Hot stamping die and apparatus with direct cooling structure, and hot stamping method

Abstract

A hot stamping die and apparatus with a direct cooling structure, and a hot stamping method, which relate to the technical field of the hot-stamping forming of sheet materials. The hot stamping die with a direct cooling structure comprises: a first die assembly and a second die assembly, wherein at least one of the first die assembly and the second die assembly is provided with a plurality of cooling flow channels parallel to a parting surface of the first die assembly and the second die assembly, and at least one cooling flow channel among the plurality of cooling flow channels is provided with a plurality of jet holes perpendicular to the at least one cooling flow channel and penetrating the parting surface; and the plurality of cooling flow channels and the plurality of jet holes are configured to accommodate a cooling medium, and the cooling medium can be sprayed through the plurality of jet holes onto the surface of a workpiece to be stamped between the first die assembly and the second die assembly. By means of the cooling flow channels and the jet holes additionally arranged on the cooling flow channels, said workpiece is cooled; and by means of the introduction of a direct spray cooling structure, local heat dissipation is accelerated, thereby suppressing excessive stretching.

Description

Hot stamping dies, equipment and methods with direct cooling structure

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese patent application No. 202510941975.2, filed on July 9, 2025, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of forming technology, specifically to the field of hot stamping technology, and more particularly to a hot stamping die, equipment, and method with a direct cooling structure. Background Technology

[0004] In hot stamping, the blank has excellent plasticity at high temperature. Under the superposition of the constraint of material flow and free stretching, strain concentration and severe thinning will occur in some areas of complex components. This typical defect will reduce the strength and service life of the stamped parts. Summary of the Invention

[0005] This disclosure provides a hot stamping die, equipment, and method with a direct cooling structure. The part to be stamped can be cooled and cooled through the cooling channel and the jet holes added on the cooling channel. By introducing a direct jet cooling structure, local heat dissipation is accelerated, thereby suppressing excessive stretching.

[0006] According to a first aspect of the present disclosure, a hot stamping die with a direct cooling structure is provided, comprising: a first die assembly and a second die assembly; wherein at least one of the first die assembly and the second die assembly has a plurality of cooling channels parallel to the mold closing surfaces of the first die assembly and the second die assembly, and at least one of the plurality of cooling channels has a plurality of jet holes perpendicular to the at least one cooling channel and penetrating the mold closing surfaces; the plurality of cooling channels and the plurality of jet holes are used to contain a cooling medium, and the cooling medium can be sprayed through the plurality of jet holes onto the surface of the workpiece to be stamped between the first die assembly and the second die assembly.

[0007] According to a second aspect of the present disclosure, a hot stamping apparatus having a direct cooling structure is provided, including a hot stamping die having a direct cooling structure as described in any of the first aspects of the present disclosure.

[0008] According to a third aspect of the present disclosure, a hot stamping method is proposed, which is performed by a hot stamping device with a direct cooling structure according to a second aspect of the present disclosure, comprising: during the relative movement of a first mold assembly and a second mold assembly until mold closing, cooling the workpiece to be stamped through multiple cooling channels and multiple jet holes, wherein the cooling channels contain cooling medium to indirectly cool the workpiece to be stamped, and the multiple jet holes spray cooling medium to directly cool the workpiece to be stamped.

[0009] According to the hot stamping die, equipment, and method with a direct cooling structure proposed in the embodiments of this disclosure, the workpiece to be stamped can be cooled and reduced through cooling channels and jet holes added to the cooling channels. By introducing a direct jet cooling structure, local heat dissipation is accelerated, thereby suppressing excessive stretching. This solution can balance the feasibility of die manufacturing and the accuracy of temperature control, significantly improve the local thinning of complex components, and enhance the uniformity of forming. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments of this disclosure, the accompanying drawings required for the description of the embodiments are introduced below. The following drawings are only some embodiments of this disclosure and do not impose specific limitations on the protection scope of this disclosure.

[0011] Figure 1 is a schematic diagram of a hot stamping die with a direct cooling structure according to an embodiment of the present disclosure;

[0012] Figure 2 is a schematic diagram of the cooling channel of a hot stamping die with a direct cooling structure according to an embodiment of the present disclosure;

[0013] Figure 3 is a schematic diagram of a cooling system for a hot stamping die with a direct cooling structure according to an embodiment of the present disclosure;

[0014] Figure 4 is a schematic diagram of the parameters of a cooling channel provided according to an embodiment of the present disclosure;

[0015] Figure 5 is a schematic diagram of parameters of a jet orifice provided according to an embodiment of the present disclosure;

[0016] Figure 6 is a schematic diagram of a hot stamping device with a direct cooling structure according to an embodiment of the present disclosure;

[0017] Figure 7 is a schematic flowchart of a hot stamping method provided according to an embodiment of the present disclosure;

[0018] Figure 8 is a schematic diagram of a complex component hot forming process using liquid nitrogen jet for high-efficiency cooling according to an embodiment of this disclosure. Detailed Implementation

[0019] This disclosure provides embodiments of a hot stamping die, apparatus, and method with a direct cooling structure.

[0020] In a first aspect, embodiments of this disclosure provide a hot stamping die with a direct cooling structure, comprising: a first die assembly and a second die assembly; wherein at least one of the first die assembly and the second die assembly has multiple cooling channels parallel to the mold closing surfaces of the first die assembly and the second die assembly, and at least one of the multiple cooling channels has multiple jet holes perpendicular to the at least one cooling channel and penetrating the mold closing surfaces; the multiple cooling channels and the multiple jet holes are used to contain a cooling medium, and the cooling medium can be sprayed through the multiple jet holes onto the surface of the workpiece to be stamped between the first die assembly and the second die assembly.

[0021] In conjunction with the embodiments of the first aspect, in some embodiments, the location or number of multiple jet holes is related to the thickness reduction rate or the thickness reduction change rate per unit time of different nodes of the part to be stamped during the hot stamping process.

[0022] In conjunction with the embodiments of the first aspect, in some embodiments, the thickness reduction rate δ at the first node of the part to be stamped is expressed as:

[0023] Where s0 is the initial sheet thickness at the first node, and s is the formed sheet thickness at the first node after stamping.

[0024] In conjunction with the embodiments of the first aspect, in some embodiments

[0025] The part to be stamped includes at least one thinning region, which is composed of multiple interconnected subsets of thinning nodes. The subsets of thinning nodes satisfy a connectivity condition, which is:

[0026] Where: σ is the preset connectivity determination distance, xp and xq are the coordinates of the thinning node, Rx is at least one thinning region, x∈[1,X], and X is the number of thinning regions; the thickness reduction rate of multiple thinning nodes is greater than or equal to the preset thinning rate;

[0027] Cooling medium injected through jet holes corresponding to at least one thinned region is used to cool at least one thinned region.

[0028] In conjunction with the embodiments of the first aspect, in some embodiments, the first mold assembly has n1 cooling channels, including n1-m1 first cooling channels U1 and m1 second cooling channels U2, with r1 jet holes on the second cooling channel U2, where n1, m1, and r1 are positive integers; the second mold assembly has n2 cooling channels, including n2-m2 third cooling channels V1 and m2 fourth cooling channels V2, with r2 jet holes on the fourth cooling channel V2, where n2, m2, and r2 are positive integers; the number of multiple cooling channels is n, and the number of multiple jet holes is r, where n = n1 + n2, and r = r1 + r2.

[0029] In conjunction with the embodiments of the first aspect, in some embodiments, the first cooling channel U1, the second cooling channel U2, the third cooling channel V1, and the fourth cooling channel V2 have a first port and a second port. The first port is used to input the cooling medium, and the second port is used to discharge the cooling medium. The first ports of the first cooling channel U1, the second cooling channel U2, the third cooling channel V1, and the fourth cooling channel V2 are sequentially connected to a distribution plate, a flow control device, and an air supply tank through a first external pipe. The second ports of the second cooling channel U2 and the fourth cooling channel V2 are connected to a switch control device through a second external pipe. The second ports of the first cooling channel U1 and the third cooling channel V1 are connected to air.

[0030] In conjunction with the embodiments of the first aspect, in some embodiments, the switch control device connected to the second port of the second cooling channel U2 and the fourth cooling channel V2 is activated at the start of cooling. The nozzles are closed sequentially to allow the cooling medium to be sprayed through multiple jet holes onto the thinned area of ​​the workpiece to be stamped, where i∈[1,u], and u represents the total number of jet cooling time points during the hot stamping process of the workpiece to be stamped; the cooling start time is... This is the statistical value of the time point corresponding to the maximum thickness reduction rate per unit time at each node in the thinning region of the part to be stamped.

[0031] In conjunction with the embodiments of the first aspect, in some embodiments, the rate of change of thickness reduction per unit time is expressed as:

[0032] Where s(t) represents the thickness of the first node at time t, and s(t+Δt) represents the thickness of the first node at time t+Δt.

[0033] In conjunction with the embodiments of the first aspect, in some embodiments, if the jet holes on the same cooling channel correspond to multiple thinning regions, the cooling start time corresponding to the multiple thinning regions is the earliest cooling start time among the multiple thinning regions.

[0034] In conjunction with the embodiments of the first aspect, in some embodiments, the switch control device at the end of cooling... Open to stop the cooling medium from being sprayed onto the surface of the workpiece through multiple jet holes, where i∈[1,u], u represents the total number of jet cooling time points during the hot stamping process of the workpiece; cooling end time This refers to the moment after the start of cooling when the temperature of the thinned region is less than or equal to the temperature threshold.

[0035] In conjunction with the embodiments of the first aspect, in some embodiments, the parameters of the cooling channels include at least one of the center-to-center distance W between two adjacent cooling channels, the diameter D of each cooling channel, and the height H of the center of each cooling channel from the mold closing surface, wherein the center-to-center distance W between two adjacent cooling channels satisfies the following condition:

[0036] Where b0 is the width of the sheet metal projected along the axis of the cooling channel of the part to be stamped.

[0037] In conjunction with the embodiments of the first aspect, in some embodiments, the cross-section of the multiple cooling channels is circular, and the diameter D of each cooling channel is expressed as:

[0038] Where V0 represents the sheet metal volume, ρ0 represents the sheet metal density, C0 represents the sheet metal specific heat capacity, T0 represents the initial temperature of the sheet metal entering the mold, T1 represents the sheet metal exiting the mold, and t b Indicates the holding time, ρ s C represents the density of the cooling medium. S V represents the specific heat capacity of the cooling medium. s T1 represents the flow rate of the cooling medium, T2 represents the outlet temperature of the cooling medium, and T4 represents the inlet temperature of the cooling medium.

[0039] In conjunction with the embodiment of the first aspect, the height H of the center of each cooling channel from the mold closing surface is expressed as:

[0040] Where, λ m Indicates the thermal conductivity of the mold, T m Indicates the mold surface temperature, T f Indicates the cooling channel wall temperature, h f Indicates the convective heat transfer coefficient of the cooling channel, T s The value represents the average temperature of the cooling medium, and W represents the center-to-center distance between two adjacent cooling channels.

[0041] In conjunction with the embodiments of the first aspect, in some embodiments, the number of multiple cooling channels satisfies the following condition:

[0042] D is related to the number of multiple cooling channels; R e1 R is the Reynolds number of the cooling medium in the first state. e2 η is the Reynolds number of the cooling medium in the second state. s v is the dynamic viscosity coefficient of the cooling medium. s ρ is the flow rate of the cooling medium. s This refers to the density of the cooling medium.

[0043] In conjunction with the embodiments of the first aspect, in some embodiments, the cross-section of the plurality of jet holes is circular, and the diameter d of each jet hole on the k-th cooling channel is... k and the center distance w between two adjacent jet holes on the k-th cooling channel. k The following conditions must be met: l k =f(d k h k ) l k ≥w k L v ≈r v w k

[0044] Where: l k f(d) is the diameter of the jet range of each jet hole on the k-th cooling channel. k h k ) is d i h i The functional relationship between h and the influence of mutual coupling on the jet range of each jet hole on the k-th cooling channel. k L is the vertical distance L between the thinned region and the mold surface of the first or second mold assembly containing the k-th cooling channel, from the moment the thinned region is formed until the start of cooling. v The length r of the v-th thinned region cooled by the k-th cooling channel along the channel direction of the k-th cooling channel. v Let v be the number of jet holes corresponding to the v-th thinning region, where v∈[1,N] and N is the total number of thinning regions cooled by the k-th cooling channel.

[0045] Secondly, embodiments of this disclosure provide a hot stamping apparatus with a direct cooling structure, including a hot stamping die with a direct cooling structure as described in any of the embodiments of the first aspect of this disclosure.

[0046] Thirdly, embodiments of this disclosure provide a hot stamping method, performed by a hot stamping apparatus with a direct cooling structure as described in the second aspect of this disclosure, comprising: during the relative movement of a first mold assembly and a second mold assembly until mold closing, cooling the thinned area of ​​the workpiece to be stamped through multiple cooling channels and multiple jet holes, wherein the cooling channels contain cooling medium to indirectly cool the workpiece to be stamped, and the multiple jet holes spray cooling medium to directly cool the workpiece to be stamped.

[0047] In conjunction with the embodiments of the third aspect, in some embodiments, the method further includes:

[0048] Based on the thickness reduction rate of different nodes of the part to be stamped during the hot stamping process, nodes with a thickness reduction rate greater than or equal to the preset thickness reduction rate are identified as multiple thinning nodes.

[0049] Based on connectivity criteria, spatial connectivity analysis is performed on multiple thinning nodes, and at least one thinning region of the part to be stamped is determined from the subset of interconnected thinning nodes; wherein the connectivity criteria are:

[0050] Where: σ is the preset connectivity determination distance, xp and xq are the coordinates of the thinning node, Rx is at least one thinning region, x∈[1,X], and X is the number of thinning regions; cooling medium is sprayed into at least one thinning region Rx through multiple cooling channels and multiple jet holes.

[0051] In conjunction with the embodiments of the third aspect, in some embodiments, the method further includes:

[0052] The stamping process is divided into different time points according to time sequence. The unit time thickness reduction rate at any time point of the j-th node in at least one thinning region Rx is determined. The unit time thickness reduction rate is expressed as:

[0053] Where s(t) represents the thickness of the first node at time t, and s(t+Δt) represents the thickness of the first node at time t+Δt.

[0054] Determine the time point corresponding to the maximum unit time thickness reduction rate of the j-th node.

[0055] Each node corresponds to Statistical analysis was performed, and the statistical value was determined as the starting time of cooling in the thinned region Rx.

[0056] In the formula, Here are the statistical formulas for each time point, where J is the number of nodes contained in the thinned region Rx;

[0057] At the start of cooling Start spraying cooling medium into at least one thinned area to cool it.

[0058] In conjunction with embodiments of the third aspect, in some embodiments, the method further includes: determining the cooling end time based on the temperature of at least one thinning region. At the end of cooling Stop spraying cooling medium into at least one thinned area.

[0059] This disclosure is not exhaustive, but merely illustrative of some embodiments, and is not intended to limit the scope of protection of this disclosure. Unless otherwise specified, each step, component, part, device, or apparatus in a particular embodiment can be implemented as an independent embodiment, and these steps, components, parts, devices, and apparatuses can be arbitrarily combined. For example, the solution after removing some steps, components, parts, devices, or apparatuses in a particular embodiment can also be implemented as an independent embodiment, and the order of steps in a particular embodiment can be arbitrarily interchanged. Furthermore, the optional implementation methods in a particular embodiment can be arbitrarily combined; moreover, the embodiments can be arbitrarily combined. For example, some or all steps, components, parts, devices, and apparatuses of different embodiments can be arbitrarily combined, and a particular embodiment can be arbitrarily combined with the optional implementation methods of other embodiments. In all embodiments of this disclosure, unless otherwise specified or logically conflicting, the terminology and / or descriptions between the embodiments are consistent and can be mutually referenced. Technical features in different embodiments can be combined to form new embodiments based on their inherent logical relationships.

[0060] The terminology used in the embodiments of this disclosure is for the purpose of describing particular embodiments only and is not intended to limit the scope of this disclosure.

[0061] Hot stamping forming technology for high-strength steel sheets is a key process in automotive lightweight manufacturing. Its core lies in heating hardenable high-strength steel sheets, such as boron steel (e.g., 22MnB5), to their austenitizing temperature, and then rapidly transferring them into a mold equipped with a cooling system for stamping and quenching. At this high temperature, the sheet exhibits excellent plasticity and low deformation resistance, allowing for the formation of complex geometric shapes. Ultimately, rapid cooling within the mold yields an ultra-high-strength martensitic structure. This process is widely used in the manufacture of critical automotive components with extremely high safety and lightweight requirements, such as A-pillars, B-pillars, and crash beams. However, the core advantage of this process—high-temperature plasticity—is highly dependent on maintaining a sufficiently uniform temperature field on the sheet during the forming stage.

[0062] With the increasing complexity of automotive structural design and the growing demand for lightweighting, the geometry of hot-stamped components is becoming increasingly complex (such as parts with deep cavities, sharp angles, abrupt flanges, or variable cross-sections). During the forming process, material flow is strongly constrained by the die geometry. Significant differences exist in the material flow state across different regions: in flat areas or shallow stretching zones, material flow is relatively free, while in the bottom of deep cavities, small-rounded transition zones, and abrupt stretching zones, the flow resistance is extremely high due to the strong constraints imposed by the die surface. This complex superposition of "constrained flow" and "free stretching" easily leads to uneven material distribution and strain distribution, exacerbating the risk of temperature drop in critical areas.

[0063] In the forming of complex components, the aforementioned regions, which are subject to strong constraints and prone to temperature drops (such as the bottom of deep cavities and small fillet corners), face a dual dilemma: on the one hand, material flow is difficult, requiring greater deformation force; on the other hand, localized temperature drops lead to reduced material plasticity and increased deformation resistance. This combined effect of "difficult flow" and "difficult deformation" results in a significantly higher actual strain in this region compared to the surrounding areas, leading to severe strain concentration. The final manifestation is often a severe reduction in material thickness in this region, far exceeding design expectations (a reduction rate of 20% or even higher). This severe localized thinning not only disrupts the uniformity of the component's wall thickness but also weakens the load-bearing capacity and fatigue resistance of this region, reducing structural strength and service life.

[0064] In related technologies, the cooling of hot stamping dies primarily relies on a complex network of cooling channels embedded within the die body and connected to an external cooling circulation system. This cooling method aims to achieve relatively uniform cooling of the entire die to ensure effective quenching and temperature control. However, this design based on an integral cooling channel system has fundamental limitations:

[0065] 1. Space constraints: In molds with extremely complex structures (such as small inserts, sharp edges, deep and narrow grooves) or in local areas that require extremely high cooling intensity, direct cooling is difficult and the cooling effect is poor.

[0066] 2. Control inertia: Cooling intensity is mainly achieved by adjusting the flow rate and temperature of the entire cooling circuit. The response speed is slow, making it difficult to independently and accurately control highly dynamic local hot spots or temperature drop zones that occur during the forming process in real time.

[0067] 3. Lack of directionality: It is impossible to apply powerful cooling capacity precisely, efficiently and intensely to specific small local areas where excessive deformation needs to be suppressed (such as the aforementioned easily thinned areas).

[0068] Therefore, facing the long-standing problem of severe localized thinning in the production of complex hot-stamped parts, there is an urgent need to develop a localized enhanced cooling technology that can achieve high strength, high precision, directional, and timed application within the mold space to compensate for the shortcomings of traditional overall cooling methods and effectively suppress excessive deformation and temperature drop risks in specific areas. This solution proposes a hot-stamping mold with a direct cooling structure. The part / sheet material to be stamped can be cooled and reduced through cooling channels and jet holes added to the cooling channels. By introducing a direct jet cooling structure, localized heat dissipation is accelerated, thereby suppressing excessive stretching. This solution balances the feasibility of mold manufacturing with temperature control accuracy, significantly improves localized thinning of complex components and enhances forming uniformity, and has significant theoretical and engineering application value for high-strength steel hot stamping and automotive lightweighting.

[0069] Figure 1 is a schematic diagram of the architecture of a hot stamping die with a direct cooling structure according to an embodiment of the present disclosure. As shown in Figure 1, it includes a first die assembly 1 and a second die assembly 2. Figure 1 shows a perspective view (a) and a top view (b) of the first die assembly 1, and a perspective view (c) and a top view (d) of the second die assembly 2, respectively.

[0070] In some embodiments, at least one of the first mold assembly and the second mold assembly has multiple cooling channels parallel to the closing surfaces of the first mold assembly and the second mold assembly. For example, as shown in FIG1, the first mold assembly has multiple cooling channels arranged parallel to a first surface of the first mold assembly (the upper surface in FIG. (a) or the surface shown in FIG. (b)). Optionally, the second mold assembly may not have cooling channels. The second mold assembly has multiple cooling channels arranged parallel to a second surface of the second mold assembly (the upper surface in FIG. (c) or the surface shown in FIG. (d)). Optionally, the first mold assembly may not have cooling channels. In other words, at least one of the first mold assembly and the second mold assembly has multiple cooling channels, thereby allowing for single-sided or double-sided cooling of the sheet metal according to cooling requirements.

[0071] It should be understood that the first surface of the first mold assembly and the second surface of the second mold assembly are considered to coincide when the mold is fully closed, and may be referred to as the closing surface in this disclosure.

[0072] Optionally, both the first mold assembly and the second mold assembly are provided with cooling channels, wherein the number of cooling channels in the first mold assembly and the number of cooling channels in the second mold assembly may be the same or different. Therefore, the arrangement of the multiple cooling channels can be determined according to the sheet metal or forming process, and this disclosure does not limit this.

[0073] Optionally, the multiple cooling channels of the first mold assembly can be parallel to each other, and the multiple cooling channels of the second mold assembly can be parallel to each other. The spacing between adjacent cooling channels of the first mold assembly can be the same as or different from the spacing between adjacent cooling channels of the second mold assembly. Optionally, the cooling channels of the first mold assembly can be parallel to the cooling channels of the second mold assembly, thereby reducing the complexity and cost of mold design. Optionally, the cooling channels of the first mold assembly can be at a certain angle to the cooling channels of the second mold assembly in space (or, in other words, the cooling channels of the first mold assembly can be non-parallel to the cooling channels of the second mold assembly), thereby achieving a larger area of ​​cooling from both surfaces of the sheet metal and improving cooling efficiency. Therefore, the arrangement of multiple cooling channels can be determined according to the forming or cooling requirements, and this disclosure does not limit this.

[0074] In some embodiments, at least one of the multiple cooling channels has a plurality of jet holes perpendicular to the cooling channel and penetrating the mold closing surface. For example, as shown in Figure 1, some cooling channels may have jet holes, while others may not. Each jet hole extends perpendicularly from the cooling channel to the mold closing surface, allowing the cooling medium in the cooling channel to be ejected from the mold body through the jet hole. In other words, each jet hole is perpendicular to its respective cooling channel and perpendicular to the mold closing surface. The cooling medium in the cooling channels with jet holes can be sprayed onto the workpiece to be stamped through the jet holes, thereby directly cooling the workpiece. Cooling channels without jet holes can indirectly cool the workpiece.

[0075] Multiple cooling channels and multiple jet holes are used to contain the cooling medium, which can be sprayed through the multiple jet holes onto the surface of the part to be stamped between the first mold assembly and the second mold assembly.

[0076] In some embodiments, the first mold assembly and the second mold assembly can be hot stamping dies. For example, the first mold assembly can be a punch and the second mold assembly can be a die. The first mold assembly and the second mold assembly can then be closed together, and the surfaces facing each other when the first mold assembly and the second mold assembly are closed together are called the closing surface. The first mold assembly and the second mold assembly can have multiple cooling channels. At least one of the multiple cooling channels can have multiple jet holes. The multiple jet holes are perpendicular to the cooling channel and penetrate the closing surface, i.e., the jet holes connect the cooling channel and the closing surface. The cooling medium can then be sprayed onto the surface of the sheet metal between the first mold assembly and the second mold assembly through the cooling channel and the jet holes.

[0077] In some embodiments, the jet orifice may be referred to as a hole, micro-hole, etc., and its cross-sectional radius may be less than a certain threshold, thereby achieving the effect of spraying the cooling medium out under a certain pressure.

[0078] In some embodiments, the jet orifices may also be arranged at an angle, for example, at an angle to the cooling channel or to the mold closing surface. For example, a single orifice within the cooling channel may have two branches, each penetrating the mold closing surface, forming a triangular structure with the mold closing surface, thereby reducing the number of openings within the cooling channel. Conversely, a single outlet on the mold closing surface may correspond to two inlets in the cooling channel, forming a triangular structure with the cooling channel, thereby increasing the jet pressure and accelerating the flow of the cooling medium within the jet orifice. These two branches can be extended to multiple branches, which is not limited in this disclosure.

[0079] In some embodiments, cooling channels can indirectly cool the part to be stamped, while jet holes can directly cool the part. Arranging cooling channels and jet holes in localized areas with high cooling requirements enables localized cooling of the part to be stamped. Furthermore, the cooling channels and jet holes can be opened or closed periodically, enabling timed cooling of the entire or a portion of the part to be stamped. The cooling medium can be at least one of liquid nitrogen, cryogenic nitrogen, and air.

[0080] In some embodiments, the part to be stamped can be a sheet metal or a blank, such as a high-strength steel sheet. During hot stamping, the part to be stamped can be a sheet metal or blank to be formed, or it can be a sheet metal or blank during the stamping process. In other words, any sheet metal or blank that needs to be cooled down before the stamping process is completed is called the part to be stamped.

[0081] In the above embodiments, the first mold assembly and the second mold assembly are metaphorical terms, and their quantity can be at least one. In other words, there can be three or more mold assemblies for mold closing, thereby manufacturing molded parts with complex structures. The structure, quantity, arrangement, and position of the cooling channels and jet holes in the three or more mold assemblies are similar to those described above, and will not be repeated here.

[0082] Figure 2 is a schematic diagram of the cooling channel of a hot stamping die with a direct cooling structure according to an embodiment of the present disclosure. It specifically shows the cooling channels with / without jet holes arranged on different die components, as well as the two ends of the cooling channels.

[0083] In some embodiments, the first mold assembly has n1 cooling channels, including n1-m1 first cooling channels U1 and m1 second cooling channels U2, with r1 jet holes on the second cooling channel U2, where n1, m1, and r1 are positive integers; the second mold assembly has n2 cooling channels, including n2-m2 third cooling channels V1 and m2 fourth cooling channels V2, with r2 jet holes on the fourth cooling channel V2, where n2, m2, and r2 are positive integers; the number of multiple cooling channels is n, and the number of multiple jet holes is r, where n = n1 + n2, and r = r1 + r2.

[0084] For example, the first mold assembly / punch can be provided with n1 parallel straight-through cooling channels along the mold closing direction as needed for cooling. Among them, m1 channels are provided with jet holes that penetrate vertically through the mold surface and connect with the cooling channels, denoted as U2. The remaining channels are not provided with jet holes, denoted as U1.

[0085] Optionally, any i-th flow channel on the first mold assembly that does not have jet holes can be represented as U. 1i For any i-th flow channel with a jet orifice in the range [1, n1-m1], the flow channel is represented as U. 2i , i∈[1,m1].

[0086] Similarly, in some embodiments, the second mold assembly / cavity can be provided with n2 parallel straight-through cooling channels along the mold closing direction as needed for cooling. Among them, m2 channels are provided with jet holes that penetrate vertically through the mold surface and connect with the cooling channels, denoted as V2. The remaining channels are not provided with jet holes, denoted as V1.

[0087] Optionally, any i-th flow channel on the second mold assembly that does not have jet holes can be represented as V. 1i For any i-th flow channel with a jet orifice in the range [1, n²-m²], the flow path is represented as V. 2i , i∈[1,m2].

[0088] Optionally, the first mold assembly and the second mold assembly have different shapes, and n1, m1, r1, n2, m2, and r2 are related to the shape of their respective mold assemblies. The quantities n1, m1, and r1 involved in the first mold assembly can be different from the corresponding quantities n2, m2, and r2 involved in the second mold assembly, thereby allowing for the layout of flow channels and jet holes based on the structure of the molded part, and targeted cooling for molded parts with different structures. Optionally, the quantities n1, m1, and r1 involved in the first mold assembly can be the same as the corresponding quantities n2, m2, and r2 involved in the second mold assembly, thereby reducing design costs.

[0089] Optionally, the n1 cooling channels are parallel to each other, and / or the n2 cooling channels are parallel to each other. The n1 and n2 cooling channels may or may not be parallel. In other words, the channels on different mold components may or may not be parallel.

[0090] In some embodiments, when the first mold assembly and the second mold assembly are fully closed, the line connecting any i-th second cooling channel U2 and the fourth cooling channel V2 closest to the i-th second cooling channel U2 forms a preset angle with the perpendicular bisector of the position of the i-th second cooling channel U2 relative to the mold closing section, and the preset angle is less than or equal to a preset threshold.

[0091] In other words, when the first mold assembly and the second mold assembly are fully closed, a certain jet hole on the first mold assembly and the nearest jet hole on the second mold assembly may not be directly opposite each other. This allows the spray range of the two jet holes to not completely overlap during the cooling process, thereby covering a larger cooling area.

[0092] It should be understood that, optionally, a jet hole on the first mold assembly and the nearest jet hole on the second mold assembly can be directly opposite each other, thereby enabling targeted and rapid cooling of that local area.

[0093] In some embodiments, as shown in FIG2, the first cooling channel U1, the second cooling channel U2, the third cooling channel V1, and the fourth cooling channel V2 have a first port and a second port. The first port is used for inputting the cooling medium, and the second port is used for discharging the cooling medium. The port shown in FIG2 is one end that penetrates the mold body. The first port can be called an inlet or air inlet, and the second port can be called an outlet or air outlet. That is, after the cooling medium enters the cooling channel from the first port, it passes through the cooling channel and is discharged from the second port.

[0094] Figure 3 is a schematic diagram of a cooling system for a hot stamping die with a direct cooling structure according to an embodiment of the present disclosure. It shows the connection between the hot stamping die and other external components through a first port and a second port. The hot stamping die and the external components together form a hot stamping cooling system.

[0095] As shown in Figure 3, in some embodiments, the first ports of the first cooling channel U1, the second cooling channel U2, the third cooling channel V1, and the fourth cooling channel V2 are sequentially connected to the distribution plate 4, the flow control device 5, and the air supply tank 6 via the first external pipe 3; the second ports of the second cooling channel U2 and the fourth cooling channel V2 are connected to the switch control device 8 via the second external pipe 7; and the second ports of the first cooling channel U1 and the third cooling channel V1 are connected to air.

[0096] In other words, all the cooling channels on the aforementioned die and punch include U... 1i U 2i V 1i V 2i U 2i V 2i The jet holes on the die and the external cooling device form the cooling system of the hot stamping die, with cooling channels U. 1i U 2i V 1i V 2i The air inlet end has an external pipeline 3, which is equipped with a distributor plate 4, a flow control device 5, and an air supply tank 6; the cooling channel U 2i V 2i The air outlet has an external pipe 7, which is equipped with a switch control device 8, and a cooling flow channel U. 1i V 1i The outlet end is not designed and is directly discharged into the air. The air supply tank can provide cooling medium, and the flow rate is regulated by the flow control device 5. The regulated cooling medium is then distributed to the cooling channels U via the distribution plate 4. 1i V 1i and cooling channel U 2i V 2i The air intake, U 2i V 2i The air outlet is connected to the external pipeline 7 to the switch control device 8, and finally to the air. The above describes the layout design of the structure and connection relationships of the hot stamping die. The following details the parameter design related to the cooling channels and jet holes in the hot stamping die, as well as the design of the jet timing for direct cooling by spraying cooling medium through the cooling channels and jet holes.

[0097] According to the present disclosure, in some embodiments, the location or number of multiple jet holes is related to the thickness reduction rate or the thickness reduction change rate per unit time of different nodes of the part to be stamped during the hot stamping process. The thickness reduction change rate per unit time refers to the rate of change of the sheet thickness per unit time, or the slope of the thickness change curve of the sheet at different time points.

[0098] Optionally, the thinning region (or severely thinning region) can be identified first, and then the key parameters of the jet timing and jet orifice can be designed based on the characteristics of the thinning region.

[0099] First, the process of determining the thinning region is introduced. In order to study the thinning situation in different regions of the part to be stamped, and thus to perform local cooling in different regions of the part to be stamped more specifically, this disclosure analyzes the thinning situation of the formed part.

[0100] In some examples, a hot stamping simulation model of the flow channel can be established to simulate the hot stamping process and calculate the thinning rate at each node of the formed part. In other examples, actual measurement data such as production data or experimental data can be analyzed to obtain the thickness of each region of the formed part and calculate the thinning rate at each node. A thinning rate threshold is set, and nodes with a thickness thinning rate greater than or equal to the threshold are identified as multiple thinning nodes. By judging the thinning nodes, a subset of interconnected thinning nodes is aggregated into a thinning region R. x .

[0101] In some embodiments, taking simulation analysis as an example, the surface of the part to be stamped can be regarded as a set of multiple feature points or nodes. Each node can be simulated using a simulation model to determine its thickness before and after stamping, thereby calculating the thinning rate of that node. For example, the thickness reduction rate δ at the first node of the part to be stamped is expressed as:

[0102] Where s0 is the initial sheet thickness at the first node, and s is the formed sheet thickness at the first node after stamping; the initial sheet thickness and the formed sheet thickness are simulated thicknesses obtained from simulation calculations based on the hot stamping simulation model, or are actual measurement data. It should be understood that the aforementioned first node refers to any one of multiple nodes.

[0103] In other words, the severely thinned area can be determined through the following steps: Establish a hot stamping simulation model with a conventional flow channel to simulate the conventional hot stamping process and analyze the thinning of the formed part; after the simulation is completed, extract the output result file, extract the thickness values ​​of all nodes along the surface of the formed part, and obtain the thickness field at the end of forming. Based on the collected thickness field data, the thinning rate of each node of the formed part can be calculated, i.e., the thickness thinning rate of multiple nodes of the part to be stamped can be determined according to the above formula.

[0104] A thinning rate threshold δ1 is set, and nodes with a thinning rate exceeding the threshold are defined as thinning nodes, thus forming a set of thinning nodes. Spatial connectivity analysis is performed on the nodes in the set, and the subset of interconnected thinning nodes that meet the connectivity criteria is aggregated into a thinning region Rx. It can be understood that the thinning region determination method can identify at least one thinning region of the part to be stamped, and the aforementioned thinning region Rx can refer to any thinning region. The arrangement of the jet holes can correspond to the positions of each thinning region. The rule for determining thinning nodes can be all nodes whose thinning rate exceeds the threshold and meets the connectivity criteria, or a redundancy value can be set to allow the thinning region to include a certain proportion of nodes that do not exceed the thinning rate threshold. The aforementioned connectivity criteria are:

[0105] Where σ is the preset connectivity determination distance, and xp and xq are the node coordinates.

[0106] In the above example, the thinning rate threshold can be the product of the material's limit thinning rate and the safety factor, which can be determined based on empirical values ​​or through model training data. σ can be determined using the fixed radius neighborhood method, taking a value of 1.0-2.0 times the average mesh size; or it can be determined using the element adjacency topology method, based on the element connection relationship of the finite element mesh to determine node connectivity.

[0107] In this disclosure, the layout of cooling channels and jet holes can be designed according to the location of the thinned region, so that the cooling medium sprayed from the jet holes corresponding to at least one thinned region is used to cool at least one thinned region.

[0108] The following describes how to determine the jetting time points for each thinning region. First, the concept of the rate of change of thickness reduction per unit time is introduced. In some embodiments, if the stamping process of each node is divided into different time points according to time sequence, then the rate of change of thickness reduction per unit time for a certain node at any given time point is expressed as:

[0109] Where s(t) represents the thickness of any node at time t, and s(t+Δt) represents the thickness at time t+Δt.

[0110] For example, the thickness-time historical data of each node in the severely thinned area can be extracted, and the thickness reduction rate curve over time during the forming process can be plotted. The slope of the change of each node over time can be calculated, which is the above-mentioned thickness reduction rate per unit time.

[0111] In some embodiments, the switch control device connected to the second port of the second cooling channel U2 and the fourth cooling channel V2 is activated at the start of cooling. The nozzles are closed sequentially to allow the cooling medium to be sprayed through multiple jet holes onto the thinned area of ​​the workpiece to be stamped, where i∈[1,u], u represents the total number of jet cooling time points during the hot stamping process of the workpiece to be stamped; the cooling start time is... This represents the statistical value of the time point corresponding to the maximum unit time thickness reduction rate of each node in the thinning region of the part to be stamped.

[0112] For example, the statistical values ​​at the above time points can be the earliest time among the corresponding time points of each node, or the average time, or the average time after removing a portion of the earliest time and a portion of the latest time. This disclosure does not limit this.

[0113] In some embodiments, the cooling start time may be the moment when the jet orifice begins to spray for cooling, or the point in time at which jet cooling is performed on the thinned area.

[0114] In some examples, for a certain thinning region, there are J nodes, and the time point corresponding to the maximum unit time thickness reduction rate at the j-th node is calculated.

[0115] Each node corresponds to The statistics are used to determine the starting time of cooling in the thinned region.

[0116] In the formula, The statistical formula for each time point is provided. In some embodiments, since the time point with the largest slope corresponds to the stage of drastic stress change, in an optional example, the statistical formula can be the earliest time point among the time points corresponding to each node in the region. Under this design, the region can start jet cooling from the earliest start time of thinning. Alternatively, the statistical value can be the average of the time points where the maximum and minimum values ​​of the slope of each node in the region are removed by 10%, which is taken as the start time of jet cooling in the region. Under this design, the region can start jet cooling from the average thinning time, which can shorten the cooling time while ensuring the cooling effect. However, it is not limited to this; the statistical value can also be other values, such as weighted average, mode, median, etc.

[0117] In some embodiments, if the jet holes on the same cooling channel correspond to multiple thinning regions, the cooling start time corresponding to the multiple thinning regions is the earliest cooling start time among the multiple thinning regions. That is, when the same channel with jet holes corresponds to multiple thinning regions, the earlier time point is taken as the jet cooling time point for the multiple regions. For example, if there are u time points in the stamping process of a sheet metal, and the i-th time point is denoted as t... i If i∈[1,u], then each thinning region can be selected from u time points to determine the time point at which the jet begins to flow in that thinning region.

[0118] Optionally, jet holes can be added to the cooling channel closest to the thinning area in the vertical direction. At the start of cooling, cooling medium is directionally sprayed into the thinning area through these jet holes, thereby directly cooling the local area.

[0119] In practical applications, the process of gas being sprayed through the jet orifice onto the thinning zone of the sheet metal takes some time. Therefore, this disclosure can also design an advance value Δt for the jet cooling time point based on the actual situation. i Then you can The timing of the cooling medium injection is precisely determined to ensure accuracy and achieve the desired cooling effect at the very moment when the thinning region begins to thin significantly.

[0120] In some embodiments, the switch control device at the end of cooling Open to stop the cooling medium from being sprayed onto the surface of the workpiece through multiple jet orifices, where i ∈ [1, u], and u represents the total number of jet cooling time points during the hot stamping process of the workpiece. In some embodiments, the cooling end time This refers to the moment after the start of cooling when the temperature of the thinned region is less than or equal to the temperature threshold.

[0121] The temperature threshold can be a safe temperature T, which means that the safe temperature of the thinning zone can be set to T. The safe temperature T can be obtained by statistical analysis of the temperature value when the sheet metal is thinned well, or it can be a temperature that is a certain temperature higher than the martensitization temperature.

[0122] During the forming process, temperature sensors can be used to monitor the temperature of the thinning zone in real time, or a temperature simulation model of the sheet metal can be used to predict the temperature change trend of each node in each thinning zone at each time point, thereby predicting the moment when each thinning zone is less than or equal to the temperature threshold. This temperature data can be fed back to the switch control device of the corresponding air outlet. When the temperature of the thinning zone is lower than the safe temperature, the corresponding switch control device is opened, and the jet cooling ends.

[0123] In summary, by plotting the thickness reduction curves of each severely thinned region during the forming process, and defining the moment when the statistical value of the unit time thickness reduction rate of each node in the thinned region of the part to be stamped is greater than or equal to the preset value as the moment when jet cooling begins, if jet holes are added to different regions of the same flow channel, then the earlier time point is taken as the jet cooling time point of the multiple regions corresponding to that flow channel.

[0124] The following describes the design of key parameters for cooling channels and jet holes. In some embodiments, in order to enable the mold to dissipate heat quickly and evenly during the forming process, and to ensure the quenching quality of the parts, the service life of the mold, and production efficiency, the key parameters of the cooling channels can be designed. The key parameters of the cooling channels of the first mold assembly and the second mold assembly can be the same or different.

[0125] Figure 4 is a schematic diagram of the parameters of a cooling channel according to an embodiment of the present disclosure. As shown in Figure 4, the cross-section of the cooling channel can be circular. The key parameters of the cooling channel include: the center distance W between two adjacent cooling channels, the diameter D of the cooling channel, and the height H of the center distance of the cooling channel from the mold closing surface.

[0126] In some embodiments, the center-to-center distance W between two adjacent cooling channels satisfies the following condition:

[0127] Where b0 is the width of the sheet metal to be stamped, n is the total number of flow channels, and n = n1 + n2.

[0128] In some embodiments, the cross-section of the multiple cooling channels is circular, and the diameter D of each cooling channel is represented as:

[0129] Where V0 represents the sheet metal volume, ρ0 represents the sheet metal density, C0 represents the sheet metal specific heat capacity, T0 represents the initial temperature of the sheet metal entering the mold, T1 represents the sheet metal exiting the mold, and t b Indicates the holding time, ρ s C represents the density of the cooling medium. S V represents the specific heat capacity of the cooling medium. s T1 represents the flow rate of the cooling medium, T2 represents the outlet temperature of the cooling medium, and T4 represents the inlet temperature of the cooling medium.

[0130] In some embodiments, the height H of the center of each cooling channel from the mold closing surface is expressed as:

[0131] Where, λ m Indicates the thermal conductivity of the mold, T m Indicates the mold surface temperature, T f Indicates the cooling channel wall temperature, h f Indicates the convective heat transfer coefficient of the cooling channel, T s The value represents the average temperature of the cooling medium, and W represents the center-to-center distance between two adjacent cooling channels.

[0132] In some embodiments, the key parameters of the cooling channels can be determined by combining the above formula with the number of channels and the mold dimensions. The selection of the number of channels must ensure the flow state of the cooling medium in the channels, that is, the number of multiple cooling channels must meet the following conditions:

[0133] D is related to the number of cooling channels; for example, D is inversely proportional to n, and the square of D is inversely proportional to n, etc. R e1 R is the Reynolds number of the cooling medium in the first state. e2 η is the Reynolds number of the cooling medium in the second state. s R is the dynamic viscosity coefficient of the cooling medium. Optionally, the first state can be a turbulent state, i.e., R e1 The first state can be the Reynolds number when the cooling medium is in turbulent flow, and the second state can be when the pressure drop rate of the cooling medium increases rapidly, i.e., R e2 It can be the Reynolds number when the pressure drop rate of the cooling medium increases rapidly.

[0134] Figure 5 is a schematic diagram of parameters of a jet orifice according to an embodiment of the present disclosure. As shown in Figure 5, the cross-section of the jet orifice is circular, and the key parameters of the jet orifice include: the diameter d of each jet orifice on the k-th cooling channel. kThe center-to-center distance w between two adjacent jet holes on the k-th cooling channel k , k∈[1,m1+m2].

[0135] In some embodiments, as shown in FIG5, the diameter d of each jet hole on the k-th cooling channel is... k and the center distance w between two adjacent jet holes on the k-th cooling channel. k The following conditions must be met: l k =f(d k h k ) l k ≥w k L v ≈r v w k

[0136] Where: l k f(d) is the diameter of the jet range of each jet hole on the k-th cooling channel. k h k ) is d i h i The functional relationship between h and the influence of mutual coupling on the jet range of each jet hole on the k-th cooling channel. k From the forming of the thinned region to the start of cooling time t i At that time, L is the vertical distance between the thinned area and the mold surface of the first mold assembly or the second mold assembly where the k-th cooling channel is located. v The length r of the v-th thinned region cooled by the k-th cooling channel along the channel direction of the k-th cooling channel. v Let v be the number of jet holes corresponding to the v-th thinning region, where v∈[1,N] and N is the total number of thinning regions cooled by the k-th cooling channel.

[0137] In summary, this disclosure presents a design method for a thermoforming die using liquid nitrogen jet for efficient cooling of complex components. Specifically, the part to be stamped can be cooled and reduced through cooling channels and jet holes added to the cooling channels. By introducing a direct jet cooling structure, local heat dissipation is accelerated, thereby suppressing excessive stretching. This solution can balance the feasibility of die manufacturing with temperature control accuracy, significantly improve the local thinning of complex components, and enhance the uniformity of forming.

[0138] This disclosure allows for the creation of jet holes within the cooling channel and implementation using the same cooling system switched to gas jet mode. This eliminates the need for additional complex piping and gas jet devices, reducing mold processing and maintenance costs while maintaining the mold's structural strength and rigidity. Furthermore, liquid nitrogen, as the cooling medium, can be directly discharged into the air, achieving efficient thermal management without the need for additional drainage facilities.

[0139] This disclosure also proposes a hot stamping device with a direct cooling structure. Figure 6 is a schematic diagram of the structure of a hot stamping device with a direct cooling structure provided according to an embodiment of this disclosure.

[0140] As shown in Figure 6, the hot stamping equipment with a direct cooling structure includes: the hot stamping die with the direct cooling structure, specifically, a first die assembly 1 and a second die assembly 2.

[0141] Optionally, as shown in Figure 6, the hot stamping equipment with a direct cooling structure further includes a positioning device 9, a sliding guide device 10, a die base 11, and a fixing plate 12. The die base 11 includes a first die base (upper die base) and a second die base (lower die base), and the fixing plate 12 includes a first fixing plate (upper fixing plate / punch fixing plate) and a second fixing plate (lower fixing plate / die fixing plate). The die base and the sliding guide device form a four-guide-pillar die frame; the second fixing plate is placed at the center of the second die base, and a second die assembly is placed in the hollow portion of the second fixing plate. Four positioning blocks slightly higher than the second die assembly are placed on the outer edge of the second die assembly, forming a positioning device; the first fixing plate is placed at the center of the first die base and is parallel to the first fixing plate, and a first die assembly is placed in the hollow portion of the first fixing plate.

[0142] Optionally, the connection between the above modules can be made by screw connection and positioning with screw pins.

[0143] This disclosure also proposes a hot stamping method. Figure 7 is a schematic flowchart of a hot stamping method according to an embodiment of this disclosure. The method can be performed by the aforementioned hot stamping equipment with a direct cooling structure, and includes the following steps:

[0144] Step 101: During the relative movement of the first mold assembly and the second mold assembly until the mold is closed, the workpiece to be stamped is cooled through multiple cooling channels and multiple jet holes.

[0145] Therefore, in this embodiment, the hot stamping equipment with a direct cooling structure can cool the part to be stamped, wherein multiple jet holes can locally and directly cool specific local areas of the part to be stamped, thereby improving cooling efficiency, having a better cooling effect, and ensuring the forming yield of the part to be stamped.

[0146] In some embodiments, the cooling channel contains cooling medium to indirectly cool the part to be stamped, and multiple jet holes spray cooling medium to directly cool the part to be stamped.

[0147] Therefore, in this embodiment, the hot stamping equipment with a direct cooling structure can directly and indirectly cool the part to be stamped. The cooling channel provides an indirect cooling effect and increases the cooling area, while the jet hole provides a direct cooling effect and improves the cooling efficiency.

[0148] In some embodiments, the method further includes: determining at least one thinning region of the part to be stamped based on the thickness reduction rate of different nodes of the part during the hot stamping process; and spraying a cooling medium onto the at least one thinning region through multiple cooling channels and multiple jet holes.

[0149] In some embodiments, the method further includes: based on the thickness reduction rate per unit time of at least one thinning region of the part to be stamped,

[0150] Nodes whose thickness reduction rate per unit time is greater than or equal to the preset thinning rate are identified as multiple thinning nodes;

[0151] Based on connectivity criteria, spatial connectivity analysis is performed on multiple thinning nodes, and at least one thinning region of the part to be stamped is determined from the subset of interconnected thinning nodes; wherein the connectivity criteria are:

[0152] Where: σ is the preset connectivity determination distance, xp and xq are the coordinates of the thinning node, Rx is any region in at least one thinning region, x∈[1,X], and X is the number of thinning regions; cooling medium is sprayed into at least one thinning region Rx through multiple cooling channels and multiple jet holes.

[0153] In other words, at the start of cooling of a certain thinning region determined by the above method, the region is locally cooled by spraying through the cooling channels and jet holes on the punch or die that are close to the thinning region in the vertical direction.

[0154] In some embodiments, the method further includes: determining the cooling end time based on the temperature of at least one thinning region. At the end of cooling Stop spraying cooling medium into at least one thinned area.

[0155] In summary, the method disclosed herein can provide cooling effects in a timely and directional manner according to the thickness reduction situation. For areas of complex components that are easy to reduce thickness, local spray cooling is implemented by using liquid nitrogen jet during the critical thinning period of the forming process, thereby reducing stress concentration and improving the thickness uniformity of the formed parts.

[0156] Figure 8 is a schematic diagram of a complex component hot forming process using liquid nitrogen jet high-efficiency cooling according to an embodiment of this disclosure. The method described above is explained using specific examples shown in Figure 8, in conjunction with the above embodiments. This disclosure proposes a complex component hot forming process using liquid nitrogen jet high-efficiency cooling, which includes the following steps:

[0157] Step 1: Cut the sheet metal according to the shape of the part to be formed, and place the cut sheet metal in a special heating furnace to heat to a temperature higher than the austenite initiation temperature Ac3, about 900–950℃, and hold for 30–120 seconds to obtain a uniform full austenitic structure.

[0158] Step 2: Next, the high-temperature sheet material, after being heated and kept at a certain temperature for a period of time, is transferred to the stamping machine.

[0159] Step 3: During the stamping process, the punch moves downward under the guidance of the sliding guide device until it closes with the die. During this period, the flow control devices on the external pipes at the air inlets of the first cooling channel U1 and the third cooling channel V1 are closed, while the flow control devices at the air inlets of the second cooling channel U2 and the fourth cooling channel V2 are opened. The cooling medium enters and exits in the second cooling channel U2 and the fourth cooling channel V2. U jet cooling time points are set, and the sheet metal is stamped to the i-th time point. After that, i∈[1,u]; the switch control devices on the external pipes of the corresponding second cooling channel U2 and fourth cooling channel V2 are closed one after another, and liquid nitrogen is sprayed out from the added jet hole to locally cool the severely thinned area.

[0160] Optionally, u jet cooling time points are set during the forming process, and at any i-th jet cooling time point... The switch control device for the external cooling channel of the corresponding cooling channel corresponding to the thinning area is closed, allowing the cooling medium to be sprayed from the jet orifice of the channel into the thinning area, thereby providing localized cooling to the thinning area. The switch control device for the corresponding cooling channel of the non-thinning area can remain open, preventing the cooling medium from being sprayed from the jet orifice in case of insufficient pressure.

[0161] Understandably, the cooling channels can be individually controlled by their on / off control devices, so that only the jet holes in the cooling channels passing through the thinned area can spray cooling medium to directly and locally cool the thinned area.

[0162] Step 4: During the stamping and holding process, the punch and die are completely closed, the flow regulating devices on the external pipes of the air inlets of cooling channels U1, U2, V1, and V2 are all turned on, and the air outlets of cooling channels U2 and V2 are also fully opened. Liquid nitrogen enters from the air inlet and generates convective heat transfer with the channel wall to achieve rapid quenching in the mold, and is finally discharged directly into the air.

[0163] Step 5: After removing the oxide scale, laser cutting, and rust prevention treatment from the demolded parts, the entire hot stamping forming process is completed.

[0164] In summary, the above embodiments of this disclosure target areas of complex components that are prone to thinning. They utilize liquid nitrogen jets to implement localized spray cooling during the critical thinning period of the forming process, thereby reducing stress concentration and improving the thickness uniformity of the formed parts.

[0165] The technical advantages of this disclosure are as follows:

[0166] 1. It achieves direct cooling during the hot stamping process, combining indirect and direct cooling for better cooling effect and higher cooling efficiency;

[0167] 2. Localized cooling is applied to severely thinned areas during the forming process to achieve real-time, precise, and independent control;

[0168] 3. The cooling capacity is precisely, efficiently and intensely concentrated and applied to specific small local areas where excessive deformation needs to be suppressed (such as the aforementioned easily thinned areas), thus solving the problem of cooling complex formed parts.

[0169] 4. It realizes a local enhanced cooling technology with high strength, high precision, directional and timed application / closing to make up for the shortcomings of traditional overall cooling methods and effectively suppress excessive deformation and temperature drop risk in specific areas.

[0170] In the embodiments of this disclosure, unless otherwise stated, elements expressed in the singular form, such as "a," "an," "the," "the aforementioned," "this," etc., can mean "one and only one," or "one or more," "at least one," etc. For example, nouns following articles such as "a," "an," and "the" in English can be understood as either singular or plural expressions.

[0171] In some embodiments, "multiple" means "two or more", "at least two", etc. The terms "at least one of A or B", "at least one of A and B", "one or more", "a plurality of", "multiple" etc. can be used interchangeably.

[0172] The prefixes "first," "second," etc., used in the embodiments of this disclosure are merely for distinguishing different descriptive objects and do not impose restrictions on the position, order, priority, quantity, or content of the descriptive objects. The description of the descriptive objects is found in the claims or the context of the embodiments, and the use of prefixes should not constitute unnecessary restrictions. For example, if the descriptive object is a "field," the ordinal numbers preceding "field" in "first field" and "second field" do not restrict the position or order of the "fields." "First" and "second" do not restrict whether the "fields" they modify are in the same message, nor do they restrict the order of "first field" and "second field." Similarly, if the descriptive object is a "level," the ordinal numbers preceding "level" in "first level" and "second level" do not restrict the priority between "levels." Furthermore, the number of descriptive objects is not limited by ordinal numbers and can be one or more. For example, in "first device," the number of "devices" can be one or more. Furthermore, the objects modified by different prefixes can be the same or different. For example, if the object being described is "device", then "first device" and "second device" can be the same device or different devices, and their types can be the same or different. Similarly, if the object being described is "information", then "first information" and "second information" can be the same information or different information, and their content can be the same or different.

[0173] In some embodiments, the terms “greater than,” “greater than or equal to,” “not less than,” “more than,” “more than or equal to,” “not less than,” “higher than,” “higher than or equal to,” “not lower than,” and “above” can be used interchangeably, as can the terms “less than,” “less than or equal to,” “not greater than,” “less than,” “less than or equal to,” “not more than,” “lower than,” “lower than or equal to,” “not higher than,” and “below”.

[0174] In some embodiments, devices, etc., may be interpreted as physical or virtual, and their names are not limited to those described in the embodiments. Terms such as “device,” “equipment,” “device,” “node,” “unit,” “section,” “system,” “entity,” and “body” are interchangeable.

[0175] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

[0176] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A hot stamping die having a direct cooling structure, characterized by, include: First mold assembly and second mold assembly; Wherein, at least one of the first mold assembly and the second mold assembly has multiple cooling channels parallel to the mold closing surface of the first mold assembly and the second mold assembly, and at least one of the multiple cooling channels has multiple jet holes perpendicular to the at least one cooling channel and penetrating the mold closing surface; The multiple cooling channels and the multiple jet holes are used to contain the cooling medium, which can be sprayed through the multiple jet holes onto the surface of the part to be stamped between the first mold assembly and the second mold assembly.

2. The hot stamping die with a direct cooling structure according to claim 1, characterized in that, The location or number of the plurality of jet holes is related to the thickness reduction rate and the thickness reduction change rate per unit time of different nodes of the part to be stamped during the hot stamping process. The thickness reduction rate δ at the first node of the piece to be punched is expressed as: Where s0 is the initial sheet thickness at the first node, and s is the formed sheet thickness at the first node after stamping.

3. The hot stamping die with a direct cooling structure according to claim 2, characterized in that, The to-be-stamped part comprises at least one thinning region, the thinning region is composed of a plurality of thinning node subsets in mutual communication, the thinning node subsets satisfy a communication judgment condition, and the communication judgment condition is: Wherein: sigma is a preset connection determination distance, x p , x q is a thinning node coordinate, R x is the at least one thinning area, x is an element in [1, X], X is the number of thinning areas; the thickness thinning rate of the plurality of thinning nodes is greater than or equal to a preset thinning rate; Cooling medium injected through jet holes corresponding to the at least one thinned region is used to cool the at least one thinned region.

4. The hot stamping die with a direct cooling structure according to claim 1, characterized in that, The first mold assembly has n1 cooling channels, the n1 cooling channels include n1-m1 first cooling channels U1 and m1 second cooling channels U2, and the second cooling channel U2 is provided with r1 jet holes, where n1, m1 and r1 are positive integers; The second mold assembly has n2 cooling channels, including n2-m2 third cooling channels V1 and m2 fourth cooling channels V2. The fourth cooling channel V2 has r2 jet holes, where n2, m2, and r2 are positive integers. The number of cooling channels is n, and the number of jet holes is r, where n = n1 + n2, and r = r1 + r2; The first cooling channel U1, the second cooling channel U2, the third cooling channel V1, and the fourth cooling channel V2 have a first port and a second port, the first port being used to input the cooling medium and the second port being used to discharge the cooling medium; The first cooling channel U1, the second cooling channel U2, the third cooling channel V1, and the fourth cooling channel V2 are connected in sequence to the distribution plate, the flow control device, and the air supply tank through the first external pipeline. The second cooling channel U2 and the second port of the fourth cooling channel V2 are connected to the switch control device through a second external pipe. The second ports of the first cooling channel U1 and the third cooling channel V1 are connected to air.

5. The hot stamping die with a direct cooling structure according to claim 4, characterized in that, The switch control device to which the second port of the second cooling flow passage U2 and the fourth cooling flow passage V2 is connected controls the start timing of cooling The nozzles are closed sequentially so that the cooling medium is sprayed through the plurality of jet holes onto the thinning area of ​​the part to be stamped, where i∈[1,u], and u represents the total number of jet cooling time points during the hot stamping process of the part to be stamped; The cooling start time The value is the statistical value of the time point corresponding to the maximum thickness reduction rate per unit time of each node in the thinning region of the part to be stamped; if the jet hole on the same cooling channel corresponds to multiple thinning regions, then the cooling start time corresponding to the multiple thinning regions is the earliest cooling start time among the multiple thinning regions.

6. The hot-stamping die having a direct cooling structure according to claim 2, characterized by, The unit time thickness thinning change rate is expressed as: Where s(t) represents the thickness of the first node at time t, and s(t+Δt) represents the thickness of the first node at time t+Δt.

7. The hot stamping die with a direct cooling structure according to claim 5, characterized in that, The switch control device at the end of cooling time Open to stop the cooling medium from being sprayed onto the surface of the workpiece through the plurality of jet holes, where i∈[1,u]; The cooling end time This refers to the moment after the cooling begins, when the temperature of the thinned region is less than or equal to a temperature threshold.

8. The hot-stamping die having a direct cooling structure according to claim 1, characterized by, The parameters of the cooling channels include at least one of the following: the center-to-center distance W between two adjacent cooling channels, the diameter D of each cooling channel, and the height H of the center of each cooling channel from the mold closing surface. The center distance W between two adjacent cooling channels satisfies the following condition: Wherein, b0 is the width of the sheet metal projected along the axis of the cooling channel of the part to be stamped; The cross section of the plurality of cooling flow channels is circular, and the diameter D of each cooling flow channel is expressed as: Where V0 represents the sheet metal volume, ρ0 represents the sheet metal density, C0 represents the sheet metal specific heat capacity, T0 represents the initial temperature of the sheet metal entering the mold, T1 represents the temperature of the sheet metal exiting the mold, and t b Indicates the holding time, ρ s C represents the density of the cooling medium. S V represents the specific heat capacity of the cooling medium. s T1 represents the flow rate of the cooling medium, T2 represents the outlet temperature of the cooling medium, and T4 represents the inlet temperature of the cooling medium. The center distance of each cooling runner from the height H of the mold clamping surface is expressed as: where λ m represents the mold thermal conductivity, T m represents the mold surface temperature, T f represents the cooling channel wall surface temperature, h f represents the cooling channel convection heat transfer coefficient, T s represents the cooling medium average temperature, and W represents the center distance between two adjacent cooling channels.

9. The hot-stamping die having a direct cooling structure according to claim 4, characterized by, The number of the plurality of cooling flow channels satisfies the following condition: Wherein D is related to the number of the multiple cooling channels; R e1 Reynolds number of the cooling medium in the first state, R e2 Reynolds number of the cooling medium in the second state, η s Dynamic viscosity coefficient of the cooling medium, v s Cooling medium flow rate, p s Cooling medium density.

10. The hot stamping die with a direct cooling structure according to claim 1, characterized in that, The cross section of the plurality of jet holes is circular, the diameter d of each jet hole on the kth cooling flow channel k and the center distance w between two adjacent jet holes on the kth cooling flow channel k satisfies the following conditions: l k = f(d k , h k ) l k ≥w k L v ≈r v w k Where: l k f(d) is the diameter of the jet range of each jet hole on the k-th cooling channel. k h k ) is d i h i The functional relationship between h and the influence of mutual coupling on the jet range of each jet hole on the k-th cooling channel. k The vertical distance L between the thinned region and the mold surface of the first or second mold assembly containing the k-th cooling channel, from the moment the thinned region is formed to the start of cooling. v r is the length of the v-th thinned region cooled by the k-th cooling channel along the channel direction of the k-th cooling channel. v Let v be the number of jet holes corresponding to the v-th thinning region, where v ∈ [1, N] and N is the total number of thinning regions cooled by the k-th cooling channel.

11. A hot stamping apparatus having a direct cooling structure, characterized by, include: The hot stamping die with a direct cooling structure as described in claim 1.

12. A hot stamping method characterized by, Performed by the hot stamping equipment having a direct cooling structure as described in claim 11, comprising: During the relative movement of the first mold assembly and the second mold assembly until the mold is closed, the thinned area of ​​the part to be stamped is cooled by the multiple cooling channels and the multiple jet holes, wherein the cooling channels contain the cooling medium to indirectly cool the part to be stamped, and the multiple jet holes spray the cooling medium to directly cool the part to be stamped.

13. The method of claim 12, wherein, The method further includes: determining nodes with a thickness reduction rate greater than or equal to a preset reduction rate as multiple thinning nodes based on the thickness reduction rate of different nodes of the part to be stamped during the hot stamping process; According to the communication judgment condition, the plurality of thinning nodes are analyzed for spatial connectivity, and a subset of the thinning nodes that are in communication with each other is determined as at least one thinning region of the to-be-stamped part; wherein the communication judgment condition is: Where: σ is the preset connectivity determination distance, xp and xq are the coordinates of the thinning node, Rx is the at least one thinning region, x∈[1,X], and X is the number of thinning regions; the cooling medium is sprayed into the at least one thinning region Rx through the multiple cooling channels and the multiple jet holes.

14. The method of claim 13, wherein, The method further includes: dividing the stamping process into different time points in chronological order, determining the at least one thinning region R x the unit time thickness thinning change amount of the jth node at any time point, which is expressed as: Where s(t) represents the thickness of the first node at time t, and s(t+Δt) represents the thickness of the first node at time t+Δt. determining a time point corresponding to a maximum value of the unit time thickness thinning change amount of the jth node corresponding to each node statistics are determined as the thinned region R x the cooling start time In the formulae, for the statistical formula for each time point, J is the reduced area R x the number of included nodes; at the start of the cooling The cooling medium is sprayed into the at least one thinned area to cool the at least one thinned area.

15. The method of claim 14, wherein, The method further includes: determining the end of cooling time instant as a function of the temperature of the at least one thinning region At the end of the cooling Stop spraying the cooling medium into the at least one thinned area.

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