Automobile aluminum alloy stamping device and method

Abstract

The application discloses a kind of automobile aluminum alloy stamping method and device, belong to metal stamping forming technical field.For the problems of wrinkling, cracking, uneven springback and high interface edge tearing rate when stamping complex parts such as aluminum alloy battery pack tray in prior art, the method provided by the application comprises: blanking and surface pretreatment of blank; Zoning coating differential lubricating medium; Using zoning variable blank holder force and progressive constraint forming drawing process, the blank holder force of each sub-zone changes with stroke gradient, and the gap between the convex and concave dies in the stiffener dense area is locally increased; Using stress release type step trimming, the process connection band is retained and cut off after local shaping; Local shaping combined with pre-compensation database for dynamic reverse compensation; Size detection data is used for iterative updating of process model.The device includes a convex die assembly and a flexible transition forming block driven independently in zones.The application can significantly inhibit cracking, reduce springback difference and improve part size consistency.

Description

Technical Field

[0001] This invention relates to the field of metal processing, and more particularly to an automotive aluminum alloy stamping apparatus and method. Background Technology

[0002] With the rapid development of lightweight technology in new energy vehicles, aluminum alloys, due to their low density, high specific strength, corrosion resistance, and easy recyclability, have gradually replaced traditional high-strength steel as the mainstream material for core components such as automotive battery pack trays and body panels. Currently, the stamping process for these parts typically employs a linear process chain: "blank blanking and surface pretreatment → lubrication coating and robotic arm positioning and loading → drawing → trimming and punching → flanging, rolling, and local shaping → deburring, cleaning, and dimensional inspection feedback." The supporting equipment is mostly traditional mechanical or hydraulic presses combined with fixed-structure molds. Process control generally relies on finite element simulation software for global springback prediction and equal-volume surface compensation. Uniformly distributed blank holder force, standard punch-die clearance, and single-material mold surface configuration are used. Through multiple rounds of empirical mold trials and manual grinding and mold repair, the part's target dimensions are gradually approximated to meet the assembly tolerances and strength requirements of the entire vehicle.

[0003] However, complex aluminum components such as battery pack trays possess spatial topological characteristics of "large planar deep cavity + four-sided sidewalls + dense multi-directional reinforcing ribs." Combined with the intrinsic material properties of aluminum alloys—low elastic modulus, limited hardening index, and significant rolling anisotropy—existing linear processes and rigid die systems face systemic limitations: First, uniformly distributed blank holder forces and fixed die boundaries cannot adapt to the drastically different strain paths and constraint gradients of the base plate, sidewalls, and reinforcing rib areas. Multi-directional coupled stresses easily induce wrinkling in high-constraint areas and thinning and cracking in low-constraint areas during synchronous forming. Second, modified models based on global equal compensation struggle to match the nonlinear springback differences between curvature abrupt change regions and stiffness jump regions, requiring orthogonal or... The superposition of reverse recovery vectors can lead to springback differences of 3-6 times between different parts of the same component, severely weakening assembly accuracy and sealing reliability. Secondly, traditional stamping equipment lacks online morphology monitoring and dynamic parameter closed-loop compensation capabilities between workstations. The minute springback after unloading is directly accumulated and transferred to the next workstation, causing additional shear stress distortion. Finally, the dense distribution of reinforcing ribs on the base plate, with their extension direction coinciding with the junction of the base plate and sidewall, causes a sudden increase in material flow resistance during one-time deep drawing and simultaneous trimming, resulting in severe stress flow interruption and redistribution. The high concentration of local strain easily induces junction tearing and secondary deformation, restricting the high-quality and stable mass production of complex aluminum structural parts.

[0004] Based on this, an automotive aluminum alloy stamping device and method are proposed. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, the present invention provides an automotive aluminum alloy stamping apparatus and method.

[0006] A method for stamping automotive aluminum alloys includes the following steps: S1: Blanking and surface pretreatment of aluminum alloy sheets by laser blanking or servo shearing, followed by plasma cleaning and surface roughness homogenization. S2: Lubrication coating and robotic arm positioning and feeding. Different lubricating media are applied to the subsequent forming areas, and the blank is introduced into the stamping station by positioning the robotic arm at preset coordinates. S3: Drawing forming employs a zoned variable blank holder force and progressive constraint forming process. The zoned variable blank holder force refers to dividing the punch assembly into multiple independent sub-regions corresponding to the blank base plate area, sidewall area, and reinforcing rib area. Each sub-region is subjected to a gradient blank holder force, either from high to low or from low to high, at different stages of drawing. The progressive constraint forming process involves: in the initial stage of drawing, setting the blank holder force in the base plate area to a higher value to suppress premature material flow, setting the blank holder force in the sidewall area to a medium value, and setting the blank holder force in the reinforcing rib area to a lower value to promote rib filling; in the middle stage of drawing, gradually reducing the blank holder force in the base plate area and increasing the blank holder force in the sidewall area based on the amount of plastic deformation that has occurred in each region, allowing material to be replenished to the sidewalls in an orderly manner; in the final stage of drawing, homogenizing the blank holder force in each sub-region to stabilize the final shape; simultaneously, dynamically adjusting the local clearance of the punch and die during the drawing process, increasing the local clearance by 10%-20% in areas with dense reinforcing ribs to reduce flow resistance, and using a standard clearance in the flat area of ​​the base plate to ensure flatness. S4: Trimming and punching. A stress-relieving step-by-step trimming and pre-compensation punching strategy is adopted. The material is cut off in sections along the stiffness transition boundary of the part in order to release the residual stress accumulated before unloading. S5: Flanging, curling and local shaping, combined with the topography prediction database, to perform dynamic reverse compensation for the springback vector that has occurred, and to redistribute local stress and fit the surface through flexible medium or variable mold surface. The specific method of dynamic reverse compensation is as follows: the part is divided into multiple feature blocks, each block is preset with a reverse springback compensation amount based on finite element iteration calculation, and in the local shaping step, non-uniform correction load is applied to each block through servo-driven segmented pressure head or deformable pad, so that each area reaches the target surface simultaneously after unloading. S6: Deburring, cleaning, and dimensional inspection. The final three-dimensional morphology data is mapped and archived with the process parameters of the entire process, which is used to iteratively update the global-local coupling compensation model for the next batch of stamping.

[0007] As a further aspect of the present invention, in the S3 drawing process, for the area where the reinforcing ribs are distributed on the base plate and extend to the junction of the base plate and the side wall, a gradient strain control strategy of first the base plate and then the side wall is adopted: by setting a pre-forming step or a flexible transition punch, the flow rate of the material at the junction towards the side wall is slowed down, so that the plastic deformation of the root of the reinforcing rib and the junction area is changed from synchronous and severe stretching to gradual extension, avoiding local strain concentration and tearing caused by one-time deep drawing.

[0008] As a further aspect of the present invention, the differentiated lubricating medium coating in S2 specifically involves: applying a high-friction coefficient damping coating to the area corresponding to the junction of the blank base plate and the sidewall, while applying a low-friction lubricant to the base plate reinforcing rib forming area; in the early stage of drawing in S3, the high frictional resistance of the junction area is used to inhibit the premature flow of material into the sidewall, and the low-friction environment of the reinforcing rib area promotes the full forming of the ribs; in the middle and late stages of drawing, the frictional resistance of the junction is gradually reduced to achieve a smooth transfer of stress path, thereby fundamentally suppressing the junction tearing caused by one-time forming.

[0009] As a further aspect of the present invention, in the middle and later stages of the S3 drawing process, the punch assembly is equipped with an independently controllable micro-partition hydraulic cylinder in the projection area of ​​the junction between the base plate and the side wall. The micro-partition is subjected to a stepped pressure reduction and stress relief operation to form a slow-release channel for material to flow into the side wall. At the same time, in conjunction with the stress dispersion structure at the rounded corner of the punch junction, the equivalent plastic strain gradient of the transition zone between the base plate and the side wall changes continuously, eliminating the stress peaks formed by the abrupt change in rigid constraints at the junction during the one-time forming process, and preventing tearing defects.

[0010] As a further aspect of the present invention, the step-by-step trimming strategy in S4 is as follows: first, perform main trimming along the contour of the non-load-bearing area and the low stiffness area, retaining the process connection strip at the junction of the bottom plate and the side wall and the root of the reinforcing rib; after the local shaping is completed in S5 and the residual stress is fully released, perform secondary fine trimming and micro-stress release cuts on the process connection strip to completely cut off the secondary deformation and edge warping caused by the original continuous stress chain.

[0011] As a further embodiment of the present invention, a morphology transfer and pre-compensation link is added between S3 and S5, which superimposes the morphology deviation after unloading at the previous station onto the mold surface or loading path of the next station in a pre-deformation manner, thereby achieving station-by-station offsetting of unloading springback and precise fitting of the curvature jump zone.

[0012] As a further aspect of the present invention, the dimensional detection data in S6 updates the partitioned variable pressure edge force mapping table and the local compensation surface database through a statistical process control method, establishes a nonlinear correlation model between material batch differences, lubrication state fluctuations and springback response, and realizes adaptive iteration of process parameters for parts in the same batch and dynamic convergence of process windows across batches.

[0013] An automotive aluminum alloy stamping apparatus, applicable to an automotive aluminum alloy stamping method, includes: a frame and a main press body; a lower die holder and a die assembly disposed on the main press worktable; an upper die holder and a punch assembly cooperating with the die assembly, the punch assembly adopting a partitioned independent drive structure, including multiple micro-partitioned hydraulic servo cylinders distributed along the contour of the sheet metal; a flexible transition forming block embedded in the lower die holder or the upper die holder; the apparatus further includes a shape transfer fixture and a central control unit disposed between adjacent stamping stations, the central control unit being electrically connected to the micro-partitioned hydraulic servo cylinders.

[0014] As a further embodiment of the present invention, the flexible transition forming block is specifically a variable stiffness composite module disposed in the region corresponding to the junction of the bottom plate and the side wall of the die assembly. Its inner layer is a high stiffness alloy support skeleton, and its outer layer is a high damping elastomer or shape memory alloy coating layer. It provides rigid positioning constraints in the early stage of drawing, and achieves strain gradient smoothing through the elastic yielding of the outer layer during the peak period of material flow at the junction edge. In conjunction with the partitioned unloading command of the central control unit, it effectively suppresses the tearing of the junction edge caused by one-time forming.

[0015] As a further aspect of the present invention, it also includes a stress-relieving trimming module integrated into the trimming station, which includes multiple sets of independent servo-driven scrap cutters and laser fine trimming heads that are opened and closed sequentially along the contour of the part; the central control unit controls the multiple sets of independent servo-driven scrap cutters to operate in a preset step sequence according to a pre-stored local residual stress distribution map, so as to realize the sequential cutting of the process connection zone and the smooth decoupling of the stress chain.

[0016] The beneficial effects of this invention are: By employing zoned variable blank holder force and progressive constraint forming in S3, the base plate, sidewalls, and reinforcing rib areas deform according to their optimal strain paths, avoiding wrinkling in high-constraint areas and thinning and cracking in low-constraint areas caused by traditional uniform blank holder force. Through step-by-step trimming and retaining connecting strips in S4, residual stress is gradually released during the local shaping stage, avoiding secondary deformation caused by stress abrupt changes after traditional one-time trimming. Dynamic reverse compensation in S5 solves the problem of global equal-quantity compensation failing to match the nonlinear springback differences in curvature and stiffness transition zones, reducing springback differences between different parts and improving assembly accuracy and sealing reliability. Data closed-loop iteration in S6 improves the quality consistency of parts within the same batch and reduces cross-batch debugging time. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the 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.

[0018] Figure 1 This is a flowchart of the steps of the present invention; Figure 2 This is a bottom view structural diagram of the concave die assembly and the convex die assembly of the present invention; Figure 3 This is a top view of the die assembly and punch assembly of the present invention. Explanation of reference numerals in the attached drawings: 1. Upper mold base; 2. Lower mold base; 31. Side wall area; 32. Base plate area; 33. Reinforcing rib area; 4. Die assembly. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Please see Figures 1-3 The present invention provides a method for stamping automotive aluminum alloys, comprising the following steps: S1: Blanking and surface pretreatment of aluminum alloy sheets by laser blanking or servo shearing, followed by plasma cleaning and surface roughness homogenization. S2: Lubrication coating and robotic arm positioning and feeding. Different lubricating media are applied to the subsequent forming areas, and the blank is introduced into the stamping station by positioning the robotic arm at preset coordinates. S3: Drawing forming, employing a zoned variable blank holder force and progressive constraint forming process. The zoned variable blank holder force refers to dividing the punch assembly into multiple independent sub-regions corresponding to the blank base plate area 32, sidewall area 31, and reinforcing rib area 33. Each sub-region is subjected to a gradient blank holder force, either from high to low or from low to high, at different stages of drawing. The progressive constraint forming process refers to: in the initial stage of drawing, the blank holder force in the base plate area 32 is set to a higher value to suppress premature material flow; the blank holder force in the sidewall area 31 is set to an intermediate value; and the blank holder force in the reinforcing rib area 33 is set to a lower value. 3. The blank holder force is set to a low value to promote the filling of the ribs; during the middle stage of drawing, the blank holder force in the bottom plate area 32 is gradually reduced and the blank holder force in the side wall area 31 is increased according to the amount of plastic deformation that has occurred in each area, so that the material is replenished to the side wall in an orderly manner; at the end of drawing, the blank holder force in each sub-area is homogenized to stabilize the final shape; at the same time, the local gap between the punch and die is dynamically adjusted during the drawing process. For areas with dense reinforcing ribs, the local gap is increased by 10%-20% to reduce flow resistance, and a standard gap is used for the flat area of ​​the bottom plate to ensure flatness. S4: Trimming and punching. A stress-relieving step-by-step trimming and pre-compensation punching strategy is adopted. The material is cut off in sections along the stiffness transition boundary of the part in order to release the residual stress accumulated before unloading. Along the boundary of the part's stiffness transition, a large cutting block is first used to remove a large area of ​​scrap material with minimal impact on the part's stiffness, while retaining the process connection bands near the sidewalls and the roots of the reinforcing ribs. These connection bands can serve as temporary constraints in subsequent local shaping stages, while allowing residual stress to be partially released through elastic deformation. During punching, small reverse compensation features are pre-set around the hole to counteract dimensional deviations caused by springback at the hole edge after unloading.

[0021] S5: Flanging, curling and local shaping, combined with the topography prediction database, to perform dynamic reverse compensation for the springback vector that has occurred, and to redistribute local stress and fit the surface through flexible medium or variable mold surface. The specific method of dynamic reverse compensation is as follows: the part is divided into multiple feature blocks, each block is preset with a reverse springback compensation amount based on finite element iteration calculation, and in the local shaping step, non-uniform correction load is applied to each block through servo-driven segmented pressure head or deformable pad, so that each area reaches the target surface simultaneously after unloading. This step does not rely on online topography scanning, but rather on a pre-established "topography prediction database"—this database obtains the springback vector field of different feature blocks of the part through finite element iterative calculations, such as the center area of ​​the base plate, the corner areas of the side walls, and the intersection areas of the reinforcing ribs. Local shaping employs a multi-axis servo indenter array, with each indenter independently controlling its stroke and pressure, or deformable polyurethane pads, using internal air pressure or mechanical push rods to change the local support stiffness. During shaping, non-uniform correction loads are applied according to the preset reverse compensation amount for each block: for example, an additional 0.5-1.0mm bend is applied at the side wall openings with large springback, and uniform leveling pressure is applied to the flat area of ​​the base plate. After unloading, each area simultaneously springs back to the target surface.

[0022] S6: Deburring, cleaning, and dimensional inspection. The final three-dimensional morphology data is mapped and archived with the process parameters of the entire process, which is used to iteratively update the global-local coupling compensation model for the next batch of stamping.

[0023] Deburring is performed using vibration or tumbling, followed by high-pressure spray cleaning. The final part is placed on a coordinate measuring machine or optical measuring table to acquire 3D topographic data. This data is compared with the target surface after S5 shaping to determine the actual deviation in each area. All deviation data and corresponding full-process parameters (clamping force sequence for each sub-area, local clearance adjustment value, lubrication medium batch, etc.) are mapped and archived for iterative updates to the global-local coupling compensation model during the next batch of stamping.

[0024] By employing zoned variable pressure force and progressive constraint forming in S3, the base plate, sidewalls, and reinforcing rib area 33 deform according to their optimal strain paths, avoiding wrinkling in high-constraint areas and thinning and cracking in low-constraint areas caused by traditional uniformly distributed pressure force. Through step-by-step trimming and retaining connecting strips in S4, residual stress is gradually released during the local shaping stage, avoiding secondary deformation caused by stress abrupt changes after traditional one-time trimming. Dynamic reverse compensation in S5 solves the problem of global equal-quantity compensation failing to match the nonlinear springback differences in curvature and stiffness transition zones, reducing springback differences between different parts and improving assembly accuracy and sealing reliability. Data closed-loop iteration in S6 improves the quality consistency of parts within the same batch and reduces cross-batch debugging time.

[0025] As a further aspect of the present invention, in the S3 drawing process, for the area where the reinforcing ribs are distributed on the base plate and extend to the junction of the base plate and the side wall, a gradient strain control strategy of first the base plate and then the side wall is adopted: by setting a pre-forming step or a flexible transition punch, the flow rate of the material at the junction towards the side wall is slowed down, so that the plastic deformation of the root of the reinforcing rib and the junction area is changed from synchronous and severe stretching to gradual extension, avoiding local strain concentration and tearing caused by one-time deep drawing.

[0026] A pre-forming step is provided in the base plate region 32 of the punch, or a flexible transition punch layer (such as a polyurethane elastic layer, 1-3 mm thick) is covered on the punch surface. In the initial stage of drawing, the punch first contacts the base plate region 32, forcing the base plate material to deform first. The material at the interface edge is temporarily not forcibly pulled towards the sidewall due to the buffering effect of the pre-forming step or the flexible layer. After most of the plastic deformation in the base plate region 32 is completed, the flexible transition layer is compressed to its limit or the pre-forming step is crossed, and the punch sidewall begins to contact and pull the material into the sidewall cavity. In this way, the material flow path at the root of the reinforcing rib and the interface edge region changes from synchronous and intense stretching to a gradual process of first extending from the base plate and then flowing into the sidewall. By delaying the flow rate of the material from the interface edge to the sidewall, the peak value of the equivalent plastic strain is reduced, and the strain gradient changes continuously, avoiding the formation of stress spikes.

[0027] As a further aspect of the present invention, the differentiated lubricating medium coating in S2 specifically involves: applying a high friction coefficient damping coating to the area corresponding to the junction of the blank base plate and the sidewall, while applying a low friction lubricant to the base plate reinforcing rib forming area; in the early stage of drawing in S3, the high friction resistance of the junction area is used to suppress the premature flow of material into the sidewall, and the low friction environment of the reinforcing rib area 33 promotes the full forming of the ribs; in the middle and late stages of drawing, the friction resistance of the junction is gradually reduced to achieve a smooth transfer of stress path, thereby fundamentally suppressing the junction tearing caused by one-time forming.

[0028] A dual-nozzle spraying system is used to apply a high-friction-coefficient damping coating to the area corresponding to the junction of the base plate and sidewall of the blank. This coating consists of an epoxy resin matrix incorporating alumina particles, with a dry film friction coefficient μ=0.25-0.30. A low-friction lubricant, such as molybdenum disulfide or graphene-modified grease, with a friction coefficient μ=0.05-0.08, is applied to the reinforcing rib forming area of ​​the base plate. In the early stage of drawing, the high frictional resistance at the junction effectively inhibits premature material flow into the sidewall, allowing the blank holder force to be concentrated on the reinforcing rib area 33, promoting the full forming of the rib. In the middle stage of drawing, when the stroke reaches 40%-60%, as the temperature and pressure increase, the high-friction coating gradually partially fails or breaks due to local micro-vibration of the punch assembly, and the friction coefficient drops to about 0.15, at which point the material begins to flow smoothly into the sidewall. In the later stage of drawing, the coating is basically ineffective, and the material flows freely to complete the final forming. The entire process requires no sensors, and the smooth transfer of stress path is achieved solely through the thermo-mechanical response characteristics of the coating material itself. By utilizing the time-temperature-pressure sensitive characteristics of the chemical coating, a dynamic variable friction function is achieved, avoiding the tearing of the interface caused by constant friction conditions in a single application.

[0029] As a further aspect of the present invention, in the middle and later stages of the S3 drawing process, the punch assembly is equipped with an independently controllable micro-partition hydraulic cylinder in the projection area of ​​the junction between the base plate and the side wall. The micro-partition is subjected to a stepped pressure reduction and stress relief operation to form a slow-release channel for material to flow into the side wall. At the same time, in conjunction with the stress dispersion structure at the rounded corner of the punch junction, the equivalent plastic strain gradient of the transition zone between the base plate and the side wall changes continuously, eliminating the stress peaks formed by the abrupt change in rigid constraints at the junction during the one-time forming process, and preventing tearing defects.

[0030] In the later stages of S3 drawing, micro-regional hydraulic cylinder control is introduced for the projection area of ​​the base plate-sidewall junction. Specifically, the punch assembly has a row of independent small-diameter hydraulic cylinders below this junction, each with individually adjustable pressure. Initially, the pressure of these micro-regional hydraulic cylinders is set the same as in the base plate area 32. When the drawing stroke reaches 50%-60%, the central control unit issues a command to gradually reduce the pressure of these micro-regional hydraulic cylinders in 3-5 steps, with each step reducing the pressure by 2-4 MPa and each step spaced 2-3 seconds apart, ultimately reducing it to 3-5 MPa. Simultaneously, the punch is designed with a stress-dispersing structure at the junction radius—for example, increasing the radius from the conventional 5mm to 8-10mm—to make the contact stress distribution at the junction more uniform. Together, these two elements form a slow-release channel for material to flow into the sidewall, changing the equivalent plastic strain gradient from a steep type to a gentle slope.

[0031] As a further aspect of the present invention, the step-by-step trimming strategy in S4 is as follows: first, perform main trimming along the contour of the non-load-bearing area and the low stiffness area, retaining the process connection strip at the junction of the bottom plate and the side wall and the root of the reinforcing rib; after the local shaping is completed in S5 and the residual stress is fully released, perform secondary fine trimming and micro-stress release cuts on the process connection strip to completely cut off the secondary deformation and edge warping caused by the original continuous stress chain.

[0032] Step 1 (Main Trimming): A large trimming die is used to remove burrs along the outer contour of the part. However, for high residual stress areas such as the junction of the base plate and side wall, and the root of the reinforcing rib, the die cutting edge is designed with a notch or segmented movable inserts are used to retain the waste material in these areas, forming a process connection strip with a width of 5-10mm and a spacing of 20-30mm. Step 2 (Secondary Fine Trimming after Local Shaping): After the S5 local shaping is completed, the part is removed from the die and undergoes natural aging or low-temperature tempering to fully release residual stress, the part is placed in the fine trimming die. The fine trimming die uses laser cutting or precision punching to cut along the center line of the process connection strip, and then cuts a U-shaped or V-shaped micro-cut at the pre-designed stress release notch at the end of the connection strip, so that the elastic strain is not suddenly released after the connection strip is cut. This avoids the problem of the part immediately warping or springback sudden change caused by the overall severing of the stress chain after traditional primary trimming. The process connection strip acts as a "temporary skeleton" in the local shaping stage, maintaining the spatial rigidity of the part.

[0033] As a further embodiment of the present invention, a morphology transfer and pre-compensation link is added between S3 and S5, which superimposes the morphology deviation after unloading at the previous station onto the mold surface or loading path of the next station in a pre-deformation manner, thereby achieving station-by-station offsetting of unloading springback and precise fitting of the curvature jump zone.

[0034] After the drawing station and before the partial forming station, a transfer fixture is set up. This fixture has a reverse support surface that is completely opposite to the theoretical shape of the part. After the drawn part is removed from the punch, it is first placed on this transfer fixture, and then manually or by a robot, it is pressed to conform to the reverse support surface. At this time, the springback deformation that occurred in the part before is forced to flatten or bend in the reverse. Then, the forming die surface of the next station is not designed according to the final theoretical shape of the part, but is processed according to the theoretical shape minus the reverse pre-deformation amount. When the part enters the forming die, it is constrained by the reverse of the die surface, and the springback after unloading just cancels out the previous residual deformation, achieving the theoretical size.

[0035] As a further aspect of the present invention, the dimensional detection data in S6 updates the partitioned variable pressure edge force mapping table and the local compensation surface database through a statistical process control method, establishes a nonlinear correlation model between material batch differences, lubrication state fluctuations and springback response, and realizes adaptive iteration of process parameters for parts in the same batch and dynamic convergence of process windows across batches.

[0036] After S6 dimensional inspection, a nonlinear correlation model between process parameters and springback response is established using statistical process control methods. Specific steps include: collecting final dimensional data from at least 30 batches (100 pieces per batch), along with corresponding process parameters for each batch, including the blank holder force settings for each sub-zone, lubricant batch number, sheet metal batch number, and local clearance adjustment values. For each part, the statistical distribution of its characteristic points, such as the center warpage of the base plate, the sidewall opening, and the height deviation of the top of the reinforcing ribs, is calculated. The model is trained using stepwise regression or an artificial neural network. This model is then embedded into the central control unit. When a new batch of sheet metal arrives, a small-scale trial punch is performed on this batch. After measuring the deviation, the data is input into the model, which automatically outputs an optimized zoned variable blank holder force mapping table and a local compensation surface database. These adjusted parameters are used for the formal production of this batch, and the model is continuously updated during production by sampling every 100 pieces.

[0037] An automotive aluminum alloy stamping apparatus, applicable to an automotive aluminum alloy stamping method, includes: a frame and a main press body; a lower die holder 2 and a die assembly disposed on the main press worktable; an upper die holder 1 and a punch assembly cooperating with the die assembly, the punch assembly adopting a partitioned independent drive structure, including multiple micro-partitioned hydraulic servo cylinders distributed along the contour of the sheet metal; a flexible transition forming block is embedded in the lower die holder 2 or the upper die holder 1; the apparatus further includes a shape transfer fixture and a central control unit disposed between adjacent stamping stations, the central control unit being electrically connected to the micro-partitioned hydraulic servo cylinders.

[0038] The machine frame and main press body: a four-column hydraulic press or a mechanical servo press is used; Lower die base 2 and die assembly: the lower die base 2 is fixed on the press worktable, and the punch is installed on the lower die base 2, with the punch surface matching the inner surface of the part. A cooling channel (circulating water) can be set inside the punch to control the forming temperature. Upper die base 1 and punch assembly: the punch assembly is a segmented and separate structure, divided into multiple independent sub-areas along the sheet metal contour. Each sub-area corresponds to one or more micro-segment hydraulic servo cylinders, and each hydraulic cylinder has a built-in displacement sensor and pressure gauge. The central control unit sends switching or analog commands to the servo valves of each hydraulic servo cylinder according to a preset timing sequence to realize open-loop or feedforward control of the blank holder force. Flexible transition forming block: set in the area corresponding to the junction of the punch base plate and the side wall. Shape transfer fixture: set between adjacent stamping stations, it is a bracket with a specific reverse curved surface. Central control unit: a PLC or industrial computer is used, electrically connected to the above-mentioned actuators. By combining independently driven punch components and flexible transition forming blocks, mechanical active control of stress and strain during the stamping process of complex aluminum alloy parts is achieved, which can significantly suppress defects such as wrinkling, cracking, uneven springback and tearing at the interface without relying on online sensors.

[0039] As a further embodiment of the present invention, the flexible transition forming block is specifically a variable stiffness composite module disposed in the region corresponding to the junction of the bottom plate and the side wall of the die assembly. Its inner layer is a high stiffness alloy support skeleton, and its outer layer is a high damping elastomer or shape memory alloy coating layer. It provides rigid positioning constraints in the early stage of drawing, and achieves strain gradient smoothing through the elastic yielding of the outer layer during the peak period of material flow at the junction edge. In conjunction with the partitioned unloading command of the central control unit, it effectively suppresses the tearing of the junction edge caused by one-time forming.

[0040] Its structure is as follows: the inner layer is made of a high-stiffness alloy to form a supporting skeleton, and the outer surface of the skeleton is covered with a layer of high-damping elastomer or shape memory alloy. This module is installed at the corresponding position of the junction between the punch base plate and the side wall, and its width is 5-10mm wider on each side than the theoretical position of the junction. In the early stage of drawing, due to the low forming temperature, the shape memory alloy is in the martensitic state or the polyurethane is in the high modulus state. This module provides rigid positioning constraints comparable to ordinary steel dies. When the drawing process reaches the middle and late stages, the sheet metal and the module generate heat through friction, or the local temperature rises above the phase transformation point through heating inside the punch. The shape memory alloy transforms into the austenitic state and produces superelasticity, or the polyurethane softens due to the temperature rise. The yielding capacity of the outer layer of the module is significantly enhanced, allowing the material near the junction to produce a small displacement outward. At this time, the central control unit simultaneously issues a micro-zone unloading command for the punch assembly. The two work together to form a soft constraint + low pressure edge condition, allowing the material to flow smoothly into the side wall. Through variable stiffness composite materials, rigid positioning is provided in the early stage of drawing to ensure shape accuracy, and flexible yielding is provided during the peak flow period to reduce the risk of tearing.

[0041] As a further aspect of the present invention, it also includes a stress-relieving trimming module integrated into the trimming station, which includes multiple sets of independent servo-driven scrap cutters and laser fine trimming heads that are opened and closed sequentially along the contour of the part; the central control unit controls the multiple sets of independent servo-driven scrap cutters to operate in a preset step sequence according to a pre-stored local residual stress distribution map, so as to realize the sequential cutting of the process connection zone and the smooth decoupling of the stress chain.

[0042] The stress-relieving trimming module includes 8-16 sets of independently servo-driven scrap cutters arranged along the part's contour. Each set of scrap cutters is driven by a small servo motor or hydraulic cylinder and can move forward / backward independently. It also includes a laser trimming head for removing small excess connecting strips. The central control unit pre-stores a residual stress distribution map of the part obtained from finite element analysis. During trimming, the central control unit operates in the following stepped sequence: First, the scrap cutters far from the high-stress area are driven to cut; then, after an interval of 1-2 seconds, the cutter blocks in the next highest stress area are driven; finally, after waiting 5-10 seconds for stress redistribution, the cutter blocks near the root of the reinforcing ribs and the junction edge are driven. After all scrap cutters have cut, the laser trimming head is activated to remove the remaining micro-connecting strips one by one. By sequentially cutting and smoothly decoupling the stress chain, the sudden stress release and part bouncing caused by the simultaneous cutting of all cutters in traditional trimming are avoided. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method of stamping an automotive aluminum alloy characterized by: Includes the following steps: S1: Blanking and surface pretreatment: Laser blanking or servo shearing is performed on aluminum alloy sheets, followed by plasma cleaning and surface roughness homogenization. S2: Lubrication Coating and Robotic Positioning and Loading: Different lubricating media are applied to the subsequent forming areas, and the blank is introduced into the stamping station by positioning the robot at preset coordinates. S3: Drawing: The process of using partitioned variable blank holder force and progressive constraint forming is adopted. The partitioned variable blank holder force refers to dividing the punch assembly into multiple independent sub-regions corresponding to the blank base plate area, side wall area and reinforcing rib area. Each sub-region is subjected to a gradient blank holder force from high to low or from low to high at different stages of drawing. The progressive constraint forming process involves setting the blank holder force in the bottom plate area to a higher value in the early stage of drawing to suppress premature material flow, setting the blank holder force in the side wall area to a medium value, and setting the blank holder force in the reinforcing rib area to a lower value to promote rib filling. During the middle stage of drawing, based on the amount of plastic deformation that has occurred in each region, the blank holder force in the bottom plate area is gradually reduced while the blank holder force in the side wall area is increased, so that the material is replenished to the side wall in an orderly manner. At the end of drawing, the blank holder force in each sub-region is homogenized to stabilize the final shape. At the same time, the local clearance of the punch and die is dynamically adjusted during the drawing process. For areas with dense reinforcing ribs, the local clearance is increased by 10%-20% to reduce flow resistance, and a standard clearance is used for the flat area of ​​the bottom plate to ensure flatness. S4: Trimming and punching: A stress-relieving step-by-step trimming and pre-compensation punching strategy is adopted to sequentially cut the material in sections along the stiffness transition boundary of the part in order to release the residual stress accumulated before unloading. S5: Flanging, Hemming and Local Shaping: Combine the topography prediction database to perform dynamic reverse compensation on the springback vector that has occurred, and perform local stress redistribution and surface fitting through flexible medium or variable mold surface. The dynamic reverse compensation includes dividing the part into multiple feature blocks, each block is preset with a reverse springback compensation amount based on finite element iteration calculation. In the local shaping step, non-uniform correction load is applied to each block through servo-driven segmented pressure head or deformable pad, so that each area reaches the target surface simultaneously after unloading. S6: Deburring, cleaning and dimensional inspection: The final three-dimensional morphology data is mapped and archived with the process parameters of the whole process, which is used to iteratively update the global-local coupling compensation model for the next batch of stamping.

2. The method of claim 1, wherein: In the S3 drawing process, a gradient strain control strategy of first the base plate and then the sidewall is adopted. By setting a pre-forming step or a flexible transition punch, the flow rate of material at the junction edge towards the sidewall is slowed down, so that the plastic deformation of the reinforcing rib root and the junction edge area extends gradually.

3. The method of claim 2, wherein: The differentiated lubricating medium coating in S2 includes coating a high friction coefficient damping coating in the area corresponding to the junction of the blank bottom plate and the side wall, and coating a low friction lubricant in the bottom plate reinforcing rib forming area. In the early stage of S3 drawing, the high frictional resistance of the boundary edge region is used to suppress the premature flow of material into the sidewall, and the low frictional environment of the reinforcing rib region promotes the full formation of the ribs. In the middle and late stages of drawing, the frictional resistance of the boundary edge is gradually reduced.

4. The method of claim 3, wherein: In the middle and late stages of the S3 drawing process, the punch assembly is equipped with an independently controllable micro-partition hydraulic cylinder in the projection area of ​​the junction between the base plate and the side wall. The micro-partition is subjected to a stepped pressure reduction and stress relief operation to form a slow-release channel for material to flow into the side wall. At the same time, in conjunction with the stress dispersion structure at the rounded corner of the punch junction, the equivalent plastic strain gradient of the transition zone between the base plate and the side wall changes continuously.

5. The automotive aluminum alloy stamping method according to claim 4, characterized in that: The step-by-step trimming strategy in S4 includes first performing main trimming along the contours of the non-load-bearing area and the low stiffness area, retaining the process connection strip at the junction of the bottom plate and the side wall and the root of the reinforcing rib; after the local shaping is completed in S5 and the residual stress is fully released, the process connection strip is then finely trimmed and micro-stress release cuts are made.

6. The automotive aluminum alloy stamping method according to claim 5, characterized in that: An inter-station shape transfer and pre-compensation link is added between S3 and S5 to superimpose the shape deviation after unloading at the previous station onto the mold surface or loading path of the next station in a pre-deformation manner.

7. The automotive aluminum alloy stamping method according to claim 6, characterized in that: The dimensional detection data in S6 is updated through statistical process control methods to update the partitioned variable pressure edge force mapping table and the local compensation surface database, and a nonlinear correlation model is established between material batch differences, lubrication state fluctuations and springback response.

8. An automotive aluminum alloy stamping apparatus, applicable to an automotive aluminum alloy stamping method as described in any one of claims 1-7, characterized in that: The device includes a frame and a main press body; a lower die holder and a die assembly mounted on the main press worktable; an upper die holder and a punch assembly that cooperate with the die assembly, wherein the punch assembly adopts a partitioned independent drive structure and includes multiple micro-partitioned hydraulic servo cylinders distributed along the contour of the sheet metal; a flexible transition forming block is embedded in the lower die holder or the upper die holder; the device also includes a shape transfer tooling and a central control unit disposed between adjacent stamping stations, wherein the central control unit is electrically connected to the micro-partitioned hydraulic servo cylinders.

9. The automotive aluminum alloy stamping device according to claim 8, characterized in that: The flexible transition forming block is specifically a variable stiffness composite module set in the area corresponding to the junction of the bottom plate and the side wall of the die assembly. Its inner layer is a high stiffness alloy support frame, and its outer layer is a high damping elastomer or shape memory alloy coating layer.

10. The automotive aluminum alloy stamping device according to claim 9, characterized in that: It also includes a stress-relieving trimming module integrated into the trimming station, which includes multiple sets of independent servo-driven scrap cutters and laser fine trimming heads that open and close sequentially along the contour of the part; the central control unit controls the multiple sets of independent servo-driven scrap cutters to operate in a preset step sequence according to a pre-stored local residual stress distribution map.

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