A hot stamping forming process and a stamping die

Abstract

The present invention relates to a hot stamping forming process and a stamping die. Among them, the hot stamping forming process includes the steps of: cutting a sheet metal blank, cutting the original sheet metal blank to obtain a sheet metal blank to be stamped; preheating, preheating the sheet metal blank to be stamped; first stamping, putting the preheated sheet metal blank to be stamped into the stamping die and performing the first stamping on the first area of the sheet metal blank to be stamped; second stamping, performing the second stamping on the second area of the sheet metal blank to be stamped, wherein the first area does not coincide with the second area. Compared with the traditional single-time hot stamping process, in this application, the first stamping is first performed on the first area, and after the first stamping is formed, the second stamping is then performed on the second area. Thus, the compressive stress on the sheet metal blank to be stamped is reasonably controlled, and a tensile stress state can be achieved, avoiding the tendency to wrinkle and eliminating the dead wrinkle area, thereby achieving the purpose of reducing the wrinkle of the sheet metal; in addition, the multi-time stamping process provides a variable path space and can improve the stamping efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of hot stamping forming processing of metal sheet materials, and particularly to a hot stamping forming process and a stamping die. Background Art

[0002] For purposes such as weight reduction and environmental protection, automotive lightweighting has become one of the mainstream development trends. According to data, for every 10% reduction in vehicle weight, fuel consumption can be saved by 3% - 7%. The use of ultra-high strength steel can significantly improve the vehicle's collision safety while achieving automotive lightweighting, and thus has gradually received wide attention.

[0003] However, ultra-high strength steel has high resistance and poor deformation ability at room temperature, and it is very difficult to use traditional cold stamping forming. Therefore, hot stamping forming is usually used for ultra-high strength steel. However, during the hot stamping forming process, various defects will inevitably occur, such as cracking, wrinkling, and springback, which seriously affect the forming quality of the material. Summary of the Invention

[0004] Based on this, it is necessary to provide a hot stamping forming process and a stamping die for the problem that existing ultra-high strength steel is prone to wrinkling during the hot stamping forming process.

[0005] In a first aspect, the present application provides a hot stamping forming process, including the steps of:

[0006] Cut the sheet material, and cut the original sheet material to obtain the sheet material to be stamped;

[0007] Preheat, preheat the sheet material to be stamped;

[0008] First stamping, put the preheated sheet material to be stamped into the stamping die, and apply pressure to the stamping die to perform the first stamping on the first area of the sheet material to be stamped;

[0009] Second stamping, continue to apply pressure to the stamping die to perform the second stamping on the second area of the sheet material to be stamped, where the first area and the second area do not overlap.

[0010] In some embodiments, the sheet material to be stamped satisfies the formula L > 0.5R / t;

[0011] Wherein, L is the width of the remaining material of the sheet material to be stamped, R is the radius of curvature of the sheet material to be stamped, and t is the thickness of the sheet material to be stamped.

[0012] In some embodiments, in the first stamping step, the first die closing speed of the stamping die is 100 mm / s - 200 mm / s, the first die closing time is 2 s - 5 s, and the first holding pressure is 100 MPa - 200 MPa.

[0013] In some embodiments, in the second stamping step, the second die closing speed of the stamping die is 100 mm / s - 200 mm / s, the second die closing time is 2 s - 5 s, and the second holding pressure is 100 MPa - 200 MPa.

[0014] In some embodiments, in the preheating step, the preheating temperature is 950 °C - 980 °C, and the preheating time is 10 min - 15 min.

[0015] In some embodiments, after the second stamping step, the method further includes the steps of:

[0016] Cooling, after the stamping die is closed and held for 10 s - 15 s, cooling down the stamping die and the blank to be stamped therein.

[0017] In some embodiments, in the cooling step, the blank to be stamped is cooled down by introducing a cooling medium into the first cooling channel and / or the second cooling channel of the stamping die, and the flow rate of the cooling medium is 400 L / min - 500 L / min.

[0018] In a second aspect, the present application provides a stamping die for operating the hot stamping forming process as described above. The stamping die includes:

[0019] A first die base and a second die base arranged at intervals along a first direction, a stamping space for accommodating the blank to be stamped is formed between the first die base and the second die base;

[0020] A movable lower die, located in the stamping space, and protruding movably along the first direction from the surface of the first die base facing the second die base;

[0021] Wherein, a recess matching the movable lower die is formed on the second die base, the movable lower die and the recess are correspondingly arranged with the first region, and other stamping regions on the first die base and the second die base are correspondingly arranged with the second region.

[0022] In some embodiments, the stamping die includes an elastic member, and the elastic member is connected between the movable lower die and the first die base.

[0023] In some embodiments, the elastic member is a nitrogen spring.

[0024] In some embodiments, a first cooling channel is formed on the first die base, and / or a second cooling channel is formed on the second die base;

[0025] Cooling medium is introduced into both the first cooling channel and the second cooling channel.

[0026] The above hot stamping process and stamping die, compared with the traditional single-time hot stamping process, first perform the first stamping on the first area. After the first stamping is completed, then perform the second stamping on the second area. Thus, the compressive stress on the sheet to be stamped can be reasonably controlled, and a tensile stress state can be achieved, avoiding the tendency to wrinkle and eliminating the dead wrinkle area, so as to achieve the purpose of reducing sheet wrinkling. In addition, the multi-stamping process provides variable path space and can improve the stamping efficiency. Brief Description of the Drawings

[0027] Figure 1 It is a flowchart of the hot stamping process in an embodiment of the present application;

[0028] Figure 2 It is a schematic diagram of the overall structure of the stamping die in an embodiment of the present application;

[0029] In the figure: 100, stamping die; 10, first die base; 20, second die base; 30, moving lower die; 40, stamping space; 50, elastic member; 11, first cooling channel; 21, recess; 22, second cooling channel; a, first direction. Detailed Embodiment

[0030] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the following will describe the specific embodiments of the present invention in detail with reference to the accompanying drawings. Many specific details are set forth in the following description in order to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0031] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0032] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, the meaning of "a plurality of" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0033] In the present invention, unless otherwise clearly specified and defined, terms such as "mounted", "connected", "coupled", "fixed", etc. should be construed in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements or the interaction relationship between two elements, unless otherwise clearly defined. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0034] In the present invention, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature may be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature may be that the first feature is directly above or obliquely above the second feature, or merely indicates that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "underneath" the second feature may be that the first feature is directly below or obliquely below the second feature, or merely indicates that the first feature has a lower horizontal height than the second feature.

[0035] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may also be an intermediate element. When an element is considered to be "connected" to another element, it may be directly connected to the other element or there may be an intermediate element at the same time. The terms "vertical", "horizontal", "up", "down", "left", "right" and similar expressions used herein are for illustrative purposes only and do not represent the only embodiments.

[0036] Figure 1 The flowchart of the hot stamping forming process in an embodiment of the present invention is shown. Figure 2 The overall structural schematic diagram of the stamping die in an embodiment of the present invention is shown. For ease of description, the drawings only show the structures related to the embodiments of the present invention.

[0037] Refer to Figure 1 and Figure 2 An embodiment of the present invention provides a hot stamping forming process, including the steps:

[0038] S10: Cutting the sheet material, cutting the original sheet material to obtain the sheet material to be punched.

[0039] S20: Preheating: preheating the sheet to be stamped.

[0040] S30: First stamping, placing the preheated sheet material to be stamped into the stamping die 100, applying pressure to the stamping die 100, and performing the first stamping on the first area of the sheet material to be stamped.

[0041] S40: Second punching, continuing to apply pressure to the punching die 100, and performing a second punching on the second area of the sheet material to be punched, wherein the first area does not overlap with the second area.

[0042] It should be noted that in the sheet cutting step S10, the original sheet can be cut according to the final part shape to be stamped, so that the sheet to be stamped after cutting can better form the target part after stamping.

[0043] Furthermore, after the cutting is completed, the sheet to be stamped needs to be preheated first, so that the sheet to be stamped is completely austenitized and kept warm for a period of time, so as to facilitate the subsequent stamping process.

[0044] Specifically, the sheet to be stamped is placed in a heating device for preheating, wherein the heating device may be a heating furnace, that is, the sheet to be stamped after cutting is placed in the heating furnace and heated. Of course, in some other embodiments, the heating device may also use other heating structures besides the heating furnace, which will not be described in detail here.

[0045] In actual use, many parts have complex curved surfaces. For such parts with complex curved surfaces, the use of a single stamping process is very likely to cause wrinkles and other defects.

[0046] Based on this, after preheating is completed, the sheet to be stamped is placed in the stamping die 100, and the first part of the stamping die 100 first contacts the first area of the sheet to be stamped, and under the action of the applied external pressure, the first area of the sheet to be stamped is stamped for the first time. After the first stamping is completed, pressure is continued to be applied to the stamping die 100. During this process, the first area of the sheet to be stamped no longer continues to deform under the support of the first part of the stamping die 100. The second part of the stamping die 100 contacts the second area of the sheet to be stamped under pressure, and the sheet to be stamped is stamped for the second time. In this way, a complete target part is formed, and the entire stamping process is completed.

[0047] When performing hot stamping forming on parts with complex curved surfaces through the above steps, since the stamping of different positions of the blank to be stamped is carried out separately in two times, the deformation process of the blank to be stamped can be made more stable, wrinkling can be reduced, and the stamping efficiency can be improved.

[0048] In some embodiments, the blank to be stamped satisfies the formula L > 0.5R / t. Wherein, L is the width of the remaining material of the blank to be stamped, R is the radius of curvature of the blank to be stamped, and t is the thickness of the blank to be stamped.

[0049] Specifically, the original blank usually has a large area. In order to manufacture various parts, the original blank needs to be cut to meet the shape requirements of the target part. However, since the blank to be stamped needs to be stamped to form the target part, during the stamping process, the blank to be stamped will deform, making it inconvenient to judge the cutting size of the blank according to the final shape of the target part.

[0050] Based on this, first calculate the size of the blank to be stamped according to the formula L > 0.5R / t, and then cut the original blank according to the calculation result, so that the cutting size of the original blank can be made more accurate, avoiding the problems of waste or shortage of the blank when forming the target part by stamping the cut blank to be stamped, not only saving materials, but also improving the stamping efficiency.

[0051] In some embodiments, in the first stamping step of S30, the first mold closing speed of the stamping die 100 is 100 mm / s - 200 mm / s, the first mold closing time is 2 s - 5 s, and the first holding pressure is 100 MPa - 200 MPa.

[0052] Specifically, in the first stamping step, under the action of pressure, the stamping die 100 performs the first mold closing. Among them, the first mold closing speed can be set to 100 mm / s - 200 mm / s, the first mold closing time can be set to 2 s - 5 s, and the first holding pressure can be set to 100 MPa - 200 MPa.

[0053] As one of the preferred embodiments, the first mold closing speed can be set to 100 mm / s, the first mold closing time can be set to 2 s, and the first holding pressure can be set to 100 MPa, so as to facilitate the contact and stamping of the first part of the stamping die 100 with the blank.

[0054] In some embodiments, in the second stamping step of S40, the second mold closing speed of the stamping die is 100 mm / s - 200 mm / s, the second mold closing time is 2 s - 5 s, and the second holding pressure is 100 MPa - 200 MPa.

[0055] Specifically, in the second stamping step, continue to apply pressure to the stamping die 100 and make it perform the second mold closing. Among them, the second mold closing speed can be set to 100 mm / s - 200 mm / s, the second mold closing time can be set to 2 s - 5 s, and the second holding pressure can be set to 100 MPa - 200 MPa.

[0056] As one of the preferred embodiments, the second mold closing speed can be set to 200 mm / s, the second mold closing time can be set to 5 s, and the second holding pressure can be set to 200 MPa, so that the second part of the stamping die 100 contacts and stamps the sheet metal under pressure.

[0057] In some embodiments, in the S20 preheating step, the preheating temperature is 950 °C - 980 °C, and the preheating time is 10 min - 15 min.

[0058] Specifically, in the preheating step, it is necessary to heat the sheet metal to be stamped until the sheet metal to be stamped is completely austenitized. Therefore, when performing hot stamping on sheet metals of different materials, different preheating temperatures and preheating times need to be adopted.

[0059] As a preferred embodiment, taking the 22MnB5 steel plate as an example, the preheating temperature can be set to 950 °C to completely austenitize the 22MnB5 steel plate and keep it warm for a period of time. The preheating time for holding can be set to 10 min to facilitate stamping the 22MnB5 steel plate.

[0060] In some embodiments, after the S40 second stamping step, the following steps are further included:

[0061] S50: Cooling. After the stamping die 100 is closed and held for 10 s - 15 s, cool down the stamping die 100 and the sheet metal to be stamped therein.

[0062] After stamping is completed, it is necessary to perform in-mold quenching on the formed part to make its structure stable. Further, in the cooling step, cool down the sheet metal to be stamped by introducing a cooling medium into the first cooling channel 11 and / or the second cooling channel 22 of the stamping die 100, and the flow rate of the cooling medium is 400 L / min - 500 L / min.

[0063] Specifically, the cooling medium can adopt cooling water, that is, introduce cooling water into the first cooling channel 11 and / or the second cooling channel 22 of the stamping die 100 for cooling, and control the cooling water flow rate to be 400 L / min - 500 L / min to ensure sufficient cooling of the internal parts of the stamping die 100.

[0064] As a preferred embodiment, after the stamping die 100 is closed, it is kept under pressure for 15 s. Meanwhile, cooling water is introduced into the stamping die 100 to cool it down, and the flow rate of the cooling water is controlled at 500 L / min to facilitate mold opening and part taking.

[0065] Based on the same concept as the above hot stamping forming process, the present application provides a stamping die 100 for operating the hot stamping forming process as described above.

[0066] Please refer to again Figure 2 , the stamping die 100 includes a first die base 10, a second die base 20, and a movable lower die 30. Among them, the first die base 10 and the second die base 20 are arranged at intervals along the first direction a, and a stamping space 40 for accommodating the sheet to be stamped is formed between them. The movable lower die 30 is located in the stamping space 40 and protrudes movably along the first direction a from the surface of the first die base 10 facing the second die base 20. In addition, a recess 21 matching the movable lower die 30 is formed on the second die base 20, the movable lower die 30 and the recess 21 are correspondingly arranged with the first area, and the other stamping areas on the first die base 10 and the second die base 20 are correspondingly arranged with the second area.

[0067] Specifically, the first die base 10 and the second die base 20 are arranged relatively at intervals, and the sheet to be stamped is placed in the stamping space 40 between the first die base 10 and the second die base 20. Thus, the first die base 10 and the second die base 20 clamp the sheet to be stamped in the stamping space 40 along the first direction a.

[0068] Pressure is applied to the first die base 10 and the second die base 20 to make the first die base 10 and the second die base 20 move towards each other. This process is the mold closing. When the pressure is applied for the first time, since the movable lower die 30 protrudes from the surface of the first die base 10 facing the second die base 20, the movable lower die 30 first contacts the sheet to be stamped, and the sheet to be stamped is first molded during the mold closing under the support of the movable lower die 30. During this process, the movable lower die 30 and the recess 21 cooperate with each other to perform the first stamping on the first area of the sheet to be stamped.

[0069] After the first stamping, the first area of the sheet to be stamped has been stamped and formed. Further, pressure is continuously applied to the first die base 10 and the second die base 20 to make the first die base 10 and the second die base 20 continue to move towards each other. At this time, the first area of the sheet to be stamped no longer deforms under the support of the movable lower die 30, while the other positions on the first die base 10 and the second die base 20 continue to close the mold under the action of the pressure, realizing the overall mold closing of the first die base 10 and the second die base 20. At this time, the sheet to be stamped realizes overall contact with the first die base 10 and the second die base 20, and the second area of the sheet to be stamped is secondarily stamped by the other areas except the movable lower die 30.

[0070] Performing two independent stampings on the stamping blank can achieve an integrated hot stamping process for parts with complex multi-curved surfaces, thereby improving the stamping efficiency, reducing the mold cost, and decreasing the cost input.

[0071] In some embodiments, the stamping die 100 includes an elastic member 50, and the elastic member 50 is connected between the movable lower die 30 and the first die base 10. The elastic member 50 can provide buffering for the stamping blank during the first stamping and the second stamping, reduce the compressive stress on the stamping blank during stamping, and prevent the stamping blank from cracking.

[0072] In some embodiments, the elastic member 50 is a nitrogen spring. Of course, in some other embodiments, the elastic member 50 can also adopt other spring structures, which will not be elaborated here.

[0073] Furthermore, a first cooling channel 11 is opened on the first die base 10, and / or a second cooling channel 22 is opened on the second die base 20, and a cooling medium is introduced into both the first cooling channel 11 and the second cooling channel 22.

[0074] Specifically in this embodiment, the cooling medium can be cooling water. It can be understood that the cooling medium can also adopt other materials other than cooling water, which will not be elaborated here.

[0075] Specifically, the first cooling channel 11 is penetrated through the first die base 10 in a direction perpendicular to the first direction a, and cooling water is introduced into the first cooling channel 11 to cool down the stamped blank, so as to facilitate mold opening and part taking.

[0076] Similarly, the second cooling channel 22 is penetrated through the second die base 20 in a direction intersecting with the first direction a, and cooling water is introduced into the second cooling channel 22. Cooperating with the first cooling channel 11 to achieve cooling, the cooling efficiency can be improved.

[0077] When this application is specifically used, a 22MnB5 steel plate with a thickness of 0.5 mm is taken as an example for illustration. First, the original blank is cut according to L>0.5R / t to obtain a stamping blank with appropriate dimensions. The stamping blank is placed in a heating furnace and heated to 950 °C to make it fully austenitized and held for 10 min.

[0078] The preheated stamping blank is transferred to the stamping die 100, and pressure is applied to the first die base 10 and the second die base 20 for the first mold closing. During this process, the first mold closing speed is controlled to be 100 mm / s, the first mold closing time is 2 s, and the first holding pressure is 100 MPa. Thus, the first region of the stamping blank is stamped for the first time under the support of the movable lower die 30.

[0079] After the first stamping, continue to apply pressure to the first die holder 10 and the second die holder 20, and perform the second mold closing. At this time, control the second mold closing speed to be 200 mm / s, the second mold closing time to be 5 s, and the second holding pressure to be 200 MPa. During the second stamping process, the first area on the sheet to be stamped no longer deforms under the support of the moving lower die 30, so that other areas on the sheet to be stamped except the first area, that is, the second area, continue to deform under the mold closing action of the first die holder 10 and the second die holder 20, and finally form the shape of the target part.

[0080] After the second stamping, cool down by introducing cooling water into the first cooling channel 11 and the second cooling channel 22 to facilitate mold opening and part taking.

[0081] In addition, verify and analyze the mechanical properties of the parts made by the above hot stamping forming process, and find that they meet the experimental expectations, and the tensile strength reaches more than 1300 MPa.

[0082] The hot stamping forming process and the stamping die 100 in the above embodiments have at least the following advantages:

[0083] 1) Stamp and form the first area and the second area of the sheet to be stamped in sequence through two stampings, reduce the wrinkling probability during the forming of complex curved surfaces, realize the integrated hot stamping process of complex multi-curvature and multi-surface, improve the stamping efficiency, reduce the die cost, and reduce the cost investment;

[0084] 2) Cut the original sheet according to the calculation result of the formula L>0.5R / t to obtain the sheet to be stamped, so that the sheet to be stamped forms a target part with appropriate dimensions after stamping, reduce the waste of the sheet, and avoid the problem of insufficient sheet after forming the target part.

[0085] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0086] The above embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.

Claims

1. A hot stamping forming process, characterized in that, Including the steps: Cut the sheet metal to obtain the sheet metal to be stamped from the original sheet metal; the sheet metal to be stamped satisfies the formula ; where L is the width of the remaining material of the sheet metal to be stamped, R is the radius of curvature of the sheet metal to be stamped, and t is the thickness of the sheet metal to be stamped; Preheating, preheating the to-be-stamped sheet material; First stamping, putting the preheated to-be-stamped sheet material into a stamping die, and applying pressure to the stamping die to perform first stamping on the first area of the to-be-stamped sheet material; Second stamping, continuously applying pressure to the stamping die to perform second stamping on the second area of the to-be-stamped sheet material, wherein the first area does not overlap with the second area.

2. The hot stamping forming process according to claim 1, wherein, In the first stamping step, the first die-closing speed of the stamping die is 100 mm / s - 200 mm / s, the first die-closing time is 2 s - 5 s, and the first holding pressure is 100 MPa - 200 MPa.

3. The hot stamping forming process according to claim 1, characterized in that In the second stamping step, the second die-closing speed of the stamping die is 100 mm / s - 200 mm / s, the second die-closing time is 2 s - 5 s, and the second holding pressure is 100 MPa - 200 MPa.

4. The hot stamping forming process according to claim 1, characterized in that, In the preheating step, the preheating temperature is 950 °C - 980 °C, and the preheating time is 10 min - 15 min.

5. The hot stamping process according to claim 1, characterized in that, After the second stamping step, it further includes the step of: Cooling, after the stamping die is closed and held for 10 s - 15 s, cooling down the stamping die and the to-be-stamped sheet material therein.

6. The hot stamping forming process according to claim 5, wherein, In the cooling step, the to-be-stamped sheet material is cooled down by introducing a cooling medium into the first cooling channel and / or the second cooling channel of the stamping die, and the flow rate of the cooling medium is 400 L / min - 500 L / min.

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