JP4153880B2 - Method and apparatus for manufacturing stepped hollow member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for producing a stepped hollow member with which the working defect in the case of forming a deformed hole projecting a large diameter step part between both cylindrical end parts and having different cross section to the circle, is reduced and working precision is improved. <P>SOLUTION: The method and the apparatus for producing the stepped hollow member, is performed through the following processes. In a preforming process, the tapered part 6 formed as the large diameter toward between both end parts in the outer periphery of a hollow blank is smoothly preformed and also, the preform member 8 is preformed so that the center hole size gradually is reduced toward both end parts of the hollow blank in the center hole 5. In a finish-forming process, the force toward the center direction of a second core die 24 with the tapered part 6 becoming the large diameter toward the large diameter step part 10 of the preformed member 8 is generated from the force in the vertical direction with a finish-forming dies 23a, 23b and the material fluidity so as to cling to a second core die 24, is smoothly generated because the center hole size is formed, so as to be smoothly reduced. <P>COPYRIGHT: (C)2005,JPO&amp;NCIPI

Description

  The present invention relates to a method and an apparatus for manufacturing a stepped hollow member in which a large-diameter stepped portion is provided between both cylindrical end portions and a deformed hole having a cross section different from a circle is penetrated on an axis.

  Conventionally, as a method for manufacturing a stepped hollow member, there is a method in which a step portion is heated to a predetermined temperature in advance and further pressed from both ends in the axial direction (see Patent Document 1). .

Further, as another manufacturing method of the stepped hollow member, both the end portions of the hollow member are drawn to a smaller outer diameter than the intermediate portion of the member, and the intermediate portion and the both end portions formed in the large diameter step portion. Is formed into a regular shape (see Patent Document 2).
Japanese Patent Laid-Open No. 2002-282991 (page 4, FIGS. 3 to 6) JP 2001-121241 A (3rd page, 4th page, FIGS. 1 to 3)

  In the above-described techniques disclosed in Japanese Patent Application Laid-Open Nos. 2002-2829191 and 2001-121241, the hollow inner diameter of the portion formed by forming a large outer diameter into a stepped portion depends on the outer diameter. Due to the large deformation, it is difficult to obtain an inner diameter with a certain size. In particular, it has been difficult to form the inner diameter shape into a different shape from the circular shape that is the outer diameter shape.

  For example, FIGS. 12a to 12e show a manufacturing process of a stepped hollow member in which the center hole has a shape different from the outer diameter shape using these manufacturing methods.

  First, a cylindrical blank 71 shown in FIG. 12a is formed into a narrow-diameter portion 72 that approximates a desired outer diameter at the lower portion by forging or the like as shown in FIG. 12b.

  Next, as shown in FIG. 12c, a substantially rectangular deformed hole 73 is formed by forging or the like, but constriction occurs in the step of forming the step 75 shown in FIG. There was a risk of reducing the strength of the stepped hollow member. For this reason, in the final step shown in FIG. 12e, a deformed hole 74 having a rectangular center hole is obtained by penetrating the bottom, but it is also difficult to form the deformed hole 74 having a predetermined size and shape.

  The present invention has been made in view of the above-mentioned problems of the prior art, and the object thereof is to gently reserve a tapered portion having a large diameter from both ends of the hollow material toward the middle on the outer periphery of the hollow material. In addition to molding, the preforming member is pre-formed so that the center hole size gradually decreases toward both ends of the hollow material in the center hole, and then the preforming member is finish-molded. From the force in the vertical direction, a force toward the center direction of the second core mold is generated by the tapered portion having a large diameter toward the large-diameter step portion of the preformed member, and the size of the center hole is also reduced gradually. The material flow that hugs the second core mold is generated smoothly, and the inner periphery of the center hole of the stepped hollow member is not constricted, and a notched annular groove is generated. To provide a method and apparatus for producing a stepped hollow member without also.

  In order to solve the above-described problem, the structural feature of the invention according to claim 1 is that a large-diameter stepped portion is provided between the cylindrical end portions, and a deformed hole having a cross-section different from a circle is penetrated on the axis. In the manufacturing method of the stepped hollow member, a hollow material is inserted into a first core mold having a cross-sectional shape corresponding to the deformed hole, and a tapered hole is formed in at least one of the opposing surfaces. The step of pressing at least one end of the hollow material with the inner peripheral surface of the taper hole is performed one or more times by enclosing a pair of preforming dies surrounding the first core mold and approaching each other. A taper portion having a large diameter is formed on the outer peripheral surface of the material between both ends of the hollow material, and the center hole dimension of the hollow material is gradually reduced toward both ends of the hollow material, and the first core Reduces to a different shape toward the mold A preforming step in which the hollow material is preliminarily finished to form a preformed member, and the preformed member is extracted from the first core mold and is inserted into a second core mold having a cross-sectional shape corresponding to the deformed hole, A pair of finish forming dies each having a step finish surface for finishing and molding the large-diameter step portion from both sides, each having a finish hole having an inner diameter corresponding to the outer diameter of each of the cylindrical end portions. By encircling the second core mold and approaching each other, the tapered portions of the preformed member are pressed by the finishing holes and the stepped surface, so that the cylindrical both end portions and the large diameter stepped portion are pressed. And forming the center hole into the deformed hole by pressing against the second core mold.

  Note that the preliminary molding step is performed for the purpose of forming tapered portions at both ends of the hollow material before the finish molding step. Therefore, the taper portions at both ends can be preformed once, or after the taper portion is formed at one end portion, the taper portion may be formed at the other end portion. Specifically, a pair of preforming dies each formed with a tapered hole that opens on each facing surface surrounds the first core die and approaches each other so that taper portions are formed at both ends of the hollow material at a time. Can be molded. Further, a taper portion is formed at one end of the hollow material by enclosing a pair of preforming dies having a tapered hole formed on one of the opposing surfaces so as to surround the first core die. A taper portion is formed at the other end of the hollow material by forming a pair of preforming dies having a tapered hole formed on the other facing surface among the facing surfaces so as to surround the first core die and approach each other. You may make it shape | mold.

  A feature of the invention according to claim 2 is the step of forming a groove extending in the axial direction at a corner portion of the deformed hole and forming an inner wall surface into an arc surface following a cylindrical shape after the finish forming step. It is that it was set as the manufacturing method of the stepped hollow member of 1 description.

  A feature of the invention according to claim 3 is that the hollow material is formed into a cylindrical shape having a center hole having a cross-sectional shape obtained by enlarging the deformed hole into a substantially similar shape, and a cylindrical blank is forged to form the hollow material. The method for producing a stepped hollow member according to claim 1 or 2 is characterized in that:

  A feature of the invention according to claim 4 is that in the manufacturing apparatus of a stepped hollow member in which a large-diameter stepped portion is provided between both cylindrical end portions and a deformed hole having a cross-section different from a circle is penetrated on the axis, A pair or a plurality of pairs each having a first core mold having a cross-sectional shape corresponding to the hole and in which a hollow material is inserted, and at least one of the facing surfaces having a tapered hole surrounding the first core mold. A taper portion having a diameter that increases from the both ends of the hollow material toward the outer peripheral surface of the hollow material by pressing the end portion of the hollow material with the inner peripheral surface of the taper hole. And forming the hollow material into a preformed member so that the center hole dimension of the hollow material gradually decreases toward both ends of the hollow material and decreases to an irregular shape toward the first core mold. Alternatively, multiple pairs of pre-molding dies and tapered portions at both ends Means for extracting the shaped preform member from the first core mold, a second core mold having a cross-sectional shape corresponding to the deformed hole, and into which the preform member is inserted; The step finished surfaces to be finished from are respectively formed to face each other, and finish holes having inner diameters corresponding to the outer diameters of both cylindrical end portions open to the step finished surfaces, respectively, A pair of finishing molds that are enclosed and detachably mounted, and press each of the finishing holes and the stepped surface to the tapered portion of the preformed member, and the cylindrical ends and the large diameter While forming a step part, it is set as the manufacturing apparatus of the stepped hollow member which has a pair of finishing shaping | molding die which presses the said center hole to the said 2nd core type | mold, and forms the said deformed hole.

  The manufacturing method of the stepped hollow member according to claim 1 configured as described above is a preforming step for obtaining a preformed member, and on the outer periphery of the hollow material, between the both ends of the hollow material from the both ends of the hollow material. The taper portion having a larger diameter is gradually preformed, and the center hole is also preformed to be reduced toward the first core mold so that the center hole size is gradually reduced toward both ends of the hollow material. ing.

  Therefore, in the finishing process for obtaining the stepped hollow member, the molding is performed as follows.

  That is, the force applied from the vertical direction by the finish mold generates a force directed toward the center of the second core mold by the tapered portion. Also, the center hole is shaped so as to be gradually reduced toward both ends of the hollow material. Therefore, a material flow that hugs the second core mold is generated smoothly, the inner periphery of the center hole of the stepped hollow member is not constricted, and a notched annular groove is not generated.

  Also, when the shape of the inner diameter of the center hole is a circle, the degree of processing when reducing the diameter of the center hole in the finish molding process is the same in the circumferential direction, but the shape of the inner diameter of the center hole is different from the circle. If the shape is irregular, the degree of processing when the center hole is reduced in the finishing process is not uniform in the circumferential direction. For this reason, when the shape of the center hole is irregular, it is difficult to mold due to the difference in the degree of processing. However, in the present invention, the center hole size is gradually reduced toward the both ends of the hollow material by the preforming process, and the material flow that hugs the second core mold in the finish molding process is smoothly generated. This eliminates the difficulty of molding due to the difference in the degree of processing.

  In the manufacturing method of the stepped hollow member according to claim 2 configured as described above, the center hole has an irregular shape that is easy to mold an axially extending groove and a circular arc surface following the cylindrical shape at the corner of the irregular hole. Is formed in the finish molding process, so when forming the groove or arc surface in the center hole, there is less plastic working margin, flow deformation also occurs smoothly, and the material yield is low-cost and high-precision. A stepped hollow member having a shape can be formed.

  In the manufacturing method of the stepped hollow member according to claim 3 configured as described above, the hollow material is not a cylindrical shape having a circular center hole, but a rough shape, that is, a deformed hole in a stage before forming the deformed hole. Since it has a cylindrical shape with a center hole with a cross-sectional shape expanded to a similar shape, the center hole can be brought close to the desired irregular shape in a stepwise manner, and there is no difficulty in fluid deformation of the material in forging It is possible to provide a stepped hollow member with high processing accuracy and few processing defects.

  In the manufacturing apparatus of the stepped member according to claim 4 configured as described above, on the outer periphery of the hollow material, the tapered portion having a large diameter gradually extends from both ends of the hollow material to both ends of the hollow material. The center hole is also preliminarily molded so as to be reduced toward the first core mold so that the center hole size is gradually reduced toward both ends of the hollow material.

  Therefore, in the finish molding step, the force applied from the up and down direction by the finish molding die generates a force toward the center direction of the second core mold by the tapered portion. In addition, since the center hole dimension is formed so as to be gradually reduced, the difficulty in forming due to the difference in processing degree is solved. Therefore, a material flow that hugs the second core mold is generated smoothly, the inner periphery of the center hole of the stepped hollow member is not constricted, and a notched annular groove is not generated.

Embodiments of a method and apparatus for manufacturing a stepped hollow member according to the present invention will be described below with reference to the drawings.

  First, FIG. 1 thru | or FIG. 3 is a figure which shows the shaping | molding process of the hollow raw material 4, and is displayed with the top view and sectional drawing.

  FIG. 1 shows a cylindrical blank 1, and FIG. 2 shows a process in which the blank 1 is forged and a center hole 2 is formed. FIG. 3 shows a process in which the bottom 3 is further punched out by pressing and the hollow material 4 is formed through the center hole 2. The hollow material 4 formed in this step has a cylindrical shape having a center hole 2 having a cross-sectional shape obtained by enlarging a deformed hole formed in the completed stepped hollow member into a substantially similar shape.

  Next, FIGS. 4 and 5 show a preforming process and apparatus for forming the hollow material 4 into the preforming member 8.

  A preforming device 31 for forming the preforming member 8 is disposed so as to be paired with a lower preform 15a placed and fixed on the base 14, and opposed to the lower preform 15a. And an upper preforming die 15b. The upper preforming die 15b is fixed to a ram 17 slidably mounted on a guide (not shown) on the base 14, and the ram 17 is configured to be interlocked with the driving of a knuckle press mechanism 16 as a driving device. Has been.

  The lower preforming die 15a is provided with a tapered hole 15d that gradually and widely opens toward the upper facing surface 15c. The hollow material 4 abuts at the lower end of the tapered hole 15d, and a first core is formed. The mold 18 is placed in a state where it is inserted.

  The upper preforming die 15b is provided with a tapered hole 15f that gradually and widely opens toward the lower facing surface 15e, and the hollow material 4 is disposed in the tapered hole 15f so as to come into contact with the upper end portion. . The upper preforming die 15b is fixed to the ram 17 at the upper end thereof, and is configured to move vertically up and down by driving the knuckle press mechanism 16.

  The tapered holes 15d and 15f do not have to be conical surfaces whose inner diameters increase linearly, and may increase gradually or stepwise.

  Further, the preforming apparatus 31 includes a first core mold 18 erected at the center of the lower preform mold 15a, and a mounting table 19 that moves slidably up and down around the first core mold 18. And an extraction mechanism 20 as an extraction means provided in the apparatus.

  The extraction mechanism 20 includes the mounting table 19, a connecting shaft 21 extending below the mounting table 19, and a cylinder mechanism 22 that slides the connecting shaft 21 up and down. The mounting table 19 is formed from the lower portion of the first core mold 18. It moves up and down.

  According to the preforming device 31, as shown in FIGS. 4 and 5, the knuckle press mechanism 16 is driven so that the upper and lower preforming dies 15a and 15b are surrounded with each other so as to surround the first core die 18. The upper and lower ends of the hollow material 4 are pressed and molded by the inner peripheral surfaces of the respective tapered holes 15d and 15f.

  In this case, the hollow material 4 is not a cylindrical shape having a circular center hole, but a cylindrical shape having a central shape 2 having a cross-sectional shape obtained by enlarging the deformed hole into a substantially similar shape, that is, a pre-stage before forming the deformed hole. Therefore, the center hole can be brought close to the desired dimensional shape in a stepwise manner, there is no difficulty in the flow deformation of the material in the forging process, the processing accuracy is high, and the processing defects are few.

  By this preforming step, the intermediate large diameter portion 7 is formed on the outer peripheral surface of the hollow material 4, and the tapered portion 6 having a large diameter toward the intermediate large diameter portion 7 is preformed. Further, the center hole size of the center hole 2 of the hollow material 4 is reduced so as to gradually become smaller from the large-diameter step portion toward both ends, and the center hole 5 is preliminarily finished to have a substantially irregular shape.

  Thus, the preformed member 8 shown in FIG. 6 is obtained.

  Next, as shown in FIG. 7, by operating the cylinder mechanism 22 of the extraction mechanism 20, the mounting table 19 is moved upward, the preforming member 8 is extracted from the first core mold 18 and conveyed to the next process. .

  Next, as shown in FIGS. 8 and 9, the finish molding device 32 for molding the preformed member 8 into the stepped hollow member 11 includes a lower finish molding die 23 a mounted and fixed on the base 14. The upper finishing mold 23b is disposed above the lower finishing mold 23a and is paired with the upper finishing mold 23b. The upper finishing mold 23b is fixed to the ram 17 for transmitting the force of the knuckle press mechanism 16 serving as a driving device. Has been.

  On the upper surface of the lower finish mold 23a, a stepped finish surface 23c for finish-molding the large-diameter stepped portion 10 is formed. At the center of the stepped finish surface 23c, the lower cylindrical end of the stepped hollow member 11 is formed. A lower finishing hole 23d corresponding to the outer diameter of 30a is opened.

  Similarly, the upper finishing mold 23b is formed with a step finished surface 23e for finishing the large-diameter stepped portion 10, and the upper cylindrical end of the stepped hollow member 11 is formed at the center of the step finished surface 23e. An upper finishing hole 23f corresponding to the outer diameter of 30b is opened. The upper finishing mold 23b is fixed to the ram 17 at the upper end thereof, and is configured to move vertically up and down by driving the knuckle press mechanism 16 so as to contact and separate from the lower finishing mold 23a.

  The finish molding apparatus 32 includes a second core mold 24 erected at the center of the lower finish molding member 23a, and a mounting table 25 that moves slidably up and down around the second core mold 24. And an extraction mechanism 26 as an extraction means provided in the apparatus.

  The cross-sectional shape of the second core mold 24 in the circumferential direction is substantially rectangular as a whole, and the portions corresponding to the four sides are formed so as to be recessed in an arc shape, and the four corners are extremely small rectangular shapes. Protrusions are formed.

  The extraction mechanism 26 includes the mounting table 25, a connecting shaft 27 extending below the mounting table 25, and a cylinder mechanism 28 that slides the connecting shaft 27 up and down. The mounting table 25 is formed from the lower part of the second core mold 24. It moves up and down.

  According to the above finish molding apparatus 32, as shown in FIG. 8, the preforming member 8 is fitted into the second core mold 24, and the preforming member 8 has a lower end at the step finish surface of the lower finishing mold 23a. It is placed in contact with 23c. Then, as shown in FIG. 9, by driving the knuckle press mechanism 16, the upper and lower finish molds 23a and 23b approach each other so as to surround the second core mold 24, and the preforming member 8 is moved to the respective parts. Press molding is performed on the inner peripheral surfaces of the finished surfaces 23c and 23e and the finishing holes 23d and 23f. At the same time, the center hole 5 of the preforming member 8 is pressed so as to hug the second core mold 24. As a result, the large-diameter step portion 10 is finish-molded on the outer peripheral surface of the stepped hollow member 11 and the rectangular deformed hole 9 following the second core mold is finish-molded.

  In this finish forming step, the preforming member 8 is gently preliminarily formed with a tapered portion 6 having a large diameter toward the large-diameter step portion 10 on the outer periphery, and the center hole size is set to the large-diameter step portion in the center hole 5. It is formed so as to be reduced toward the first core mold so as to be gradually reduced from the portion toward both ends. Therefore, the force applied from the upper and lower directions by the finish molds 23 a and 23 b generates a force toward the center direction of the second core mold 24 by the tapered portion 6. In addition, since the center hole dimension is formed so as to be gradually reduced, partial hardness unevenness due to the difference in the degree of processing hardly occurs. Therefore, the material flow that hugs the second core mold 24 is generated smoothly, the inner periphery of the center hole 9 of the stepped hollow member 11 is not constricted, and the notched annular groove is not generated. In addition, the stepped hollow member 11 of FIG. 10 is obtained by this finish molding process.

  Next, as shown in FIG. 11, grooves 12 extending in the axial direction are formed at four corners of the center hole 9 of the stepped hollow member 11 by a manufacturing process by ironing (not shown). The inner wall surface is formed on a circular arc surface 13 that follows a cylindrical shape. In this case, the center hole 9 of the stepped hollow member 11 formed in the finish forming step is substantially rectangular as a whole in the cross-sectional shape in the circumferential direction, and the portions corresponding to the four sides are each formed in an arc shape. The four corners are formed with extremely small rectangular recesses. Therefore, when the groove 12 is formed in the corner portion and the arc surface 13 is formed in the portion corresponding to the side, excess material in the portion corresponding to the side is smoothly flowed to the corner portion where the material is insufficient, as shown in FIG. The stepped hollow member 11 having such a desired size and shape is formed. Therefore, it is possible to provide a stepped hollow member having a small dimension and shape with low cost and high accuracy, which requires less plastic working margin and has a high material yield.

  In the above-described embodiment, the center hole 9 of the stepped hollow member 11 is a rectangular deformed hole. However, the present invention can be applied to a stepped hollow member having a triangular or other polygonal center hole. .

  In the embodiment described above, the grooves 12 are formed at the four corners of the center hole 9, respectively, but the number of grooves is not limited, and any number may be used as necessary.

The top view and sectional drawing of a blank. The top view and sectional drawing which show the process which drilled the center hole in the blank. The top view and sectional drawing which show the process which punched the bottom part and shape | molded the hollow raw material. Sectional drawing which shows a preforming apparatus. The figure which shows the state which shape | molded the preforming member. The top view and sectional drawing which show a preforming member. Sectional drawing which shows the state which extracted the preforming member from the core type | mold. Sectional drawing which shows a finish molding apparatus. The figure which shows the state which shape | molded the stepped hollow member. The top view and sectional drawing which show a stepped hollow member. The top view and sectional drawing which show the stepped hollow member by which the groove | channel and the circular arc surface were shape | molded. Sectional drawing which shows the blank of a prior art. Sectional drawing which shows the formation process of the lower end small diameter part of the stepped hollow member of a prior art. The top view and sectional drawing which show the drilling process of the stepped hollow member of a prior art. The top view and sectional drawing which show the formation process of the large diameter step part of the stepped hollow member of a prior art. The top view and sectional drawing which show the formation process of the center hole of the stepped hollow member of a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Blank, 2 ... Center hole, 4 ... Hollow material, 5 ... Center hole, 6 ... Tapered part, 7 ... Intermediate | middle large diameter part, 8 ... Pre-forming member, 9 ... Center hole, 10 ... Large diameter step part, 11 ... Stepped hollow member, 12 ... Groove, 13 ... Arc surface, 15a ... Lower preform, 15b ... Upper preform, 15c ... Opposite surface, 15d ... Taper hole, 15e ... Opposite surface, 15f ... Taper hole, 16 ... Knuckle press mechanism (drive device), 18 ... first core mold, 20 ... drawing mechanism (drawing means), 23a ... lower finish mold, 23b ... upper finish mold, 23c ... stepped surface, 23d ... lower finish hole , 23e: Stepped surface, 23f: Upper finishing hole, 24: Second core type, 30a: Lower cylindrical end, 30b: Upper cylindrical end.

Claims (4)

In the method of manufacturing a stepped hollow member in which a large-diameter stepped portion protrudes between both cylindrical ends and a deformed hole having a cross-section different from a circle on the axis is penetrated,
A hollow material is inserted into a first core mold having a cross-sectional shape corresponding to the deformed hole,
At least one end of the hollow material is formed by enclosing a pair of preforming dies in which tapered holes are formed in at least one of the opposing surfaces so as to surround the first core die and approach each other. And pressing the taper hole inner peripheral surface one or more times to form a tapered portion having a large diameter from both ends of the hollow material to the space between the both ends on the outer peripheral surface of the hollow material, A preforming step in which the hollow material is preliminarily finished to form a preformed member so that the center hole size of the hollow material gradually decreases toward both ends of the hollow material and decreases to an irregular shape toward the first core mold. When,
The preformed member is extracted from the first core mold, and is inserted into a second core mold having a cross-sectional shape corresponding to the deformed hole,
A pair of finish forming dies each having a step finish surface for finishing and molding the large-diameter step portion from both sides, each having a finish hole having an inner diameter corresponding to the outer diameter of each of the cylindrical end portions. By encircling the second core mold and approaching each other, the tapered portions of the preformed member are pressed by the finishing holes and the stepped surface, so that the cylindrical both end portions and the large diameter stepped portion are pressed. A method of manufacturing a stepped hollow member including forming and forming the center hole into the deformed hole by pressing against the second core mold. After the finish molding process,
The manufacturing method of the stepped hollow member of Claim 1 which has the process of forming in the corner | angular part of the said odd-shaped hole the groove | channel extended in an axial direction, and forming the inner wall surface in the circular arc surface which follows a column shape. The hollow material is formed into a cylindrical shape having a center hole having a cross-sectional shape obtained by enlarging the deformed hole into a substantially similar shape, and the hollow material is formed by forging a columnar blank. The manufacturing method of the stepped hollow member of Claim 2. In the manufacturing apparatus of a stepped hollow member in which a large-diameter stepped portion is projected between both cylindrical end portions and a deformed hole having a cross-section different from a circle is penetrated on the axis line,
A first core type having a cross-sectional shape corresponding to the deformed hole, into which a hollow material is inserted,
A pair or a plurality of pairs of preforming dies in which a tapered hole surrounding the first core mold is opened on at least one of the opposing surfaces, and the end of the hollow material is pressed by the inner peripheral surface of the tapered hole In addition, a taper portion having a large diameter is formed on the outer peripheral surface of the hollow material from both ends of the hollow material, and the center hole size of the hollow material gradually decreases toward both ends of the hollow material. And a pair or a plurality of pairs of preforming molds for forming the hollow material into a preformed member so as to decrease in an irregular shape toward the first core mold,
Means for extracting from the first core mold a preformed member having tapered portions formed at both ends;
A second core mold having a cross-sectional shape corresponding to the deformed hole, and into which the preformed member is inserted;
Stepped finish surfaces for finishing and molding the large-diameter stepped portion from both sides are formed opposite to each other, and finish holes having inner diameters corresponding to the outer diameters of the cylindrical end portions open to the respective stepped finished surfaces. A pair of finish molds surrounding the second core mold so as to be able to come into contact with and separating from the second core mold, wherein the finishing holes and the stepped surface are pressed against the tapered portion of the preformed member. An apparatus for manufacturing a stepped hollow member having a pair of finish forming dies that form both cylindrical end portions and a large-diameter stepped portion and press the center hole against the second core die to form the deformed hole.

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