Method for improving cold stamping forming surface quality of outer plate of aluminum alloy automobile covering part

Abstract

The invention discloses an aluminum alloy automobile covering part outer plate cold stamping forming surface quality improving method, and relates to the technical field of automobile stamping dies. The method sequentially comprises the seven steps of parting compensation treatment, dynamic flow control treatment, mold difference hardness treatment, molded surface superfinishing, difference strong pressure shaping, structured lubrication dust retention treatment and forming process reconstruction. Through a full-process integrated forming control scheme, surface product defects such as scratches, slip lines, viscosity and concave-convex points in the cold stamping process of the aluminum alloy outer plate can be effectively eliminated, the large-angle vertical face and fillet resilience is controlled to be within 0.5 mm, the die debugging difficulty and the bench worker workload are greatly reduced, the die manufacturing period is shortened, and the production efficiency is improved. And the mass production yield and forming stability of parts are improved, and the large-scale mass production requirements of new energy automobiles are met.

Description

Technical Field

[0001] This invention relates to the field of automotive mold technology, and in particular to a method for improving the surface quality of aluminum alloy automotive body panels during cold stamping. It provides a complete, low-cost, mass-producible method for improving surface quality and high-precision forming control, which addresses defects such as surface scratches, slip lines, springback distortion, stickiness, and trimming deformation that are prone to occur in the cold stamping process of aluminum alloy automotive body panels. Background Technology

[0002] With the continuous increase in the demand for lightweighting in new energy vehicles, aluminum alloys have become the mainstream material for automotive body panels due to their excellent lightweight properties. However, in the molding and manufacturing of automotive body panels, the large area, high appearance requirements, multiple rounded corners, and complex surface structure of these parts, coupled with the inherent characteristics of aluminum alloys—softness, high coefficient of friction, large springback, and easy sticking to the mold—lead to many common industry challenges in the cold stamping process of aluminum alloy body panels, severely restricting their high-quality, large-scale application.

[0003] In actual production, existing technologies have the following drawbacks: Conventional draw beads are mostly fixed structures, which can easily lead to excessively fast or slow material flow in certain areas of the die, resulting in surface defects such as wrinkling, cracking, and slip lines; for large-angle vertical surfaces and transition rounded corner areas with angles ≥30°, springback is difficult to control precisely, often resulting in uneven surfaces, unclear edges, and uneven surfaces, seriously affecting appearance quality; the die surface is prone to scratches and sticking, with sticking in the main forming area and excessive resistance in the material feeding area, making it difficult to control micro-deformation of the parts; the conventional "trimming before shaping" process causes trimming stress to be directly transmitted to the already formed surface, resulting in surface deformation. Issues such as shape and surface defects exist; meanwhile, existing technologies mostly focus on improvements in single aspects, such as material performance optimization, adjustment of single compensation methods, or upgrading of production equipment, without forming a complete integrated solution from source-level parting compensation, dynamic process flow control, mold performance optimization, precision assurance, lubrication protection to process stress management. This makes it impossible to simultaneously meet the mass production requirements of high surface quality, low defect rate, low cost, and fast cycle time, resulting in high part quality defect rate, long mold production cycle, and high manufacturing cost. It also requires a large number of highly skilled craftsmen to perform manual debugging, which seriously increases the mold development cost and restricts the large-scale application of aluminum alloy materials in high-quality automotive exterior body panels.

[0004] It should be noted that the analysis of the above technical information is the result of creative labor. The detailed description of it in the background section is only intended to deepen the understanding of the non-obviousness of the overall background of this application by those skilled in the art, and should not be regarded as an admission or in any form an implication that the above technical information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] To address the shortcomings in the aforementioned background technology, this invention proposes a method for improving the surface quality of aluminum alloy automotive body panel cold stamping forming. The technical problem to be solved is: given the lack of a fully integrated forming control scheme for the existing aluminum alloy automotive body panel cold stamping forming technology, how to simultaneously achieve high surface quality, low defect rate, low cost, and adaptability to large-scale mass production.

[0006] To address the aforementioned issues, this invention, through a systematic review of the molding process and batch-combined testing of numerous molding technologies and craftsmanship experience, continuously optimizes parameter configurations and process settings based on these experiments. It innovates an integrated improvement method encompassing parting line CAE compensation, flow control, gradient hardness, ultra-precise surface treatment, and process optimization. This method comprehensively eliminates surface scratches, slip lines, orange peel texture, stickiness, and unevenness in various scenarios, precisely controlling the springback and distortion of large-angle facades and rounded corners, thereby improving surface quality stability and mass production yield. This forms a systematic and innovative optimal solution for the entire process, significantly reducing mold debugging difficulty and fitter workload without increasing equipment and material costs, shortening mold manufacturing cycles, improving part quality controllability and production efficiency, and creating a high-quality, short-cycle systematic technical solution. This provides a simplified operating solution for the application of new materials and significant cost reduction in the automotive industry, and also offers strong technical support for the automotive industry's pursuit of lightweighting, green and low-carbon development, and sustainable upgrading.

[0007] This invention, based on traditional outer panel forming, innovates configuration through experimental combination and integration of craftsmanship experience. It uses parting processing to break down key features at the source, forming differentiated processing solutions. During the forming process, it changes the traditional fixed material flow pattern, adopting dynamic flow control to adjust the flow pattern and promote the uniformity of the forming material. It mitigates the interference of micro-deformation of the material through mold surface strengthening, eliminates the influence of surface hard spots through precision assurance, and maximizes the protection of the molded surface through process reconstruction. This systematically solves the problems of outer panel surface quality and forming defects. The main steps include seven key steps: parting processing, dynamic flow control, differential pressure, ultra-precision machining, lubrication and dust retention, differential hardness, and process reconstruction. The aluminum alloys used in the experiments of this invention are 5- and 6-series, and the thickness of the experimental plates is 0.6–1.2 mm.

[0008] The basic technical solution provided by this invention is as follows:

[0009] A method for improving the surface quality of aluminum alloy automotive body panels through cold stamping includes the following steps:

[0010] S1 parting compensation treatment: Based on the product characteristics in the stamping direction, the process surface of the aluminum alloy automotive body panel is classified and a differentiated CAE process compensation treatment is adopted accordingly.

[0011] S2 Dynamic Flow Control: It adopts a movable drawbead structure, and dynamically adjusts the blanking resistance of the drawbead according to different stages of stamping to achieve balanced material flow in the forming process.

[0012] S3 Difference Hardness Treatment for Molds: Based on the molding function requirements of different areas of the mold, the hardness of different areas of the mold surface is adjusted differently.

[0013] S4 surface ultra-precision machining: high-speed, light-cut ultra-precision machining of the mold forming area surface;

[0014] S5 Differential High-Pressure Shaping: Graded and differentiated high-pressure treatment is carried out for areas and key appearance surfaces of the outer panel that are prone to forming defects.

[0015] S6 Structured Lubrication and Dust Retention Treatment: A closed-loop lubrication groove structure is set in the die surface area corresponding to the draw bead, which is used in conjunction with the stamping process for lubrication and dust removal.

[0016] S7 Molding Process Restructuring: Based on the molding requirements of different areas of the outer panel, the order of trimming and shaping processes is adjusted, and a process mode of shaping first and then trimming or secondary trimming is adopted.

[0017] The beneficial effects of the above-mentioned basic technical solution are as follows: This solution constructs a fully integrated molding control system that covers the entire process, from process compensation at the molding source, dynamic flow control during molding, mold body performance optimization, surface accuracy assurance, appearance protection to stress control in the final process. Each step cooperates and works synergistically, rather than being a simple superposition of individual steps. Through parting compensation, it precisely controls the springback and molding defects of different characteristic surfaces from the source. Dynamic flow control solves the core problem of uneven material flow in fixed draw beads. Differential hardness treatment matches the wear resistance, anti-sticking properties, and material flow requirements of different areas. This system addresses common industry challenges in the cold stamping process of aluminum alloy outer panels, such as surface scratches, slip lines, springback distortion, sticking, and trimming deformation. It eliminates the impact of machining tool marks on surface quality through ultra-precision machining, prioritizes protection of critical appearance surfaces through differential pressure, reduces the risk of mold sticking and scratches through structured lubrication and dust retention, and avoids the impact of trimming stress on the appearance surface through process reconstruction. It requires no additional production equipment or auxiliary material costs, significantly reduces the difficulty of mold debugging and the amount of manual labor for fitters, shortens the mold manufacturing cycle, and improves the controllability of part forming quality and production efficiency.

[0018] Furthermore, in the parting compensation process, the process surface is divided into three categories and corresponding differentiated compensation is adopted. Specifically, for areas with a gentle overall shape and a planar shape around the drawbeam, conventional process compensation is adopted; for facade areas with a continuous length ≥200mm and an overall downward angle ≥30°, curvature compensation is adopted; and for feature areas with isolated high points or pits, floating molding of movable inserts is adopted.

[0019] The further beneficial effects of this solution are: it allows for precise classification and differentiated compensation for surfaces with different structural features, avoiding uneven forming caused by a one-size-fits-all process compensation. It also allows for precise pre-control of springback and forming defects in different areas from the source of process design. In particular, it enables targeted pre-control of springback on large-angle facades and sudden forming problems of island-like features, thus significantly improving forming accuracy.

[0020] Furthermore, the dynamic flow control process adopts either of the following two modes depending on the size and structural complexity of the outer plate: Adjustable dynamic flow control mode, in which the drawbead is made into a movable insert, and a series of nitrogen cylinders are set below the insert. The pressure of the nitrogen cylinders is adjusted to achieve differentiated adjustment of the pressing resistance in the stamping flow stage and the forming stage; Fixed dynamic flow control mode, in which the drawbead is made into a symmetrically arranged movable insert, and an elastic pad is set below the insert. The pressing resistance in different stages of stamping is dynamically adjusted by changing the compression of the elastic pad.

[0021] The further beneficial effects of this solution are as follows: it provides an adaptable dynamic flow control solution for outer panel products of different sizes and complexities, realizing differentiated control of the pressure resistance at different stages of stamping, resulting in less resistance and smoother sheet flow during the material flow stage, and greater resistance and more precise sheet shaping during the forming and holding pressure stage. This solves the industry pain point that fixed draw beads cannot simultaneously meet the requirements of material flow smoothness and forming and holding pressure, effectively avoiding defects such as wrinkling, cracking, and slip lines caused by uneven material flow, while significantly reducing the workload of subsequent mold debugging.

[0022] Furthermore, in the differential hardness treatment of the mold, the mold surface is divided into three types of areas and correspondingly differentiated hardness control is performed. Specifically, high hardness quenching treatment is performed on the main forming rounded corners and appearance edge areas; medium hardness quenching treatment is performed on the auxiliary edge areas and key forming surface areas; and low hardness quenching treatment is performed on the draw beads and material feeding management surface areas. The low hardness is the lower limit hardness that meets the forming requirements.

[0023] Further benefits of this solution include: differentiated hardness matching based on the molding function requirements of different areas of the mold; high hardness in the main molding fillets and appearance edge areas ensures the wear resistance and anti-adhesion of the edges, maintaining clear edges even in long-term mass production; medium hardness in auxiliary edges and key molding surfaces balances precision retention and molding adaptability; and low hardness in the draw beads and feed surface reduces frictional resistance, ensures smooth sheet flow, and avoids adhesion and material jamming. This achieves a synergistic matching of multiple requirements for wear resistance, anti-adhesion, and smooth material flow, extending the mold's service life and reducing the surface defect rate.

[0024] Furthermore, ultra-precision machining is a high-speed light cutting process with the following machining parameters: spindle speed 8000-12000 r / min, feed rate 6000-8000 mm / min, machining step distance 0.3-0.5 mm, using a combination of inclined axis forward and reverse milling, and tool inclination angle of 25°-40°.

[0025] The further beneficial effects of this solution are as follows: through high-speed light cutting ultra-precision machining process, the machining marks and tool deflection defects of conventional precision machining are effectively eliminated, the continuity and smoothness of the mold surface are greatly improved, the transmission of machining marks to the surface of the part is avoided, the A-level curved surface appearance requirements of the part are guaranteed from the perspective of mold precision, and the adaptation machining for concave rounded corners ensures the smoothness of material flow in the rounded corner area.

[0026] Furthermore, the differential pressure shaping is divided into three levels of pressure treatment: for facade areas with a downward angle ≥30°, a level two pressure treatment is adopted, with a pressure allowance of 0.06-0.1mm; for key appearance edge areas, a level one pressure treatment is adopted, with the pressure range extending outward from the edge 30-50mm, and a pressure allowance of 0.08-0.15mm; for the surface area adjacent to the flange line, a progressive pressure treatment is adopted, with a progressive pressure structure set in a range of 120-150mm inward along the flange edge line, and the pressure allowance linearly decreasing from 0.12mm at the flange edge line to 0 inward.

[0027] The further beneficial effects of this solution are as follows: it implements graded and differentiated high-pressure shaping for areas and key appearance surfaces that are prone to molding defects, thus achieving priority protection for key areas. The high-pressure treatment ensures full fit and precise shaping of key appearance surfaces, effectively avoiding problems such as surface rebound, unclear edges, and surface collapse in the flanged area. At the same time, the progressive high-pressure avoids the problem of surface irregularities caused by sudden changes in high pressure, balancing shaping accuracy and surface smoothness.

[0028] Furthermore, in the structured lubrication and dust retention treatment, the closed-loop lubrication groove structure includes a double-line main lubrication groove arranged parallel to both sides of the drawbeam, and a guide line arranged perpendicular to the main lubrication groove at intervals; the main lubrication groove is continuously connected along the extension direction of the drawbeam to form a closed loop, with a groove width of 1mm and a groove depth of 0.2-0.4mm, the distance between the two main lubrication grooves is 5mm, and the distance between each groove and the side of the drawbeam is 3mm; the guide line is spaced 50mm apart, and its end extends to the joint of the movable insert of the drawbeam.

[0029] Further benefits of this solution include: the closed-loop lubrication groove structure enables uniform retention and micro-coating of lubricating oil, ensuring continuous and stable lubrication in the draw bead area and reducing the surface stickiness of the aluminum alloy sheet; at the same time, the drainage line removes surface dust and excess lubricating oil that falls off the aluminum alloy sheet during the stamping process, avoiding surface scratches and mold sticking caused by dust, and effectively improving the surface quality stability during continuous stamping production.

[0030] Furthermore, in the reconstruction of the molding process, the specific process mode is as follows: For areas with secondary molding requirements, a secondary trimming mode is adopted. The initial trimming leaves a margin of 20-40mm. After the shaping and setting process is completed, a secondary trimming is performed to the design size. For areas without secondary molding interference, a shaping-then-trimming mode is adopted. The surface shaping and setting process is completed first, and then the trimming process is performed. For surface areas with rapid curvature changes, a secondary trimming mode is preferred.

[0031] The further beneficial effects of this solution are: it overturns the conventional process arrangement of "trimming first and then shaping". By reconstructing the process of shaping first and then trimming or trimming twice, it avoids the transmission and influence of trimming stress release on the already formed appearance surface, effectively solves the problems of surface deformation, surface collapse and edge offset caused by trimming, and greatly improves the final dimensional accuracy and surface quality stability of the parts.

[0032] Furthermore, curvature compensation is divided into two forms: when the overall trend shape of the facade area is arc-shaped, reverse arc compensation is used, and the curvature and length of the reverse arc are 30%-50% of the curvature and length of the corresponding facade area arc; when the overall trend shape of the facade area is linear, extension compensation is used. When the area length is ≥100mm, the extension base is 40mm, and the extension amount increases by 5mm for every 15° increase in angle; when the area length is <100mm, the extension base is 30% of the area length, and the extension amount increases by 5mm for every 15° increase in angle.

[0033] The further beneficial effects of this solution are as follows: it provides a precise curvature compensation method for large-angle facades with different trend shapes, offsets the rebound stress after the arc-shaped facade is formed by reverse arc compensation, and precisely controls the rebound deformation of linear facades by extending compensation, thereby achieving precise pre-control of the rebound of large-angle facades and controlling the amount of facade rebound within 0.5mm.

[0034] Furthermore, in the adjustable dynamic flow control mode, the rated pressure of the nitrogen cylinder group is 1.5 times the clamping force required for conventional fixed drawbeads.

[0035] The further beneficial effects of this solution are: it ensures that the adjustable draw beads have sufficient pressure adjustment margin, can adapt to the pressure requirements of different plates and different forming stages, and improves the adaptability and adjustment accuracy of dynamic flow control.

[0036] In summary, the present invention has the following significant beneficial effects:

[0037] 1. The surface quality of parts is significantly improved. Through full-process surface quality control, surface defects such as scratches, slip lines, orange peel, stickiness, and bumps during the molding process can be effectively eliminated. The surface smoothness of the parts reaches the A-level curved surface standard, and the mass production yield is greatly improved.

[0038] 2. The controllability of molding precision is significantly enhanced. Through coordinated measures such as source parting compensation and process pressure shaping, the springback of large-angle facades and rounded corners can be controlled within 0.5mm, ensuring clear edges and stable surfaces of parts without the need for large-scale manual finishing.

[0039] 3. Excellent mass production adaptability: Through dynamic flow control of active draw beads, gradient hardness treatment, and structured lubrication, the active draw beads reduce the difficulty of debugging, and the gradient hardness extends the mold life and reduces surface stickiness, resulting in good mass production adaptability. The material flow is balanced, with no sticking to the mold and no trimming deformation, enabling continuous and stable mass production. It effectively solves problems such as sticking to the mold, uneven material flow, and trimming deformation in the mass production process, and can achieve continuous and stable mass production, which is suitable for the fast pace and low cost requirements of mass production of new energy vehicles.

[0040] 4. The mold development efficiency is greatly improved. This solution does not require additional equipment and auxiliary material costs, significantly reduces the difficulty of mold debugging and the amount of manual work for fitters, and shortens the mold manufacturing cycle. At the same time, core technologies such as parting compensation, flow control, gradient hardness, and lubrication grooves can be extended to the forming and manufacturing of various aluminum alloy stamping parts, and have broad industry application value. Attached Figure Description

[0041] To more clearly illustrate the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a process flow diagram of the method for improving the surface quality of aluminum alloy automotive body panel cold stamping forming according to an embodiment of the present invention. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the core concept of the present invention and the following embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] These embodiments are provided to make the application thorough and complete, and to fully express the scope of the application to those skilled in the art. It should be noted that, unless otherwise specifically stated, the relative arrangement of components and steps, material composition, numerical expressions, and values ​​illustrated in these embodiments should be interpreted as merely exemplary and not as limiting.

[0045] A method for improving the surface quality of aluminum alloy automotive body panel outer sheet formed by cold stamping, wherein the aluminum alloy automotive body panel outer sheet is hereinafter referred to as the outer sheet, such as... Figure 1 As shown, it includes the following steps:

[0046] 1. The classification process mainly involves classifying and processing the process surfaces of the outer panel based on CAE analysis and forming experience. This processing method is primarily based on the part characteristics of the outer panel. During the process data establishment phase, after confirming the important directions, the classification process is carried out according to the product characteristics in the stamping direction, resulting in the following three processing methods:

[0047] 1) Normal treatment: The overall shape is relatively flat, and the outer plate shape around the lower drawbar is mostly a planar shape. The process compensation is carried out in the conventional way and the normal treatment is performed.

[0048] 2) Curvature Compensation: If the outer panel has many vertical surfaces or continuous areas exceeding 200mm in length, and the downward angle of the product's trend shape (ignoring small edges and bends, and considering the overall shape of an area) is greater than 30 degrees, curvature compensation is required for that area. There are two forms: First, if the outer panel's trend shape is arc-shaped, a reverse arc shape needs to be created downwards, with reverse stretching to compensate for the stress caused by forward forming. To save material, the curvature and length of the reverse arc should ideally be 30%–50% of the outer panel's area shape. Specific adjustments can be made based on the simulation results. Second, if the outer panel's trend shape is linear, the extension is directly based on the area's length. When the area's length is greater than 100mm, the base extension is 40mm, and for every 15-degree increase in angle above 30 degrees, the extension increases by 5mm. When the area's length is less than 100mm, the base extension is 30% of the trend shape's length, and for every 15-degree increase in angle above 30 degrees, the extension increases by 5mm.

[0049] 3) Floating molding: For areas with isolated high points or low points (such as the door handle area on the outer panel of a car door), it is necessary to perform floating molding of the abruptly changed island area. The method is to set the area as an insert and install an auxiliary pressure source below it to make it start molding first.

[0050] 2. Dynamic Flow Control: The purpose of dynamic flow control is to reduce localized stress concentration during the molding process, while simultaneously configuring differentiated flow control during the material flow and molding stages. This aims to achieve uniform material flow and smooth pressure distribution, reducing issues such as uneven stress, material viscosity, and poor material control during molding caused by fixed material flow, which can lead to distortion, surface damage, and warping / cracking. Its implementation modes are as follows:

[0051] 1) Adjustable dynamic flow control is used for large outer plates and outer plates with large curvature fluctuations. The simulation analysis of these outer plates shows large differences and the problems are relatively concentrated. Dynamic flow control needs to be verified. Adjustable flow control can significantly reduce the workload of subsequent technicians. The implementation mode is to make the drawbead into a movable insert and install a series of nitrogen cylinders under the insert, so that the drawbead area is in an independent adjustable state. At the same time, during the mold forming process, the flow stage and the forming stage have different pressures due to the different timing and pressure gradient of the upper die falling, so that the drawbead pressure is reduced in the early stage and increased in the later stage. The nitrogen cylinder pressure range of the drawbead should be selected as 1.5 times the normal drawbead required pressure to have sufficient adjustment margin.

[0052] 2) Fixed dynamic flow control: This is mainly for small outer panels or relatively simple outer panels. In this case, the drawbars can be made into movable inserts, and then elastic pads can be installed under the inserts to achieve fixed dynamic flow control. Note that for fixed dynamic flow control, the movable inserts of the drawbars should be arranged as symmetrically as possible to promote the balance of forces.

[0053] 3. Differential pressure; the key surfaces and areas prone to molding problems of the outer panel are directional. Quality control of the relevant areas should adopt priority protection measures to ensure overall quality. The following methods can be used to prioritize the protection of areas prone to molding problems and key surfaces.

[0054] 1) For facade areas prone to quality problems (simple boundaries can be defined by a trend shape greater than 30 degrees, with auxiliary simulation analysis as the basis for judgment), perform secondary strong coloring and strong pressure. The method is to make strong pressure bulges during the model surface processing. The range is the range extracted along the local surface edge. The strong pressure is reserved at 0.06-0.1mm, and the value is determined according to the angle and simulation analysis.

[0055] 2) For the critical ridge area, apply first-level strong coloring and strong pressure. The range is centered on the raised ridge and extends outward by 30-50mm. Since the ridge is a region prone to process wear, the amount of strong pressure needs to be increased. The strong pressure reserve is 0.08-0.15mm to form hard coloring in the critical area.

[0056] 3) The adjacent surfaces of the flange line are concentrated areas of surface quality, which need to be treated in a focused manner without affecting the smoothness of the overall surface. Therefore, a progressive strong pressing method is required. The method is to apply progressive strong coloring 120-150mm inward along the flange edge, with a 0.12mm reserve at the edge edge until it returns to zero at 120-150mm inward.

[0057] 4. Ultra-finishing: To reduce the impact of machining marks on surface quality and enhance the continuity and smoothness of the surface, an ultra-finishing process is performed on the forming area after the surface finishing is completed. This improves surface quality and eliminates the effect of tool deflection. The ultra-finishing parameters are set as follows:

[0058] 1) Ultra-precision machining is high-speed light cutting, requiring a rotational speed of 8000-12000 r / min and a feed rate of 6000-8000 mm / min to achieve the effect of high-speed light cutting.

[0059] 2) For ultra-precision machining with a step distance between 0.3 and 0.5 mm, the inclined axis machining method should be selected, and the combined forward and reverse milling should be used. The tool inclination angle should be 25-40 degrees.

[0060] 3) When performing multi-path ultra-precision machining on concave fillets on the surface, the concave fillets need to be enlarged by R0.5 for machining to ensure the smoothness of high-pressure shaping and fillet material flow.

[0061] 5. Lubrication and Dust Retention: To achieve smooth material flow and reduce the surface viscosity of aluminum alloy materials, while continuously eliminating the microscopic forming effects and adhesion caused by particle shedding from the sheet surface during continuous stamping, and reducing surface processing, a lubrication and dust retention method is adopted by using lubrication grooves in the draw bead area. The lubrication groove settings and oil spraying method are as follows:

[0062] 1) The lubrication groove is made by laser engraving or high-precision CNC scribing. The lubrication groove is set on both sides of the draw bead. Parallel double-line lubrication grooves are laser engraved at a position of 3mm on each side of the draw bead. The groove is 1mm wide, 0.2-0.4mm deep, and the double line spacing is 5mm. They are continuous and form a closed loop.

[0063] 2) Since the drawbead is a movable insert, in order to allow the lubrication groove to retain and microscopically apply lubricating oil while removing particles that fall off the surface of the aluminum alloy material, and to prevent the impact of easy peeling and scratches on the surface of the aluminum alloy material, it is necessary to make drainage lines at 50mm intervals towards the joint of the drawbead insert, and to make vertical lubrication grooves from the lubrication groove towards the joint of the drawbead insert, so as to drain excess lubricating oil and remove surface dust.

[0064] An oil spray nozzle is installed on the outside of the upper die draw bead, and oil is sprayed with oil with each stroke (consistent with the conventional mode, and will not be described in detail).

[0065] 6. Differential Hardness: Since the outer panel is a high-precision component, its forming is significantly affected by microscopic forces. When considering the forming process of each area, comprehensive control of hardness and corresponding friction helps improve the overall product quality of the component, achieving the goals of wear resistance, anti-adhesion, smooth material flow, and protection of critical surface forming. Experiments have shown that differential hardness has a positive impact on the surface quality of the outer panel. The implementation method is as follows:

[0066] 1) Main forming rounded corners and appearance edge areas: Implement high hardness and high smoothness to achieve the effect of high hardness and low friction. Laser quenching can be used to form high hardness, wear-resistant and non-stick edge lines, achieving high smoothness and non-sticking effect.

[0067] 2) For auxiliary edge areas and key forming surface areas, maintain medium hardness. Induction hardening or other hardening methods can be used to ensure accuracy and durability, while also creating a priority effect for key areas.

[0068] 3) For the draw beads and material feeding management area, the requirements should be low. The quenching hardness should be close to the lower limit of the production requirements but within the qualified range, in order to reduce frictional resistance, ensure the order of micro-deformation material feeding, and avoid adhesion and material flow jamming.

[0069] 7. Process Restructuring: The inherent difficulty in controlling the deformation of aluminum alloy materials leads to challenges in controlling the stress release during secondary forming, especially when large-scale stress release occurs during trimming. Because the effect of trimming stress on the already shaped surface is diminished, process adjustments and restructuring are necessary to ensure surface accuracy and product dimensional accuracy, reducing the impact of trimming deformation, surface collapse, and edge misalignment. The main operational differences are as follows:

[0070] 1) For areas that require trimming to create gaps or secondary forming, perform a secondary trimming operation. Leave an initial trimming allowance of 20-40mm (which can be determined based on simulation analysis of springback). Then perform a shaping and setting operation. After the shaping operation is completed, perform a secondary trimming and setting operation to maintain surface quality and change the original trimming-then-setting mode.

[0071] 2) For areas that will not be affected by subsequent processes, the process can be reversed directly, and the shaping and trimming methods can be adopted. The shaping operation is performed first, and the trimming is performed after the shape is finalized.

[0072] 3) Consider whether there are abrupt changes in curvature of the surface shape. If there are abrupt changes, the secondary trimming mode should be used first.

[0073] All aspects not detailed in this invention are conventional technical means known to those skilled in the art.

[0074] The above content shows and describes the basic principles, main features, and beneficial effects of the present invention. The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for improving the surface quality of aluminum alloy automotive body panels during cold stamping, characterized in that, Includes the following steps: S1 parting compensation treatment: Based on the product characteristics in the stamping direction, the process surface of the aluminum alloy automotive body panel is classified and a differentiated CAE process compensation treatment is adopted accordingly. S2 Dynamic Flow Control: It adopts a movable drawbead structure, and dynamically adjusts the blanking resistance of the drawbead according to different stages of stamping to achieve balanced material flow in the forming process. S3 Difference Hardness Treatment for Molds: Based on the molding function requirements of different areas of the mold, the hardness of different areas of the mold surface is adjusted differently. S4 surface ultra-precision machining: high-speed, light-cut ultra-precision machining of the mold forming area surface; S5 Differential High-Pressure Shaping: Graded and differentiated high-pressure treatment is carried out for areas and key appearance surfaces of the outer panel that are prone to forming defects. S6 Structured Lubrication and Dust Retention Treatment: A closed-loop lubrication groove structure is set in the die surface area corresponding to the draw bead, which is used in conjunction with the stamping process for lubrication and dust removal. S7 Molding Process Restructuring: Based on the molding requirements of different areas of the outer panel, the order of trimming and shaping processes is adjusted, and a process mode of shaping first and then trimming or secondary trimming is adopted.

2. The method for improving the surface quality of aluminum alloy automotive body panels by cold stamping as described in claim 1, characterized in that, In the type-splitting compensation process of step S1, the process surface is divided into three categories and corresponding differentiated compensation is applied, specifically as follows: For areas with a gentle overall shape and a planar perimeter around the drawbeads, conventional compensation processes are used. For facade areas with a continuous length ≥200mm and an overall downward angle ≥30°, curvature compensation is applied. For feature areas with isolated high points or depressions, floating molding with movable inserts is used.

3. The method for improving the surface quality of aluminum alloy automotive body panels by cold stamping according to claim 1 or 2, characterized in that, The dynamic flow control processing in step S2 adopts either of the following two modes, depending on the size and structural complexity of the outer panel: Adjustable dynamic flow control mode: The draw bead is made into a movable insert, and a series of nitrogen cylinders are set below the insert. The pressure of the nitrogen cylinders is controlled to achieve differential adjustment of the pressing resistance between the stamping flow stage and the forming stage. Fixed dynamic flow control mode: The draw beads are made into symmetrically arranged movable inserts, and elastic pads are set under the inserts. By changing the compression of the elastic pads, the pressure resistance of the material at different stages of stamping can be dynamically adjusted.

4. The method for improving the surface quality of aluminum alloy automotive body panels by cold stamping as described in claim 3, characterized in that, In step S3, the mold differential hardness processing involves dividing the mold surface into three regions and adjusting their corresponding differential hardness, specifically as follows: High-hardness quenching treatment is applied to the main forming fillet and appearance edge areas. For auxiliary edges and key forming surfaces, medium-hardness quenching treatment is performed; For the drawbead and feed management area, a low-hardness quenching treatment is performed, wherein the low hardness is the lower limit hardness that meets the forming requirements.

5. The method for improving the surface quality of aluminum alloy automotive body panel cold stamping as described in any one of claims 1, 2, and 4, characterized in that, The ultra-precision machining in step S4 is a high-speed light cutting machining process. The machining parameters are: spindle speed 8000-12000 r / min, feed rate 6000-8000 mm / min, machining step distance 0.3-0.5 mm, and a combination of inclined axis forward and reverse milling method is adopted. The tool inclination angle is 25°-40°.

6. The method for improving the surface quality of aluminum alloy automotive body panels by cold stamping according to any one of claims 5, characterized in that, The differential pressure shaping in step S5 is divided into three levels of pressure treatment, specifically: For facade areas with a downward angle ≥30°, a two-stage high-pressure treatment is adopted, with a high-pressure allowance of 0.06-0.1mm; For critical appearance edge areas, a first-level high-pressure treatment is applied, with the high-pressure range extending outward from the edge 30-50mm, and the high-pressure allowance being 0.08-0.15mm. For the adjacent surface area of ​​the flange line, a progressive strong pressure treatment is adopted. A progressive strong pressure structure is set in the range of 120-150mm inward along the flange edge line. The strong pressure allowance decreases linearly from 0.12mm at the flange edge line to 0 inward.

7. The method for improving the surface quality of aluminum alloy automotive body panels by cold stamping according to any one of claims 1, 2, 4, and 6, characterized in that, In the structured lubrication and dust retention treatment of step S6, the closed-loop lubrication groove structure includes a double-line main lubrication groove arranged parallel to both sides of the drawbeam, and a guide line arranged perpendicular to the main lubrication groove at intervals; the main lubrication groove is continuously connected along the extension direction of the drawbeam to form a closed loop, with a groove width of 1mm and a groove depth of 0.2-0.4mm, the distance between the two main lubrication grooves is 5mm, and the distance between each groove and the side of the drawbeam is 3mm; the guide line is spaced 50mm apart, and its end extends to the joint of the movable insert of the drawbeam.

8. The method for improving the surface quality of aluminum alloy automotive body panels by cold stamping as described in claim 7, characterized in that, In the reconstructed molding process of step S7, the specific process mode is as follows: For areas requiring secondary forming, a secondary trimming mode is adopted. The initial trimming leaves a margin of 20-40mm. After the shaping and setting process is completed, a secondary trimming is performed to the design size. For areas without secondary forming interference, a shaping-then-trimming approach is adopted, where the surface shaping and setting process is completed first, followed by the trimming process. For surface regions with abrupt changes in curvature, a secondary trimming mode is preferred.

9. The method for improving the surface quality of aluminum alloy automotive body panels by cold stamping according to claim 2, characterized in that, The curvature compensation process is divided into two forms: When the overall trend shape of the facade area is arc-shaped, a reverse arc compensation is used. The curvature and length of the reverse arc are 30%-50% of the curvature and length of the corresponding facade area arc. When the overall trend shape of the facade area is linear, extension compensation is adopted. When the area length is ≥100mm, the extension base is 40mm, and the extension amount increases by 5mm for every 15° increase in angle. When the area length is <100mm, the extension base is 30% of the area length, and the extension amount increases by 5mm for every 15° increase in angle.

10. The method for improving the surface quality of aluminum alloy automotive body panels by cold stamping according to claim 3, characterized in that, In the adjustable dynamic flow control mode, the rated pressure of the nitrogen cylinder group is 1.5 times the clamping force required for conventional fixed drawbeams.

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