JP2019089132A - Mold for hot press, hot press device, and production method of hot press molded article - Google Patents

Abstract

To remove effectively generation of a crack on a vertical wall of a hot press molded article having a hat-shaped or ditch-type cross section.SOLUTION: A hot press molded article 13 is produced by performing hot press molding to a blank 20 by using a mold 15 for hot press including a punch apex 15a and two punch shoulder R parts 15b, and including an inner pad 21 arranged protrusively as long as a prescribed amount from the punch apex 15a and stored in the punch apex 15a at a molding bottom dead center.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a mold for hot pressing, a hot pressing apparatus and a method for producing a hot press-formed product, and more specifically, a top plate, a ridge line continuous to the top plate, and a vertical wall continuous to the ridge line The present invention relates to a technology for suppressing vertical wall cracking in the case of producing a hot press-formed product having a cross section (e.g., hat cross section or grooved cross section).

  In recent years, in order to reduce the weight of automobiles, it has been promoted to increase the strength of steel materials and to reduce the weight used. In thin steel plates widely used in automobiles, as the strength increases, the press formability decreases, and it has become difficult to manufacture complicated shapes. Specifically, a high strength blank is reduced in ductility to cause breakage at a portion having a high degree of processing, or springback or wall warpage is increased to deteriorate the dimensional accuracy of a press-formed product. For this reason, it is not easy to perform cold press forming on a blank made of a steel plate having a high strength, in particular, a tensile strength of 780 MPa or more to manufacture a press-formed product having a desired shape. According to roll forming instead of press forming, although processing of a high strength steel plate is possible, only parts having a uniform cross section in the longitudinal direction can be manufactured.

  On the other hand, Patent Document 1 discloses a method called hot press forming in which press forming is performed on a blank made of a heated steel plate, and Patent Document 2 discloses that the blank is preformed into a predetermined shape at room temperature. A hot press forming method (pre-press quenching method) is disclosed that simultaneously achieves high strength and formability of a steel sheet by heating to an austenite region and quenching in a press forming die.

  In hot press forming, since the steel plate at the time of forming is high temperature, soft and high ductility, it is possible to manufacture a press-formed product having a complicated shape with good dimensional accuracy. Furthermore, by heating the steel plate to the austenite region and quenching (quenching) in the press forming die, high strengthening of the steel plate by martensitic transformation is simultaneously achieved.

  As described above, although the degree of freedom for forming a high strength steel plate is greatly increased by the hot press forming, cracking may occur during the press forming even if the hot press forming is performed.

  FIG. 8 (a) is a perspective view showing the hot press-formed product 1 causing such a crack, and FIG. 8 (b) is a half cross section of the press-forming apparatus 3 of the hot press-formed product 1. FIG. FIG. 9 (a) is a perspective view showing a hot press-formed product 2 which causes a similar crack, and FIG. 9 (b) is a half sectional view of the press-forming apparatus 4 of the hot press-formed product 2. 9 (c) is an explanatory view showing a cross section corresponding to the cross section AA 'in FIG. 9 (a) in the press-forming apparatus 4 before the start of the press-forming. The two straight lines in FIG. 9A and FIG. 9C indicate that the positions indicated by the two lines correspond to the positions before and after press molding.

  As shown in FIG. 8 (b), the blank 8 is subjected to hot press forming by drawing using the punch 5, the die 6, and the blank holder 7 of the press forming apparatus 3 as shown in FIG. 8 (a). For example, a cross section (for example, a hat cross section or a groove) having a top plate 1a, two ridge lines 1b and 1b continuous to the top plate 1a, and two vertical walls 1c and 1c continuous to two ridge lines 1b and 1b, respectively. In the case of manufacturing a hot press-formed product 1 having a mold cross section) and a curved portion 1 d having a ridge line 1 b which is projected to the outside of the top plate 1 a in plan view in the pressing direction In the vertical wall 1c continuous with the top plate 1a of the portion 1d, a crack is likely to occur during hot press forming.

  Further, as shown in FIGS. 9 (b) and 9 (c), the blank 8 is subjected to hot press forming by bending using the punch 5 and the die 6 of the press forming apparatus 3, and FIG. 9 (a) For example, as shown in FIG. 1, a cross section having a top 2a, two ridges 2b and 2b continuous to the top 2a, and two vertical walls 2c and 2c continuous to two ridges 2b and 2b (for example, When manufacturing a hot press-formed product 2 having a hat cross section or a groove cross section and a step 2e in the pressing direction (direction orthogonal to the top 2a) on the top plate 2a, the top plate near the step 2e A crack is likely to occur during hot pressing in the vertical wall 2c that is continuous with 2a (in particular, the top plate 2a present at a low position bordering on the step 2e).

  A large number of inventions have been proposed for the purpose of preventing cracking of press-formed products. Patent Document 3 discloses a method of manufacturing a cold press-formed product of a member having a hat-shaped cross section which is curved in a plan view with a line of sight orthogonal to a top plate, and Patent Document 4 discloses a cross-sectional hat by hot press molding. A method is disclosed in which an arc-shaped separate-acting punch is incorporated in a mold (punch) when forming a mold member, and the separate-acting punch is operated at the forming bottom dead center. A draw forming hot press forming method is disclosed that improves formability by cooling specific portions of the material using a cooling catalyst.

British Patent Publication No. 1490535 Japanese Patent Application Laid-Open No. 10-96031 WO 2014-106932 pamphlet JP, 2015-20175, A JP, 2014-208374, A

  However, when the manufacturing method disclosed by patent document 3 is applied to hot press forming, a crack may generate | occur | produce in a punch shoulder part.

  The method disclosed by Patent Document 4 can not suppress the warping of the vertical wall that occurs before reaching the molding bottom dead center. Further, in order to operate the separate-acting punch, it is necessary to separately provide an operating device and the like of the separate-acting punch, which inevitably raises the cost of the apparatus.

  Furthermore, although the method of suppressing the crack of a vertical wall is prescribed | regulated certainly by patent document 5, the raise of the apparatus cost is not avoided also by this method.

  As described above, in the prior art, it is not possible to suppress the cracking of the vertical wall due to the extension strain generated in the vertical wall during hot press forming described with reference to FIGS. 8 and 9 without increasing the manufacturing cost.

  Cracking of the blank in hot press forming often occurs due to the local temperature drop of the blank caused by the contact between the blank and the die (punch, die). The temperature reduction portion in contact with the mold in the blank is high in hardness and difficult to deform as compared to the non-temperature reduction portion (high temperature portion) not in contact with the mold in the blank. It will be done.

  The present inventors earnestly studied in order to solve the above-mentioned subject based on such a premise, as a result of obtaining knowledge AK listed in the following, the present invention was completed.

  (A) FIG. 10 (a) shows the contour by numerical analysis of the thickness reduction rate at the bottom dead point of the hot press-formed product 1 hot pressed by the press-forming apparatus 3 shown in FIG. 8 (b). 10 (b) is a graph showing the temperature of each part at a position 10 mm above the bottom dead center of the hot press-formed product 1 hot pressed by the press-forming apparatus 3 shown in FIG. 8 (b). It is a contour figure by numerical analysis. The numbers in FIG. 10A indicate the thickness reduction rate in the indicated area.

As shown in FIG. 10 (a), the vertical wall 1c on the outer peripheral side of the curved portion 1d in which cracking easily occurs in hot press forming is
(I) It is a site to which tension is applied not only in the press direction but also in the direction orthogonal to the press direction during molding;
(Ii) It is a part kept at high temperature because it does not contact with the molds 5 and 6, and (iii) It is a part sandwiched by the die shoulder R and the punch shoulder R of the mold which the blank 8 contacts. It is characterized by

  (B) From these features (i) to (iii), the longitudinal wall 1c on the outer peripheral side of the curved portion 1d is likely to be cracked because the plate thickness is greatly reduced because the strain is concentrated at the time of molding. Therefore, in order to suppress the cracking of the vertical wall 1c, local concentration of strain is alleviated by expanding the area of the non-temperature decreasing portion (high temperature portion) of the vertical wall 1c on the outer peripheral side of the curved portion 1d. Is effective.

  (C) Two ridgelines 1b and 1b continuous to the top plate 1a and two vertical walls 1c and 1c continuous to the two ridgelines 1b and 1b on the top plate 1a When the curved portion 1d is provided with the ridge line 1b that protrudes and is bent, concentration of strain on the vertical wall 1c on the outer peripheral side of the curved portion 1d is significantly generated. When the ridgeline 1b is bent, the flow of the blank at the time of press molding becomes uneven.

  (D) FIG. 10 (c) is a contour diagram by numerical analysis of a thickness reduction rate at a forming bottom dead point in a hot press-formed product 10 hot-pressed by a press-forming apparatus according to the present invention described later. FIG. 10 (d) is a contour diagram by numerical analysis of the temperature of each portion at a position 10 mm above the forming bottom dead point in the hot press-formed product 10 hot-pressed by the press-forming apparatus according to the present invention. is there. The numbers in FIG. 10C indicate the thickness reduction rate in the indicated area.

  As understood from comparison of FIG. 10 (c) and FIG. 10 (d) with FIG. 10 (a) and FIG. 10 (d), the hot press-formed product 10 is manufactured by hot press forming. In this case, a punch having an inner pad attached to the top of the punch is used. Specifically, a portion of the blank formed in the curved portion 10d of the top plate 10a in plan view in the press direction is used as the punch top. The area of the non-temperature reduction portion (high temperature portion) of the vertical wall 1c on the outer peripheral side of the curved portion 10d is expanded by performing hot press forming using a punch and a die supported by the inner pad freely mounted. As a result, since local concentration of strain can be alleviated and the reduction rate of the plate thickness can be suppressed, it is possible to effectively eliminate the occurrence of cracks in the vertical wall 10c on the outer peripheral side of the curved portion 10d.

  (E) The above findings (A) to (D) show that when there is only one ridge line of the top plate, that is, from an annular ridge line such as a circle, an ellipse, or a polygon in plan view in the press direction with respect to the blank. The present invention can also be applied to the case of hot press forming a top plate to be formed.

  (F) FIG. 5 (a) shows the molding drop in the hot press-formed product 2 having a step 2e on the top plate 2a, which is hot-pressed using the press-forming apparatus 4 shown in FIG. 9 (b) (c). FIG. 5 (b) is a contour diagram of the top plate 2a hot pressed by the press forming apparatus 4 shown in FIGS. 9 (b) and 9 (c). It is a contour figure by numerical analysis of each part temperature in a 4 mm upper position from the molding bottom dead center in the hot press-formed article 2 with 2e. Here, the level | step difference 2e is a boundary part from which the shaping | molding height of the top 2a changes.

As shown in FIG. 5 (a), the top plate 2a near the step 2e (the top plate 2a present at a low position bordering the step 2e, in particular the punch side of the boundary of the step 2e) (A) and (b) on the vertical wall 2c continuous with the convex portion), similarly to the curved portion 1d shown in FIG.
(I) It is a site to which tension is applied not only in the press direction but also in the direction orthogonal to the press direction during molding;
(Ii) It is a part kept at high temperature because it does not contact with the molds 5 and 6, and (iii) it is pinched by the die shoulder R and punch shoulder R of the molds 5 and 6 with which the blank 8 contacts. It has the feature of being a part.

  (G) From these features (i) to (iii), the longitudinal wall 2c of the step portion 2e of the top plate 2a is likely to be cracked because the plate thickness is greatly reduced because the strain is concentrated at the time of molding. The reason will be described in more detail.

  FIG. 6 (a) is an explanatory view showing the shape of the blank 20 at a position 20 mm above the bottom dead center when molding the hot press-formed product 14 by the press-forming apparatus 12 according to the present invention. b) is explanatory drawing which shows the cross section of the press molding apparatus 12 at this time.

  As shown in FIGS. 6 (a) and 6 (b), when there is a step in the portion 8a of the blank 8 formed on the top plate 2a, the portion 8a located on the convex side 5a of the punch 5 is punched at the beginning of forming It will be restrained earlier than the portion 8b located on the concave side 5b of 5. For this reason, when the molding proceeds and the portion 8b located on the concave side 5b of the punch 5 is molded, the portion 8a located on the convex side 5a of the punch 5 is restrained, and the inflow of the material It is short and cracking is likely to occur in the portion formed on the vertical wall 2c which is continuous with the portion 8b. In particular, in the hot press forming, the area of the non-temperature reduction portion (high temperature portion) of the portion formed on the vertical wall 2c in the blank 8 at the time of forming becomes smaller, so the blank 8 is restrained more than the cold press forming. As a result, in the portion formed on the vertical wall 2c, which is continuous with the portion 8b, cracking is more likely to occur.

  (H) For this reason, in order to suppress the crack in the vertical wall 2e in the hot press-formed product 2 having the step 2e on the top plate 2a, the non-temperature decrease of the vertical wall 2c continuing to the step 2e on the top plate 2a It is effective to reduce local concentration of strain by expanding the area of the part (high temperature part).

  FIG. 7A is an explanatory view showing the shape of the blank 20 at a position above the lower dead point of molding 20 mm when the hot press-formed product 14 is formed by the press-forming apparatus 12 according to the present invention described later. 7 (b) is an explanatory view showing a cross section of the press forming device 12 at this time.

  As shown in FIG. 7B, using the punch 16 having the inner pad 21 mounted on the top of the punch, specifically, it is formed on the top plate 14a of the hot press-formed product 14 in the blank 20. A portion 20a of the blank 20 located on the convex side 16a of the punch 16 by supporting the vicinity of the portion to be formed into the step 14e by the inner pad 21 and performing hot press forming using the punch 16 and the die 18. Also, the portion 20b located on the concave side 16b of the punch 16 is formed substantially simultaneously, and the restraint of the blank 20 at the time of forming the portion 20b is reduced.

  (I) FIG.5 (c) is a contour figure by numerical analysis of the thickness reduction rate in the forming bottom dead point in the hot press-formed product 14 hot-pressed by the press-forming apparatus based on this invention mentioned later. FIG. 5 (d) is a contour diagram by numerical analysis of the temperature of each portion at a position 4 mm above the forming bottom dead point in the hot press-formed product 14 hot pressed by the press forming apparatus according to the present invention. is there.

  As understood from comparison of FIG. 5C and FIG. 5D with FIG. 5A and FIG. 5B, a hot press having a step 14e on the top plate 14a by hot press forming When manufacturing the molded article 14, a punch having an inner pad attached to the top of the punch is used. Specifically, it is molded on the top plate 14a on the side lower in height with the step 14e as the boundary in the blank. Of the portion to be formed on the vertical wall 14c in the vicinity of the step 14e in the blank 20 by supporting the portion by the inner pad attached to the top of the punch so as to be able to move in and out and performing hot press forming using the punch and die. Since the region of the non-temperature reduction portion (high temperature portion) can be expanded, and thereby local concentration of strain can be alleviated and reduction of the plate thickness can be suppressed, generation of cracks in the vertical wall 14c near the step 14e The can be effectively resolved.

  (J) Thus, the restraint of the blank 20 at the time of molding of the portion 20 b is reduced by using the inner pad 21, and the non-temperature reduction portion (high temperature portion) of the portion formed on the vertical wall 14 c in the blank 20 By the synergetic effect of the expansion of the region of (4), the formability is significantly improved, and cracking at the vertical wall 14c in the vicinity 14d of the step 14e is suppressed. That is, when manufacturing the hot press-formed product 14 having a step in the press direction (the height of the formed product 14) on the top plate 14 a of the hat-shaped cross section or the grooved cross section by performing hot press forming on the blank 20 In addition, by using the inner pad 21, it is possible to effectively suppress the occurrence of cracks in the vertical wall 14c which is continuous with the top plate 14a having a low height with the step 14e as a boundary.

  (K) As described above, when hot pressing to a hat-shaped or groove-shaped cross section or when forming a convex portion having a top plate with respect to a blank by hot pressing, the vicinity of the punch shoulder R portion in the blank If the part to be formed on the vertical wall is a part that is concerned about cracking due to tension being applied in the direction orthogonal to the pressing direction, the vicinity of the blank part is supported by the inner pad However, by performing hot press forming, cracking of the blank at this site can be avoided.

The present invention is as listed below.
(1) In a hot press die including a punch top and a punch shoulder R continuous with the punch top, the punch top is disposed so as to protrude by a predetermined amount from the punch top and at the forming bottom dead center A mold for hot pressing comprising an inner pad housed at the top of a punch.

  (2) The inner pad is a portion at which tension is applied in a direction perpendicular to the pressing direction to a portion of the blank formed on the vertical wall in the vicinity of the punch shoulder R portion (in the punch for applying tension to the blank The mold for hot pressing as described in 1 above, which is disposed in a part).

  (3) The hot-pressing mold according to the item 2, wherein the portion is a portion where the edge of the punch top portion protrudes and bends to the outside of the punch in a plan view in the pressing direction.

  (4) The hot press described in item 2 is the low-order portion (lower portion of the punch) in which the height of the punch is low at the step portion formed in the punch height direction at the top of the punch. Mold.

  (5) A hot pressing apparatus comprising the hot pressing die described in any one of the items 1 to 4.

  (6) The heated blank is subjected to press forming using the punch and die, which are the molds for hot pressing described in any one of items 1 to 4, to obtain a top plate, a top plate, and a top plate. A method of manufacturing a hot press-formed article having a cross section comprising a ridge line continuous to a plate and a vertical wall continuous to the ridge line, the press forming being formed on the top plate of the heated blank A hot press is performed by bringing the punch relatively close to the die and clamping the part while supporting the part by the inner pad disposed so as to project from the top of the punch by a predetermined amount. Method of producing a molded article.

  The "hot press-formed product" in the present invention is a large number as a component of an automobile body or an automobile part, and for example, a center pillar inner panel and center pillar outer panel, side sill inner panel and side sill outer panel, A pillar inner panel and A pillar outer panel The roof rail inner panel, the roof cross, the front side member and the rear side member, the sub frame (suspension member) and the like are exemplified.

According to the present invention, the non-temperature reduction portion (high temperature portion) of the portion formed on the vertical wall portion is expanded by performing the hot press forming using the punch and the die having the inner pad attached to the punch top portion freely. As a result, the occurrence of cracks in the vertical wall can be effectively eliminated.
More specifically, in the blank, the inner pad freely attached to the top of the punch is brought into contact with the place where the top plate protrudes outward in a plan view in the press direction and the place where the top plate has a step. By performing hot press forming using the above, it is possible to eliminate the occurrence of cracking of the portion formed on the vertical wall of the relevant portion.

FIG. 1 is an explanatory view schematically showing a hot press apparatus according to the present invention and a press-formed product produced therefrom. FIG. 2: is explanatory drawing which shows typically the hot-press apparatus which concerns on this invention, and the press-formed article manufactured by these. FIG. 3 is an explanatory view showing a situation in which a blank is subjected to hot press forming using a conventional hot press apparatus provided with a punch and a die. FIG. 4: is explanatory drawing which shows the condition which hot press-molds to a blank using the hot press apparatus which concerns on this invention. FIG. 5 (a) is based on numerical analysis of the plate thickness reduction rate distribution at the bottom dead point of the press-formed product shown in FIG. 9 (a) manufactured by the conventional hot press-forming method without using the inner pad. FIG. 5 (b) is a contour view, which is 4 mm above the molding bottom dead center of the press-formed product shown in FIG. 9 (a) manufactured by the conventional hot press-forming method without using the inner pad. FIG. 5 (c) is a bottom view of the press-formed product shown in FIG. 2 (a) manufactured by the hot press-forming method according to the present invention using the inner pad. It is a contour figure by numerical analysis of board thickness reduction rate distribution in a dead center, and Drawing 5 (d) shows in Drawing 2 (a) manufactured by the hot press-forming method concerning the present invention which uses an inner pad. 4 mm above the molding bottom dead center of the press-formed product It is a contour diagram in accordance with the numerical analysis of each part temperature at location. FIG. 6 (a) is an explanatory view showing the shape of a blank at a position 20 mm above the bottom dead center when forming a hot press-formed product by the press-forming apparatus according to the present invention, and FIG. It is explanatory drawing which shows the cross section of the press molding apparatus at this time. FIG. 7 (a) is an explanatory view showing the shape of a blank at a position above the bottom dead center of molding 20 mm when a hot press-formed product is formed by a press-forming apparatus according to the present invention described later. ) Is an explanatory view showing a cross section of the press forming apparatus at this time. Fig.8 (a) is a perspective view which shows the hot press-formed product which produces a crack, FIG.8 (b) is explanatory drawing which shows the half cross section of the press-forming apparatus of a hot press-formed product. Fig.9 (a) is a perspective view which shows the hot press-formed product which produces the same crack, FIG.9 (b) is explanatory drawing which shows the half cross section of the press-forming apparatus of a hot press-formed product. FIG. 9C is an explanatory view showing a cross section corresponding to the cross section AA 'in FIG. 9A in the press-forming apparatus before the start of the press-forming. Fig.10 (a) is a contour figure by numerical analysis of the plate | board thickness reduction rate in the shaping | molding bottom dead point in the hot press-formed product hot-press-formed by the press-forming apparatus shown in FIG. 10) is a contour diagram by numerical analysis of the temperature of each part at a position 10 mm above the forming bottom dead point in a hot press-formed product which is hot-pressed using a press forming apparatus shown in FIG. FIG. 10 (d) is a contour diagram by numerical analysis of a thickness reduction rate at a forming bottom dead point in a hot press-formed product which is hot-pressed by a press-forming apparatus according to the present invention. It is a contour figure by numerical analysis of each part temperature in a 10-mm upper position above a forming bottom dead point in a hot press-formed product hot-press formed by a press-forming device according to.

The invention will be described with reference to the accompanying drawings.
1. Hot press apparatus 11, 12 according to the present invention
Fig.1 (a) is explanatory drawing which shows typically the press-formed article 13 manufactured by the hot-press apparatus 11 which concerns on this invention, FIG.1 (b) is the hot-press apparatus 11 which concerns on this invention. FIG. 2 (a) is an explanatory view schematically showing a press-formed product 14 manufactured by the hot press 12 according to the present invention, and FIG. 2 (b) is a hot press according to the present invention. FIG. 2 is an explanatory view showing a device 12;

  Hereinafter, the hot press devices 11 and 12 will be collectively described with reference to FIGS. 1 (a) and 1 (b), 2 (a) and 2 (b).

  As shown in FIG. 1 (b) and FIG. 2 (b), the hot pressing devices 11 and 12 are provided with the punches 15 and 16 which are dies for hot pressing, and the dies 17 and 18, respectively. The apparatus 11 further comprises a blank holder 19.

  The hot press device 11 performs hot press forming by draw forming on the blank 20 using the punch 15, the die 17, and the blank holder 19 to form two ridge lines continuous with the top plate 13 a and the top plate 13 a. 13b, 13b and two vertical walls 13c, 13c continuous with the two ridgelines 13b, 13b, respectively, having a cross section (for example, hat cross section or grooved cross section), and also two ridges 13b, 13b and two vertical walls A hot press-formed product 13 having a bent portion 13d in which at least one of the ridges 13c and 13c and the vertical wall 13c of the 13c and 13c protrudes and bends to the outside of the top plate 13a in plan view in the press direction is manufactured.

  On the other hand, the hot press 12 performs hot press forming on the blank 20 by bending using the punch 16 and the die 18 to form the top plate 14a and two ridge lines 14b and 14b continuous to the top plate 14a. , And a cross section (for example, a hat cross section or a groove type cross section) including two vertical walls 14c and 14c continuous to two ridge lines 14b and 14b, and the top plate 14a has a height direction of the hot press-formed product 14 A hot press-formed product 14 having a step 14 e to a direction (a direction substantially orthogonal to the top plate 14 a) is manufactured. The top plate 14a is divided into a portion with a high height and a portion with a low height with the step 14e as a boundary, and the height changes in the step 14e.

  The mold for hot pressing according to the present invention is used for the punches 15 and 16. That is, the punches 15 and 16 have punch tops 15a and 16a, and two punch shoulder R-portions 15b and 16b continuous to the punch tops 15a and 16a.

  In the hot pressing device 11, at least one of the two punch shoulder R portions 15b has a curved portion in plan view in the pressing direction. The curved portion is for forming the curved portion 13 d of the hot press-formed product 13. FIG. 1 shows a cross section at the position of the bend of the punch 15.

  In the press-formed product 14 formed by the hot press 12, the ridge line 14 b formed by the two punch shoulder R portions 16 b collides with another vertical wall portion, and a step 14 e is generated on the top plate 14 a. FIG. 2B shows a cross section in the vicinity of the ridge line 14b formed by the punch shoulder R portion 16b abutting another vertical wall portion, that is, the lower portion of the top plate 14a with the step 14e as a boundary.

  The punches 15 and 16 have inner pads 21 and 21 which are disposed so as to protrude from the punch tops 15a and 16a by a predetermined amount in FIGS. 1 (b) and 2 (b). The inner pads 21 and 21 are parts of portions of the blank 20 formed on the top plates 13 a and 14 a (portions of the blank 20 formed on the vertical walls 13 c and 14 c near the punch shoulder R portion are orthogonal to the pressing direction. (In the vicinity of the point where the tension is applied), but the remaining part (e.g. all) except this part may also be supported.

  Housing holes 15c, 16c for housing the inner pads 21, 21 are formed in the punch tops 15a, 16a, and the inner pads 21, 21 are punched in the bottom portions 15d, 16d of the housing holes 15c, 16c. Suitable pressing mechanisms such as springs 15e, 16e or gas cushions are provided for positioning by projecting a predetermined amount from the tops 15a, 16a.

  The inner pads 21 and 21 are disposed at the positions shown in FIG. 1 (b) and FIG. 2 (b) at the start of press molding, and as the dies 17 and 18 approach the punches 15 and 16 after the start of press molding. It is urged by the dies 17 and 18 and gradually moves from the above position toward the bottoms 15d and 16d of the accommodation holes 15c and 16c, and is completely accommodated in the punch tops 15a and 16a at the forming bottom dead center. , 16a are arranged.

As shown in FIG. 1, it is preferable to hold the blank 20 between the die pad 17a and the inner pad 21 using the die pad 17a supported by the die 17 or the like. Also in FIG. 2 (b) (not shown), it is desirable to have a die pad as well.
The hot pressing devices 11, 12 according to the present invention are configured as described above.

2. Manufacturing method according to the present invention In the present invention, as shown in FIGS. 1 (a) and 1 (b), 2 (a) and 2 (b), the heated blanks 20, 20 are hot pressed The hot press-formed articles 13 and 14 are manufactured by press-forming using 11 and 12.

  FIG. 3 is an explanatory view showing a situation in which the blank 20 is hot-pressed using the conventional hot-pressing apparatus 30 including the punch 31 and the die 32. FIG. 4 is a hot-pressing apparatus according to the present invention It is explanatory drawing which shows the condition which hot press-molds to the blank 20 using 11,12.

  As shown in FIG. 3, during the conventional hot press forming using the hot press 30, the first portion 20a of the blank 20 is cooled by coming into contact with the die R portion 32a, and the second portion 20b Is cooled by contact with the punch shoulder R portion 31a. Therefore, in the blank 20, the third portion (the portion formed on the vertical wall of the press-formed product) 20c between the first portion 20a and the second portion 20b has a narrow range of non-temperature reduction ( In the region of the high temperature portion), strain concentrates at the portion where the curved portion 13d or the step 14e is formed (i.e., 14d).

  On the other hand, as shown in FIG. 4, in the present invention, the hot press forming of the top plate 14a on the top side with a low height bordering on the curved portion 13d and the step 14e is performed on the top plates 13a and 14a of the blank 20. By holding the punches 15 and 16 relatively close to the dies 17 and 18 while supporting the portions to be molded by the inner pads 21 arranged so as to protrude from the punch tops 15 a and 16 a by a predetermined amount Sip Is done.

  The first portion 20a of the blank 20 is cooled by contact with the die R portions 17a and 18a, and the second portion 20b contacts the inner pad shoulder R portion 21a instead of the punch shoulder R portions 15a and 16a. It is cooled by

  At this time, since the blank 20 is supported by the inner pad 21 at a position approaching the dies 17 and 18 by a predetermined amount, the third portion between the first portion 20 a and the second portion 20 b of the blank 20 is The portion 20c (portion formed on the vertical wall of the press-formed product) 20c has a non-temperature-reduced portion (high-temperature portion) region formed in a wider range than the conventional example shown in FIG. The concentration of strain at the time of molding is alleviated at the forming location of 14e, whereby the thickness reduction rate is reduced and cracking is eliminated.

  FIG. 5 (a) is a numerical analysis of the plate thickness reduction rate distribution at the bottom dead point of the press-formed product 2 shown in FIG. 9 (a) manufactured by the conventional hot press-forming method without using the inner pad. FIG. 5 (b) is 4 mm above the molding bottom dead center of the press-formed product 2 shown in FIG. 9 (a) manufactured by the conventional hot press-forming method without using the inner pad. FIG. 5 (c) is a contour figure by numerical analysis of each part temperature at the position, and FIG. 5 (c) is a press-formed product 14 shown in FIG. 2 (a) manufactured by the hot press forming method according to the present invention using the inner pad. FIG. 5 (d) is a contour diagram by the numerical analysis of the plate thickness reduction rate distribution at the forming bottom dead center of FIG. 5 (d) is manufactured by the hot press forming method according to the present invention using the inner pad, FIG. From the molding bottom dead center of the press-formed product 14 shown in It is a contour diagram in accordance with the numerical analysis of each part temperature at 4mm upper position.

  As understood from the comparison of FIGS. 5 (b) and 5 (d), the present invention is the step difference portion of the press-formed product 14 at a position 4 mm above the molding bottom dead center than the conventional example. The non-temperature reduction part (high temperature part) of the part shape | molded by the vertical wall 14c is expanded.

  Therefore, as shown in FIGS. 5 (a) and 5 (b), in the conventional example, the thickness reduction rate of the vertical wall 14c of the step portion of the press-formed product 14 reaches 28.9% indicating cracking. However, in the present invention, the reduction in thickness is suppressed to 18.6%, and it can be seen that no cracks occur in the vertical wall 14c of the step portion.

13 Hot press-formed product 15 Hot press mold 15a Punch top 15b Punch shoulder R 20 Blank 21 Inner pad

Claims (7)

A punch top, a punch shoulder R continuous with the punch top, and an inner pad disposed so as to project from the punch top by a predetermined amount outside the punch top and being accommodated in the punch top at a forming bottom dead center; And punches,
A die for pressing a blank in cooperation with the punch;
A free end arrangement space forming portion for making the outer peripheral edge portion a non-restricting free end until the outer peripheral edge of the blank is sandwiched between the punch and the die at the time of the pressing;
A mold for hot pressing characterized by comprising: The punch and the die form the blank into a press-formed product by the pressing.
And the ridge line includes a grooved cross section having a top plate, a pair of ridge lines provided on the top plate, and a pair of vertical walls respectively continuous with the corresponding ridge lines, and The hot press according to claim 1, wherein the punch and the die are arranged such that both ends of the grooved cross section in the extending direction have a shape opened in the extending direction of the ridge line. Mold. A punch top, a punch shoulder R continuous with the punch top, and an inner pad disposed so as to project from the punch top by a predetermined amount outside the punch top and being accommodated in the punch top at a forming bottom dead center; And punches,
A die for pressing a blank in cooperation with the punch;
A die pad disposed so as to project from the recess formed in the die toward the punch by a predetermined amount, and accommodated in the recess at the molding bottom dead center;
Equipped with
The press work is performed by relatively moving the punch top portion and the die in a state in which the die pad and the inner pad sandwich the blank. The blank for forming a press-formed product, wherein the punch and the die include a top plate, a ridge line provided on the top plate, and a vertical wall continuous to the ridge line and extending to intersect the die. Configured to be pressed,
The punch top portion is provided as a portion forming a part of the top plate,
The punch shoulder R portion is provided as a portion forming the ridge line,
The punch further includes a portion continuous with the punch shoulder R portion to form the vertical wall,
The hot press die according to any one of claims 1 to 3, wherein the inner pad is disposed adjacent to a portion forming the vertical wall.   The hot press die according to claim 4, wherein the inner pad is disposed at a position where an edge of the punch top portion protrudes and bends to the outside of the punch in a plan view in a press direction.   A hot press comprising the hot press die according to any one of claims 1 to 5. A method for producing a hot press-formed product, comprising press-forming a heated blank using the hot-pressing die according to any one of claims 1 to 5.

Images