JP2004017107A - Die and method for forming hollow shaft with projection - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a die with which a hollow shaft with a projection is formed at small internal pressure load without generating inside surface flaws and outside fins, and a forming method for the shaft. <P>SOLUTION: Upper and lower dies 2, 3 are respectively provided with at least one or more sets of projection part forming dies 1. The projection part forming die 1 is composed of dies 2c, 2e, 3c, 3e for forming the side wall of the projection part and dies 2d, 3d for forming the upper surface of the projection part. The dies 2c, 2e, 3c, 3e for forming the side wall are bisected in the direction perpendicular to a housed metallic tube stock A. The dies 2d, 3d for forming the upper surface of the projection part are fit into the side wall forming dies 2c, 2e, 3c, 3e so that a caliber of an inside surface shape having the same shape as the contour shape of the projection part is formed together with the side wall forming dies 2c, 2e, 3c, 3e and the each die is made slidable in the axial direction of the housed metallic tube stock A. <P>COPYRIGHT: (C)2004,JPO

Description

【００５９】
成形後、突起部を目視にて観察して噛み出しの発生の有無を調べると共に、突起部先端の曲率半径Ｒを測定した。その結果を、成形条件と共に表１に示す。
【００６０】
なお、金属管内に負荷した圧力は、第１加工では最高３００ＭＰａ、第２加工も最高３００ＭＰａであった。
表１に示す結果から明らかなように、第１工程の液圧バルジ加工と第２の型寄せ液圧バルジ加工とを本発明で規定する金型を用いておこなった試番１〜４では、低い内圧付与で外面に噛み出しを発生することなく目標通の曲率半径Ｒを有する突起部を備えた突起付き中空軸が得られた。
【００６１】
これに対し、図８に示すような突起部の側壁成形用金型と突起部の上面成形用金型とが嵌合していない金型を用いて加工をおこなった試番５と６では、外面に図８のＥ部に示すような噛み出しが発生した。なお、試番１〜６のいずれにも、しわや割れなどの内面疵の発生は認められなかった。
【００６２】
【発明の効果】
本発明の成形金型および方法によれば、低い内圧負荷で突起部先端の軸方向角部外面の曲率半径が金属素管の肉厚以下と小さい突起部を有する突起付き中空軸を噛み出しの発生をさせることなく成形ができる。
【図面の簡単な説明】
【図１】本発明の突起付き中空軸の成形用金型の一例を示す縦断面図である。
【図２】図１に示した成型用金型を用いた第１工程の液圧バルジ加工後の状態を示す金型の縦断面図である。
【図３】′図１に示した成型用金型を用いた第２工程の型寄せ加工後の状態を示す金型の縦断面図である。
【図４】本発明の突起付き中空軸の成形用金型の他の例を示す縦断面図である。
【図５】実験結果の一例を整理して示す図で、突起部の拡管率が３０％のときにおける寸法ｄｌ、Ｌｌ、ｄ２おびＬ２が突起部の軸方向角部外面の曲率半径Ｒに及ぼす影響を示す図である。
【図６】図５と同様の図で、突起部の拡管率が１０％の時における図である。
【図７】金属素管、膨出加工品、突起付き中空軸品の模式的縦断面および横断面図である。
【図８】嵌合部を備えない分割型での噛み出し状況を示す図である
【図９】実施例で成形した膨出加工品、突起付き中空軸品の模式的縦断面および横断面図である。
【符号の説明】
Ａ　金属素管
Ｂ　膨出加工品
Ｃ　突起付き中空軸
Ｄ　分割型験合部
Ｅ　噛み出し部
１　金型
２　上金型
３　下金型、
２ａ、３ａ　取付け板、
２ｄ、３ｄ　突起部の上面成形用金型
２ｃ、２ｅ　３ｃ、３ｅ　突起部側壁成形用金型
７ａ、７ｂ　管端拘束治具
７ｃ、７ｄ　加工液導入路
８ａ、８ｂ　型移動用治具、[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a molding die and a molding method for a hollow shaft with a projection such as a camshaft provided with a cam portion for opening and closing intake and exhaust valves of a four-cycle reciprocating engine.
[0002]
[Prior art]
Conventionally, for example, a camshaft, which is a rotating shaft having a cam for driving an intake valve and an exhaust valve of a four-cycle reciprocating engine, is formed by machining a solid material into a rough shape by casting or forging, and then machining the final shape by machining. Was served. However, since the camshaft manufactured by the above-described processing method is a solid material, there is a problem that the camshaft is heavy and contravenes the weight reduction of the axle.
[0003]
In order to reduce the weight of the axle, a cam that requires abrasion resistance is manufactured as a hollow member using a sintered alloy, and the rotating shaft is manufactured as a hollow shaft, and these are integrated by welding, brazing, or mechanical fixing. The technology for making and assembling camshafts was developed. However, when performing welding or brazing, the respective materials of the cam member and the rotating shaft are limited, and an optimum material cannot be used. Further, the mechanical fixing method needs to repeat the fixing operation as many times as the number of the cam members, and thus has a problem of low productivity.
[0004]
Japanese Patent Application Laid-Open Nos. 57-206530 and 2000-192805 disclose a method and an apparatus for manufacturing a hollow shaft with a hollow projection formed from a metal tube for the purpose of reducing the weight of an axle and improving productivity. And JP-A-2000-210726.
[0005]
JP-A-57-206530 discloses that a metal tube is housed in a die having an inner surface provided with a concave groove corresponding to the outer shape of a projection, and the metal tube has a hydraulic bulge formed by hydraulic pressure and axial compression. A method of forming a hollow shaft with a projection by performing processing is disclosed. However, since this method is a method of forming a projection only by bulging by hydraulic bulging, the thickness of the projection is greatly reduced, and it is difficult to obtain sufficient product strength, and further, has the following disadvantages.
[0006]
That is, when the thickness of the metal tube is set to to and the radius of curvature R of the outer surface of the corner in the axial direction at the tip of the protruding portion (see FIG. 7C described later), an attempt is made to form a protruding portion in which R is equivalent to to. In this case, the radius of curvature of the inner surface corner corresponding to R becomes zero, and in order to form the projection having such a shape only by bulging, it is theoretically necessary to apply an infinite internal pressure. For this reason, a hollow shaft with a projection having an R / to of 1 or less cannot be manufactured by the above method.
[0007]
Here, the reason why the radius of curvature R is preferably small is as follows. That is, the projection may be required to have a flat surface with a constant width at the tip thereof, but the larger the R, the smaller the flat surface. Even if R is large, it is possible to secure a flat surface of a predetermined width by increasing the width of the entire protrusion. However, such a hollow shaft hinders a reduction in the size of the entire device such as an engine and an obstacle in reducing the weight of the device.
[0008]
Japanese Patent Application Laid-Open No. 2000-192805 discloses a method of forming a hollow shaft with projections by using a mold having a divided structure, reducing the diameter of a part of a metal tube, and then performing bulging. ing. However, in this method, a separate step of reducing the diameter of the metal tube is required, and if there is a flaw on the inner surface of the metal tube, the flaw may increase due to the reduction. Therefore, it is necessary to finish the inner surface of the raw tube smoothly, and there is a disadvantage that the production cost is increased. In addition, at the time of the mold approaching process with the divided molds, biting occurs between the divided molds, and it is impossible to mold into a desired shape, or the outer surface has galling flaws. There is also a drawback that requires.
[0009]
Japanese Patent Application Laid-Open No. 2000-210726 discloses that after a metal tube accommodated in a split mold that is divided into a plurality of pieces in an axial direction and set at a predetermined distance from each other, is subjected to swelling processing, A method of forming a hollow shaft with projections while suppressing the thickness reduction of the projections by shifting the mold in the axial direction and applying axial compression to the bulging portion is disclosed.
[0010]
However, in this method, at the time of the mold approaching process with the split molds, biting occurs between the split molds, and a desired shape cannot be formed, or an eaves are formed on the outer surface, so that care in a separate process is required. It has the disadvantage that it becomes necessary.
[0011]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and the problem is that a hollow shaft with a projection in which the projection and the shaft are integrated can be molded with a small internal pressure, without causing the inner surface eaves and the outer surface to bite out, An object of the present invention is to provide a molding die and a molding method suitable for manufacturing a hollow shaft with a projection in which the radius of curvature R of the axial corner outer surface of the tip of the projection is equal to or less than the thickness of the metal tube.
[0012]
Note that the outer surface biting will be described in more detail below.
[0013]
FIG. 8 is a longitudinal sectional view of a mold in the process of being processed by a mold in which the mold for forming the side wall of the projection and the mold for forming the upper surface are not fitted.
[0014]
The mold is composed of an upper mold 2 and a lower mold 3, and the upper and lower molds are respectively molds 2c, 2d, 2e, 3c, 3d, 3e for forming projections, and molds for molding shafts provided adjacent thereto. 2b, 2f, 3b and 3f, and the projection molding die is composed of a projection side wall molding die 2c, 2e, 3c and 3e, and a projection upper surface molding die 2d and 3d. The mold for forming the side wall is divided into two parts in the circumferential direction of the metal tube accommodated therein, and the mold for forming the upper surface of the protrusion forms the outer shape of the protrusion with the mold for forming the side wall. Are arranged as follows. Each of these molds is slidable in the axial direction of the stored metal tube. Although FIG. 8 shows a state in which the projection is being formed, the mold for forming the side wall of the projection and the mold for forming the upper surface are not fitted to each other. The start E portion (dotted circle) has occurred. In the method described in Japanese Patent Application Laid-Open No. 2000-210726, biting occurs between the split molds at the time of moving the mold in the same manner as described above.
[0015]
[Means for Solving the Problems]
The present inventor has proposed a steel pipe made of carbon steel for mechanical structure specified in JIS G 4051, G 4052 and G 4805, structural steel with guaranteed hardenability, and high carbon chromium bearing steel in order to solve the above problems. As a result of repeated experiments of hydraulic bulge processing using the same, the following findings (a) to (d) were obtained.
(A) In order to prevent the occurrence of biting between the dies as shown in FIG. 8, the outer shape of the protrusion is formed by the upper surface forming die and the side wall forming die of the protrusion. It is necessary to fit the upper surface forming die of the projection into the side wall forming die to eliminate the gap between the dies.
(B) In order to form a projection having a small radius of curvature R at the outer end of the axial corner portion with a small internal pressure load, the length of the external line in the axial direction of the bulge after the hydraulic bulging in the first step is set to L. _l (Mm), the axial length of the outer surface in the axial direction of the protrusion after the hydraulic bulging in the second step is L ₂ (Mm), L in the hydraulic bulging in the first step _l Is L ₂ It is effective to form a bulge larger than that.
(C) Further, the outer peripheral length at the axial center position of the bulging portion after the hydraulic bulging in the first step is d. _l (Mm), the outer peripheral length at the axial center position of the protruding portion after the bulging in the second step is d ₂ (Mm), the ratio (d) _l / D ₂ ) And L _l And L ₂ And the ratio (L ₁ / L ₂ ) Is a parameter that determines the magnitude of the radius of curvature R during the hydraulic bulging in the second step.
(D) Assuming that the radius of curvature of the outer surface of the corner portion in the axial direction of the tip of the projection to be formed is R (mm), the hydraulic bulge processing in the first step and the mold approach liquid in the second step are performed under the following conditions. When pressure bulging is performed, the radius of curvature R of the outer surface of the axial corner at the tip of the projection becomes smaller than the thickness to (mm) of the metal tube at a small applied internal pressure, and the hollow shaft with projections having no inner surface flaws. Manufacturing becomes possible.
[0016]
1.2−0.2 × (R / t.) ≦ (d _l / D ₂ ) × (L _l / L ₂ ) ≦ 1.4
(E) The wall thinning generated at the time of the bulging process of the projection is suppressed by the abset effect at the time of the pallet processing at the second step.
[0017]
The present invention has been made based on such findings, and the gist is as follows.
[0018]
(1) Hydraulic bulging is performed on a metal tube accommodated in a hole mold formed by an upper mold and a lower mold to form a hollow shaft with a projection in which a projection and a shaft are integrated. Upper and lower molds each include at least one or more sets of protrusion forming molds, and the protrusion forming molds include side wall forming molds for forming side walls of the protrusions. The side wall forming mold is divided into two parts in a direction orthogonal to the axial direction of the accommodated metal tube, and the upper surface forming metal The mold is fitted into the side wall forming mold so that a hole having the same inner surface shape as the outer shape of the projection can be formed with the side wall forming mold. The upper surface forming mold is a mold for forming a hollow shaft with a protrusion which can slide in the axial direction of the metal tube.
[0019]
(2) A metal hollow pipe formed by an upper mold and a lower mold is subjected to hydraulic bulging to form a hollow shaft with a projection in which the projection and the shaft are integrated. Upper and lower dies each include at least one set of protrusion forming dies, and the protrusion forming dies form a part of a side wall and an upper surface of the protrusion. And a sidewall molding die for molding the remaining side wall, and the sidewall molding die has the same shape as the outer shape of the projection with the sidewall upper surface molding die. The mold for forming the side wall and the mold for forming the upper surface of the side wall are fitted with a hollow shaft with a protrusion that is slidable in the axial direction of the metal tube. Mold for molding.
[0020]
(3) A method for molding a hollow shaft with a projection in which a projection and a shaft are integrated with each other, using the mold for molding a hollow shaft with a projection according to (1) above, wherein the mold for sidewall molding is formed. The upper mold and the upper mold are set with a predetermined gap between both molds, and a liquid pressure is applied to the inside of the metal tube housed between the upper mold and the lower mold to form the side wall mold. A hydraulic bulging process of the first step in which a part of the metal tube is swelled in a hole formed by the metal mold and the upper surface forming die, and a state in which hydraulic pressure is applied to the inside of the metal tube after the processing And forming a hollow shaft with projections in a second step of closing the gap between the dies to form a bulge in the die into a target projection shape.
[0021]
(4) A method for molding a hollow shaft with a projection in which the projection and the shaft are integrated with each other by using the mold for molding a hollow shaft with a projection according to the above (2), wherein the mold for sidewall molding is provided. And the side wall upper surface forming mold are set with a predetermined gap between both the molds, and a liquid pressure is applied to the inside of the metal tube housed between the upper mold and the lower mold to form the side wall forming mold. Hydraulic bulging in the first step in which a part of the metal tube is swelled into a hole formed by the mold and the side wall upper surface forming die, and after the processing, hydraulic pressure is applied to the inside of the metal tube. A method of forming a hollow shaft with projections, comprising performing a mold-pulling hydraulic bulge process in a second step of narrowing a gap between the dies and forming a bulge portion in the die into a target projection shape in the formed state.
[0022]
(5) When the target radius of curvature of the outer surface of the corner portion in the axial direction at the tip of the protrusion after the bulging hydraulic bulge processing in the second step is R (mm), the hydraulic bulge in the first step under the condition satisfying the following equation: The method for producing a hollow shaft with projections according to the above (3) or (4), wherein the processing and the second-step hydraulic bulging process are performed.
[0023]
1.2−0.2 × (R / t ₀ ) ≦ (d ₁ / D ₂ ) × (L _l / L ₂ ) ≦ 1.4
Where t ₀ : Thickness of metal tube (mm)
d ₁ : Perimeter length (mm) at the axial center of the bulge after the first step
d ₂ : Outer peripheral length (mm) at the axial center position of the protrusion after the second step
L ₁ : Axial outer surface line length (mm) of the swollen portion after the first step
L ₂ : Axial outer surface line length of the protrusion after the second step (mm)
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a longitudinal sectional view showing an example of a mold for forming a hollow shaft with a projection according to the present invention. FIG. 1 shows a state immediately before molding in which a metal tube A is housed in a hole formed by upper and lower molds. Show.
[0025]
The mold of the present invention is a mold provided with at least one or more sets of protrusion forming molds in each of the upper mold 2 and the lower mold 3. In the mold shown in FIG. 1, a pair of molds for forming a protrusion is a mold for forming a side wall of the protrusion (upper mold: 2c, 2e, lower mold: 3c, 3e) and an upper surface of the protrusion. Molding mold (upper mold: 2d, lower mold: 3d), and the side wall molding mold is divided into two parts 2c and 2e in the direction perpendicular to the metal tube A accommodated (in the case of the lower mold: 3c and 3e), and the upper surface forming die of the protrusion is formed with the side wall forming die so that a mold having the same inner surface shape as the outer shape of the protrusion of the product can be formed. It is fitted in the mold (FIG. 1D). Further, the protrusion forming dies 2c, 2e, 2d and 3c, 3e, 3d are respectively attached to the mounting plates 2a, 3a by an appropriate means such as a dovetail groove mechanism. It is mounted so that it can slide in the axial direction.
[0026]
In addition, b in FIG. 1 shows a breaking line, a part of the longitudinal direction of the mold is omitted, and one set of protrusion forming molds is shown in each of the upper and lower molds. When a hollow shaft having a plurality of protrusions is formed, a mold having a plurality of sets of protrusion-forming dies is naturally used. The molds 2b, 2f, 3b, and 3f are molds for molding the tube end portion. For example, in the case of 2b, the molds may be molds for molding a side wall of a projection, such as 2c, or may be a normal movable mold for molding a shaft. It may be a mold.
[0027]
As shown in FIG. 1, the mold according to the present invention has protrusions formed in the side wall forming molds 2c, 2e, 3c, 3e of the protrusions in which the protrusion molding die is divided into two in the circumferential direction of the raw tube. It is a great feature that the upper surface forming molds 2d and 3d are fitted (D part). With such a configuration, the outer surface between the molds as shown in FIG. Does not occur.
[0028]
FIG. 4 is a longitudinal sectional view showing another example of a mold for molding a hollow shaft with a projection of the present invention. This mold is the same as the mold shown in FIG. 1 except that the upper molds 2d and 3d shown in FIG. 1 and one of the side wall molds 2e and 3e are integrated. . The same effect as the mold shown in FIG. 1 can be obtained also by using the side wall upper mold 2g as shown in FIG. 4 in which one of the side wall molds and the upper mold is integrated.
[0029]
Next, the molding method of the present invention will be described. Hereinafter, the case where the mold shown in FIG. 1 is used will be described, but the same applies to the mold shown in FIG.
[0030]
At the time of hydraulic bulging, since a force is applied to divide the upper and lower molds by the pressure applied to the metal tube, the hydraulic bulging is performed while pressing the upper and lower molds from above and below by a press mechanism (not shown). It is. Either or both of the upper mold 1 and the lower mold 2 are moved up and down by the vertical movement of the press mechanism, whereby the metal tube A is carried into the mold and the hollow shaft C with the projection after the processing is completed. Is carried out of the mold.
[0031]
In the hydraulic bulging process, first, an upper mold 2 and a lower mold 3 are opened by operating a press mechanism (not shown), and the respective molds are arranged and fixed as shown in FIG. Is accommodated in the mold, and the upper mold 2 and the lower mold 3 are closed. At this time, the side wall forming molds 2c, 2e and 3c, 3e of the protrusion are fitted to the upper surface forming molds 2d and 3d of the protrusion, respectively, and a predetermined gap is provided. Set.
[0032]
Both ends of the metal tube A are kept airtight by the tube end restraining jigs 7a and 7b. The pipe end restraining jig is connected to an appropriate pressing mechanism such as a hydraulic ring (not shown), and can apply a compressive force in the axial direction from both ends of the metal pipe during hydraulic bulging.
[0033]
After the mold is set in the state shown in FIG. 1, the metal tube A is subjected to a first step hydraulic bulging and a second step hydraulic bulging described below.
[0034]
That is, in the hydraulic bulging process in the first step, the positions of the upper surface forming dies 2d and 3d of the protrusion and the side wall forming dies 2c, 2e and 3c and 3e of the protrusion are adjusted as appropriate by a hydraulic cylinder or the like. The state shown in FIG. 1 is fixed and held by mold moving jigs 8a and 8b having a pressing mechanism. Each mold is fixed at a predetermined position according to the shape of the product.
[0035]
Then, while the high-pressure processing liquid is injected into the inside of the metal pipe A from the processing liquid introduction paths 7c and 7d provided at the axis of the pipe end restraining jigs 7a and 7b, the pipe end restraining jigs 7a and 7b 7b, the metal tube A is expanded and deformed by applying an axial compressive force from both sides of the metal tube.
[0036]
FIG. 2 is a longitudinal sectional view of the mold shown in FIG. 1 after the hydraulic bulging in the first step using the mold for forming a hollow shaft with a projection.
[0037]
In the hydraulic bulging process of the first step, even when an axial compressive force is applied from only one side only by the pipe end restraining jig 7a or 7b, the pipe bulging deformation of the metal pipe A is possible. When the deformability of the metal tube A to be used is high or when the amount of expanded tube swelling is small, the axial compression force by the tube end restraining jigs 7a and 7b is not applied, and the metal tube A is applied only by applying the internal pressure. It is also possible to bulge the tube A.
[0038]
Next, in the mold approach hydraulic bulging process of the second step, the mold moving jigs 8a and 8b are operated to move the side wall forming dies 2c, 2e and 3c and 3e of the protrusion to the upper surface forming metal of the protrusion. Move from both sides toward dies 2d and 3d. At this time, the injection of the working fluid from the working fluid introduction passages 7c and 7d provided at the axis of the pipe end restraining jigs 7a and 7b and the application of the axial compressive force are continuously performed to further expand the bulging processed product B. Expand and bulge.
[0039]
FIG. 3 is a longitudinal sectional view of a mold showing a state after a mold approach hydraulic bulge processing in a second step using the mold for forming a hollow shaft with a projection shown in FIG. When the state shown in FIG. 3 is attained, the mold approach hydraulic bulging is completed.
[0040]
More specifically, the side wall forming molds 2c, 2e and 3c, 3e of the protrusion are in contact with each other in a fitted state, and the side wall of the protrusion is opposed to the upper surface forming molds 2d and 3d of the protrusion. Hydraulic bulging is completed when the protrusions of the hollow shaft with protrusions fill the inner surface of the hole mold in which the molding dies 2c, 2e and 3c, 3e are abutted and integrated.
In the bulging hydraulic bulging in the second step, the application of the axial compressive force by the pipe end restraining jigs 7a and 7b is performed by only one of them similarly to the hydraulic bulging in the first step. When the deformability of the metal pipe A used is high or when the expanded pipe swelling amount is small, it may be omitted, and the metal pipe A may be simply moved to follow the movement of the mold.
[0041]
Also, when performing the mold approach hydraulic bulging process, the approach movement of the mold may be performed by operating only one mold moving jig and fixing the other mold moving jig.
[0042]
In addition, the gap between the side wall molding die and the upper surface molding die (or the side wall upper surface molding die) set before molding is determined in the first step when the gap is reduced to zero. It is preferable that the gap is formed so that the processed bulging portion can be filled in the mold.
[0043]
As described above, the hydraulic bulging process for the metal pipe A is performed in two steps, so that the expanded area in the axial direction of the metal pipe formed in the hydraulic bulging processing in the first step is only vertically. It is longer than in the case of using the divided conventional hydraulic bulging die. When the internal pressure applied to the metal pipe A is the same, the swelling amount and the material volume also increase. The expanded area of the expanded product B, which is longer in the pipe axis direction and has a larger amount of expansion and a larger material volume, is subjected to compression processing by the second-step die-sliding hydraulic bulging process. Accordingly, a decrease in the thickness of the bulging portion is prevented. Further, since bending in the tube axis direction is given by the mold shift, the outer radius of the corner in the tube axis direction can be formed with a small internal pressure.
[0044]
At the time of the hydraulic bulging in the second step, the internal pressure applied to the inside of the bulged product B depends on the outer shape of the projection and the expanded bulged product B after the hydraulic bulging in the second step. Although it is determined by the overhanging shape of the portion, in the mold closing hydraulic bulging in the second step, the higher the internal pressure applied, the better the shape after molding. For this reason, it is preferable that the internal pressure applied to the inside of the bulging product B be as high as possible in the bulging hydraulic bulging in the second step.
[0045]
After the hydraulic bulging process in the second step is completed, the upper mold 2 and the lower mold 3 are opened by operating the press, and the hollow boss C with hydraulic bulging is carried out of the mold 1.
[0046]
As described above, the hydraulic bulging in the first step and the hydraulic bulging in the second step are performed in a state where the side wall forming die and the upper surface forming die are fitted to each other, that is, between the two dies. Since there is no gap in the hydraulic bulge processing in the first step and the hydraulic bulge processing in the second step, biting can be prevented. In addition, since the method of the present invention is basically a bulging process, there is no occurrence of an inner surface flaw generated in the case of the diameter reducing process.
[0047]
According to the method of the present invention, a hollow shaft with projections can be formed as described above. In particular, the hydraulic bulging in the first step and the hydraulic bulging in the second step can be performed under the following conditions. The target radius of curvature R (see FIG. 7 (c)) of the outer surface of the corner portion in the axial direction at the tip of the projection of the hollow shaft with projection is reduced while preventing the bite from being formed. ₀ [See FIG. 7 (a)] The following hollow shaft with projection can be manufactured.
1.2−0.2 × (R / t.) ≦ (d ₁ / D ₂ ) × (L ₁ / L ₂ ) ≦ 1.4
Where t ₀ : Wall pressure of metal pipe (mm)
d ₁ : Perimeter length (mm) at the axial center of the bulge after the first step
d ₂ : Outer peripheral length (mm) at the axial center position of the protrusion after the second step
L ₁ : Axial outer surface line length (mm) of the swollen portion after the first step
L ₁ : Axial outer surface line length of the protrusion after the second step (mm)
This has been clarified from the following experimental results.
[0048]
7A and 7B show a longitudinal section and a sectional view of a metal tube, a bulged product, and a hollow shaft with a projection. FIG. 7A is a sectional view of the metal tube A, and FIG. FIG. 3C is a cross-sectional view of a processed product B, and FIG.
[0049]
As shown in FIG. 7, the wall thickness of the metal pipe A is to, the outer peripheral length is do, and the outer peripheral length at the axial center position of the expanded portion of the expanded product B is d. _l , The line length of the outer surface in the axial direction is L _l , And the outer peripheral length at the axial center position of the projection of the hollow shaft C with the projection is d. ₂ , The line length of the outer surface in the axial direction is L ₂ And
[0050]
FIG. 5 shows that the expansion ratio of the protrusion is 30%, in other words, the ratio (do / d ₂ ) Is 0.77 and the ratio (R / to) is 0.6. _l , L _l , D ₂ , And L ₂ Is a graph showing the effect of R on R. In the figure, a circle indicates that a protrusion having the desired R could be formed, a triangle indicates that a protrusion could not be formed, and a hydraulic bulging process in the second step. It is the figure shown by x mark when buckling that the width of the tip of the bulging part sometimes becomes smaller than the width of the tip part, or the tip surface is dented occurs.
[0051]
FIG. 6 shows that the expansion ratio of the projection is 10%, in other words, the ratio (do / d ₂ ) Is 0.91 and the ratio (R / t.) Is 0.6 when forming a hollow shaft C with projections having a ratio of 0.6. _l , L _l , D ₂ , And L ₂ FIG. 6 is a diagram similar to FIG.
[0052]
Note that the ratio (d _l / D ₂ ) Is d _l = Lower limit value (do / d ₂ ), D _l = D ₂ , The maximum value is 1 and (d ₀ / D ₂ ) ≦ (d ₁ , / D ₂ ) ≦ 1.
[0053]
As can be seen from the results shown in FIGS. 5 and 6, 1.2−0.2 × (R / t.)> (D ₁ / D ₂ ) × (L ₁ / L ₂ In the condition of ()), the mark is a mark, and the projection having the target radius of curvature R cannot be formed. Also, (d ₁ / D ₂ ) × (L _l / L ₂ )> 1.4 under the condition of 1.4, and buckling occurs at the bulging portion during the hydraulic bulging in the second step.
[0054]
On the other hand, 1.2−0.2 × (R / to) ≦ (d _l / D ₂ ) × (L _l / L ₂ In the condition of ≦≦ 1.4, the mark “○” indicates that a projection having the target radius of curvature R is obtained.
[0055]
Examples of the metal pipe A that can be formed include carbon steel for machine structural use and its equivalent steel specified in JIS G4051, G4052 and G4805, structural steel and its equivalent steel with guaranteed hardenability, and high carbon chromium. It is not limited to a steel pipe made of bearing steel and its equivalent steel, but may also be a Fe-based alloy pipe or Ni-based alloy pipe other than those described above, and a non-ferrous pipe or a non-ferrous alloy pipe represented by aluminum and its alloys.
[0056]
【Example】
9A and 9B are longitudinal sectional views of the hollow shaft with projections formed in the example. FIG. 9A is a sectional view of a bulged product after the second hydraulic bulge processing, and FIG. It is sectional drawing of the hollow shaft with a protrusion of an article.
[0057]
Using a metal tube of carbon steel for machine structure having an outer diameter of 30 mm and a wall thickness of 3 mm as a raw tube, a hydraulic bulging process in the first step shown in FIGS. The hollow shaft with protrusions shown in FIG. 9 (b) is formed into a processed product by a hydraulic bulging process in a second step of changing the state shown in FIG. 2 to the state shown in FIG. Molded. Also, the first hydraulic bulge processing and the second hydraulic bulge processing were performed under the same conditions as those of the present invention except that the mold shown in FIG. 8 was used as a comparative example.
[0058]
[Table 1]

[0059]
After the molding, the protrusions were visually observed to check for occurrence of biting, and the radius of curvature R at the tip of the protrusions was measured. The results are shown in Table 1 together with the molding conditions.
[0060]
The pressure applied to the inside of the metal pipe was 300 MPa at the maximum in the first processing and 300 MPa at the second processing.
As is clear from the results shown in Table 1, in Test Nos. 1 to 4 in which the hydraulic bulging in the first step and the second hydraulic bulging in the second mold were performed using the mold defined in the present invention, A hollow shaft with a projection having a projection having a target radius of curvature R was obtained without application of a low internal pressure to the outer surface of the projection.
[0061]
On the other hand, in Test Nos. 5 and 6, which were performed using a mold in which the mold for forming the side wall of the protrusion and the mold for forming the upper surface of the protrusion were not fitted as shown in FIG. A biting as shown in a portion E in FIG. 8 occurred on the outer surface. In addition, generation | occurrence | production of the internal surface flaws, such as a wrinkle and a crack, was not recognized in any of the test numbers 1-6.
[0062]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the molding die and method of this invention, the radius of curvature of the axial corner outer surface of the tip of the projection at the low internal pressure load is less than the thickness of the metal pipe, and the hollow shaft with the projection having the projection is small. Molding can be performed without causing generation.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing an example of a mold for molding a hollow shaft with a projection of the present invention.
FIG. 2 is a longitudinal sectional view of a mold showing a state after a hydraulic bulging process in a first step using the molding mold shown in FIG. 1;
FIG. 3 is a longitudinal sectional view of the mold showing a state after a mold shifting process in a second step using the molding mold shown in FIG. 1;
FIG. 4 is a longitudinal sectional view showing another example of a mold for molding a hollow shaft with a projection of the present invention.
FIG. 5 is a diagram showing an example of the experimental results, in which dimensions dl, L1, d2 and L2 affect the radius of curvature R of the outer surface of the protrusion in the axial direction when the expansion ratio of the protrusion is 30%. It is a figure showing an influence.
FIG. 6 is a view similar to FIG. 5, but when the expansion ratio of the protrusion is 10%.
FIG. 7 is a schematic longitudinal sectional view and a transverse sectional view of a metal tube, a bulged product, and a hollow shaft product with a projection.
FIG. 8 is a diagram showing a state of biting in a split type having no fitting portion.
FIG. 9 is a schematic vertical cross-sectional view and a cross-sectional view of a bulged product and a hollow shaft product with a protrusion formed in the example.
[Explanation of symbols]
A Metal tube
B bulge product
C Hollow shaft with projection
D Split type joint
E Ejection part
1 Mold
2 Upper mold
3 Lower mold,
2a, 3a mounting plate,
2d, 3d Mold for molding top surface of protrusion
2c, 2e 3c, 3e Mold for forming side wall of projection
7a, 7b Pipe end restraining jig
7c, 7d machining fluid introduction path
8a, 8b type moving jig,

Claims (5)

A metal for forming a hollow shaft with a projection in which a projection and a shaft are integrated by subjecting a metal tube housed in a hole mold formed by an upper mold and a lower mold to a hydraulic bulging process. The upper and lower molds each include at least one or more sets of protrusion forming molds, and the protrusion forming molds include a side wall forming mold and a protrusion for forming side walls of the protrusions. An upper surface forming die for forming the upper surface of the portion is formed, and the side wall forming die is divided into two parts in a direction orthogonal to the axial direction of the accommodated metal tube, and the upper surface forming die is formed of a side wall. It is fitted in the side wall forming mold so that a hole having the same inner surface shape as the outer shape of the projection can be formed with the forming die, and the side wall forming mold and the upper surface forming mold are fitted. A mold for forming a hollow shaft with a protrusion, wherein the mold is slidable in the axial direction of the metal tube. A metal for forming a hollow shaft with a projection in which a projection and a shaft are integrated by subjecting a metal tube accommodated in a hole mold formed by an upper mold and a lower mold to hydraulic bulging. A mold, wherein the upper and lower molds each include at least one or more sets of protrusion forming molds, and the protrusion forming molds have side walls for forming a part of the side walls of the protrusions and the upper surface. An upper surface forming die and a side wall forming die for forming the remaining side wall. The side wall forming die has the same inner shape as the outer shape of the projection with the side wall upper surface forming die. A hollow having a protrusion, which is fitted so that a hole mold can be formed, wherein the side wall forming mold and the side wall upper surface forming mold are slidable in the axial direction of the metal tube. Mold for molding shafts. A method for molding a hollow shaft with a projection in which a projection and a shaft are integrated with each other using the mold for molding a hollow shaft with a projection according to claim 1, wherein the mold for forming a side wall and the molding for an upper surface are formed. The mold and the mold are set with a predetermined gap between them, and a liquid pressure is applied to the inside of the metal tube housed between the upper mold and the lower mold to mold the side wall mold and the upper mold. A hydraulic bulging process in a first step for swelling a part of the metal tube into a die formed by a mold, and after the working, pressurizing the metal tube while applying a hydraulic pressure inside the metal tube. And forming a bulging portion in the die in a second step of forming a bulge portion in the die into a target projection shape. A method for molding a hollow shaft with a projection in which a projection and a shaft are integrated with each other using the mold for molding a hollow shaft with a projection according to claim 2, wherein the sidewall molding die and the sidewall upper surface molding are formed. The mold is set with a predetermined gap between the two molds, and a liquid pressure is applied to the inside of the metal tube accommodated between the upper mold and the lower mold to form the side wall forming mold and the upper surface of the side wall. A hydraulic bulging process in a first step of bulging a part of the metal tube into a hole formed by a molding die, and after the processing, a hydraulic pressure is applied to the inside of the metal tube. A method of forming a hollow shaft with projections, comprising performing a mold-pulling hydraulic bulge process in a second step of narrowing a gap between the dies and forming a bulge portion in the die into a target projection shape. Assuming that the target radius of curvature of the outer surface of the corner portion in the axial direction at the tip of the protrusion after the hydraulic bulging in the second step is R (mm), the hydraulic bulging in the first step and the hydraulic bulging in the first step are performed under the following conditions. The method for producing a hollow shaft with protrusions according to claim 3 or 4, wherein a two-step hydraulic bulging process is performed.
1.2−0.2 × (R / t ₀ ) ≦ (d ₁ / d ₂ ) × (L ₁ / L ₂ ) ≦ 1.4
Here, t _{0 is} the wall thickness (mm) of the metal tube.
d ₁ : outer peripheral length (mm) at the center position in the axial direction of the swollen portion after the first step
d ₂ : outer peripheral length (mm) at the axial center position of the protrusion after the second step
L ₁ : Line length (mm) of the outer surface in the axial direction of the swollen portion after the first step
L _2: axial outer surface line length of the projecting portion after the second step (mm)

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