Precise molding process for shielding case

Abstract

The invention relates to a precise forming process for a shielding case. The process comprises the following steps: constructing a finite element simulation model to output a material pressing force distribution curve and shearing time sequence parameters; synchronous shearing is executed in the stroke that the forming punch drives the plate to deform, and the shearing advancing speed and the side wall deformation speed are controlled to be synchronous so as to relieve the lateral tensile stress; a multi-stage floating material pressing system is used for applying differential material pressing force to different stretching stations, and material inflow resistance is controlled to restrain wrinkling or prevent cracking; a closed shaping cavity of which the geometric volume is smaller than the volume of a solid material is constructed by utilizing a mold, and a prefabricated upwarp angle is eliminated and a gap of a shaping groove is filled by utilizing the creep characteristic of the material in cooperation with servo pressure maintaining. The device has the advantages that dynamic stress decoupling is achieved while the feeding precision is kept, the complex stretching forming quality is considered, and shielding case side wall seam physical closing is achieved.

Description

Technical Field

[0001] This application relates to the field of precision manufacturing, and in particular to a precision molding process for a shielding cover. Background Technology

[0002] In the fields of mobile communication and precision electronic equipment manufacturing, metal shielding covers are key components for suppressing electromagnetic interference. These parts are typically made of thin sheet materials such as nickel silver or stainless steel, and are formed by multi-station continuous stamping using progressive dies. As electronic products become thinner and more complex, the stretching depth of the shielding covers is increasing and their shapes are becoming increasingly irregular, which places higher demands on the precision control of the forming process.

[0003] Existing progressive stamping processes primarily rely on connecting strips on the strip skeleton to transport and position the sheet metal between stations. In the critical stretching process, the sheet metal, driven by the punch, undergoes significant plastic flow into the die cavity to form sidewalls. However, the fixed connecting strips restrict the free flow of the sheet metal, resulting in significant lateral tensile stress between the workpiece and the strip skeleton. This stress coupling effect often causes necking deformation or even tearing at the connection point. If the connecting strips are cut prematurely to relieve stress, the workpiece loses its positioning support and is prone to displacement under high-speed stamping, leading to dimensional deviations.

[0004] Furthermore, traditional stamping dies typically employ blank holders with constant stiffness, making it difficult to adapt to the varying material flow resistance requirements at different stages of the drawing process. In the initial drawing stage, insufficient blank holder force can lead to wrinkling in the flange area, while excessive blank holder force during deep drawing can cause sidewall cracking. This contradiction between positioning constraints and stress release, as well as the mismatch between a single blank holder mode and complex rheological requirements, makes it difficult for existing processes to stably produce high-precision deep-drawn shields, and results in significant residual stress after forming, making springback control challenging. Therefore, a precision forming process is needed that can decouple feed stress in real time and precisely control material flow. Summary of the Invention

[0005] In order to decouple feed stress in real time and precisely control material flow, this application provides a precision forming process for shielding covers.

[0006] This application provides a precision molding process for a shielding cover, which employs the following technical solution: A precision molding process for a shielding cover includes the following steps: S1. Digital Process Optimization: Before physical mold opening, a finite element simulation model is constructed, including the upper mold assembly, the lower mold assembly, and the sheet material to be processed; based on the material rheological properties of the sheet material, the dynamic stress distribution during the stretching process is simulated; and based on the simulation results, the blanking force distribution curve and shearing timing parameters are output. S2. Synchronous Shearing and Decoupled Feeding: The sheet metal is conveyed to the bearing surface of the lower die assembly; the upper die assembly is driven downward, and the forming punch set on the upper die assembly drives the sheet metal to produce plastic deformation to form a workpiece semi-finished product; during the stroke of the forming punch contacting the sheet metal and starting to stretch, the connecting strip at the edge of the sheet metal is cut off by the synchronous shearing mechanism based on the shearing timing parameters; the vertical velocity of the shearing entry point of the synchronous shearing mechanism is controlled to be equal to the vertical sinking velocity of the neutral layer in the deformation zone of the side wall of the workpiece semi-finished product, so as to eliminate lateral tensile stress while cutting off the connecting strip; S3. Variable Resistance Progressive Stretching: The workpiece semi-finished product is continuously stretched using a multi-stage floating pressure system configured in the mold; the multi-stage floating pressure system includes at least two floating pressure units with different elastic coefficients arranged sequentially along the feeding direction; based on the pressure force distribution curve, each of the floating pressure units applies an independently set pressure force to the flange area of ​​the workpiece semi-finished product at different stretching positions to control the frictional resistance of the workpiece semi-finished product flowing into the mold cavity, and to form a pre-formed warp corner feature at the end of the side wall of the workpiece semi-finished product at the end of the stretching. S4. Closed-volume servo shaping: When the upper die assembly descends to the position where the servo press slide reaches the bottom dead center, the forming punch and the shaping groove on the lower die assembly enclose each other to form a closed shaping cavity; the geometric volume of the closed shaping cavity is configured to be smaller than the solid material volume of the workpiece semi-finished product at the bottom dead center position, and a hydrostatic pressure field is established in the closed shaping cavity; the servo press slide is controlled to maintain a preset pressure holding period at the bottom dead center position, and the hydrostatic pressure field is used to drive the metal material of the workpiece semi-finished product to creep flow until the pre-formed warp feature is eliminated and the geometric gap of the shaping groove is filled.

[0007] By employing the above technical solution, a finite element simulation model incorporating mold geometry parameters and the rheological properties of the metal material is constructed to simulate the dynamic stress distribution throughout the stretching process and output shearing timing parameters to guide physical forming control. In the synchronous shearing and decoupled feeding steps, a synchronous shearing mechanism is used to cut the connecting strip based on these parameters, and the vertical velocity of the shearing entry point is controlled to equal the vertical sinking velocity of the neutral layer in the deformation zone of the workpiece's semi-finished sidewall. This technique ensures that the side connecting strip maintains its positioning function in the initial contact of the forming punch with the sheet metal and is cut off simultaneously with substantial plastic deformation of the sidewall. This maintains feeding accuracy while removing the lateral rigid constraint of the strip skeleton on the workpiece, avoiding sidewall necking or tearing caused by tensile stress coupling.

[0008] A multi-stage floating blanking system with floating blanking units of different elastic coefficients is used to apply differentiated blanking forces at different stretching stations based on the blanking force distribution curve determined by simulation. By independently setting the blanking force at each station, the frictional resistance of the workpiece semi-finished product flowing from the flange area into the mold cavity is precisely controlled to adapt to the differentiated requirements of material flowability for different stretching depths. This solves the technical contradiction that a single blanking force cannot simultaneously suppress wrinkling and prevent cracking, and retains a pre-formed warp feature at the end of the sidewall at the end of stretching as material allowance for subsequent shaping.

[0009] When the upper die assembly descends to the bottom dead center position of the servo press slide, the forming punch and the forming groove enclose a closed forming cavity, and the geometric volume of this cavity is configured to be smaller than the solid material volume of the workpiece semi-finished product. In conjunction with the servo press's pressure-holding program, a hydrostatic pressure field is established within the cavity and maintained for a preset time period. Utilizing the creep characteristics of the metal material, the material undergoes directional flow, filling the geometric gaps in the forming groove and eliminating pre-formed warping features. This method converts elastic rebound stress into plastic deformation, achieving physical closure of the shielding cover sidewall joints, and improving the structural density and electromagnetic shielding performance of the workpiece.

[0010] Optionally, S1 includes the following sub-steps: S11. Establish the dynamic contact boundary equation between the workpiece semi-finished product and the forming punch on the upper die assembly, the die unit on the lower die assembly, and the floating pressure unit using the penalty function method or the Lagrange multiplier method, and input the preset downward stamping speed of the forming punch and the friction coefficient parameters of the contact interface between the workpiece semi-finished product and the die assembly; wherein, the dynamic contact boundary equation is used to characterize the real-time physical contact state between the workpiece semi-finished product and the contact interface of each component of the die during the deformation process; S12. Generate a forming limit diagram, and identify potential wrinkling and cracking regions on the simulation model based on the forming limit diagram; wherein, the forming limit diagram is used to characterize the forming safety boundary of the metal material under different strain paths; S13. Adjust the fillet radius and friction coefficient of the contact interface of the die unit or forming punch according to the identification results, and re-execute the simulation until the wrinkled area and the cracked area disappear. Output the shearing timing parameters and the pressure setting value of the floating pressure unit at this time as the pressure force distribution curve; wherein, the pressure force distribution curve is used to characterize the relationship between the pressure force applied by the floating pressure unit to the workpiece semi-finished product and the stroke or time.

[0011] By employing the above technical solutions and utilizing the penalty function method or the Lagrange multiplier method to establish the dynamic contact boundary equation between the workpiece semi-finished product and the mold assembly, the real-time physical state of the complex contact interface during deformation is accurately characterized, providing a high-fidelity physical basis for numerical calculations. Based on the generated forming limit diagram, the forming safety boundary of the metal material under different strain paths is quantified, thereby accurately identifying potential wrinkling and cracking risk areas in the simulation model.

[0012] Based on the identification results, the mold geometry parameters and contact interface friction coefficients are iteratively adjusted to eliminate molding defects and lock in the optimal process window in a virtual environment. This process transforms traditional trial-and-error experience into quantifiable process control data, outputting precise shearing timing parameters and blank holder force distribution curves. This provides optimized input parameters for subsequent physical synchronous shearing and variable resistance progressive stretching, effectively reducing actual mold trial costs and improving the predictability of molding quality.

[0013] Optionally, step S2 includes the following sub-steps: S21. Progressive shearing: The wavy shearing blade edge of the forming punch sidewall is used to contact the connecting strip. The wavy shearing blade edge has a blade edge inclination angle of 1° to 2°. The shearing force is converted into a tangential component force through point contact cutting. S22. Negative pressure waste stripping: During the shearing stroke, a negative pressure airflow is established below the shearing fracture surface through an embedded vacuum waste suction channel connected to an external negative pressure source. The negative pressure airflow is used to pull the cut waste into the waste discharge path inside the lower mold assembly.

[0014] By adopting the above technical solution, and utilizing a wavy shearing cutting edge with a cutting edge inclination angle of 1° to 2° on the sidewall of the forming punch, the traditional instantaneous full-segment shearing is transformed into a progressive point-contact cutting mode. This geometric feature effectively decomposes the vertical shearing impact force into a tangential component force, reducing the instantaneous impact load and mechanical vibration during the shearing action, thereby ensuring the smoothness of the die movement and optimizing the fracture quality during precision stretching.

[0015] The embedded vacuum waste suction channel creates a negative pressure airflow below the shear fracture surface, applying active traction force to the cut waste material during the synchronous period of the shear stroke. This pneumatic stripping mechanism overcomes the risk of waste material remaining in the mold cavity due to electrostatic adsorption or elastic rebound, forcing the waste material to be discharged along a preset waste discharge path. This effectively prevents product damage or mold edge damage caused by small metal fragments getting stuck in the mold gap, ensuring the stability of continuous progressive stamping.

[0016] Optionally, step S3 includes the following sub-steps: S31. High-resistance initial stretching: In the initial stretching station, a first floating pressure unit is used to provide a first order of magnitude of pressure force; wherein, the first floating pressure unit uses a high-stiffness gas spring as an elastic element, and in the initial stage of plastic deformation when the workpiece semi-finished product begins to flow into the mold cavity, it presses the flange area of ​​the workpiece semi-finished product against the concave surface of the lower mold assembly, thereby straightening the material fibers and suppressing wrinkling by increasing the feeding friction resistance of the workpiece semi-finished product from the flange area to the mold cavity; S32. Low-resistance secondary stretching: In the secondary stretching station, a second floating pressure unit is used to provide a second level of pressure force; wherein, the second floating pressure unit uses a helical spring as an elastic element, and the second level of pressure force is less than the first level of pressure force; during the continuous stage of plastic deformation in which the material of the workpiece semi-finished product continuously flows into the mold cavity and forms the sidewall, the second floating pressure unit sinks synchronously with the bottom of the workpiece semi-finished product to prevent excessive thinning of the sidewall.

[0017] By employing the above technical solution, a high-stiffness gas spring drives the first floating pressure unit at the initial stretching station, applying a first-order level of high pressure during the initial stage of plastic deformation. This tightly presses the flange area of ​​the semi-finished workpiece onto the die surface. This high-pressure constraint significantly increases the feeding friction resistance of the material flowing into the die cavity, forcing the material fibers to straighten under tensile stress. This effectively suppresses flange wrinkling caused by uneven material flow or excessive tangential compressive stress in the early stages of stretching.

[0018] In the secondary stretching station, a helical spring drives a second floating blank holder unit, applying a second-order blank holder force less than that of the first, and it sinks synchronously with the bottom of the workpiece during the continuous plastic deformation stage. This flexible support mechanism reduces the frictional resistance of material flow, avoiding stress concentration and excessive thinning of the sidewalls due to excessive blank holder force during deep drawing, thus preventing sidewall necking or cracking while ensuring the forming depth. This graded variable resistance control strategy utilizes the physical properties of different elastic elements to match the rheological requirements of different stages of the stretching process, resolving the technical contradiction that a single blank holder force cannot simultaneously suppress wrinkling and prevent cracking.

[0019] Optionally, step S4 includes the following sub-steps: S41. Interference Volume Construction: Calculate the target volume based on the negative tolerance limit of the sheet thickness of the semi-finished workpiece, and set the volume of the closed shaping cavity to be equal to the target volume; and connect an overflow relief groove with a depth of less than 0.05mm to the non-sealed area of ​​the shaping groove. S42. Directional creep filling and monitoring: The servo press slider is controlled to maintain a pressure holding period of 50ms to 100ms at the bottom dead center position; during this period, the molding load value of the mold is monitored in real time; if the molding load value exceeds the preset safety threshold, the interference pressure is used to drive the excess metal material to plastically flow into the overflow relief groove. S43. Load attenuation determination: During the pressure holding period, real-time load signals are collected and the load attenuation rate is calculated; S44. Flexible return: When the absolute value of the load attenuation rate is less than the preset relaxation convergence threshold, the servo press slider is controlled to start the return action according to the S-shaped speed curve.

[0020] By adopting the above technical solution, and setting the target volume of the closed forming cavity based on the negative tolerance limit of the workpiece semi-finished sheet thickness, sufficient mechanical interference can be constructed within the cavity even under the thinnest material thickness conditions, thereby maintaining an effective high-pressure stress field to drive material filling. Combined with a micron-deep overflow relief groove in the non-sealed area of ​​the forming groove, an adaptive tolerance protection mechanism is constructed. When the sheet thickness is within the positive tolerance range, causing the forming load to exceed the safety threshold, the interference pressure drives excess metal to flow plastically into the overflow relief groove, ensuring filling density while releasing mold overload stress and preventing mold damage due to excessive pressure.

[0021] The servo press slider is controlled to maintain pressure at the bottom dead center for a period of 50ms to 100ms, utilizing the creep characteristics of the metallic material to eliminate residual stress and fill geometric gaps under hydrostatic pressure. During this period, real-time load signals are acquired and the attenuation rate is calculated to quantify the relaxation state of the internal stress of the material. Only when the absolute value of the load attenuation rate is less than a preset threshold, indicating that the material has reached rheological equilibrium, is the slider controlled to initiate a flexible return stroke according to an S-shaped velocity curve. This closed-loop control strategy based on rheological state feedback avoids rebound deformation caused by premature unloading and elastic impact caused by sudden load changes, ensuring the dimensional stability and accuracy of the shield sidewall joint closure structure.

[0022] Optionally, the workpiece semi-finished product has at least two independent stretching regions and connecting ribs connecting the two independent stretching regions; the following steps are also included before performing step S3: Pre-fabricated pressure relief cut: A pressure relief cut with a non-closed contour is punched at the location of the connecting rib; Geometric deformation transformation: During the stretching process in step S3, the synchronous sinking action of the two independent stretching regions is used to drive the pressure relief cut to open and deform. The geometric displacement of the pressure relief cut absorbs the material displacement difference between the two independent stretching regions, thereby blocking the transmission of tensile stress at the connecting rib.

[0023] By employing the above technical solution, a pressure-relieving notch with a non-closed contour is pre-cut at the connecting rib position connecting two independent tensile regions, altering the stress transfer path of the material in that region during subsequent tensile processes. During variable-resistance progressive tensile testing, as the two independent tensile regions simultaneously sink under pressure, the tensile strain originally applied to the connecting rib position is forcibly converted into the opening deformation of the pressure-relieving notch. This geometric deformation conversion mechanism utilizes the spatial displacement generated by the opening of the notch edge to physically absorb the displacement difference between the two independent tensile regions caused by material flow.

[0024] This technique effectively blocks the superposition and transmission of bidirectional tensile stress at the connecting ribs, preventing necking or fracture due to insufficient material replenishment and excessive tensile stress. This achieves stress decoupling in complex multi-cavity structures during synchronous stretching and forming, ensuring the integrity and dimensional accuracy of the multifunctional integrated component connection structure.

[0025] Optionally, the mold includes: The upper die assembly is configured as a slider fixedly connected to the servo press, and the upper die assembly is provided with a plurality of forming punches and shaping punches in sequence along the feeding direction; The lower die assembly is fixedly mounted on the worktable and has a die unit and a shaping groove corresponding to the positions of the forming punch and the shaping punch. A multi-stage floating pressure system is slidably disposed within the die unit; the system includes a first floating pressure unit located at the primary stretching station and a second floating pressure unit located at the secondary stretching station; the first floating pressure unit is connected to a first elastic element, the second floating pressure unit is connected to a second elastic element, and the elastic coefficient of the first elastic element is greater than the elastic coefficient of the second elastic element; The synchronous shearing mechanism includes a wave-shaped shearing blade integrally formed on the side wall of the forming punch, and an embedded vacuum waste suction channel that penetrates the interior of the lower die assembly. The closed extrusion forming structure is composed of the forming punch and the forming groove; when the mold is closed to the bottom dead center, the forming punch and the forming groove enclose the closed forming cavity.

[0026] By adopting the above technical solution, and configuring an upper die assembly connected to the servo press slide and a lower die assembly fixed to the worktable, a physical foundation platform for multi-station progressive stamping is constructed. The multi-stage floating blank holder system, slidingly positioned within the die unit, utilizes a configuration where the elastic coefficient of the first elastic element is greater than that of the second elastic element, providing graded and differentiated blank holder force output in its physical structure. This hardware characteristic ensures that the die can output high pressure at the initial stretching station to suppress flange wrinkling, while outputting low pressure at the secondary stretching station to prevent excessive sidewall thinning, thus achieving the process requirement of variable resistance material flow control at the equipment level.

[0027] The synchronous shearing mechanism integrates the wavy shearing blade into the sidewall of the forming punch, and, in conjunction with the embedded vacuum waste suction channel inside the lower die assembly, achieves a structural integration of shearing and forming actions. The wavy blade design optimizes the shearing contact mode, while the embedded channel provides the shortest negative pressure discharge path for the waste, effectively preventing die damage caused by waste rebound or retention. The closed extrusion forming structure, composed of the forming punch and forming groove, constructs a geometrically closed forming cavity when the die closes to the bottom dead center. This provides the necessary rigid volumetric constraint boundary for the creep flow of the metal material, which is the physical prerequisite for using hydrostatic pressure to eliminate pre-formed warp corners and close sidewall seams.

[0028] Optionally, the mold further includes: A hard limiting component includes a precision limiting block disposed on an upper mold assembly and a limiting support disposed on a lower mold assembly; the contact surface between the precision limiting block and the limiting support defines the bottom dead center position of the mold. The indentation rib is protruding from the bottom edge of the forming punch and extends along the bending line trajectory of the workpiece semi-finished product. When the hard limiting component is in a rigid contact state, the height of the indentation rib protruding from the bottom surface of the shaping groove is such that the indentation rib penetrates 10% to 15% of the thickness of the workpiece semi-finished material.

[0029] By adopting the above technical solution, a precision limiting block and a limiting support are set between the upper and lower die components. The rigid contact between the two components physically defines the bottom dead center position of the die, thereby eliminating the influence of fluctuations in the servo press slide motion accuracy on the final closing height and providing an absolute geometric reference for precision forming. Under the constraint of this rigid reference, the depth of the indentation rib on the bottom surface of the forming punch penetrating into the bending root of the workpiece semi-finished product is forcibly set to be stable at 10% to 15% of the material thickness. This controlled micro-penetration action generates concentrated local pressure on the bending trajectory, forcing the material root to undergo severe plastic deformation and produce a work hardening effect. This effectively destroys the elastic recovery memory inside the metal material and reconstructs the stress distribution, thereby offsetting the springback torque after unloading. While ensuring the bending angle accuracy, the final forming size of the workpiece is locked.

[0030] Optionally, the surface of the lower mold assembly is recessed with an overflow pressure relief groove; one end of the overflow pressure relief groove is connected to the non-sealed area of ​​the shaping groove, and the other end is connected to the outside of the mold; the depth dimension of the overflow pressure relief groove is smaller than the closing gap dimension of the closed shaping cavity, forming a throttling structure that allows metal flow only under overload pressure.

[0031] By adopting the above technical solution, a passive overload protection mechanism based on the difference in flow channel resistance is constructed by setting a micron-deep overflow relief groove on the surface of the lower mold assembly, and designing its depth dimension to be smaller than the closed gap dimension of the closed forming cavity. This dimensional difference causes the overflow relief groove to have a significant throttling effect on the metal flow, ensuring that under standard material thickness and normal forming pressure, the metal material preferentially fills the geometric gap of the forming groove to complete the precision forming, and does not easily overflow, thereby ensuring the high-pressure environment required for the forming process.

[0032] When the thickness of the semi-finished sheet metal is within the positive tolerance range, resulting in excess solid material volume within the closed cavity, the hydrostatic pressure inside the cavity rises sharply and exceeds the flow resistance threshold of the overflow relief groove. At this point, the overload pressure drives the excess metal material to overcome the throttling resistance and undergo directional plastic flow towards the overflow relief groove, converting the volume potential energy that could have caused the mold to break into material displacement work. This mechanism adaptively releases abnormal overload stress during the mold closing process without relying on external active control, effectively preventing the risk of mold damage caused by material thickness fluctuations and improving the process robustness and service life of the precision progressive stamping system.

[0033] Optionally, the mold further includes: A piezoelectric load sensor is installed on the force transmission path of the forming punch or lower die assembly to collect real-time forming load. A micro-displacement sensor is installed between the guide mechanism of the upper mold assembly and the lower mold assembly to monitor the mold closing stroke; both the piezoelectric load sensor and the micro-displacement sensor are electrically connected to the control system of the servo press.

[0034] By adopting the above technical solution, a real-time force-displacement dual-parameter feedback monitoring system for the mold is constructed by setting piezoelectric load sensors on the force transmission path of the forming punch or lower die assembly and installing micro-displacement sensors between the guiding mechanisms. The piezoelectric load sensors can capture millisecond-level changes in forming load, providing necessary data support for identifying the rheological equilibrium state of the metal material and triggering overload protection; the micro-displacement sensors enable precise monitoring of the actual closing height between the upper and lower die assemblies. Electrically connecting both to the servo press control system realizes closed-loop control logic based on real-time data, enabling the system to dynamically correlate pressure and position information, thereby automatically compensating for closing errors caused by mold thermal expansion and adaptively adjusting the pressure holding strategy based on load feedback, ensuring the stability and consistency of the precision forming process under complex working conditions.

[0035] In summary, this application includes at least one of the following beneficial technical effects: 1. This application utilizes a synchronous shearing and decoupled feeding process, employing a synchronous shearing mechanism to strictly synchronize the vertical advance speed of the shearing entry point with the sinking speed of the neutral layer in the workpiece sidewall deformation. This technique maintains the positioning function of the connecting strip in the initial stage of the forming punch contacting the sheet metal, and cuts off the connecting strip while substantial plastic deformation occurs in the sidewall. This ensures feeding accuracy while simultaneously releasing the lateral rigid constraint of the strip skeleton on the workpiece, effectively avoiding sidewall necking or tearing problems caused by tensile stress coupling, and improving the forming stability of high-speed progressive stamping. 2. This application employs a variable resistance progressive drawing process, utilizing a multi-stage floating blanking system with different elastic coefficients (high-stiffness gas springs and low-stiffness helical springs). Based on simulation results, differentiated blanking forces are applied at different drawing stations. By applying high resistance in the initial drawing stage to straighten the fibers and suppress wrinkling, and applying low resistance in the deep drawing stage to provide flexible support and prevent breakage, this graded control strategy successfully resolves the technical contradiction that a single constant blanking force cannot simultaneously address wrinkling in shallow drawing and breakage in deep drawing, significantly improving the yield of drawing complex irregular shielding covers. 3. This application utilizes a closed-volume servo forming process, employing a mold to construct a closed forming cavity with a geometric volume smaller than the solid material volume, and establishing a hydrostatic pressure field through a long-term pressure holding program of a servo press. This process leverages the creep characteristics of metallic materials to drive directional plastic flow of the material under interference pressure, filling the geometric gaps in the forming groove and eliminating pre-fabricated warping. This not only completely transforms elastic rebound stress into plastic deformation, solving the springback problem of traditional bending, but also achieves physically dense closure of the shielding cover sidewall joints, achieving excellent electromagnetic shielding performance without subsequent welding; simultaneously, combined with the overflow pressure relief groove design, it achieves adaptive overload protection against raw material thickness fluctuations, extending the mold's service life. Attached Figure Description

[0036] Figure 1 A flowchart illustrating a precision molding process for a shielding cover in one embodiment of the present invention is shown. Detailed Implementation

[0037] The present application will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the application and are not intended to limit the scope of the application.

[0038] In the following description, numerous specific details are set forth for purposes of explanation in order to provide a thorough understanding of the inventive concept. As part of this specification, some of the accompanying drawings of this disclosure are block diagrams illustrating structures and devices to avoid complicating the disclosed principles. For clarity, not all features of the actual embodiment need to be described. Furthermore, the language used in this disclosure has been primarily chosen for readability and instructional purposes and may not have been chosen to define or limit the subject matter of the invention, thus requiring the necessary claims to determine such inventive subject matter. References to “an embodiment” or “an embodiment” in this disclosure mean that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment, and multiple references to “an embodiment” or “an embodiment” should not be construed as necessarily referring to the same embodiment.

[0039] Unless explicitly defined, the terms “a,” “an,” and “the” are not intended to refer to a singular entity, but rather to include a general category whose specific examples can be used for illustration. Therefore, the use of the terms “a” or “an” can mean any number of at least one, including “a,” “one or more,” “at least one,” and “one or more.” The term “or” means any of the options and any combination of the options, including all options unless explicitly indicated that the options are mutually exclusive. The phrase “at least one of” when combined with a list of items refers to a single item in the list or any combination of items in the list. The phrase does not require all items listed unless explicitly defined as such.

[0040] In existing technologies, the molding of shielding covers often faces the contradiction between positioning and stress release, as well as the technical problem of controlling material flow in complex stretching structures. Therefore, this application discloses a precision molding process for shielding covers, which can be applied to a precision molding mold for shielding covers. This mold, through specific structural matching, can meet the high-precision molding requirements. Specifically, the mold needs to have functional structures that can achieve dynamic stress decoupling during stretching, provide differentiated pressure resistance for different stretching stages, and construct a closed high-pressure field at the molding endpoint to eliminate springback.

[0041] Specifically, in one embodiment, the precision forming mold for the shielding cover includes an upper mold assembly, a lower mold assembly, a multi-stage floating pressure system, a synchronous shearing mechanism, a closed extrusion forming structure, a hard limiting assembly, an indentation rib, a piezoelectric load sensor, and a micro-displacement sensor. The upper and lower mold assemblies form the basic closed frame of the mold, supporting each forming unit. The multi-stage floating pressure system, in conjunction with the die unit, applies variable flange constraint force to the sheet metal during progressive stretching. The synchronous shearing mechanism cuts the connecting strip synchronously during the forming action. The closed extrusion forming structure, in conjunction with the hard limiting assembly and the indentation rib, performs volumetric closed-loop forced forming of the workpiece at the bottom dead center. The piezoelectric load sensor and the micro-displacement sensor provide real-time feedback on the forming status to assist servo control.

[0042] The upper die assembly is configured as a slider fixedly connected to the servo press, reciprocating up and down with the slider. The upper die assembly is typically a rectangular or square plate structure, and its material can be high-strength mold steel. The upper die assembly is located directly above the lower die assembly, its upper surface locked to the press slider by a die shank or screws, and its lower surface supports the punches for each process. In one embodiment, the upper die assembly can be a single die base plate; in another embodiment, the upper die assembly can also be composed of an upper die base, a backing plate, and a clamping plate stacked together, as long as a stable mounting base can be provided.

[0043] The upper die assembly has multiple forming punches and shaping punches arranged sequentially along the feeding direction. These punches are fixed vertically downwards to the bottom surface of the upper die assembly. The cross-sectional shape of the forming punches and shaping punches is adapted to the inner contour shape of the shield to be processed, such as rectangular, polygonal, or L-shaped irregular structures. The bottom edge of the forming punch usually has smooth stretching fillets to facilitate material flow; while the shaping punch has a sharper shape for final shaping. In terms of connection, the punches can be embedded into the upper die fixing plate by means of a mounting plate, or they can be directly locked to the upper die base by bolts.

[0044] The lower die assembly is fixedly mounted on the worktable, serving as the base of the die. The lower die assembly typically includes a lower die base and a lower template fixed to it. Its overall shape corresponds to that of the upper die assembly, usually being a rectangular steel block of a certain thickness. The lower die assembly is positioned precisely at the center of the press's worktable and is fixed by pressure plates or bolts to maintain absolute stillness during the stamping process, providing a precise alignment reference for the closing of the upper die assembly.

[0045] The lower die assembly has die cavity units and forming grooves. The positions of the die cavity units correspond one-to-one with the positions of the forming punches, and the positions of the forming grooves correspond to the positions of the forming punches. The die cavity units and forming grooves are cavity structures recessed into the upper surface of the lower die assembly. The inner cavity size of the die cavity unit is slightly larger than the corresponding forming punch, and the gap between them is equal to or slightly larger than the material thickness. The forming groove has a specific inwardly tapering profile (such as a negative angle inner wall). In one embodiment, the die cavity units and forming grooves can be directly machined onto the lower die plate; in another embodiment, for ease of maintenance and replacement, they can also be designed as independent insert structures (die inserts), which are fixedly installed in the grooves of the lower die base by tight fit or screws.

[0046] The die unit has a multi-stage floating pressure system that slides internally. This system mainly consists of a forming float body, a guiding mechanism, and a limiting mechanism. In one embodiment, the forming float body can be guided vertically by a precision guide post and guide sleeve located within the lower die assembly; in another embodiment, guidance can be achieved through a precision clearance fit between the outer wall of the forming float body and the inner wall of the die unit. To prevent the float from ejecting from the die cavity under elastic force during mold opening, the system is also equipped with a limiting mechanism. This limiting mechanism can be, for example, a height-limiting screw connected between the bottom of the float and the lower die base, or a stepped structure designed on the side wall of the float, which abuts against a corresponding countersunk step on the die unit to limit the maximum upward stroke.

[0047] The system includes a first floating pressure unit located at the initial stretching station and a second floating pressure unit located at the secondary stretching station. The shape features of these two units are adapted to the specific structure of the workpiece. For example, in one embodiment, they can be designed as annular floating plates surrounding a shaping groove; in another embodiment, for irregularly shaped shields, they can be designed as separate, block-shaped floating keys. The top surface shape of the first floating pressure unit is designed to adapt to the flat flange profile of the workpiece in the initial stretching stage, while the top surface shape of the second floating pressure unit adapts to the bottom profile of the workpiece in the secondary stretching stage, ensuring uniform transmission of contact area and pressure.

[0048] The bottom of the first floating pressure unit is connected to a first elastic element, and the bottom of the second floating pressure unit is connected to a second elastic element. In one embodiment, the bottom of the floating pressure unit may have a countersunk hole for receiving, and the top of the elastic element is embedded in the countersunk hole to prevent lateral slippage; in another embodiment, the top of the elastic element may directly abut against the flat bottom surface of the floating pressure unit, or be fixedly connected by screws. The other end (bottom end) of the elastic element requires stable support. For example, it may be supported on the surface of the lower mold base, on a heat-treated high-hardness pad, or, when using pneumatic components, mounted on a specially designed nitrogen gas communication plate.

[0049] The elastic coefficient of the first elastic element is set to be greater than that of the second elastic element. This difference in elastic coefficient manifests in different morphological characteristics in the physical structure, such as differences in the diameter of the spring steel wire, or differences in the cylinder diameter and inflation pressure. For example, in one embodiment, to provide the strong pressing force required to suppress wrinkling, the first elastic element can be a high-stiffness gas spring, a nitrogen spring, or a high-strength rectangular cross-section mold spring (such as a heavy-duty spring with a red or brown color code). To provide flexible support to prevent breakage, the second elastic element can be a low-stiffness helical spring, a common round wire spring, a polyurethane rubber block, or a disc spring assembly. The key is to ensure that the supporting force provided by the first elastic element is significantly greater than that provided by the second elastic element to achieve the technical requirement of variable resistance control.

[0050] The synchronous shearing mechanism is usually located on the side of the forming punch and at the corresponding position of the lower die assembly in the mold. Its function is to maintain positioning while cutting the connecting strip during the stretching process.

[0051] The synchronous shearing mechanism includes a wavy shearing blade integrally formed on the side wall of the forming punch, and an embedded vacuum waste suction channel extending through the lower die assembly. In one embodiment, the wavy shearing blade can be a blade structure directly ground on the side of the forming punch; in another embodiment, it can also be a separate shearing insert locked in a groove on the side of the forming punch, as long as it can move synchronously with the forming punch. The specific shape of the wavy shape can be designed as a sine wave, a sawtooth shape, or a beveled blade, and the blade has an inclination angle of 1° to 2° to achieve point contact shearing. The specific orientation of the embedded vacuum waste suction channel can be, for example, perpendicularly passing through the lower die insert, the lower die plate, and the lower die base; its connection method is, for example, by providing an air pipe connector at the outlet to connect to an external negative pressure source, a vacuum pump, or a venturi tube.

[0052] An embedded vacuum waste suction channel is located directly below the wavy shearing blade to collect waste generated during shearing. The cross-section of the waste suction channel inlet can completely cover the projected area of ​​the shearing blade, and the inlet can be designed as an inverted cone to prevent blockage. The waste is sucked in and discharged outside the mold under the action of negative pressure airflow.

[0053] The forming punch and forming groove constitute a closed extrusion forming structure. In addition to the forming punch and forming groove, this structure may also include auxiliary sealing structures depending on sealing requirements. The forming groove has specific shape characteristics, such as an inwardly tapering negative angle inner wall profile, the angle of which can be designed to be 88° to 89°, or a right-angle profile.

[0054] When the mold closes to the bottom dead center (BDC) state, the forming punch and the forming groove enclose each other, forming a closed forming cavity. Here, the bottom dead center state refers to the rigid contact state of the hard-limiting components. Specifically, the enclosed state means that the sidewall of the forming punch and the inner wall of the forming groove form a zero-clearance or micro-clearance fit. The volume of this closed forming cavity is configured to be smaller than the solid material volume of the workpiece semi-finished product at the BDC, thereby creating a mechanical interference fit within the cavity. In other embodiments, the cavity shape can be adjusted according to the R-angle requirements of the shielding cover, as long as a hydrostatic pressure field can be established.

[0055] To precisely control the mold's closing height, a hard limit component is installed. The function of the hard limit component is to eliminate the positional error of the servo press slide, ensuring the consistency and stability of the cavity closing height during the closed forming process by providing an absolute mechanical positional reference.

[0056] The rigid limiting assembly includes a precision limiting block disposed on the upper mold assembly and a limiting support disposed on the lower mold assembly. In one embodiment, the precision limiting block may be a pad structure made of high-hardness alloy steel and fixed to the non-forming area of ​​the upper mold base or stripper plate by screws; the limiting support is designed as a rigid cylindrical or square column fixed to the lower mold base. To ensure a balanced distribution of the clamping force, the precision limiting block and the limiting support are typically evenly distributed around the four corners of the mold or the center of force.

[0057] The precision limiting block and the limiting support are aligned vertically, and their contact surface defines the bottom dead center (BDC) position of the mold. The BDC position refers to the extreme mechanical position where the upper mold assembly is rigidly blocked by the hard limiting component and cannot continue descending. The contact surface is usually precision ground to ensure flatness, or adjustable shims are provided at the contact point to fine-tune the closing height during mold maintenance or adjustment.

[0058] In addition, the bottom edge of the forming punch is provided with an indentation rib, which extends along the bending line trajectory of the workpiece semi-finished product. Regarding the specific structural features of the indentation rib, in one embodiment, its cross-sectional shape can be designed as a small V-shape, trapezoid, or semi-circle. Extending along the bending line trajectory means that the length direction of the indentation rib covers the root area of ​​the bending angle that needs to be locked on the side wall of the workpiece. The indentation rib can be manufactured by integrally forming it with the forming punch using electrical discharge machining to ensure connection strength; in another embodiment, to facilitate replacement after wear, the indentation rib can also be designed as an independent carbide insert, embedded in the bottom of the punch.

[0059] When the precision limiting block and the limiting support are in rigid contact, the height of the indentation rib protruding from the bottom surface of the forming groove allows the indentation rib to penetrate 10% to 15% of the thickness of the workpiece semi-finished material. This height refers to a pre-designed dimensional difference; that is, when the rigid limiting component locks and causes the die to stop moving, the actual distance between the bottom surface of the forming punch and the bottom surface of the forming groove is slightly less than the thickness of the sheet metal. Using this penetration depth, the die can generate localized high contact pressure at the root of the bend, forcing the material in that area to undergo severe work hardening. For example, for a 0.15mm thick nickel silver material, the penetration depth can be set to approximately 0.015mm to 0.0225mm. The key to this depth setting is that it is sufficient to disrupt the elastic memory within the material, thereby maintaining the stability of the bending angle after unloading.

[0060] To monitor the forming process, the mold is equipped with a sensing system. This sensing system typically consists of a data acquisition unit, a signal transmission unit, and a processing unit. Its purpose is to transform mold debugging and production from traditional experience-based trial molding to data-driven control, especially to achieve real-time sensing and digital feedback of the rheological state of the metal material during stretching and shaping.

[0061] A piezoelectric load sensor is installed along the force transmission path of the forming punch or lower die assembly to collect real-time forming loads. Regarding the specific location of the force transmission path, in one embodiment, the sensor can be embedded in the back plate or pad of the forming punch to directly measure the force on the punch during the forming process; in another embodiment, the sensor can also be installed at the pressure-bearing center of the lower die base or at the bottom of the nitrogen spring. For sensor selection, a quartz piezoelectric sensor with high response frequency and good rigidity is typically chosen to capture millisecond-level stress relaxation changes during the pressure holding phase. The data type collected by this sensor is typically a pressure-time curve that reflects the dynamic change of load over time.

[0062] A micro-displacement sensor is installed between the guide mechanisms of the upper and lower mold assemblies to monitor the mold closing stroke. Regarding the specific attachment structure, the micro-displacement sensor can be fixed to the side of the guide pillar or guide sleeve. The sensor type can be an eddy current displacement sensor, a linear encoder, or an LVDT linear differential transformer; any displacement measuring element capable of achieving micron-level measurement accuracy is suitable. The specific physical quantity monitored by this sensor is the real-time distance between the upper mold assembly and the lower mold assembly. In particular, it can accurately capture the absolute positional change of the bottom dead center, thereby detecting and compensating for the mold's thermal expansion caused by continuous production.

[0063] Both the piezoelectric load cell and the micro-displacement sensor are electrically connected to the control system of the servo press. Regarding the specific connection method, in one embodiment, the sensor can be connected to a high-precision A / D conversion module via an anti-interference shielded cable to convert the acquired analog signals into digital signals, which are then processed by a PLC (Programmable Logic Controller) or industrial computer. The control system receives these real-time feedback signals and automatically adjusts the motion trajectory of the servo slider, the bottom dead center correction value, or the holding time according to preset algorithm logic—such as the load attenuation judgment logic mentioned in the claims—thereby achieving closed-loop control of the molding process.

[0064] The lower die assembly has a recessed overflow relief groove on its surface. This recess can be machined using precision electrical discharge machining (EDM) or high-speed milling to ensure micron-level depth accuracy. The cross-sectional shape of the overflow relief groove can be designed as a semi-circular, trapezoidal, or rectangular channel to optimize material flow guidance. In terms of layout, the overflow relief groove is typically located around the periphery of the forming groove to facilitate lateral reception of overflowing material.

[0065] One end of the overflow relief groove connects to the non-sealed area of ​​the forming groove, and the other end connects to the outside of the mold. The non-sealed area refers to the non-critical functional surfaces on the shield, such as the area of ​​process waste that will be removed in subsequent processes, the flange edge of non-mating surfaces, or the side area that does not require a strict right-angle closure. The outside of the mold refers to the space that leads to the atmospheric environment or a dedicated waste collection area to ensure that there is sufficient space to accommodate the overflowing metal material and to avoid mold blockage.

[0066] The depth of the overflow relief groove is smaller than the closing gap of the closed forming cavity, thus forming a throttling structure that allows metal flow only under overload pressure. The principle behind this throttling structure is that, due to the extremely shallow depth of the overflow relief groove—for example, 0.02 mm to 0.05 mm in one embodiment—it provides significant resistance to the flow of high-viscosity metal fluids. Under normal forming pressure, the metal material cannot overcome this resistance to flow into the groove, thus ensuring the sealing of the forming cavity and the required high-pressure environment. Only when an overload pressure condition occurs, i.e., when a positive tolerance in the workpiece material thickness causes a sharp increase in the hydrostatic pressure within the cavity and exceeds the flow resistance threshold, will the metal material be forced to flow into the overflow relief groove. This design acts like a fuse in a circuit within the mold structure, automatically releasing overload energy by sacrificing a small amount of material overflow, protecting the precision mold from damage.

[0067] In another embodiment, a precision molding process for a shielding cover is disclosed, referring to... Figure 1 This includes the following steps S1-S4.

[0068] S1. Digital Process Optimization: Before physical mold opening, a finite element simulation model is constructed, including the upper mold assembly, the lower mold assembly, and the sheet material to be processed; based on the material rheological properties of the sheet material, the dynamic stress distribution during the stretching process is simulated; and based on the simulation results, the blanking force distribution curve and shearing timing parameters are output.

[0069] In this step, a finite element simulation model is first constructed. This model needs to accurately map the boundary conditions of the physical world, specifically including the geometric data of the die, such as the CAD models of the punch, die, and blank holder; material properties, such as the stress-strain curve and anisotropy coefficient r value of C7521 nickel silver; and process parameters, such as blank holder force, friction coefficient, and stamping speed. Based on the material rheological properties of the sheet metal, that is, the dynamic relationship between stress, strain, strain rate, and temperature during the deformation process of the metal, the dynamic stress distribution during the tensile process is simulated. By understanding the variation of stress with time and deformation depth, potential cracking or wrinkling risk areas can be accurately predicted.

[0070] Taking the development of a complex, irregularly shaped shield with a depth of 5mm as an example, in stage S1, the 3D model is first imported into simulation software such as Dynaform or AutoForm, and material parameters are set. Simulation results show that when the stretching depth reaches 3mm, the stress concentration at the corners exceeds the tensile strength of the material. Based on this, the process parameters are adjusted in the software until there is no risk of breakage throughout the process, and finally an optimized process plan is output: for example, it is recommended to use a blank holder force of 2000N in the 0-2mm stroke, reduce it to 1000N in the 2-5mm stroke, and start the shearing action when the stroke reaches 2.5mm. These parameters constitute the blank holder force distribution curve and shearing timing parameters that guide the subsequent physical production.

[0071] Specifically, S1 includes the following sub-steps S11-S13.

[0072] S11. Establish the dynamic contact boundary equation between the workpiece semi-finished product and the forming punch on the upper die assembly, the die unit on the lower die assembly, and the floating pressure unit using the penalty function method or the Lagrange multiplier method, and input the preset downward stamping speed of the forming punch and the friction coefficient parameters of the contact interface between the workpiece semi-finished product and the die assembly; wherein, the dynamic contact boundary equation is used to characterize the real-time physical contact state of the contact interface between the workpiece semi-finished product and each component of the die during the deformation process.

[0073] In this step, the penalty function method or the Lagrange multiplier method is used to establish the dynamic contact boundary equations between the semi-finished workpiece and the forming punch on the upper die assembly, the die unit on the lower die assembly, and the floating blank holder unit. These dynamic contact boundary equations mathematically describe the contact relationship between the sheet metal and the die contact area during stamping, ensuring that material nodes do not penetrate the die surface during calculation. The penalty function method, by introducing virtual spring stiffness to limit node penetration, has high computational efficiency and is suitable for complex large deformation problems; the Lagrange multiplier method, by introducing additional variables to accurately satisfy the constraints, has high computational accuracy. This scheme allows for flexible selection of the appropriate algorithm based on the complexity of the model.

[0074] Simultaneously, preset parameters for the downward stamping speed of the forming punch and the friction coefficient at the interface between the workpiece semi-finished product and the die assembly are input. Because metallic materials are sensitive to strain rate, the faster the stamping speed, the more pronounced the material hardening and the greater the flow resistance. Therefore, inputting the actual speed allows the simulation results to more closely approximate actual production conditions. The friction coefficient parameter determines the resistance to material flow; different lubrication conditions correspond to different friction coefficients. This parameter directly determines whether the material can smoothly flow into the die unit and is a key variable affecting wrinkling and cracking.

[0075] Following the aforementioned shielding development embodiment, when establishing the mathematical model, the mold assembly is set as a rigid body, and the sheet metal as an elasto-plastic body. The contact algorithm is defined as the penalty function method, and a penalty factor is set to balance calculation speed and accuracy. The speed curve of the servo punch is input, which shows a trend of being fast at first and then slowing down, and the speed at material contact is set to 50 mm / s. The friction coefficient of the contact interface is set to 0.12 to correspond to the oil lubrication state in actual production. Based on these input parameters, the system calculates the distance between the sheet metal node and the mold surface at each time step. Once contact is detected, a reaction force is generated, thereby simulating real physical contact behavior.

[0076] S12. Generate a forming limit diagram, and identify potential wrinkling and cracking regions on the simulation model based on the forming limit diagram; wherein, the forming limit diagram is used to characterize the forming safety boundary of the metal material under different strain paths.

[0077] In this step, the system generates a forming limit diagram. The horizontal axis of the forming limit diagram typically represents the short-axis principal strain, and the vertical axis represents the long-axis principal strain. The diagram contains a forming limit curve. This curve defines the forming safety boundary for a specific metallic material under different strain paths and serves as a quantitative benchmark for determining the feasibility of a forming process.

[0078] Based on the generated forming limit diagram, potential wrinkling and cracking regions on the simulation model can be identified. The specific identification logic is as follows: if the strain point coordinates of a certain unit node obtained from the simulation calculation are above the forming limit curve, it indicates that the deformation at that point exceeds the physical bearing limit of the material, and the region is determined to be a cracking region; if the strain point is located in a specific compressive instability region in the lower left of the diagram, it indicates that the material is subjected to excessive tangential compressive stress, and the region is determined to be a wrinkling region; only when the strain point falls within the safe region below the forming limit curve is it determined to be a qualified forming state.

[0079] Following the above embodiment, after the simulation calculation is completed, the software generates a strain contour map with color markings. By comparing this map with the forming limit curve, if the radius (R-angle) of the shield model is displayed in red and its corresponding strain point exceeds the forming limit curve, the system determines that there is a high risk of breakage at that radius; if the flange edge is displayed in purple and its strain point falls into the wrinkling zone, the system determines that there is a risk of wrinkling at that flange edge. This process achieves precise location of forming defects.

[0080] S13. Adjust the fillet radius and friction coefficient of the contact interface of the die unit or forming punch according to the identification results, and re-execute the simulation until the wrinkled area and the cracked area disappear. Output the shearing timing parameters and the pressure setting value of the floating pressure unit at this time as the pressure force distribution curve; wherein, the pressure force distribution curve is used to characterize the relationship between the pressure force applied by the floating pressure unit to the workpiece semi-finished product and the stroke or time.

[0081] In this step, the fillet radius of the die unit or forming punch and the friction coefficient of the contact interface are adjusted based on the identification results of S12, and the simulation is re-executed. The logic of the adjustment is as follows: if a crack in the R-corner is identified, it indicates that the material flow resistance is too high or the local deformation is too severe. The material flow can be improved by increasing the fillet radius of the die, or the local stress concentration can be reduced by increasing the fillet radius of the punch. If wrinkling is identified, it indicates that the material flow velocity is too fast or the tangential compressive stress is not effectively suppressed. The friction resistance can be increased by increasing the roughness of the blank holder or increasing the initial blanking force. Conversely, if cracking occurs and the fillet adjustment is ineffective, it may be necessary to reduce the friction coefficient by improving the lubrication conditions. This is an iterative optimization process of identifying problems, correcting parameters, and verifying again, until all cracked and wrinkled areas in the simulation cloud map completely disappear and the simulation becomes a qualified and safe state.

[0082] Finally, this step outputs the shearing timing parameters and the corresponding pressure setpoint of the floating pressure unit as a pressure force distribution curve. This pressure force distribution curve is not a single fixed value, but rather a function characterizing the relationship between the pressure applied to the workpiece semi-finished product by the floating pressure unit and the stroke or time. For example, the curve can be set to apply higher pressure in the first half of the stretching stroke to suppress wrinkling, and then linearly reduce the pressure in the second half to prevent sidewall cracking. This provides precise process control data for subsequent variable resistance progressive stretching steps.

[0083] Following the above embodiments, to address the risk of R-corner cracking discovered in S12, the radius of the die fillet was adjusted from R0.5mm to R0.8mm in the simulation model; to address the risk of flange wrinkling, the initial clamping force of the first floating clamping unit was increased from 1000N to 1500N. After running the simulation again, it was found that the cracked area disappeared, but slight wrinkling still existed. Therefore, the process parameters were further optimized, maintaining the initial clamping force at 1500N, but setting the clamping force to decrease in the latter half of the stroke to facilitate material flow. After a third simulation verification, all forming indicators met the qualification standard. At this point, the software output the final process plan, determining that the shearing action should be triggered when the stretching stroke reaches 3.0mm, and generating a specific curve F(t) showing the change of clamping force with stroke, thus completing the locking from virtual simulation to physical process parameters.

[0084] S2. Synchronous Shearing and Decoupled Feeding: The sheet metal is conveyed to the bearing surface of the lower die assembly; the upper die assembly is driven downward, and the forming punch set on the upper die assembly drives the sheet metal to produce plastic deformation to form a workpiece semi-finished product; during the stroke when the forming punch contacts the sheet metal and begins to stretch, the connecting strip at the edge of the sheet metal is cut off by the synchronous shearing mechanism based on the shearing timing parameters; the vertical velocity of the shearing entry point of the synchronous shearing mechanism is controlled to be equal to the vertical sinking velocity of the neutral layer in the deformation zone of the side wall of the workpiece semi-finished product, so as to eliminate lateral tensile stress while cutting off the connecting strip.

[0085] In traditional processes, sheet metal is connected to the strip skeleton by a connecting strip. If it is not cut before stretching, the connecting strip will restrict the material from flowing into the die, causing the sidewall to crack. If it is cut too early, the workpiece will shift position due to loss of traction.

[0086] Therefore, this step implements a synchronous shearing strategy, meaning the shearing and stretching actions occur simultaneously within the same time window. The core logic lies in controlling the vertical velocity of the shearing entry point of the synchronous shearing mechanism to equal the vertical sinking velocity of the neutral layer in the deformation zone of the workpiece's semi-finished sidewall. The neutral layer, acting as a reference layer that neither elongates nor compresses during the metal sheet's deformation process, represents the true displacement rhythm of the material's deformation. The significance of velocity matching is that if the shearing speed is faster than the material sinking, the cutter will crush the material; if it is slower, the material will be torn. Only when the speeds are perfectly matched is the shearing action "transparent" to the material's tensile deformation, thus achieving flexible cutting with zero relative displacement.

[0087] Following the above embodiment, after the sheet metal is conveyed to the lower die assembly, the upper die assembly drives the forming punch downwards to contact the sheet metal. The instant the punch begins to press into the sheet metal, causing plastic deformation, the synchronous shearing mechanism is activated based on the shearing timing parameters output by S1. At this time, the downward speed of the shearing blade is precisely controlled to be synchronized with the downward speed of the sidewall material. This is analogous to stretching a piece of clay with strings attached to both ends; as the punch presses down on the clay, the scissors follow at the same speed and cut the strings. In this way, the clay remains positioned one millisecond before cutting, and at the moment of cutting, due to the synchronized speed, it is not subjected to a reverse pulling force, thus perfectly resolving the contradiction between positioning and stress relief.

[0088] Specifically, S2 includes the following sub-steps S21-S22.

[0089] S21. Progressive shearing: The wavy shearing blade edge of the forming punch sidewall is used to contact the connecting strip. The wavy shearing blade edge has a blade edge inclination angle of 1° to 2°. The shearing force is converted into a tangential component force through point contact cutting.

[0090] In this step, the purpose of designing a wavy cutting edge is to replace the traditional straight-edge contact mode, because a straight edge generates the greatest resistance and impact vibration at the moment of contact, and is prone to burrs. The wavy design breaks up the contact line, increases the rigidity of the cutting edge, and can generate a specific bending moment on the scrap at the moment of cutting to facilitate separation. At the same time, the wavy shearing cutting edge has a cutting edge inclination angle of 1° to 2°. This extremely small inclination angle physically decomposes the originally huge vertically downward punching force into a vertical cutting force and a horizontal tangential component, realizing a point contact cutting method. This method changes the force pattern of instantaneous cutting, gradually shearing from a single point, significantly reducing the maximum stamping load and reducing die vibration.

[0091] Following the above embodiment, assume the connecting strip width is 5mm. If a flat-blade shearing method is used, the shear strength of the entire 5mm length must be overcome at the moment of contact, with an impact force assumed to be 100kg. However, with a 1.5° bevel angle, the cutting edge only contacts a very small point of the material at any given moment, and the instantaneous force may drop to 10kg. This cutting process is smooth and continuous, resulting in a cleaner fracture and effectively protecting the stability of precision forming.

[0092] S22. Negative pressure waste stripping: During the shearing stroke, a negative pressure airflow is established below the shearing fracture surface through an embedded vacuum waste suction channel connected to an external negative pressure source. The negative pressure airflow is used to pull the cut waste into the waste discharge path inside the lower mold assembly.

[0093] In this step, negative pressure scrap stripping is performed. During the shearing stroke, a negative pressure airflow is established below the shearing fracture surface through an embedded vacuum scrap suction channel connected to an external negative pressure source. Due to the adhesive force or electrostatic effect of the stamping oil, the small scrap pieces cut off are very easy to adhere to the punch and rise with the die or fall onto the die surface, which can lead to product damage or die damage. The embedded channel opens directly below the shearing edge, is the closest and has the strongest suction, and uses the aerodynamic drag force generated by the high-speed airflow to actively pull the scrap, rather than relying on gravity to fall.

[0094] Within milliseconds of the shearing process, a powerful external vacuum pump activates, creating a strong negative pressure field below the shearing nozzle. At the instant of disconnection, before the waste material can adhere to the punch due to oil film, it is instantly sucked deep into the lower die by the powerful airflow and discharged through pipes to a collection box outside the die. This proactive defense mechanism ensures a clean molding environment and prevents potential hazards caused by waste material retention.

[0095] Specifically, the semi-finished workpiece has at least two independent stretching regions and connecting ribs connecting the two independent stretching regions; the following steps are also included before performing step S3: Pre-fabricated pressure relief cut: A pressure relief cut with a non-closed contour is punched at the location of the connecting rib; Geometric deformation transformation: During the stretching process in step S3, the synchronous sinking action of the two independent stretching regions is used to drive the pressure relief cut to open and deform. The geometric displacement of the pressure relief cut absorbs the material displacement difference between the two independent stretching regions, thereby blocking the transmission of tensile stress at the connecting rib.

[0096] Pre-fabricated pressure relief notches are used to address stress competition during simultaneous tensile testing of multiple cavities. When there are two deep pit structures on the shield that need to be stretched simultaneously, the connecting rib in the middle will be subjected to tensile forces to the left and right. The material in this area needs to fill both the left and right cavities, making it highly susceptible to necking fracture due to the superimposed tensile stress. Pre-fabricated pressure relief notches are created by cutting I-shaped or S-shaped slits in the rib before stretching, without removing the material, thus forming a physically disconnected, non-closed contour.

[0097] During the stretching process in step S3, the synchronous downward movement of the two independent stretching regions drives the pressure relief incision to open and deform. The physical mechanism involves forcibly converting the intense elongation deformation originally applied to the connecting rib material into displacement deformation of the pressure relief incision, i.e., an increase in the incision width. The geometric displacement of the pressure relief incision absorbs the material displacement difference between the two independent stretching regions, thereby blocking the transmission of tensile stress at the connecting rib. The opening of the incision effectively absorbs the displacement difference, causing the tensile force on the left side to stop at the left edge of the incision, and the tensile force on the right side to stop at the right edge of the incision. The rib in the middle no longer bears superimposed stress, thus protecting the integrity of the connection structure.

[0098] Taking the stretching of a dual-cavity shield as an example, if stretched directly, the connecting strip in the middle will inevitably break. With this process, as the two cavities are formed, the pre-fabricated linear cuts gradually open into rhomboid or circular holes. This method of using hole expansion instead of material stretching not only solves the problem of forming cracks, but also allows the pre-fabricated cuts to be directly used as heat dissipation holes or process positioning holes after forming, achieving an organic combination of process function and product function.

[0099] S3. Variable Resistance Progressive Stretching: The workpiece semi-finished product is continuously stretched using a multi-stage floating pressure system configured within the mold; the multi-stage floating pressure system includes at least two floating pressure units with different elastic coefficients arranged sequentially along the feeding direction; based on the pressure force distribution curve, each of the floating pressure units applies independently set pressure forces to the flange area of ​​the workpiece semi-finished product at different stretching stations to control the frictional resistance of the workpiece semi-finished product flowing into the mold cavity, and to form a pre-formed warp corner feature at the end of the side wall of the workpiece semi-finished product at the end of the stretching.

[0100] During process implementation, based on the blanking force distribution curve output from step S1, each floating blanking unit applies independently set blanking forces to the flange area of ​​the workpiece semi-finished product at different stretching stations. The core of its control lies in precisely controlling the frictional resistance of the workpiece semi-finished product flowing into the mold cavity by adjusting the blanking force, and forming a pre-formed warp corner feature at the end of the side wall of the workpiece semi-finished product at the end of stretching.

[0101] In traditional progressive drawing, a uniform nitrogen spring or rubber is typically used to provide a constant blank holder force. However, the physical requirements of metal flow at different stages of the drawing process are diametrically opposed: high resistance is needed initially to suppress wrinkling, while low resistance is needed later to prevent tearing. Constant pressure cannot simultaneously meet these two requirements. The multi-stage floating blank holder system of this application adopts a physical divide-and-conquer strategy. By deploying multiple independent floating units within the die and equipping each unit with a power source with a different stiffness coefficient, it achieves decoupling of pressure in spatial distribution and time sequence. The essence of drawing is material flow; the positive pressure generated by the blank holder force is converted into frictional resistance. By controlling the blank holder force in stages, it is essentially precisely adjusting the flow threshold of material into the die cavity.

[0102] At the end of S3, the process goal is not to achieve perfectly vertical sidewalls, but rather to intentionally retain an outward-flaring, trumpet-shaped feature. This pre-formed upturn is not a forming defect, but rather a reserve of interference material for the closed-loop forming in step S4. Without this upturn, the subsequent interference forming step would be unable to effectively fill the joint due to a lack of excess metal.

[0103] Following the aforementioned stretching case of the 5mm deep shield, the stretching process was planned to be carried out in stages. Station A was responsible for the initial stretching to a depth of 2mm, and station B was responsible for the final stretching to a depth of 5mm. Although both are stretching processes, the elastic elements under stations A and B are configured completely differently. Station A is equipped with high-stiffness elastic elements to provide strong edge clamping, ensuring that the material is firmly held in place during the initial flow to prevent wrinkling; station B is equipped with low-stiffness elastic elements to provide flexible support, reducing resistance and preventing sidewall breakage. The final stretched product retains a small outward flare of about 3 degrees at the root of the sidewall, which is the geometric feature preset to achieve zero-gap closure.

[0104] Specifically, S3 includes the following sub-steps S31-S32.

[0105] S31. High-resistance initial stretching: In the initial stretching station, a first floating pressure unit is used to provide a first order of magnitude of pressure force; wherein, the first floating pressure unit uses a high-stiffness gas spring as an elastic element, and in the initial stage of plastic deformation when the workpiece semi-finished product begins to flow into the mold cavity, it presses the flange area of ​​the workpiece semi-finished product against the concave surface of the lower mold assembly, thereby straightening the material fibers and suppressing wrinkling by increasing the feeding friction resistance of the workpiece semi-finished product from the flange area to the mold cavity.

[0106] In the initial stretching stage, a first floating pressure unit provides the initial pressure force. To achieve this high pressure, the first floating pressure unit uses a high-stiffness gas spring as the elastic element. Its physical mechanism addresses the risk of wrinkling during the initial stretching stage. When the flat workpiece semi-finished product begins to flow into the cylindrical mold cavity, the material in the outer flange area is subjected to severe tangential compressive stress, making it highly susceptible to structural instability and resulting in folding and arching, i.e., wrinkling. The gas spring possesses extremely high initial force and a constant force curve characteristic, capable of providing pressure exceeding tons at the moment of material contact—something difficult to achieve with ordinary helical springs.

[0107] In the initial stage of plastic deformation, when the workpiece semi-finished product begins to flow into the mold cavity, the first floating blank holder unit, driven by the aforementioned high-rigidity gas spring, tightly presses the flange area of ​​the workpiece semi-finished product against the die surface of the lower mold assembly. The enormous blank holder force is converted into significant feeding friction resistance. Under the combined action of the downward ejection force of the punch and the resistance applied by the blank holder ring, the metal material fibers are forcibly straightened, and this straightening effect effectively counteracts the tangential compressive stress that causes wrinkling.

[0108] Following the stretching embodiment of station A described above, in the first stretching step responsible for the 0-2mm stroke, a nitrogen spring with a pressure set to 2000N was selected as the first elastic element. Within the 0-2mm stroke range when the forming punch contacts the material and begins its downward movement, before the material undergoes significant arching deformation, it is tightly pressed against the die surface by a constant pressure of 2000N. Constrained by high frictional resistance, the material can only smoothly slide into the cavity while adhering to the die surface. Any slight tendency to wrinkle is eliminated by the high pressure in its initial stage, thus ensuring the surface quality of the initial stretching.

[0109] S32. Low-resistance secondary stretching: In the secondary stretching station, a second floating pressure unit is used to provide a second level of pressure force; wherein, the second floating pressure unit uses a helical spring as an elastic element, and the second level of pressure force is less than the first level of pressure force; during the continuous stage of plastic deformation in which the material of the workpiece semi-finished product continuously flows into the mold cavity and forms the sidewall, the second floating pressure unit sinks synchronously with the bottom of the workpiece semi-finished product to prevent excessive thinning of the sidewall.

[0110] In the secondary stretching stage, a second floating pressure unit provides a second level of pressure. To achieve this low pressure, the second floating pressure unit uses a helical spring as the elastic element, and the second level of pressure is set to be significantly lower than the first level. This configuration is based on the rheological characteristics of the deep stretching stage: as the stretching depth increases, a large amount of material flows into the die to form the sidewalls, and the forming force required for further stretching is mainly transmitted through the sidewalls. If the high edge force from the initial stretching stage is maintained at this point, the huge feed friction resistance will cause the tensile stress on the sidewalls to exceed the tensile limit of the material, leading to excessive thinning, necking, or even fracture of the sidewalls. Compared to gas springs, helical springs have lower stiffness and their pressure increases linearly with the stroke, resulting in a smaller initial force, making them suitable for providing flexible support at this stage.

[0111] During the continuous plastic deformation stage where the material of the workpiece semi-finished product flows into the mold cavity and forms the sidewall, the second floating pressure unit sinks synchronously with the bottom of the workpiece semi-finished product. At this time, the function of the floating pressure unit changes from strong pressing to bottom support and guidance. Its following action not only prevents the bottom of the workpiece from collapsing and deforming due to suspended force, but also ensures that the material in the flange area can flow smoothly into the cavity under low resistance, thus protecting the thickness of the sidewall.

[0112] Following the stretching embodiment of station B described above, in the second stretching step responsible for stretching from 2mm to 5mm depth, the elastic element below the floating pressure unit is replaced with a lower-stiffness helical spring, and its pressure force is set to only 500N. At this point, although the material continues to flow, the feed friction resistance is reduced to about one-quarter of that in the first stretching step. The sidewall does not need to bear a huge tensile force to draw the flange material in, thus ensuring the safety of the deep stretching process. The final product has a uniform sidewall thickness, with no signs of thinning or breakage.

[0113] S4. Closed-volume servo shaping: When the upper die assembly descends to the position where the servo press slide reaches the bottom dead center, the forming punch and the shaping groove on the lower die assembly enclose each other to form a closed shaping cavity; the geometric volume of the closed shaping cavity is configured to be smaller than the solid material volume of the workpiece semi-finished product at the bottom dead center position, and a hydrostatic pressure field is established in the closed shaping cavity; the servo press slide is controlled to maintain a preset pressure holding period at the bottom dead center position, and the hydrostatic pressure field is used to drive the metal material of the workpiece semi-finished product to creep flow until the pre-formed warp feature is eliminated and the geometric gap of the shaping groove is filled.

[0114] When the upper die assembly descends, driving the servo press slide to the bottom dead center position, the forming punch and the shaping groove on the lower die assembly enclose each other to construct a closed shaping cavity. The key process parameter configuration for this step is that the geometric volume of the closed shaping cavity is strictly smaller than the solid material volume of the workpiece semi-finished product at the bottom dead center position. Here, the solid material volume specifically refers to the total volume of the metal material, including the reserved pre-formed warp corner portion. By creating a volume difference where the volume is smaller than the solid material volume, a mechanical interference state is physically created within the rigid cavity.

[0115] Based on this mechanical interference state, a hydrostatic pressure field is established within the closed forming cavity. Under this environment, the metallic material is subjected to extremely high pressure stress from all directions, and its stress state is similar to that of a fluid under pressure. This triaxial compressive stress state significantly improves the plasticity of the metal, activates its flow potential, and makes it exhibit flow characteristics similar to high-viscosity fluids. Simultaneously, this process utilizes the creep characteristics of metallic materials. In the high-pressure cold forming environment of this process, creep refers to the phenomenon that dislocation slip and grain boundary slip within metal crystals continue to occur over time under constant high stress. Utilizing this characteristic, directional migration at the microscopic level of the material can be achieved without disrupting the material's continuity.

[0116] During execution, the servo press slider is controlled to maintain a preset pressure holding period at the bottom dead center position, for example, by using the position locking function of the servo system to forcibly maintain the mold in a closed state. At this time, the pre-formed warp corner, as a reserved interference fit material, is forcibly squeezed under the drive of the hydrostatic pressure field and flows to the tiny geometric dead angles or gaps in the shaping groove. For example, for a shielding cover requiring extremely high sealing performance, the approximately 3-degree warp corner material reserved in step S3 will gradually flow to the V-shaped gap on the inside of the bend or the right angle part with a radius of 0.05mm during the pressure holding process until it is completely filled. This process eliminates the characteristics of the pre-formed warp corner and fills the geometric gaps in the shaping groove. It not only eliminates springback through intense plastic flow but also forms a physically continuous and dense right-angle structure, achieving zero-gap closure.

[0117] Specifically, S4 includes the following sub-steps S41-S44.

[0118] S41. Interference Volume Construction: Calculate the target volume based on the negative tolerance limit of the sheet thickness of the semi-finished workpiece, and set the volume of the closed shaping cavity to be equal to the target volume; and connect an overflow relief groove with a depth of less than 0.05mm to the non-sealed area of ​​the shaping groove.

[0119] This step first calculates the target volume based on the negative tolerance limit of the sheet metal thickness of the semi-finished workpiece, and then sets the volume of the closed forming cavity to be equal to this target volume. This design strategy aims to address tolerance fluctuations in sheet metal thickness. Taking a sheet metal with a standard thickness of 0.15mm and a tolerance of ±0.01mm as an example, if the volume is designed according to the standard thickness, when processing the thinnest sheet metal of 0.14mm, an effective mechanical interference fit may not be formed, leading to failure in establishing the hydrostatic pressure field and forming failure. By designing the cavity volume based on the negative tolerance limit of 0.14mm, it is ensured that even with the thinnest material, the cavity volume is still less than or equal to the volume of the solid material, thereby guaranteeing that a mechanical interference fit can be constructed under any material thickness condition.

[0120] Furthermore, this step also involves connecting an overflow pressure relief groove with a depth of less than 0.05 mm to the non-sealed area of ​​the forming groove. This overflow pressure relief groove is typically located in the trimming waste area or on the edge of the non-sealed flange, serving as a tiny fluid channel. The physical significance of setting its depth to be extremely shallow (e.g., less than 0.05 mm) is to create extremely high flow resistance. Under normal forming pressure, the metal material is unlikely to overcome this resistance to flow into the groove, thus ensuring the sealing of the closed cavity and the required high-pressure environment. Only when the pressure inside the cavity abnormally rises to the overload threshold due to excessive interference fit can the metal material be forcibly squeezed into this channel.

[0121] Following the above embodiment, if the mold cavity height is designed with a negative tolerance limit of 0.14mm, the material will be just compacted when processing 0.14mm sheet metal. When processing 0.16mm sheet metal with a positive tolerance, the excess 0.02mm of material volume will cause the cavity pressure to spike dramatically. At this point, the overflow relief groove with a depth of 0.03mm comes into play. The excessive pressure drives the excess metal to overcome the flow channel resistance and be squeezed into the groove to form an extremely thin flash, thereby releasing the excessive internal pressure and preventing the mold from being damaged by bursting. It acts as an overload protection similar to a circuit fuse.

[0122] S42. Directional creep filling and monitoring: The servo press slider is controlled to maintain a pressure holding period of 50ms to 100ms at the bottom dead center position; during this period, the molding load value of the mold is monitored in real time; if the molding load value exceeds the preset safety threshold, the interference pressure is used to drive the excess metal material to plastically flow into the overflow relief groove.

[0123] In this step, directional creep filling and monitoring are performed. The specific control logic is as follows: the servo press slider is controlled to maintain a holding pressure period of 50ms to 100ms at the bottom dead center. The scientific basis for setting this time window is to match the cold rheological characteristics of the metal material. If the holding time is less than 50ms, the stress release inside the material is often insufficient, resulting in incomplete elimination of springback; if the holding time exceeds 100ms, the marginal contribution to molding quality decreases, and it will significantly reduce strokes per minute (SPM), affecting production efficiency. Therefore, this time range is the optimal process window that balances molding quality and production efficiency.

[0124] During this pressure holding period, the system monitors the molding load value of the mold in real time. The molding load value directly reflects the pressure state inside the closed cavity, and monitoring this value aims to determine in real time whether an overload has occurred. If the molding load value exceeds the preset safety threshold, an adaptive mechanism that drives excess metal flow through interference pressure is triggered. For example, when encountering ultra-thick sheet metal, the pressure inside the cavity may instantly exceed the safety threshold (e.g., 300 tons). At this time, the extremely high internal pressure is sufficient to overcome the preset flow channel resistance of the overflow relief groove, forcing the metal material in the weakest position (usually located in the non-sealed area) to undergo plastic flow and be squeezed into the groove. This constructs an adaptive protection mechanism based on physical principles, rather than simply relying on the shutdown protection of the electronic control system.

[0125] Following the above embodiment, in actual production, the servo slider remains stationary at the bottom dead center position for a duration set to 75ms. During this 75ms pressure holding period, the sensor reading shows a stable pressure of 200 tons, indicating that the filling process is normal. If a sheet of material with an abnormal thickness (e.g., 0.17mm) is suddenly fed in, the monitored pressure will instantly surge to 350 tons. At this point, without waiting for the system to execute a stop command, the excessive interference pressure directly drives the excess metal into the overflow relief groove, thereby clamping the internal pressure of the mold within a safe range and effectively protecting the expensive precision inserts and hard limiting structures from damage.

[0126] S43. Load attenuation determination: During the pressure holding period, real-time load signals are collected and the load attenuation rate is calculated.

[0127] S44. Flexible return: When the absolute value of the load attenuation rate is less than the preset relaxation convergence threshold, the servo press slider is controlled to start the return action according to the S-shaped speed curve.

[0128] During the pressure holding period, the system collects real-time load signals through sensors and calculates the load decay rate. The load decay rate refers to the rate at which the external pressure required to maintain the same deformation gradually decreases during the pressure holding process, as the metal material fills the voids and undergoes internal lattice rearrangement, resulting in stress relaxation; in other words, how quickly the pressure decreases over time. The purpose of calculating this rate is to use it as a microscopic physical indicator to determine whether the forming process is complete. A large decay rate indicates that the material is still in a stage of vigorous flow and adjustment; when the decay rate approaches zero, it indicates that the material has become stable internally, and the internal stress has been largely released.

[0129] When the absolute value of the calculated load decay rate is less than a preset relaxation convergence threshold, the servo press slider is controlled to start the return stroke according to an S-shaped speed curve. The relaxation convergence threshold is a preset critical value, for example, 0.01 tons / millisecond. When the decay rate is lower than this value, the system determines that the metal material has reached rheological equilibrium, i.e., the molding is complete. The significance of using an S-shaped speed curve return stroke is to avoid the instantaneous release of the elastic potential energy accumulated in the mold caused by directly and rapidly lifting the slider. The shock wave generated by such an instantaneous release may damage precision-molded parts or cause micro-cracks. The S-shaped curve is characterized by slow start and fast acceleration, allowing the elastic deformation of the mold to recover slowly, achieving flexible stress relief.

[0130] Following the above embodiment, assume the initial molding load at the start of the holding pressure is 200 tons. At 10ms after the start of the holding pressure, the load drops to 195 tons, at which point the decay rate is relatively fast. By 60ms, the load drops to 190 tons and remains almost constant for the next 10ms. The system calculates that the load decay rate at this point is below a preset threshold, determining that the metal has reached rheological equilibrium. It then instructs the slider to move upwards a very slow distance, e.g., 0.1mm, at an extremely slow speed, e.g., 1mm / s, to first release the elastic tension of the mold, and then accelerates its return stroke. The shield produced using this control logic exhibits high dimensional stability, no springback, and effectively extends the mold's service life.

[0131] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0132] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A precision molding process for a shielding cover, characterized in that, Includes the following steps: S1. Digital Process Optimization: Before physical mold opening, a finite element simulation model is constructed, including the upper mold assembly, the lower mold assembly, and the sheet material to be processed; based on the material rheological properties of the sheet material, the dynamic stress distribution during the stretching process is simulated; and based on the simulation results, the blanking force distribution curve and shearing timing parameters are output. S2. Synchronous Shearing and Decoupled Feeding: The sheet metal is conveyed to the bearing surface of the lower die assembly; the upper die assembly is driven downward, and the forming punch set on the upper die assembly drives the sheet metal to produce plastic deformation to form a workpiece semi-finished product; during the stroke of the forming punch contacting the sheet metal and starting to stretch, the connecting strip at the edge of the sheet metal is cut off by the synchronous shearing mechanism based on the shearing timing parameters; the vertical velocity of the shearing entry point of the synchronous shearing mechanism is controlled to be equal to the vertical sinking velocity of the neutral layer in the deformation zone of the side wall of the workpiece semi-finished product, so as to eliminate lateral tensile stress while cutting off the connecting strip; S3. Variable Resistance Progressive Stretching: The workpiece semi-finished product is continuously stretched using a multi-stage floating pressure system configured in the mold; the multi-stage floating pressure system includes at least two floating pressure units with different elastic coefficients arranged sequentially along the feeding direction; based on the pressure force distribution curve, each of the floating pressure units applies an independently set pressure force to the flange area of ​​the workpiece semi-finished product at different stretching positions to control the frictional resistance of the workpiece semi-finished product flowing into the mold cavity, and to form a pre-formed warp corner feature at the end of the side wall of the workpiece semi-finished product at the end of the stretching. S4. Closed-volume servo shaping: When the upper die assembly descends to the position where the servo press slide reaches the bottom dead center, the forming punch and the shaping groove on the lower die assembly enclose each other to form a closed shaping cavity; the geometric volume of the closed shaping cavity is configured to be smaller than the solid material volume of the workpiece semi-finished product at the bottom dead center position, and a hydrostatic pressure field is established in the closed shaping cavity; the servo press slide is controlled to maintain a preset pressure holding period at the bottom dead center position, and the hydrostatic pressure field is used to drive the metal material of the workpiece semi-finished product to creep flow until the pre-formed warp feature is eliminated and the geometric gap of the shaping groove is filled.

2. The precision molding process for the shielding cover according to claim 1, characterized in that, S1 includes the following sub-steps: S11. Establish the dynamic contact boundary equation between the workpiece semi-finished product and the forming punch on the upper die assembly, the die unit on the lower die assembly, and the floating pressure unit using the penalty function method or the Lagrange multiplier method, and input the preset downward stamping speed of the forming punch and the friction coefficient parameters of the contact interface between the workpiece semi-finished product and the die assembly; wherein, the dynamic contact boundary equation is used to characterize the real-time physical contact state between the workpiece semi-finished product and the contact interface of each component of the die during the deformation process; S12. Generate a forming limit diagram, and identify potential wrinkling and cracking regions on the simulation model based on the forming limit diagram; wherein, the forming limit diagram is used to characterize the forming safety boundary of the metal material under different strain paths; S13. Adjust the fillet radius and friction coefficient of the contact interface of the die unit or forming punch according to the identification results, and re-execute the simulation until the wrinkled area and the cracked area disappear. Output the shearing timing parameters and the pressure setting value of the floating pressure unit at this time as the pressure force distribution curve; wherein, the pressure force distribution curve is used to characterize the relationship between the pressure force applied by the floating pressure unit to the workpiece semi-finished product and the stroke or time.

3. The precision molding process for the shielding cover according to claim 1, characterized in that, S2 includes the following sub-steps: S21. Progressive shearing: The wavy shearing blade edge of the forming punch sidewall is used to contact the connecting strip. The wavy shearing blade edge has a blade edge inclination angle of 1° to 2°. The shearing force is converted into a tangential component force through point contact cutting. S22. Negative pressure waste stripping: During the shearing stroke, a negative pressure airflow is established below the shearing fracture surface through an embedded vacuum waste suction channel connected to an external negative pressure source. The negative pressure airflow is used to pull the cut waste into the waste discharge path inside the lower mold assembly.

4. The precision molding process for the shielding cover according to claim 1, characterized in that, S3 includes the following sub-steps: S31. High-resistance initial stretching: In the initial stretching station, a first floating pressure unit is used to provide a first order of magnitude of pressure force; wherein, the first floating pressure unit uses a high-stiffness gas spring as an elastic element, and in the initial stage of plastic deformation when the workpiece semi-finished product begins to flow into the mold cavity, it presses the flange area of ​​the workpiece semi-finished product against the concave surface of the lower mold assembly, thereby straightening the material fibers and suppressing wrinkling by increasing the feeding friction resistance of the workpiece semi-finished product from the flange area to the mold cavity; S32. Low-resistance secondary stretching: In the secondary stretching station, a second floating pressure unit is used to provide a second level of pressure force; wherein, the second floating pressure unit uses a helical spring as an elastic element, and the second level of pressure force is less than the first level of pressure force; during the continuous stage of plastic deformation in which the material of the workpiece semi-finished product continuously flows into the mold cavity and forms the sidewall, the second floating pressure unit sinks synchronously with the bottom of the workpiece semi-finished product to prevent excessive thinning of the sidewall.

5. The precision molding process for the shielding cover according to claim 1, characterized in that, S4 includes the following sub-steps: S41. Interference Volume Construction: Calculate the target volume based on the negative tolerance limit of the sheet thickness of the semi-finished workpiece, and set the volume of the closed shaping cavity to be equal to the target volume; and connect an overflow relief groove with a depth of less than 0.05mm to the non-sealed area of ​​the shaping groove. S42. Directional creep filling and monitoring: Control the servo press slider to maintain a pressure holding period of 50ms to 100ms at the bottom dead center position; during this period, monitor the molding load value of the mold in real time; If the molding load value exceeds the preset safety threshold, the interference pressure is used to drive the excess metal material to plastically flow into the overflow relief groove. S43. Load attenuation determination: During the pressure holding period, real-time load signals are collected and the load attenuation rate is calculated; S44. Flexible return: When the absolute value of the load attenuation rate is less than the preset relaxation convergence threshold, the servo press slider is controlled to start the return action according to the S-shaped speed curve.

6. The precision molding process for the shielding cover according to claim 1, characterized in that, The semi-finished workpiece has at least two independent stretching regions and connecting ribs connecting the two independent stretching regions; the following steps are also included before performing step S3: Pre-fabricated pressure relief cut: A pressure relief cut with a non-closed contour is punched at the location of the connecting rib; Geometric deformation transformation: During the stretching process in step S3, the synchronous sinking action of the two independent stretching regions is used to drive the pressure relief cut to open and deform. The geometric displacement of the pressure relief cut absorbs the material displacement difference between the two independent stretching regions, thereby blocking the transmission of tensile stress at the connecting rib.

7. The precision molding process for the shielding cover according to claim 1, characterized in that, The mold includes: The upper die assembly is configured as a slider fixedly connected to the servo press, and the upper die assembly is provided with a plurality of forming punches and shaping punches in sequence along the feeding direction; The lower die assembly is fixedly mounted on the worktable and has a die unit and a shaping groove corresponding to the positions of the forming punch and the shaping punch. A multi-stage floating pressure system is slidably disposed within the die unit; the system includes a first floating pressure unit located at the primary stretching station and a second floating pressure unit located at the secondary stretching station; the first floating pressure unit is connected to a first elastic element, the second floating pressure unit is connected to a second elastic element, and the elastic coefficient of the first elastic element is greater than the elastic coefficient of the second elastic element; The synchronous shearing mechanism includes a wave-shaped shearing blade integrally formed on the side wall of the forming punch, and an embedded vacuum waste suction channel that penetrates the interior of the lower die assembly. The closed extrusion forming structure is composed of the forming punch and the forming groove; when the mold is closed to the bottom dead center, the forming punch and the forming groove enclose the closed forming cavity.

8. The precision molding process for the shielding cover according to claim 7, characterized in that, The mold also includes: A hard limiting component includes a precision limiting block disposed on an upper mold assembly and a limiting support disposed on a lower mold assembly; the contact surface between the precision limiting block and the limiting support defines the bottom dead center position of the mold. The indentation rib is protruding from the bottom edge of the forming punch and extends along the bending line trajectory of the workpiece semi-finished product. When the hard limiting component is in a rigid contact state, the height of the indentation rib protruding from the bottom surface of the shaping groove is such that the indentation rib penetrates 10% to 15% of the thickness of the workpiece semi-finished material.

9. The precision molding process for the shielding cover according to claim 8, characterized in that, The surface of the lower mold assembly is recessed with an overflow pressure relief groove; one end of the overflow pressure relief groove is connected to the non-sealed area of ​​the shaping groove, and the other end is connected to the outside of the mold; the depth dimension of the overflow pressure relief groove is smaller than the closing gap dimension of the closed shaping cavity, forming a throttling structure that allows metal flow only under overload pressure.

10. The precision molding process for the shielding cover according to claim 9, characterized in that, The mold also includes: A piezoelectric load sensor is installed on the force transmission path of the forming punch or lower die assembly to collect real-time forming load. A micro-displacement sensor is installed between the guide mechanism of the upper mold assembly and the lower mold assembly to monitor the mold closing stroke; both the piezoelectric load sensor and the micro-displacement sensor are electrically connected to the control system of the servo press.

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