Technical field
[0001]
　The present invention comprises a hot pressing method, to hot-press systems to perform this hot pressing.
BACKGROUND
[0002]
　For example, structural members for automobiles, from the viewpoint of passenger protection viewpoint of fuel efficiency, can reduce the weight has been required while achieving maintaining or improving the mechanical strength. In general, materials having a high mechanical strength, low moldability during molding processing such as press working, it is difficult to process into complex shapes. As a processing method for improving the moldability of the material having a high mechanical strength, molding as described in Patent Documents 1 and 2, heated material (blank material or pre press-molded article) in a pressing mold quenched with a so-called hot pressing method (hot stamping method, hot pressing method, sometimes called a die quenching method). According to the hot press method, the material at the time of molding is excellent in moldability because they soften at high temperatures, the press-formed product of high mechanical strength by being quenched are quenched in a press mold is obtained.
[0003]
　However, by hot press method, which may crack the press molded article may occur. To prevent cracking of the press-Patent Document 3, a cold method for producing a press-molded product of the cross-section hat-shaped member which is curved in plan view of the line of sight perpendicular to the top plate is disclosed. Patent Document 4, a method of the mold (punch) upon forming the cross-sectional hat-shaped member by a hot press forming is incorporated arcuate Betsudo punch, to run a different dynamic punch in the forming bottom dead center is disclosed It is. Patent Document 5, the hot press forming method by drawing to improve the formability by the specific portion of the material is cooled with a cooling catalyst is disclosed in the molding process. However, when applied to hot press method the method described in Patent Document 3, there is a case where a crack occurs in the punch shoulder. Further, in the method described in Patent Document 4, it can not be suppressed cracking upright wall portion occurring before reaching the molding bottom dead center.
[0004]
　Further, in the press forming using a pair of molds, there is that the method of supporting the blank by the inner pad provided on the mold used. For example, Patent Documents 5-7, configured to press the blank is disclosed by the inner pad provided in the mold during press molding. However, such inner pad from the volume is small compared to the main body of the mold, the temperature is likely to rise. When performing hot press-forming in a state where the temperature of the inner pad is increased, the degree of quenching of the press-molded product to be produced is low, the mechanical strength may be lowered. In particular, in the case of manufacturing a plurality of press-molded product by repeating the hot press forming, since the temperature of the inner pad is maintained in a state of increased, the mechanical strength of the press-molded product to be produced is reduced there is.
CITATION
Patent Document
[0005]
Patent Document 1: British Patent Publication 1,490,535 Pat
Patent Document 2: JP-A 10-96031 discloses
Patent Document 3: WO 2014-106932 pamphlet
Patent Document 4: JP 2015-20175 JP
Patent Document 5: JP HirakiAkira 57-31417 JP
Patent Document 6: JP 2010-149184 Patent Publication
Patent Document 7: real-Open 5-84418 JP
Summary of the Invention
Problems that the Invention is to Solve
[0006]
　In view of the above circumstances, an object of the present invention is to provide is to provide a hot press method and the hot press system can be improved and that the strength to suppress the cracking of the press-molded product.
Means for Solving the Problems
[0007]
　The present inventors have intensively studied and, as a result, have conceived to aspects of the invention described below.
[0008]
(1)
　using the upper and lower molds, the inner pad is biased to a state of protruding toward the upper die is movably accommodated in the lower mold, a mold having a hot blank material a pressed hot press method for producing a press-molded article,
　wherein the interior of the inner pad is provided with the path of the refrigerant,
　by flowing a coolant in the path of the refrigerant, the gold of the press molded product removed from the mold until set next blank in the mold, the surface temperature of the inner pad, hot, characterized in that cooling to a temperature satisfying the following formula to 100 ° C. the upper limit press method.

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

　where,

　　T: surface temperature
　　(℃) h: the inner pad pressing dimension
　　(mm) t: thickness of the blank (mm)
　　lambda: thermal conductivity of inner pad (W / mK)
　　W: volume ratio of the refrigerant path in the interior of the inner pad (mm 3 / mm 3
　　) S: refrigerant flow rate of the refrigerant in the path (mm / sec)
[0009]
(2)
　said that by taking out the press-molded product from the mold the time to set the next blank in the mold, characterized in that the time that satisfies the following formula 5 seconds as the lower limit ( hot press method according to 1).

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

where,

　　A: Remove the press-molded product from the mold following time the blank until the set in a mold
　　(sec) h: pressing direction dimension of the inner pad
　　(mm) t: thickness of the blank (mm)
　　lambda: thermal conductivity of inner pad (W /
　　mK) W : volume ratio of the refrigerant path in the interior of the inner pad (mm 3 / mm 3
　　) S: flow rate of refrigerant in the refrigerant passage (mm / sec)
[0010]
(3)
　pressing direction dimension of the inner pad, hot press method according to (1) or (2), characterized in that to satisfy the following formula to 100mm as the lower limit.

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

where,

　　h: pressing direction dimension of inner pad
　　(mm) t: thickness of the blank (mm)
　　lambda: thermal conductivity of inner pad (W /
　　mK) W: volume ratio of the refrigerant path in the interior of the inner pad (mm 3 / mm 3
　　) S: flow rate of refrigerant in the refrigerant passage (mm / sec)
[0011]
(4)
　and characterized in that taking out the press-molded product from the mold until set next blank in the mold, cooling the inner pad by spraying the refrigerant fluid in the inner pad hot press method according to any one of (1) to (3) to be.
[0012]
(5)
　wherein the upper mold, the and the refrigerant ejection port is provided which can inject coolant toward the inner pad,
　until taken out of the press molded product from the mold set next blank in the mold between, the upper die is approached to said lower die, by injecting refrigerant from the refrigerant ejection port toward the inner pad provided in the lower die, characterized by cooling the inner pad hot press method according to any one of (1) to (4).
[0013]
(6)
　the upper and lower molds, a mold having, an inner pad path of the refrigerant is provided within which is movably accommodated biased to a state of protruding toward the upper die to the lower die a press for hot pressing the blank material, with
　a cooling control unit for controlling the supply of coolant for cooling the inner pad,
　has,
　the cooling control unit, flowing the refrigerant in the path of the refrigerant by cooling, until set is taken out of the press molded product from the mold the next blank in the mold, the surface temperature of the inner pad, the temperature satisfying the following formula to 100 ° C. the upper limit hot pressing system, characterized by.

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

　where,

　　T: surface temperature
　　(℃) h: the inner pad pressing dimension
　　(mm) t: thickness of the blank (mm)
　　lambda: thermal conductivity of inner pad (W /
　　mK) W: volume ratio of the refrigerant path in the interior of the inner pad (mm 3 / mm 3
　　) S: refrigerant flow rate of the refrigerant in the path (mm / sec)
[0014]
(7)
　said that by taking out the press-molded product from the mold the time to set the next blank in the mold, characterized in that the time that satisfies the following formula 5 seconds as the lower limit ( hot press system according to 6).

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

where,

　　A: Remove the press-molded product from the mold following time the blank until the set in a mold
　　(sec) h: pressing direction dimension of the inner pad
　　(mm) t: thickness of the blank (mm)
　　lambda: thermal conductivity of inner pad (W /
　　mK) W : volume ratio of the refrigerant path in the interior of the inner pad (mm 3 / mm 3
　　) S: flow rate of refrigerant in the refrigerant passage (mm / sec)
[0015]
(8)
　pressing dimension of the inner pad, hot press system according to (6) or (7), characterized in that to satisfy the following formula to 100mm as the lower limit.

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

　where,

　　h: pressing direction dimension of inner pad
　　(mm) t: thickness of the blank (mm)
　　lambda: thermal conductivity of inner pad (W /
　　mK) W: volume ratio of the refrigerant path in the interior of the inner pad (mm 3 / mm 3
　　) S: flow rate of refrigerant in the refrigerant passage (mm / sec)
[0016]
(9)
　further comprises a coolant injection unit for injecting a coolant into the inner pad,
　the refrigerant ejection unit takes out the press-molded product from the mold until set next blank in the mold the hot press system according to any of injecting refrigerant fluid in the inner pad above, wherein the cooling the inner pad (6) (8).
[0017]
(10)
　The said upper mold, said and refrigerant injection hole is provided which can inject coolant toward the inner pad,
　until taken out of the press molded product from the mold set next blank in the mold between, the press machine is caused to approach the upper die to the lower die, by the cooling control unit is possible to inject coolant toward the inner pad provided in the lower mold from the refrigerant ejection port, the inner hot pressing system according to any of above, wherein the cooling pad (6) (9).
Effect of the invention
[0018]
　According to the present invention, it is possible to suppress the cracking of the press-molded product, and the strength improvements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019]
[1] Figure 1 is a diagram illustrating a configuration example of a first press molded article schematically.
FIG. 2 is a diagram showing a configuration example of a second press-molded product schematically.
[Figure 3A] Figure 3A is a configuration example of a first mold used in the manufacture of the first press-molded product is a cross-sectional view schematically showing.
[Figure 3B] Figure 3B is a configuration example of a first mold punch used in the manufacture of the first press-molded product is a perspective view schematically showing.
FIG. 4 is a configuration example of a second mold used in the production of the second press-molded product is a cross-sectional view schematically showing.
FIG. 5 is a diagram schematically showing a configuration example of a hot press system.
FIG. 6 is a diagram showing another configuration example of the inner pad cooling mechanism schematically.
[Figure 7A] Figure 7A shows a state at a predetermined timing hot press method using a first mold is a cross-sectional view schematically showing.
[Figure 7B] Figure 7B shows a state at a predetermined timing hot press method using a first mold is a cross-sectional view schematically showing.
[Figure 7C] Figure 7C, the state at a predetermined timing hot press method using a first mold is a cross-sectional view schematically showing.
[Figure 7D] Figure 7D, the state at a predetermined timing hot press method using a first mold is a cross-sectional view schematically showing.
FIG 7E] Figure 7E, the state at a predetermined timing hot press method using a first mold is a cross-sectional view schematically showing.
[FIG. 8A] Figure 8A, the state at a predetermined timing hot press method using a second die is a cross-sectional view schematically showing.
[Figure 8B] Figure 8B shows the state at a predetermined timing hot press method using a second die is a cross-sectional view schematically showing.
[Figure 8C] Figure 8C shows the state at a predetermined timing hot press method using a second die is a cross-sectional view schematically showing.
[Figure 8D] Figure 8D, the state at a predetermined timing hot press method using a second die is a cross-sectional view schematically showing.
FIG 8E] FIG. 8E, the state at a predetermined timing hot press method using a second die is a cross-sectional view schematically showing.
[9] FIG. 9 is a sectional view showing a configuration example of the mold of the first comparative example schematically.
FIG 10A] FIG 10A is a contour diagram in accordance with the numerical analysis of the sheet thickness reduction rate in the case of producing the first press-molded article using a first mold.
[FIG. 10B] FIG 10B is a contour diagram in accordance with the numerical analysis of the sheet thickness reduction rate in the case of producing the first press-molded article by using a mold of the first comparative example.
[FIG. 10C] FIG 10C is a contour diagram in accordance with the numerical analysis of the temperature of each part of the case of producing the first press-molded article using a first mold.
[FIG. 10D] FIG 10D is a contour diagram in accordance with the numerical analysis of the temperature of each part of the case of producing the first press-molded article by using a mold of the first comparative example.
[11] FIG 11 is a diagram showing a configuration example of the mold of the second comparative example schematically.
FIG 12A] FIG 12A is a contour diagram in accordance with the sheet thickness reduction rate of the numerical analysis of the case of producing the second of the press-molded product using the second mold.
[Figure 12B] Figure 12B is a contour diagram in accordance with the numerical analysis of the sheet thickness reduction rate in the case of producing a second press-molded product using a mold of the second comparative example.
[FIG. 12C] FIG 12C is a contour diagram in accordance with the numerical analysis of the temperature of each part of the case of producing the second of the press-molded product using the second mold.
FIG 12D] FIG 12D is a contour diagram in accordance with the numerical analysis of the temperature of each part of the case of producing the second of the press-molded product using a mold of the second comparative example.
FIG. 13 is a surface temperature T of the inner pad top at the timing to set the blank in a mold, the relationship between the mechanical strength of the portion in contact with the inner pad top of the manufactured press-molded product it is a graph showing a.
[14] FIG 14 is a graph showing the relationship between the surface temperature T of the waiting time A and the inner pad top.
[15] FIG 15 is a graph showing the relationship between the surface temperature T of the press dimension h and inner pad top of the inner pad.
DESCRIPTION OF THE INVENTION
[0020]
　Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In an embodiment of the present invention, showing the example of producing the first press-molded article using a first mold, an example of manufacturing the second press-molded product using the second mold. For convenience of explanation, simply referred to as "mold" is a "first mold" is intended to include both "second mold", when referred to as "press-molded product" is "first press molded product "and intended to include both" second press-molded product ". Then, in the embodiment of the present invention is to produce one of the press-molded product in a single hot press forming cycle, continuously manufacturing a plurality of press-molded product by repeating the cycle of hot press forming . Further, in each drawing, showing a pressing direction by the arrow P. Note that pressing direction P is intended to refer to a relative moving direction of the upper and lower molds at the time of hot press forming, in the embodiment of the present invention is assumed to be a vertical direction.
[0021]

　First, a configuration example of the press-formed product 8,9 manufactured by hot press method according to an embodiment of the present invention. As hot press-formed product 8,9 produced by pressing method according to the embodiment of the present invention, the first press-molded product 8 shown in FIG. 1, a second press-molded product 9 shown in FIG. 2 cases to show. First press molded article 8 and the second press-molded product 9, a steel plate is a blank 7 is manufactured by hot press forming. The blank 7, from 0.09 to 0.50% carbon content for the hardenability in mass%, preferably 0.11% or more, thickness in the range of 0.6 ~ 3.2 mm, preferably steel of approximately 2.3mm applies.
[0022]
　As shown in FIGS. 1 and 2, the press-molded product 8,9 each have a portion of the hat shape. Portion of the hat shape, a top plate 81 and 91, and two ridge portions 82 and 92 formed continuously on both sides of the top plate portion 81 and 91, are formed continuously to each of the two ridge portions that having two vertical wall portions 83, 93. Top plate 81 and 91 is, for example, a plate-like portion that extends in a substantially perpendicular direction to the pressing direction P. Ridge 82 and 92 is a portion which is curved or bent at a predetermined curvature. The vertical wall portion 83 and 93, either inclined at a predetermined angle with respect to the pressing direction P, or a portion parallel to the pressing direction P.
[0023]
　More first press molded product 8, as shown in FIG. 1, the two ridge portions 82 and the respective at least one of the two vertical wall portions 83, bent so as to project in a predetermined direction in the pressing direction when viewed or curved portion 84 is provided is bent. Further, the top plate portion 91 of the second press-molded product 9, as shown in FIG. 2, has a height direction position (pressing direction position) are different parts from each other. The height higher portion of the top plate portion 91 (hereinafter, referred to as "top plate height section 911") and the lower portion height (hereinafter referred to as "the top plate lower portion 912"), step-like portion partitioned by the top plate stepped portion 913 is.
[0024]
　Incidentally, the press-molded product 8,9 shown in Figure 1 and Figure 2 are both exemplary of the press-molded product manufactured by hot press method according to an embodiment of the present invention. Press-molded articles produced by hot press method according to an embodiment of the present invention is not limited to the shape shown in FIGS. 1 and 2.
[0025]

　Next, an example of the structure of the mold 2, 3 used in the hot press method according to an embodiment of the present invention will be described with reference to FIGS. 3A ~ 4. Figure 3A is a first configuration example of a mold 2 used in the manufacture of the first press-molded product 8 is a sectional view schematically showing the top plate portion 81 of the punch curved portion 216 for molding the bent portion 84 it is a cross-sectional view taken along a plane perpendicular to the longitudinal direction of. 3B is an example of the configuration of the first mold 2 punch 21 is a perspective view showing schematically a view showing a portion for forming a curved portion 84. Figure 4 is a second configuration example of the mold 3 used in the manufacture of the second press-molded product 9 is a sectional view schematically showing the top plate height portion 911 and the top plate stepped portion 913 and the top plate a low a portion for molding the parts 912, is a cross-sectional view taken along a plane parallel to their alignment direction.
[0026]
　As shown in FIGS. 3A and 3B and Figure 4, the mold 2, 3, respectively, the punches 21 and 31 is a lower die, a die 22, 32 is an upper mold, the pressing direction P in the punch 21 and 31 having an inner pad 23, 33 provided for reciprocal movement, and a biasing mechanism 24, 34 for urging the inner pad 23, 33 on the side of the die 22, 32.
[0027]
　Punch 21 and 31 continuously, the punch projection 211, 311 projecting toward the side of the die 22 and 32, a punch top 212 and 312 provided at the tip of the punch projections 211 and 311, the punch top 212, 312 with the two punch shoulder R portion 213, 313 which are provided, two provided continuously to each of the two punches shoulder R portion 213, 313 and a punch vertical wall portion 214, 314. Punch apex 212, 312 is a portion for forming the top plate portion 81, 91 of the press-molded product 8,9, having a substantially perpendicular planar configuration pressing direction P, for example. Punch shoulder R portion 213, 313 is a portion for forming the ridge portion 82, 92 of the press-molded product 8,9, it has a curved configuration having a predetermined radius of curvature. Punch vertical wall portion 214, 314 is a portion for forming the vertical wall portion 83, 93 of the press-molded product 8,9, planar inclined at an angle in a predetermined in the pressing direction P, or parallel to the pressing direction P having a planar configuration. The specific shape of each part of the punch 21 and 31 is intended to be defined in accordance with the shape of the press-molded product 8,9 of manufacturing is not limited to the shape shown in FIG. 3A or FIG. 3B and FIG. 4 .
[0028]
　As shown in FIG. 3B, in the first mold 2, each of the least one of the two punch shoulder R portion 213 and two punch vertical wall portion 214, in order to mold the curved portion 84, the pressing direction punch bent portion 216 which is curved or bent so as to project in a predetermined direction is provided in view. Further, as shown in FIG. 4, in the second mold 3, to shape the top plate height portion 911 and the top plate lower portion 912 mutually different heights of the top plate portion 91, to each other in the punch top 312 portions different heights are provided. Specifically, the partial height higher punch height apex 316 is for molding the top plate height portion 911, a punch lower apex 317 is lower portions at a height for forming the top plate lower portion 912 It is provided.
[0029]
　As shown in FIG. 3A, the punch top 212 of the first die 2 of the punch 21, it is provided with inner pad housing hole 215, this inner pad housing hole 215, the punch 21 of the separate inner pad 23 a member is reciprocally movably accommodated in the pressing direction P. The inner pad 23, the side of the inner pad top 231 facing the die 22, the inner pad shoulder R portion 232 is provided contiguous to both sides of the inner pad top 231. Inner pad shoulder R portion 232 has a curved configuration having a predetermined radius of curvature.
[0030]
　The inner pad 23 is urged toward the side of the die 22 by the urging mechanism 24, inner pad top 231 and the inner pad shoulder R portion 232 protrudes a predetermined dimension on the side of the die 22 than the punch top 212 It is maintained in the state. Projecting dimension of the inner pad 23, in a state where the blank 7 is placed placed in the inner pad top 231, blank 7 is set to a dimension that does not contact the punches top 212 and the punch shoulder R portion 213. However, the specific protruding dimension is not particularly limited. Further, the inner pad 23, when it is pressed from the side of the die 22 enters the inside of the inner pad housing hole 215, 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 is flush. In this state, inner pad top 231 is part of the punch top 212.
[0031]
　As shown in FIG. 4, also punching the top 312 of the punch 31 of the second mold 3, the inner pad accommodation hole 315 provided in the inner pad housing hole 315, and the punch 31 in a separate member there inner pad 33 is reciprocally movably accommodated in the pressing direction P. In the second mold 3, the inner pad housing hole 315 is provided a punch in the low top 317 (the portion for molding the top plate lower portion 912). Further, as shown in FIG. 4, the punch height top 316 and the inner pad 33 are separated at a predetermined distance in the perpendicular direction (left-right in the plane of FIG. 4 direction) pressing direction P. For example, as shown in FIG. 4, between the punch and high top 316 and inner pad 33, a punch lower apex 317 is interposed. This distance, in a state where the blank 7 is placed placed in the inner pad top 231 and the punch height top 316, parts (especially the vertical wall portion 93 comprising a top plate stepped portion 913 and the vertical wall portion 93 of the blank 7 a portion located in the vicinity of the top plate stepped portion 913) is set to a distance that does not contact the inner pad 33 and the punch height top 316 among.
[0032]
　State and, in the second mold 3, the inner pad 33 is biased toward the biasing mechanism 34 on the side of the die 32, the inner pad top 331 is projected to the side of the die 32 than the punch lower apex 317 It is maintained in. The projecting dimension is in a state where the blank 7 is placed placed in the inner pad top 331 and the punch height top 316, blank 7 is set to a dimension that does not contact the punches low top 317. Further, the inner pad 33, when it is pressed from the side of the die 32 enters into the inner pad housing hole 315, the inner pad top 331 and the punch lower apex 317 have the same height. In this state, inner pad top 331, a portion of the punch lower apex 317.
[0033]
　Incidentally, the inner pad 23, 33 may have a configuration capable of supporting hot at least a portion comprising part of the top plate 81, 91 after the press forming of the blank 7. In particular, inner pad 23 and 33, at the time of hot press forming, it is sufficient to the pressing direction P of the blank 7 a configuration capable of supporting a portion or the vicinity thereof applied tension in a direction perpendicular. Further, it may be a configuration capable of supporting the entire hot portion to be a top plate 81 and 91 after the press forming of the blank 7. In Figure 3B, but shows the configuration which the inner pad 23 is provided on the punch curved portion 216 and the vicinity thereof, the inner pad may be configured to be provided over the entire length of the punch top 212.
[0034]
　Further, the biasing mechanism 24, 34 may have a configuration capable of urging the inner pad 23, 33 on the side of the die 22 and 32, specific configurations are not limited. The biasing mechanism 24 and 34, for example, such as a spring or a gas cushion, various known biasing mechanisms can be applied.
[0035]
　The die 22 and 32, die recesses 221, 321 which can be punched projections 211, 311 is writing fits is provided. The edge of the die recess 221, 321 die shoulder R portion 222, 322 is provided. Die shoulder R portion 222 and 322 has a curved configuration having a predetermined radius of curvature. The refrigerant in the bottom of the die recesses 221, 321, at a position facing the inner pad 23, 33 is accommodated in the inner pad housing hole 215, 315 is a coolant jetting portion for jetting the refrigerant toward the inner pad 23 injection holes 223 and 323 are provided. Refrigerant ejection port 223, 323 are part of the inner pad cooling mechanism 13 for cooling the inner pad 23, 33 (described later). From the refrigerant injection holes 223 and 323 toward the inner pad 23, 33 by injecting a coolant such as water or air, it can be cooled inner pad 23 and 33.
[0036]

　Here, a detailed configuration example and a method of cooling the inner pad 23, 33. In an embodiment of the present invention, the temperature range of 700 ~ 950 ° C., a preferred blank material 7 is heated to about 750 ° C., by cooling with molded using a mold 2, press-molded product 8 , to produce 9. Then, at the time of hot press forming is formed into a predetermined shape by the punch 21, 31 and the die 22, 32 while supporting the blank 7 by the inner pad 23, 33. Therefore, at the time of hot press forming, a part of the blank 7 is in contact with the inner pad 23 and 33.
[0037]
　In press-molded product 8, 9 is thus produced, the strength of the portion in contact with the inner pad 23 and 33 at the time of hot press forming in order to more 1500MPa is the cooling rate of the part 30 ° C. / sec to be not less than. However, since the inner pad 23, 33 has a smaller volume compared to the punches 21, 31 and die 22, 32, the temperature tends to rise during the hot press forming. Particularly, in the case of continuously producing a plurality of press-moldings 8,9 by repeating the cycle of hot press forming it is likely to be maintained in the inner pad 23, 33 is heated. When carrying out the hot press forming in a state in which the inner pad 23, 33 is heated, the cooling rate of the portion in contact with the inner pad 23, 33 of the blank 7 is reduced, to obtain a predetermined strength it can not be. Therefore, in the embodiment of the present invention, by the structure and method of cooling the inner pad 23 and 33 as follows, the cooling rate of the portion in contact with the inner pad 23, 33 of the blank 7 increased, so that it is possible to obtain a predetermined strength.
[0038]
　But are not limited to particular materials of the inner pad 23, 33 by the thermal conductivity λ is 30 W / mK or more, and a specific heat C is a more materials 4.3J / g · K. Such materials can be applied, for example tool steel. Further, as shown in FIGS. 3A and 4, inside the inner pad 23 and 33, refrigerant passages 233,333 in line shape (i.e., hollow shape) is provided. Refrigerant passages 233,333 have a structure capable of flowing a coolant fluid such as water or air. (= Spatial volume of the refrigerant passages 233,333 (mm volume ratio W of the refrigerant path 233,333 3 volume) / inner pad 23, 33 (mm 3 )) is preferably from 0.01-0.10 . The depth of the inner pad top 231 and 331 to the refrigerant passage 233,333 is preferably 10 ~ 30 mm. According to such a configuration, by supplying the refrigerant to the refrigerant passage 233,333 provided inside the inner pad 23 and 33, the next blank after removing the press-molded product 8,9 from the mold 2, 3 until sets 7, it can be cooled to a predetermined temperature to be described later the surface temperature of the inner pad top 231 and 331 (i.e., the surface temperature of the surface which contacts the blank 7).
[0039]
　Also, pressing dimension (height) h of the inner pad 23 and 33, the lower limit of 100 mm, dimensions that satisfy the following formula (1) is applied.

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

　where,

　　h: protruding dimension of the inner pad
　　(mm) t: blank thickness (mm)
　　lambda: thermal conductivity of inner pad (W /
　　mK) W: volume ratio of the refrigerant path in the interior of the inner pad (mm 3 / mm 3
　　) S: flow rate of refrigerant in the refrigerant passage (mm / sec)

is.
[0040]
　The area of the inner pad top 231 and 331 (the surface which contacts the blank 7) is defined in accordance with the dimensions of the press-molded product 8,9 to manufacture, for example, 3000 ~ 20000 mm 2 applied in the range of can, preferably 5000 mm 2 can be applied about. By defining the size of the inner pad 23 and 33 in this manner, the temperature rise of the inner pad 23 and 33 during the hot press forming was suppressed, thereby suppressing a decrease in the cooling rate of the blank 7. That is, when the volume of the inner pad 23, 33 is small, the time of hot press forming was heated by the heat of the blank 7 becomes small cooling rate of the blank 7, there is a possibility that the quenching becomes insufficient . Therefore, the inner pad 23, 33 With such a dimension, for example, if the blank 7 the thickness of 0.6 ~ 3.2 mm, can be secured cooling rate of more than 30 ° C. / sec.
[0041]
　Further, as described above, to the tensile strength of the portion in contact with the inner pad 23 and 33 at the time of hot press forming the above 1500MPa must the cooling rate of the partial and 30 ° C. / sec or higher. Therefore, before the start of the hot press forming (i.e., the time to set the blank 7 into the mold 2, 3) in, so that the surface temperature T of the inner pad top 231 and 331 is equal to or less than a predetermined temperature, the inner flowing a refrigerant for cooling the refrigerant passage 233,333 of the pad 23, 33. Specifically, the surface temperature T of the inner pad top 231 and 331 before the start of the hot press forming, the upper limit is set to 100 ° C., cooled to satisfy the following formula (2).

　T ≦ 100 × (2.3 / t ) × (h / 100) × (λ / 30) × (W / 2) × S
　　　　　　　　　　　　　　　　　　　　　　Equation (2)

　where,

　　T: surface temperature of the inner pad (°
　　C.) t: the thickness of the blank
　　(mm) h: protruding dimension of the inner pad (mm)
　　lambda: thermal conductivity of inner pad (W /
　　mK) W: volume ratio of the refrigerant path in the interior of the inner pad (mm 3 / mm 3 )
　　S: flow rate of refrigerant in the refrigerant passage (mm / sec)

is. When the surface temperature T of the inner pad top 231 and 331 before the start of the hot press forming to satisfy the above equation (2) to 100 ° C. as the upper limit, the tensile portion in contact with the inner pad 23 and 33 at the time of hot press forming can the strength to more than 1500MPa.
[0042]
　When manufacturing a plurality of press-molded product 8,9 repeat cycle of hot press forming, to satisfy the temperature conditions, press-formed article produced by hot press forming in the previous 8,9 to removal from the mold 2, 3 until set next blank 7 into the mold 2, 3, the time for cooling the inner pad 23, 33 (hereinafter, referred to as "standby time a") and It must be provided. In an embodiment of the present invention, the waiting time A, the time indicated by the following equation 5 seconds as the lower limit (3).

　A ≧ 5 × (t / 2.3 ) × (100 / h) × (30 / λ) × (2 / W) × (1 / s)
　　　　　　　　　　　　　　　　　　　　Equation (3)

where,

　　A: standby time
　　(sec) t : thickness of the blank
　　(mm) h: pressing direction dimension of the inner pad (mm)
　　lambda: thermal conductivity of inner pad (W /
　　mK) W: volume ratio of the refrigerant path in the interior of the inner pad (mm 3 / mm 3 )
　　S: flow rate of refrigerant in the refrigerant passage (mm / sec)

is. Thus, the surface temperature T of the inner pad top 231 and 331 before the start of the hot press forming can be a temperature of above.
[0043]

　Next, a configuration example of the hot press system 1 can perform a hot press method according to an embodiment of the present invention. Figure 5 is a diagram schematically showing a configuration example of a hot press system 1. As shown in FIG. 5, the hot press system 1 includes a press 11 to hot press molding the blank material 7 using a mold 2, a press control unit 12 for controlling the press machine 11, inner pad the inner pad cooling mechanism 13 for cooling the 23 and 33, configured to include a cooling control unit 14 that controls the inner pad cooling mechanism 13. The mold 2, 3 of the press 11, when manufacturing the first press-molded article 8 is applied first mold 2, in the case of producing the second of the press-molded product 9 is second mold 3 is applied. Further, the hot press system 1 includes a workpiece transfer mechanism 15 for removal from the mold of the press-molded product 8,9 molded and set into the mold 2, 3 of the blank 7, the workpiece transport device 15 a workpiece transfer control unit 16 that controls may have.
[0044]
　Press 11, by using a mold 2,3 it may have a configuration in which the blank 7 can hot press molding, specific configurations are not particularly limited. The press machine 11 can be applied various known pressing machine. Workpiece transport device 15, it is only necessary to perform the extraction from the mold 2, 3 of the set of the blank 7 into the mold 2, 3 and the press-molded product 8,9, specific configurations are not particularly limited. For example, the workpiece transfer mechanism 15, various known transport device and the transport robot can be applied.
[0045]
　Inner pad cooling mechanism 13 includes a refrigerant passage 233,333 of the inner pad 23, 33, and the refrigerant ejection port 223 and 323 provided in the die 22 and 32, the refrigerant in the refrigerant passage 233,333 and the refrigerant ejection port 223, 323 configured to include a coolant supply source 131 for supplying. In an embodiment of the present invention, fluid applied such as water or air as the coolant. The temperature of the coolant may be a normal temperature (room temperature), but may be used refrigerant cooled to a temperature lower than the room temperature. In this case, the inner pad cooling mechanism 13 has a refrigerant cooling mechanism to further cool the refrigerant. In an embodiment of the present invention, the cooling control unit 14, by controlling the supply of the refrigerant, controlling the cooling of the inner pad 23, 33. For example, the cooling control unit 14, the flow rate of the timing and the coolant supplying refrigerant to the refrigerant paths 233,333 of the inner pad 23, 33, the timing and the injection for injecting refrigerant from the refrigerant ejection port 223, 323 of the die 22 and 32 to control the amount of refrigerant.
[0046]
　Incidentally, the inner pad cooling mechanism 13, the refrigerant ejection port 223, 323 is not limited to the configuration provided in the die 22, 32. Here, a description will be given of another configuration example of the inner pad cooling mechanism 13. Figure 6 is a diagram schematically showing another example of the configuration of the inner pad cooling mechanism 13. As shown in FIG. 6, the inner pad cooling mechanism 13, as a refrigerant injection unit for injecting a coolant, in place of the refrigerant ejection port 223 and 323 provided in the die 22 and 32 has a coolant jetting nozzle 132. Coolant jetting nozzle 132 (coolant jetting unit), to allow injection of coolant toward the inner pad 23, 33, provided in the vicinity of the mold 2, 3. In this case, the cooling control unit 14 controls the timing and the injection amount of injected refrigerant from the refrigerant injection nozzle 132. The specific configuration of the refrigerant injection nozzle 132 is not limited in particular, it can be applied various known nozzle. The refrigerant injection nozzle 132 may be a movable movable by the moving mechanism. In this case, the moving mechanism according to the control by the cooling control unit 14, to approximate coolant jetting nozzle 132 to the inner pad 23, 33 when injecting the coolant into the inner pad 23 and 33, when performing hot press-forming to retract the coolant jetting nozzle 132 so as not to interfere with the mold 2, 3. Thus, refrigerant injection unit for injecting a refrigerant into the inner pad 23, 33 may be configured to be provided in the mold 2, 3, the mold 2,3 may be provided separately be configured .
[0047]
　The press control unit 12 and the cooling control unit 14 and the workpiece transfer control unit 16, respectively, device is applied with a computer including a CPU, a ROM, and a RAM. The ROM of the press control unit 12 computer, a computer program for controlling a press machine is stored in advance. Then, CPU reads the computer program stored in the ROM, executes using the RAM as a work area. Thus, the press 11 is controlled. The same applies to the cooling control unit 14 and the workpiece transfer control unit 16. Then, by working computer together the press control unit 12 and the cooling control unit 14 and the workpiece transfer control unit 16, the hot pressing method is performed in accordance with an embodiment of the present invention.
[0048]

　Next, a description will be given hot pressing method according to the embodiment of the present invention. FIGS 7A ~-7E are cross-sectional views illustrating a hot press method using a first mold 2 schematically. Figure 8A ~ 8E are sectional views illustrating a hot press method using a second mold 3 schematically.
[0049]
　In an embodiment of the present invention, the temperature range of the temperature of the blank 7 at the timing to be set in the mold 2,3 700 ~ 950 ° C., preferably about 750 ° C.. The surface temperature of the mold 2, 3 at the timing of setting the blank 7 into the mold 2, 3 and 100 ° C. or less. In particular, the surface temperature T of the inner pad top 231, 331 is a temperature which satisfies the equation (2) up to a maximum of 100 ° C. as described above. Accordingly, the cooling rate of the blank 7 at the time of hot press forming can be a 30 ° C. / sec or more, it can be produced press-molded product 8,9 having a predetermined mechanical strength.
[0050]
　First, a description will be given of a case of using the first mold 2. As shown in FIG. 7A, at the timing before the start of the press molding, it is maintained from the punch top 212 in a predetermined state in which the size projected by the biasing mechanism 24 inner pad 23. Therefore, at the timing before the start of the hot press forming, of the first mold 2 blank material 7 is set to, areas of ridge 82 and the vertical wall portion 83 of the first press-formed article 8 It is maintained in a state not in contact with the punch top 212. Therefore, this part before the start of the hot press forming that is lowered temperatures is prevented or suppressed.
[0051]
　Then, as shown in FIG. 7B, the press control unit 12 controls the press 11 to approach the die 22 to punch 21. When the die 22 approaches the punch 21, a die shoulder R portion 222 comes into contact with the blank 7. The portions of the blank 7 is referred to as a "die shoulder contacting portion 71 '. However, at the timing immediately after the die shoulder R portion 222 is in contact with the die shoulder contacting portion 71 of the blank 7, the portion (the portion in contact with the inner pad shoulder R portion 232 of the blank 7, "inner pad shoulders a portion between the contact portion 72 "and referred) and the die shoulder contacting portion 71 (this portion is referred to as" non-contact portion 73 ") is in a state not in contact with any of the punch 21 and the die 22. Therefore, the temperature drop of the non-contact portion 73 is prevented or suppressed. The blank 7 is the configuration which is supported in a position close to the die 22 than the punch top 212 by the inner pad 23, increasing the distance between the die shoulder contacting portion 71 and the inner pad shoulder contacting portion 72 of the blank 7, range of non-contact portion 73, i.e., the range of the partial decrease of the temperature is prevented or suppressed can be increased.
[0052]
　Figure 7C shows the timing of the die 22 is positioned at the bottom dead center. If the die 22 from the state of the timing shown in Figure 7B is further closer to the punch 21, as shown in FIG. 7C, the non-contact portion 73 of the blank 7 is pressed against the punch top 212 and the punch shoulder R portion 213. Along with access to the punch 21 of the die 22, inner pad 23 is pressed, the projecting dimension from the punch top 212 of the inner pad 23 becomes smaller. If the die 22 reaches the bottom dead center, inner pad top 231 becomes flush with the punch top 212, a portion of the punch top 212. The non-contact portion 73, it becomes ridge portion 82 and the vertical wall portion 83 of the first press-molded product 8 is quenched is cooled by contact with the punch top 212 and the punch shoulder R portion 213. Incidentally, the die shoulder contacting portion 71 of the blank 7 is quenched is cooled by contact with the die shoulder R portion 222, inner pad shoulder contacting portion 72 inner pad shoulder R portion 232 and not the punch shoulder R portion 213 is quenched is cooled by contact with the vicinity.
[0053]
　Thus, the inner pad top 231 at the start of the hot press forming, on a side closer to the punch top 212 to the die 22 protrudes a predetermined size, the blank with the die 22 approaches the punch 21 projecting dimension is pressed against the die 22 via a 7 decreases, the die 22 reaches the bottom dead center is part of the punch top 212. Then, in the hot press method according to an embodiment of the present invention, while it is supporting the blank 7 by the inner pad 23, to produce a first of the press-molded product 8 by approaching the die 22 to punch 21.
[0054]
　Then, as shown in Figure 7D, the press control unit 12 controls the press 11 to move the die 22 to the top dead center. The workpiece transfer mechanism 15 under the control of the workpiece transport control section 16 retrieves the first of the press-molded product 8 produced from the first mold 2. Thereafter, as shown in FIG. 7E, the press control unit 12 controls the press 11 to approximate the die 22 to punch 21, the cooling control unit 14 that state, the refrigerant ejection port 223 provided in the die 22 cooling the inner pad 23 by ejecting coolant. In an embodiment of the present invention, the surface temperature T of the inner pad top 231 cools to a temperature indicated by the equation (2) to 100 ° C. as the upper limit. By approaching the die 22 to the inner pad 23 (moving to the bottom dead center from the top dead center) when injecting the refrigerant, increasing the flow rate of the refrigerant in the surface of the inner pad top 231, said has inner pad top 231 It can reduce the time to be cooled to a temperature. After cooling the inner pad top 231, press control unit 12 controls the press 11 to move the die 22 to the top dead center. Thus, one cycle of hot press forming is completed.
[0055]
　The workpiece transfer mechanism 15 in accordance with control by the workpiece conveyance control unit 16, when the standby time A has satisfies Equation 5 seconds as the lower limit (3), the following blank 7 into the first mold 2 set. Thus, the first surface temperature of the mold 2 is 100 ° C. or less, in particular, in a state where the surface temperature T of the inner pad top 231 is cooled to a temperature indicated by the equation (2) to 100 ° C. as the upper limit, the following of the blank 7 is set to the first mold 2. Therefore, the next blank material 7 when hot press molding, the cooling rate of the portion in contact with the inner pad top 231 can be a 30 ° C. / sec or more, a predetermined intensity (here above 1500MPa is) strength can be produced first press molded product 8 with.
[0056]
　Next, an example of using the second mold 3. Note that the same method using the first mold 2 is omitted. Figure 8A corresponds to FIG. 7A, a timing before the start of the hot press forming, showing a state where the blank 7 is set to 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 from the punch lower top 317 by the biasing mechanism 34 to a state of predetermined dimensions protruding toward the side of the die 32. Therefore, at the timing before the start of the hot press forming, of the second mold 3 is set to the blank 7, the portion and the vertical wall portion 93 which is a ridgeline portion 92 of the second press-molded product 9 comprising part (especially, the portion adjacent to the top plate stepped portion 913 of the vertical wall portion 93) is maintained in a state not in contact with the punch lower apex 317, the temperature drop in before the start of the hot press forming is prevented or It is suppressed.
[0057]
　As shown in FIG. 8B, the press control unit 12 controls the press 11 to approach the die 32 to punch 31. When the die 32 approaches the punch 31, a die shoulder R portion 322 is in contact with the predetermined portion of the blank 7 (die shoulder contacting portion 71). As shown, the blank 7 is crowded pressed by the In'napatto top 331 and the die 32 before reaching the bottom dead center. Therefore, it is possible to draw a blank positioned on the punch height top 316 on the punch lower top 317 before reaching the bottom dead center. Thus, it is possible to reduce the ridge portion 92 and the vertical wall portion 93 perpendicular tension to the pressing direction P occurring blank to be molded into the top plate lower portion 912 in the vicinity of BDC (left-right direction tension) possible to become.
[0058]
　Figure 8C shows a timing when the die 32 is positioned at the bottom dead center. Approaching the state of the timing to the die 32 is further punch 31 shown in FIG. 8B, as shown in FIG. 8C, when the die 32 reaches the bottom dead center, inner pad top 331 becomes flush with the punch lower apex 317, the part of the punch lower apex 317.
[0059]
　Figure 8D is a view corresponding to FIG. 7D. As shown in FIG. 8D, the press control unit 12 controls the press 11 to move the die 32 to the top dead center. The workpiece transfer mechanism 15 in accordance with control by the workpiece transport control section 16 retrieves the second press-molded article 9 made from the second mold 3.
[0060]
　Thereafter, as shown in FIG. 8E (Figure 8E is a diagram corresponding to FIG. 7E), press control unit 12 is the bottom dead center from the approximated allowed (top dead center to the punch 31 die 32 by controlling the press machine 11 It moved to the side), in this state, the cooling control unit 14 cools the inner pad 33 by injecting the refrigerant from the refrigerant ejection port 323 provided in the die 32. Cooling temperature is the same as the case of using the first mold 2. After cooling of the inner pad 33, the press control unit 12 controls the press 11 to move the die 32 to the top dead center. Thus, one cycle of hot press forming is completed.
[0061]
　Then, after completion of the hot press forming cycle, to perform a cycle of the following hot press forming. Incidentally, the waiting time A is the same as the case of using the first mold 2. According to this method, the same effect as the case of using the first mold 2.
[0062]

　Next, the function of suppressing the cracking of the press-molded product 8,9 by inner pad 23 and 33, using the dies 5 and 6 of the comparative example without the inner pad 23, 33 It is described in comparison with an example. Is formed in a hat-type, such as a first press molded product 8, and, in a shape having a curved portion 84, cracking is likely to occur at the outer peripheral side vertical wall portion 83 of the bending portion 84. Further, as the second of the press-molded product 9, if it is shaped top plate stepped portion 913 to the top plate portion 91 of the hat shape is provided, the portion close to the top plate stepped portion 913 of the vertical wall portion 93 cracking is likely to occur in. These parts are characterized in the following (i) ~ (iii).
　(I) in hot press forming, not pressing direction P only, tension is applied in the direction perpendicular to the pressing direction P.
　(Ii) it is maintained at a high temperature for not contacting the mold 2,3.
　(Iii) sandwiched die shoulder R portion 222 and the punch shoulder R portion 213 of the mold 2, 3.
[0063]
　Then, in the first press-formed article 8, the vertical wall portion 83 of the outer peripheral side of the curved portion 84, the strain at the time of hot press forming is concentrated. In the second of the press-molded product 9, a portion close to the top plate stepped portion 913 of the vertical wall portion 93 (the portion where the height of the top plate portion 91 is changed), the strain at the time of hot press forming is concentrated to. Therefore, the thickness reduction rate is increased in these portions, cracks are likely to occur. Therefore, in the hot press method according to an embodiment of the present invention, by using the inner pad 23 and 33, of the blank 7, or the portion which becomes the outer peripheral side vertical wall portion 83 of the bending portion 84, the vertical wall portion in part to become part close to the top plate stepped portion 913 of the 93, to expand the range of temperature drop is prevented or suppressed. Thus, preventing or inhibiting the occurrence of cracks by suppressing local concentration of strain.
[0064]
　Figure 9 is an example of the configuration of the mold 5 of the first comparative example is a sectional view schematically showing, a configuration example of a mold without the inner pad 23. Incidentally, the same structure as the first die 2 are denoted by the same reference numerals, and description thereof is omitted. As shown in FIG. 9, the inner pad 23 is not provided on the punch 51 of the die 5 of the first comparative example, the die 52 is not provided the refrigerant ejection port 223. Otherwise, the same configuration as that of the first mold 2 is applied.
[0065]
　When manufacturing the first of the press-molded product 8 using a mold 5 of the first comparative example having no inner pad 23, the blank 7 to be hot press-formed while being supported by the punch top 212 become. Then, the die shoulder contacting portion 71 of the blank 7 is cooled by contact with the die shoulder R portion 222, (it means a portion in contact with the punch shoulder R portion 213 of the blank 7) Punch shoulder contacting portion 74 It is cooled by contact with the punch shoulder R portion 213. With such a structure, the non-contact portions 73 between the die shoulder contacting portion 71 and the punch shoulder contacting portion 74, a narrow range compared with the method using a first mold 2 having inner pad 23 . That is, the range of the portion where the temperature decrease is suppressed small. Since the strain is concentrated on this small range, cracking it becomes high sheet thickness reduction rate is likely to occur. Further, when the bending portion 84 in the first press-molded product 8 is a configuration provided, the strain concentration to the portion located curved portion 84 of the vertical wall portion 83 is generated conspicuously. This is because the ridge portions 82 when bent in the pressing direction as viewed, the flow of the blank 7 is not uniform at the time of hot press forming.
[0066]
　In contrast, as shown in FIG. 7B, in the embodiment of the present invention, using the first mold 2 having inner pad 23, the areas of the top plate portion 81 of the blank 7, inner pad supporting the punch top 212 at a position protruding a predetermined dimension on the side of the die 22 by 23. In this state, in the pressing direction as viewed, the distance between the die shoulder R portion 222 and the inner pad shoulder R portion 232 is greater than the distance between the die shoulder R portion 222 and the punch shoulder R portion 213. With such a configuration, compared to the method using a mold 5 of the first comparative example, it can increase the range of the non-contact portion 73.
[0067]
　Then while maintaining this state, by clamping by relatively approaching the punch 21 and the die 22 to produce a first of the press-molded product 8. At this time, the die shoulder contacting portion 71 of the blank 7 is cooled by contact with the die shoulder R portion 222, inner pad shoulder contacting portion 72 contacts the inner pad shoulder R portion 232 rather than the punch shoulder R portion 213 It is cooled by. According to this structure, the non-contact portion 73 (i.e., the portion reduced in temperature can be prevented or suppressed) from the range of possible increased, in areas of curved portion 84 of the blank 7, hot press concentrating the strain at the time of molding is suppressed. Thus, thickness reduction ratio is reduced, the generation of cracks is suppressed.
[0068]
　Figure 10A and Figure 10B is a contour diagram in accordance with the sheet thickness reduction rate of the numerical analysis of the case of producing the first of the press-molded product 8. Each Figure 10A shows the case of using the first mold 2, FIG. 10B shows a case of using a metal mold 5 of the first comparative example. Numerical values ​​surrounded by squares in the figure indicates a sheet thickness reduction ratio. Figure 10C and Figure 10D is a contour diagram in accordance with the numerical analysis of the temperature of each part of the case of producing the first of the press-molded product 8. Respectively Figure 10C shows a case of using the first mold 2, FIG. 10D shows a case of using a metal mold 5 of the first comparative example. In Figure 10C and Figure 10D, the area of ​​solid black coating shows a region the temperature is above 650 ° C. in a state where the die 22 is located 10mm above the bottom dead center.
[0069]
　Figure 10A and 10B, the and 10C and as FIG. 10D and the comparison clear and when manufacturing the first press-molded article 8 by hot press forming, the method using a first mold 2 According, as compared to the method using a mold 5 of the first comparative example, in a portion positioned in the curved portion 84 of the vertical wall portion 83, you can expand the range of parts that temperature drop can be suppressed. Thus, the local concentration of strain can be suppressed relaxation to sheet thickness reduction rate, can be prevented or suppress the occurrence of cracks at the curved portion 84 of the vertical wall portion 83.
[0070]
　In the embodiment of the present invention, the first press-molded product 8 has a curved portion 84 which is bent in the pressing direction as viewed, shows a method of preventing or inhibiting the occurrence of cracks in the bending portion 84, the even press-molded article other than shape, such as, it is possible to prevent or suppress the crack generation. For example, hot press method according to an embodiment of the present invention, in the pressing direction as viewed, round, oval, to the production of a press molded article having a ridge line portion of the annular such polygon is applicable, of these shapes the occurrence of even cracks in the press-molded product can be prevented or suppressed.
[0071]
　Figure 11 is an example of the structure of the mold 6 of the second comparative example is a diagram schematically showing, an example of a mold without the inner pad 33. As shown in FIG. 11, the inner pad 33 is not provided on the punch 61 of the die 6 of the second comparative example, the die 62 is not provided the refrigerant ejection port 323.
[0072]
　As shown in FIG. 11, when manufacturing the second press-molded article 9 by using a mold 6 of the second comparative example, the punch height top 316 comes into contact with the blank 7 before the punch lower apex 317, top plate height portion 911 is formed prior to the top plate lower portion 912. Then, punch the low top 317 hot press forming progresses When the timing of contacting the blank 7, the blank 7 is restrained by the punch height top 316 molded. Therefore, insufficient flow of material in the portion close to the top plate stepped portion 913 of the vertical wall portion 93, since the tension in the left-right direction is generated, cracks in the part is likely to occur.
[0073]
　In an embodiment of the present invention, prevented by using a second mold 3 having the inner pad 33, the areas of the vertical wall portion 93 (in particular, the portion close to the top plate stepped portion 913), reduction in temperature or to expand the range of parts to be suppressed. Accordingly, by relaxing the local strain concentration can be prevented or suppress the occurrence of cracks. Furthermore, as shown in FIG. 8A, the portion and the vicinity thereof becomes part and the top plate stepped portion 913 formed of the top plate portion 91 of the blank 7, performs hot press forming while being supported by the inner pad 33. Thus, among the blank 7, a portion which is located above the punch height top 316, a punch and a portion located above the lower top 317, top plate height portion 911 substantially at the same time the top plate lower portion It is molded into a 912. Therefore, at the time of hot press forming, it is possible to reduce the left-right direction of the tension generated in the non-contact portion 73.
[0074]
　Then, the effect of reducing the tension generated on the blank 7 by the inner pad 33, by the action of expanding the range of non-contact portion 73 of the blank 7, the formability is greatly improved. Thus, in producing the second of the press-molded product 9 and top plate height portion 911 and the top plate lower portion 912 is provided, by using a second mold 3 having the inner pad 33, the vertical in part (vertical wall portion 93 continuous with the top plate lower portion 912) adjacent to the top plate stepped portion 913 of the wall portion 93, preventing the occurrence of cracks due to the tension applied to the direction perpendicular to the pressing direction P or It can be suppressed.
[0075]
　Figure 12A and Figure 12B is a contour diagram in accordance with the sheet thickness reduction rate of the numerical analysis of the case of producing the second of the press-molded product 9. Numerical boxed in the drawing shows a sheet thickness reduction ratio. Each Figure 12A shows the case of using the second mold 3, FIG. 12B shows a case using a mold 6 of the second comparative example. Figure 12C and Figure 12D is a case of producing the second of the press-molded product 9, a temperature in a state where the die 32 is located 4mm above the bottom dead center is a diagram showing the following areas 650 ° C.. Respectively Figure 12C shows a case of using a second mold 3, FIG. 12D shows a case of using a mold 6 of the second comparative example. The area of ​​the solid black paint is temperature indicates the region of 650 ° C. or less.
[0076]
　Figure 12A and 12B, the and as FIG. 12C and the clear from a comparison Figure 12D, the use of the second mold 3, as compared with the case of using a mold 6 of the second comparative example, the blank You can expand the scope of the non-contact portion 73 of 7, thereby, an increase in the sheet thickness reduction rate by relaxing the local concentration of strain can be suppressed. This prevents or suppress the crack generation at the portion close to the top plate stepped portion 913 of the vertical wall portion 93.
[0077]

　Next, a description will be given of an embodiment. In an embodiment of the present invention, the target tensile strength to produce a press-formed product as 1500 MPa, was measured for the following (1) (2). (1) to the mold 2, 3 and the surface temperature T of the inner pad top 231 and 331 at the timing of setting the blank 7, part of which in contact with the inner pad top 231 and 331 of the press-molded product 8,9 produced mechanical strength. (2) standby time A (time from taking out the press-molded product 8,9 from the mold 2, 3 until set next blank 7) and the relationship between the surface temperature T of the inner pad top 231 and 331.
[0078]
　The measurement conditions are as follows. The contact area of the blank 7 and the inner pad 23, 33 is 5000 mm 2 is. Press direction dimension h of the inner pad 23, 33 is 100mm. Inner pad 23, 33 is a tool steel, the thermal conductivity λ is 30 W / mK, specific heat C is 4.3J / g · K. Volume ratio W of the refrigerant paths 233,333 inside the inner pad 23, 33 is 0.02. Depth from the surface of the inner pad 23, 33 to the refrigerant passage 233,333 is 20 mm. As the blank 7, the thickness t 0.11% carbon content by mass% was used a plate material of carbon steel 2.3 mm. Temperature of the blank 7 of the blank 7 at the time of the set to the mold 2, 3 was 750 ° C.. Water was used as a refrigerant. The flow rate of refrigerant in 233,333 in the refrigerant passage was 1 m / s.
[0079]
　13 parts, and the surface temperature T of the inner pad top 231 and 331 at the timing of setting the blank 7 into the mold 2, 3, in contact with the inner pad top 231 and 331 of the press-molded product 8,9 produced is a graph showing the mechanical strength of the relationship. The surface temperature T of the inner pad top 231, 331 is a value calculated using the equation (2). As shown in FIG. 13, at a timing of setting the blank 7 into the mold 2, the surface temperature T of the inner pad top 231 and 331 is at 100 ° C. or less, inner pad top 231 at the time of hot press forming , the tensile strength of the portion in contact with the 331 was confirmed to be a more 1500 MPa. In particular, since the sudden tensile strength was higher at 100 ° C. vicinity, it is preferable to satisfy the equation (2) the upper limit of the surface temperature T of the inner pad top 231, 331 as 100 ° C. was confirmed.
[0080]
　14, the waiting time A (time from taking out the press-molded product 8,9 from the mold 2, 3 until set next blank 7) and the relationship between the surface temperature T of the inner pad top 231 and 331 it is a graph showing a. Incidentally, the waiting time A is a value calculated using Equation (3). As shown in FIG. 14, according to the waiting time A is longer, the surface temperature T of the inner pad top 231 and 331 is gradually lowered. Then, in the range where the waiting time A exceeds 5 seconds, the surface temperature T of the inner pad top 231 and 331 it is almost not reduced. Thus, the waiting time A, it is preferred to satisfy the equation (3) as the lower limit is confirmed 5 seconds.
[0081]
　Figure 15 is a graph showing the relationship between the surface temperature T of the press dimension of the inner pad 23, 33 h and the inner pad top 231 and 331. The measurement conditions are the same as the condition. The value of the pressing direction dimension h is a value calculated using Equation (1). According pressing dimension h of the inner pad 23, 33 is increased, the surface temperature T of the inner pad top 231 and 331 goes low. Then, press dimension h of the inner pad 23, 33 in the range of more than 100 mm, the surface temperature T of the press dimension h is the inner pad top even larger 231 and 331 is almost not reduced. Thus, the press dimension h of the inner pad 23 and 33, it may be preferable to satisfy the equation (1) to 100mm as the lower limit is confirmed.
[0082]
　Although the embodiments of the present invention has been described in detail with reference to the accompanying drawings. However, the above-described embodiment is merely an example for implementing the present invention. The present invention is not limited to the above-described embodiments can be carried out by changing the embodiment described above without departing from the scope and spirit thereof as appropriate.
Industrial Applicability
[0083]
　The present invention can be used as hot press method, the industry in which the hot-press systems to perform hot pressing.

The scope of the claims
[Requested item 1]
　The upper and lower molds, the inner pad is movably accommodated is biased to a state of protruding toward the upper mold, a mold having a reference to the lower die, the blank and hot pressed a hot press method for producing a press-molded product,
　the inside of the inner pad is provided with the path of the refrigerant,
　by flowing a coolant in the path of the refrigerant takes the press-molded product from the mold Te until set next blank in the mold, the surface temperature of the inner pad, hot pressing method, characterized by cooling to a temperature satisfying the following formula to 100 ° C. as the upper limit.

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

　where,

　　T: surface temperature
　　(℃) h: the inner pad pressing dimension
　　(mm) t: thickness of the blank (mm)
　　lambda: thermal conductivity of inner pad (W /
　　mK) W: volume ratio of the refrigerant path in the interior of the inner pad (mm 3 / mm 3
　　) S: refrigerant flow rate of the refrigerant in the path (mm / sec)
[Requested item 2]
　Wherein the press-molded article according to claim 1, characterized in that the time that satisfies the following formula for the next blank is taken out from the mold the time to set the mold, the 5 seconds as the lower limit pressing method between the heat.

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

where,

　　A: Remove the press-molded product from the mold following time the blank until the set in a mold
　　(sec) h: pressing direction dimension of the inner pad
　　(mm) t: thickness of the blank (mm)
　　lambda: thermal conductivity of inner pad (W /
　　mK) W : volume ratio of the refrigerant path in the interior of the inner pad (mm 3 / mm 3
　　) S: flow rate of refrigerant in the refrigerant passage (mm / sec)
[Requested item 3]
　The press dimension of the inner pad, hot press method according to claim 1 or 2, characterized in that to satisfy the following formula to 100mm as the lower limit.

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

where,

　　h: pressing direction dimension of inner pad
　　(mm) t: thickness of the blank (mm)
　　lambda: thermal conductivity of inner pad (W /
　　mK) W: volume ratio of the refrigerant path in the interior of the inner pad (mm 3 / mm 3
　　) S: flow rate of refrigerant in the refrigerant passage (mm / sec)
[Requested item 4]
　Claims taken out of the press molded product from the mold until set next blank in the mold, and injecting the refrigerant fluid in the inner pad, wherein the cooling the inner pad hot press method according to any one of 1 to 3.
[Requested item 5]
　Wherein the upper mold, the and the refrigerant ejection port is provided which can inject coolant toward the inner pad,
　take out the press-molded product from the mold until set next blank in the mold , the upper die is approached to said lower die, by injecting refrigerant from the refrigerant ejection port toward the inner pad provided in the lower die, according to claim 1, characterized by cooling the inner pad hot press method according to any one of 4.
[Requested item 6]
　By using the upper and lower molds, a mold having a an inner pad path of the refrigerant is provided inside is urged in a state of protruding toward the upper die is movably accommodated in the lower die a press for hot pressing the blank material,
　and a cooling control unit for controlling the supply of coolant for cooling the inner pad
　has,
　the cooling control unit, by flowing the refrigerant in the path of the refrigerant, the press the molded article until set next blank in the mold is taken out from the mold, the surface temperature of the inner pad, the cooling to a temperature satisfying the following formula to 100 ° C. the upper limit hot pressing system comprising.

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

　where,

　　T: surface temperature
　　(℃) h: the inner pad pressing dimension
　　(mm) t: thickness of the blank (mm)
　　lambda: thermal conductivity of inner pad (W / mK)
　　W: volume ratio of the refrigerant path in the interior of the inner pad (mm 3 / mm 3
　　) S: refrigerant flow rate of the refrigerant in the path (mm / sec)
[Requested item 7]
　Wherein take out the press-molded product from the mold to claim 6, characterized in that the time to place the next blank in the mold, the time that satisfies the following formula 5 seconds as the lower limit hot-press system.

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

where,

　　A: Remove the press-molded product from the mold following time the blank until the set in a mold
　　(sec) h: pressing direction dimension of the inner pad
　　(mm) t: thickness of the blank (mm)
　　lambda: thermal conductivity of inner pad (W /
　　mK) W : volume ratio of the refrigerant path in the interior of the inner pad (mm 3 / mm 3
　　) S: flow rate of refrigerant in the refrigerant passage (mm / sec)
[Requested item 8]
　The press dimension of the inner pad, hot press system according to claim 6 or 7, characterized in that to satisfy the following formula to 100mm as the lower limit.

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

　where,

　　h: pressing direction dimension of inner pad
　　(mm) t: thickness of the blank (mm)
　　lambda: thermal conductivity of inner pad (W /
　　mK) W: volume ratio of the refrigerant path in the interior of the inner pad (mm 3 / mm 3
　　) S: flow rate of refrigerant in the refrigerant passage (mm / sec)
[Requested item 9]
　Further comprising a coolant jetting unit for jetting the refrigerant to the inner pad,
　the refrigerant injection unit, until taken out of the press molded product from the mold set next blank in the mold, the inner hot pressing system according to any one of claims 6 8, by injecting coolant fluid to the pad, characterized in that cooling the inner pad.
[Requested item 10]
　Wherein the upper mold, the and the refrigerant ejection port is provided which can inject coolant toward the inner pad,
　take out the press-molded product from the mold until set next blank in the mold the press machine so that close the upper die to the lower die, by the cooling control unit is possible to inject coolant toward the inner pad provided in the lower mold from the refrigerant ejection port, cooling said inner pad hot pressing system according to any one of claims 6 9, characterized by.