High-tension steel plate deep drawing forming anti-cracking method

Abstract

The invention discloses a deep drawing forming anti-cracking method for a high-tension steel plate, and belongs to the field of drawing forming anti-cracking methods. S2, optimizing a deep drawing mold; s3, dynamically controlling the blank holder force; s4, controlling the tensile strain rate in stages; s5, lubrication and environment control; s6, performing a 3D modeling and simulation technology; according to the method, through tempering pretreatment, the hardness of the steel plate is reduced, the round corner and surface state of the die is optimized, the blank holder force and the stretching speed are dynamically regulated and controlled, the deep drawing forming cracking rate of the SAPH440 steel plate is effectively reduced, and the percent of pass is effectively increased; the passive mode of'full-inspection rejection of defective products' is avoided, the waste rate of raw materials is greatly reduced, meanwhile, the service life of the mold is prolonged through the combination of the SKD11 mold and the carbide coating, and the mold replacement cost is reduced; and the consistency of process parameters in batch production is ensured through 3D simulation crack risk pre-judgment, environment constant temperature and humidity control and equipment regular calibration.

Description

Technical Field

[0001] This invention belongs to the field of tensile forming crack prevention methods, specifically, it relates to a deep drawing forming method for high-tensile steel plates to prevent cracking. Background Technology

[0002] High-tensile SAPH440 series steel plates are widely used in industrial production due to their high strength, good weldability, and formability. However, this series of steel plates faces significant cracking problems during deep drawing: SAPH440 material itself has high hardness (initial hardness 90-95HRB) and low elongation, requiring greater pressure to achieve plastic deformation during the deep drawing and flanging process, which easily leads to springback cracking in stress concentration areas; at the same time, in existing deep drawing processes, the mold cores are mostly made of ordinary domestic Cr12 mold steel (hardness after heat treatment is only HRC55-58), which has poor wear resistance. After long-term use, the surface wear of the mold core is prone to causing tensile scratches on the steel plate, further aggravating the risk of cracking.

[0003] To address these issues, existing technologies often employ a passive approach of "full inspection and rejection of defective products": after deep drawing and molding, cracked workpieces are screened out manually or using machine vision and scrapped directly. This method not only fails to prevent cracking at its source but also results in a raw material waste rate as high as 15%-20%, significantly increasing production failure costs. Some improvement solutions attempt to adjust the blank holder force or lubrication conditions, but these lack systematic optimization based on the material characteristics of SAPH440 steel plates, leading to unstable crack prevention effects and failing to meet the demands of industrialized mass production. Summary of the Invention

[0004] To address the aforementioned problems and technical deficiencies, this invention employs the following technical solution: a method for preventing cracking in deep drawing of high-tensile steel plates, specifically comprising the following steps: S1. Tempering pretreatment of steel plates: The high-tensile SAPH440 series steel sheet (2-5mm thick, initial hardness 90-95HRB) to be processed is placed in a box-type resistance furnace and heated to 180℃ at a heating rate of 10℃ / min to ensure uniform softening of the internal structure of the steel sheet. After the holding time, the steel sheet is removed and placed in a room temperature (20±5℃) environment to cool naturally. During the cooling process, wind or water spraying should be avoided to accelerate cooling and prevent thermal stress from being generated inside the steel sheet. After this treatment, the hardness of the steel sheet is reduced to HRB≤65, and the toughness is increased by 20%-30%, meeting the basic requirements of deep drawing for material plasticity and reducing the risk of tensile fracture caused by excessive hardness from the root. S2, Deep Drawing Mold Optimization: S2.1. The flanged area of ​​the deep drawing mold is machined using a CNC milling machine, increasing the original flange radius (R) from R0.5mm to R1mm. During machining, a 10mm diameter ball end mill is used, with a milling speed set to 2000 r / min and a feed rate of 500 mm / min to ensure a smooth, stepless transition at the fillet. After machining, the fillet radius is checked using a coordinate measuring machine, with the error controlled within ±0.05mm. The increased R angle optimizes the material flow path at the flange, reducing the local stress concentration factor by 30%-40% and significantly reducing the probability of flange cracking. S2.2 The deep drawing mold is made of high-quality SKD11 carbon steel. The new SKD11 mold is subjected to vacuum heat treatment. First, it is preheated at 850℃ for 2 hours, then heated to 1050℃ and held for 1.5 hours, and finally tempered at 500℃ for 2 hours. After treatment, the mold core hardness reaches HRC58-62, and the wear resistance is improved by more than 50% compared with the original Cr12 material, avoiding scratches on the steel plate and local stress concentration cracking caused by mold core wear. S2.3. The heat-treated SKD11 mold core undergoes a thermal diffusion method for carbide coating treatment (carbide coating treatment): The mold core is placed in a molten salt bath (mainly composed of vanadium carbide) and held at 850℃ for 4 hours, forming a vanadium carbide coating with a thickness of 5-10 μm on the mold core surface. After coating treatment, the mold core surface is polished with a diamond wheel at a polishing speed of 1500 r / min, ultimately achieving a surface hardness of approximately HV3200 and a surface roughness Ra≤0.2μm. This coating can reduce the coefficient of friction between the mold and the steel plate from 0.15-0.20 to 0.08-0.10, reducing tensile resistance during deep drawing and preventing tearing defects at the bends. S3. Dynamic control of blank holder force: A 400-ton servo punch press is used in conjunction with a hydraulic servo system, and the blank holder force is controlled in coordination with the hydraulic pad and the proportional pressure valve. S3.1 Obtain the yield strength (typical value 340MPa) of the high-tensile steel plate through material mechanical property testing, and set the initial blank holder force to 30%-40% of the yield strength, i.e. 102-136kN; the blank holder force is output through the hydraulic cushion of the punch press and the proportional pressure valve, and the pressure accuracy is controlled within ±0.5kN. S3.2 During the deep drawing process, the displacement sensor of the punch press collects the slide stroke in real time, and the blank holder force changes linearly with the slide stroke: 0-30% of the slide stroke is the initial forming stage, and the blank holder force maintains the initial value; 3%-70% of the slide stroke is the deep forming stage, and the blank holder force increases at a rate of 0.5kN / mm; 70%-100% of the slide stroke is the final forming stage, and the blank holder force maintains the maximum value. Simultaneously, the slide position is monitored in real time using a pre-stroke comparison method, controlling the positional deviation within ±0.1mm to ensure precise matching between the blank holder force and the mold cavity position, avoiding material wrinkling due to insufficient blank holder force or excessive stretching and cracking due to excessive blank holder force. The response time of the hydraulic servo system is ≤50ms, which can compensate for pressure fluctuations caused by changes in material flow in real time. S4. Staged control of tensile strain rate: Based on the mechanical properties of the steel plate at different forming stages, the tensile strain rate is controlled in stages, specifically corresponding to the slide movement speed of the punch press. S4.1, Elastic Stage (Slider Stroke 0-10%): Tensile strain rate controlled at ≤0.00025s. -1 The corresponding slider speed is ≤0.5mm / s to avoid dynamic effects interfering with the determination of the material yield point and to ensure uniform elastic deformation. S4.2, Yield Stage (slider stroke 10%-50%): Tensile strain rate controlled at 0.00025-0.0025s. -1 The corresponding slider speed is 0.5-5mm / s (adjusted according to the actual hardness of the steel plate: 0.5-3mm / s when the hardness is 60-65HRB, and 3-5mm / s when the hardness is ≤60HRB), to ensure that the plastic deformation is fully developed and to balance work hardening and deformation uniformity. S4.3, Strengthening to fracture stage (slider stroke 50%-100%): tensile strain rate controlled at ≤0.0083s. -1 The corresponding slider speed is ≤8mm / s to control the stability of the necking process and reduce the risk of breakage. The overall stretching speed corresponds to a machine operation frequency of 10-30 times / minute to ensure that the material has sufficient time to flow and avoid cracking caused by instantaneous stress concentration.

[0005] S5. Lubrication and Environmental Control: S5.1. A special oil-based deep-drawing lubricant is used, with the following formula: oil phase: 25%, a mixture of mineral oil, animal fat, or vegetable oil (C18-C24 series hydrocarbons) to provide basic lubricity. Soap / Fat: 5%, soap base (fatty acid salt), forms an adsorption film between the metal and the mold. Water: 25%, forms an emulsion system with oil and soap, adjusts viscosity and helps disperse solids. Solids (fillers): 45%, including graphite, limestone (calcium carbonate / lime powder), zinc oxide, carbonates, borates, etc., to enhance boundary lubrication and reduce friction. Additives: defoamers, bactericides, inorganic buffers, non-ferrous metal passivators, etc., are used to improve the stability, anti-foaming, and anti-corrosion properties of lubricants.

[0006] The lubricant is evenly sprayed onto the surface of the mold cavity and the contact area between the blank and the mold using an automatic spraying device. The spraying thickness is controlled at 8-12 μm, and the spraying pressure is 0.3 MPa. Mixing with other types of lubricating oil is strictly prohibited to prevent lubricant film failure. Simultaneously, because the mold surface has undergone carbide coating treatment to achieve a smoothness Ra≤0.2 μm, lubricant consumption is reduced, ensuring the stability of the lubricating film under high temperature and high pressure. S5.2. Control the ambient temperature of the deep drawing process at 20±5℃ and the humidity at 40%-60%; S6. Before the deep drawing operation, a deep drawing forming model of the high-tensile steel plate is constructed using finite element analysis software, specifically including: S6.1 Import the actual material properties of the steel plate: elastic modulus 205 GPa, Poisson's ratio 0.3, yield strength 340 MPa, tensile strength 440 MPa, elongation at break 22%, and work hardening curve (obtained based on tensile test).

[0007] S6.2 Mesh generation uses 0.5-1mm quadrilateral reduced integral elements to simulate material flow trajectory and stress-strain distribution. Crack-prone areas (stress values ​​> 380MPa) are highlighted in red. For crack-prone areas, adjust the die fillet radius, blank holder force, or stretching speed parameters. For example, if the simulation shows that the stress at the die inlet is too high, further increase the inlet fillet radius to R1.2mm, or reduce the blank holder force in that area by 5%-10%.

[0008] S6.3. Based on simulation results, control the maximum depth-to-diameter ratio of a single deep drawing to ≤2.5 (depth-to-diameter ratio = forming depth / workpiece opening diameter); if the deep drawing requirement exceeds this depth-to-diameter ratio (e.g., depth-to-diameter ratio 3.0), then adopt a multi-stage forming process, for example, forming in two stages: the first stage forming to a depth-to-diameter ratio of 1.8, and the second stage forming to a depth-to-diameter ratio of 3.0. If the tensile deformation in each pass exceeds 20%, then perform intermediate annealing between adjacent passes: place the steel plate in a box furnace, hold at 550℃ for 60 minutes, and allow it to cool naturally at room temperature to restore the material's ductility and avoid the risk of work hardening exacerbating cracking. S7. After deep drawing, the formed workpiece is placed in an aging furnace, heated to 180℃, and held for 60 minutes, then cooled to room temperature in the furnace (cooling rate 5℃ / min). This treatment can eliminate 60%-70% of the residual stress inside the workpiece, improve strength stability, and prevent deformation or cracking due to stress release during subsequent use; the yield strength of the workpiece after treatment is controlled to increase by 5%-8%, ensuring a balance between strength and plasticity. Before each batch of production, the speed accuracy of the tensile testing machine is calibrated (error ≤ ±1%) to ensure the accuracy of process parameters; after deep drawing, a combination of eddy current testing and visual inspection is used to inspect the workpiece quality: the eddy current testing frequency is set to 50-60kHz, which can identify surface and near-surface cracks with a depth ≥0.1mm and a length ≥1mm; visual inspection uses a 20x magnifying glass to observe the workpiece surface to ensure there are no defects such as cracks, wrinkles, or scratches.

[0009] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention demonstrates significant crack prevention: by reducing the hardness of the steel plate through tempering pretreatment, optimizing the rounded corners and surface condition of the mold, and dynamically controlling the blank holder force and stretching speed, the cracking rate of deep drawing of SAPH440 steel plates is effectively reduced, and the pass rate is significantly improved. It avoids the passive mode of "rejecting all defective products," greatly reducing raw material waste. Simultaneously, the combination of the SKD11 mold and carbide coating extends mold life and reduces mold replacement costs. Through 3D simulation to predict cracking risk, constant temperature and humidity control of the environment, and regular equipment calibration, the consistency of process parameters in mass production is ensured. This method is designed specifically for the material characteristics of SAPH440 steel plates and can be adapted to the deep drawing requirements of other high-tensile steel plates by adjusting parameters such as tempering temperature and blank holder force ratio, making it widely applicable.

[0010] This invention achieves a four-dimensional dynamic demonstration of construction information, full life-cycle quality traceability, and intelligent, user-friendly, and efficient document generation by uploading daily construction reports from the project site, conducting automatic big data analysis, and sharing data with BIM models. It assists construction units and other participating parties in efficiently managing rail transit projects, realizes efficient integration of offline data and online digitization, greatly simplifies the digitization path of construction information, facilitates operation for construction personnel, and enriches the usage scenarios for construction units and other participating parties. It has good economic and social benefits and broad application prospects. Attached Figure Description

[0011] In the attached diagram: Figure 1 This is a schematic diagram of the method flow according to an embodiment of the present invention. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Generally, the components of the embodiments of the present invention described and shown in the accompanying drawings can be arranged and designed in various different configurations.

[0013] A method for preventing cracking in deep drawing of high-tensile steel plates, specifically including the following steps: S1. Tempering pretreatment of steel plates: The high-tensile SAPH440 series steel sheet (2-5mm thick, initial hardness 72-75HRB) to be processed is placed in a box-type resistance furnace and heated to 180℃ at a heating rate of 10℃ / min, and held at this temperature for 1 hour to ensure uniform softening of the internal structure of the steel sheet. After the holding time, the steel sheet is removed and placed in a room temperature (20±5℃) environment to cool naturally. During the cooling process, wind or water spraying should be avoided to accelerate cooling and prevent thermal stress from being generated inside the steel sheet. After this treatment, the hardness of the steel sheet is reduced to HRB≤65, and the toughness is increased by 20%-30%, meeting the basic requirements of deep drawing for material plasticity and reducing the risk of tensile fracture caused by excessive hardness from the root. S2, Deep Drawing Mold Optimization: S2.1. The flanged area of ​​the deep drawing mold is machined using a CNC milling machine, increasing the original flange radius (R) from R0.5mm to R1mm. During machining, a 10mm diameter ball end mill is used, with a milling speed set to 2000 r / min and a feed rate of 500 mm / min to ensure a smooth, stepless transition at the fillet. After machining, the fillet radius is checked using a coordinate measuring machine, with the error controlled within ±0.05mm. The increased R angle optimizes the material flow path at the flange, reducing the local stress concentration factor by 30%-40% and significantly reducing the probability of flange cracking. S2.2 The deep drawing mold is made of high-quality SKD11 carbon steel. The new SKD11 mold is subjected to vacuum heat treatment. First, it is preheated at 850℃ for 2 hours, then heated to 1050℃ and held for 1.5 hours, and finally tempered at 500℃ for 2 hours. After treatment, the mold core hardness reaches HRC58-62, and the wear resistance is improved by more than 50% compared with the original Cr12 material, avoiding scratches on the steel plate and local stress concentration cracking caused by mold core wear. S2.3. The heat-treated SKD11 mold core undergoes a thermal diffusion method for carbide coating treatment (carbide coating treatment): The mold core is placed in a molten salt bath (mainly composed of vanadium carbide) and held at 850℃ for 4 hours, forming a vanadium carbide coating with a thickness of 5-10 μm on the mold core surface. After coating treatment, the mold core surface is polished with a diamond wheel at a polishing speed of 1500 r / min, ultimately achieving a surface hardness of approximately HV3200 and a surface roughness Ra≤0.8μm. This coating can reduce the coefficient of friction between the mold and the steel plate from 0.15-0.20 to 0.08-0.10, reducing tensile resistance during deep drawing and preventing tearing defects at the bends. S3. Dynamic control of blank holder force: A 400-ton servo punch press is used in conjunction with a hydraulic servo system, and the blank holder force is controlled in coordination with the hydraulic pad and the proportional pressure valve. S3.1 Obtain the yield strength (typical value 340MPa) of the high-tensile steel plate through material mechanical property testing, and set the initial blank holder force to 30%-40% of the yield strength, i.e. 102-136kN; the blank holder force is output through the hydraulic cushion of the punch press and the proportional pressure valve, and the pressure accuracy is controlled within ±0.5kN. S3.2 During the deep drawing process, the displacement sensor of the punch press collects the slide stroke in real time, and the blank holder force changes linearly with the slide stroke: 0-30% of the slide stroke is the initial forming stage, and the blank holder force maintains the initial value; 3%-70% of the slide stroke is the deep forming stage, and the blank holder force increases at a rate of 0.5kN / mm; 70%-100% of the slide stroke is the final forming stage, and the blank holder force maintains the maximum value. Simultaneously, the slide position is monitored in real time using a pre-stroke comparison method, controlling the positional deviation within ±0.1mm to ensure precise matching between the blank holder force and the mold cavity position, avoiding material wrinkling due to insufficient blank holder force or excessive stretching and cracking due to excessive blank holder force. The response time of the hydraulic servo system is ≤50ms, which can compensate for pressure fluctuations caused by changes in material flow in real time. S4. Staged control of tensile strain rate: Based on the mechanical properties of the steel plate at different forming stages, the tensile strain rate is controlled in stages, specifically corresponding to the slide movement speed of the punch press. S4.1, Elastic Stage (Slider Stroke 0-10%): Tensile strain rate controlled at ≤0.00025s. -1 The corresponding slider speed is ≤0.5mm / s to avoid dynamic effects interfering with the determination of the material yield point and to ensure uniform elastic deformation. S4.2, Yield Stage (slider stroke 10%-50%): Tensile strain rate controlled at 0.00025-0.0025s. -1The corresponding slider speed is 0.5-5mm / s (adjusted according to the actual hardness of the steel plate: 0.5-3mm / s when the hardness is 60-65HRB, and 3-5mm / s when the hardness is ≤60HRB), to ensure that the plastic deformation is fully developed and to balance work hardening and deformation uniformity. S4.3, Strengthening to fracture stage (slider stroke 50%-100%): tensile strain rate controlled at ≤0.0083s. -1 The corresponding slider speed is ≤8mm / s to control the stability of the necking process and reduce the risk of breakage. The overall stretching speed corresponds to a machine operation frequency of 10-30 times / minute to ensure that the material has sufficient time to flow and avoid cracking caused by instantaneous stress concentration.

[0014] S5. Lubrication and Environmental Control: S5.1. Use a special oil-based deep-drawing lubricant, the formula of which is: oil phase, soap / grease, water, solid (filler), additives (defoamer, bactericide, inorganic buffer, non-ferrous metal passivator).

[0015] The lubricant is evenly sprayed onto the surface of the mold cavity and the contact area between the blank and the mold using an automatic spraying device. The spraying thickness is controlled at 8-12 μm, and the spraying pressure is 0.3 MPa. Mixing with other types of lubricating oil is strictly prohibited to prevent lubricant film failure. Simultaneously, because the mold surface has undergone carbide coating treatment to achieve a smoothness Ra≤0.2 μm, lubricant consumption is reduced, ensuring the stability of the lubricating film under high temperature and high pressure. S5.2. Control the ambient temperature of the deep drawing process at 20±5℃ and the humidity at 40%-60%; S6. Before the deep drawing operation, a deep drawing forming model of the high-tensile steel plate is constructed using finite element analysis software, specifically including: S6.1 Import the actual material properties of the steel plate: elastic modulus 205 GPa, Poisson's ratio 0.3, yield strength 340 MPa, tensile strength 440 MPa, elongation at break 22%, and work hardening curve (obtained based on tensile test).

[0016] S6.2 Mesh generation uses 0.5-1mm quadrilateral reduced integral elements to simulate material flow trajectory and stress-strain distribution. Crack-prone areas (stress values ​​> 380MPa) are highlighted in red. For crack-prone areas, adjust the die fillet radius, blank holder force, or stretching speed parameters. For example, if the simulation shows that the stress at the die inlet is too high, further increase the inlet fillet radius to R1.2mm, or reduce the blank holder force in that area by 5%-10%.

[0017] S6.3. Based on simulation results, control the maximum depth-to-diameter ratio of a single deep drawing to ≤2.5 (depth-to-diameter ratio = forming depth / workpiece opening diameter); if the deep drawing requirement exceeds this depth-to-diameter ratio (e.g., depth-to-diameter ratio 3.0), then adopt a multi-stage forming process, for example, forming in two stages: the first stage forming to a depth-to-diameter ratio of 1.8, and the second stage forming to a depth-to-diameter ratio of 3.0. If the tensile deformation in each pass exceeds 20%, then perform intermediate annealing between adjacent passes: place the steel plate in a box furnace, hold at 550℃ for 60 minutes, and then air cool to restore the material's ductility and avoid the risk of work hardening exacerbating cracking. S7. After deep drawing, the formed workpiece is placed in an aging furnace, heated to 180℃, and held for 1 hour, then cooled to room temperature in the furnace (cooling rate 5℃ / min). This treatment can eliminate 60%-70% of the residual stress inside the workpiece, improve strength stability, and avoid deformation or cracking due to stress release during subsequent use; the yield strength of the workpiece after treatment is controlled to increase by 5%-8%, ensuring a balance between strength and plasticity. Before each batch of production, the speed accuracy of the tensile testing machine is calibrated (error ≤ ±1%) to ensure the accuracy of process parameters; after deep drawing, a combination of eddy current testing and visual inspection is used to inspect the workpiece quality: the eddy current testing frequency is set to 50-60kHz, which can identify surface and near-surface cracks with a depth ≥0.1mm and a length ≥1mm; visual inspection uses a 20x magnifying glass to observe the workpiece surface to ensure there are no defects such as cracks, wrinkles, or scratches.

[0018] Example 1: Step 1: Place the steel plate (initial hardness 73HRB) into a box-type resistance furnace, heat it to 180℃ at 10℃ / min, hold it at that temperature for 1 hour, and then let it cool naturally at room temperature. After cooling, the hardness is measured to be 62HRB, and the toughness is increased by 25% compared to the initial state.

[0019] Step 2: Mold corner radius: The flange radius is machined to 1mm, with a three-coordinate measuring machine error of ±0.03mm; Mold material: changed to SKD11 steel, with a hardness of HRC59 after heat treatment; Carbide coating treatment: salt bath temperature 850℃, heat preservation for 4h, coating thickness 8μm, surface roughness Ra=0.15μm after polishing.

[0020] Step 3: Initial blank holder force: SAPH440 yield strength 340MPa, initial blank holder force = 340MPa × 35% × (workpiece projected area 0.02m²) = 23.8kN; The blank holder force is 23.8kN for 0-30% of the slider stroke; 43.8kN for 30%-70% of the slider stroke, increasing by 0.5kN / mm; and 43.8kN for 70%-100% of the slider stroke. The slider position deviation is controlled within ±0.08mm.

[0021] Step 4: Elastic Stage (0-10%): Slider speed 0.5 mm / s (strain rate 0.00025 s) -1 ); Yield stage (10%-50%): slider speed 3mm / s (strain rate 0.0015s) -1 ); Strengthening stage (50%-100%): slider speed 6mm / s (strain rate 0.006s) -1 ); Machine operating frequency: 20 times / minute.

[0022] Step 5: Lubricant spraying: 10μm thickness, spraying pressure 0.3MPa; Environmental parameters: temperature 22℃, humidity 50%.

[0023] Step 6: 3D Simulation and Forming Optimization: Simulation results: The crack-prone area is at the die inlet (stress 360MPa), and no parameter adjustment is required; Forming times: Single forming (depth-to-diameter ratio 2.2 ≤ 2.5).

[0024] Step 7: Post-processing and quality inspection of the workpiece: Aging treatment: Hold at 180℃ for 1 hour, then cool with the furnace; Quality inspection: Eddy current testing found no cracks, and visual inspection showed no wrinkles or scratches, effectively improving the pass rate.

[0025] This invention exhibits significant crack prevention effects: by reducing the hardness of the steel plate through tempering pretreatment, optimizing the rounded corners and surface condition of the mold, and dynamically controlling the blank holder force and stretching speed, the cracking rate of deep drawing of SAPH440 steel plate is effectively reduced, and the pass rate is significantly improved; it avoids the passive mode of rejecting defective products through full inspection, greatly reducing the waste rate of raw materials. At the same time, the combination of SKD11 mold and carbide coating extends the mold life and reduces mold replacement costs; by predicting cracking risk through 3D simulation, controlling the constant temperature and humidity of the environment, and regularly calibrating the equipment, the consistency of process parameters in mass production is ensured; This method is designed for the material properties of SAPH440 steel plates. By adjusting parameters such as tempering temperature and blank holder force ratio, it can be adapted to the deep drawing requirements of other high-tensile steel plates, making it widely applicable.

[0026] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications, improvements, and substitutions without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for preventing cracking during deep drawing and forming of high-tensile steel plates, characterized in that, Specifically, the following steps are included: S1. Stress-relieving tempering pretreatment of steel plates: Heat the steel plate to 180℃, hold for 30 minutes, then allow it to cool naturally at room temperature. To relieve stamping stress (50%-70%), maintain material strength, avoid low-temperature brittleness, and prevent a decrease in steel plate hardness; S2, Deep Drawing Mold Optimization: S2.1 Increase the flange radius of the deep drawing mold to R1; S2.2 The deep drawing mold is made of SKD11 high-quality carbon steel; S2.3 The bending punch and drawing die of the mold are treated with carbide coating by thermal diffusion method; S3. Dynamic control of blank holder force: A large-tonnage servo punch press is used in conjunction with a hydraulic servo system, and the blank holder force is controlled in coordination with the hydraulic pad and the proportional pressure valve. S3.1 The initial blank holder force is taken as 30%-40% of the yield strength of the high-tensile steel plate; S3.2 The blank holder force is dynamically adjusted with an accuracy of ±0.1MPa within the range of 0-20MPa as the deep drawing depth increases, with a response time of ≤50ms. The blank holder force changes linearly with the stroke of the punch press slide, and the slide position deviation is controlled within ±0.1mm by the pre-stroke comparison method. S4. Staged control of tensile strain rate: S4.1, Elastic stage: Tensile strain rate ≤ 0.00025s -1 ; S4.2, Yield Stage: The tensile strain rate is controlled between 0.00025 and 0.0025 s. -1 ; S5. Lubrication and Environmental Control: S5.

1. Apply oil-based deep drawing lubricant evenly to the concave die surface and the contact area between the blank and the die, while ensuring that the surface finish of the die reaches Ra≤0.2μm. S5.

2. Control the ambient temperature of the deep drawing process at 20±5℃ and the humidity at 40%-60%; S6. Using 3D modeling and simulation technology, import the material performance parameters of the steel plate before the deep drawing operation, simulate the material flow trajectory and stress-strain distribution, identify crack-prone areas and optimize machine parameters; control the maximum depth-to-diameter ratio of a single deep drawing to ≤2.

5. If it exceeds this depth-to-diameter ratio, adopt a multi-stage forming process. When the tensile deformation of each pass exceeds 20%, keep it at 550℃ for 60 minutes between adjacent passes, and allow it to cool naturally at room temperature to restore the material's ductility. S7. After the deep drawing operation is completed, the formed workpiece is subjected to aging treatment to eliminate internal residual stress.

2. The method for preventing cracking in deep drawing of high-tensile steel plates according to claim 1, characterized in that, In step S2.3, the carbide coating process has a coating thickness of 5-10 μm, and the mold surface is polished after the process.

3. The method for preventing cracking in deep drawing of high-tensile steel plates according to claim 1, characterized in that, In step S3, the hydraulic servo system is equipped with a pressure feedback module to collect the blank holder force data of each area in real time. When the blank holder force in a certain area fluctuates beyond ±0.3MPa, the system automatically adjusts the output of the proportional pressure valve.

4. The method for preventing cracking in deep drawing of high-tensile steel plates according to claim 1, characterized in that, The oily deep-drawing lubricant in step S5.1 includes: Oil phase: 25%, a mixture of mineral oil, animal fat, or vegetable oil (C18-C24 series hydrocarbons), providing basic lubrication. Soap / Fat: 5%, soap base (fatty acid salt), forms an adsorption film between the metal and the mold. Water: 25%, forms an emulsion system with oil and soap, adjusts viscosity and helps disperse solids. Solids (fillers): 45%, including graphite, limestone (calcium carbonate / lime powder), zinc oxide, carbonates, borates, etc., to enhance boundary lubrication and reduce friction. Additives: defoamers, bactericides, inorganic buffers, non-ferrous metal passivators, etc., are used to improve the stability, anti-foaming, and anti-corrosion properties of lubricants.

5. The method for preventing cracking in deep drawing of high-tensile steel plates according to claim 1, characterized in that, In step S6, 3D modeling and simulation are performed using finite element analysis software, with mesh generation accuracy controlled within 0.5-1mm. The work hardening curve of the steel plate is introduced during the simulation process.

6. The method for preventing cracking in deep drawing of high-tensile steel plates according to claim 5, characterized in that, In step S6, the interval between adjacent forming processes is 10-15 minutes. During the interval, compressed air is used to clean the residual lubricant and impurities on the steel plate surface. At the same time, visual inspection is used to preliminarily check whether there are microcracks on the steel plate surface. If microcracks are found, the subsequent forming is stopped and the microcracked areas are locally repaired.

7. The method for preventing cracking in deep drawing of high-tensile steel plates according to claim 1, characterized in that, The aging process in step 7 specifically involves heating the molded workpiece to 550°C and holding it at that temperature for 60 minutes, then allowing it to cool naturally to room temperature.

8. The method for preventing cracking in deep drawing of high-tensile steel plates according to claim 1, characterized in that, Before the tempering pretreatment in step 1, the steel plate billet is edge-treated. After the billet is cut by laser cutting, the edges of the billet are chamfered with a chamfer radius of 0.3-0.5mm to remove edge burrs and tear strips.

9. The method for preventing cracking in deep drawing of high-tensile steel plates according to claim 1, characterized in that, In step 3, the servo punch press is equipped with a displacement monitoring module to monitor the slider movement trajectory in real time. When the slider movement speed fluctuates beyond ±0.1mm / s, the system automatically adjusts the drive parameters.

10. The method for preventing cracking in deep drawing of high-tensile steel plates according to claim 1, characterized in that, After the deep drawing operation is completed, the quality of the workpiece is inspected by a combination of eddy current testing and visual inspection. The eddy current testing frequency is set to 50-60kHz.

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