Method for forming outwardly convex closed corners and flanges on a metal panel and forming die

Abstract

The present invention belongs to the field of automobiles, and particularly relates to a method and a forming die for forming an outwardly convex closed corner and a flange on a metal panel. The method comprises the following steps: providing a die assembly composed of a first die and a second die which are arranged to open and close relative to each other, wherein the first die and the second die respectively comprise an outer peripheral blank holder and a second flat portion which open and close relative to each other; placing the metal panel between the first die and the second die; moving the first die and the second die closer to each other; in the initial stage of deformation of the metal panel, keeping the outer peripheral blank holder in a state of not being closed with the second flat portion; when the metal panel in the outer region of the outwardly convex closed corner is about to have obvious wrinkles, closing the outer peripheral blank holder with the second flat portion to form a flange at the edge of the housing. The present invention avoids the problem of the failure of the simultaneous engineering result of the hot forming coated plate part.

Description

Technical Field

[0001] The present invention belongs to the field of automobiles, and particularly relates to a method and a forming die for forming an outward convex closed corner and a flange on a metal panel. Background Art

[0002] As a main means of vehicle lightweighting, hot-formed parts are increasingly widely used in a white body. Due to small springback and strong anti-wrinkle ability of hot-formed parts, hot-formed parts generally have good manufacturability.

[0003] For hot-forming materials with Al-Si coating plates and bare plate materials without Al-Si coating, the 22MnB5 material curves and friction coefficients of the previous stamping SE analysis are the same. For beam parts with open cross-sections, there is no significant difference in formability between the two; however, for parts designed with a closed outward convex corner and a long flange surface at the closed outward convex corner, the forming effects of the two are different. As Figure 1 、 2 A schematic diagram of a part designed with an outward convex corner and a long flange surface. According to the conventional process design scheme: the pad1 parting line for controlling wrinkles on the corner flange surface is designed in the rounded corner area at the root of the corner, the clearance value of pad1 is designed to be 0.5 mm, and the working stroke is greater than the forming depth of the part (designed to be 70 mm); for hot-forming materials with Al-Si coating plates and bare plate materials without Al-Si coating, the part formability of the previous simultaneous engineering stamping SE analysis is qualified and there is no cracking risk, but the actual debugging verification shows that serious cracking occurs in the hot-forming of Al-Si coating plates, while the bare plate parts do not crack; moreover, when adjusting process parameters such as the clearance value and working stroke of pad1, the quality problem of cracking cannot be improved and solved.

[0004] For outward convex corner parts, the Al-Si coating weakens the formability of the 22MnB5 matrix or increases friction. At the same time, the wrinkling trend during the forming of the outward convex corner area causes the preset clearance of the process plan to fail, and the material of the flange surface prematurely pressed by pad1 cannot improve the material flow in this area. Under the action of pad1 and pad2, a material bulging area is formed in the corner side wall area; the previous stamping SE of the part cannot analyze this difference, resulting in serious cracking of the part in the industrialization stage; the cracking problem in the side wall area cannot be improved by adjusting process parameters such as the clearance and stroke of pad1, and large design changes and die modification are required for the part, resulting in an increase in part cost and cycle. Summary of the Invention

[0005] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a method and a forming die for forming an outwardly convex closed corner and a flange on a metal panel, so as to solve the problems that the synchronous engineering cannot identify the differences in the matrix properties and friction coefficients of the hot-formed Al-Si coated plate and the bare plate in the outwardly convex corner area of the part, and the stamping SE cannot correctly predict the cracking risk in the outwardly convex corner area of the part, resulting in the quality problem of cracking at the outwardly convex corner position of the hot-formed Al-Si coated plate parts in the industrialization stage.

[0006] To achieve the above object and other related objects, the present invention provides a method for forming an outwardly convex closed corner and a flange on a metal panel, comprising the following steps:

[0007] Providing a die assembly composed of a first die and a second die that are arranged to open and close relative to each other, wherein one of the first die and the second die is formed with a convex part, and the other of the first die and the second die is formed with a concave part, and the convex part and the concave part are arranged opposite to each other, so that when the first die and the second die approach each other, a shell-shaped cavity can be formed between the convex part and the concave part, and the shell-shaped cavity has an outwardly convex closed corner; an outer peripheral blank holder is provided outside the die of the first die and the second die that is formed with the convex part, and a first preset distance is provided between the outer peripheral blank holder and the edge of the convex part; a first flat part extending outward is formed at the edge of the convex part, and a second flat part extending outward is formed at the edge of the concave part, and the first flat part and the second flat part are substantially perpendicular to the opening and closing direction of the first die and the second die;

[0008] Placing the metal panel between the first die and the second die;

[0009] Moving the first die and the second die closer to each other, so that the metal panel is deformed under the action of the convex part and the concave part to form a shell with an outwardly convex closed corner; in the initial stage of the deformation of the metal panel, the outer peripheral blank holder is kept in a state of not being closed with the second flat part;

[0010] Continuing to move the first die and the second die closer to each other, and when the metal panel in the outer area of the outwardly convex closed corner is about to have obvious wrinkles, closing the outer peripheral blank holder with the second flat part;

[0011] Continuing to move the first die and the second die closer to each other until the first flat part, the metal panel, and the second flat part are sequentially attached to form a flange at the edge of the shell.

[0012] In an alternative embodiment of the present invention, the mold assembly further includes a first elastic unit, which is configured to apply an elastic force to the outer peripheral blank holder, and the direction of the elastic force is towards the second planar portion; when the outer peripheral blank holder and the second planar portion are closed, the outer peripheral blank holder has a margin of movement along the opening and closing direction of the first mold and the second mold, so that after the first planar portion, the metal panel and the second planar portion are fitted, the edge of the metal panel can be completely withdrawn from the area between the outer peripheral blank holder and the second planar portion.

[0013] In an alternative embodiment of the present invention, the step of placing the metal panel between the first mold and the second mold includes:

[0014] Performing a heat treatment on the metal panel;

[0015] Placing the heated metal panel between the first mold and the second mold.

[0016] In an alternative embodiment of the present invention, the surface of the metal panel has an Al-Si coating.

[0017] In an alternative embodiment of the present invention, a middle blank holder is provided on the one of the first mold and the second mold that forms the concave portion, and the middle blank holder is located inside the concave portion; in the initial stage when the first mold and the second mold approach each other, the convex portion first closes with the middle blank holder to clamp the metal panel, and then the middle blank holder and the convex portion move downward synchronously, so that the middle portion of the metal panel remains clamped during the deformation process of the metal panel.

[0018] To achieve the above and other related purposes, the present invention also provides a forming mold, including:

[0019] A first mold, on the surface of which a convex portion is formed;

[0020] A second mold, on the surface of which a concave portion is formed;

[0021] The first mold and the second mold are arranged to open and close relative to each other, and the convex portion and the concave portion are respectively arranged on opposite sides of the first mold and the second mold, so that when the first mold and the second mold are closed, a shell-shaped cavity with an outwardly convex closed corner can be formed between the convex portion and the concave portion;

[0022] An outer peripheral blank holder is provided on the outer side of the first mold. The outer peripheral blank holder is spaced from the edge of the convex portion by a first preset distance. A first planar portion formed on the surface of the first mold is provided between the edge of the convex portion and the outer peripheral blank holder; a second planar portion formed on the surface of the second mold and opposite to the first planar portion and the outer peripheral blank holder is provided at the edge of the concave portion;

[0023] The outer peripheral blank holder is movably connected to the first mold, and the moving direction is parallel to the opening and closing direction of the first mold and the second mold.

[0024] In an optional embodiment of the present invention, a first elastic unit is provided between the outer peripheral blank holder and the first mold. The first elastic unit is assembled such that the elastic force acting on the outer peripheral blank holder is directed towards the direction where the second planar portion is located.

[0025] In an optional embodiment of the present invention, the outer peripheral blank holder is assembled such that when the first mold and the second mold are in a separated state, the outer peripheral blank holder is spaced from one end of the convex portion close to the concave portion in the opening and closing direction of the first mold and the second mold by a second preset distance, so that in the initial stage when the convex portion and the concave portion approach each other, the outer peripheral blank holder can be in an unclosed state with the second planar portion.

[0026] In an optional embodiment of the present invention, the outer peripheral blank holder is assembled such that when the convex portion and the concave portion are completely closed, there is still a movable margin between the outer peripheral blank holder and the first mold.

[0027] In an optional embodiment of the present invention, a middle blank holder is provided on the second mold. The middle blank holder is located inside the concave portion. The middle blank holder is movably connected to the second mold, and the moving direction is parallel to the opening and closing direction of the first mold and the second mold; the middle blank holder protrudes from the second planar portion or is flush with the second planar portion.

[0028] The technical effect of the present invention is as follows:

[0029] The outer peripheral blank holder of the present invention can not only control the generation of flange surface wrinkles at the outer convex corner position, but also ensure that the material of the flange surface flows into the die opening and complete the forming of the outer convex corner side wall area; it avoids the problem that hard points are formed between the outer peripheral blank holder and the die according to the conventional design scheme and the outer convex corner flange material cannot flow into the die opening. Under the action of the outer peripheral blank holder and the middle blank holder, the outer convex corner side wall area is bulged and formed. The actual forming process of the material is consistent with the stamping SE process of the synchronous engineering and its tooling settings, avoiding the problem of the failure of the synchronous engineering result of the hot forming Al-Si coated plate part.

[0030] For parts designed with closed convex corners and long flange surfaces at the convex corners, the parting line of the peripheral blank holder used to control corner wrinkles in the present invention is designed 5-10 mm from the outer edge of the part. On the premise of no wrinkling in the corner area, the stroke of the peripheral blank holder is designed to be the minimum value as much as possible; the part obtains a larger forming area on the punch and die, avoiding the peripheral blank holder pressing the blank rigidly at the corner position, resulting in the corner side wall area being completely formed by the material properties through bulging.

[0031] The present invention makes the results of the early synchronous engineering consistent with the state in the industrialization stage, avoiding the stamping SE being unable to predict part cracking and causing serious cracking of parts in the industrialization stage; adjusting process parameters such as the pressure and stroke of the peripheral blank holder can improve quality problems such as cracking or wrinkling that occur in industrialization, avoiding the need to solve problems only through large product design changes and die modifications in the industrialization stage, which is beneficial to saving the industrialization cycle, cost, and controlling the production quality of parts.

[0032] The present invention solves the problem that the synchronous engineering cannot identify the differences in matrix properties and friction coefficients between the hot-formed Al-Si coated plate and the bare plate in the outer convex corner area of the part, and the stamping SE cannot correctly predict the cracking risk in the outer convex corner area of the part, resulting in the quality problem of cracking at the outer convex corner position of the hot-formed Al-Si coated plate parts in the industrialization stage. Description of the Drawings

[0033] Figure 1 is a schematic diagram of the distribution of the parting line of the existing outer convex closed corner and flange forming process;

[0034] Figure 2 is Figure 1 the A-A cross-sectional view of

[0035] Figure 3 is a schematic diagram of the distribution of the parting line of the outer convex closed corner and flange forming method provided by the embodiment of the present invention;

[0036] Figure 4 is the schematic diagram of the forming die provided by the embodiment of the present invention. Detailed Embodiments

[0037] The following illustrates the implementation manners of the present invention through specific specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0038] It should be noted that the illustrations provided in the following embodiments only schematically illustrate the basic concept of the present invention. Therefore, only the components related to the present invention are shown in the illustrations, rather than being drawn according to the number, shape, and size of the components in actual implementation. The types, quantities, and proportions of the components in actual implementation can be arbitrarily changed, and the layout type of the components may also be more complex.

[0039] Please refer to Figure 3 、 4 As shown, in combination with the forming process of a hot-formed Al-Si coated plate part, the technical solution of the present invention will be described in detail. Figure 3 What is shown is a partial structure of a vehicle A-pillar. This part has obvious outward convex closed corners, and flanges are provided at the edges of the part. It can be understood that the present invention is not only applicable to this part. In fact, as long as the body part has obvious outward convex closed corners, the technical solution of the present invention is applicable. The present invention can effectively avoid the problems of wrinkles and cracks that occur during the forming process of these parts.

[0040] Please refer to Figure 4 As shown, the present invention provides a forming die, including a first die 10 and a second die 20. In a specific embodiment, a convex portion 11 is formed on the surface of the first die 10 for use as a punch; a concave portion 21 is formed on the surface of the second die 20 for use as a die; in this embodiment, the first die 10 is located above the second die 20. It can be understood that such a setting of the positional relationship is not necessary. For example, the first die 10 can also be arranged below the second die 20. In this embodiment, the die is arranged below mainly to facilitate the placement of the metal panel, so that the metal panel can be laid flat on the die before forming.

[0041] Please refer to Figure 4 As shown, the first die 10 and the second die 20 are arranged to open and close relatively. The convex portion 11 and the concave portion 21 are respectively arranged on the opposite sides of the first die 10 and the second die 20, so that when the first die 10 and the second die 20 are closed, a shell-shaped cavity with an outward convex closed corner can be formed between the convex portion 11 and the concave portion 21; in a specific embodiment, for example, the second die 20 can be fixedly arranged, and the first die 10 can be arranged to reciprocate vertically. The first die 10 can be driven by a hydraulic cylinder, for example. It can be understood that the action modes of the first die 10 and the second die 20 are not unique. In fact, as long as a relative opening and closing action can be generated between the two, for example, the first die 10 can also be fixed, the second die 20 can reciprocate vertically, or both the first die 10 and the second die 20 can reciprocate vertically.

[0042] Please refer toFigure 3 , 4 As shown in 4 , an outer peripheral blank holder 30 is provided on the outer side of the first mold 10. The outer peripheral blank holder 30 is spaced from the edge of the convex portion 11 by a first preset distance. A first flat portion 12 formed on the surface of the first mold 10 is provided between the edge of the convex portion 11 and the outer peripheral blank holder 30. A second flat portion 22 formed on the surface of the second mold 20 and opposite to the first flat portion 12 and the outer peripheral blank holder 30 is provided at the edge of the concave portion 21. In a specific embodiment, the outer peripheral blank holder 30 is movably connected to the first mold 10, and the moving direction is parallel to the opening and closing direction of the first mold 10 and the second mold 20. A first elastic unit (such as a compression spring, not shown in the figure) is provided between the outer peripheral blank holder 30 and the first mold 10, and the first elastic unit is assembled so that the elastic force acting on the outer peripheral blank holder 30 is directed toward the direction where the second flat portion 22 is located.

[0043] It can be understood that the parting line between the outer peripheral blank holder 30 and the first mold 10 is set outside the part flange surface. In this embodiment, the distance L from the parting line to the part edge is 5 - 10 mm. The position where the convex portion 11 is far from the corner side wall is prone to cracking. In the initial stage of stamping forming, the part has a larger area on the convex and concave dies. At the end stage of stamping, the sheet metal can completely break away from the control of the outer peripheral blank holder 30, and the blanking is inside the parting line.

[0044] Please refer to Figure 4 As shown in Figure 4 , the outer peripheral blank holder 30 is assembled so that when the first mold 10 and the second mold 20 are in a separated state, the outer peripheral blank holder 30 is spaced from one end of the convex portion 11 close to the concave portion 21 by a second preset distance in the opening and closing direction of the first mold 10 and the second mold 20, so that in the initial stage when the convex portion 11 and the concave portion 21 approach each other, the outer peripheral blank holder 30 can be in an unclosed state with the second flat portion 22. The outer peripheral blank holder 30 is assembled so that when the convex portion 11 and the concave portion 21 are completely closed, there is still a movable margin between the outer peripheral blank holder 30 and the first mold 10. In a specific embodiment, the working stroke of the outer peripheral blank holder 30 is set to 40 mm. When there is no obvious wrinkle at the corner position (the thickening rate is about 10%), the stroke of the outer peripheral blank holder 30 is as small as possible. At the same time, the clearance value between the outer peripheral blank holder 30 and the second mold 20 is set to 0.5 mm to ensure that the material can flow into the die orifice more easily for forming.

[0045] It should be noted that the various specific parameters provided in the above embodiments, such as the distance from the parting line to the edge of the part, the working stroke of the outer peripheral blank holder 30, the clearance value between the outer peripheral blank holder 30 and the second die 20, etc., are only one of the optional configurations given for the convenience of explaining the present invention. In the actual application process, these parameters can be appropriately selected according to factors such as the type of part, the design parameters of the part, the material and thickness of the metal panel, etc. The present invention does not limit these specific parameters, and those skilled in the art can select appropriate parameters based on general knowledge to achieve the purpose of the present invention.

[0046] Please refer to Figure 3 、 4 As shown, a middle blank holder 40 is provided on the second die 20. The middle blank holder 40 is located inside the concave portion 21. The middle blank holder 40 is movably connected to the second die 20, and the moving direction is parallel to the opening and closing direction of the first die 10 and the second die 20; the middle blank holder 40 protrudes from the second flat portion 22 or is flush with the second flat portion 22.

[0047] Based on the above forming die, the specific method for forming the outward convex closed corner 1 and the flange 2 on the metal panel of the present invention is as follows:

[0048] Step 1: Provide a die assembly composed of a first die 10 and a second die 20 that are arranged to open and close relative to each other.

[0049] Step 2: Place the heated metal panel between the first die 10 and the second die 20; the initial position of the sheet material is on the middle blank holder 40.

[0050] Step 3: Move the first die 10 and the second die 20 closer to each other, so that the metal panel is deformed under the action of the convex portion 11 and the concave portion 21. The sheet material flows into the convex and concave die clearance along the die opening of the second die 20 for part forming to form a shell with an outward convex closed corner 1; in the initial stage of the deformation of the metal panel, keep the outer peripheral blank holder 30 in a state where it is not closed with the second flat portion 22; while the material at the position of the flange 2 surface of the outward convex corner flows into the convex and concave die clearance along the die opening of the second die 20, the material on the flange 2 surface is subjected to a transverse shear force and has a tendency to wrinkle.

[0051] Step 4: Continue to move the first mold 10 closer to the second mold 20. At the position immediately before obvious wrinkles occur on the surface of the corner flange 2 (in this part, it is the position 40 mm before reaching the bottom), the outer peripheral blank holder 30 starts to contact the second mold 20 and press the material on the surface of the flange 2 to control the generation of wrinkles; the position of the convex corner flange 2 surface is controlled by the outer peripheral blank holder 30 and no longer generates wrinkles; at the same time, there is a gap of 0.5 mm between the outer peripheral blank holder 30 and the second mold 20 to ensure that the material can still flow into the die opening of the second mold 20 for forming under the control of the outer peripheral blank holder 30.

[0052] Step 5: Continue to move the first mold 10 closer to the second mold 20 until the first flat portion 12, the metal panel, and the second flat portion 22 are sequentially attached to form a flange 2 at the edge of the housing; since the parting line of the outer peripheral blank holder 30 is outside the part and away from the corner area, the material of the outer peripheral blank holder 30 has a larger forming corner. Compared with the conventional process design: the thickening trend of the material in the area of the outer peripheral blank holder 30 is reduced; at the same time, at the end stage of stamping, all the sheet metal in the area of the outer peripheral blank holder 30 flows into the die opening, avoiding the formation of hard points between the outer peripheral blank holder 30 and the second mold 20.

[0053] In summary, the outer peripheral blank holder 30 of the present invention can not only control the generation of wrinkles on the surface of the flange 2 at the convex corner position, but also ensure that the material on the surface of the flange 2 flows into the die opening to complete the forming of the convex corner side wall area; it avoids the problems of forming hard points between the outer peripheral blank holder 30 and the die and the material of the convex corner flange 2 being unable to flow into the die opening according to the conventional design scheme. Under the action of the outer peripheral blank holder 30 and the middle blank holder 40, the convex corner side wall area is bulged and formed. The actual forming process of the material is consistent with the stamping SE process of the concurrent engineering and the setting of its tooling, avoiding the problem of the failure of the concurrent engineering results of the hot-formed Al-Si coated sheet parts.

[0054] For parts designed with a closed convex corner and a long flange 2 surface at the convex corner, the parting line of the outer peripheral blank holder 30 for controlling corner wrinkles in the present invention is designed 5 - 10 mm from the outer edge of the part. On the premise of no wrinkling in the corner area, the stroke of the outer peripheral blank holder 30 is designed to be the minimum as much as possible; the part obtains a larger forming area on the convex and concave dies, avoiding the outer peripheral blank holder 30 pressing the sheet metal rigidly at the corner position and causing the corner side wall area to be formed entirely by the material properties through bulging.

[0055] The present invention makes the results of the early synchronous engineering consistent with the state in the industrialization stage, avoiding the situation that stamping SE cannot predict part cracking and causing serious cracking of parts in the industrialization stage. Adjusting process parameters such as the pressure and stroke of the outer peripheral binder plate 30 can improve quality problems such as cracking or wrinkling occurring in industrialization, avoiding the need to solve problems only through major product design changes and die modifications in the industrialization stage, which is beneficial to saving the industrialization cycle, cost and controlling the production quality of parts.

[0056] The present invention solves the problem that synchronous engineering cannot identify the differences in matrix properties and friction coefficients between hot-formed Al-Si coated plates and bare plates in the outer convex corner area of parts, and stamping SE cannot correctly predict the cracking risk in the outer convex corner area of parts, resulting in the quality problem of cracking at the outer convex corner position of hot-formed Al-Si coated plate parts in the industrialization stage.

[0057] The above embodiments are only illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A method for forming outwardly convex closed corners and flanges on a metal panel, characterized in that, The method includes the following steps: Providing a mold assembly composed of a first mold and a second mold which are arranged to open and close relative to each other. One of the first mold and the second mold is formed with a convex part, and the other of the first mold and the second mold is formed with a concave part. The convex part and the concave part are arranged opposite to each other so that when the first mold and the second mold approach each other, a shell-shaped cavity can be formed between the convex part and the concave part. The shell-shaped cavity has an outwardly convex closed corner. An outer peripheral blank holder is provided on the outer side of the mold of the first mold and the second mold that is formed with the convex part. A first preset distance is provided between the outer peripheral blank holder and the edge of the convex part. The edge of the convex part is formed with a first planar part extending outward, and the edge of the concave part is formed with a second planar part extending outward. The first planar part and the second planar part are substantially perpendicular to the opening and closing direction of the first mold and the second mold. Placing a metal panel between the first mold and the second mold; Moving the first mold and the second mold closer to each other so that the metal panel is deformed under the action of the convex part and the concave part to form a shell with an outwardly convex closed corner; At the initial stage when the metal panel is deformed, keeping the outer peripheral blank holder in a state where it is not closed with the second planar part; Continuing to move the first mold and the second mold closer to each other. When the metal panel in the outer region of the outwardly convex closed corner is about to have obvious wrinkles, closing the outer peripheral blank holder with the second planar part; Continuing to move the first mold and the second mold closer to each other until the first planar part, the metal panel, and the second planar part are sequentially attached to form a flange at the edge of the shell; The parting line between the outer peripheral blank holder and the first mold is arranged outside the part flange surface; The surface of the metal panel has an Al-Si coating.

2. The method for forming an outwardly convex closed corner and flange on a metal panel according to claim 1, characterized in that, The mold assembly further includes a first elastic unit which is configured to be able to apply an elastic force to the outer peripheral blank holder, and the direction of the elastic force is towards the second planar part. When the outer peripheral blank holder is closed with the second planar part, the outer peripheral blank holder has a movement margin along the opening and closing direction of the first mold and the second mold so that after the first planar part, the metal panel, and the second planar part are attached, the edge of the metal panel can be completely withdrawn from the region between the outer peripheral blank holder and the second planar part.

3. The method for forming an outwardly convex closed corner and flange on a metal panel according to claim 1, characterized in that, The step of placing the metal panel between the first mold and the second mold includes: Performing a heat treatment on the metal panel; Placing the metal panel in the heated state between the first mold and the second mold.

4. The method for forming an outwardly convex closed corner and a flange on a metal panel according to claim 1, wherein A middle pressure plate is provided on one of the first mold and the second mold that forms a concave part, and the middle pressure plate is located inside the concave part; in the initial stage when the first mold and the second mold approach each other, the convex part first closes with the middle pressure plate to clamp the metal panel, and then the middle pressure plate and the convex part move downward synchronously so that the middle part of the metal panel remains clamped during the deformation process of the metal panel.

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