Two-pass bending die

Abstract

The invention relates to the technical field of metal forging, and particularly discloses a two-pass bending die which comprises an upper fixing plate and a lower fixing plate, a one-pass bending upper die and a two-pass bending upper die are arranged on the upper fixing plate, and a one-pass bending lower die and a two-pass bending lower die are arranged on the lower fixing plate. A primary blank cavity is formed in the primary bending lower die and is used for carrying out primary bending forming on two end parts close to a blank; and a secondary blank cavity is arranged on the secondary bending lower die and is used for carrying out secondary bending forming on the middle part of the blank. According to the bending die, the die for two-pass bending is arranged to split the part, needing to be bent, of the forge piece, the bending die for one-pass bending and the bending die for two-pass bending are designed, and bending of a bar with multiple bending sections and a large-angle bending long supporting arm can be achieved. By means of the two-pass bending mode, reciprocating alternating stress borne by the blank can be reduced in the distributed bending process, and the service life of the die is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of metal forging and forming, in particular to a two-pass bending die. Background Art

[0002] In the process of metal forging, products with complex structures usually require corresponding blank making processes, such as drawing, upsetting, bending, flattening, etc. The blank making process is to maximize the shape and structure of the original material before forging to be similar to the shape and structure of the product, so as to improve material utilization and improve the fullness and success rate of the forging process.

[0003] Forging of aluminum alloy wishbone parts for automobile chassis, especially forgings with multiple bends and deep U-shaped structures, a bending process is usually required during the billet making process.

[0004] Because for aluminum alloy fork arms, the original forging materials are mostly aluminum alloy extruded round bars, and due to the particularity of aluminum alloy materials, there may be some problems in performing deep U-shaped arm bending on ordinary bending machines. For example, deformation is prone to occur during the bending process when multiple bends and deep U-shaped structures are performed at the same time. Because the overall required bending angle is large, and during the bending process, the stress is mainly concentrated at the bending point, which may cause local excessive deformation or cracks. The main body deformation during the bending process is not uniform, which can easily lead to excessive deviation of the product size after bending.

[0005] Although the existing bending machine molds can meet the bending requirements, they are usually achieved by selecting special bending equipment and designing special bending molds. For example, local support auxiliary devices are added to the openings on both sides of the lower mold, usually a pair of rollers or bearings. The rollers or bearings can convert the friction between the blank and the mold from sliding friction to rolling friction, reducing friction and stress during the deformation process, and facilitating the bending of forgings with multiple bending sections and deep U-shaped arms.

[0006] At the same time, because auxiliary devices such as rollers or bearings are added to the mold, the average life of the entire mold depends on the life of the auxiliary devices or the connection mechanism between the auxiliary devices and the mold, which greatly reduces the life of the entire mold. Especially for the metal forging industry, the metal surface temperature is usually four or five hundred degrees during the bending process, and auxiliary mechanisms such as rollers or bearings are subjected to reciprocating alternating stress, and fatigue life will also affect the use of the entire mold.

[0007] In summary, the existing bending machines have poor bending effects and are prone to deformation when performing bending with multiple bending sections and deep U-shaped structures. At the same time, the molds that select special bending equipment and design special bending molds to add local support devices such as rollers or bearings have a low mold life when performing bending forming. Summary of the invention

[0008] The purpose of the present invention is to provide a two-pass bending die to solve the technical problems in the prior art that the existing bending machines have poor bending effects and are prone to deformation when performing bending with multiple bending sections and deep U-shaped structures, and at the same time, the molds with special bending equipment and special bending molds with added local support devices such as rollers or bearings have a low mold life when performing bending forming.

[0009] In order to solve the above technical problems, the present invention specifically provides the following technical solutions:

[0010] A two-pass bending die comprises an upper fixed plate and a lower fixed plate, wherein a first-pass bending upper die and a second-pass bending upper die are arranged side by side on the lower surface of the upper fixed plate, and a first-pass bending lower die and a second-pass bending lower die are arranged side by side on the upper surface of the lower fixed plate;

[0011] A primary blank cavity is provided on the one-stage bending lower die, and the primary blank cavity is used to perform a primary bending forming on the two end portions of the blank when the one-stage bending upper die and the primary blank cavity are clamped;

[0012] A secondary blank cavity is arranged on the second-pass bending lower die, and the secondary blank cavity is used for performing secondary bending forming on the middle of the blank when the second-pass bending upper die and the secondary blank cavity are clamped.

[0013] As a preferred solution of the present invention, the primary blank cavity comprises a first intermediate cavity, primary bending cavities are arranged at both ends of the first intermediate cavity, and the primary bending cavities located at both ends of the first intermediate cavity are centrally symmetrical;

[0014] Wherein, when the primary bending upper die and the primary blank cavity are molded together, the primary bending cavity performs a primary bending on the two end portions close to the blank;

[0015] The first intermediate cavity is matched with and symmetrical to the bottom surface of the one-stage bending upper die.

[0016] As a preferred solution of the present invention, the end of the primary bending cavity away from the first intermediate cavity horizontally extends toward the side of the primary bending lower mold to form a positioning groove.

[0017] As a preferred solution of the present invention, calibration holes are provided on both sides of the single-pass bending upper die, the single-pass bending lower die, the second-pass bending upper die, and the second-pass bending lower die, and the calibration holes on the same side of the single-pass bending upper die and the single-pass bending lower die, the second-pass bending upper die, and the second-pass bending lower die are collinear in the vertical direction.

[0018] As a preferred solution of the present invention, the secondary blank cavity comprises a second intermediate cavity, and the primary bending cavity is arranged at both ends of the second intermediate cavity;

[0019] The second-pass bending upper die includes an upper die body, the bottom of which is configured to form a curved surface structure that cooperates with the second intermediate cavity, and the curved surface structure cooperates with the second intermediate cavity to perform secondary bending on the middle of the blank.

[0020] As a preferred solution of the present invention, positioning blocks are provided at both ends of the upper mold body, and the bottom of the positioning blocks is provided with an inclined surface, and a connecting block is provided on the top of the positioning block, one end of the connecting block is rotatably connected to the upper mold body through a rotating shaft, and an elastic corner piece is provided on the side of the upper mold body, and one side of the elastic corner piece is connected to the positioning block;

[0021] Wherein, the inclined surface is used to match the end surface of the blank, and rotates around the rotating shaft when the upper part of the connecting block is subjected to downward pressure. The elastic angle piece supports the positioning block to be close to the upper mold body, and when the downward pressure disappears, the elastic angle piece restores the positioning block to its initial position.

[0022] As a preferred solution of the present invention, a guide groove is provided in the middle of the inclined surface, the guide groove is along the length direction of the inclined surface, and the guide groove has the same structure as the primary bending cavity.

[0023] As a preferred solution of the present invention, a pressure plate is arranged above the upper fixed plate, the bottom of the pressure plate cooperates with the upper surface of the upper fixed plate, a pressure spindle is arranged in the middle of the pressure plate, a connecting seat is installed on the pressure spindle, and a plurality of pressure relief devices are arranged on the connecting seat;

[0024] The pressure relief device includes an electromagnetic drive part and a first guide rod. A through hole matching the first guide rod is arranged on the pressure plate, a second guide rod is arranged above the through hole, an electromagnet is arranged on the top of the second guide rod, the bottom of the second guide rod is connected to the third guide rod, a guide hole matching the third guide rod is arranged axially of the first guide rod, and a pressure spring is mounted on the rod body of the third guide rod.

[0025] As a preferred solution of the present invention, a first wedge-shaped body is provided at the bottom of the second guide rods on both sides of the upper mold body, a countersunk hole is provided on the connecting blocks on both sides of the upper mold body, a second wedge-shaped body that matches the first wedge-shaped body is provided in the countersunk hole, and the first wedge-shaped body and the second wedge-shaped body form a wedge surface transmission pair;

[0026] Wherein, the wedge surface transmission pair composed of the first wedge-shaped body and the second wedge-shaped body drives the connecting block to rotate around the rotating shaft.

[0027] As a preferred solution of the present invention, before the pressure plate contacts the upper fixed plate, the electromagnetic driving part is used to linearly increase the force applied to the electromagnet, so that the second guide rod drives the first guide rod to contact the upper fixed plate through the third guide rod under the action of the pressure spring.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention separates the mold of the part of the forging that needs to be bent by setting a two-pass bending mold to form a one-pass bending and a two-pass bending, that is, the deep U-shaped structure bending and the small arc bending are bent separately. By bending in steps and designing a two-pass bending mold, the bending of the bar with multiple bending sections and large-angle bending long arms can be achieved.

[0030] The two-pass bending method of the present invention can reduce the reciprocating stress on the blank during the distributed bending process.

[0031] The bending die provided by the present invention does not need to add too many auxiliary devices as a whole, and at the same time can ensure the bending quality and reduce the occurrence of blank die jamming during the bending process. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0033] Figure 1 A schematic diagram of the overall structure of a mold according to an embodiment of the present invention;

[0034] Figure 2 It is a schematic diagram of the overall right side structure of an embodiment of the present invention;

[0035] Figure 3 It is a structural schematic diagram of a longitudinal section of a one-stage bending upper die and a one-stage bending lower die according to an embodiment of the present invention;

[0036] Figure 4 It is a schematic diagram of the overall longitudinal section structure of the two-pass bending upper die and the two-pass bending lower die according to an embodiment of the present invention;

[0037] Figure 5It is a structural schematic diagram of a pressure relief device disposed above an upper fixed plate according to an embodiment of the present invention;

[0038] Figure 6 It is a schematic diagram of the overall structure of an embodiment of the present invention, which is provided with a connecting block, a positioning block and a pressure relief device;

[0039] Figure 7 It is a schematic diagram of a blank bent by two-pass bending dies and the final formed structure of the blank according to an embodiment of the present invention.

[0040] The numbers in the figure represent the following:

[0041] 10-upper fixed plate; 11-pressure plate; 12-pressure spindle; 13-connecting seat; 20-lower fixed plate; 30-first-pass bending upper die; 40-second-pass bending upper die; 41-upper die body; 42-positioning block; 43-inclined surface; 45-rotating shaft; 46-elastic angle piece; 47-guide groove; 50-first-pass bending lower die; 51-first blank cavity; 52-first intermediate cavity; 53-first bending cavity; 54-positioning groove; 60-second-pass bending lower die; 61-second blank cavity; 70-calibration hole; 80-pressure relief device; 81-electromagnetic drive unit; 82-first guide rod; 83-through hole; 84-second guide rod; 85-third guide rod; 86-guide hole; 87-pressure spring; 88-first wedge; 89-countersunk hole. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] like Figures 1 to 7 As shown, the present invention provides a two-pass bending mold, including an upper fixed plate 10 and a lower fixed plate 20, a first-pass bending upper mold 30 and a second-pass bending upper mold 40 are arranged side by side on the lower surface of the upper fixed plate 10, and a first-pass bending lower mold 50 and a second-pass bending lower mold 60 are arranged side by side on the upper surface of the lower fixed plate 20.

[0044] A primary blank cavity 51 is provided on the one-stage bending lower die 50, and the primary blank cavity 51 is used to perform a primary bending forming on the two end portions of the blank when the one-stage bending upper die 30 and the primary blank cavity 51 are molded together;

[0045] A secondary blank cavity 61 is provided on the second-pass bending lower die 60 , and the secondary blank cavity 61 is used to perform secondary bending forming on the middle of the blank when the second-pass bending upper die 40 and the secondary blank cavity 61 are clamped.

[0046] by Figure 7 The numbers in the figure are as follows: P101-D=50mm x L=600mm original cylindrical bar as an example; P102-the blank obtained after the first bending pass; P103-the blank obtained after the second bending pass.

[0047] During the specific operation of this embodiment: the original extruded aluminum alloy cylindrical bar P101 is heated to a certain temperature, at which the aluminum alloy is suitable for forging and has sufficiently high process plasticity; the original cylindrical bar is placed on the mold for a bending process; the first bending process is performed, and a primary billet cavity 51 is provided on the primary bending lower die 50, and the primary billet cavity 51 is used to perform a primary bending forming on the two end portions close to the billet when the primary bending upper die 30 is molded with the primary billet cavity 51, so as to obtain a billet with local bending at both ends, which is called a primary bending billet; after the first bending process is completed, a second bending process is performed to obtain a secondary bending billet, and a secondary billet cavity 61 is provided on the second bending lower die 60, and the secondary billet cavity 61 is used to perform a secondary bending forming on the middle of the billet when the second bending upper die 40 is molded with the secondary billet cavity 61, i.e., a deep U-shaped arm product structure billet.

[0048] That is, the middle section of the final blank formed by bending of the mold in this embodiment has a larger curvature or depth compared with the ends of the formed blank, while both sides of the middle section have small curvature bends.

[0049] In particular, two heating holes are set on the upper die of the primary bending and two heating holes are set on the lower die of the primary bending to heat the mold. Specifically, the mold electric heating tube is placed in the hole to make the mold temperature reach 200-300℃. At this temperature, the surface and internal structure of the bent blank are denser.

[0050] The primary bending cavity 53 in this embodiment is aimed at the bending forming of a specific target blank, that is, Figure 7 Of course, if the target blank has an asymmetrical bending structure, it is still necessary to perform a single bending forming according to the bending parts at both ends of the bending structure with a larger depth and curvature (such as a deep U-shaped structure part). In other words, this embodiment divides the order of single bending and second bending based on the bending degree of the target blank.

[0051] To this end, the primary blank cavity 51 in this embodiment includes a first intermediate cavity 52 , and primary bending cavities 53 are provided at both ends of the first intermediate cavity 52 , and the primary bending cavities 53 located at both ends of the first intermediate cavity 52 are centrally symmetrical.

[0052] The primary bending cavity 53 performs a primary bending on the two end portions close to the blank when the secondary bending upper die 30 and the primary blank cavity 51 are molded together.

[0053] The first intermediate cavity 52 is matched and symmetrical with the bottom surface of the first bending upper die 30. In order to release the stress of the blank generated during the first bending process, a concave arc structure to a certain extent can be set in the middle of the first intermediate cavity 52, such as Figure 3 As shown, further, the middle part of the blank is not bent, so a symmetrical concave arc structure is also provided in the middle of the bottom surface of the secondary bending upper die 30. In this way, the stress generated by the bending at both ends of the blank is released in the middle part of the blank.

[0054] The end of the primary bending cavity 53 is away from the first intermediate cavity 52 and extends horizontally toward the side of the secondary bending lower die 50 to form a positioning groove 54. The positioning groove 54 can also extend to the end surface of the secondary bending lower die 50 to form an open mouth or incompletely extend to form a guard edge. The positioning groove 54 is used to position the end of the blank, so that the blank can maintain accurate positioning during the primary bending and secondary bending processes.

[0055] Calibration holes 70 are provided on both sides of the single-pass bending upper mold 30, the single-pass bending lower mold 50, the second-pass bending upper mold 40, and the second-pass bending lower mold 60, and the calibration holes 70 located on the same side of the single-pass bending upper mold 30 and the single-pass bending lower mold 50, the second-pass bending upper mold 40, and the second-pass bending lower mold 60 are collinear in the vertical direction.

[0056] In this embodiment, it can be arranged according to the actual structure of the mold. The calibration hole 70 can be used to lock the upper mold and the lower mold of the mold, and the single-pass bending upper mold 30 and the second-pass bending upper mold 40 as well as the single-pass bending lower mold 50 and the second-pass bending lower mold 60 can be connected by correspondingly arranging the calibration holes 70 on the single-pass bending upper mold 30 and the second-pass bending upper mold 40. Specifically, the calibration hole 70 can be a threaded hole, which is connected by installing a screw in the threaded hole, and then the single-pass bending upper mold 30 and the second-pass bending upper mold 40 as well as the single-pass bending lower mold 50 and the second-pass bending lower mold 60 can be locked by rotating the screw.

[0057] The secondary blank cavity 61 includes a second intermediate cavity 62, and a primary bending cavity 53 is set at both ends of the second intermediate cavity 62. During the second bending process, it is still necessary to use the primary bending cavity 53 to reshape and position the blank after the first bending during the second bending process. The advantage is that if only a larger depth bending or a deep U-shaped structure bending is performed on the middle part of the blank during the second bending process, the bending process will inevitably affect the structure that has been bent into shape by the first bending.

[0058] To this end, the second-pass bending upper mold 40 in this embodiment includes an upper mold body 41, and the bottom of the upper mold body 41 is configured to have a curved surface structure that cooperates with the second intermediate cavity 62. The curved surface structure cooperates with the second intermediate cavity 62 to perform secondary bending on the middle of the blank.

[0059] Since the deformation of the blank is large during the second bending process, the process involves the deformation of the overall structure of the blank and the change of the positions of the two sections of the blank.

[0060] To this end, in order to cooperate with the deformation of the two ends of the blank during the second bending process, in this embodiment, positioning blocks 42 are provided at both ends of the upper mold body 41, and an inclined surface 43 is provided at the bottom of the positioning block 42, and a connecting block 44 is provided on the top of the positioning block 42. One end of the connecting block 44 is rotatably connected to the upper mold body 41 through a rotating shaft 45. An elastic angle piece 46 is provided on the side of the upper mold body 41, and one side of the elastic angle piece 46 is connected to the positioning block 42.

[0061] The elastic corner piece 46 in this embodiment is specifically a metal spring piece with memory metal, specifically a rectangular structure, wherein one side of the metal spring piece is connected to the bottom of the connection seat 13, and the other side is connected to the side of the upper mold body 41, and both can be designed to be detachably connected. Therefore, the elastic corner piece 46 can be used as a consumable part and can be replaced without affecting the performance of the mold itself.

[0062] Among them, the inclined surface 43 is used to match the end surface of the blank, and rotates around the rotating shaft 45 when the upper part of the connecting block 44 is subjected to downward pressure. The elastic angle piece 46 supports the positioning block 42 close to the upper mold body 41, and when the downward pressure disappears, the elastic angle piece 46 restores the positioning block 42 to its original position.

[0063] A guide groove 47 is provided in the middle of the inclined surface 43 . The guide groove 47 is along the length direction of the inclined surface 43 , and the guide groove 47 has the same structure as the primary bending cavity 53 .

[0064] A pressure plate 11 is arranged above the upper fixed plate 10, and the bottom of the pressure plate 11 cooperates with the upper surface of the upper fixed plate 10. A pressure main shaft 12 is arranged in the middle of the pressure plate 11, and a connecting seat 13 is installed on the pressure main shaft 12. A plurality of pressure relief devices 80 are arranged on the connecting seat 13.

[0065] Furthermore, in this embodiment, a pressure relief device 80 is provided including an electromagnetic drive part 81 and a first guide rod 82, a through hole 83 matching the first guide rod 82 is provided on the pressure plate 11, a second guide rod 84 is provided above the through hole 83, an electromagnet is provided on the top of the second guide rod 84, the bottom of the second guide rod 84 is connected to the third guide rod 85, a guide hole 86 matching the third guide rod 85 is provided axially of the first guide rod 86, and a pressure spring 87 is mounted on the rod body of the third guide rod 85.

[0066] A first wedge 88 is disposed at the bottom of the second guide rod 17 on both sides of the upper die body 41, and a countersunk hole 89 is disposed on the connecting block 44 on both sides of the upper die body 41. A second wedge 88 is disposed in the countersunk hole 89 to match the first wedge 88. The first wedge 88 and the second wedge constitute a wedge surface transmission pair.

[0067] The wedge surface transmission pair composed of the first wedge-shaped body 88 and the second wedge-shaped body drives the connecting block 44 to rotate around the rotating shaft 45 .

[0068] Before the pressure plate 11 contacts the upper fixed plate 10 , the electromagnetic driving part 81 is used to linearly increase the force on the electromagnet, so that the second guide rod 84 drives the first guide rod 82 to contact the upper fixed plate 10 through the third guide rod 85 under the action of the pressure spring 87 .

[0069] The above embodiments are only exemplary embodiments of the present application and are not intended to limit the present application. The protection scope of the present application is defined by the claims. Those skilled in the art may make various modifications or equivalent substitutions to the present application within the essence and protection scope of the present application, and such modifications or equivalent substitutions shall also be deemed to fall within the protection scope of the present application.

Claims

1. A two-pass bending die, comprising an upper fixed plate (10) and a lower fixed plate (20), wherein a first-pass bending upper die (30) and a second-pass bending upper die (40) are arranged side by side on the lower surface of the upper fixed plate (10), and a first-pass bending lower die (50) and a second-pass bending lower die (60) are arranged side by side on the upper surface of the lower fixed plate (20), characterized in that: A primary blank cavity (51) is provided on the one-stage bending lower die (50), and the primary blank cavity (51) is used to perform a primary bending forming on the two end portions of the blank when the one-stage bending upper die (30) and the primary blank cavity (51) are molded together; A secondary blank cavity (61) is provided on the secondary bending lower die (60), and the secondary blank cavity (61) is used to perform secondary bending forming on the middle of the blank when the secondary bending upper die (40) and the secondary blank cavity (61) are closed.

2. A two-pass bending die according to claim 1, characterized in that: The primary blank cavity (51) comprises a first intermediate cavity (52), and primary bending cavities (53) are arranged at both ends of the first intermediate cavity (52), and the primary bending cavities (53) located at both ends of the first intermediate cavity (52) are centrally symmetrical; Wherein, when the primary bending upper die (30) and the primary blank die cavity (51) are molded together, the primary bending cavity (53) performs a primary bending on the two end portions close to the blank; The first intermediate cavity (52) is matched with and symmetrical to the bottom surface of the one-stage bending upper die (30).

3. A two-pass bending die according to claim 2, characterized in that: The end of the primary bending cavity (53) away from the first intermediate cavity (52) extends horizontally toward the side of the primary bending lower die (50) to form a positioning groove (54).

4. A two-pass bending die according to claim 1, characterized in that: Calibration holes (70) are provided on both sides of the first-pass bending upper die (30), the first-pass bending lower die (50), the second-pass bending upper die (40), and the second-pass bending lower die (60), and the calibration holes (70) located on the same side of the first-pass bending upper die (30) and the first-pass bending lower die (50), the second-pass bending upper die (40), and the second-pass bending lower die (60) are collinear in the vertical direction.

5. A two-pass bending die according to claim 2, characterized in that: The secondary blank cavity (61) comprises a second intermediate cavity (62), and the primary bending cavity (53) is arranged at both ends of the second intermediate cavity (62); The second-pass bending upper die (40) comprises an upper die body (41), the bottom of which is configured to form a curved surface structure that cooperates with the second intermediate cavity (62), and the curved surface structure cooperates with the second intermediate cavity (62) to perform secondary bending on the middle of the blank.

6. A two-pass bending die according to claim 1, characterized in that: Positioning blocks (42) are arranged at both ends of the upper mold body (41), and an inclined surface (43) is arranged at the bottom of the positioning block (42), a connecting block (44) is arranged at the top of the positioning block (42), one end of the connecting block (44) is rotatably connected to the upper mold body (41) through a rotating shaft (45), and an elastic corner piece (46) is arranged on the side of the upper mold body (41), and one side of the elastic corner piece (46) is connected to the positioning block (42); The inclined surface (43) is used to match the end surface of the blank, and rotates around the rotating shaft (45) when the upper part of the connecting block (44) is subjected to downward pressure. The elastic angle piece (46) supports the positioning block (42) close to the upper mold body (41), and when the downward pressure disappears, the elastic angle piece (46) restores the positioning block (42) to its initial position.

7. A two-pass bending die according to claim 1, characterized in that: A guide groove (47) is provided in the middle of the inclined surface (43), the guide groove (47) is along the length direction of the inclined surface (43), and the guide groove (47) has the same structure as the primary bending cavity (53).

8. A two-pass bending die according to claim 6, characterized in that: A pressure plate (11) is arranged above the upper fixed plate (10), the bottom of the pressure plate (11) cooperates with the upper surface of the upper fixed plate (10), a pressure main shaft (12) is arranged in the middle of the pressure plate (11), a connecting seat (13) is installed on the pressure main shaft (12), and a plurality of pressure relief devices (80) are arranged on the connecting seat (13); The pressure relief device (80) includes an electromagnetic drive part (81) and a first guide rod (82), a through hole (83) matching the first guide rod (82) is provided on the pressure plate (11), a second guide rod (84) is provided above the through hole (83), an electromagnet is provided at the top of the second guide rod (84), the bottom of the second guide rod (84) is connected to the third guide rod (85), a guide hole (86) matching the third guide rod (85) is provided axially of the first guide rod (86), and a pressure spring (87) is mounted on the rod body of the third guide rod (85).

9. A two-pass bending die according to claim 8, characterized in that: A first wedge-shaped body (88) is disposed at the bottom of the second guide rod (84) located on both sides of the upper mold body (41), a countersunk hole (89) is disposed on the connecting block (44) on both sides of the upper mold body (41), and a second wedge-shaped body that cooperates with the first wedge-shaped body (88) is disposed in the countersunk hole (89), and the first wedge-shaped body (88) and the second wedge-shaped body form a wedge surface transmission pair; The wedge surface transmission pair composed of the first wedge-shaped body (88) and the second wedge-shaped body drives the connecting block (44) to rotate around the rotating shaft (45).

10. A two-pass bending die according to claim 8, characterized in that: Before the pressure plate (11) contacts the upper fixed plate (10), the electromagnetic drive unit (81) is used to linearly increase the force applied to the electromagnet, so that the second guide rod (84) drives the first guide rod (82) to contact the upper fixed plate (10) through the third guide rod (85) under the action of the pressure spring (87).

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