Forming method

Abstract

To improve heating efficiency of an end face of an open punching end.SOLUTION: A forming method includes: a punching step of punching a steel plate, and thereby forming an open punching end where a part of an end face of the steel plate is opened; and a heating step of arranging a heating coil in a non-contact state along the end face of the open punching end formed by the punching step so as to sandwich the end face of the open punching end, allowing AC current to flow through the heating coil and generating an induction electromotive force in the steel plate, and thereby heating the end face of the open punching end. A current direction of the heating coil arranged on one side of the end face of the open punching end is opposite to a current direction of the heating coil arranged on the other side of the end face of the open punching end.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a forming method for forming a steel sheet. [Background technology]

[0002] One of the problems in press forming of high tensile steel is stretch flange cracking, which occurs due to residual strain on the shear end surface, such as the punched end, during the punching process.

[0003] As a method for reducing this residual distortion, a forming method has been proposed in which a loop-shaped heating coil is positioned along and opposed to the end face of the end punched out by the punching process in a non-contact state, and an alternating current is passed through the heating coil to generate an induced electromotive force in the steel sheet, thereby heating the end face (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent application 2021-003691 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the end face of the punched end of the steel sheet, which is partially open, is heated by the above-mentioned loop-shaped heating coil, a current flows at the end face, but the current leaves the end face, disperses inside the steel sheet, and flows in the opposite direction to form a loop, which may reduce the current density at the end face and the heating efficiency.

[0006] The present invention has been made to solve the above problems, and has as its main object to provide a forming method capable of improving the heating efficiency of the end face of the open punched end. [Means for solving the problem]

[0007] In order to achieve the above object, one aspect of the present invention is to A punching process of punching a steel plate to form an open punched end in which a part of an end surface of the steel plate is opened; a heating step of disposing a heating coil along an end surface of the open punched end produced by the punching step in a non-contact state so as to sandwich the end surface of the open punched end, and passing an alternating current through the heating coil to generate an induced electromotive force in the steel sheet, thereby heating the end surface of the open punched end; Including, the current direction of the heating coil arranged on one side of the end face of the open punched end is opposite to the current direction of the heating coil arranged on the other side of the end face of the open punched end; Molding method It is. In this embodiment, In the heating step, A heating coil on one side of the end face of the open punched end is disposed on the open side; The heating coil on the other side of the end face of the open punched end may be disposed on the steel plate side. In this embodiment, In the heating step, The heating coil on one side is disposed on an upper side, and the heating coil on the other side is disposed on a lower side, 1 is a cross-sectional view of the open punched end, upper and lower heating coils; When viewed from the top-bottom direction, a cross section of the upper heating coil may not overlap a cross section of the open punched end, and a cross section of the lower heating coil may overlap a cross section of the open punched end. In this embodiment, The upper heating coil is disposed within an upper appropriate range of a rectangular shape having a length of a and a width of b, The lower heating coil is disposed within a lower appropriate range of a rectangular shape having a length c and a width d. The upper appropriate range is set to start from an upper corner of the end surface of the open punched end, The lower appropriate range is set to a position that is a predetermined distance α away from a lower corner of the end surface of the open punched end, The upper and lower heating coils may have a diameter D that satisfies the following relationship: 0≦a≦1.5×D 0≦b≦1.5×D α≦c≦1.2×D 0≦d≦1.5×D, In this embodiment, The method further includes forming a stretch flange on the open punched end, In the forming process, the distance between the central axis of a heating coil arranged on the side of the steel plate being stretched and the end face of the open punched end may be closer than the distance between the central axis of a heating coil arranged on the opposite side to the side being stretched and the end face of the open punched end. In this embodiment, In the heating step, the steel plate punched in the punching step is placed in a heating jig and then heated by the heating coil, The heating jig has a positioning guide on which the steel plate punched in the punching process is placed and which positions the steel plate at a predetermined position, and the heating coil which heats an end face of an open punched end of the steel plate positioned by the positioning guide, When the steel plate punched in the punching step is placed on the positioning guide, the heating coil located on the front side may be offset to the outside of the steel plate. In this embodiment, The method further includes forming a stretch flange on the open punched end, In the heating step, the heating coil may heat a curved flange forming portion of a frame member made of high tensile steel of a vehicle formed in the forming step. In this embodiment, The heating step may be carried out during any step in the press. In this embodiment, The method further includes a forming step of forming a stretch flange on the punched end, The heating step may be performed in an idling step in which a conveying pitch is adjusted when the steel plate is conveyed from the punching step to the forming step. In this embodiment, In the press machine, the steel plate formed product is continuously transported by a gripping unit, and at least the punching process and the idling process are continuously performed at a predetermined transport pitch, The idling step may be replaced with the heating step by disposing a heating jig including the heating coil at a position corresponding to the idling step. Effect of the Invention

[0008] According to the present invention, it is possible to provide a forming method capable of improving the heating efficiency of the end face of the open punched end. [Brief description of the drawings]

[0009] [Figure 1] 1A to 1C are schematic diagrams illustrating steps of a molding method according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram illustrating a heating step. [Diagram 3] FIG. 2 is a perspective view showing a heating coil according to the embodiment. [Figure 4] FIG. 2 is a top view of the heating coil according to the embodiment; [Diagram 5] FIG. 2 is a cross-sectional view taken vertically through a heating coil disposed at an open punched end. [Figure 6] FIG. 13 illustrates the magnetic field strength at the open punched end. [Figure 7] FIG. 13 shows the current density at the open punched end. [Figure 8] FIG. 13 illustrates proper placement of upper and lower heating coils. [Figure 9] FIG. 13 is a diagram showing the state in which the open punched end of the steel plate is placed against the heating coil of the heating jig. [Figure 10] FIG. 13 is a diagram showing a configuration in which two heating coils are arranged on the upper side and two heating coils are arranged on the lower side. [Figure 11] FIG. 13 is a diagram showing a configuration in which the upper coil and the lower coil overlap when viewed from above. [Figure 12]FIG. 11 is a diagram showing the results of heating using a conventional heating coil and the heating coil according to the present embodiment. [Figure 13] FIG. 13 is a diagram showing the relationship between the upper and lower heating coils and the temperature distribution, which is an experimental result. [Figure 14] FIG. 2 is a diagram showing a molded product including a stretch flange forming portion. [Figure 15] FIG. 1 is a diagram showing a specific example of a molded product of a FR lower arm. [Figure 16] FIG. 1 is a diagram showing a specific example of a molded part for an A-pillar lower. [Figure 17] FIG. 1 is a diagram showing a specific example of a molded product of a B-pillar outer lower. [Figure 18] FIG. 1 is a diagram showing an example of a heating jig. [Figure 19] 1 is a diagram comparing steps of a molding method according to the present embodiment with steps of a conventional molding method. [Figure 20] FIG. 2 is a diagram showing an example of a process in a press machine. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention will be described below through embodiments of the invention, but the invention according to the claims is not limited to the following embodiments. Furthermore, not all of the configurations described in the embodiments are necessarily essential as means for solving the problems.

[0011] EMBODIMENT 1 1 is a schematic diagram showing the steps of the forming method according to the present embodiment. In the forming method described below, a steel sheet 100 as a workpiece is formed with an open punched end 101, part of whose end face is open, and the periphery of the open punched end 101 is deformed to form a stretch flange 102.

[0012] The forming method according to this embodiment includes, for example, as shown in FIG. 1 , a punching process of forming an open punched end 101 by punching a steel plate, a heating process of heating the open punched end 101, a cooling process of cooling the heat generated by the heating process, and a forming process of forming a stretch flange 102 from the open punched end 101.

[0013] The punching process is a process in which a steel sheet 100 fixed to a punching die (not shown) is punched out by a punch (not shown). The heating process is a process in which the open punched end 101 formed in the punching process is heated, as will be described in detail later.

[0014] In the heating step, as shown in Fig. 2, the punched steel sheet 100 is placed on a positioning guide 3 of a heating jig 200. Then, induction heating is performed on the open punched end 101 of the steel sheet 100 by a heating coil 2. In this embodiment, for example, it is preferable to perform high-frequency induction heating in which a high-frequency alternating current is passed through the heating coil 2 to generate an induced electromotive force in the steel sheet 100. After being heated by the heating coil 2, the steel sheet 100 is removed from the heating jig 200.

[0015] The heating temperature by the heating coil 2 is adjusted so that the punched end 101 is at least 200°C and less than the Ac1 point, for example. Heating within this temperature range allows for proper removal of residual strain. In particular, if the steel sheet 100 is heated to the Ac1 point or higher, austenitic transformation occurs in the steel sheet 100, which softens and reduces strength when air-cooled, and increases hardness and reduces formability in the forming process when rapidly cooled by running water, etc., so it is preferable to keep the temperature below the Ac1 point.

[0016] As shown in Fig. 1, the cooling step is a step of cooling the open punched end 101 heated in the heating step. Specifically, the steel sheet 100 is left in a room temperature environment for a certain period of time. Note that in the forming method according to this embodiment, the cooling step may be omitted. In this case, the forming step described below is carried out after the heating step. The forming step (burring step) is a step of plastically deforming the open punched end 101 using a flange die or the like to form a stretch flange 102.

[0017] Residual strain generated in the peripheral portion of the open punched end 101 by the punching process is removed in the heating process. After cooling, the forming process is introduced. This makes it possible to reduce damage caused by a flange die or the like compared to performing the process on a steel sheet 100 in a heated state. Furthermore, in this embodiment, as will be described later, the open punched end 101 can be locally heated, so that residual strain can be effectively removed while heating efficiency is also improved.

[0018] Conventionally, when the end face of an open punched end of a steel sheet is heated by a loop-shaped heating coil, a current flows at the end face, but the current leaves the end face, disperses inside the steel sheet, and flows in the opposite direction to form a loop, which may reduce the current density at the end face and reduce the heating efficiency.

[0019] Fig. 3 is a perspective view showing the heating coil according to the present embodiment, and Fig. 4 is a top view showing the heating coil according to the present embodiment.

[0020] In response to the above problem, in the heating step of the forming method according to the present embodiment, for example, as shown in Fig. 3 and Fig. 4, a heating coil 2 is arranged along an end face 103 of an open punched end 101 produced by the punching step in a non-contact state and so as to sandwich the end face 103 of the open punched end 101. Then, an alternating current is passed through the heating coil 2 to generate an induced electromotive force in the steel sheet 100, thereby heating the end face 103 of the open punched end 101. Furthermore, the current direction of the heating coil 21 arranged on one side (upper side) of the end face 103 of the open punched end 101 is opposite to the current direction of the heating coil 22 arranged on the other side (lower side) of the end face 103 of the open punched end 101.

[0021] This allows a current loop to be formed along the end surface 103 of the open punched end 101, and the current to be concentrated at this end surface 103. This allows the current density at the end surface 103 of the open punched end 101 to be increased, and the heating efficiency of this end surface 103 to be improved.

[0022] 5 is a vertical cross-sectional view of the heating coils arranged at the open punched end. In the heating process, as shown in FIG. 5, the heating coil 21 above the end face 103 of the open punched end 101 is arranged on the open side, and the heating coil 22 below the end face 103 of the open punched end 101 is arranged on the steel sheet side.

[0023] As a result, the open punched end 101 is sandwiched diagonally between the upper heating coil 21 and the lower heating coil 22, and is sandwiched in a magnetic field diagonally, as shown in Fig. 6. Therefore, stable heating can be performed even if the upper and lower heating coils 21, 22 are slightly displaced from their set positions. In addition, as shown in Fig. 7, a strong current flows starting from the upper corner 104 of the end face 103 of the open punched end 101, and the heating efficiency of the end face 103 of the open punched end 101 can be further improved.

[0024] In general, when the end face of the open punched end is sandwiched between upper and lower heating coils and heated, the temperature peak occurs directly below the upper and lower heating coils. Therefore, if the relative positional relationship between the upper and lower heating coils and the end face of the open punched end changes, the position of the temperature peak also changes. Therefore, in order to heat the end face of the open punched end in a concentrated manner, it is particularly important to manage the relative positional relationship.

[0025] In contrast, in this embodiment, as described above, the open punched end 101 is sandwiched in an oblique direction between the upper heating coil 21 and the lower heating coil 22. As a result, the temperature peak occurs starting from the upper corner 104 of the end face 103 of the open punched end 101, so that the management of the relative positional relationship between the upper and lower heating coils 21, 22 and the end face 103 of the open punched end 101 becomes insensitive. Therefore, even if the relative positional relationship is slightly changed from the set relationship, the end face 103 of the open punched end 101 can be heated intensively.

[0026] Next, a detailed description will be given of the proper relative positional relationship between the upper and lower heating coils 21, 22 and the end surface 103 of the open punched end 101. Figure 8 is a diagram showing the proper arrangement of the upper and lower heating coils.

[0027] 8, in a cross-sectional view of the open punched end 101 and the upper and lower heating coils 21, 22, it is preferable that, when viewed from the top-bottom direction, the cross section of the upper heating coil 21 does not overlap with the cross section of the open punched end 101, and the cross section of the lower heating coil 22 overlaps with the cross section of the open punched end 101. As a result, the open punched end 101 is sandwiched obliquely between the upper heating coil 21 and the lower heating coil 22, and stable heating can be performed even if the upper and lower heating coils 21, 22 are slightly deviated from their set positions.

[0028] The upper heating coil 21 is preferably disposed within a rectangular upper appropriate range X1 having a length a and a width b, and the lower heating coil 22 is preferably disposed within a rectangular lower appropriate range X2 having a length c and a width d.

[0029] The upper appropriate range X1 is set upward and to the left from the upper corner 104 of the end face 103 of the open punched end 101. The lower appropriate range X2 is set downward and to the right from a position a predetermined distance α away from the lower corner 105 of the end face 103 of the open punched end 101.

[0030] It is preferable that the diameter of the upper and lower heating coils 21, 22 is D and that the following relationship is satisfied: The predetermined distance α is set in consideration of processing errors of the open punched end 101, and is set to, for example, about 0.5 mm. 0≦a≦1.5×D 0≦b≦1.5×D α≦c≦1.2×D 0≦d≦1.5×D

[0031] As described above, by arranging the upper heating coil 21 within the upper appropriate range X1 and the lower heating coil 22 within the lower appropriate range X2 and heating the end surface 103 of the open punched end 101, high heating efficiency can be maintained.

[0032] The upper heating coil 21 is more preferably disposed closest to the end face 103 of the open punched end 101 within the upper appropriate range X1, taking into consideration the processing error of the open punched end 101. Similarly, the lower heating coil 22 is more preferably disposed closest to the end face 103 of the open punched end 101 within the lower appropriate range X2, taking into consideration the processing error of the open punched end 101. This can further increase the heating efficiency.

[0033] Furthermore, when the punched steel sheet 100 is placed on the heating jig 200 in the punching process, it is preferable that the upper heating coil 21 is offset to the outside of the steel sheet 100 as shown in Fig. 5. This allows the steel sheet 100 to be simply lowered straight down when the open punched end 101 of the steel sheet 100 is placed against the heating coil 2 of the heating jig 200 in the heating process, as shown in Fig. 9, for example, and therefore improves the ease of installation of the steel sheet 100.

[0034] In the above embodiment, the distance between the central axis of the heating coil 2 arranged on the side of the steel plate 100 being stretched during the forming process and the end face 103 of the open punched end 101 may be closer than the distance between the central axis of the heating coil 2 arranged on the side opposite the side of the steel plate 100 being stretched and the end face 103 of the open punched end 101.

[0035] As a result, by bringing the heating coil 2 arranged on the side of the steel plate 100 being stretched in the forming process closer to the end face 103 of the open punched end 101, the portion of the steel plate 100 being stretched can be heated more to a greater extent, thereby improving workability.

[0036] In addition, in the above embodiment, as shown in FIG. 3, one heating coil 21 is arranged on the upper side and one heating coil 22 is arranged on the lower side, and the upper and lower heating coils 21, 22 form a loop, but this is not limited to this.

[0037] For example, as shown in FIG. 10, two heating coils 23 may be arranged on the upper side and two heating coils 24 may be arranged on the lower side, with the upper and lower heating coils 23, 24 forming a loop.

[0038] This increases the coil inductance and the heating efficiency. Also, the range of influence of the magnetic field by the upper and lower heating coils 23, 24 is wider, so that the robustness of the relative positional relationship between the upper and lower heating coils 23, 24 and the end surface 103 of the open punched end 101 is improved, enabling more stable heating.

[0039] The upper view of Fig. 10 is a perspective view of the upper and lower heating coils arranged at the open punched end 101, as viewed from an oblique direction. The lower view of Fig. 10 is a perspective view of the upper and lower heating coils, as viewed from an oblique direction.

[0040] As shown in Fig. 10, the two upper heating coils 23 and the two lower heating coils 24 are arranged along the end face 103 of the open punched end 101 in a non-contact state and so as to sandwich the end face 103 of the open punched end 101. The two upper heating coils 23 are arranged on the open side, and the two lower heating coils 24 are arranged on the steel sheet side. The direction of current flow in the two upper heating coils 23 is opposite to the direction of current flow in the two lower heating coils 24.

[0041] As a result, a current loop is formed along the end surface 103 of the open punched end 101 by the two upper heating coils 23 and the two lower heating coils 24, and the current can be concentrated on this end surface 103. As a result, the current density on the end surface 103 of the open punched end 101 can be increased, and the heating efficiency of this end surface 103 can be improved.

[0042] Furthermore, in the above embodiment, as shown in Fig. 4, the upper heating coil 21 is disposed on the open side, the lower heating coil 22 is disposed on the steel plate side, and the upper heating coil 21 and the lower heating coil 22 are offset when viewed from above. However, the present invention is not limited to this. For example, as shown in Fig. 11, the upper heating coil 21 and the lower heating coil 22 may be overlapped without being offset when viewed from above.

[0043] The upper diagram of Fig. 11 is a diagram of the upper and lower heating coils 21, 22 arranged at the open punched end 101 as viewed from above. The lower diagram of Fig. 11 is a perspective view of the upper and lower heating coils 21, 22 as viewed from an oblique direction. As shown in Fig. 11, the upper and lower heating coils 21, 22 are arranged along the end face 103 of the open punched end 101 in a non-contact state and so as to sandwich the end face 103 of the open punched end 101.

[0044] This allows a current loop to be formed along the end surface 103 of the open punched end 101, and the current to be concentrated at this end surface 103. This allows the current density at the end surface 103 of the open punched end 101 to be increased, and the heating efficiency of this end surface 103 to be improved.

[0045] Next, the end surface 103 of the open punched end 101 was heated by the conventional heating coil and the heating coil 2 according to this embodiment, respectively, and the heating results were compared. Fig. 12 is a diagram showing the heating results when heating was performed by the conventional heating coil and the heating coil according to this embodiment. In this experiment, the temperature distribution, magnetic field strength distribution, and current density distribution and vector of the open punched end 101 of the steel sheet 100 when an AC current with a frequency of 340 kHz was passed through the heating coil 2 at a constant voltage of 200 V for 1 second were analyzed.

[0046] In Figure 12, (a) the left side shows experimental results for a conventional heating coil configuration having a shape that follows the end surface 103 of the open punched end 101, (b) the center shows a configuration in which the upper heating coil 21 and the lower heating coil 22 of this embodiment are not offset when viewed from above, and (c) the right side shows a configuration in which the upper heating coil 21 and the lower heating coil 22 of this embodiment are offset when viewed from above.

[0047] In addition, in FIG. 12, the second row shows the temperature distribution, the row below that shows the magnetic field strength distribution, and the row below that shows the current density distribution and vectors.

[0048] As shown in the temperature distribution in Figure 12, the configurations of this embodiment (b) and (c) show a significant increase in temperature of the end face 103 of the open punched end 101 compared to the conventional configuration (a), confirming that the heating efficiency is good.

[0049] Furthermore, compared to the configuration (b) of this embodiment without offset, the configuration (c) of this embodiment with offset is subjected to a stronger magnetic field originating from the upper corner 104 of the end face 103 of the open punched end 101, and therefore it can be confirmed that there is a greater temperature rise originating from the upper corner 104.

[0050] When the end face 103 of the open punched end 101 is sandwiched between the upper and lower heating coils 21 and 22 for heating, the temperature peaks directly below the upper and lower heating coils 21 and 22 .

[0051] For this reason, (b) in the case of the non-offset configuration of this embodiment, it is necessary to position the upper and lower heating coils 21, 22 with pinpoint accuracy relative to the end face 103 of the open punched end 101, and to accurately align the relative positional relationship between the upper and lower heating coils 21, 22 and the end face 103 of the open punched end 101.

[0052] On the other hand, in the case of the offset configuration of the present embodiment (c), the open punched end 101 is sandwiched diagonally between the upper heating coil 21 and the lower heating coil 22. As a result, the upper corner 104 of the end face 103 of the open punched end 101 becomes the starting point and becomes the temperature peak, so that the management of the relative positional relationship between the upper and lower heating coils 21, 22 and the end face 103 of the open punched end 101 becomes insensitive.

[0053] Therefore, from the viewpoint of such robustness, (c) the configuration with offset of this embodiment is considered to be superior to (b) the configuration without offset of this embodiment.

[0054] Furthermore, as shown by the current density distribution and vectors in FIG. 12, (a) in the case of the conventional configuration, the induced current that flows through the end face 103 of the open punched end 101 along the heating coil leaves the end face 103, disperses inside the steel sheet, and flows in the opposite direction to form a loop, resulting in a decrease in heating efficiency.

[0055] On the other hand, in the case of the configurations of this embodiment (b) and (c), the induced current flows concentratedly through the end face 103 of the open punched end 101 directly below the heating coils 21, 22, so that the temperature peak almost coincides with the end face 103 of the open punched end 101 to be heated, and it can be seen that the heating efficiency is high.

[0056] In particular, in the case of the configuration of this embodiment (c), an induced current flows from the upper corner 104 of the open punched end 101 and the current flows on the opposite side of the plate thickness, so that a temperature peak is formed from this upper corner 104, and it can be seen that the end surface 103 of the open punched end 101 can be heated more intensively.

[0057] Next, an experiment was conducted to observe the change in temperature distribution by moving the upper and lower heating coils 21, 22 while heating for (b) a configuration without offset of this embodiment and (c) a configuration with offset of this embodiment.

[0058] In this experiment, (b) for the configuration without offset of this embodiment, the upper and lower heating coils were moved from the reference position to the outside of the steel plate, and Inside We analyzed the change in temperature distribution when moving the heater to the side and when moving the heater to the side.

[0059] Similarly, (c) for the configuration with offset of this embodiment, the change in temperature distribution was analyzed when the upper and lower heating coils 21, 22 were moved from the reference position to the outside of the steel plate 100 and when they were moved to the below of the steel plate 100.

[0060] Fig. 13 is a diagram showing the relationship between the upper and lower heating coils and the temperature distribution, which is the result of the above experiment. In Fig. 13, the left side shows (b) the change in temperature distribution in the configuration without offset of this embodiment, and the right side shows (b) the change in temperature distribution in the configuration with offset of this embodiment.

[0061] 13, (b) in the configuration without offset of this embodiment, when the upper and lower heating coils 21, 22 are moved from the reference position to the outside or inside of the steel sheet 100, the relative positional relationship between the upper and lower heating coils 21, 22 and the end face 103 of the open punched end 101 changes, and the position of the temperature peak also changes. Therefore, in order to intensively heat the end face 103 of the open punched end 101, it is particularly important to manage the relative positional relationship between the upper and lower heating coils 21, 22 and the end face 103 of the open punched end 101.

[0062] On the other hand, (c) in the configuration with offset of this embodiment, when the upper and lower heating coils 21, 22 are moved from the reference position to the outside or below the steel sheet 100, the relative positional relationship between the upper and lower heating coils 21, 22 and the end face 103 of the open punched end 101 changes, but it is found that the position of the temperature peak does not change very much. Therefore, even if the relative positional relationship between the upper and lower heating coils 21, 22 and the end face 103 of the open punched end 101 changes slightly, the end face 103 of the open punched end 101 can be heated in a concentrated manner, so that heating can be performed more stably.

[0063] Next, an example of a molded product produced by the molding method according to the present embodiment will be described. The molded product produced by the molding method according to the present embodiment is, for example, a molded product including a stretch flange forming portion, such as a flange forming portion where a curvature flange is erected, as shown in Fig. 14, and is a molded product including a forming portion where the line length of the end face 103 before and after processing is significantly enlarged.

[0064] In the above-mentioned heating step, it is preferable that the heating coil 2 heats, for example, a curved flange forming portion of a high tensile steel frame member of a vehicle formed in the forming step. This makes it possible to process the forming portion in which the line length of the end face is significantly enlarged before and after heating.

[0065] A specific molded product is assumed to be a FR lower arm used in a vehicle suspension, as shown in Fig. 15. In Fig. 15, a flange molding portion such as a crotch portion surrounded by a dotted line may be molded by the molding method according to this embodiment.

[0066] In the forming process, for example, a flange die or the like is pressed against the open punched end 101 from which the unnecessary portion has been cut off to form a stretch flange. As described below, the flange forming portions of the A-pillar lower and the B-pillar outer lower are formed in this manner.

[0067] As the molded product, an A-pillar lower used for a window pillar of a vehicle is assumed as shown in Fig. 16. In Fig. 16, a flange molding portion such as a corner portion surrounded by a dotted line may be molded by the molding method according to this embodiment.

[0068] As an example of the other molded product, a B-pillar outer lower of a vehicle is assumed, as shown in Fig. 17. In Fig. 17, a flange molding portion such as a corner portion surrounded by a dotted line may be molded by the molding method according to this embodiment.

[0069] As described above, the forming method according to this embodiment includes a punching process in which a steel sheet 100 is punched to form an open punched end 101 in which a part of an end surface 103 of the steel sheet 100 is opened, and a heating process in which a heating coil 2 is arranged along the end surface 103 of the open punched end 101 produced in the punching process in a non-contact state so as to sandwich the end surface 103 of the open punched end 101, and an alternating current is passed through the heating coil 2 to generate an induced electromotive force in the steel sheet 100, thereby heating the end surface 103 of the open punched end 101. The current direction of the heating coil 21 arranged on one side of the end surface 103 of the open punched end 101 is opposite to the current direction of the heating coil 22 arranged on the other side of the end surface 103 of the open punched end 101.

[0070] This allows a current loop to be formed along the end surface 103 of the open punched end 101, and the current to be concentrated at this end surface 103. This allows the current density at the end surface 103 of the open punched end 101 to be increased, and the heating efficiency of this end surface 103 to be improved.

[0071] EMBODIMENT 2 Fig. 18 is a diagram showing an example of a heating jig. The left side of Fig. 18 shows a state before the steel plate molded product X is placed in the heating jig 200, and the right side shows a state after the steel plate molded product X is placed in the heating jig 200. In this embodiment, the steel plate molded product punched out in the punching step is placed in the heating jig 200 in the heating step, and heated.

[0072] 18, the heating jig 200 has a heating coil 2 for heating the open punched end 101 of the steel plate molded product X, a positioning guide 3 for positioning the steel plate molded product X at a predetermined position, and a base part 4. The heating coil 2 is connected to an AC power source 5 for supplying power to the heating coil 2.

[0073] The shape and arrangement of the positioning guide 3 are set so that the position of the steel plate molded product X is automatically set by simply placing the steel plate molded product X on the positioning guide 3. The heating coil 2 and the positioning guide 3 are arranged on the base part 4 in accordance with the shape of the steel plate molded product X and the position of the heating portion.

[0074] The position, number, and shape of the heating coil 2 are not limited to the example shown in Fig. 18, and can be set arbitrarily. Similarly, the position, number, and shape of the positioning guide 3 are not limited to the example shown in Fig. 18, and can be set arbitrarily.

[0075] By using the heating jig 200 according to this embodiment, it is no longer necessary to heat the steel plate molded product X from above and below while holding it, as in the conventional method, and the steel plate molded product X can be simply placed on the heating jig 200 and heated.

[0076] The heating step according to this embodiment may be performed in an idling step between the punching step and the forming step, as shown in Fig. 19. The idling step is a step for adjusting the conveying pitch when conveying the steel plate formed product X from the punching step to the forming step, and is a waiting step in which no processing is performed.

[0077] This makes it possible to efficiently heat the steel plate molded product X by utilizing the idling process in which the punched steel plate molded product X was kept waiting after the punching process and before the forming process in the past. Therefore, there is no need to introduce an additional heating process, and productivity is improved.

[0078] Furthermore, according to this embodiment, by simply arranging the heating jig 200 in an idling process in a normal press machine, the idling process can be converted into a heating process, so that the number of processes does not increase.

[0079] Fig. 20 is a schematic diagram showing an example of processes in a press machine. In a press machine 500, for example, a forming process, a punching process, an idling process, an idling process, and a punching process shown in the upper part of Fig. 20 are performed successively at a predetermined conveying pitch while a steel sheet formed product X is continuously conveyed by fingers (gripping parts) 501 shown in the lower part of Fig. 20. Therefore, the idling process in the press machine 500 can be easily replaced with a heating process by simply placing a heating jig 200 at a position corresponding to the idling process.

[0080] The heating step may be performed during any step in the press machine 500, such as during a molding step or punching step, as long as the heating jig 200 can be placed there.

[0081] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0082] 2 heating coil, 3 positioning guide, 4 base portion, 5 AC power source, 21 heating coil, 22 heating coil, 23 heating coil, 24 heating coil, 100 steel plate, 101 open punched end, 102 stretch flange, 103 end face, 104 upper corner, 105 lower corner, 200 heating jig, 500 press machine

Claims

1. A punching process of punching a steel plate to form an open punched end in which a part of an end surface of the steel plate is opened; a heating step of heating the end face of the open punched end by passing an alternating current through a heating coil, the heating coil being formed by deforming a straight coil wire so as to extend along the shape of the end face of the open punched end, the one coil wire being arranged on one side of the end face of the open punched end and the other coil wire being arranged on the other side of the end face of the open punched end so as to sandwich the end face of the open punched end in a non-contact state with the end face of the open punched end, thereby generating an induced electromotive force in the steel sheet; After the heating step, a forming step of forming a stretch flange on the punched end; Including, a current direction of one coil wire of the heating coil arranged on one side of the end face of the open punched end is opposite to a current direction of the other coil wire of the heating coil arranged on the other side of the end face of the open punched end; In the heating step, 1 is a cross-sectional view of the open punched end, one coil of the heating wire, and the other coil of the heating wire; One of the one and the other coil wires is disposed on the open side of the end face of the punched end, so that, when viewed from above and below, a cross section of the one coil wire does not overlap a cross section of the open punched end, and a cross section of the other coil wire overlaps a cross section of the open punched end. Molding processing method.

2. The molding method according to claim 1, In the heating step, one coil wire is disposed on the upper side and the other coil wire is disposed on the lower side; 1 is a cross-sectional view of the open punched end, upper and lower heating coils; When viewed from the top-bottom direction, a cross section of the upper coil wire does not overlap a cross section of the open punched end, and a cross section of the lower coil wire overlaps a cross section of the open punched end. Molding processing method.

3. The molding method according to claim 2, One of the coil wires on the upper side of the heating coil is disposed within an upper appropriate range of a rectangular shape having a length a and a width b, The other coil wire below the heating coil is disposed within a lower appropriate range of a rectangular shape having a length c and a width d. The upper appropriate range is set to start from an upper corner of the end surface of the open punched end, The lower appropriate range is set to a position that is a predetermined distance α away from a lower corner of the end surface of the open punched end, The diameter of the coil wire of one of the heating coils and the other of the heating coils is D, and the following relationship is satisfied: 0≦a≦1.5×D 0≦b≦1.5×D α≦c≦1.2×D 0≦d≦1.5×D, Molding processing method.

4. The molding method according to claim 1 or 2, In the forming process, the distance between the central axis of the coil wire of the heating coil arranged on the side of the steel sheet to be stretched and the end face of the open punched end is shorter than the distance between the central axis of the coil wire of the heating coil arranged on the opposite side to the side to be stretched and the end face of the open punched end. Molding processing method.

5. The molding method according to claim 1 or 2, In the heating step, the steel plate punched in the punching step is placed in a heating jig and then heated by the heating coil, The heating jig has a positioning guide on which the steel plate punched in the punching process is placed and which positions the steel plate at a predetermined position, and the heating coil which heats an end face of the open punched end of the steel plate positioned by the positioning guide, When the steel plate punched in the punching process is placed on the positioning guide, the coil wire of the heating coil located on the front side is offset to the outside of the steel plate. Molding processing method.

6. The molding method according to claim 1 or 2, In the heating step, the heating coil heats a curved flange forming portion of a frame member made of a high tensile steel of a vehicle formed in the forming step. Molding processing method.

7. The molding method according to claim 4, The heating step is carried out during any step in the press; Molding processing method.

8. The molding method according to claim 5, The heating process is carried out in an idling process for adjusting a conveying pitch when conveying the steel plate from the punching process to the forming process. Molding processing method.

9. The molding method according to claim 8, In the press machine, the steel plate formed product is continuously transported by a gripping unit, and at least the punching step and the idling step are continuously performed at a predetermined transport pitch, The heating jig is disposed at a position corresponding to the idling step, thereby replacing the idling step with the heating step. Molding processing method.

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