Hot stamping method and device

Abstract

The application relates to the technical field of automobile body part production, and provides a hot stamping forming method and device. The hot stamping forming method comprises the following steps: heating a metal sheet to an austenitizing temperature and keeping the temperature, austenitizing the metal sheet, transferring the austenitized metal sheet to a sheet placing space in a hot stamping forming device, cooling the metal sheet to a preset forming temperature under a steam atmosphere formed in the sheet placing space, and controlling an upper die and a lower die in the hot stamping forming device to be closed, and performing stamping work on the metal sheet cooled to the preset forming temperature. The application can control the heat loss rate of the sheet, can guarantee the temperature of the metal sheet before stamping, and is favorable for improving the hot stamping forming quality of the metal sheet with a plating layer on the surface.

Description

Technical Field

[0001] This application relates to the field of automotive body manufacturing technology, and in particular to a hot stamping forming method and apparatus. Background Technology

[0002] Among the metal materials used to manufacture body parts, taking metal sheets with zinc-based coatings as an example, zinc-based coated metal sheets generally refer to metal sheets made by coating the surface of steel substrates with zinc or its alloys as the main coating components. Due to their good corrosion resistance and weldability, they have been widely used in body manufacturing.

[0003] Currently, when manufacturing body parts from zinc-based coated metal sheets, the water bath hot stamping process is commonly used. However, this process is prone to defects such as sheet cracking and insufficient forming precision during production, which is not conducive to improving the forming quality of the metal sheets. Summary of the Invention

[0004] In view of this, this application aims to provide a hot stamping forming method to improve the hot stamping forming quality of metal sheets with coatings on the surface.

[0005] To achieve the above objectives, the technical solution of this application is implemented as follows:

[0006] A hot stamping forming method for hot stamping forming of metal sheets with a coating on the surface, the method comprising:

[0007] The metal sheet is heated to the austenitizing temperature and held at that temperature to austenitize the metal sheet.

[0008] The austenitized metal sheet is transferred to the sheet placement space in the hot stamping forming device, and the metal sheet is cooled to the preset forming temperature under the steam atmosphere formed in the sheet placement space.

[0009] The upper and lower dies in the hot stamping forming device are controlled to close, and the metal sheet material that has been cooled to the preset forming temperature is stamped.

[0010] Furthermore, the hot stamping forming apparatus includes a water tank with a temperature control system, the lower mold is located inside the water tank, and the water in the water tank is heated by the temperature control system to form the steam atmosphere in the sheet metal placement space.

[0011] Furthermore, the surface area Br of the water in the tank and the surface area Bb of one side of the metal sheet satisfy Br / Bb≥1.0; and / or,

[0012] The water temperature X in the water tank satisfies X≥set temperature threshold. The set temperature threshold is calculated by multiplying the quotient of the actual atmospheric pressure at the production site and the first basic threshold, the quotient of the second basic threshold and the actual ambient humidity at the production site, and the third basic threshold. The result is the set temperature threshold.

[0013] Furthermore, the transfer time T1 for transferring the austenitized metal sheet to the hot stamping forming apparatus satisfies T1≤4s; and / or,

[0014] The closing time between the upper mold and the lower mold is between 2s and 3s.

[0015] Furthermore, the method also includes:

[0016] After stamping, the upper and lower dies are controlled to maintain pressure for a preset duration, and demolding and unloading are performed after the pressure is maintained.

[0017] Furthermore, the holding pressure By after stamping is calculated as follows: the surface area of ​​one side of the metal sheet is multiplied by the basic tonnage threshold, and the result is the holding pressure By; and / or,

[0018] The preset pressure holding time is between 13s and 17s.

[0019] Compared with related technologies, this application has the following advantages:

[0020] (1) The hot stamping forming method described in this application forms a steam atmosphere in the space where the sheet is placed, and cools the austenitized metal sheet to a preset forming temperature in the steam atmosphere before stamping. This allows the tiny droplets suspended in the steam to trigger the Leiden-Frost effect on the surface of the high-temperature metal sheet, forming a continuous steam film. Combined with the "air curtain" formed by the surrounding steam, the synergistic effect of the formed steam film and the steam air curtain can effectively block the direct heat transfer between the metal sheet and the surrounding air, actively delaying the heat loss rate of the metal sheet. This allows the metal sheet to be cooled stably and controllably to the preset forming temperature required by the process, effectively preventing the metal sheet from undergoing a martensitic phase transformation due to low temperature, which would cause a sharp drop in the elongation of the metal sheet. This can also prevent defects such as cracking and insufficient forming accuracy of the metal sheet during stamping, thus improving the hot stamping forming quality of the metal sheet with a coating on the surface.

[0021] (2) By setting up a water tank with a temperature control system and heating the water in the water tank to form a steam atmosphere in the plate placement space, not only can the steam atmosphere required for the controllable cooling of the metal plate be stably constructed by continuously heating the water in the water tank, but it also does not require the use of other steam sources, which helps to reduce the overall cost of the device.

[0022] (3) By limiting the ratio between the area of ​​the water surface in the water tank and the surface area of ​​the metal plate on one side, the amount of steam can be sufficient, a good steam atmosphere can be formed, and the uneven cooling of the metal plate due to insufficient local steam can be avoided.

[0023] By combining the actual atmospheric pressure and ambient humidity at the production site, the water temperature in the water tank is limited, which can ensure that sufficient steam can be generated stably under different production environments, thereby expanding the scope of application of the process and improving its robustness.

[0024] (4) By controlling the transfer time of the metal sheet into the hot stamping forming device, the temperature loss of the metal sheet during the transfer process can be avoided, and the temperature of the metal sheet when it enters the hot stamping forming device can be guaranteed, which helps to avoid the martensitic phase transformation of the metal sheet.

[0025] By controlling the mold closing time between the upper and lower dies, the stamping operation can be completed quickly and smoothly, avoiding excessive temperature drop in the metal sheet and ensuring the stamping quality of the metal sheet.

[0026] (5) After stamping, controlling the upper and lower dies to hold pressure for a preset holding time can make the metal sheet fully quenched in the mold, so that the internal structure of the metal sheet can be uniformly transformed, which can improve the strength and dimensional stability of the sheet after forming, effectively suppress springback, warping and deformation of the sheet after forming, and help improve the accuracy and pass rate of the finished product.

[0027] (6) By matching the holding pressure according to the surface area of ​​the metal sheet, it can be ensured that the metal sheet and the mold are fully in contact during stamping, which can make the sheet quenching and cooling uniform, and the martensite transformation sufficient, which is beneficial to improving the quenching quality of the formed sheet.

[0028] By limiting the holding time, quenching efficiency and production cycle can be reasonably balanced. This ensures that the martensitic transformation is fully achieved and the microstructure and dimensional stability of the formed sheet are guaranteed, while avoiding excessive holding time that would reduce production efficiency.

[0029] Another objective of this application is to provide a hot stamping forming apparatus for hot stamping forming metal sheets with a coating on the surface and heated to austenitization, comprising a water tank with a temperature control system, a lower die located in the water tank, and an upper die arranged corresponding to the lower die.

[0030] The water tank is equipped with multiple brackets arranged around the lower mold. The multiple brackets can lift the metal sheet in the sheet placement space located above the lower mold, and the temperature control system heats the water in the water tank to create a steam atmosphere in the sheet placement space.

[0031] The metal sheet being lifted can be cooled to a preset forming temperature in the steam atmosphere, and the upper mold and the lower mold can be closed to perform a stamping operation on the metal sheet cooled to the preset forming temperature.

[0032] Furthermore, the temperature control system includes a controller, a water level detection unit, a temperature detection unit, and a heating unit disposed in the water tank, as well as a water inlet control valve disposed at the water inlet on the water tank;

[0033] The water level detection unit, the temperature detection unit, the heating unit, and the water inlet control valve are all connected to the controller, and the heating unit is a frequency-controlled electric heater.

[0034] Furthermore, both the upper mold and the lower mold are provided with several steam guiding channels;

[0035] One end of the steam guiding channel passes through the side wall of the upper mold or the lower mold and is connected to the inside of the water tank. The other end of the steam guiding channel passes through multiple micro-holes to the forming surface of the upper mold or the lower mold.

[0036] Furthermore, a guide plate is provided at the edge of the top of the water tank;

[0037] The guide plate is inclined towards the water tank to guide the steam in the water tank to flow into the plate placement space, and the water tank is provided with an adjustment mechanism to adjust the tilt angle of the guide plate.

[0038] The hot stamping forming apparatus described in this application, on the one hand, by setting up a sheet metal placement space with a steam atmosphere inside the water tank, allows the austenitized metal sheet to be cooled to a preset forming temperature in the steam atmosphere, and the cooled metal sheet to be stamped. Utilizing the Leidenfrost effect, a steam film that blocks heat transfer and a steam curtain are formed on the surface of the metal sheet, ensuring uniform cooling of the metal sheet before stamping. This stable and controllable cooling effectively prevents the metal sheet from undergoing martensitic transformation at low temperatures, which would cause a sharp drop in elongation and avoid defects such as cracking and insufficient forming accuracy during stamping. On the other hand, by heating water in the water tank through a temperature control system to create a steam atmosphere in the sheet metal placement space, not only can the steam atmosphere required for controlled cooling of the metal sheet be stably constructed, but also the use of other steam sources is eliminated, contributing to a reduction in apparatus costs.

[0039] In addition, the temperature control system uses a water level detection unit, a temperature detection unit, a heating unit, and an inlet control valve, which are connected to the controller respectively. The heating unit uses a frequency converter-controlled electric heater, which can not only realize fully automatic closed-loop control of water temperature and water level in the water tank to ensure stable and uninterrupted steam production, but also dynamically adjust the heating power according to the water volume in the water tank and steam demand through frequency converter heating, so as to obtain better temperature control accuracy and better energy saving effect.

[0040] Furthermore, by setting steam guiding channels in the upper and lower molds, and by having the steam guiding channels penetrate to the mold forming surface through micropores, steam can be guided and distributed to the mold forming surface, ensuring the steam coverage effect on the metal sheet surface. This also helps to avoid insufficient local steam volume when the mold is closed, which would lead to a decrease in the cooling rate of the sheet during quenching, thus improving the quality stability of the formed sheet.

[0041] In addition, an inclined baffle plate is installed on the top of the water tank to guide the steam in the water tank to flow towards the plate placement space, ensuring the amount of steam above the metal plate and reducing the amount of steam escaping from the water tank, thus improving the steam utilization rate. At the same time, the angle of the baffle plate is adjustable to adapt to different water levels in the water tank, so that the steam flows to the plate placement space in a concentrated manner, which helps to create a better steam atmosphere. Attached Figure Description

[0042] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0043] Figure 1 This is a schematic diagram of the hot stamping forming apparatus described in the embodiments of this application;

[0044] Figure 2 This is a schematic diagram of the upper and lower molds being closed as described in the embodiments of this application;

[0045] Figure 3 This is a schematic diagram of the bracket structure described in the embodiments of this application;

[0046] Figure 4 This is a schematic diagram illustrating the arrangement of the steam guiding channel as described in an embodiment of this application;

[0047] Figure 5 This is a schematic diagram illustrating the arrangement of the guide vane according to an embodiment of this application;

[0048] Figure 6 This is a schematic flowchart of the hot stamping forming method described in the embodiments of this application;

[0049] Explanation of reference numerals in the attached figures:

[0050] 100. Hot stamping forming device; 200. Sheet metal placement space; 300. Steam guide channel;

[0051] 1. Water tank; 2. Upper mold; 3. Lower mold; 4. Bracket; 5. Controller; 6. Water level detection unit; 7. Temperature detection unit; 8. Heating unit; 9. Inlet control valve; 10. Metal sheet; 11. Guide plate; 12. Adjustment mechanism; 13. Outlet control valve;

[0052] 41. Support; 42. Block; 43. Shaft; 44. Tie rod; 45. Spring; 46. Hinge shaft. Detailed Implementation

[0053] To make the technical solution and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0054] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0055] Furthermore, it should be noted that in the description of this application, if terms such as "upper," "lower," "inner," or "outer" appear, indicating orientation or positional relationship, these are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In addition, if terms such as "first" or "second" appear, they are also used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0056] Furthermore, in the description of this application, unless otherwise expressly defined, the terms "installation," "connection," "joining," and "connector" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application in light of the specific circumstances.

[0057] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0058] The present application will now be described in detail through exemplary embodiments. However, it should be understood that, without further description, elements, structures, and features in one embodiment may be advantageously incorporated into other embodiments.

[0059] An embodiment of the first aspect of this application provides a hot stamping forming apparatus 100 for hot stamping forming a metal sheet 10 with a coating on its surface and heated to austenitization. Through the innovative design of this hot stamping forming apparatus 100, this embodiment can achieve hot stamping forming of the metal sheet 10 while also controlling the heat dissipation rate of the sheet, ensuring the temperature of the metal sheet 10 before stamping, which is beneficial to improving the hot stamping forming quality of the metal sheet 10 with a coating on its surface.

[0060] In related technologies, taking a metal sheet 10 with a zinc-based coating on its surface as an example, when using this metal sheet 10 to manufacture vehicle body parts, the conventional method is usually a water bath hot stamping process. In this process, after the metal sheet 10 is austenitized and removed from the furnace (heating furnace), an uncontrolled air cooling method is used, and the cooling rate of the sheet is significantly affected by the ambient temperature. In particular, when the ambient temperature is ≤0℃, the metal sheet 10 is prone to cool to below the martensitic transformation initiation temperature before entering the water bath, and martensitic phase transformation begins to occur.

[0061] If the metal sheet 10 undergoes a martensitic phase transformation, its elongation will drop sharply. During subsequent water bath stamping, defects such as sheet cracking and insufficient forming accuracy are likely to occur, which is detrimental to improving the forming quality of the metal sheet 10. At the same time, due to the large difference in the cooling rate of the sheet under different ambient temperatures, the process window before the stamping process is also prone to frequent fluctuations, making it difficult to meet the stability requirements of large-scale production.

[0062] Furthermore, in related technologies, there are also methods for cooling and quenching wear-resistant balls with coatings, specifically during the heat treatment after casting. This involves spraying water vapor onto the casting for cooling and quenching, and controlling the steam spray rate to regulate the cooling speed of the wear-resistant balls, allowing them to cool to the reheating temperature or holding temperature. However, this method of cooling with water vapor is used in the quenching process after casting, which differs from the pre-cooling of metal sheets before hot stamping. Additionally, the varying distances between the steam nozzle and different parts of the product can cause different parts of the product to not contact the steam simultaneously, leading to inconsistent cooling and potentially product defects.

[0063] In view of this, in order to overcome the shortcomings of the related technology, the hot stamping forming apparatus 100 of this embodiment combines... Figure 1 and Figure 2 As shown, it includes a water tank 1 with a temperature control system, a lower mold 3 located inside the water tank 1, and an upper mold 2 arranged corresponding to the lower mold 3.

[0064] The water tank 1 is equipped with multiple brackets 4 arranged around the lower mold 3. The multiple brackets 4 can lift the austenitized metal sheet 10 into the sheet placement space 200 located above the lower mold 3. The temperature control system heats the water in the water tank 1 and can also create a steam atmosphere in the sheet placement space 200.

[0065] In addition, the metal sheet 10 being lifted can be cooled to a preset forming temperature in a steam atmosphere, and when the upper mold 2 and the lower mold 3 are closed, the metal sheet 10 cooled to the preset forming temperature can also be stamped in a steam atmosphere to achieve hot stamping forming of the metal sheet 10.

[0066] Therefore, as described above, it can be understood that in the hot stamping forming apparatus 100 of this embodiment, by forming a steam atmosphere in the sheet metal placement space 200 within the water tank 1, the austenitized metal sheet 10 can be cooled to a preset forming temperature in the steam atmosphere, and the cooled metal sheet 10 can be stamped. This allows the contact between tiny droplets in the inner steam and the metal sheet 10 to trigger the Leidenfrost effect (the Leidenfrost effect is the rapid vaporization of a liquid or droplet on a high-temperature solid surface when it comes into contact with the solid surface, forming a continuous vapor film). This effectively blocks heat exchange between solids and liquids, i.e., between the outside world. A vapor film that blocks heat transfer is formed on the surface of the metal sheet 10, and an air curtain that also blocks heat transfer is formed by using external vapor. The two work together to allow the metal sheet 10 to be cooled stably and controllably before stamping. This effectively prevents the metal sheet 10 from undergoing a martensitic phase transformation due to low temperature, which would cause a sharp drop in the elongation of the metal sheet 10. This can prevent defects such as cracking and insufficient forming accuracy of the metal sheet 10 during stamping, and help ensure the hot stamping forming quality of the metal sheet 10.

[0067] Meanwhile, by using a water tank 1 with a temperature control system, the water in the water tank 1 is heated by the temperature control system to form a steam atmosphere in the sheet metal placement space 200. Obviously, this embodiment can not only stably construct the steam atmosphere required for the controllable cooling of the metal sheet 10 in the sheet metal placement space 200 in the water tank 1, but also use the water in the water tank 1 to heat and evaporate to form water vapor. This embodiment can also ensure that different parts of the metal sheet 10 can come into contact with water vapor at the same time under the steam atmosphere. This can avoid the pre-cooling effect of the metal sheet 10 being affected by the sequential contact with water vapor, and help to ensure the hot stamping quality of the subsequent metal sheet 10.

[0068] Of course, since no other steam source is needed, this embodiment also helps to reduce the overall cost of the hot stamping forming apparatus 100. At the same time, compared with the existing traditional water bath thermoforming process, the hot stamping forming apparatus 100 of this embodiment cools down the metal sheet 10 by creating a steam atmosphere in the sheet placement space 200 and performing subsequent stamping operations on the metal sheet 10. It does not require the metal sheet 10 to be directly immersed in boiling water. It can also be understood that it can fundamentally avoid the risk of burns and on-site pollution caused by boiling water overflow and splashing in the traditional water bath process, and can significantly improve the safety of the metal sheet 10 during hot stamping forming.

[0069] Based on the above overview, it is worth noting that the sheet metal placement space 200, as the name suggests, is the space formed within the water tank 1 for placing the metal sheet 10 to be stamped. This space is located above the lower die 3, and the metal sheet 10 is specifically placed on the bracket 4. Furthermore, the steam atmosphere formed within the sheet metal placement space 200 is generally water vapor filling the space, thereby "enveloping" the metal sheet 10 in steam.

[0070] Furthermore, the metal sheet 10 in this embodiment is generally a hot-formed steel sheet for automobiles, such as 22MnB5. The coating on the surface of the metal sheet 10 in this embodiment can be, for example, a zinc-based coating or an aluminum-silicon coating, and this embodiment will be described using a zinc-based coating as an example.

[0071] Meanwhile, due to the high temperature of the metal sheet 10, the steam will quickly form a stable steam film after contacting the metal sheet 10. This steam film can effectively block the contact between the metal sheet 10 and the surrounding water vapor, and can significantly inhibit the possible chemical reaction between the metal sheet 10 and the water vapor. In addition, after the metal sheet 10 is heated, an oxide layer will also form on its surface, which will also isolate the sheet substrate from the water. Therefore, when the metal sheet 10 enters the steam atmosphere, it will not react with the steam and will not cause any side effects to the metal sheet 10.

[0072] In this embodiment, the water tank 1 adopts a box structure with an open top, and it can generally be made of stainless steel to have good resistance to high temperature water corrosion.

[0073] At the same time, still combined Figure 1 and Figure 2 As shown, the upper mold 2 and lower mold 3 can be set up by referring to conventional hot stamping dies in the field. The lower mold 3 can be fixed in the water tank 1 by its mold base. The upper mold 2 is located directly above the lower mold 3 and is arranged corresponding to the lower mold 3. The upper mold 2 is connected to an external press and can move up and down in the vertical direction under the drive of the press.

[0074] The press described above can be arranged in the same way as conventional settings in this field. When the press drives the upper die 2 to move downward, the upper die 2 and the lower die 3 close together, which can perform stamping operations on the metal sheet 10. When the press drives the upper die 2 to move upward, the upper die 2 and the lower die 3 can be opened.

[0075] It should be noted that, in Figure 1 and Figure 2 The diagram only schematically illustrates the arrangement of the lower mold 3 in the water tank 1, as well as the relative positional relationship between the upper mold 2 and the lower mold 3 in the mold-open and mold-closed states. Figure 1 and Figure 2The upper mold 2 and lower mold 3 shown are not intended to limit the shape and structure of the mold. In specific implementation, as mentioned above, those skilled in the art can refer to the conventional hot stamping mold structure in the field and adopt appropriate upper mold 2 and lower mold 3.

[0076] In addition, it is worth noting that since no water bath is required, for the mold in this embodiment that includes the upper mold 2 and the lower mold 3, it is not necessary to open additional cooling water channels in the upper mold 2 and the lower mold 3. Compared with the traditional water bath hot stamping process, this can reduce the cost of the mold to a certain extent.

[0077] In this embodiment, in some exemplary implementations, the following are still combined Figure 1 and Figure 2 As shown, the temperature control system specifically includes a controller 5, a water level detection unit 6, a temperature detection unit 7 and a heating unit 8 installed in the water tank 1, and a water inlet control valve 9 installed at the water inlet on the water tank 1.

[0078] The water level detection unit 6, temperature detection unit 7, heating unit 8, and inlet control valve 9 are all connected to the controller 5, and the heating unit 8 is an electric heater controlled by frequency conversion. In addition to the inlet with inlet control valve 9 on the water tank 1, in practice, the water tank 1 is also usually equipped with an outlet with outlet control valve 13.

[0079] The above-mentioned water inlets can be connected to a water source via suitable water pipes. As a preferred embodiment, to ensure the water in water tank 1 reaches the required temperature as quickly as possible and reduces heating time, the water source can, for example, be warm water with a certain temperature. The above-mentioned water outlets are used to drain water from water tank 1 when adjusting the water level or during equipment maintenance. The outlets can also be connected to a sewage pipe via suitable water pipes.

[0080] In specific implementation, it is worth noting that the water level detection unit 6 mentioned above can, for example, be an ultrasonic water level sensor installed in the water tank 1. When the water level detection unit 6 detects that the water level in the water tank 1 is lower than the set low water level threshold, the controller 5 controls the water inlet control valve 9 to open and inject water into the water tank 1. After the water level is detected to reach the set high water level threshold, the water inlet control valve 9 can be closed.

[0081] The temperature detection unit 7 described above can be, for example, a PT100 platinum resistance temperature sensor, or other suitable sensors for detecting hot water temperature. The electric heater constituting the heating unit 8 can be, for example, a stainless steel tubular electric heating tube, and can be equipped with a suitable frequency converter to achieve frequency conversion adjustment of the heating power of the electric heater.

[0082] The aforementioned inlet control valve 9 and outlet control valve 13 may be electrically controlled shut-off valves, and the aforementioned controller 5 may be a PLC control system, or other suitable control systems.

[0083] In addition, to ensure the heating efficiency of the water in the water tank 1, the heating unit 8 can generally be multiple units distributed at different positions on the bottom of the water tank 1. Similarly, to ensure the reliability of the water temperature detection in the water tank 1, the temperature detection unit 7 can also be multiple units distributed at different positions in the water tank 1. Each temperature detection unit 7 can be set at the bottom of the water tank 1 or on the side wall of the water tank 1. When multiple temperature detection units 7 are used, the average value of the temperature detection values ​​of multiple temperature detection units 7 can usually be taken as the water temperature detection result.

[0084] It is understood that this embodiment uses a water level detection unit 6, a temperature detection unit 7, a heating unit 8, and a water inlet control valve 9, which are respectively connected to the controller 5, and the heating unit 8 is a frequency-controlled electric heater. This not only enables fully automatic closed-loop control of the water temperature and water level in the water tank 1, but also enables automatic and precise control of the water level and water temperature in the water tank 1 by timely adjustment of the water level and water temperature in the water tank 1, so as to ensure stable and uninterrupted steam production, thereby allowing steam to fill the board placement space 200 and form a better steam atmosphere in the board placement space 200.

[0085] At the same time, by using frequency conversion heating for heating unit 8, this embodiment can also dynamically adjust the heating power of electric heater according to the water volume in water tank 1 and steam demand. This not only achieves better temperature control accuracy, but also achieves better energy-saving effect, which is conducive to reducing production costs.

[0086] In this embodiment, it is worth noting that, in order to reliably support the metal sheet 10, the aforementioned brackets 4 are generally multiple and arranged inside the water tank 1, with multiple brackets 4 distributed around the lower mold 3, thereby forming a sheet placement space 200 above the lower mold 3 for temporarily placing the metal sheet 10. In terms of specific structure, the aforementioned brackets 4 can be suitable products capable of supporting the metal sheet 10 and allowing the metal sheet 10 to detach from the support when the mold is closed.

[0087] In practical implementation, as a structural example, combined with Figure 3 As shown, the bracket 4 may include, for example, a support 41, a support block 42, a pull rod 44, and a spring 45.

[0088] The support 41 is fixed to the bottom of the water tank 1 and forms the main structure of the bracket 4. The support block 42 is rotatably mounted on the top of the support 41 via the rotating shaft 43. A slot is also provided on the upper part of the support 41, which is arranged radially along the rotating shaft 43, so that the support block 42 can rotate relative to the support 41.

[0089] In addition, with Figure 3 Based on the orientation shown, the support block 42 also has protruding parts that bulge outward to the left and right sides of the support 41 respectively. The protruding part on the right side of the support 41 is used to support the metal sheet 10 placed in the sheet placement space 200, and the protruding part on the left side of the support 41 is used to connect with the pull rod 44.

[0090] Specifically, the top end of the pull rod 44 is connected to the protruding part on the left side of the support block 42 via the hinge shaft 46, and the bottom end of the pull rod 44 is connected to one end of the spring 45, while the other end of the spring 45 is connected to the support 41.

[0091] With the above structure, it can be understood that by using a spring 45 of suitable specifications, the support block 42 can be made to move as described above. Figure 1 As shown, the metal sheet 10 is supported within the sheet placement space 200 so that the metal sheet 10 is cooled by the vapor atmosphere in the sheet placement space 200.

[0092] When the mold closes, the downward-moving upper mold 2 presses down on the metal sheet 10. The pressure on the metal sheet 10 causes the support block 42 to rotate. The rotating support block 42 pulls the spring 45, causing the spring 45 to deform and store energy. As the lower mold 2 continues to move the metal sheet 10 downward, the rotation angle of the support block 42 gradually increases. Eventually, the metal sheet 10 can separate from the support block 42 and fall onto the lower mold 3. After the metal sheet 10 separates, the support block 42, driven by the elastic restoring force of the spring 45, can rotate back to its original position to continue receiving the next metal sheet 10.

[0093] It should be noted that, in this embodiment, Figure 1 , Figure 2 The accompanying drawings only schematically show the position and height of the bracket 4. It is understood that, in specific implementation, those skilled in the art can reasonably design the number, position and height of the bracket 4 based on the exemplary description of this embodiment, so as to provide stable support for the metal sheet 10, and at the same time, so that the metal sheet 10, after being separated from the bracket 4, can fall smoothly onto the lower mold 3 when the mold is closed.

[0094] Continue to combine Figure 4 As shown, in the hot stamping forming apparatus 100 of this embodiment, steam guide channels 300 can be further provided in the upper mold 2 and the lower mold 3.

[0095] One end of the steam guide channel 300 passes through the side wall of the upper mold 2 or the lower mold 3 and is connected to the water tank 1. The other end of the steam guide channel 300 passes through multiple micro-holes to the forming surface of the upper mold 2 or the lower mold 3.

[0096] At this point, it can be understood that by setting steam guide channels 300 in the upper mold 2 and the lower mold 3, and by having the steam guide channels 300 penetrate through micropores to the mold forming surface, this embodiment can not only guide and distribute steam to the mold forming surface to ensure the coverage effect of steam on the surface of the metal sheet 10, but also help to avoid insufficient local steam volume when the mold is closed, which would lead to a decrease in the cooling rate of the sheet during quenching, and thus help to improve the quality stability of the formed sheet.

[0097] In practical implementation, it is worth noting that, since the upper and lower dies of a stamping die generally contain die inserts fixed on the die support, and the die forming surface is also located on the surface of the die inserts, the steam guide channel 300 can be set on the die inserts in the upper die 2 and the lower die 3 by means of machining.

[0098] Meanwhile, to achieve better steam diversion and fully distribute steam to the forming surfaces of the upper mold 2 and lower mold 3, multiple steam diversion channels 300 can be provided in the lower mold 3, especially in the upper mold 2. Each steam diversion channel 300 is distributed at different positions on the mold insert to guide and distribute steam to different areas of the forming surface of the mold.

[0099] In addition, the micro-holes that connect the steam guide channel 300 with the mold forming surface can be round holes or elongated holes on the mold forming surface. Multiple micro-holes can be arranged in a regular matrix. Taking round holes as an example, the diameter of the micro-holes can generally be 0.5mm-1mm.

[0100] Furthermore, it should be noted that the microholes provided on the forming surface of the mold will not affect the overall formability of the metal sheet 10. At the same time, the stamping marks caused by the microholes on the surface of the metal sheet 10 during the stamping process will disappear after shot blasting and other surface treatments are performed after the stamping process, thus ensuring the surface condition of the final product.

[0101] Continue to combine Figure 5 As shown, in the hot stamping forming apparatus 100 of this embodiment, a guide plate 11 can be provided at the top edge of the water tank 1. The guide plate 11 is arranged at an inclination towards the water tank 1 to guide the steam in the water tank 1 to flow into the sheet material placement space 200. Furthermore, an adjustment mechanism 12 for adjusting the inclination angle of the guide plate 11 can also be provided on the water tank 1.

[0102] At this time, by setting an inclined guide plate 11 on the top of the water tank 1, this embodiment can guide the upward flowing steam in the water tank 1 to flow into the plate placement space 200, thereby ensuring the amount of steam above the metal plate 10.

[0103] With the addition of the baffle plate 11 at the top of the water tank 1, it is understood that this embodiment can also prevent steam from flowing out of the water tank 1, thereby reducing the amount of steam escaping from the water tank 1 and improving steam utilization.

[0104] Meanwhile, by setting an adjustment mechanism 12, the angle of the guide plate 11 can be adjusted under the drive of the adjustment mechanism 12. This embodiment can adapt to different water level heights in the water tank 1, so that the steam always flows to the plate placement space 200, which helps to form a better steam atmosphere in the plate placement space 200.

[0105] In specific implementation, it is worth noting that guide plates 11 should usually be installed at each side edge of the top of the water tank 1. The guide plates 11 can be made of stainless steel, for example, and since they are only used to guide the direction of steam flow, the guide plates 11 can be made of thin stainless steel sheets.

[0106] The aforementioned adjustment mechanism 12 can be, for example, a swing motor mounted on the top of the water tank 1, or a combination of a commonly used stepper motor and a linkage mechanism. Taking the swing motor as an example, the swing motor is also connected to the controller 5, and one end of the guide plate 11 is fixed to the drive end of the swing motor. The controller 5 controls the rotation of the swing motor based on preset parameters or the detection of the water level in the water tank 1, thereby adjusting the tilt angle of the guide plate 11.

[0107] In specific production, when the water level in water tank 1 is high, the steam rises a short distance, which makes the angle of inclination of the guide plate 11 into water tank 1 smaller. When the water level in water tank 1 is low, the steam rises a longer path, which increases the angle of inclination of the guide plate 11 into water tank 1, preventing the steam from escaping to the outside and allowing it to flow into the plate placement space 200.

[0108] The hot stamping forming apparatus 100 of this embodiment adopts the above design. When in use, under the control of the controller 5, water is first injected into the water tank 1. After the water injection is completed, the heating unit 8 is controlled to work to heat the water in the water tank 1 to the set temperature, so that the water in the water tank 1 continues to evaporate and fills the sheet metal placement space 200 above the lower mold 3. Then, the austenitized metal sheet 10 can be hot stamped.

[0109] At this time, when the hot stamping forming apparatus 100 of this embodiment is specifically used for hot stamping forming of metal sheet 10 with a coating on the surface, such as a zinc-based coating, the forming method can be referred to the description in the second aspect embodiment below.

[0110] The second aspect of this application provides a hot stamping forming method for hot stamping forming of a metal sheet 10 with a coating on its surface, and in terms of overall design, combined with Figure 6 As shown, it mainly includes the following steps:

[0111] Step s1: Heat the metal sheet 10 to the austenitizing temperature and hold it at that temperature to austenitize the metal sheet 10.

[0112] In step s1, the heating of the metal sheet 10 can generally be carried out in a nitrogen-protected atmosphere roller hearth continuous heating furnace. For the metal sheet 10 with a zinc-based coating on the surface, its austenitizing temperature is generally between 890℃ and 900℃. At the same time, the holding time after heating to the austenitizing temperature can be between 3 min and 10 min.

[0113] For example, the austenitizing temperature of the metal sheet 10 can be 890℃, 895℃ or 900℃, etc., and the holding time after heating to the austenitizing temperature can be 3min, 4min, 5min, 6min, 8min, 9min or 10min, etc.

[0114] Step s2: Transfer the austenitized metal sheet 10 to the sheet placement space 200 in the hot stamping forming device 100, and cool the metal sheet 10 to the preset forming temperature under the steam atmosphere formed in the sheet placement space 200.

[0115] In step s2, after the metal sheet 10 exits the furnace, it can generally be picked up by a robotic arm to transfer it to the hot stamping forming device 100.

[0116] Furthermore, based on the hot stamping forming apparatus 100 in the first aspect embodiment described above, it is worth noting that in the method of this embodiment, before the metal sheet 10 is transferred, the water temperature X after heating in the water tank 1 can specifically satisfy X≥ a set temperature threshold. The calculation method of the set temperature threshold is as follows: multiply the quotient of the actual atmospheric pressure value at the production site and the first basic threshold, the quotient of the second basic threshold and the actual ambient humidity at the production site, and the third basic threshold, and the result is the set temperature threshold.

[0117] In specific implementation, the first basic threshold is generally set to 101.3, the second basic threshold is generally set to 50%, and the third basic threshold is generally set to 90. Therefore, the calculation method for setting the temperature thresholds is represented by a formula, i.e., setting the temperature thresholds... .

[0118] In the above formula, QY represents the actual atmospheric pressure at the production site, and SD represents the actual ambient humidity at the production site. Furthermore, the water temperature in water tank 1 should generally be above 90℃, such as 90℃, 91℃, 92℃, 95℃, 96℃, 98℃, 100℃, etc.

[0119] Understandably, by combining the actual atmospheric pressure and ambient humidity of the production site to limit the water temperature in water tank 1, it can ensure that sufficient steam can be generated stably under different production environments. This can create a better steam atmosphere in the board placement space 200, while also expanding the scope of process applicability and improving the robustness of the process.

[0120] In addition, it is worth noting that in specific implementation, in order to ensure sufficient steam volume and form a good steam atmosphere in the plate placement space 200, and to avoid uneven cooling of the metal plate 10 due to insufficient local steam, in this embodiment, it is generally set such that the area Br of the water surface in the water tank 1 and the surface area Bb of one side of the metal plate 10 satisfy Br / Bb≥1.0.

[0121] As an example, the ratio between the area Br of the water surface in the water tank 1 and the surface area Bb of one side of the metal sheet 10 can be, for example, 1.0, 1.1, 1.2, 1.3, or 1.5. Furthermore, in practice, the dimensions of the metal sheet 10 to be stamped (i.e., its surface area Bb) are fixed. Therefore, based on the surface area Bb of the metal sheet 10, the dimensions of the water tank 1 are designed accordingly to meet the design requirement of Br / Bb ≥ 1.0.

[0122] Meanwhile, in this embodiment, in step s2, the transfer time T1 for transferring the austenitized metal sheet 10 to the hot stamping forming apparatus 100 is generally T1≤4s.

[0123] Furthermore, as a preferred embodiment, the aforementioned transition time T1 can specifically be 3s≤T1≤4s, and based on this, as an example, the aforementioned transition time T1 can be, for example, 3s, 3.2s, 3.5s, or 3.8s, 4s, etc.

[0124] By controlling the transfer time of the metal sheet 10 into the hot stamping forming apparatus 100, it can be understood that this embodiment can avoid excessive temperature loss of the metal sheet 10 during the transfer process, and can ensure the temperature of the metal sheet 10 when it enters the hot stamping forming apparatus 100. This helps to avoid the metal sheet 10 from undergoing martensitic phase transformation due to excessive cooling, which would affect the subsequent stamping quality.

[0125] In this embodiment, in step s2, the preset forming temperature for the metal sheet 10 with the zinc-based coating is generally 650℃-700℃, and the specific temperature can be determined according to the thickness of the metal sheet 10.

[0126] Furthermore, in specific implementation, this embodiment can generally transfer the metal sheet 10 to the sheet placement space 200 and support it on the bracket 4, and then use an infrared pyrometer to measure the temperature of the metal sheet 10 in real time to determine when the metal sheet 10 has cooled down and when subsequent stamping operations can be carried out.

[0127] Meanwhile, based on the real-time measurement of the temperature of the metal sheet 10, in the hot stamping forming method of this embodiment, under the control of the controller 5, the cooling rate of the metal sheet 10 can also be calculated by the change in the temperature of the metal sheet 10, and the water temperature in the water tank 1 can be adjusted according to the real-time cooling rate of the metal sheet 10.

[0128] As an example, if the cooling rate of the metal sheet 10 calculated by the controller 5 is large (e.g., exceeding the set threshold), it indicates that the vapor film formed on the surface of the metal sheet 10 has broken, which means that the steam content is insufficient. At this time, the heating power of the heating unit 8 can be increased, and the angle of the guide plate 11 can be adjusted to increase the amount of steam in the sheet placement space 200 until the vapor film is restored and the cooling rate of the metal sheet 10 becomes normal (e.g., maintained within the set range).

[0129] The aforementioned threshold and set range can generally be determined based on the continuous cooling transformation curve (CCT) of the metal sheet 10. The CCT curve is a comprehensive kinetic curve describing the transformation start temperature, end temperature, and transformation products of supercooled austenite at different cooling rates. It can be used to determine the critical cooling rate required for the steel to obtain a specific microstructure. Specifically, the aforementioned threshold can be, for example, the critical cooling rate determined by the CCT curve to avoid martensitic transformation in the metal sheet 10. The aforementioned set range can be determined based on this critical cooling rate, the preset forming temperature, and the transfer time. This ensures that the metal sheet 10 does not undergo martensitic transformation due to low temperature and that excessive temperature loss during the transfer process is avoided, thus maintaining the preset forming temperature of the metal sheet 10 before stamping.

[0130] As an example, taking the metal sheet 10 with 22MnB5 and a zinc-based coating used in the preparation example below of this embodiment, the aforementioned threshold value can be, for example, 15°C / s, and the aforementioned range can be 5°C / s-10°C / s. Of course, those skilled in the art can also use other values ​​and ranges that meet the thermoforming requirements of the metal sheet 10 according to specific forming needs.

[0131] On the other hand, given the time T2 it takes for the metal sheet 10 to cool from its initial temperature upon entering the sheet placement space 200 (i.e., the hot stamping forming apparatus 100) to the preset forming temperature, it generally satisfies... .

[0132] In the above formula, W0 is the ambient temperature of the production site (usually the stamping production workshop), W1 is the initial temperature of the metal sheet 10 when it enters the sheet placement space 200, W2 is the preset forming temperature, A is the heat exchange surface area of ​​the metal sheet 10, V is the volume of the metal sheet 10, ρ is the density of the metal sheet 10, c is the specific heat capacity of the metal sheet 10, and h is the convective heat transfer coefficient between the metal sheet 10 and the surrounding environment.

[0133] It is evident that by triggering the Leidenfrost effect to produce a vapor film on the surface of the metal sheet 10 in a steam atmosphere, the convective heat transfer coefficient h can be controlled, and consequently, the aforementioned time T2 can be controlled to meet the requirements. Therefore, this embodiment can increase the time from when the austenitized metal sheet 10 exits the furnace to before die-forming, effectively solving the problem of no process window before stamping without affecting the subsequent stamping quality of the metal sheet 10. This is particularly important when the production environment is ≤0℃.

[0134] Step s3: Control the upper mold 2 and lower mold 3 in the hot stamping forming device 100 to close the mold and perform stamping operation on the metal sheet 10 that has been cooled to the preset forming temperature.

[0135] In step s3, the upper die 2 moves downward under the drive of the press, first causing the metal sheet 10 to separate from the bracket 4. Then, the upper die 2 and the lower die 3 close together, thus completing the hot stamping of the metal sheet 10.

[0136] In practical implementation, the mold closing time of the upper mold 2 and the lower mold 3 should generally be between 2s and 3s. For example, the mold closing time can be 2s, 2.5s or 3s, and preferably 2s.

[0137] By controlling the mold closing time between the upper mold 2 and the lower mold 3, it can be understood that this embodiment enables the stamping operation to be completed quickly and smoothly, avoids excessive temperature drop of the metal sheet 10 during the mold closing process, and also helps to ensure the stamping quality of the metal sheet 10.

[0138] Furthermore, it is worth noting that during the mold closing process, the upper mold 2 first contacts the metal sheet 10, and then the metal sheet 10 quickly contacts the lower mold 3. As the upper mold 2 continues to move downward relative to the lower mold 3, the mold closing and stamping process is completed. After mold closing, the vapor film on the surface of the metal sheet 10 comes into contact with the upper mold 2 and the lower mold 3 (both of which are generally slightly higher than the ambient temperature). Due to the huge temperature difference between the upper and lower molds and the metal sheet 10, under the combined action of pressure and temperature difference, the vapor film is rapidly crushed and condensed to form a continuous liquid water film.

[0139] In this way, by utilizing the above liquid water film, rapid heat exchange can be achieved between the metal sheet 10 and the upper and lower dies to reach the martensitic transformation temperature, thereby completing the quenching process, realizing the martensitic transformation of the metal sheet 10, and ensuring that the martensitic structure is free of segregation, thus improving the tensile strength of the metal sheet 10 after forming.

[0140] See also Figure 6 As shown, the hot stamping forming method of this embodiment may further include the following steps:

[0141] Step s4: After stamping, control the upper die 2 and lower die 3 to hold pressure for a preset holding time, and demold and unload the material after the holding pressure is completed.

[0142] In step s4, by controlling the upper die 2 and lower die 3 to hold pressure for a preset duration after stamping, it can be understood that this embodiment can enable the metal sheet 10 to be fully quenched in the mold, so that the internal structure of the metal sheet 10 can be uniformly transformed. This not only improves the strength and dimensional stability of the sheet after forming, but also effectively suppresses springback, warping and deformation of the sheet after forming, thus helping to improve the accuracy and pass rate of stamped products.

[0143] In addition, in specific implementation, the calculation method for the holding pressure By after stamping is generally as follows: multiply the surface area of ​​one side of the metal sheet 10 by the basic tonnage threshold, and the result is the holding pressure By.

[0144] The basic tonnage threshold is generally taken as (750±50)t, and as an example, the basic tonnage threshold can be 800t (i.e. 800 tons of force). Therefore, the calculation method of the above-mentioned holding pressure By is represented by the formula By=Bb×800t.

[0145] At this time, by setting the holding pressure according to the surface area of ​​the metal sheet 10, this embodiment can ensure that the metal sheet 10 and the mold are fully in contact during stamping, which can make the sheet quenching and cooling uniform, and the martensite transformation sufficient, which is also conducive to improving the quenching quality of the formed sheet.

[0146] In step s4, the preset pressure holding time can generally be between 13s and 17s. For example, the preset pressure holding time can be 13s, 14s, 15s, 16s or 17s, and preferably 15s.

[0147] Furthermore, by limiting the holding time as described above, this embodiment can reasonably balance quenching efficiency and production cycle during production. It can ensure that the formed sheet material achieves sufficient martensitic transformation and guarantees the structural and dimensional stability of the formed sheet material, while avoiding excessive holding time that would reduce production efficiency.

[0148] The hot stamping forming method of this embodiment adopts the above design and uses the hot stamping forming apparatus 100 of the first aspect embodiment. It can utilize the vapor film formed by the Leidenfrost effect triggered on the surface of the metal sheet 10 and the air curtain formed by the surrounding steam to effectively block the direct heat transfer between the metal sheet 10 and the surrounding air, actively delaying the heat loss rate of the metal sheet 10. This allows the metal sheet 10 to be cooled stably and controllably to the preset forming temperature required by the process. It can not only obtain a suitable process window before stamping and effectively avoid excessive temperature drop of the metal sheet 10, but also avoid defects such as cracking and insufficient forming accuracy of the metal sheet 10 during stamping. This is beneficial to improving the hot stamping forming quality of the metal sheet 10 with a coating on the surface and has good practicality.

[0149] Meanwhile, as a specific preparation example, using steps s1 to s4 of the aforementioned hot stamping method, a plate with a thickness of 1.5 mm and a single-sided surface area of ​​0.5 m² is prepared. 2 The zinc-based coated metal sheet 10 (22MnB5) is hot-stamped and formed. Specifically, the austenitizing temperature is 900℃, the holding temperature is 10min, the water temperature in the water tank 1 is maintained at about 95℃, the water level is kept flush with the mold base of the lower mold 3, the guide plate 11 is tilted at 42.5°, and the metal sheet 10 is cooled to 650℃ in the water tank 1. Then it is transferred to the hot stamping forming device 100. The transfer time T1 is 3.5s, the mold closing time is 2s, the holding pressure time is 15s, and the demolding and unloading are completed after holding pressure.

[0150] As a comparative example of the hot stamping forming method in this embodiment, a traditional water bath hot stamping process is used in this comparative example. Specifically, the hot stamping forming process in this comparative example includes forming a plate with a thickness of 1.5 mm and a single-sided surface area of ​​0.5 m². 2The zinc-based coated metal sheet 10 (22MnB5) is heated to 900℃ and held for 10 minutes to austenitize it. Then, the austenitized metal sheet 10 is directly transferred in about 5 seconds and immersed in boiling water (about 100℃) for water bath cooling for 3 seconds. Then, the metal sheet 10 is transferred to the hot stamping forming device 100 for 5 seconds. The mold closing time is 2.5 seconds and the pressure holding time is 15 seconds. After the pressure holding is completed, the sheet is demolded and unloaded.

[0151] The hot-stamped products prepared in the production examples using the hot stamping method of this embodiment were compared with the hot-stamped products prepared using the traditional water bath hot stamping process in the comparative examples. The mechanical properties and appearance quality of the products were tested. Some test results are shown in Table 1 below.

[0152]

[0153] The test results above show that, compared with the traditional water bath hot stamping process, the hot stamping method of this embodiment can make the molded products have better mechanical properties and appearance quality. The products prepared by the hot stamping method of this embodiment have better molding quality, which can well meet the application requirements of body parts and has good practicality.

[0154] The above descriptions are merely some embodiments of this application and are not intended to limit this application. The technical features or structures in the foregoing different embodiments can be arbitrarily combined to form other specific technical solutions as needed. For those skilled in the art, this application can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of the claims of this application.

Claims

1. A hot stamping forming method for hot stamping forming of a metal sheet (10) with a coating on its surface, characterized in that, The method includes: The metal sheet (10) is heated to the austenitizing temperature and held at that temperature to austenitize the metal sheet (10); The austenitized metal sheet (10) is transferred to the sheet placement space (200) in the hot stamping forming apparatus (100), and the metal sheet (10) is cooled to the preset forming temperature under the steam atmosphere formed in the sheet placement space (200). The upper die (2) and lower die (3) in the hot stamping forming device (100) are controlled to close, and the metal sheet (10) cooled to the preset forming temperature is stamped.

2. The hot stamping forming method according to claim 1, characterized in that: The hot stamping forming apparatus (100) includes a water tank (1) with a temperature control system. The lower mold (3) is located inside the water tank (1) and heats the water in the water tank (1) through the temperature control system to form the steam atmosphere in the sheet material placement space (200).

3. The hot stamping forming method according to claim 2, characterized in that: The surface area Br of the water in the water tank (1) and the surface area Bb of one side of the metal plate (10) satisfy Br / Bb≥1.0; and / or, The water temperature X in the water tank (1) satisfies X≥ set temperature threshold. The set temperature threshold is calculated by multiplying the quotient of the actual atmospheric pressure value at the production site and the first basic threshold, the quotient of the second basic threshold and the actual ambient humidity at the production site, and the third basic threshold. The result is the set temperature threshold.

4. The hot stamping forming method according to claim 1, characterized in that: The transfer time T1 for transferring the austenitized metal sheet (10) into the hot stamping forming apparatus (100) satisfies T1≤4s; and / or, The closing time between the upper mold (2) and the lower mold (3) is between 2s and 3s.

5. The hot stamping forming method according to any one of claims 1 to 4, characterized in that, The method also includes: After stamping, the upper die (2) and the lower die (3) are controlled to maintain pressure for a preset holding time, and demolding and unloading are performed after the pressure is maintained.

6. The hot stamping forming method according to claim 5, characterized in that: The method for calculating the holding pressure By after stamping is as follows: the surface area of ​​one side of the metal sheet (10) is multiplied by the basic tonnage threshold, and the result is the holding pressure By; and / or, The preset pressure holding time is between 13s and 17s.

7. A hot stamping forming apparatus (100) for hot stamping forming a metal sheet (10) with a coating on its surface and heated to austenitization, characterized in that: It includes a water tank (1) with a temperature control system, a lower mold (3) located inside the water tank (1), and an upper mold (2) arranged corresponding to the lower mold (3); The water tank (1) is provided with a plurality of brackets (4) arranged around the lower mold (3). The plurality of brackets (4) can lift the metal sheet (10) in the sheet placement space (200) located above the lower mold (3). The temperature control system heats the water in the water tank (1) and can form a steam atmosphere in the sheet placement space (200). The metal sheet (10) being lifted can be cooled down to a preset forming temperature in the steam atmosphere, and the upper mold (2) and the lower mold (3) are controlled to close, so that the metal sheet (10) cooled down to the preset forming temperature can be stamped.

8. The hot stamping forming apparatus (100) according to claim 7, characterized in that: The temperature control system includes a controller (5), a water level detection unit (6), a temperature detection unit (7) and a heating unit (8) located in the water tank (1), and an inlet control valve (9) located at the inlet of the water tank. The water level detection unit (6), the temperature detection unit (7), the heating unit (8) and the water inlet control valve (9) are all connected to the controller (5), and the heating unit (8) is a frequency-controlled electric heater.

9. The hot stamping forming apparatus (100) according to claim 7, characterized in that: Both the upper mold (2) and the lower mold (3) are provided with several steam guiding channels (300). One end of the steam guide channel (300) passes through the side wall of the upper mold (2) or the lower mold (3) and is connected to the inside of the water tank (1). The other end of the steam guide channel (300) passes through multiple micro-holes to the forming surface of the upper mold (2) or the lower mold (3).

10. The hot stamping forming apparatus (100) according to any one of claims 7 to 9, characterized in that: A guide plate (11) is provided at the edge of the top of the water tank (1); The guide plate (11) is inclined toward the water tank (1) to guide the steam in the water tank (1) to flow toward the plate placement space (200), and the water tank (1) is provided with an adjustment mechanism (12) for adjusting the tilt angle of the guide plate (11).

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