A method for improving shape accuracy of hot stamped parts

Abstract

The application relates to a method for improving the shape precision of a hot stamping part, and belongs to the technical field of hot stamping processes. The method comprises the following steps: obtaining a hot forming steel plate; according to the surface state of the hot forming steel plate, high-temperature friction coefficient detection is carried out to perform simulation analysis; according to the simulation analysis result, a plate material is prepared; according to the surface state of the hot forming steel plate, hot stamping process parameters are determined; the plate material is subjected to hot stamping to generate a hot forming part; the hot forming part is subjected to hot cutting to generate an initial part; the initial part is subjected to pressure holding quenching to generate a target part; and the target part is subjected to shape precision and performance detection. Through a series of innovative measures, the size precision problem encountered by the hot forming steel plate in the hot stamping process is effectively solved, the production efficiency and the part performance are improved, and technical support is provided for the high-quality development of the automobile manufacturing industry.

Description

Technical Field

[0001] This application relates to the field of hot stamping technology, and in particular to a method for improving the shape accuracy of hot stamped parts. Background Technology

[0002] To improve the strength and lightweighting of automobile bodies, hot-formed steel and hot stamping technology play a crucial role in the manufacturing of body components. With the rapid development of the automotive industry, the demands for vehicle safety and fuel economy are increasing, making lightweighting a key measure for reducing energy consumption and emissions. Hot-formed steel, due to its high strength and excellent formability, has become an important material for achieving automotive lightweighting. After being heated to an austenitic state, hot-formed steel is stamped using a die and then rapidly quenched to obtain a martensitic structure with ultra-high strength, significantly improving the load-bearing capacity and collision resistance of parts. This technology is particularly suitable for manufacturing automotive body structural components, such as A-pillars, B-pillars, and anti-collision beams—critical safety components.

[0003] However, during hot stamping, the setting of process parameters has a crucial impact on the performance and forming accuracy of the parts. To avoid the oxide scale problem that occurs in traditional bare sheets during heating and stamping, surface treatment technologies such as aluminum-silicon coatings and zinc-based coatings have been developed and applied. These coatings not only effectively reduce oxide scale formation but also provide additional corrosion resistance, thereby further expanding the application range of hot-formed steel.

[0004] Nevertheless, hot-formed steels with different coating conditions exhibit variations in high-temperature formability and the performance of parts after hot stamping. Therefore, different process parameters need to be set according to the characteristics of the coating. Furthermore, with the increasing design and application of large-size hot-formed parts, controlling the dimensional accuracy of parts after hot stamping has become a major challenge. Especially in the edge areas of parts, large shape deviations often occur due to the accumulation of dimensional accuracy errors. Summary of the Invention

[0005] This application provides a method for improving the shape accuracy of hot-stamped parts to solve the following technical problem: how to improve the shape accuracy of hot-stamped parts.

[0006] This application provides a method for improving the formability of hot-stamped parts, the method comprising:

[0007] To obtain hot-formed steel sheets;

[0008] Based on the surface condition of the hot-formed steel sheet, the high-temperature friction coefficient was tested for simulation analysis.

[0009] Based on the results of the simulation analysis, the sheet metal is prepared.

[0010] The hot stamping process parameters are determined based on the surface condition of the hot-formed steel sheet;

[0011] The sheet metal is hot-stamped to produce a thermoformed part;

[0012] The thermoformed part is hot-stamped to produce an initial part;

[0013] The initial part is subjected to pressure holding quenching to generate the target part;

[0014] The target part is subjected to shape accuracy and performance testing.

[0015] Optionally, the shape accuracy and performance testing of the target part includes:

[0016] Obtain the absolute value S0 of the maximum allowable shape error of the target part;

[0017] Determine the absolute value S1 of the actual shape error of the hot-stamped part;

[0018] Compare the absolute value of the maximum shape error S0 with the absolute value of the actual shape error S1;

[0019] Based on the comparison results, determine whether the hot stamping process parameters need to be adjusted.

[0020] Optionally, determining whether to adjust the hot stamping process parameters based on the comparison results includes:

[0021] Determine whether S1 is less than S0;

[0022] If so, the target part is determined to have acceptable shape accuracy, and no adjustment of hot stamping process parameters is required;

[0023] If not, the target part is determined to be unqualified in terms of shape accuracy, and the hot stamping process parameters need to be adjusted.

[0024] Optionally, determining that the target part's shape accuracy is unqualified and that hot stamping process parameters need to be adjusted includes:

[0025] The shape error deviation S2 of the target part is obtained, where S2 = S1 - S0;

[0026] The shape error deviation ratio S3 of the target part is obtained, where S3 = S2 / S0;

[0027] Adjust the mold cooling water flow rate L2 according to S3, where L2=L1*(1-A*S3), and L1 is the initial water flow rate of the mold;

[0028] If the hot-formed steel sheet is a bare sheet, A = 1;

[0029] If the hot-formed steel sheet is an aluminum-silicon coated steel sheet, A = 1.1;

[0030] If the hot-formed steel sheet is a zinc-based coated steel sheet, A = 1.25.

[0031] Optionally, the step of performing high-temperature friction coefficient testing based on the surface condition of the hot-formed steel sheet for simulation analysis includes:

[0032] If the hot-formed steel sheet is a bare sheet, the heating temperature for the high-temperature friction coefficient test is 880-960℃, and the holding time is 2-10 minutes.

[0033] If the hot-formed steel sheet is an aluminum-silicon coated steel sheet, the heating temperature for the high-temperature friction coefficient test is 880-950℃, and the holding time is 3-8 minutes.

[0034] If the hot-formed steel sheet is a zinc-based coated steel sheet, the heating temperature for the high-temperature friction coefficient test is 880-910℃, and the holding time is 3-12 minutes.

[0035] Optionally, determining the hot stamping process parameters based on the surface condition of the hot-formed steel sheet includes:

[0036] If the hot-formed steel sheet is a bare sheet, the hot stamping process parameters include: heating temperature of 880℃~960℃, holding time of 2min~10min, and initial cooling water flow rate of the die of 1.2m³ / min. 3 / h~7.2m 3 / h;

[0037] If the hot-formed steel sheet is an aluminum-silicon coated steel sheet, the hot stamping process parameters include: a heating temperature of 880℃~950℃, a holding time of 3min~8min, and an initial cooling water flow rate of 1.1m³ / min for the mold. 3 / h~7.2m 3 / h;

[0038] If the hot-formed steel sheet is a zinc-based coated steel sheet, the hot stamping process parameters include: heating temperature of 860–910℃, holding time of 3–12 minutes, initial temperature of the sheet entering the mold not exceeding 770℃, and initial cooling water flow rate of the mold of 1 m³ / min. 3 / h~7.2m 3 / h.

[0039] Optionally, the step of performing pressure holding quenching on the initial part to generate the target part includes:

[0040] If the hot-formed steel sheet is a bare sheet, the holding time for the pressure quenching is 4s to 20s;

[0041] If the hot-formed steel sheet is an aluminum-silicon coated steel sheet, the holding time for the pressure quenching is 4s to 20s;

[0042] If the hot-formed steel sheet is a zinc-based coated steel sheet, the holding time for the pressure quenching is 4s to 18s.

[0043] Optionally, the step of performing pressure holding quenching on the initial part to generate the target part includes:

[0044] If the target part is a non-opening part, the initial part is subjected to pressure holding quenching, and then rapidly cooled after mold opening to generate the target part; the pressure holding time of the pressure holding quenching is 0.2s to 10s, and the cooling rate of the rapid cooling is 100℃ / s to 300℃ / s.

[0045] Optionally, the step of hot-punching the thermoformed part to generate an initial part includes:

[0046] If the strength grade of the hot-formed steel sheet is ≤950MPa, the gap value of the hot punching is 0.1mm~0.36mm; if the strength grade of the hot-formed steel sheet is >950MPa, the gap value of the hot punching is 0.15mm~0.8mm.

[0047] If the thickness of the sheet metal is ≤1.6mm, the gap value of the hot punching is 0.1mm~0.36mm; if the thickness of the sheet metal is >1.6mm, the gap value of the hot punching is 0.15mm~0.9mm.

[0048] The technical solutions provided in this application have the following advantages compared with the prior art:

[0049] This application provides a method for improving the formability of hot-stamped parts. The method includes: obtaining a hot-formed steel sheet; performing high-temperature friction coefficient testing based on the surface condition of the hot-formed steel sheet for simulation analysis; preparing the sheet metal based on the simulation analysis results; determining hot-stamping process parameters based on the surface condition of the hot-formed steel sheet; hot-stamping the sheet metal to generate a hot-formed part; hot-cutting the hot-formed part to generate an initial part; performing pressure-holding quenching on the initial part to generate a target part; and testing the shape accuracy and performance of the target part. By setting hot-stamping process parameters specifically based on the surface condition of the hot-formed steel sheet, it helps to improve the forming accuracy and surface quality of hot-stamped parts. Furthermore, by scientifically adjusting the hot-stamping process parameters based on subsequent shape accuracy testing results, the shape accuracy of the parts can be optimized, reducing rework and scrap caused by substandard dimensional accuracy, producing high-quality parts that better meet market demands, thereby enhancing the product's market competitiveness. Attached Figure Description

[0050] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0051] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0052] Figure 1 This is a flowchart illustrating a method for improving the formability of hot-stamped parts, as provided in an embodiment of this application. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0054] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1 to 6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "comprise" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0055] Figure 1 This is a flowchart illustrating a method for improving the formability of hot-stamped parts, as provided in an embodiment of this application.

[0056] like Figure 1 As shown in the figure, this application provides a method for improving the formability of hot-stamped parts, the method comprising:

[0057] S1. Obtain hot-formed steel sheet;

[0058] S2. Based on the surface condition of the hot-formed steel plate, the high-temperature friction coefficient is tested for simulation analysis.

[0059] The coefficient of friction varies at high temperatures for hot-formed steel sheets with different surface conditions. Setting appropriate high-temperature friction coefficient testing parameters (such as heating temperature and holding time) for each surface condition allows for more accurate measurement of the friction coefficient under that condition. Accurate friction coefficient data is fundamental to establishing a simulation model, directly affecting the accuracy and reliability of the simulation analysis. Therefore, this step provides solid data support for subsequent simulation optimization.

[0060] In some embodiments, the step of performing high-temperature friction coefficient testing based on the surface condition of the hot-formed steel sheet for simulation analysis includes:

[0061] If the hot-formed steel sheet is a bare sheet, the heating temperature for the high-temperature friction coefficient test is 880-960℃, and the holding time is 2-10 minutes.

[0062] If the hot-formed steel sheet is an aluminum-silicon coated steel sheet, the heating temperature for the high-temperature friction coefficient test is 880-950℃, and the holding time is 3-8 minutes.

[0063] If the hot-formed steel sheet is a zinc-based coated steel sheet, the heating temperature for the high-temperature friction coefficient test is 880-910℃, and the holding time is 3-12 minutes.

[0064] In the friction coefficient test, a linear stretching method can be used. During the stretching process, two clamps are used to apply a certain pressure to the sheet material, and a tension is applied to one side of the sheet. The high-temperature friction coefficient value is obtained by collecting the tension and pressure.

[0065] S3. Based on the results of the simulation analysis, prepare the sheet metal.

[0066] By testing the friction coefficient of the material at high temperatures and combining it with the geometric model of the part, a simulation model is established to simulate the frictional heat generation process, and then simulation analysis and optimization are performed. The optimal sheet metal profile and process parameters are determined, and sheet metal is prepared according to the designed hot-stamped part. Sheet metal preparation methods mainly include blanking; for welded or patched parts, the sheet metal is prepared by welding or spot welding the patch.

[0067] S4. Determine the hot stamping process parameters based on the surface condition of the hot-formed steel sheet;

[0068] The forming behavior of hot-formed steel sheets with different surface conditions varies during the hot stamping process. For each surface condition of hot-formed steel sheet, by precisely setting the hot stamping process parameters (such as heating temperature, holding time, and initial cooling water flow rate of the die), the material microstructure transformation and forming process can be more effectively controlled, thereby reducing the dimensional deviation and shape error of the parts.

[0069] In some embodiments, determining the hot stamping process parameters based on the surface condition of the hot-formed steel sheet includes:

[0070] If the hot-formed steel sheet is a bare sheet, the hot stamping process parameters include: heating temperature of 880℃~960℃, holding time of 2min~10min, and initial cooling water flow rate of the die of 1.2m³ / min. 3 / h~7.2m 3 / h;

[0071] If the hot-formed steel sheet is an aluminum-silicon coated steel sheet, the hot stamping process parameters include: a heating temperature of 880℃~950℃, a holding time of 3min~8min, and an initial cooling water flow rate of 1.1m³ / min for the mold. 3 / h~7.2m 3 / h;

[0072] If the hot-formed steel sheet is a zinc-based coated steel sheet, the hot stamping process parameters include: heating temperature of 860–910℃, holding time of 3–12 minutes, initial temperature of the sheet entering the mold not exceeding 770℃, and initial cooling water flow rate of the mold of 1 m³ / min. 3 / h~7.2m 3 / h.

[0073] S5. The sheet metal is hot-stamped to produce a thermoformed part;

[0074] According to the determined hot stamping process parameters, hot stamping is performed, mainly including heating the sheet metal, transferring the sheet metal after heating and holding it at the correct temperature, and then transferring the sheet metal by a robotic arm to the hot stamping die for hot stamping forming. For zinc-based coated hot-formed steel sheets, pre-cooling can be performed during the transfer process to reduce the surface temperature of the sheet metal.

[0075] S6. Perform hot punching on the thermoformed part to generate an initial part;

[0076] Hot stamping can remove excess scrap and hole material. The hot stamping process needs to be optimized for different hot stamping production lines. When the hot stamping production line has a scrap collection and processing design, all scrap can be stamped and punched away, allowing for on-line scrap collection and processing. When the hot stamping production line does not have a scrap collection and processing design, the hot stamping and punching process cannot remove all scrap; a portion must be retained so that a small part of the scrap remains connected to the part. The part is then fed into a subsequent laser cutting stage where the scrap is removed by laser cutting.

[0077] Setting the appropriate hot stamping clearance value has a direct impact on the quality and accuracy of the stamped edge. When hot stamping hot-formed parts to produce the initial part, the hot stamping clearance value can be set according to the strength grade and thickness of the hot-formed steel sheet to ensure that the gap between the cutting edge and the material is moderate during the stamping process. If the gap is too large, it will easily lead to more burrs on the stamped edge, while if it is too small, it may aggravate die wear or increase the stamping force. Setting it appropriately can ensure that the stamped edge is flat and smooth, thereby improving the overall appearance quality and dimensional accuracy of the part.

[0078] In some embodiments, hot punching the thermoformed part to generate an initial part includes:

[0079] If the strength grade of the hot-formed steel sheet is ≤950MPa, the gap value of the hot punching is 0.1mm~0.36mm; if the strength grade of the hot-formed steel sheet is >950MPa, the gap value of the hot punching is 0.15mm~0.8mm.

[0080] If the thickness of the sheet metal is ≤1.6mm, the gap value of the hot punching is 0.1mm~0.36mm; if the thickness of the sheet metal is >1.6mm, the gap value of the hot punching is 0.15mm~0.9mm.

[0081] For bare steel plates, aluminum-silicon coated steel plates, and zinc-based coated steel plates, by setting a reasonable holding quenching time, it is possible to ensure that the microstructure of the parts is uniformly transformed during the quenching process and reduce dimensional accuracy errors caused by quenching deformation.

[0082] S7. Perform pressure holding quenching on the initial part to generate the target part;

[0083] In some embodiments, the step of performing pressure holding quenching on the initial part to generate the target part includes:

[0084] If the hot-formed steel sheet is a bare sheet, the holding time for the pressure quenching is 4s to 20s;

[0085] If the hot-formed steel sheet is an aluminum-silicon coated steel sheet, the holding time for the pressure quenching is 4s to 20s;

[0086] If the hot-formed steel sheet is a zinc-based coated steel sheet, the holding time for the pressure quenching is 4s to 18s.

[0087] In some embodiments, the step of performing pressure holding quenching on the initial part to generate the target part includes:

[0088] If the target part is a non-opening part, the initial part is subjected to pressure holding quenching, and then rapidly cooled after mold opening to generate the target part; the pressure holding time of the pressure holding quenching is 0.2s to 10s, and the cooling rate of the rapid cooling is 100℃ / s to 300℃ / s.

[0089] For non-opening parts, this application proposes a hybrid cooling method (rapid cooling after pressure quenching and mold opening) to improve production efficiency. Non-opening parts typically have high geometric stiffness. The hybrid cooling method promotes the formation of fine, uniform lath martensite in materials such as low-carbon steel during rapid cooling. This structure possesses high strength and good toughness. By controlling the cooling rate and temperature, the morphology and distribution of martensite can be optimized, thereby improving the stiffness and strength of the part, effectively suppressing springback after forming, and ensuring the dimensional stability and shape accuracy of the part.

[0090] In this embodiment, after the non-opening part is hot-stamped, it can be opened after a short holding-pressure quenching time (0.2s to 10s) and then rapidly cooled. Controlling the holding-pressure quenching time within the short range of 0.2s to 10s allows for rapid completion of the quenching process, reducing the time the part spends in the mold and thus improving production efficiency; preferably, it is 0.2s to 5s. Simultaneously, rapid cooling (cooling rate of 100℃ / s to 300℃ / s) enables the part temperature to quickly reach the martensitic transformation completion point (M). f The temperature should be below 95%, and the martensite content should be greater than 95% to further shorten the production cycle. Rapid cooling can be achieved through direct water quenching or water mist cooling.

[0091] Water mist cooling technology relies on specialized equipment. This equipment can be installed on the side of the mold, or the water mist function can be achieved by designing dedicated water channels through perforations in the mold, or it can be specifically installed on the side of the press. If water mist devices are installed on both sides of the mold, after pressure holding and quenching, the part is clamped and then rapidly sprayed with water mist. If water mist channels are opened on the mold, after pressure holding and quenching, the part is rapidly cooled by water mist sprayed through these channels. If a dedicated water mist device is installed on the side of the press, the part is clamped and moved to the water mist device for water mist spraying. Here, it is required that the pressure holding and quenching process and the water mist spraying process be closely connected, and that water mist be sprayed rapidly after pressure holding and quenching. At the same time, the uniformity of the water mist spray must be ensured. If there is a lot of residual moisture on the surface of the part, it can be dried by baking or blowing air.

[0092] S8. Perform shape accuracy and performance testing on the target part.

[0093] In some embodiments, the shape accuracy and performance testing of the target part includes:

[0094] Obtain the absolute value S0 of the maximum allowable shape error of the target part;

[0095] Determine the absolute value S1 of the actual shape error of the hot-stamped part;

[0096] Compare the absolute value of the maximum shape error S0 with the absolute value of the actual shape error S1;

[0097] Based on the comparison results, determine whether the hot stamping process parameters need to be adjusted.

[0098] The absolute value S0 of the maximum allowable shape error of the target part can be obtained according to the GB / T 13914—2002 standard for dimensional tolerances of stamped parts. The absolute value S1 of the actual shape error of the hot-stamped part can be determined by using tools such as steel rulers and vernier calipers, or by using a handheld laser scanner and computer data processing.

[0099] Surface treatment is performed on parts, primarily targeting bare steel sheets and hot-formed steel with zinc-based coatings, as well as hot-formed steel with zinc as the main coating component. This is because bare steel sheets come into contact with oxygen during heating, transfer, and stamping, causing surface oxidation and the formation of oxide scale. Zinc-based coated steel sheets also come into contact with oxygen during heating, transfer, and stamping, resulting in surface oxidation and the formation of oxides such as zinc oxide. These oxides can affect subsequent coating performance, thus requiring surface treatment. For bare steel sheets, shot blasting can remove the surface oxide scale. For zinc-based coated hot-formed steel and hot-formed steel with zinc as the main coating component, light sandblasting can remove surface oxides such as zinc oxide.

[0100] After the surface treatment of the part, the shape contour of the part surface is obtained by a special scanning device, such as a blue light scanning device. Then, the scanned part surface contour is compared with the three-dimensional digital model of the part to obtain the absolute value S1 of the actual shape error of the part. Usually, the actual shape error is larger at the edges and corners of the part because the shape accuracy error of the part accumulates continuously, and the accuracy error is the largest at the edges and corners of the part. This error is recorded after it is obtained.

[0101] The absolute value S0 of the maximum permissible shape error in the part's design or manufacturing requirements is determined as the benchmark for judging whether the part's shape accuracy is acceptable. When designing parts, the critical dimensions and their permissible error ranges are usually clearly specified to ensure machining accuracy. For example, the dimensional accuracy of CNC-machined hardware parts can reach tolerances of ±0.01mm or less, and the surface roughness can achieve Ra0.8μm or less. Furthermore, some industries or customers may have specific requirements for the shape accuracy of parts, such as parallelism and perpendicularity typically requiring a tolerance within 0.02mm, and hole diameter accuracy reaching H7 level. These requirements must be referenced to relevant standards or agreements to meet specific design and machining requirements.

[0102] By directly comparing S1 and S0, and determining whether the shape accuracy is acceptable, it can be determined whether the hot stamping process parameters need to be adjusted to optimize the shape accuracy of the part.

[0103] In some embodiments, determining whether the hot stamping process parameters need to be adjusted based on the comparison results includes:

[0104] Determine whether S1 is less than S0;

[0105] If so, the target part is determined to have acceptable shape accuracy, and no adjustment of hot stamping process parameters is required;

[0106] If not, the target part is determined to be unqualified in terms of shape accuracy, and the hot stamping process parameters need to be adjusted.

[0107] In some implementations, determining that the target part's shape accuracy is unqualified and requiring adjustment of hot stamping process parameters includes:

[0108] The shape error deviation S2 of the target part is obtained, where S2 = S1 - S0;

[0109] The shape error deviation ratio S3 of the target part is obtained, where S3 = S2 / S0;

[0110] Adjust the mold cooling water flow rate L2 according to S3, where L2=L1*(1-A*S3), and L1 is the initial water flow rate of the mold;

[0111] If the hot-formed steel sheet is a bare sheet, A = 1;

[0112] If the hot-formed steel sheet is an aluminum-silicon coated steel sheet, A = 1.1;

[0113] If the hot-formed steel sheet is a zinc-based coated steel sheet, A = 1.25.

[0114] In the hot stamping process, experimental studies have shown that moderately reducing the cooling water flow rate can reduce the shape accuracy error of hot stamped parts. However, excessive reduction in the cooling water flow rate may weaken the cooling capacity of the mold, thereby affecting the mechanical properties of the material. Therefore, in order to ensure the shape accuracy and material properties of the parts, the cooling water flow rate must be scientifically adjusted to achieve the best cooling effect. In the embodiments of this application, the adjusted mold cooling water flow rate L2 can be calculated according to the formula L2=L1*(1-A*S3), where L1 is the initial water flow rate and A is the adjustment coefficient (affected by the coating state).

[0115] Based on the adjusted mold cooling water flow rate, stamping production and product shape accuracy inspection are performed. Then, based on the shape accuracy error, it is determined whether to continue adjusting the process parameters, thereby ensuring the accuracy of the part's forming precision. This method effectively ensures the forming precision and performance quality of the parts, and qualified parts can then be sent to subsequent processing stages.

[0116] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national / industry standards; if there is no corresponding national / industry standard, they are performed according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0117] Example 1

[0118] The aluminum-silicon coated hot-formed steel is heated to 930℃ and held at that temperature for 5 minutes. It is then removed from the furnace and transferred to a hot stamping die for hot stamping. The cooling water flow rate is 3 m³ / min. 3 / h. This part is a large beam-type component, with a maximum permissible absolute value of 4.0 mm for shape accuracy. Shape accuracy testing revealed a significant springback at the corners, reaching 5.1 mm. Therefore, the part's shape accuracy is substandard. The out-of-tolerance amount is 1.1 mm, resulting in an out-of-tolerance rate of 27.5%.

[0119] Therefore, the cooling water flow rate of the mold needs to be adjusted. Since the coating is an aluminum-silicon coating, the adjustment coefficient A is 1.1. Based on the shape error tolerance ratio, the adjusted water flow rate is L2 = L1 * (1 - A * S3) = 3 * (1 - 1.1 * 27.5%) = 2.0925 m³ / s. 3 / h, rounded up to 2.1m 3 / h. After adjusting the new parameters, the actual maximum shape error of the part was reduced to 3.2mm, meeting the requirements of subsequent stamping production.

[0120] Example 2

[0121] The zinc-based coated hot-formed steel is heated to 880℃ and held at that temperature for 6 minutes. It is then removed from the furnace and transferred to a hot stamping die for hot stamping. The cooling water flow rate is 3 m³ / min.3 The maximum allowable absolute value of the shape error for this column-type part is 0.5mm, but the measured edge position error is 0.7mm, exceeding the allowable range by 0.2mm, with an out-of-tolerance rate as high as 40%.

[0122] Therefore, the cooling water flow rate of the mold needs to be adjusted. Since the coating is zinc-based, the adjustment coefficient A is 1.25. Based on the shape error tolerance ratio, the adjusted water flow rate is L2 = L1 * (1 - A * S3) = 3 * (1 - 1.25 * 40%) = 1.5 m. 3 / h, rounded up to 1.5m 3 / h. After parameter adjustment, the maximum shape error of the part has been reduced to 0.45mm, which meets the standards for subsequent stamping production.

[0123] Example 3

[0124] For a non-opening part, hot-formed steel was heated to 930℃ and held at that temperature for 5 minutes. It was then rapidly transferred to a die for hot stamping, followed by pressure quenching for 4 seconds. The die was then opened, and the part was water-quenched for 2 seconds. A tensile sample was taken for testing, and the tensile strength was 1530 MPa, which is higher than the required value of 1350 MPa, thus meeting the strength standard.

[0125] Comparative Example 1

[0126] The aluminum-silicon coated hot-formed steel is heated to 930℃ and held at that temperature for 5 minutes. It is then removed from the furnace and transferred to a hot stamping die for hot stamping. The cooling water flow rate is 3 m³ / min. 3 / h. This part is a large beam-type component, with a maximum permissible absolute value of 4.0 mm for shape accuracy. Shape accuracy testing revealed a significant springback at the corners, reaching 5.1 mm. Therefore, the part's shape accuracy is substandard. The out-of-tolerance amount is 1.1 mm, resulting in an out-of-tolerance rate of 27.5%.

[0127] Therefore, it is necessary to adjust the mold cooling water flow rate. This can be achieved by increasing the water flow rate to 4m³ / h. 3 / h, the rebound amount is increased to 6mm.

[0128] Comparative Example 2

[0129] The zinc-based coated hot-formed steel is heated to 880℃ and held at that temperature for 6 minutes. It is then removed from the furnace and transferred to a hot stamping die for hot stamping. The cooling water flow rate is 3 m³ / min. 3 The maximum allowable absolute value of the shape error for this column-type part is 0.5mm, but the measured edge position error is 0.7mm, exceeding the allowable range by 0.2mm, with an out-of-tolerance rate as high as 40%.

[0130] Therefore, it is necessary to adjust the mold cooling water flow rate. The flow rate should be increased to 3.5m. 3 / h, the rebound amount increases to 1mm.

[0131] Comparative Example 3

[0132] For a non-opening part, hot-formed steel was heated to 930℃ and held at that temperature for 5 minutes. It was then quickly transferred to a mold for hot stamping, followed by mold-holding quenching for 8 seconds. The mold was then opened, and a tensile sample was taken for testing. The tensile strength was 1420 MPa, which is higher than the required value of 1350 MPa, indicating that the strength is qualified. Compared to Example 3, the total production time was extended by 2 seconds.

[0133] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0134] In this embodiment of the invention, the application of hot punching process and hybrid cooling method shortens the production cycle and improves overall production efficiency.

[0135] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.

Claims

1. A method for improving the shape accuracy of hot-stamped parts, the method comprising: To obtain hot-formed steel sheets; Based on the surface condition of the hot-formed steel sheet, the high-temperature friction coefficient was tested for simulation analysis. Based on the results of the simulation analysis, the sheet metal is prepared. The hot stamping process parameters are determined based on the surface condition of the hot-formed steel sheet; The sheet metal is hot-stamped to produce a thermoformed part; The thermoformed part is hot-stamped to produce an initial part; The initial part is subjected to pressure holding quenching to generate the target part; The target part is subjected to shape accuracy and performance testing; The shape accuracy and performance testing of the target part includes: Obtain the absolute value S0 of the maximum allowable shape error of the target part; Determine the absolute value S1 of the actual shape error of the hot-stamped part; Compare the absolute value of the maximum shape error S0 with the absolute value of the actual shape error S1; Based on the comparison results, determine whether the hot stamping process parameters need to be adjusted; The step of determining whether the hot stamping process parameters need to be adjusted based on the comparison results includes: Determine whether S1 is less than S0; If so, the target part is determined to have acceptable shape accuracy, and no adjustment of hot stamping process parameters is required; If not, the target part is determined to be unqualified in shape accuracy, and the hot stamping process parameters need to be adjusted. The determination that the target part's shape accuracy is unqualified requires adjustment of the hot stamping process parameters, including: The shape error deviation S2 of the target part is obtained, where S2 = S1 - S0; The shape error deviation ratio S3 of the target part is obtained, where S3 = S2 / S0; Adjust the mold cooling water flow rate L2 according to S3, where L2 = L1 * (1 - A * S3), and L1 is the initial water flow rate of the mold; If the hot-formed steel sheet is a bare sheet, A=1; If the hot-formed steel sheet is an aluminum-silicon coated steel sheet, A=1.1; If the hot-formed steel sheet is a zinc-based coated steel sheet, A=1.

25.

2. The method according to claim 1, characterized in that, The step of performing high-temperature friction coefficient testing based on the surface condition of the hot-formed steel sheet for simulation analysis includes: If the hot-formed steel sheet is a bare sheet, the heating temperature for the high-temperature friction coefficient test is 880-960℃, and the holding time is 2-10 minutes. If the hot-formed steel sheet is an aluminum-silicon coated steel sheet, the heating temperature for the high-temperature friction coefficient test is 880-950℃, and the holding time is 3-8 minutes. If the hot-formed steel sheet is a zinc-based coated steel sheet, the heating temperature for the high-temperature friction coefficient test is 880-910℃, and the holding time is 3-12 minutes.

3. The method according to claim 1, characterized in that, The step of determining the hot stamping process parameters based on the surface condition of the hot-formed steel sheet includes: If the hot-formed steel sheet is a bare sheet, the hot stamping process parameters include: heating temperature of 880℃~960℃, holding time of 2min~10min, and initial cooling water flow rate of the die of 1.2m³ / min. 3 / h~7.2m 3 / h; If the hot-formed steel sheet is an aluminum-silicon coated steel sheet, the hot stamping process parameters include: a heating temperature of 880℃~950℃, a holding time of 3min~8min, and an initial cooling water flow rate of 1.1m³ / min for the mold. 3 / h~7.2m 3 / h; If the hot-formed steel sheet is a zinc-based coated steel sheet, the hot stamping process parameters include: heating temperature of 860–910℃, holding time of 3–12 minutes, initial temperature of the sheet entering the mold not exceeding 770℃, and initial cooling water flow rate of the mold of 1 m³ / min. 3 / h~7.2m 3 / h.

4. The method according to claim 1, characterized in that, The step of performing pressure holding quenching on the initial part to generate the target part includes: If the hot-formed steel sheet is a bare sheet, the holding time for the pressure quenching is 4s to 20s; If the hot-formed steel sheet is an aluminum-silicon coated steel sheet, the holding time for the pressure quenching is 4s to 20s; If the hot-formed steel sheet is a zinc-based coated steel sheet, the holding time for the pressure quenching is 4s to 18s.

5. The method according to claim 1, characterized in that, The step of performing pressure holding quenching on the initial part to generate the target part includes: If the target part is a non-opening part, the initial part is subjected to pressure holding quenching, and then rapidly cooled after mold opening to generate the target part.

6. The method according to claim 5, characterized in that, The holding time for the pressure quenching is 0.2s to 10s, and the cooling rate for the rapid cooling is 100℃ / s to 300℃ / s.

7. The method according to claim 1, characterized in that, The process of hot-stamping the thermoformed part to generate an initial part includes: If the strength grade of the hot-formed steel sheet is ≤950MPa, the gap value of the hot punching is 0.1mm~0.36mm; if the strength grade of the hot-formed steel sheet is >950MPa, the gap value of the hot punching is 0.15mm~0.8mm. If the thickness of the sheet metal is ≤1.6mm, the gap value of the hot punching is 0.1mm~0.36mm; if the thickness of the sheet metal is >1.6mm, the gap value of the hot punching is 0.15mm~0.9mm.

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