Mold for high-temperature molding

Abstract

To provide a mold for high-temperature molding, which enables easy taking-out of a workpiece and easy management.SOLUTION: A mold 2A for high-temperature molding comprises: an outer die 3 including an inner wall surface 301 which serves as a holding surfacer; and an inner die 3 including an outer surface 401 at least a part of which is adjacent to the inner wall surface 301 and an inner surface 402 which forms a molding chamber 20. The relationship of the following expression (1) is satisfied, in which T denotes the temperature of the outer and inner dies 3 and 4 before the high-temperature molding, ΔT denotes a temperature increase accompanying the high-temperature molding, α denotes the coefficient of thermal expansion of the inner die 4 in a temperature region of the temperature T to a temperature T+ΔT, and β denotes the coefficient of thermal expansion of the outer die 3: (1)α>β.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a mold for shaping a workpiece at high temperature.

Background Art

[0002] In high-temperature forming using a mold, it may be difficult to remove the workpiece from the mold due to the influence of thermal expansion. During high-temperature forming, the mold expands thermally and becomes larger than its initial dimensions due to elastic deformation caused by the forming load. When the high-temperature environment is removed by cooling after forming, if the amount of thermal shrinkage and elastic deformation of the mold is larger than that of the workpiece, the workpiece cannot be removed from the mold. For this reason, a tapered mold structure is known in which the mold has a two-layer structure of an inner mold and an outer mold, the inner mold is a split mold, and the inner mold and the outer mold are tapered and fitted together (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, a tapered mold requires machining into a tapered shape during production, making it difficult to achieve high precision and tending to result in high processing costs. In addition, finishing work may be required for actual assembly of the inner mold and the outer mold. In this case, it is essential to use and store the inner mold and the outer mold as a set adjusted on-site. Therefore, in a molding apparatus or the like that performs hot forming using a large number of molds, there is a problem that the labor for managing and storing the molds increases.

[0005] An object of the present invention is to provide a high-temperature forming mold that allows easy removal of a workpiece and easy management.

Means for Solving the Problems

[0006] The mold for hot forming according to one aspect of the present invention includes an outer mold including a holding surface, an outer surface at least partially adjacent to the holding surface, and an inner mold including an inner surface partitioning a forming chamber. When the temperatures of the outer mold and the inner mold before hot forming are T, the temperature rise accompanying hot forming is ΔT, the coefficient of thermal expansion of the inner mold in the temperature range from temperature T to temperature T + ΔT is α, and the coefficient of thermal expansion of the outer mold is β, the relationship of the following formula (1) is satisfied. (1) α > β

[0007] According to this aspect, since the coefficient of thermal expansion α of the inner mold is larger than the coefficient of thermal expansion β of the outer mold, the inner mold expands in a state where the surroundings are constrained by the outer mold during hot working. Therefore, when the workpiece is placed in the forming chamber and heated and pressed, the pressing force of the workpiece against the inner wall surface of the inner mold increases, and precise processing can be performed. That is, the inner surface shape of the forming chamber can be favorably transferred to the workpiece. On the other hand, when the temperature is lowered from hot to cold, the degree of thermal contraction of the inner mold becomes larger than that of the outer mold. For this reason, a gap is likely to occur between the inner mold and the outer mold, and the inner mold can be easily removed from the outer mold. In addition, since the improvement of the forming accuracy and the removal of the workpiece are realized by utilizing the difference in the coefficient of thermal expansion between the inner mold and the outer mold, the fitting finish processing between the inner mold and the outer mold such as a tapered mold is unnecessary. Therefore, the management and storage of the inner mold and the outer mold as a set are unnecessary, and the management of the mold can be facilitated.

[0008] In the above mold for hot forming, when the holding surface is an inner wall surface surrounding the inner mold, the outer dimension of the inner mold in the direction along the center line passing through the center of the forming chamber is A, and the inner dimension of the outer mold is B, it is desirable to satisfy the relationship of the following formula (2). (2) α × A × ΔT > β × B × ΔT

[0009] According to this aspect, regarding the amount of thermal expansion and contraction in the temperature range of ΔT, the outer dimension of the inner mold is larger than the inner dimension of the outer mold. For this reason, during hot working, the inner mold presses against the outer mold and becomes an interference fit, improving the strength of the mold. On the other hand, when the temperature is lowered from hot to cold, since the inner mold contracts more than the outer mold, the inner mold can be surely removed from the outer mold.

[0010] In the above-described mold for hot forming, it is desirable that the inner mold is a split-type inner mold formed by an assembly of a plurality of split molds.

[0011] According to this aspect, since the inner mold is of the split type, the molded product after hot forming the workpiece can be easily demolded from the inner mold.

[0012] In the above-described mold for hot forming, the plurality of split molds include a pair of first split molds arranged to face each other with the center line of the molding chamber interposed therebetween, and a pair of second split molds arranged to face each other so as to intersect the center line and be adjacent to one end and the other end of the pair of first split molds, respectively. When the dimension of the first split mold along the center line is A1 and one dimension of the second split mold along the center line is A2, it is preferable to adopt a configuration that satisfies the following formula (3). (3) α × A1 × ΔT + 2 × (α × A2 × ΔT) > β × B × ΔT

[0013] According to this aspect, the inner mold is composed of a pair of first split molds and a pair of second split molds. Regarding the thermal expansion amount in the temperature range of ΔT, the total outer dimension of the split mold pair constituting the inner mold is larger than the inner dimension of the outer mold. Therefore, the molding accuracy can be improved, and the inner mold composed of the split mold pair can be surely demolded from the outer mold.

[0014] In the above-described mold for hot forming, when the thermal expansion coefficient of the first split mold in the temperature region from temperature T to temperature T + ΔT is α1 and the thermal expansion coefficient of the second split mold is α2, it is preferable to adopt a configuration that satisfies the following formula (4). (4) α1 × A1 × ΔT + 2 × (α2 × A2 × ΔT) > β × B × ΔT (where α1 > β, α2 > β)

[0015] According to this aspect, even when the inner mold is composed of a pair of first split molds and second split molds and their thermal expansion coefficients are different, the molding accuracy can be improved, and the inner mold composed of the split mold pair can be surely demolded from the outer mold.

[0016] In the above-described mold for high-temperature forming, the plurality of split molds are arc-shaped split molds obtained by dividing a cylindrical inner mold centered on the center of the molding chamber into a plurality of parts in the circumferential direction, and include a pair of arc-shaped split molds facing each other along the center line of the molding chamber. When the distance between the pair of arc-shaped split molds on the center line is A3 and one dimension of the arc-shaped split mold along the center line is A4, it is preferable to adopt a configuration that satisfies the following formula (5). (5) α × (A3 + 2 × A4) × ΔT > β × B × ΔT

[0017] According to this aspect, in the case where the inner mold is constituted by a combination of arc-shaped split molds, regarding the thermal expansion amount in the temperature range of ΔT, the outer dimension of the inner mold is larger than the inner dimension of the outer mold. Therefore, the molding accuracy can be improved, and the inner mold composed of the split mold pair can be surely released from the outer mold.

[0018] In the above-described mold for high-temperature forming, the plurality of split molds are arranged along the inner wall surface partitioned by the pair of first split molds and the pair of second split molds, and further include a pair of third split molds and a pair of fourth split molds that partition the molding chamber. The pair of third split molds are arranged to face each other with the center line of the molding chamber interposed therebetween, and the pair of fourth split molds intersect the center line and are arranged to face each other so as to be adjacent to one end and the other end of the pair of third split molds respectively. When the thermal expansion coefficient of the third split mold and the fourth split mold in the temperature range from temperature T to temperature T + ΔT is γ, the dimension of the third split mold along the center line is C1, and one dimension of the fourth split mold along the center line is C2, it is preferable to adopt a configuration that satisfies the following formula (6) or (7). (6) α × A1 × ΔT + 2 × (α × A2 × ΔT) > β × B × ΔT (where α > γ) (7) 2 × (α × A2 × ΔT) + γ × C1 × ΔT + 2 × (γ × C2 × ΔT) > β × B × ΔT (where α < γ)

[0019] According to this aspect, the inner mold is arranged in an outer mold composed of a pair of first split molds and a pair of second split molds, and further has a multi-layer structure in which an inner mold composed of a pair of third split molds and a pair of fourth split molds is arranged. Also, based on the difference in the coefficient of thermal expansion between the outer mold and the inner mold, the total outer dimension of the inner mold is set to be larger than the inner dimension of the outer mold with respect to the amount of thermal expansion and contraction in the temperature range of ΔT. Therefore, the forming accuracy can be improved, and the inner mold composed of the first to fourth split molds can be reliably removed from the outer mold.

[0020] In the above-described mold for high-temperature forming, a partition plate may be further provided inside the forming chamber, which divides the forming chamber into a plurality of compartments.

[0021] According to this aspect, one forming chamber can be divided into a plurality of compartments by a partition plate. Therefore, the production efficiency of the formed product can be improved.

Effect of the Invention

[0022] According to the present invention, it is possible to provide a mold for high-temperature forming in which the workpiece can be easily taken out and which is easy to manage.

Brief Description of the Drawings

[0023]

Figure 1

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Embodiments for Carrying Out the Invention

[0024] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The mold according to the present invention is used for sintering sintering materials such as powders and solid pieces of metals and ceramics, die-casting for pressure-molding molten metals, diffusion bonding for joining different or the same material types, etc., and is a high-temperature molding die used at a high temperature of about several hundred °C. That is, it is a high-temperature molding die used for pressing a heated workpiece housed in the mold to transfer the shape of the inner wall surface of the mold to the workpiece and produce a highly accurate molded product.

[0025] FIG. 1 is a longitudinal sectional view schematically showing a molding apparatus 1 used for molding a sintered product or the like, and is a view showing a preferred application of a mold 2 for high-temperature molding according to the present invention. The mold 2 has a molding chamber 20 for molding a workpiece MP. The mold 2 has at least a two-layer structure of an inner mold and an outer mold in a direction from the molding chamber 20 toward the outside. Details of the mold structure will be described later.

[0026] The molding apparatus 1 includes an upper punch 11 that presses the workpiece MP in the molding chamber 20, and a lower punch 12 that receives the workpiece MP to be pressed. An upper backing 13 to which a pressing force is applied is attached to the upper punch 11. The lower punch 12 may be provided with a backing for receiving a pressing load, or may be provided with a lower backing 14 supported by a cushion mechanism for controlling the load applied to the workpiece as shown in FIG. 1. The molding apparatus 1 further includes a heating means for the mold 2. The heating means is, for example, an electric heating or induction heating device for the mold 2, or a heating furnace that houses the molding apparatus 1.

[0027] In the case of high-temperature molding using the mold 2 as described above, when molding by pressing the workpiece MP and pressing it against the inner wall surface of the molding chamber 20, the mold 2 thermally expands and becomes larger than its initial dimensions due to elastic deformation by the molding load of the press. Upon cooling after molding, the dimensions of the mold 2 and the workpiece MP contract from the high-temperature environment. However, if the amount of thermal shrinkage of the mold 2 is larger than the amount of thermal shrinkage of the workpiece MP, the workpiece MP cannot be removed from the mold 2.

[0028] One means for solving this problem is the use of a tapered mold, but as described above, there are problems in that finishing is required and mold management is troublesome. In the present invention, by providing a difference in coefficient of thermal expansion in the constituent materials of the inner mold and the outer mold, a mold 2 for high-temperature molding is provided that can easily achieve accuracy and removal of the workpiece MP, and can also simplify the labor of mold management. Hereinafter, various specific examples of such a mold 2 will be described.

[0029] [First Embodiment] Figure 2 is a horizontal cross-sectional view showing a high-temperature forming die 2A having a forming chamber with a rectangular cross-section according to the first embodiment of the present invention. The die 2A has a forming chamber 20 with a rectangular cross-section that finally houses a workpiece MP that becomes a formed product. The die 2A is composed of an outer die 3 and an inner die 4 surrounded by the outer die 3.

[0030] The outer die 3 has a shape of a rectangular frame in a cross-sectional view and has a rectangular inner wall surface 301 that serves as a holding surface of the inner die 4. The inner die 4 includes an outer surface 401 adjacent to the inner wall surface 301 of the outer die 3 and an inner surface 402 that partitions the forming chamber 20. The inner wall surface 301 surrounds the four side surfaces of the inner die 4. The inner die 4 also has a shape of a rectangular frame in a cross-sectional view. Examples of die materials constituting the outer die 3 and the inner die 4 include metal-based materials, non-metal-based materials, composite materials of metal-based materials and non-metal-based materials, cermet-based materials, and ceramic-based materials. Examples of metal-based materials include, for example, carbide alloys, tool steels, aluminum alloys, copper alloys, magnesium alloys, etc. Examples of non-metal-based materials include graphite, plastic foamed carbon, CFRP, and carbon composites. Examples of cermet-based materials include titanium carbonitride, and examples of ceramic-based materials include alumina, silicon nitride, zirconia, etc.

[0031] Among the above-mentioned die materials, as the constituent material of the inner die 4, a material with a greater thermal expansion and contraction than the constituent material of the outer die 3 is selected in a predetermined temperature range. Here, let the temperature of the outer die 3 and the inner die 4 before high-temperature forming be T, and the temperature rise accompanying high-temperature forming be ΔT. The temperature T is also the temperature at the time of taking out the formed product from the die 2A. ΔT is the temperature difference between the time of high-temperature forming and the time of taking out the formed product. Also, let the coefficient of thermal expansion of the inner die 4 in the temperature range from temperature T to temperature T + ΔT be α, and the coefficient of thermal expansion of the outer die 3 be β. At this time, the die 2A satisfies the relationship of the following formula (1). (1) α > β

[0032] Furthermore, let the outer dimension of the inner die 4 be A and the inner dimension of the outer die 3 be B in the direction along a center line CL passing through the center of the forming chamber 20. At this time, it is desirable that the die 2A satisfies the relationship of the following formula (2). (2) α × A × ΔT > β × B × ΔT

[0033] According to the above-described mold 2A, as shown in Equation (1), since the coefficient of thermal expansion α of the inner mold 4 is larger than the coefficient of thermal expansion β of the outer mold 3, during hot forming where high-temperature forming is performed, the inner mold 4 expands inward in a state where the surroundings are constrained by the outer mold 3. Therefore, when the workpiece MP (FIG. 1) is placed in the forming chamber 20 and heated and pressed, the pressing force of the workpiece MP against the inner surface 402 of the inner mold 4 increases. Therefore, the inner surface shape of the forming chamber 20 can be favorably transferred to the workpiece MP, and high-precision machining can be performed. Also, during hot forming, the inner mold 4 presses against the outer mold 3 to achieve an interference fit, which also has the advantage of improving the strength of the mold 2A.

[0034] On the other hand, during cold forming after the mold is cooled, the degree of thermal contraction of the inner mold 4 is greater than that of the outer mold 3. That is, as shown in Equation (2), regarding the amount of thermal expansion and contraction in the temperature range of ΔT, the outer dimension A of the inner mold 4 is larger than the inner dimension B of the outer mold 3. That is, when the temperature is lowered from hot to cold, the inner mold 4 contracts more than the outer mold 3. For this reason, a gap is likely to occur between the outer surface 401 of the inner mold 4 and the inner wall surface 301 of the outer mold 3, and the inner mold 4 can be easily removed from the outer mold 3. If the coefficient of thermal expansion α of the inner mold 4 is set to be smaller than the coefficient of thermal expansion of the workpiece MP, the workpiece MP contracts more than the inner mold 4 in the forming chamber 20. Therefore, even for the non-divided inner mold 4, the formed product of the workpiece MP can be easily taken out from the inner mold 4.

[0035] As described above, in the mold 2A, improvement in forming accuracy and removal of the workpiece MP are realized by utilizing the difference in the coefficient of thermal expansion between the inner mold 4 and the outer mold 3. For this reason, finish machining such as a taper mold is unnecessary. Therefore, it is not necessary to manage and store the inner mold 4 and the outer mold 3 as a set, and the management of the mold can be facilitated.

[0036] FIG. 3 is a cross-sectional view showing a high-temperature molding die 2B having a circular molding chamber 20 in a horizontal cross-sectional view, which is a modified example of the first embodiment. The die 2B is composed of an outer shape 3 having a shape of a frame body with a circular cross-section and an inner shape 4 surrounded by the outer shape 3. The inner shape 4 includes a cylindrical outer surface 401 adjacent to the cylindrical inner wall surface 301 of the outer shape 3 and a cylindrical inner surface 402 partitioning the molding chamber 20.

[0037] In the die 2B, the relationship between the coefficient of thermal expansion α of the inner shape 4 and the coefficient of thermal expansion β of the outer shape 3 is as shown in the above formula (1). Also, the relationship between the outer dimension of the inner shape 4 and the inner dimension of the outer shape 3 along the center line CL passing through the center of the molding chamber 20, that is, the relationship of the thermal expansion and contraction amount in the temperature range of ΔT when the diameter of the inner shape 4 is A and the inner diameter of the outer shape is B, is as shown in the above formula (2). Even in a die with a circular cross-section such as the die 2B, by satisfying the relationships of formula (1) and further formula (2), the inner shape 4 shrinks more than the outer shape 3 in the cold state. Therefore, the removability of the molded product of the workpiece MP from the die 2B can be improved.

[0038] FIG. 4 is a cross-sectional view showing a high-temperature molding die 2C according to another modified example of the first embodiment. The structures of the outer shape 3 and the inner shape 4 of the die 2C itself are the same as those of the die 2A shown in FIG. 2 above. The difference is that a partition plate 5 is arranged in the molding chamber 20 of the inner shape 4. FIG. 4 shows an example in which two partition plates 5 are arranged at equal intervals in the direction of the center line CL. By the two partition plates 5, the molding chamber 20 is partitioned into three small chambers 20A. The workpiece MP is loaded into each small chamber 20A, and high-temperature molding is performed. That is, the die 2C can produce three molded products simultaneously in one molding.

[0039] [Second Embodiment] FIG. 5 is a horizontal cross-sectional view showing a high-temperature molding die 2D according to the second embodiment, in which a molding chamber 20 having a rectangular cross-section is partitioned by a split inner mold. The mold 2D is composed of an outer mold 3 and an inner mold 4A surrounded by the outer mold 3. The inner mold 4A has an outer surface 401 adjacent to the inner wall surface 301 of the outer mold 3 and an inner surface 402 partitioning the molding chamber 20 having a rectangular cross-section. The above points are the same as those of the mold 2A of the first embodiment. The mold 2D is different from the mold 2A of the first embodiment in that the inner mold 4A of the mold 2D is a split mold formed by an assembly of a pair of first split molds 41 and a pair of second split molds 42. By adopting the split inner mold 4A, the molded product after high-temperature molding of the workpiece MP can be easily taken out from the inner mold 4A.

[0040] The pair of first split molds 41 are each a mold piece having a rectangular cross-section, and are arranged opposite to each other with the center line CL of the molding chamber 20 interposed therebetween. The pair of second split molds 42 are each a mold piece having a rectangular cross-section, and are arranged in a direction intersecting the center line CL, more specifically, in a direction perpendicular to the center line CL. One second split mold 42 is arranged adjacent to one end 411 of the first split mold 41 and closes the space between the pair of one ends 411. The other second split mold 42 is arranged adjacent to the other end 412 of the first split mold 41 and closes the space between the pair of the other ends 412.

[0041] The first split mold 41 and the second split mold 42 are formed of the same mold material. That is, the coefficient of thermal expansion of the first split mold 41 and the second split mold 42 in the temperature range from temperature T to temperature T + ΔT is α. The coefficient of thermal expansion of the outer mold 3 is β, and the relationship α>β is set as shown in Equation (1). Regarding the thermal expansion amount of the mold 2D, when the dimension of the first split mold 41 along the center line CL is A1 and one dimension of the second split mold 42 along the center line CL is A2, the following relationship of Equation (3) is satisfied. (3) α×A1×ΔT+2×(α×A2×ΔT)>β×B×ΔT

[0042] According to the mold 2D of the second embodiment, an inner mold 4A composed of a pair of first split molds 41 and a pair of second split molds 42 is used. And in the temperature range of ΔT, the total thermal expansion amount of the outer dimensions A1 + 2×A2 of the split mold pair constituting the inner mold 4A is larger than the thermal expansion amount of the inner dimension B of the outer mold 3. Therefore, the forming accuracy of the workpiece MP can be improved, and the inner mold 4A composed of the split mold pair can be surely released from the outer mold 3. Also, it becomes easy to take out the formed product from the inner mold 4A.

[0043] FIG. 6 is a horizontal cross-sectional view showing a high-temperature forming mold 2E which is a modified example of the second embodiment and in which a forming chamber 20 having a circular cross-section is partitioned by a split inner mold 4B. The mold 2E is composed of an outer mold 3 having the shape of a frame body with a circular cross-section and an inner mold 4B having the shape of a frame body with a circular cross-section surrounded by the outer mold 3. The split inner mold 4B is composed of arc-shaped split pieces obtained by dividing a cylindrical body having the center of the forming chamber 20 as the center of the circle into a plurality of parts in the circumferential direction. In FIG. 6, an inner mold 4B equally divided into 4 parts in the circumferential direction is illustrated. The inner mold 4B includes a cylindrical outer surface 401 adjacent to the cylindrical inner wall surface 301 of the outer mold 3 and a cylindrical inner surface 402 partitioning the forming chamber 20. The mode of division of the inner mold 4B is arbitrary, and it may be 3 or less divisions, 5 or more divisions, or may not be equally divided.

[0044] Specifically, the inner mold 4B is composed of a pair of first arc split molds 45 facing each other along a single center line CL passing through the center of the forming chamber 20 and a pair of second arc split molds 46 arranged to face each other with the center line CL interposed therebetween. The annular inner mold 4B is configured in such a manner that the pair of second arc split molds 46 close the two gaps in the circumferential direction of the pair of first arc split molds 45 respectively.

[0045] The first arc-divided type 45 and the second arc-divided type 46 are formed of the same mold material. That is, the coefficient of thermal expansion of the first arc-divided type 45 and the second arc-divided type 46 in the temperature range from temperature T to temperature T + ΔT is α. The coefficient of thermal expansion of the outer mold 3 is β, and the relationship of α>β is set as in formula (1). Regarding the amount of thermal expansion and contraction of the mold 2E, when the distance between the first arc-divided types 45 on the center line CL is A3 and one dimension (thickness) of the first arc-divided type 45 along the center line CL is A4, the following formula (5) is satisfied. (5) α×(A3 + 2×A4)×ΔT>β×B×ΔT

[0046] According to the mold 2E of FIG. 6, when the inner mold 4B is constituted by the combination of the first arc-divided type 45 and the second arc-divided type 46, in the temperature range of ΔT, the amount of thermal expansion and contraction of the outer dimension A3 + 2×A4 of the inner mold 4B is larger than the amount of thermal expansion and contraction of the inner dimension B of the outer mold. Therefore, the accuracy of forming the workpiece MP can be improved, and the inner mold 4B composed of the split mold pair can be reliably removed from the outer mold 3. Further, since the inner mold 4B is a split mold, it is also easy to take out the molded product from the inner mold 4B.

[0047] FIG. 7 is a horizontal cross-sectional view showing a high-temperature molding die 2F using an inner mold 4A of a split mold with different coefficients of thermal expansion, which is a modification of the second embodiment. The structure of the outer mold 3 and the split inner mold 4A of the mold 2F itself is the same as that of the mold 2D shown in FIG. 5 above. The difference is that the coefficient of thermal expansion of the first split mold 41 and the coefficient of thermal expansion of the second split mold 42 are different. For example, depending on the shape of the molded product, that is, the shape of the molding chamber 20, the amount of thermal expansion and contraction may differ greatly in the direction along the center line CL and the direction perpendicular to the center line CL. In this case, in the split inner mold 4A, it is possible to improve the ejectability of the molded product by adjusting the coefficients of thermal expansion of the first split mold 41 and the second split mold 42.

[0048] Regarding the amount of thermal expansion and contraction of the mold 2F, when the coefficient of thermal expansion of the first split mold 41 is α1 and the coefficient of thermal expansion of the second split mold 42 is α2 in the temperature range from temperature T to temperature T + ΔT, the following formula (4) is satisfied. (4) α1 × A1 × ΔT + 2 × (α2 × A2 × ΔT) > β × B × ΔT (provided that α1 > β, α2 > β)

[0049] FIG. 8 is a cross-sectional view showing a mold 2G for hot forming according to another modification of the second embodiment. The structure of the outer shape 3 of the mold 2G and the inner shape 4A of the split mold itself is the same as that of the mold 2D shown in FIG. 5 above. The difference is that two partition plates 5 are arranged in the molding chamber 20 of the inner shape 4A. By the two partition plates 5, the molding chamber 20 is partitioned into three small chambers 20A. The workpiece MP is loaded into each small chamber 20A, and hot forming is performed. That is, the mold 2G can simultaneously produce three molded products in one molding operation.

[0050] In the mold 2G, the thermal expansion rate of the contents in the molding chamber 20 may be considered. In the mold 2G, the partition plate 5 and the workpiece MP loaded in the small chamber 20A are the contents. When the thermal expansion and contraction amount of the contents along the center line CL is smaller than the thermal expansion and contraction amount of the first split mold 41 along the center line CL, mold release of the inner shape 4A from the outer shape 3 may be inhibited. For example, when transitioning from hot to cold, if the thermal contraction amount of the contents is smaller than the thermal contraction amount of the first split mold 41, a phenomenon may occur in which the contents press against the second split mold 42 on the inner wall surface 301 of the outer shape 3. In this case, it is desirable to set the thermal expansion and contraction amount of the inner shape 4A including the contents to be larger than the thermal expansion and contraction amount of the outer shape. That is, in addition to the thermal expansion and contraction amount of the first split mold 41 along the center line CL, the thermal expansion and contraction amount of the contents may be taken into consideration.

[0051] Here, when the thermal expansion rate of the partition plate 5 is δ, the thermal expansion rate of the workpiece MP loaded in the small chamber 20A is ε, the dimension of the partition plate 5 along the center line CL is D, the dimension of the small chamber 20A along the center line CL is E, the number of parallel partition plates 5 is N1, and the number of parallel small chambers 20A is N2, in addition to the above formula (3), a configuration that further satisfies the following relationship of formula (3-1) may be adopted. (3-1) 2 × (α × A2 × ΔT) + δ × D × ΔT × N1 + ε × E × ΔT × N2 > β × B × ΔT

[0052] [Third Embodiment] FIG. 9 is a cross-sectional view showing a high-temperature mold 2H according to the third embodiment, in which a molding chamber 20 having a rectangular cross-section is partitioned by a two-layer split inner mold. The mold 2H is composed of an outer mold 3 and an inner mold 4C surrounded by the outer mold 3. The inner mold 4C is a split frame body, and has a two-layer structure including a first inner mold layer 40A and a second inner mold layer 40B surrounded by the first inner mold layer 40A. The mold 2H is a mode in which a split inner mold is further arranged inside the inner mold 4A of the mold 2D shown in FIG. 5.

[0053] The first inner mold layer 40A of the inner mold 4C is formed by an assembly of a pair of first split molds 41 and a pair of second split molds 42. The pair of first split molds 41 are arranged to face each other with the center line CL of the molding chamber 20 interposed therebetween. The pair of second split molds 42 are arranged in a direction orthogonal to the center line CL. One second split mold 42 is arranged adjacent to one end 411 of the first split mold 41 and closes the space between the pair of one ends 411. The other second split mold 42 is arranged adjacent to the other end 412 of the first split mold 41 and closes the space between the pair of the other ends 412.

[0054] The second inner mold layer 40B partitions the molding chamber 20. The second inner mold layer 40B is formed by an assembly of a pair of third split molds 43 and a pair of fourth split molds 44 arranged along the inner surface 402 of the region partitioned by the first inner mold layer 40A. The pair of third split molds 43 are each a mold piece having a rectangular cross-section and are arranged to face each other with the center line CL of the molding chamber 20 interposed therebetween. The pair of second split molds 42 are each a mold piece having a rectangular cross-section and are arranged in a direction orthogonal to the center line CL. One fourth split mold 44 is arranged adjacent to one end 431 of the third split mold 43 and closes the space between the pair of one ends 431. The other fourth split mold 44 is arranged adjacent to the other end 432 of the third split mold 43 and closes the space between the pair of the other ends 432. The outer surface 403 of the second inner mold layer 40B abuts against the inner surface 402 of the first inner mold layer 40A. The inner surface 404 of the second inner mold layer 40B serves as an inner wall surface that partitions the molding chamber 20.

[0055] In the hot mold 2H, the first inner mold layer 40A, whose outward bulge is restricted by the outer mold 3, expands inward and pushes the second inner mold layer 40B inward. In the extending direction of the center line CL, one end 431 and the other end 432 of the third split mold 43 of the second inner mold layer 40B abut against the fourth split mold 44. In the direction intersecting the center line CL, the side surface of the second inner mold layer 40B abuts against the inner side surface 402 of the first inner mold layer 40A. Therefore, according to the mold 2H provided with the two-layer structured split inner mold 4C, the dimensions in the molding chamber 20 become the designed dimensions, and since no gap is generated between the split molds, there is an advantage that burr generation can be suppressed.

[0056] In the mold 2H, the thermal expansion rates of the first split mold 41 and the second split mold 42 in the temperature range from temperature T to temperature T + ΔT are both α. Also, the thermal expansion rates of the third split mold 43 and the fourth split mold 44 in the temperature range from temperature T to temperature T + ΔT are both γ. Note that α = γ may be satisfied. The thermal expansion rate of the outer mold 3 is β, and it is set to at least the relationship of α > β as shown in Equation (1). Regarding the thermal expansion amount, for the mold 2H, when the dimension of the first split mold 41 along the center line CL is A1, one dimension of the second split mold 42 along the center line CL is A2, the dimension of the third split mold 43 along the center line CL is C1, and one dimension of the fourth split mold 44 along the center line CL is C2, it is set to satisfy the relationship of the following Equation (6) or (7). (6) α × A1 × ΔT + 2 × (α × A2 × ΔT) > β × B × ΔT (where α > γ) (7) 2 × (α × A2 × ΔT) + γ × C1 × ΔT + 2 × (γ × C2 × ΔT) > β × B × ΔT (where α < γ)

[0057] According to the mold 2H, the inner mold 4C has a multi-layer structure in which a second inner mold layer 40B composed of a pair of third split molds 43 and a pair of fourth split molds 44 is disposed within a first inner mold layer 40A composed of a pair of first split molds 41 and a pair of second split molds 42. Also, in consideration of the difference in the coefficient of thermal expansion between the first inner mold layer 40A and the second inner mold layer 40B, the total outer dimension of the inner mold 4C is set to be larger than the inner dimension of the outer mold 3 with respect to the amount of thermal expansion and contraction in the temperature range of ΔT. Therefore, the molding accuracy can be improved, and the inner mold 4C formed of the two-layer split mold can be surely released from the outer mold 3. In the third embodiment as well, the partition plate 5 may be disposed in the molding chamber 20 to partition a plurality of small chambers 20A as in the modified example of the second embodiment in FIG. 8. Thereby, a plurality of molded products can be simultaneously produced in one molding operation.

[0058] FIG. 10 is a cross-sectional view showing a high-temperature molding die 2I including an inner mold 4C formed using split molds having different coefficients of thermal expansion, which is a modified example of the third embodiment. The structure of the outer mold 3 and the inner mold 4C of the split mold of the mold 2I itself is the same as that of the mold 2H shown in FIG. 9 above. The difference is that the coefficient of thermal expansion of the first split mold 41 of the first inner mold layer 40A is different from the coefficient of thermal expansion of the second split mold 42. The coefficients of thermal expansion of the third split mold 43 and the fourth split mold 44 of the second inner mold layer 40B are the same value = γ.

[0059] Regarding the amount of thermal expansion and contraction, when the coefficient of thermal expansion of the first split mold 41 is α1 and the coefficient of thermal expansion of the second split mold 42 is α2 in the temperature range from temperature T to temperature T + ΔT in the mold 2I, the mold 2I is set to satisfy the relationship of Expression (6-1) or (7-1) obtained by rewriting the above-described Expressions (6) and (7) as follows. (6-1) α1×A1×ΔT+2×(α2×A2×ΔT)>β×B×ΔT (where α1>γ) (7-1) 2×(α2×A2×ΔT)+γ×C1×ΔT+2×(γ×C2×ΔT)>β×B×ΔT (where α1<γ) In this modified example as well, the partition plate 5 may be disposed in the molding chamber 20 to partition a plurality of small chambers 20A as in the modified example of the second embodiment in FIG. 8. Thereby, a plurality of molded products can be simultaneously produced in one molding operation.

[0060] FIG. 11 is a cross-sectional view showing a high-temperature molding die 2J including an inner die 4C formed using split types having different coefficients of thermal expansion, which is another modification of the third embodiment. The structure of the outer die 3 of the die 2J and the inner die 4C of the split type itself is the same as that of the die 2H shown in FIG. 9 above. The difference is that the coefficient of thermal expansion of the first split die 41 of the first inner die layer 40A is different from that of the second split die 42, and the coefficient of thermal expansion of the third split die 43 of the second inner die layer 40B is different from that of the fourth split die 44. Further, two partition plates 5 are arranged in the molding chamber 20.

[0061] In the die 2J, assume that the coefficient of thermal expansion of the first split die 41 in the temperature range from temperature T to temperature T + ΔT is α1, the coefficient of thermal expansion of the second split die 42 is α2, the coefficient of thermal expansion of the third split die 43 is γ1, and the coefficient of thermal expansion of the fourth split die 44 is γ2. In this case, for the die 2J with respect to the thermal expansion amount, it is set to satisfy the relationship of Equation (6-2) or (7-2) obtained by rewriting the above-mentioned Equations (6) and (7) as follows. (6-2) α1×A1×ΔT+2×(α2×A2×ΔT)>β×B×ΔT(where α1×A1 > γ1×C1+2×γ2×C2) (7-2) 2×(α2×A2×ΔT)+γ1×C1×ΔT+2×(γ2×C2×ΔT)>β×B×ΔT(where α1×A1 < γ1×C1+2×γ2×C2)

[0062] As yet another modification of the third embodiment, a high-temperature molding die may be used in which the coefficients of thermal expansion of the first split die 41 and the second split die 42 in the temperature range from temperature T to temperature T + ΔT are the same value = α, the coefficient of thermal expansion of the third split die 43 is γ1, and the coefficient of thermal expansion of the fourth split die 44 is γ2 (γ1≠γ2). Further, by arranging the partition plate 5 in the molding chamber 20 to partition the small chamber 20A, a plurality of molded products can be produced simultaneously in one molding.

[0063] [Modification example of the outer die] Next, a modified example of the outer mold 3 is shown. In the above-described embodiment, the outer mold 3 was exemplified in a mode that completely surrounds the four sides of the inner mold 4. The outer mold 3 does not have to be a completely surrounding type as described above, and it suffices if it has a holding surface for holding the inner mold 4.

[0064] FIG. 12(A) is a top view showing a hot forming die 2K having an outer mold 3A according to a modified example, and FIG. 12(B) is a cross-sectional view taken along line XIIB-XIIB of FIG. 12(A). The die 2K is composed of an outer mold 3A and an inner mold 4D held by this outer mold 3A. The outer mold 3A includes an outer mold base 31 having a substantially square rectangular parallelepiped shape in a top view, and a regulating plate 32 erected from the outer mold base 31. The regulating plate 32 is a rectangular parallelepiped with a rectangular cross-section, and is erected from the central regions of the four sides of the outer mold base 31, respectively. The inner surface of the regulating plate 32 is a holding surface 32A for holding the inner mold 4.

[0065] The inner mold 4D is formed by a pair of first split molds 41A and a pair of second split molds 42A, and partitions the molding chamber 20. The outer surfaces of the first split mold 41A and the second split mold 42A are adjacent to the holding surfaces 32A of the regulating plates 32 arranged corresponding thereto, respectively. The first split mold 41A and the second split mold 42A are each smaller in size than the regulating plate 32, and spacers 6 for filling the size difference between the two are disposed at the four corners of the inner mold 4D.

[0066] In the die 2K, let the coefficient of thermal expansion of the first split mold 41A and the second split mold 42A of the inner mold 4D in the temperature range from temperature T to temperature T + ΔT be α, and the coefficient of thermal expansion of the outer mold 3A be β. In this case, a relationship of α>β is set as in formula (1). Regarding the amount of thermal expansion and contraction, the relationship of the die 2D shown in FIG. 5 can be applied mutatis mutandis. That is, when the dimension of the first split mold 41A is A1, one dimension of the second split mold 42A is A2, and the dimension between the holding surfaces 32A of the pair of opposing regulating plates 32 is B, the die 2K satisfies the relationship of the above-described formula (3).

[0067] FIG. 13(A) is a top view showing a mold 2L for hot forming having an outer shape 3B according to another modified example, and FIG. 13(B) is a cross-sectional view taken along line XIIIB-XIIIB of FIG. 13(A). The mold 2L is composed of an outer shape 3B and an inner shape 4E held by the outer shape 3B. The outer shape 3B includes an outer shape base 310 having a substantially square rectangular parallelepiped shape in a top view, and a regulating bar 33 erected from the outer shape base 310. The regulating bar 33 is a cylinder, and two regulating bars are erected from each of the four sides of the outer shape base 310.

[0068] The inner shape 4E is formed by a pair of first split molds 41B and a pair of second split molds 42B, and partitions the molding chamber 20. The outer surfaces of the first split mold 41B and the second split mold 42B are adjacent to the inner circumferential surfaces of the regulating bars 33 arranged correspondingly thereto. In this modified example, the inner circumferential surface of the regulating bar 33 is the holding surface of the inner shape 4E.

[0069] In the mold 2L, let the coefficient of thermal expansion of the first split mold 41B and the second split mold 42B of the inner shape 4E in the temperature range from temperature T to temperature T + ΔT be α, and the coefficient of thermal expansion of the outer shape 3B be β. In this case, the relationship of α>β is set as shown in Equation (1). Regarding the amount of thermal expansion and contraction, the relationship of the mold 2D shown in FIG. 5 can be applied mutatis mutandis. That is, when the dimension of the first split mold 41B is A1, one dimension of the second split mold 42B is A2, and the dimension between the inner circumferential surfaces of a pair of opposing regulating bars 33 is B, the mold 2L satisfies the relationship of the above-mentioned Equation (3).

[0070] In each of the above-described embodiments, the molding chamber 20 has been described as having a rectangular or circular shape in a horizontal cross-sectional view, but the cross-sectional shape is not limited to these. The cross-sectional shape of the molding chamber 20 is appropriately set according to the contour of the molded product. Therefore, the cross-sectional view shape of the inner shape exemplified in each of the above-described embodiments is appropriately set according to the contour of the molded product.

Explanation of Reference Numerals

[0071] 1 Molding apparatus 1 2, 2A~2L Molds 20 Molding chamber 20A Compartments (multiple compartments) 3, 3A, 3B Outer shapes 301 Inner wall surface (holding surface) 4, 4A to 4E Inner mold 401 Outer surface 402 Inner surface 40A First inner mold layer 40B Second inner mold layer 41 First segmented type 411 One end 412 The other end 42 Second segmented type 43 Third segmented type 44 Fourth segmented type 45 First arc segmented type 46 Second arc segmented type 5 Partition plate

Claims

1. An outer mold including a holding surface, an inner mold including an outer surface at least partially adjacent to the holding surface and an inner surface partitioning a molding chamber, wherein when the temperatures of the outer mold and the inner mold before high-temperature molding are T, the temperature rise accompanying high-temperature molding is ΔT, the coefficient of thermal expansion of the inner mold in the temperature range from temperature T to temperature T + ΔT is α, and the coefficient of thermal expansion of the outer mold is β, a mold for high-temperature molding satisfying the relationship of the following formula (1). （１）α＞β

2. In the mold for high-temperature molding according to Claim 1, wherein the holding surface is an inner wall surface surrounding the inner mold, when the outer dimension of the inner mold in the direction along the center line passing through the center of the molding chamber is A and the inner dimension of the outer mold is B, a mold for high-temperature molding satisfying the relationship of the following formula (2). (2) α × A × ΔT > β × B × ΔT

3. In the mold for high-temperature molding according to Claim 2, wherein the inner mold is a split-type inner mold formed of an assembly of a plurality of split molds, a mold for high-temperature molding.

4. In the mold for high-temperature molding according to Claim 3, wherein the plurality of split molds include a pair of first split molds arranged to face each other with the center line of the molding chamber interposed therebetween, and a pair of second split molds arranged to face each other so as to intersect the center line and be adjacent to one end and the other end of the pair of first split molds, respectively, when the dimension of the first split mold along the center line is A1 and one dimension of the second split mold along the center line is A2, a mold for high-temperature molding satisfying the relationship of the following formula (3). (3) α × A1 × ΔT + 2 × (α × A2 × ΔT) > β × B × ΔT

5. In the mold for high-temperature molding according to Claim 4, when the coefficient of thermal expansion of the first split mold in the temperature range from temperature T to temperature T + ΔT is α1 and the coefficient of thermal expansion of the second split mold is α2, a mold for high-temperature molding satisfying the relationship of the following formula (4). (4) α1 × A1 × ΔT + 2 × (α2 × A2 × ΔT) > β × B × ΔT (where α1 > β, α2 > β)

6. In the mold for high-temperature molding according to Claim 3, wherein the plurality of split molds are arc-shaped split molds obtained by circumferentially dividing a cylindrical inner mold having the center of the molding chamber as the center of a circle, and include a pair of arc split molds facing each other along the center line of the molding chamber, when the distance between the pair of arc split molds on the center line is A3 and one dimension of the arc split mold along the center line is A4, a mold for high-temperature molding satisfying the relationship of the following formula (5). (5) α × (A3 + 2 × A4) × ΔT > β × B × ΔT

7. In the mold for high-temperature forming according to claim 4, the plurality of split molds are arranged along the inner wall surface partitioned by the pair of first split molds and the pair of second split molds, and further include a pair of third split molds and a pair of fourth split molds that partition the molding chamber, the pair of third split molds are arranged opposite to each other with the center line of the molding chamber interposed therebetween, the pair of fourth split molds intersect the center line and are arranged opposite to each other so as to be adjacent to one end and the other end of the pair of third split molds respectively, when the coefficient of thermal expansion of the third split mold and the fourth split mold in the temperature range from temperature T to temperature T+ΔT is γ, the dimension of the third split mold along the center line is C1, and one dimension of the fourth split mold along the center line is C2, a mold for high-temperature forming that satisfies the relationship of the following formula (6) or (7). (6) α×A1×ΔT + 2×(α×A2×ΔT) > β×B×ΔT (where α < γ) (7) 2×(α×A2×ΔT) + γ×C1×ΔT + 2×(γ×C2×ΔT) > β×B×ΔT (where α > γ)

8. In the mold for high-temperature forming according to any one of claims 1 to 7, a mold for high-temperature forming, further comprising a partition plate disposed inside the molding chamber and dividing the molding chamber into a plurality of compartments.

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