Patent Grant
11590547
The present invention relates to a method of manufacturing a variable wall thickness steel pipe and a variable wall thickness steel pipe.
Priority is claimed on Japanese Patent Application No. 2016-048657, filed on Mar. 11, 2016 and Japanese Patent Application No. 2016-245864, filed on Dec. 19, 2016, the contents of which are incorporated herein by reference.
It is desired that a vehicle body member constituting a vehicle body of an automobile has a part which absorbs collision energy by being crushed by impact load when an impact such as a collision is received, and a part which protects the vehicle body without being crushed. In order to provide such a vehicle body member, utilization of a variable wall thickness steel pipe having a thickness varying in a longitudinal direction has been studied.
For example, as a method of manufacturing a drawn steel pipe having a plurality of diameters, FIG. 7 of Patent Document 1 discloses a method of manufacturing a stepped drawn pipe having predetermined inner diameters and outer diameters in a plurality of locations. In the method, a die and a tap are fixed to be movable in a drawing direction and a steel pipe is drawn while being pressure-clamped by bearing surfaces facing each other.
In addition, FIG. 7 of Patent Document 2 discloses a method of manufacturing a variable wall thickness steel pipe using a die and a plug each having two steps of diameters. The method includes a step of forming a base steel pipe restricted in size by a bearing diameter d2 (small diameter) of the die and a bearing diameter d3 (small diameter) of the plug, a step of forming a base steel pipe restricted in size by the bearing diameter d2 (small diameter) of the die and a bearing diameter d4 (large diameter) of the plug, and a step of forming a base steel pipe restricted in size by a bearing diameter d1 (large diameter) of the die and the bearing diameter d4 (large diameter) of the plug.
Incidentally, some vehicle body members or vehicle body components constituting a vehicle body of an automobile are obtained by performing bending with respect to a member having a hollow closed cross-sectional shape and partially forming a bent part. In variable wall thickness steel pipes obtained by manufacturing methods in Patent Document 1 or Patent Document 2, working is performed with respect to an entire raw pipe in a longitudinal direction. Accordingly, the entirety is in a work-hardened state. In order to perform bending or the like with respect to such a variable wall thickness steel pipe which has been entirely work-hardened, there is a need to soften the work-hardening of variable wall thickness steel pipe by performing heat treatment in advance. If such heat treatment becomes unnecessary, considerable labor-saving can be expected when a variable wall thickness steel pipe is worked into a vehicle body member. In addition, since heat treatment is omitted, degeneration in the steel structure of the variable wall thickness steel pipe can also be prevented.
The present invention has been made in consideration of the foregoing circumstances and an object thereof is to provide a variable wall thickness steel pipe and a method of manufacturing a variable wall thickness steel pipe, in which a working amount at the time of manufacturing is small and heat treatment such as annealing becomes unnecessary when post-working such as bending is performed.
In order to achieve the object, the present invention employs each of the following aspects.
(1) According to an aspect of the present invention, there is provided a method of manufacturing a variable wall thickness steel pipe with a hollow tubular raw pipe. The method includes locking the raw pipe in a die by thrusting a plug into the raw pipe from an one end side so as to expand an outer shape on the one end side, in a state where the raw pipe is disposed inside the die and movement of the raw pipe in a longitudinal direction is restricted; and performing ironing in which an inner shape of the raw pipe is expanded while the outer shape is maintained so that a thin portion is formed by further thrusting the plug toward the other end side of the raw pipe while the locked state of the raw pipe is maintained, whereas the restriction on the raw pipe is relaxed.
(2) In the method of manufacturing a variable wall thickness steel pipe according to (1), in the performing ironing, an unprocessed portion may remain on the other end side of the raw pipe by stopping thrusting the plug in the middle.
(3) In the method of manufacturing a variable wall thickness steel pipe according to (1) or (2), a thickness reduction rate of the thin portion in the performing ironing may be within a range from 10% to 90%.
(4) In the method of manufacturing a variable wall thickness steel pipe according to any one of (1) to (3), the plug used in the locking and the performing ironing may include a tip end portion having an outer shape size smaller than an inner shape size of the raw pipe, a base end portion having an outer shape size larger than the inner shape size of the raw pipe and smaller than an outer shape size of the raw pipe, and a tapered portion being provided between the tip end portion and the base end portion to be tapered from the base end portion toward the tip end portion.
(5) In the method of manufacturing a variable wall thickness steel pipe according to any one of (1) to (3), the plug used in the locking and the performing ironing may include a base end portion having an outer shape size larger than an inner shape size of the raw pipe and smaller than an outer shape size of the raw pipe, and a tip end portion leading to a tip end side of the base end portion and being tapered as being separated from the base end portion.
(6) In the method of manufacturing a variable wall thickness steel pipe according to (4) or (5), the base end portion may have a large-sized base end portion being disposed on the tip end portion side, and a small-sized base end portion having an outer shape size smaller than an outer shape size of the large-sized base end portion.
(7) According to another aspect of the present invention, there is provided a method of manufacturing a variable wall thickness steel pipe with a hollow tubular raw pipe. The method includes locking the raw pipe in a die by thrusting a first plug into the raw pipe from one end side, so as to expand an outer shape size on the one end side, in a state where the raw pipe is disposed inside the die and movement of the raw pipe in a longitudinal direction is restricted; pulling the first plug from the raw pipe; and performing ironing in which an inner shape of the raw pipe is expanded while an outer shape of the raw pipe is maintained so that a thin portion is formed by thrusting a second plug, which has an outer shape different from the outer shape of the first plug, from the one end side of the raw pipe toward the other end side while the locked state of the raw pipe is maintained, whereas the restriction on the raw pipe is relaxed.
(8) In the method of manufacturing a variable wall thickness steel pipe according to (7), the second plug used in the performing ironing may include a small-sized tip end portion smaller than an inner shape size of the raw pipe, an intermediate-sized portion having an outer shape size larger than the inner shape size of the raw pipe, a large-sized portion having an outer shape size larger than the outer shape size of the intermediate-sized portion and smaller than an outer shape size of the raw pipe, a first tapered portion being provided between the small-sized tip end portion and the intermediate-sized portion, and a second tapered portion being provided between the intermediate-sized portion and the large-sized portion.
(9) In the method of manufacturing a variable wall thickness steel pipe according to (7), the second plug used in the performing ironing may include a base end portion having an outer shape size larger than the inner shape size of the raw pipe and smaller than an outer shape size of the raw pipe, and a third tapered portion being tapered from the base end portion toward a tip end portion.
(10) In the method of manufacturing a variable wall thickness steel pipe according to any one of (1) to (9), the die may include a hollow small-sized portion having an inner shape size corresponding to the outer shape size of the raw pipe, a hollow large-sized portion having an inner shape size larger than the outer shape size of the raw pipe, and a hollow tapered portion being provided between the hollow small-sized portion and the hollow large-sized portion and being tapered from the hollow large-sized portion toward the hollow small-sized portion.
(11) In the method of manufacturing a variable wall thickness steel pipe according to (10), the die may further include a hollow intermediate-diameter portion being provided in a part of the hollow small-sized portion in the longitudinal direction and having an inner shape size larger than the outer shape size of the raw pipe.
(12) The method of manufacturing a variable wall thickness steel pipe according to any one of (1) to (11) may further include drawing the raw pipe after performing ironing.
(13) According to another aspect of the present invention, there is provided a method of manufacturing a variable wall thickness steel pipe with a hollow tubular raw pipe. The method includes locking the raw pipe in a die by simultaneously or alternately thrusting plugs into the raw pipe respectively from one end side and the other end side of the raw pipe, so as to expand an outer shape on the one end side and an outer shape on the other end side; pulling the plug on the other end side while the plug is inserted on the one end side; performing first ironing in which an inner shape of the raw pipe is expanded while the outer shape is maintained so that a first thin portion is formed by further thrusting the plug, which is inserted on the one end side, toward the other end side of the raw pipe while the one end side is locked in the die; inserting and pulling the plugs such that the plug is inserted on the other end side, whereas the plug on the one end side is pulled out; and performing second ironing in which the inner shape of the raw pipe is expanded while the outer shape is maintained so that a second thin portion is formed by further thrusting the plug on the other end side toward the one end side of the raw pipe while the other end side is locked in the die. In the locking, the raw pipe freely moves in a longitudinal direction of the raw pipe in a case where the plugs are simultaneously thrust, and movement of the raw pipe in a thrusting direction of the plugs is restricted in a case where the plugs are alternately thrust.
(14) The method of manufacturing a variable wall thickness steel pipe according to (13) may further include drawing the raw pipe after performing second ironing.
(15) In the method of manufacturing a variable wall thickness steel pipe according to any one of (1) to (14), the raw pipe may be a seamless steel pipe.
(16) According to an aspect of the present invention, there is provided a variable wall thickness steel pipe which employs the following configuration including an expanded portion that is provided on one side in a longitudinal direction and has a largest outer shape size in a case of being seen in a cross section perpendicular to the longitudinal direction, and a thin portion that is provided on the other side of the expanded portion in a case of being seen in the longitudinal direction and has a thickness smaller than a thickness of the expanded portion. In a case where an average value of hardness of the expanded portion is H1 and an average value of hardness of the thin portion is H2, H2>H1 may be satisfied.
As a way of obtaining each of the average values of hardness according to the specification of this application, the average value is obtained by measuring hardness of five spots on a part of a manufactured variable wall thickness steel pipe at a central position in a thickness direction at intervals of 1 mm in the longitudinal direction of the same variable wall thickness steel pipe, and calculating the average value of hardness of the five spots. In a case where if it is difficult to obtain five measurement spots due to the small size, hardness of five spots may be measured at intervals of 1 mm in the circumferential direction of the variable wall thickness steel pipe, and the average value of the five spots may be calculated and used.
(17) The variable wall thickness steel pipe according to (16) may employ the following configuration further including a thick portion that is disposed on the other side of the thin portion in a case of being seen in the longitudinal direction and has a thickness greater than the thickness of the thin portion. In a case where an average value of hardness of the thick portion is H3, H2>H1≥H3 may be satisfied.
(18) The variable wall thickness steel pipe according to (17) may employ the following configuration. The thin portion includes a straight pipe portion having a smallest thickness in the thin portion, a first tapered portion being provided between the straight pipe portion and the expanded portion and having an outer shape expanded toward the expanded portion, and a second tapered portion being provided between the straight pipe portion and the thick portion and having a thickness increasing toward the thick portion. In a case where an average value of hardness of the first tapered portion is H4, an average value of hardness of the straight pipe portion is H5, and an average value of hardness of the second tapered portion is H6, both expressions H5>H6≥H3 and H5>H4>H1 may be satisfied.
(19) In the variable wall thickness steel pipe according to any one of (16) to (18), the thickness of the thin portion may be partially increased in a case of being seen in the longitudinal direction.
(20) In the variable wall thickness steel pipe according to (16), combinations of the expanded portions and the thin portions may be symmetrically provided at both ends in the longitudinal direction.
(21) The variable wall thickness steel pipe according to (20) may employ the following configuration further including a thick portion that is disposed between a pair of the thin portions and has a thickness greater than the thickness of the thin portion. In a case where an average value of hardness of the thick portion is H7, H2>H1≥H7 may be satisfied.
(22) According to another aspect of the present invention, there is provided a variable wall thickness steel pipe which employs the following configuration including a thick portion that is provided on one side in a longitudinal direction and has a greatest thickness in a case of being seen in a cross section perpendicular to the longitudinal direction, and a thin portion that is provided on the other side of the thick portion and has a thickness smaller than the thickness of the thick portion. An outer shape size in the longitudinal direction is constant. In a case where an average value of hardness of the thick portion is H8 and an average value of hardness of the thin portion is H9, H9>H8 is satisfied.
(23) In the variable wall thickness steel pipe according to any one of (16) to (22), in a case where the thin portion is seen in a circumferential direction of the thin portion in a cross section perpendicular to the longitudinal direction, the thin portion may have a rotationally symmetric shape in which regions having a relatively small thickness and relatively high hardness and regions having a relatively great thickness and relatively low hardness alternate with each other in the circumferential direction.
(24) In the variable wall thickness steel pipe according to any one of (16) to (23), a seamless steel pipe may be used as a material.
As the various types of hardness above, for example, Vickers hardness may be used.
According to the present invention, for example, in the method of manufacturing a variable wall thickness steel pipe according to (1), it is possible to perform ironing in which the inner shape is expanded while the outer shape of the raw pipe is maintained by thrusting the plug into the raw pipe from one end side while the outer shape of the raw pipe on one end side is expanded and the raw pipe is locked in the die. Thus, the working amount to be applied to one end side of the raw pipe can be reduced to a working amount as small as the outer shape size thereof is expanded. Therefore, since work-hardening is small on one end side of the raw pipe, heat treatment such as annealing can be made unnecessary when post-working such as bending is performed.
In addition, since ironing is performed by thrusting the plug into the raw pipe while one end side of the raw pipe is locked in the die, there is no need to fix the raw pipe itself to the die, and ironing can be carried out by only relatively moving the plug with respect to the die.
Therefore, in the method of manufacturing a variable wall thickness steel pipe according to the aspect of the present invention, it is possible to easily manufacture a variable wall thickness steel pipe in which a part having a great thickness on one end side and a thin portion subjected to ironing are formed.
Particularly, in the method of manufacturing a variable wall thickness steel pipe according to (2), since an unprocessed portion having a zero working amount can remain on the other end side of the raw pipe, heat treatment such as annealing can be made unnecessary when post-working such as bending is performed with respect to the unprocessed portion.
In addition, in the method of manufacturing a variable wall thickness steel pipe according to (7), for example, two regions, of which the inner shape sizes are different from each other, can be provided inside the thin portion, and it is possible to manufacture a variable wall thickness steel pipe in which the thickness and strength vary in stages in the longitudinal direction.
A variable wall thickness steel pipe and a method of manufacturing a variable wall thickness steel pipe according to each of embodiments of the present invention will be described below with reference to the drawings. In each of the embodiments, a raw pipe 1 having tensile strength of 290 MPa or higher is preferably used as a material.
A method of manufacturing a variable wall thickness steel pipe according to the first embodiment includes a step of forming a diameter-increasing portion by performing pipe expanding with respect to a part on one end side of a raw pipe using a die and a plug, and a step of ironing a middle portion on the other end side of the diameter-increasing portion such that the inner diameter of the raw pipe is increased while the outer diameter is maintained. Examples of a raw pipe as a working target in the present embodiment can include a hollow tubular metal pipe. Particularly, a round steel pipe is preferably used. As the round steel pipe, any of a seamless steel pipe, a UO pipe, a spiral pipe, and an electric resistance welded steel pipe can be applied.
Next, the die and the plug used in the manufacturing method of the present embodiment will be described with reference to
A tapered portion 21c of a plug 21 in
The plug 21 according to the present embodiment is configured to include a small-diameter tip end portion 21a corresponding to an inner diameter d2 of the raw pipe 1, a large-diameter base end portion 21b having a diameter larger than the inner diameter d2 of the raw pipe 1 and a diameter smaller than the inner diameter of the hollow small-diameter portion 11a of the die 11, and the tapered portion 21c being provided between the small-diameter tip end portion 21a and the large-diameter base end portion 21b. The outer diameter of the large-diameter base end portion 21b is set to have a size smaller than the inner diameter d1 of the hollow small-diameter portion 11a of the die 11.
In order to manufacture a variable wall thickness steel pipe according to the present embodiment, first, as shown in
After the raw pipe 1 is fixed inside the die 11, the small-diameter tip end portion 21a of the plug 21 is inserted from the one end portion 1a side of the raw pipe 1 toward a hollow portion 1b of the raw pipe 1.
Next, as shown in
For example, it is possible to manage whether or not the tapered portion 21c has reached the position of the tapered portion 11c by measuring the amount of a thrusting stroke of the plug 21 or reaction increasing in response to a thrust of the plug 21.
At the point of time of
When the diameter-increasing portion 1c is formed, a slight pulling strain is applied to the one end portion 1a of the raw pipe 1 in the circumferential direction.
Next, as shown in
As the plug 21 is further thrust, the large-diameter base end portion 21b of the plug 21 is thrust toward the other end portion 1d side of the raw pipe 1. In the middle portion 1e of the raw pipe 1 in which the large-diameter base end portion 21b of the plug 21 is thrust, the original inner diameter d2 of the raw pipe 1 is increased to a size corresponding to the diameter of the large-diameter base end portion 21b of the plug 21. On the other hand, since the middle portion 1e of the raw pipe 1 is positioned inside the hollow small-diameter portion 11a of the die 11 and its outer diameter size is restricted due to the surroundings, the outer diameter d1 of the middle portion 1e is not increased. Therefore, the middle portion 1e of the raw pipe 1 is subjected to ironing while the original outer diameter d1 of the raw pipe 1 is maintained.
The reason for releasing the stemmed state of the raw pipe 1 immediately before ironing starts is that a flow of the thickness of the raw pipe 1 entailed in ironing is not to be hindered. That is, when the middle portion 1e of the raw pipe 1 is reduced in thickness through ironing, in order to ensure as much room for the quantity as thickness reduction, the stemmed state of the raw pipe 1 is released. Accordingly, a part of the raw pipe 1 on the sheet left side is prevented from being buckled. In the present embodiment, since the quantity of thickness reduction of the raw pipe 1 due to ironing flows toward the sheet left side, the entire length of the raw pipe 1 becomes slightly longer than that before working.
In order to achieve an effect of improving strength of the middle portion 1e due to ironing, the thickness reduction rate of the raw pipe 1 due to ironing is required to be 10% or higher. Meanwhile, if the thickness reduction rate of the raw pipe 1 due to ironing exceeds 90%, there is concern that a fracture, burning, or the like is caused. Therefore, it is favorable that the thickness reduction rate of the raw pipe 1 due to ironing is within a range from 10% to 90%. Preferably, it is favorable that the thickness reduction rate is within a range from 20% to 80%. When the thickness of the raw pipe 1 before ironing is d0 and the thickness of the middle portion 1e after ironing is d, the thickness reduction rate (%) is expressed by (d0−d)/d0×100(%).
Here, in a case where the thickness d of the middle portion 1e after ironing is not uniform when seen in the longitudinal direction of the raw pipe 1, and there is a distribution, the numerical value obtained in a location having the greatest amount of thickness reduction is employed as the thickness reduction rate. That is, in the middle portion 1e, the value obtained in a location in which the difference (equivalent strain amount) obtained by subtracting d from d0 is the greatest in a case of being seen in its longitudinal direction is employed as the thickness reduction rate described above. Furthermore, in a case where the amount of thickness reduction is not uniform in the circumferential direction of the raw pipe 1 and there is a distribution, the value obtained in a location in which the amount of thickness reduction is the greatest in the distribution in the circumferential direction is employed as the thickness reduction rate described above.
The thickness reduction rate can be adjusted by changing the diameter of the large-diameter base end portion 21b of the plug 21. The above-described appropriate range related to the thickness reduction rate in ironing is the same in other embodiments to be described below.
In the example shown in
The variable wall thickness steel pipe 31 shown in
In
In the diameter-increasing portion 31c and the middle portion 31e, a hollow portion 31b of the variable wall thickness steel pipe 31 is further increased in diameter than the original inner diameter d2 of the raw pipe 1. In the unprocessed portion 31f, the original inner diameter d2 of the raw pipe 1 remains unchanged. In addition, the outer diameter of the variable wall thickness steel pipe 31 is gradually increased from the outer diameter d1 of the raw pipe 1 in the lock portion 31e1. Then, in the diameter-increasing portion 31c, the outer diameter thereof is constant while being further increased than the outer diameter d1 of the raw pipe 1. Meanwhile, a part excluding the lock portion 31e1 in the middle portion 31e, and the unprocessed portion 31f remain having an outer diameter equal to the outer diameter d1 of the raw pipe 1. Accordingly, the variable wall thickness steel pipe 31 has a comparatively great thickness in the diameter-increasing portion 31c and the unprocessed portion 31f and has a comparatively small thickness in the middle portion 31e.
In the variable wall thickness steel pipe 31 shown in
In addition, since a large working amount is applied to the middle portion 31e of the variable wall thickness steel pipe 31, the middle portion 31e has comparatively high strength due to work hardening. That is, as seen in a hardness distribution (Vickers hardness distribution, determination can also be made through a tensile strength distribution instead of Vickers hardness distribution) in the longitudinal direction of the variable wall thickness steel pipe 31, the unprocessed portion 31f has the lowest hardness, and the diameter-increasing portion 31c has hardness slightly higher than hardness of the unprocessed portion 31f. Then, the middle portion 31e has hardness higher than hardness of the diameter-increasing portion 31c. Therefore, since the middle portion 31e has the highest hardness, it is preferable to be used for a portion requiring high mechanical strength. In addition, the unprocessed portion 31f and the diameter-increasing portion 31c having relatively low hardness are preferable to be used as portions requiring post-working such as bending.
In addition, the inner surface of the middle portion 31e has small surface roughness by being subjected to ironing. If the surface roughness is reduced, fatigue properties increase. Accordingly, in addition to improvement of strength due to work hardening, the middle portion 31e can also achieve improvement of fatigue properties due to the reduced surface roughness on the inner surface, thereby realizing weight reduction and high strength. Such a synergistic effect cannot be achieved in thinning through simple cutting.
In addition,
The variable wall thickness steel pipe 41 shown in
In a hollow portion 41b of the variable wall thickness steel pipe 41, the entire inner diameter in its longitudinal direction is further increased than the inner diameter d2 of the raw pipe 1. In addition, the outer diameter of the variable wall thickness steel pipe 41 is gradually increased from the outer diameter d1 of the raw pipe 1 in the lock portion 41e1. Then, in the diameter-increasing portion 41c, the outer diameter thereof is constant while being further increased than the outer diameter d1 of the raw pipe 1. Meanwhile, a part excluding the lock portion 41e1 in the middle portion 41e, and the other end part 41f remain having an outer diameter equal to the outer diameter d1 of the raw pipe 1. Accordingly, the variable wall thickness steel pipe 41 has a comparatively great thickness in the lock portion 41e1 and the diameter-increasing portion 41c and has a comparatively small thickness in a part excluding the lock portion 41e1 in the middle portion 41e, and the other end part 41f.
In the variable wall thickness steel pipe 41 shown in
In addition, since a large working amount is applied to the middle portion 41e and the other end part 41f of the variable wall thickness steel pipe 41, the middle portion 41e and the other end part 41f have comparatively high strength due to work hardening.
As described above, in the embodiment shown in
In addition, since ironing is performed by thrusting the plug 21 into the raw pipe 1 while the diameter-increasing portion 1c is locked in the die 11, ironing can be carried out by only relatively moving the die 11 and the plug 21 without requiring labor and tools for fixing the raw pipe 1 itself.
In addition, since a part of the raw pipe 1 on the other end portion 1d side of the middle portion 1e is caused to be the unprocessed portion 31f which remains unprocessed, the working amount with respect to a part on the other end portion 1d side becomes zero, so that heat treatment such as annealing can be made unnecessary when post-working such as bending is performed with respect to the unprocessed portion 31f.
In addition, in the variable wall thickness steel pipe 31 manufactured by the method described above, since the diameter-increasing portion 31c and the unprocessed portion 31f have a small working amount, the thickness is large and strength is comparatively low. Meanwhile, in the middle portion 31e, since the working amount thereof is large, the thickness is small and strength is comparatively high. Therefore, the diameter-increasing portion 31c and the unprocessed portion 31f are in a state where deformability remains, compared to the middle portion 31e, and these parts form the variable wall thickness steel pipe 31 having excellent post-workability such as bending. In addition, since the middle portion 31e has small inner surface roughness by being subjected to ironing, this part forms the variable wall thickness steel pipe 31 having excellent fatigue properties.
A method of manufacturing a variable wall thickness steel pipe of a second embodiment is configured to include a step of forming a diameter-increasing portion by performing pipe expanding with respect to a part on one end side of a raw pipe using a die and a plug, and a step of ironing a middle portion on the other end side of the diameter-increasing portion such that the inner diameter of the raw pipe is increased while the outer diameter is maintained after the plug is replaced with another plug. A raw pipe as a working target of the present embodiment may be similar to that of the first embodiment.
In the present embodiment, a die and a plug similar to those of the first embodiment are used in the step of forming the diameter-increasing portion, which is performed first.
That is, similar to the case of the first embodiment, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
Then, as shown in
As the plug 51 is thrust to the position shown in
In addition, as shown in
In the diameter-increasing portion 61c and the middle portion 61e, the inner diameter of a hollow portion 61b of the variable wall thickness steel pipe 61 is further increased than the inner diameter d2 of the raw pipe 1. Then, in the unprocessed portion 61f, the inner diameter of a hollow portion 61b of the variable wall thickness steel pipe 61 remains the inner diameter d2 of the raw pipe 1. In addition, in the middle portion 61e, the inner diameter of a part on the one end portion 61a side is increased by the large-diameter base end portion 51c of the plug 51, and the inner diameter of a part on the other end portion 61d side is increased by the intermediate-diameter portion 51b of the plug 51. Furthermore, inner diameter of a part on the one end portion 61a side and the inner diameter of a part on the other end portion 61d side are different from each other. In addition, in the lock portion 61e1 and the diameter-increasing portion 61c, the outer diameter of the variable wall thickness steel pipe 61 is further increased than the outer diameter d1 of the raw pipe 1. Meanwhile, the outer diameters of a part excluding the lock portion 61e1 in the middle portion 61e, and the unprocessed portion 61f remain unchanged as the outer diameter d1 of the raw pipe 1. Accordingly, the variable wall thickness steel pipe 61 has a comparatively great thickness in the diameter-increasing portion 61c and the unprocessed portion 61f and has a comparatively small thickness in the middle portion 61e.
In the variable wall thickness steel pipe 61 shown in
In addition, since a comparatively large working amount is applied to the middle portion 61e of the variable wall thickness steel pipe 61, the middle portion 61e has comparatively high strength due to work hardening.
In the present embodiment as described above, ironing is performed with respect to the middle portion 1e of the raw pipe 1 using the plug 51. In this case, in the middle portion 1e, the diameter-increasing amount of a region on the diameter-increasing portion 1c side is larger than the diameter-increasing amount of a region on the other end portion 1d side, so that two regions of which the inner diameters and strengths are different from each other can be provided inside the middle portion 1e.
In addition, the variable wall thickness steel pipe 61 manufactured by the method described above has the middle portion 61e in which the diameter-increasing amount of a region on the diameter-increasing portion 61c side is larger than the diameter-increasing amount of a region on the other end portion 61d side, and the working amount of a region on the diameter-increasing portion 61c side is larger than the working amount of a region on the other end portion 61d side. Therefore, the variable wall thickness steel pipe 61 has regions of which the thicknesses and strength are different from each other in the middle portion 61e.
A method of manufacturing a variable wall thickness steel pipe of a third embodiment will be described with reference to
As shown in
In the present embodiment, similar to the first embodiment, as shown in
Next, as shown in
Since the plug 71 in the present embodiment is configured to include the tapered tip end portion 71c and the base end portion 71b and does not include the small-diameter tip end portion 21a shown in the first embodiment, its length in the longitudinal direction is comparatively short. Therefore, compared to the first embodiment, the required stroke amount of the plug 71 when inserting the plug 71 into the raw pipe 1 or when pulling out the plug 71 from the raw pipe 1 becomes short. As a result, the work hour for taking out and putting in the plug 71 can be shortened, and a hydraulic cylinder (not shown) having a simple structure for taking out and putting in the plug 71 can be employed. Therefore, it is possible to perform working even with comparatively small manufacturing equipment.
The variable wall thickness steel pipe which has been manufactured via the steps shown in
In the present embodiment as described above, since the variable wall thickness steel pipe is manufactured by using the plug 71 having a comparatively short length in the longitudinal direction, compared to the first embodiment, it is possible to comparatively reduce the required stroke amount of the plug 71 at the time of manufacturing.
Next, a method of manufacturing a variable wall thickness steel pipe of a fourth embodiment will be described. The method of manufacturing a variable wall thickness steel pipe of the present embodiment is configured to include a step similar to that of the second embodiment. In the present embodiment, ironing is performed by using a plug 81 different from the plug 51 used in the ironing step of the second embodiment. Since other configurations are similar to those of the second embodiment, a description will be omitted.
First, in the present embodiment, similar to the second embodiment, the lock portion 1e1 and the diameter-increasing portion 1c are formed in the raw pipe 1. Next, as shown in
Then, as shown in
As the plug 81 is thrust to the position shown in
Since the plug 81 used in the present embodiment includes the tapered tip end portion 81c having a comparatively long taper length, the inner diameter of the middle portion 1e of the raw pipe 1 becomes the same as the outer diameter of the tapered tip end portion 81c of the plug 81 over the entire length. That is, the inner diameter of the middle portion 1e of the raw pipe 1 is gradually increased from the other end portion 1d side to the one end portion 1a side.
In the diameter-increasing portion 91c and the middle portion 91e, the inner diameter of a hollow portion 91b of the variable wall thickness steel pipe 91 is further increased than the inner diameter d2 of the raw pipe 1. In the unprocessed portion 91f, the inner diameter d2 of the raw pipe remains unchanged. In addition, in a lock portion 91e1 and the diameter-increasing portion 91c, the outer diameter of the variable wall thickness steel pipe 91 is further increased than the outer diameter d1 of the raw pipe 1. A part excluding the lock portion 91e1 in the middle portion 91e, and the unprocessed portion 91f remain unchanged as the outer diameter d1 of the raw pipe 1. In addition, the inner diameter in the middle portion 91e gradually increases from the other end portion 1d side to the one end portion 1a side. Accordingly, the diameter-increasing portion 91c and the unprocessed portion 91f have a comparatively great thickness. In addition, in a case where the thickness of the middle portion 91e is seen from the diameter-increasing portion 91c toward the unprocessed portion 91f, the thickness is gradually reduced in the lock portion 91e1 and gradually increases in parts other than the lock portion 91e1.
In the variable wall thickness steel pipe 91 shown in
In addition, in the middle portion 91e of the variable wall thickness steel pipe 91, since the working amount is gradually reduced from the diameter-increasing portion 91c to the unprocessed portion 91f, hardness is comparatively high on the diameter-increasing portion 91c side of the middle portion 91e, and hardness is comparatively low on the unprocessed portion 91f side.
As described above, in the present embodiment, ironing is performed with respect to the middle portion 1e of the raw pipe 1 by using the plug 81 having the tapered tip end portion 81c which is comparatively long. Therefore, it is possible to manufacture the variable wall thickness steel pipe in which the inner diameter is gradually reduced from the diameter-increasing portion 1c side to the other end portion 1d side in the middle portion 1e.
A method of manufacturing a variable wall thickness steel pipe of a fifth embodiment is configured to include a step of forming diameter-increasing portions 1c and 1f by performing pipe expanding with respect to both end parts of the raw pipe 1 using one die and two plugs; a step of performing first ironing in which a plug 22 on the other end side is pulled while the plug 21 on one end side is inserted in the raw pipe 1, and the inner diameter of a middle portion 1g on the other end side of the diameter-increasing portion 1c on one end side is increased while the outer diameter of the raw pipe 1 is maintained; and a step of performing second ironing in which the plug 21 on one end side is pulled from the raw pipe 1, the plug 22 on the other end side is inserted into the raw pipe 1, and the inner diameter of a middle portion 1h on one end side of the diameter-increasing portion 1f on the other end side is increased while the outer diameter of the raw pipe 1 is maintained. The raw pipe 1 as a working target of the present embodiment may be similar to that of the first embodiment.
In the present embodiment, a die 12 shown in
The one-dot chained lines vertically shown in
Since the plug 21 shown in
In order to manufacture the variable wall thickness steel pipe according to the present embodiment, first, as shown in
Next, as the diameter-increasing step, as shown in
Next, while the plug 21 on the one end portion 1a side remains unchanged, the plug 22 on the other end portion 1d side is pulled out from the raw pipe 1. Thereafter, as shown in
In the example shown in
Next, the plug 21 pulled out from the raw pipe 1, and the plug 22 is inserted into the raw pipe 1 on the other end portion 1d side. Then, as shown in
In the example shown in
The first working part 11g also includes parts subjected to working by the tapered portions 12c and 21c of the die 12 and the plug 21 at each of boundaries with respect to the diameter-increasing portion 111c and the unprocessed portion 111i. That is, the first working part 111g includes a lock portion 111g1 (1g1) leading to the diameter-increasing portion 111c, and a tapered portion 111g2 leading to the unprocessed portion 111i.
The second working part 111h also includes parts subjected to working by the tapered portions 12c and 22c of the die 12 and the plug 22 at each of boundaries with respect to the diameter-increasing portion 111f and the unprocessed portion 111i. That is, the second working part 111h includes a lock portion 111h1 (1h1) leading to the diameter-increasing portion 111f, and a tapered portion 111h2 leading to the unprocessed portion 111i.
A hollow portion 111b of the variable wall thickness steel pipe 111 is further increased in diameter than the original inner diameter d2 of the raw pipe 1 in the diameter-increasing portion 111c, the first working part 111g, the diameter-increasing portion 111f, and the second working part 111h. Meanwhile, in the unprocessed portion 111i, the original inner diameter d2 of the raw pipe 1 remains unchanged. In addition, the outer diameter of the variable wall thickness steel pipe 111 is further increased than the outer diameter d1 of the raw pipe 1 in the diameter-increasing portion 111c, a lock portion 111g1, the diameter-increasing portion 111f, and the lock portion 111h1. Meanwhile, a part excluding the lock portion 111g1 in the first working part 111g, a part excluding the lock portion 111h1 in the second working part 111h, and the unprocessed portion 111i remain unchanged as the outer diameter d1 of the raw pipe 1.
In addition, in regard to the thickness, the variable wall thickness steel pipe has a comparatively great thickness in the diameter-increasing portion 111c, the diameter-increasing portion 111f, and the unprocessed portion 111i and has a comparatively small thickness in the first working part 111g and the second working part 111h.
In the variable wall thickness steel pipe 111 shown in
In addition, since a comparatively large working amount is applied to the first working part 111g and the second working part 111h, the first working part 111g and the second working part 111h have comparatively high strength due to work hardening.
The variable wall thickness steel pipe 121 shown in
In a hollow portion 121b of the variable wall thickness steel pipe 121, the entire inner diameter in its longitudinal direction is further increased than the inner diameter d2 of the raw pipe 1. In addition, the outer diameter of the variable wall thickness steel pipe 121 is further increased than the outer diameter d1 of the raw pipe 1 in the diameter-increasing portion 121c, lock portions 121e1 and 121e2 located at both ends of the middle portion 121e, and the diameter-increasing portion 121f. Moreover, a part excluding the lock portions 121e1 and 121e2 from the middle portion 121e remains unchanged as the outer diameter d1 of the raw pipe 1. Accordingly, the variable wall thickness steel pipe 121 has a comparatively great thickness in the diameter-increasing portion 121c and the diameter-increasing portion 121f and has a comparatively small thickness in the middle portion 41e.
In the variable wall thickness steel pipe 121 shown in
In addition, since a comparatively large working amount is applied to the middle portion 121e, the middle portion 121e has comparatively high strength due to work hardening.
As described above, in the embodiment shown in
In the fifth embodiment described above, the variable wall thickness steel pipe 111 is manufactured by using the die 12 in a line symmetric shape having the one-dot chained line in
Next, a method of manufacturing a variable wall thickness steel pipe of a sixth embodiment will be described with reference to
As shown in
The thickly-formed portion 13e is configured to include a hollow intermediate-diameter portion 13f, a tapered portion 13h being provided between the hollow intermediate-diameter portion 13f and the first hollow small-diameter portion 13a, and a tapered portion 13g being provided between the hollow intermediate-diameter portion 13f and the second hollow small-diameter portion 13b. The inner diameter d3 of the hollow intermediate-diameter portion 13f is set to be an inner diameter larger than the outer diameter d1 of the raw pipe 1 and to be an inner diameter smaller than the inner diameter of the hollow large-diameter portion 13d. If the inner diameter d3 of the hollow intermediate-diameter portion 13f is larger than the inner diameter of the hollow large-diameter portion 13d, the raw pipe 1 is only subjected to pipe expanding in the hollow intermediate-diameter portion 13f during the ironing step without being subjected to thinning. Therefore, the thickness of the raw pipe 1 in the thickly-formed portion 13e remains unchanged as the original thickness of the raw pipe 1.
Next, similar to the first embodiment, as shown in
Next, as shown in
A hollow portion 141b of the variable wall thickness steel pipe 141 remains unchanged as the inner diameter d2 of the raw pipe 1 in the unprocessed portion 141g, whereas a hollow portion 141b of the variable wall thickness steel pipe 141 is further increased in diameter than the inner diameter d2 of the raw pipe 1 in the diameter-increasing portion 141c and the middle portion 141e. In addition, in the diameter-increasing portion 141c, a lock portion 141e1, and the thick portion 141f, the outer diameter of the variable wall thickness steel pipe 141 is further increased than the outer diameter d1 of the raw pipe 1. In a part other than the thick portion 141f and the lock portion 141e1 in the middle portion 141e, and the unprocessed portion 141g, the outer diameter d1 of the raw pipe 1 remains unchanged. Therefore, in a case of being seen in the longitudinal direction, the variable wall thickness steel pipe 141 has a constant inner diameter in the shape-increasing portion 141g and a part of the middle portion 141e excluding a portion thereof. Furthermore, the thick portion 141f and the diameter-increasing portion 141c have outer diameters different from each other.
In the variable wall thickness steel pipe 141 shown in
In addition, since a comparatively large working amount is applied to the middle portion 141e of the variable wall thickness steel pipe 141, the middle portion 141e has comparatively high strength due to work hardening.
The variable wall thickness steel pipe 151 shown in
In a hollow portion 151b of the variable wall thickness steel pipe 151, the entire inner diameter in its longitudinal direction is further increased than the inner diameter d2 of the raw pipe 1. In addition, the outer diameter of the variable wall thickness steel pipe 151 is further increased than the outer diameter d1 of the raw pipe 1 in the diameter-increasing portion 151c and the thick portion 151f. In the middle portion 151e and the other end part 151g other than the thick portion 151f, the outer diameter d1 of the raw pipe 1 remains unchanged. Therefore, the variable wall thickness steel pipe 151 has an entirely constant inner diameter in the longitudinal direction and has a plurality of parts of which the outer diameters are different from each other.
In the variable wall thickness steel pipe 151 shown in
In addition, since a comparatively large working amount is applied to the middle portion 151e and the other end part 151g of the variable wall thickness steel pipe 151, the middle portion 151e and the other end part 151g have comparatively high strength due to work hardening.
As described above, in the embodiment shown in
In addition, in the variable wall thickness steel pipe 141, since the working amount is comparatively small on the other end portion 1d (141d) side of the diameter-increasing portion 1c and the middle portion 1e, strength is low. Meanwhile, in the middle portion 1e including the thick portion 1j, since the working amount is comparatively large, strength is high.
Next, a method of manufacturing a variable wall thickness steel pipe of a seventh embodiment will be described with reference to
As shown in
Similar to the first embodiment, as the diameter-increasing step shown in
Next, as the ironing step shown in
If the plug 161 is thrust as shown in
It is preferable that the difference (d5−d4) between the diameter d4 of the small-diameter base end portion 161e of the plug 161 in
A variable wall thickness steel pipe manufactured via the steps shown in
As described above, in the present embodiment, as a variable wall thickness steel pipe is manufactured by using the plug 161 provided with the small-diameter base end portion 161e having a diameter smaller than the diameter of the large-diameter portion 161c, the ironing step can be performed without having the small-diameter base end portion 161e and a part of the raw pipe 1 subjected to ironing coming into contact with each other in the ironing step. That is, when the plug 161 is thrust, only the tapered tip end portion 161b and the large-diameter portion 161c come into slide contact with the inner surface of the raw pipe 1. In addition, when the plug 161 is pulled out, only the large-diameter portion 161c mainly comes into slide contact with the inner surface of the raw pipe 1. In this manner, when the plug 161 is taken out and put in, since the small-diameter base end portion 161e does not come into slide contact with the inner surface of the raw pipe 1, compared to the first embodiment, frictional resistance between the raw pipe 1 and the plug 161 can be reduced when the plug 161 is taken out and put in the ironing step, and a force required for working can be prevented from being excessive.
A method of manufacturing a variable wall thickness steel pipe of an eighth embodiment has a step of performing drawing after ironing of the first to fourth embodiments and the sixth and seventh embodiments. In the present embodiment, as an example, the variable wall thickness steel pipe 61 manufactured via the step of the second embodiment is taken as an intermediate product 15, and drawing is performed with respect to the intermediate product 15.
First, a die 14 and the intermediate product 15 used in the present embodiment will be described with reference to
The die 14 shown in
Since the outer diameters of the unprocessed portion 15f and the middle portion 15e of the intermediate product 15 are the same as the outer diameter d1 of the raw pipe 1, the inner diameter of the hollow small-diameter portion 14b corresponds to the outer diameter d1 of the raw pipe 1. The inner diameter of the tapered portion 14c becomes the largest diameter on one end portion 14a side of the die 14, and an inner diameter d6 at this position is set to a size larger than the outer diameter of the diameter-increasing portion 15c of the intermediate product 15.
Next, the method of manufacturing a variable wall thickness steel pipe according to the present embodiment will be described. First, the intermediate product 15 is manufactured. Since the method of manufacturing the intermediate product 15 is similar to that of the second embodiment, a description will be omitted.
Next, as shown in
If the intermediate product 15 is thrust to the position shown in
In a hollow portion 181b of the variable wall thickness steel pipe 181, the entire outer diameter in its the longitudinal direction remains unchanged as the outer diameter of the raw pipe 1. In addition, in the diameter-reducing portion 181c and the unprocessed portion 181f, the inner diameter of the variable wall thickness steel pipe 181 remains unchanged as the inner diameter d2 of the raw pipe 1. In the middle portion 181e, the inner diameter thereof is further increased than the inner diameter d2 of the raw pipe 1. Therefore, the variable wall thickness steel pipe 181 has an entirely constant outer diameter in the longitudinal direction and has a plurality of regions of which the inner diameters are different from each other at positions in the longitudinal direction.
The variable wall thickness steel pipe 181 has a comparatively great thickness in the diameter-reducing portion 181c and the unprocessed portion 181f and has a comparatively small thickness in the middle portion 181e.
In addition, in the variable wall thickness steel pipe 181, since a small working amount is applied to the unprocessed portion 181f, no work hardening has occurred in this part, or even if work hardening has occurred, it is very insignificant. Therefore, the unprocessed portion 181f has comparatively low strength. Accordingly, even in a case where post-working such as bending is performed with respect to this part, annealing treatment or the like for softening work hardening becomes unnecessary.
In the present embodiment, as an example of the intermediate product 15, the variable wall thickness steel pipe 61 manufactured in accordance with the second embodiment is employed. However, the present embodiment is not limited to only this example. For example, an intermediate product of the present embodiment may be the variable wall thickness steel pipe 31 which is manufactured in accordance with the first embodiment as shown in
In addition, So that drawing is performed with respect to the entire outer surface of the intermediate product 15, the inner diameter of the hollow small-diameter portion 14b of the die 14 used in the present embodiment may be an inner diameter smaller than the outer diameter of the raw pipe 1. In this case, if the inner diameter of the hollow small-diameter portion 14b of the die 14 is excessively small with respect to the outer diameter of the raw pipe 1, an opening drawing rate becomes excessively significant, so that there is concern that buckling may occur at the time of drawing. The opening drawing rate in this case will be described below.
Generally, as steel pipes for automobiles, steel pipes of which a ratio of the steel pipe thickness to the steel pipe outer diameter (t/D0, t: thickness of raw pipe and D0: outer diameter of raw pipe) ranges from 0.001 to 0.15 are used. The inventors have minutely investigated the opening drawing rate in a case where drawing is performed with respect to a steel pipe having this size. As a result, it is ascertained that the opening drawing rate is favorably 0.4 or lower. Therefore, in a case where drawing is performed with respect to the entire outer surface of the intermediate product 15, it is favorable that the inner diameter of the hollow small-diameter portion 14b of the die 14 is set such that the opening drawing rate becomes 0.4 or lower. The opening drawing rate is expressed by the following Expression (1). The factor κ in the following Expression (1) indicates an opening drawing rate, the factor D0 indicates an outer diameter of a steel pipe before drawing, and the factor D indicates the outer diameter of the steel pipe after drawing.
K=(D0−D)/D0 (1)
As described above, in the present embodiment, it is possible to manufacture the variable wall thickness steel pipe 181 having an entirely constant outer diameter of the raw pipe 1 in the longitudinal direction and having a plurality of regions of which the inner diameters are different from each other. In this variable wall thickness steel pipe 181, since a comparatively small working amount is applied to the unprocessed portion 181f, strength in this region is comparatively low. In addition, since a comparatively large working amount is applied to the diameter-reducing portion 181c and the middle portion 181e, strength in these regions is comparatively high.
In addition, it is possible to manufacture a variable wall thickness steel pipe in which working is performed with respect to the entire region in the longitudinal direction, by performing drawing with respect to the entire outer surface of the intermediate product 15 in the longitudinal direction. In addition, it is possible to manufacture a variable wall thickness steel pipe having an entirely constant outer diameter in the longitudinal direction and having a plurality of regions of which the inner diameters are different from each other. In this variable wall thickness steel pipe, since working is performed with respect to the entire region of the raw pipe 1 in the longitudinal direction, the strength of the entire region is higher than the original strength of the raw pipe 1.
A ninth embodiment will be described. A method of manufacturing a variable wall thickness steel pipe of the present embodiment is configured to include a step similar to that of the first embodiment. In the present embodiment, the variable wall thickness steel pipe is manufactured by using a plug different from the plug 21 used in the first embodiment and the die 11 used in the first embodiment. Alternatively, the variable wall thickness steel pipe is manufactured by using a die different from the die 11 used in the first embodiment and the plug 21 used in the first embodiment. Since other configurations are similar to those of the first embodiment, a description will be omitted. Hereinafter, as an example of the ninth embodiment, the method of manufacturing a variable wall thickness steel pipe, in which a plug different from the plug 21 used in the first embodiment and the die 11 used in the first embodiment are used, will be described.
A plug 19 shown in
A diagonal length d7 of a cross section orthogonal to the longitudinal direction in the small-sized tip end portion 19a is a diameter corresponding to the inner diameter d2 of the raw pipe 1. In a cross section orthogonal to the longitudinal direction in the large-sized base end portion 19b, a side length d8 of the quadrangular shape with rounded corners corresponds to the inner diameter d2 of the raw pipe 1, and a diagonal length d9 is greater than the inner diameter d2 of the raw pipe 1 and is smaller than the inner diameter d1 of the hollow small-diameter portion 11a of the die 11.
If a variable wall thickness steel pipe is manufactured through a step similar to that of the first embodiment using the plug 19, a schematic view of a cross section orthogonal to the longitudinal direction in a middle portion subjected to ironing exhibits a shape as shown in
In the ninth embodiment described above, the variable wall thickness steel pipe 20A is manufactured through a step similar to the first embodiment using the plug 19 of which the shape of a cross section orthogonal to the longitudinal direction is a quadrangular shape with rounded corners, and the die 11. However, a plug having a different shape of a cross section orthogonal to the longitudinal direction may be used. However, it is favorable that a cross section orthogonal to the longitudinal direction of the plug has a rotationally symmetric shape. The reason is that in a case where a cross section orthogonal to the longitudinal direction of the plug does not have a rotationally symmetric shape, the diameter-increasing portion cannot be sufficiently formed by performing pipe expanding and the raw pipe 1 cannot be locked in the tapered portion 11c of the die 11.
As described above, in the present embodiment, the variable wall thickness steel pipe may be manufactured by using a die different from the die 11 used in the first embodiment and the plug 21 used in the first embodiment. It is favorable that the die used in this case has a rotationally symmetric shape of a cross section orthogonal to the longitudinal direction of the die such that pipe expanding can be sufficiently performed. In addition, the outer shape of the raw pipe 1 has to be a shape corresponding to the die.
For example, if a variable wall thickness steel pipe 20D is manufactured by using a square-shaped steel pipe, a die having a shape corresponding to the square-shaped steel pipe, and the plug 21 similar to that of the first embodiment in a manner similar to that of the first embodiment, the shape of a cross section orthogonal to the longitudinal direction in the middle portion of the variable wall thickness steel pipe 20D becomes a shape as shown in
As described above, according to the ninth embodiment, it is possible to manufacture the variable wall thickness steel pipe 20A alternately having parts which are subjected to ironing and parts which remain unprocessed in the circumferential direction, in a middle portion subjected to ironing. In addition, in the variable wall thickness steel pipe 20A, since the thickness of the parts subjected to ironing is small and the working amount is large, strength thereof is comparatively significant. Meanwhile, since the thickness of the parts which remain unprocessed is large and the working amount is small, strength thereof is comparatively small.
As described above, in the method of manufacturing a variable wall thickness steel pipe according to each of the embodiments of the present invention, the lock portion is provided by performing pipe expanding with respect to the raw pipe, and ironing is performed with respect to the middle portion on the other end side of the diameter-increasing portion of the raw pipe such that the inner diameter of the raw pipe is increased while the outer diameter is maintained, by thrusting the plug into the raw pipe while the lock portion is locked in the die. Therefore, the working amount with respect to the diameter-increasing portion can be reduced, so that heat treatment such as annealing can be made unnecessary when post-working such as bending is performed with respect to the diameter-increasing portion.
In addition, since ironing is performed by thrusting the plug into the raw pipe while the lock portion is locked in the die, ironing can be carried out by only relatively moving the die and the plug without fixing the raw pipe itself at the time of ironing.
In addition, it is possible to form parts having a small thickness and comparatively high strength and parts having a large thickness and comparatively low strength in the longitudinal direction of the variable wall thickness steel pipe. Therefore, heat treatment such as annealing can be made unnecessary when post-working such as bending is performed with respect to a part having a large thickness and comparatively small strength.
Application examples of the variable wall thickness steel pipe in each of the embodiments of the present invention for automobile components include a frame member such as a cross-member, a suspension member, and a suspension arm; a collision countermeasure component such as a perimeter and a side impact bar; and a drive system pipe component such as a drive shaft.
In the frame member such as a cross-member, a suspension arm, and a suspension member, there are many cases where a large thickness is particularly required in attachment parts for other components. Therefore, by using the variable wall thickness steel pipe in each of the embodiments of the present invention it is possible to employ a light-weight structure in which only a required location is thickened. In addition, in these components, there are cases where pressing or bending is performed when performing post-working in which the thick portion is formed into a predetermined shape. In these cases, if a part to be subjected to working has a large thickness and low strength, it is easy to perform working. Therefore, it is possible to preferably use the variable wall thickness steel pipe in each of the embodiments of the present invention.
A side impact bar is a member which is installed inside a door panel and transmits collision energy at the time of a collision to both sides of a door, and it is desired that the side impact bar does not break at the time of a collision. Therefore, if a central portion is thickened by using the variable wall thickness steel pipe in each of the embodiments of the present invention, it is possible to realize a light-weight structure.
A perimeter is a frame member in the front part of a vehicle body, and the member becomes a load transmission path at the time of a frontal collision. The member can be further reduced in weight by causing a bending shape portion or the like which is likely to be bent at the time of a collision to be a thick portion. In addition, when a thick portion is bent, if the thick portion has low strength, it is easy to perform working. Therefore, it is possible to preferably use variable wall thickness steel pipe in each of the embodiments of the present invention.
In a drive shaft, there are cases where splining is performed with respect to variable wall thickness portions at pipe ends. If this part has a large thickness and low strength, it is easy to perform working. Therefore, it is possible to preferably use variable wall thickness steel pipe in each of the embodiments of the present invention.
Essentials of the above-described embodiments will be summarized below.
(1) For example, the method of manufacturing a variable wall thickness steel pipe according to the first embodiment described by using
(2) Then, as shown in
(3) In addition, as shown in
(4) In addition, as shown in
(5) In addition, for example, as in the third embodiment described by using
(6) In addition, for example, as in the seventh embodiment described by using
(7) For example, the method of manufacturing a variable wall thickness steel pipe according to the second embodiment described by using
(8) Then, as shown in
(9) In addition, as in the fourth embodiment described by using
(10) As in the first embodiment described by using
(11) As in the sixth embodiment described by using
(12) As in the eighth embodiment described by using
(13) For example, the method of manufacturing a variable wall thickness steel pipe according to the fifth embodiment described by using
(14) According to the fifth embodiment shown in
(15) According to each of the embodiments, in the method of manufacturing a variable wall thickness steel pipe according to any one of (1) to (14), the raw pipe 1 may be a seamless steel pipe.
(16) For example, according to the first embodiment described by using
(17) The variable wall thickness steel pipe 31 according to (16) may employ the following configuration further including a thick portion (unprocessed portion 31f) that is disposed on the other side of the thin portion (middle portion 31e) in a case of being seen in the longitudinal direction and has a thickness greater than the thickness of the thin portion (middle portion 31e). In a case where an average value of hardness of the thick portion (unprocessed portion 31f) is H3, H2>H1≥H3 may be satisfied.
(18) For example, the variable wall thickness steel pipe 31 according to (17) may employ the following configuration in which the thin portion (middle portion 31e) includes a straight pipe portion 31e2 having a smallest thickness in the thin portion (middle portion 31e), a first tapered portion (lock portion 31e1) being provided between the straight pipe portion 31e2 and the expanded portion (diameter-increasing portion 31c) and having an outer shape (outer diameter) expanded toward the expanded portion (diameter-increasing portion 31c), and a second tapered portion (tapered portion 31e3) being provided between the straight pipe portion 31e2 and the thick portion (unprocessed portion 31f) and having a thickness increasing toward the thick portion (unprocessed portion 31f). In a case where an average value of hardness of the first tapered portion (lock portion 31e1) is H4, an average value of hardness of the straight pipe portion 31e2 is H5, and an average value of hardness of the second tapered portion (tapered portion 31e3) is H6, both expressions H5>H6≥H3 and H5>H4>H1 may be satisfied.
(19) According to the sixth embodiment described by using
(20) According to the fifth embodiment described by using
(21) The variable wall thickness steel pipe 111 according to (20) may employ the following configuration further including a thick portion (unprocessed portion 111i) that is disposed between a pair of the thin portions (middle portions 111g and 111h) and has a thickness greater than the thickness of the thin portion (middle portions 111g and 111h). In a case where an average value of hardness of the thick portion (unprocessed portion 111i) is H7, H2>H1≥H7 may be satisfied.
(22) For example, according to the eighth embodiment described by using
(23) According to the ninth embodiment described by using
(24) In the variable wall thickness steel pipe according to any one of (16) to (23), a seamless steel pipe may be used as a material.
According to the present invention, it is possible to provide a method of manufacturing a variable wall thickness steel pipe, in which a working amount at the time of manufacturing is small and heat treatment such as annealing becomes unnecessary when post-working such as bending is performed, and a variable wall thickness steel pipe.
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| Filing Document | Filing Date | Country | Kind |
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| PCT/JP2017/005278 | 2/14/2017 | WO |
| Publishing Document | Publishing Date | Country | Kind |
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| WO2017/154481 | 9/14/2017 | WO | A |
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| 20190076902 A1 | Mar 2019 | US |
