Method and device for reducing edge cracking in high strength steel stamping forming process

Abstract

The application discloses a method and device for reducing edge cracking in a high-strength steel stamping forming process, comprising a concave die and a blank holder for clamping a material plate, and a punch die for bending the material plate; an edge control mechanism is arranged on the side wall of the concave die, and the edge control mechanism bears the part of the material plate to be bent; the edge control mechanism is movably arranged on the side wall of the concave die, and during the stamping process, the edge control mechanism continuously applies a reverse force on the bottom of the material plate to control the stress state of the edge region of the material plate. The insert block structure with variable force control is used to change the stress state of the edge region of the material from tensile stress to compressive stress, thereby improving the fracture limit of the material and reducing the edge cracking. By changing the stress state of the edge region of the high-strength steel material in the stamping forming process, the local plastic deformation capacity of the material is improved, the edge cracking rate is effectively reduced, the qualified rate in the high-strength steel stamping forming process is improved, the application range of the high-strength steel material is widened, and the application has important practical value.

Description

Technical Field

[0001] This invention belongs to the field of metal plastic processing technology, specifically relating to a method and apparatus for reducing edge cracking during the stamping process of high-strength steel. Background Technology

[0002] To achieve lightweight design of automobile bodies, using advanced high-strength steel with higher strength and performance is one of the important ways to reduce the weight of body parts. Advanced high-strength steel, especially third-generation high-strength steel, combines good formability, impact energy absorption, and economy, and has great application potential in automotive lightweighting. Due to the complex phase composition and chemical composition of high-strength steel, it has the characteristic of being sensitive to edge forming and often exhibits hydrogen embrittlement delayed cracking or failure during processing and service, which limits its application range.

[0003] After high-strength steel sheet coils are blanked and sheared, they form blanks with damaged sheared edges. During the subsequent flanging process, the side subjected to tensile stress fails first, which is the main reason for its through cracking and component failure.

[0004] As the strength of materials increases, their plasticity and machinability inevitably decrease. During the forming process after shearing, the edge cracking problem of sheet metal becomes serious, such as bending cracking of sheared sections, edge cracking of roll bending, and cracking of expanded holes and flanging, which increases the scrap rate and affects the safety and fatigue performance of parts.

[0005] Edge cracking is essentially a failure phenomenon that occurs when a localized area at the edge of a material reaches or exceeds its fracture limit due to plastic deformation. The process of edge cracking is fundamentally a result of the interaction between the material's global formability and its local formability. Therefore, improving the local stress state and formability limit properties of the cracked area is key to improving its edge formability. Summary of the Invention

[0006] In view of the problems existing in the background technology, the purpose of the present invention is to provide a method and apparatus for reducing edge cracking during the stamping process of high-strength steel that is easy to implement and low in cost.

[0007] To achieve the above objectives, in a first aspect, the device for reducing edge cracking during the stamping process of high-strength steel designed in this invention includes a die for holding the material plate and a blank holder die, wherein the die bends the material plate.

[0008] The die sidewall is provided with an edge control mechanism, which supports the portion of the material plate to be bent. The edge control mechanism is movably disposed on the die sidewall. During the stamping process, the edge control mechanism continuously applies a reverse force to the bottom of the material plate to control the stress state of the edge area of ​​the material plate.

[0009] Preferably, the edge control mechanism is equipped with an induction heating component, which heats the edge area of ​​the material plate. This allows for appropriate heating of the localized area of ​​the material's flange, based on the material and its deformation, thereby reducing cracking of the sheet material.

[0010] Preferably, the edge control mechanism is an edge insert with one end hinged to the side wall of the die cavity, and an adjustable bearing is disposed between the edge insert and the die cavity to provide a continuous reverse force.

[0011] More preferably, the continuous directional force is less than the punching force of the die, and is 80% to 90% of the punching force.

[0012] Preferably, the edge insert extends beyond the end of the material plate.

[0013] More preferably, the edge insert extends 3-8 mm beyond the end of the material plate.

[0014] Secondly, the method for reducing edge cracking during the stamping process of high-strength steel, as designed in this invention, includes the following steps:

[0015] S1, place the material plate flat on the die cavity, with the edge of the material plate extending out of the die cavity to the edge control mechanism;

[0016] S2, the blank holder die holds the material plate, and the edge forming force is set according to the material strength and mold structure;

[0017] S3, the material plate completes edge forming under the action of the punching die and the edge control mechanism;

[0018] S4, mold reset.

[0019] Preferably, in step S1, the end of the edge control mechanism extends 3-8 mm beyond the end of the material plate.

[0020] Preferably, step S2' is further included between steps S2 and S3:

[0021] Heating is applied to the edge area of ​​the material plate, and the temperature of the edge area is controlled between 200 and 300°C.

[0022] Further preferred, step S2' is applied to materials with a strength exceeding 1000 MPa or low edge shear quality, depending on the molding effect.

[0023] The beneficial effects of the present invention are as follows: The present invention adopts a block structure with variable force control, which changes the stress state of the material edge area from tensile stress to compressive stress, thereby improving the fracture limit of the material and reducing edge cracking.

[0024] This invention improves the local plastic deformation capacity of high-strength steel by changing the stress state of the edge region during the stamping process, effectively reducing the edge cracking rate and increasing the pass rate of high-strength steel stamping, thus expanding the application range of high-strength steel materials and having important practical value.

[0025] This invention uses a pressure-controlled spring to change the edge stress state of the material during the forming process, that is, from the original tensile stress state to the compressive stress state, thereby increasing the material's fracture limit, that is, raising the threshold for material fracture and cracking.

[0026] The variable force control mold edge insert structure of this invention realizes key control over the stress state of high-strength steel material flanging forming process, which can significantly reduce the failure phenomenon in the edge forming process of high-strength steel material. It has the characteristics of easy implementation, good effect, low cost and high efficiency. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the present invention—before deformation;

[0028] Figure 2 This is a schematic diagram of the structure of the present invention—after deformation; Detailed Implementation

[0029] The technical solutions (including preferred technical solutions) of the present invention will be further described in detail below with reference to the accompanying drawings and by way of listing some optional embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] like Figure 1 and Figure 2 As shown, the device for reducing edge cracking during the stamping process of high-strength steel includes a die 3 for clamping the material plate 4 and a blank holder 2, and the punch 1 bends the material plate 4.

[0031] The die 3 is provided with an edge control mechanism on its side wall. The edge control mechanism supports the portion of the material plate to be bent. The edge control mechanism is movably disposed on the side wall of the die 3. During the stamping process, the edge control mechanism continuously applies a reverse force to the bottom of the material plate 4 to control the stress state of the edge area of ​​the material plate.

[0032] In some optional embodiments of the present invention, the edge control mechanism is provided with an induction heating component, which heats the edge area of ​​the material plate. Thus, the temperature of the localized area of ​​the material edge can be appropriately increased according to the material and the magnitude of its deformation, reducing cracking of the sheet material.

[0033] In some optional embodiments of the present invention, the edge control mechanism is an edge insert 5 with one end hinged to the side wall of the die 3, and an adjustable bearing 6 is disposed between the edge insert 5 and the die 3 to provide a continuous counterforce. The edge insert 5 is hinged to the side wall of the die 3 via a shaft and can rotate freely around the die 3 at a certain angle.

[0034] Preferably, the adjustable bearing 6 is a nitrogen spring or an air spring; the pressure of the spring is adjustable and controllable, and the maximum value is determined according to the strength of the material being formed, the size of the formed part, and the insert structure; one end of the spring is hinged to the side wall of the die 3, and the other end of the spring is hinged to the bottom of the edge insert 5, so as to keep the edge of the edge insert 6 smoothly connected to the die 3.

[0035] During the forming process of the edge of the sheet metal 4 under the action of the die 1, the die 1, the sheet metal 4, and the edge insert 5 always remain in close contact, and the magnitude of the contact force between the three is controlled by the spring 6. In principle, the force is slightly less than the downward force of the die punch, with 80-90% being optimal.

[0036] Preferably, the edge insert extends beyond the end of the material plate.

[0037] More preferably, the edge insert extends 3-8 mm beyond the end of the material plate.

[0038] The method for reducing edge cracking during the stamping process of high-strength steel, as designed in this invention, includes the following steps:

[0039] Step 1: Place the material plate 4 flat on the cavity mold 3, with the edge of the material plate 4 extending out of the cavity mold 3 to the edge control mechanism; the edge of the material plate 4 should be slightly shorter than the edge of the edge insert 5, preferably by 3 to 8 mm.

[0040] Step 2: The key to improving the formability of the edge region material in Step 1 lies in designing a variable force control edge control mechanism. This mechanism can adjust the stress state at the material edge and also control the temperature during the material forming process.

[0041] A reasonable edge forming force should be set according to the material strength and mold structure. The forming force is adjustable and controllable. The maximum value is determined by the strength of the forming material, the size of the forming part and the insert structure. In principle, the force should be slightly less than the downward force of the mold punch, with 80-90% being optimal.

[0042] Step 3: For materials with a strength exceeding 1000MPa or low edge shear quality, activate the induction heating function according to the forming effect, and appropriately raise the temperature of the local area of ​​the material flanging, with the temperature being 200-300 degrees Celsius.

[0043] Step 4: Under the combined action of the die and the edge forming force, the die 1, sheet 4 and edge insert 5 remain in close contact to complete the edge forming process.

[0044] Step 6: Edge insert 5 automatically resets under the action of spring force.

[0045] By innovating the structure of the molds and designing the edge forming process, the edge cracking phenomenon during the stamping process of high-strength steel materials can be significantly reduced, thereby improving the pass rate of high-strength steel parts.

[0046] It will be readily understood by those skilled in the art that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, combinations, substitutions, improvements, etc., made under the spirit and principles of the present invention are included within the protection scope of the present invention.

Claims

1. A device for reducing edge cracking during the stamping process of high-strength steel, characterized in that: Includes a die for holding the material plate and a blank holder, and a punch for bending the material plate; The die sidewall is provided with an edge control mechanism, which supports the portion of the material plate to be bent. The edge control mechanism is movably disposed on the die sidewall. During the stamping process, the edge control mechanism continuously applies a reverse force to the bottom of the material plate to control the stress state of the edge area of ​​the material plate. The edge control mechanism is an edge insert with one end hinged to the side wall of the die cavity, and an adjustable bearing is provided between the edge insert and the die cavity to provide a continuous reverse force. The edge insert is hinged to the side wall of the die cavity via a shaft, and can rotate freely around the die cavity at a certain angle; The edge insert extends beyond the end of the material plate; During the forming process under the action of the die, the die, the material plate, and the edge insert remain in close contact.

2. The device for reducing edge cracking during high-strength steel stamping as described in claim 1, characterized in that: The edge control mechanism is equipped with an induction heating component, which heats the edge area of ​​the material plate.

3. The device for reducing edge cracking during high-strength steel stamping as described in claim 1, characterized in that: The continuous reverse force is less than the punching force of the die, and is 80% to 90% of the punching force.

4. The device for reducing edge cracking during high-strength steel stamping as described in claim 1, characterized in that: The edge insert extends 3-8 mm beyond the end of the material plate.

5. A method using the apparatus for reducing edge cracking during high-strength steel stamping as described in any one of claims 1 to 4, comprising the following steps: S1, the material plate is placed flat on the die cavity, and the edge of the material plate extends out of the die cavity to the edge control mechanism; the edge of the material plate is slightly shorter than the edge of the edge insert, and the end of the edge insert extends out of the end of the material plate by 3 to 8 mm; S2, the blank holder die holds the material plate, and the edge forming force is set according to the material strength and mold structure; S3, under the combined action of the die and the edge forming force, the die, the material plate and the edge insert remain in close contact to complete the edge forming process; S4, mold reset.

6. The method for reducing edge cracking during high-strength steel stamping as described in claim 5, characterized in that: The step S2' is also included between steps S2 and S3: Heating is applied to the edge area of ​​the material plate, and the temperature of the edge area is controlled between 200 and 300°C.

7. The method for reducing edge cracking during high-strength steel stamping as described in claim 6, characterized in that: For materials with a strength exceeding 1000 MPa or low edge shear quality, step S2' is applied based on the molding effect.

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