Thermoforming method, production method and thermoformed part

Abstract

The application provides a hot forming method, a preparation method and a hot formed part, which are applied to the technical field of interior and exterior decoration and place a zinc-based hot forming material in a heating device, control the temperature of the heating device to increase from an initial temperature to a first constant temperature, and maintain the constant temperature at the first constant temperature for a first constant time period; the initial temperature is 700-740 DEG C, and the first constant temperature is 750-770 DEG C; continue to control the temperature of the heating device to increase from the first constant temperature to a second constant temperature, and maintain the constant temperature at the second constant temperature for a second constant time period, and the second constant temperature is 885-895 DEG C; the heated zinc-based hot forming material is taken out from the heating device, the appropriate initial temperature, the first constant temperature and the second constant temperature are controlled, the volatilization and oxidation rate of the zinc layer is reduced, the surface whitening defect of the zinc-based hot forming material is reduced, and the strength of the part is ensured.

Description

Technical Field

[0001] This application relates to the field of interior and exterior trim technology, and in particular to a thermoforming method, preparation method and thermoformed part. Background Technology

[0002] In the hot forming process of zinc-based hot forming materials, the zinc-based hot forming materials need to be heated in a roller hearth furnace. During the heating process in the roller hearth furnace, the zinc layer on the surface of the zinc-based hot forming material is very prone to oxidation, combustion, or even volatilization under high temperature environment, resulting in defects such as whitening and graying on the surface of the steel plate material, which affects the subsequent stamping forming accuracy and surface quality. Summary of the Invention

[0003] In view of this, the purpose of this application is to provide a thermoforming method, a preparation method, and a thermoformed part to solve or partially solve the technical problems raised in the background art.

[0004] To achieve the above objectives, the first aspect of this application provides a thermoforming method, comprising:

[0005] The zinc-based thermoforming material is placed in a heating device, and the temperature of the heating device is controlled to rise from an initial temperature to a first constant temperature, and the temperature is maintained at the first constant temperature until the constant temperature duration reaches the first constant temperature duration; wherein, the initial temperature is 700~740℃, and the first constant temperature is 750~770℃. Continue to control the temperature of the heating device to rise from the first constant temperature to the second constant temperature, and maintain the temperature at the second constant temperature until the constant temperature duration reaches the second constant temperature duration, wherein the second constant temperature is 885~895℃; The heated zinc-based thermoforming material is removed from the heating device.

[0006] In this application, by controlling the initial temperature to 700~740℃, the first constant temperature to 750~770℃, and the second constant temperature to 885~895℃, the initial heating temperature (i.e., the initial temperature), the intermediate constant temperature (i.e., the first constant temperature), and the final heating temperature (i.e., the second constant temperature) of the zinc-based thermoforming material are all appropriately controlled. The appropriate initial and intermediate constant temperatures ensure that the temperature of the zinc-based thermoforming material first rises from the initial temperature to the first constant temperature. This prevents the zinc-based thermoforming material from being rapidly heated directly from room temperature, which could lead to extensive oxidation, combustion, or even volatilization of the zinc layer. The appropriate initial heating temperature (usually 800℃ and above) ensures that the zinc-based hot forming material does not undergo severe oxidation. A suitable intermediate isothermal temperature ensures that the zinc-based hot forming material has a sufficient temperature transition in the temperature range below 800℃, thereby reducing the rate of zinc layer volatilization and oxidation and reducing whitening defects on the surface of the zinc-based hot forming material. A suitable termination heating temperature ensures that the zinc-based hot forming material can be fully austenitized to meet the strength requirements of the parts. Therefore, suitable initial heating temperature, intermediate isothermal temperature and termination heating temperature can ensure that the zinc-based hot forming material does not have whitening defects during the hot forming process and improve the forming accuracy.

[0007] In some embodiments, the initial temperature is 710~730℃, the first isothermal temperature is 755~765℃, and the second isothermal temperature is 887~893℃. Thus, by controlling the initial temperature, the first isothermal temperature, and the second isothermal temperature more effectively, the rate of zinc layer volatilization and oxidation can be significantly reduced, the whitening defect on the surface of zinc-based thermoforming materials can be significantly reduced, and the whitening defect can be ensured to be eliminated during the thermoforming process, thereby improving the forming accuracy.

[0008] In some embodiments, the second isothermal duration is 150-200 seconds, and the first isothermal duration is 40-80 seconds. By controlling the appropriate second isothermal duration, sufficient heating time is ensured for the zinc-based hot-formed material in the temperature range above 800°C, thereby ensuring that the zinc-based hot-formed material can be fully austenitized and meet the strength requirements of the part. By controlling the appropriate first isothermal duration, sufficient temperature transition time is allowed for the zinc-based hot-formed material in the temperature range below 800°C, thereby significantly reducing the zinc layer volatilization and oxidation rate and reducing surface whitening defects.

[0009] In some embodiments, when the thickness of the zinc-based thermoforming material is less than the first preset thickness, the first isothermal duration is 50-80s, and the second isothermal duration is 150-180s; Alternatively, when the thickness of the zinc-based thermoforming material is greater than or equal to the first preset thickness, the first isothermal duration is 40-50 seconds, and the second isothermal duration is 160-200 seconds.

[0010] Thus, by applying different first and second holding times based on different thicknesses, it is ensured that thicker zinc-based hot-formed materials can be fully austenitized, thereby ensuring that the strength of the parts meets the requirements. At the same time, the overall heating rate of thicker zinc-based hot-formed materials is slower, so even if the first holding time is shorter, it will not result in a short heating transition time, thus still ensuring sufficient heating transition time in the temperature range below 800℃.

[0011] Based on the same inventive concept, a second aspect of this application provides a method for preparing a thermoformed part, comprising: thermoforming, stamping and demolding the zinc-based thermoformed material according to the thermoforming method described in any one of the first aspects above, to obtain a thermoformed part.

[0012] In this application, because the temperature of each step in the thermoforming process is precisely controlled, the zinc-based thermoforming material after thermoforming will not have whitening defects, nor will it have residual oxidized zinc oxide layer on the surface. This ensures that the zinc-based thermoforming material after thermoforming will not stick to the mold, wrinkle or crack during subsequent stamping and demolding processes, thus improving the dimensional consistency of the product.

[0013] In some embodiments, the process of thermoforming, stamping, and demolding the zinc-based thermoforming material based on the thermoforming method according to any one of the first aspects above to obtain a thermoformed part includes: The zinc-based thermoforming material is thermoformed according to any one of the first aspects described above to obtain a thermoformed part; The thermoformed part is immersed in the lower mold for cooling, and then the molding, pressure holding, and demolding are performed sequentially to obtain the demolded part; wherein, the lower mold contains a coolant at a temperature of 85~100℃, and the pressure holding time is 6~10s; The demolded part is subjected to blowing, shot blasting and oiling in sequence to obtain zinc-based thermoforming material.

[0014] Thus, blowing air onto the demolded part can accelerate the evaporation of residual moisture inside the demolded part, thereby solving defects such as rust spots and color differences caused by moisture remaining on the surface or internal structure of the demolded part. After blowing air, shot blasting and oiling the demolded part can ensure that a protective oil film quickly forms on the surface of the part after shot blasting, further preventing oxidation and rust.

[0015] In some embodiments, during the demolding process, the demolding time is controlled to be 30-45 seconds, and the demolding temperature is ≤200℃. This allows for the initial evaporation of moisture from the surface of the part, preventing moisture from remaining on the surface or inside the structure of the part due to immediate transfer.

[0016] In some embodiments, blowing air onto the demolded part includes: In response to the demolding component including a target area, the demolding component is blown with a first wind speed and the target area of ​​the demolding component is blown with a second wind speed, the second wind speed being greater than the first wind speed, the target area being a groove area and / or a weld seam area. Alternatively, in response to the demolding component not including the target area, the demolding component is blown with a first wind speed.

[0017] In this way, a lower first wind speed is used to blow air onto the entire demolded part to remove moisture from its surface, while a higher second wind speed is used to blow air directionally onto the target area that is prone to water accumulation, so as to focus on cleaning the target area and accelerate the evaporation of moisture in the target area, thereby preventing moisture residue from causing rust.

[0018] In some embodiments, during the shot blasting process, the shot blasting time is 120-180 s, and the shot blasting machine power is 50-70 kW; and / or, during the oiling process, the spraying pressure is 0.5-0.7 MPa, and the oiling amount is 0.5-1.0 g / m³. 2 .

[0019] In this way, by controlling the parameters in the shot blasting and oiling process, it is ensured that a protective oil film quickly forms on the surface of the parts after shot blasting, preventing oxidation and rust.

[0020] Based on the same inventive concept, a third aspect of this application provides a thermoformed part, which is prepared by the preparation method described in any one of the second aspects above.

[0021] As can be seen from the above, the thermoforming method, preparation method, and thermoformed parts provided in this application, by controlling the initial temperature to 700~740℃, the first isothermal temperature to 750~770℃, and the second isothermal temperature to 885~895℃, effectively control the initial heating temperature (i.e., the initial temperature), the intermediate isothermal temperature (i.e., the first isothermal temperature), and the final heating temperature (i.e., the second isothermal temperature) of the zinc-based thermoforming material. The suitable initial and intermediate isothermal temperatures prevent the temperature of the zinc-based thermoforming material from being rapidly heated directly from room temperature to a temperature that would cause extensive oxidation, combustion, or even volatilization of the zinc layer. (Typically 800℃ and above), thus preventing severe oxidation of zinc-based hot-forming materials; a suitable intermediate isothermal temperature ensures sufficient temperature transition for zinc-based hot-forming materials in the temperature range below 800℃, thereby significantly reducing the rate of zinc layer volatilization and oxidation, and reducing whitening defects on the surface of zinc-based hot-forming materials; a suitable termination heating temperature ensures that zinc-based hot-forming materials can be fully austenitized to meet the strength requirements of parts. Therefore, suitable initial heating temperature, intermediate isothermal temperature, and termination heating temperature can ensure that zinc-based hot-forming materials do not exhibit whitening defects during hot forming, improving forming accuracy. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in this application or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic flowchart of a thermoforming method according to an embodiment of this application; Figure 2 This is a schematic flowchart illustrating the method for preparing a thermoformed part according to an embodiment of this application. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments.

[0025] It should be noted that, unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods, unless otherwise specified, are conventional methods.

[0026] The thermoforming process of zinc-based thermoforming materials, simply put, involves heating a steel plate covered with a "zinc alloy coat," then rapidly forming and quenching it in a mold to turn it into a lightweight, strong, and rust-free car "skeleton."

[0027] This process cleverly combines the advantages of both "thermoforming" and "zinc-based coating": Hot forming solves the problem of processing high-strength steel: ultra-high-strength steel sheets are very brittle at room temperature, making it difficult to stamp into complex automotive parts. The hot forming process first heats the steel sheet to above its austenitizing temperature (typically 880–950°C) to completely soften it, then rapidly shapes it in a mold and quenches it to obtain parts with strengths exceeding 1500 MPa. Simultaneously, heating, stamping, and quenching are performed in one continuous process, ensuring the finished product's ultra-high strength and dimensional accuracy.

[0028] The zinc-based coating provides dual protection: covering the steel surface with a zinc-based coating offers two main benefits: Anti-oxidation: When heated at high temperatures, the zinc coating will preferentially react with oxygen, acting like a "protective film" to prevent the steel plate surface from rusting or decarburizing, eliminating the need for shot peening to remove oxide scale after hot forming.

[0029] Corrosion resistance: The zinc coating provides long-term cathodic protection for parts, preventing the substrate from rusting even if the surface is scratched, which is crucial for car bodies that require high corrosion resistance.

[0030] However, this seemingly perfect combination also has its drawbacks: in the hot forming process of zinc-based hot forming materials, the materials need to be heated in a roller hearth furnace. During the heating process in the roller hearth furnace, the zinc layer on the surface of the zinc-based hot forming material is very prone to oxidation, combustion, or even volatilization at high temperatures, resulting in defects such as whitening and graying on the surface of the steel plate, which affects the accuracy and surface quality of subsequent stamping.

[0031] Currently, the industry's solutions to the above problems are mostly empirical adjustments or local optimizations, such as reducing heating temperature and shortening molding time. However, these methods lack systematicity and repeatability, making them difficult to apply stably in large-scale production.

[0032] Therefore, there is an urgent need for a systematic, quantifiable, and controllable hot forming method to solve the core problem of zinc layer oxidation and whitening, and to improve the stability and consistency of the surface quality of high-strength steel parts.

[0033] Based on this, the inventors of this application discovered that the conventional heating process window for existing thermoforming materials is 880℃~920℃, which is a very high heating temperature. When zinc-based thermoforming materials are in the thermoforming process, the temperature of the zinc-based thermoforming materials will rapidly rise to 800℃ and above, causing the zinc layer to oxidize, burn, or even volatilize rapidly and in large quantities. Ultimately, the oxidized zinc oxide residue remains on the surface of the steel plate, resulting in defects such as whitening and graying on the surface of the steel plate material. In addition, the oxidized zinc oxide residue on the surface of the steel plate can cause mold adhesion, wrinkling, or cracking during the forming process, seriously affecting the dimensional consistency of the final product.

[0034] Therefore, see Figure 1 This application proposes a thermoforming method, comprising: Step S100: Place the zinc-based thermoforming material in a heating device, control the temperature of the heating device to rise from the initial temperature to the first constant temperature, and maintain the temperature at the first constant temperature until the constant temperature duration reaches the first constant temperature duration; wherein, the initial temperature is 700~740℃, and the first constant temperature is 750~770℃. Step S200: Continue to control the temperature of the heating device to rise from the first constant temperature to the second constant temperature, and maintain the temperature at the second constant temperature until the constant temperature duration reaches the second constant temperature duration, wherein the second constant temperature is 885~895℃; Step S300: Remove the heated zinc-based thermoforming material from the heating device.

[0035] Specifically, firstly, the zinc-based thermoforming material is placed in a heating device, which can be a roller hearth furnace or a heating furnace, etc.

[0036] Zinc-based thermoforming materials can be of any shape. For example, zinc-based thermoforming materials can be zinc-based thermoforming plates, zinc-based thermoforming rings, zinc-based thermoforming blocks, zinc-based thermoforming parts, etc.

[0037] Zinc-based thermoforming materials include a substrate and a zinc layer on the substrate. The substrate can be made of steel, aluminum alloy, carbon fiber / glass fiber composite material, etc., which are suitable for thermoforming.

[0038] Secondly, the temperature of the heating device is controlled to rise from the initial temperature to the first constant temperature, and then maintained at the first constant temperature for a duration of time until the temperature reaches the first constant temperature duration. In this way, the temperature of the zinc-based thermoforming material in the heating device can be heated from the initial temperature until it reaches the first constant temperature, and then maintained at the first constant temperature for a duration of time.

[0039] Next, the temperature of the heating device is controlled to rise from the first constant temperature to the second constant temperature, and then maintained at the second constant temperature for the second constant temperature duration. In this way, the temperature of the zinc-based thermoforming material in the heating device can continue to be heated from the first constant temperature until it reaches the second constant temperature, and then maintained at the second constant temperature for the second constant temperature duration.

[0040] The initial temperature is 700-740℃, the first constant temperature is 750-770℃, and the second constant temperature is 885-895℃. Specifically, in this application, the temperature of the zinc-based thermoforming material located in the heating device is raised from the initial temperature of 700-740℃ to the first constant temperature of 750-770℃, held at that temperature for a first constant time, then further heated to the second constant temperature of 885-895℃, held at that temperature for a second constant time, and finally the heated zinc-based thermoforming material is removed from the heating device, completing the thermoforming process of the zinc-based thermoforming material.

[0041] Throughout the thermoforming process, the initial heating temperature is controlled at 700~740℃. Compared to the heating temperature of 880℃~920℃ in existing thermoforming processes, the initial heating temperature in this application is lower, significantly lower than the initial heating temperature of 880℃ in existing thermoforming processes. This results in a lower initial heating temperature for the zinc-based thermoforming material, preventing the temperature of the zinc-based thermoforming material from being rapidly heated directly from room temperature to a very high temperature (usually 800℃ and above). Therefore, the rapid and extensive oxidation, combustion, or even volatilization of the zinc layer caused by the rapid temperature rise of the zinc-based thermoforming material to above 800℃ will not occur, thus ensuring that defects such as whitening or graying will not appear on the surface of the zinc-based thermoforming material.

[0042] When the initial temperature is below 700℃, it is too low, resulting in an excessively long heating time and increased process costs for thermoforming. When the initial temperature is above 740℃, it is too high, causing the initial heating temperature of the zinc-based thermoforming material to be too high. Consequently, the temperature of the zinc-based thermoforming material is rapidly heated from room temperature to a relatively high temperature, leading to a drastic temperature change and rapid oxidation and whitening.

[0043] For example, the initial temperature can be 700℃, 705℃, 710℃, 715℃, 720℃, 725℃, 730℃, 735℃, 740℃, etc.

[0044] Furthermore, during the heating process, the temperature of the zinc-based thermoforming material located in the heating device is raised from an initial temperature of 700~740℃ to a first constant temperature of 750~770℃ and held at that temperature for a first constant temperature duration. That is, the temperature of the zinc-based thermoforming material is raised from a lower initial temperature to a slightly higher first constant temperature and held at that temperature for a first constant temperature duration. Since the first constant temperature of 750~770℃ is also significantly lower than the initial heating temperature of 880℃ in the thermoforming process, the temperature of the zinc-based thermoforming material can be maintained at a temperature below 800℃ for a longer period of time. This ensures that the zinc-based thermoforming material has sufficient temperature rise transition time in the temperature range below 800℃, thereby significantly reducing the rate of zinc layer volatilization and oxidation and reducing the whitening defect on the surface of the zinc-based thermoforming material.

[0045] Furthermore, during the heating process, when the coating begins to liquefy, the Al used to form the inhibition layer dissolves and diffuses to the coating surface to form Al2O3, thereby preventing the coating from being oxidized. When the heating temperature rises to 550℃, the formation of some intermetallic phases causes some Al2O3 to break down, and ZnO begins to form in the broken areas. When the temperature continues to rise to 700℃, the transformation from the δ phase to the Γ phase leads to further breakage of the Al2O3 layer, resulting in the formation of more ZnO on the surface. The oxides generated on the coating surface can prevent Zn volatilization. Therefore, controlling the first constant temperature at 750~770℃ can maintain the temperature of the zinc-based thermoforming material at the first constant temperature. This allows more oxides to be generated on the coating surface to prevent Zn volatilization, while also ensuring that the temperature of the zinc-based thermoforming material does not rise rapidly to above 800℃ to further reduce Zn volatilization. At the same time, holding the first constant temperature at 750~770℃ for a period of time allows the Γ phase to undergo a stable transformation, controlling the coating liquefaction rate and the mutual diffusion rate with the zinc-based thermoforming material, thus ensuring the Zn content in the coating.

[0046] When the first isothermal temperature is less than 750℃, the temperature is too low, which prevents the formation of more oxides on the coating surface or results in a low rate of oxide formation, thus failing to effectively prevent Zn volatilization. When the first isothermal temperature is greater than 770℃, the temperature is too high, approaching or exceeding 800℃, leading to more severe Zn volatilization. This results in a decrease in the Zn content and coating thickness in the final coating, thereby weakening the cathodic protection effect of the coating on the steel substrate.

[0047] For example, the first constant temperature can be 750℃, 751℃, 752℃, 753℃, 754℃, 755℃, 756℃, 757℃, 758℃, 759℃, 760℃, 761℃, 762℃, 763℃, 764℃, 765℃, 766℃, 767℃, 768℃, 769℃, 770℃, etc.

[0048] After the first constant temperature period, continue heating to the second constant temperature of 885~895℃ and maintain the temperature for the second constant temperature period. In this way, the temperature of the zinc-based thermoforming material located in the heating device can be heated to the final second constant temperature of 885~895℃ and maintained for the second constant temperature period. Finally, the zinc-based thermoforming material is removed from the heating device, completing the thermoforming process.

[0049] The termination heating temperature in this application is a second isothermal temperature of 885~895℃. This temperature is significantly lower than the termination heating temperature of 950℃ in existing hot forming processes, but it reaches the austenitizing temperature (generally 880~950℃). This ensures that the zinc-based hot forming material can be austenitized. Simultaneously, maintaining the second isothermal temperature for the second duration ensures sufficient heating time for the zinc-based hot forming material above 800℃, thereby guaranteeing full austenitization and meeting the strength requirements of the parts.

[0050] In addition, a significant reason for blistering on the surface of zinc-based thermoforming materials is the relatively low boiling point of Zn (907°C). When the heating temperature is high, the Zn in the coating becomes very unstable as it approaches the boiling point. Furthermore, stress concentration exists at the edges of the cut zinc-based thermoforming materials, leading to damage to the coating at the edges of the materials at high temperatures. This results in Zn leakage and boiling, causing blistering.

[0051] Furthermore, at very high heating temperatures, severe powdering occurs on the coating surface, making the coating more prone to peeling off. At high temperatures, liquid zinc volatilizes, leading to a decrease in the final Zn content and coating thickness, thus weakening the coating's cathodic protection of the steel substrate.

[0052] Therefore, controlling the second constant temperature to 885~895℃ can keep the Zn in the coating stable and prevent it from boiling and bubbling, and can also reduce or even eliminate the volatilization of liquid zinc, ensuring that the Zn content in the coating will hardly decrease and the coating thickness will hardly decrease, thus ensuring that the coating will not affect the cathodic protection of the steel substrate.

[0053] When the second constant temperature is greater than 895℃, the termination heating temperature is too high, almost approaching the boiling point of Zn. This will cause the Zn in the coating to boil and blister. At the same time, the evaporation of liquid zinc will reduce the Zn content and coating thickness in the final coating, thereby weakening the cathodic protection of the coating on the steel substrate.

[0054] When the second constant temperature is less than 885℃, the termination heating temperature is too low. Although it can ensure that Zn will not boil or volatilize, the termination temperature is too low to reach the austenitizing temperature (generally 880~950℃). This makes it impossible for zinc-based hot-formed materials to austenitize. After quenching and cooling, a complete martensitic structure cannot be obtained, resulting in a tensile strength of the part <1350MPa, which does not meet the strength requirements of the part.

[0055] For example, the second constant temperature can be 885℃, 886℃, 887℃, 888℃, 889℃, 890℃, 891℃, 892℃, 893℃, 894℃, 895℃, etc.

[0056] In this application, by controlling the initial temperature to 700~740℃, the first constant temperature to 750~770℃, and the second constant temperature to 885~895℃, the initial heating temperature (i.e., the initial temperature), the intermediate constant temperature (i.e., the first constant temperature), and the final heating temperature (i.e., the second constant temperature) of the zinc-based thermoforming material are all appropriately controlled. The appropriate initial temperature prevents the temperature of the zinc-based thermoforming material from being rapidly heated directly from room temperature to a very high temperature, thus preventing severe oxidation of the zinc-based thermoforming material. The appropriate intermediate constant temperature ensures that the zinc-based thermoforming material has sufficient temperature rise transition time in the temperature range below 800℃, thereby significantly reducing the rate of zinc layer volatilization and oxidation and reducing whitening defects on the surface of the zinc-based thermoforming material. The appropriate final heating temperature ensures that the zinc-based thermoforming material can be fully austenitized to meet the strength requirements of the parts. Therefore, the appropriate initial heating temperature, intermediate constant temperature, and final heating temperature can ensure that the zinc-based thermoforming material does not exhibit whitening defects during the thermoforming process, improving the forming accuracy.

[0057] In some embodiments, the initial temperature is 710~730℃, the first constant temperature is 755~765℃, and the second constant temperature is 887~893℃.

[0058] Specifically, when the initial temperature is 710~730℃, the range of the initial temperature is more suitable, which allows the temperature of the zinc-based thermoforming material to be heated from room temperature to a more suitable temperature, ensuring that it is not heated directly from room temperature to a very high temperature, and thus preventing severe oxidation of the zinc-based thermoforming material.

[0059] Preferably, the initial temperature is 720°C, which is the optimal initial temperature. This temperature will not excessively increase the heating time of the zinc-based thermoforming material, and it will also ensure that the temperature of the zinc-based thermoforming material does not rise rapidly to a very high temperature, thus preventing severe oxidation of the zinc-based thermoforming material.

[0060] When the first constant temperature is 755~765℃, it is more suitable to ensure that the zinc-based thermoforming material has sufficient temperature rise transition in the temperature range below 800℃, thereby significantly reducing the volatilization and oxidation rate of the zinc layer and reducing the whitening defect on the surface of the zinc-based thermoforming material.

[0061] Preferably, the first constant temperature is 760°C, which is the optimal intermediate constant temperature. This ensures that the zinc-based thermoforming material has sufficient temperature rise transition in the temperature range below 800°C, thereby significantly reducing the rate of zinc layer volatilization and oxidation, and significantly reducing the whitening defect on the surface of the zinc-based thermoforming material.

[0062] When the second constant temperature is 887~893℃, it is more suitable to ensure that the zinc-based thermoforming material can be fully austenitized to meet the strength requirements of the parts.

[0063] Preferably, when the second isothermal temperature is 890°C, this is the optimal termination temperature, which can ensure that the zinc-based thermoforming material can be fully austenitized without causing Zn to boil or the Zn liquid to volatilize.

[0064] In some embodiments, the second isothermal duration is 150-200s, and the first isothermal duration is 40-80s.

[0065] Specifically, when the first isothermal duration is 40~80s, the first isothermal duration is appropriate. The heat preservation within the first isothermal duration allows the zinc-based thermoforming material to have sufficient temperature transition time in the temperature range below 800℃, thereby significantly reducing the volatilization and oxidation rate of the zinc layer and reducing surface whitening defects.

[0066] For example, the first constant temperature duration can be 40s, 45s, 50s, 55s, 60s, 65s, 70s, 75s, 80s, etc.

[0067] When the first isothermal duration is less than 40 seconds, the first isothermal duration is too short, resulting in insufficient heating transition time for the zinc-based thermoforming material in the temperature range below 800°C. As a result, the rate of zinc layer volatilization and oxidation cannot be significantly reduced, and the surface whitening defect cannot be effectively reduced.

[0068] When the first isothermal duration is greater than 80s, the first isothermal duration is too long. Under the condition that the total heating duration is constant, the first isothermal duration is too long, which will lead to the subsequent heating duration being too short. As a result, it is impossible to ensure the full austenitization of the zinc-based thermoforming material during the subsequent heating process, so as not to meet the strength requirements of the zinc-based thermoforming material parts after thermoforming.

[0069] When the second isothermal duration is 150~200s, the second isothermal duration is appropriate and can ensure that the zinc-based thermoforming material has sufficient heating time in the temperature range above 800℃, thereby ensuring that the zinc-based thermoforming material can be fully austenitized and meet the strength requirements of the parts.

[0070] For example, the second constant temperature duration can be 150s, 155s, 160s, 165s, 170s, 175s, 180s, 185s, 190s, 195s, 200s, etc.

[0071] When the second isothermal duration is less than 150s, the second isothermal duration is too short, which results in the zinc-based thermoforming material having too short a heating time in the temperature range above 800℃. Consequently, the zinc-based thermoforming material cannot be sufficiently austenitized, and thus ultimately cannot meet the strength requirements of the parts.

[0072] When the second isothermal duration exceeds 200s, it is too long. On the basis that the zinc-based thermoforming material has been sufficiently austenitized, continuing to extend the second isothermal duration will only increase heating costs and will not further improve the strength of the parts.

[0073] In some embodiments, when the thickness of the zinc-based thermoforming material is less than the first preset thickness, the first isothermal duration is 50-80s and the second isothermal duration is 150-180s; or, when the thickness of the zinc-based thermoforming material is greater than or equal to the first preset thickness, the first isothermal duration is 40-50s and the second isothermal duration is 160-200s.

[0074] Specifically, the first preset thickness is a thickness obtained based on actual testing experience. For example, the first preset thickness can be 1.5mm, 1.6mm, or 1.8mm, etc.

[0075] Compared to zinc-based hot-formed materials with a thickness less than the first preset thickness, zinc-based hot-formed materials with a thickness greater than or equal to the first preset thickness have a shorter first isothermal duration and a longer second isothermal duration. This is because the thicker the zinc-based hot-formed material, the longer it requires to achieve full austenitization. Therefore, a longer second isothermal duration ensures that the thicker zinc-based hot-formed material can achieve full austenitization, thereby ensuring that the strength of the part meets the requirements. At the same time, the thicker zinc-based hot-formed material has a slower overall heating rate. Even if the first holding time is shorter, it will not result in a short heating transition time, thus still ensuring sufficient heating transition time in the temperature range below 800°C.

[0076] In some embodiments, when the thickness of the zinc-based thermoforming material is in the range of 1.2~1.6 mm (excluding 1.6 mm) for the part thickness, the first isothermal duration is 50~80 s, and the second isothermal duration is 150~180 s. When the thickness of the zinc-based thermoforming material is in the range of 1.6~2.0 mm, the first isothermal duration is 40~50 s, and the second isothermal duration is 160~200 s.

[0077] In some embodiments, during the process of controlling the temperature of the heating device to rise from an initial temperature to a first constant temperature and from the first constant temperature to a second constant temperature, the temperature gradient can be controlled to rise once every preset fixed time interval (exemplarily, 18~22s), and the magnitude of each temperature rise can be the same or different.

[0078] For example, during the process of controlling the temperature of the heating device to rise from the initial temperature to the first constant temperature, the temperature can be increased by 20°C or 25°C at preset fixed intervals. During the process of controlling the temperature of the heating device to rise from the first constant temperature to the second constant temperature, the temperature can be increased by 30°C or 40°C at preset fixed intervals.

[0079] See Figure 2 This application also provides a method for preparing a thermoformed part, comprising: thermoforming, stamping and demolding the zinc-based thermoformed material based on the thermoforming method described in any of the above embodiments to obtain a thermoformed part.

[0080] Specifically, a thermoforming material with a set chemical composition can be obtained first, and then the thermoforming material can be hot-dip galvanized to obtain a zinc-based thermoforming material.

[0081] The specified chemical composition includes: C, Si, Mn, Al, Ti, V, Cr, B, P, S, N, and Fe; by mass fraction, the content of C is 0.1%–0.4%, the content of Si is 0.2%–2.0%, the content of Mn is 1%–4%, the content of Al is 0.05%–0.5%, the content of Ti is 0.01%–0.1%, the content of V is 0.01%–0.2%, the content of Cr is 0.2%–2.0%, the content of B is 0.001%–0.005%, the content of P is ≤0.005%, the content of S is ≤0.005%, and the content of N is ≤0.005%.

[0082] For example, the content of C can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, etc. The content of Si can be 0.2%, 0.5%, 1.0%, 1.5%, 2.0%, etc. The content of Mn can be 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 4.0%, etc. The content of Al can be 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.50%, etc. The content of Ti can be 0.001%, 0.003%, 0.005%, 0.007%, 0.10%, etc.

[0083] The hot-formed material is hot-dip galvanized to obtain a zinc-based hot-formed material. The hot-dip galvanizing bath composition includes Al and Zn, wherein the Al content is 0.1% to 0.25% by mass fraction, and the Zn content is 99.75% to 99.9%. Exemplarily, the Al content can be 0.1%, 0.15%, 0.25%, etc., and the Zn content can be 99.75%, 99.85%, 99.9%, etc.

[0084] After obtaining the zinc-based thermoforming material, the zinc-based thermoforming material is thermoformed, stamped, and demolded according to the thermoforming method described in any of the above embodiments to obtain thermoformed parts. In this way, the entire process from thermoforming material to thermoformed parts is completed.

[0085] In this application, because the temperature of each step in the thermoforming process is precisely controlled, the zinc-based thermoforming material after thermoforming will not have whitening defects, nor will it have residual oxidized zinc oxide layer on the surface. This ensures that the zinc-based thermoforming material after thermoforming will not stick to the mold, wrinkle or crack during subsequent stamping and demolding processes, thus improving the dimensional consistency of the product.

[0086] Generally, for zinc-based thermoformed materials after thermoforming, a mechanical gripper is used to hold the red-hot zinc-based thermoformed material and quickly move it into a mold with a cooling system for stamping and forming, while maintaining pressure at a temperature greater than 27°C / s. -1 The cooling rate allows for rapid quenching within the mold, resulting in a fully martensitic structure that significantly improves the strength of the parts. This enables the production of stamped parts with tensile strengths up to 1500 MPa.

[0087] In the specific implementation process, the inventors found that for large-sized parts (such as laser-welded door rings), after the water bath forming in the mold is completed, due to their complex structure and the presence of grooves or welding seams on the edges, water is easily trapped in the mold, that is, water is retained on the surface or in the internal structure of the parts.

[0088] Because these parts are large in size and have a wide surface area, manual wiping is inefficient and they are difficult to dry quickly in workshop environments (such as high humidity and large temperature fluctuations). They are prone to oxidation and rust in a short period of time, resulting in defects such as rust spots and color differences on the surface of the parts, which seriously affect the surface quality of the final product and the adhesion of subsequent coating processes.

[0089] Based on this, in some embodiments, the thermoforming method based on any of the above embodiments performs thermoforming, stamping, and demolding on the zinc-based thermoforming material to obtain thermoformed parts, including: The zinc-based thermoforming material is thermoformed using the thermoforming method described in any of the above embodiments to obtain a thermoformed part; The thermoformed part is immersed in the lower mold for cooling, and then the molding, pressure holding, and demolding are performed sequentially to obtain the demolded part; wherein, the lower mold contains a coolant at a temperature of 85~100℃, and the pressure holding time is 6~10s; The demolded part is subjected to blowing, shot blasting and oiling in sequence to obtain zinc-based thermoforming material.

[0090] Specifically, after obtaining the thermoformed part, the thermoformed part is first immersed in the lower mold for cooling, and then the molding, pressure holding, and demolding are performed in sequence to obtain the demolded part; wherein, the lower mold contains a coolant with a temperature of 85~100℃, and the pressure holding time is 6~10s.

[0091] For example, the coolant may be water.

[0092] The temperature of the coolant is controlled at 85~100℃ to ensure a suitable temperature. During this process, film boiling occurs on the surface of the thermoformed part, and the oxide layer on the surface of the thermoformed part is cleaned by bubbles. At the same time, the generated bubbles merge to form a stable gas film. Because the heat transfer coefficient of gas is small, the thermoformed part dissipates heat slowly, thus ensuring that the temperature is below 700℃ when the mold is closed, while remaining above the Ms transformation temperature line, which guarantees the forming and strength of the part.

[0093] If the coolant temperature is less than 85°C, the coolant temperature is too low, causing the thermoformed part to cool down too quickly. As a result, the thermoformed part will enter the Ms transformation temperature line before the mold is closed, which will lead to increased strength and decreased plasticity of the thermoformed part, and there is a risk of stamping cracking.

[0094] For example, the temperature of the coolant can be 85℃, 86℃, 87℃, 88℃, 89℃, 90℃, 91℃, 92℃, 93℃, 94℃, 95℃, 96℃, 97℃, 98℃, 99℃, 100℃, etc.

[0095] When the holding time is 6~10s, the holding time is appropriate, ensuring that the hot-formed part can be quickly quenched in the mold to obtain a fully martensitic structure, which greatly improves the strength of the part.

[0096] When the holding time is less than 6 seconds, the holding time is too short, and the thermoformed part will spring back, affecting the accuracy of the final part. When the holding time is greater than 10 seconds, the holding time is too long. Although it does not affect the accuracy of the part, it will lead to a longer production cycle and affect production efficiency.

[0097] For example, the pressure holding time can be 6s, 7s, 8s, 9s, 10s, etc.

[0098] After obtaining the demolded part, the demolded part is subjected to blowing, shot blasting and oiling in sequence to obtain zinc-based thermoforming material.

[0099] Blowing air onto the demolded part can accelerate the evaporation of residual moisture inside, thereby solving defects such as rust spots and color differences caused by moisture remaining on the surface or internal structure of the demolded part. Shot blasting and oiling of the demolded parts after air blowing can ensure that a protective oil film quickly forms on the surface of the parts after shot blasting, further preventing oxidation and rust.

[0100] In some embodiments, during the demolding process, the demolding time is controlled to be 30~45s, and the demolding temperature is ≤200℃.

[0101] Specifically, the demolding time is controlled at 30-45 seconds. For the existing demolding process, the demolding time is deliberately increased so that the moisture on the surface of the part can be initially evaporated, avoiding the moisture from remaining on the surface or in the internal structure of the part due to immediate transfer.

[0102] For example, the demolding time can be 30s, 31s, 32s, 33s, 34s, 35s, 36s, 37s, 38s, 39s, 40s, 41s, 42s, 43s, 44s, 45s, etc.

[0103] The demolding temperature is ≤200℃, meaning the temperature of the demolded part after demolding is less than or equal to 200℃. This ensures that the strength and plasticity of the demolded part meet the requirements and facilitates subsequent processes.

[0104] In some embodiments, blowing air onto the demolded part includes: In response to the demolding component including a target area, the demolding component is blown with a first wind speed and the target area of ​​the demolding component is blown with a second wind speed, the second wind speed being greater than the first wind speed, the target area being a groove area and / or a weld seam area. Alternatively, in response to the demolding component not including the target area, the demolding component is blown with a first wind speed.

[0105] Specifically, the target area is a grooved area and / or a welded seam area, which are prone to water accumulation. Therefore, when the demolding component includes the target area, the demolding component is blown with a first wind speed, and the target area of ​​the demolding component is blown with a second wind speed, where the second wind speed is greater than the first wind speed. In this way, the lower first wind speed blows on the entire demolding component to remove moisture from its surface, while the higher second wind speed blows directional air onto the target area, focusing on cleaning the target area and accelerating the evaporation of moisture in the target area to prevent moisture residue from causing rust.

[0106] When the demolding part does not include the target area, the demolding part is blown with a first wind speed to blow the entire demolding part with a smaller first wind speed to remove moisture from the surface of the demolding part, accelerate moisture evaporation, and avoid moisture residue that may cause rust.

[0107] For example, the second wind speed is greater than or equal to 15 m / s. The first wind speed is greater than or equal to 10 m / s.

[0108] In some embodiments, during the shot blasting process, the shot blasting time is 120-180 s, and the shot blasting machine power is 50-70 kW; and / or, during the oiling process, the spraying pressure is 0.5-0.7 MPa, and the oiling amount is 0.5-1.0 g / m³.2 In this way, by controlling the parameters during the shot blasting and oiling processes, a protective oil film can be quickly formed on the surface of the parts after shot blasting to prevent oxidation and rust.

[0109] For example, the shot blasting time can be 120s, 130s, 140s, 150s, 160s, 170s, 180s, etc. The shot blasting machine power can be 50kW, 60kW, 70kW, etc. The spraying pressure can be 0.5MPa, 0.6MPa, 0.7MPa, etc. The oil application rate can be 0.5g / m³. 2 0.6g / m 2 0.7g / m 2 0.8g / m 2 0.9g / m 2 1.0g / m 2 wait.

[0110] This application also provides a thermoformed part, which is prepared by any one of the preparation methods described above. The specific steps of the preparation method for this thermoformed part can be referred to the above embodiments. Since this thermoformed part adopts some or all of the technical solutions of the above embodiments, it at least has all the beneficial effects brought about by the technical solutions of the above embodiments, and will not be elaborated further here.

[0111] The following discussion uses zinc-based steel sheet as an example to further illustrate the technical methods and effects of this application through specific embodiments.

[0112] Example 1 A method for hot forming zinc-based hot-formable steel, comprising: A zinc-based steel sheet is placed in a heating furnace, and the temperature of the heating furnace is controlled to rise from an initial temperature to a first constant temperature, and maintained at the first constant temperature for a first constant temperature duration; wherein, the initial temperature is 720°C, the first constant temperature is 760°C, and the first constant temperature duration is 80s. The temperature of the heating furnace is continuously controlled to rise from the first constant temperature to the second constant temperature, and maintained at the second constant temperature until the constant temperature duration reaches the second constant temperature duration, wherein the second constant temperature is 890℃ and the second constant temperature duration is 120s.

[0113] The heated zinc-based steel sheet is removed from the heating furnace.

[0114] The temperatures throughout the heating process are shown in Table 1 below.

[0115] Example 2 A hot forming method for zinc-based hot-formed steel, which differs from Example 1 in that: the first isothermal duration is 60s; the second isothermal temperature is 885℃, and the second isothermal duration is 140s.

[0116] The temperatures throughout the heating process are shown in Table 1 below.

[0117] Example 3 A hot forming method for zinc-based hot-formed steel, which differs from Example 1 in that: the initial temperature is 700℃, the first constant temperature is 750℃, and the first constant temperature duration is 80s; the second constant temperature is 885℃, and the second constant temperature duration is 140s.

[0118] The temperatures throughout the heating process are shown in Table 1 below.

[0119] Example 4 A hot forming method for zinc-based hot-formed steel, which differs from Example 1 in that: the initial temperature is 740°C, the first constant temperature is 770°C, and the first constant temperature duration is 40s; the second constant temperature is 895°C, and the second constant temperature duration is 200s.

[0120] The temperatures throughout the heating process are shown in Table 1 below.

[0121] Comparative Example 1 A hot forming method for zinc-based hot-formed steel, which differs from Example 1 in that: the initial temperature is 780°C, the first constant temperature is 810°C, the first constant temperature duration is 40s, and the second constant temperature duration is 160s.

[0122] The temperatures throughout the heating process are shown in Table 1 below.

[0123] Comparative Example 2 A hot forming method for zinc-based hot-formed steel, which differs from Example 1 in that the first constant temperature is 810°C.

[0124] The temperatures throughout the heating process are shown in Table 1 below.

[0125] Comparative Example 3 A hot forming method for zinc-based hot-formed steel, which differs from Example 1 in that: the initial temperature is 880°C, the first constant temperature is 900°C, and the first constant temperature duration is 60s; the second constant temperature is 920°C, and the second constant temperature duration is 160s.

[0126] Comparative Example 4 A hot forming method for zinc-based hot-formed steel, which differs from Example 1 in that: the initial temperature is 880°C, the first constant temperature is 900°C, and the second constant temperature is 920°C.

[0127] The temperatures throughout the heating process are shown in Table 1 below.

[0128] Comparative Example 5 A hot forming method for zinc-based hot-formed steel, which differs from Example 1 in that the second isothermal temperature is 880°C.

[0129] The temperatures throughout the heating process are shown in Table 1 below.

[0130] The same zinc-based steel sheet was thermoformed, stamped, and demolded according to the thermoforming methods of Examples 1-4 and Comparative Examples 1-3, respectively. All process parameters in the stamping and demolding steps were kept consistent to obtain thermoformed parts, which were named the formed parts of Example 1, Example 2, Example 3, Example 4, Comparative Example 1, Comparative Example 2, and Comparative Example 3, respectively.

[0131] The tensile strength, metallographic structure, and surface condition of the molded parts obtained in each embodiment and comparative example were tested and observed. The test and observation results are shown in Table 2 below.

[0132] Table 1. Temperatures during the heating process in each embodiment and comparative example.

[0133] In the table above, the time interval between heating temperatures in each column is 20 seconds. That is, taking Example 1 as an example, the initial temperature of the heating furnace is 720°C. After 20 seconds, the temperature of the heating furnace is controlled to rise to 740°C. After another 20 seconds, the temperature of the heating furnace is controlled to continue rising to 760°C and held at 760°C for 80 seconds. The temperature of the heating furnace is then controlled to continue rising to 790°C. After another 20 seconds, the temperature of the heating furnace is controlled to continue rising to 820°C. After another 20 seconds, the temperature of the heating furnace is controlled to continue rising to 860°C. After another 20 seconds, the temperature of the heating furnace is controlled to continue rising to 760°C. After another 20 seconds, the temperature of the heating furnace is controlled to continue rising to 890°C and held at 890°C for 120 seconds.

[0134] Table 2. List of test results for the molded parts obtained from each embodiment and comparative example.

[0135] Referring to Tables 1 and 2 above, it can be seen that by strictly controlling the initial temperature to 700~740℃, the first isothermal temperature to 750~770℃, the second isothermal temperature to 885~895℃, the second isothermal duration to 150~200s, and the first isothermal duration to 40~80s, only a few small areas of the molded parts of the final prepared embodiments showed white powder on their surfaces, while the vast majority of the surfaces did not show any whitening defects. Furthermore, the metallographic structure of the molded parts of each embodiment was mainly martensite with a very small amount of ferrite, indicating that the entire zinc-based steel sheet was fully austenitized after hot forming and rapidly quenched in the mold to obtain a fully martensitic structure, and its tensile strength met the actual requirements (≥1350MPa).

[0136] In Comparative Example 1, although both the first and second isothermal durations were suitable compared to Example 1, the initial temperature was close to 800°C and the first isothermal temperature was greater than 800°C. That is, both the initial temperature and the first isothermal temperature were high, which caused the temperature of the zinc-based steel plate to be rapidly heated from room temperature to above 800°C. This resulted in a faster oxidation rate of the zinc layer, ultimately leading to multiple whitening defects on the surface of the zinc-based steel plate.

[0137] In Comparative Example 2, although the initial temperature was lower than in Example 1, the first constant temperature was a higher 810°C. This resulted in the zinc-based steel plate not having sufficient time to rise and transition in the temperature range below 800°C. Instead, it rapidly rose to 810°C and was held at that temperature, causing the zinc layer to volatilize and oxidize, ultimately leading to localized whitening defects on the surface of the zinc-based steel plate.

[0138] In Comparative Examples 3 and 4, although the first and second isothermal durations were suitable compared to Example 1, the initial temperature exceeded 800°C, the first isothermal temperature reached 900°C, and the second isothermal temperature reached 920°C. These very high initial, first, and second isothermal temperatures caused the zinc-based steel plate to be rapidly heated from room temperature to above 800°C and maintained thereafter. This resulted in rapid and extensive oxidation, combustion, and even volatilization of the zinc layer, ultimately leading to a large area of ​​white powder on the surface of the zinc-based steel plate. Compared to Comparative Example 1, the higher initial, first, and second isothermal temperatures in Comparative Examples 3 and 4 resulted in a greater degree of oxidation and whitening, thus causing the appearance of a large area of ​​white powder.

[0139] In Comparative Example 5, although the initial temperature and the first isothermal temperature were relatively low, preventing the zinc layer from volatilizing and oxidizing, the surface of the formed part in Comparative Example 5 only showed white powder in a few isolated locations, without any whitening defects. However, due to the low second isothermal temperature, the zinc-based steel plate could not be austenitized, and a fully martensitic structure could not be obtained after quenching and cooling, ultimately resulting in a tensile strength <1350MPa, which did not meet the strength requirements of the part.

[0140] In this application, by controlling the initial temperature to 700~740℃, the first constant temperature to 750~770℃, and the second constant temperature to 885~895℃, the initial heating temperature (i.e., the initial temperature), the intermediate constant temperature (i.e., the first constant temperature), and the final heating temperature (i.e., the second constant temperature) of the zinc-based steel sheet are all appropriately controlled. The appropriate initial temperature prevents the temperature of the zinc-based steel sheet from being rapidly heated directly from room temperature to a very high temperature, thus preventing severe oxidation of the zinc-based steel sheet. The appropriate intermediate constant temperature ensures that the zinc-based steel sheet has sufficient temperature rise transition in the temperature range below 800℃, thereby significantly reducing the rate of zinc layer volatilization and oxidation and reducing whitening defects on the surface of the zinc-based steel sheet. The appropriate final heating temperature ensures that the zinc-based steel sheet can be fully austenitized to meet the strength requirements of the parts. Therefore, the appropriate initial heating temperature, intermediate constant temperature, and final heating temperature can ensure that the zinc-based steel sheet will not have whitening defects during hot forming, improving the forming accuracy.

[0141] Precise temperature control at each stage is key to solving the problem of severe oxidation and whitening of the zinc layer on zinc-based steel sheets, while post-demolding air blowing is the core method to solve the water trapping problem. Standardization of shot blasting and oiling process parameters (time, power, oil volume) ensures the surface protection effect. The entire process forms a closed-loop control, realizing full-process quality control from heating to protection.

[0142] By precisely setting the heating temperature of the roller hearth furnace, "window control" of the zinc oxide process is achieved, avoiding prolonged exposure to high-temperature sections and effectively suppressing whitening defects. A high-volume fan is introduced for directional blowing during the demolding process, combined with extended dwell time, systematically solving the problem of water trapping in large-sized parts. The entire process forms a standardized workflow that is replicable, monitorable, and traceable, suitable for complex, large-sized parts such as laser-welded door rings.

[0143] The thermoforming method and the preparation method of thermoformed parts described in this application significantly improve the surface quality of the final thermoformed parts, eliminating whitening and rust, meeting the pretreatment requirements for coating, and improving the adhesion and corrosion resistance of subsequent coating processes. This provides a quantifiable implementation plan for the thermoforming of complex structural parts such as laser welding.

[0144] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this application (including the claims) is limited to these examples; within the framework of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the embodiments of this application as described above, which are not provided in the details for the sake of brevity.

[0145] The embodiments of this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiments of this application should be included within the protection scope of this application.

Claims

1. A thermoforming method, characterized in that, include: The zinc-based thermoforming material is placed in a heating device, and the temperature of the heating device is controlled to rise from an initial temperature to a first constant temperature, and the temperature is maintained at the first constant temperature until the constant temperature duration reaches the first constant temperature duration; wherein, the initial temperature is 700~740℃, and the first constant temperature is 750~770℃. Continue to control the temperature of the heating device to rise from the first constant temperature to the second constant temperature, and maintain the temperature at the second constant temperature until the constant temperature duration reaches the second constant temperature duration, wherein the second constant temperature is 885~895℃; The heated zinc-based thermoforming material is removed from the heating device.

2. The thermoforming method according to claim 1, characterized in that, The initial temperature is 710~730℃, the first constant temperature is 755~765℃, and the second constant temperature is 887~893℃.

3. The thermoforming method according to claim 1, characterized in that, The second constant temperature duration is 150~200s, and the first constant temperature duration is 40~80s.

4. The thermoforming method according to claim 1, characterized in that, When the thickness of the zinc-based thermoforming material is less than the first preset thickness, the first isothermal duration is 50~80s, and the second isothermal duration is 150~180s; Alternatively, when the thickness of the zinc-based thermoforming material is greater than or equal to the first preset thickness, the first isothermal duration is 40-50 seconds, and the second isothermal duration is 160-200 seconds.

5. A method for preparing a thermoformed part, characterized in that, include: The zinc-based thermoforming material is thermoformed, stamped, and demolded using the thermoforming method according to any one of claims 1 to 4 to obtain thermoformed parts.

6. The preparation method according to claim 5, characterized in that, The method described in any one of claims 1 to 4, which involves thermoforming, stamping, and demolding the zinc-based thermoforming material to obtain a thermoformed part, includes: The zinc-based thermoforming material is thermoformed according to any one of claims 1 to 4 to obtain a thermoformed part; The thermoformed part is immersed in the lower mold for cooling, and then the molding, pressure holding, and demolding are performed sequentially to obtain the demolded part; wherein, the lower mold contains a coolant at a temperature of 85~100℃, and the pressure holding time is 6~10s; The demolded part is subjected to blowing, shot blasting and oiling in sequence to obtain zinc-based thermoforming material.

7. The preparation method according to claim 6, characterized in that, During the demolding process, the demolding time is controlled to be 30~45s, and the demolding temperature is ≤200℃.

8. The preparation method according to claim 6, characterized in that, The blowing of air onto the demolded part includes: In response to the demolding component including a target area, the demolding component is blown with a first wind speed and the target area of ​​the demolding component is blown with a second wind speed, the second wind speed being greater than the first wind speed, the target area being a groove area and / or a weld seam area. Alternatively, in response to the demolding component not including the target area, the demolding component is blown with a first wind speed.

9. The preparation method according to claim 6, characterized in that, During the shot blasting process, the shot blasting time is 120~180s, and the shot blasting machine power is 50~70kW; And / or, during the oiling process, the spraying pressure is 0.5-0.7 MPa, and the oil application rate is 0.5-1.0 g / m³. 2 .

10. A thermoformed part, characterized in that, The thermoformed part is prepared by the preparation method according to any one of claims 5 to 9.

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