Method for manufacturing press-formed products, and trays and hot press manufacturing lines used in the manufacture of press-formed products.

Abstract

This press-molded article production method comprises a heating step, a conveyance step, and a press step. In the heating step, a plate-like heat storage material 5 and a plate-like workpiece W1 placed above the heat storage material 5 are heated by a heating device 14 in a state of overlapping with each other in a direction normal to the planar face of the workpiece W1. In a first conveyance step, the heat storage material 5 and the workpiece W1 placed above the heat storage material 5 are, in the state of overlapping with each other, conveyed from the heating device 14 to a lifting position. In a second conveyance step, the workpiece W1 placed above the heat storage material 5 is lifted at the lifting position by a conveyance device 46 and then conveyed to a pressing position at a pressing machine 20. In the press step, the workpiece W1 is subjected to processing by the pressing machine 20.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a press-formed product including heating, conveying, and pressing steps, a tray used for manufacturing a press-formed product, and a hot press production line.

Background Art

[0002] Conventionally, a technique of pressing a material heated to a predetermined temperature with a press machine has been used. For example, in hot pressing, a hot press steel sheet as a material is heated to the austenite region (about 900 °C or higher) and press-formed hot. Thereby, quenching treatment is performed together with the forming process, and a press-formed product having a strength of 1500 MPa class or higher can be obtained. In a general hot stamping, quenching is performed by being rapidly cooled by contact heat transfer with a mold during press forming. Therefore, in order to obtain a sufficient quenching effect, it is necessary to ensure that the temperature of the material at the start of press forming, which approximately corresponds to the quenching start temperature, is at a predetermined temperature or higher. In this case, the predetermined temperature at the start of press forming is, for example, 700 °C or higher depending on the material.

[0003] Patent Publication No. 5910305 and Patent Publication No. 5910306 disclose a hot press forming method having a step of heating a plurality of stacked conductive plate-like workpieces by attaching electrodes thereto and energizing them. The plurality of heated plate-like workpieces are arranged at a predetermined press position different from the energization position. The plurality of plate-like workpieces arranged at the press position are each press-formed. By simultaneously heating the plurality of plate-like workpieces by energization, productivity is improved.

[0004] In the above prior art, heat dissipates during the conveyance of the workpiece, and the temperature of the workpiece decreases. As a result, when the workpiece is carried into the mold of the press machine, the required temperature of the workpiece cannot be maintained, and there is a possibility that the quenching of the press-formed product is not sufficient.

[0005] Therefore, Japanese Patent Publication No. 5814669 discloses a hot pressing conveying device that holds and conveys heated panel-shaped objects between each process in a hot pressing production line. The hot pressing conveying device conveys the heated objects while covering them with an insulating cover. This maintains the objects at the temperature required for quenching during transport.

[0006] Furthermore, the hot press forming apparatus disclosed in Japanese Patent Publication No. 4673656 includes a primary heating means by induction heating or electric heating and a secondary heating means by radiant heat transfer as a heating device for the metal sheet to be processed. The secondary heating means by radiant heat transfer is arranged in the conveying device from the primary heating means to the hot press forming die. By performing secondary heating by radiant heat transfer, the metal sheet can be heated uniformly and the temperature deviation of the metal sheet can be reduced. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 5910305 [Patent Document 2] Patent No. 5910306 [Patent Document 3] Patent No. 5814669 [Patent Document 4] Patent No. 4673656 [Overview of the project] [Problems that the invention aims to solve]

[0008] The inventors realized that when the material used for hot pressing is made thinner, the temperature drop during transport from the heated material to the press machine can affect the quality of the press-formed product. Therefore, they investigated methods to suppress the temperature drop of the material during transport. In their investigation, they found that simply covering the material with an insulating cover during transport, as in the conventional technology described above, is not always sufficient to suppress the temperature drop. Another option is to provide a secondary heating means to heat the material during transport. However, in this case, it would be necessary to add equipment including a heat source for the secondary heating means along the transport path. This would lead to larger equipment and potentially increase equipment costs and operating costs.

[0009] Therefore, this application discloses a method for manufacturing press-formed products and a tray that can easily mitigate the temperature drop of the material during the transport time from the time the material is heated until the start of press forming in hot press forming. [Means for solving the problem]

[0010] A method for manufacturing a press-formed product according to an embodiment of the present invention comprises a heating step, a first conveying step, a second conveying step, and a pressing step. In the heating step, a plate-shaped heat storage material and a plate-shaped workpiece placed above the heat storage material are heated by a heating device while they are overlapping in the direction normal to the surface of the workpiece. In the first conveying step, the heat storage material and the workpiece placed above the heat storage material are conveyed from the heating device to a lifting position while they are overlapping in the direction normal to the surface of the workpiece. In the second conveying step, at the lifting position, the workpiece placed above the heat storage material is lifted upward by a conveying device and conveyed to the pressing position of a press machine. In the pressing step, the workpiece is processed by the press machine. [Effects of the Invention]

[0011] According to this disclosure, the temperature drop of the material during the transport time from when the material is heated until press forming begins in hot press forming can be easily mitigated. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a diagram showing an overview of a hot press manufacturing line according to this embodiment. [Figure 2] Figure 2 is a top view of the tray of this embodiment as seen from above. [Figure 3] Figure 3 is a side view of the tray shown in Figure 2 as seen from the direction of arrow F. [Figure 4] Figure 4 is a side view showing an example of a support column when the workpiece is not a flat plate. [Figure 5] Figure 5 is a top view showing another example of the arrangement of the support columns. [Figure 6] Figure 6 is a side view of the tray shown in Figure 5 as seen from the direction of arrow F. [Figure 7] Figure 7 is a side view showing a modified example of the support column. [Figure 8] Figure 8 is a side view showing an example when the workpiece is a stepped plate. [Figure 9] Figure 9 is a side view showing another example when the workpiece is a stepped plate. [Figure 10] Figure 10 is a top view showing a configuration example of a tray provided with a shielding plate. [Figure 11] Figure 11 is a side view of the tray shown in Figure 10 as seen from the direction of arrow F. [Figure 12] Figure 12 is a side view showing a modified example of the tray of this embodiment. [Figure 13] Figure 13 is a side view showing a modified example of the tray of this embodiment. [Figure 14] Figure 14 is a side view showing a modified example of the tray of this embodiment. [Figure 15] Figure 15 is a side view showing a modified example of the heat storage material of this embodiment. [Figure 16] Figure 16 is a side view showing a modified example of the heat storage material of this embodiment. [Figure 17] Figure 17 is a diagram showing a modified example of the hot press manufacturing line of this embodiment. [Figure 18A]FIG. 18A is a diagram showing the configuration of the conveying device shown in FIG. 17. [Figure 18B] FIG. 18B is a diagram showing the state in which the second arm of the conveying device shown in FIG. 18A is open. [Figure 19] FIG. 19 shows the temperature measurement positions in the experimental example. [Figure 20] FIG. 20 is a graph of the average temperature drop rate as a measurement result. [Figure 21] FIG. 21 is a graph showing the range targeted for the derivation of the average temperature drop rate.

Embodiments for Carrying Out the Invention

[0013] In hot press forming, the temperature at the start of press forming depends on the heating temperature of the material and how much the temperature drops within the time from when the material is heated to when it is conveyed to the mold for press forming. The heating temperature of the material is determined by metallurgical conditions. Also, the conveyance time to the mold after heating is determined by the equipment configuration and specifications. The amount of temperature drop during that conveyance depends on the heat capacity of the material. For example, in the case of a steel plate, heat escapes mainly by heat transfer from the front and back surfaces to the atmosphere and heat radiation. The inventors noticed that the amount of temperature drop during conveyance depends greatly on the thickness of the material. That is, as described above, when the thickness of the material becomes thinner, even with the same conveyance time, the amount of temperature drop becomes larger, and it may become difficult to ensure the forming start temperature required for quenching. As a result, there may be cases where the required part strength of the press-formed product cannot be obtained.

[0014] The inventors considered a method of suppressing the temperature drop during conveyance without adding a heat source. When a plate-shaped material (workpiece) is heated by a heating device, the workpiece is conveyed by a conveyance path such as rollers from the heating device to a position where it is lifted by the conveying device. The workpiece is lifted by the conveying device and lowered to the press position of the press machine. The inventors focused on the state of the workpiece from when it is heated by the heating device until it is lifted by the conveying device, and considered suppressing the temperature drop of the workpiece in this conveyance process.

[0015] After careful consideration, we devised a method to arrange a plate-shaped workpiece and a plate-shaped heat storage material so that they overlap vertically, heat them in a heating device, and then remove them from the heating device while still stacked vertically. This allows the workpiece and heat storage material to compensate for each other's heat loss through radiant heat during transport after heating. The workpiece's heat loss is mitigated by the radiant heat from the heat storage material, reducing the temperature drop during transport. In addition, the heat storage material also receives radiant heat from the workpiece, mitigating its temperature drop during transport. Therefore, the mitigation of the workpiece's temperature drop through radiant heat from the heat storage material to the workpiece can be performed more efficiently. Furthermore, in addition to radiant heat, heat is transferred from the workpiece and heat storage material to the surrounding air through heat transfer. For example, if the workpiece and heat storage material are placed in contact with each other and overlapped perpendicular to the surface of the workpiece, the contact area does not come into contact with the air, thus reducing the transfer of heat from the workpiece and heat storage material to the air through heat transfer. Furthermore, when the workpiece and heat storage material are placed with a gap between them and overlapping perpendicular to the surface of the workpiece, air heated by heat transfer from the workpiece and heat storage material accumulates in the space between the heated workpiece and the heat storage material. The presence of this heated, stagnant air between the workpiece and the heat storage material reduces the temperature difference between the air and the workpiece, thereby reducing the transfer of heat from the workpiece to the air and achieving a heat retention effect. As a result, the temperature drop of the workpiece during transport can be mitigated. The following embodiment is based on this finding.

[0016] A method for manufacturing a press-formed product according to an embodiment of the present invention comprises a heating step, a first conveying step, a second conveying step, and a pressing step. In the heating step, a plate-shaped heat storage material and a plate-shaped workpiece placed above the heat storage material are heated by a heating device while they are overlapping in the direction normal to the surface of the workpiece. In the first conveying step, the heat storage material and the workpiece placed above the heat storage material are conveyed from the heating device to a lifting position while they are overlapping in the direction normal to the surface of the workpiece. In the second conveying step, at the lifting position, the workpiece placed above the heat storage material is lifted upward by a conveying device and conveyed to the pressing position of a press machine. In the pressing step, the workpiece is processed by the press machine.

[0017] In the above manufacturing method, a plate-shaped heat storage material and a plate-shaped workpiece are heated in a heating device while stacked vertically. After heating, the heat storage material and workpiece are transported from the heating device to a lifting position. Therefore, until they are lifted from the heating device to the transport device, the heat storage material and workpiece are stacked vertically with the top surface of the heat storage material and the bottom surface of the workpiece facing each other. In other words, the heat storage material and workpiece are stacked in the direction normal to the plate surface of the workpiece (perpendicular to the plate surface). For example, the top surface of the heat storage material and the bottom surface of the workpiece face each other. As a result, from the end of heating until they are lifted by the transport device, the heat storage material and workpiece can compensate for each other's heat loss by receiving radiant heat from each other. Furthermore, for example, if the heat storage material and workpiece are stacked with a gap between them, a heat retention effect can be obtained by allowing air warmed by heat transfer from the workpiece and heat storage material to accumulate in the space between the opposing workpiece and heat storage material. Therefore, the temperature drop of the workpiece during the transport time from when the workpiece is heated until the start of press forming in hot press forming can be easily mitigated.

[0018] The workpiece is the material used for hot pressing, i.e., the material to be pressed, while the heat storage material is not the material used for hot pressing. The heat storage material is not a heat source that generates thermal energy on its own, like a heater. The heat storage material may be a simple rigid body in the shape of a plate. The plate-shaped heat storage material is not limited to a flat plate. For example, the plate-shaped heat storage material may be a plate with protrusions projecting in the direction normal to the plate surface, a plate with a hollow section penetrating the plate, or a curved plate, etc. The plate-shaped workpiece is also not limited to a flat plate. The plate-shaped workpiece may be, for example, a plate with protrusions projecting in the direction normal to the plate surface, a plate with a hollow section penetrating the plate, or a curved plate, etc. The workpiece may be, for example, an intermediate molded product formed or processed from a flat plate (blank).

[0019] In the first transport process, it is preferable that the heat storage material and the workpiece placed above the heat storage material are transported overlapping each other with a gap between them in the direction normal to the surface of the workpiece. This allows the top and bottom surfaces of the workpiece to be exposed to the air during transport. Therefore, the difference in conditions between the top and bottom surfaces of the workpiece during transport is reduced compared to when the heat storage material and the workpiece are in contact with each other. As a result, the difference in quality between the top and bottom surfaces of the workpiece can be suppressed.

[0020] In the heating step, the heat storage material may be placed on the tray body, and the workpiece may be heated while placed on at least three first support columns that extend upward from the tray body or the heat storage material to a position higher than the upper surface of the heat storage material. In this case, in the first transport step, the heat storage material placed on the tray body and the workpiece placed on the at least three first support columns may be transported together with the tray body from the heating device to the lifting position.

[0021] On the tray, the heat storage material and the workpiece are heated and transported while maintaining their relative positions. This allows the heat storage material and the workpiece to compensate for each other's heat loss through radiant heat from the end of heating until they are lifted by the transport device. The workpiece is placed on a group of first support columns that extend to a position higher than the top surface of the heat storage material. The group of first support columns is formed by extending upward from the tray body or the heat storage material. Therefore, the support columns do not obstruct the transport device when it lifts the workpiece placed on the group of first support columns upward. The lifting operation can be performed easily and quickly.

[0022] The heat storage material may have a protrusion that projects upward. In the heating step, the workpiece may be heated while placed on the protrusion of the heat storage material. In the first conveying step, the workpiece may be conveyed from the heating device to the lifting position while placed on the protrusion of the heat storage material.

[0023] This allows the heat storage material and the workpiece to compensate for each other's heat loss through radiant heat from the end of heating until they are lifted by the conveying device. Furthermore, the workpiece is placed on an upwardly protruding convex portion. Therefore, the conveying device can easily and quickly lift the workpiece upwards.

[0024] In the heating step and the first conveying step, the heat storage material may be placed on at least three second support columns extending upward from the tray body, and may be positioned to overlap the tray body vertically with a gap between them. This can suppress thermal deformation of the tray body.

[0025] The tray body may have a shape that extends vertically in the vertical direction and may be configured to include a hollow section that penetrates vertically. This makes it easier for heat from below the tray body to be transferred to the heat storage material and the workpiece during the heating process.

[0026] In the heating step and the first conveying step, it is preferable that, when viewed from above, the outer edge of the heat storage material is located outside the outer edge of the workpiece. This allows the entire workpiece to receive radiant heat from the heat storage material. As a result, the temperature of the entire workpiece is more easily maintained uniformly.

[0027] The workpiece may be a plate with a difference in thickness, including a thick section and a thin section. In this case, during the heating step and the first conveying step, at least a portion of the thin section of the workpiece may overlap with the heat storage material when viewed from above. This suppresses the temperature drop of the thin section of the workpiece, which has a relatively small heat capacity and cools down easily. Therefore, the temperature difference between the thin section and the thick section of the workpiece can be efficiently suppressed.

[0028] The workpiece is a plate with a difference in thickness, including a thick section and a thin section, and the heat storage material may also be a plate with a difference in thickness, including a thick section and a thin section. In this case, during the heating step and the first conveying step, at least a portion of the thin section of the workpiece may overlap with the thick section of the heat storage material when viewed from above. As a result, the thin section of the workpiece, which has a relatively small heat capacity and cools down easily, receives radiant heat from the thick section of the heat storage material, which has a relatively large heat capacity and radiates a large amount of heat, to replenish its heat. Therefore, the temperature drop of the thin section of the workpiece can be suppressed more effectively. Consequently, the temperature difference between the thin section and the thick section of the workpiece can be efficiently suppressed, and the temperature drop of the workpiece as a whole can be efficiently suppressed.

[0029] In the first transport step, the heat storage material and the workpiece may be transported with their fronts in the transport direction covered by a shielding plate. The shielding plate prevents air from hitting the front surface of the workpiece in the transport direction. This reduces the temperature drop from the end face of the workpiece at the front surface in the transport direction, and also suppresses the movement of stagnant air between the workpiece and the heat storage material, which has been warmed by heat transfer between the workpiece and the heat storage material, to the outside. Therefore, the heat retention effect can be maintained. In other words, the temperature drop of the workpiece during transport is further suppressed.

[0030] For example, the thickness of the heat storage material may be greater than the thickness of the workpiece. In this case, the temperature drop of the thin workpiece is suppressed by the radiant heat from the heat storage material, which has a relatively large heat capacity. Therefore, the temperature drop of the workpiece can be effectively suppressed.

[0031] For example, the minimum plate thickness t1 (mm) of the thinnest part of the workpiece and the minimum plate thickness t2 (mm) of the thinnest part of the heat storage material may be related by the following formula. This effectively suppresses the temperature drop of the workpiece.

[0032] 0.8 ≤ t2 / t1 ≤ 20 In the heating step and the first conveying step, the maximum vertical distance D (mm) between the heat storage material and the workpiece and the minimum plate thickness t1 (mm) of the thinnest part of the workpiece may be related by the following formula. This effectively suppresses the temperature drop of the workpiece.

[0033] D≦120t1 In the heating step and the first conveying step, the distance ΔW between the edge of the heat storage material as viewed from above and the edge of the workpiece as viewed from above is preferably 10 to 200 mm. This effectively suppresses the temperature drop of the workpiece. In particular, when viewed from above, if the outer edge of the heat storage material is located outside the outer edge of the workpiece, setting the distance ΔW to 10 to 200 mm will further enhance this effect.

[0034] In the heating step and the first conveying step, a portion of the heat storage material may extend upward on the outer edge of the workpiece when viewed from above. This allows the radiant heat between the lateral end of the workpiece and the upward-extending portion of the heat storage material to compensate for each other's heat. This effectively suppresses the temperature drop of the workpiece. As an example, a portion of the heat storage material may extend upward on the outer edge of the workpiece when viewed from above, reaching at least the same height as the workpiece. This covers the side of the workpiece with the heat storage material. Therefore, in addition to the compensation of heat through mutual radiant heat between the lateral end of the workpiece and the upward-extending portion of the heat storage material, it is possible to mitigate the temperature drop from the end face of the workpiece on the front side in the conveying direction, similar to the case where a shielding plate is provided, and to suppress the movement of stagnant air between the workpiece and the heat storage material, which has been warmed by heat transfer from the workpiece to the outside. This effectively maintains the heat retention effect of the workpiece.

[0035] In the heating step, the workpieces placed above the heat storage material and heated by the heating device may include a first workpiece and a second workpiece. In the first conveying step, the workpieces placed above the heat storage material and conveyed may include a first workpiece and a second workpiece. In this case, the second conveying step is: The process involves driving a pair of first arms, which are rotatably mounted on a base frame of the transport device, to support and lift the lower surfaces of both ends of the first workpiece among the at least two workpieces using the claws of the pair of first arms, The process involves driving a pair of second arms, which are rotatably mounted on the base frame of the conveying device, in a system different from that of the pair of first arms, and using the claws of the pair of second arms to support and lift the lower surfaces of both ends of the second workpiece among the at least two workpieces; A process of transporting the first workpiece, whose lower surfaces at both ends are supported by the claws of the pair of first arms of the transport device, and the second workpiece, whose lower surfaces at both ends are supported by the claws of the pair of second arms, such that they overlap each other in the direction normal to the surface of the first workpiece. The process involves driving the pair of first arms to lower the first workpiece, which is supported by the pair of first arms, to the press position of the press machine, The process may also include the step of driving the pair of second arms in a system different from the pair of first arms to lower the second workpiece supported by the pair of second arms to the press position of the press machine.

[0036] The above-described conveying device conveys the first workpiece with its underside supported by the claws of a pair of first arms at both ends, and the second workpiece with its underside supported by the claws of a pair of second arms at both ends. This ensures that the distance between the two workpieces is stably maintained during conveyance. Furthermore, because the rotation of the first and second arms positions the first and second claws on the underside of both ends of the workpiece, the lifting and lowering operations of the workpieces can be performed simply and reliably. In other words, with a simple device configuration, the first and second workpieces can be conveyed in a state where they can efficiently receive heat radiation from each other. In addition, the first drive unit drives the first arm, and independently of this, i.e., in a separate system, the second drive unit drives the second arm. Therefore, the first and second workpieces can be lifted sequentially, and the first and second workpieces can be lowered sequentially to different press positions. In this way, the conveying device can convey the first and second workpieces simply and efficiently while suppressing the temperature drop. Therefore, the temperature drop of the workpiece during the transport time from when the workpiece is heated until the start of press forming in hot press forming can be easily mitigated.

[0037] The lateral direction of the base frame is the direction in the plane perpendicular to the vertical direction. The lateral direction in which the pair of first arms are aligned and the lateral direction in which the pair of second arms are aligned may be the same, or they may be different in the plane perpendicular to the vertical direction.

[0038] The tray in the embodiment of the present invention comprises a tray body, a plate-shaped heat storage material placed on the tray body, and at least three first support columns extending upward from the tray body or the heat storage material to a position higher than the upper surface of the heat storage material. The first support columns are arranged such that, when viewed from above, the imaginary straight lines connecting the columns form at least one triangle.

[0039] According to the above configuration, the heat storage material placed on the tray body and the workpiece placed on the first support column group are supported on the tray in a state where they overlap vertically, that is, in the direction normal to the surface of the workpiece. Therefore, the heat storage material and the workpiece can be heated by the heating device while they are overlapping vertically, and then transported from the heating device to the lifting position. The first support column group is formed extending upward from the tray body or the heat storage material. Therefore, the first support column group does not get in the way when the workpiece placed on the first support column group is lifted upward by the transport device. The lifting operation can be performed easily and quickly. As a result, from the end of heating until it is lifted by the transport device, the heat storage material and the workpiece can compensate for each other's heat loss by receiving radiant heat from each other. Consequently, the temperature drop of the workpiece during the transport time from after heating of the workpiece to the start of press forming in hot press forming can be easily mitigated. In other words, a tray for heating and transporting materials for hot press forming is provided that can easily mitigate the temperature drop of the material during transport time.

[0040] The support columns may be fixed to the tray body or the heat storage material. That is, the support columns may be attached in a fixed state to the tray body or the heat storage material. This simplifies the tray structure. In contrast, if, for example, the height of each support column relative to the tray body is made variable, a heat-resistant drive mechanism is required. In this case, the configuration becomes more complex and manufacturing costs increase.

[0041] The tray in the embodiment of the present invention comprises a tray body and a plate-shaped heat storage material placed on the tray body. The heat storage material may have a protrusion that projects upward and on which a plate-shaped workpiece can be placed. With this configuration, the heat storage material placed on the tray body and the workpiece placed on the protrusion of the heat storage material are supported on the tray in a state where they overlap vertically, that is, in the direction normal to the plate surface of the workpiece. As a result, from the end of heating until the workpiece is lifted by the conveying device, the heat storage material and the workpiece can compensate for each other's heat by receiving radiant heat from each other. Consequently, the temperature drop of the workpiece during the conveying time from the end of heating of the workpiece to the start of press forming in hot press forming can be easily mitigated.

[0042] The tray may also include at least three second support columns that extend upward from the tray body and are positioned differently from the first support column group when viewed from above. The heat storage material is placed on the second support column group and is positioned to overlap the tray body vertically with a gap between them. This helps to suppress thermal deformation of the tray body.

[0043] The tray body has a shape that extends vertically in the vertical direction and may include a hollow section that penetrates vertically. This makes it easier for heat from below the tray body to be transferred to the heat storage material and the workpiece during the heating process.

[0044] The tray body may be configured such that, when viewed from above, the hollow area is wider than the constituent members of the tray body. This makes it easier for heat from below the tray body to be transferred to the heat storage material and the workpiece during the heating process. At least one of the first and second support column groups may be located between the hollow areas of the tray body when viewed from above. This makes it easier for heat from below the tray body to be transferred through the hollow areas around the first and / or second support column groups to the workpiece placed in the first support column group and / or the heat storage material placed in the second support column group.

[0045] The height ΔH (mm) of the tallest support column among the first support column group from the top surface of the heat storage material and the minimum plate thickness t2 (mm) of the thinnest part of the heat storage material may be related by the following formula. This effectively suppresses the temperature drop of the workpiece.

[0046] ΔH / t² ≤ 30 When viewed from above, the first group of support columns may be arranged inside the outer edge of the heat storage material placed on the tray body. This allows the workpiece to be positioned so as to overlap with the heat storage material, when viewed from above, inside the outer edge of the heat storage material.

[0047] The tray may further include a shielding plate that covers the height region from the top surface of the heat storage material to the top end of the tallest support column among the first support column group from a vertical direction. The shielding plate prevents air from hitting the front surface of the workpiece in the direction of transport, thereby mitigating the temperature drop from the end face of the workpiece at the front surface in the direction of transport, and also suppressing the movement of stagnant air between the workpiece and the heat storage material, which has been warmed by heat transfer between the workpiece and the heat storage material, to the outside. As a result, the heat retention effect can be maintained. In other words, the temperature drop of the workpiece while it is being transported on the tray is further suppressed.

[0048] The shielding plate may have an inclined surface that slopes closer to the first group of support columns as it approaches the edges from the center. This allows the air hitting the shielding plate to flow along the inclined surface away from the heat storage material and the workpiece during transport with the workpiece on the tray. As a result, the effect of suppressing the temperature drop of the workpiece during transport is enhanced.

[0049] The tray body may have a long and short direction when viewed from above. The shielding plate may be configured to cover the long direction of the tray body when viewed from above. By covering the long direction of the tray body with the shielding plate, the effect of suppressing temperature drop of the workpieces placed on the tray and transported can be further enhanced.

[0050] The hot press manufacturing line in an embodiment of the present invention comprises the above-mentioned tray, a heating device for heating a workpiece placed on the tray, a transport path disposed between the heating device and the lifting position of the workpiece for transporting the tray from the heating device to the lifting position, a transport device for supporting the workpiece placed on the tray and lifting it upward at the lifting position, at least one press machine having at least one pair of molds, and a moving device for moving the transport device between the lifting position and the press position between the at least one pair of molds.

[0051] The conveying device may include a base frame that is movable horizontally and vertically, a pair of first arms rotatably mounted on the base frame, a pair of second arms rotatably mounted on the base frame, a first drive unit for driving the first arms, and a second drive unit for driving the second arms. The pair of first arms are arranged laterally on the base frame and have a pair of first bases extending vertically from the base frame, and a first claw extending laterally from each of the pair of first bases. The pair of second arms are aligned laterally with respect to the base frame and have a pair of second bases extending vertically from the base frame, and a second claw extending laterally from each of the pair of second bases. The first drive unit rotates the pair of first arms relative to the base frame, thereby changing the lateral distance between the pair of first claws. The second drive unit rotates the pair of second arms relative to the base frame, thereby changing the lateral distance between the pair of second claws. The first drive unit and the second drive unit are configured to independently control the rotation of the first arm and the rotation of the second arm, respectively. The pair of first claws are configured to support the lower surfaces of both lateral ends of the first workpiece while being close to each other in the lateral direction. The pair of second claws are configured to support the lower surfaces of both lateral ends of the second workpiece while being close to each other in the lateral direction. The vertical positions of the pair of first claws and the vertical positions of the pair of second claws are different from each other.

[0052] Embodiments of the present invention will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated. The dimensional ratios between the components shown in each drawing do not necessarily represent the actual dimensional ratios.

[0053] [Example of device configuration] Figure 1 is a schematic diagram of a hot press manufacturing line 10 according to this embodiment. The hot press manufacturing line 10 comprises a heating device 14, a transfer table 16, a manipulator 44, a transfer device 46, a press machine 20, and a controller 22. The transfer table 16 is located near the outlet 14A of the heating device 14. The transfer table 16 is located between the heating device 14 and the press machine 20.

[0054] In the heating device 14, the heat storage material 5 and the workpiece W1 are placed on a single tray 1, stacked one on top of the other. After the heat storage material 5 and workpiece W1 on the tray 1 are heated in the heating device 14, the tray 1 is removed from the heating device 14. The tray 1, carrying the heat storage material 5 and workpiece W1, is then transported on the transport table 16 to a position where it can be lifted by the transport device 46.

[0055] (heating device) The heating device 14 is a device for heating an object to be heated. Examples of the heating device 14 include resistance heating furnaces, gas heating furnaces, far-infrared heating furnaces, and near-infrared heating furnaces. The heating device 14 is not limited to heating furnaces, and may be, for example, a high-frequency induction heating device, a low-frequency induction heating device, or an energized heating device that heats the object to be heated by directly applying electricity to it. The heating device 14 may have a heating chamber. The heating device 14 may have a plurality of indoor rollers 13 inside the heating chamber that are rotationally driven by a drive mechanism (not shown). By rotating the indoor rollers 13, the object to be heated (i.e., the heat storage material 5 and the workpiece W1) on the indoor rollers 13 is conveyed. An outlet 14A and an inlet 14B of the heating device 14 are provided at the front and rear of the heating chamber in the direction of conveyance of the object to be heated.

[0056] (Transport table) The transport table 16 is equipped with multiple transport rollers 26 that are rotationally driven by a drive mechanism (not shown). Each transport roller 26 rotates in sync with the indoor roller 13, allowing the transported object to be transported between the transport table 16 and the heating chamber of the heating device 14. The multiple transport rollers 26 are arranged at intervals. The transport table 16 is an example of a transport path that transports the heated workpiece W1 and the tray 1 on which the heat storage material 5 is placed from the heating device 14 to the lifting position. The lifting position for the workpiece by the transport device 46 is provided on the transport table 16. Note that the configuration of the transport path is not limited to the transport table 16 shown in Figure 1. For example, the transport path may be a belt conveyor or rails, etc. Also, in the example shown in Figure 1, the lifting position is on the transport path, but the lifting position does not have to be on the transport path. The lifting position may be on a platform or the like provided at the destination, separate from the transport path.

[0057] (Press machine) The press machine 20 comprises a lower die 23 and an upper die 21 for press-forming the workpiece. The lower die 23 is, for example, a punch die, and the upper die 21 is, for example, a die die. Coolant passages may be provided in the upper die 21 and the lower die 23. This allows heat absorbed from the workpiece during press-forming to be released via the coolant. The workpiece is placed between the lower die 23 and the upper die 21 of the press machine 20. With the workpiece in place, the lower die 23 and the upper die 21 are brought relatively close together and moved to the bottom dead center, thereby press-forming the workpiece. The operation of the lower die 23 and the upper die 21 can be controlled, for example, by a controller 22. The lower die 23 and the upper die 21 of the press machine 20 may be shaped to press-form multiple workpieces simultaneously and manufacture multiple press-formed products at the same time. Alternatively, multiple press machines 20 may be provided. For example, two press machines, each equipped with a pair of dies, may be provided.

[0058] (manipulator) The manipulator 44 uses a conveying device 46 to transport an object between the conveying table 16 and the press machine 20. The manipulator 44 is an example of a moving device. The conveying device 46 lifts, holds, and places the workpiece, which is the object to be transported. The manipulator 44 controls the position and orientation of the conveying device 46. The conveying device 46 may also be the end effector of the manipulator 44. The manipulator 44 moves the conveying device 46 between a lifted position on the conveying table 16 and a pressed position between a pair of dies (upper die 21 and lower die 23) of the press machine 20. The manipulator 44 comprises a base rotatable about at least one axis and an arm extending from the base and having at least one joint. The conveying device 46 is rotatably attached to the end of the arm. Note that the moving device for moving the conveying device 46 is not limited to a manipulator. For example, the moving device may include a rail connecting the transport table 16 and the press machine 20, and a suspension device that suspends the transport device 46 on the rail so that it can move up and down.

[0059] (controller) The controller 22 controls the heating device 14, the transport table 16, the press machine 20, and the manipulator 44 (transport device 46). The controller 22 is composed of, for example, one or more computers equipped with a processor and memory. These controls can be achieved by the processor executing a program stored in memory. The controller 22 transmits control signals or control data to the heating device 14, the transport table 16, the press machine 20, and the manipulator 44 (transport device 46). The controller 22 may also receive signals or data indicating the status of these devices. As an example, the controller 22 may include control units (for example, composed of circuits or processors) provided in each of the heating device 14, the transport table 16, the manipulator 44, and the press machine 20 to control each device. In this case, the controller 22 may include a global control computer that supplies control information to the control units of each device and controls the overall operation of the hot press manufacturing line 10. The operation of the arm 71 of the transport device 46, which will be described later, may be controlled by a part of the controller 22, for example, the control unit of the manipulator 44.

[0060] (Conveyor device) The transport device 46 comprises a base frame 48 and at least one pair of arms 71 rotatably mounted on the base frame 48. A joint 56 connected to the manipulator 44 is provided on the upper surface of the base frame 48. The joint 56 is connected so that the base frame 48 can rotate relative to the manipulator 44 on an axis in the vertical direction.

[0061] The pair of arms 71 are positioned spaced apart from the base frame 48 in the lateral direction (perpendicular to the vertical direction). Each of the pair of arms 71 has a base extending vertically from the base frame 48 and a claw extending laterally from the base. By controlling the rotation of the arms 71 relative to the base frame 48, the claws of the pair of arms 71 can be controlled to be in a closed state, where they are close together, and in an open state, where they are far apart.

[0062] (Tray) Figure 2 is a top view of tray 1, seen from above. Figure 3 is a side view of tray 1, as shown in Figure 2, seen from the direction of arrow F. Tray 1 is a tray for heating and transporting materials (workpieces) for hot pressing. Tray 1 is configured to withstand the heating temperature of the workpieces. In the example shown in Figure 2, the tray body 2 has a shape that extends along a plane perpendicular to the vertical direction and includes a hollow section 2G that penetrates vertically. Viewed from above, the area of ​​the hollow section 2G is larger than the area of ​​the constituent members of the tray body 2. Tray 1 has a heat storage material 5 placed on top of the tray body 2. Tray 1 has a plurality of support columns 3 that extend above the heat storage material 5.

[0063] (Tray body) In the example shown in Figure 2, the tray body 2 has a frame 2c and rod members 2f that span the inside of the frame 2c. The frame 2c includes a pair of vertical frames 2b and a pair of horizontal frames 2a. The pair of vertical frames 2b are arranged parallel to each other and spaced apart in the horizontal direction. The pair of horizontal frames 2a are arranged parallel to each other and spaced apart in the vertical direction between the pair of vertical frames 2b. The pair of vertical frames 2b and horizontal frames 2a form a rectangular frame 2c when viewed from above. The rod members 2f include vertical rod members 2d and horizontal rod members 2e. The vertical rod members 2d are spanned between the pair of horizontal frames 2a. The horizontal rod members 2e are spanned between the pair of vertical frames 2b. The rod members 2f are arranged in a grid pattern within the frame 2c.

[0064] The rod member 2f (at least one of the vertical rod member 2d and the horizontal rod member 2e) may be configured to allow adjustment of its position within the frame 2c. For example, the frame 2c may be provided with multiple positioning holes or locking pieces. In this case, the rod member 2f is fixed to the holes or locking pieces of the frame 2c using fasteners or the like as needed. By changing the position of the holes or locking pieces that fix the rod member 2f, the position of the rod member 2f within the frame 2c can be adjusted.

[0065] Note that the configuration of the tray body 2 is not limited to the example shown in Figure 2. For example, the tray body may be formed in a ladder shape having a pair of vertical bar members spaced apart and arranged substantially parallel to each other, and a plurality of horizontal bar members bridged between the pair of vertical bar members in a direction intersecting the pair of vertical bar members. Alternatively, the tray body may be formed as a hollow portion of a plate-like member having a plurality of holes that penetrate vertically.

[0066] The components of the tray body 2 (frame 2c and rod member 2f in the example in Figure 2) may be pipe material or solid material. Furthermore, the components of the tray body 2 may be angle material with an L-shaped cross-section or channel material with a U-shaped cross-section. The material of the components of the tray body 2 is not particularly limited, but it should be made of a heat-resistant material, such as heat-resistant steel or ceramics. The maximum operating temperature of the components should preferably be in the range of 900°C or higher, which is the normal operating temperature for heating devices, and 1050°C or lower, which is the upper limit setting temperature of the heating device. Examples of heat-resistant steel (heat-resistant alloy steel) that can be used as components include SCH22 (0.4C-25Cr-20Ni) and SCH24 (0.4C-25Cr-35Ni-Mo,Si). Forming the components of the tray body 2 from heat-resistant alloy steel facilitates processing and manufacturing.

[0067] (Heat storage material) The heat storage material 5 is placed on top of the tray body 2. The heat storage material 5 is a plate-shaped member. When viewed from above, the heat storage material 5 has a rectangular shape. The heat storage material 5 has a through hole for the support column 3 to pass through. The support column 3 extends upward through the through hole in the heat storage material 5 placed on top of the tray body 2. The support column 3 may be fixed to the tray body 2. For example, the support column 3 may be attached to the tray body 2 by being inserted into a hole in the tray body 2. In this case, the support column 3 is fixed to the tray body 2 by being inserted into both the hole in the tray body 2 and the through hole in the heat storage material. As another example, the support column 3 may be fixed to the tray body 2 by the engagement of a male screw on the outer circumference of the end of the support column 3 with a female screw on the inner circumference of the hole in the tray body 2. Alternatively, the support column 3 may be press-fitted into the hole in the tray body 2. Note that the means of fixing the support column 3 is not limited to the hole in the tray body 2. The support column 3 may be fixed to the tray body 2 by other means of fastening. Alternatively, the support column 3 may be fixed to the heat storage material 5 by being inserted into a hole in the heat storage material 5. In this case, the hole in the heat storage material 5 into which the support column 3 is inserted may be a through hole or a recessed hole that does not go all the way through.

[0068] The material of the heat storage material 5 is not particularly limited, but it is made of a heat-resistant material, such as a heat-resistant metal or ceramic. Examples of heat-resistant metals that can be used as the material for the heat storage material 5 include Fe-based materials such as heat-resistant steel, stainless steel, and carbon steel, or Al-based, Ti-based materials, or Ni-based alloys and other alloys. The material of the heat storage material may be the same as the material of the workpiece. Furthermore, it is preferable that the heat storage material 5 has a low thermal conductivity. A low thermal conductivity makes it difficult for the temperature to drop, and the effect of heat replenishment by radiant heat on the workpiece W1 can be sustained for a longer period. For example, the heat storage material 5 may be made of a material having a thermal conductivity of the same or lower than that of the workpiece to be heated. The thermal conductivity of the heat storage material 5 is not limited to this, but for example, it is preferably 200 W / mK or less, more preferably 100 W / mK or less, and even more preferably 70 W / mK or less. Furthermore, after the workpiece W1 is lifted by the conveying device 46 and conveyed to the press position, the heat storage material 5 and tray 1 may be used in the heating and conveying processes of other workpieces.

[0069] (post) The support columns 3 are formed extending upward from the tray body 2 to a position higher than the upper surface of the heat storage material 5. The multiple support columns 3 are arranged such that, when viewed from above, the imaginary lines connecting the support columns 3 form at least one triangle. The multiple support columns 3 are configured to allow the workpiece W1 to be placed on top of the heat storage material 5 with a gap between them. In the example shown in Figure 2, all of the multiple support columns 3 are located between the hollow portions 2G of the tray body 2 when viewed from above. That is, the support columns 3 are provided on the structural members of the tray body 2 that are sandwiched between the hollow portions 2G.

[0070] In the example shown in Figure 3, multiple support columns 3 penetrate the heat storage material 5. The heat storage material 5 has through holes for the multiple support columns 3 to pass through. This allows the multiple support columns 3 to be positioned inside the outer edge of the heat storage material 5 when viewed from above, as shown in Figure 2. In this case, the workpiece W1, which has a smaller area than the heat storage material 5, can be placed on the multiple support columns 3 so that the entire workpiece W1 overlaps with the heat storage material 5 when viewed from above. In the example shown in Figure 3, the heat storage material 5 is a flat plate, but the shape of the heat storage material 5 may be, for example, a shape corresponding to the workpiece W1. In this case, the distance between the workpiece W1 and the heat storage material 5 can be made uniformly closer across the entire surface.

[0071] (Examples of multiple support posts of different heights) In the examples shown in Figures 2 and 3, the workpiece W1 is a flat plate. In this case, the heights of the multiple support columns 3 are all the same. If the workpiece W1 is not a flat plate but a bent intermediate molded product, the multiple support columns 3 will include columns of different heights. Figure 4 is a side view showing an example of support columns when the workpiece W1 is not a flat plate. In this example, the cross-sectional shape of the workpiece W1 is hat-shaped. In this example, multiple support columns 3 of different heights are provided according to the shape of the workpiece W1.

[0072] (Example of support columns for workpieces and heat storage materials) Support columns for placing the heat storage material 5 may be provided on the tray body 2. Figure 5 is a top view showing an example of a tray 1 having support columns for supporting the heat storage material 5. Figure 6 is a side view of the tray 1 shown in Figure 5, viewed from the direction of arrow F. In the examples shown in Figures 5 and 6, the multiple support columns 3 include a first group of support columns 3a for placing the workpiece W1 and a second group of support columns 3b for placing the heat storage material 5. The second group of support columns 3b extends upward from the tray body 2. The heat storage material 5 is placed on the second group of support columns 3b. As a result, the second group of support columns 3b supports the heat storage material 5 with a gap between it and the tray body 2.

[0073] The first support group 3a includes at least three support columns that, when viewed from above, form a triangle with imaginary lines connecting them. The second support group 3b also includes at least three support columns that, when viewed from above, form a triangle with imaginary lines connecting them. All of the columns in the second support group 3b are positioned differently from those in the first support group 3a when viewed from above. All of the columns in the first support group 3a are taller than the shortest column in the second support group 3b. This allows the first support group 3a to support the workpiece W1 above the heat storage material 5 supported by the second support group 3b, with a gap between them.

[0074] The number of columns in the first support group 3a and the second support group 3b is not particularly limited. The number of columns in the first support group 3a and the number of columns in the second support group 3b may be the same or different. For example, if it is desired to strengthen the support of the workpiece W1 more than the support of the heat storage material 5, taking into consideration the characteristics and support positions of the workpiece W1 and the heat storage material 5, the number of columns in the first support group 3a may be greater than the number of columns in the second support group 3b.

[0075] (Example of a support column extending from a heat storage material) Figure 7 is a side view showing an example of a support column formed extending upward from the heat storage material 5. In the example shown in Figure 7, a projection extending upward from the upper surface of the heat storage material 5 forms the support column 3. In this example, the heat storage material 5 and the support column 3 are integrally formed. In addition to this example, another configuration for providing a support column to the heat storage material 5 is to insert the support column into a recess (hole) formed on the upper surface of the heat storage material 5. In the configuration shown in Figure 7, the tray body 2 may be omitted, and the heat storage material 5 may also perform the function of the tray body 2. Furthermore, the support column 3 shown in Figure 7 is also an example of a protruding part of the heat storage material that projects upward.

[0076] The support column 3 is formed in a columnar shape, such as a cylinder or a rectangular prism, or in a conical shape, such as a cone or a pyramidal pyramid. The support column 3 may be made of solid material or pipe material. The material of the support column 3 is not particularly limited, but it is made of a heat-resistant material, such as heat-resistant steel or ceramics. The maximum operating temperature of the support column 3 is preferably in the range of 900°C or higher, which is the normal operating temperature for heating devices, and 1050°C or lower, which is the upper limit setting temperature of the heating device. Examples of heat-resistant steel (heat-resistant alloy steel) that can be used as a component of the support column 3 include SCH22 (0.4C-25Cr-20Ni) and SCH24 (0.4C-25Cr-35Ni-Mo,Si).

[0077] The support column 3 may be configured to be detachable from the tray body 2 or the heat storage material 5. For example, the support column 3 can be attached to the tray body 2 by inserting it into a hole formed in a component of the tray body 2 (frame 2c and rod member 2f in the example in Figure 2) or the heat storage material 5. In this case, a female thread may be formed on the inner surface of the hole in the tray body 2 or the heat storage material 5, and a male thread may be formed on the end of the support column 3. This allows the support column 3 to be fixed to the tray body 2 or the heat storage material 5 by the screw.

[0078] (Example of arrangement of heat storage material and workpiece) In the example shown in Figure 3, the height of the support column 3 from the top surface of the heat storage material 5 (the vertical length, i.e., the dimension from the top surface of the heat storage material 5 to the top end of the support column 3) is ΔH. In this way, at least three support columns can be provided that are ΔH higher than the heat storage material 5. This allows the heat storage material 5 and the workpiece W1 to be placed on top of each other with a vertical gap of ΔH. For example, as in the examples in Figures 3, 6, and 7, when the workpiece W1 is a flat plate, all the columns of the support column 3 (first support column group 3a) are the same height. Therefore, all of the support columns 3 (first support column group 3a) are ΔH higher than the top surface of the heat storage material 5.

[0079] The distance between the heat storage material 5 placed on tray 1 and the workpiece W1 is determined by the height ΔH from the top surface of the heat storage material 5 to the top end of the support column 3. That is, ΔH determines the vertical distance D between the heat storage material 5 and the workpiece W1 on tray 1 during heating and transport. The distance D on tray 1 during heating and transport is preferably 100 mm or less. A smaller distance D is preferable from the viewpoint of suppressing temperature drop by allowing the heat storage material 5 and the workpiece W1 placed on tray 1 to receive radiant heat from each other. The maximum value of the distance D is more preferably 50 mm or less, even more preferably 30 mm or less, and still more preferably 10 mm or less. The lower limit of the distance D is not particularly limited, but the distance required for the operation of placing and lifting the workpiece W1 onto tray 1 is the lower limit of the distance D. The preferred range of ΔH is the same as the preferred range of the distance D.

[0080] Preferably, the maximum vertical distance D (mm) between the heat storage material 5 placed on the tray body 2 and the workpiece W1 placed on the support column 3, and the minimum plate thickness t1 (mm) of the thinnest part of the workpiece W1, are related by the following formula. This effectively suppresses the temperature drop of the workpiece W1 on the tray 1 during transport.

[0081] D≦120t1 The greater the thickness t2 of the heat storage material 5, the greater the effect of suppressing the temperature drop of the workpiece W1 during transport. On the other hand, the greater the thickness t2 of the heat storage material 5, the greater the energy required to heat the workpiece W1 and the heat storage material 5 to a predetermined temperature during the heating process. Also, the degree of temperature drop of the workpiece W1 on the tray 1 during transport depends on both the thickness t1 of the workpiece W1 and the thickness t2 of the heat storage material 5. From these viewpoints, it is preferable that t2 / t1 is, for example, 0.8 ≤ t2 / t1 ≤ 20. The lower limit of t2 / t1 is more preferably 1.0, and even more preferably 2.0. The upper limit of t2 / t1 is more preferably 15, and even more preferably 10. If there are multiple parts with different thicknesses in a single workpiece W1, the smallest thickness in the workpiece W1 is taken as the thickness t1. If the heat storage material 5 contains multiple parts with different thicknesses, the smallest thickness in the heat storage material 5 is taken as the thickness t2.

[0082] In the examples shown in Figures 2 to 7, when viewed from above, the edge of the heat storage material 5 is located outside the edge of the workpiece W1. Furthermore, in these examples, the top-view area of ​​the heat storage material 5 is larger than the top-view area of ​​the workpiece W1. As a result, almost the entire underside of the workpiece W1 can receive radiant heat from the heat storage material 5. Thus, the workpiece W1 and the heat storage material 5 placed on the tray 1 may have different sizes when viewed from above. The heat storage material 5 overlaps almost the entire workpiece W1 in the vertical direction.

[0083] The distance ΔW between the edge of the heat storage material 5 placed on the tray body 2, as viewed from above, and the edge of the workpiece W1 placed on the first support column group 3a, as viewed from above, is not particularly limited, but is preferably 10 to 200 mm. If ΔW is too short, the effect of suppressing the temperature drop at the edge of the workpiece W1 is reduced. From this viewpoint, the minimum value of ΔW is more preferably 20 mm or more, and even more preferably 30 mm or more. If ΔW is too long, the amount of energy required to heat the workpiece W1 and the heat storage material 5 increases. From this viewpoint, the maximum value of ΔW is more preferably 150 mm or less, and even more preferably 100 mm or less.

[0084] ΔW is defined as the distance from the edge of the workpiece to the edge of the heat storage material in a direction perpendicular to the edge of the workpiece (or in the direction of the normal if the edge is curved) when viewed from above. Furthermore, even if the workpiece W1 is not a flat plate but a bent intermediate molded product, the heat storage material 5 and workpiece W1 can be positioned such that, when viewed from above, the edge of the heat storage material 5 is located outside the edge of the workpiece W1. In this case as well, ΔW is defined as the distance between the edge of the heat storage material 5 and the edge of the workpiece W1 when viewed from above. Moreover, the area of ​​the heat storage material 5 placed on the tray body 2 when viewed from above may be larger than the area of ​​the workpiece W1 placed on the support column 3 when viewed from above.

[0085] (Example of arrangement of thickness difference plates) The workpiece W1 may be a plate with a difference in thickness, including a thick section and a thin section. Figure 8 is a side view showing an example of the arrangement of the workpiece W1, which is a plate with a difference in thickness, and the heat storage material 5. In the example shown in Figure 8, the heat storage material 5 is provided so as to overlap only a part of the workpiece W1, not the entirety of it. The heat storage material 5 is positioned so as to overlap the thin section of the workpiece W1, which is placed on the support column 3, when viewed from above. This makes it possible to suppress the temperature drop of the thin section of the workpiece W1. In addition, the area of ​​the heat storage material 5 can be reduced compared to the case where the heat storage material 5 is provided so as to overlap the entire thin section of the workpiece W1 when viewed from above. This reduces the energy required to heat the heat storage material 5. From the viewpoint of suppressing the temperature drop of the thin section, it is preferable to arrange the heat storage material 5 so as to overlap the entire thin section of the workpiece W1 when viewed from above. However, even if the heat storage material 5 is arranged so as to overlap only a part of the thin section of the workpiece W1 when viewed from above, the effect of suppressing the temperature drop of the thin section can still be obtained. For example, if the thin-walled portion of workpiece W1 includes the edge of the plate, the edge of the thin-walled portion is particularly prone to temperature drop. Therefore, by arranging the heat storage material 5 so that it overlaps with the edge of the plate, which is part of the thin-walled portion of workpiece W1, when viewed from above, the temperature drop in the thin-walled portion can be efficiently suppressed.

[0086] Figure 9 is a side view showing another example of the arrangement of the workpiece W1, which is a plate with a difference in thickness, and the heat storage material 5. In the example shown in Figure 9, the heat storage material 5 is also a plate with a difference in thickness, having a thick section and a thin section. In the example shown in Figure 9, the thick section of the heat storage material 5 placed on the tray body 2 and the thin section of the workpiece W1 placed on the support column 3 overlap when viewed from above. As a result, the thick section of the heat storage material 5 is conveyed facing the thin section of the workpiece W1. The thin section of the workpiece W1 has a thin plate thickness and its temperature drops easily. The thick section of the heat storage material 5 has a relatively large heat capacity and radiates a large amount of heat. Therefore, it can more effectively suppress the temperature drop of the thin section of the workpiece W1. As a result, the temperature drop of the entire workpiece W1 can be efficiently suppressed, and the temperature difference between the thin section and the thick section of the workpiece W1 can be efficiently suppressed.

[0087] The plate with varying thickness may be, for example, a tailored blank made by joining the ends of steel plates of different thicknesses. Alternatively, the plate with varying thickness may be a patchwork tailored blank made by overlapping and joining steel plates of different dimensions. Alternatively, the plate with varying thickness may be a tailored rolled blank made by partially changing the thickness of a single steel plate through processing such as rolling.

[0088] (shielding plate) Figure 10 is a top view showing an example configuration of tray 1 equipped with shielding plates 4 (4A-4D). Figure 11 is a side view of tray 1 shown in Figure 10, viewed from the direction of arrow F. Tray 1 shown in Figures 10 and 11 is a configuration in which shielding plates 4 (4A-4D) are added to tray 1 shown in Figures 2 and 3. As shown in Figure 10, shielding plates 4A-4D are provided so as to surround the entire circumference of the tray body 2 when viewed from above. The shielding plates 4 include a pair of shielding plates 4A, 4C that cover the short side of the tray body 2 when viewed from above, and a pair of shielding plates 4B, 4D that cover the long side.

[0089] As shown in Figure 11, each of the shielding plates 4A to 4D covers the height region between the top surface of the heat storage material 5 and the top end of the highest support column 3 from the side (in a direction perpendicular to the vertical direction). That is, the shielding plates 4A to 4D are formed to extend at least from the heat storage material 5 to the highest point of the support column 3. This prevents air from flowing into the space between the heat storage material 5 placed on the tray body 2 and the workpiece W1 placed on the support column 3.

[0090] The shielding plates 4A to 4D are attached to the tray body 2. In the example shown in Figure 11, the shielding plates 4B and 4D are connected to the sides of the tray body 2 and extend upward. The shielding plates 4 are connected to the tray body 2 by fasteners such as welding or bolts. The shielding plates 4 may be detachable from the tray body 2.

[0091] In the examples shown in Figures 10 and 11, each of the shielding plates 4A to 4D has an inclined surface that slopes closer to the support column 3, i.e., the workpiece W1 and the heat storage material 5, as it approaches the edge from the center. In other words, each of the shielding plates 4A to 4D has a curved shape in which the central part protrudes outward and the edge is located inward from the central part. This allows the air hitting the shielding plate 4 to be directed away from the workpiece W1 placed on the tray 1. As shown in Figures 10 and 11, the shielding plates 4B and 4D are configured so that the central part is located outward from the edge, whether viewed from above or from the side.

[0092] The shape of the shielding plate is not limited to the examples above. For example, the shielding plate 4 may be made of a flat plate. It may also have a shape in which the central part is located outside the edges in either a side view or a top view.

[0093] The positions in which the shielding plates 4 are provided are not limited to the examples shown in Figures 10 and 11. In the example shown in Figure 10, shielding plates 4B and 4D are provided to cover the longitudinal direction, and shielding plates 4A and 4C are provided to cover the short direction. It is also possible to have a configuration in which at least one of the longitudinal and short directions is covered by the shielding plates 4. By covering the longitudinal direction with the shielding plates 4, the inflow of air can be blocked over a wide area. It is also possible to have a configuration in which at least the front in the conveying direction is covered by the shielding plates 4. This makes it possible to block the inflow of air during conveying more efficiently.

[0094] [Example of a manufacturing process for press-formed products] Referring again to Figure 1, an example of the process for manufacturing press-formed products using the hot press manufacturing line 10 described above will be explained. The manufacturing process for press-formed products in this embodiment includes a heating step for heating the workpiece W1, a conveying step for transporting the workpiece W1, and a pressing step for pressing the workpiece W1.

[0095] (Heating process) In the heating process, the heat storage material 5 and the workpiece W1 are heated in the heating device 14 while placed on the tray 1. For example, as shown in Figures 2 to 11, the heat storage material 5 is placed on the tray body 2, and the workpiece W1 is placed on multiple support columns 3. The heat storage material 5 and the workpiece W1 placed on the tray 1 overlap in the vertical direction, that is, in the direction normal to the surface of the workpiece W1.

[0096] The tray body 2 has a hollow section 2G that penetrates vertically. Therefore, even if there is a heat source below the tray 1, the transfer of heat from the heat source to the heat storage material 5 and the workpiece W1 is less likely to be obstructed by the tray body 2.

[0097] The tray 1, on which the heat storage material 5 and workpiece W1 are placed, enters the heating chamber of the heating device 14 through the inlet 14B. The tray 1 is transported to the outlet 14A by the indoor rollers 13. The heating device 14 heats the heat storage material 5 and workpiece W1 to a predetermined heating temperature while transporting them. This heating temperature is, for example, set to be above the Ac3 transformation point, which is the temperature at which the ferrite of the steel material constituting the workpiece W1 completes its transformation to austenite.

[0098] Furthermore, a conveying device and manipulator may be provided to place the workpiece W1 on the tray 1 before it is placed in the heating device 14. This conveying device places the workpiece W1 on the support columns 3 of the tray 1. This conveying device can have a configuration similar to, for example, the conveying device 46 shown in Figure 1, which lifts the workpiece W1 on the tray 1 and places it in the pressing position. This conveying device is located upstream of the heating device 14.

[0099] (First transport process) In the first transport process, the heat storage material 5 and the workpiece W1 are placed on tray 1 and removed from the heating device 14, and transported to the transfer point to the transport device 46, i.e., the lifting position. As a result, the heat storage material 5 is placed on the tray body 2, and the workpiece W1 is placed on the support column 3 and stacked on top of the heat storage material 5, and are transported together with tray 1 from the heating device 14 to the lifting position. Outside the heating device 14, tray 1 is transported near the press machine 20 by transport rollers 26. For example, as shown in Figures 2 to 11, the heat storage material 5 and the workpiece W1 are placed on tray 1 and transported from the heating device 14 to the lifting position. The positional relationship between the workpiece W1 and the heat storage material 5 in the first transport process is the same as their positional relationship in the heating process. That is, tray 1 allows the workpiece W1 to be transported to the lifting position in the first transport process while maintaining the positional relationship between the workpiece W1 and the heat storage material 5 during heating. This mitigates the temperature drop of the workpiece W1 during transport. Furthermore, the temperature drop of the workpiece W1 during transport can be mitigated without the need to install a heat source such as a heater that generates thermal energy along the transport path. Therefore, temperature drop can be easily mitigated.

[0100] (Second transport process) In the second transport process, the workpiece W1 placed on the support column 3 is lifted by the transport device 46 near the press machine 20. As described above, the transport device 46 moves upward while holding the workpiece W1 with the arm 71. The workpiece W1 moves upward while maintaining the same posture as when it was placed on the support column 3. At this time, since the support column 3 is formed to extend upward, it does not get caught on the workpiece W1 being lifted upward by the transport device 46. Therefore, the control or device configuration for lifting the workpiece W1 can be simplified.

[0101] The workpiece W1, lifted by the conveying device 46, is set in the press position. The press position is, for example, between the upper die 21 and the lower die 23 of the press machine 20.

[0102] (Pressing process) The press machine 20 press-forms the workpiece W1 using the upper die 21 and the lower die 23. Here, the workpiece W1 to be pressed is the workpiece W1 that has been heated to above the Ac3 transformation point by the heating device 14 and then transported to the press position by the transport table 16 and the transport device 46. The press machine 20 can start press-forming on this workpiece W1, perform the forming process and also perform a quenching treatment. Specifically, with the workpiece W1 positioned between the upper die 21 and the lower die 23, the press machine 20 moves the upper die 21 relatively closer to the lower die 23 and moves it to the bottom dead center to form the workpiece. After reaching the bottom dead center, with the molds clamped, the upper die 21 and the lower die 23 come into contact with the workpiece W1 and rapidly remove heat from the workpiece W1. This causes the workpiece W1 to undergo martensitic or bainite transformation. As a result, the workpiece W1 can be formed into a quenched product with a shape corresponding to the upper die 21 and the lower die 23.

[0103] The present invention is not limited to the embodiments described above. For example, in the embodiments described above, one workpiece is placed on top of the heat storage material 5 in tray 1, but two or more workpieces may be placed on top of the heat storage material 5.

[0104] [Tray variations] Figures 12 to 14 are side views showing modified versions of tray 1. In the examples shown in Figures 12 to 14, tray 1 comprises a tray body 2 and a plate-shaped heat storage material 5 placed on top of the tray body 2. In Figures 12 to 14, the configuration of the tray body 2 may be the same as in Figures 2, 5, or 10. The heat storage material 5 shown in Figures 12 to 14 are all modified versions of the plate-shaped heat storage material 5.

[0105] In the example shown in Figure 12, the heat storage material 5 has a protrusion 5a that projects upward. The protrusion 5a is shaped to support the workpiece W1. The workpiece W1 is placed on the heat storage material 5 in contact with the protrusion 5a. The protrusion 5a has a flat top surface. The workpiece W1 is in contact with the top surface. That is, the top surface of the protrusion 5a becomes the mounting surface on which the workpiece W1 is in contact. The top view area of ​​the mounting surface is smaller than the top view area of ​​the entire heat storage material 5.

[0106] Viewed from above, at least a portion of the edge 5ae of the mounting surface is located inward from the edge of the workpiece W1. This creates a space between the edge of the workpiece W1 and the heat storage material 5. The arm 71 of the conveying device 46 can be inserted into this space and the arm 71 can support the lower surface of the workpiece W1. This facilitates the lifting operation of the workpiece W1 by the conveying device 46. The range of the vertical dimension ΔT1 of the space between the workpiece W1 and the heat storage material 5 at the edge of the workpiece W1 is not particularly limited, but it is preferable to set it to a range similar to ΔH described above.

[0107] Furthermore, the distance ΔW between the edge of the heat storage material 5 placed on the tray body 2 as viewed from above and the edge of the workpiece W1 placed on the protrusion 5a as viewed from above is not particularly limited, but is preferably 10 to 200 mm, as described above. The maximum value of the distance ΔV between the edge of the workpiece W1 placed on the protrusion 5a as viewed from above and the edge 5ae as viewed from the mounting surface of the protrusion 5a is not particularly limited, but is preferably 100 mm or less, and more preferably 50 mm or less.

[0108] In the example shown in Figure 13, the heat storage material 5 has a plurality of protrusions 5a that project upward. The plurality of protrusions 5a are arranged in a line in one direction. Each of the plurality of protrusions 5a forms a ridge that extends in a direction intersecting the direction in which the plurality of protrusions 5a are aligned (in Figure 13, the direction perpendicular to the plane of the paper). In this way, the heat storage material 5 can also be configured such that the workpiece W1 is placed on the ridge formed by the protrusions 5a.

[0109] In the example shown in Figure 14, the heat storage material 5 is a plate with a curved shape that protrudes upward. In the heat storage material 5, the thickness of the protrusion 5a is approximately the same as the thickness of the parts other than the protrusion 5a. Thus, the protrusion 5a can be a part formed by bending the plate so that it protrudes upward. In the example shown in Figure 14, the workpiece W1 is an intermediate molded product obtained by molding a flat plate. The heat storage material 5 has a shape that corresponds to the shape of the workpiece W1. The heat storage material 5 can be obtained, for example, by molding a flat plate.

[0110] In the configurations shown in Figures 12 to 14, the heat storage material 5 may be placed on a support column extending upward from the tray body 2. Alternatively, in the configurations shown in Figures 12 to 14, the tray body 2 may be omitted, and the heat storage material 5 may also perform the function of the tray body 2.

[0111] [Modified examples of heat storage materials] Figures 15 and 16 are side views showing modified examples of the heat storage material 5. In the examples shown in Figures 15 and 16, the tray 1 comprises a tray body 2, a plate-shaped heat storage material 5 placed on the tray body 2, and a support column 3 for placing the workpiece W1. In Figures 15 and 16, the configuration of the tray body 2 and the support column 3 may be the same as in Figure 2. The heat storage material 5 shown in Figures 15 and 16 are all modified examples of the plate-shaped heat storage material 5. In the examples shown in Figures 15 and 16, when viewed from above, a vertical wall 5b is formed on the outside of the edge (border) of the workpiece W1, with a portion of the heat storage material 5 extending upward. That is, the heat storage material 5 has a vertical wall 5b extending upward on the outside of the area where the workpiece W1 is placed. The vertical wall 5b is provided, for example, in at least a part of the area surrounding the area where the support column 3 is placed. The vertical wall 5b shown in Figure 15 extends substantially vertically from the top surface of the heat storage material 5. The inner surface of the vertical wall 5b shown in Figure 16 is inclined.

[0112] The upper end of the vertical wall 5b can be the same height as or higher than the upper end of the support column 3. That is, the height ΔT2 from the upper surface of the heat storage material 5 can be the same height as or higher than the height of the workpiece W1 placed on the support column 3. For example, the vertical wall 5b can cover the sides of the workpiece W1. As a result, the heat loss at the side ends of the workpiece W1 is compensated by radiant heat from the vertical wall 5b of the heat storage material 5, and the temperature drop at the ends of the workpiece W1 can be suppressed more effectively. Furthermore, for example, the same effect as when a shielding plate 4 is provided on the side, as shown in Figures 10 and 11, can be obtained.

[0113] A space is provided between the vertical wall 5b and the workpiece W1 placed on the support column 3. The arm 71 of the conveying device 46 can be inserted into this space. This facilitates the lifting operation of the workpiece W1 by the conveying device 46. From the viewpoint of the heat retention function of the workpiece W1, it is preferable that the space between the vertical wall 5b and the workpiece W1 placed on the support column 3 be small. The maximum value of the distance ΔU between the vertical wall 5b and the end of the workpiece W1 when viewed from above is not particularly limited, but for example, it is preferably 200 mm or less, and more preferably 100 mm or less.

[0114] [Materials for the work] The workpiece material can be any formable metal. While not limited to these, examples of workpiece materials include Fe-based materials such as carbon steel and stainless steel, as well as Al-based and Ti-based materials. The workpiece may also have a plating layer. For example, the workpiece may be a plated steel sheet. Examples of plating layers include aluminum alloys, aluminum-based alloys, zinc alloys, or zinc-based alloys.

[0115] When the workpiece is a plated steel sheet, it is preferable because oxide scale is less likely to form during transport. When the workpiece W1 is transported stacked on top of the heat storage material 5, if oxide scale forms on the underside of the workpiece W1, the oxide scale may fall off and land on the top surface of the heat storage material 5. In this case, if the heat storage material 5 and tray 1 are used repeatedly in a continuous manner, oxide scale may accumulate on the heat storage material 5, potentially leading to contamination. Therefore, by using a plated steel sheet as the workpiece, the formation of oxide scale during transport can be suppressed, and contamination of the heat storage material 5 can be reduced.

[0116] [Effects of transporting workpieces with a gap between them and the heat storage material] In the example above, the heat storage material 5 and the workpiece W1 are transported on the tray 1, stacked with a gap between them in the vertical direction. This helps to suppress variations in the characteristics of the top and bottom surfaces of the workpiece W1.

[0117] When the heat storage material 5 and the workpiece W1 are stacked without any gaps and transported together, the exposure time to air differs between the bottom surface of the workpiece W1 (the overlapping surface with the heat storage material 5) and the top surface (the opposite surface). In this case, if the workpiece W1 is an unplated steel sheet, the amount of oxide scale generated may also differ between the top and bottom surfaces. If the amount of oxide scale differs between the top and bottom surfaces, differences in friction characteristics between the top and bottom surfaces may occur. As a result, the time required for die adjustment and forming condition setting in press forming may increase. Furthermore, when a plated steel sheet workpiece W1 is heated in the heating process with no gaps between the workpiece W1 and the heat storage material 5, the heating rate may differ between the overlapping surface of the workpiece W1 and the opposite surface, potentially resulting in differences in temperature history. In this case, differences in alloying between the plating and the base material may occur between the top and bottom surfaces of the workpiece W1, potentially resulting in differences in plating quality. Therefore, by heating and transporting the workpiece W1 and the heat storage material 5 with a gap between them, variations in properties such as friction characteristics and plating quality between the top and bottom surfaces of the workpiece W1 can be reduced.

[0118] [Modified examples of hot press manufacturing lines] Figure 17 shows a modified example of the hot press manufacturing line 10. The hot press manufacturing line 10 shown in Figure 17 includes a heating device 14, a transfer table 16, a manipulator 44, a transfer device 46, a press machine 20, and a controller 22. In the hot press manufacturing line 10 of Figure 17, all components except the transfer device 46 and the press machine 20 can be configured in the same way as in Figure 1.

[0119] In the example shown in Figure 17, the press machine 20 can accommodate two workpieces W1 and W2 between the upper die 21 and the lower die 23. The upper die 21 and the lower die 23 are relatively movable. With the two workpieces W1 and W2 positioned between the upper die 21 and the lower die 23, the press machine 20 moves the upper die 21 and the lower die 23 closer together to press-form the two workpieces W1 and W2 simultaneously.

[0120] (Conveyor device) Figure 18A is a side view showing an example configuration of the conveying device 46 in Figure 17 as seen from the side (y-direction). Figure 18B is a diagram showing the second arm 72 of the conveying device 46 in Figure 18A in the outward-opening position.

[0121] (Base frame) In the example shown in Figures 18A and 18B, the transport device 46 comprises a base frame 48, a pair of first arms 71 and a pair of second arms 72 rotatably mounted on the base frame 48. The shape of the base frame 48 is rectangular when viewed from above. In this example, the vertical direction is defined as the z direction. The direction in the plane perpendicular to the vertical direction is defined as the transverse direction. Within the transverse direction, the long side of the base frame 48 is defined as the y direction, and the short side is defined as the x direction.

[0122] A joint 56 is provided on the upper surface of the base frame 48, which is connected to the manipulator 44. The joint 56 is connected so that the base frame 48 can rotate around the manipulator 44 in the vertical direction.

[0123] (First arm and second arm) A pair of first arms 71 are arranged spaced apart in the lateral direction (x direction). Each of the pair of first arms 71 has a first base 71a extending vertically from the base frame 48 and a first claw 71b extending laterally by bending from the first base 71a. Each first arm 71 is rotatably mounted to the base frame 48 about a rotation axis 60 in the y direction. One end of the first base 71a is rotatably connected to the base frame 48, and the first claw 71b extends from the other end.

[0124] A pair of second arms 72 are arranged spaced apart in the lateral direction (x direction). Each of the pair of second arms 72 has a second base 72a extending vertically from the base frame 48 and a second claw 72b extending laterally by bending from the second base 72a. Each second arm 72 is rotatably mounted to the base frame 48 about a rotation axis 60 in the y direction. One end of the second base 72a is rotatably connected to the base frame 48, and the second claw 72b extends from the other end.

[0125] The vertical positions of the pair of first claws 71b and the pair of second claws 72b are different from each other. In the example shown in Figures 18A and 18B, the first base portion 71a is shorter than the second base portion 72a in the vertical direction. The first claws 71b are located closer to the base frame 48 than the second claws 72b.

[0126] In the example shown in Figures 18A and 18B, the rotation axis 60 of the first arm 71 and the rotation axis 60 of the second arm 72 are coaxial. This allows the first arm 71 and the second arm 72 to be efficiently positioned on the base frame 48. Note that the rotation axis 60 of the first arm 71 and the rotation axis 60 of the second arm 72 do not necessarily have to be coaxial.

[0127] (Drive unit) The pair of second arms 72 are driven by a second drive unit. The second drive unit rotates the pair of second arms 72 relative to the base frame 48, thereby changing the lateral (x-direction) distance between the pair of second claws 72b. In the example shown in Figures 18A and 18B, the second drive unit consists of actuators 82 provided for each second arm 72.

[0128] The actuator 82 is, for example, an air cylinder. The actuator 82 adjusts the amount of extension of the axially moving operating shaft 82A. A pin 82B is provided at the end of the operating shaft 82A. The pin 82B is movably and rotatably inserted into an elongated hole in a link 90 fixed to the second arm 72.

[0129] When each actuator 82 extends its operating shaft 82A, as shown in Figure 18A, the corresponding second arm 72 extends downward, and the pair of second claws 72b of the pair of second arms 72 move closer to each other, resulting in a closed state. When each actuator 82 retracts its operating shaft 82A, as shown in Figure 18B, the pair of second claws 72b of the pair of second arms 72 move apart from each other, resulting in an open state.

[0130] The pair of first arms 71 are driven by a first drive unit (not shown). The first drive unit rotates the pair of first arms 71 relative to the base frame 48, thereby changing the lateral (x-direction) distance between the pair of first claws 71b. The first drive unit that drives the first arms 71 can also be configured to include an actuator similar to the actuator 82 shown in Figures 18A and 18B. The pair of first arms 71 are also controlled by the first drive unit to be in a closed state where the pair of first claws 71b are close to each other, or in an open state where the pair of first claws 71b are further apart than in the closed state. Note that the actuators of the first and second drive units are not limited to air cylinders, but may be motors or hydraulic cylinders, for example.

[0131] The pair of first claws 71b are capable of supporting the lower surfaces of both lateral ends of the first workpiece W1 when they are positioned close to each other in the lateral direction, i.e., in a closed state. The pair of second claws 72b are capable of supporting the lower surfaces of both lateral ends of the second workpiece W2 when they are positioned close to each other in the lateral direction, i.e., in a closed state.

[0132] [Example of a manufacturing process for press-formed products] An example of a process for manufacturing press-formed products using the hot press manufacturing line 10 shown in Figure 17 will be explained. The manufacturing process for press-formed products includes a heating process, a first conveying process, a second conveying process, and a pressing process. The heating process and the first conveying process can be the same as the manufacturing process of the hot press manufacturing line 10 shown in Figure 1.

[0133] (Heating process) In the heating process, the heat storage material 5, the first workpiece W1, and the second workpiece W2 are heated in the heating device 14 while placed on the tray body 2. The first workpiece W1 and the second workpiece W2 are each heated above the heat storage material 5, overlapping with the heat storage material 5 in the direction normal to the plate surface. The first workpiece W1 and the second workpiece W2 are each placed on at least three support columns 3. The support columns 3 extend upward from the tray body 2.

[0134] (First transport process) In the first transport process, the heat storage material 5, the first workpiece W1, and the second workpiece W2 are transported by the transport table 16 from the heating device 14 to the lifting position by the transport device 46 while placed on the tray body 2.

[0135] (Second transport process) The second conveying process includes the steps of the conveying device 46 lifting the first workpiece W1, the conveying device 46 lifting the second workpiece W2, the conveying of the first and second workpieces W1 and W2, the lowering of the first workpiece W1 to the press position, and the lowering of the second workpiece W2 to the press position.

[0136] Figure 17 shows how the conveying device 46 lifts the first workpiece W1. A pair of first arms 71, rotatably mounted on the base frame 48 of the conveying device 46, are driven to support and lift the lower surfaces of both ends of the first workpiece W1 with the claws of the pair of first arms 71. At this time, the pair of first arms 71 and the pair of second arms 72 are opened, and the conveying device 46 is lowered to approach the first workpiece W1 on the conveying rollers 26 of the conveying table 16. By rotating the pair of first arms 71 to the closed position, the claws (first claws 71b) of the pair of first arms 71 are inserted under the lower surfaces of both ends of the first workpiece W1. In this state, the conveying device 46 is raised to support and lift the lower surfaces of both ends of the first workpiece W1 with the first claws 71b of the pair of first arms 71.

[0137] When lifting the second workpiece W2, the conveying device 46 supports and holds the lower surface of the first workpiece W1 with a pair of first arms 71, and then drives a pair of second arms 72 to lift the second workpiece W2. Similar to the lifting operation of the first workpiece W1, the conveying device 46 uses the claws of the pair of second arms 72 to support and lift the lower surfaces of both ends of the second workpiece W2.

[0138] The conveying device 46 conveys the first workpiece W1, whose lower surface is supported by the claws of a pair of first arms 71, and the second workpiece W2, whose lower surface is supported by the claws of a pair of second arms 72, in a state where they overlap each other with a gap in the direction normal to the surface of the first workpiece W1.

[0139] Figure 17 shows the transfer device 46 lowering the second workpiece W2 to the press position. The transfer device 46 moves to the press position of the second workpiece W2. With the lower surface of the first workpiece W1 supported and held by the pair of first arms 71, the transfer device 46 drives the pair of second arms 72 to open them and lowers the second workpiece W2 to the press position of the press machine 20. Subsequently, the transfer device 46 moves to the press position of the first workpiece W1, drives the pair of first arms 71 to open them and lowers the first workpiece W1 to the press position of the press machine 20.

[0140] In the example shown in Figure 17, two workpieces are placed in the upper die 21 and lower die 23 of a single press machine, and the two workpieces are press-formed simultaneously. In this case, the first workpiece W1 and the second workpiece W2 are lowered to different pressing positions between the upper die 21 and the lower die 23. The manner in which the conveying device 46 lowers the two held workpieces to their respective pressing positions is not limited to this. For example, the first workpiece W1 and the second workpiece W2 may be lowered to the respective pressing positions of two press machines.

[0141] (Example of experiment) The temperature change after heating was measured under different conditions after heating of steel plates. Specifically, the following experiment was conducted. 1.5 GPa class hot-press steel plates with thicknesses of 0.8 mm and 1.6 mm were used as test materials, and thermocouples were attached to the surface of the steel plates to measure the temperature. The steel plates were heated to 950°C in a heating furnace, and the temperature drop during air cooling after removal from the furnace was measured. Comparative Example 1 involved heating and cooling a single 1.6 mm thick steel plate alone, Comparative Example 2 involved heating and cooling a single 0.8 mm thick steel plate alone, and an example involved stacking two 0.8 mm thick steel plates in the direction normal to the plate surface, spaced apart by a predetermined distance D, and fixed in place. In the case of stacking two steel plates, the distance D was set to three levels: 10 mm, 30 mm, and 50 mm, and these were designated as Example 1, Example 2, and Example 3, respectively. Figure 19 shows the temperature measurement positions. The temperature of the upper and lower steel plates was measured at 5mm, 20mm, 30mm, and 50mm from the edge of the steel plate, as well as at the center of the steel plate.

[0142] Figure 20 is a graph of the average cooling rate as a measurement result. The average cooling rate was derived in the section from 800°C to 750°C in the measured temperature drop curve. Figure 21 is a graph showing the range targeted for the derivation of the average cooling rate. From the results shown in Figure 20, it was confirmed that the average cooling rate of Examples 1 to 3, which used two 0.8 mm thick steel plates stacked on top of each other, was reduced compared to Comparative Example 1, which used a single 0.8 mm thick steel plate, at all measurement locations. Furthermore, it was confirmed that when two steel plates are stacked, a smaller gap D between the two steel plates reduces the average cooling rate near the edges of the steel plates, and also shows a greater improvement in the average cooling rate at all measurement locations. In Example 3, where the gap D was set to 50 mm, the cooling rate improved to about an intermediate level between Comparative Example 1, which used a single 0.8 mm thick steel plate, and Comparative Example 2, which used a single 1.6 mm thick steel plate. In Example 1, where the spacing D was set to 10 mm, the cooling rate improved to the same level as Comparative Example 2, which used a single 1.6 mm thick steel plate. By appropriately setting the spacing D between the two stacked steel plates, it was possible to obtain cooling characteristics equivalent to those of a steel plate with twice the thickness, i.e., twice the heat capacity.

[0143] From the results above, it was found that the rate of cooling can be reduced by stacking plates heated in the same way as the workpieces in the vertical direction above the workpieces when transporting them. In the above embodiment, the spacing between the plate-shaped heat storage material and the workpieces placed on tray 1 can be stably maintained with a simple configuration during the heating process and the subsequent transport process. Therefore, the workpieces can be transported simply and efficiently while suppressing the temperature drop. [Explanation of symbols]

[0144] 1 tray 2 Tray body 3 pillars 3a 1st pillar group 3b 2nd pillar group W1 Work 5. Heat storage material

Claims

1. A heating step in which a plate-shaped heat storage material and a plate-shaped workpiece placed above the heat storage material are heated in the heating chamber of a heating device while overlapping in the direction normal to the plate surface of the workpiece, A first transport step involves transporting the heat storage material and the workpiece placed above the heat storage material from the heating chamber of the heating device to a lifting position outside the heating chamber, with the workpiece and the heat storage material overlapping in the direction normal to the surface of the workpiece. A second transport step involves lifting the workpiece, which is placed above the heat storage material at the aforementioned lifting position, upward using a transport device and transporting it to the press position of the press machine. The process includes a pressing step in which the workpiece is processed by the press machine, In the heating step, the heat storage material is placed on the tray body, and the workpiece is heated while placed on at least three first support columns that extend upward from the tray body or the heat storage material to a position higher than the upper surface of the heat storage material. A method for manufacturing a press-formed product, wherein in the first transport step, the heat storage material placed on the tray body and the workpiece placed on the group of at least three first support columns are transported together with the tray body from the heating chamber of the heating device to the lifting position.

2. A heating step in which a plate-shaped heat storage material and a plate-shaped workpiece placed above the heat storage material are heated in the heating chamber of a heating device while overlapping in the direction normal to the plate surface of the workpiece, A first transport step involves transporting the heat storage material and the workpiece placed above the heat storage material from the heating chamber of the heating device to a lifting position outside the heating chamber, with the workpiece and the heat storage material overlapping in the direction normal to the surface of the workpiece. A second transport step involves lifting the workpiece, which is placed above the heat storage material at the aforementioned lifting position, upward using a transport device and transporting it to the press position of the press machine. The process includes a pressing step in which the workpiece is processed by the press machine, The heat storage material has a protrusion that extends upward, In the heating step, the workpiece is heated while placed on the protrusions of the heat storage material. A method for manufacturing a press-formed product, wherein in the first transport step, the workpiece is transported from the heating chamber of the heating device to the lifting position while placed on the protrusion of the heat storage material.

3. A method for manufacturing a press-formed article according to claim 1, In the heating step and the first conveying step, A method for manufacturing a press-formed product, wherein the heat storage material is placed on at least three second support columns extending upward from the tray body and is positioned to overlap the tray body vertically with a gap between them.

4. A method for manufacturing a press-formed article according to claim 1 or 3, A method for manufacturing a press-formed product, wherein the tray body has a shape that extends vertically in the vertical direction and includes a hollow portion that penetrates vertically.

5. A method for manufacturing a press-formed article according to any one of claims 1 to 4, In the heating step and the first conveying step, A method for manufacturing a press-formed product, wherein, when viewed from above, the outer edge of the heat storage material is located outside the outer edge of the workpiece.

6. A method for manufacturing a press-formed article according to any one of claims 1 to 5, The aforementioned workpiece is a plate with a difference in thickness, including a thick-walled portion and a thin-walled portion. A method for manufacturing a press-formed product, wherein in the heating step and the first conveying step, at least a portion of the thin-walled portion of the workpiece overlaps with the heat storage material when viewed from above.

7. A heating step in which a plate-shaped heat storage material and a plate-shaped workpiece placed above the heat storage material are heated in the heating chamber of a heating device while overlapping in the direction normal to the plate surface of the workpiece, A first transport step involves transporting the heat storage material and the workpiece placed above the heat storage material from the heating chamber of the heating device to a lifting position outside the heating chamber, with the workpiece and the heat storage material overlapping in the direction normal to the surface of the workpiece. A second transport step involves lifting the workpiece, which is placed above the heat storage material at the aforementioned lifting position, upward using a transport device and transporting it to the press position of the press machine. The process includes a pressing step in which the workpiece is processed by the press machine, The aforementioned workpiece is a plate with a difference in thickness, including a thick-walled portion and a thin-walled portion. The heat storage material is a plate with a difference in thickness, including a thick section and a thin section. A method for manufacturing a press-formed product, wherein in the heating step and the first conveying step, at least a portion of the thin-walled portion of the workpiece overlaps with the thick-walled portion of the heat storage material when viewed from above.

8. A heating step in which a plate-shaped heat storage material and a plate-shaped workpiece placed above the heat storage material are heated in the heating chamber of a heating device while overlapping in the direction normal to the plate surface of the workpiece, A first transport step involves transporting the heat storage material and the workpiece placed above the heat storage material from the heating chamber of the heating device to a lifting position outside the heating chamber, with the workpiece and the heat storage material overlapping in the direction normal to the surface of the workpiece. A second transport step involves lifting the workpiece, which is placed above the heat storage material at the aforementioned lifting position, upward using a transport device and transporting it to the press position of the press machine. The process includes a pressing step in which the workpiece is processed by the press machine, A method for manufacturing a press-formed product, wherein in the first transport step, the heat storage material and the workpiece are transported with their fronts in the transport direction covered by a shielding plate.

9. A method for manufacturing a press-formed article according to any one of claims 1 to 8, A method for manufacturing a press-formed product, wherein the minimum plate thickness t1 (mm) of the thinnest part of the workpiece and the minimum plate thickness t2 (mm) of the thinnest part of the heat storage material are related by the following formula. 0.8 ≤ t² / t¹ ≤ 20

10. A heating step in which a plate-shaped heat storage material and a plate-shaped workpiece placed above the heat storage material are heated in the heating chamber of a heating device while overlapping in the direction normal to the plate surface of the workpiece, A first transport step involves transporting the heat storage material and the workpiece placed above the heat storage material from the heating chamber of the heating device to a lifting position outside the heating chamber, with the workpiece and the heat storage material overlapping in the direction normal to the surface of the workpiece. A second transport step involves lifting the workpiece, which is placed above the heat storage material at the aforementioned lifting position, upward using a transport device and transporting it to the press position of the press machine. The process includes a pressing step in which the workpiece is processed by the press machine, A method for manufacturing a press-formed product, wherein, in the heating step and the first conveying step, the maximum vertical distance D (mm) between the heat storage material and the workpiece and the minimum plate thickness t1 (mm) of the thinnest part of the workpiece are related by the following formula. 0 < D ≤ 120t1

11. A method for manufacturing a press-formed article according to any one of claims 1 to 10, A method for manufacturing a press-formed product, wherein in the heating step and the first conveying step, the distance ΔW between the edge of the heat storage material as viewed from above and the edge of the workpiece as viewed from above is 10 to 200 mm.

12. A heating step in which a plate-shaped heat storage material and a plate-shaped workpiece placed above the heat storage material are heated in the heating chamber of a heating device while overlapping in the direction normal to the plate surface of the workpiece, A first transport step involves transporting the heat storage material and the workpiece placed above the heat storage material from the heating chamber of the heating device to a lifting position outside the heating chamber, with the workpiece and the heat storage material overlapping in the direction normal to the surface of the workpiece. A second transport step involves lifting the workpiece, which is placed above the heat storage material at the aforementioned lifting position, upward using a transport device and transporting it to the press position of the press machine. The process includes a pressing step in which the workpiece is processed by the press machine, A method for manufacturing a press-formed product, wherein, in the heating step and the first conveying step, a portion of the heat storage material extends upward on the outer edge of the workpiece when viewed from above.

13. A tray for heating and transporting workpieces, which are materials for hot press forming, The tray body and A plate-shaped heat storage material placed on the tray body, The tray body or the heat storage material comprises at least three groups of first support columns that extend upward to a position higher than the upper surface of the heat storage material, The first group of support columns is arranged such that, when viewed from above, the imaginary straight lines connecting the columns form at least one triangle, in a tray for heating and conveying hot press-formed materials.

14. A tray for heating and transporting workpieces, which are materials for hot press forming, The tray body and The tray body is equipped with a plate-shaped heat storage material placed on top of it, The heat storage material is a tray for heating and conveying hot press-formed materials, having a protrusion that projects upward and on which a plate-shaped workpiece can be placed.

15. A tray according to claim 13, The tray body is provided with at least three second support columns that extend upward and are positioned at a different location from the first support column group when viewed from above, The heat storage material is placed on the second group of support columns and positioned to overlap the tray body vertically with a gap between them.

16. A tray according to any one of claims 13 to 15, The tray body has a shape that extends vertically in the vertical direction and includes a hollow section that penetrates vertically.

17. A tray according to claim 13 or 15, A tray in which, when viewed from above, the first group of support columns is positioned inside the outer edge of the heat storage material placed on the tray body.

18. A tray according to any one of claims 13, 15, and 17, A tray further comprising a shielding plate that covers the height region from the upper surface of the heat storage material to the upper end of the tallest support column among the first group of support columns from a vertical direction.

19. Hot press manufacturing line, A tray according to any one of claims 13 to 18, A heating device for heating the workpiece placed on the tray, A transport path is provided between the heating device and the lifting position of the workpiece, and transports the tray from the heating device to the lifting position. A conveying device that supports the workpiece placed on the tray and lifts it upward at the aforementioned lifting position, A press machine having at least one pair of molds, A hot press manufacturing line comprising a transfer device for moving the transfer device between the lifting position and the pressing position between the at least pair of dies.

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