TWI623361B - Hot pressing method and hot pressing system - Google Patents

Abstract

The hot pressing method of the present invention is a method of manufacturing a press-formed product by hot pressing a blank having a punch, a die and an inner pad, wherein the inner pad is given a potential energy to be protruded toward the die; the heat of the present invention The pressing method is performed by allowing the refrigerant to flow in the refrigerant path so that the surface temperature T of the inner pad is taken out from the mold to the next billet, and the next billet is placed between the molds, and cooled to an upper limit of 100 ° C and satisfying the following number Temperature. T£100 ́(2.3/t) ́(h/100) ́(l/30) ́(W/2) ́ST: surface temperature of the inner pad (°C) h: dimension of the inner pad (mm) t: thickness of the blank (mm) l: thermal conductivity of the inner pad (W/mK) W: volume ratio of the refrigerant path inside the inner pad (mm ³ /mm ³ ) S: flow rate of the refrigerant in the refrigerant path (mm/ Sec)

Description

Hot pressing method and hot pressing system

FIELD OF THE INVENTION The present invention relates to a hot pressing method and a hot pressing system that performs the hot pressing method.

Background of the Invention For example, from the viewpoint of improving fuel consumption and protecting a rider, it is required to maintain or increase mechanical strength of a structural member for an automobile, and to reduce weight. In general, when the material has high mechanical strength, moldability at the time of molding processing such as press working is low, and it is difficult to process into a complicated shape. A processing method for improving the moldability of a material having a high mechanical strength, such as the hot press method described in Patent Document 1 or Patent Document 2 (sometimes referred to as a hot stamping method, a hot press method, a press hardening method, etc.) The hot pressing method is to form a heated material (binder or pre-molded product) by press molding and rapidly cooling. According to the hot press method, since the material is softened by high temperature during molding, the moldability is excellent, and it is quenched by rapid cooling in a press molding die, whereby a press-molded product having high mechanical strength can be obtained.

However, even with the hot pressing method, the press-formed product sometimes produces cracks. In order to prevent cracking of the press-formed product, Patent Document 3 discloses a method for producing a press-formed product, which has a cross-sectional hat shape and is curved in a plan view orthogonal to the line of sight of the top plate. Patent Document 4 discloses a case in which a cross-sectional hat-shaped member is formed by hot press forming, and an arc-shaped independent action punch is built in a die (punch), and an independent action punch is activated at a bottom dead center of the molding. Methods. Patent Document 5 discloses a concentrated press forming process which uses a cooling catalyst to cool a specific portion of a material by a molding step to improve moldability. However, if the method described in Patent Document 3 is applied to the hot pressing method, cracking may occur in the shoulder of the punch. Further, in the method described in Patent Document 4, it is not possible to suppress the cracking of the standing wall portion before reaching the bottom dead center of the molding.

Further, in press molding using a pair of dies, a method of supporting a billet by an inner mat provided on a mold may be employed. For example, Patent Documents 5 to 7 disclose a configuration in which a billet is pressed by an inner pad provided in a mold at the time of press molding. However, the inner pad has a smaller volume than the mold main body, so the temperature is liable to rise. Then, when hot press forming is performed in a state where the inner mat temperature is raised, the degree of quenching of the produced press-formed product is lowered, and the mechanical strength may be lowered. In particular, when the plurality of press-molded articles are produced by repeating hot press forming, since the inner pad temperature is maintained in an ascending state, the mechanical strength of the produced press-formed product may be lowered. Advanced technical literature

Patent Document 1: Japanese Patent Publication No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. Japanese Laid-Open Patent Publication No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei.

Summary of invention

In view of the above circumstances, an object of the present invention is to provide a hot press method and a hot press system, which can solve the cracking of the press molded product and increase the strength.

The inventors of the present invention have thought of the following aspects of the invention as a result of a keen review.

(1) A hot pressing method in which a billet is heat-pressed using a mold having an upper mold, a lower mold, and an inner mat, wherein the inner mat is movably received in the lower mold, and is given potential energy. a state in which the upper mold protrudes; wherein: a path of the refrigerant is provided inside the inner pad; and a surface of the inner pad is removed from the mold by allowing a refrigerant to flow in the path of the refrigerant The molded product was pressed until the next blank was placed between the above-mentioned dies, and cooled to a temperature of 100 ° C as the upper limit and satisfying the following formula. T£100 ́(2.3/t) ́(h/100) ́(l/30) ́(W/2) ́S

here,

T: surface temperature of the inner pad (°C)

h: the pressing direction dimension of the inner pad (mm)

t: thickness of the billet (mm)

λ: thermal conductivity of the inner pad (W/mK)

W: volume ratio of the refrigerant path inside the inner pad (mm ³ /mm ³ )

S: refrigerant flow rate in the refrigerant path (mm/sec)

(2) The hot press method according to the above (1), characterized in that the time from which the press-formed product is taken out from the mold to the time when the next blank is placed on the mold is set to a lower limit of 5 seconds and satisfies the following The time of the number.

A 5 × (t / 2.3) × (100 / h) × (30 / λ) × (2 / W) × (1/S)

here,

A: The time from the removal of the press-formed product from the mold to the time when the next blank is placed in the mold (sec)

h: the pressing direction dimension of the inner pad (mm)

t: thickness of the billet (mm)

λ: thermal conductivity of the inner pad (W/mK)

W: volume ratio of the refrigerant path inside the inner pad (mm ³ /mm ³ )

S: refrigerant flow rate in the refrigerant path (mm/sec)

(3) The hot press method according to the above (1) or (2), wherein the inner pad has a pressing direction dimension of 100 mm as a lower limit and satisfies the following formula.

h 100 × (t / 2.3) × (30 / λ) × (2 / W) × (1/S)

here,

h: the pressing direction dimension of the inner pad (mm)

t: thickness of the billet (mm)

l: thermal conductivity of the inner pad (W/mK)

W: volume ratio of the refrigerant path inside the inner pad (mm ³ /mm ³ )

S: refrigerant flow rate in the refrigerant path (mm/sec)

(4) The hot press method according to any one of (1) to (3), wherein the press-molded article is taken out from the mold until the next blank is placed between the molds, The inner pad ejects a fluid refrigerant to cool the inner pad.

(5) The hot press method according to any one of (1) to (4), wherein a refrigerant injection hole is provided in the upper mold, and the refrigerant injection hole is capable of injecting a refrigerant toward the inner pad; The mold takes out the press-formed product until the next blank is placed between the molds, and the upper mold is brought close to the lower mold, and the refrigerant is sprayed from the refrigerant injection hole toward the inner liner provided in the lower mold. The aforementioned inner cushion.

(6) A hot pressing system, comprising: a press machine, wherein a billet is heat-pressed using a mold having an upper mold, a lower mold, and an inner mat, wherein the inner mat is movably received in the lower mold, The potential energy is provided in a state of protruding toward the upper mold, and a path of the refrigerant is provided therein; and a cooling control unit controls supply of the refrigerant that cools the inner pad, and the cooling control unit is configured to allow the refrigerant to flow through the refrigerant. The surface temperature of the inner mat is set between the press mold and the next billet between the molds, and is cooled to a temperature of 100 ° C as an upper limit and satisfying the following formula. T£100 ́(2.3/t) ́(h/100) ́(l/30) ́(W/2) ́S

here,

T: surface temperature of the inner pad (°C)

h: the pressing direction dimension of the inner pad (mm)

t: thickness of the billet (mm)

λ: thermal conductivity of the inner pad (W/mK)

W: volume ratio of the refrigerant path inside the inner pad (mm ³ /mm ³ )

S: refrigerant flow rate in the refrigerant path (mm/sec)

(7) The hot press system according to the above (6), wherein the time from which the press-formed product is taken out from the mold to the time when the next blank is placed on the mold is set to a lower limit of 5 seconds and satisfies the following The time of the number.

A 5 × (t / 2.3) × (100 / h) × (30 / λ) × (2 / W) × (1/S)

here,

A: The time from the removal of the press-formed product from the mold to the time when the next blank is placed in the mold (sec)

h: the pressing direction dimension of the inner pad (mm)

t: thickness of the billet (mm)

λ: thermal conductivity of the inner pad (W/mK)

W: volume ratio of the refrigerant path inside the inner pad (mm ³ /mm ³ )

S: refrigerant flow rate in the refrigerant path (mm/sec)

(8) The hot press system according to the above (6) or (7), wherein the inner pad has a pressing direction dimension of 100 mm as a lower limit and satisfies the following formula.

h 100 × (t / 2.3) × (30 / λ) × (2 / W) × (1/S)

Here, h: the direction of the pressing direction of the inner pad (mm) t: the thickness of the blank (mm) l: the thermal conductivity of the inner pad (W/mK) W: the volume ratio of the refrigerant path inside the inner pad (mm ³ /mm ³ ) S: Flow rate of refrigerant in the refrigerant path (mm/sec)

(9) The hot press system according to any one of the aspects of the present invention, characterized in that the refrigerant injection unit further includes a refrigerant injection unit that injects a refrigerant into the inner pad, and the refrigerant injection unit is in a slave The mold takes out the press-formed product until the next blank is placed between the molds, and the fluid is sprayed on the inner mat to cool the inner mat.

(10) The hot press system according to any one of the preceding aspects, wherein the upper mold is provided with a refrigerant injection hole that can inject a refrigerant toward the inner pad; The mold takes out the press-formed product until the next blank is placed between the molds, and the press brings the upper mold closer to the lower mold, and the cooling control unit causes the refrigerant to pass from the refrigerant injection hole toward the lower mold. The aforementioned inner pad is sprayed, thereby cooling the aforementioned inner pad.

According to the present invention, it is possible to suppress cracking and strength improvement of the press-formed product.

MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the embodiment of the present invention, an example in which the first press-molded article is produced using the first die and an example in which the second press-molded article is produced using the second die are shown. For the sake of explanation, the "first mold" and the "second mold" are both referred to as "the first mold" and the "second press molded product". . Then, in the embodiment of the present invention, one press-molded article is produced by one cycle of hot press forming, and a plurality of press-molded articles are continuously produced by repeating the hot press forming cycle. Moreover, in each figure, the pressurization direction is shown by the arrow P. In addition, the pressurization direction P means the relative movement direction of the upper mold and the lower mold at the time of hot press forming, and is an up-down direction in embodiment of this invention.

<Pressure Molded Article> First, a configuration example of the press-molded articles 8 and 9 produced by the hot press method according to the embodiment of the present invention will be described. The press-molded articles 8 and 9 produced by the hot press method according to the embodiment of the present invention are exemplified by the first press-molded article 8 shown in Fig. 1 and the second press-molded article 9 shown in Fig. 2 . The first press-molded article 8 and the second press-molded article 9 are produced by hot press forming a steel sheet of the billet 7. The steel sheet to which the blank 7 is applied has a carbon content of 0.09 to 0.50%, more preferably 0.11% or more, and a thickness of 0.6 to 3.2 mm, more preferably about 2.3 mm, for the hardenability.

As shown in FIGS. 1 and 2, the press-molded articles 8 and 9 each have a cap-shaped portion. The cap-shaped portion has: top plate portions 81, 91; two ridge portions 82, 92 which are formed continuously on both sides of the top plate portions 81, 91; and two vertical wall portions 83, 93 which are continuous with two ridge portions Each formed. The top plate portions 81 and 91 are, for example, plate-like portions extending in a direction substantially perpendicular to the pressing direction P. The ridge portions 82, 92 are portions that are bent or flexed with a predetermined curvature. The vertical wall portions 83, 93 are portions that are inclined at a predetermined angle with respect to the pressing direction P or parallel to the pressing direction P.

In the first press-molded article 8, as shown in FIG. 1, at least one of the two ridge portions 82 and the two vertical wall portions 83 is provided with a curved portion 84, which is viewed from the viewpoint of the pressurization direction. Bending or flexing to extend in a predetermined direction. Further, as shown in FIG. 2, the top plate portion 91 of the second press-molded article 9 has a portion in which the height direction position (pressure direction position) is different. Then, a portion having a higher height of the top plate portion 91 (hereinafter referred to as "top plate high portion 911") and a portion having a lower height (hereinafter referred to as "top plate lower portion 912") are step portions of the step portion of the stepped portion. 913 to divide.

Further, both of the press-molded articles 8 and 9 shown in Fig. 1 and Fig. 2 are exemplified by a press-molded article produced by the hot press method of the embodiment of the present invention. The press-molded article produced by the hot press method according to the embodiment of the present invention is not limited to the shape shown in Fig. 1 or Fig. 2 .

<Mold> Next, a configuration example of the molds 2 and 3 used in the hot press method according to the embodiment of the present invention will be described with reference to Figs. 3A to 4 . 3A is a cross-sectional view schematically showing a configuration example of the first metal mold 2 used for manufacturing the first press-molded product 8, and is a punch that cuts the molded curved portion 84 at a right angle to the longitudinal direction of the top plate portion 81. A cross-sectional view of the curved portion 216. 3B is a perspective view schematically showing a configuration example of the punch 21 for manufacturing the first metal mold 2, and is a view showing a portion of the curved curved portion 84. 4 is a cross-sectional view schematically showing a configuration example of the second mold 3 used for manufacturing the second press-molded article 9, and is a portion in which the top plate height portion 911, the top plate step portion 913, and the top plate lower portion 912 are formed in parallel. A cross-sectional view taken along the plane of the alignment direction.

As shown in FIG. 3A, FIG. 3B and FIG. 4, the molds 2, 3 respectively have: punches 21, 31 as lower molds; dies 22, 32 as upper molds; inner pads 23, 33, which can be moved back and forth The punches 21 and 31 are provided in the pressing direction P; and the potential energy mechanisms 24 and 34 are provided, and the inner pads 23 and 33 are biased toward the dies 22 and 32.

The punches 21, 31 have punch projections 211, 311 which protrude toward the die 22, 32 side; punch tops 212, 312 which are provided at the front ends of the punch projections 211, 311; and two punch shoulders R The corner portions 213 and 313 are continuously disposed on the punch top portions 212 and 312, and the two punch vertical wall portions 214 and 314 are continuously provided in each of the two punch shoulder R corner portions 213 and 313. The punch tops 212 and 312 are portions of the top plate portions 81 and 91 of the press-molded products 8 and 9, and have a planar configuration which is substantially perpendicular to the pressing direction P, for example. The punch shoulder R corner portions 213 and 313 are portions of the ridge portions 82 and 92 of the press-formed products 8 and 9, and have a curved shape having a predetermined radius of curvature. The punch vertical wall portions 214 and 314 are portions of the vertical wall portions 83 and 93 of the press-formed products 8 and 9, and have a planar shape inclined at a predetermined angle toward the pressurizing direction P, or a plane parallel to the pressurizing direction P. Shaped. Further, the specific shape of each of the punches 21 and 31 is defined by the shape of the press-molded articles 8 and 9 to be manufactured, and is not limited to the shape shown in FIG. 3A, FIG. 3B or FIG.

As shown in FIG. 3B, in the first mold 2, at least one of the two punch shoulder R corner portions 213 and the two punch vertical wall portions 214 is provided with a punch curved portion 216 for forming the curved portion 84. The punch curved portion 216 is bent or bent to protrude in a predetermined direction from the viewpoint of the pressurizing direction. Further, as shown in FIG. 4, in the second mold 3, in order to form the top plate height portion 911 and the top plate lower portion 912 having different heights of the top plate portion 91, portions having different heights are provided on the punch top portion 312. Specifically, a punch high top 316 and a punch low top 317 are provided. The punch high top 316 is a portion for forming the top plate high portion 911, and the height is high, and the punch low top portion 317 is used to form the top plate low. The portion of the portion 912 has a lower height.

As shown in FIG. 3A, an inner pad receiving hole 215 is provided in the punch top 212 of the punch 21 of the first die 2, and the inner pad 23 is accommodated so as to be movable back and forth in the pressing direction P. The inner pad 23 is an additional member that is different from the punch 21. The inner pad 23 is provided with an inner pad top 231 located on the opposite side from the die 22, and an inner pad R corner 232 continuing from both sides of the inner pad top 231. The inner pad shoulder R corner portion 232 has a curved shape, and the curved shape has a predetermined radius of curvature.

Then, the inner pad 23 is biased toward the die 22 by the potential energy supply mechanism 24, and the inner pad top portion 231 and the inner pad shoulder R corner portion 232 are maintained to protrude from the punch top portion 212 toward the die 22 side by a predetermined size. The protruding dimension of the inner pad 23 is set such that the blank 7 does not contact the size of the punch top 212 and the punch shoulder R corner 213 in a state where the blank 7 is placed on the inner pad top 231. However, the specific protruding size is not particularly limited. Further, when the inner pad 23 is pressed from the side of the die 22, it enters the inside of the inner pad receiving hole 215, and the inner pad top 231 and the punch top 212 have the same height. In other words, the inner pad top 231 and the punch top 212 are flush planes. In this state, the inner pad top 231 becomes part of the punch top 212.

As shown in FIG. 4, an inner pad receiving hole 315 is also provided in the punch top 312 of the punch 31 of the second die 3, and the inner pad 33 is accommodated so as to be movable back and forth in the pressing direction. P, the inner pad 33 is an additional member different from the punch 31. Further, in the second mold 3, the inner pad receiving hole 315 is provided in the punch lower top portion 317 (the portion where the top plate lower portion 912 is formed). Further, as shown in Fig. 4, the punch high top portion 316 and the inner pad 33 are separated from each other by a predetermined distance in a direction perpendicular to the pressing direction P (the paper surface in Fig. 4 is a left-right direction). For example, as shown in FIG. 4, the punch low top 317 is interposed between the punch top 316 and the inner pad 33. This distance is set to a portion of the top step portion 913 and the vertical wall portion 93 in the billet 7 in a state where the billet 7 is placed on the inner top portion 231 and the punch top portion 316 (particularly, the vertical wall portion 93). The portion located near the top step portion 913 does not contact the distance between the inner pad 33 and the punch high top 316.

Then, in the second mold 3, the inner pad 33 is provided with the potential energy mechanism 34, and the potential energy is applied toward the die 32 side, and the inner pad top portion 331 is maintained in a state of being protruded toward the die 32 side from the punch lower top portion 317. The protruding dimension is set such that if the blank 7 is placed on the inner pad top 331 and the punch high top 316, the blank 7 does not contact the size of the punch lower top 317. Further, when the inner pad 33 is pressed from the side of the die 32, it enters the inside of the inner pad receiving hole 315, and the inner pad top 331 and the punch lower top 317 have the same height. In this state, the inner pad top 331 becomes part of the punch low top 317.

Further, the inner pads 23 and 33 may be configured to support at least a part of the top plate portions 81 and 91 after the hot press forming. In particular, when the inner pads 23 and 33 are formed during the hot press forming, the blank 7 can be supported, and the portion to be applied by tension or the vicinity thereof in the direction perpendicular to the pressurizing direction P may be used. Further, the configuration may be such that the main material 7 can be supported, and the entire portions of the top plate portions 81 and 91 may be formed after hot press forming. FIG. 3B shows a configuration in which the inner pad 23 is provided in the punch curved portion 216 and its vicinity, but the inner pad may be provided over the entire length of the punch top portion 212.

Further, the configuration of the potential energy mechanisms 24 and 34 may be such that the inner pads 23 and 33 can be provided with potential energy toward the dies 22 and 32, and the specific configuration is not limited. For the energy-enhancing mechanisms 24 and 34, various types of potential-enhancing mechanisms such as springs or air cushions can be applied.

The dies 22 and 32 are provided with die recesses 221 and 321 into which the punch projections 211 and 311 can be fitted. Die edge R corner portions 222 and 322 are provided at the edge portions of the die recesses 221 and 321 . The die shoulder R corner portions 222, 322 have a curved shape having a predetermined radius of curvature. The refrigerant injection holes 223 and 323 are provided at the bottoms of the die recesses 221 and 321 at positions facing the inner pads 23 and 33 accommodated in the inner pad receiving holes 215 and 315 for injecting the refrigerant toward the inner pad 23. The refrigerant injection holes 223 and 323 are a part of the inner pad cooling mechanism 13 (described later) that cools the inner pads 23 and 33. The inner pads 23 and 33 can be cooled by ejecting a refrigerant such as water or air from the refrigerant injection holes 223 and 323 toward the inner pads 23 and 33.

<Inner Pad Configuration and Cooling Method> Here, a detailed configuration example of the inner pads 23 and 33 and a cooling method will be described. In the embodiment of the present invention, by using the molds 2 and 3, the billet 7 which is heated to a temperature range of 700 to 950 ° C and heated to a temperature of about 750 ° C is molded and cooled to produce a press-molded product 8 . 9. Then, at the time of hot press forming, the blank 7 is supported by the inner pads 23, 33, and formed into a predetermined shape by the punches 21, 31 and the dies 22, 32. Therefore, at the time of hot press forming, a part of the blank 7 comes into contact with the inner pads 23, 33.

In the press-molded articles 8 and 9 thus produced, in order to make the strength of the hot press-molding contact inner pads 23 and 33 to be 1500 MPa or more, the cooling rate of the portion must be 30 ° C/sec or more. However, since the inner pads 23, 33 are small in volume compared to the punches 21, 31 or the dies 22, 32, the temperature tends to rise during hot press forming. In particular, when a plurality of press-molded articles 8 and 9 are continuously produced by repeating the cycle of hot press forming, the inner pads 23 and 33 are easily maintained in a temperature rising state. Then, when hot press forming is performed in a state where the inner pads 23 and 33 are heated, the cooling rate of the portion of the blank 7 contacting the inner pads 23 and 33 is slowed down, and a predetermined strength cannot be obtained. Therefore, in the embodiment of the present invention, by adopting the following configuration of the inner pads 23, 33 and the cooling method, the cooling rate of the portion of the blank 7 contacting the inner pads 23, 33 can be accelerated, and the predetermined strength can be obtained.

The material of the inner pads 23 and 33 is not particularly limited, and is preferably a material having a thermal conductivity l of 30 W/mK or more and a specific heat C of 4.3 J/g×K or more. Such materials can be applied, for example, to tool steel or the like. Further, as shown in FIG. 3A and FIG. 4, in the inside of the inner pads 23 and 33, the refrigerant paths 233 and 333 which are pipe-shaped (that is, hollow) are provided. The refrigerant paths 233 and 333 have a configuration in which a fluid refrigerant such as water or air can flow. The volume ratio W of the refrigerant paths 233 and 333 (=the volume of the refrigerant paths 233 and 333 (mm ³ ) / the volume of the inner pads 23 and 33 (mm ³ )) is preferably 0.01 to 0.10. Further, the depth from the inner pad tops 231, 331 to the refrigerant paths 233, 333 is preferably 10 to 30 mm. According to this configuration, the surface temperature of the inner pad tops 231, 331 (that is, the surface temperature of the surface contacting the blank 7) is caused by the refrigerant flowing through the refrigerant paths 233, 333 provided inside the inner pads 23, 33. The preforms 8 and 9 are taken out from the molds 2 and 3, and the next billet 7 is placed, and cooled to a predetermined temperature to be described later.

Moreover, the dimension (height) h in the pressing direction of the inner pads 23 and 33 is preferably a size of 100 mm as the lower limit and satisfies the following formula (1). H3100 ́(t/2.3) ́(30/l) ́(2/W) ́(1/S) Equation (1) Here, h: the protruding dimension of the inner pad (mm) t: the thickness of the blank ( Mm) l: thermal conductivity of the inner pad (W/mK) W: volume ratio of the refrigerant path inside the inner pad (mm ³ /mm ³ ) S: flow rate of the refrigerant in the refrigerant path (mm/sec)

Further, the area of the inner pad tops 231 and 331 (the surface contacting the blank 7) is defined by the shape of the press-molded articles 8 and 9 to be produced, and the like, and is applicable, for example, in the range of 3,000 to ^20,000 mm ² , and more preferably to the extent of 5000 mm ² . . By specifying the sizes of the inner pads 23 and 33 in this manner, it is possible to suppress an increase in the temperature of the inner pads 23 and 33 during the hot press forming, and to suppress a decrease in the cooling rate of the billet 7. That is, when the volume of the inner pads 23, 33 is small, the temperature of the blank 7 is raised during hot press forming, and the cooling rate of the blank 7 is slowed down, so that the quenching is insufficient. Therefore, by setting the inner pads 23 and 33 to have such a size, for example, the blank 7 having a thickness of 0.6 mm to 3.2 mm can secure a cooling rate of 30° C./sec or more.

Further, as described above, in order to allow the tensile strength of the portion contacting the inner pads 23 and 33 to be 1500 MPa or more during hot press forming, the cooling rate of the portion must be 30 ° C/sec or more. Therefore, before the hot press forming (that is, when the blank 7 is placed on the molds 2, 3), the refrigerant flows through the refrigerant paths 233, 333 of the inner pads 23, 33 to cool the inner tops 231, 331 of the inner pads. The surface temperature T becomes equal to or lower than a predetermined temperature. Specifically, the surface temperature T of the inner pad tops 231 and 331 before the start of the hot press forming is cooled to an upper limit of 100° C. and satisfies the following formula (2). T£100 ́(2.3/t) ́(h/100) ́(l/30) ́(W/2) ́S Equation (2) Here, T: surface temperature of the inner pad (°C) t: embryo Thickness of material (mm) h: Outburst size of inner pad (mm) l: Thermal conductivity of inner pad (W/mK) W: volume ratio of refrigerant path inside inner pad (mm ³ /mm ³ )

S: the flow rate of the refrigerant in the refrigerant path (mm/sec). If the surface temperature T of the inner pad tops 231, 331 before the start of the hot press forming is the upper limit of 100 ° C, and the above formula (2) is satisfied, the hot pressing can be performed. At the time of molding, the tensile strength of the portion contacting the inner pads 23, 33 is 1500 MPa or more.

Then, when a plurality of press-molded articles 8 and 9 are produced by repeating the cycle of hot press forming, in order to satisfy the above temperature conditions, it is necessary to take out the press-molded articles produced by the previous hot press forming from the molds 2 and 3. 8 and 9, the time for cooling the inner pads 23, 33 (hereinafter referred to as "standby time A") is set until the next blank 7 is placed in the molds 2, 3. In the embodiment of the present invention, the standby time A is a time represented by the following formula (3) with a lower limit of 5 seconds.

here,

A: Standby time (sec)

t: thickness of the billet (mm)

h: protruding size of the inner pad (mm)

λ: thermal conductivity of the inner pad (W/mK)

W: volume ratio of the refrigerant path inside the inner pad (mm ³ /mm ³ )

S: The flow rate (mm/sec) of the refrigerant in the refrigerant path is such that the surface temperature T of the inner pad tops 231 and 331 before the start of the hot press forming can be the above temperature.

<Hot Press System>

Next, a configuration example of a hot press system 1 according to an embodiment of the present invention can be described. FIG. 5 is a view schematically showing a configuration example of the hot press system 1. As shown in Fig. 5, the configuration of the hot press system 1 includes a press 11 which press-forms the billet 7 using the molds 2, 3, a pressurization control unit 12 which controls the press 11 and an inner pad cooling mechanism 13 The cooling inner pads 23, 33 and the cooling control portion 14 control the inner pad cooling mechanism 13. When the first press-molded product 8 is used in the molds 2 and 3 of the press 11, the first mold 2 is applied, and when the second press-molded product 9 is produced, the second mold 3 is applied. Further, the hot press system 1 may further include a workpiece transfer mechanism 15 that sets the blanks 7 to the molds 2, 3 and takes out the formed press-formed products 8, 9 from the mold; and the workpiece transfer control portion 16, which controls the workpiece Transport mechanism 15.

The press 11 may have a configuration in which the blanks 7 can be formed by using the molds 2 and 3, and the blank 7 is not particularly limited. The press 11 can be applied to various conventional presses. The workpiece transfer mechanism 15 may be provided with the blanks 7 for the molds 2 and 3, and the formed press-molded articles 8 and 9 may be taken out from the molds 2 and 3, and the specific configuration is not particularly limited. For example, various types of conveying apparatuses, conveying robots, and the like can be applied to the workpiece conveying mechanism 15.

The inner pad cooling mechanism 13 includes refrigerant paths 233 and 333 of the inner pads 23 and 33, refrigerant injection holes 223 and 323 provided in the dies 22 and 32, and supply of the refrigerant paths 233 and 333 and the refrigerant injection holes 223 and 323. The refrigerant supply source 131 of the refrigerant. In the embodiment of the present invention, a fluid such as water or air can be applied to the refrigerant. Further, the temperature of the refrigerant may be normal temperature (room temperature), but it may be cooled to a temperature lower than normal temperature using a temperature. At this time, the inner pad cooling mechanism 13 further has a refrigerant cooling mechanism that cools the refrigerant. In the embodiment of the present invention, the cooling control unit 14 controls the cooling of the inner pads 23 and 33 by controlling the supply of the refrigerant. For example, the cooling control unit 14 controls the timing of supplying the refrigerant to the refrigerant paths 233 and 333 of the inner pads 23 and 33, and the flow rate of the refrigerant, and controls the timing of injecting the refrigerant from the refrigerant injection holes 223 and 323 of the dies 22 and 32 and the injected refrigerant. the amount.

Further, the inner pad cooling mechanism 13 is not limited to the configuration in which the refrigerant injection holes 223 and 323 are provided in the dies 22 and 32. Here, another configuration example of the inner pad cooling mechanism 13 will be described. FIG. 6 is a view schematically showing another configuration example of the inner pad cooling mechanism 13. As shown in FIG. 6, the inner pad cooling mechanism 13 has a refrigerant injection nozzle 132 as a refrigerant injection portion for injecting a refrigerant, instead of the refrigerant injection holes 223 and 323 provided in the dies 22 and 32. The refrigerant injection nozzle 132 (refrigerant injection portion) is provided in the vicinity of the molds 2, 3 so that the refrigerant can be sprayed toward the inner pads 23, 33. At this time, the cooling control unit 14 controls the timing at which the refrigerant is injected from the refrigerant injection nozzle 132 and the injection amount. Further, the specific configuration of the refrigerant injection nozzle 132 is not particularly limited, and various conventional nozzles can be applied. Further, the refrigerant injection nozzle 132 can also be movable, which can be moved by a moving mechanism. At this time, the moving mechanism causes the refrigerant injection nozzle 132 to approach the inner pads 23 and 33 when the refrigerant is injected into the inner pads 23 and 33 in accordance with the control of the cooling control unit 14, and the refrigerant injection nozzle 132 is retracted during the hot press forming. So as not to interfere with the molds 2, 3. In this manner, the refrigerant ejecting portion that ejects the refrigerant to the inner pads 23 and 33 may be configured to be provided in the molds 2 and 3, or may be provided separately from the molds 2 and 3.

A device having a computer including a CPU, a ROM, and a RAM is applied to each of the pressurization control unit 12, the cooling control unit 14, and the workpiece transfer control unit 16. A computer program for controlling the press is stored in advance in the ROM of the computer of the pressurization control unit 12. Then, the CPU reads out the computer program stored in the ROM and executes the RAM as a work area. Thereby the press 11 is controlled. The same applies to the cooling control unit 14 and the workpiece transfer control unit 16. Then, the hot press method according to the embodiment of the present invention is executed by the cooperation of the computer of the pressurization control unit 12, the cooling control unit 14, and the workpiece transport control unit 16.

<Hot Pressing Method> Next, a hot press method according to an embodiment of the present invention will be described. 7A to 7E are cross-sectional views schematically showing a hot pressing method using the first mold 2. 8A to 8E are cross-sectional views schematically showing a hot pressing method using the second mold 3.

In the present embodiment, at the timing set in the molds 2, 3, the temperature of the billet 7 is in the temperature range of 700 to 950 ° C, more preferably about 750 ° C. Further, at the timing when the blank 7 is placed on the molds 2 and 3, the surface temperatures of the molds 2 and 3 are set to 100 ° C or lower. In particular, as described above, the surface temperature T of the inner pad tops 231 and 331 is set to an upper limit of 100° C. and satisfies the temperature of the above formula (2). Thereby, the cooling rate of the billet 7 at the time of hot press forming can be made 30 ° C /sec or more, and the press-molded products 8 and 9 with predetermined mechanical strength can be manufactured.

First, the case where the first mold 2 is used will be described. As shown in FIG. 7A, at the timing before the start of press molding, the inner pad 23 is maintained in a state of being protruded from the punch top portion 212 by the given potential energy mechanism 24 by a predetermined size. Therefore, at the timing before the start of the hot press forming, the portion of the blank 7 provided in the first die 2 that is the ridge line portion 82 and the vertical wall portion 83 of the first press-molded article 8 is maintained at the top of the punchless contact 212. status. Therefore, it is prevented or suppressed that the temperature of the portion is lowered before the start of hot press forming.

Next, as shown in FIG. 7B, the pressurization control unit 12 controls the press 11 to bring the die 22 close to the punch 21. When the die 22 approaches the die 21, the die shoulder R corner 222 contacts the blank 7. This portion of the blank 7 is referred to as "die shoulder contact portion 71". Here, at the timing immediately after the die shoulder R corner portion 222 is in contact with the die shoulder contact portion 71 of the blank 7, the portion of the blank 7 that is in contact with the inner shoulder R corner portion 232 (this portion is referred to as "inner pad shoulder contact portion 72" The portion between the die shoulder contact portion 71 (this portion is referred to as "non-contact portion 73") is in a state where both the punch 21 and the die 22 are not contacted. Therefore, the temperature drop of the non-contact portion 73 is prevented or suppressed. Then, the blank 7 is supported by the inner pad 23 at a position closer to the die 22 than the punch top 212. With this configuration, the distance between the die shoulder contact portion 71 of the blank 7 and the inner pad shoulder contact portion 72 can be increased, and the distance is increased. The range of the non-contact portion 73 can also increase the range of preventing or suppressing the temperature-reducing portion.

Fig. 7C shows the timing at which the die 22 is at the bottom dead center. If the die 22 is further approached from the state shown in FIG. 7B, the non-contact portion 73 of the blank 7 is pushed to the punch top 212 and the punch shoulder R corner portion 213 as shown in FIG. 7C. Further, as the die 22 approaches the punch 21, the inner pad 23 is pressed, and the inner pad 23 becomes smaller from the protruding size of the punch top 212. If the die 22 reaches the bottom dead center, the inner pad top 231 and the punch top 212 are the same height and become part of the punch top 212. Then, the non-contact portion 73 becomes the ridge portion 82 and the vertical wall portion 83 of the first press-molded article 8, and is cooled and quenched by contacting the punch top portion 212 and the punch shoulder R corner portion 213. Furthermore, the die shoulder contact portion 71 of the blank 7 is cooled and quenched by contact with the die shoulder R corner portion 222, and the inner pad shoulder contact portion 72 does not contact the punch shoulder R corner portion 213 by contacting the inner shoulder pad R corner portion 232. It is cooled and quenched in the vicinity.

Thus, at the beginning of the hot press forming, the inner pad top portion 231 protrudes from the punch top portion 212 toward the die 22 side by a predetermined size, and as the die 22 approaches the punch 21, it is pushed toward the die 22 via the blank 7 to protrude the size. It becomes smaller, and if the die 22 reaches the bottom dead center, it becomes a part of the punch top 212. Then, in the hot press method according to the embodiment of the present invention, the first press-molded article 8 is produced by supporting the blank 7 with the inner pad 23 while bringing the die 22 close to the punch 21.

Next, as shown in Fig. 7D, the pressurization control unit 12 controls the press 11 to move the die 22 to the top dead center. Then, the workpiece conveyance mechanism 15 takes out the manufactured first press-molded article 8 from the first mold 2 in accordance with the control of the workpiece conveyance control unit 16. Then, as shown in FIG. 7E, the pressurization control unit 12 controls the press 11 to bring the die 22 closer to the punch 21. In this state, the cooling control unit 14 injects the refrigerant from the refrigerant injection hole 223 provided in the die 22 to cool it. Inner pad 23. In the embodiment of the present invention, the surface temperature T of the inner pad top portion 231 is cooled to an upper limit of 100 ° C and satisfies the temperature indicated by the above formula (2). When the refrigerant is injected, the die 22 is brought close to the inner pad 23 (moving from the top dead center to the bottom dead center side), whereby the flow rate of the refrigerant on the surface of the inner pad top 231 can be increased, and the time during which the inner pad top portion 231 is cooled to the aforementioned temperature can be shortened. After the inner pad top portion 231 is cooled, the pressurization control portion 12 controls the press 11 to move the die 22 to the top dead center. Thereby, a cycle of hot press forming is completed.

Then, the workpiece transport mechanism 15 sets the next blank 7 in the first mold 2 when the standby time A is 5 seconds as the lower limit and the numerical formula (3) is satisfied in accordance with the control of the workpiece transport control unit 16. With this, the surface temperature of the first mold 2 is 100° C. or lower, and in particular, the surface temperature T of the inner pad top 231 is cooled to a temperature of 100° C. and satisfies the temperature expressed by the above formula (2). 1 Mold 2 sets the next blank 7 . Therefore, when the next blank 7 is subjected to hot press forming, the cooling temperature of the portion contacting the inner pad top 231 can be made 30 ° C /sec or more, and the first strength of the predetermined strength (here, 1500 MPa or more) can be produced. Press molded product 8.

Next, an example in which the second mold 3 is used will be described. In addition, about the same method as the method of using the 1st metal mold|die 2, it abbreviate|omits description. FIG. 8A corresponds to FIG. 7A and shows the timing before the start of hot press forming, and the blank 7 is placed in the state of the second mold 3. As shown in FIG. 8A, at the timing before the start of the hot press forming, the inner pad 33 is maintained by the energizing potential mechanism 34 in a state of protruding from the lower end 317 of the punch toward the die 32 side by a predetermined size. In this way, the ridge line portion 92 and the vertical wall portion 93 of the second press-molded product 9 are provided in the blank 7 of the second metal mold 3 at the timing before the start of the hot press forming (in particular, the vertical wall portion 93) The portion close to the top step portion 913 is maintained in a state where it does not contact the lower top portion 317 of the punch, and prevents or suppresses a temperature drop before the start of thermoforming.

As shown in FIG. 8B, the pressurization control unit 12 controls the press 11 to bring the die 32 close to the punch 31. When the die 32 approaches the die 31, the die shoulder R corner 322 contacts a predetermined portion of the blank 7 (die shoulder contact portion 71). As shown, the blank 7 is pressed by the inner pad top 331 and the die 32 before reaching the bottom dead center. Thus, the blank at the top 316 of the punch can be pulled into the lower top 317 of the punch before reaching the bottom dead center. Thereby, it is possible to reduce the tension generated in the direction perpendicular to the pressing direction P (the tension in the left-right direction of the paper surface) in the vicinity of the bottom dead center in the ridge portion 92 and the vertical wall portion 93 formed in the lower portion 912 of the top plate.

Fig. 8C shows the timing at which the die 32 is at the bottom dead center. If the die 32 is closer to the punch 31 from the state of the timing shown in FIG. 8B, as shown in FIG. 8C, if the die 32 reaches the bottom dead center, the inner pad top 331 and the lower punch top 317 have the same height, which becomes a low punch. Part of the top 317.

Fig. 8D is a view corresponding to Fig. 7D. As shown in Fig. 8D, the pressurization control unit 12 controls the press 11 to move the die 32 to the top dead center. Then, the workpiece conveyance mechanism 15 takes out the manufactured second press-molded product 9 from the second mold 3 in accordance with the control of the workpiece conveyance control unit 16.

Thereafter, as shown in Fig. 8E (Fig. 8E is a view corresponding to Fig. 7E), the pressurization control unit 12 controls the press 11 to bring the die 32 close to the punch 31 (from the top dead center to the bottom dead center side), In this state, the cooling control unit 14 injects the refrigerant from the refrigerant injection hole 323 provided in the die 32 to cool the inner pad 33. The cooling temperature is the same as that in the case of using the first mold 2. After the inner pad 33 is cooled, the pressurization control unit 12 controls the press 11 to move the die 32 to the top dead center. Thereby, a cycle of hot press forming is completed.

Then, after the cycle of the hot press forming is completed, the cycle of the next hot press forming is performed. Further, the standby time A is the same as that when the first mold 2 is used. According to this method, the same effects as those in the case of using the first mold 2 are exhibited.

<Suppression of cracking by the inner pad> Next, the crack suppression of the press-molded articles 8 and 9 of the inner pads 23 and 33 will be described in comparison with the example of the molds 5 and 6 of the comparative example having no inner pads 23 and 33. Features. When formed into a hat shape such as the first press-molded article 8 and has the shape of the curved portion 84, the vertical wall portion 83 on the outer peripheral side of the curved portion 84 is likely to be cracked. Further, when the second press-molded article 9 is provided with the shape of the top step portion 913 in the hat-shaped top plate portion 91, the portion of the vertical wall portion 93 that is close to the top step portion 913 is likely to be cracked. These parts have the following features (i) to (iii). (i) In the hot press forming, the tension is applied not only to the pressing direction P but also to a direction perpendicular to the pressing direction P. (ii) Since it is not in contact with the molds 2 and 3, it is maintained at a high temperature. (iii) being sandwiched by the die shoulder R corner portion 222 of the molds 2, 3 and the punch shoulder R corner portion 213.

Then, at the time of hot press forming of the first press-molded article 8, the deformation is concentrated on the vertical wall portion 83 on the outer peripheral side of the curved portion 84. In the second press-molded article 9, at the time of hot press forming, the deformation is concentrated on a portion close to the top step portion 913 (the portion where the height of the top plate portion 91 changes) of the vertical wall portion 93. Therefore, in these portions, the plate thickness reduction rate becomes high, and cracking easily occurs. Therefore, in the hot press method according to the embodiment of the present invention, the inner pad 23, 33 is used as the portion of the vertical wall portion 83 on the outer peripheral side of the curved portion 84 or the vertical wall portion 93 among the blanks 7. The portion which is close to the portion of the top step portion 913 is expanded to prevent or suppress the range in which the temperature is lowered. Thereby, the deformation is suppressed from being concentrated locally, and cracking is prevented or suppressed.

FIG. 9 is a cross-sectional view showing a configuration example of the mold 5 of the first comparative example, and is a configuration example schematically showing a mold having no inner pad 23. The same components as those of the first mold 2 are denoted by the same reference numerals and will not be described. As shown in FIG. 9, in the punch 51 of the mold 5 of the first comparative example, the inner pad 23 is not provided, and the refrigerant injection hole 223 is not provided in the die 52. Other than this, the same configuration as that of the first mold 2 is applied.

When the first press-molded article 8 is produced using the mold 5 of the first comparative example having no inner pad 23, the blank 7 is hot-pressed in a state of being supported by the punch top portion 212. Then, the die shoulder contact portion 71 of the blank 7 is cooled by contacting the die shoulder R corner portion 222, and the punch shoulder contact portion 74 (the portion of the billet 7 that contacts the punch shoulder R corner portion 213) is contact-punched. The head and shoulder R corners 213 are cooled. According to this configuration, the range of the non-contact portion 73 between the die shoulder contact portion 71 and the punch shoulder contact portion 74 is narrower than that of the first mold 2 having the inner pad 23. That is, the range in which the temperature reduction is suppressed is narrow. Then, the deformation is concentrated in the small range, so the plate thickness reduction rate becomes high, and cracking easily occurs. In other words, when the curved portion 84 is provided in the first press-molded article 8, the deformation is concentrated on the portion of the curved portion 84 of the vertical wall portion 83. This is because when the ridge portion 82 is bent as viewed from the viewpoint of the pressurizing direction, the flow of the billet 7 becomes uneven at the time of hot press forming.

On the other hand, as shown in FIG. 7B, in the embodiment of the present invention, the first mold 2 having the inner pad 23 is used, and the inner pad 23 supports the portion of the blank 7 which becomes the top plate portion 81. The head top portion 212 protrudes toward the die 22 side by a predetermined size. In this state, the distance between the die shoulder R angle portion 222 and the inner shoulder R angle portion 232 is larger than the distance between the die shoulder R corner portion 222 and the punch shoulder R corner portion 213 from the viewpoint of the pressurizing direction. According to this configuration, the range of the non-contact portion 73 can be increased as compared with the mold 5 of the first comparative example.

Then, while maintaining the state, the punch 21 and the die 22 are relatively close to each other and clamped, whereby the first press-molded article 8 is produced. At this time, the die shoulder contact portion 71 of the blank 7 is cooled by contacting the die shoulder R corner portion 222, and the inner pad shoulder contact portion 72 is not cooled by contacting the punch shoulder R corner portion 213 by contacting the inner shoulder pad R The corners 232 are cooled. According to this configuration, the range of the range of the non-contact portion 73 (that is, the portion that prevents or suppresses the temperature drop) can be increased. Therefore, the portion of the billet 7 that becomes the curved portion 84 suppresses the concentration of deformation during hot press forming. Therefore, the plate thickness reduction rate is reduced, and cracking is suppressed.

10A and 10B are contour maps showing numerical analysis of the thickness reduction rate when the first press-molded article 8 is produced. In each case, FIG. 10A shows a case where the first mold 2 is used, and FIG. 10B shows a case where the mold 5 of the first comparative example is used. Moreover, the numerical value enclosed by the four corners in the figure indicates the plate thickness reduction rate. 10C and 10D are contour maps showing numerical analysis of the temperature of each part when the first press-molded article 8 is manufactured. In each case, FIG. 10C shows a case where the first mold 2 is used, and FIG. 10D shows a case where the mold 5 of the first comparative example is used. In FIGS. 10C and 10D, the black-coated region indicates a region in which the die 22 is located at 10 mm above the bottom dead center and has a temperature of 650 ° C or higher.

10A and FIG. 10B, and FIG. 10C and FIG. 10D, it can be seen that when the first press-molded article 8 is produced by hot press forming, the method of using the first die 2 is compared with the use of the first comparative example. In the method of the mold 5, the portion of the vertical wall portion 83 located at the curved portion 84 can expand the range of the portion where the temperature drop is suppressed. In this way, the deformation can be concentrated locally, and the reduction rate of the thickness can be suppressed, and the cracking of the curved portion 84 of the vertical wall portion 83 can be prevented or suppressed.

Further, in the embodiment of the present invention, the first press-molded article 8 has a curved portion 84 which is curved in the direction of the pressurization direction, and is shown in the curved portion 84, and prevents or suppresses the occurrence of cracking, but even It is a press-formed product other than this type of shape, and it can prevent or suppress the occurrence of cracking. For example, the hot press method according to the embodiment of the present invention can be applied to a press-formed product having an annular ridge portion such as a circular shape, an elliptical shape, or a polygonal shape as viewed from the viewpoint of the pressurization direction; It can prevent or inhibit the occurrence of cracking.

FIG. 11 is a view schematically showing a configuration example of the mold 6 of the second comparative example, and shows an example of a mold having no inner pad 33. As shown in Fig. 11, in the punch 61 of the mold 6 of the second comparative example, the inner pad 33 is not provided, and the refrigerant injection hole 323 is not provided in the die 62.

As shown in Fig. 11, when the second press-molded article 9 is produced using the mold 6 of the second comparative example, the punch high top portion 316 is in contact with the blank 7 before the punch lower top portion 317, and the top plate high portion 911 is lower than the top plate lower portion 912. Formed first. Then, as the hot press forming progresses, the point 7 of the punch lower top 317 is in contact with the blank 7, and the blank 7 is limited by the formed punch high top 316. Therefore, in the portion of the vertical wall portion 93 that is close to the top step portion 913, the material inflow is insufficient, and tension occurs in the left and right direction of the paper surface, so that cracking easily occurs in the portion.

In the embodiment of the present invention, by using the second mold 3 having the inner pad 33, the portion of the vertical wall portion 93 (particularly the portion close to the top step portion 913) is expanded to prevent or suppress the temperature drop. . Thereby, the deformation can be moderated to the local area, and cracking can be prevented or suppressed. Further, as shown in FIG. 8A, the inner pad 33 supports the portion of the blank 7 which becomes the top plate portion 91 and the portion which becomes the top step portion 913 and the vicinity thereof, and is subjected to hot press forming. Thereby, the portion of the blank 7 on the upper side of the punch top 316 and the portion on the upper side of the lower top 317 of the top plate are formed substantially simultaneously into the top plate upper portion 911 and the top plate lower portion 912. Therefore, at the time of hot press forming, the tension in the left-right direction of the paper surface generated in the non-contact portion 73 can be reduced.

Then, by the inner pad 33, the action of the aforementioned tension generated in the blank 7 and the action of expanding the range of the non-contact portion 73 of the blank 7 are greatly enhanced, and the moldability is greatly improved. When the second press-molded article 9 including the top plate height portion 911 and the top plate low portion 912 is manufactured, the second mold 3 having the inner pad 33 can be used to approach the top plate step portion 913 among the vertical wall portions 93. The portion (continuous to the vertical wall portion 93 of the lower portion 912 of the top plate) prevents or suppress the occurrence of cracking due to the application of the tension in a direction perpendicular to the pressing direction P.

12A and 12B are contour maps showing numerical analysis of the thickness reduction rate when the second press-molded product 9 is produced. The numerical value surrounded by a square in the figure indicates the plate thickness reduction rate. In each case, FIG. 12A shows a case where the second mold 3 is used, and FIG. 12B shows a case where the mold 6 of the second comparative example is used. 12C and FIG. 12D are views showing a region where the temperature of the die 32 is 650 ° C or higher in a state where the die 32 is placed 4 mm above the bottom dead center when the second press-molded article 9 is produced. In each case, FIG. 12C shows a case where the second mold 3 is used, and FIG. 12D shows a case where the mold 6 of the second comparative example is used. Further, the black-coated region indicates a region having a temperature of 650 ° C or lower.

12A and FIG. 12B, and FIG. 12C and FIG. 12D, it can be seen that when the second mold 3 is used, the range of the non-contact portion 73 of the blank 7 can be expanded compared to the mold 6 of the second comparative example. This can alleviate the deformation and concentrate on the local part, and suppress the increase in the thickness reduction rate. Therefore, it is possible to prevent or suppress the cracking of the portion of the vertical wall portion 93 that is close to the top step portion 913.

<Embodiment> Next, an embodiment will be described. In the examples of the present invention, the tensile strength was set to 1500 MPa, and a press-molded article was produced, which was measured for the following (1) and (2). (1) The mechanical strength of the portion where the press-formed products 8, 9 are brought into contact with the inner top portions 231, 331 of the inner molded top portions 231, 331 at the timing when the blank 7 is placed on the molds 2, 3. (2) The relationship between the standby time A (the time from which the press-molded articles 8, 9 are taken out from the molds 2, 3 to the time when the next blank 7 is set) and the surface temperature T of the inner pad tops 231, 331.

The measurement conditions are as follows. The contact area of the blank 7 with the inner pads 23, 33 was 5000 mm ² . The pressing direction dimension h of the inner pads 23, 33 is 100 mm. The inner pads 23, 33 are tool steels having a thermal conductivity l of 30 W/mK and a specific heat C of 4.3 J/g x K. The volume ratio W of the refrigerant paths 233, 333 inside the inner pads 23, 33 is 0.02. The depth from the surface of the inner pads 23, 33 to the refrigerant paths 233, 333 is 20 mm. The billet 7 used a carbon steel sheet having a mass percentage of 0.11% and a thickness t of 2.3 mm. When the blank 7 was placed on the molds 2, 3, the temperature of the blank 7 was 750 °C. The refrigerant uses water. The refrigerant flow rate in 233, 333 in the refrigerant path is 1 m/s.

Fig. 13 is a view showing the surface temperature T of the inner pad tops 231, 331 at the timing at which the blank 7 is placed on the dies 2, 3, and the mechanical strength of the portions of the manufactured press-molded articles 8, 9 which are in contact with the inner pad tops 231, 331 Diagram of the relationship. Further, the surface temperature T of the inner pad tops 231, 331 is a value calculated by the above formula (2). As shown in Fig. 13, it is confirmed that the timing at which the blank 7 is placed on the molds 2, 3 is such that if the surface temperature T of the inner pad tops 231, 331 is 100 ° C or less, the portions of the inner pad top portions 231, 331 which are in contact with the inner pad during hot press molding are formed. The tensile strength is 1500 MPa or more. In particular, in the vicinity of 100 ° C, the tensile strength is rapidly increased. Therefore, it is confirmed that the upper limit of the surface temperature T of the inner pad tops 231 and 331 is set to 100 ° C and the above formula (2) is satisfied.

Fig. 14 is a graph showing the relationship between the standby time A (the time from which the press-molded articles 8, 9 are taken out from the molds 2, 3 to the time when the next blank 7 is set) and the surface temperature T of the inner pad tops 231, 331. Furthermore, the standby time A is a value calculated by the above equation (3). As shown in FIG. 14, as the standby time A becomes longer, the surface temperature T of the inner pad tops 231, 331 becomes lower. Then, in the range where the standby time A exceeds 5 seconds, the surface temperature T of the inner pad tops 231, 331 hardly decreases. In this way, it is preferable to confirm that the standby time A is set to the lower limit of 5 seconds and the above equation (3) is satisfied.

Fig. 15 is a view showing the relationship between the pressing direction dimension h of the inner pads 23, 33 and the surface temperature T of the inner pad tops 231, 331. Furthermore, the measurement conditions are the same as those described above. Moreover, the value of the pressurization direction dimension h is a value calculated by the above formula (1). As the pressing direction dimension h of the inner pads 23, 33 becomes larger, the surface temperature T of the inner pad tops 231, 331 becomes lower. When the pressing direction dimension h of the inner pads 23 and 33 is in the range of 100 mm or more, the surface temperature T of the inner pad tops 231 and 331 hardly decreases even if the pressing direction dimension h becomes large. In this way, it is confirmed that the dimension h of the pressing direction of the inner pads 23 and 33 is set to a lower limit of 100 mm and satisfies the above formula (1).

Embodiments of the present invention have been described in detail above with reference to the drawings. However, the above embodiments are merely illustrative of the implementation of the present invention. The present invention is not limited to the above-described embodiments, and the above embodiments can be modified as appropriate without departing from the scope of the invention.

Industrial Applicability The present invention can be utilized in an industry related to a hot press method and a hot press system that performs a hot press method.

1...Hot press system 2...first mold 3...second mold 5,6...mold 7...binder 8...first press molded product 9...second press molded product 11...press machine 12...pressurization control unit 13... Inner pad cooling mechanism 14 ... cooling control unit 15 ... workpiece transfer mechanism 16 ... workpiece transfer control unit 21 , 31 , 51 ... punches 22 , 32 , 52 ... dies 23 , 33 ... inner pads 24 , 34 ... are provided with potential energy mechanisms 71 ... Die shoulder contact portion 72... inner pad contact portion 73... non-contact portion 74... punch shoulder contact portion 81, 91... top plate portion 82, 92... ridge portion 83, 93... vertical wall portion 84... curved portion 131... refrigerant supply source 132...refrigerant injection nozzles 211, 311... punch projections 212, 312... punch tops 213, 313... punch shoulders R corners 214, 314... punch vertical wall portions 215, 315... inner cushion receiving holes 216... Head curved portions 221, 321 ... die recesses 222, 322 ... die shoulder R corner portions 223, 323 ... refrigerant injection holes 231 ... inner pad top 232 ... inner pad shoulder R corner portions 233, 333 ... refrigerant path 316 ... punch high top 317 ...punch low top 911... top plate high portion 912... top plate lower portion 913... top plate step portion A... standby time h... pressurization direction of inner pad Inch pad P S ... ... pad pressing direction of the refrigerant in the refrigerant flow path inside surface temperature T t ... pad refrigerant path inside the billet thickness W is ... ... ... L the volume ratio of the thermal conductivity

FIG. 1 is a view schematically showing a configuration example of a first press-molded article. FIG. 2 is a view schematically showing a configuration example of a second press-molded article. 3A is a cross-sectional view schematically showing a configuration example of a first mold used for producing a first press-molded article. 3B is a perspective view schematically showing a configuration example of a punch for manufacturing a first mold for use in a first press-molded article. 4 is a cross-sectional view schematically showing a configuration example of a second mold used for manufacturing the second press-molded article. Fig. 5 is a view schematically showing a configuration example of a hot press system. Fig. 6 is a view schematically showing another configuration example of the inner pad cooling mechanism. Fig. 7A is a cross-sectional view schematically showing a state in which a hot press method using a first mold is at a predetermined timing. Fig. 7B is a cross-sectional view schematically showing a state in which a hot press method using a first mold is at a predetermined timing. Fig. 7C is a cross-sectional view schematically showing a state in which a hot press method using a first mold is at a predetermined timing. Fig. 7D is a cross-sectional view schematically showing a state in which a hot press method using a first mold is at a predetermined timing. Fig. 7E is a cross-sectional view schematically showing a state in which a hot press method using a first mold is at a predetermined timing. Fig. 8A is a cross-sectional view schematically showing a state in which a hot press method using a second mold is at a predetermined timing. Fig. 8B is a cross-sectional view schematically showing a state in which a hot press method using a second mold is at a predetermined timing. 8C is a cross-sectional view schematically showing a state in which a hot press method using a second mold is at a predetermined timing. 8D is a cross-sectional view schematically showing a state in which a hot press method using a second mold is at a predetermined timing. 8E is a cross-sectional view schematically showing a state in which a hot press method using a second mold is at a predetermined timing. FIG. 9 is a cross-sectional view schematically showing a configuration example of a mold of a first comparative example. FIG. 10A is a contour diagram showing numerical analysis of a plate thickness reduction rate when a first press-molded article is produced using a first mold. FIG. 10B is a contour diagram showing numerical analysis of the thickness reduction rate when the first press-molded article is produced using the mold of the first comparative example. FIG. 10C is a contour diagram showing numerical analysis of each part temperature when the first press-molded article is produced using the first mold. FIG. 10D is a contour diagram showing numerical analysis of each part temperature when the first press-molded article is produced using the mold of the first comparative example. FIG. 11 is a view schematically showing an example of a mold configuration of a second comparative example. Fig. 12A is a contour diagram showing numerical analysis of a plate thickness reduction rate when a second press-molded article is produced using a second mold. FIG. 12B is a contour diagram showing numerical analysis of the thickness reduction rate when the second press-molded article is produced using the mold of the second comparative example. Fig. 12C is a contour diagram showing numerical analysis of the temperature of each part when the second press-molded article is produced using the second mold. 12D is a contour diagram showing numerical analysis of the temperature of each part when the second press-molded article is produced using the mold of the second comparative example. Fig. 13 is a view showing the relationship between the surface temperature T of the top of the inner pad at the time when the blank is placed on the mold, and the mechanical strength of the portion of the press-formed product which is in contact with the top of the inner pad. Fig. 14 is a graph showing the relationship between the standby time A and the surface temperature T of the top of the inner pad. Fig. 15 is a view showing the relationship between the pressing direction dimension h of the inner pad and the surface temperature T of the inner pad top.

Claims (10)

A hot pressing method for producing a press-formed product by hot pressing a blank having a mold having an upper mold, a lower mold, and an inner mat, wherein the inner cushion is movably received in the lower mold, and the potential energy is imparted toward the foregoing a state in which the upper mold is protruded; characterized in that: a path of the refrigerant is provided inside the inner pad; and the surface temperature of the inner pad is caused by the flow of the refrigerant in the refrigerant, and the press-molded product is taken out from the mold Until the next blank is placed between the aforementioned molds, and cooled to a temperature of 100 ° C and satisfying the following formula; 100 × (2.3 / t) × (h / 100) × (λ / 30) × (W / 2) × S Here, T: surface temperature of the inner pad (°C) h: size of the inner pad's pressing direction ( Mm)t: thickness of the blank (mm) λ: thermal conductivity of the inner pad (W/mK) W: volume ratio of the refrigerant path inside the inner pad (mm ³ /mm ³ ) S: flow rate of the refrigerant in the refrigerant path ( Mm/sec). The hot pressing method of claim 1, wherein the time from which the press-formed product is taken out from the mold to the time when the next blank is placed on the mold is set to a time limit of 5 seconds and a time of the following formula is satisfied; 5 × (t / 2.3) × (100 / h) × (30 / λ) × (2 / W) × (1/S) Here, A: take out the press-molded product from the mold to set the next blank to Time of the mold (sec)h: dimension of the pressing direction of the inner pad (mm) t: thickness of the blank (mm) λ: thermal conductivity of the inner pad (W/mK) W: volume ratio of the refrigerant path inside the inner pad (mm ³ /mm ³ )S: The flow rate of the refrigerant in the refrigerant path (mm/sec). The hot pressing method of claim 1, wherein the pressing direction dimension of the inner pad is a lower limit of 100 mm and satisfies the following formula; 100 × (t / 2.3) × (30 / λ) × (2 / W) × (1/S) Here, h: the direction of the pressing direction of the inner pad (mm) t: the thickness of the blank (mm) λ : Thermal conductivity (W/mK) of the inner pad W: volume ratio of the refrigerant path inside the inner pad (mm ³ /mm ³ ) S: flow rate of the refrigerant in the refrigerant path (mm/sec). The hot pressing method of claim 1, wherein the fluid is sprayed on the inner pad to cool the inner pad, after the press-molded article is taken out from the mold to the next one of the molds. The hot pressing method of claim 1, wherein a refrigerant injection hole is provided in the upper mold, the refrigerant injection hole may spray the refrigerant toward the inner liner; and the press molded product is taken out from the mold to set the next blank to the mold The upper mold is brought close to the lower mold, and the refrigerant is ejected from the refrigerant injection hole toward the inner pad provided in the lower mold. Cool the aforementioned inner pad. A hot pressing system, comprising: a press machine, wherein a billet is heat-pressed using a mold having an upper mold, a lower mold and an inner mat, wherein the inner mat is movably received in the lower mold, and the potential energy is imparted a direction in which the upper mold protrudes, and a path in which a refrigerant is provided inside; and a cooling control unit that controls supply of the refrigerant that cools the inner pad, wherein the cooling control unit causes a flow of the refrigerant to flow through the refrigerant so that The surface temperature of the inner mat is set between the press mold and the next billet between the molds, and is cooled to a temperature of 100 ° C and satisfying the following formula; 100 × (2.3 / t) × (h / 100) × (λ / 30) × (W / 2) × S Here, T: surface temperature of the inner pad (°C) h: size of the inner pad's pressing direction ( Mm)t: thickness of the blank (mm) λ: thermal conductivity of the inner pad (W/mK) W: volume ratio of the refrigerant path inside the inner pad (mm ³ /mm ³ ) S: flow rate of the refrigerant in the refrigerant path ( Mm/sec). The hot pressing system of claim 6, wherein the time from which the press-formed product is taken out from the mold to the time when the next blank is placed on the mold is set to a time limit of 5 seconds and a time of the following formula is satisfied; 5 × (t / 2.3) × (100 / h) × (30 / λ) × (2 / W) × (1/S) Here, A: take out the press-molded product from the mold to set the next blank to Time of the mold (sec)h: dimension of the pressing direction of the inner pad (mm) t: thickness of the blank (mm) λ: thermal conductivity of the inner pad (W/mK) W: volume ratio of the refrigerant path inside the inner pad (mm ³ /mm ³ )S: The flow rate of the refrigerant in the refrigerant path (mm/sec). The hot pressing system of claim 6, wherein the pressing direction dimension of the inner pad is a lower limit of 100 mm and satisfies the following formula; 100 × (t / 2.3) × (30 / λ) × (2 / W) × (1/S) Here, h: the direction of the pressing direction of the inner pad (mm) t: the thickness of the blank (mm) λ : Thermal conductivity (W/mK) of the inner pad W: volume ratio of the refrigerant path inside the inner pad (mm ³ /mm ³ ) S: flow rate of the refrigerant in the refrigerant path (mm/sec). A hot press system according to claim 6, further comprising a refrigerant ejecting portion that ejects the refrigerant to the inner pad; the refrigerant ejecting portion is configured to take the press molded product from the mold to set the next billet to the mold The refrigerant is sprayed on the inner pad to cool the inner pad. The hot pressing system of claim 6, wherein a refrigerant injection hole is provided in the upper mold, the refrigerant injection hole may spray the refrigerant toward the inner liner; and the press molded product is taken out from the mold to set the next blank Between the dies, the press brings the upper mold closer to the lower mold, and the cooling control unit ejects the refrigerant from the refrigerant injection hole toward the inner pad provided in the lower mold, thereby cooling the inner mat.