JP2011104623A - Method of producing tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of producing tubes, in which a plurality of small forming dies are used, also ones which are simple in the structures of respective forming dies, light in weight and inexpensive are used and the tubes are quickly formable without requiring large pressurizing force. <P>SOLUTION: The forming dies P1, ... used in respective processes are small, furthermore, made into shape structure in which the ridge lines of the die faces K1, ... in the respective forming dies P1, ... are extended in a straight line from the beginning to the terminal in the feeding direction of a workpiece and also the forming dies P1, ... in the respective processes are arranged in series with prescribed intervals L1, .... The respective forming dies P1, ... are operated simultaneously in principle and the workpiece W which is present between the respective forming dies is deformed by the pressurizing force of the respective forming dies which are adjacent each other. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a method for manufacturing a tube by pressing a metal strip-shaped workpiece into a cylindrical tube.

  As a method of manufacturing a cylindrical tube from a strip, there are a roll forming method and a press die method. Although the former has a high forming speed, it requires a large facility, and it is difficult to cope with changes in the diameter and thickness of the tube to be manufactured, and is not versatile. On the other hand, the latter has a large mold and requires a large pressure, but it is easy to cope with changes in various pipe diameters and plate thickness, is versatile, and suitable for high-mix low-volume production. ,Attention has been paid.

  For example, as the latter method, as disclosed in Patent Document 1 below, one large mold is used, and the lower mold is a concave groove that is continuous from the start end on the workpiece insertion side to the end on the workpiece carry-out side. The upper mold has a shape that matches the groove of the lower mold from the start side to the end side, and the end portion has a semicircular recess that forms a tube together with the lower mold semicircle. It has a shape. The shape of the concave groove formed in the lower mold of this mold has a wide U-shape at the start end side, and the width becomes narrower toward the end side, and finally becomes a semicircular shape. The shape gradually changed.

  In addition, what is disclosed in the following Patent Document 2 is to form a tube having a rectangular cross section, and a lower die (die) and an upper die (punch) are used, and a cross section is formed above the lower die (die). A head having a rectangular part or a pentagonal cross section is formed, and after a work is woven along the outer surface of the head, the tube is finally finished into a rectangular cross section.

Japanese Examined Patent Publication No. 2-61333 Japanese Patent No. 3347573

  However, all of the conventional methods for manufacturing a tube using a press die are a single die, and a groove whose width and cross-sectional shape gradually change from the start side to the end side on the die surface. Alternatively, it has a head, and is difficult to mold and expensive. Further, when a long or large-diameter pipe is formed, the mold itself becomes large, and when this is driven, a large driving force is required.

  In particular, since the workpiece is fed from the beginning to the end while being in contact with the mold, the tube matches the shape of the mold and has a good appearance, but the processing speed during molding is high. Is slow and unfavorable in terms of production capacity.

  The present invention was made in order to solve the problems associated with the above-described conventional technology. In addition to using a plurality of small molds, the structure of each mold is simple, lightweight and inexpensive, and a large pressure is applied. It aims at providing the manufacturing method of the pipe | tube which can shape | mold a pipe | tube in a short time without requiring.

  The method of manufacturing a pipe according to the present invention that achieves the above object mainly forms a pipe through a forming process, a bending process, and a wrist-like process, and a small mold is used in each process, and each The ridge line of the recess in the mold is linearly extended from the start end to the end in the workpiece feed direction, and the molds in each step are arranged at predetermined intervals in series, and the respective molds are simultaneously It is characterized in that the work existing between the respective molds is deformed by the pressing force of the respective molds adjacent to each other.

  In particular, if the molding dies for each process are arranged at a predetermined interval and are simultaneously operated to mold the workpiece, the rear end side of the workpiece existing between the molding dies is held by the molding die that is behind the workpiece feed direction. As a result, the tip side is preliminarily deformed under the influence of the pressing force of the mold that is in front of the feed direction, making molding easier than molding from zero, and molding speed Even if it raises, it can shape | mold according to this. In addition, even if the workpiece to be sequentially fed is a large single die, a large resistance acts on feeding, but if it is a small molding die, the workpiece W can be fed in a very smooth manner, and the forming speed of the tube Is greatly improved.

  According to the method for manufacturing a pipe according to the present invention, since the ridge line of the concave portion of the small mold used in each process is linearly extended from the start end to the end in the feed direction of the workpiece, the mold structure is It becomes extremely simple and inexpensive.

  In addition, since these molds are arranged at a predetermined interval from each other, and these are simultaneously operated to process workpieces that are sequentially fed, the workpieces existing between the molds can be freely deformed. This free deformation supplements the molding ability of each mold. In other words, the workpiece is deformed by the pressing force of the mutually adjacent molding dies even between the respective molding dies, and when the next molding die is entered, the previously molded workpiece is shaped. The molding of each mold becomes easy, and since the molding is performed in several steps, not only the molding mold itself is reduced, but also the contact between the workpiece and the mold is reduced. The speed can also be increased.

  In addition, each mold is reduced in size and weight, so the stroke can be reduced, the machining speed can be increased, the force required for machining is small, the mold can be operated quickly, and rapid machining is possible. It becomes possible.

  In addition, by changing the workpiece, even pipes with different thicknesses can be processed and become versatile.

  In the invention of claim 2, since the notch process is performed before the work is fed into the first mold, and the separate process is performed when the work is fed out from the third mold, the work feed amount is adjusted. The length of the tube to be molded can be freely selected or adjusted.

  In the invention of claim 3, since the preliminary step of forming the concave portion and the convex portion that mesh with each other is performed before the work is fed into the first mold, the engagement of the rectangular convex portion and the concave portion is performed. As a result, the connection of the side end portions of the work after forming becomes strong, and it is possible to form a pipe excellent in strength without being welded.

  In the invention of claim 4, the convex part and the concave part have a rectangular shape, the front side edge in the workpiece feeding direction is inclined backward, and the rear side edge is formed substantially perpendicular to the workpiece feeding direction. Therefore, the convex portion and the concave portion are smoothly meshed, and a tube having excellent strength can be easily formed.

  In the invention of claim 5, since the piercing process of opening a plurality of through holes is performed before feeding the workpiece into the first mold, it is possible to easily manufacture a light-weight pipe.

It is a schematic perspective view which shows the manufacturing process of the pipe | tube which concerns on the 1st Embodiment of this invention. It is a schematic perspective view which shows the manufacturing process of the pipe | tube which concerns on the 1st Embodiment of this invention. It is a schematic perspective view which shows the shaping | molding state of the workpiece | work by the embodiment. It is sectional drawing which follows the 3-3 line of FIG. It is sectional drawing which follows the 4-4 line of FIG. 1 (A). It is sectional drawing which follows the 5-5 line | wire of FIG. 1 (A). FIG. 6 is a cross-sectional view taken along line 6-6 in FIG. It is sectional drawing which follows the 7-7 line | wire of FIG. 1 (B). It is sectional drawing which follows the 8-8 line | wire of FIG. 1 (B). It is a schematic perspective view which shows the shaping | molding state of the workpiece | work by the 2nd Embodiment of this invention. FIG. 10 is an enlarged developed plan view showing a main part of FIG. 9.

Embodiments of the present invention will be described below with reference to the drawings.
<First Embodiment>
1 (A) and 1 (B), the pipe manufacturing method according to the present embodiment generally includes a plurality of small molds P1 to P9 arranged in series on the same axis at predetermined intervals L1 to L8. A belt-shaped workpiece W is formed into a cylindrical tube while being conveyed at a predetermined feed speed along the line. For example, it is excellent in appearance such as a rod used in a vehicle suspension. Regardless of the case, it is suitable for the manufacture of a tube that substantially exhibits strength or function. Note that the distances L1 to L8 between the molds P1 to P9 may be equal or may be different from each other.

  The forming dies P1 to P9 used in the present embodiment can be described in order from the start end side in the feeding direction of the strip-shaped workpiece W. Pierces for opening a plurality of through holes O in the workpiece W to reduce the weight. And a preforming mold P1 for performing a preliminary molding process similar to this, and a notch for forming a connecting portion D by inserting a cut C extending from a side end portion of the workpiece W in a direction perpendicular to the feeding direction of the workpiece. A forming die P2, a forming die P3 for forming mainly so as to abut the center and side edges of the workpiece, and first to third forming dies for bending the formed workpiece W into an arc shape. P4, P5, P6, first and second molding dies P7, P8 for wrist-like pressurizing and deforming the bent workpiece into an arc shape, and a cylindrical workpiece fed from the second molding die P8 Between A truncated P9 for separate disconnecting the connecting portion D, and a has.

  Further details will be described. As shown in FIG. 1, the preforming mold P1 includes a lower mold 1d provided with a large number of circular openings O and an upper mold (not shown) having punches provided corresponding to the openings O. It is configured. Since the workpiece W of the present embodiment is a tube that is preferably reduced in weight, such as a rod used in a vehicle suspension, for example, the preforming mold P1 is indispensable. Some of them do not require piercing or other preforming. In such a case, the mold P1 is not necessarily required. Needless to say, the shape of the opening O to be pierced is not necessarily limited to a circle but can be selected from various shapes.

  As shown in FIG. 1, the notch mold P <b> 2 has a pair of recesses extending inward from the side ends so as to form a connecting portion D by inserting a cut C perpendicular to the feed direction of the workpiece W. A lower mold 2d having 2a and an upper mold (not shown) having a punch portion provided corresponding to the recess 2a. The interval between the notches C inserted in the notch mold P2 corresponds to the length M of the tube to be formed. When forming a long tube, the notch C is inserted at a long interval, and in the case of a short tube. Make cuts C at short intervals. Therefore, in the case of a strip-shaped workpiece having a length equal to or longer than the axial length of the tube to be molded, it is preferable to provide this molding die P2, but the strip-shaped workpiece cut in accordance with the length of the tube to be molded. When the workpiece is used, the notch forming die P2 is not always necessary. In addition, although the work in the latter case cannot be sent continuously, it may be fed using a robot hand or the like.

  As shown in FIGS. 1A and 3, the forming mold P3 includes a pair of upper and lower molds 3u and 3d. The forming mold P3 is formed in the feed direction of the workpiece W by the convex portion 31 of the upper die 3u and the concave portion 32 of the lower die 3d. A forming process is performed in which the center portion and both side edge portions of the work in a direction orthogonal to each other are auctioned. Each ridgeline R (see FIG. 1A) of the convex portion 31 of the upper die 3u and the concave portion 32 of the lower die 3d extends linearly in the feed direction of the workpiece W, and both the upper die 3u and the lower die 3d are relatively simple. The mold surface K3.

  As shown in FIGS. 1A and 4, the first molding die P4 for bending is composed of a pair of upper and lower dies 4u and 4d, and includes a convex portion 41 of the upper die 4u and a concave portion 42 of the lower die 4d. A bending step of forming the workpiece W formed by forming into a U-shaped cross section is performed. Also in the first bending mold P4, the ridgeline R (see FIG. 1A) of the convex part 41 of the upper mold 4u and the concave part 42 of the lower mold 4d extends linearly in the feed direction of the workpiece W. Both 4u and lower mold 4d have a relatively simple mold surface K4.

  However, in the first molding die P4, a punch member 44 urged by the spring member 43 is provided at the center portion of the lower die 4d, and the punch member 44 is further lowered from the die surface K4 of the lower die 4d during pressurization. The central portion of the workpiece W is more easily formed into an arc shape.

  As shown in FIGS. 1A and 5, the second forming die P5 for bending is composed of a pair of upper and lower dies 5u and 5d, and includes a convex portion 51 of the upper die 5u and a concave portion 52 of the lower die 5d. The second stage bending process is performed so that the workpiece W bent into a U-shaped cross section is brought close to an arc shape.

  Also in the second molding die P5, the ridgeline R (see FIG. 1A) of the convex portion 51 of the upper die 5u and the concave portion 52 of the lower die 5d extends linearly in the feed direction of the workpiece W, and the upper die 5u, The lower mold 5d has a relatively simple mold surface K5. Also in the second molding die 5, a punch member 54 urged by a spring member 53 is provided in the central portion of the lower die 5 d, and the punch member 54 is pressed by the convex portion 51 of the upper die 5 u during pressurization. It is further lowered from the mold surface K5 of 5d so that the central portion of the workpiece W approaches an arc shape.

  As shown in FIGS. 1B and 6, the third molding die P6 for bending is composed of a pair of upper and lower dies 6u and 6d, and includes a convex portion 61 of the upper die 6u and a concave portion 62 of the lower die 6d. A third-stage bending process is performed so that the second-stage bent workpiece W is brought close to an arc shape. Also in the third molding die P6, the ridgeline R (see FIG. 1B) of the convex portion 61 of the upper die 6u and the concave portion 62 of the lower die 6d extends linearly in the feed direction of the workpiece W, and the upper die 6u, The lower mold 6d is a relatively simple mold surface K6.

  Also in the third molding die P6, the punch member 64 urged by the spring member 63 is provided in the central portion of the lower die 6d, but the shape of the convex portion 61 of the upper die 6u is such that both side edges of the workpiece W are The lower end is a cylindrical portion 65 whose axis extends in the feed direction of the workpiece W so that it can be more easily formed into an arc shape.

  As shown in FIG. 1B and FIG. 7, the first molding die P7 for wrist-like is composed of a pair of upper and lower dies 7u and 7d. The upper die 7u has a semicircular recess 71 and the lower die 7d has an upper portion. A concave portion 72 having a substantially circular shape is provided with the concave portion 71 of the mold 7u, respectively, and the first step list so that both the concave portions 71 and 72 approach the arc-shaped workpiece W bent in the third step in the previous step. The like process is performed.

  Also in the first molding die P7, the ridgeline R (see FIG. 1B) of the upper and lower concave portions 71 and 72 extends linearly in the feed direction of the workpiece W, and both the upper die 7u and the lower die 7d are relatively relatively long. It is a simple mold surface K7. The concave portion 72 of the lower mold 7d is configured such that the upper end portion of the side edge portion 74 slightly enters the mouth edge portion of the concave portion 71 of the upper mold 7u at the time of wristwatch, so that the workpiece W that has a nearly circular shape is formed. The molding is performed by tightening from the outer periphery and approaching the arc shape.

  As shown in FIG. 1B and FIG. 8, the second molding die P8 for wrist-like is composed of a pair of upper and lower molds 8u and 8d, and the upper and lower molds 8u and 8d have semicircular recesses 81 and 82, respectively. The two recesses 81 and 82 are both formed in a substantially circular shape, and a second-stage restructuring process for finishing the workpiece W in a circular cross section by the both recesses 81 and 82 is performed.

  Also in the second molding die P8, the ridgeline R (see FIG. 1B) of the upper and lower concave portions 81, 82 extends linearly in the feed direction of the workpiece W, and both the upper die 8u and the lower die 8d are relatively relatively long. It is a simple mold surface K8.

  Each of the molds P1 to P9 (except for the notch mold P2) is operated in synchronism so as to simultaneously mold the workpiece W so that the workpiece W is also transferred simultaneously from the front end to the rear end. Since it has connected via the connection part D (refer FIG. 2), in order to make this into a final molded product, the connection part D must be cut | disconnected. Therefore, as shown in FIG. 1B, the cutting die P9 of the present embodiment is a cutter for cutting off the connecting portion D of the workpiece W finished in a cylindrical shape sent out from the second forming die P8 in the previous step. 9u and cradle 9d.

  Next, the manufacturing method of the pipe | tube which concerns on this embodiment is demonstrated.

  First, for example, the work W around which a band plate is wound in a roll shape is fed into a preforming mold P1 while being drawn out at a predetermined speed using a pair of rollers or the like. In the mold P1 of the present embodiment, piercing is performed on the workpiece W to open a large number of openings O.

  Then, the workpiece W is fed forward, and when the workpiece W passes over the recess 2a of the notch mold P2 and reaches from the tip of the workpiece W to the recess 2a reaches the pipe length M (see FIG. 2), the notch The molding die P2 is operated, and a cut C perpendicular to the feed direction of the workpiece W is made. Thereby, it becomes the workpiece | work W connected by the connection part D for every predetermined length M. FIG.

  In this case, when the workpiece W reaches the forming mold P3 or the first bending mold P4, all the molds P1 to P9 except the notch mold P2 are simultaneously operated. As shown in FIG. 4, inside the forming mold P3, the workpiece W competes between the center portion and the side edge portion in the direction orthogonal to the feed direction of the workpiece W by the pressure of the upper die 3u and the lower die 3d. It is formed into a raised shape, and is bent into a U-shaped section by pressurization of the upper mold 4u and the lower mold 4d inside the first mold P4 for bending.

  However, since the work W existing between the forming mold P3 and the first bending mold P4 is the one immediately after being formed into the mold P3 on the rear end side, the mold surface K3 of the mold P3. As a result, it is the same as the state held by the molding die P3, and the tip side is affected by the pressing force of the molding die P4 and does not have a U-shaped cross section. The side edge portions are bent and deformed in directions close to each other. That is, the work W between the forming mold P3 and the first bending mold P4 is preliminarily bent and formed by the pressure of the first forming mold P4 before entering the first forming mold P4. Become. Therefore, the molding by the first mold P4 is easier to mold than completely from zero, and even if the molding speed is increased, the molding can follow the molding. In addition, even when the workpiece W is sequentially fed, a large resistance acts on feeding in the case of a large single die. However, if the small molding dies P1 to P9 are used as in the present embodiment, the workpiece W is very smooth. Since W can be sequentially fed, the forming speed of the tube is greatly improved.

  This is because between the first molding die P4 for folding and the second molding die P5, between the second molding die P5 for folding and the third molding die P6, the third molding die P6 for folding and the second one for wrist-like. The same operation is performed between the first molding die P7 and all of the first molding die P7 and the second molding die P8.

  When the workpiece W bent into a U-shaped cross section by the first forming die P4 for bending is fed to the second forming die P5, as shown in FIG. 5, the convex portion 51 of the upper die 5u and the punch are formed. The workpiece W faces downward in a state where the substantially central portion is sandwiched between the member 54 and the upper mold 5u and the lower mold 5d of the second mold P5 are pressed, and the work W follows the mold surface K5 of the lower mold 5d. And bent. In this case, the subsequent workpiece W that is sequentially fed to the second mold P5 is bent and deformed in advance in the direction in which the side edges are close to each other by the pressure applied by the folding molds P4 and P5. Compared with molding from scratch, molding becomes easier, and even if the molding speed is increased, molding can be performed following this.

  As shown in FIG. 5, the workpiece bent in this way is formed in a substantially semicircular shape at the center and pressure-deformed so that the side end portions are close to each other. Since W is not yet circular in cross section, in this embodiment, it is further pressure-deformed by the third mold P6 and approaches the circular cross section.

  When the workpiece W bent and formed by the second forming die P5 for bending is fed to the third forming die P6 and pressurized by the third forming die P6, as shown in FIG. 6, the convex portion of the upper die 6u. 61 and the punch member 64 are pressed downward with a substantially central portion sandwiched therebetween, and the mold surface K6 of the lower mold 6d is pressed by the upper mold 6u and the lower mold 6d of the third mold P6. And the bottom part is closer to a semicircular shape, and the upper side edges are further closer to each other.

  In the first molding die P7 for wrist-like, the workpiece W fed in this state has mutual side end portions due to the semicircular recess 71 of the upper die 7u and the semicircular recess 72 of the lower die 7d. It is restricked to abut. However, the cross-sectional shape is not yet completely circular.

  Then, the workpiece W fed to the second molding die P8 for wrist-like is re-striated by the semicircular concave portion 81 of the upper die 8u and the semicircular concave portion 82 of the lower die 7d. It becomes a circle.

  Since the workpieces W thus formed are connected to each other by the connecting portion D, finally, the connecting portion D is formed by the cutter 9u and the receiving base 9d of the cutting die P9 shown in FIG. Is cut into a tube of a predetermined length M.

  The tube formed in this way has a fast forward speed and the entire work piece is not reliably in contact with the mold, so that the outer surface has irregularities and the appearance is good. However, since it has substantial strength and function as a tube, it is extremely preferable as a tube used at a site where the appearance is not questioned.

  An attempt was made to manufacture a pipe using a normal steel plate having a thickness of 2.3 mm and a normal steel plate having a thickness of 4.0 mm as a work W by the method for manufacturing a pipe according to the present embodiment. Each workpiece W was performed without changing the lifting stroke of the mold. As a result, although the outer surface had irregularities, the tube could be formed normally.

In addition, when manufacturing a pipe | tube with the workpiece | work W whose plate | board thickness is still thicker, it can cope to some extent by changing the raising / lowering stroke of each shaping | molding die.
<Second Embodiment>
FIG. 9 is a schematic perspective view showing a molding state of a workpiece according to the second embodiment of the present invention, and FIG. 10 is an enlarged plan view showing a main part of FIG.

  In the first embodiment, a plurality of through holes O are opened in the workpiece W by using the preforming mold P1 to reduce the weight, but the side end portion of the workpiece W is not processed. When made into a cylindrical tube, the ends on both sides are simply close together. Therefore, if strong torsion or axial force is applied, the adjacent side ends may be separated and the strength may be insufficient. To make a strong pipe, both ends must be welded together. Sometimes it is necessary.

  In the present embodiment, as shown in FIG. 9, when a convex portion T is formed at one end portion of the work W and a concave portion H is formed at the other end portion to form a cylindrical tube, the convex portion T is formed. And the concave portion H mesh with each other, forming a tube that is excellent in strength against torsion and axial force and does not require welding. The workpiece W of this embodiment forms a plurality of convex portions T having a substantially rectangular shape at one end portion of the workpiece W using the preforming mold P1, and the convex portion T at the other end portion. The number of concave portions H having a substantially rectangular shape corresponding to the number of the convex portions T is formed so that the convex portions T and the concave portions H mesh with each other.

  In particular, in determining the shape of the convex portion T and the concave portion H, it has been experimentally found that if the end edge portions Ta and Ha are formed so as not to be orthogonal to the feeding direction, the meshing of both ends smoothly. . This is because the workpiece W is preliminarily molded at an intermediate portion such as between the first molding die P7 and the second molding die P8 for wrist-like, and the convex portion T and the concave portion H on the tip side in the feed direction. It seems that the points that are engaged while approaching each other have an influence.

  That is, in this embodiment, as shown in FIG. 10, the front side edge Hf of the concave portion H in the workpiece W feeding direction (the direction of the white arrow) is tilted backward, and the rear side edge Hb is set to the workpiece. It is formed substantially perpendicular to the feed direction of W. However, the corners of the convex portion T and the concave portion H are formed into smooth arcs so that they can smoothly mesh with each other. In this way, the engagement of the rectangular convex portion T and the concave portion H strengthens the connection of the side end portions of the workpiece, and it is possible to form a tube having excellent strength without welding. it can.

  Here, when the backward inclination angle θ (inclination angle with respect to the direction orthogonal to the feeding direction of the workpiece W) is verified by experiment, it has been found that 0 to 10 degrees is preferable. When the angle was 0 ° or less, insufficient strength against torsion or axial force was generated, and when the angle was 10 ° or more, interference was likely to occur when the convex portion T and the concave portion H were engaged.

  The convex portions T and the concave portions H are substantially rectangular, and it is preferable to form a plurality of the convex portions T and the concave portions H so as to have a wave shape as shown in the figure. Any shape can be used as long as it is easy to shape. For example, a triangular shape is a zigzag shape, or individual convex portions T and concave portions H have various shapes. It may be. When the preforming mold P1 is used, a large number of openings O may be formed at the same time as in the previous embodiment.

  The present invention is not limited to the above-described embodiments, and various modifications can be made by those skilled in the art within the technical idea of the present invention. For example, in the above-described embodiment, the rod used in the suspension of a passenger car has been described. However, the present invention is not limited to this, and can be used as a pipe material used in various parts.

  In addition, as a method for manufacturing a pipe according to the present invention, it is not always necessary to use a plurality of pairs of forming dies for each step in the forming process, the bending process, and the restructuring process, and at least one pair of forming dies is provided. Just do it.

  The present invention can be suitably used for manufacturing a tube such as a rod used in a vehicle suspension, for example.

1 ... Forming mold,
H ... concave part,
Ha ... side edge of concave part,
L1-L9 ... interval,
P3: Forming mold,
P4 to P6 ... Bending mold
P7, P8 ... Wrist-like mold,
T: Convex part,
Ta: side edge of convex part,
W ... Work.

Claims (5)

A method of manufacturing a tube for forming a strip-shaped workpiece into a cylindrical tube,
A forming step of forming with a pair of forming molds provided with a mold surface that has a shape in which the center part and the side edge part in a direction perpendicular to the feeding direction of the workpiece are contested;
A bending step of forming with at least a pair of bending molds having a mold surface that is bent in the direction in which the central portion of the workpiece formed in the forming step is recessed and the side edges are brought close to each other;
The central part of the workpiece formed in the bending step is formed in a semicircular shape, and is formed by at least a pair of wrist-like molds having a mold surface that is pressure-deformed so that the side end portions are in contact with each other. Restorative process,
Have
The forming die in each step has a configuration in which a ridge line on each die surface extends linearly from the start end to the end in the feed direction of the workpiece, and the forming die, the bending die, and the In a state where a predetermined interval is arranged in series in the order of the wrist mold, the workpiece is sequentially fed from the forming mold to the wrist mold and the molds are simultaneously operated. A method for manufacturing a pipe, characterized in that a workpiece existing between the molding dies is deformed by the pressure of the molding dies adjacent to each other.   A notch step for making a notch extending from a side end of the workpiece in a direction perpendicular to the feeding direction of the workpiece before feeding the workpiece into the first molding die; and the workpiece is fed out from the third molding die. The manufacturing method of the pipe | tube of Claim 1 which has a separate process which cuts off and the said notch part.   Before feeding the workpiece into the first mold, a preliminary step of forming at least one concave portion at one end of the workpiece and a convex portion engaging with the concave portion at the other end of the workpiece. The method of manufacturing a pipe according to claim 1, wherein the pipe has a structure.   The convex portion and the concave portion are rectangular, and the front side edge in the workpiece feeding direction is inclined backward, and the rear side edge is formed substantially perpendicular to the workpiece feeding direction. The manufacturing method of the pipe | tube of Claim 3.   The method for manufacturing a pipe according to any one of claims 1 to 4, further comprising a preliminary step of opening a plurality of through holes in the work before the work is fed into the first mold.

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