Patent Publication Number: US-6983770-B2

Title: Method of manufacturing pipe body and pipe body manufactured by the method

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is a continuation of applicants&#39; application Ser. No. 09/776,119, filed Feb. 2, 2001, now U.S. Pat. No. 6,601,427. 

   TECHNICAL FIELD 
   The present invention relates to manufacture a pipe body by performing a bending operation on a metal plate. 
   BACKGROUND OF THE INVENTION 
   Conventionally, there is disclosed a technique by which a pipe body, for example, a prism pipe body is made by bending a metal plate, such as in Japanese Patent Laid-Open No. Hei 11-290940. 
   In Japanese Patent Laid-Open No. Hei 11-290940, a prism pipe body is manufactured by using a rectangular metal plate as a material by means of pressing. 
   The method of manufacturing prism pipe body includes a first bending step, a second bending step, and a re-striking step. In the first bending step, a primary intermediate product is formed of a metal plate. In the second bending step, the primary intermediate product is processed to form a secondary intermediate product. In the re-striking step, the secondary intermediate product is processed to form a prism pipe body as a final product. 
   In the first bending step, both width direction sides of the metal plate are bent at the right angle in length direction. Accordingly, the primary intermediate product which includes flanges and a bottom plate is formed. The flanges face to each other. The bottom plate connects the flanges to each other. 
   In the second bending step, a concave surface having a predetermined width is formed on the bottom plate of the primary intermediate product lengthwise, and at the same time, both ends of the concave surface is bent at the right angle to inside. Accordingly, the secondary intermediate product is formed. The secondary intermediate product includes a pair of side walls which facing to each other. The cross section of the secondary intermediate product is U shape. 
   In the re-striking step, edges of a pair of flanges (seam) are contacted together by pressing a pair of side walls of the secondary intermediate product inside. Accordingly, a prism pipe body as a final product is formed. 
   According to this method of manufacturing the prism pipe body, the concave surface which is formed on bottom plate of secondary intermediate product, has a function to restrict a spring back force generated by pressing the pair of side walls together to inside. Accordingly a prism pipe body with square cross section, in which edges of the flanges closely contact together, can be manufactured only by pressing without welding edges of the flanges. 
   PROBLEMS TO BE SOLVED 
   However, in this conventional method of manufacturing prism pipe body, even though the concave surface of secondary intermediate product has a function to restrict spring back force, spring back force which tends to open to outside still remains at the pair of side walls. Accordingly, it is difficult to stably manufacture without deflection the prism pipe body whose edges of flange (wall including the seam) closely contacts for mass production. 
   When testing a prism pipe body manufactured by the conventional working method, if edges of flanges are contacted each other or not, some are closely contacted each other, but many of them have gaps in the seam due to the spring back force appearing at the pair of side walls. 
   It is an object of the present invention to solve the above mentioned problems and to provide an method of manufacturing pipe body and pipe body manufactured by the method having capability of manufacturing pipe body stably without deflection in which a seam is tightly contacted by pressing when mass production the pipe body. 
   SUMMARY OF THE INVENTION 
   In order to achieve the above objects, according to one aspect of the present invention, a method of manufacturing a metal pipe body by bending a flat metal plate at predetermined angles, comprising the steps of: bending a portion near at least one end of the plate along an axis of the completed metal pipe body so as to have a predetermined angle of a corner of the completed metal pipe body; bending the same side as said bent portion of said metal plate at points which correspond to some integer times of one side of the completed metal pipe body in the same bending direction as said bent portion along the axis of completed metal pipe with an angle more than said predetermined angle; making one of the portion made by said second bending, concave toward the center of completed metal pipe body; pressing portions including edges of the plate towards the center of completed metal pipe body along the bottom surface of said portions including edges so as for said edges to get close contact and at the same time modifying said angles more than the predetermined angle into said predetermined angle; generating a modifying operation of said concave portion into convex form toward outside against center of the completed metal pipe accompanied with said angle modifying operation; accumulating inner stress for said concave portions tending back to said convex form through said modifying operation by making said concave portions flat thereby making a close contacting operation of said portions including edges by operation for all sides other than said convex portion and portions including edges enforcing towards the center of completed metal pipe; and maintaining said edges contacting together and said originally concave portion flat, is provided. 
   According to another aspect of the present invention, a method of manufacturing a metal pipe body by bending a flat metal plate at an angle, comprising the steps of: bending a portion of the flat metal plate near at least one end of the flat metal plate along an axis of the completed metal pipe body so as to have a predetermined angle of a corner of the completed metal pipe body; bending the same side as said bent portion of said metal plate at points which correspond to some integer times of one side of the completed metal pipe body in the same bending direction as said bent portion along the axis to be completed metal pipe with an obtuse angle more than said predetermined angle; making one of the portion made by said second bending, concave toward the center portion of completed metal pipe body; pressing portions including edges of the plate towards center of the completed metal pipe body along the bottom surface of said portions including edges so as to get close contact of said edges and at the same time modifying said angles more than predetermined angle into said predetermined angle; modifying said concave portion into convex form toward outside against center of the completed metal pipe accompanied with said angle modifying operation; modifying said convex portion into flat by pressing said bottom surface and the surface facing to said surface with convex form towards center of completed metal pipe body with said portions including edges contacting together; accumulating inner stress for said concave portions tending back to said convex form through said modifying operation by making said concave portions flat thereby making a close contacting operation of said portions including edges; and maintaining said edges contacting together and said originally concave portion flat, is provided. 
   According to other aspect of the present invention, a method of manufacturing pipe body having a seam and circular shaped cross section made of a rectangular metal plate, comprising the steps of: by bending said metal plate, forming a curved pipe-like intermediate product of oval-like cross section in which a pair of edges of said metal plate to be a seam of said pipe is still not contacted and located at one end of longer axis of said oval and extending along the axis of the completed pipe; and modifying the curved intermediate product by applying a force along the longer axis of said oval so as to force said edges contacted tightly with spring back force tending to return to the original oval shape, is provided. 
   According to still other aspect of the present invention, a method for manufacturing pipe body having a seam and polygonal cross section made of a rectangular metal plate, comprising the steps of: by bending said plate at plurality of points along its edge direction, forming a pipe-like intermediate product in which a pair of edges of said metal plate to be a seam of said pipe are still not contacted together and both end angles of one specified wall are greater than the predetermined value for angle of the completed pipe; making said pair of edges close contact by forcing said one specified wall convex to outside; and modifying convex said one specified wall flat so as to force said edges contacted tightly with spring back force tending to return to the convex shape, is provided. 
   The above stated methods makes possible to manufacture either a prism or cylindrical pipe body made of metal plate with the polygonal or circular cross section in which the seam of plate edges is closely contacted by aggressively utilizing a force which the convex and concave surface tend to return to the original shapes. 
   According to still other aspect of the present invention, a method for manufacturing pipe body having a seam and polygonal cross section made of a rectangular metal plate, comprising the steps of: a first processing step of forming a seam including wall by standing at least one portion of a pair of edges of said metal plate along its edge direction; a second processing step of forming remaining walls other than said seam including wall and making a pipe-like intermediate product in which a pair of edges of said metal plate to be a seam of said pipe are still not contacted and both end angles of one specified wall are greater than the predetermined value for angle of the completed pipe; a third processing step of making said pair of edges close contact by forcing said one specified wall convex to outside; and a fourth processing step of modifying convex said one specified wall flat so as to force said edges contacted tightly with spring back force tending to return to the convex shape, is provided. 
   The method makes it possible that a primary intermediate product having a wall including seam is formed at the first processing step, and a secondary intermediate product having remaining walls other than the wall including seam is formed at the second processing step, and by using the secondary intermediate product, pipe bodies having various shapes are formed. 
   According to still other aspect of the present invention, a pipe body having a seam and polygonal cross section made of rectangular metal plate, characterized by: being made through a pipe-like intermediate product prepared by bending said plate at plurality of points along its edge direction, in which a pair of edges of said metal plate to be a seam of said pipe is still not contacted and both end angles of one specified wall are greater than the predetermined value for angle of the completed pipe; and said pair of edges are closely contacted by forcing said one specified wall convex to outside and convex said one specified wall are flat so as to force said edges contacted tightly with spring back force tending to return to the convex shape, is provided. 
   By the above stated pipe body according to present invention, it is possible to make the seam closely contacted together without welding. 
   The seam may be located at the center of the wall including seam. And, the seam may be located between the wall including seam and adjoining wall. Further, the seam may be located at the center of three walls. 
   Moreover, according to the method, it is possible to manufacture a pipe body whose shape of cross section is triangle, pentagonal, hexagon, or octagon shape. 
   Preferably, the one specified wall comprises a flat portion and a curved portion. When the curved portion is formed between the adjoining wall and the flat portion and the curved convex surface is modified to be flat, flatness of it can be ensured. 
   In the method of manufacturing pipe body, it is more preferable to use the pipe body having a cross section of a rectangle shape, and it is also preferable that an angle between the one specified wall and the adjoining wall of the intermediate product is an obtuse angle when forming a curved convex surface. 
   When the cross section of the pipe body is rectangular, it is preferable that defining each of the walls of the pipe body as a bottom wall, a pair of side walls adjacent to the bottom wall and a upper wall facing to the bottom wall, and the seam is formed on the upper wall. 
   Preferably, the metal plate includes engaging concave portion such as tapped holes or notch for installation previously formed on the wall in order to use the pipe body as a supporting member for, image forming apparatus, such as copy machine, for example, without further work after assembling. 
   Preferably, a forming process of the pipe body is performed under consideration of extension when bending the metal plate. 
   According to still other aspect of the present invention, a pipe body having a seam and circular cross section made of rectangular metal plate, characterized by: being made through a curved pipe-like intermediate product of oval-like cross section made by bending said metal plate in which a pair of edges of said metal plate to be a seam of said pipe is still not contacted and located at one end of longer axis of said oval and extending along the axis of the completed pipe; and formed by modifying the curved intermediate product by applying a force along the longer axis of said oval so as to force said edges contacted tightly with spring back force tending to return to the original oval shape, is provided. 
   According to still other aspect of the present invention, a pipe body having a seam and polygonal cross section made of a rectangular metal plate, characterized by: being made through a pipe-like intermediate product prepared by bending said plate at plurality of points along its edge direction, in which a pair of edges of said metal plate to be a seam of said pipe are still not contacted together and both end angles of one specified wall are greater than the predetermined value for angle of the completed pipe; said pair of edges are closely contacted by forcing said one specified wall convex to outside; and convex said one specified wall is modified flat so as to force said edges contacted together tightly with spring back force tending to return to the convex shape, is provided. 
   According to the above described pipe body, it is possible to closely contact the seam together without welding. 
   According to still other aspect of the present invention, a prism pipe body having a seam extending along axis direction of said pipe body made of a rectangular metal plate, characterized by pair of edges of said plate consisting said seam are closely contacted by spring back force and having a fastening plate formed on a surface to be tied with other materials, is provided. 
   According to still other aspect of the present invention, a prism pipe body made of a rectangular metal plate, comprising a bottom wall, a pair of adjoining walls to said bottom wall and upper walls one of which includes a seam confronting with said bottom wall, wherein: said seam is closely contacted by spring back force; said walls are extending along the direction of axis of the pipe body; and a fastening plate is formed on a surface to be tied with other materials, is provided. 
   In the above described pipe bodies, because the fastening plate is formed integrally, fastening strength can be improved more than any prism pipe bodies of prior art fastened with other materials using a bracket. 
   According to still other aspect of the present invention, a prism pipe body made of a rectangular metal plate, comprising a bottom wall, a pair of adjoining walls to said bottom wall and upper walls including seam which is confronting with said bottom wall, characterized by a first residual stress distortion appeared at corners portion between said pair of adjoining walls and said bottom wall which makes said seam open, a second residual stress distortion appeared at center portion of said bottom wall induced by plastic deformation which has counter direction of said first residual distortion, wherein said seam is closely contacted by said second residual stress distortion which makes said bottom wall convex to outside, and an area exists between said corner and said center of bottom wall which has a low residual stress distortion, is provided. 
   According to still other aspect of the present invention, a prism pipe body characterized by: being made through a pipe-like intermediate product comprising one specified wall, a pair of side walls adjoining to said specified wall and other walls, wherein: the angles between said specified wall and said adjoining walls are obtuse, and said specified wall concave into inside; a stress distortion toward inside generated on said intermediate product through making said specified wall convex to outside by deforming said pair of walls of said intermediate product toward inside; forcing the angle between said specified wall and said pair of walls square by making plastic distortion so as for said specified wall to be deformed flat with making center portion of said specified wall as fulcrum, through forcing top wall including seam which is confronted to said bottom wall with restricting said pair of walls and making said intermediate product completed pipe body of which bottom wall corresponds to said specified wall and a pair of side walls adjoining said bottom wall correspond to said pair of side walls; wherein said bottom wall deforms convex to outside by a residual stress distortion generated at center of said specified wall which has counter direction of another residual stress distortion generated at corners between said pair of adjoining walls and said bottom wall making said seam open; said seam is closely contacted by said another residual stress distortion; and an area exists between said corner and said center of bottom wall having a low residual stress distortion, is provided. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be better understood and its various objects and advantages will be more fully appreciated from the following description taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a perspective view showing an external shape of a prism pipe body according to the present invention; 
       FIG. 2  is a side view of the prism pipe body depicted in  FIG. 1 ; 
       FIG. 3  is a plane view of a metal plate used for forming the pipe body depicted in  FIGS. 1 and 2 ; 
       FIG. 4  is a side view of a primary intermediate product; 
       FIG. 5  is a schematic diagram showing one example of pressing apparatus used for pressing of the primary intermediate product according to the present invention, wherein  FIG. 5(   a ) shows a state of mounting the metal plate on a driving plate, and  FIG. 5(   b ) shows a state that the primary intermediate product is manufactured by pressing the metal plate; 
       FIG. 6  is a side view of a secondary intermediate product, wherein  FIG. 6(   a ) shows the whole shape of the secondary intermediate product, and  FIG. 6(   b ) is a partial enlarged view of the secondary intermediate product; 
       FIG. 7  is a perspective view showing one external shape of the secondary intermediate product according to the present invention; 
       FIG. 8  is a side view showing another shape of the secondary intermediate product according to the present invention; 
       FIG. 9  is a schematic view showing one example of pressing apparatus used for pressing operation of the secondary intermediate product depicted in  FIGS. 6 and 7 , wherein  FIG. 9(   a ) shows mounting the primary intermediate product on a driving plate, and  FIG. 9(   b ) shows manufacturing of the secondary intermediate product by pressing the primary intermediate product; 
       FIG. 10  is a schematic view showing one example of pressing apparatus for pressing operation of the secondary intermediate product depicted in  FIG. 8 ; 
       FIG. 11(   a ) is a schematic view showing another example of the pressing apparatus depicted in  FIG. 10 , and  FIG. 11(   b ) is a schematic view showing another example of the pressing apparatus depicted in  FIG. 9 ; 
       FIG. 12  is a explanatory view illustrating a pipe body according to the present invention whose cross section is rectangular; 
       FIG. 13  is a schematic diagram showing example  1  of the apparatus applied to a method of manufacturing pipe body according to the present invention and shows the secondary intermediate product set at the apparatus depicted in  FIG. 6 ; 
       FIG. 14  is a partial enlarged view showing a punching member of side wall former contacting at a bent portion of the secondary intermediate product depicted in  FIG. 6 ; 
       FIG. 15  is a partial enlarged view showing convex portion formed on one specified wall of the secondary intermediate product depicted in  FIG. 6 ; 
       FIG. 16  is a view showing a pair of side walls with an adjoining wall standing to form the secondary intermediate product depicted in  FIG. 6 ; 
       FIG. 17  is views illustrating a degree of opening of the seam of the secondary intermediate product by a spring back force generated at a pair of side walls, wherein  FIG. 17(   a ) shows the secondary intermediate product with close contacted seam, and  FIG. 17(   b ) shows that with open seam by the spring back force generated at the pair of side walls; 
       FIG. 18  shows a pipe body formed by the apparatus depicted in  FIG. 13 ; 
       FIG. 19  is a view illustrating an operation of the pipe body depicted in  FIG. 18 ; 
       FIG. 20  is a partial enlarged view illustrating an angle of corner portion of the pipe body formed by the pressing apparatus depicted in  FIG. 13 ; 
       FIG. 21  is a schematic diagram of example 2 of an apparatus using the method of manufacturing prism pipe body according to the present invention, wherein the secondary intermediate product depicted in  FIG. 6  is set at an apparatus; 
       FIG. 22  shows a press punching member in contact with a bent portion of the secondary intermediate product depicted in  FIG. 21 ; 
       FIG. 23  is a view illustrating an external force applied on the secondary intermediate product depicted in  FIG. 21 ; 
       FIG. 24  is a view illustrating a modification process of the secondary intermediate product depicted in  FIG. 21 ; 
       FIG. 25  is a view showing a pair of press punching members of the apparatus in its standing state depicted in  FIG. 21 ; 
       FIG. 26  is views showing a prism pipe body manufactured by the apparatus depicted in  FIG. 21  and illustrating the opening of seam of the secondary intermediate product by a spring back force generated at a pair of side walls, wherein  FIG. 26(   a ) shows the prism pipe body with closely contacted seam,  FIG. 26(   b ) is a view illustrating that the seam is virtually opened by a spring back force f 2  tending to open the seam generated at the bottom wall and  FIG. 26(   c ) is a view illustrating a degree of closing of the seam by a spring back force r 2  tending to close the seam generated at the bottom wall. 
       FIG. 27  shows an example of modification of the apparatus depicted in  FIG. 21 ; 
       FIG. 28  is a schematic diagram showing example 3 of an apparatus used in the method of manufacturing prism pipe body according to the present invention, wherein the schematic diagram shows that the secondary intermediate product depicted in  FIG. 6  is set on the apparatus; 
       FIG. 29  is a perspective view of the prism pipe body manufactured by the apparatus depicted in  FIG. 28 ; 
       FIG. 29A  is a perspective view of another prism pipe body; 
       FIG. 30  is a front view of the prism pipe body manufactured by the apparatus depicted in  FIG. 28 ; 
       FIG. 31  is a partial sectional view of the secondary intermediate product depicted in  FIG. 28 ; 
       FIG. 32  is views illustrating the pressing apparatus used for forming the secondary intermediate product depicted in  FIG. 28 , wherein  FIG. 32(   a ) is a view before forming, and  FIG. 32(   b ) is a view after forming; 
       FIG. 33  is a view showing the press punching member contacted with a bent portion of the secondary intermediate product depicted in  FIG. 28 ; 
       FIG. 34  is a view showing a pair of press punching members of the apparatus in its standing state depicted in  FIG. 28 ; 
       FIG. 35  is a view showing the press punching member depicted in  FIG. 28  contacted with the upper wall; 
       FIG. 36  is a view illustrating an operation of the spring back force generated at the prism pipe body depicted in  FIG. 30 ; 
       FIG. 37  is a diagram illustrating a spring back force generated at a prism pipe body without convex portion; 
       FIG. 38  is a separated and emphasized explanatory views for effect of the spring back force of the prism pipe body depicted in  FIG. 36 , wherein  FIG. 38(   a ) shows effects of the spring back force generated at the bottom wall, and  FIG. 38(   b ) shows effects of the spring back force generated at the convex portion; 
       FIG. 39  is a diagram illustrating a spring back force generated at a prism pipe body having convex portion near by an upper wall; 
       FIG. 40  is a illustrative view showing an modified example of the prism pipe body forming apparatus shown in  FIG. 28  and the apparatus makes the convex portion at the bottom wall; 
       FIG. 41  is views showing a prism pipe body with a fastening plate integrally formed, wherein  FIG. 41(   a ) shows a side wall of the prism pipe body at which a pair of fastening plates are formed,  FIG. 41(   b ) is a view showing the prism pipe body depicted in  FIG. 41(   a ) tightly attached to a member having a “U” shaped cross section, and  FIG. 41(   c ) is a view showing a bent fastening plate formed on the bottom wall; 
       FIG. 42  is views showing a prism pipe body with a fastening plate integrally formed, wherein  FIG. 42(   a ) shows a prism pipe body with a pair of bent fastening plates which is formed by bending outside on a side wall,  FIG. 42(   b ) is a view showing the prism pipe body depicted in  FIG. 42(   a ) attached to a member having a “U” shape cross section, and  FIG. 42(   c ) is a view showing the prism pipe body depicted in  FIG. 42(   a ) attached to a base member; 
       FIG. 43  is views showing a prism pipe body with a fastening plate integrally formed, wherein  FIG. 43(   a ) shows a prism pipe body at which a pair of bent fastening plates bent toward an external side of a side wall are formed, and  FIG. 43(   b ) is a view showing the prism pipe body depicted in  FIG. 43(   a ) attached to a member having a “U” cross section; 
       FIG. 44  is views showing a prism pipe body with a fastening plate integrally formed, wherein  FIG. 44(   a ) shows a prism pipe body having a perpendicular fastening plate which is formed on a pair of side walls and a bottom wall, and  FIG. 44(   b ) is a view showing the prism pipe body depicted in  FIG. 44(   a ) attached to a corner of a base member; 
       FIG. 45  is views showing a prism pipe body with a fastening plate integrally formed, wherein  FIG. 45(   a ) shows a prism pipe body having a perpendicular fastening plate which is formed on a pair of side walls and a bottom wall, and  FIG. 45(   b ) is a view showing the prism pipe body depicted in  FIG. 45(   a ) attached to a corner of a base member at three ways; 
       FIG. 46  is views showing a prism pipe body with a fastening plate integrally formed, wherein  FIG. 46(   a ) shows a prism pipe body having a “L” shaped fastening plate which is formed on a pair of side walls and a bottom wall, and  FIG. 46(   b ) is a view showing the prism pipe body depicted in  FIG. 46(   a ) attached to a corner of base member; 
       FIG. 47  is views showing a prism pipe body with fastening plates integrally formed, wherein  FIG. 47(   a ) is a view showing a prism pipe body having “L” shaped fastening plate which is formed on a pair of side walls and a bottom wall, and a bent fastening plate formed on one of the “L” shaped fastening plate,  FIG. 47(   b ) is a view showing a prism pipe body having “L” shaped fastening plate which is formed on one of the pair of side walls and a bottom wall, and a bent fastening plate formed on other one of the pair of side wall, and  FIG. 47(   c ) is a view showing the prism pipe body depicted in  FIG. 47(   b ) attached to a corner of an attaching member; 
       FIG. 48  is a plane view of a metal plate used for manufacturing the prism pipe body depicted in  FIG. 41 ; 
       FIG. 49  is a front view of a primary intermediate product formed by using the metal plate depicted in  FIG. 41 ; 
       FIG. 50  is a perspective view of a secondary intermediate product formed by using the primary intermediate product depicted in  FIG. 49 ; 
       FIG. 51  is a front view of a primary intermediate product used for manufacturing of the prism pipe body depicted in  FIG. 42 ; 
       FIG. 52  is a perspective view of a secondary intermediate product formed by using the primary intermediate product depicted in  FIG. 51 ; 
       FIG. 53  is a plane view of a metal plate used for manufacturing the prism pipe body depicted in  FIG. 43 ; 
       FIG. 54  is a front view of a primary intermediate product formed by using the metal plate depicted in  FIG. 53 ; 
       FIG. 55  is a perspective view of a secondary intermediate product formed by using the primary intermediate product depicted in  FIG. 54 ; 
       FIG. 56  is a plane view of a metal plate used for manufacturing of the prism pipe body depicted in  FIG. 44 ; 
       FIG. 57  is a plane view of a metal plate used for manufacturing of the prism pipe body depicted in  FIG. 45 ; 
       FIG. 58  is a plane view of a metal plate used for manufacturing of the prism pipe body depicted in  FIG. 46 ; 
       FIG. 59  is a plane view of a metal plate used for manufacturing of the prism pipe body depicted in  FIG. 47(   a ); 
       FIG. 60  is a perspective view of a prism pipe body according to the present invention having a portion for tolerance; 
       FIG. 61  is a perspective view of a prism pipe body having a portion for tolerance of the prior art; 
       FIG. 62  is a plane view of a metal plate used for manufacturing of the prism pipe body depicted in  FIG. 60 ; 
       FIG. 63  is a perspective view of a pressing apparatus used for manufacturing of the primary intermediate product depicted in  FIG. 64 ; 
       FIG. 64  is a perspective view of a primary intermediate product formed by using the metal plate depicted in  FIG. 62 ; 
       FIG. 65  is a perspective view of a secondary intermediate product formed by using the primary intermediate product depicted in  FIG. 64 ; 
       FIG. 66  is a perspective view showing another example of the prism pipe body depicted in  FIG. 60 ; 
       FIG. 67  is a plane view of a metal plate used for manufacturing of the prism pipe body depicted in  FIG. 68 ; 
       FIG. 68  is views illustrating a prism pipe body with a wall including seam which is consisted by engagement, wherein  FIG. 68(   a ) is a partial enlarged view showing a state before engagement,  FIG. 68(   b ) is a partial enlarged view showing a state after engagement, and  FIG. 68(   c ) is a perspective view showing the whole structure; 
       FIG. 69  shows various examples of engaging protrusion and engaging dent depicted in  FIG. 68 , wherein  FIG. 69(   a ) shows a wall including seam with the engaging dent having a guide portion on an opened end,  69 ( b ) shows a wall including seam with the engaging protrusion having a guide portion on front end, and  FIG. 69(   c ) shows a wall including seam with guide portions at both ends; 
       FIG. 70  illustrates a prism pipe body with fork type engaging protrusion, wherein  FIG. 70(   a ) is a perspective view thereof,  FIG. 70(   b ) is a partial enlarged view before engagement, and  FIG. 70(   c ) is a partial enlarged view after engagement; 
       FIG. 71  is a plane view of a metal plate used for manufacturing of the prism pipe body depicted in  FIG. 70 ; 
       FIG. 72  shows various modified examples of the engaging protrusion and the engaging dent depicted in  FIG. 71 , wherein  FIG. 72(   a ) shows one example of forming the guide portion at a fastening wall,  FIG. 72(   b ) shows an example of forming the fork type guide portion at the engaging dent,  FIG. 72(   c ) shows an example of forming the guide portion at the outer side of the front end of the fork type protrusion;  FIG. 72(   d ) shows an example of forming the guide portion at the inner side of the front end of the fork type protrusion;  FIG. 72(   e ) shows an example of forming a half circular notch at the base portion of the fork type protrusion; and  FIG. 72(   f ) shows an example of forming a circular notch at the base portion of the fork type protrusion; 
       FIG. 73  shows a metal plate with plurality of engaging protrusion and engaging dent formed on each sides; 
       FIG. 74  shows a metal plate with plurality of fork type engaging protrusion and engaging dent formed on each sides; 
       FIG. 75  shows a metal plate with engaging protrusions and dents formed alternately on each sides; 
       FIG. 76  shows a metal plate with fork type engaging protrusions and dents formed alternately on each sides; 
       FIG. 77  is a partial enlarged view of a prism pipe body with a male engaging portion and a female engaging portion; 
       FIG. 78  is views illustrating the operation of the male engaging portion and the female engaging portion, wherein  FIG. 78(   a ) illustrates the male engaging portion and the female engaging portion being about to engage, and  FIG. 78(   b ) illustrates the male engaging portion and the female engaging portion being engaged; 
       FIG. 79  is a side view illustrating an other position of the seam of the pipe body according to the present invention; 
       FIG. 80  shows a method of manufacturing prism pipe body having a triangular cross section, wherein  FIG. 80(   a ) is a view showing a secondary immediate intermediate product set on a manufacturing apparatus,  FIG. 80(   b ) is a view showing a protrusion formed by pressure of a pair of press punching members, and  FIG. 80(   c ) is a view showing a completed prism pipe body; 
       FIG. 81  shows a method of manufacturing prism pipe body having a pentagonal cross section, wherein  FIG. 81(   a ) is a view showing a secondary immediate intermediate product set on a manufacturing apparatus,  FIG. 81(   b ) is a view showing a protrusion formed by pressure of a pair of press punching members, and  FIG. 81(   c ) is a view showing a completed prism pipe body; 
       FIG. 82  shows a method of manufacturing prism pipe body having a hexagonal cross section, wherein  FIG. 82(   a ) is a view showing a secondary immediate intermediate product set on a manufacturing apparatus,  FIG. 82(   b ) is a view showing a protrusion formed by pressure of a pair of press punching members, and  FIG. 82(   c ) is a view showing a completed prism pipe body; 
       FIG. 83  shows a method of manufacturing prism pipe body having a octagonal cross section, wherein  FIG. 83(   a ) is a view showing a secondary immediate intermediate product set on a manufacturing apparatus,  FIG. 83(   b ) is a view showing a protrusion formed by pressure of a pair of press punching members, and  FIG. 83(   c ) is a view showing a completed prism pipe body; 
       FIG. 84  is a view showing a cylindrical pipe body; 
       FIG. 85  shows an example of using the prism pipe body depicted in  FIG. 1  for a support frame of copy machine, wherein  FIG. 85(   a ) is a perspective view of the supporting frame, and  FIG. 85(   b ) is a side view of the supporting frame; 
       FIG. 86  is a perspective view showing a frame structure made of various prism pipe bodies having engaging portion and portion for tolerance viewing the prism pipe body with portion for tolerance from a direction where the seam can be seen; 
       FIG. 87  is a perspective view showing a frame structure made of various prism pipe bodies having engaging portion and portion for tolerance viewing the prism pipe body with portion for tolerance from a direction where the bottom wall can be seen; 
       FIG. 88  is a perspective view of the frame structure depicted in  FIG. 87  form its diagonally looking up direction. 
       FIG. 89  is a view of the frame structure depicted in  FIG. 87  after 90 degree of clock wise rotation; 
       FIG. 90  is a perspective view of the frame structure depicted in  FIG. 86  form its diagonally looking up direction. 
       FIG. 91  is a view of the frame structure depicted in  FIG. 90  after 90 degree of clock wise rotation; 
       FIG. 92  is a view of the frame structure viewing from the same direction as  FIG. 89 ; 
       FIG. 93  is a view of the frame structure depicted in  FIG. 87  after 180 degree of rotation; 
       FIG. 94  is a partial enlarged view of a prism pipe body used for a frame structure; 
       FIG. 95  is a view showing a shell element used for stress distortion analysis with a pair of rigid bodies contacting the bent portion of it; 
       FIG. 96  is an explanatory view of stress distortion generated on one specified wall corresponding to the bottom wall by slight movement of a pair of rigid bodies in approaching direction; 
       FIG. 97  is an explanatory view of one specified wall corresponding to the bottom wall deformed almost flat by further movement of the pair of rigid bodies in approaching direction; 
       FIG. 98  is an explanatory view of one specified wall corresponding to the bottom wall deformed convex outside by still further movement of the pair of rigid bodies in approaching direction; 
       FIG. 99  is a view showing a wall including seam closed by still further movement of the pair of rigid bodies in approaching direction; 
       FIG. 100  is a view showing the wall including seam tending to open when the pair of rigid bodies of  FIG. 99  moves in separating direction; 
       FIG. 101  is a view showing a wall including seam when it is pressed down when the rigid body is moved down; 
       FIG. 102  is a view showing the one specified wall corresponding to the bottom wall getting a plastic deformation when the rigid body further moves down from the state depicted in  FIG. 101 ; 
       FIG. 103  is a view showing the one specified wall corresponding to the bottom wall getting flat by the plastic deformation when the rigid body further moves down from the state depicted in  FIG. 102 ; and 
       FIG. 104  is a view showing the one specified wall corresponding to the bottom wall getting flat by the plastic deformation when each rigid bodies are removed. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Preferred embodiments of the present invention will be illustrated as follows:
     (1) [Prism Pipe Body]   (2) [Method of Manufacturing the Prim Pipe Body of Item(1)]   

   (The Primary Intermediate Product Used for Manufacturing of the Prism Pipe Body) 
   (The Secondary Intermediate Product Used for Manufacturing the Prism Pipe Body) 
   [Example 1 of Apparatus for Manufacturing the Prism Pipe Body] 
   (Stress Distribution Analysis of the Prism Pipe Body  1 ) 
   [Example 2 of Apparatus for Manufacturing the Prism Pipe Body] 
   [Example 3 of Apparatus for Manufacturing the Prism Pipe Body]
     (3) [Example 1 of a Prism Pipe Body Having a Fastening Plate]   

   [Method of Manufacturing the Prism Pipe Body of Item (3)]
     (4) [Example 2 of a Prism Pipe Body Having a Fastening Plate]   

   [Method of Manufacturing the Prism Pipe Body of Item (4)]
     (5) [Prism Pipe Body Having a Portion for Tolerance]   

   [Method of Manufacturing the Prism Pipe Body Having a Portion for Tolerance]
     (6) [Prism Pipe Body Having a Cock]   (7) [Other Prism Pipe Bodies]   

   (Deformation Example of the Prism Pipe Body Shown in  FIG. 1 ) 
   (Prism Pipe Body Having a Polygon Shaped Section) 
   (Cylindrical Pipe Body)
     (8) [Example of Using a Prism Pipe Body]   

   (Example 1 of Using the Prism Pipe Body) 
   (Example 2 of Using the Prism Pipe Body)
     (1) [Prism Pipe Body]   

     FIG. 1  is a perspective view showing a prism pipe body having a closed section with the square pillar shape, and  FIG. 2  is a side view of the prism pipe body. 
   In  FIGS. 1 and 2 , the numeral  1  is the prism pipe body. A closed section of the prism pipe body  1  is geometrically square shaped (e.g., such as a shape of a perfect square). The prism pipe body  1  includes a bottom wall  2 , a pair of side walls  3  and  4  which neighbor to the bottom wall  2 , and an upper wall  5  which faces the bottom wall  2 . 
   The upper wall  5  includes a pair of wall including seams  5   a  and  5   b.    
   Two end surfaces  5   c  and  5   d  of each of the pair of wall including seams  5   a  and  5   b  contact to each other, such that a seam  5   e  is formed on the center of upper wall  5 .
     (2) [Method of Manufacturing Prism Pipe Body of Item (1)]   

   As a material for manufacturing the prism pipe body  1 , a rectangular shaped metal plate (sheet metal)  6  depicted in  FIG. 3  is used. And, the prism pipe body  1  is formed by pressing. Tapped holes  6   a  and  6   a  for installation have been formed in advance at suitable portions of the metal plate  6 . The tapped holes  6   a  and  6   a  are used as supporting means which will be described below when attaching the prism pipe body  1  to a copy machine (not depicted). 
   (Primary Intermediate Product Used for Manufacturing Prism Pipe Body) 
   First, in the second processing step, the pair of wall including seams  5   a  and  5   b  including a seam  5   e  are formed by using the metal plate  6 . 
   In order to form the wall including seams, the pair of side portions  6   b  and  6   b  are bent at the right angle (90 degree) of lengthwise along the bending lines  6   c  and  6   c  extended along the sides of them to be stood up. And, numeral  6   e  denotes a pair of sides of the metal plate. 
   That is, as shown in  FIG. 4 , the primary intermediate product  8  is extended in the direction which the sides  6   b  and  6   b  of the wall including seams  5   a  and  5   b  are extended and faced with each other. In  FIG. 4 , numeral  9  is an end-bent portion. 
   For pressing operation the primary intermediate product  8 , for example, a presser  10  is used, as shown in  FIG. 5(   a ). The presser  10  substantially includes a fixed plate  11 , a press punching member  12  and a movable plate  12 ′. The movable plate  12 ′ is slidably installed into a concave portion  13  of a fixed plate  11 . 
   Side movable plate  12 ′ is elastically and upwardly supported by a hydraulic pressure of a presser body (not depicted). The metal plate  6  is mounted on the movable plate  12 ′. Said metal plate  6  is apart from the fixed plate  11  at a distance H to be in a floating state. The press punching member  12  is placed over the movable plate  12 ′. 
   The primary intermediate product  8  makes the movement of the press punching member  12  downwardly, then the metal plate  6 , between the press punching member  12  and the movable plate  12 ′, is contacted and supported and pressed, as shown in  FIG. 5(   b ). 
   (Secondary Intermediate Product of Using for Manufacturing the Prism Pipe Body) 
   Then, in the second processing step, an end-bent portion  9 , of the primary intermediate product  8 , is bent along the bending lines  6   d  and  6   d  depicted in  FIG. 4 . Therefore, the second intermediate product  14  in  FIG. 6(   a ) and  FIG. 7  is formed. The size of said metal plate  6  and the place of bending line are designed by estimating the degree of extension of the metal plate  6  in pressing operation. 
   Thus, as residual walls other than the wall including seams  5   a  and  5   b,  one specified wall  15  corresponding to the bottom wall  2  and a pair of adjoining walls  16  and  16  corresponding to the pair of side walls  3  and  4  neighboring with the bottom wall  2  are formed. The seam  5   e  of said secondary intermediate product  14  is in non-contacted state plate. 
   As shown and enlarged in  FIG. 6(   b ), said one specified wall  15  includes flat plate  15   a  and  15   b  and a curved portion  15   c.  The curved portion  15   c  is placed between the two flat plate  15   a  and  15   b,  and the flat plate  15   a  is next to the adjoining wall  16 . 
   The angle θ 1 , between said flat plate  15   a  and the adjoining wall  16 , is larger than that θ (see  FIG. 2 ) between the bottom wall  2  and a pair of side walls  3  and  4 , when the prism pipe body  1  shown in  FIG. 1  is completed. The angle θ is the right angle and the angle θ 1  is an obtuse angle. 
   As shown in  FIGS. 6 and 7 , the curved portion  15   c  is formed on the one specified wall  15  of the secondary intermediate product  14 . However, as shown in  FIG. 8 , the secondary intermediate product  14 , in which the curved portion  15   c  is not formed, may be used to form the prism pipe body  1 . 
   However, to establish a plane nature when forming the bottom wall  2  using a manufacture apparatus which will be illustrated below, it is rather preferable to form the curved portion  15   c  into the secondary intermediate assembling product  14 . Further, when the angle θ 1  is the same, the widened degree between the wall including seams  5   a  and  5   b  may be increased by forming the curved portion  15   c.    
   As shown in  FIGS. 6 and 7 , for example, the presser  17  depicted in  FIG. 9(   a ) is used for pressing operation the secondary intermediate product  14 . The presser  17  substantially includes a fixed plate  19 , a press punching member  20  and a movable plate  20 ′. The movable plate  20 ′ is slidably installed into an concave portion of the fixed plate  19  and is elastically and upwardly supported by a hydraulic pressure of a presser (not depicted). 
   A circumferential wall  19   a  of the concave portion of said fixed plate  19  is tapered shaped. The angle between the circumferential wall  19   a  of the concave portion and the upper surface of the fixed plate  19  is almost the same angle θ 1 . The press punching member  20  has a punching portion  20   a.  A circumferential wall  20   b  of the punching portion  20   a  has a shape corresponding to the circumferential wall  19   a  of the concave portion. 
   A bottom surface of the punching portion  20   a  is upwardly concave shaped to form a shape of the one specified wall  15  of the secondary intermediate product  14 . An upper surface  20   a′  of the movable plate  20 ′ is upwardly convex shaped corresponding to the bottom surface of the punching portion  20   a.    
   The primary intermediate product  8  is mounted on the movable plate  20 ′ and is apart from the fixed plate  19  at a distance H′ to be in a floating state. By downwardly moving the press punching member  20 , the one specified wall of the primary intermediate product  14  is contacted and supported and then pressed between and by the movable plate  20 ′, and the press punching member  20 , as shown in  FIG. 9(   b ), such that the secondary intermediate product  14  is formed. 
   After upwardly raising the press punching member  20 , the secondary intermediate product  14  is taken out of the concave portion  16 . Then, the secondary intermediate product  14  is drawn out the press punching member  20  lengthwise right angle to the ground, and is separated from the press punching member  20 . When the secondary intermediate product  14  depicted in  FIG. 8  is manufactured, a presser  17 , having the bottom surface  20   c  of the punching portion  20   a  and the upper surface  20   a′  of the movable plate  20 ′ which are flat, is used as shown in  FIG. 10 . 
   In the presser  17  depicted in  FIGS. 9 and 10 , it is impossible to separate the secondary intermediate product  14  from the press punching member  20  without taking the secondary intermediate product  14  out of the press punching member  20 . 
   However, as shown in  FIGS. 11(   a ) and  11 ( b ), if the angle θ 2 , between the adjoining wall  16  of the secondary intermediate product  14  and the one specified wall  15 , is greater than that angle θ 1 , between the adjoining wall  16  of the secondary intermediate product  14  and the one specified wall  15  depicted in  FIGS. 6 and 7 , by only raising the press punching member  20 , the secondary intermediate product  14  can be separated from the press punching member  20 . 
   Therefore, in case of the secondary intermediate product  14  depicted in  FIG. 11 , it is possible to omit the process of taking the secondary intermediate product  14  out of the press punching member  20  lengthwise thereof. According to the secondary intermediate product  14  depicted in  FIG. 11 , the improvement in efficiency of pressing is accomplished. 
   Hereinafter, the cross section of the pipe body  1  which has a shape of perfect square will be described. However, when the cross section has a shape of rectangle, as depicted in  FIG. 12 , the length of the adjoining wall  16  corresponding to the lengthwise side of rectangle is increased, and the widened degree of a pair of wall including seams  5   a  and  5   b  of the upper wall  5  corresponding to the short side of rectangle is increased. Therefore, the secondary intermediate product  14  may be separated from the press punching member  20  by only raising the press punching member  20  when the angle between the adjoining wall  16  of the secondary intermediate product  14  and the one specified wall  15  is even at the angle of θ 1 . 
   [Example 1 of Apparatus for Manufacturing the Prism Pipe Body] 
   Then, said secondary intermediate product  14  is set at the press forming apparatus (a body of apparatus)  21  depicted in  FIG. 13  to form the prism pipe body  1  as a finished product. 
   Said press forming apparatus  21  includes a lower mold (fixed mold)  22  and an upper mold (movable mold)  23 . The lower mold  22  has a fixed plate  24 , and the upper mold  23  has a movable mold  25 . A pair of stopper members  26  and  26  and a pair of press punching members  27  and  27  are installed at the fixed plate  24 , respectively. 
   The press punching members  27  and  27  are slidably mounted on a sliding rail (not shown), and is elastically supported by a spring member not depicted in a direction away from each other. The press punching members  27  and  27  are moved on the sliding rail being away from or approaching each other. The secondary intermediate product  14  depicted in  FIG. 7  is set at an opposite space  28  of the press punching members  27  and  27  to allow the one specified wall  15  to look downward. 
   Driving members  29  and  29  for driving the press punching members  27  and  27  and a press punching member  30  for pressing the pair of wall including seams  5   a  and  5   b  are attached to the movable plate  25 , respectively. 
   Taper portions  29   a  and  29   a  are formed at a lower end portion of said driving members  29  and  29 . Taper portions  27   a  and  27   a  are formed at an upper end portion of driving the press punching members  27  and  27  and engaging into the taper portions  29   a  and  29   a.    
   The state of the secondary intermediate product  14  is set in the faced space  28  with the lower mold  24  and the upper mold  25  being away from each other is shown in  FIG. 13 . When the upper mold  23  moves down along the direction of an arrow A 1 , the taper portions  29   a  and  29   a  of the driving members  29  and  29  are engaging into the taper portions  27   a  and  27   a  of the press punching members  27  and  27 , as shown in  FIG. 14 . Thus, the press punching members  27  and  27  are moved in a close direction to each other. 
   Then, punching surfaces  27   b  and  27   b  of the press punching members  27  and  27  come in contact with a curved portion  31  of the wall including seams  5   a  and  5   b  and the adjoining walls  16  and  16 , such that a pair of adjoining walls  16  and  16  is pressed by an external force in a close direction to each other. That is, the press punching members  27  and  27  take part of side walls forming punching member forming side walls by contacting with the adjoining walls  16  and  16 . 
   The press punching members  27  and  27  are moved in the near direction to each other. Thus, the curved portion  31  depicted in  FIG. 15  is slid into an upper side of the punching surfaces  27   b  and  27   b.  A pair of walls  16  stands up, and at the same time, the one specified wall  15  downwardly swells up toward an outside to have convex curved surface  32 . 
   When the upper mold  23  has fallen down more, the state of the taper portions  27   a  and  27   a  of the press punching members  27  and  27  and the taper portions  29   a  and  29   a  of the driving members  29  and  29  which are engaging into each other is released. As a result, as shown in  FIG. 16 , the driving of the press punching members  27  and  27  is interrupted. Thus, the ends of the wall including seams  5   a  and  5   b  are close to each other to form the upper wall  5  to which the seam  5   e  is close, and at the same time, a pair of side walls  3  and  4  are formed. 
   This is the third processing step. In the third processing step, the press punching member  30  is not yet in contact with the pair of side walls  5   a  and  5   b.  The secondary intermediate product  14 , having the upper wall  5  in which a pair of side walls  3  and  4  and the seam  5   e  are close to each other, is shown in  FIG. 17   a.  In the above state, when the press punching members  27  and  27  are moved in the direction away from each other, as shown in  FIG. 17(   b ), the end surfaces  5   c  and  5   d  of the wall including seams  5   a  and  5   b  are separated from a pair of side walls (a pair of adjoining walls)  3  and  4  by a spring back force f 1  and f 1  which is generated by a pair of side walls  3  and  4 . Thus the seam  5   e  is opened. An degree of opening of the seam  5   e  is called δ 1 . 
   Then, as shown in  FIG. 18 , after interrupting the driving of the pair of press punching members  27  and  27 , the upper mold  23  is caused to be continuously dropped down to a state of maintaining the pressure applied to the side walls  3  and  4 . Then, the press punching member  30  comes in contact with a pair of wall including seams  5   a  and  5   b,  such that the wall including seams  5   a  and  5   b  are pressed. The convex-curved surface  32  is modified and planed by the fixed plate  24  to which a repelling power developed by the pressure of the press punching member  30  is applied, so the bottom wall  2  is formed. This pressing step is the fourth processing step. 
   The press punching member  30  fulfills a function of pressing the wall including seams  5   a  and  5   b  and one specified wall  15  as the press punching member of the wall including seam. 
   Then, when the upper mold  23  is raised, the press punching member  30  becomes more distant from a pair of wall including seams  5   a  and  5   b.  At the same time, the fitting and fastening between the driving members  29  and  29  and the press punching members  27  and  27  are released. The press punching members  27  and  27  are moved in the direction away from each other, so the prism pipe body  1  is formed, as shown in  FIGS. 1 and 2 . 
     FIG. 19  illustrates the operation of the prism pipe body  1  formed as above. As shown in  FIG. 19 , a spring back force f 3  is applied to the lower assembling member  2  of the prism pipe body  1  to be restored to the convex-curved surface  32  denoted by broken lines. 
   Thus, a force is applied to the wall including seams  5   a  and  5   b  in a direction (closing direction) of approaching each other. When a degree of closing δ 2  of the seams  5   e  of the spring back force f 3  is set greater than the degree of opening δ 1  of the seams  5   e  of the spring back force f 1 , an external force applied to the side walls  3  and  4  by the press punching members  27  and  27  is removed. The state of the seams  5   e  adhering closely to each other maintained. 
   The angle θ 3 , between an inner surface of an corner of the bottom wall  2  and each inner surface of corner of the side walls  3  and  4  of the prism pipe body  1  (the angle between the flat part  15   a  and each of the side walls  3  and  4 ) is maintained in the angle θ 1 , between the one specified wall  15  and the adjoining wall  16  of the secondary intermediate product  14 , as depicted and enlarged in FIG.  20 , by hardening the form of the secondary intermediate product  14 . 
   (Stress Distribution Analysis of the Prism Pipe Body) 
     FIG. 95  shows a shell element  200  used in an analysis model of a stress distortion. The shell element  200  corresponds to the shape of an end of the secondary intermediate product  14 . The thickness of metal plate for using the secondary intermediate product  14  is 1.2 mm, and after completion, the external dimension of the prism pipe body  1  is 30 mm×20 mm. 
   Reference numeral  201  is a rigid body corresponding to the fixed plate  24 , reference numerals  202  and  203  are rigid bodies corresponding to the punching surfaces  27   b  and  27   b,  and reference numeral  204  is a rigid body corresponding to the press punching member  30 . Regarding to each portion of the composed the shell element  200 , the same reference numerals regarding them for each portions of the secondary intermediate product  14  are used. 
   For the stress distribution analysis of the prism pipe body  1 , a limited mediocre element program (MARC K6.3) for non-linear structure analysis has been used. 
   The physical properties of the shell element  200  are as follows: 
   Young&#39;s modulus: 2.068×1011 (N/mm) 
   Poisson&#39;s ratio: 0.29 
   Density: 7.82×103 (kg(m3) 
   Yield ratio: 2.48×108 (Pa). 
   Further, a residual stress remains in the secondary intermediate product  14 , but the residual stress is not considered in the present description. 
     FIG. 95  shows a state just after causing the rigid bodies  202  and  203  to come in contact with curved part  31  and  31 . Assuming that the axis X is horizontal, the axis Y is vertical, and the transport quantity of the rigid bodies  202  and  203  is “0”. 
   The state of causing the rigid bodies  202  and  203  to approach each other within 0.05 mm respectively is shown in  FIG. 96 . A stress distortion is concentrated into an area of the one specified wall  15  of the secondary intermediate product  14 , and the range thereof is about 6.147×10[6]–1.434×10[7] (Pa). The stress distortion is low at the upper side, the curved parts  31  and  31 , a pair of wall including seams  5   a  and  5   b  of a pair of adjoining walls  16 . 
   Further, when the rigid bodies  202  and  203  are caused to approach each other within 3 mm respectively, the one specified wall  15  is modified to be planed by the stress distortion, as shown in  FIG. 97 . At this time, the stress distortion being generated at the area  205  of the one specified wall  15  is about 3.025×10[8]–4.321×10[8] (Pa). The greatest stress distortion is generated at the central portion of the one specified wall  15  and is about 3.899×10[8]–4.32110[8] (Pa). The stress distortion, about 4.321×10[8]–2.593×10[8] (Pa), has been upwardly generated at a lower area  206  of the pair of adjoining wall  16  which forms a lower portion. 
   Further, when the rigid bodies  202  and  203  are caused to approach within 7.5 mm, respectively, the one specified wall  15  becomes convex toward outer direction, as shown in  FIG. 98 . At this time, the stress distortion of about 3.882×10[8]–4.854×10[8] (Pa) is generated substantially and equally at the area  205 , but, the greatest stress distortions are generated at inner and outer sides of the central area  205 ′. The value of stress distortion at the area  206  shown in  FIG. 98  is almost equal to that at the area  205  of the secondary intermediate product  14  which is at the state shown in  FIG. 97 . 
   When the rigid bodies  202  and  203  are caused to approach by both 10.45 mm respectively, the rigid bodies  202  and  203  come in contact with the seam  5   e  of a pair of wall including seams  5   a  and  5   b,  as shown in  FIG. 99 . At this time, the stress distortion, 3.972×10[8]–4.974×10[8] (Pa), is equally generated at the area  205 . The stress distortion at the inner and outer sides of the area  205 ′ is greater than that of the range at the area  205 . Also, the stress distortion at the area of the pair of wall including seams  5   a  and  5   b  is in a range of 1.968×10[8]–4.473×10[8] (Pa). At this time, the movement of rigid bodies  202  and  203  is stopped. 
   At a point in time shown in  FIG. 99 ,  FIG. 100  shows a state that the rigid bodies  202  and  203  are transferred in a direction to be apart from each other at 5 mm. Thus, the seam  5   e  is open. This is the reason that the stress distortion generated at the area  205  is reduced. 
   Comparing  FIG. 99  with  FIG. 100 , the convex shape, of the one specified wall  15  which is formed by plastic deformation of the one specified wall  15  corresponding to the bottom wall  2 , is maintained. Therefore, it is estimated that the seam  5   e  is opened by the stress distortion which remains at the corner  208  between the adjoining wall  16  and the one specified wall  15 . 
   A residual stress distortion remaining at the area  205  is about 8.025×10[7]–1.607×10[8] (Pa). 
     FIG. 101  shows the state that the wall including seams  5   a  and  5   b  is pressed by the rigid body  204  which is in contact with a pair of wall including seams  5   a  and  5   b.  A stress distortion, 3.945×10[8]–4.383×10[8] (Pa) is generated at the each corner  208 ,  208  of the area  205 . A stress distortion which is generated at the each corner  208  and  208  of the area  205 ′ is lower than that of the each corners  208  and  208  and that is 4.383×10[7]–3.068×10[8] (Pa). It is estimated that this resulted by the start of plastic deformation at the central portion of the one specified wall  15 . Since the stress distortion of the area  207  is increased by receiving the pressure of the rigid body  204 , the value is 3.945×10[8]–4.383×10[8] (Pa) at the area  207 . 
   At the state shown in  FIG. 101 , and as shown in  FIG. 102 , when the rigid body  204  is caused to be drawn down about 0.65 mm, the plastic deformation of the one specified wall (the bottom wall  2 )  15  is progressed, and the bottom wall  2  is plastically deformed to be planed from the central portion thereof. An area of the plastic deformation is transferred from the central portion toward the sides of one specified walls  16  and  16  and is denoted by numerals  209  and  209 . Also, the area  205 ′ of the central portion is increased under the influence of pressure. The stress distortion of the area  205 ′ is the degree of 4.734×10[8]–5.260×10[8] (Pa). The stress distortion at the corners  208  and  208  of the area  205  is the same degree, and the stress distortion at the areas  209  and  209  is the degree of 5.260×10[7]–2.630×10[8] (Pa). The stress distortion of area  207  is about 3.682×10[8]–5.260×10[8] (Pa). 
   At the state shown in  FIG. 102 , when the rigid body  204  is caused to be more drawn down about 1.65 mm, a pair of side walls  3  and  4  are restrained and the upper wall  5  having the seam  5   e  is pressed to be faced with the bottom wall  2 , such that the bottom wall  2  is plastically deformed from the central portion thereof, as shown in  FIG. 103 . 
   Thus, the bottom wall  2  is right angle to the side walls  3  and  4 . Also, residual stress distortion remains in the central portion area  205 ′ of the bottom wall  2  in the direction against the stress distortion which is at the each corners  208  and  208  between a pair of side walls  3  and  4  and the bottom wall  2  to cause the seam  5   e  to be open. 
   The lower residual stress distortion remains in the area  209  between the corner  208  of the bottom wall  2  and the central portion area  205 ′. 
   Further, with a pair of side walls  3  and  4  restrained, since the bottom wall  2  is plastically deformed to be planed, the stress distortions at the areas  210  and  210  of the pair of side walls  3  and  4  are increased. The stress distortion at the area  205 ′ is about 4.398×10[8]–5.497×10[8] (Pa), the stress distortion at the area  207  is about 4.398×10[8]–4.947×10[8] (Pa), the stress distortion at the each corners  208  and  208  is about 5.497×10[7]–1.649×10[8] (Pa), and the stress distortion at the areas  210  and  210  is about 3.848×10[8]–4.947×10[8] (Pa). 
   At the state shown in  FIG. 103 , the rigid bodies  202  and  203  part from each other in separate directions and are stopped at the position 8.75 mm, and at the same time, as shown in  FIG. 104  the rigid body  204  is raised to the position 0.855 mm. 
   At the state that the rigid bodies  202  through  204  are separated from one another, the prism pipe body  1  maintains the shape that the seam  5   e  is attached thereto. This is a reason that the bottom wall  2  has plastically been deformed. 
   The stress distortions are reduced on the whole as a result of drawing back the rigid bodies  202  through  204 , and the stress distortion at the areas  207  and  209  are reduced to the range 4.491×10[7]–1.347×10[8] (Pa). Since only a pair of wall including seams  5   e  and  5   e  is collided with the curved part  31  of the areas  207  through  210 , the residual stress distortion of 1.347×10[8]–2.695×10[8] (Pa) is generated. 
   Further, a residual stress distortion remains at the central portion  205 ′ of the bottom wall  2  to outer direction that the bottom wall  2  becomes convex, and the value is about 1.796×10[8]–3.144×10[8] (Pa). Further, a residual stress distortion of about 3.593×10[8]–4.042×10[8] (Pa) is generated by both the residual stress distortions of which one is generated by colliding the conjunction walls  5   a  and  5   b  at the corner  208  of the area  205  and the other remains at the central area  205 ′. Further, a residual stress distortion area  209 ′ which is lower than that of the central area  205 ′ is created at the bottom wall  2  toward an outer direction. 
   Further, since the outside of the bottom wall  2  is restricted by the rigid body  201 , a prominent shape  211  resulting from a plastic deformation is generated at inside. 
   As shown in  FIGS. 101 through 104 , since a pair of side walls  2  and  3  are restricted and the bottom wall  2  is plastically deformed from the central portion of the bottom wall  2  to be planed, the stress becomes concentrated at the corner  208  between a pair of side walls  3  and  4  and the bottom wall  2 , and the bottom wall  2  is modified to be the right angle to the pair of side walls  3  and  4 . 
   Therefore, without contacting a core bar jig into the secondary intermediate product  14  for pressing a bending portion for the right angle modifying, by right angle bending the secondary intermediate product  14 , the prism pipe body  1  can be formed. 
   Though the above description is illustrated with the stress distortion, the values of the stress distortions are not absolute, but relative. 
   Further, at the left side of  FIGS. 95 through 104 , a bar graph in which the range of stress distortion values is classified by dividing them into ten equal parts is illustrated. In the second intermediate product  14  (shell elements) in  FIG. 95 through 104  indicated the stress distortion in color by classification of bar graph. In this regard, the color views corresponding to  FIGS. 95 through 104  follow by a further matter submission document. 
   [Example 2 of Apparatus for Manufacturing the Prism Pipe Body] 
     FIG. 21  shows another example of an apparatus for manufacturing the prism pipe body  1  depicted in  FIG. 1 . The manufacturing apparatus depicted in  FIG. 21  includes a driving plate  25  not having a press punching member  30  for pressing the pair of wall including seams  5   a  and  5   b.  Instead, frictional contact members  27   c  and  27   c  are formed at the punching surfaces  27   b  and  27   b  of the press punching members  27  and  27 . 
     FIG. 21  shows the state that the secondary intermediate product  14  having the lower mold  24  and the upper mold  25  separated from each other is set in a space opposite. When the upper mold  23  is drawn down along the arrow A 1 , as shown in  FIG. 22 , the taper portions  29   a  and  29   a  of the driving members  29  and  29  are engaging into the taper portions  27   a  and  27   a  of the press punching members  27  and  27 . Thus, the press punching members  27  and  27  move by approaching each other, and the frictional contact members  27   c  and  27   c  of the press punching members  27  and  27  contact with the corner  31  between the adjoining walls  16  and  16  and the wall including seams  5   a  and  5   b,  such that a pair of adjoining walls  16  and  16  are pressed to approach with each other by an external force F 1 . 
   Therefore, though the stress is concentrated at the one specified wall  15 , since the border portions between the adjoining wall  14  and the curved portion  15   a  and between the curved portion  15   a  and flat part  15   b  are difficult to deform by hiding, the force F 2  works in the direction to allow the flat part  15   b  to come in contact with the fixed plate  26 . 
   As shown in  FIG. 23 , a reaction force R 1  works at the bending member  15   a  to raise the intermediate product  14 . When selecting a material of the friction contact member  27   c  so that a static friction force F 3  between the friction contact member  27   c  and bending member  31  is greater than the reaction force R 1 , contact between the bending member  15   a  and fixing plate  26  is maintained. 
   While maintaining the contact state, the pressure punch members  27  and  27  are moved in such a manner that they approach each other, as shown in  FIG. 24 , the curved portion  31  is gotten out slightly of an upper direction of punch surfaces  27   b  and  27   b  and a pair of walls  16  rise. At the same time, the flat part  15   b  is transformed in a direction by which a gap between the flat part  15   b  and fixed plate  26  disappears. The flat part  15   b  comes in contact with the fixing plate  26 . 
   By the flat part  15   b  coming in contact with the fixed plate  26 , a second reaction force R 2  works at the flat part  15   b.  When a static friction force F 3  between the friction contact member  27   c  and bending member is greater than the sum of the first reaction force R 1  and second reaction force R 2 , the contact between the flat part  15   b  and fixed plate  26  is maintained. And the flat part  15   b  is further transformed in a direction when it contacts the fixed plate  26 . 
   Also, when the fixed plate  26  is absent, a pair of press punching members  27  move into a direction in which they approach each other until a junction port  5   e  contacts thereto. And when the pair of press punching members  27  move in a direction in which they are separated from each other, a reference numeral δ 1 ′ is a degree of opening based on a spring back force that one specified wall  15  returns to an original curved convex shape. A reference numeral δ 2 ′ is a degree of closing based on a spring back force which will be described later. 
   When the upper forming portion  23  descends in a state shown in  FIG. 24 , the fastening between taper portions  27   a  and  27   a  of press punching members  27  and  27  and taper portions  29   a  and  29   a  of driving members  29  and  29  is terminated. Accordingly, as shown in  FIG. 25 , movements of press punching members  27  and  27  stop so that sections of wall including seams  5   a  and  5   b  are contact to each other. As a result, an upper wall  5  to which a seam  5   e  contacts to is formed. At the same time, a pair of side walls  3  and  4  and a bottom wall  2  are formed. In a process from a state shown in  FIG. 24  to a state shown in  FIG. 25 , the seam  5   e  is displaced by an amount corresponding to the degree of closing δ 2 ′. 
   When the upper forming portion  23  ascends, the fastening between the press punching members  27  and  27  and driving members  29  and  29  is terminated. By means of the fastening termination, the press punching members  27  and  27  move in a direction in which they separate from each other. And a first external force F 1  having been pressed to side walls  3  and  4 , a second external force F 2 , first and second reaction forces R 1  and R 2  having pressed to the bottom wall  2  are terminated to form an prism pipe body  1  shown in  FIGS. 1 and 2 . 
     FIG. 26  is a view for ill slating an operation of the prism pipe body formed by a manufacturing apparatus shown in  FIG. 21 . A first spring back force f 2 ′ is generated at the bottom surface wall  2  of prism pipe body  1  shown in  FIG. 26(   a ). The spring back force f 2 ′ is a force which tends to return to an original shape by removing the second external force F 2  as shown in  FIG. 26(   b ). Accordingly, wall including seams  5   a  and  5   b  are displaced into a direction by which they are separated from each other so that the seam  5   e  is opened by the open amount δ 1 ′. 
   On the other hand, a second spring back force r 2  is generated at the bottom wall  2  as shown in  FIG. 26(   c ). The second spring back force r 2  is a force which tends to return to an original shape by removing the second reaction force R 2 . When the degree of closing δ 2 ′ of the seam  5   e  based on the second spring back force r 2  is set more than the open amount δ 1 ′ of the seam  5   e  based on the first spring back force f 2 ′, an engaging state between seams  5   e  is maintained even though an external force pressed to the side walls  3  and  4  by means of press punching members  27  and  27  is terminated. 
   In an apparatus for manufacturing the prism pipe body  1 , the friction contact member  27   c  is installed at a press punching member  27  so that contact occurs between one specified wall  15  and a fixed plate  24  while pressing a pair of adjoining walls  16  of the intermediate product  14 . 
   Instead of forming the friction contact member  27   c  at the pressure punch member  27 , as shown in  FIG. 27 , by forming a keeper protrusion  27   c′  at the pressure punch member  27 , contact maintains between one specified wall  15  and a fixed plate  24  while pressing a pair of adjoining walls  16  of the intermediate product  14 . 
   [Example of 3 of Apparatus for Manufacturing Prism Pipe Body] 
     FIG. 28  shows another example of the apparatus for manufacturing prism pipe body  1  shown in  FIG. 1 . 
   When the apparatus for manufacturing the prism pipe body  1  shown in  FIG. 28  is used, as shown in  FIGS. 29 and 30 , convex portions  3   a  and  4   a  are located in lengthwise at regular intervals in a pair of side walls  3  and  4  and are symmetrically formed on the right and left based on a central line O 1  passing the seam  5   e.    
   A metal plate  6  shown in  FIG. 3  is used for a material of the prism pipe body  1  shown in  FIGS. 29 and 30 . A primary intermediate product  8  shown in  FIG. 4  is formed by a working device shown in  FIG. 5 . 
   In a second processing step, a secondary intermediate product  14  shown in  FIG. 7  and a second intermediate product having the same as the secondary intermediate forming portion  14  are formed. As shown in  FIG. 31 , the flat part  15   a  and adjoining wall  16  are vertically formed to each other. 
   A presser shown in  FIG. 32  is used to form the secondary intermediate forming portion  14 . The only difference between the pressers shown in  FIGS. 9 and 32  is that the bottom surface shape of the press punching member  20  and an upper surface shape of a movable plate  20 ′. The remaining elements are identical with each other, thus detailed description of the presser shown in  FIG. 32  is omitted by using identical reference numerals. 
   In an apparatus for manufacturing the prism pipe body  1  shown in  FIG. 28 , a protrusion forming convex portion  27   d  is located in lengthwise of the prism pipe body  1  shown in  FIG. 29  at regular intervals in punch surfaces  27   b  and  27   b  of a pair of press punching members  27  and  27  and are formed at the right angle to the ground at regular intervals. The protrusion forming convex portion  27   d  serves to define protrusions  3   a  and  4   a.    
   The remaining elements in the apparatus for manufacturing the prism pipe body  1  shown in  FIG. 28  are the same as that of the apparatus shown in  FIG. 13 . A detailed description of the apparatus shown in  FIG. 28  is omitted. An operation thereof will be described with reference to  FIGS. 33 through 35 . 
   As shown in  FIG. 28 , a second intermediate product  14  is set in a space  28  opposite the pressure punch members  27  and  27  to direct the bottom wall  2  in a lower direction in a third processing step. 
   When the upper forming portion  23  descends in the direction of arrow A 1  in the state, taper portions  29   a  and  29   a  of driving members  29  and  29  fasten to taper portions  27   a  and  27   a  of press punching members  27  and  27 . Accordingly, as shown in  FIG. 33 , the press punching members  27  and  27  are moved and approach each other by resisting an elastic force of a spring member. 
   Accordingly, the punch surfaces  27   b  and  27   b  of press punching members  27  and  27  come in contact with a bending parts  31  and  31  which is a boundary of side walls  3  and  4  and junction walls  5   a  and  5   b.  Thus, the side walls  3  and  4  are pressed and approach each other by an external force pressed by means of the punch surfaces  27   b  and  27   b.    
   When the press punching members  27  and  27  are further driven in a direction in which they are approach to each other, a curve of the bottom wall  2  is terminated and sections  5   c  and  5   d  approach and finally contact to each other. Accordingly, as shown in  FIG. 34 , the upper wall  5  is formed. At the same time, convex portions  3   a  and  4   a  are formed at a place (at least a place under a height direction center of a side surface walls  3  and  4 ) near to the bottom wall  2  of side walls  3  and  4  by the protrusion forming convex portion  27   c.    
   Then, in a fourth processing step, the upper forming portion  23  further descends, and the fastening between taper portions  27   a  and  27   a  of press punching members  27  and  27  and taper portions  29   a  and  29   a  of driving members  29  and  29  is released. Accordingly, the press punching members  27  and  27  stop in that location. When the upper mold  23  further descends in by applying the pressure to the side walls  3  and  4 , the pressure punching member  30  contacts to the upper wall  5 , as shown in  FIG. 35 , and pressure is applied to the upper wall  5 . By applying pressure to the press punching member  30 , the upper wall  5  and bottom wall  2  are surely become planed. However, the fourth processing step is not indispensable. 
   And, when the upper mold  23  ascends and separates from the lower mold  22 , the press punching members  27  and  27  are estranged from each other to thereby obtain the prism pipe body  1  shown in  FIG. 29 . 
     FIG. 36  is a view for illustrating the prism pipe body  1  manufactured by the manufacturing apparatus shown in  FIG. 28 .  FIG. 37  shows a prism pipe body  1 A not having convex portion, for comparison. The only difference between the prism pipe body  1  shown in  FIG. 36  and the prism pipe body  1 A shown in  FIG. 37  is that the prism pipe body  1 A has convex portion in the third processing step and the remaining elements are identical with the prism pipe body  1  shown in  FIG. 36 . Parts corresponding to the prism pipe body  1  in the prism pipe body  1 A are allotted to the same reference numeral of the prism pipe body  1 . 
   Generally, when transforming manufactured products by means of a press work (bending work), spring back is generated. The spring back means a phenomenon that the transformation returns to an original state after a working force is removed. Accordingly, the prism pipe body  1  and the bottom wall  2  of prism pipe body  1 A tend to return to a curved surface shown as a chain line in  FIG. 37  by a stress generated according to spring back (spring back force). 
   That is, after the external force by the press punching members  27  and  27  is removed, the sections  5   c  and  5   d  of wall including seams  5   a  and  5   b  tend to separate from each other. In the prism pipe body  1 A shown in  FIG. 37 , it is difficult to exactly prevent a gap between the sections  5   c  and  5   d  without performing welding operation. However, it is easy to exactly prevent the gap between the sections  5   c  and  5   d  by the above mentioned study. 
   However, in the prism pipe body  1  manufactured by the manufacturing apparatus shown in  FIG. 28 , convex portions  3   a  and  4   a  are formed on the side walls  3  and  4 . As shown in  FIG. 36 , the spring back force f 1 ″ is generated at a place in which the convex portions  3   a  and  4   a  are formed. Accordingly, the spring back force f 1 ″ offsets the spring back force which is generated at the bottom surface wall  2 . Or, the spring back force f 1 ″ operates to close the seam  5   e  by a force greater than the spring back force in the bottom wall  2 . 
   Accordingly, adhering sections  5   c  and  5   d  without performing the welding operation can prevent the gap. Concretely, as shown in  FIG. 38(   a ), open amount between sections  5   c  and  5   d  by the spring back force is generated at the bottom surface wall  2  is δ 1 ″. As shown in  FIG. 38(   b ), if degree of closing between sections  5   c  and  5   d  by the spring back force f 1 ″ is set to δ 2 ″ (under condition that sections  5   c  and  5   d  can freely move without interference by each other), the sections  5   c  and  5   d  contact to each other when δ 1 ″≦δ 2 ″. 
   Also, since the convex portions  3   a  and  4   a  is formed near the bottom wall  2  meaning far from the seam  5   e,  as shown in  FIG. 39 , a force in a direction close between sections  5   c  and  5   d  can apply to the convex portions  3   a  and  4   a  in this case more efficiently than the convex portions  3   a  and  4   a  in another case whereby the convex portions  3   a  and  4   a  are formed near the wall including seam  5  and formed at a side near to the seam  5   e.  Also, since convex portions  3   a  and  4   a  are located at the right and left based on a seam  5   e,  a force in a direction close between sections  5   c  and  5   d  can apply to the convex portions  3   a  and  4   a  with a good balance. 
   The prism pipe body  1  shown in  FIG. 28  can be manufactured by forming protrusions  27   c  and  27   c  at a conventional presser. Since conventional equipment is efficiently used, precision of a product is improved by controlling equipment investment. 
   Also, in a press forming device  21  of the apparatus for manufacturing the prism pipe body  1 , convex portion is formed on a surface (side walls  3  and  4 ) other than the upper wall  5  having wall including seams  5   a  and  5   b.  Thus, the wall including seams  5   a  and  5   b  are prevented by an influence of pressing force from getting out of the prism pipe body  1 , and thus not to form the upper wall  5 . 
   Also, in the apparatus for manufacturing the prism pipe body  1  shown in  FIG. 28 , the convex portion  3   a  and  4   a  is formed on the side walls  3  and  4  of the prism pipe body  1 . However, the convex portion  3   a  and  4   a  can be formed on the bottom wall  2  instead of at the side walls  3  and  4  of the prism pipe body  1 . 
   In this case, as shown in  FIG. 40 , convex portion forming protrusion  22   a  is formed at a fixed plate  22 . And, when pressing the secondary intermediate product  14  from an upper direction by means of the press punching member  30 , the convex portion  2   a  is formed on the center of the bottom wall  2 . 
   Also, as shown in  FIG. 29 , plural numbers of convex portions  3   a  and  4   a  are formed at predetermined intervals lengthwise of the pipe. However, line convex portions  3   b  and  4   b  extending lengthwise of the metal pipe may be formed on the side walls  3  and  4 , respectively, as shown in  FIG. 29A .
     (3) [Example 1 of Prism Pipe Body Having a Fastening Plate]   

     FIGS. 41 through 43  show the prism pipe body having a fastening plate. 
   A pair of parallel fastening plates  1   b  and  1   b  are formed on a section portion  1   a  of the prism pipe body  1  shown in  FIG. 41(   a ). The parallel fastening plates  1   b  and  1   b  protrude parallel from the side walls  3  and  4 . Tapped holes  1   c  and  1   c  are formed on the parallel fastening plates  1   b  and  1   b,  respectively. 
   The prism pipe body  1  shown in  FIG. 41(   b ) is screwed to a “U” shaped section member  50 . The “U” shaped section member  50  includes a bottom surface portion  50   a  and a pair of standing walls  50   b  and  50   b.    
   The prism pipe body  1  is fixed to a bottom surface portion  50   a  of the “U” shaped section member  50 , by facing to a section portion to  1   c  thereof the bottom surface portion  50   a  and facing to the parallel fastening plates  1   b  and  1   b  pair of standing walls  50   b  and  50   b  to screw the pair of standing walls  50   b  and  50   b  and fastening plates  1   b  and  1   b.    
   A pair of curved fastening plates  1   d  and  1   d  are formed on a section portion  1   a  of the prism pipe body  1  shown in  FIG. 42(   a ). The curved fastening plates  1   d  and  1   d  are formed by bending the parallel fastening plates  1   c  and  1   c  shown in  FIG. 41(   a ) in an outer direction. 
   The prism pipe body  1  shown in  FIG. 42(   a ) is fixed to a bottom surface portion  50   a  of the “U” shaped section member  50 , for example, as shown in  FIG. 42(   b ), by facing to the “U” shaped section member  50  and the curved fastening plates  1   d  and  1   d  to the bottom surface portion  50   a  thereof to screw the curved fastening plates  1   d,    1   d  and the bottom surface portion  50  thereof. 
   The prism pipe body  1  shown in  FIG. 42(   a ) is fixed to an upper surface portion  51   a  of a rectangular block member  51 , for example, by facing to a section portion  1   a  thereof to the upper surface  51   a  of a rectangular block member  51  and facing to the curved fastening plates  1   d  and  1   d  each other to screw the curved fastening plates  1   d  and  1   d  and the upper surface portion  51   a  of a rectangular block member  51 . 
   A pair of curved fastening plates  1   e  and  1   e  are formed on a section portion  1   a  of the prism pipe body  1  shown in  FIG. 43(   a ). The curved fastening plates  1   e  and  1   e  are formed by bending the parallel fastening plates  1   b  and  1   b  shown in  FIG. 41(   a ) in an inner direction. 
   The prism pipe body  1  shown in  FIG. 43(   a ) is fixed to a bottom surface  50   a  of the “U” shaped section member  50 , for example, by facing to the curved fastening plates  1   e  and  1   e  to the bottom surface  50   a  of the “U” shaped section member  50  to screw the curved fastening plates  1   e,    1   e  and the bottom surface  50   a  thereof. 
   Since fastening plates are formed on a section portion of the prism pipe body  1  shown in  FIGS. 41 through 43 , the prism pipe body  1  can be fastened to another member without using a fastening bracket member. 
   As shown in  FIGS. 41 through 43 , shapes of the fastening plates can be changed, and freedom of fastening the prism pipe body  1  to another member is improved. 
   Also, fastening the prism pipe body  1  to another member occurs by integrally forming fastening plates on the section portion  1   a  of the prism pipe body  1 . Accordingly, when comparing the prism pipe body  1  shown in  FIGS. 41 through 43  with the prism pipe body  1  shown in  FIG. 1(   a ), fastening plates are not integrally formed on the section portion thereof. In the prism pipe body  1  shown in  FIGS. 41 through 43 , fastening strength is improved. 
   Also, in the prism pipe body  1  shown in  FIGS. 41(   a ),  41 ( b ),  42 , and  43 , since fastening plates are located far from the bottom wall  2  causing insufficient processing transformation and the upper wall  5  has a seam, size precision of the fastening plates can be guaranteed. 
   When forming the bottom wall  2  at the fastening plates, since the curved fastening plate  1   f  is formed by protruding and bending a front end  1   c  of the fastening plate from a section portion as shown in  FIG. 41(   c ) parallel, size precision of the fastening plates can be guaranteed. 
   When processing and forming the prism pipe body  1 , since the bottom wall  2  receives a concave and convex transformation, it is difficult to form the curved fastening portion in the previous process. However, as shown in  FIG. 41(   c ), the curved fastening plate is easily formed on the bottom wall  2  by forming a parallel protrusion and bending it later as shown in  FIG. 41(   c ). 
   [Method for Manufacturing the Prism Pipe Body of Item (3)] 
   In manufacturing the prism pipe body  1  shown in  FIG. 41 , a metal plate  6  shown in  FIG. 48  is used. A pair of parallel fastening plates  1   b  and  1   b  are previously formed on the metal plate  6  by means of a punching operation. 
   The metal plate  6  is mounted to a presser  10  shown in  FIG. 5  and is pressed by means of the presser  10  to thereby form a first intermediate product  8  shown in  FIG. 49 . Then the first intermediate product  8  shown in  FIG. 49  is mounted to a presser  17  shown in  FIG. 9  and is pressed by means of the presser  17  to thereby form a secondary intermediate product  14  shown in  FIG. 50 . 
   Then the secondary intermediate product  14  shown in  FIG. 50  is mounted to any one of pressers  21  shown in  FIGS. 13 ,  21 , and  28  and is pressed by means of the presser  21  to thereby form a prism pipe body  1  shown in  FIG. 41(   a ). 
   The prism pipe body  1  shown in  FIG. 42  is obtained by standing the parallel fastening plate  1   b  formed on the metal plate  6  shown in  FIG. 48  in an outer side, mounting and pressing it to and by the presser  10  shown in  FIG. 5 . 
   Accordingly, the primary intermediate product  8  shown in  FIG. 51  is formed. Then the primary intermediate product  8  shown in  FIG. 51  is pressed by the presser  17  shown in  FIG. 9  to form the second intermediate product  14  shown in  FIG. 52 . Then the secondary intermediate product  14  is mounted and pressed to and by means of any one of pressers  21  shown in  FIGS. 13 ,  21 , and  28  to thereby form a prism pipe body  1  shown in  FIG. 42 . 
   In manufacturing the prism pipe body  1  shown in  FIG. 43 , a metal plate  6  shown in  FIG. 53  is used. A pair of fastening plates  1   b′  and  1   b′  are previously formed on the metal plate  6  by means of a punching operation. Before a primary intermediate product  8 , the pair of fastening plates  1   b′  and  1   b′  of metal plate  6  stand in inside. 
   Then the metal plate  6  is mounted to a presser  10  shown in  FIG. 5  and is pressed by means of the presser  10  to form a primary intermediate product  8  shown in  FIG. 54 . Then the primary intermediate product  8  shown in  FIG. 54  is mounted to a presser  17  shown in  FIG. 9  and is pressed by means of the presser  17  to thereby form a secondary intermediate product  14  shown in  FIG. 55 . 
   Then the secondary intermediate product  14  shown in  FIG. 55  is mounted and pressed to and by means of any one of pressers  21  shown in  FIGS. 13 ,  21 , and  28  to thereby form a prism pipe body  1  shown in  FIG. 43 .
     (4) [Example 2 of a Prism Pipe Body Having a Fastening Plate]   

   Rectangular fastening plates  1   f  and  1   g  are formed on a section portion  1   a  of the prism pipe body  1  shown in  FIG. 44(   a ). The rectangular fastening plates  1   f  and  1   g  are formed rectangular to each other. The rectangular fastening plate  1   f  protrudes parallel from the bottom wall  2 . The rectangular fastening plate  1   g  protrudes parallel from one side wall  4 . 
   The prism pipe body  1  shown in  FIG. 44(   a ) is fixed to a corner  51   b  of an upper portion  51   a  of the rectangular block member  51 , by facing to a section portion  1   a  thereof to the corner  51   b  and facing to the rectangular fastening plates  1   f  and  1   g  to side portions  51   c  and  51   c  of the rectangular block member  51  to screw the rectangular fastening plates  1   f  and  1   g  to the side portions  51   c,  as shown in  FIG. 44(   b ). 
   According to the prism pipe body  1  shown in  FIG. 44(   a ), since the prism pipe body  1  can be mounted to the rectangular block member  51  from two directions right angle to each other, a mounting strength of the prism pipe body  1  shown in  FIG. 44(   a ) is improved compare with a fastening plate structure shown in  FIGS. 41 through 43 . 
   The prism pipe body  1  shown in  FIG. 45(   a ) has a curved fastening plate  1   d  which is further curved to an outer side of a side wall  3  in another direction of the prism pipe body  1  shown in  FIG. 44(   a ). The curved fastening plate  1   d  is the right angle to rectangular fastening plates  1   f  and  1   g.    
   The prism pipe body  1  shown in  FIG. 45(   a ) is fixed to a corner  51   b  of an upper portion  51   a  of the rectangular block member  51 , by facing to a section portion  1   a  thereof with a curved fastening plate  1   d  to the upper portion  51   a,  and facing to the rectangular fastening plates  1   f  and  1   g  to side portions  51   c  and  51   c  of the rectangular block member  51  to screw the curved fastening plate  1   d  to the upper portion  51   a  and to screw the rectangular fastening plates  1   f  and  1   g  to the side portions  51   c  and  51   c.    
   According to the prism pipe body  1  shown in  FIG. 45(   a ), since the prism pipe body  1  can be mounted to the rectangular block member  51  from three directions right angle to one another, a mounting strength of the prism pipe body  1  shown in  FIG. 45(   a ) is improved comparing with a fastening plate structure shown in  FIG. 44(   a ). 
   The prism pipe body  1  shown in  FIG. 46(   a ) has L shaped fastening plates  1   h  and  1   i  which are formed on a bottom wall  2  and a side wall  4  and the L shaped fastening plates  1   h  and  1   i  are perpendicular to each other. The L shaped fastening plates  1   h  and  1   i  extend in a direction which the side portion  51   c  extends. 
   The prism pipe body  1  shown in  FIG. 46(   a ) is fixed to a corner  51   b  of the rectangular shaped block member  51 , for example, by facing to a section portion  1   c  of the prism pipe body  1  to the corner  51   b  of the rectangular shaped block member  51  and screwing the L shaped fastening plates  1   h  and  1   i  along the side portion  51   c,  as shown in  FIG. 46(   b ). 
   According to the prism pipe body  1  shown in  FIG. 46(   a ), since a junction area between a fastening plate and the side portion  51   c  can readily be assured, a mounting strength of the prism pipe body  1  shown in  FIG. 46(   a ) is improved when comparing with the prism pipe body  1  shown in  FIG. 44(   a ). 
   The prism pipe body  1  shown in  FIG. 47(   a ) includes a curved fastening plate  1   j  additionally which is further formed on the L shaped fastening plate  1   i  of the prism pipe body shown in  FIG. 46(   a ). The curved fastening plate  1   j  is a right angle to the L shaped fastening plate  1   i.    
   The prism pipe body  1  shown in  FIG. 47(   b ) includes a curved fastening plate  1   d  which is formed on a side wall  3  in the other direction of the prism pipe body  1  shown in  FIG. 46(   a ). 
   The prism pipe body  1  shown in  FIG. 47(   b ) is fixed to a mounted member  52 , for example, by screwing the L shaped fastening plates  1   h  and  1   i  to side portions  52   c  and  52   c  of the mounted member  52  and screwing the curved fastening plate  1   d  to an upper side  52   a.    
   According to the prism pipe body  1  shown in  FIGS. 47(   a ) and  47 ( b ), since the prism pipe body  1  can be screwed to another member from three directions right angle to one another, a mounting strength of the prism pipe body  1  shown in  FIGS. 47(   a ) and  47 ( b ) is more improved when comparing with a fastening plate structure shown in  FIG. 46(   a ). 
   According to the prism pipe body  1  shown in  FIGS. 44 through 47 , when the prism pipe body  1  is mounted to the mounted member to form a frame assembly which will be described later, the seam  5   e  is formed in an inner direction so that it is difficult to be seen from an outer side. Therefore, an external appearance of the frame assembly is improved. 
   [Method for Manufacturing Prism Pipe Body of Item (4)] 
   In manufacturing the prism pipe body  1  shown in  FIG. 44 , a metal plate  6  shown in  FIG. 56  is used. In manufacturing the prism pipe body  1  shown in FIG.  45 , a metal plate  6  shown in  FIG. 57  is used. In manufacturing the prism pipe body  1  shown in  FIG. 46 , a metal plate  6  shown in  FIG. 58  is used. 
   The metal plate  6  is pressed by the same pressing method to form a first intermediate product  8  and a second intermediate product  14 . The second intermediate product  14  is mounted and pressed to and by a presser  21  shown in  FIGS. 13 ,  21 , and  28  to form the prism pipe body  1  shown in  FIGS. 44 through 46 . 
   Also, in the prism pipe body  1  shown in  FIG. 47(   a ), a metal plate  6  shown in  FIG. 59  is stood in advance along a broken line  6   f  and is pressed to form a primary intermediate product  8 . The description of the metal plate  6  used for manufacturing of the prism pipe body  1  shown in  FIG. 47(   b ) is omitted. 
   However, when forming L shaped fastening plates  1   h  and  1   i  at wall including seams  5   a  and  5   b,  since a width of the prism pipe body  1  is not efficiently used, a problem with mounting strength of the prism pipe body  1  is generated. 
   That is, when forming fastening plates at wall including seams  5   a  and  5   b,  since a width W 2  from a broken line  6   c  to a side  6   e  is about half of a width W 1  from a broken line  6   d  to a broken line  6   c,  a mounting strength of the fastening plates is decreased. But, since the prism pipe body  1  shown in  FIGS. 44 through 47 , the fastening plates are formed on walls other than junction walls  5   a  and  5   b,  accordingly, as shown in  FIG. 59 , the width W 1  (a width of a surface of the prism pipe body  1 ) from the broken line  6   d  to the broken line  6   c  can be efficiently used so that a mounting strength of fastening plates in this case is more improved than a case in which the fastening plates are formed on wall including seams  5   a  and  5   b.    
   Also, according to the prism pipe body  1  shown in  FIGS. 44 through 47 , the fastening plates are formed on walls other than wall including seams  5   a  and  5   b.  Accordingly, a width W 3  of a rectangular metal plate  6  which is used as a material to form the prism pipe body  1  can be efficiently used. 
   That is, in the prism pipe body  1  shown in  FIGS. 44 through 47 , in order to form L shaped fastening plates  1   i  and  1   h  having a length of about (W 1 +W 2 +W 4 ), a metal plate having a width of (W 3 +W 4 ) may be used. However, in order to form the fastening plates at wall including seams  5   a  and  5   b,  a metal plate having a width of (W 1 +W 4 +W 3 ) should be used. Thus, a material having a broad width by width (W 1 +W 4 ) needs to thereby decrease an application of a material.
     (5) [Prism Pipe Body Having a Portion for Tolerance]   

   A closed section shape of a prism pipe body  1  shown in  FIG. 60  is a rectangular shape. An interference preventing portion for tolerance  53  is formed on an upper wall  5  of the prism pipe body  1 . The interference preventing portion for tolerance  53  is formed from below explanation. 
   The prism pipe body  1  is used as a component which manufactures a frame assembly such as a copy machine. The frame assembly includes a copy machine forming unit as an image forming device. 
   The copy machine forming unit has a complex shape. Accordingly, when a copy machine forming unit is received in the frame assembly, the prism pipe body  1  and the copy machine forming unit are apt to interfere with each other. 
   Also, in order to substitute another copy machine forming unit for the copy machine forming unit received in the prism pipe body  1 , when separating the received copy machine forming unit therefrom, the copy machine forming unit can interfere with the prism pipe body such as contacting with the prism pipe body  1 . Also, when maintaining the received copy machine forming unit, a maintenance tool can contact with the prism pipe body  1 . 
   Because of these kinds of reasons, the interference preventing portion for tolerance  53  is formed at the prism pipe body  1 . 
   The upper wall  5  of the prism pipe body  1  includes continuous curved walls having different heights to the bottom wall  2  in order to form the interference preventing portion for tolerance  53 . 
   That is, the upper wall  5  includes flat surfaces  53   a  and  53   a  and slope portions  53   c  and  53   c.  The flat surfaces  53   a  are located at both sides of the interference preventing portion for tolerance  53 . The slope portions  53   c  forms the interference preventing portion for tolerance  53  with the flat surfaces  53   b.  The slope portions  53   c  are continuously connected to the flat surfaces  53   a  through a curved portion  53   d.  The slope portions  53   c  are continuously connected to the flat surfaces  53   b  through a curved portion  53   e.    
   An opening portion  53   f  is formed on the curved portions  53   d  and  53   e.  The reason that the opening portion  53   f  is formed will be described when describing the method for manufacturing the prism pipe body  1  later. 
   According to the prism pipe body  1 , while avoiding a decline of a local strength caused by forming the interference preventing portion for tolerance  53  at the prism pipe body  1 , the interference preventing portion for tolerance  53  can be formed at the prism pipe body  1 . 
   That is, as shown in  FIG. 61 , a conventional prism pipe body  1 B not having a seam is used for a frame assembly. An electric sewing pipe body or pressing material is an example of the conventional prism pipe body  1 B. 
   In the prism pipe body  1 B shown in  FIG. 61 , in order to form an interference preventing portion for tolerance  53 ″ at a upper wall  5 ″, when cutting a part of the upper wall  5 ″, a hole  54  is opened at a place corresponding to the interference preventing portion for tolerance  53 ″. Accordingly, when forming the interference preventing portion for tolerance  53 ″ at the prism pipe body  1 B, a strength of a forming place of the interference preventing portion for tolerance  53 ″ is decreased. 
   That is, in the frame assembly formed by using the prism pipe body  1 B shown in  FIG. 61 , shaking based on a bending transformation and vibration is apt to increase. Accordingly, when the frame assembly is used as the copy machine without using any hands, an image stress distortion is apt to be generated. Also, in  FIG. 61 , a reference numeral  2 ″ represents a bottom wall, and reference numerals  3 ″ and  4 ″ represent side walls. 
   Conventionally, in order to solve the problem, a reinforcement countermeasure of the frame assembly has been performed. 
   Accordingly, the number of processes and a cost are increased. On the contrary, when the prism pipe body  1  shown in  FIG. 60  is used, in manufacturing the prism pipe body  1 , since the prism pipe body can have the interference preventing portion for tolerance  53  having continuous curved walls, an increase in the cost can be prevented. 
   [Method for Manufacturing Prism Pipe Body Having a Portion for Tolerance] 
   In manufacturing the prism pipe body  1  shown in  FIG. 60 , the metal plate  6  shown in  FIG. 62  is used. In the metal plate  6 , a slot  6   g  is formed at a place corresponding to a place at which curved portions  53   d  and  53   e  are formed. 
   The metal plate  6  is mounted and pressed to and by a press forming device  10  shown in  FIG. 63  to form a primary intermediate product  8  shown in  FIG. 64 . In  FIG. 64 , the same reference numerals are allotted to the same configuration elements shown in  FIG. 4  as the primary intermediate product  8 . 
   When wall including seams  5   a  and  5   b  are stood up and formed by a presser  10  shown in  FIG. 63 , flat portions  53   a  and  53   b,  a slope portion  53   c,  and curved portions  53   d  and  53   e  are formed at a primary intermediate product  8  shown in  FIG. 64 . 
   Punch surfaces of the fixed plate  11 , press punching member  12 , and movable plate  12 ′ have shapes corresponding to an outer shape of the primary intermediate product  8  shown in  FIG. 64 . 
   When the primary intermediate product  8  is formed by a press forming operation, a stress distortion transformation (for example, expansion) is generated at an end edge  53   d′  of the curved portion  53   d.  The slot  6   g  is formed to remove the transformation of the end edge  53   d′.    
   Then the primary intermediate product  8  is mounted and pressed to and by the press forming device  17  shown in  FIG. 9  to form a secondary intermediate product  14  shown in  FIG. 65 . Then the secondary intermediate product  14  is mounted and processed to and by any one of press forming devices  21  shown in  FIGS. 13 ,  21 , and  28  to finally obtain a prism pipe body  1  shown in  FIG. 60 . 
   Also, the prism pipe body  1  shown in  FIG. 66  is a modified example of the square pipe body  1  shown in  FIG. 60 . An engaging protrusion  35  is formed on a wall including seam  5   a.  An engaging concave portion  36  is formed on the wall including seam  5   b.  A protrusion  37  is tapered into the engaging concave portion  36  so that adhesion of the wall including seam  5   a  is guaranteed. The prism pipe body  1  will be described in detail by using a prism pipe body  1  shown in  FIG. 67 .
     (6) [Prism Pipe Body Having Caulking]   

   In the above mentioned description, the prism pipe body  1  is excluded shown in  FIG. 66 , and an adhesion state of a seam  5   e  is assured based on a spring back force. However, as shown in  FIG. 67 , engaging protrusion  35  and engaging concave portion  36  as engaging portion are formed on sides  6   b  and  6   b  of a metal plate  6 . A triangular taper protrusion  37  is formed on the engaging concave portion  36  shown in  FIG. 68(   a ) and is tapered into the engaging protrusion  35 . And enlarged as shown in  FIG. 68(   b ), the engaging protrusion  35  is contacted and fitted into the engaging concave portion  36 . The engaging protrusion  35  is transformed by the triangular taper protrusion  37 , and a pair of wall including seams  5   a  and  5   b  engage with each other.  FIG. 68(   c ) shows a prism pipe body  1  formed by the method. 
   In the triangular taper protrusion  37 , as shown in  FIG. 68(   b ), an end portion of engaging protrusion  35  of the prism pipe body  1  is transformed toward both side edges of the engaging concave portion  36 . The transformation causes a part of the engaging protrusion  35  to come in contact with both side edges of the engaging concave portion  36 . 
   According to the prism pipe body  1 , adhesion of a pair of wall including seams  5   a  and  5   b  based on spring back force generated is assured when it returns to a curved convex portion. In addition to this, the adhesion of the pair of wall including seams  5   a  and  5   b  is assured by fitting and fastening between engaging portions. 
   As shown in  FIG. 69(   a ), a guide portion  1   z  is formed on an open end of the engaging concave portion  36 . The guide portion  1   z  is open toward an open-end side of the engaging concave portion  36 . The configuration in which the engaging protrusion  35  can be easily entered into the engaging concave portion  36  can be designed. Also, as shown in  FIG. 69(   b ), a slope shape guide portion  1   y  can be formed on a front end of the engaging protrusion  35 . Also, as shown in  FIG. 69(   c ), two guide portions  1   z  and  1   y  can be formed. 
   The prism pipe body  1  shown in  FIG. 70(   a ) includes engaging protrusion  35  having two division protrusions (division members)  35   a  and  35   b.  Enlarged as shown in  FIG. 70(   b ), protrusion walls  36   a  and  36   b  are formed on an open end of the engaging concave portion  36 . The protrusion walls  36   a  and  36   b  protrude from a direction in which they approach each other. The two division protrusions  35   a  and  35   b  are, as shown in  FIG. 70(   c ), transformed into directions by which they separate from each other by the taper protrusion  37  and the two division protrusions  35   a  and  35   b  come in contact with the protrusion walls  36   a  and  36   b  to prevent a secession.  FIG. 71  shows a metal plate  6  which is used for manufacturing of the prism pipe body  1  shown in  FIG. 70 . 
   As shown in  FIG. 72(   a ), a guide portion  1   z  is formed on engaging concave portion  36 . Otherwise, as shown in  FIG. 72(   b ), a front end of the taper protrusion  37  extends into a side  6   e,  and two division shape guide portions  36 ′ is formed on the engaging concave portion  36 . The two division shape guide portions  36 ′ transforms the two division protrusions  35   a  and  35   b  to separate from it. 
   Also, as shown in  FIG. 72(   c ), a slope shape guide portion  1   z  is formed on an outer side of the two division protrusions  35   a  and  35   b.  Otherwise, as shown in  FIG. 72(   d ), a sliding guide portion  1   x  is formed on inside of the two division protrusions  35   a  and  35   b.  When an angle of a pair of sliding guide portions  1   x  approximately coincides with a peak angle of the taper protrusion  37 , an initial contact area of the taper protrusion  37  to two division protrusions  35   a  and  35   b  can be widely assured so that transformations of the two division protrusions  35   a  and  35   b  can be easily designed. 
   Also, as shown in  FIG. 72(   e ), by forming a slot  1   q  of a half circular arc at bases of the two division protrusions  35   a  and  35   b,  transformations of the two division protrusions  35   a  and  35   b  can be easily designed. Also, as shown in  FIG. 72(   f ), a circular arc shape slot  1   q′  is formed extending from the bases of the two division protrusions  35   a  and  35   b  so that transformations of the two division protrusions  35   a  and  35   b  can be easily designed. The prism pipe body  1  can be formed by a metal plate  6  which is a suitable combination of elements shown in  FIGS. 72(   a ) through  72 ( e ). 
   As mentioned above, in the prism pipe body  1  shown in  FIGS. 70 through 72 , the prism pipe body  1  is formed by engaging protrusion  35  and engaging concave portion  36 . However, as shown in  FIG. 73 , a plurality of engaging concave portions  36  and taper protrusions  37  are formed in a direction in which one side  6   e  extends at one side  6   e  of the metal plate  6  by predetermined intervals. A plurality of engaging protrusions  35  corresponding to a plurality of engaging concave portions  36  and taper protrusions  37  are formed on the other side  6   e  of the metal plate  6 . Also, as shown in  FIG. 74 , a pair of fastening walls  36   a  and  36   b  are formed on each of engaging concave portions  36  at the one side  6   e  of the metal plate. A plurality of division protrusions  35   a  and  35   b  are formed on the other side  6   e  of the metal plate  6 . 
   Also, as shown in  FIG. 75 , the engaging concave portions  36  and engaging protrusions  35  can be formed on each side  6   e  by turns. And as shown in  FIG. 76 , the division protrusions  35   a  and  35   b  and the engaging concave portion  36  can be formed on each side  6   e  by turns. 
   Also, as shown in  FIG. 77 , a male side engaging portion  35 ′ is formed on a wall including seam  5   a  of one direction. A female side engaging portion  36 ′ is formed on a wall including seam  5   b  of the other direction. The male side engaging portion  35 ′ includes two division protrusions  35   a′  and  35   a′,  engaging concave portions  35   b′  and  35   b′,  and engaging concave portion  35   c′.  The female side engaging portion  36 ′ includes engaging protrusion  36   a′,  and engaging concave portions  36   b′  and  36   b′,  and engaging protrusions  36   c′  and  36   c′.  The engaging protrusion  36   a′  engages with the engaging concave portion  35   c′.  The two division protrusions  35   a′  and  35   a′  are engaging to engaging concave portions  36   b′  and  36   b′.  The engaging protrusions  36   c′  and  36   c′  are right angle to the division protrusions  35   a′  and  35   a′.    
   The engaging protrusion  36   a′  includes slope portions  36   d′  and  36   d′.  The engaging protrusions  36   c′  and  36   c′  include shoulders  36   e′  and  36   e′.  The division protrusions  35   a′  and  35   a′  include slope portions  35   d′  and  35   d′.  As the slope portions  35   d′  and  35   d′  become wider as directing toward an open. A shoulder  35   e′  is formed on the wall including seam  5   a  and engages with a shoulder  36   e′.  When the wall including seams  5   a  and  5   b  approach each other as shown in  FIG. 78(   a ), engaging protrusion  36   a′  engages with the engaging concave portion  35   c′.  The shoulder  36   e′  engages with the shoulder  35   e′.  The division protrusions  35   a′  and  35   a′  are engaging to engaging concave portions  36   b′  and  36   b′.  When the wall including seams  5   a  and  5   b  approach more closely to each other, as shown in  FIG. 78(   b ), the two division protrusions  35   a′  and  35   a′  are transformed to a direction by which they separate from each other by tapering of the engaging protrusion  36   a′.  At the same time, the engaging protrusions  36   c′  and  36   c′  are pressed by the shoulders  35   e′  and  35   e′  and transformed into a pressed direction. As shown in  FIG. 78(   b ), an upper portion of the seam  5   e  and a vicinity thereof are substantially filled with a male mold engaging portion  35 ′ and a female mold engaging portion  36 ′. 
   When engaging protrusion with engaging concave portion, it can prevent the wall including seam with respect to a stress distortion from being separated.
     (7) [Other Prism Pipe Bodies]   

   (Deformation Example of the Prism Pipe Body Shown in  FIG. 1 ) 
   In a prism pipe body  1 , a seam  5   e  is formed at the center of an upper wall  5 . However, as shown in  FIG. 79 , for example, a seam  5   e  is formed at a section of the upper wall  5  and a section of the side wall  3 , that is, a corner of the upper and side walls  5  and  3 . In this case, at lease one direction of sides  6   b  of the metal plate  6  preferably stands up. 
   (Prism Pipe Body Having a Polygon Shaped Section) 
     FIG. 80  shows a method for manufacturing pipe body having a triangular section.  FIG. 81  shows a method for manufacturing prism pipe body  1  having a pentagonal section.  FIG. 82  shows a method for manufacturing prism pipe body  1  having a hexagonal section.  FIG. 83  shows a method for manufacturing prism pipe body  1  having an octagonal section. In each  FIGS. 80 through 83 , (a) represents a state when a second intermediate product is mounted to a press forming device, (b) represents a state when the second intermediate product is pressed by a pressure punch member to form convex portion, and (c) shows a completed square pillar  1  having a many-sided shape. Reference numerals shown in each Figure corresponds to reference numerals of each element in a method for manufacturing prism pipe body. 
   That is, a reference numeral  1  represents a prism pipe body. A reference numeral  2  represents a curved surface in a step to form a second intermediate product  14 . Reference numerals  3  and  4  are surfaces on which convex portions  3   a  and  4   a  are formed. Reference numerals  5   a  and  5   b  represent wall including seams. Reference numerals  5   c  and  5   d  represent sections. A reference numeral  5  is a surface having a seam  5   e.  A reference numeral  24  is a fixing plate. A reference numeral  27  represents a pressure punch member. Reference numerals  27   c  is a protrusion forming protrusion. A reference numeral  5 ′ represents a surface other than surfaces  2 ,  3 ,  4 , and  5  of the pipe body. Each pipe body  1  is symmetrical including convex portions  3   a  and  4   a,  and a seam  5   e.  Sections  5   c  and  5   d  of the pipe body  1  are contacted to each other by a spring back force generated in the convex portions  3   a  and  4   a.    
   What these types of shaped prism pipe bodies can be formed without forming convex portions  3   a  and  4   a  can be understood from the above-mentioned description. 
   (Cylindrical Pipe Body) 
   As shown in  FIG. 84 , a geometrical shape of a closed section can form a circular pipe body  1 . 
   In this case, at first, by bending the metal plate  6 , a seam  5   e  long extends in a non-adhesion state, a pair of sides  6   a  long extends, and an elliptical pipe body  34  are formed as a curved intermediate product having a curved convex portion  33  which is expanded into an outer side. Then, while approximately maintaining a shape of a shorter diameter direction of the elliptical pipe body  34 , an external force is applied to a curved convex portion  33  which is present at a longer diameter direction in a direction which a curvature thereof becomes smaller to transform the elliptical pipe body  34 . In this case, the spring back force f 5  to return to original curved convex portion  33  occurs and based on this spring back force f 5 , the prism pipe body, engaging to the seam  5   e.  
     (8) [Example of Using a Prism Pipe Body]   

   (Example 1 of Using a Prism Pipe Body) 
   The prism pipe body  1  shown in  FIG. 1  is, for example, as shown in  FIGS. 85(   a ) and  85 ( b ), used for a cantilever type frame assembly  38  as a support means of a facsimile combined copy machine. A loading frame  39  is mounted to the prism pipe body  1 . For example, scanner unit (not shown) is loaded into the loading frame  39 . 
   (Example 2 of Using a Prism Pipe Body) 
     FIGS. 86 through 93  show one example of frame assembling formed by a prism pipe body having a seam. 
   In  FIGS. 86 through 93 , a reference numeral  61  represents a square base member. Reference numerals  62  through  69  represent prism pipe bodies. L shaped fastening plates  62   a  and  62   b  and at the same time, a curved fastening plate  62   c  are formed at one end of the prism pipe body  62 . 
   The prism pipe body  62  is fastened and fixed to a corner of the square base member  61 , for example, by a fastening member. 
   That is, after contacting the L shaped fastening plate  62   a  with one side  61   b,  contacting the L shaped fastening plate  62   b  with the other side  61   b,  contacting the curved fastening plate  62   c  with a upper surface  61   c,  they are fastened and fixed to the square base member  61  by a screw member (not shown). 
   As shown in  FIG. 87 , the L shaped fastening plate  65   a  and  65   b  and the curved fastening plate  65   c  are formed at the prism pipe body  65 . The curved fastening plate  65   c  is screwed to upper surface  61   c,  the L shaped fastening  65   a  is screwed to one side  61   d,  and the L shaped fastening plate  65   b  is screwed to the other side  61   f.    
   A stretch fastening plate  63   a  and a curved fastening plate  63   b  are formed on one end of the prism pipe body  63 . The stretch fastening plate  63   a  is screwed to one side  61   f  and the curved fastening plate  63   b  is screwed to the upper surface  61   c.    
   As shown in  FIG. 88 , an interference preventing portion for tolerance  53  is formed at a longitudinal center of the prism pipe body  64 . At the right angle fastening plates  64   a  and  64   b  and a curved fastening plate  64   c  are formed at one end of the prism pipe body  1 . 
   Also, by screwing at the right angle fastening plate  64   a  to one side  61   b  of a prism pipe body  64 , by screwing at the right angle fastening plate  61   d  to one side  61   b  of a prism pipe body  64 , by screwing the curved fastening plate  64   c  to the upper surface  61   c,  the prism pipe body  64  is fixed to a corner of a rectangular base member  61 . 
   As shown in  FIGS. 89 and 90 , an L shaped fastening plate  66   a  is formed at one end of the prism pipe body  66 . An L shaped fastening plate  66   b  shown in  FIG. 90  and a parallel fastening plate  66   c  shown in  FIGS. 89 and 92  are formed at the other end of the prism pipe body  66 . One end of prism pipe body  66  is fixed to the other end of the prism pipe body  62  and the other end of the prism pipe body  66  is fixed to the other end of the prism pipe body  63 . 
   A curved fastening plate  67   a  shown in  FIG. 91  is formed at one end of the prism pipe body  67 . A curved fastening plate  67   b  and a parallel fastening plate  67   c  are formed at the other end of the prism pipe body  67 . Also, a location determination engaging protrusion  67   d  is formed at a section of the prism pipe body  67 . An interference preventing portion for tolerance  53  is formed at the other end of the prism pipe body  67 . The location determination engaging protrusion  67   d  and engaging concave are formed at the other end of the prism pipe body  65 . One end of the prism pipe body  67  is fixed to the other end of the prism pipe body  64 . The other end of the prism pipe body  67  is fixed to the other end of the prism pipe body  65 . 
   As shown in  FIG. 92 , parallel fastening plates  68   a  and  68   a  are formed at both ends of the prism pipe body  68 . A half circular concave portion  68   b  is formed on each of the parallel fastening plates  68   a  enlarged as shown in  FIG. 94 . A location determination support pin  70  is formed at the other ends of the prism pipe bodies  62  and  64 . The location determination support pin  70  engages with the half circular concave portion  68   b  to determine and support a location of the prism pipe body  68 . 
   By suspending one end of the prism pipe body  68  to a location determination support pin  70  of the prism pipe body  64 , suspending the other end of the prism pipe body  68  to a location determination support pin  70  of the prism pipe body  62 , and screwing parallel fastening plates  68   a  and  68   a  to other end of the prism pipe bodies  62  and  64 , the prism pipe body  68  is fixed to a prism pipe body  62  and prism pipe body  64 . 
   As shown in  FIGS. 89 ,  91 , and  93 , a curved fastening plates  69   a  are formed at both ends of the prism pipe body  69 . The curved fastening plate  69   a  of the prism pipe body  69  is screwed and fixed to the other ends of the prism pipe bodies  63  and  65 , so that the prism pipe body  69  is fastened and fixed between the prism pipe body  63  and prism pipe body  65 . 
   Also, it is preferable when loading an image forming unit on a upper surface of the frame assembly, the prism pipe body  68 , side surface walls  3  and  4  of which become a upper side is formed parallel. The reason is that a working stress of the side walls  3  and  4  during the process of the prism pipe body are smaller than the remainder wall. The flat degree thereof is guaranteed, so that the side walls  3  and  4  is suitable as a location determination base surface. 
   In accordance with a method of manufacturing pipe body and pipe body manufactured by the method, according to the present invention, when mass production them, a pipe body to which a seam is tightly contacted can be uniformly manufactured without deflections. 
   In any products, for example support member, a frame assembly, and an image forming device, in which the piping structure in accordance with present invention is utilized, a cost for structure maintaining materials for those products such as image forming device, can be decreased. 
   For easy notation, the powers of ten is described as “10 [k]” in the above description, since, 10 [3] means third power of 10 (=1000).