JP3724317B2 - Method for forming hollow rack shaft and core bar therefor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hollow rack shaft used in a steering apparatus for automobiles, a rack tooth forming method for a hollow rack shaft, and a mold (core metal) for the method.
[0002]
[Prior art]
A rack and pinion system is frequently used for a steering apparatus of an automobile. In this method, the rotation of the steering wheel operated by the driver is transmitted to the pinion. The rotation of the pinion is transmitted to the rack shaft meshing with the pinion, and converted into a movement in the lateral direction (the length direction of the rack). Since the rack shaft is coupled to the steering rod, the direction of the front wheel is changed by the lateral movement of the rack shaft. Since such a steering mechanism is well known, further explanation is omitted.
[0003]
Conventionally, the rack shaft has been obtained by cutting a rod-shaped material. However, in recent years, as much as possible, plastic processing technology has been incorporated in order to eliminate cutting as much as possible in the manufacture of the rack shaft. As a result, the rack shaft has become hollow. JP-A-9-246379, JP-B-4-28582, and JP-A-11-180318 disclose examples of rack shaft manufacturing methods incorporating such a plastic working technique.
[0004]
In the manufacturing method disclosed in Japanese Patent Application Laid-Open No. 9-246379, a first mold split mold is inserted into a tube material, primary molding is performed by a press mold, and then teeth corresponding to rack teeth are formed on a part of the inner surface. A primary molding material is inserted into a secondary molding split mold, a semicircular mandrel is press-fitted from one end, and rack teeth are molded.
[0005]
In addition, a manufacturing method disclosed in Japanese Patent Publication No. 4-28582 is a mold having a tooth corresponding to a rack tooth in a state where a core metal is inserted into a tube material and the periphery of the tube is surrounded by a fixed mold. Is pressed into the outer shape of the tube to form rack teeth.
[0006]
The manufacturing method disclosed in JP-A-11-180318 is an invention made by Okubo, one of the inventors of the present invention.
[0007]
FIG. 1 is an external view showing a hollow rack shaft completed by the above manufacturing method. The completed hollow rack shaft has substantially no change in appearance even if it is a hollow rack shaft completed according to the present invention.
[0008]
According to the manufacturing method disclosed in this publication, a substantially strip-shaped plate material is used as the material. In the first step, the plate material is bent into a U shape having a semicircular cross section in the vicinity of both ends along the longitudinal center, and in a U shape at the center. Thereafter, in the second step, rack teeth are formed by plastic working on the U-shaped portion at the center. FIG. 2 shows a state in which the rack teeth are formed, that is, the workpiece (half-processed plate material) 3 after the second step, (a) is a front sectional view, and (b) is a central portion. The cross section of the U-shaped part in which the rack tooth of this was formed is shown.
[0009]
Thereafter, in the third step, the U-shaped part in the center and the U-shaped part in the vicinity of both ends are bent into an arc shape so that the ends (edges) of both legs are abutted with each other. As a whole, it is formed into a tube shape. 3A and 3B are views showing a state after the workpiece 3 is bent, that is, a state after the third step is finished, in which FIG. 3A is a front sectional view and FIG. 3B is a rack tooth at the center. The cross section of the U-shaped part in which is formed, (c) shows the cross section of the U-shaped part in the vicinity of both ends. In addition, as can be seen from FIG. 3 (c), the leg portion is bent so as to be smoothly connected to the semicircular arc portion of the U-shaped portion in the vicinity of both ends, and is formed into a cylindrical shape.
[0010]
In the third step, in order to bend the leg portions of the U-shaped portion and the U-shaped portion into an arc shape, the following method is currently used. For this reason, in practice, there has been a phenomenon in which it is not correctly bent into an arc.
[0011]
7, 8, and 9 show a method of forming a tube by bending a leg portion of the U-shaped portion and the U-shaped portion into an arc shape along the progress of the processing. In each figure, (a) is a front cross-sectional view of a mold and a workpiece, and (b) and (c) in each figure are II cross-section, II-II cross-section, III-III of each front cross-sectional view. It is sectional drawing in a cross section, IV-IV cross section, VV cross section, and VI-VI cross section.
[0012]
2 and 3, the work 3 is drawn with the legs facing downward. However, in FIGS. 7, 8, and 9, the work 3 is drawn with the legs facing up. ing.
[0013]
As shown in FIG. 7, the workpiece 3 is a surface on which a rack tooth portion already formed in the second step is placed, and a rack sub-tooth mold 1 having a surface complementary to this tooth shape, On the both sides of the rack sub-tooth mold 1, the released legs 6 are placed on the arc-under mold 5 having a surface complementary to the arc of the U-shaped section formed in the first step. Can be placed on top.
[0014]
The upper mold 4 has an arc-shaped surface having a diameter substantially equal to the width of the leg portion of the workpiece 3 on the lower side, and is pushed down toward the rack sub-mold 1 and the arc-lower mold 5.
[0015]
As the upper die 4 descends, the workpiece 3 is guided by the arc surface of the upper die 4 and receives a bending force toward the inside to be deformed, but as shown in FIGS. 8B and 8C, Deformation occurs only near the base of the leg 6, and the entire leg 6 does not deform along the arc surface of the upper mold 4.
[0016]
For this reason, even if the upper die 4 is completely lowered as shown in FIG. 9, a straight portion 7 that is not deformed in an arc shape remains in a part of the leg portion 6. That is, a back surface that is not a perfect circle is formed on the rack shaft. Further, since the end faces of the abutting portions do not face each other, the end faces are inclined and a V-shaped groove is formed, which hinders subsequent welding such as laser welding.
[0017]
The original U-shaped part and the arc of the upper mold 4 are connected to form one circle, and the U-shaped part (the part with rack teeth) is designed to connect smoothly to the arc. However, the deformation that actually occurs is such a distorted cross-sectional shape.
[0018]
In this way, when the cylindrical portion of the rack shaft end and the semicircular portion of the rack portion are plastically processed into a distorted cross-sectional shape, the machining allowance in the subsequent grinding process is increased in order to make this distorted cross-sectional shape a correct arc. In addition to increasing the manufacturing cost, there is a problem in that the strength of the rack shaft is reduced due to the large machining allowance, and the rack shaft is broken or the service life is shortened.
[0019]
Further, if the thickness of the plate material is increased in order to prevent the strength from being lowered, the other part of the completed hollow rack shaft has an unnecessarily thick thickness, which is contrary to the trend of weight reduction. It was.
[0020]
[Problems to be solved by the invention]
As described above, the present invention improves the tube forming process that could not be formed into a correct arc in the conventional plastic working, so that the arc part on the back of the rack part and both ends of the rack shaft are closer to a perfect circle (or semicircle). It is an object of the present invention to provide a rack shaft forming method that can be formed into a single piece and a mold for the method.
[0021]
[Means for Solving the Problems]
The above-described problems are solved by the invention having the following solution means. That is,
The first invention is a method of forming a hollow rack shaft,
An intermediate material for manufacturing a hollow rack shaft in which a rack tooth shape is formed in a portion having a U-shaped cross section in the central portion, and U-shaped cross section portions are formed on both sides thereof. When the U-shaped and U-shaped leg portions are bent into an arc shape and the end portions of the leg portions are butted and plastically processed into a tube shape, between the U-shaped and U-shaped leg portions, , which has an arc shape of a hollow inner surface of the hollow rack shaft that is both shaped, circular for each cylinder portion of the D-shaped core metal and the hollow rack shaft with a flat portion for contacting the top of the rack tooth profile A cored bar portion is provided, and a cored bar made up of at least two separate parts is inserted in order to extract the cored bar after molding .
[0022]
The core bar of the second invention is
An intermediate material for manufacturing a hollow rack shaft in which a rack tooth shape is formed in a portion having a U-shaped cross section in the central portion, and U-shaped cross section portions are formed on both sides thereof. In order to bend the U-shaped and U-shaped leg portions into an arc shape and to plastically process them into a tube shape by abutting the end portions of the leg portions, between the respective U-shaped and U-shaped leg portions. a metal core to be inserted, the metal core is, D Katachishinkin which together with the arc shape of the hollow inner surface of the hollow rack shaft are both formed, each with a flat portion for contacting the top of the rack tooth profile And a circular cored bar part for the cylindrical part of the hollow rack shaft, and is made up of at least two separate parts for extracting it after molding .
[0023]
[0024]
In the present invention, the leg is not bent only at the base by the above-described cored bar, and the whole is bent in an arc shape so as to follow the shape of the cored bar. There are no straight lines left on the legs.
[0025]
For this reason, the cylindrical portion of the end portion of the hollow rack and the semicircular portion of the rack portion can be plastically processed without distortion, and the distorted cross-sectional shape is made into a correct arc. Therefore, it is not necessary to make a large machining allowance in the subsequent grinding process, and the manufacturing cost can be reduced. Further, this does not cause a decrease in strength, and it is not necessary to increase the thickness of the original plate material, so that the weight reduction of the hollow rack shaft is not impaired.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
4, 5, and 6 show a method of forming a tube by bending a leg portion of a U-shaped portion and a U-shaped portion into an arc shape, which is adopted in the embodiment of the present invention. Shown along the course. In each figure, (a) is a front sectional view of a mold and a workpiece, and (b) and (c) in each figure are VII-VII section, VIII-VIII section, IX-IX section of each front section view, It is sectional drawing in a XX cross section, a XI-XI cross section, and a XII-XII cross section.
[0027]
2 and 3, the workpiece 3 is drawn with the legs facing downward. However, in FIGS. 4, 5 and 6, the workpiece 3 is drawn with the legs facing upward. This is the same as the description of the conventional example.
[0028]
As shown in FIG. 4, the workpiece 3 is a surface on which a rack tooth portion already formed in the second step is placed, and a rack sub-tooth mold 1 having a surface complementary to this tooth shape, On the both sides of the rack sub-tooth mold 1, the released legs 6 are placed on the arc-under mold 5 having a surface complementary to the arc of the U-shaped section formed in the first step. Can be placed on top.
[0029]
The upper mold 4 has an arcuate surface having a diameter substantially equal to the width of the leg portion 6 of the workpiece 3 on the lower side. The circular cored bar 2 a is a cored bar having a diameter equal to the semicircular part of the U-shaped part at both ends of the work 3. The D-shaped cored bar 2b includes an arc part having the same diameter as the circular cored bar 2a and a downward flat part.
[0030]
The flat portion is an inner surface of the rack tooth (work 3), and comes into contact with each of the top portions protruding upward in a wave shape in FIG. 4 and receives a force applied from above during bending of the leg portion 6 described later. One of the two circular cored bars 2a and the D-shaped cored bar 2b can be integrated, but since the cored bar is extracted from the rack shaft (workpiece 3) after the leg 6 is bent, all are integrated. I can't do it.
[0031]
In bending, the work 3 is placed on the rack sub-cavity mold 1 and the arc lower mold 5 with the released leg 6 facing upward, and the circular core is placed between the released leg 6 of the work 3. The metal mold 2a and the D-shaped metal core 2b are placed, and the upper mold 4 is set above the metal mold 2a (the state shown in FIG. 4).
[0032]
From this state, when the upper mold 4 starts to descend, the end of the leg 6 is guided by the arc surface of the upper mold 4, and the two legs 6 receive bending force toward the inside and undergo bending deformation. Begins. At this time, since the circular cored bar 2a and the D-shaped cored bar 2b are interposed, the bending force applied only to the base of the leg 6 at the beginning is changed to the leg 6a as the bending progresses. While the contact points to the arc surface of 2b move upward, a bending force is received at each contact point (state of FIG. 5).
[0033]
Immediately before the lowermost point of the lowering of the upper mold 4 (state shown in FIG. 6), contact is made in the vicinity of the uppermost part of the circular arc surface, so that even the end of the leg part 6 is subjected to bending. In this way, as shown in FIG. 6, the two leg end surfaces are bent along the arc surface of the core bar and in close contact with the arc surface of the upper mold 4 over the entire leg portion of the leg portion 6. Are faced to face each other.
[0034]
When the bending process is finished, the respective cored bars are pulled out from the work 3 in the left-right direction of FIG. 4A, for example. In order to make it possible to pull out the cored bar, either one of the D-shaped cored bar 2b and the circular cored bar 2a is combined (or assembled separately), or the center of the D-shaped cored bar 2b The D-shaped cored bar 2b and the left and right circular cored bars 2a can be assembled to form an integrated object (or created as an integrated object from the beginning).
[0035]
The work 3 that has been bent has an unavoidable springback (when the work 3 is removed from each mold, the work 3 tends to return to its original shape slightly, but the butt portion opens slightly). Since a slight gap is generated between the cored bar and the workpiece 3, each cored bar can be easily pulled out through the gap. Since the butt portion slightly opened by the spring back is easily closed by applying a light force, roundness can be ensured by welding the butt portion in this state (for example, laser welding).
[0036]
In this way, the leg portion 6 of the work 3 is provided with an arc shape that accurately follows the arc surface of each mold. As a result, the distorted sectional shape as in the prior art is improved and the roundness is improved. A rack shaft can be obtained.
[0037]
【The invention's effect】
As described above, the present invention can plastically process the cylindrical portion of the end portion of the hollow rack and the semicircular portion of the rack portion into a cross-sectional shape with high roundness without distorting the distorted cross-sectional shape. In order to obtain a correct arc, it is not necessary to increase the machining allowance in the subsequent grinding process, and the manufacturing cost can be reduced. In addition, there is an effect that the strength is not reduced and the original plate material does not need to be thickened, so that weight reduction is not impaired.
[Brief description of the drawings]
FIG. 1 is an external view showing a completed hollow rack shaft.
FIG. 2 shows a state of a work (half-processed plate material) 3 on which rack teeth are formed, (a) is a front cross-sectional view, and (b) is a U-shape on which rack teeth at the center are formed. It is sectional drawing which shows the cross section of a shaped part.
FIGS. 3A and 3B are views showing a state after the workpiece 3 is bent, that is, a state after the third step is completed, in which FIG. 3A is a front sectional view, and FIG. The cross section of the U-shaped part in which the tooth | gear is formed, (c) is sectional drawing which shows the cross section of the U-shaped part near the both ends.
4 and FIG. 6 together with FIG. 5 and FIG. 6 illustrate a method of forming a tube by bending a U-shaped portion and a leg portion of a U-shaped portion into an arc shape in the embodiment of the present invention. (A) is front sectional drawing of a metal mold | die and a workpiece | work, (b), (c) is sectional drawing in a VII-VII cross section and a VIII-VIII cross section.
5 and FIG. 6 together with FIG. 4 and FIG. 6 illustrate a method of forming a tube by bending a leg portion of a U-shaped portion and a U-shaped portion into an arc shape, which is adopted in the embodiment of the present invention. (A) is front sectional drawing of a metal mold | die and a workpiece | work, (b), (c) is sectional drawing in an IX-IX cross section and an XX cross section.
6 and FIG. 5 together with FIG. 4 and FIG. 5 illustrate a method of forming a tube by bending a leg portion of a U-shaped portion and a U-shaped portion into an arc shape, which is adopted in the embodiment of the present invention. (A) is front sectional drawing of a metal mold | die and a workpiece | work, (b), (c) is sectional drawing in a XI-XI cross section and a XII-XII cross section.
FIG. 7 and FIG. 9 show that the method of forming a tube by bending a leg portion of a U-shaped portion and a U-shaped portion into an arc shape, which is adopted in the prior art, in the course of processing. (A) is front sectional drawing of a metal mold | die and a workpiece | work, (b), (c) is sectional drawing in an II cross section and an II-II cross section.
8 and 9 together with FIGS. 7 and 9, the method of bending the U-shaped portion and the leg portion of the U-shaped portion into an arc shape to form a tube is used in the process. (A) is front sectional drawing of a metal mold | die and a workpiece | work, (b), (c) is sectional drawing in a III-III cross section and an IV-IV cross section.
9 and 8 together with FIGS. 7 and 8, the method of bending the U-shaped portion and the leg portion of the U-shaped portion into an arc shape to form a tube is used in the process. (A) is front sectional drawing of a metal mold | die and a workpiece | work, (b), (c) is sectional drawing in a VV cross section and a VI-VI cross section.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Rack sub-mold 2a Circular core 2b D-shaped core 3 Workpiece 4 Upper mold 5 Arc lower mold 6 Leg 7 Straight part

Claims (2)

An intermediate material for manufacturing a hollow rack shaft in which a rack tooth shape is formed in a portion having a U-shaped cross section in the central portion, and U-shaped cross section portions are formed on both sides thereof. When the U-shaped and U-shaped leg portions are bent into an arc shape and the end portions of the leg portions are butted and plastically processed into a tube shape, between the U-shaped and U-shaped leg portions, , which has an arc shape of a hollow inner surface of the hollow rack shaft that is both shaped, circular for each cylinder portion of the D-shaped core metal and the hollow rack shaft with a flat portion for contacting the top of the rack tooth profile A method for forming a hollow rack shaft, comprising: a cored bar portion, wherein a cored bar comprising at least two separate parts is inserted in order to extract the cored bar part after molding. An intermediate material for manufacturing a hollow rack shaft in which a rack tooth shape is formed in a portion having a U-shaped cross section in the central portion, and U-shaped cross section portions are formed on both sides thereof. In order to bend the U-shaped and U-shaped leg portions into an arc shape and to plastically process them into a tube shape by abutting the end portions of the leg portions, between the respective U-shaped and U-shaped leg portions. a metal core to be inserted, the metal core is, D Katachishinkin which together with the arc shape of the hollow inner surface of the hollow rack shaft are both formed, each with a flat portion for contacting the top of the rack tooth profile And forming a hollow rack shaft characterized in that it comprises at least two separate parts for extracting the metal core after the molding. For the core.

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