JP2022153042A - Manufacturing method of cylindrical member - Google Patents

Abstract

To manufacture a cylindrical member with precision in an extrusion method.SOLUTION: A manufacturing method of a cylindrical member includes a preparation step for preparing a cylindrical material, and a machining step for machining the cylindrical member by extruding the prepared cylindrical material from an extrusion port of a mold. When the cylindrical member is viewed in the view of a cross section orthogonal to an axis thereof, on an outer peripheral surface, a protrusion 20 that protrudes outward and a recess 22 that recesses inward are alternately formed in a circumferential direction, and on an inner peripheral surface, a maximum part 24 with a distance from the axis having a maximum value and a minimum part 26 with a distance from the axis having a minimum value are alternately formed in the circumferential direction. As specifying a value when the distance from the axis to the protrusion becomes the largest as D1 and a value when the distance from the axis to the recess becomes the smallest as D2, respectively, a position in the circumferential direction of the maximum part is positioned in an angular range in which the distance from the axis to the outer peripheral surface is (D1+D2)/2 or more, and a position in the circumferential direction of the minimum part is positioned in an angular range in which the distance from the axis to the outer peripheral surface is less than (D1+D2)/2.SELECTED DRAWING: Figure 3

Description

The technology disclosed in this specification relates to a method for manufacturing a tubular member. More particularly, it relates to a method of manufacturing a tubular member having a special cross-sectional shape.

A processing method (so-called extrusion method) is known in which a material is extruded from an extrusion port of a mold and processed into a cylindrical member. In the extrusion method, a cylindrical member having a special cross-sectional shape can be manufactured by adjusting the shape of the extrusion port of the mold. For example, Patent Literature 1 discloses a method of manufacturing a tubular member by an extrusion method.

JP 2014-237164 A

When forming a tubular member by an extrusion method, when the thickness (dimension in the radial direction) of the tubular member changes in the circumferential direction, the extrusion resistance of the material changes in the circumferential direction, There may be unevenness on the edge of the If the end portion of the tubular member becomes uneven, when the tubular member is released from the mold, a uniform force cannot be applied to the entire end portion of the tubular member, resulting in deformation of the tubular member. was there. If the cylindrical member has a special cross-sectional shape, a special processing method is required to correct the deformed cylindrical member to desired dimensions by cutting or the like. A technology for manufacturing by an extrusion method is desired.

This specification discloses a technique for manufacturing a tubular member with high accuracy by an extrusion method.

The method for manufacturing a cylindrical member disclosed herein includes a preparation step of preparing a cylindrical material, and a processing step of extruding the prepared cylindrical material from an extrusion port of a mold and processing it into a cylindrical member. ing. When the tubular member is viewed in a cross section perpendicular to its axis, the outer peripheral surface of the tubular member has an outwardly convex portion and an inwardly concave portion with respect to the convex portion in the circumferential direction. While a predetermined number are alternately formed on the inner peripheral surface of the cylindrical member, a maximum portion where the distance from the axis is the maximum value and a minimum portion where the distance from the axis is the minimum value are circles. The predetermined number are formed alternately in the circumferential direction. At the tip of the extrusion port of the mold, the maximum distance from the axis to the protrusion is D1, and the minimum distance from the axis to the recess is D2. The position of the direction is in the angular range where the distance from the axis to the outer peripheral surface is (D1 + D2) / 2 or more, and the position of the minimum portion in the circumferential direction is the distance from the axis to the outer peripheral surface is (D1 + D2) /2 or less.

In the method for manufacturing a cylindrical member, the cylindrical member is prepared, and the prepared cylindrical member is extruded through the extrusion port of the mold to be processed into the cylindrical member. By processing a cylindrical member into a cylindrical member, the overall processing rate can be reduced. In addition, in the cylindrical member, the maximum part of the inner peripheral surface is formed in the angle range where the convex part is formed on the outer peripheral surface (the angular range of (D1 + D2) / 2 or more), and the angle at which the concave part is formed on the outer peripheral surface A minimum portion of the inner peripheral surface is formed in the range (angle range less than (D1+D2)/2). Therefore, it is possible to reduce the difference in processing rate between the convex portion and the concave portion. As a result, the lubricating coating is formed satisfactorily over the entire circumference of the cylindrical member, and the occurrence of irregularities at the ends of the cylindrical member can be suppressed. Since it is possible to suppress the occurrence of unevenness in the end portion of the tubular member, it is possible to suppress deformation of the tubular member when the tubular member is released from the mold.

FIG. 4 is a vertical cross-sectional view of a cylindrical member used in the manufacturing method according to Example 1; FIG. 2 is a vertical cross-sectional view of a cylindrical member manufactured by the manufacturing method according to Example 1; FIG. 3 is a cross-sectional view of the cylindrical member shown in FIG. 2 (more specifically, a cross-sectional view taken along line III-III in FIG. 2); FIG. 5 is a diagram showing a state in which a cylindrical member is installed in a mold in the manufacturing method according to the first embodiment; FIG. 5 is a diagram showing the relationship between the cylindrical member and the insert punch in the state shown in FIG. 4; The figure which expanded the part (VI) enclosed by the two-dot chain line of FIG. FIG. 5 is a diagram showing a state after extrusion molding of a cylindrical member placed in a mold and before releasing from the mold in the manufacturing method according to the first embodiment; The figure which shows the insert punch used with the manufacturing method which concerns on a modification. FIG. 11 is a cross-sectional view of a cylindrical member manufactured by a manufacturing method according to a modification;

(Feature 1) In the method for manufacturing a cylindrical member disclosed in the present specification, in the preparatory step, the cylindrical material may be formed by cold drawing. In the working step, the cylindrical material may be cold worked into a tubular member. With such a configuration, it is possible to improve the dimensional accuracy of the cylindrical material, thereby improving the dimensional accuracy of the tubular member.

(Feature 2) In the manufacturing method of the tubular member disclosed in the present specification, the cross-sectional area of the extrusion port may be tapered so as to gradually decrease from the base end to the tip end. Then, in the working process, the cylindrical material may be extruded in a direction from the proximal end to the distal end. According to such a configuration, it is possible to improve the dimensional accuracy of the cylindrical member after molding.

(Feature 3) In the method for manufacturing a tubular member disclosed in the present specification, the mold includes a die for molding the outer peripheral surface of the tubular member, and a die arranged inside the die to form the inner peripheral surface of the tubular member. and a punch positioned between the die and the insert punch to press against the cylindrical material. The extrusion port may be formed by the inner peripheral surface of the die and the outer peripheral surface of the insert punch. In the processing step, the punch presses one end of the cylindrical material placed between the die and the insert punch, and the punch and the insert punch are moved toward the extrusion port, thereby forming the cylindrical material into a cylindrical member. may According to such a configuration, it is possible to efficiently manufacture the cylindrical member from the cylindrical member.

(Feature 4) In the method for manufacturing a cylindrical member disclosed in the present specification, the portion of the inner peripheral surface of the die that corresponds to the convex portion coincides with the outer peripheral surface of the cylindrical material, and the inner peripheral surface of the die The portion corresponding to the concave portion is located outside the inner peripheral surface of the cylindrical material, and the portion of the outer peripheral surface of the insert punch corresponding to the maximum portion is aligned with or inside the inner peripheral surface of the cylindrical material. It is located outside the peripheral surface, and the portion of the outer peripheral surface of the insert punch corresponding to the minimum portion may be located inside the inner peripheral surface of the cylindrical material. According to such a configuration, the difference between the processing rate of the convex portion and the processing rate of the concave portion when the cylindrical member is formed into the tubular member is reduced, and the dimensional accuracy of the formed tubular member can be improved. .

(Example 1) Hereinafter, a method for manufacturing a tubular member according to Example 1 will be described. First, the tubular member manufactured by the manufacturing method of Example 1 will be described. The cylindrical member of Example 1 is a key ring used in an automobile steering device. That is, in an automobile steering device, the key ring is fitted on the outer peripheral surface of the column shaft, and the key ring and the column shaft normally rotate together. A key groove is formed on the outer peripheral surface of the key ring. When the ignition key is turned off, the lock key engages with the key groove of the key ring to restrict the rotation of the column shaft. When a large rotational force is applied to the steering wheel in this state, the column shaft is allowed to rotate relative to the key ring, thereby preventing damage to the key ring.

Specifically, as shown in FIGS. 2 and 3, the key ring 10 of this embodiment includes a key groove portion 12 having a key groove formed on the outer peripheral surface, an outer peripheral tapered portion 14 having a circular cross section, and an inner peripheral tapered portion 14 having a circular cross section. A tapered portion 16 and a cylindrical portion 18 are provided. A cylindrical portion 18 is provided at one end of the key ring 10 . The outer diameter of the cylindrical portion 18 is D1, and the inner diameter of the cylindrical portion 18 is D4. The inner diameter D4 of the cylindrical portion 18 is larger than the outer diameter of the column shaft. Therefore, when the key ring 10 is attached to the column shaft, the cylindrical portion 18 does not come into contact with the column shaft.

The inner peripheral tapered portion 16 is provided adjacent to the cylindrical portion 18 . The inner peripheral taper portion 16 has an inner diameter that gradually decreases from the cylindrical portion 18 side toward the key groove portion 12 side. Specifically, the inner diameter of the inner peripheral tapered portion 16 is D4 at the end on the cylindrical portion 18 side and D3 (<D4) at the end on the key groove portion 12 side. D3 is slightly larger than the outer diameter of the column shaft. Therefore, when the key ring 10 is attached to the column shaft, the inner peripheral tapered portion 16 does not come into contact with the column shaft. The outer diameter of the inner peripheral tapered portion 16 is the same as the outer diameter of the cylindrical portion 18 and is D1.

The outer tapered portion 14 is provided adjacent to the inner tapered portion 16 . The outer diameter of the outer peripheral taper portion 14 gradually decreases from the cylindrical portion 18 side toward the key groove portion 12 side. Specifically, the outer diameter of the outer peripheral tapered portion 14 is D1 at the end on the cylindrical portion 18 side and D2 (<D1 and >D4) at the end on the key groove portion 12 side. The inner diameter of the outer peripheral tapered portion 14 is the same as the inner diameter of the end portion of the inner peripheral tapered portion 16 on the key groove portion 12 side, which is D3. Therefore, like the inner tapered portion 16, the outer tapered portion 14 does not come into contact with the column shaft.

The key groove portion 12 is provided adjacent to the outer peripheral tapered portion 14 . As shown in FIG. 3, on the outer peripheral surface of the key groove portion 12, a convex portion 20 that protrudes outward and a key groove 22 (an example of a concave portion in the claims) that is concave inward with respect to the convex portion 20 are formed. A predetermined number (12 pieces in this embodiment) are formed alternately in the circumferential direction. Each of the plurality of protrusions 20 is formed in the same shape and arranged at regular intervals in the circumferential direction. In the cross section shown in FIG. 3 (the cross section orthogonal to the axis of the key ring 10), the top of the projection 20 is formed in an arc shape centering on the axis of the key ring 10. As shown in FIG. Also, the diameter from the axis of the key ring 10 to the top of the projection 20 is D1.

Each of the plurality of key grooves 22 is formed in the same shape. Since the plurality of protrusions 20 have the same shape and are arranged at equal intervals in the circumferential direction, the plurality of key grooves 22 are also arranged at equal intervals in the circumferential direction. In the cross section shown in FIG. 3, the bottom of the key groove 22 is formed in an arc shape centering on the axis of the key ring 10. As shown in FIG. The diameter from the axis of the key ring 10 to the bottom of the key groove 22 is D2. A surface connecting the top of the projection 20 and the bottom of the key groove 22 extends radially from the axis of the key ring 10 .

On the other hand, the inner peripheral surface of the key groove portion 12 is formed in a regular polygonal prism shape by a predetermined number (12 pieces in this embodiment) of flat portions 25 . 3 (a cross section orthogonal to the axis of the key ring 10), the inner peripheral surface of the key groove portion 12 has a contour line of a regular dodecagon, and each side of the regular dodecagon and straight portions 24 located at the respective vertices of the regular dodecagon. That is, the straight portions 24 are positioned at the intersections of the adjacent flat portions 25 . As is clear from FIG. 3, the distance from the axis of the key ring 10 to the inner peripheral surface of the key groove portion 12 is maximum at each vertex of the regular dodecagon (that is, the straight line portion 24), and The minimum value occurs at the midpoint of the side (that is, the center line 26 of the flat portion 25). In other words, the distance from the axis to the inner peripheral surface of the key groove portion 12 is a function that changes in the circumferential direction, and takes a maximum value r2 (maximum portion) at each vertex of the regular dodecagon (that is, the straight portion 24). , a minimum value r1 (minimum portion) at the midpoint of each side of the regular dodecagon (ie, the center line 26 of the plane portion 25). As is clear from the figure, each vertex (maximum portion) and the midpoint (minimum portion) of each side of the regular dodecagon are alternately arranged at equal intervals in the circumferential direction.

Moreover, as is clear from FIG. 3, the positions of the vertices of the regular dodecagon (that is, the linear portions 24) in the circumferential direction are located at the center of the convex portion 20 in the circumferential direction. Therefore, the positions of the vertices of the regular dodecagon in the circumferential direction are located in the angular range where the distance from the axis to the outer peripheral surface is D1 (>(D1+D2)/2). On the other hand, the midpoint of each side of the regular dodecagon (that is, the center line 26 of the plane portion 25) is located at the center of the key groove 22 in the circumferential direction. Therefore, the position of the midpoint of each side of the regular dodecagon in the circumferential direction is located in the angular range where the distance from the axis to the outer peripheral surface is D2 (<(D1+D2)/2).

Here, the length r2 from the axis of the key ring 10 to the maximal portion (linear portion 24) is slightly larger than the radius of the column shaft (specifically, 1/2 of the inner diameter D3 of the outer peripheral tapered portion 14). , the length r1 from the axis of the key ring 10 to the minimum portion (center line 26 of the flat portion 25) is slightly smaller than the radius of the column shaft. Therefore, when the key ring 10 is attached to the column shaft (that is, when it is press-fitted), the key ring 10 is elastically deformed by the press fitting, and a clearance is formed between the key ring 10 and the column shaft at its maximum portion. A very small portion of the key ring 10 and its vicinity are in contact with the column shaft. The frictional force generated between the key ring 10 and the column shaft normally causes the key ring 10 and the column shaft to rotate together. On the other hand, when a large rotational force is applied to the steering wheel while the lock key is engaged with the key groove 22 of the key ring 10, the key ring 10 is further elastically deformed to prevent the column shaft from rotating (sliding). allow. This prevents the key ring 10 from being damaged. As is clear from the above description, by adjusting the contact area between the inner peripheral surface of the key ring 10 and the column shaft, the torque (acting on the column shaft) when the column shaft rotates (sliding) with respect to the key ring 10 can be adjusted. torque) can be controlled.

Next, a method for manufacturing the key ring 10 described above will be described. To manufacture the key ring 10, first a cylindrical material 30 is provided. The dimensions of the cylindrical material 30 to be prepared are, as shown in FIG. 1, an outer diameter D1, an inner diameter D4, and an axial length L2. Therefore, the outer diameter D1 of the cylindrical material 30 is the same as the diameter up to the top of the protrusion 20 of the key ring 10, and the inner diameter D4 of the cylindrical material 30 is the same as the inner diameter of the cylindrical portion 18. . Further, the axial length L2 of the cylindrical material 30 is smaller than the axial length L1 of the key ring 10, and is set so that the volume of the cylindrical material 30 and the volume of the key ring 10 are the same. By preparing the cylindrical material 30 having such dimensions, it is possible to reduce the processing rate when the cylindrical material 30 is plastically deformed into the key ring 10, and the key ring 10 can be molded with high accuracy. The cylindrical material 30 can be prepared by various methods, for example, it can be formed by cold drawing. If the cylindrical material 30 is formed by cold drawing, the dimensional accuracy of the cylindrical material 30 can be increased, and as a result, the dimensional accuracy of the key ring 10 formed from the cylindrical material 30 can be increased.

Next, the prepared cylindrical material 30 is extruded through the extrusion port of the mold and processed into the key ring 10 . First, a mold for processing the key ring 10 will be described. As shown in FIG. 4, the mold for processing the key ring 10 includes a die 32 and an insert punch 40. As shown in FIG. The die 32 has a through-hole into which the cylindrical material 30 and the insert punch 40 are inserted, and a die-side forming portion 34 is formed on the inner peripheral surface of the through-hole. The die-side molding portion 34 is provided below the die 32 and has a shape for forming the outer peripheral surface of the key ring 10 . That is, the die-side molded portion 34 has a shape corresponding to the protrusion 20 and the key groove 22 of the key ring 10 and the like. A tapered portion (portion indicated by L14 in FIG. 4) corresponding to the shape of the outer peripheral tapered portion 14 is formed at the upper end of the die-side forming portion 34 .

The insert punch 40 can be inserted into the through-hole of the cylindrical material 30, and has a punch-side molding portion 42 formed on its outer peripheral surface. The punch-side molding portion 42 is provided below the insert punch 40 and has a shape for forming the inner peripheral surface of the key ring 10 . That is, the punch-side formed portion 42 has a shape (that is, the punch-side flat portion 45 and the punch-side straight portion 44) corresponding to the flat portion 25 and the straight portion 24 of the key ring 10. A tapered portion (a portion indicated by L16 in FIG. 4) corresponding to the shape of the inner peripheral tapered portion 16 is formed at the upper end of the portion 42. As is clear from the above description, the die side molding portion of the die 32 is formed. 34 and the punch-side forming portion 42 of the insert punch 40 form an extrusion port for extruding the cylindrical material 30 .

In order to mold the key ring 10 using the mold described above, first, the insert punch 40 is set at a predetermined initial position with respect to the die 32, and a cylindrical member is placed in the space between the die 32 and the insert punch 40. 30 is installed (state shown in FIG. 4). A punch 38 for pressing the cylindrical member 30 downward is arranged above the cylindrical member 30 . In the state shown in FIG. 4 (the state before starting processing), the cylindrical member 30 is positioned above the die-side molding portion 34 . Moreover, as shown in FIGS. 5 and 6, the insert punch 40 is partially in contact with the inner peripheral surface of the cylindrical member 30 . Specifically, the punch-side straight portion 44 (the portion corresponding to the vertex of the regular dodecagon when viewed in cross section) contacts the inner peripheral surface of the cylindrical member 30, while the punch-side flat portion 45 (viewed in cross section) A clearance S is formed between the inner peripheral surface of the cylindrical member 30 and the portion corresponding to the side of the regular dodecagon.

Next, the cylindrical material 30 is pressed downward by the punch 38, and the cylindrical material 30 is cold extruded from the extrusion port of the die (the gap between the die-side molding portion 34 and the punch-side molding portion 42). . At this time, the punch 38 moves downward as the cylindrical material 30 is extruded from the ejection port of the mold, and the insert punch 40 also moves downward. Then, the punch 38 and the insert punch 40 are lowered to the lowest point, so that the cylindrical material 30 is formed into the key ring 10 (state shown in FIG. 7). After the molding of the cylindrical material 30 is finished, the cylindrical material 30 (that is, the key ring 10) is removed from the mold by a knockout punch (not shown).

In the manufacturing method of the key ring 10 according to this embodiment, the cylindrical material 30 is prepared based on the shape of the key ring 10, and the cylindrical material 30 is formed into the key ring 10 by extrusion. Therefore, the processing rate of the cylindrical material 30 can be reduced as a whole, and the key ring 10 can be molded with high accuracy. In addition, linear portions 24 (that is, each vertex of the regular dodecagon) are arranged corresponding to the convex portions 20 on the outer peripheral surface of the key ring 10, and corresponding to the key grooves 22 on the outer peripheral surface of the key ring 10. The center line 26 of the inner peripheral surface (that is, the midpoint of each side of the regular dodecagon) is arranged thereon. As a result, the processing rate of the cylindrical material 30 is made uniform in the circumferential direction (uniform in the convex portion 20 and the key groove 22), and a lubricating film is well formed on the surface of the cylindrical material 30, and the post-extrusion The end face of the cylindrical material 30 can be made flat. As a result, deformation of the molded cylindrical material 30 when released from the mold can be suppressed, and the key ring 10 can be accurately molded.

In the above-described embodiment, the upper end of the punch-side molding portion 42 of the insert punch 40 is formed with a tapered portion (the portion indicated by L16 in FIG. 4) corresponding to the inner peripheral tapered portion 16, which is disclosed in this specification. is not limited to such an example. For example, as in an insert punch 54 shown in FIG. 8, multistage tapered portions 48 and 49 may be provided at the base end portion (the right end portion in FIG. 8) of the punch-side forming portion. Specifically, in the example shown in FIG. 8, a first tapered portion 48 tapered at a first angle and a second tapered portion 49 tapered at a second angle larger than the first angle are formed. . By providing the tapered portion in multiple stages in this manner, the cylindrical material is gradually deformed according to the movement of the insert punch 54 . Therefore, the roundness of the cylindrical material after molding is improved, and the key ring can be molded with high accuracy.

In the above-described embodiment, each vertex of the regular dodecagon on the inner peripheral surface of the key ring 10 (that is, the linear portion 24) is positioned at the circumferential center of the convex portion 20. The midpoint of each side of the square (that is, the center line 26 of the flat portion 25) in the circumferential direction was positioned at the center of the keyway 22 in the circumferential direction, but the technology disclosed in this specification It is not limited to such examples. For example, the circumferential position of each vertex of the regular dodecagon on the inner peripheral surface of the key ring 10 may be arbitrarily set within the angular range in which the convex portion 20 is formed, or the regular dodecagon of the key ring 10 may be set arbitrarily within the angular range in which the key groove 22 is formed. With such a configuration as well, the difference in processing rate between the convex portion 20 and the key groove 22 can be reduced, and the key ring can be molded with high accuracy.

Further, in the above-described embodiment, the outer diameter of the portion 44 corresponding to the maximum portion of the outer peripheral surface of the insert punch 40 matches the diameter of the inner peripheral surface of the cylindrical material 30, but is disclosed in this specification. is not limited to such an example. For example, the outer diameter of the portion corresponding to the maximum portion of the insert punch may be positioned outside the inner peripheral surface of the cylindrical material.

Further, in the above embodiment, the cylindrical material 30 is extruded forward to form the key ring 10, but the cylindrical material may be extruded backward to form the key ring.

In the above embodiment, the method of manufacturing the cylindrical member (key ring 10) having the projection 20 and the key groove 22 formed on the outer peripheral surface and the inner peripheral surface having a regular polygonal transverse cross-sectional shape is described in the present invention. The technology disclosed in the specification is not limited to such examples. For example, as shown in FIG. 9, a convex portion 62 that protrudes toward the axis and a concave portion 64 that becomes concave toward the axis are formed on the inner peripheral surface, while the cross-sectional shape of the outer peripheral surface The technique disclosed in this specification can be applied to the method of manufacturing the tubular member 60 having a regular polygonal shape. In this case as well, the minimum portion 68 (the midpoint of the side of the regular polygon) is positioned according to the convex portion 62 on the inner peripheral surface, and the maximum portion 66 ( By adjusting so that the apexes of the regular polygon are positioned, the processing rate when forming the cylindrical member 60 from the cylindrical material can be made uniform in the circumferential direction, and the cylindrical member 60 can be formed with high accuracy. can do.

Although specific examples of the technology disclosed in this specification have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. In addition, the technical elements described in this specification or in the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing.

10 Key ring 12 Key groove portion 14 Outer circumference taper portion 16 Inner circumference taper portion 18 Cylindrical portion 20 Convex portion 22 Key groove 24 Straight portion (vertex)
25 Flat part (side)
26 Center line 30 Cylindrical material 32 Die 34 Die side forming part 36 Die side taper part 38 Punch 40 Insert punch 42 Punch side forming part 44 Punch side straight part 45 Punch side flat part 46 Punch side taper part 47 Punch side midpoint part 48 First taper portion 49 Second taper portion 54 Insert punch 60 Cylindrical member 62 Protruding portion 64 Groove portion 66 Straight portion (vertex)
68 Flat part (side)

Claims (5)

a preparation step of preparing a cylindrical material;
and a processing step of extruding the prepared cylindrical material from an extrusion port of a mold to process it into a cylindrical member,
When the tubular member is viewed in a cross section perpendicular to its axis,
A predetermined number of protrusions that protrude outward and recesses that are recessed inward with respect to the protrusions are formed alternately in the circumferential direction on the outer peripheral surface of the cylindrical member,
On the inner peripheral surface of the cylindrical member, the predetermined number of maximum portions with a maximum distance from the axis and minimum portions with a minimum distance from the axis are alternately formed in the circumferential direction. and
The tip of the extrusion port of the mold is
Let D1 be the value when the distance from the axis to the projection is maximum, and let D2 be the value when the distance from the axis to the recess is minimum.
The position of the maximum portion in the circumferential direction is located in an angular range in which the distance from the axis to the outer peripheral surface is (D1+D2)/2 or more, and
A method of manufacturing a cylindrical member, wherein the minimum portion is positioned in the circumferential direction in an angular range in which the distance from the axis to the outer peripheral surface is less than (D1+D2)/2. In the preparation step, the cylindrical material is formed by cold drawing,
2. The method of manufacturing a cylindrical member according to claim 1, wherein in said processing step, said cylindrical material is cold-processed into said cylindrical member. The cross-sectional area of the extrusion port is tapered so as to gradually decrease from the base end to the tip end,
3. The method of manufacturing a tubular member according to claim 1, wherein in said processing step, said cylindrical material is extruded in a direction from said base end toward said tip end. The mold is
a die for forming the outer peripheral surface of the tubular member;
an insert punch disposed inside the die for forming the inner peripheral surface of the tubular member;
a punch disposed between the die and the insert punch for pressing the cylindrical material;
The extrusion port is formed by an inner peripheral surface of the die and an outer peripheral surface of the insert punch,
In the processing step, one end of the cylindrical material arranged between the die and the insert punch is pressed by the punch, and the punch and the insert punch are moved toward the extrusion port, whereby the cylindrical material is The method for manufacturing a tubular member according to any one of claims 1 to 3, wherein a shaped material is molded into the tubular member. A portion of the inner peripheral surface of the die that corresponds to the convex portion coincides with the outer peripheral surface of the cylindrical material,
a portion of the inner peripheral surface of the die corresponding to the recess is located outside the inner peripheral surface of the cylindrical material;
A portion of the outer peripheral surface of the insert punch that corresponds to the maximum portion coincides with the inner peripheral surface of the cylindrical material or is located outside the inner peripheral surface,
5. The method of manufacturing a tubular member according to claim 4, wherein a portion of the outer peripheral surface of said insert punch corresponding to said minimum portion is located inside an inner peripheral surface of said cylindrical material.

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