the first eccentrically expanding step of the present example; 
           [0022]      FIG. 3  is a cross-sectional view illustrating the end of the pipe in a second eccentric die before starting a second eccentrically expanding step of the present example; 
           [0023]      FIG. 4  is a cross-sectional view illustrating an expanded pipe part in the second eccentric die after the second eccentrically expanding step of the present example; 
           [0024]      FIG. 5  is a cross-sectional view illustrating the end of the pipe in an eccentric die before starting the first eccentrically expanding step of another example; 
           [0025]      FIG. 6  is a cross-sectional view illustrating the end of the pipe in the eccentric die after the first eccentrically expanding step of another example; 
           [0026]      FIG. 7  is a cross-sectional view illustrating the end of the pipe in the eccentric die before starting the second eccentrically expanding step of another example; 
           [0027]      FIG. 8  is a cross-sectional view illustrating the expanded pipe part in the eccentric die after the second eccentrically expanding step of another example; 
           [0028]      FIG. 9  is a view illustrating a first eccentric punch of  FIGS. 1 and 5  in an enlarged manner; and 
           [0029]      FIG. 10  is a view illustrating a second eccentric punch of  FIGS. 3 and 7  in an enlarged manner. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    Embodiments of the present invention will be described with reference to the drawings.  FIGS. 1 to 4  illustrate an example (present example) of a manufacturing method using a first eccentric die  31  in a first eccentrically expanding step, and a second eccentric die  41  in a second eccentrically expanding step. Specifically,  FIG. 1  is a cross-sectional view illustrating an end  11  of a pipe  1  in the first eccentric die  31  before starting the first eccentrically expanding step of the present example,  FIG. 2  is a cross-sectional view illustrating the end  11  of the pipe  1  in the first eccentric die  31  after the first eccentrically expanding step of the present example,  FIG. 3  is a cross-sectional view illustrating the end  11  of the pipe  1  in the second eccentric die  41  before starting the second eccentrically expanding step of the present example, and  FIG. 4  is a cross-sectional view illustrating an expanded pipe part  2  in the second eccentric die  41  after the second eccentrically expanding step of the present example. In this example, the first eccentrically expanding step and the second eccentrically expanding step are performed in order on the end  11  subjected to the concentrically expanding step in advance in an aim of earning the expanding rate.  FIG. 9  is a view illustrating a first eccentric punch of  FIG. 1  in an enlarged manner.  FIG. 10  is a view illustrating a second eccentric punch of  FIG. 3  in an enlarged manner. 
         [0031]    As described above, the method for manufacturing the eccentrically expanded pipe of the present invention has a feature in mainly bulging out a peripheral surface on the small expanding side  21  through the first eccentrically expanding step preceding the second eccentrically expanding step corresponding to the conventional eccentrically expanding step. Specifically, as illustrated in  FIGS. 1  and  9 , the first eccentric punch  32  made eccentric to the small expanding side with respect to an axis of a tapered portion  321  of the punch than the large expanding side is fitted with pressure to the end  11  of the pipe  1 , with the end  11  of the pipe  1 , which is subjected to the concentric expanding processing in advance to earn the expanding rate, projecting to be in a range of an inner surface on the small expanding side  311  of the first eccentric die  31 , and as illustrated in  FIG. 2 , an axis Om of the end  11  is made eccentric to the small expanding side with respect to an axis Oo of the pipe  1  to greatly bulge out the peripheral surface on the small expanding side  21  and stretch the plate of the peripheral surface on the small expanding side  21 . In this case, the peripheral surface on the large expanding side  22  is brought into contact with an inner surface on the large expanding side  312  of the first eccentric die  31 , and thus the axis is not made eccentric to the large expanding side and the axis become eccentric to the small expanding side. 
         [0032]    The first eccentric punch  32  used in the first eccentrically expanding step has a bus of a tapered portion  321  set long on the small expanding side (see L 2  of  FIG. 9 ) and a bus of the tapered portion  321  set short on the large expanding side (see L 1  of  FIG. 9 ) to allow the peripheral surface on the small expanding side  21  to bulge out. Therefore, an intermediate portion  12  of the pipe  1  expanded by the first eccentric punch  32  becomes a tapered portion having a long bus on the small expanding side and a short bus on the large expanding side copying the tapered portion  321  of the first eccentric punch  32  (see  FIG. 2 ), where an boundary edge  23  is inclined to diagonally right such that the bus on the small expanding side of the intermediate portion  12  of the pipe  1  becomes long while maintaining an boundary edge  13 , separating pipe  1  portion from the intermediate portion  12 , to a circle equal to an outer diameter of the pipe  1 . This means that the peripheral surface on the small expanding side  21  is pulled and stretched, where an end face  14  of the end  11  after the first eccentrically expanding step is inclined opposite to the boundary edge  23 , that is, to diagonally left. The peripheral surface on the small expanding side  21  of the end of the pipe  1  is stretched (plate thickness is thinned) by the first eccentrically expanding step, thereby earning the expanding rate. Since the plate thickness of the peripheral surface on the large expanding side  22  does not change (not thinned) in the first eccentrically expanding step, the target expanding rate can be achieved through stretching the large expanding side (thinning the plate thickness) of the pipe  1  in the following second eccentrically expanding step. 
         [0033]    The first eccentric punch  32  used in the present invention will now be described with reference to  FIG. 9 . The length of the buses of the first eccentric punch  32  of the present invention is preferably L 1 &lt;L 2 . In this embodiment L 1  is 27.9 mm and L 2  is 54.5 mm. If the angle (θ 1 +θ 2 ) of the tip of the tapered portion  321  of the first eccentric punch  32  is too small, the overall compression of the pipe  1  in the axial direction becomes small, whereas if the angle is too large, the pipe  1  tends to easily buckle in the axial direction. In this context the angle of the tip is preferably around 15 to 55°. In the present example, θ 1 +θ 2 =51.9°. The first eccentric punch  32  of the present invention has a feature in that the axis of the cylindrical body of the first eccentric punch is made eccentric to the small expanding side (downward direction in  FIG. 9 ) with respect to the axis of the tapered portion  321  of the punch, where an extent of eccentricity (δ 1 ) of an axis line of the tapered portion  321  of the first eccentric punch  32  and an axis line of the cylindrical body  322  in the present example is δ 1 =5 mm. The present example is designed to achieve θ 1 =θ 2 , α 1 =α 2  (α 1  and α 2  are angles at the boundary of the cylindrical body  322  and the apered portion  321 ). In the present example, α 1 =α 2 =154°. In the present example, the first eccentric punch  32  in which the diameter of the cylindrical body  322  is 43.3 mm with respect to the pipe  1  of 35.7 mm is used. The change in expanding rate in this case is +21%. 
         [0034]    The first eccentric die  31  used in the present invention will now be described with reference to  FIG. 1 . The first eccentric die  31  of the present invention is designed so that a inner surface on the large expanding side  312  of the first eccentric die  31  and the peripheral surface on the large expanding side  22  of the pipe  1  contact when the pipe  1  subjected to concentric expanding processing is mounted on the die  31 . The inner surface on the small expanding side  311  of the first eccentric die  31  is designed so that a gap forms between the inner surface on the small expanding side  311  and the peripheral surface on the small expanding side  21  when the pipe  1  subjected to concentric expanding processing is mounted on the die  31 . This gap becomes a space for the peripheral surface on the small expanding side  21  to expand the pipe to the small expanding side when the first eccentric punch  32  is fitted with pressure in the first eccentrically expanding step. The space defined by the inner surface on the small expanding side  311 , the inner surface on the large expanding side  312 , an inclined inner surface on the small expanding side  313 , and an inclined inner surface on the large expanding side  314  is formed to a shape copying the outer shape of the first eccentric punch  32 . Therefore, since the shape copies the outer shape of the first eccentric punch  32 , the length in the axial direction of inclined inner surface on the small expanding side  313  becomes longer than the length in the axial direction of the pipe  1  of the inclined inner surface on the large expanding side  314 . 
         [0035]    As illustrated in  FIG. 3 , the end  11  of the pipe  1  after the first eccentrically expanding step is fitted with pressure with the second eccentric punch  42 . The second eccentric punch  42  is eccentric to the large expanding side than the small expanding side (the axis of the punch  42  is eccentric to large expanding side in view of the axis of the tapered portion  421 ). The second eccentric punch  42  is fitted with pressure to the end  11  of the pipe  1  fixed on the second eccentric die  41  in the state that the end  11  of the pipe  1  projects to a range of a inner surface on the small expanding side  411 . As illustrated in  FIG. 3  and  FIG. 4 , by fitting the second eccentric punch  42  to the end  11  on the die  41 , the axis Om of the end  11  shift to the axis Oe over the axis Oo of the pipe  1  to greatly bulge out the peripheral surface on the large expanding side  22 , and achieve the target expanding rate. The end  11  after the second eccentrically expanding step becomes the expanded pipe part  2  as a product. The plate thickness of the peripheral surface on the small expanding side  21  is barely changed in the second eccentrically expanding step, but the plate thickness of the peripheral surface on the large expanding side  22  is stretched and thinned. Consequently, the eccentrically expanded pipe having equal plate thickness in circumferential direction is obtained. The shift of the axis (Om to Oe) is realized through a plastic deformation of the pipe  1  which causes the end  11  relatively projecting to the small expanding side to project to the large expanding side. 
         [0036]    The pipe  1  after the first eccentrically expanding step has a shape in which the peripheral surface on the small expanding side  21  is greatly bulged out than the peripheral surface on the large expanding side  22 , as described above. Therefore, when such a deformed pipe  1  is inserted to the second eccentric die  41 , the boundary edge  23  interferes with the inner surface on the small expanding side  411  of the second eccentric die  41 , and the pipe  1  bends to the large expanding side, as illustrated in  FIG. 3 . In this case, the periphery of the intermediate portion  12  on the large expanding side  12  bends so that the plate thickness increases, which becomes the stretch amount of when the intermediate portion  12  on the large expanding side is stretched in the following second eccentrically expanding step. The first eccentrically expanding step of bending the end  11  acts to further reinforce the effect of the present invention and contributes to preventing production of cracks and necking at the expanded pipe part  2 . As to the length of the end  11 , the length of the peripheral surface on the small expanding side  21  executed the first eccentrically expanding step is compressed in the axial direction as illustrated in the  FIG. 2 . In the following second eccentrically expanding step, the length of the peripheral surface on the large expanding side  22  is also compressed as illustrated in the  FIG. 4 . As a result, the thickness of the end  11  is prevented from being uneven, especially, plate thickness of the peripheral surface on the large expanding side  22  is prevented from being thin. The present invention suppresses biased reduction of plate thickness by cancelling out the biased pulling and the biased axial compression of the small expanding side and the large expanding side by combining the first eccentrically expanding step and the second eccentrically expanding step. 
         [0037]    The second eccentric punch  42  used in the second eccentrically expanding step has a bus on the large expanding side of a tapered portion  421  set long (see L 4  of  FIG. 10 ) and a bus on the small expanding side set short (see L 3  of  FIG. 10 ) to allow the peripheral, surface on the large expanding side  22  to bulge out. Therefore, the intermediate portion  12  of the pipe  1  connecting the pipe  1  and the end  11  becomes a tapered portion having a long bus on the large expanding side and a short bus on the small expanding side copying the tapered portion  421  of the second eccentric punch  42 , where the boundary edge  23  is inclined to diagonally left such that the bus on the large expanding side becomes long while maintaining the boundary edge  13  separating the pipe  1  from the intermediate portion  12  to a circle equal to the outer diameter of the pipe  1 . This means that the peripheral surface on the large expanding side  22  is pulled and stretched, where the end face  14  of the expanded pipe part  2  formed after the second eccentrically expanding step again returns to an orientation orthogonal to the axis center Oe from the inclined orientation. 
         [0038]    The length of the buses of the second eccentric punch  42  is L 3 &lt;L 4  (see  FIG. 10 ), where the eccentrically expanded pipe in which the peripheral surface on the large expanding side  22  and the peripheral surface on the small expanding side  21  are equally stretched can be manufactured by using the second eccentric punch  42  in which the short and long (L 1 , L 2 ) of the bus on the large expanding side and the bus on the small expanding side of the tapered portion  321  of the first eccentric punch  32  are switched between the large expanding side and the small expanding side. Furthermore, since the second eccentric punch  42  is molded to an outer shape copying the outer shape of the expanded pipe part  2 , which is the final product, punching should be performed in the order of the first eccentric punch  32  and the second eccentric punch  42 . In the present example, L 3 =20.4 mm and L 4 =47.1 mm. The extent of eccentricity (δ 2 ) between an axis line of a tapered portion  421  of the second eccentric punch  42  and an axis line of the cylindrical body  422  is δ 2 =6 mm. In the second eccentric punch  42 , α 3 =α 4  and θ 3 =θ 4 . More specifically, in the case of the present example, θ 3 +θ 4 =48.7°, and α 3 =α 4 =155.7°. Furthermore, in the present example, the second eccentric punch  42  in which diameter of the cylindrical body of the punch is 47.5 mm with respect to the end (43.3 mm) of the pipe  1  expanded by the first eccentrically expanding step is used. The change in expanding rate in this case is +10%. θ 3 +θ 4  is desirably between 15 and 55°, similar to the first eccentric punch  32 . 
         [0039]    The second eccentric die  41  of the present example has a an inner surface on the large expanding side  412  and an inclined inner surface on the large expanding side  414  copying the outer shape of the peripheral surface on the large expanding side  22  of the expanded pipe part  2 , which is the final product. On the other hand, an inner surface on the small expanding side  411  and an inclined inner surface on the small expanding side  413  are formed to a shape one size larger than the outer shape of the peripheral surface on the small expanding side  21  of each expanded pipe part  2  which is the final product, and a gap is formed between the peripheral surface on the small expanding side  21  and inner surface on the small expanding side  411  after the second eccentrically expanding step as in  FIG. 4 . As illustrated in  FIG. 3 , the second eccentric die  41  of the present example is formed so that redundant space is formed on the small expanding side. This space functions as a space for preventing the pipe  1  from being excessively bent when inserting the pipe  1 , having the peripheral surface on the small expanding side  21  greatly bulged out, to the second eccentric die  41 . 
         [0040]      FIG. 5 to 8  illustrate an example (another example) of a manufacturing method using an eccentric die  51  in both the first eccentrically expanding step and the second eccentrically expanding step. Specifically,  FIG. 5  is a cross-sectional view illustrating the end  11  of the pipe  1  in the eccentric die  51  before starting the first eccentrically expanding step of another example,  FIG. 6  is a cross-sectional view illustrating the end  11  of the pipe  1  in the eccentric die  51  after the first eccentrically expanding step of another example,  FIG. 7  is a cross-sectional view illustrating the end  11  of the pipe  1  in the eccentric die  51  before starting the second eccentrically expanding step of another example, and  FIG. 8  is a cross-sectional view illustrating the expanded pipe part  2  in the eccentric die  51  after the second eccentrically expanding step of another example. In another example, the first eccentrically expanding step and the second eccentrically expanding step are performed in order on the end  11  subjected to the concentrically expanding step in advance in an aim of earning the expanding rate, similar to the above described example (present example, see  FIG. 1 to 4 ). The first eccentric punch  32  and the second eccentric punch  42  similar to those in the above-described example (present example, see  FIGS. 1 to 4 ) are used. 
         [0041]    In the present invention, the peripheral surface on the small expanding side  21  is first relatively bulged out than the peripheral surface on the large expanding side  22  to reduce the plate thickness of the peripheral surface on the small expanding side  21 , and then the peripheral surface on the large expanding side  22  is relatively bulged out than the peripheral surface on the small expanding side  21  to thinly stretch and reduce the plate thickness of the peripheral surface on the large expanding side  22 . Also in another example of this invention, the first eccentrically expanding step is relatively bulging out the peripheral surface on the small expanding side  21  than the peripheral surface on the large expanding side  22 , and the second eccentrically expanding step is relatively bulging out the peripheral surface on the large expanding side  22  than the peripheral surface on the small expanding side  21 . In another example, axis of the end  11  of the pipe  1  firstly shifts to the large expanded side (Om as represented in the  FIG. 6 ) through the first eccentrically expanding step, and then shifts to the large expanded side again (Oe as represented in the  FIG. 8 ) through the second eccentrically expanding step. Specifically, as illustrated in  FIG. 5 , the first eccentric punch  32  made eccentric to the small expanding side than the large expanding side with respect to the axis of the tapered portion  321  is fitted with pressure to the end  11  of the pipe  1 . The end  11  of the pipe  1  was subjected to concentric expanding processing in advance to earn the expanding rate in this example. The pipe  1  is set to the second eccentric die so that the end  11  projects to the range of an inner surface on the small expanding side  511  of the eccentric die  51 . As illustrated in  FIG. 6 , the peripheral surface on the small expanding side  21  is greatly bulged out while making the axis Om of the end  11  eccentric to the large expanding side with respect to the axis Oo of the pipe  1 . 
         [0042]    In order to implement the manufacturing method for another example, the eccentric die  51  is used in both steps, namely the first eccentrically expanding step and the second eccentrically expanding step. When the pipe  1  is set in the eccentric die  51 , a gap forms between the peripheral surface on the large expanding side  22  and an inner surface on the large expanding side  512  of the eccentric die  51  as illustrated in  FIG. 5 . When the first eccentric punch  32  is fitted with pressure to the end face  14  of the pipe in this state, the peripheral surface on the small expanding side  21  can be bulged out while making the axis eccentric to the large expanding side. In other words, since the bulging out of the peripheral surface on the large expanding side  22  is not restricted by the inner surface on the large expanding side  512  of the eccentric die  51  as in the case of the pipe  1  being set in the first eccentric die  31  illustrated in  FIG. 1 , the axis is made eccentric to the large expanding side. 
         [0043]    In another example, following eccentric die  51  is used. That is the die having a large gap formed between the inner surface on the large expanding side  512  of the die  51  and the peripheral surface  22  on the large expanding side of the end  11  when the pipe  1  is installed on the die  51  ( FIG. 5 ). The eccentric die  51  has an inner surface defined by the inner surface on the large expanding side  512 , an inclined inner surface on the large expanding side  513 , an inclined inner surface on the small expanding side  514 , and the inner surface on the small expanding side  511 . The defined space is similar to the shape of the expanded pipe part  2  of the final product, and has a shape slightly larger (about one size larger) than the expanded pipe part  2 . As illustrated in the  FIG. 8 , a thin gap are formed between the expanded pipe part  2  and inner surface of the die  51  (the inner surface on the large expanding side  512  and the inner surface on the small expanding side  511 ) after the second eccentrically expanding step. Since the end  11  bulges out to the small expanding side without contacting the peripheral surface on the small expanding side  21  to the inner surface on the small expanding side  511  and the inclined inner surface on the small expanding side  514  in the first eccentrically expanding step of the another example, a bend boundary edge  24  formed at the intermediate portion  12  becomes a baggy shape (illustrated in  FIG. 6 ) However, such bagginess does not arise any problems as it is pushed and stretched by the second eccentric punch  42  in the following second eccentrically expanding step. Since the common eccentric die  51  is used in the first eccentrically expanding step and the second eccentrically expanding step in another example, the manufacturing cost of the die is reduced, and furthermore, the end  11  does not need to be re-inserted in another die in the second eccentrically expanding step (the second eccentrically expanding step). Therefore, the process can proceed to the second eccentrically expanding step immediately right after the termination of the first eccentrically expanding step. 
         [0044]    Right after the termination of the first eccentrically expanding step, the second eccentric punch  42  made eccentric to the large expanding side than the small expanding side with respect to the axis of the tapered portion  421  is fitted with pressure to the end  11  of the pipe ( FIGS. 7 and 8 ). The end  11  of pipe  1  projects to the range of the inner surface on the small expanding side  511  of the eccentric die  51 ; and as illustrated in  FIG. 8 , the peripheral surface on the large expanding side  22  is greatly bulged out to form the expanded pipe part  2  while making the axis Om of the end  11  eccentric to the large expanding side with respect to the axis Oo of the pipe  1 . The eccentric direction (the direction in which the axis of the end  11  shifts) of the axis Om of the end  11  during the first eccentrically expanding step and that of the axis Oe of the end  11  during the second eccentrically expanding step is identical (toward the large expanded side) in another example, but the eccentric amount does not always same. Although the axis Oe of the expanded pipe part  2  become eccentric toward the large expanding side in the second eccentrically expanding step, the amount of axis shift is rather small, because the axis of the end  2  of the pipe  1  already became eccentric toward the large expanding side in the first eccentrically expanding step (shifted from the position of Oo to Om). The manufacturing method of the another example stretches the plate of the peripheral surface on the small expanding side  21  in the first eccentrically expanding step to earn the expanding rate, and stretches the plate of the peripheral surface on the large expanding side  22  in the following second eccentrically expanding step to achieve the target expanding rate. Since the small expanding side and the large expanding side are expanded in two steps, biased reduction in plate thickness is suppressed, and production of cracks and necking at the expanded pipe part  2  is prevented. 
       EXAMPLES 
       [0045]    In order to verify a validity of this invention, variation of thickness of the expanded pipe part was measured at the three point (terminal portion A, middle portion B and edge portion C, see  FIG. 11 ). The result of the measurement was summarized in the following table. Plate thickness of the original pipe, which meant a pipe not undergone any expanding procedures, was set at 100%. The measurement was conducted on the large expanding side and the small expanding side. In the table, Example 1 indicates result of the eccentrically expanded pipe part which was formed through the present example of this invention. Example 2 indicates result of the eccentrically expanded pipe part which was formed through another example of this invention. Comparison 1 indicates the result of the eccentrically expanded pipe part which was formed using an ordinal method to form eccentrically expanded pipes. The ordinal method was to expand end of pipe eccentrically by inserting a known eccentric punchs, whose axis is eccentric to the large expanding side, into the end of pipe two times, thereby forming an eccentrically expanded pipe. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Variation of thickness (%) 
                 A 
                 B 
                 C 
                 Average 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Example 1 
                 Large expanding 
                 91.5% 
                 91.3% 
                 85.2% 
                 89.3% 
               
               
                   
                 side 
               
               
                   
                 Small expanding 
                 83.2% 
                 90.1% 
                 90.6% 
                 88.0% 
               
               
                   
                 side 
               
               
                 Example 2 
                 Large expanding 
                 102.3% 
                 86.0% 
                 83.8% 
                 90.7% 
               
               
                   
                 side 
               
               
                   
                 Small expanding 
                 83.6% 
                 96.1% 
                 92.3% 
                 90.7% 
               
               
                   
                 side 
               
               
                 Comparison 
                 Large expanding 
                 69.3% 
                 68.3% 
                 69.9% 
                 69.2% 
               
               
                   
                 side 
               
               
                   
                 Small expanding 
                 107.0% 
                 106.1% 
                 106.8% 
                 106.6% 
               
               
                   
                 side 
               
               
                   
               
             
          
         
       
     
         [0046]    It was verified that the eccentrically expanded pipe manufactured through this invention (Example 1 and 2) has the evenly expanded pipe (average expanding rate of Example 2 is equal on the large expanding side and small expanding side, 90.7% and that of Example 1 was nearly equal on the large expanding side and small expanding side, 89.3% and 88.0%). Contrast to this, the, eccentrically expanded pipe manufactured through the ordinal method (Comparison) was the unevenly expanded. Particularly, significant difference was observed at the edge portion C. The variation of plate thickness at the edge portion C of Example 1 was 85.2% on the large expanded side and 90.6% on the small expanding side. That of Example 2 was 83.8% on the large expanding side and 92.3% on the small expanding side. Contrast to this, that of the large expanding side was 69.9% and that of the small expanding side was 106.8%.