JP6299365B2 - Automotive wheel disc and method of manufacturing the same - Google Patents

Description

  The present invention relates to an automobile wheel disk formed by plastic working of a steel plate (hereinafter also referred to as “wheel disk”), and in particular, an automobile wheel disk formed by utilizing bulge processing, also referred to as hydroforming, and It relates to the manufacturing method.

  In general, an automobile wheel is composed of a cylindrical rim for mounting and holding a tire, and a disk-like disk that supports the rim and is attached to the hub of the automobile. Although these wheel rim and wheel disc can be molded integrally, they are often joined by welding separately molded ones.

  FIG. 1 is a cross-sectional view showing an example of an automobile wheel disk. As shown in the figure, the wheel disk 1 is formed by plastic working of a steel plate, and is concentrically in order from the disk center side, and includes a hub mounting part 2, an inner curved part 3, a hat part 4, an outer curved part 5 and a flange. Part 6. A hub hole 2 a is formed in the center of the hub attachment portion 2. The hub mounting portion 2 is formed with a flat nut seat 2b around the hub hole 2a. The nut seat 2b has a plurality of bolts at equal intervals on the same circumference centered on the hub hole 2a. A hole 2c is formed. The hat portion 4 protrudes from the outer periphery of the hub attachment portion 2 to the disk surface side through the inner curved portion 3. The flange portion 6 extends from the outer periphery of the hat portion 4 to the disc back surface side through the outer curved portion 5.

  In the wheel disc 1, the flange portion 6 is fitted inside the wheel rim and joined by welding or the like, whereby the wheel disc 1 and the wheel rim are integrated to form an automobile wheel. In the automobile wheel, the center boss of the automobile hub is inserted into the hub hole 2a of the hub attachment portion 2, and the bolt from the automobile hub is inserted into each bolt hole 2c of the hub attachment portion 2, and a nut is screwed into each bolt. And fastened to the automobile hub.

  While the automobile is running, a bending moment acts on the automobile wheel so as to bend the wheel disc 1 in the front and back direction. With respect to this bending moment, the rigidity of the wheel disk 1 is enhanced by the hat portion 4 to suppress deformation.

  Generally, a wheel disk is formed by pressing a steel plate as a raw material (for example, refer to Patent Documents 1 and 2). At this time, since the shape of the wheel disk is complicated, the molding by press working is performed in multiple stages, and it is necessary to use several types of dies that are different for each stage. For example, a flat steel plate is drawn and then drawn in the opposite direction to form a rough shape with a protruding hat, and then a pair of gold engraved wheel disk shapes. Pressing is performed according to the mold. In practice, the final product wheel disc is manufactured through post-processing such as trimming, bending, punching, coining, and the like.

JP-A 64-66032 JP 2000-225432 A

Eisaku Sakurada and two others, “Influence of surface friction on fatigue property”, CAMP-ISIJ, Vol.22, 2009, p.546

  As described above, the deformation of the wheel disk is suppressed by the hat portion while the automobile is running. For this reason, the wheel disk is subjected to repeated bending stress particularly on the hat portion, and is required to have excellent fatigue characteristics at the hat portion.

  By the way, the material of the wheel disc is mainly a hot-rolled steel sheet. A hot-rolled steel sheet has a rougher surface and larger surface irregularities than a cold-rolled steel sheet. When pressing such a hot-rolled steel sheet, both the front and back surfaces of the steel sheet are strongly pressed against each other and rubbed against the mold, so that the convex part of the surface irregularities is cut and smoothed. Thus, the concave portion becomes a sharp micropore. If there are micropores on the smooth surface, stress concentrates on the micropores when a load is applied, so that the press-formed product has a lower fatigue strength than the raw steel plate (hot-rolled steel plate) and deteriorates fatigue characteristics. This is described in Non-Patent Document 1.

  Then, when forming a hot-rolled steel sheet into a wheel disk by pressing, the front and back surfaces of the wheel disk including the hat part are smoothed by friction with the mold, and sharp holes are generated on the smooth surface. Therefore, improvement in fatigue characteristics at the hat portion cannot be expected.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an automotive wheel disk capable of improving fatigue characteristics at a hat portion and a method for manufacturing the same.

  The gist of the present invention resides in the following (I) automobile wheel disc and the following (II) and (III) automobile wheel disc production methods.

(I) It is a disk for an automobile wheel, which is formed by plastic processing of a steel plate and has a hub attachment part, an inner curved part, a hat part, an outer curved part and a flange part, concentrically in order from the disk center side,
It is the disk for motor vehicle wheels whose surface roughness of the back surface of the said hat part is 0.7 micrometer or more by arithmetic mean roughness Ra.

  The hub attachment portion of the wheel disk of (I) has a hub attachment outer peripheral portion that is bent adjacent to the inner curved portion and is connected to the inner curved portion. The surface roughness of the rear surface of the hub mounting outer peripheral portion is preferably 0.7 μm or more in terms of arithmetic average roughness Ra.

(II) A method for producing a disc for an automobile wheel having a hub mounting portion, an inner curved portion, a hat portion, an outer curved portion and a flange portion, concentrically in order from the disc center side,
Preparing two hot-rolled steel sheets as work materials, and forming a through hole in the edge of one of the steel sheets; and
Stacking the steel plates, welding process for welding the periphery of each other over the entire circumference,
And a bulge processing step of forming the disk by expanding the steel plate.

Here, the bulge processing step is
An inner molding die comprising a pair of engraved parts engraved with surface shapes of the hub mounting part, the inner curved part and the hat part, and arranged opposite to each other;
An outer molding die that has a pair of opposingly arranged adjacent to the outer periphery of the inner molding die, and has an engraving portion in which the outer curved portion and the surface shape of the flange portion are engraved,
A step of using a workpiece holding mold, which is composed of a pair arranged opposite to each other adjacent to the outer periphery of the outer forming mold, and which slidably holds the peripheral edge of the steel plate,
A first step of sandwiching a peripheral edge of the steel plate by the workpiece holding mold in a state where the inner molding die and the outer molding die are retracted from a predetermined position;
Subsequent to the first step, a second step of inflating the steel sheet by introducing a liquid between the steel sheets from the through hole of the steel sheet to give a liquid pressure,
Following this second step, a third step of advancing the outer molding die to a predetermined position;
Following this third step, a fourth step of advancing the inner mold to a predetermined position;
Subsequent to the fourth step, the fifth step includes increasing the hydraulic pressure and inflating the steel sheet until it extends along the engraving portion of the inner molding die and the engraving portion of the outer molding die. .

In the method of manufacturing a wheel disc of (II) above,
In the second step of the bulge processing step, the total extension in the radial cross section of the bulge portion of the steel plate is the hub mounting portion, the inner curved portion, the hat portion, the outer curved portion and the flange of the disk. It is preferable to swell the steel sheet so as to be 90 to 110% of the total extension in the radial section of the part.

(III) A method for manufacturing a disk for an automobile wheel having a hub attachment part, an inner curved part, a hat part, an outer curved part and a flange part, concentrically in order from the disk center side,
A preparation step of preparing one hot-rolled steel sheet as a workpiece;
A preliminary processing step of performing a drawing process for raising a region corresponding to the outer curved portion and the flange portion in the steel plate;
And a bulge processing step of forming the disk by expanding the steel plate.

Here, the preliminary processing step is
A first mold for holding a workpiece that non-slidably holds a region corresponding to the hub mounting portion, the inner curved portion, and the hat portion of the steel plate;
It consists of a pair arranged opposite to each other with an area corresponding to the outer curved portion and the flange portion in the steel plate from the outer periphery of the first mold for holding the work material, and can slide on the peripheral portion of the steel plate A second mold for holding the workpiece to be clamped;
A step of using an annular punch disposed in a region corresponding to the outer curved portion and the flange portion in the steel plate,
A first preliminary processing step of sandwiching the steel sheet by the first mold for holding the workpiece and the second mold for holding the workpiece;
Subsequent to the first preliminary processing step, a second preliminary processing step of pushing the punch into the steel plate and raising a region corresponding to the outer curved portion and the flange portion of the steel plate is included.

And the bulge processing step is
An inner molding die having an engraved portion in which surface shapes of the hub attaching portion, the inner curved portion and the hat portion are engraved;
An outer molding die that is arranged adjacent to the outer periphery of the inner molding die and has an engraving portion in which the outer curved portion and the surface shape of the flange portion are engraved;
A pressing die disposed adjacent to the outer periphery of the outer molding die, and a raised surface of the steel plate disposed opposite to the pressing die, the inner molding die and the outer molding die; Consists of a pedestal mold addressed to the opposite surface, and a process of using a workpiece holding mold that holds the peripheral edge of the steel plate in a non-slidable manner,
A first step of sandwiching a peripheral edge of the steel plate by the workpiece holding mold in a state where the inner molding die and the outer molding die are retracted from a predetermined position;
Subsequent to the first step, a second step of introducing a liquid between the steel plate and the pedestal mold to apply a hydraulic pressure and inflating the steel plate,
Following this second step, a third step of advancing the outer molding die to a predetermined position;
Following this third step, a fourth step of advancing the inner mold to a predetermined position;
Subsequent to the fourth step, the fifth step includes increasing the hydraulic pressure and inflating the steel sheet until it extends along the engraving portion of the inner molding die and the engraving portion of the outer molding die. .

In the method for producing a wheel disc of (III) above,
In the second preliminary processing step of the preliminary processing step, the total extension in the radial cross section of the hub mounting portion, the portion of the inner curved portion corresponding to the inner curved portion and the hat portion, and the raised portion in the steel plate, It is preferable that the steel plate is raised so as to be 90 to 110% of the total extension in the radial section of the hub mounting portion, the inner curved portion, the hat portion, the outer curved portion and the flange portion of the disk. .

In the wheel disk manufacturing method according to (II) and (III) above, when the hub attachment portion has a hub attachment outer peripheral portion that is bent adjacent to the inner curved portion and is connected to the inner curved portion,
The inner molding die includes a first inner molding die arranged on the center side, and a second inner molding die arranged adjacent to the outer periphery of the first inner molding die. ,
The outer side surface of the first inner molding die and the inner side surface of the second inner molding die are located at a portion corresponding to the hub mounting outer peripheral portion of the disc;
For the state in which the fourth step corresponds to the final shape of the disk of the first and second inner molding dies, the first inner molding dies are moved from the second inner molding dies. And a step of causing the second inner molding die to advance to a predetermined position in a state of protruding downward by a predetermined length,
It is preferable that the manufacturing method further includes, after the fifth step, a sixth step of retracting the first inner molding die by the predetermined length with respect to the second inner molding die. .

  In this case, it is preferable that the ratio of the plate thickness change amount before and after the bulge processing to the thickness of the steel plate at the hub mounting outer peripheral portion is 3.5% or more on average in the bulge processing step.

In the method for producing a wheel disk of (II) and (III) above,
It is preferable that the ratio of the plate thickness change amount before and after the bulge processing to the thickness of the steel plate in the hat portion is 3.5% or more on average by the bulge processing step.

  In the vehicle wheel disc of the present invention, the surface roughness of the back surface of the hat portion is maintained at the same level as the surface roughness of the material steel plate, and it is not smoothed and sharpened micropores are not generated. It is possible to improve fatigue characteristics at the part. Moreover, since the manufacturing method of the disk for motor vehicle wheels of this invention utilizes a bulge process, the wheel disk of this invention can be manufactured effectively.

It is sectional drawing which shows an example of the disk for motor vehicle wheels. It is sectional drawing which shows the outline of the process of a basic test. It is a photograph which shows the external appearance of each front and back of the molded article obtained by the basic test. It is the micro observation photograph which expanded a part of back of the molded article obtained by the basic test. It is a figure which shows an example of the cross-sectional profile of the back surface of a raw material steel plate, a press molded product, and a bulge molded product as a result of a basic test. It is the figure which put together the surface roughness of the back surface of a raw material steel plate, a press molded product, and a bulge molded product as a result of a basic test. It is sectional drawing which expands and shows the area | region of the hat part of the disk for motor vehicle wheels. It is sectional drawing which expands and shows the hub attachment part periphery of the disk for motor vehicle wheels. It is sectional drawing which shows typically the manufacturing process for demonstrating the manufacturing method of the disk for motor vehicle wheels which is 1st Embodiment of this invention. It is sectional drawing which shows typically the manufacturing process for demonstrating the manufacturing method of the disk for motor vehicle wheels which is 2nd Embodiment of this invention. It is sectional drawing which shows typically the manufacturing process for demonstrating the manufacturing method of the disk for motor vehicle wheels which is 3rd Embodiment of this invention. It is a figure which shows distribution of the plate | board thickness change rate in a wheel disc as a test result of the Example in 1st Embodiment. It is a figure which shows distribution of the plate | board thickness change rate in a wheel disc as a test result of the Example in 3rd Embodiment.

  As mentioned above, conventional wheel discs are made from hot-rolled steel sheets and are formed by pressing the hot-rolled steel sheets, so the front and back surfaces, including the hat, are smoothed during the pressing process. In addition, sharp micropores are generated on the smooth surface. That is, the surface roughness of the conventional wheel disc is remarkably small on both the front and back surfaces as compared with the raw steel plate (hot rolled steel plate) before forming. Such smoothing correlates with deterioration of fatigue characteristics at the hat portion.

  Therefore, the present inventors focused on this point, and thought that if the surface roughness of the material steel plate can be maintained as much as possible at the hat portion of the formed wheel disc, the fatigue characteristics can be improved. . Based on this idea, as a result of intensive studies on a plastic working method for forming a raw steel plate into a wheel disk, the following findings (1) and (2) were obtained.

  (1) When bulging is applied as a plastic working method to bulge a hot-rolled steel sheet, the steel sheet is given a hydraulic pressure from one of the front and back surfaces, for example, the back surface, and thereby swells. Then, the steel plate is pressed against the other surface of the front and back surfaces, for example, a mold engraving portion arranged to face the surface, and is formed into the shape of the engraving portion. In this case, in the steel plate, one surface to which hydraulic pressure is applied is neither pressed against the mold nor rubbed with the mold, so that the surface roughness of the material steel plate is maintained without being smoothed and sharpened. No micropores are generated.

  In order to verify this, as shown below, a basic test was conducted to investigate the surface properties of the molded product by pressing and by bulging.

  FIG. 2 is a cross-sectional view schematically showing the basic test process. FIG. 3 is a photograph showing the appearance of the front and back surfaces of the molded product obtained in the basic test, and FIG. 4 is a micro-observation photograph in which a part of the back surface of the molded product is enlarged. In any of FIGS. 2 to 4, (a) shows a case by press working, and (b) shows a case by bulge processing.

  In the press working, a 440 MPa class general-purpose hot-rolled steel plate (SPH440) with a thickness of 2.3 mm and a 150 mm-square size is used as the raw material, and in the bulge processing, a hot-rolled steel plate of 250 mm square size with the same thickness and steel type is adopted. did. And as shown in FIG. 2, the overhang | projection part with a substantially hemispherical shape and 25 mm in height was shape | molded in the steel plate 7 of the raw material. That is, in the case of press working, as shown in FIG. 2A, an upper die 51 having a hole 51a having a diameter of 100 mm formed in the center and a punch 53 having a tip radius of curvature of 50 mm accommodated in the center. The peripheral edge of the material steel plate 7 was firmly held by the mold 52 so as not to slide, and in this state, the punch 53 was pushed up against the back surface of the material steel plate 7 and pushed up. In the case of bulge processing, as shown in FIG. 2B, an upper die 41 having a hole 41a having a diameter of 100 mm at the center and a lower die 42 having a recess 42a filled with a liquid at the center are formed. In this state, the peripheral edge portion of the material steel plate 7 is firmly held in a non-slidable manner, and the liquid 43 is introduced into the recess 42a of the lower mold 42 to apply hydraulic pressure to the material steel plate 7 from the back surface. Inflated.

  As shown in FIG. 3 (a), the molded product obtained by press working is dotted with white regions on the same circumference of about 20 mm from the top of the overhang, particularly on the back surface where the punch contacts. I can see that This white area indicates that the convex portion of the surface layer is scraped and flattened by rubbing with the mold (punch). A white region is widely recognized in the micro observation photograph of FIG. 4A in which the white region is enlarged. For this reason, according to press work, it can confirm that planarization has arisen in the steel plate surface layer which contacts a metallic mold.

  On the other hand, as shown in FIG. 3B and FIG. 4B, in the molded product obtained by bulging, there is no specific white area on the back surface to which the hydraulic pressure is applied. For this reason, according to the bulge processing, it can be confirmed that flattening does not occur in the steel sheet surface layer to which the hydraulic pressure is applied.

  Prior to the basic test, the cross-sectional profile of the material steel plate was measured with a contact-type surface roughness meter. Then, for the press-formed product obtained by pressing the steel plate and the bulge-formed product obtained by bulging, each back surface (in the case of a press-formed product, the surface in contact with the punch, the bulge-formed product In this case, the cross-sectional profile of the surface to which the hydraulic pressure was applied was measured with a contact-type surface roughness meter. Furthermore, arithmetic mean roughness Ra was calculated | required from each measurement result as surface roughness of each of a raw steel plate, a press-formed product, and a bulge-formed product according to JIS B0601.

  FIG. 5 is a diagram showing an example of a cross-sectional profile of the back surface of a raw steel plate, a press-formed product, and a bulge-formed product as a result of the basic test. FIG. 5 (a) shows the case of the raw steel plate, and FIG. In the case of a press-molded product, FIG. 7C shows the case of a bulge molded product. FIG. 6 is a table summarizing the surface roughness of the back surface of the material steel plate, press-formed product, and bulge-formed product. Note that the surface roughness Ra shown in FIG. 6 is obtained by measuring the profile of each target material at a total of 8 locations of 4 locations in the circumferential direction and 4 locations in the radial direction at a position of about 20 mm from the top of the overhang portion. It is the average value of the surface roughness Ra obtained from

  As shown in FIGS. 5A and 5B, in the case of a press-formed product, it can be seen that the convex portions of the surface unevenness are cut and smoothed as compared with the raw steel plate. On the other hand, as shown in FIGS. 5 (a) and 5 (c), in the case of a bulge molded product, it can be seen that the unevenness of the surface layer is equivalent to that of the material steel plate and hardly changes.

  Further, as shown in FIG. 6, the surface roughness Ra is about 0.9 μm in the case of a raw steel plate. However, in the case of a press-formed product, it is about 0.5 μm, which is significantly smaller than the raw steel plate, and is far below 0.7 μm. The surface roughness Ra of the bulge molded product is about 0.8 μm, which is slightly smaller than that of the raw steel plate, and exceeds 0.7 μm.

  From these test results, if bulging is used to form a wheel disk from a hot-rolled steel sheet, the back surface of the front and back surfaces of the hat part is not smoothed and the surface roughness of the material steel sheet is maintained. And since the surface roughness is ensured by arithmetic mean roughness Ra to 0.7 micrometer or more, the improvement of the fatigue characteristic in a hat part can be anticipated.

  As will be described later, in the hub mounting portion, a portion that is bent adjacent to the inner curved portion and is connected to the inner curved portion (hub mounting outer peripheral portion) is also required to have excellent fatigue characteristics like the hat portion. If bulging is used to form a wheel disc from a hot-rolled steel sheet, the back surface of the outer periphery of the hub mounting will not be smoothed, and the surface roughness of the material steel sheet will be maintained. Since the thickness Ra is ensured to be 0.7 μm or more, an improvement in fatigue characteristics at the outer periphery of the hub can be expected.

  (2) When bulging is used to form a wheel disc, the material steel plate swells by applying hydraulic pressure, and there is an advantage that distortion is uniform because it is deformed biaxially without generating frictional force. However, when forming a wheel disc by inflating the material steel plate at a time according to the normal bulge processing technique, excessive liquid is used to form a detailed shape having a small corner R such as a hub attachment part or a hat part. It is necessary to apply pressure. In addition, the plate thickness of the details is excessively reduced, and there is a possibility that the fatigue characteristics particularly in the hat portion may be adversely affected.

  The inconvenience in such bulge processing is that a mold having an engraved part in which the surface shape of a wheel disk is engraved is used as an inner mold for forming the shape of the hub mounting part, the inner curved part and the hat part. The problem is solved by dividing the outer bending mold and the outer molding mold for shaping the shapes of the outer curved section and the flange section, and individually controlling the operations of the inner molding mold and the outer molding mold. It is possible.

  Specifically, first, a hydraulic pressure is applied to the material steel plate in a state where both the inner forming die and the outer forming die are retracted from predetermined positions, and the steel plate is expanded to some extent. Thereafter, the outer molding die is advanced to a predetermined position, then the inner molding die is advanced to a predetermined position, and the outer molding die and the inner molding die are pressed in this order against the bulging portion of the steel plate. Thereby, the bulge part of a steel plate becomes the shape which the area | region corresponding to a hat part bent and protruded, and the shape in general along the shape of a wheel disc is modeled as a whole. And the hydraulic pressure given to a steel plate is raised, and a steel plate is expanded until it follows the engraving part of the inner side shaping | molding die and an outer side shaping | molding die. In this way, a hat portion having a small corner R can be formed without applying an excessive hydraulic pressure, and the thickness of the hat portion is not excessively reduced.

  The present invention has been completed based on the above findings. Below, the preferable aspect is demonstrated about the wheel disc of this invention, and its manufacturing method.

1. Wheel Disc As in the case of the wheel disc 1 shown in FIG. 1, the wheel disc of the present invention is concentrically in order from the disc center side, and includes a hub attachment portion 2, an inner curved portion 3, a hat portion 4, an outer curved portion 5, and It has a flange portion 6. In particular, the wheel disk 1 of the present invention is formed by using a hot-rolled steel sheet as a raw material and plastically processing the hot-rolled steel sheet, and the surface roughness of the back surface of the hat portion 4 is 0 in terms of arithmetic average roughness Ra. .7 μm or more. That is, the back surface of the hat portion 4 is maintained at the same surface roughness as the surface roughness of the material steel plate (hot rolled steel plate) and is not smoothed. For this reason, the wheel disc 1 of the present invention can improve the fatigue characteristics at the hat portion 4.

  When the surface roughness Ra of the back surface of the hat portion 4 is less than 0.7 μm, it can be said that the back surface of the hat portion 4 is smoothed and sharp holes are present on the smooth surface, so that improvement in fatigue characteristics cannot be expected. . For this reason, the surface roughness Ra of the back surface of the hat portion 4 is set to 0.7 μm or more as described above. More preferably, it is 0.8 μm or more. In addition, since the surface roughness Ra of the hot-rolled steel sheet applied to the raw steel sheet is at most about 3.0 μm, the upper limit of the surface roughness Ra on the back surface of the hat portion 4 is practically 3.0 μm. It is as follows.

  Here, an example of a specific range of the hat portion 4 will be described with reference to FIG. 7A below.

FIG. 7A is a cross-sectional view showing an enlarged region of a hat portion of a vehicle wheel disk. As shown in the figure, in the radial cross section of the wheel disc, the hat portion 4 is a region protruding to the disc surface side. Specifically, with the nut seat 2b of the hub mounting portion 2 as a reference, a portion that protrudes most to the surface side in a direction perpendicular to the nut seat 2b is defined as a hat top portion 4a. When the hat top 4a curvatures nut seat 2b in a direction parallel at the corner R portion of the range of 6mm around the is R _ave, nuts seat 2b in a direction parallel to the center of the hat top portion 4a of the 2R _ave The range region can be defined as the hat portion 4.

The reason for defining the area of the hat portion 4 in this way is that fatigue cracks are likely to occur in this area. That is, the fatigue crack of the hat portion 4 is generated when a bending is applied such that the curvature of the hat portion 4 increases or decreases. This has a close relationship with the curvature radius in the vicinity of the hat top portion 4a. This is because fatigue cracks are likely to occur in a region in the range of 2 _{Rave about} the hat top 4a.

  FIG. 7B is an enlarged cross-sectional view showing the periphery of the hub attachment portion 2 of FIG. The hub attachment portion 2 includes a flat portion 2d. The nut seat 2b is connected to the flat portion 2d via the inclined portion 2e and protrudes from the flat portion 2d to the disk surface side. The nut seat 2 b and the inclined portion 2 e have a generally truncated cone shape, and a plurality of nut seats 2 b and the inclined portion 2 e are formed around the central axis of the wheel disk 1. In the cross section of FIG. 7B, the flat portion 2d exists on the hub hole 2a side and the inner curved portion 3 side with respect to the nut seat 2b, but the nut seat 2b and the inclined portion 2e are not formed. In the cross section, it exists in a continuous region. The hub hole 2a is formed in the hub mounting portion 2 at a portion protruding from the flat portion 2d to the disk surface side.

  In the flat portion 2d, the inclined portion 2e, the nut seat 2b, and the inner curved portion 3, a corner R portion (a rounded bent portion) is formed in an adjacent portion. Among these, the hub mounting outer peripheral portion 2h, which is a corner R portion adjacent to the inner bending portion 3 between the flat portion 2d and the inner bending portion 3, that is, in the hub mounting portion 2, is the same as the hat portion 4. In addition, a large bending stress acts repeatedly, and fatigue cracks are likely to occur. This is because, in the wheel disk 1, the portion closer to the center than the hub mounting outer peripheral portion 2h is fixed in close contact with the axle and hardly deforms, whereas the hub mounting outer peripheral portion 2h and farther from the center than that. This is because the portion is not fixed to other members and is easily deformed. Since the hub mounting outer peripheral portion 2h is adjacent to a portion fixed to another member, a large bending stress can be generated.

  The range of the hub mounting outer periphery is from the first inflection point to the second inflection point when the cross-sectional profile is measured from the flat portion 2d adjacent to the hub mounting outer periphery 2h toward the inner curved portion 3. Can be defined as the area between. The surface roughness of the back surface of the hub mounting outer peripheral portion 2h is 0.7 μm or more in terms of arithmetic average roughness Ra. In other words, the surface roughness of the rear surface of the hub mounting outer peripheral portion 2h is maintained at the same level as the surface roughness of the material steel plate (hot rolled steel plate) and is not smoothed. For this reason, this wheel disk 1 can improve fatigue characteristics even at the hub mounting outer peripheral portion 2h.

  The wheel disk 1 of the present invention can be formed by, for example, a plastic working method utilizing bulge processing as shown below.

2. Wheel Disk Manufacturing Method <First Embodiment>
FIG. 8 is a cross-sectional view schematically showing a manufacturing process for explaining the method for manufacturing the vehicle wheel disk according to the first embodiment of the present invention. As shown in FIG. 8A, the manufacturing method according to the first embodiment includes a preparation step of preparing two hot-rolled steel plates 7 as workpieces (materials) and welding for joining both steel plates 7 together by welding. Process. Further, as shown in FIGS. 8B to 8F, a bulging process is included in which both the steel plates 7 are simultaneously expanded to form each of them into the wheel disk 1.

  In the preparation step, as shown in FIG. 8A, two hot-rolled steel plates 7 are prepared, and through holes 7 b are formed in the edge portion 7 a of one of the steel plates 7. The through hole 7b serves as a liquid inlet for applying a hydraulic pressure to the steel plates 7 in the bulge processing step. The steel plate 7 may be rectangular or circular. Furthermore, in a welding process, as shown to Fig.8 (a), both the steel plates 7 are piled up and a mutual peripheral edge is weld-joined over a perimeter. The weld 8 plays a role of preventing liquid leakage when a hydraulic pressure is applied to both steel plates 7 in the bulge processing step.

  Next, in the bulge processing step, as shown in FIGS. 8B to 8F, an inner molding die 11, an outer molding die 12, and a workpiece holding die 13 are configured. Use split mold. The inner molding die 11 according to the first embodiment is composed of a pair which are arranged to face each other vertically. The inner molding die 11 has an engraving portion 11a in which the surface shapes of the hub attachment portion 2, the inner curved portion 3 and the hat portion 4 of the wheel disk 1 are engraved.

  The outer molding die 12 is composed of a pair adjacent to the outer periphery of the inner molding die 11 and arranged vertically opposite each other. The outer molding die 12 has an engraving portion 12a in which the outer curved portion 5 of the wheel disk 1 and the surface shape of the flange portion 6 are engraved.

  The workpiece holding mold 13 is composed of a pair adjacent to the outer periphery of the outer molding mold 12 and arranged to face each other vertically. The workpiece holding mold 13 plays a role of slidably holding the peripheral edge portion 7a of the steel plate 7.

  The bulging process using these split molds goes through the following first to fifth steps in order. First, in the first step, as shown in FIG. 8B, both the inner molding die 11 and the outer molding die 12 are retracted from predetermined positions, and in this state, the workpiece is held. The peripheral edge 7a of the steel plate 7 is held by the mold 13 for use. As a result, a greatly expanded space is formed between the inner molding die 11 and the outer molding die 12 and the steel plate 7. The peripheral edge portion 7 a of the steel plate 7 is sandwiched by a workpiece holding mold 13 with a relatively loose pressure, and is allowed to slide with respect to the workpiece holding mold 13.

  Then, in a 2nd process, as shown in FIG.8 (c), the liquid 14 is introduce | transduced between the steel plates 7, and a hydraulic pressure is provided. The introduction of the liquid 14 is performed from the liquid supply path 15 provided in the workpiece holding mold 13 through the through hole 7 b of the steel plate 7. Thereby, the steel plate 7 swells to some extent in the wide space between the inner molding die 11 and the outer molding die 12 in the retracted state. At this time, the peripheral edge portion 7a of the steel plate 7 is sandwiched by the workpiece holding mold 13 and a part thereof is drawn into the space between the retracted outer molding mold 12. For this reason, a reduction in the plate thickness is suppressed at the swollen portion of the steel plate 7.

  8 (c) to 8 (f), the steel plate 7 that is paired up and down, the inner forming die 11, the outer forming die 12, and the workpiece holding die 13 are arranged on the lower side. Illustration of the arrangement is omitted. This is because their behavior is subject to top and bottom.

  Subsequently, in the third step, as shown in FIG. 8D, only the outer molding die 12 is advanced to a predetermined position. As a result, the engraving portion 12a of the outer forming die 12 is pressed against the outer portion of the bulging portion of the steel plate 7, and a shape generally conforming to the shapes of the outer curved portion 5 and the flange portion 6 is formed. At the same time, the outer curved portion 5 side of the region corresponding to the hat portion 4 is steeply raised. At that time, the hydraulic pressure by the liquid 14 is continuously applied to the back surface of the bulging portion of the steel plate 7.

  Then, in a 4th process, as shown in FIG.8 (e), the inner side metal mold | die 11 is advanced to a predetermined position. As a result, the engraving portion 11a of the inner molding die 11 is pressed against the remaining inner portion of the bulging portion of the steel plate 7, and generally follows the shapes of the hub mounting portion 2, the inner curved portion 3, and the hat portion 4. The shape is shaped. At the same time, the region corresponding to the hat portion 4 is bent and protrudes. At that time, the hydraulic pressure by the liquid 14 is continuously applied to the back surface of the bulging portion of the steel plate 7.

  Subsequently, in the fifth step, as shown in FIG. 8F, the liquid 14 is further introduced to increase the hydraulic pressure. Thereby, the swelling part of the steel plate 7 swells along the engraving part 11 a of the inner molding die 11 and the engraving part 12 a of the outer molding die 12. This completes the bulging process.

  In this way, the wheel disk 1 shown in FIG. 8 (g) can be formed. Then, the final product wheel disk 1 is manufactured through post-processes such as trimming, bending, punching and coining.

  According to the manufacturing method of the first embodiment, in the bulge processing step, the operation of the inner molding die and the outer molding die is individually controlled as described above, so that excessive hydraulic pressure is not applied. Also, the hat portion can be formed. In addition, since only the hydraulic pressure is applied to the back surface of the hat portion during molding, the surface roughness of the raw steel plate is maintained without being smoothed, and sharpened micropores are not generated. Furthermore, since the hat portion is formed by once expanding the steel plate while suppressing the decrease in the plate thickness in the bulging process and bending the expanded portion, the plate thickness of the hat portion does not excessively decrease.

  Moreover, according to the manufacturing method of 1st Embodiment, the number of metal mold | dies can be reduced compared with the case by the conventional press work.

  In addition to these, the manufacturing method according to the first embodiment also has an advantage that two wheel disks can be formed simultaneously.

  By the way, in the case of the manufacturing method of the first embodiment, in the second step of the bulging process, the total extension in the radial section of the bulge portion of the steel plate (hereinafter referred to as “total extension of the bulge portion of the steel plate”) is a wheel disk. The steel plate should be 90% to 110% of the total extension in the radial section of the hub mounting part, inner curved part, hat part, outer curved part and flange part (hereinafter referred to as "total extension of the wheel disc"). It is preferable to inflate. The reason is as follows.

  If the total length of the bulge portion of the steel plate is too short, the gap between the bulge portion of the steel plate and the inner and outer molds in the third and fourth steps following the second step of the bulge processing step. Becomes wider. For this reason, in the subsequent fifth step, the plate thickness decreases as the steel plate expands, and as a result, the plate thickness of the hat portion may excessively decrease. On the other hand, if the total extension of the bulge portion of the steel plate is too long, the bulge portion of the steel plate becomes excessive in the third to fifth steps following the second step of the bulge processing step, which may cause quality defects such as fogging. . Therefore, the total extension of the steel plate bulge portion is preferably in the range of 90 to 110% of the total extension of the wheel disk.

Here, when the plate thickness of the material steel plate is t ₀ and the plate thickness of the formed wheel disc is t ₁ , the plate thickness before and after the bulge processing with respect to the plate thickness of the material steel plate expressed by the following equation (1) Consider the change rate ratio (hereinafter referred to as “plate thickness change rate”) T (%).
T = (t ₁ −t ₀ ) / t ₀ × 100 (1)

  When the plate thickness change rate T is + (plus), it means that the plate thickness has increased with respect to the material steel plate, and conversely, when-(minus), the plate thickness has decreased with respect to the material steel plate. Means that When the thickness of the hat portion increases relative to the thickness of the material steel plate, the fatigue characteristics at the hat portion are further improved. For this reason, it is preferable that the average thickness change rate T in a hat part is 3.5% or more. As a result, the maximum principal stress generated in the hat portion is reduced and the occurrence of fatigue cracks can be suppressed.

  In order to secure an average thickness change rate T in the hat portion of 3.5% or more, the total length of the bulge portion of the steel plate may be set to 100% or more of the total length of the wheel disk.

Second Embodiment
FIG. 9 is a cross-sectional view schematically showing a manufacturing process for explaining a method for manufacturing a vehicle wheel disk according to the second embodiment of the present invention. As shown in FIG. 9A, the manufacturing method of the second embodiment includes a preparation step of preparing one hot-rolled steel sheet 7 as a workpiece (raw material), and FIGS. 9B and 9C. As shown in FIG. 4, a preliminary processing step of drawing the steel plate 7 is included. Further, as shown in FIGS. 9D to 9H, a bulge processing step is included in which the pre-processed steel plate 7 is expanded and formed into the wheel disk 1.

  In the preparation step, as shown in FIG. 9A, one simple hot-rolled steel sheet 7 is prepared.

  Next, in the preliminary processing step, as shown in FIGS. 9B and 9C, a first workpiece holding mold 21, a workpiece holding second mold 22, and an annular punch 23 are used. And are used. The first workpiece-holding mold 21 is composed of a pair that are vertically opposed to each other. The first workpiece holding die 21 plays a role of slidably holding regions corresponding to the hub mounting portion, the inner curved portion, and the hat portion of the steel plate 7.

  The second workpiece holding mold 22 is made up of a pair of upper and lower opposingly spaced apart areas corresponding to the outer curved portion and the flange portion of the steel plate 7 from the outer periphery of the first workpiece holding mold 21. Become. The 2nd metal mold | die 22 for to-be-processed material bears the role which clamps the peripheral part 7a of the steel plate 7 so that sliding is possible.

  The punch 23 is concentrically between the region corresponding to the outer curved portion and the flange portion of the steel plate 7, that is, between the lower workpiece holding first mold 21 and the workpiece holding second mold 22. Be placed.

  The preliminary processing step using these molds goes through a first preliminary processing step and a second preliminary processing step described below in order. First, in the first preliminary processing step, as shown in FIG. 9B, the steel plate 7 is sandwiched between the first workpiece holding mold 21 and the second workpiece holding mold 22. At this time, the inner region of the steel plate 7 is sandwiched with a strong pressure by the first mold 21 for holding the workpiece, and the sliding with respect to the first mold 21 for holding the workpiece is prevented. Yes. On the other hand, the peripheral edge portion 7a of the steel plate 7 is sandwiched between the second mold 22 for holding the workpiece, and is allowed to slide with respect to the second mold 22 for holding the workpiece. ing.

  Subsequently, in the second preliminary processing step, as shown in FIG. 9C, the punch 23 is pushed up. As a result, the punch 23 is pushed into the steel plate 7, and the steel plate 7 is raised in areas corresponding to the outer curved portion and the flange portion. At this time, the peripheral edge portion 7a of the steel plate 7 is sandwiched by the second workpiece holding mold 22 while a part thereof is a workpiece holding first mold 21 and a workpiece holding second mold. 22 is drawn into the space between. For this reason, a reduction in the plate thickness is suppressed at the raised portion of the steel plate 7.

  Next, in the bulge processing step, as shown in FIGS. 9D to 9H, an inner molding die 11, an outer molding die 12, and a workpiece holding die 13 are configured. Use split mold. The inner molding die 11 of the second embodiment is disposed only upward. The inner molding die 11 has an engraving portion 11a in which the surface shapes of the hub attachment portion 2, the inner curved portion 3 and the hat portion 4 of the wheel disk 1 are engraved.

  The outer molding die 12 is disposed adjacent to the outer periphery of the inner molding die 11. The outer molding die 12 has an engraving portion 12a in which the outer curved portion 5 of the wheel disk 1 and the surface shape of the flange portion 6 are engraved.

  The workpiece holding mold 13 includes a pressing mold 16 and a base mold 17. The holding die 16 is disposed adjacent to the outer periphery of the outer molding die 12. The pedestal die 17 is disposed below the pressing die 16, the inner molding die 11 and the outer molding die 12, and is opposite to the raised surface (front surface) of the steel plate 7 after the preliminary processing ( It is addressed to the back side. The workpiece holding die 13 of the second embodiment plays a role of sandwiching the peripheral edge portion 7a of the steel plate 7 so as not to slide.

  The bulging process using these split molds is performed through the first to fifth steps, which are substantially the same as those in the first embodiment. Hereinafter, the description overlapping with the first embodiment will be omitted as appropriate.

  First, in the first step, as shown in FIG. 9 (d), the inner molding die 11 and the outer molding die 12 are both retracted from predetermined positions, and in this state, the workpiece is held. The peripheral edge portion 7a of the steel plate 7 after the preliminary processing is held by the metal mold 13. At this time, the peripheral edge portion 7 a of the steel plate 7 is prevented from sliding with respect to the workpiece holding mold 13. This sliding prevention can be performed by providing an annular protrusion and a groove (so-called lock beads) that fit into each other in the holding die 16 and the base die 17 constituting the workpiece holding mold 13. Further, the clamping pressure by the workpiece holding mold 13 may be increased.

  Then, in a 2nd process, as shown in FIG.9 (e), the liquid 14 is introduce | transduced between the steel plate 7 and the base mold | type 17, and a hydraulic pressure is provided. The introduction of the liquid 14 is performed through the liquid supply path 15 provided in the base mold 17. Thereby, the pre-processed steel plate 7 swells to some extent in a wide space between the retracted inner molding die 11 and the outer molding die 12. At this time, rather than the raised portion, the recessed region inside the steel plate 7 swells mainly, and the thickness of the swelled portion hardly decreases.

  Subsequently, as in the first embodiment described above, in the third step, as shown in FIG. 9 (f), only the outer mold 12 is advanced to a predetermined position, and subsequently, the fourth step. 9 (g), the inner molding die 11 is advanced to a predetermined position. Thereby, the bulging part of the steel plate 7 has a shape in which a region corresponding to the hat portion 4 is bent and protrudes, and the shape generally conforming to the shape of the wheel disk 1 is formed as a whole.

  Subsequently, in the fifth step, as shown in FIG. 9H, the liquid 14 is further introduced to increase the hydraulic pressure. Thereby, the bulging part (including the raised part) of the steel plate 7 swells along the engraving part 11 a of the inner molding die 11 and the engraving part 12 a of the outer molding die 12. Thus, the bulging process is completed, and the wheel disk 1 shown in FIG. 9 (i) can be formed. Then, the final product wheel disk 1 is manufactured through post-processes such as trimming, bending, punching and coining.

  Also by the manufacturing method of the second embodiment, the same effects as those of the first embodiment described above can be obtained. However, in the manufacturing method of the second embodiment, the back surface of the steel plate and the punch are rubbed in the preliminary processing step, but the rubbed region is limited to the region corresponding to the outer curved portion and the flange portion of the wheel disk, so the hat portion It does not affect the surface properties of the back side of the film.

  In addition, in the first embodiment, two wheel disks can be formed at the same time, but the manufacturing method of the second embodiment is advantageous in that a complicated welding process as in the first embodiment is not required. is there.

  Further, in the case of the manufacturing method of the second embodiment, for the same reason as in the first embodiment, in the second preliminary processing step, the portion of the region corresponding to the hub mounting portion, the inner curved portion and the hat portion in the steel plate, In addition, the total extension in the radial section of the raised portion (hereinafter referred to as “total extension including the steel plate raised portion”), that is, the “total extension of the steel plate bulge portion” in the first embodiment is the total extension of the wheel disk. It is preferable that the steel plate is raised so that it becomes 90 to 110% of the total. In order to secure the average thickness change rate T in the hat portion to 3.5% or more, the total extension including the steel plate raised portion may be set to 100% or more of the total extension of the wheel disk.

<Third Embodiment>
FIG. 10: is sectional drawing which shows typically the manufacturing process for demonstrating the manufacturing method of the disk for motor vehicle wheels which is 3rd Embodiment of this invention. The third embodiment is a modification of the second embodiment shown in FIG. 9. In FIG. 10, parts corresponding to the components shown in FIG. 9 are given the same reference numerals as those in FIG. Omitted. As in the second embodiment, the manufacturing method of the third embodiment includes a preparation step (see FIG. 9A) for preparing one hot-rolled steel plate 7 as a workpiece (raw material), and the steel plate 7. And a preliminary processing step (see FIGS. 9B and 9C) for drawing, and further includes a bulge processing step that is partially different from the second embodiment.

  In the bulge processing step, as shown in FIG. 10, as the inner molding die, the first inner molding die 11A disposed on the center side and the outer periphery of the first inner molding die 11A are disposed adjacent to each other. A split mold comprising a second inner mold 11B, an outer mold 12 and a workpiece holding mold 13 is used.

  11A of 1st inner side shaping | molding molds have 11 Aa of engraving parts by which the surface shape of most hub attachment parts 2 of the wheel disc 1 was carved. The second inner molding die 11B has an engraving portion 11Ba in which the surface shapes of the inner curved portion 3 and the hat portion 4 are engraved. The outer side surface of the first inner molding die 11A and the inner side surface of the second inner molding die 11B are located at portions corresponding to the hub mounting outer peripheral portion 2h of the wheel disc 1.

  First, the first to third steps are performed in the same manner as in the second embodiment. That is, the peripheral edge of the steel plate 7 is sandwiched between the pedestal mold 17 and the workpiece holding mold 13, and the first and second inner molding dies 11A and 11B and the outer molding mold 12 are A state in which the steel sheet 7 is retracted from the predetermined position (see FIG. 10A) is introduced, the liquid 14 is introduced between the steel plate 7 and the pedestal mold 17, and a hydraulic pressure is applied to the steel plate 7 to expand the steel plate 7 (FIG. 10). (See (b)). Then, the outer molding die 12 is advanced to a predetermined position, and a part of the bulging portion of the steel plate 7 is shaped along the engraving portion 12a of the outer molding die 12 (see FIG. 10C).

  Next, in the fourth step, as shown in FIG. 10 (d), the first inner molding die is in a state corresponding to the final shape of the disk of the first and second inner molding dies 11A and 11B. Maintaining the state where the mold 11A protrudes downward from the second inner molding die 11B by a predetermined length D, the second inner molding die 11B is advanced to a predetermined position (FIG. 10 (e)). reference)

  Accordingly, the engraving portion 11Aa of the first inner molding die 11A or the second inner side of the bulging portion of the steel plate 7 other than the portion where the engraving portion 12a of the outer molding die 12 is pressed. The engraving portion 11Ba of the molding die 11B is pressed, and a shape substantially conforming to the shapes of the hub mounting portion 2, the inner curved portion 3, and the hat portion 4 is formed. At the same time, the region corresponding to the hat portion 4 is bent and protrudes. At that time, the hydraulic pressure by the liquid 14 is continuously applied to the back surface of the bulging portion of the steel plate 7.

  Subsequently, in the fifth step, as shown in FIG. 10F, the liquid 14 is further introduced to increase the hydraulic pressure. Thereby, the bulging part of the steel plate 7 extends along the engraving portion 11Aa of the first inner molding die 11A, the engraving portion 11Ba of the second inner molding die 11B, and the engraving portion 12a of the outer molding die 12. Swell. In the portion where the first inner molding die 11A and the second inner molding die 11B are adjacent to each other, the first inner molding die 11A protrudes downward in the above-described manner, whereby the inclination of the steel plate 7 is inclined. It is larger (see FIG. 10 (g)).

  Further, in the third embodiment, the first inner molding die 11A is retracted by a predetermined length D with respect to the second inner molding die 11B while the hydraulic pressure is applied to the steel plate 7. As a result, the first inner molding die 11A and the second inner molding die 11B are in a state corresponding to the final shape of the disk.

  The portion of the steel plate 7 in contact with the first inner molding die 11A retreats together with the first inner molding die 11A (in FIG. 10 (h), the steel plate 7 before retraction is indicated by a broken line, and the steel plate 7 after retraction. Is indicated by a solid line). At this time, in the vicinity of the portion where the first inner molding die 11A and the second inner molding die 11B are adjacent to each other, the length of the steel plate 7 along the surface is shortened, and as a result, the portion is increased in thickness. (In FIG. 10 (h), the portion to be thickened is indicated by the symbol “T”). In order to perform such processing, the plate thickness of the steel plate 7 is preferably 1 to 10 mm, and the predetermined length D is the actual length (in the surface) in the radial section of the portion to be thickened. The length along the length; mm) is preferably 0.5 to 1.5 times. This completes the bulging process.

  According to the manufacturing method of the third embodiment, since the back surface of the hat portion and the outer peripheral portion of the hub attachment is only given hydraulic pressure during forming, the surface roughness of the raw steel plate is maintained without being smoothed. In addition, sharpened micropores are not generated. Furthermore, since the hub mounting outer peripheral portion is thickened in the bulge processing step, a hub mounting outer peripheral portion having a large plate thickness can be obtained.

  In the case of the manufacturing method of the third embodiment, as in the case of the second embodiment, in the second step of the bulge processing step, the total extension of the steel plate bulge portion is 90 to 110% of the total extension of the wheel disk. Furthermore, it is preferable to swell the steel plate.

  In order to enhance the fatigue characteristics at the hub mounting outer periphery, the average thickness change rate T (see the above formula (1)) at the hub mounting outer periphery is preferably 3.5% or more. As a result, the maximum principal stress generated in the hub mounting outer peripheral portion is reduced, and the occurrence of fatigue cracks can be suppressed.

  Also in the first embodiment, instead of the inner mold 11, a mold including the first inner mold 11 </ b> A and the second inner mold 11 </ b> B is used. Processes similar to those in the third embodiment can be performed. Also in this case, the hat portion and the back surface of the hub mounting outer peripheral portion are not smoothed, the surface roughness of the material steel plate is maintained, and sharpened micropores are not generated. Furthermore, also in this case, since the hub mounting outer peripheral portion is increased in thickness in the bulging process, a hub mounting outer peripheral portion having a large plate thickness can be obtained.

  Even when the first embodiment is modified as described above, in the second step of the bulge processing step, the steel plate is expanded so that the total extension of the steel plate expansion portion is 90 to 110% of the total extension of the wheel disk. It is preferable.

<Example 1>
In order to confirm the effect of the present invention, a numerical analysis simulation was performed on the assumption that the wheel disk was formed by utilizing the bulge processing by employing the manufacturing method of the first embodiment shown in FIG. At that time, in the second step of the bulging process, the steel plate was expanded so that the total length of the expanded portion of the steel plate was 100% of the total length of the wheel disk. For comparison, a numerical analysis simulation was performed on the assumption that a wheel disk having the same shape was formed by conventional press working. As the material steel plate, a 440 MPa class general-purpose hot-rolled steel plate (SPH440) having a plate thickness of 2.3 mm was used.

  As a wheel disk obtained by utilizing bulge processing as an example of the present invention, cross-sectional profiles of the front surface and the back surface were extracted along the radial direction. As a comparative example, the cross-sectional profiles of the front surface and the back surface were extracted along the radial direction of the wheel disk obtained by press working. In the comparative example, extraction was performed in two directions shifted by 45 degrees around the center of the disk. And from each result, plate | board thickness was computed for every radial direction distance from a disk center, and plate | board thickness change rate T was calculated | required according to said (1) Formula.

  FIG. 11 is a diagram showing the distribution of the plate thickness change rate in the wheel disc examined using the LS-DYNA version 971 of general-purpose FEM software as an example. As shown in the figure, in the example of the present invention, the average thickness change rate T in the hat portion is 3.5% or more, and the thickness of the hat portion can be significantly increased from the thickness of the material steel plate. did it. On the other hand, in the comparative example, the average thickness change rate T in the hat portion was much lower than 3.5%, and the thickness of the hat portion rather decreased than the thickness of the material steel plate.

<Example 2>
The manufacturing method of the third embodiment shown in FIG. 10 was adopted, and a numerical analysis simulation was performed assuming that a wheel disk was formed by utilizing bulge processing. At that time, in the second step of the bulging process, the steel plate was expanded so that the total length of the expanded portion of the steel plate was 100% of the total length of the wheel disk. For comparison, a numerical analysis simulation was performed on the assumption that a wheel disk having the same shape was formed by conventional press working. As the material steel plate, a 440 MPa class general-purpose hot-rolled steel plate (SPH440) having a plate thickness of 2.3 mm was used.

  As a wheel disk obtained by utilizing bulge processing as an example of the present invention, cross-sectional profiles of the front surface and the back surface were extracted along the radial direction. As a comparative example, the cross-sectional profiles of the front surface and the back surface were extracted along the radial direction of the wheel disk obtained by press working. In the comparative example, extraction was performed in two directions shifted by 45 degrees around the center of the disk. And from each result, plate | board thickness was computed for every radial direction distance from a disk center, and plate | board thickness change rate T was calculated | required according to said (1) Formula.

  FIG. 12 is a diagram showing the distribution of the plate thickness change rate in the wheel disc examined using the LS-DYNA version 971 of general-purpose FEM software as an example. As shown in the figure, in the example of the present invention, the average plate thickness change rate T at the hub mounting outer peripheral portion is 3.5% or more, and the plate thickness of the hat portion is greatly increased from the plate thickness of the material steel plate. I was able to. On the other hand, in the comparative example, the average plate thickness change rate T in the outer periphery of the hub attachment was far below 3.5%, and the thickness of the outer periphery of the hub attachment decreased rather than the thickness of the material steel plate.

  INDUSTRIAL APPLICABILITY The present invention can be effectively used for automobile wheel discs and their manufacture.

1: wheel disc, 2: hub mounting part, 2a: hub hole,
2b: nut seat, 2c: bolt hole, 2h: outer periphery of hub mounting,
3: inner curved part, 4: hat part, 4a: hat top part, 5: outer curved part,
6: flange portion, 7: steel plate, 7a: peripheral portion of steel plate, 7b: through hole,
8: welded part,
11: Inner mold, 11a: Engraving section, 11A: First inner mold,
11B: second inner mold, 12: outer mold, 12a: engraving part,
13: Workpiece holding mold, 14: Liquid, 15: Liquid supply path,
16: Presser type, 17: Pedestal type,
21: A first mold for holding a workpiece, 22: A second mold for holding a workpiece,
23: annular punch

Claims (9)

It is a disk for an automobile wheel that is formed by plastic working a steel plate, and in order from the center of the disk, concentrically, a hub mounting part, an inner curved part, a hat part, an outer curved part and a flange part,
A disk for an automobile wheel, wherein the surface roughness of the back surface of the hat portion is 0.7 μm or more and 3.0 μm or less in terms of arithmetic average roughness Ra. The hub mounting portion has a hub mounting outer peripheral portion bent adjacent to the inner curved portion and connected to the inner curved portion;
The disk for automobile wheels according to claim 1, wherein the surface roughness of the rear surface of the outer peripheral portion of the hub mounting is 0.7 µm or more and 3.0 µm or less in terms of arithmetic average roughness Ra. In order from the disk center side, concentrically, a manufacturing method of a disk for an automobile wheel having a hub mounting part, an inner curved part, a hat part, an outer curved part and a flange part,
Preparing two hot-rolled steel sheets as work materials, and forming a through hole in the edge of one of the steel sheets; and
Stacking the steel plates, welding process for welding the periphery of each other over the entire circumference,
A bulge processing step of forming the disk by inflating the steel plate, and
The bulging process includes
An inner molding die comprising a pair of engraved parts engraved with surface shapes of the hub mounting part, the inner curved part and the hat part, and arranged opposite to each other;
An outer molding die that has a pair of opposingly arranged adjacent to the outer periphery of the inner molding die, and has an engraving portion in which the outer curved portion and the surface shape of the flange portion are engraved,
A step of using a workpiece holding mold, which is composed of a pair arranged opposite to each other adjacent to the outer periphery of the outer forming mold, and which slidably holds the peripheral edge of the steel plate,
A first step of sandwiching a peripheral edge of the steel plate by the workpiece holding mold in a state where the inner molding die and the outer molding die are retracted from a predetermined position;
Subsequent to the first step, a second step of inflating the steel sheet by introducing a liquid between the steel sheets from the through hole of the steel sheet to give a liquid pressure,
Following this second step, a third step of advancing the outer molding die to a predetermined position;
Following this third step, a fourth step of advancing the inner mold to a predetermined position;
Subsequent to the fourth step, the fifth step includes increasing the hydraulic pressure and inflating the steel sheet until it extends along the engraving portion of the inner molding die and the engraving portion of the outer molding die. The manufacturing method of the disk for motor vehicle wheels characterized by the above-mentioned. In the second step of the bulge processing step, the total extension in the radial cross section of the bulge portion of the steel plate is the hub mounting portion, the inner curved portion, the hat portion, the outer curved portion and the flange of the disk. The method for manufacturing a disk for an automobile wheel according to claim 3, wherein the steel sheet is expanded so as to be 90 to 110% of the total extension in the radial section of the portion. In order from the disk center side, concentrically, a manufacturing method of a disk for an automobile wheel having a hub mounting part, an inner curved part, a hat part, an outer curved part and a flange part,
A preparation step of preparing one hot-rolled steel sheet as a workpiece;
A preliminary processing step of performing a drawing process for raising a region corresponding to the outer curved portion and the flange portion in the steel plate;
A bulge processing step of forming the disk by inflating the steel plate, and
The preliminary processing step includes
A first mold for holding a workpiece that non-slidably holds a region corresponding to the hub mounting portion, the inner curved portion, and the hat portion of the steel plate;
It consists of a pair arranged opposite to each other with an area corresponding to the outer curved portion and the flange portion in the steel plate from the outer periphery of the first mold for holding the work material, and can slide on the peripheral portion of the steel plate A second mold for holding the workpiece to be clamped;
A step of using an annular punch disposed in a region corresponding to the outer curved portion and the flange portion in the steel plate,
A first preliminary processing step of sandwiching the steel sheet by the first mold for holding the workpiece and the second mold for holding the workpiece;
Subsequent to this first preliminary processing step, the second preliminary processing step of pushing the punch into the steel plate and raising the region corresponding to the outer curved portion and the flange portion in the steel plate,
The bulging process includes
An inner molding die having an engraved portion in which surface shapes of the hub attaching portion, the inner curved portion and the hat portion are engraved;
An outer molding die that is arranged adjacent to the outer periphery of the inner molding die and has an engraving portion in which the outer curved portion and the surface shape of the flange portion are engraved;
A pressing die disposed adjacent to the outer periphery of the outer molding die, and a raised surface of the steel plate disposed opposite to the pressing die, the inner molding die and the outer molding die; Consists of a pedestal mold addressed to the opposite surface, and a process of using a workpiece holding mold that holds the peripheral edge of the steel plate in a non-slidable manner,
A first step of sandwiching a peripheral edge of the steel plate by the workpiece holding mold in a state where the inner molding die and the outer molding die are retracted from a predetermined position;
Subsequent to the first step, a second step of introducing a liquid between the steel plate and the pedestal mold to apply a hydraulic pressure and inflating the steel plate,
Following this second step, a third step of advancing the outer molding die to a predetermined position;
Following this third step, a fourth step of advancing the inner mold to a predetermined position;
Subsequent to the fourth step, the fifth step includes increasing the hydraulic pressure and inflating the steel sheet until it extends along the engraving portion of the inner molding die and the engraving portion of the outer molding die. The manufacturing method of the disk for motor vehicle wheels characterized by the above-mentioned. In the second preliminary processing step of the preliminary processing step, the total extension in the radial cross section of the hub mounting portion, the portion of the inner curved portion corresponding to the inner curved portion and the hat portion, and the raised portion in the steel plate, The steel plate is raised so as to be 90 to 110% of the total extension in the radial section of the hub mounting portion, the inner curved portion, the hat portion, the outer curved portion, and the flange portion of the disk. The manufacturing method of the disk for motor vehicle wheels of Claim 5. The hub mounting portion has a hub mounting outer peripheral portion bent adjacent to the inner curved portion and connected to the inner curved portion;
The inner molding die includes a first inner molding die arranged on the center side, and a second inner molding die arranged adjacent to the outer periphery of the first inner molding die. ,
The outer side surface of the first inner molding die and the inner side surface of the second inner molding die are located at a portion corresponding to the hub mounting outer peripheral portion of the disc;
For the state in which the fourth step corresponds to the final shape of the disk of the first and second inner molding dies, the first inner molding dies are moved from the second inner molding dies. And a step of causing the second inner molding die to advance to a predetermined position in a state of protruding downward by a predetermined length,
In the manufacturing method, following the fifth step, the first inner mold is set to the predetermined length with respect to the second inner mold while the hydraulic pressure is applied to the steel plate. The method of manufacturing a disk for an automobile wheel according to any one of claims 3 to 6, further comprising a sixth step of retreating. The automobile according to claim 7, wherein the ratio of the plate thickness change amount before and after the bulge processing to the thickness of the steel plate at the hub mounting outer peripheral portion is 3.5% or more on average by the bulge processing step. A method of manufacturing a disk for a wheel. 9. The ratio of the thickness change amount before and after bulging to the thickness of the steel plate in the hat portion is set to 3.5% or more on average by the bulging step. The manufacturing method of the disk for motor vehicle wheels of description.