Die for hot stamping forming and hot stamping forming method

Abstract

The invention provides a hot stamping forming die and a hot stamping forming method, belongs to the technical field of hot stamping, solves the problems of wrinkling and stacking of stamped plates, and adopts the scheme that the hot stamping forming die comprises a die steel block 2 used for hot stamping forming, the die steel block 2 is further provided with air blowing holes 1, and the air blowing holes 1 are communicated with the die steel block 2. The blowing hole 1 is a risk area determined according to the hot stamping forming of the plate 7, and the risk area refers to a small-range thinning excessive out-of-tolerance area or a cracking area of the plate 7 in the hot stamping forming process or a risk area determined when the hot stamping forming plate is subjected to simulation analysis in the early stage; and one end of the air channel pipe 4 penetrates through the die steel block 2 to be connected with the air blowing hole 1, and the air channel pipe 4 is used for cooling the hot stamping forming plate 7 through the air blowing hole. The cooling system is added for the risk area, so that the local temperature of the plate is lower than that of other parts, the austenite conversion rate is higher than that of other parts, and the tensile strength of the area is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of hot stamping, and in particular to a hot stamping forming die and a hot stamping forming method. Background Art

[0002] This section is intended to provide background or context for the embodiments of the invention set forth in the claims. The descriptions herein may include concepts that may be explored, but not necessarily concepts that have been previously thought of or explored. Therefore, unless otherwise noted herein, the content described in this section is not prior art with respect to the specification and claims of this application, and is not admitted to be prior art by inclusion in this section.

[0003] Hot stamping / Hot press forming, also known as press hardening, is a new technology that has emerged in recent years and is specifically used for stamping high-strength steel plate parts for automobiles. It is also one of the key technical processes for achieving lightweight automobile production. Hot-formed products have almost no rebound after forming, and the product precision is high. Using hot stamping forming technology, the strength of the stamped parts can be as high as 1300Mpa-2000MPa, and they can better absorb vehicle collision energy, reduce vehicle collision deformation, protect the safety of occupants to the greatest extent, and achieve lightweight body. Therefore, it has attracted widespread attention in the industry and quickly became a popular technology in the field of automobile manufacturing. It is widely used in the production of safety parts such as door anti-collision beams, front and rear bumpers, and body structural parts such as A-pillars, B-pillars, C-pillars, and center channels.

[0004] With the continuous improvement of the design and manufacturing level of automobile sheet materials in my country, many of the original cold stamping sheets have begun to develop towards hot forming.

[0005] Hot stamping generally means that the plate is heated to between 810℃-930℃ and kept heated for a certain time to austenitize the steel. After complete austenitization, it is transferred to the hot stamping die by mechanical transfer. Due to heat loss during transfer, the temperature of the steel sheet during stamping is between 630℃-750℃. At this time, the physical properties of the steel sheet are softer, which is more conducive to forming. After cooling, the steel has high strength and can meet the predetermined requirements.

[0006] Since the physical properties of steel become soft after heating, it is easy to tear during the forming process. If the sheet is thinned too much, the stamped sheet will crack, wrinkle, and overlap, which will affect the quality of the product and lead to low output of hot stamping sheets. Therefore, how to improve product quality and increase product output is a technical problem that needs to be solved. Summary of the invention

[0007] In order to solve the problems of cracking of hot stamping sheet materials in the prior art, the purpose of the present invention is to provide a hot stamping die and a hot stamping method.

[0008] To solve the above technical problems, in a first aspect, according to some embodiments, the present invention provides a hot stamping die, comprising a die steel block 2 for hot stamping;

[0009] The mold steel block 2 also has a blowing hole 1, and the position of the blowing hole 1 is based on the position of the mold steel block 2 corresponding to the risk area determined when the hot stamping sheet 7 is formed. The risk area refers to a small range of excessive thinning or cracking area of ​​the sheet during the hot stamping process, or a risk area determined in the early stage of the simulation analysis of the hot stamping sheet;

[0010] An air pipe 4, one end of which passes through the mold steel block 2 and is connected to the blowing hole 1, and the air pipe 4 is used to cool the hot stamping formed plate 7 through the blowing hole;

[0011] The other end of the air pipe 4 is connected to an air source, and the air source cools the hot stamping formed sheet 7 along the air pipe 4 through the blowing holes; or,

[0012] The other end of the air pipe 4 is connected to a water source, and the water source cools the hot stamping formed plate 7 along the air pipe 4 through the blowing holes.

[0013] Optionally, in some embodiments, there are multiple blowing holes 1 and multiple air pipes 4.

[0014] Optionally, in some embodiments, when the air pipe 4 passes through the mold steel block 2, the air pipe joint 3 is used to connect the air pipe 4 outside the mold steel block 2 with the air pipe 4 inside the mold steel block.

[0015] Optionally, in some embodiments, it further includes: an air-water circuit adapter block 5, wherein the air-water circuit adapter block 5 is connected to the other end of the air circuit pipe 4 to control the input of gas or liquid into the air circuit pipe 4.

[0016] Optionally, in some embodiments, the mold further includes: an air circuit external plug 6, which is located on the air circuit and water circuit adapter block 5, one end of which is connected to the air circuit and water circuit adapter block 5, and the other end is an air port, which is connected to the air source through the air port.

[0017] Optionally, in some embodiments, the gas generated by the gas source is high-pressure gas.

[0018] In a second aspect, an embodiment of the present invention further provides a hot stamping forming method, using the mold described in the first aspect, comprising:

[0019] Determining a risk area of ​​the hot stamping formed sheet;

[0020] Performing cooling analysis on the risk area and the cooling conditions of the hot stamping formed sheet;

[0021] According to the analyzed data, the position of the blowing hole on the mold steel block and the blowing rate are determined;

[0022] Performing hot stamping on the hot stamping sheet, and, according to the analyzed data, performing a cooling treatment on the risk area of ​​the sheet by using the blowing holes during the hot stamping process;

[0023] Obtain the sheet material after hot stamping.

[0024] Optionally, in some embodiments, determining the risk area of ​​the hot stamping formed sheet material specifically includes:

[0025] Using a computer to simulate and analyze the hot stamping sheet material to identify the current sheet material thinning risk area during the hot stamping process; or,

[0026] Perform hot stamping on the existing hot stamping sheet to determine the current risk area of ​​sheet thinning.

[0027] The above technical solution of the present invention has at least the following beneficial technical effects:

[0028] According to the technical solution of the embodiment of the present invention, during the hot stamping process, the material is torn or thinned too much, and cooling is used to solve the problem of tearing and excessive thinning. For the risk area of ​​cracking prone area or small-scale excessive thinning of the plate during hot stamping, an additional cooling system is added, which is equivalent to using the additional cooling to quench the material and increase the hardness of the material, thereby reducing or solving the problem of wrinkling and stacking. Since the physical properties of the steel become soft after heating, it is easy to tear during the local forming process and the plate is too thin. By using the cooling during the forming process, the steel is cooled down in advance to increase the strength, thereby realizing the forming process. According to the technical solution of the present invention, by adding a blowing hole to the mold, the local temperature of the plate is lower than that of other parts, so that the transformation rate of austenite is better than that of other parts, the risk area can have more martensite in advance, thereby improving the tensile strength of the area, and to a certain extent, the thickness of the plate in the current risk area is guaranteed, so that the risk of excessive thinning in the cracking prone area or local small-scale excessive thinning is reduced, effectively solving the problem of wrinkling and stacking of the stamped material plate, improving the quality of the product, and also increasing the output of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the conventional technology, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 This is a view of the axis of a hot stamping die provided in an embodiment of the present invention.

[0031] Figure 2 It is a partial cross-sectional view of a hot stamping die provided in an embodiment of the present invention.

[0032] Figure 3 It is a schematic diagram of the gas / liquid flow direction of a hot stamping die provided in an embodiment of the present invention.

[0033] Figure 4 A partial cross-sectional schematic diagram of the gas / liquid flow direction of a hot stamping die provided by an embodiment of the present invention

[0034] Figure 5 It is a curve diagram of plate material changes during the blowing process of a hot stamping forming method provided by an embodiment of the present invention.

[0035] Figure 6 It is a process flow chart of a hot stamping forming method provided by an embodiment of the present invention.

[0036] in, Figures 1 to 6 The corresponding relationship between the reference numerals and component names in the figure is:

[0037] 1-blowing hole; 2-mold steel block; 3-gas pipe joint; 4-gas pipe; 5-gas and water channel adapter block; 6-gas external plug; 7-plate. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] Furthermore, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily obscuring the concepts of the present invention.

[0040] If there are descriptions involving "first", "second", etc. in the embodiments of the present application, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features; the technical solutions between the various embodiments can be combined with each other, based on the ability of ordinary technicians in the field to implement.

[0041] In the embodiments of the present application, when A and / or B are mentioned, it means A, B, and A and B.

[0042] It should be noted that the sequence numbers mentioned in this application do not necessarily mean that the steps must be strictly followed in the actual implementation process. The sequence numbers are used to distinguish each step for ease of explanation and to avoid confusion.

[0043] The accompanying drawings show schematic diagrams of layer structures according to embodiments of the present invention. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clarity. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0044] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0045] With the continuous improvement of the design and manufacturing level of automobile sheet materials in my country, many original cold stamping sheets have begun to develop towards hot forming. In the past, in the formability analysis standards for different sheets, the thinning thresholds for sheets of different thicknesses were also different; usually, for sheets whose thinning exceeded this threshold, the shape and epitaxial surface of the sheet were modified in the early process stage to reduce the thinning rate; but under the influence of automobile assembly and vehicle CAE, the shape modification of the sheet itself has great limitations, which requires a new technology that can increase the thinning threshold of the sheet in the analysis without changing the product, and reduce the problem of excessive thinning and cracking on site;

[0046] During the hot stamping process, the stamped material (sheet metal) will have wrinkles and overlap. After analysis, it was found that during the hot stamping process, after high temperature cooling, there will be a transformation process from austenite to martensite. This process is a temperature and time dependent process, which involves many factors such as carbon content, cooling rate, etc. These factors will affect the start and end temperatures (Ms and Mf) of the transformation, as well as the type and quantity of the transformation products.

[0047] During the transformation from austenite to martensite, the strength usually changes. This is because martensite has higher hardness and strength than austenite. The key points about the strength change of austenite to martensite are as follows:

[0048] 1. Transition start and end temperatures (Ms and Mf):

[0049] Ms represents the starting temperature of the transformation from austenite to martensite, Mt represents the end temperature of the transformation, and Mf represents the end temperature of the transformation.

[0050] Carbon content (Wc) has a significant effect on Ms and Mf. As Wc increases, Ms and Mf generally decrease, but at different rates (for example, when Wc < 0.6%, Mf decreases faster than Ms).

[0051] 2. Type and quantity of transformation products:

[0052] The transformation of austenite to martensite may produce different types of martensite (such as lath martensite, twinned martensite, etc.), and these different types of martensite may contribute differently to the strength.

[0053] The number of transformation products also affects the overall strength.

[0054] Generally, more martensitic transformation means higher strength.

[0055] 3. Changes in intensity during the transition process:

[0056] During the transformation from austenite to martensite, the strength of the material will gradually increase. This is because martensite has higher hardness and strength.

[0057] However, the strength change during the transformation process is not linear, but is affected by many factors, such as temperature, time, cooling rate, etc.

[0058] Based on the above information, an austenite to martensite strength graph might show the following trends:

[0059] (a) As the temperature decreases (from the austenite stable zone to the martensite transformation zone), the strength gradually increases.

[0060] (b) Near the transformation start temperature (Ms), the rate of strength increase may accelerate because martensite begins to form. As the martensite transformation continues, the strength continues to increase until the transformation end temperature (Mf) is reached.

[0061] Based on the above theoretical basis, the present invention adds an additional cooling system to the crack-prone area or the small-scale over-thinning area to accelerate the cooling rate of the risk area, so that the current risk area has more martensite in advance, thereby improving the tensile strength of the area.

[0062] Therefore, the main technical concept of the present invention is to accelerate the transformation rate of local austenite better than other parts, and quickly improve the tensile strength of this position, so the thinning rate of the surrounding area will be increased. Therefore, the present invention only targets the problem of excessive thinning or cracking in a small local area, such as thinning in areas such as rounded corners, which can effectively solve the problems of wrinkling and stacking during hot stamping and improve the quality of hot stamping sheets.

[0063] In order to solve the above problems, an embodiment of the present invention provides a hot stamping die, see Figure 1-Figure 5 As shown, it includes a die steel block 2 for hot stamping forming, including:

[0064] The mold steel block 2 also has a blowing hole 1, and the position of the blowing hole 1 is based on the position of the mold steel block 2 corresponding to the risk area determined during the hot stamping of the sheet 7. The risk area refers to a small-scale over-thinning and over-tolerance area or a cracking area of ​​the sheet 7 during the hot stamping process, or a risk area determined during the early simulation analysis of the hot stamping sheet;

[0065] An air pipe 4, one end of which passes through the mold steel block 2 and is connected to the blowing hole 1, and the air pipe 4 is used to cool the hot stamping formed plate 7 through the blowing hole;

[0066] The other end of the air pipe 4 is connected to an air source, and the air source cools the hot stamping formed sheet 7 along the air pipe 4 through the blowing holes; or,

[0067] The other end of the air pipe 4 is connected to a water source, and the water source cools the hot stamping formed plate 7 along the air pipe 4 through the blowing holes.

[0068] According to the technical solution of the embodiment of the present invention, during the hot stamping process, the material is torn or thinned too much, and cooling is used to solve the problem of tearing and excessive thinning. For the risk area of ​​cracking prone area or small-scale excessive thinning of the plate during hot stamping, an additional cooling system is added, which is equivalent to using the additional cooling to quench the material and increase the hardness of the material, thereby reducing or solving the problem of wrinkling and stacking. Since the physical properties of the steel become soft after heating, it is easy to tear during the forming process and the plate is thinned too much. By using the cooling during the forming process, the steel is cooled down in advance to increase the strength, thereby realizing the forming process. According to the technical solution of the present invention, by adding a blowing hole on the mold, the local temperature of the plate is lower than that of other parts, so that the transformation rate of austenite is better than that of other parts, the risk area can have more martensite in advance, thereby improving the tensile strength of the area, and to a certain extent, the thickness of the plate in the current risk area is guaranteed, so that the risk of excessive thinning in the cracking prone area or the local small-scale excessive thinning is reduced, effectively solving the problem of wrinkling and stacking of the stamped material plate, improving the quality of the product, and also increasing the output of the product.

[0069] Optionally, as one embodiment, the other end of the air pipe 4 is connected to an air source, and the air source cools the hot stamping formed sheet 7 along the air pipe 4 through the blowing holes.

[0070] Optionally, as one embodiment, the other end of the air pipe 4 is connected to a water source, and the water source flows along the air pipe 4 through the blowing holes to cool the hot stamping formed plate 7 by water.

[0071] The current technical solution can adopt a water cooling method or an air cooling method. Preferably, air cooling is recommended.

[0072] Optionally, as one embodiment, there are multiple blowing holes 1 and multiple air pipes 4.

[0073] like Figure 1 As shown, there are two gas pipes 4 in the current figure, which can be freely adjusted according to actual needs.

[0074] Specifically, Figure 2 As shown in more detail, the blowing hole 1 can have a plurality of small blowing ports.

[0075] Optionally, as one of the embodiments, when the air pipe 4 passes through the mold steel block 2, the air pipe joint 3 is used to connect the air pipe 4 outside the mold steel block 2 with the air pipe 4 inside the mold steel block.

[0076] Optionally, as one of the embodiments, an air-water circuit adapter block 5 is provided, wherein the air-water circuit adapter block 5 is connected to the other end of the air circuit pipe 4 to control the input of gas or liquid into the air circuit pipe 4 .

[0077] Optionally, as one of the embodiments, the gas circuit external plug 6 is located on the gas circuit and water circuit adapter block 5, one end of which is connected to the gas circuit and water circuit adapter block 5, and the other end is an air port, which is connected to the air source through the air port.

[0078] Optionally, as one embodiment, the gas generated by the gas source is high-pressure gas.

[0079] Usually, the normal range of the pressure of high-pressure gas is between 0.6MPa and 1.4MPa.

[0080] For reference Figure 3 and Figure 4 As shown, Figure 3 The arrows in the figure indicate the direction of the gas or liquid. The gas is connected to the gas-water adapter block 5 through the gas circuit external connector 6, enters the gas circuit pipe 4, and blows toward the plate through the blowing hole 1. The high-pressure gas enters the gas circuit pipe 4 through the gas circuit external connector 6 and is ejected from the blowing hole 1. The high-pressure airflow acts on the heated plate to cool the steel plate with air or water.

[0081] The experimental results obtained by using the technical solution of the embodiment of the present invention are as follows Figure 5 As shown, Figure 5 A curve graph of , where:

[0082] Vertical axis: degrees Celsius;

[0083] Horizontal axis: time, in seconds. 10 to the power of 1 is 10 seconds, 10 to the power of 2 is 100 seconds, and 10 to the power of 3 is 1000 seconds.

[0084] Zone A: austenite zone;

[0085] Zone B: bainite zone;

[0086] F zone: ferrite zone;

[0087] P zone: pearlite zone;

[0088] M zone: martensite zone;

[0089] Each downward curve represents the results achieved by different cooling rates, and the value in the circle is the hardness;

[0090] The dotted line "Cooling rate = 25 ° C / sec" represents the critical cooling rate for obtaining full martensite (this is the CCT curve of 22MnB5, and the materials of Baosteel and Benxi Steel are not much different). It can be seen that in the solution of the embodiment of the present invention, austenite can be converted into martensite earlier, that is, the physical properties of the steel become softer after the current material is heated (at this time, tearing is likely to occur during the forming process, and the plate is too thinned), and during the air cooling process, the steel is cooled down in advance, the strength is increased, and the forming process is realized.

[0091] The embodiment of the present invention further provides a hot stamping forming method, using the mold described in the above embodiment, such as Figure 6 As shown, including:

[0092] S601: Determine the risk area of ​​the hot stamping formed sheet;

[0093] S602: performing cooling analysis on the cooling conditions of the risk area and the hot stamping formed sheet;

[0094] S603: Determine the position of the blowing hole on the mold steel block and the blowing rate according to the analyzed data;

[0095] S604: hot stamping the hot stamping sheet, and, according to the analyzed data, using the blowing holes to cool down the risk area of ​​the sheet during the hot stamping process;

[0096] S605: Obtain the sheet after hot stamping.

[0097] Optionally, as one embodiment, determining the risk area of ​​the hot stamping formed sheet material specifically includes:

[0098] Using a computer to simulate and analyze the hot stamping sheet material to identify the current sheet material thinning risk area during the hot stamping process; or,

[0099] Perform hot stamping on the existing hot stamping sheet to determine the current risk area of ​​sheet thinning.

[0100] There are at least two ways to determine the risk area for sheet thinning mentioned above. One is to determine it using CAE analysis. However, the simulation analysis of CAE may deviate from the actual situation to a certain extent. Therefore, another way is to select a sheet that is the same as the sheet to be stamped, and perform hot stamping first to obtain accurate wrinkling and stacking positions. The risk area is determined based on the wrinkling and stacking positions. Because it is the same sheet to be stamped (the result of industrial mass production), the actual result is basically the same as the subsequent hot stamping result of the same sheet. The approximate position can also be confirmed by CAE first, and then determined in combination with the actual hot stamping results.

[0101] Obviously, the described embodiments are only some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0102] It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, and do not constitute a limitation of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all changes and modifications that fall within the scope and boundaries of the appended claims, or the equivalent forms of such scope and boundaries.

Claims

1. A hot stamping die, comprising a die steel block (2), used for hot stamping, characterized in that: The mold steel block (2) also has a blowing hole (1), and the position of the blowing hole (1) is based on the position of the mold steel block (2) corresponding to the risk area determined when the hot stamping sheet (7) is formed, and the risk area refers to a small-scale over-thinning and over-tolerance area or a cracking area of ​​the sheet (7) during the hot stamping process, or a risk area determined in the early stage of the simulation analysis of the hot stamping sheet; An air pipe (4), one end of which passes through the mold steel block (2) and is connected to the blowing hole (1), and the air pipe (4) is used to cool the hot stamping formed plate (7) through the blowing hole; The other end of the air pipe (4) is connected to an air source, and the air source is passed along the air pipe (4) through the blowing holes to cool the hot stamping formed sheet (7); or, The other end of the air pipe (4) is connected to a water source, and the water source flows along the air pipe (4) through the blowing holes to cool the hot stamping formed plate (7) by water.

2. The mold according to claim 1, characterized in that: The blowing hole (1) and the air pipe (4) are provided in plurality.

3. The mold according to claim 1, characterized in that: When the gas pipe (4) passes through the mold steel block (2), the gas pipe joint (3) is used to connect the gas pipe (4) outside the mold steel block (2) with the gas pipe (4) inside the mold steel block.

4. The mold according to claim 1, characterized in that: Also includes: An air-water circuit adapter block (5) is connected to the other end of the air circuit pipe (4) to control the input of gas or water into the air circuit pipe (4).

5. The mold according to claim 4, characterized in that: The mold further comprises: an air circuit external connection plug (6), which is located on the air circuit and water circuit adapter block (5), one end of which is connected to the air circuit and water circuit adapter block (5), and the other end of which is an air port, and is connected to the air source through the air port.

6. The mold according to claim 1, characterized in that: The gas generated by the gas source is high-pressure gas.

7. A hot stamping forming method, characterized in that: The mold according to claim 1 to claim 6 is characterized in that: Determining a risk area of ​​the hot stamping formed sheet; Performing cooling analysis on the risk area and the cooling conditions of the hot stamping formed sheet; According to the analyzed data, the position of the blowing hole on the mold steel block and the blowing rate are determined; Performing hot stamping on the hot stamping sheet, and, according to the analyzed data, performing a cooling treatment on the risk area of ​​the sheet by using the blowing holes during the hot stamping process; Obtain the sheet material after hot stamping.

8. The method according to claim 7, characterized in that Determining the risk area of ​​the hot stamping formed sheet specifically includes: Using a computer to simulate and analyze the hot stamping sheet material to identify the current sheet material thinning risk area during the hot stamping process; or, Perform hot stamping on the existing hot stamping sheet to determine the current risk area of ​​sheet thinning.

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