Hot press molding device, automobile body component, hot press molding method, and automobile body component manufacturing method

Abstract

A hot press forming device includes an upper die (14) having a forming surface for forming a to-be-formed portion (4) of a metal sheet (2) and further having a blade (32a) serving as a punch (32), a lower die (13) having a forming surface (21) for holding and forming the to-be-formed portion in cooperation with the upper die, and a trim die (16) configured to cooperate with an edge of the upper die to separate a trimming portion (3) positioned outside the formed portion of the metal sheet from the formed portion resulting from forming the to-be-formed portion by the upper die and the lower die. An outside surface (14a) of the upper die is formed to extend in a cutting direction of the punch, and defines a cooling suppression space (62) at a side of the upper die in which the trimming portion is exposed so as to suppress cooling of the trimming portion. A hot press forming device capable of preventing delayed fracture from occurring in a formed product can be provided.

Description

TECHNICAL FIELD

[0001] The present application relates to a hot press forming apparatus for forming a metal sheet and trimming unnecessary portions, an automobile body component formed by the hot press forming apparatus, a hot press forming method of forming a metal sheet and trimming unnecessary portions, and an automobile body component manufacturing method. BACKGROUND

[0002] Patent Literature 1 describes an example of a conventional hot press forming apparatus capable of forming a metal sheet and trimming unnecessary portions. The hot press forming apparatus disclosed in Patent Literature 1 is configured so that a die functions as both a punch and a die. A metal sheet to be loaded into the hot press forming apparatus includes a formed portion to be formed into a predetermined shape by the die and a trimming portion that is an unnecessary portion outside the formed portion.

[0003] The die is formed so as to overlap the entire area of the metal sheet and has a recessed portion for forming. The punch is formed so as to fit in the recessed portion of the die while overlapping the formed portion of the metal sheet. Further, a retainer that holds the trimming portion of the metal sheet by clamping the trimming portion in cooperation with the die from the start of forming to the end of trimming is movably installed on the side portion of the punch. The retainer is biased toward the die by a spring force of a spring and is configured to hold the trimming portion in cooperation with the die from the start of forming to the end of trimming.

[0004] The hot press forming apparatus described in Patent Literature 1 has a configuration that suppresses occurrence of delayed fracture by performing trimming in a state where the metal sheet is not hardened. Delayed fracture refers to a phenomenon in which, at room temperature, under the action of a static load, a sudden fracture occurs after a given time elapses.

[0005] RELATED ART LITERATURE

[0006] PATENT LITERATURE

[0007] Patent Literature 1: International Publication No. 2018 / 083814 SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] Unfortunately, when trimming is simply performed in a non-hardened state, the effect of preventing delayed fracture is insufficient. This can be because, in the hot press forming apparatus described in Patent Literature 1, the trimming portion is clamped between the retainer and the die from the start of trimming. When the trimming portion is thus clamped between the retainer and the die, the temperature of the trimming portion decreases, and this makes it difficult to cut the trimming portion during trimming. Therefore, tensile residual stress, which is one cause of the occurrence of delayed fracture, increases in the end portion of the formed product after trimming.

[0010] An object of the present application is to provide a hot press forming device, an automobile body component, a hot press forming method, and an automobile body component manufacturing method, each of which can prevent occurrence of delayed fracture in a formed product.

[0011] Solution to the problem

[0012] To achieve this object, a hot press forming device according to the present application includes:

[0013] a first die configured to form a metal sheet heated to a predetermined temperature, and having a forming surface for forming a portion to be formed of the metal sheet and a blade serving as a punch in an outer end portion of the forming surface;

[0014] a second die having a forming surface for clamping and forming the portion to be formed in cooperation with the first die; and

[0015] a die configured to cooperate with the blade of the first die to separate a trimming portion positioned outside the portion to be formed of the metal sheet, in which the portion to be formed is formed by the first die and the second die, from the portion to be formed,

[0016] wherein an outer side surface of the first die is formed to extend in a cutting direction of the punch, and a cooling suppression space is defined on one side of the first die, the trimming portion is exposed to the cooling suppression space and the cooling suppression space suppresses cooling of the trimming portion.

[0017] An automobile body component according to the present application is an automobile body component in which a portion to be formed is formed into a predetermined shape, and a trimming portion outside the portion to be formed is cut by the above-described hot press forming device, wherein a cut end surface of the portion to be formed includes a sheared surface, and a residual stress of the cut end surface measured by an X-ray diffraction method is 50 MPa or more and 250 MPa or less.

[0018] A hot press forming method according to the present application is a method performed by:

[0019] stacking a portion to be formed of a metal sheet heated to a predetermined temperature on a first die, and clamping and holding an outer edge portion of a trimming portion positioned outside the portion to be formed of the metal sheet by using a holder, thereby forming a cooling suppression space between the first die and the holder, the cooling suppression space extending from the trimming portion along an outer side surface of the first die in a cutting direction of a punch, and the cooling suppression space suppressing cooling of an inner portion of the trimming portion which is not held by the holder;

[0020] a step of forming the to-be-formed portion of the metal sheet by clamping the to-be-formed portion between the first die and the second die; and

[0021] moving the formed metal sheet in the cutting direction together with the holding member, the first die, and the second die, and separating the trimming portion from the to-be-formed portion by using a punch die constituting a cutting mechanism in cooperation with a punch formed by the outer end portion of the forming surface of the first die.

[0022] The automobile body component manufacturing method according to the present application is a method executed by the following steps:

[0023] a step of stacking a metal sheet for an automobile body component heated to a predetermined temperature between a first die and a second die of the hot press forming apparatus, and

[0024] a step of forming the metal sheet for an automobile body component by a hot press forming method using the hot press forming apparatus.

[0025] Effects of the Invention

[0026] In the present application, the trimming portion of the metal sheet is hardly cooled because the trimming portion is exposed to the cooling inhibition space without contacting any other member. Therefore, the punch and the punch die can cut the boundary portion between the trimming portion and the to-be-formed portion at a high temperature. The tensile residual stress of the formed product trimmed at a high temperature is thus reduced.

[0027] Therefore, it is possible to provide a hot press forming apparatus and a hot press forming method each of which can prevent occurrence of delayed fracture in a formed product. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a front view showing a part of the hot press forming apparatus according to the first embodiment;

[0029] Figure 2 is a front view showing a part of the hot press forming apparatus in a forming process;

[0030] Figure 3 is a front view showing a part of the hot press forming apparatus at the completion of forming;

[0031] Figure 4 is a front view showing a part of the hot press forming apparatus when trimming is completed;

[0032] Figure 5 is a side view of the punch die and the lower die;

[0033] Figure 6is a flowchart for explaining a hot press forming method according to the present application;

[0034] Figure 7 is a flowchart for explaining a method of manufacturing an automobile body part according to the present application;

[0035] Figure 8 is a perspective view showing an example of an automobile body part;

[0036] Figure 9 is a front view showing a part of a hot press forming device according to a second embodiment;

[0037] Figure 10 is a micrograph of a cut end surface;

[0038] Figure 11 is a graph for explaining a relationship between presence / absence of a cooling inhibition space and residual stress; and

[0039] Figure 12 is a perspective view showing an outline of a configuration of an automobile body frame. DETAILED DESCRIPTION

[0040] (First Embodiment)

[0041] For the purpose of explaining the present application, first, refer to Figures 1 to 8 Embodiments capable of explaining all the claims of the present application will be described in detail as a first embodiment. Figures 1 to 4 Only a left half of the hot press forming device viewed in a longitudinal direction of the material to be formed is shown. Note that, Figures 1 to 5 The hot press forming device is schematically shown so that the configuration of the present application is easily understood, and thus a metal sheet as the material to be formed is drawn thicker than the actual material.

[0042] Figure 1 The hot press forming device 1 shown in FIG. 1 forms a metal sheet 2 (material to be formed) heated to a predetermined temperature into a predetermined shape and performs trimming of the metal sheet 2. As the metal sheet 2, a metal sheet for an automobile body part or 22MnB5 (boron steel) can be used. The thickness of the metal sheet 2 is preferably 0.8 mm to 2.9 mm.

[0043] The trimming referred to herein is to separate a trimming portion 3, which is an unnecessary portion of the metal sheet 2, from a portion to be formed 4. Figure 1 A state immediately before forming is shown. The portion to be formed 4 is a portion to be formed into a predetermined shape by the hot press forming device 1.

[0044] The hot press forming device 1 according to the present embodiment includes, for example, a first elevator 12 that supports a first mold 10 and a second mold 20 via a second elevator 22, and a first mold moving mechanism 14 that moves the first mold 10 in a horizontal direction. Figure 1a lower die 13 shown on the base 11 at the lowermost portion of the machine, an upper die 14 facing the lower die 13, a blank holder 15 arranged in alignment with the lower die 13 and the upper die 14, and a punch 16 arranged between the lower die 13 and the blank holder 15.

[0045] The first lifter 12 has a configuration that regulates the lowering of the lower die 13 during the forming process, and allows the lower die 13 to be lowered during the trimming process so that the lower die 13 is lowered together with the upper die 14. Although not shown in detail, the first lifter 12 as described above can be configured by using, for example, a compression coil spring, a hydraulic cylinder, or a servo motor as a power source.

[0046] A forming surface 21 for cooperating with the upper die 14 (to be described later) to form the metal sheet 2 is formed on the upper end of the lower die 13. That is, the lower die 13 is configured to be movable in the thickness direction of the metal sheet 2. In the present embodiment, the lower die 13 corresponds to the "second die" of the present application.

[0047] The lower die 13 and the upper die 14 are configured to form the metal sheet 2 into a hat-shaped cross-sectional shape that protrudes upward. To this end, the lower die 13 includes a first forming surface 21a that extends laterally at the highest position, a second forming surface 21b that is an inclined surface extending obliquely downward from the first forming surface 21a, and a third forming surface 21c that extends laterally from the lower end of the first forming surface 21b. In addition, the lower die 13 has a refrigerant passage 22 so as to cool the first forming surface 21a to the third forming surface 21c to a predetermined temperature.

[0048] The upper die 14 has a forming surface 23 facing the lower die 13, and is supported by an upper die holder 24. The forming surface 23 of the upper die 14 is formed in a shape in which the protruding portion of the lower die 13 fits therein. The forming surface 23 includes a first forming surface 23a facing the first forming surface 21a of the lower die 13, a second forming surface 23b that is an inclined surface extending obliquely downward from the first forming surface 23a, and a third forming surface 23c extending laterally from the lower end of the second forming surface 23b. The upper die 14 has a refrigerant passage 25 for cooling the first forming surface 23a to the third forming surface 23c to a predetermined temperature. Although not shown, the upper die 14 can be divided into a plurality of portions so as to accurately perform forming on each forming surface.

[0049] When the upper mold 14 is divided into multiple parts, it can be divided into, for example, a first upper mold having a first forming surface 23a and a second upper mold having a second forming surface 23b and a third forming surface 23c. In this case, the first upper mold moves only in the vertical direction (the thickness direction of the metal sheet 2) and presses the metal sheet 2 onto the first forming surface 21a of the lower mold 13. The second upper mold moves in a direction perpendicular to the second forming surface 23b, in the horizontal direction, and in the vertical direction, and presses the metal sheet 2 onto the second forming surface 21b and the third forming surface 21c of the lower mold 13.

[0050] The lower end portion of the third forming surface 23c of the upper die 14 and the outer end portion adjacent to the blank holder 15 (described later) are formed as a punch 32, which is configured to cooperate with the die 16 (described later) to form a cutting mechanism 31. More specifically, the upper die 14 has a blade 32a serving as the punch 32 in the outer end portion of the forming surface 23.

[0051] The punch 32 is formed such that the direction from the upper die 14 to the lower die 13 is the cutting direction. The outer surface 14a of the upper die 14, extending upward from the punch 32, is parallel to the forming direction (…). Figure 1 The plane is formed in the vertical direction.

[0052] The upper mold holder 24, which supports the upper mold 14, is connected to a pressurizing device (not shown) and moves up and down by the drive of the pressurizing device. The upper mold holder 24... Figure 1 The initial position shown moves downwards for forming and trimming, and then moves upwards back to the initial position after the continuous trimming from the end of forming is completed. That is, the upper die 14 is configured to move in the cutting direction of the punch 32. In this embodiment, the upper die 14 corresponds to the "first die" of the present invention.

[0053] The blank holder 15 includes a lower holder 33 and an upper holder 34 that clamp and hold the outer edge portion 3a of the trimmed portion 3 of the metal sheet 2. In this embodiment, the blank holder 15 is equivalent to the "holder" of the present invention.

[0054] The lower retainer 33 is supported on the base 11 for vertical movement via the second lift 35. The second lift 35 is configured such that a substantially constant load is applied from the lower retainer 33 to the trimmed portion 3 of the metal sheet 2 regardless of its vertical position. Such a second lift 35 can be configured using, for example, a compression coil spring, a hydraulic cylinder, or a servo motor as a power source.

[0055] The upper retainer 34 is positioned laterally spaced from the upper die 14 by a predetermined distance and is fixed to the upper die retainer 24. Therefore, the upper retainer 34 and the lower retainer 33 move synchronously with the lower die 13 and the upper die 14 in the cutting direction of the punch 32.

[0056] The upper retainer 34 is formed in the longitudinal direction of the metal sheet 2 (perpendicular to) Figure 1 The direction of the paper surface extends continuously from one end of the metal sheet 2 to the other end.

[0057] The length of the upper retainer 34 in the vertical direction is substantially equal to the length of the upper mold 14 in the vertical direction. Therefore, as Figure 1 As shown, when the trimmed portion 3 of the metal sheet 2 is clamped and held by the lower retainer 33 and the upper retainer 34, the portion 4 of the metal sheet 2 to be formed overlaps with the third forming surface 23c of the upper mold 14. In this state, a cooling suppression space 36 is formed between the upper mold 14 and the blank holder 15. This cooling suppression space is the space extending from the trimmed portion 3 to the outer surface 14a of the upper mold 14 in the cutting direction of the punch 32 (vertical direction in this embodiment). As will be described in detail later, the cooling suppression space 36 is the space in which the inner portion 3b of the metal sheet 2 not held by the blank holder 15 is exposed, and this cooling suppression space suppresses the cooling of the inner portion 3b on one side of the upper mold 14.

[0058] The cooling suppression space 36 is surrounded, for example, by the outer surface 14a of the upper mold 14, the inner surface 34a of the upper retainer 34, the upper mold retainer 24, and the trimmed portion 3 of the metal sheet 2, and on both sides of the metal sheet 2 in the longitudinal direction. Figure 1 The front and rear sides of the paper surface are open to the atmosphere. According to this embodiment, the upper retainer 34 is spaced from the upper mold 14 by a length approximately 5 to 7 times the thickness of the metal sheet 2, such that the cooling suppression space 36 has sufficient volume. For example, when the thickness of the metal sheet 2 is 2 mm, the distance between the upper mold 14 and the upper retainer 34 is approximately 10 mm. The distance between the upper mold 14 and the upper retainer 34, i.e., the width of the cooling suppression space 36, is preferably 10 mm to 30 mm. Note that, although not shown, the upper end of the upper retainer 34 and the upper end of the upper mold 14 can also be connected by a connecting portion extending in the lateral direction.

[0059] The die 16 and the punch 32 of the upper die 14 cooperate to form a cutting mechanism 31. The die 16 has a trimming blade 41 at its upper end and is fixed to the base 11, so that the die 16 is positioned near one side of the lower die 13. When forming is completed, the height of the die 16, that is, the height of the highest point of the trimming blade 41, is lower than the third forming surface 21c of the lower die 13 (see...). Figure 3This means that when forming is complete, the metal sheet 2 is spaced apart from the die 16. Therefore, the lower die 13, the upper die 14, and the blank holder 15 are configured such that the metal sheet 2 moves toward the die 16 after forming is complete, thereby separating the trimmed portion 3 from the portion to be formed 4. Note that the height of the die 16 can also be set such that the trimming blade 41 contacts the metal sheet 2 before forming is complete. That is, the metal sheet 2 is preferably spaced apart from the die 16 until forming is complete, but it can also contact the die 16 during forming.

[0060] The width of the upper end of the die 16, including the trimming blade 41 (the width in the direction in which the die 16 and the lower die 13 are aligned), is slightly narrower than the width of the aforementioned cooling suppression space 36 (the gap between the upper die 14 and the upper retainer 34). Figure 4 As shown, the reason for forming the die 16 as described above is to prevent contact between the die 16 and the upper retainer 34 during the cutting process (described later). That is, the upper end portion of the die 16, including the trimming blade 41, is configured such that the blank retainer 15 can enter the cooling suppression space 36 while clamping and holding the outer edge portion of the trimmed portion 3.

[0061] According to this embodiment, the outer surface 16a of the upper end portion of the die 16 is inclined, such that the thickness of the die 16 gradually increases toward the base 11. This improves the rigidity of the die 16. The outer surface 16a is preferably formed to be inclined at 20° to 25° with respect to the vertical direction.

[0062] like Figure 5 As shown, the blade edge 41a of the trimming blade 41 is formed with a shearing angle, which forms a predetermined height H relative to the third forming surface 21c of the lower mold 13. The third forming surface 21c is perpendicular to the forming direction (in... Figure 5 It extends in the vertical direction. The height H is... Figure 5 The difference between the lowest part of the valley-shaped trimming blade 41 shown in the side view and the highest part of the two ends of the trimming blade 41. This shearing angle height is 1 / 3 to 1 times the thickness of the metal sheet 2.

[0063] The trimming blade 41 is formed at a position lower than the third forming surface 21c of the lower mold 13 in the forming position. Note that the shape of the trimming blade 41 is not limited to... Figure 5 The valley shape shown can also be, for example, a mountain shape with a higher central portion, a shape that extends linearly from one end to the other, or a shape without a shear angle.

[0064] Next, the hot pressing forming method for forming and trimming the metal sheet 2 using the aforementioned hot pressing forming apparatus 1 will be explained. This hot pressing forming method is as follows:Figure 6 The execution is shown in the flowchart. In the hot pressing apparatus 1 used to perform this hot pressing method, refrigerant is always supplied to refrigerant channels 22 and 25, and the temperature of the lower mold 13 and the upper mold 14 is maintained at a predetermined temperature. In order to perform the hot pressing method, the metal sheet 2 is first loaded into the hot pressing apparatus 1, thereby forming a cooling suppression space 36 (step S1).

[0065] In other words, the trimmed portion 3 of the metal sheet 2, heated to a predetermined temperature, is clamped and held by the lower retainer 33 and the upper retainer 34 of the blank holder 15, and the portion 4 of the metal sheet 2 to be formed is stacked on the third forming surface 23c of the upper mold 14. This cooling suppression space formation step can be performed while the metal sheet 2 is in contact with the lower mold 13 and the upper mold 14, such as... Figure 1 As shown, or performed with a gap formed between the metal sheet 2 and the lower mold 13 (although not shown).

[0066] Thus, by loading the metal sheet 2 into the thermoforming apparatus 1, the internal portion 3b of the trimmed portion 3 that is not held by the lower retainer 33 and the upper retainer 34 (see...) Figure 1 It is exposed to the cooling inhibition space 36 without contacting any other components. This keeps the temperature of the inner part 3b of the trimmed part 3 at a high temperature before molding.

[0067] Then, the hot press forming apparatus 1 performs forming (step S2). Forming is performed by moving the upper holding member 24 downwards using a pressure device. When the upper holding member 24 moves downwards... Figure 1 The state shown becomes Figure 2 The state shown is as follows. That is, the portion 4 of the metal sheet 2 to be formed is held in its initial position by being supported by the first forming surface 21a of the lower mold 13, and is pushed downward by the third forming surface 23c of the upper mold 14. As a result, the portion 4 to be formed bends along the second forming surfaces 21b and 23b. In this state, the lower retainer 33 and the upper retainer 34 of the blank holder 15 move downward while clamping the trimmed portion 3, so as to follow the upper mold 14.

[0068] Subsequently, as Figure 3 As shown, the upper mold holder 24 descends until the first forming surface 23a to the third forming surface 23c of the upper mold 14 pushes the metal sheet 2 onto the first forming surface 21a to the third forming surface 21c of the lower mold 13, thereby forming the metal sheet 2 into a shape consistent with the first forming surface 21a, 23a to the third forming surface 21c, 23c, and quenching the metal sheet 2 by rapidly cooling it through contact with the lower mold 13 and the upper mold 14. Figure 3The trimming blade 41 of the punch 16 is spaced apart from the metal sheet 2 in the finished state of the forming. However, the trimming blade 41 can also be in contact with the metal sheet 2 in the finished state of the forming.

[0069] After the forming and quenching are thus performed, trimming is performed by further lowering the upper holder 24 (step S3).

[0070] The trimming is performed by lowering the lower die 13, the upper die 14, the lower holder 33, and the upper holder 34 in a state where they clamp and hold the metal sheet 2 so that they are positioned below the punch 16. Since the metal sheet 2 is positioned below the forming position, as Figure 4 As shown in the finished state of the forming, the trimming blade 41 of the punch 16 cuts the boundary portion between the to-be-formed portion 4 and the trimming portion 3, thereby separating the trimming portion 3 from the to-be-formed portion 4. In this state, the upper end portion of the punch 16 including the trimming blade 41 enters the cooling inhibition space 36, while the lower holder 33 and the upper holder 34 clamp and hold the outer edge portion of the trimming portion 3. Further, even after the trimming is completed, the inner portion 3b of the trimming portion 3 is exposed to the cooling inhibition space 36. That is, the inner portion 3b is always exposed to the cooling inhibition space 36.

[0071] In the trimming portion 3 of the metal sheet 2, the inner portion 3b that is not held by the blank holder 15 is hardly cooled because it is not in contact with any other member and is always exposed to the cooling inhibition space 36. Therefore, the punch 32 and the punch 16 can cut the boundary portion between the trimming portion 3 and the to-be-formed portion 4 at a high temperature. The tensile residual stress of the formed product that is trimmed at a high temperature as described above is reduced.

[0072] Therefore, the present embodiment can provide a hot press forming apparatus and a hot press forming method each of which can prevent occurrence of delayed fracture in a formed product.

[0073] The lower die 13 (second die), the upper die 14 (first die), and the blank holder 15 according to the present embodiment are configured so that the metal sheet 2 moves toward the punch 16 after the forming is completed, thereby separating the trimming portion 3 from the to-be-formed portion 4.

[0074] Therefore, since the trimming portion 3 of the metal sheet 2 is not cooled by the punch 16 during the forming, the temperature drop of the trimming portion 3 can be reduced as much as possible. Therefore, it is more difficult for delayed fracture to occur.

[0075] The punch 16 according to the present embodiment has a shear angle with a predetermined height H. This makes it possible to reduce the shear load in the cutting process and further reduce the tensile residual stress of the metal sheet 2, thereby more reliably preventing occurrence of delayed fracture.

[0076] AsFigure 7 The automobile body part can be manufactured by using the hot press forming apparatus 1 disclosed in the above-described embodiments, as shown in the flowchart. Note that, in the following explanation, the same reference numerals as those explained with reference to Figures 1 to 6 the same drawings will indicate the same or equivalent components, and detailed explanation thereof will be appropriately omitted.

[0077] To manufacture the automobile body part by using the hot press forming apparatus 1 disclosed in the above-described embodiments, first, the metal sheet 2 for the automobile body part is loaded into the hot press forming apparatus 1 and stacked on the third forming surface 23c of the upper die 14 (step Pl). The cooling suppression space 36 is thus formed by loading the metal sheet 2 into the hot press forming apparatus 1. Then, the metal sheet 2 is clamped between the upper die 14 and the lower die 13 and formed by a hot stamping process (step P2). Subsequently, trimming is performed by moving the upper die 14, the lower die 13, and the blank holder 15 downward so that the metal sheet 2 comes into contact with the die 16 (step P3). This trimming cuts the trimming portion 3 outside the to-be-formed portion 4 (see Figure 8 ).

[0078] After the trimming is performed, by unloading the metal sheet 2 from the hot press forming apparatus 1, the automobile body part 51 as shown in Figure 8 can be obtained.

[0079] The cut end surface 52 of the to-be-formed portion 4 of the automobile body part 51 after the trimming includes a shear surface (to be described later), and it is generally known that a cut end surface cut by a punch and a die forms an "undercut" when a blade cuts into a plate, and includes a "shear surface" as a mark formed when a blade cuts into a plate, a "fracture surface" as a simultaneously separated portion, and a "burr" generated by a gap between an upper blade and a lower blade at the time of separation.

[0080] (Second Embodiment)

[0081] An example of the hot press forming apparatus according to the present invention described in claim 1 will be explained below with reference to Figure 9 the same reference numerals as those explained with reference to Figures 1 to 5 the same drawings will indicate the same or equivalent components, and detailed explanation thereof will be appropriately omitted. Figure 9

[0082] Figure 9 The hot press forming apparatus 61 as shown in

[0083] ​On one side of the upper die 14 of the hot press forming device 61 according to the present embodiment, a cooling suppression space 62, which is a space in which the trimming portion 3 of the metal sheet 2 is exposed, is formed. That is, the outer side surface 14a of the upper die 14 is formed so as to extend in the cutting direction of the punch 32, and the cooling suppression space 62, in which the trimming portion 3 is exposed, is defined on one side of the upper die 14, and the cooling suppression space suppresses the cooling of the trimming portion 3.

[0084] Therefore, even when this embodiment is employed, the trimming portion 3 of the metal sheet 2 is hardly cooled because it is exposed to the cooling suppression space 62 without contacting any other member. Therefore, the boundary portion between the trimming portion 3 and the portion to be formed 4 can be cut by the punch 32 and the die 16 at a high temperature. The tensile residual stress of the formed product thus trimmed at a high temperature is reduced.

[0085] This makes it possible to provide a hot press forming device capable of preventing delayed fracture from occurring in a formed product also in the present embodiment.

[0086] Figure 10 A cut end surface formed when the trimming portion 3 is trimmed by using the punch 32 and the die 16 without holding the trimming portion 3 as disclosed in the present embodiment is shown. Referring to Figure 10 , the range indicated by reference symbol A is a so-called "undercut" portion, the range indicated by reference symbol B is a so-called "sheared surface" portion, and the range indicated by reference symbol C is a so-called "fractured surface" portion.

[0087] As shown in Figure 11 , the results are obtained when the trimming portion 3 of the metal sheet 2 is trimmed by using the hot press forming device 61 disclosed in the second embodiment and the residual stress of the cut end surface of the portion to be formed 4 is examined. The residual stress is measured in the range enclosed by the white circle in Figure 10 . The white circle in Figure 10 is a circle having a diameter of 1 mm, and is centered on the "sheared surface" positioned in the central portion of the cut end surface. As test conditions for performing the X-ray diffraction method, the X-ray stress measurement method is a sin 2 φ method, and the scanning method is an equi-inclination method. The stress constant (K [MPa / deg]) is -318.

[0088] When the residual stress is examined, only one residual stress is examined when the entire region of the trimming portion 3 is held by the holder as in the conventional hot press forming device by using the residual stress when there is no cooling suppression space. When the entire front surface and the rear surface of the trimming portion 3 are exposed to the cooling suppression space 62, that is, when there is the cooling suppression space, the residual stress is examined for five samples. As shown inFigure 11 As shown, when there is no cooling inhibition space, the residual stress is about 500 MPa. On the other hand, when there is a cooling inhibition space, by taking into account the change in the gap between the upper die 14 and the punch 31 during trimming and the change in the temperature of the metal sheet 2 and the like, the residual stress is greater than or equal to 50 MPa and less than or equal to 250 MPa.

[0089] Therefore, in the automobile body member 51 (see FIG. 1) in which the to-be-molded portion 4 is molded into a predetermined shape and the trimming portion 3 outside the to-be-molded portion 4 is cut by the hot press molding device 61 disclosed in the second embodiment, the residual stress of the cut end face 52 measured by the X-ray diffraction method is greater than or equal to 50 MPa and less than or equal to 250 MPa. Figure 8

[0090] Figure 11 All of the residual stresses of the five samples shown in Table 1 are less than or equal to 200 MPa. Therefore, the hot press molding device, the hot press molding method, and the automobile body member manufacturing method according to the present application can manufacture an automobile body member that does not undergo delayed fracture due to the residual stress of the cut end face being less than or equal to 200 MPa.

[0091] When the hot press molding device 61 disclosed in the second embodiment is used, that is, when molding and trimming are simultaneously performed in a state in which the entire front surface and the entire rear surface of the trimming portion 3 are exposed to the cooling inhibition space 62, the hardness (Vickers hardness) of the cut end face is 503 Hv on the upstream side in the cutting direction, 472 Hv in the central portion in the cutting direction, and 507 Hv on the downstream side in the cutting direction, that is, it satisfies the company quality standard that the hardness on the end face is 450 Hv or more.

[0092] As shown in Table 2, the automobile body member 51 can be used as, for example, a center pillar 72 of a vehicle frame 71 of an automobile, and can also be used as a side beam 73. The center pillar 72 is a body member for connecting the side beam 73 and a roof 74. The side beam 73 is a body member that extends in the front-rear direction of the body in both end portions in the left-right direction of the body. A lower end portion of a front pillar 75, a lower end portion of the center pillar 72, and a lower end portion of a rear pillar 76 are welded to the side beam 73. Figure 12

[0093] ​​In the above-described embodiments, the hot press molding apparatus 1 having a structure in which the upper mold holder 24 approaches and moves away from the non-moving base 11 has been explained, but the present application is not limited thereto. That is, a configuration in which the upper mold holder 24 is non-movable and the base 11 approaches and moves away from the upper mold holder 24 can also be adopted. In this case, the upper mold holder 24 is disposed in a lower end portion of the apparatus, and the base 11 is disposed in an upper end portion of the apparatus. The upper mold 14 and the upper holder 34 are mounted on the upper mold holder 24, and the lower mold 13, the punch 16, and the lower holder 33 are disposed below the base 11.

[0094] Explanation of Reference Signs and Symbols

[0095] 1, 61 … hot press molding apparatus, 2 … metal sheet, 3 … trimming portion, 3a … outer edge portion, 3b … inner portion, 4 … portion to be molded, 13 … lower mold (second mold), 14 … upper mold (first mold), 14a … outer side surface, 16 … punch, 31 … cutting mechanism, 32 … punch head, 32a … blade, 36, 62 … cooling inhibition space, 51 … automobile body part, 52 … cut end surface, S1 … cooling inhibition space forming step, S2, P2 … molding step, S3, P3 … trimming step, P1 … cooling inhibition space forming step

Claims

1. A hot press forming apparatus comprising: a first die configured to form a metal sheet heated to a predetermined temperature, the first die having a forming surface for forming a portion to be formed of the metal sheet and a blade provided in an outer end portion of the forming surface and configured to function as a punch; a second die having a forming surface for clamping and forming the portion to be formed in cooperation with the first die; a die punch configured to separate a trimming portion positioned outside the portion to be formed of the metal sheet from the portion to be formed, and a holder arranged in alignment with the first die and the second die, the holder configured to move in a cutting direction of the punch in synchronization with the first die and the second die while clamping and holding an outer edge portion of the trimming portion, wherein an outer side surface of the first die is formed to extend in the cutting direction of the punch and defines a cooling inhibition space on one side of the first die, the trimming portion is exposed to the cooling inhibition space and the cooling inhibition space inhibits cooling of the trimming portion, the holder has an inner side surface facing the outer side surface of the first die, the cooling inhibition space is surrounded by the outer side surface, the inner side surface, and an inner portion of the trimming portion that is not held by the holder, and the inner portion of the trimming portion that is not held by the holder is always exposed to the cooling inhibition space.

2. The hot press forming apparatus according to claim 1, wherein the die punch has a trimming blade in an end facing the metal sheet, and one end portion of the die punch including the trimming blade is configured to enter the cooling inhibition space in a state where the holder clamps and holds the outer edge portion of the trimming portion.

3. The hot press forming apparatus according to claim 1 or 2, wherein the first die, the second die, and the holder are configured such that the metal sheet is moved toward the die punch after forming is completed, and the trimming portion is separated from the portion to be formed.

4. The hot press forming apparatus according to claim 1 or 2, wherein the die punch has a shear angle with a predetermined height.

5. An automotive body part, wherein, a portion to be formed is formed into a predetermined shape and a trimming portion outside the portion to be formed is cut by the hot press forming apparatus according to claim 1 or 2, wherein a cut end surface of the portion to be formed includes a shear surface, and a residual stress of the cut end surface measured by an X-ray diffraction method is not less than 50 MPa and not more than 250 MPa.

6. A hot press forming method comprising: stacking a to-be-formed portion of a metal sheet heated to a predetermined temperature on a first die, and clamping and holding an outer edge portion of a trimming portion positioned outside the to-be-formed portion of the metal sheet by using a holder, thereby forming a cooling inhibition space between the first die and the holder, the cooling inhibition space extending from the trimming portion along an outer side surface of the first die in a cutting direction of a punch, and the cooling inhibition space inhibiting cooling of an inner portion of the trimming portion which is not held by the holder; forming the to-be-formed portion of the metal sheet by clamping the to-be-formed portion between the first die and a second die; and moving the formed metal sheet in the cutting direction of the punch together with the holder, the first die, and the second die, and separating the trimming portion from the to-be-formed portion by using a die constituting a cutting mechanism in cooperation with the punch formed by an outer end portion of a forming surface of the first die.

7. The hot press forming method according to claim 6, wherein the step of separating the trimming portion from the to-be-formed portion is performed by using a die having a trimming blade in one end facing the metal sheet, and in the step of separating the trimming portion from the to-be-formed portion, one end portion of the die including the trimming blade enters the cooling inhibition space in a state where the holder clamps and holds the outer edge portion of the trimming portion.

8. A method of manufacturing an automobile body component, comprising: a step of stacking a metal sheet for an automobile body component heated to a predetermined temperature between a first die and a second die of a hot press forming apparatus according to 1 or 2; and a step of forming the metal sheet for an automobile body component by a hot press process by using the hot press forming apparatus.

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