JPH10156479A - Thread forming method and press forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the method for forming a thread with reduced number of processes at high speed. SOLUTION: An inner tool 5, which consists of plural inner tool divided bodies 6, 7 arranged on a circumference of circle coaxially to a circumference of circle of an outer tool 3 and is movable to a reducing position and an expanding position of an outer tool 3 in the radial direction, is constructed so that a connecting part between the divided bodied 6, 7 of first/second groups makes the first group divided body 6 movable to the reducing position and a movement of this first group divided body 6 to the reducing position makes a subsequent movement of the second group divided body 7 to the reducing position. In thread forming, the second group divided body 7 among the inner tool divided bodies 6, 7 is moved to the expanding position, successively, the first group divided body 6 is moved to the expanding position, at the same time, the outer tool divided body 4 is moved to the reducing position and presses the cylindrical part of a sheet press part, thus, a continuous thread is press- formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw forming method and a press forming apparatus for press-forming a screw on a cylindrical portion of a sheet metal molded product used for a bathroom lamp case or the like.

[0002]

2. Description of the Related Art As an example of a sheet metal molded product, as shown in FIG. 10, a steel plate is drawn in a hat shape, and a cylindrical portion 1a is formed.
And a flange portion 1b and a top surface portion 1c. FIG. 11 shows a screw-formed product 2 in which the screw 2a is formed in the cylindrical portion 1a.

As shown in FIG. 12, a conventional screw forming apparatus of this type is a columnar member which is attached to a chuck 51 of a lathe and has a spiral groove forming portion 52a formed on an outer peripheral portion, and is drawn in a hat shape. A core 52 fitted to the inner surface of the cylindrical portion 1a of the sheet metal molded product 1, a holding member 53 for fixing the molded product 1 to the chuck 51, and a screw 2a pressed against the cylindrical portion 1a attached to a carriage 54 of a lathe. And a tool 55 for molding.

[0004] In the screw forming method according to this configuration, a sheet metal molded product 1 drawn and formed in a hat shape by another press machine is connected to a core 5.
2, the tool 55 is pressed from the outer peripheral side against the portion of the cylindrical portion 1a facing the concave portion of the spiral groove forming portion 52a while the lathe is started and rotated around the center L of the circumference. The carriage 54 is synchronized with the rotation of the lathe so that the core 5
The screw 2a is pressed and formed on the cylindrical portion 1a by feeding and moving the screw 2a in accordance with the pitch of the second spiral groove forming portion 52a. And after the screw molding is completed,
Stop the lathe, remove the retainer 53, and complete the screw molding 2
Is rotated along the spiral groove forming portion 52a with respect to the core 52, and is removed to start screw forming of the next sheet metal molded product 1.

[0005]

However, in the conventional screw forming apparatus and the conventional screw forming method, the core 5 of the sheet metal molded product 1 is used.
The number of steps is large, and the time required for each step is large, such as mounting on the mounting member 2, fixing the holding member 53, forming the screw 2 a by moving the carriage 54 on the lathe, and rotating the screw-formed product 2. Therefore, the speed-up of screw forming was not sufficient.

In view of the above problems, an object of the present invention is to provide a screw forming method and a press forming apparatus capable of forming a screw at a high speed with a small number of steps.

[0007]

In order to achieve the above object, a screw forming method and a press forming apparatus according to the present invention provide an external tool that contacts an outer peripheral surface of a cylindrical portion of a sheet metal molded product and an inner tool that contacts an outer peripheral surface thereof. The outer tool is formed of a plurality of outer tool divided bodies arranged on a circumference, and each outer tool divided body is radially reduced in diameter. The inner peripheral surface can be moved to a position and an enlarged diameter position, and at the reduced diameter position, the respective inner peripheral surfaces are connected to each other in a circular shape, and a continuous spiral groove forming portion is formed on these inner peripheral surfaces. It consists of a plurality of inner tool divided bodies arranged on a circumference concentric with the circumference of the tool, and each inner tool divided body is movable in a radial direction between a reduced diameter position and an increased diameter position, and has an increased diameter position. In this case, the respective outer peripheral surfaces are connected to each other in a circular shape, and a spiral groove forming portion continuous with these outer peripheral surfaces is formed. The divided bodies of the first group and the divided bodies of the second group are alternately arranged among the inner tool divided bodies, and the connection between the divided bodies of the first and second groups is formed by the first group. To move the divided body to the reduced diameter position,
The movement of the divided body of the first group to the reduced diameter position allows the subsequent movement of the divided body of the second group to the reduced diameter position. Of the divided bodies, the divided bodies of the second group move to the enlarged diameter position, and then the divided bodies of the first group move to the enlarged diameter position, and the outer tool divided bodies move to the reduced diameter position. The cylindrical part of the molded product is pressed and a screw continuous to this cylindrical part is press-formed. After the completion of the screw forming, the outer tool divided body moves to the diameter expanding position, and the inner tool divided body of the first group The divided body moves to the reduced diameter position, and thereafter, the divided body of the second group moves to the reduced diameter position to remove the screw-formed product.

According to the screw forming method and the press forming apparatus of the present invention, even if the continuous spiral groove forming portion is provided on the outer peripheral surface of the inner tool divided body, the divided body of the first group among the inner tool divided bodies is provided. Can be moved to the reduced-diameter position, and then the divided body of the second group can be moved to the reduced-diameter position, and the outer tool divided body can be moved to the increased-diameter position. It is possible to attach and remove the screw-formed product without rotating it. Then, among the inner tool divided bodies, the divided body of the second group is moved to the diameter increasing position, and then the divided body of the first group is moved to the enlarged diameter position, and the outer tool divided body is moved to the reduced diameter position. Since a continuous screw can be formed on the cylindrical portion of the sheet metal molded product by the pressing operation to be moved, the screws on the entire circumference of the cylindrical portion can be press-formed at once. Therefore, screw molding can be performed at a high speed with a small number of steps.

In the press forming apparatus according to the present invention, the outer tool support is provided with a biasing means for supporting the outer tool divided body so that the outer tool can be reduced in diameter and expanding the diameter and constantly biasing the outer tool in the radial direction. A ram provided with an urging means which is supported movably up and down and always urges in a descending direction, and an outer ram fixed to the ram for reducing the diameter of the outer tool divided body and expanding the diameter thereof as the outer tool support is lowered and raised. A cam, an inner tool support base provided with biasing means for supporting the inner tool divided body so as to be able to reduce and expand the diameter and constantly biasing it in the diameter reducing direction. A bolster provided with a biasing means for biasing in the direction, an inner cam fixed to the bolster and reducing and expanding the inner tool divided body as the inner tool support rises and descends, and a ram facing the bolster. Driving means for moving the outer cam up and down, and The inner tool is configured to always abut against the surface and to move the outer tool segments in their respective radial directions to reduce and increase the inner diameter thereof, and to provide a connection between the first and second groups of inner tool segments. The surface is constituted by a surface inclined with respect to a line connecting the center of the circumference and the center of the divided body, and the inclined surface enables the divided body of the first group to move to the reduced diameter position, The movement of the divided body of the first group to the reduced diameter position is configured to allow the subsequent movement of the divided body of the second group to the reduced diameter position, and the inner cam is configured to move the inner circumference of the inner tool divided body. When the diameter is reduced, the divided body of the first group is moved to the reduced diameter position, and then the divided body of the second group is moved to the reduced diameter position. After moving the divided body to the enlarged position, the divided body of the first group is moved to the enlarged position. Then, the same effect as above can be performed by one step of the vertical movement of the ram by the drive means. The means for converting the vertical movement of the ram into the movement of the outer tool divided body and the inner tool divided body to the reduced diameter and increased diameter positions can be realized with a simple configuration of the cam and the urging means.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIGS. 1 to 9, the press forming apparatus of the present invention comprises an outer tool 3 contacting an outer peripheral surface of a cylindrical portion 1a of a sheet metal molded product 1 and an inner tool 5 contacting an inner peripheral surface thereof. The present invention relates to a press forming apparatus for press-forming a screw 2a by using the above method.

The press forming apparatus includes an outer tool 3 composed of four outer tool divided bodies 4 arranged on a circumference, and eight outer tools 3 arranged on a circumference concentric with the circumference of the outer tool 3. Inner tool split 6,
7, an outer tool support 8 that supports the outer tool divided body 4 so as to be able to reduce and expand the diameter, a ram 18 that supports the outer tool support 8 movably up and down, and is fixed to the ram 18. The outer cam 11 for reducing and increasing the diameter of the outer tool segment 4 as the outer tool support 8 moves up and down with respect to the ram 18, and the inner cam for supporting the inner tool segments 6 and 7 so as to reduce and increase the diameter. A tool support 9, a bolster 19 for vertically supporting the inner tool support 9, and an inner tool support 9 fixed to the bolster 19;
An inner cam 12 for reducing the diameter of the inner tool divided bodies 6 and 7 as the bolster 19 moves up and down with respect to the bolster 19, and a driving means (not shown) for moving the ram 18 up and down opposite to the bolster 19 are provided.

As shown in FIGS. 1 and 3, the outer tool divided body 4 has a sliding portion 4 so that each of the outer tool divided bodies 4 does not fall down.
c is supported by the guide groove 8a of the outer tool support 8 and is movable along the guide groove 8a in the radial direction between the reduced diameter position and the increased diameter position. At the reduced diameter position, the respective inner peripheral surfaces are connected to each other. A spiral groove forming portion 4a is formed on the inner peripheral surface, which is a continuous circle. In addition, a contact slope 4d, a reduced-diameter contact surface 4e, and a larger-diameter contact surface 4f are provided on the outer peripheral surface that contacts the outer cam 11.

As shown in FIGS. 1 and 4, each of the inner tool divided bodies 6 and 7 has a slide portion 6c and 7c, respectively.
Are guided by the guide grooves 9b and 9c.
b, 9c can be moved in the radial direction between a reduced diameter position and an increased diameter position. At the increased diameter position, the outer peripheral surface and the inner peripheral surface are connected to each other in a circular shape, and the spiral groove is continuous with these outer peripheral surfaces. Forming portions 6a and 7a are configured. Also, the inner cam 12
On the inner peripheral surface that comes into contact with, there are provided contact slopes 6d, 7d, reduced-diameter contact surfaces 6e, 7e, and enlarged-diameter contact surfaces 6f, 7f.

As shown in FIG. 2, four of the inner tool divided bodies 6, 7 are divided into the first group 6 and the remaining four
And the divided bodies 7 of the first group are alternately arranged one by one on the circumference, and the connecting surface A between the divided bodies 6 and 7 of the first and second groups is arranged.
Is constituted by an inclined surface whose inner peripheral side is wider than its outer peripheral side with respect to a plane including the center L of the circumference and the center of the divided body 6 of the first group, and this inclined surface is The movement of the divided body 6 of the group to the reduced diameter position is enabled, and the movement of the divided body 6 of the first group to the reduced diameter position is subsequently moved to the reduced diameter position of the divided body 7 of the second group. Is possible.

The outer tool support 8 is provided with a guide groove 8a for guiding the slide portion 4c of the outer tool divided body 4, and holds the outer tool divided body 4 so as to be movable only in the radial direction. The guide groove 8a accommodates a spring 13 that constantly urges the outer tool divided body 4 in the radially expanding direction and presses the outer tool divided body 4 against the outer cam 11. Also, the top surface 1 of the sheet metal molded product 1 before and after the screw molding.
A retaining plate 21 for suppressing the floating of c is held by a retaining bolt 22 so as to be vertically movable, and is constantly urged by a spring 23 in a downward direction.

The ram 18 includes a retaining bolt 20 for vertically moving the outer tool support 8 so as not to fall down, and a spring 14 for constantly urging the outer tool support 8 in a downward direction. An outer cam 11 that is provided and reduces and expands the diameter of the outer tool divided body 4 with the vertical movement of the outer tool support 8 is fixed.

The outer cam 11 has a cam surface 11a which comes into contact with the reduced-diameter contact surface 4e at the reduced-diameter position of the outer-tool divided member 4 and abuts against the enlarged-diameter contact surface 4f at the increased-diameter position. 4 and a cam slope 11b that comes into contact with the abutment slope 4d when the diameter is reduced and increased.

The inner tool support 9 has inner tool divisions 6 and 7
Guide grooves 9b, 9 for guiding the sliding portions 6c, 7c
c is provided to hold the inner tool divided bodies 6 and 7 movably only in the radial direction. In these guide grooves 9b and 9c,
The inner tool splits 6 and 7 are constantly urged in the radially decreasing direction so that the inner cam 1
2 are housed.

The bolster 19 is provided with a spring 17 which supports the inner tool support 9 in a vertically movable manner and constantly urges the ascending direction. With this vertical movement, the inner tool divided bodies 6 and 7 are reduced in diameter and diameter. The inner cam 12 for expanding the diameter is fixed.

As shown in FIGS. 1 and 5, the inner cam 12 comes into contact with the reduced diameter contact surfaces 6e and 7e at the reduced diameter position of the inner tool divided bodies 6 and 7 and at the enlarged diameter position. Surface 6f,
The cam surface 12a which comes into contact with 7f, and the first surface which comes into contact with the contact slope 6d when the diameter of the divided body 6 of the first group is reduced and expanded.
The cam slope 12b and the second cam slope 12 which comes into contact with the contact slope 7d when the diameter of the divided body 7 of the second group is reduced and expanded.
c is provided.

The first cam slope 12b is disposed below the second cam slope 12c.
When the diameter is reduced due to the rise of the diameter, the divided body 6 of the first group is reduced in diameter first, and then the diameter of the divided body 7 of the second group is reduced. When the diameter is increased, the second group of divided bodies 7 is expanded first, and thereafter the first group of divided bodies 6 can be expanded. Further, as shown in FIG. 5, the moving amount of the first group of divided bodies 6 in the diameter reducing direction is larger than the moving amount of the second group of divided bodies 7 in the diameter reducing direction. The upper space 12d is provided with a size large enough to allow the inner peripheral side of the divided body 6 of the first group at the reduced diameter position to enter.

The screw forming method according to the above configuration will be described below with reference to the drawings.

When the ram 18 is slightly raised by the driving means, as shown in FIGS.
The outer tool divided body 4 is urged in the radially increasing direction by the spring 13 because the outer tool 11 is urged by the outer cam 11 and fixed to the ram 18 so that the outer tool divided body 4 is expanded. 4f and the cam surface 11a of the outer cam 11 come into contact with each other and move to the diameter increasing position.
Then, since the inner tool support 9 is urged by the spring 17 and rises with respect to the inner cam 12 fixed to the bolster 19,
The divided body 6 of the first group of the inner tool 5 is urged by the spring 15, and the reduced diameter contact surface 6e of the divided body 6 and the cam surface 12a of the inner cam 12 come into contact with each other and move to the reduced diameter position. . As shown in FIG. 7, the movement of the divided body 6 of the first group to the reduced diameter position enables the movement of the next divided body 7 of the second group to the reduced diameter position.

When the ram 18 is further raised, FIGS.
As shown in the figure, the outer tool divided body 4 is separated upward from the inner tool divided bodies 6 and 7. And the inner tool support 9 is a spring 17
Is further raised with respect to the inner cam 12 fixed to the bolster 19, so that the divided body 7 of the second group of the inner tool 5 is urged by the spring 16 to reduce the diameter of the divided body 7. The contact surface 7e and the cam surface 12a of the inner cam 12 come into contact with each other and move to the reduced diameter position.

Here, the sheet metal molded product 1 is mounted on the inner tool divided bodies 6 and 7 so as to cover the cylindrical portion 1a. At this time, since the inner tool divided bodies 6 and 7 are both reduced in diameter, the mounting of the sheet metal molded product 1 is extremely easy. In practice, only the operation of placing on the inner tool divided bodies 6 and 7 is required, and automation is also possible. Easy.

Next, when the driving means is activated and the ram 18 is lowered, the holding plate 21 is lowered, and the lower surface of the holding plate 21 and the upper surfaces 6b, 7b of the inner tool divided bodies 6, 7 are used for sheet metal. The lift of the molded product 1 is suppressed by sandwiching the top surface 1c of the molded product 1, and the outer tool divided body 4 located at the enlarged diameter position is formed by the cylindrical portion 1a of the sheet metal molded product 1.
, So that the lower surface 4b of the outer tool divided body 4 and the upper surface 9a of the inner tool support 9 sandwich the flange portion 1b of the sheet metal molded product 1 and suppress the floating thereof.

6 and 7 when the ram 18 is further lowered.
Since the inner tool support 9 descends with respect to the inner cam 12 fixed to the bolster 19, as shown in FIG.
The second cam slope 12c of the inner cam 12 pushes and expands the contact slope 7d of the divided body 7 of the group
The enlarged diameter contact surface 7f and the cam surface 12a of the inner cam 12 come into contact with each other, and the divided body 7 moves to the enlarged diameter position, and the spiral groove forming portion 7a of the divided body 7 1a. As shown in FIG. 7, the movement of the divided bodies 7 of the second group to the expanded position enables the movement of the next divided body 6 of the first group to the expanded position.

When the ram 18 is lowered to the lower limit position, the inner tool support 9 is further lowered with respect to the inner cam 12, as shown in FIGS. 6, the first cam slope 12b of the inner cam 12 pushes the contact slope 6d, so that the enlarged diameter contact surface 6f of the divided body 6 and the cam surface 12a of the inner cam 12 come into contact with each other. Moves to the diameter-expanding position, and the spiral groove forming portion 6a of the divided body 6 fits into the inner surface of the cylindrical portion 1a of the sheet metal molded product 1. Thereafter, the outer tool support 8 is raised with respect to the outer cam 11 fixed to the ram 18, so that the contact slope 4d of the outer tool divided body 4 is
The first cam slope 11b narrows in the diameter reducing direction, and the reduced diameter contact surface 4e of the outer tool divided body 4 comes into contact with the cam surface 11a of the outer cam 11, so that the outer tool divided body 4 moves to the reduced diameter position. The cylindrical portion 1a of the sheet metal molded product 1 is pressed to press-mold a screw 2a continuous with the cylindrical portion 1a.

When the ram 18 is raised again, as described above, the outer tool divided body 4 moves to the radially enlarged position and is separated upward, and the divided body 6 of the first group of the inner tool 5 is moved to the radially reduced position. Then, the divided bodies 7 of the second group move to the diameter reducing position, so that the screw-formed product 2 can be removed upward without rotating. And the next sheet metal molding 1
And screw driving can be performed by activating the driving means.

In the above embodiment, the outer tool 3 is constituted by the four outer tool divided bodies 4. However, the present invention is not limited to this. For example, the outer tool 3 may be constituted by three outer tool divided bodies. Is also good. Further, although the inner tool 5 is constituted by the eight inner tool divided bodies 6 and 7, the present invention is not limited to this, and may be constituted by, for example, four inner tool divided bodies.

Further, in the above embodiment, the inner tool divided bodies 6 and 7 are enlarged in diameter, and then the outer tool divided body 4 is reduced in diameter and screw-formed. However, the present invention is not limited to this. Alternatively, the diameter of the outer tool divided body may be reduced first, and then the diameter of the inner tool divided body may be increased to form a screw.

In the above embodiment, the continuous screw 2a is formed, but the present invention is not limited to this, and a partial screw may be formed.

[0034]

According to the screw forming method and the press forming apparatus of the present invention, even if the continuous spiral groove forming portion is provided on the outer peripheral surface of the inner tool divided body, the first group of the inner tool divided body is formed. After the divided body is moved to the reduced diameter position, the divided body of the second group can be moved to the reduced diameter position, and the outer tool divided body can be moved to the increased diameter position. This makes it possible to easily attach and remove the screw-formed product without rotating it. Then, among the inner tool divided bodies, the divided body of the second group is moved to the diameter increasing position, and then the divided body of the first group is moved to the enlarged diameter position, and the outer tool divided body is moved to the reduced diameter position. Since a continuous screw can be formed on the cylindrical portion of the sheet metal molded product by the pressing operation to be moved, the screws on the entire circumference of the cylindrical portion can be press-formed at once. Therefore, screw molding can be performed at a high speed with a small number of steps.

In the press forming apparatus according to the present invention, the outer tool support is provided with an urging means for supporting the outer tool divided body so that the outer tool can be reduced in diameter and expanding the diameter, and constantly urging the outer tool divided body in the diameter increasing direction. A ram provided with an urging means which is supported movably up and down and always urges in a descending direction, and an outer ram fixed to the ram for reducing the diameter of the outer tool divided body and expanding the diameter thereof as the outer tool support is lowered and raised. A cam, an inner tool support base provided with biasing means for supporting the inner tool divided body so as to be able to reduce and expand the diameter and constantly biasing it in the diameter reducing direction. A bolster provided with a biasing means for biasing in the direction, an inner cam fixed to the bolster and reducing and expanding the inner tool divided body as the inner tool support rises and descends, and a ram facing the bolster. Driving means for moving the outer cam up and down, and The inner tool is configured to always abut against the surface and to move the outer tool segments in their respective radial directions to reduce and increase the inner diameter thereof, and to provide a connection between the first and second groups of inner tool segments. The surface is constituted by a surface inclined with respect to a line connecting the center of the circumference and the center of the divided body, and the inclined surface enables the divided body of the first group to move to the reduced diameter position, The movement of the divided body of the first group to the reduced diameter position is configured to allow the subsequent movement of the divided body of the second group to the reduced diameter position, and the inner cam is configured to move the inner circumference of the inner tool divided body. When the diameter is reduced, the divided body of the first group is moved to the reduced diameter position, and then the divided body of the second group is moved to the reduced diameter position. After moving the divided body to the enlarged position, the divided body of the first group is moved to the enlarged position. Then, the same effect as above can be performed by one step of the vertical movement of the ram by the drive means. The means for converting the vertical movement of the ram into the movement of the outer tool divided body and the inner tool divided body to the reduced diameter and increased diameter positions can be realized with a simple configuration of the cam and the urging means.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an embodiment of the present invention.

FIG. 2 is a schematic plan sectional view showing an outer tool and an inner tool according to one embodiment of the present invention.

FIG. 3 is a partial bottom view showing the external tool according to the embodiment of the present invention and the vicinity thereof.

FIG. 4 is a partial plan view showing the inner tool and its vicinity according to the embodiment of the present invention.

FIG. 5 is a schematic perspective view showing an inner cam according to one embodiment of the present invention.

FIG. 6 is a view for explaining a state in which the ram according to the embodiment of the present invention is in the middle of descending position, in which the outer tool divided body expands, the inner tool first group divided body decreases in diameter, and The schematic plan sectional view showing the state where the diameter of the divided object of the 2nd group of tools was expanded.

FIG. 7 is a schematic plan sectional view showing the outer tool and the inner tool in the state of FIG. 6;

FIG. 8 is a view for explaining a state in which the ram is at the lowermost lower limit position according to the embodiment of the present invention, in which the divided bodies of the first and second groups of the inner tool are expanded, and the outer tool divided bodies are reduced in diameter. FIG.

FIG. 9 is a schematic plan sectional view showing the outer tool and the inner tool in the state of FIG. 8;

FIG. 10 is a perspective view showing an example of a sheet metal molded product.

FIG. 11 is a perspective view showing an example of a screw-formed product.

FIG. 12 is a schematic plan view showing a conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 sheet metal molded product 1 a cylindrical portion 2 screw-completed product 2 a screw formed into cylindrical portion 3 outer tool 4 outer tool divided body 4 a spiral groove forming portion of outer tool divided body 5 inner tool 6 inner tool of first group Divided body 6a Spiral groove forming part of divided body of first group of inner tools 7 Divided body of second group of inner tool 7a Spiral groove forming part of divided body of second group of inner tool 8 Outer tool support Reference Signs List 9 inner tool support 11 outer cam 12 inner cam 13-17 spring (biasing means) 18 ram 19 bolster A connection between divided bodies of first and second groups L center of circumference

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Atsushi Takekawa 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (5)

[Claims] 1. A screw forming method for press-forming a screw on a cylindrical portion of a sheet metal molded product using an outer tool contacting an outer peripheral surface thereof and an inner tool contacting an inner peripheral surface thereof, wherein the outer tool comprises: It is composed of a plurality of outer tool divided bodies arranged on the circumference, and each outer tool divided body can be moved in the radial direction between the reduced diameter position and the increased diameter position, and at the reduced diameter position, each inner peripheral surface is moved. A spiral groove forming portion is formed on the inner peripheral surface, which is a circle connected to each other, and the inner tool is formed from a plurality of inner tool divided bodies arranged on a circumference concentric with the circumference of the outer tool. Each of the inner tool divided bodies can be moved in a radial direction between a reduced diameter position and an increased diameter position. At the increased diameter position, the respective outer peripheral surfaces are circularly connected to each other, and spiral grooves continuous with these outer peripheral surfaces are formed. A forming unit is configured, and the divided body of the first group and the divided body of the second group among the inner tool divided bodies are formed. And the connecting portions between the divided bodies of the first and second groups allow the divided bodies of the first group to move to the reduced diameter position. The movement to the reduced diameter position is configured to enable the subsequent movement of the divided body of the second group to the reduced diameter position. At the time of screw forming, the second group of the inner tool divided body is formed. The divided body moves to the enlarged diameter position, and then the divided body of the first group moves to the enlarged diameter position, and the outer tool divided body moves to the reduced diameter position, and presses the cylindrical portion of the sheet metal molded product. Press forming a continuous screw on this cylindrical part, and after the screw forming is completed, the outer tool divided body moves to the expanded position,
A screw wherein a divided body of a first group of the inner tool divided bodies moves to a reduced diameter position, and thereafter a divided body of a second group moves to a reduced diameter position to remove a screw formed product. Molding method. 2. The inner tool has a substantially cylindrical shape as a whole at the time of diameter reduction, and a connecting surface between the divided bodies of the first and second groups is formed with respect to a line connecting the center of the circumference and the center of the divided body. The inclined surface is configured to allow the first group of divided bodies to move to the reduced-diameter position, and the movement of the first group of divided bodies to the reduced-diameter position is performed by the second group. 2. The screw forming method according to claim 1, wherein the group divided body can be moved to a reduced diameter position. 3. The outer tool comprises four outer tool splits,
3. The screw forming method according to claim 1, wherein the inner tool comprises eight inner tool divided bodies. 4. A press-forming apparatus for press-forming a screw on an outer peripheral surface of a cylindrical portion of a sheet metal molded product and an inner tool contacting an inner peripheral surface thereof, wherein the outer tool comprises: It is composed of a plurality of outer tool divided bodies arranged on the circumference, and each outer tool divided body can be moved in the radial direction between the reduced diameter position and the increased diameter position, and at the reduced diameter position, each inner peripheral surface is moved. A spiral groove forming portion is formed on the inner peripheral surface, which is a circle connected to each other, and the inner tool is formed from a plurality of inner tool divided bodies arranged on a circumference concentric with the circumference of the outer tool. Each of the inner tool divided bodies can be moved in a radial direction between a reduced diameter position and an increased diameter position. At the increased diameter position, the respective outer peripheral surfaces are circularly connected to each other, and spiral grooves continuous with these outer peripheral surfaces are formed. A forming unit is configured, and the divided body of the first group and the divided body of the second group among the inner tool divided bodies are formed. The divided bodies are alternately arranged, and the connection between the divided bodies of the first and second groups enables the divided bodies of the first group to move to the reduced diameter position, and the divided bodies of the first group are divided. The press forming apparatus is configured such that the movement of the divided body of the second group to the reduced diameter position can be performed thereafter. 5. An outer tool support base provided with a biasing means for supporting the outer tool divided body so as to be able to reduce the diameter and expanding the diameter and constantly biasing the outer tool divided body in the radial direction, and supporting the outer tool support base so as to be vertically movable. A ram provided with a biasing means for constantly biasing in a downward direction, an outer cam fixed to the ram and reducing and expanding the diameter of the outer tool divided body as the outer tool support is lowered and raised; An inner tool support base provided with an urging means for supporting the body so that the body can be reduced in diameter and expanding and constantly urging the body in the diameter reducing direction, A bolster provided with a biasing means, an inner cam fixed to the bolster and reducing and expanding the inner tool divided body as the inner tool support moves upward and downward, and a drive for moving the ram up and down in opposition to the bolster The outer cam always contacts the outer peripheral surface of the outer tool split, and the outer tool split Are moved in the respective radial directions to reduce and increase the inner diameter, and the connection surface between the divided bodies of the first and second groups of the inner tool is:
It is constituted by a surface inclined with respect to a line connecting the center of the circumference and the center of the divided body, and the inclined surface enables the divided body of the first group to move to the reduced diameter position, and the first group The movement of the divided body of the second group to the reduced diameter position is configured to allow the subsequent movement of the divided body of the second group to the reduced diameter position, and the inner cam is always provided on the inner peripheral surface of the inner tool divided body. When the diameter is reduced, the divided body of the first group is moved to the reduced diameter position, and then the divided body of the second group is moved to the reduced diameter position. When the diameter is increased, the divided body of the second group is moved. 5. The press-forming apparatus according to claim 4, wherein the first group of divided bodies is moved to the diameter increasing position after being moved to the diameter increasing position.