Die for hot press forming, and method for manufacturing hot press formed products.

Abstract

The present invention provides a mold for hot press forming and a method for manufacturing a hot press-formed product that can more reliably suppress the occurrence of wrinkles when deep drawing is performed by hot pressing. The mold 24 is for performing deep drawing on a heated blank 30 by hot pressing and comprises a first mold 26 having a first forming surface 26S and an outer peripheral surface 44 disposed outside the first forming surface 26S, and a second mold 28 disposed opposite the first mold 26 and having a second forming surface 28S corresponding to the first forming surface 26. A guide portion 45 is provided on the outer peripheral surface 44. The guide portion 45 protrudes from the second mold 28 and has a top portion 47 that extends from the outer edge of the first mold 26 toward the inside of the first mold 26. The guide portion 45 has a pair of guide surfaces 45S that are inclined from the top portion 47 toward the outer peripheral surface 44 on the side intersecting the direction of extension of the top portion 47.

Description

Technical Field

[0006] , , ,

[0007] ,

[0001] The present invention relates to a mold for hot press forming and a method for manufacturing a hot press formed product.

Background Art

[0002] In hot press forming, various manufacturing methods for suppressing the generation of wrinkles have been proposed. For example, Patent Document 1 discloses a hot press deep drawing forming method using a holder that sandwiches and holds the outer edge portion of a blank between the mold.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When performing drawing forming by hot press, it is required to more reliably suppress the generation of wrinkles.

[0005] An object of the present invention is to provide a mold for hot press forming and a method for manufacturing a hot press formed product that can more reliably suppress the generation of wrinkles when performing drawing forming by hot press.

Means for Solving the Problems

[0008] According to the present invention, when deep drawing is performed by hot pressing, the occurrence of wrinkles can be suppressed more reliably. [Brief explanation of the drawing]

[0009] [Figure 1] This is a front view of a wheel equipped with a wheel disc according to this embodiment. [Figure 2] This is a longitudinal cross-sectional view of a wheel equipped with a wheel disc according to this embodiment. [Figure 3] This is a schematic perspective view showing the wheel disc according to this embodiment. [Figure 4] This is a schematic central longitudinal cross-sectional view showing the wheel disc according to this embodiment. [Figure 5] This is a schematic perspective view showing a mold for forming the wheel disc according to this embodiment. [Figure 6] This is a schematic cross-sectional view showing the state in which a blank is set in the mold according to this embodiment. [Figure 7] It is a cross-sectional view schematically showing a state in which a blank is drawn and formed by the mold according to this embodiment, and is a view showing a state in which the blank has started to deform. [Figure 8] It is a schematic view seen from the outside of the mold in the state of FIG. 5 to the outer edge of the blank. [Figure 9] It is a cross-sectional view schematically showing a state in which the mold according to this embodiment is operated to the bottom dead center. [Figure 10] It is a perspective view schematically showing a mold for forming a wheel disk according to a modification. [Figure 11] It is a perspective view showing a hot press molded product according to another modification.

MODE FOR CARRYING OUT THE INVENTION

[0010] Embodiments of the present invention relate to the following aspects.

[0011] [Wheel] Referring to FIGS. 1 and 2, a two-piece type automotive wheel 1 including a wheel disk 10 as a hot press molded product will be described. The wheel 1 includes a rim 2 and a wheel disk 10. The rim 2 has a substantially cylindrical shape centered on the central axis Z, and has a drop portion 3, bead seat portions 4 provided on both sides in the central axis Z direction from the drop portion 3, and further flange portions respectively provided on the outer edges in the central axis Z direction of each bead seat portion 4. 5. A tire is mounted on the outer circumference of the rim 2.

[0012] The wheel disk 10 is fitted into the inner circumference of the rim 2. The wheel disk 10 has a substantially disk shape centered on the central axis Z, and has a hub mounting portion 12 as a concave portion at the center, and an annular inclined portion 14 and a peripheral edge fixing portion 16 as a vertical wall portion in order from the hub mounting portion 12 toward the radially outer side. Although not shown, the hub mounting portion 12 is formed with a hub hole and a plurality of bolt holes.

[0013] The peripheral fixing portion 16 of the wheel disc 10 is welded to the drop portion 3 of the rim 2 while fitted into the inner circumference of the drop portion 3 of the rim 2. The wheel disc 10 is positioned on one side of the rim 2 in the direction of the central axis Z. The wheel 1 has a space 6 formed by the rim 2 and the wheel disc 10 on the other side of the rim 2 in the direction of the central axis Z.

[0014] [Wheel Disc] The wheel disc 10 will be described with reference to Figures 3 and 4. The central axis Z passes through the center of the wheel disc 10 and is parallel to the thickness direction of the blank before press forming. In the following description, one side and one direction parallel to the central axis Z will be referred to as the upper side and the upward direction in Figure 3, and the other side and other direction of the central axis Z will be referred to as the lower side and the downward direction in Figure 3. In the direction perpendicular to the central axis Z, the side and direction approaching the central axis Z will be referred to as the inward and inward direction, and the side and direction moving away from the central axis Z will be referred to as the outward and outward direction. The direction of rotation around the central axis Z will be the circumferential direction. "Orthogonal" and "parallel" include the cases of "approximately orthogonal" and "approximately parallel," respectively. Also, angles will be considered inferior angles.

[0015] Figure 3 is a schematic perspective view of the wheel disc 10 according to this embodiment, as seen from the outer surface.

[0016] The wheel disc 10 is roughly disc-shaped. In Figure 3, the outer surface shown is the outer surface 10A, and the opposite back surface is the inner surface 10B.

[0017] The hub mounting portion 12 is located in the center of the wheel disc 10 and is recessed in a mortar shape. The hub mounting portion 12 has a bottom portion 18 and an inclined cylindrical portion 20. The bottom portion 18 includes the central axis Z and has a circular outer edge 18A (Figure 5) perpendicular to the central axis Z, and a bottom surface 18S surrounded by the outer edge 18A.

[0018] The inclined cylindrical portion 20 is shaped like an inverted truncated cone, having a circular lower edge 20A as viewed from the central axis Z, an upper edge 20B having a larger diameter than the lower edge 20A and positioned above the lower edge 20A, and an inclined cylindrical surface 20S connecting the lower edge 20A and the upper edge 20B. The lower edge 20A is connected to the outer edge 18A of the base 18. The inclined cylindrical portion 20 is inclined outward from the lower edge 20A toward the upper edge 20B. The connection portion between the outer edge 18A of the base 18 and the lower edge 20A of the inclined cylindrical portion 20 may have a cross-sectional radius (R). The diameter of the lower edge 20A of the inclined cylindrical portion 20 is, for example, 40 mm or more and 200 mm or less. The diameter of the upper edge 20B of the inclined cylindrical portion 20 is, for example, 60 mm or more and 250 mm or less.

[0019] The annular inclined portion 14 is provided on the outside of the hub mounting portion 12 so as to surround the hub mounting portion 12, and is positioned above the bottom portion 18. The annular inclined portion 14 is provided concentrically with the hub mounting portion 12 and is annular when viewed from the central axis Z. The annular inclined portion 14 has an inner edge 14A, an outer edge 14B positioned outside and below the inner edge 14A, and an inclined surface 14S connecting the inner edge 14A and the outer edge 14B.

[0020] The inner edge 14A of the annular inclined portion 14 is connected to the upper edge 20B of the inclined cylindrical portion 20. The outer edge 14B of the annular inclined portion 14 is also the outer edge of the wheel disc 10. The inclined surface 14S is a gently curved surface that slopes downward from the inner edge 14A to the outer edge 14B and is convex upward. The outer edge 14B of the annular inclined portion 14 is, for example, 250 mm or more and 500 mm or less.

[0021] The annular inclined portion 14 may have a plurality of through holes 22 in the inclined surface 14S. In the inclined surface 14S shown in Figure 3, four through holes 22 are formed evenly in the circumferential direction. The through holes 22 are in the shape of an annular sector when viewed from the central axis Z.

[0022] The peripheral fixing portion 16 is provided on the outside of the annular inclined portion 14 so as to surround the annular inclined portion 14. The peripheral fixing portion 16 is provided concentrically with the annular inclined portion 14 and is cylindrical in shape, having a circular upper edge 16A when viewed from the central axis Z, a lower edge 16B located below the upper edge 16A and having the same diameter as the upper edge 16A, and a cylindrical surface 16S connecting the upper edge 16A and the lower edge 16B. The upper edge 16A of the peripheral fixing portion 16 is connected to the outer edge 14B of the annular inclined portion 14. The lower edge 16B of the peripheral fixing portion 16 is open.

[0023] The height H1 of the hub mounting portion 12, that is, the vertical distance between the bottom surface 18S and the upper edge 20B of the inclined cylindrical portion 20, is, for example, 15 mm or more and 80 mm or less. The height H2 of the annular inclined portion 14, that is, the vertical distance between the inner edge 14A and the outer edge 14B of the annular inclined portion 14, is, for example, 5 mm or more and 70 mm or less.

[0024] [Mold] The mold 24 used in the manufacturing method of the wheel disc 10 according to this embodiment will be described with reference to Figures 5 and 6. The mold 24 is installed in the press machine of a hot press device, although it is not shown in the figures. The mold 24 is used to perform hot press forming on a blank when manufacturing a wheel disc 10 having a mortar-shaped hub mounting portion 12, an annular inclined portion 14 provided so as to surround the hub mounting portion 12, and a cylindrical peripheral edge fixing portion 16 provided so as to surround the annular inclined portion 14.

[0025] The mold 24 shown in Figure 5 comprises a first mold 26 and a second mold 28. Figures 5 and 6 show a blank 30 positioned between the upper mold, which is the first mold 26, and the lower mold, which is the second mold 28. In this specification, the central axis Z of the mold 24, the upper side and upward direction, the lower side and downward direction, the inner side and inward direction, and the outer side and outward direction are assumed to be the same as those of the wheel disc 10. The first mold 26 and the second mold 28 are circular when viewed with respect to the central axis Z.

[0026] (First mold) The first mold 26 is equipped with a refrigerant flow path (not shown). The first mold 26 has a size corresponding to the size of the wheel disc 10. The first mold 26 has a first molding surface 26S and an outer peripheral surface 44 located outside the first molding surface 26S on the side facing the second mold 28 across the blank 30. The first molding surface 26S is in contact with the first surface 30F of the blank 30.

[0027] The first molding surface 26S is provided with an inner protrusion 32 and an outer peripheral recess 34. The inner protrusion 32 is columnar, located in the center of the first molding surface 26S, and protrudes downward relative to the second mold 28. The outer peripheral recess 34 is positioned outside the inner protrusion 32 so as to surround it, and is recessed upward relative to the second mold 28. The outer peripheral recess 34 is provided concentrically with the inner protrusion 32 and is annular when viewed from the central axis Z.

[0028] The first molding surface 26S includes a central axis Z and has a tip surface 36 that is circular when viewed from the central axis Z. The outer edge 36A of the tip surface 36 is connected to a first inner inclined surface 38. The first inner inclined surface 38 has a lower edge 38A connected to the outer edge 36A of the tip surface 36, and an upper edge 38B having a larger diameter than the lower edge 38A and positioned above the tip surface 36. The first inner inclined surface 38 is inclined outward from the lower edge 38A toward the upper edge 38B. The connection between the outer edge 36A of the tip surface 36 and the lower edge 38A of the first inner inclined surface 38 may have a cross-sectional radius (R).

[0029] The upper edge 38B of the first inner inclined surface 38 is connected to the first outer inclined surface 40. The first outer inclined surface 40 has an inner edge 40A connected to the upper edge 38B of the first inner inclined surface 38, and an outer edge 40B having a larger diameter than the inner edge 40A and positioned below the inner edge 40A. The first outer inclined surface 40 is a curved surface that slopes downward from the inner edge 40A to the outer edge 40B and is gently concave upward. The connection portion between the upper edge 38B of the first inner inclined surface 38 and the inner edge 40A of the first outer inclined surface 40 may have a cross-sectional radius (R).

[0030] The first outer inclined surface 40 is connected to the first wall surface 42. The first wall surface 42 has an upper edge 42A connected to the outer edge 40B of the first outer inclined surface 40, and a lower edge 42B positioned downward from the upper edge 42A parallel to the central axis Z. The first wall surface 42 has the shape of the inner surface of a cylinder.

[0031] The outer circumferential surface 44 is positioned outside the first wall surface 42 so as to surround the first wall surface 42. The outer circumferential surface 44 has an inner edge 44A connected to the lower edge 42B of the first wall surface 42, and an outer edge 44B positioned outward from the inner edge 44A perpendicular to the central axis Z. The outer circumferential surface 44 is annular with respect to the central axis Z and has a surface perpendicular to the central axis Z.

[0032] A guide portion 45 is provided on the outer circumferential surface 44. The guide portion 45 has an inverted V-shape when viewed from the outside of the first mold 26. The guide portion 45 has a apex portion 47 that protrudes relative to the second mold 28. The apex portion 47 extends in a direction toward the inside of the first mold 26 from the outer edge of the first mold 26. The apex portion 47 may be inclined toward the side away from the second mold 28 toward the inside of the first mold 26 from the outer edge of the first mold 26 (Figure 6). In the cross-section shown in Figure 6, the angle α between the extending direction of the apex portion 47 and the direction perpendicular to the central axis Z is preferably 0° or more and 15° or less, and more preferably 5° or more and 10° or less. The apex portion 47 is curved and protrudes relative to the second mold 28 when viewed from the outside of the first mold 26.

[0033] The guide portion 45 has a pair of guide surfaces 45S. The guide surfaces 45S are provided on both sides in the circumferential direction, flanking the top portion 47. Each guide surface 45S is inclined upward from the top portion 47 toward the outer peripheral surfaces 44 on both sides intersecting the direction of extension of the top portion 47, i.e., on both sides in the circumferential direction relative to the top portion 47. When viewing the guide portion 45 from the outside in a direction perpendicular to the central axis Z, the angle β between the extension of the tangent line touching the guide surface 45 and the outer peripheral surface 44 is preferably 10° or more and 60° or less, and more preferably 10° or more and 45° or less.

[0034] As described above, the inner protrusion 32 is formed to protrude from the second mold 28 by the tip surface 36 and the first inner inclined surface 38. The outer peripheral recess 34 is formed to be recessed from the second mold 28 by the first inner inclined surface 38 and the first outer inclined surface 40. The first mold 26 forms the bottom surface 18S and the inclined cylindrical surface 20S of the hub mounting portion 12 by the tip surface 36 and the first inner inclined surface 38, the inclined surface 14S of the annular inclined portion 14 by the first outer inclined surface 40, and the cylindrical surface 16S of the peripheral fixing portion 16 by the first wall surface 42.

[0035] (Second mold) The second mold 28 is equipped with a refrigerant flow path (not shown). The second mold 28 has a size corresponding to the size of the wheel disc 10. The second mold 28 has a second molding surface 28S on the side facing the first mold 26 across the blank 30, which corresponds to the first molding surface 26S. The second molding surface 28S is in contact with the second surface 30R of the blank 30.

[0036] The second molding surface 28S is provided with an inner recess 46 and an outer peripheral protrusion 48. The inner recess 46 is located in the center of the second molding surface 28S and is recessed downward relative to the first mold 26. The inner recess 46 is provided complementary to the inner protrusion 32 of the first mold 26. The outer peripheral protrusion 48 is positioned outside the inner recess 46 so as to surround it and protrudes upward relative to the first mold 26. The outer peripheral protrusion 48 is provided concentrically with the inner recess 46 and is annular when viewed from the central axis Z. The outer peripheral protrusion 48 is provided complementary to the outer peripheral recess 34 of the first mold 26.

[0037] The second molding surface 28S includes a central axis Z and has a concave bottom surface 50 that is circular when viewed from the central axis Z. The outer edge 50A of the concave bottom surface 50 is connected to a second inner inclined surface 52. The second inner inclined surface 52 has a lower edge 52A connected to the outer edge 50A of the concave bottom surface 50, and an upper edge 52B having a larger diameter than the lower edge 52A and positioned above the concave bottom surface 50. The second inner inclined surface 52 is inclined outward from the lower edge 52A toward the upper edge 52B. The connection between the outer edge 50A of the concave bottom surface 50 and the lower edge 52A of the second inner inclined surface 52 may have a cross-sectional radius (R).

[0038] The upper edge 52B of the second inner inclined surface 52 is connected to the second outer inclined surface 54. The second outer inclined surface 54 has an inner edge 54A connected to the upper edge 52B of the second inner inclined surface 52, and an outer edge 54B having a larger diameter than the inner edge 54A and positioned below the inner edge 54A. The second outer inclined surface 54 is a curved surface that slopes downward from the inner edge 54A to the outer edge 54B and gently protrudes upward. The connection portion between the upper edge 52B of the second inner inclined surface 52 and the inner edge 54A of the second outer inclined surface 54 may have a cross-sectional radius (R).

[0039] The second outer inclined surface 54 is connected to the second wall surface 56. The second wall surface 56 has an upper edge 56A connected to the outer edge 54B of the second outer inclined surface 54, and a lower edge 56B positioned downward from the upper edge 56A parallel to the central axis Z. The second wall surface 56 is cylindrical in shape.

[0040] (Relationship between mold and wheel disc) The front surface 36 of the first mold 26 and the concave bottom surface 50 of the second mold 28 form the bottom portion 18 of the wheel disc 10. The first inner inclined surface 38 of the first mold 26 and the second inner inclined surface 52 of the second mold 28 form the inclined cylindrical portion 20 of the wheel disc 10. The first outer inclined surface 40 of the first mold 26 and the second outer inclined surface 54 of the second mold 28 form the annular inclined portion 14 of the wheel disc 10. The first wall surface 42 of the first mold 26 and the second wall surface 56 of the second mold 28 form the peripheral edge fixing portion 16 of the wheel disc 10. The guide surface 45S of the first mold 26 appropriately relieves the circumferential compressive force of the outer edge portion 30P of the blank 30 during hot press forming, thereby more reliably suppressing the occurrence of wrinkles in the peripheral edge fixing portion 16 and the annular inclined portion 14 of the wheel disc 10.

[0041] [blank] The blank 30 is, for example, a steel plate with a thickness of 1 mm to 5 mm. After hot press forming, the first surface 30F of the blank 30 becomes the outer surface 10A, and the second surface 30R becomes the inner surface 10B. Preferably, the blank 30 has a tensile strength of 1000 MPa or more after quenching. The blank 30 has a circular shape when viewed from the thickness direction. The blank 30 has a plurality of through holes 22P. The through holes 22P shown in Figure 5 are in the shape of a circular fan, and four of them are evenly arranged in the circumferential direction of the blank 30. The through holes 22P become through holes 22 in the wheel disc 10 after hot press forming. In the blank 30, the circular area centered on the central axis Z from the radial center to the inner edge 22A of the through hole 22P is called the central portion 30C, the annular area centered on the central axis Z from the inner edge 22A to the outer edge 22B of the through hole 22P is called the outer peripheral portion 30M, and the annular area centered on the central axis Z from the outer edge 22B of the through hole 22P to the outer edge of the blank 30 is called the outer edge portion 30P.

[0042] The steel material used as this blank 30 has a chemical composition of, for example, C: 0.1% to 0.8% by mass, Si: 0.001% to 2.0%, Mn: 0.5% to 3.0%, P: 0.15% or less, and S: 0.01% or less.

[0043] Furthermore, the steel material preferably contains, by mass%, sol.Al: 0.001% to 1.0%, N: 0.01% or less, and B: 0.01% or less as a chemical composition, with the remainder being Fe and impurities. Alternatively, the above chemical composition may include, in place of a portion of Fe, one or more elements selected from the group consisting of Ti, Nb, V, Cr, Mo, Cu, and Ni.

[0044] Other additive elements such as Ti, Nb, V, Cr, Mo, Cu, and Ni may be added as needed to improve the hardenability of the steel and to ensure stable strength after quenching.

[0045] [Manufacturing method] Next, a method for manufacturing the wheel disc 10 by hot pressing will be described. The method for manufacturing the wheel disc 10 includes a heating step and a hardening step.

[0046] (Heating process) In the heating process, the blank 30 is heated to a temperature above its Ac3 transformation point to austenitize it.

[0047] The Ac3 transformation point, which indicates the austenitization transformation temperature, is the temperature at which the blank 30 made of the aforementioned steel material is completely austenitized, and is shown as follows as an example.

[0048] Ac3(℃)=910-203×√C(mass%)+44.7×Si(mass%)-30×Mn(mass%)-11×Cr(mass%)+700×S(mass%)+400×Al(mass%)+50×Ti(mass%) Here, C represents carbon, Si represents silicon, Mn represents manganese, Cr represents chromium, S represents sulfur, Al represents aluminum, and Ti represents titanium.

[0049] (Heat treatment process) The blank 30, heated to above the Ac3 transformation point in the heating process, is hot press-formed using the mold 24 installed in the press machine of the hot press apparatus. After hot press forming, the wheel disc 10 is rapidly cooled by removing heat from the press-formed product using the first mold 26 and the second mold 28 while the molds are clamped, thereby causing the wheel disc 10 to undergo martensitic transformation. In other words, the quenching process includes the steps of setting, deep drawing, and cooling.

[0050] ·set As shown in Figure 6, the blank 30, which has been heated to above the Ac3 transformation point in the heating process, is set between the first mold 26 and the second mold 28. At this time, the blank 30 is positioned in the mold 24 by positioning pins (not shown).

[0051] • Deep drawing The deep drawing process consists of a first step and a second step. First, in the first step, as shown in Figure 7, the first mold 26 is moved downward toward the second mold 28. As a result, the central part 30C of the blank 30 is pushed downward by the inner protrusion 32 of the first mold and drawn, and at the same time, the outer peripheral part 30M around it is pushed upward by the outer peripheral protrusion 48 of the second mold 28, causing the blank 30 to be drawn in the reverse direction (hereinafter sometimes referred to as "reverse drawing"). In this way, when drawing is started on the blank 30 at a temperature above the Ac3 transformation point, the blank 30 begins to deform.

[0052] As the deep drawing process begins, a shrinkage flange deformation occurs at the outer edge 30P of the blank 30, in which the blank 30 is compressed in the circumferential direction and pulled towards the central part 30C. Specifically, as shown in Figure 8, the outer edge 30P of the blank 30 may deform into a wavy shape that oscillates vertically. The wavy deformed outer edge 30P moves inward toward the central axis Z while a portion of it contacts the guide surface 45S.

[0053] Then, in the second step, as shown in Figure 9, the first mold 26 is moved downward to its bottom dead center, and the drawing of the blank 30 is completed while it is sandwiched between the first mold 26 and the second mold 28. Between the first and second steps, the outer edge 30P of the blank 30 continues to move inward along the outer peripheral surface 44 and the guide surface 45S toward the central axis Z, and is drawn between the first wall surface 42 and the second wall surface 56, becoming the peripheral fixing portion 16 of the wheel disc 10.

[0054] ·cooling When the first mold 26 reaches its bottom dead center, the formed blank 30 is in close contact with the first mold 26 and the second mold 28. This state is called mold clamping. In the clamped state, the heat of the blank 30 is rapidly removed by the first mold 26 and the second mold 28. As a result, the blank 30 undergoes martensitic transformation. That is, the blank 30 is hardened, and thus becomes a wheel disc 10.

[0055] One method for removing heat from the blank 30 is to indirectly cool it using a refrigerant flowing through the inside of the first mold 26 and the second mold 28. Another method for removing heat is to directly cool the blank 30 by injecting a refrigerant from the first mold 26 and the second mold 28.

[0056] The time from the heating process to the start of cooling shall be within 15 seconds. That is, the time from when the blank 30 heated in the heating process leaves the heating furnace until the first mold 26 reaches its bottom dead center shall be within 15 seconds.

[0057] [Mechanism of Action and Effects] The operation and effects of the mold 24 for hot press forming and the manufacturing method of the wheel disc 10 according to the above embodiment will be explained.

[0058] In the first step of deep drawing, the blank 30 is subjected to deep drawing. At this time, the outer edge 30P of the blank 30 is not held. Therefore, in the initial stage of deep drawing, the blank 30 is smoothly pulled into the central part 30C, thereby suppressing the reduction in plate thickness in the central part 30C.

[0059] As the drawing process progresses and shrinkage flange deformation occurs at the outer edge 30P of the blank 30, a portion of the corrugated outer edge 30P comes into contact with the guide surface 45S. In this way, a portion of the outer edge 30P moves inward along the guide surface 45S toward the central axis Z, thereby partially relieving the circumferential compressive force on the outer edge 30. This restricts the circumferential movement of the outer edge 30P and prevents the outer edge 30P from overlapping and increasing the plate thickness.

[0060] The guide surface 45S is inclined from the top portion 47 toward the outer peripheral surface 44 on the side intersecting the extending direction of the top portion 47, making it easy for the corrugated outer edge portion 30P to come into surface contact with it. As a result, the outer edge portion 30P moves easily along the guide surface 45S, which can more reliably alleviate the circumferential compressive force on the outer edge portion 30P. In this way, in this embodiment, the occurrence of wrinkles in the peripheral fixing portion 16 can be more reliably suppressed.

[0061] The top portion 47 is inclined toward the inside of the first mold 26 and away from the second mold 28 from the outer edge portion 30P of the first mold 26, thereby enabling more reliable surface contact with the outer edge portion 30P, which has deformed into a wavy shape as the deep drawing process progresses.

[0062] In this embodiment, by performing unidirectional drawing and reverse drawing in the opposite direction in a single press operation, localized temperature drops in the blank 30 can be suppressed. Therefore, the strength of the wheel disc 10 after quenching can be ensured.

[0063] [Differentiation] The present invention is not limited to the embodiments described above, and can be modified as appropriate within the scope of the spirit of the invention. The examples provided below can be implemented individually or in combination with the above embodiments as appropriate.

[0064] For example, the mold according to this embodiment may include a bead portion for forming a bead on the wheel disc. A modified mold will be described with reference to Figure 10, which uses the same reference numerals for the same configuration as in Figure 4. Note that the same reference numerals are used for the same configuration as in the above embodiment, and detailed descriptions will be omitted. The mold 24A shown in Figure 10 includes a first mold 26A and a second mold 28A.

[0065] The first mold 26A has a first molding surface 26SA and an outer peripheral surface 44SA located outside the first molding surface 26SA, on the side facing the second mold 28A. The first molding surface 26SA has a tip surface 36, a first inner inclined surface 38, a first outer inclined surface 40SA, and a first wall surface 42SA. The outer peripheral surface 44SA is located outside the first wall surface 42SA so as to surround it. A guide portion 45 is provided on the outer peripheral surface 44SA. The guide portion 45 has guide surfaces 45S on both sides in the circumferential direction, with the top portion 47 in between.

[0066] The first mold 26A has a plurality of first bead portions 58 between the first wall surface 42SA and the outer peripheral surface 44SA. One first bead portion 58 is provided on each of the circumferential sides of the guide portion 45 provided on the outer peripheral surface 44SA. The first bead portions 58 have a recessed first bead surface 58S relative to the second mold 28A.

[0067] The second mold 28A has a second molding surface 28SA on the side facing the first mold 26A, which corresponds to the first molding surface 26SA. The second molding surface 28SA has a concave bottom surface 50, a second inner inclined surface 52, a second outer inclined surface 54, and a second wall surface 56SA.

[0068] The second mold 28A has a plurality of second bead portions 60 on the second wall surface 56SA. The second bead portions 60 are located in positions corresponding to the first bead portions 58 and are provided complementary to the first bead portions 58. The second bead portions 60 have a second bead surface 60S that protrudes relative to the first mold 26.

[0069] The first bead portion 58 and the second bead portion 60, although not shown in the figure, form a plurality of bead portions that protrude outward from the wheel disc.

[0070] The mold 24A according to this modified example can obtain the same effects as the above embodiment because the guide surface 45S is provided on the guide portion 45.

[0071] In hot press forming, as deep drawing progresses and shrinkage flange deformation occurs at the outer edge 30P of the blank 30, a portion of the corrugated outer edge 30P moves along the guide surface 45S toward the central axis Z. At a position corresponding to the inner edge 44A of the outer peripheral surface 44SA, a large compressive force acts on the blank 30 in the circumferential direction, making it easy for the plate thickness to increase. The mold 24A in this modified example suppresses localized increases in plate thickness by allowing the material of the blank 30 to escape into the first bead portion 58 and the second bead portion 60. As a result, the mold 24A in this modified example and the method for manufacturing a wheel disc using the mold 24A can more reliably suppress the occurrence of wrinkles.

[0072] In the above embodiment, the wheel disc was described as having through holes in the annular inclined portion that are in the shape of a circular fan. However, the present invention is not limited to this, and the through holes may be circular or polygonal. Furthermore, although the above embodiment described as having four through holes formed in the annular inclined portion, the present invention is not limited to this, and there may be three or fewer, or five or more through holes. Moreover, the wheel disc does not need to have through holes in the annular inclined portion.

[0073] In the above embodiment, the case where the first mold is the upper mold and the second mold is the lower mold has been described, but the present invention is not limited to this, and the first mold may be the lower mold and the second mold may be the upper mold.

[0074] In the above embodiment, the first mold and the second mold were described as being circular when viewed from the central axis Z, but the present invention is not limited to this, and the first mold and the second mold may be rectangular when viewed from the central axis.

[0075] In the above embodiment, the top of the guide portion is described as being curved and protruding from the second mold when viewed from the outside of the first mold, but the present invention is not limited to this. The top of the guide portion may be the intersection of guide surfaces provided on both sides of the top in the circumferential direction. In this case, the guide portion is in the shape of an inverted triangle when viewed from the outside of the first mold. The top may also have a surface perpendicular to the central axis Z. In this case, the guide portion is in the shape of an inverted trapezoid when viewed from the outside of the first mold.

[0076] In the above embodiment, the case where the hot-press-formed product is a disc for an automobile wheel was described, but the present invention is not limited to this, and may be, for example, a part formed by deep drawing and having large irregularities in the direction of the central axis.

[0077] Furthermore, for example, the hot-pressed product may be the cover 68 of the torque converter 66, as shown in Figure 11. The cover 68 of the torque converter 66 shown in Figure 11 is filled with fluid. The cover 68 rotates in response to engine input from the front. The cover 68 has a front cover 70 positioned at the front and a rear cover 72 connected to the rear end of the front cover 70. Regarding the front cover 70, although the surface shape is not shown in Figure 11, both the front cover 70 and the rear cover 72 are substantially disc-shaped with a central axis Z, and are provided with a recess 74, an annular inclined portion 76, and a vertical wall portion 78 in order from the central axis Z outward. The cover 68 of the torque converter 66 according to this modified example can be manufactured using the same manufacturing method, mold, and manufacturing apparatus as in the above embodiment, and the same effects as in the above embodiment can be obtained.

[0078] The above embodiments describe the case of manufacturing a substantially disc-shaped hot press-formed product, but the present invention is not limited thereto. That is, the present invention is suitable for deep drawing, and the external shape in plan view is not particularly limited; for example, the external shape in plan view may be elliptical, rectangular, polygonal, etc.

[0079] In the above embodiment, the hot-pressed product was described as having a recess and an annular inclined portion formed to surround the recess in a plan view, but the present invention is not limited to this. For example, the present invention may be applied to a hot-pressed product having one or more recesses or one or more protrusions.

[0080] Furthermore, the present invention may be applied to a hot press-formed product having a convex portion and an annular recess formed to surround the convex portion. In this case, the first mold is provided with a recessed inner recess and a protruding outer peripheral convex portion relative to the second mold, and the outer peripheral convex portion may be provided to surround the inner recess. Alternatively, the second mold may be provided with a protruding inner convex portion and a recessed outer peripheral recess relative to the first mold, with the inner convex portion being positioned opposite the inner recess, and the outer peripheral recess being positioned opposite the outer peripheral convex portion and surrounding the inner convex portion. [Explanation of symbols]

[0081] 1 Wheel 2 rims 3 Drop section 4. Bead seat section 5. Flange section 6 Space 10 Wheel discs (hot press-formed products) 10A Outer surface 10B Inner surface 12 Hub mounting area (recess) 14 Annular inclined section 14A Inner edge 14B Outer edge 14S Slope 16 Peripheral fixing part (vertical wall part) 16A Upper edge 16B Lower edge 16S Cylindrical surface 18 Bottom 18A Outer edge 18S bottom 20 Inclined cylinder part 20A Lower edge 20B Upper edge 20S inclined cylinder surface 22 Through holes (wheel discs) 22P Through Hole (Blank) 22A Inner edge 22B Outer edge 24, 24A mold 26, 26A First mold 26S, 26SA 1st molding surface 28, 28A Second mold 28S, 28SA 2nd molding surface 30 Blank 30F 1st page 30R 2nd side 30C central part 30M outer circumference 30P outer edge 30E outer edge 30PH holding area 30PN non-retention area 32 Inner protrusion 34 Outer peripheral recess 36 Tip surface 36A Outer edge 38 1st inner slope 38A lower edge 38B Upper edge 40, 40SA 1st outer slope 40A inner edge 40B Outer edge 42, 42SA, Wall 1 42A Upper edge 42B Lower edge 44, 44SA outer surface 44A Inner edge 44B Outer edge 45 Guide section 45S Guide surface 46 Inner recess 47 Top 48 Outer peripheral protrusion 50 concave bottom 50A outer edge 52 2nd inner slope 52A Lower edge 52B Upper edge 54 Second outer slope 54A Inner edge 54B Outer edge 56, 56SA Second Wall 56A Upper edge 56B Lower edge 58 First Bead Section 58S First bead surface 60 Second bead section 60S Second bead surface 66 Torque Converter 68 Cover 70 Front Cover 72 Rear Cover 74 recess 76 Annular inclined section 78 Vertical wall section H1 Height (hub mounting part) H2 Height (ring-shaped inclined section) Z center axis α, β angles

Claims

1. A die for performing deep drawing by hot pressing on a heated blank, A first mold having a first molding surface and an outer peripheral surface disposed outside the first molding surface, The present invention comprises a second mold positioned opposite the first mold and having a second molding surface corresponding to the first molding surface, A guide portion is provided on the outer surface, The guide portion protrudes from the second mold and has a top portion that extends in a direction toward the inside of the first mold from the outer edge of the first mold. The mold for hot press forming has a pair of guide surfaces that are inclined from the top toward the outer peripheral surface on the side intersecting the extending direction of the top.

2. The top portion is inclined away from the second mold from the outer edge of the first mold toward the inside of the first mold, according to claim 1.

3. The first molding surface of the first mold is provided with an inner projection that protrudes relative to the second mold and an outer recess that is recessed, and the outer recess is provided so as to surround the inner projection. The second molding surface of the second mold is provided with an inner recess that is recessed relative to the first mold and an outer projection that protrudes, wherein the inner recess is positioned opposite the inner projection, and the outer projection is positioned opposite the outer recess and surrounds the inner recess. A mold for hot press forming according to claim 1 or 2.

4. The mold for hot press forming according to claim 3, wherein the inner protrusion is columnar, and the outer recess and the outer protrusion are annular.

5. The first mold is provided with a first bead portion at the connection point between the pair of guide surfaces and the outer peripheral surface. The second mold is provided with a second bead portion that forms a bead on the blank between itself and the first bead portion. A mold for hot press forming according to claim 1 or 2.

6. The mold according to claim 1 or 2, wherein a wheel disc is formed by the hot press described above.

7. A method for manufacturing a hot press-formed product using the mold according to Claim 1, The first step involves starting deep drawing press forming on a heated blank, The process includes a second step of performing a drawing press forming while restricting the circumferential movement of the blank with respect to at least a portion of the outer edge, including the outer edge of the blank, using the guide surface, after the blank has started to deform. A method for manufacturing hot-pressed products.

8. The method for manufacturing a hot press-formed product according to claim 7, wherein the deep drawing press forming includes deep drawing in which the central portion of the blank, which is inward from the outer edge, protrudes in one direction relative to the heated blank, and reverse deep drawing in which the outer periphery between the outer edge and the central portion protrudes in the opposite direction to the one direction.

9. The method for manufacturing a hot press-formed product according to claim 7 or 8, wherein the hot press-formed product is a wheel disc.

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