Hot forming die

Abstract

To provide a hot forming die capable of processing a workpiece with high accuracy and suppressing breakage of the workpiece due to overpressure.SOLUTION: The hot forming die 1 includes an outer die 2, an inner die 3, and a lower plate 4 as a regulating member. The outer mold 2 includes an inner surface 21 that defines an internal space R in which the workpiece MP is molded. The inner die 3 includes a first end surface 31 adjacent to the inner surface 21 and a second end surface 32 adjacent to the workpiece MP, and compresses the workpiece MP by thermal expansion during hot working. The lower plate 4 is a member which is disposed in the internal space R and thermally expands in a hot state, includes abutting surfaces 41, 42 abutting on the second end surface 32 from a direction opposite to a compression direction F of the workpiece MP by the inner die 3, and restricts thermal expansion of the inner die 3 within a predetermined range so that a dimension of the workpiece MP in the compression direction F becomes a predetermined value.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a die for hot forming a workpiece. [Background technology]

[0002] Hot forming using a mold is used to form various workpieces. For example, Patent Document 1 discloses a jig that sandwiches a stack of multiple plate materials between a fixing member, a thermal expansion plate, and a holding member from different directions, and diffusion-bonds the stack. In this jig, the expansion force of the thermal expansion plate during heating is used as a compressive force on the stack. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-43566 Summary of the Invention [Problem to be solved by the invention]

[0004] In hot forming, workpieces must be processed with high dimensional accuracy. The technique of using thermal expansion force, such as the jig in Patent Document 1, has the advantage of being able to transfer the inner shape of the mold to the workpiece by the action of compressive force due to thermal expansion. However, the compressive force may act excessively on the workpiece, causing damage to the workpiece.

[0005] An object of the present invention is to provide a hot forming die that can process a workpiece with high precision while suppressing damage to the workpiece due to overpressure. [Means for solving the problem]

[0006] A hot forming die according to one aspect of the present invention is a hot forming die for compression-molding a workpiece while hot, and comprises: an outer die including an inner surface defining an internal space in which the workpiece is molded; an inner die including a first end face adjacent to the inner surface and a second end face adjacent to the workpiece, and which thermally expands when hot to compress the workpiece; and a regulating member that is disposed in the internal space and thermally expands when hot, and which includes an abutment surface that abuts against the second end face from a direction opposite to the compression direction of the workpiece by the inner die, and which regulates the thermal expansion of the inner die within a predetermined range so that the dimensions of the workpiece in the compression direction become predetermined values.

[0007] According to this embodiment, the inner mold thermally expands during heating while being constrained by the outer mold. Therefore, when a workpiece is placed in the internal space that serves as the molding chamber and heated, a compressive force due to the thermal expansion of the inner mold acts on the workpiece, enabling highly accurate processing. In other words, the inner surface shape of the molding chamber can be transferred to the workpiece with precision. Meanwhile, a regulating member is also disposed in the internal space as another component that thermally expands during heating. The regulating member includes a contact surface that contacts the second end surface of the inner mold, allowing the thermal expansion of the inner mold to be restricted within a predetermined range. In other words, the thermal expansion of the inner mold is permitted up to a predetermined range, but thermal expansion beyond that range is restricted by the regulating member. Therefore, it is possible to set the dimensions of the workpiece to a predetermined value and prevent excessive pressure from being applied to the workpiece.

[0008] In the above-described hot forming die, it is desirable that the dimension of the regulating member in the cold state is set so that the dimension in the compression direction in the hot state is the same as the dimension of the workpiece in the compression direction.

[0009] According to this aspect, the dimensions of the restricting member in the hot state are the same as the dimensions of the workpiece after compression, so that the workpiece can be processed to the desired finished dimensions.

[0010] In the above-mentioned hot forming mold, when the temperature before hot forming is T, the temperature rise due to hot forming is ΔT, and the thermal expansion coefficients of the outer mold, the inner mold, and the regulating member in the temperature range from temperature T to temperature T + ΔT are α, β, and γ, respectively, it is desirable that the relationship of the following formula (1) be satisfied: β>α, γ>α (1)

[0011] According to this embodiment, since the relationship of formula (1) is satisfied, the inner mold and the restricting member undergo greater thermal expansion than the outer mold. That is, since the relationship between the thermal expansion coefficients of the inner mold and the outer mold is β>α, the workpiece can be compressed by the compressive force caused by the thermal expansion of the inner mold during hot working. Furthermore, since the relationship between the thermal expansion coefficients of the restricting member and the outer mold is γ>α, the restricting member is press-fit into the internal space during hot working. Therefore, the restricting member can restrict the thermal expansion of the inner mold during hot working.

[0012] In the above-mentioned hot forming die, when the cold dimensions are A, the dimension of the internal space in the compression direction of the outer die is B, and the dimension of the regulating member in the compression direction is C, the relationship of the following formula (2) is satisfied: B+C+(B×ΔT×β)+(C×ΔT×γ)>A+(A×ΔT×α) ···(2) It is desirable that the regulating member has a side surface along the compression direction, and that the side surface is in contact with the workpiece when hot, and is pressed into between the second end surface of the inner mold and the inner surface of the outer mold.

[0013] According to this embodiment, since the relationship of formula (2) is satisfied, the total thermal expansion of the inner mold and the restraining member is greater than the thermal expansion of the outer mold during hot working. Therefore, the restraining member is in a press-fit state during hot working, which can suppress excessive pressure on the workpiece due to the thermal expansion of the inner mold. Furthermore, the restraining member is in the press-fit state with its side surface abutting the workpiece. Therefore, when the workpiece is a stack of multiple plate materials and is to be diffusion bonded, it is possible to prevent the stack from becoming disorganized, buckling, or lifting up of the inner and outer molds.

[0014] The above-mentioned hot forming die may further include an alignment member arranged in the internal space, wherein the regulating member abuts against a first side surface of the workpiece facing a direction perpendicular to the compression direction, and the alignment member abuts against a second side surface of the workpiece opposite the first side surface.

[0015] According to this aspect, the workpiece is sandwiched between the restricting member and the aligning member in the internal space, so that, if the workpiece is, for example, a stack of multiple plate materials, it is possible to prevent the stack from becoming disarrayed or buckling.

[0016] In the above hot forming die, the matching member is a member that thermally expands when hot, and includes an opposing surface that abuts against the inner die from a direction opposite to the compression direction of the workpiece by the inner die, and satisfies the relationship of the following formula (3), where D is the dimension of the matching member in the compression direction and δ is its thermal expansion coefficient: B+D+(B×ΔT×β)+(D×ΔT×δ)>A+(A×ΔT×α) ···(3) It is desirable that the alignment member be pressed between the second end surface of the inner mold and the inner surface of the outer mold when hot, with the opposing surface abutting the workpiece along the compression direction.

[0017] According to this embodiment, since the relationship of formula (3) is satisfied, the total thermal expansion of the inner mold and the matching member is greater than the thermal expansion of the outer mold during hot working. Therefore, the matching member is pressed into the workpiece during hot working, which further effectively prevents the workpiece from being distorted or buckled.

[0018] In the above-mentioned hot forming die, the inner die may include a first inner die arranged adjacent to a first pressure-receiving surface in the compression direction of the workpiece, and a second inner die arranged adjacent to a second pressure-receiving surface opposite the first pressure-receiving surface, and the regulating member may include a first abutment surface abutting the second end surface of the first inner die, and a second abutment surface abutting the second end surface of the second inner die.

[0019] According to this embodiment, the workpiece is sandwiched between the first inner die and the second inner die. Therefore, compressive forces can be easily applied to the workpiece in a balanced manner from both the first pressure-receiving surface and the second pressure-receiving surface. Furthermore, since both of these inner dies abut against the restricting member, thermal expansion is restricted, and excessive pressure can be prevented from being applied to the workpiece.

[0020] In the above-mentioned hot forming mold, it is desirable that the inner mold further includes a third inner mold arranged adjacent to a third side surface facing a direction perpendicular to the compression direction of the workpiece, and that the regulating member also regulates the thermal expansion of the third inner mold within a predetermined range so that the dimensions of the workpiece in the direction perpendicular to the compression direction become predetermined values.

[0021] According to this aspect, the third inner die can apply a compressive force to the workpiece from the third side surface perpendicular to the compression direction. The restricting member also restricts the thermal expansion of the third inner die within a predetermined range. This improves the dimensional accuracy of the workpiece in the perpendicular direction and suppresses excessive pressure in the perpendicular direction.

[0022] In the above-mentioned hot forming die, the inner die may further include a fourth inner die arranged adjacent to a fourth side surface that is perpendicular to both the first pressure-receiving surface and the second pressure-receiving surface of the workpiece and the third side surface.

[0023] According to this embodiment, it is possible to enclose the workpiece with the inner mold, thereby enabling more accurate machining.

[0024] The hot forming die may further include a pressing mechanism that presses the alignment member toward the workpiece.

[0025] According to this aspect, the workpiece can be pressed through the alignment member, that is, the alignment member can also be used as a mold member that applies a compressive force to the workpiece. [Effects of the Invention]

[0026] According to the present invention, it is possible to provide a hot forming die that can process a workpiece with high precision while suppressing damage to the workpiece due to overpressure. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 is a plan view showing a hot forming die according to a first embodiment of the present invention. [Figure 2] FIG. 2 is an exploded plan view of the hot forming die of the first embodiment. [Figure 3] 3A is a cross-sectional view taken along line IIIA-IIIA in FIG. 1, and FIG. 3B is a cross-sectional view taken along line IIIB-IIIB in FIG. 3A. [Figure 4] FIG. 4 is a cross-sectional view showing how a stack of multiple plate materials buckles during hot forming. [Figure 5] FIG. 5 is a cross-sectional view showing a modified example of the first embodiment. [Figure 6] FIG. 6(A) is a plan view of a hot forming die according to the second embodiment, FIG. 6(B) is a cross-sectional view taken along line VIB-VIB in FIG. 6(A), and FIG. 6(C) is a cross-sectional view taken along line VIC-VIC in FIG. 6(A). [Figure 7] FIG. 7 is a plan view showing a modified example of the second embodiment. [Figure 8] FIG. 8 is a partially cutaway plan view of a hot-forming die according to the third embodiment. [Figure 9] 9A is a cross-sectional view taken along line IXA-IXA in FIG. 8, and FIG. 9B is a cross-sectional view taken along line IXB-IXB in FIG. [Figure 10] FIG. 10 is a plan view showing a modified example of the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0028] Embodiments of the present invention will be described in detail below with reference to the drawings. The hot-forming die according to the present invention can be used at high temperatures ranging from several hundred degrees Celsius to 2,000 degrees Celsius and can be used in various hot-forming processes for workpieces. Among hot-forming processes, the die is particularly suitable for diffusion bonding, which bonds different or identical materials. During diffusion bonding, the die loaded with the workpiece can be heated in a heating furnace or induction heating furnace in an appropriate atmospheric environment without applying a press load, utilizing internal stress due to thermal expansion. Alternatively, a hot press can be used as an auxiliary to achieve stronger diffusion bonding. In the latter case, the surface perpendicular to the compression direction of the workpiece is hot-pressed. The hot-forming die according to the present invention enables forming without the use of a hot press, thereby reducing equipment and forming costs. Even when a hot press is used, it is used only as an auxiliary, simplifying equipment. Furthermore, the die according to the present invention can improve the dimensional accuracy after hot forming to a level that eliminates or reduces the need for post-processing. Examples of the workpiece include sintered parts, clad materials, cast parts, and powders.

[0029] [First embodiment] FIG. 1 is a plan view of the lower surface of a hot-forming die 1 according to a first embodiment of the present invention, and FIG. 2 is an exploded plan view of the hot-forming die 1. FIG. 3(A) is a cross-sectional view taken along line IIIA-IIIA in FIG. 1, and FIG. 3(B) is a cross-sectional view taken along line IIIB-IIIB in FIG. 3(A). The hot-forming die 1 is used to compression-form a workpiece MP in a hot state. Here, an example is shown in which the workpiece MP, which is a stack of multiple plate materials P, is diffusion-bonded using the die 1. Directions X, Y, and Z are indicated in FIGS. 1 to 3 and the following drawings. The X direction is the compression direction of the workpiece MP, the Y direction is the width direction of the workpiece MP perpendicular to the X direction, and the Z direction is the direction perpendicular to both the X and Y directions. Note that +Z is sometimes referred to as up and -Z as down, but this is for convenience of explanation and does not limit the manner in which the die 1 is used.

[0030] <Mold configuration> The mold 1 includes an outer mold 2, an inner mold 3, a lower plate 4 (regulating member), and an upper plate 5 (aligning member). The outer mold 2 is made of, for example, graphite and has a rectangular frame shape in a plan view. The outer mold 2 has an inner surface 21 that defines an internal space R in which the workpiece MP is molded. The inner surface 21 has a rectangular shape that is long in the X direction in a plan view. The area of ​​the internal space R excluding the -X end and +X end becomes a molding area RA in which the workpiece MP is compression molded. A plurality of plate materials P are arranged in the X direction and placed in the molding area RA.

[0031] The inner die 3 is made of, for example, cemented carbide and has a rectangular parallelepiped shape. The inner die 3 is placed in the internal space R and functions to compress the workpiece MP by thermally expanding when hot. The inner die 3 includes a first end face 31 adjacent to the inner surface 21 of the outer die 2 and a second end face 32 adjacent to the workpiece MP. Here, "adjacent" not only refers to a state in which the first end face 31 and the second end face 32 are always in contact with each other, but also includes a state in which there is a gap between them when cold but they are in contact when hot.

[0032] In this embodiment, the inner mold 3 is configured as a pair of a first inner mold 3A disposed on the -X side of the internal space R and a second inner mold 3B disposed on the +X side. The first inner mold 3A is disposed adjacent to a first pressure-receiving surface MP1, which is one side of the workpiece MP in the compression direction, i.e., the -X side. The second inner mold 3B is disposed adjacent to a second pressure-receiving surface MP2, which is the side of the workpiece MP opposite the first pressure-receiving surface MP1, i.e., the +X side. During hot processing, due to thermal expansion of the first inner mold 3A, the first end surface 31 of the first inner mold 3A abuts against the inner surface 21 on the -X side of the outer mold 2, and the second end surface 32 presses against the first pressure-receiving surface MP1. Furthermore, the first end surface 31 of the second inner mold 3B abuts against the inner surface 21 on the +X side of the outer mold 2, and the second end surface 32 presses against the second pressure-receiving surface MP2.

[0033] The lower plate 4 is made of, for example, a ceramic plate and has a rectangular shape elongated in the X direction in plan view. The lower plate 4 is disposed in the internal space R and thermally expands when heated. The lower plate 4 is disposed between the first inner mold 3A and the second inner mold 3B and below the workpiece MP. The lower plate 4 includes a first contact surface 41 and a second contact surface 42 that contact the second end surface 32 of the inner mold 3 from the direction opposite to the compression direction F of the workpiece MP by the inner mold 3. The lower plate 4 restricts the thermal expansion of the inner mold 3 within a predetermined range so that the dimensions of the workpiece MP in the compression direction F, i.e., the X direction, are predetermined values.

[0034] Specifically, the first contact surface 41 faces the second end surface 32 of the first inner die 3A, which applies a compressive force to the first pressure-receiving surface MP1 of the workpiece MP. In the hot state, the compression direction F of the second end surface 32 of the first inner die 3A is the +X direction. The first contact surface 41 presses the second end surface 32 from the opposite -X direction. In the hot state, the compression direction F of the second end surface 32 of the second inner die 3B is the -X direction. The second contact surface 42 presses the second end surface 32 in the +X direction. The upper side surface 43 of the lower plate 4 abuts against the first side surface MP3, which faces the -Z direction, which is perpendicular to the compression direction F of the workpiece MP.

[0035] The upper plate 5 is formed, for example, from a ceramic plate and, like the lower plate 4, has a rectangular shape elongated in the X direction in plan view. The upper plate 5 is located between the first inner mold 3A and the second inner mold 3B in the internal space R and above the workpiece MP. The -X and +X side surfaces of the upper plate 5 are abutment surfaces 51 that face the second end surfaces 32 of the first inner mold 3A and the second inner mold 3B, respectively. The opposing surface 52, which is the lower surface of the upper plate 5, abuts against the side of the workpiece MP facing the +Z direction, i.e., the second side surface MP4 opposite the first side surface MP3. The upper plate 5 is also preferably made of a material that thermally expands when hot. In this case, the abutment surface 51 abuts against the second end surface 32 from the direction opposite to the compression direction F.

[0036] <Mold behavior and desirable characteristics of mold constituent materials> With the mold 1 having the above configuration, during heating, the inner mold 3 thermally expands while its periphery is constrained by the outer mold 2. The workpiece MP is accommodated in a molding chamber corresponding to the molding area RA. This molding chamber is defined by the inner surface 21 of the outer mold 2, the second end surfaces 32 of the first inner mold 3A and the second inner mold 3B, the upper surface 43 of the lower plate 4, and the opposing surface 52 of the upper plate 5. When the workpiece MP is accommodated in the molding area RA and heated, a compressive force due to the thermal expansion of the inner mold 3 acts on the workpiece MP, allowing for highly accurate processing. In other words, the inner shape of the molding chamber can be accurately transferred to the workpiece.

[0037] Meanwhile, a lower plate 4, an example of a restricting member, is also disposed in the internal space R as another member that thermally expands when heated. The lower plate 4 includes a first contact surface 41 and a second contact surface 42 that respectively contact the second end surface 32 of the inner mold 3, and is press-fit between the pair of second end surfaces 32 when thermally expanded when heated. The lower plate 4 restricts the thermal expansion of the inner mold 3 within a predetermined range. In other words, the thermal expansion of the inner mold 3 is permitted up to a predetermined range, but thermal expansion beyond this range is restricted by the lower plate 4. If there is no member that is press-fit between the pair of inner molds 3A and 3B, the inner molds 3A and 3B will thermally expand without restriction according to their inherent thermal behavior. In this case, excessive compressive load acts on the workpiece MP, potentially damaging the workpiece MP. However, in this embodiment, the lower plate 4 regulates the thermal expansion of the inner molds 3A and 3B, so it is possible to set the dimensions of the workpiece MP to a predetermined value while preventing excessive pressure from being applied to the workpiece MP.

[0038] The cold dimensions of the lower plate 4 are desirably set so that the dimensions in the compression direction F when hot are the same as the dimensions of the workpiece MP in the compression direction F. In other words, the finished dimensions of the workpiece MP in the compression direction F when hot are made the same as the dimensions of the lower plate 4 after thermal expansion. This restricts the thermal expansion of the inner dies 3A, 3B to a range in which the distance between the pair of second end faces 32 of the inner dies 3A, 3B when hot is the same as the dimensions of the workpiece MP after compression. As a result, the workpiece MP can be machined to the desired finished dimensions, i.e., highly accurate machining can be performed.

[0039] Next, the desirable relationship between the thermal expansion coefficients of the outer mold 2, inner mold 3, and lower plate 4 will be shown. The temperature before hot forming is T, the temperature rise due to hot forming is ΔT, and the thermal expansion coefficients of the outer mold 2, inner mold 3, and lower plate 4 in the temperature range from temperature T to temperature T + ΔT are α, β, and γ, respectively. In this case, it is desirable to satisfy the relationship of the following formula (1). β>α, γ>α (1)

[0040] When the relationship of Equation (1) is satisfied, the inner mold 3 and the lower plate 4 undergo greater thermal expansion than the outer mold 2. In other words, since the thermal expansion coefficients of the inner mold 3 and the outer mold 2 have a relationship of β > α, the workpiece MP can be compressed by the compressive force caused by the thermal expansion of the inner mold 3 during heating. In other words, while the thermal expansion of the first end face 31 of the inner mold 3 is restricted by the inner surface 21 of the outer mold 2, the second end face 32 presses the pressure-receiving surfaces MP1 and MP2 of the workpiece MP in the compression direction F. Meanwhile, since the thermal expansion coefficients of the lower plate 4 and the outer mold 2 have a relationship of γ > α, the lower plate 4 is pressed into the internal space R during heating. Therefore, the lower plate 4 can restrict the thermal expansion of the inner mold 3 during heating. The relationship between the thermal expansion coefficient β of the inner mold 3 and the thermal expansion coefficient γ of the lower plate 4 is arbitrary. β and γ are selected appropriately depending on the amount of restriction of the thermal expansion of the inner mold 3.

[0041] The desirable dimensional relationship between the outer die 2, inner die 3, and lower plate 4 is as follows. Referring to FIG. 3(A), the dimensions in the compression direction F during cold operation are defined as A, B, and C, respectively, for the dimension of the internal space R of the outer die 2, B for the inner die 3, and C for the lower plate 4. In this embodiment, the dimension B of the inner die 3 is the sum of the dimension B1 of the first inner die 3A and the dimension B2 of the second inner die 3B in the compression direction F. In this case, it is desirable to satisfy the relationship of the following formula (2): B+C+(B×ΔT×β)+(C×ΔT×γ)>A+(A×ΔT×α) ···(2)

[0042] When the relationship of formula (2) is satisfied, the total thermal expansion of the inner mold 3 and the lower plate 4 is greater than the thermal expansion of the outer mold 2 during hot processing. Therefore, during hot processing, the lower plate 4 is press-fit between the pair of inner molds 3A and 3B. This prevents excessive pressure from being applied to the workpiece MP due to the thermal expansion of the inner molds 3A and 3B.

[0043] Furthermore, satisfying the relationship of Equation (2) can suppress misalignment and buckling of the workpiece MP, which is a stack of plate materials P, during diffusion bonding. Figure 4 is a cross-sectional view showing how the workpiece MP, which is composed of multiple plate materials P stacked in the compression direction F, buckles during hot forming. Figure 4 illustrates a comparative example in which the plate 400 disposed between the pair of inner molds 3A and 3B is not pressed into place during hot forming, i.e., the relationship of Equation (2) is not satisfied. Because the plate 400 does not function as a stopper against the thermal expansion of the inner molds 3A and 3B, the workpiece MP is subjected to excessive pressure. As a result, as illustrated in Figure 4, the center of the stack of plate materials P rises, causing the workpiece MP to buckle upward, convex. Contrary to the example in Figure 4, if the workpiece MP buckles downward, the inner molds 3A and 3B and the outer mold 2 will be lifted.

[0044] In this embodiment, the lower plate 4, which is disposed between the pair of inner molds 3A, 3B, is in a press-fit state during hot working, so that excessive pressure is not applied to the workpiece MP. This makes it possible to suppress the misalignment of the plate material P and the buckling of the workpiece MP. In particular, the lower plate 4 has an upper surface 43 that extends along the compression direction F, and this upper surface 43 is disposed so as to abut against the first side surface MP3 of the workpiece MP. Therefore, in addition to being in a press-fit state as described above, the lower plate 4 directly restricts the movement of the workpiece MP in the -Z direction, making it easier to suppress the misalignment and buckling.

[0045] One purpose of placing the upper plate 5 in the internal space R in addition to the lower plate 4 is to further suppress the disordering of the sheet materials P and the buckling of the workpieces MP. The upper plate 5 has an opposing surface 52 extending along the compression direction F, and is positioned so that this opposing surface 52 abuts against the second side surface MP4 of the workpieces MP. In other words, the upper plate 5 directly restricts the movement of the workpieces MP in the +Z direction. As a result, the workpieces MP are sandwiched between the lower plate 4 on the -Z side and the upper plate 5 on the +Z side in the internal space R. Therefore, the disordering of the workpieces MP, which are a stack of multiple sheet materials P, and the buckling of the workpieces MP can be effectively suppressed.

[0046] It is desirable that the upper plate 5 also thermally expands when hot and is pressed into the pair of inner dies 3A, 3B. As described above, the upper plate 5 has an abutment surface 51 that abuts against the inner dies from the direction opposite to the compression direction F of the workpiece MP by the inner dies 3A, 3B. In this case, it is desirable that the relationship of the following formula (3) be satisfied, where D is the dimension of the upper plate 5 in the compression direction F and δ is the thermal expansion coefficient. Similarly to formula (2), the dimension B of the inner die 3 is the sum of the dimension B1 of the first inner die 3A and the dimension B2 of the second inner die 3B in the compression direction F. B+D+(B×ΔT×β)+(D×ΔT×δ)>A+(A×ΔT×α) ···(3)

[0047] By satisfying the relationship of formula (3), the upper plate 5 is pressed between the second end faces 32 of the pair of inner dies 3A, 3B when hot, with the opposing surface 52 abutting against the second side surface MP4 of the workpiece MP along the compression direction F. In other words, the total amount of thermal expansion of the inner die 3 and the upper plate 5 is greater than the amount of thermal expansion of the outer die 2 when hot. By pressing the upper plate 5 into the pressed state when hot, buckling and other problems of the workpiece MP can be more effectively suppressed.

[0048] The upper plate 5 may be a plate that is not press-fitted when hot. In other words, a gap may be formed between the abutment surface 51 and the second end surface 32 when hot. In this case, it is desirable to provide a pressing mechanism that presses the upper plate 5 in the -Z direction. Furthermore, if the placement of the lower plate 4 can sufficiently suppress buckling of the workpiece MP, the placement of the upper plate 5 in the internal space R may be omitted.

[0049] <Modification of the first embodiment> Fig. 5 is a cross-sectional view showing a hot-forming die 1A according to a modified example of the first embodiment. In the embodiment shown in Figs. 1 to 3(B), an example is shown in which the inner die 3 is configured as a pair of a first inner die 3A on the -X side and a second inner die 3B on the +X side, which are arranged to sandwich the workpiece MP. The inner die 3 may be arranged at either the -X side end or the +X side end of the workpiece MP. The modified example of Fig. 5 shows an example in which one inner die 3 is arranged only at the +X side end of the workpiece MP.

[0050] Similar to the second inner die 3B of the previously described die 1, the inner die 3 of the die 1A has a first end face 31 adjacent to the inner face 21 of the outer die 2 and a second end face 32 adjacent to the second pressure-receiving face MP2 of the workpiece MP. Meanwhile, the first pressure-receiving face MP1 on the -X side is adjacent to the inner face 21 on the -X side of the outer die 2. The inner die 3 thermally expands when heated, pressing the workpiece MP in the compression direction F. In this case, the compression direction F is only the -X direction. The configuration of this modified example can be adopted when sufficient compressive force can be generated by the thermal expansion of one inner die 3.

[0051] In the mold 1A, the lower plate 4 is press-fit between the second end surface 32 of the inner mold 3 and the inner surface 21 of the outer mold 2 during hot working. The second abutment surface 42 of the lower plate 4 faces the second end surface 32 of the inner mold 3, as in the previously described mold 1. Meanwhile, the first abutment surface 41 directly faces the inner surface 21 on the -X side of the outer mold 2. During hot working, the lower plate 4 thermally expands, and the first abutment surface 41 abuts against the inner surface 21, and the second abutment surface 42 abuts against the second end surface 32, thereby restricting the thermal expansion of the inner mold 3 within a predetermined range. In this way, the press-fit state of the lower plate 4 may be formed such that the first abutment surface 41 abuts directly against the inner surface 21, as in this modified example, or such that the first abutment surface 41 abuts indirectly against the inner surface 21 via the first inner mold 3A, as in the first embodiment.

[0052] The upper plate 5 of the mold 1A is also desirably press-fit between the second end face 32 of the inner mold 3 and the inner surface 21 of the outer mold 2 during hot working. That is, it is desirable that the abutment surface 51 on the -X side abuts against the inner surface 21 and the abutment surface 51 on the +X side abuts against the second end face 32, thereby enhancing the buckling prevention of the workpiece MP. In this way, the press-fit state of the upper plate 5 may be formed such that the abutment surface 51 on the -X side abuts against the inner surface 21 directly, or may be formed such that the abutment surface 51 on the -X side abuts against the inner surface 21 indirectly via the first inner mold 3A.

[0053] <Ease of removal after molding> After hot forming, when the mold 1 or mold 1A is cooled, the outer mold 2, inner mold 3, and lower plate 4 undergo thermal contraction. If the relationship of the above formula (1) regarding the thermal expansion coefficient is satisfied, the pressed-in state is released due to the difference in thermal contraction between the outer mold 2, the inner mold 3, and the lower plate 4. The workpiece MP itself also undergoes thermal contraction. Therefore, the workpiece MP can be easily removed from the mold 1 or 1A after forming. This also applies to the embodiments described below.

[0054] [Second embodiment] Fig. 6(A) is a plan view of a hot forming die 1B according to a second embodiment, Fig. 6(B) is a cross-sectional view taken along line VIB-VIB in Fig. 6(A), and Fig. 6(C) is a cross-sectional view taken along line VIC-VIC in Fig. 6(A). The die 1B comprises an outer die 2, an inner die 3, a lower plate 4 (regulating member), and an upper plate 5 (aligning member). The difference from the die 1 of the first embodiment is that the inner die 3 includes a pair of third inner die 3C in addition to a first inner die 3A and a second inner die 3B.

[0055] The pair of third inner dies 3C are made of, for example, cemented carbide and have a rectangular parallelepiped shape elongated in the X direction. The X-direction length of the third inner dies 3C is slightly shorter than the X-direction length of the inner surface 21 of the outer die 2, and the Z-direction length is equal to the Z-direction length of the inner surface 21. The workpiece MP has a third side surface MP5 facing in the Y direction, which is perpendicular to the compression direction F. The +Y-side third inner dies 3C are adjacent to the +Y-side third side surface MP5, and the -Y-side third inner dies 3C are adjacent to the -Y-side third side surface MP5. The pair of third inner dies 3C can apply a compressive force in the Y direction (compression direction FY) to the workpiece MP from the third side surface MP5 facing in the Y direction, which is perpendicular to the compression direction F. This improves the dimensional accuracy of the workpiece MP in the Y direction.

[0056] The third inner mold 3C has a third end surface 33 and a fourth end surface 34 facing in the Y direction. The third end surface 33 is adjacent to the inner surface 21 of the outer mold 2. The fourth end surface 34 defines a portion of the forming area RA of the workpiece MP and is adjacent to the third side surface MP5 of the workpiece MP and the Y sides of the lower plate 4 and upper plate 5. The third inner mold 3C thermally expands in the Y direction during heating, compressing the third side surface MP5 of the workpiece MP. However, since the lower plate 4 also thermally expands in the Y direction, the third inner mold 3C is in a press-fit state, restricting its thermal expansion within a predetermined range. Desirably, the cold dimensions of the lower plate 4 are set so that the Y-direction dimension of the workpiece MP during heating is a predetermined value in the Y direction. This improves the dimensional accuracy of the workpiece MP in the Y direction. It also prevents excessive pressure from being applied to the workpiece MP from the Y direction.

[0057] In the hot forming die 1B of the second embodiment, one of the pair of third inner dies 3C may be omitted. In this case, either the third side surface MP5 on the +Y side or the -Y side of the workpiece MP will abut against the inner surface 21 of the outer die 2 during hot forming. If dimensional accuracy in the Y direction is not required, a gap may be provided between the third side surface MP5 and the inner surface 21. This allows the compressed and deformed portion of the workpiece MP to escape into the gap when the workpiece MP is compressed due to thermal expansion of the first inner die 3A and the second inner die 3B.

[0058] The member that restricts the thermal expansion of the third inner mold 3C in the Y direction may be the upper plate 5. In this case, the upper plate 5 is press-fit between the pair of third inner molds 3C in the Y direction when hot. Furthermore, the X-direction dimension of the third inner mold 3C may be reduced to approximately the same as the X-direction dimension of the workpiece MP, or the Y-direction dimension of the first inner mold 3A and the second inner mold 3B may be set shorter than the Y-direction dimension of the workpiece MP.

[0059] 7 is a plan view showing a hot-forming die 1C according to a modified example of the second embodiment. Unlike the die 1B described above, the die 1C does not include the third inner die 3C on the +Y side. Instead, a pressing mechanism 6 is attached to the first side surface MP3 on the +Y side of the workpiece MP. The +Y side surfaces of the first inner die 3A and the second inner die 3B are adjacent to the inner surface 21 of the outer die 2.

[0060] The pressing mechanism 6 includes a first pressing plate 61, a second pressing plate 62, and a spring 63. The first pressing plate 61 contacts the inner surface 21 of the outer mold 2. The second pressing plate 62 contacts the third side surface MP5 on the +Y side of the workpiece MP. The spring 63 is disposed between the first pressing plate 61 and the second pressing plate 62 and biases both plates. That is, the biasing force of the spring 63 presses the first pressing plate 61 against the inner surface 21 and the second pressing plate 62 against the third side surface MP5. According to the modified mold 1C, even if the third inner mold 3C is disposed only on one of the third side surfaces MP5, the pressing force of the pressing mechanism 6 can ensure the alignment of the sheet material P on the other third side surface MP5. Note that the spring 63 may be replaced with a cushioning material or elastic member having compressive recovery properties.

[0061] [Third embodiment] FIG. 8 is a partially cutaway plan view of a hot-forming die 1D according to a third embodiment. FIG. 9(A) is a cross-sectional view taken along line IXA-IXA in FIG. 8, and FIG. 9(B) is a cross-sectional view taken along line IXB-IXB in FIG. 8. The die 1D includes an outer guide 71 and a cushion block 72 in addition to the die 1B of the second embodiment shown in FIG. 6. As shown in FIG. 9(A), the workpiece MP includes a second side surface MP4 that faces the Z direction and is perpendicular to both the pressure-receiving surfaces MP1 and MP2 and the third side surface MP5. The outer guide 71 and the cushion block 72 are positioned to apply a compressive force to the second side surface MP4 via the upper plate 5. In other words, the upper plate 5, together with the first inner mold 3A, the second inner mold 3B, and the third inner mold 3C, functions as a fourth inner mold that applies a compressive force to the workpiece MP. The outer guide 71 and the cushion block 72 function as a pressing mechanism that presses the upper plate 5 toward the workpiece MP.

[0062] The outer guide 71 is a block having a hollow portion through which the mold 1B is inserted in the X direction and capable of accommodating the cushion block 72. The outer guide 71 may be made of any material having a predetermined strength, such as a carbon-based material, a carbon fiber-reinforced carbon composite, ceramics, cemented carbide, hot work die steel, or stainless steel. The cushion block 72 is made of a material having a predetermined strength and a thermal expansion coefficient greater than that of the outer guide 71. Due to this difference in thermal expansion, a compressive force can be applied from the cushion block 72 to the second side surface MP4 via the upper plate 5 during hot working. The cushion block 72 may be made of, for example, a carbon-based composite, a ceramic-based composite, cemented carbide, or hot work die steel.

[0063] The cushion block 72 includes a first surface 721 on the +Z side and a second surface 722 on the -Z side. The first surface 721 is adjacent to the inner surface 711 on the +Z side of the outer guide 71. The X-direction dimension of the cushion block 72 is longer than the X-direction dimension of the workpiece MP, with the -X end overlapping the upper surface 35 of the first inner die 3A and the +X end overlapping the upper surface 35 of the second inner die 3B. The second surface 722 abuts against the upper surface of the upper plate 5. A gap G exists between the second surface 722 and the upper surface 35 of each of the first inner die 3A and the second inner die 3B in the cold state as a compression allowance.

[0064] As explained in the second embodiment, during hot working, the first inner mold 3A and the second inner mold 3B apply a pressing force in the X direction (compression direction F) to the pressure-receiving surfaces MP1 and MP2, and the pair of third inner molds 3C apply a pressing force in the Y direction (compression direction FY) to the third side surface MP5, compressing the workpiece MP. In addition, the fourth inner mold, consisting of the outer guide 71, cushion block 72, and upper plate 5, applies a pressing force in the Z direction (compression direction FZ) to the second side surface MP4. In other words, the workpiece MP is compressed from three directions: X, Y, and Z. This improves the processing accuracy of the entire surface of the workpiece MP.

[0065] The amount of thermal expansion of the cushion block 72 in the Z direction is restricted to the length of the gap G. That is, the first surface 721 of the cushion block 72 abuts against the inner surface 711 of the outer guide 71, restricting its expansion, so only the second surface 722 thermally expands in the -Z direction. However, once the cushion block 72 thermally expands by the length of the gap G, the second surface 722 abuts against the upper surface 35, restricting further thermal expansion. Therefore, no overpressure acts on the second side surface MP4 of the workpiece MP.

[0066] FIG. 10 is a cross-sectional view showing a hot-forming die 1E according to a modified example of the third embodiment. The die 1E uses a pressing member 73 that integrates the upper plate 5 and cushion block 72 of the die 1D described above. The pressing member 73 includes a protrusion 731 protruding in the -Z direction and a shoulder 732 that serves as the protrusion base of the protrusion 731. The protrusion 731 has an X-direction dimension that allows it to fit between the pair of inner dies 3A and 3B. The shoulder 732 is connected to the -X and +X sides of the protrusion 731 and faces the upper surfaces 35 of the inner dies 3A and 3B. The upper surface 733 of the pressing member 73 is adjacent to the inner surface 711 of the outer guide 71, and the lower surface 734 abuts against the second side surface MP4 of the workpiece MP. A gap G, which serves as a compression allowance, exists between the shoulder 732 and the upper surface 35 in the cold state.

[0067] The thermal expansion coefficient of the pressing member 73 is set to be larger than that of the outer guide 71. When heated, the pressing member 73 thermally expands, and the lower surface 734 applies a pressing force to the second side surface MP4 in the Z direction, which is the compression direction FZ. The amount of thermal expansion of the pressing member 73 in the Z direction is restricted to the length of the gap G. When the pressing member 73 thermally expands by the length of the gap G, the shoulder portion 732 abuts against the upper surface 35, so further thermal expansion is restricted. Therefore, no excessive pressure acts on the second side surface MP4 of the workpiece MP. [Explanation of symbols]

[0068] 1, 1A~1E Hot forming mold 2 Outer mold 21 Inner 3 Inner mold 3A, 3B, 3C 1st inner mold, 2nd inner mold, 3rd inner mold 31 First end surface 32 Second end face 33 Third end face 34 4th end face 35 Top 4 Lower plate (regulating member) 41 First contact surface 42 Second contact surface 5 Upper plate (alignment member / fourth inner die) 52 Opposite surface 6 Pressing mechanism 71 Outer guide 72 Cushion block (pressure mechanism) F Compression direction MP work material MP1, MP2 First pressure receiving surface, second pressure receiving surface MP3, MP4 1st side, 2nd side (4th side) MP5 3rd side R Interior space

Claims

1. A hot forming die for compression molding a workpiece in a hot state, an outer mold including an inner surface defining an interior space into which the workpiece is molded; an inner mold including a first end surface adjacent to the inner surface and a second end surface adjacent to the workpiece, the inner mold thermally expanding when heated to compress the workpiece; a restricting member that is disposed in the internal space and that thermally expands when hot, the restricting member including a contact surface that contacts the second end surface from a direction opposite to the compression direction of the workpiece by the inner mold, and that restricts the thermal expansion of the inner mold within a predetermined range so that the dimension of the workpiece in the compression direction becomes a predetermined value; A hot forming die comprising:

2. The hot forming die according to claim 1, A hot forming die, wherein the dimension of the regulating member in the cold state is set so that the dimension in the compression direction in the hot state is the same as the dimension of the workpiece in the compression direction.

3. The hot forming die according to claim 2, A hot forming mold that satisfies the relationship of the following formula (1), where T is the temperature before hot forming, ΔT is the temperature rise due to hot forming, and α, β, and γ are the thermal expansion coefficients of the outer mold, the inner mold, and the regulating member in the temperature range from temperature T to temperature T+ΔT, respectively. β>α, γ>α ...(1)

4. The hot forming die according to claim 3, As dimensions in a cold state, when the dimension of the internal space of the outer mold in the compression direction is A, the dimension of the inner mold in the compression direction is B, and the dimension of the regulating member in the compression direction is C, the relationship of the following formula (2) is satisfied, B+C+(B×ΔT×β)+(C×ΔT×γ)>A+(A×ΔT×α)...(2) The regulating member has a side surface along the compression direction, and is pressed into between the second end surface of the inner mold and the inner surface of the outer mold with the side surface abutting the workpiece when hot.

5. The hot forming die according to claim 3 or 4, further comprising an alignment member disposed in the internal space, A hot forming die, wherein the regulating member is arranged in the internal space so as to abut against a first side surface of the workpiece facing a direction perpendicular to the compression direction, and the alignment member is arranged in the internal space so as to abut against a second side surface of the workpiece opposite the first side surface.

6. The hot forming die according to claim 5, the aligning member is a member that thermally expands when hot, and includes an opposing surface that abuts against the inner die from a direction opposite to a compression direction of the workpiece by the inner die, When the dimension of the matching member in the compression direction is D and the thermal expansion coefficient is δ, the relationship of the following formula (3) is satisfied: B+D+(B×ΔT×β)+(D×ΔT×δ)>A+(A×ΔT×α)...(3) The alignment member is pressed between the second end surface of the inner mold and the inner surface of the outer mold with the opposing surface abutting the workpiece along the compression direction during hot forming.

7. The hot forming die according to any one of claims 1 to 4, the inner mold includes a first inner mold disposed adjacent to a first pressure-receiving surface in the compression direction of the workpiece, and a second inner mold disposed adjacent to a second pressure-receiving surface opposite to the first pressure-receiving surface, The regulating member includes a first contact surface that contacts the second end surface of the first inner mold and a second contact surface that contacts the second end surface of the second inner mold.

8. The hot forming die according to claim 7, The inner mold further includes a third inner mold disposed adjacent to a third side surface facing a direction perpendicular to the compression direction of the workpiece, The regulating member also regulates the thermal expansion of the third inner die within a predetermined range so that the dimension of the workpiece in a direction perpendicular to the compression direction becomes a predetermined value.

9. The hot forming die according to claim 8, The hot forming die, wherein the inner die further includes a fourth inner die arranged adjacent to a fourth side surface that is perpendicular to both the first pressure-receiving surface and the second pressure-receiving surface of the workpiece and the third side surface.

10. The hot forming die according to claim 5, The hot forming die further comprises a pressing mechanism that presses the alignment member toward the workpiece.

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