Shielding case progressive die device with zero-gap bending forming function and method

Abstract

The invention relates to a shielding case progressive die device with a zero-gap bending forming function, the device comprises a lower die assembly, an upper die assembly and a forming bending punch, the side wall of the punch is provided with a shearing edge, and the shearing edge is matched with a lower die to cut off a side edge connecting belt in the bending stroke so as to maintain positioning; the lower die is provided with a shaping groove corresponding to a prefabricated upwarp angle of a product, and when the die is closed to a bottom dead center, the shaping groove and the punch enclose to form a closed extrusion cavity with the volume smaller than that of a material, so that the upwarp angle material is forced to plastically flow and backfill a joint. The method has the advantages that the physical zero gap of the side wall is achieved through the mold closing force, electromagnetic leakage can be blocked without the welding procedure, and the forming precision is high.

Description

Technical Field

[0001] This application relates to the field of stamping dies, and in particular to a progressive die device and method for a shield cover with zero-gap bending forming function. Background Technology

[0002] In the manufacturing of mobile communication terminals and precision electronic equipment, metal shielding covers are fundamental components for ensuring the electromagnetic compatibility (EMC) of circuit systems. These components are typically made of thin sheets of stainless steel or nickel silver, and their main function is to physically isolate sensitive components such as internal radio frequency chips and power management units from the external electromagnetic environment by constructing a sealed conductive shell, thereby preventing the entry and exit of electromagnetic interference signals. As communication technology evolves towards higher frequency bands, the market has raised the bar for the sealing performance of shielding covers, requiring them to form a closed space with good electrical continuity after installation.

[0003] Existing shielding cover forming processes generally employ progressive dies for automated production, with core steps typically including unpacking and bending. In traditional bending processes, metal sheets are bent along a pre-set bending line under the action of the die to form sidewalls. However, due to the inherent elastic modulus of metal materials, the sheet often experiences a certain degree of elastic recovery, or springback, when the external force is unloaded after bending. This springback makes it difficult for the shielding cover's sidewalls to maintain an ideal vertical state. More importantly, at the junction of two adjacent sidewalls, due to the coexistence of tensile and compressive deformation of the material, traditional processes struggle to achieve a tight fit between the edges of adjacent sidewalls. Typically, a V-shaped or irregularly shaped gap that gradually widens from the root to the top naturally forms at the joint between these two sidewalls.

[0004] For low-frequency signals, minute structural gaps may have little impact, but in high-frequency communication scenarios, even minute geometric gaps can become channels for electromagnetic wave leakage, leading to a significant decrease in shielding effectiveness. To address this gap issue, existing technologies often require additional post-processing steps, such as laser welding or soldering to fill the corners after bending. This not only increases production costs and process complexity but may also cause product deformation due to heat-affected zones, affecting subsequent surface mount yield. Furthermore, some processes attempt to force the gap closed by increasing bending pressure, but this can easily lead to accelerated mold wear and product dimensional tolerance exceeding limits. Summary of the Invention

[0005] In order to achieve physical closure of the bending corner and eliminate the risk of electromagnetic leakage by improving the structure and process of the stamping die without adding subsequent welding processes, this application provides a shielding cover progressive die device and method with zero-gap bending forming function.

[0006] Firstly, the shielding cover progressive die device with zero-gap bending forming function provided in this application adopts the following technical solution: A shielding cover progressive die device with zero-gap bending forming function includes a lower die assembly, an upper die assembly, an elastically set forming stripping float, and a forming bending punch. The lower mold assembly is a fixed mold base, and the upper mold assembly is located above the lower mold assembly and can reciprocate vertically relative to the lower mold assembly; the forming stripping float is elastically disposed within the lower mold assembly to support the shielding cover product to be processed and provide elastic floating stroke in the vertical direction; the forming bending punch is fixedly disposed on the upper mold assembly and is located directly above the forming stripping float; The side wall of the forming and bending punch is provided with a shearing edge. The shearing edge is located at the vertical projection position corresponding to the side connecting strip of the shield product. When the upper die assembly drives the forming and bending punch to perform the bending stroke, the shearing edge cooperates with the corresponding edge on the lower die assembly to cut off or partially cut off the side connecting strip, so as to maintain the positioning connection between the product and the material strip skeleton during the forming process. The lower die assembly has a shaping groove at the pre-formed upturned corner position corresponding to the bending angle of the shield product. The shaping groove has an inwardly contracting negative angle or right angle inner wall profile. When the upper die assembly moves down to the lower dead point position relative to the lower die assembly, the forming bending punch and the shaping groove of the lower die assembly enclose each other to form a closed extrusion cavity. The volume of the closed extrusion cavity is smaller than the volume of the metal material containing the pre-formed upturned corner. The closing locking force of the upper die assembly is used to apply lateral extrusion to the pre-formed upturned corner, forcing the metal material at the upturned corner to undergo plastic flow and backfill to the bending joint, so as to physically close the side wall gap of the shield.

[0007] By adopting the above technical solution, this invention utilizes the shearing edge of the forming bending punch's sidewall to cut or partially cut the side connecting strip during the bending stroke, achieving continuous positioning and connection between the product and the material strip skeleton during the forming process. This avoids positioning offset caused by complete material separation in traditional single-process bending. Simultaneously, the closed extrusion cavity, smaller than the volume of the metal material, formed by the shaping groove of the lower die assembly and the forming bending punch at the bottom dead center, transforms the vertical closing locking force of the upper die assembly into a lateral extrusion force on the pre-formed warped corner. This forces the metal material to undergo plastic flow and directionally backfill to the bending joint, achieving physical closure of the shielding cover's sidewall gaps without adding subsequent welding processes, effectively blocking electromagnetic wave leakage channels.

[0008] Optionally, the forming bending punch is provided with a hard limiting step, and the lower die assembly is provided with a corresponding limiting post; the height difference between the hard limiting step and the limiting post is set such that when the die is closed, the pressing depth of the forming bending punch into the bending root of the product is 10% to 15% of the material thickness, so as to cooperate with the material flow of the pre-formed corner to lock the bending angle.

[0009] By adopting the above technical solution, a precise mechanical reference for the bottom dead center of the mold is established by the rigid contact between the hard limiting step and the limiting post, ensuring the consistency of the forming height. By setting the indentation depth at the root of the bend to 10%~15% of the material thickness, an indentation effect is generated in the stress concentration area of ​​the bend, which changes the stress distribution inside the material and converts elastic strain energy into plastic deformation. This effectively suppresses the springback phenomenon after the metal material is unloaded, locks the bending angle to ensure geometric accuracy, and provides a stable geometric boundary for the plastic flow of the pre-formed warp corner, ensuring the reliability of the filling.

[0010] Optionally, the lower die assembly is provided with a vacuum waste suction channel directly below the shearing blade, and the shearing blade is designed as a 1°~2° wavy oblique blade to prevent the cut connecting waste from jumping up and getting stuck in the shaping groove when the side continuous shearing action occurs.

[0011] By adopting the above technical solution, the 1°~2° wavy oblique blade design transforms the instantaneous full-segment shearing into a gradual point-contact shearing, effectively reducing the impact load and vibration during punching and minimizing the initial rebound kinetic energy imparted to the cut waste. Combined with the vacuum waste suction channel directly below, a negative pressure field is established on the shear fracture surface. Pneumatic suction applies a directional downward traction force to the small waste particles, forcing them to detach from the die working surface and enter the discharge channel. This synergistic effect of mechanical shock absorption and pneumatic adsorption eliminates the risk of waste entering the precision forming groove due to elastic rebound or electrostatic adsorption, preventing surface damage to the product or damage to the die cutting edge, and ensuring the stability and yield of the zero-gap forming structure during high-speed continuous stamping.

[0012] Secondly, the zero-gap forming method for a shielding cover provided in this application adopts the following technical solution: A method for forming a shield with zero gaps, used in the aforementioned progressive mold device for forming a shield with zero gap bending function, includes the following steps: S1. The semi-finished shielding cover with pre-made upturned corners is conveyed into the mold through the side connecting belt; S2. Control the slide of the servo press to decelerate, and press the product surface through the forming stripping float; wherein, the slide is the power output component of the servo press, connected to the upper mold assembly and driving the upper mold assembly to reciprocate vertically relative to the lower mold assembly; S3. Control the slider to descend at a constant low speed, and simultaneously complete the shearing and release of the side connecting strip and the bending of the product side wall through the forming and bending punch; S4. When the slider reaches the bottom dead center, the servo pressure holding program is executed to control the slider to stop moving and maintain the preset pressure holding time. During this pressure holding time, the mold device maintains the forced extrusion state on the pre-made warped corner, and utilizes the creep characteristics of the metal material to make the warped corner material flow fully and fill the bending joint to form a seamless closed structure.

[0013] By adopting the above technical solution, this invention optimizes the dynamics of stamping by utilizing the programmable motion characteristics of a servo press. During the blanking stage, controlling the slide deceleration reduces the inertial impact when the forming ejector block contacts the product surface, avoiding interference with positioning accuracy caused by vibrations from high-speed collisions. During the forming stage, a constant low-speed descent ensures strain rate stability during shearing release and bending deformation, preventing material tearing and dimensional deviations caused by speed fluctuations or instantaneous stress concentration.

[0014] The servo-controlled pressure holding program, executed at the bottom dead center, transforms traditional instantaneous mechanical forming into a material rheological process that incorporates a time dimension. By maintaining the rigid locking and forced extrusion of the pre-formed warped corner with the mold for a preset pressure holding time, a continuous high-pressure stress boundary condition is constructed, inducing lattice slip and microstructure rearrangement by utilizing the creep characteristics of metallic materials. This time-dependent plastic flow mechanism allows the metallic material at the warped corner to fully extend and migrate directionally to fill the geometric gaps at the bending joint, effectively overcoming the elastic rebound caused by instantaneous unloading. A seamless closed structure of the shield sidewall is achieved solely through mechanical plastic deformation.

[0015] Optionally, the pressure holding time in step S4 is set to 50ms to 100ms; Furthermore, in step S4, a micron-level displacement sensor installed inside the mold is used to monitor the closing height in real time. If the deviation of the closing height caused by thermal expansion exceeds ±0.005mm, the servo control system automatically adjusts the bottom dead center position of the slider to ensure that the extrusion pressure of the forced filling is constant.

[0016] By adopting the above technical solution, this invention subdivides the traditional static pressure holding process into two distinct stages: physical filling and stress relaxation. During the first pressure holding period, by controlling the slider to reach the bottom dead center at a near-zero speed, the inertial impact during the rigid closure of the hard-limiting structure is eliminated, protecting the fitting accuracy of the mold components. Simultaneously, the indentation ribs apply initial pressure to the root of the bend, establishing a high-pressure stress field within the closed space formed by the pre-formed warp and the shaping groove. This forces the metal lattice to slip along a preset path, generating directional plastic flow pointing towards the inner joint of the bend, achieving physical filling of the negative angle space of the shaping groove, and closing the structural gaps at the microscopic level.

[0017] During the second pressure holding period, a closed-loop control logic based on the material rheological state was constructed by introducing a pressure sensor. The decay rate of the forming load was used as a criterion to monitor the release of elastic stress within the metal material in real time. The system only determines that the springback stress has been completely converted into plastic deformation and releases the slider lock when the load change tends to stabilize and the rate of change is below a threshold. This real-time feedback-based decision-making mechanism overcomes the shortcomings of fixed-time control in adapting to batch-to-batch material differences, ensuring that the mold opens in a material rheological equilibrium state, effectively preventing springback deformation after unloading, and guaranteeing the dimensional accuracy and structural stability of the final product.

[0018] Optionally, step S4 includes the following sub-steps: S41. Control the slider to reach the bottom dead center position at a near-zero final speed, so that the hard limit step and the limit post in the mold are rigidly closed; at the same time, apply the initial impact pressure to the root of the bend through the indentation ribs set on the forming bending punch, and establish a high pressure stress field in the closed space formed by the pre-made warp and the forming groove. S42. During the first pressure holding period while keeping the slider position locked, the high-pressure stress field is used to force the metal lattice at the prefabricated corner to slip, generating directional plastic flow pointing towards the inner joint of the bend, until the flowing metal material completely fills the negative angle space of the shaping groove; wherein, the preset pressure holding time consists of a continuous first pressure holding period and a second pressure holding period; S43. During the subsequent second pressure holding period, the attenuation rate of the forming load is monitored in real time using a pressure sensor. When the forming load is detected to decrease from its peak and tend to stabilize, and the rate of change is lower than the preset threshold, it is determined that the elastic rebound stress inside the metal material has been converted into plastic deformation. At this time, the locking state of the slider is released, and the final shaping is completed.

[0019] By adopting the above technical solution, this invention subdivides the traditional static pressure holding process into two distinct stages: physical filling and stress relaxation. During the first pressure holding period, by controlling the slider to reach the bottom dead center at a near-zero speed, the inertial impact during the rigid closure of the hard-limiting structure is eliminated, protecting the fitting accuracy of the mold components. Simultaneously, the indentation ribs apply initial pressure to the root of the bend, establishing a high-pressure stress field within the closed space formed by the pre-formed warp and the shaping groove. This forces the metal lattice to slip along a preset path, generating directional plastic flow pointing towards the inner joint of the bend, achieving physical filling of the negative angle space of the shaping groove, and closing the structural gaps at the microscopic level.

[0020] During the second pressure holding period, a closed-loop control logic based on the material rheological state was constructed by introducing a pressure sensor. The decay rate of the forming load was used as a criterion to monitor the release of elastic stress within the metal material in real time. The system only determines that the springback stress has been completely converted into plastic deformation and releases the slider lock when the load change tends to stabilize and the rate of change is below a threshold. This real-time feedback-based decision-making mechanism overcomes the shortcomings of fixed-time control in adapting to batch-to-batch material differences, ensuring that the mold opens in a material rheological equilibrium state, effectively preventing springback deformation after unloading, and guaranteeing the dimensional accuracy and structural stability of the final product.

[0021] Optionally, S41 includes the following sub-steps: S411. Within the micro-range before the slider reaches the bottom dead center, a non-linear deceleration program is executed to dissipate the kinetic energy of the slider below the impact threshold, ensuring that the hard limit step and the limit post do not generate inertial impact that causes elastic vibration of the mold assembly when they contact and lock; wherein, the micro-range is 0.05mm-0.1mm. S412. By using the rigid locking of the hard limiting step and the limiting post, the final closing height between the forming bending punch and the lower die forming groove is forcibly set, so that the mold cavity size at the final closing height is smaller than the original thickness of the shielding material to be processed, so as to create a mechanical interference state in the closed space. S413. Based on the aforementioned mechanical interference state, the indentation ribs on the driving forming bending punch penetrate into the metal surface layer at the root of the bend. By utilizing the penetration action, the local contact pressure of the metal surface layer is instantly increased to above the yield strength of the metal material, so as to physically activate the phase transition potential energy of the material from elastic deformation to plastic flow, and complete the establishment of a high-pressure stress field.

[0022] By adopting the above technical solution, this invention performs a nonlinear deceleration program within a micro-distance range of 0.05mm to 0.1mm before the slider reaches the bottom dead center, effectively dissipating the slider's kinetic energy, eliminating the inertial impact of the hard limit structure at the moment of rigid contact, avoiding fluctuations in the closing reference caused by elastic vibration of the mold assembly, and ensuring the accuracy and stability of the final closing height. Based on this, the rigid locking of the hard limit structure forces the setting of a mold cavity size smaller than the original material thickness, constructing a defined mechanical interference state within the closed space.

[0023] Based on this interference fit, the indentation ribs on the forming bending punch are forcibly driven into the metal surface at the root of the bend, instantly raising the local contact pressure to above the yield strength of the metal material. This sudden change in contact pressure disrupts the elastic balance within the material, physically activating the phase transition potential energy of the metal from elastic deformation to plastic flow. This provides the necessary energy threshold for establishing a high-pressure stress field within the enclosed space, ensuring that the subsequent metal material can overcome deformation resistance and undergo directional rheology along a predetermined path towards the negative angle space of the forming groove.

[0024] Optionally, S42 includes the following sub-steps: S421. When the precast warp corner begins to deform under pressure, the negative angle or right angle inner wall of the shaping groove is used as a rigid boundary to block the outward expansion deformation path of the warp corner material, and the original extension trend of the material along the tangential direction is forcibly transformed into a reverse flow vector pointing to the inner rounded corner area of ​​the bend. S422. Maintain a constant volume constraint during the first pressure holding period, and use the pressure gradient formed between the high pressure zone at the indentation rib at the root of the bend and the low pressure zone at the bend joint gap to drive the metal material in the plastic state to migrate from the high pressure zone to the low pressure zone along the reverse flow vector. S423. By filling the natural geometric gaps at the inner rounded corners of the bend through the volume migration until the migrated metal material completely fits the right-angle vertex of the shaping groove, the bend angle of the shield is reconstructed from a rounded transition shape to a microscopic orthogonal right-angle closed shape, thereby physically cutting off the leakage channel of electromagnetic waves.

[0025] By employing the above technical solution, this invention utilizes the rigid inner wall of the shaping groove to construct a physical barrier, effectively blocking the outward expansion path of the prefabricated warped corner material under pressure deformation, and forcibly transforming the material's extension trend into a reverse flow vector pointing towards the inner rounded corner region of the bend. Utilizing the pressure gradient constructed between the high-pressure zone at the bend root and the low-pressure zone in the joint gap, the metal material in a plastic state is driven to overcome deformation resistance and undergo directional volume migration along the reverse flow vector. This controlled volume migration fills the geometric gaps of the inner rounded corners that cannot be eliminated by traditional bending processes, reconstructing the originally smoothly transitioned bend angle into a microscopically orthogonal right-angled closed shape, completely cutting off the electromagnetic wave leakage path in terms of physical structure, and achieving high shielding effectiveness.

[0026] Optionally, S43 includes the following sub-steps: S431. During the second pressure holding period, a piezoelectric sensor is used to collect the real-time load signal under the closed state of the mold at a sampling frequency of kilohertz, and a low-pass filtering algorithm is used to filter out the mechanical vibration noise from the servo motor, and a denoised force-time characteristic curve reflecting the internal stress state of the metal material is constructed. S432. Perform real-time differential operation on the noise reduction force-time characteristic curve to calculate the decay rate of the forming load over time; compare the decay rate with a preset stress relaxation convergence threshold, and determine that the metal material has reached the rheological equilibrium state and the bending springback potential energy has been completely dissipated only when the absolute value of the decay rate is continuously less than the stress relaxation convergence threshold and the duration reaches a preset confirmation time window. S433. Once the rheological equilibrium state is determined, the original pressure holding time is interrupted, and the slider is controlled to start a micro-return action with a non-linear S-shaped speed curve. While releasing the mold locking force, the instantaneous release of the mold elastic deformation energy caused by the sudden unloading of the load is avoided, which would impact the already shaped shield product.

[0027] By employing the above technical solution, this invention utilizes high-frequency sampling and low-pass filtering algorithms to construct a denoised force-time characteristic curve that accurately reflects the internal stress state of the metal, eliminating the interference of mechanical vibration noise on the judgment logic. Through real-time differential calculation and threshold comparison of the forming load attenuation rate, the rheological state of the metal material is precisely quantified, ensuring that the pressure holding only ends after the bending springback potential energy is fully dissipated. After confirmation of the final shape, a nonlinear S-shaped velocity curve is used to control the slider return stroke, achieving a flexible release of the mold locking force. This avoids the reverse impact caused by the release of the mold's elastic deformation energy due to instantaneous load unloading, protecting the dimensional accuracy and surface quality of the finalized shielding product.

[0028] Optionally, step S3 includes the following sub-steps: S31. Control the slider to move downwards and use the pre-set beveled or wavy shearing edge on the side wall of the forming bending punch to cut into the side connecting strip in a point contact manner; at the moment of cutting in, the vertical punching impact force is converted into a tangential shearing force along the metal sheet plane of the side connecting strip, and the integrity of the stress transmission structure of the side connecting strip is destroyed in advance before the bending action causes lateral tensile deformation of the metal sheet of the side connecting strip. S32. As the slider continues to descend, it drives the product sidewall to bend and deform. The shearing blade advances downward in sync and cuts off the side connecting strip. During this process, the vertical advance speed of the shearing cut point is kept synchronized with the sinking speed of the bending neutral layer, so as to decouple the lateral tensile stress of the strip skeleton on the product sidewall in real time and prevent necking or tearing of the bending edge in the plastic deformation zone. S33. While the shearing blade cuts the side connecting strip, the vacuum generator in the lower die assembly is activated to establish a negative pressure field below the shearing fracture surface. Using the pneumatic suction force generated by the negative pressure field, the cut continuous shearing waste is pulled out of the bending and forming station along the preset vacuum suction channel direction to prevent the waste from being trapped in the fitting gap between the die assemblies during the pressure holding process in subsequent steps.

[0029] By employing the above technical solution, this invention alters the force transmission path through the point-contact cutting method of the shearing blade, transforming the vertical stamping impact force into a tangential shearing force along the sheet metal plane. This preemptively disrupts the integrity of the stress transmission structure before the side connecting strip undergoes lateral tensile deformation. By maintaining real-time synchronization between the vertical advance speed of the shearing point and the sinking speed of the bending neutral layer, dynamic decoupling of the lateral tensile stress applied to the product sidewall by the strip skeleton is achieved, effectively preventing necking or tearing at the bending edge in the plastic deformation zone. Combined with the negative pressure field below the shear fracture surface, pneumatic suction is used to achieve directional stripping and discharge of continuous shearing waste, eliminating the risk of small waste particles being trapped in the gaps between mold components during subsequent high-pressure holding, thus ensuring the stability of precision forming.

[0030] In summary, this application includes at least one of the following beneficial technical effects: 1. This application employs a side-sliding and bending process, utilizing the cooperation of the shearing blade and the lower die assembly to simultaneously cut the side connecting strip during the bending stroke, maintaining the positioning connection between the product and the material strip skeleton. This effectively solves the positioning offset problem caused by complete material separation in traditional single-process bending. At the same time, by coordinating the synchronous control of the shearing advance speed and the bending sinking speed, real-time decoupling of lateral tensile stress is achieved, preventing necking or tearing of the product sidewall in the plastic deformation zone, and ensuring the forming stability during high-speed continuous stamping.

[0031] 2. This application constructs a closed extrusion cavity with a negative angle or right angle inner wall profile in the lower die assembly, and uses a forming bending punch to create a cavity with a volume smaller than the material volume. The mold closing and locking force is used to apply lateral extrusion to the pre-formed warp corner, forcing the metal material to undergo plastic flow and directionally backfill to the bending joint. This forced filling mechanism reconstructs the natural arc transition in the traditional bending process into a microscopic orthogonal right-angle closed shape, realizing the physical closure of the shielding cover sidewall without the need for subsequent welding processes, and significantly improving the electromagnetic shielding effectiveness of the device in high-frequency environments.

[0032] 3. This application employs a servo-mechanical coupling control method to execute a servo-based pressure holding program at the bottom dead center, which includes physical filling and stress relaxation stages. It utilizes a high-pressure stress field to induce metal lattice slippage to fill geometric gaps and determines the rheological equilibrium state based on real-time monitoring of the molding load decay rate, effectively overcoming the elastic rebound of the metal material after unloading. Combined with closed-loop feedback from a micron-level displacement sensor, it automatically compensates for the closing height deviation caused by the thermal expansion of the mold, ensuring the constancy of the forced filling extrusion pressure and the stability of product dimensional accuracy during mass production. Attached Figure Description

[0033] Figure 1A schematic diagram of the internal structure of a shielding cover progressive mold device with zero-gap bending forming function is shown in one embodiment of the present invention.

[0034] Figure 2 A flowchart illustrating the zero-gap forming method of the shielding cover in one embodiment of the present invention is shown.

[0035] Explanation of reference numerals in the attached figures: 1. Lower mold assembly; 2. Upper mold assembly; 3. Forming stripping float; 4. Forming bending punch; 5. Spring; 6. Shielding cover. Detailed Implementation

[0036] 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.

[0037] 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.

[0038] 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.

[0039] In the electronics and communications industry, a shielding cover (6) is a key structural component used to isolate electromagnetic interference. It is typically a five-sided enclosed box structure, including a top surface and vertically bent sidewalls. The material is often thin metal sheets such as stainless steel or nickel silver. Current shielding cover production typically employs progressive die devices. The production process generally includes punching, trimming, pre-bending, and final bending of the material strip. The sheet metal is connected and transported between different die stations via a material strip frame. However, with this traditional die structure and process, after the sidewalls are bent, due to the springback characteristics of the metal material and the bending geometry, the junctions of adjacent sidewalls often cannot fit tightly, leaving V-shaped or irregular structural gaps. These gaps become electromagnetic leakage channels under high-frequency signals, leading to a decrease in shielding effectiveness. Therefore, subsequent processes such as laser welding are often required to fill these gaps, but this increases costs and may cause thermal deformation.

[0040] Therefore, this embodiment provides a progressive die device for a shielding cover 6 with zero-gap bending forming function. This device is mainly used in the automated stamping production of metal shielding covers 6 in precision electronic equipment. Through a special structural design, this die device achieves the physical closure of the seams of the sidewalls of the shielding cover 6 through mechanical plastic deformation without adding welding processes.

[0041] It should be stated beforehand that, in this embodiment, the semi-finished shield 6 entering the mold device for processing is an intermediate process part after the metal coil (such as nickel silver or stainless steel strip with a thickness of 0.15mm-0.2mm) has undergone a preceding progressive stamping process (including blanking, stretching, pre-bending, etc.). This semi-finished shield 6 is not a completely independent entity in its spatial topology, but rather exists suspended as part of the strip system. Specifically, the semi-finished shield 6 mainly consists of four parts: the top surface body, the side wall bending edge, the prefabricated corner structure, and the side connecting strip. The spatial positions and connection relationships of each part are as follows: The top surface (the central part of shielding cover 6) constitutes the geometric reference surface of the entire workpiece. It is usually rectangular, polygonal, or an irregular stepped flat plate structure designed to avoid high and low components on the PCB board. The surface flatness of the top surface is strictly controlled (e.g., flatness tolerance less than 0.05mm) to serve as the reference for suction cups. At the edges of the top surface, several bending reference lines are defined, which physically separate the top surface from the bending edges of the surrounding side walls, but maintain a unified material continuity.

[0042] The sidewall bend (the product's sidewall portion) is a plate-like structure extending outward from the perimeter of the main body of the top surface. Upon entering this workstation, the sidewall bend is not in its final vertical state (i.e., at a 90° angle to the main body of the top surface), but rather in an intermediate state of "almost bent" or "pre-bent." For example, the angle with the main body of the top surface may be between 45° and 85°, or although it is close to vertical, the root radius (R-angle) has not yet been fully compressed. This state preserves the material's plastic deformation allowance. The length of the sidewall bend extends along the bending baseline, and its height determines the final internal accommodating height of the shielding cover 6.

[0043] The prefabricated upturned corner structure (prefabricated upturned corner section) is located at the intersection of the longitudinal ends of two adjacent sidewall bending edges. Unlike the straight sidewall ends in traditional processes, the prefabricated upturned corner in this embodiment exhibits a micro-geometric shape of an outward-opening "trumpet mouth" or "outward-flaring lip". Specifically, based on the ideal sidewall plane perpendicular to the top surface of the main body, the end of the prefabricated upturned corner is tilted and deviated outward from the mold cavity, forming an opening angle of approximately 3° to 5°. Furthermore, the metal material in this area is not removed; instead, a greater amount of metal (i.e., volume redundancy) is retained than the theoretically required right-angle closure. This special geometric shape is intentionally manufactured by the preceding mold through extrusion or molding processes. Its purpose is to provide a source of flowing metal solid for forced filling at the moment of subsequent bottom dead center closure.

[0044] The side connecting strip (side connecting strip section) is the only physical force transmission bridge between the semi-finished shield 6 and the external material strip skeleton. It is usually located in the middle or non-corner area of ​​the outer edge of the side wall bending edge, and is in the shape of a narrow bridge-like connecting rib, with a width of only 0.5mm to 1.5mm. One end of the side connecting strip is integrally connected to the edge of the side wall bending edge, and the other end merges into the continuously transported material strip skeleton. It is particularly important to note that the connection point between the side connecting strip and the side wall bending edge is designed to be above the cutting trajectory of the shearing blade. This specific positional relationship ensures that in the initial stage of the bending punch 4's downward contact with the product, the side connecting strip can apply lateral tension to the side wall like a cable, preventing the product from warping or shifting under the bending moment; and at the end of the bending stroke, it can be precisely cut to release the product.

[0045] Reference Figure 1 The progressive die assembly for the shielding cover includes a lower die assembly 1, an upper die assembly 2, a forming and stripping float 3, and a forming and bending punch 4. The lower die assembly 1 serves as a fixed die base, bolted to the worktable of the punch press. The punch press described here is a servo press capable of precisely controlling the slide movement curve through programming. The upper die assembly 2 is positioned above the lower die assembly 1 and connected to the slide of the servo press, enabling it to reciprocate vertically relative to the lower die assembly 1.

[0046] The forming stripper float 3 is elastically positioned within the lower mold assembly 1. Specifically, a high-strength spring 5 or a nitrogen spring 5 is connected to the bottom of the forming stripper float 3, giving it a vertical elastic floating stroke. The top surface shape of the forming stripper float 3 is adapted to the plate shape of the shielding cover 6 product to be processed, serving to support the shielding cover 6 product. In the initial stage of mold closure, the forming stripper float 3 contacts the product before other forming components, and under the force of the spring 5, presses the product between the upper mold assembly 2 and the forming stripper float 3, preventing the product from shifting during subsequent processing.

[0047] The forming and bending punch 4 is fixedly mounted on the upper die assembly 2 and positioned directly above the forming and stripping float 3. The forming and bending punch 4 can be made of high wear-resistant die steel such as SKD11 or DC53, and can undergo PVD coating treatment to reduce the coefficient of friction. In terms of specific shape, the forming and bending punch 4 can be designed as a rectangular block, T-shaped, or other irregular shape according to the internal structure of the shield 6, with its bottom edge having an R-angle matching the bending radius.

[0048] The core of this embodiment lies in the cooperation between the side continuous shearing mechanism and the forced filling structure.

[0049] Regarding the side-mounted shearing mechanism, the side wall of the forming bending punch 4 is equipped with a shearing blade. This shearing blade does not penetrate the entire side wall, but is located at the vertical projection position corresponding to the side connecting strip of the shield cover 6 product. The lower die assembly 1 is equipped with a lower die mating blade at the corresponding position. When the upper die assembly 2 drives the forming bending punch 4 downward to perform the bending stroke, the forming bending punch 4 first pushes the side wall of the product to bend and deform. Subsequently, by using the shearing blade to cooperate with the corresponding blade on the lower die assembly 1, the side connecting strip is cut off or partially cut off. This design ensures that in the initial stage of bending deformation, since the connecting strip has not been completely cut off, the product is still subjected to the lateral tension of the strip skeleton, thereby maintaining the accuracy of positioning and avoiding lateral slippage during simple bending. Cutting off the connection when the bending is about to be completed eliminates the stress interference of the strip on the formed product. In order to reduce the impact of punching, the shearing blade is preferably designed as a 1°~2° wavy oblique blade or a unidirectional oblique blade, which transforms the instantaneous surface contact shearing into a gradual point contact shearing.

[0050] The continuous shearing action generates tiny connecting scraps, typically in the form of thin strips or flakes. To handle these scraps, the lower die assembly 1 has a vacuum suction channel directly below the shearing blade. This channel runs through the lower die insert and the lower die base, and its diameter is slightly larger than the maximum size of the scrap to prevent blockage. A negative pressure generating device, such as an industrial vacuum pump or venturi tube, located outside or at the bottom of the die, is connected to the suction channel via piping. During the continuous shearing action, a strong airflow is generated to quickly suck away the cut connecting scraps, preventing them from jumping up and getting stuck in the die gaps. To further reduce the risk of blockage, the inner wall of the suction channel can be polished and designed with a tapered structure that gradually widens downwards.

[0051] Regarding the forced seam filling structure, its purpose is to eliminate the seams on the bent sidewalls. Before entering the mold station described in this embodiment, the bent corner of the shield 6 product has been pre-machined with an outwardly flared pre-formed corner, the flare angle of which can be 3°~5°. Here, the mold station refers to the working position in the progressive die where specific processing steps are completed. The purpose of pre-machined corner is to provide additional metal volume redundancy at the final forming station. Without this pre-formed structure, subsequent extrusion will lack sufficient material flow to the seam. In this embodiment, the lower die assembly 1 has a shaping groove at the pre-formed corner position corresponding to the bent corner of the shield 6 product. This shaping groove has an inwardly tapering negative angle or right angle inner wall profile. For example, the inner wall angle can be designed to be 88° to 90°.

[0052] When the upper die assembly 2 descends to the bottom dead center position relative to the lower die assembly 1, the forming bending punch 4 and the shaping groove of the lower die assembly 1 enclose each other to form a closed extrusion cavity. The bottom dead center refers to the lowest point of the press slide stroke, which is also the position where the die is most tightly closed and the pressure is greatest. Crucially, the volume of this closed extrusion cavity is designed to be smaller than the volume of the metal material containing the pre-formed warp, and this volume difference creates a mechanical interference fit. Therefore, using the closing locking force of the upper die assembly 2, i.e., the rated load provided by the press at the bottom dead center, the die applies lateral extrusion to the pre-formed warp, forcing the metal material at the warp to undergo plastic flow. Since the outer side of the shaping groove is a rigid steel dead wall, the flowing metal material cannot diffuse outwards and can only backfill the gap at the bending joint along the path of least resistance, thus physically closing the side wall gaps of the shield 6 and forming a microscopically orthogonal right-angled closed shape.

[0053] To ensure the stability of the extrusion effect, the forming bending punch 4 is equipped with a hard limiting step, typically a precision-ground boss surface; the lower die assembly 1 is equipped with a corresponding limiting post, typically a cylindrical or square prism-shaped hardened steel part. The height difference between the hard limiting step and the limiting post is precisely set so that when the die closes to the hard limiting contact, the pressing depth of the forming bending punch 4 into the root of the product bend is 10%~15% of the material thickness. The forming bending punch 4 is also equipped with tiny indentation ribs, which are tiny protrusions extending along the bending line. This pressing depth generates work hardening at the root of the bend, that is, increases the dislocation density through intense plastic deformation, improves the local yield strength, and, in conjunction with the material flow of the pre-formed warp, effectively changes the stress distribution in the bending area, counteracts the springback moment, thereby locking the bending angle and preventing springback.

[0054] Based on the mold device structure described in the above embodiments, although it provides a structural foundation for zero-gap forming through the design of mechanical hard limiting and forced gap filling structure, in actual high-speed automated stamping production, without a precise servo control strategy, simply relying on the mechanical movement of the mold is often insufficient to cope with complex working condition changes. If a traditional mechanical press or a servo press without optimized control is used, the slide usually moves according to a fixed sine curve, often accompanied by high instantaneous speed and kinetic energy when reaching the bottom dead center. This high-speed impact directly acts on the hard limiting step and limiting post, producing violent rigid collisions and elastic vibrations. This mechanical vibration not only disrupts the stability of the high-pressure stress field within the closed extrusion cavity, causing the plastic flow of the metal material to be interrupted or diverged, failing to completely fill the negative angle space of the forming groove, but also accelerates the wear of the precision cutting edge and indentation rib of the mold, reducing mold life and leading to a decrease in product dimensional consistency.

[0055] Furthermore, if the parameters in the stamping process fail to meet standards or adapt to environmental changes, serious quality problems can result. During continuous production, the die components experience thermal expansion due to friction and deformation heat, causing a micrometer-level drift in the closing height. Without real-time monitoring and compensation from a closed-loop control system, thermal expansion can cause the actual pressing depth to exceed the preset value, leading to die overload or even breakage. Conversely, if the closing gap is too large during cold start-up, sufficient mechanical interference cannot be established, resulting in contact pressure at the pre-formed corner being lower than the yield strength, failing to activate phase transformation potential energy, and ultimately preventing the bending joint from closing. Simultaneously, the thickness tolerance and material hardness fluctuations of metal coils are inherent, and a fixed holding time cannot ensure that the elastic rebound stress of each batch of material is completely converted into plastic deformation. If the die is opened prematurely before the internal stress has dissipated, the residual elastic potential energy will cause uncontrollable rebound of the sidewalls, disrupting the formed right-angle shape, making the flatness and dimensional tolerances of the shield 6 unable to meet the assembly requirements of precision electronic equipment.

[0056] Therefore, in another embodiment, a zero-gap molding method for a shielding cover based on servo and mechanical coupling control is provided. This method utilizes the aforementioned progressive mold device for the shielding cover, combined with the programmable motion characteristics of a servo press, to achieve high-precision molding control.

[0057] Specifically, refer to Figure 2 The zero-gap forming method for the shielding cover includes the following steps S1-S4.

[0058] S1. The semi-finished shield with pre-made upturned corners is conveyed into the mold through the side connecting belt.

[0059] During the conveying process, the side connecting belts play a role in suspension and transmission. The servo feeder drives the external material belt skeleton to feed intermittently according to a preset step distance. The material belt skeleton drives the suspended shielding cover semi-finished product to move synchronously through the rigid side connecting belts, accurately feeding it into the working area of ​​the forming mold. To ensure that the shielding cover falls accurately on the forming and stripping float of the lower mold assembly, guide pins are set inside the mold. When the material belt is conveyed to the approximate position, the guide pins are inserted into the reference guide holes on the material belt skeleton to perform micron-level XY axis precision positioning of the semi-finished product. Then, the floating device inside the mold descends, allowing the semi-finished product to sit smoothly on the top surface of the forming and stripping float.

[0060] To prevent interference between the pre-formed warp corners and the forming stripper float, which could lead to misalignment, the four corners of the forming stripper float are designed with special chamfers or clearance notches. Because the root of the pre-formed warp corner may have slight inward bulges or deformations caused by previous extrusion, if the float's outline perfectly matches the theoretical right angle, it may cause the product to jam or fail to adhere properly to the top surface of the float. By reserving clearance space, it is ensured that the float only contacts the flat inner surface of the center part of the shielding cover, eliminating the interference of irregular corner shapes on the positioning reference surface and guaranteeing the absolute perpendicularity and fit between the semi-finished product and the lower mold assembly in the Z-axis direction.

[0061] S2. Control the slide of the servo press to decelerate, and press the product surface through the forming stripping float; wherein, the slide is the power output component of the servo press, connected to the upper mold assembly and driving the upper mold assembly to reciprocate vertically relative to the lower mold assembly.

[0062] In terms of specific timing, once the feeding action is confirmed as complete, i.e., the semi-finished shielding cover accurately stops at the forming station, the servo control system instructs the slider to start from the top dead center. The top dead center refers to the highest position that the press slider can reach during the vertical reciprocating motion of the upper mold assembly. To balance production efficiency and forming quality, the slider first rapidly approaches the mold closing area at a preset high speed to shorten the idle stroke time. When the slider reaches a preset buffer distance above the contact point (e.g., 5mm to 10mm), the control system switches the motion curve, and the slider begins to execute a deceleration program from the high-speed motion state, smoothly transitioning to the low-speed contact state.

[0063] After the slide of the servo press decelerates, it can achieve flexible and stable pressing. This is because the deceleration significantly reduces the kinetic energy and inertial impact when the upper die assembly contacts the forming stripper and the product surface. If the slide directly impacts at high speed, the huge impact force will cause the spring in the lower die assembly to vibrate violently or even rebound momentarily, causing the shielding cover semi-finished product to bounce or shift slightly after it has just been placed. By achieving a soft landing through deceleration, the pressing process of the upper die assembly on the product becomes a linear loading quasi-static process. The spring force under the forming stripper is released smoothly and gradually increases, thus firmly clamping the top surface of the shielding cover semi-finished product between the upper die assembly (usually the stripper plate or the bottom of the punch) and the forming stripper, establishing the Z-axis reference for subsequent bending processing.

[0064] During this clamping process, the side connecting strip plays a role in auxiliary positioning and posture maintenance. Although the forming and stripping float initially provides the main clamping force, the side connecting strip maintains a rigid connection between the product and the external material strip skeleton at the moment the clamping force is established. It restricts the product's rotational or axial movement freedom in the X and Y axis planes, ensuring that the product does not tilt due to uneven force distribution in the initial stage of vertical pressure, and guaranteeing the relative positional accuracy between the product sidewall and the subsequent cutting edge.

[0065] S3. Control the slider to descend at a constant low speed, and simultaneously complete the shearing and release of the side connecting strip and the bending of the product side wall through the forming and bending punch.

[0066] In terms of timing, once the forming stripper in S2 has fully pressed the product surface, ensuring that the product's Z-axis freedom is locked, the servo control system controls the slider to enter the processing area. At this point, the slider's speed no longer changes, but remains at a constant low speed (e.g., 10%~20% of the rated speed) as it continues to descend. Switching to a constant low speed at this point ensures that subsequent shearing and bending actions are performed under stable strain rate conditions, avoiding uneven material rheology or a decrease in the quality of the punched section due to speed fluctuations. It also provides a stable time reference for the synchronized actions, complementing the precise position control of the servo system.

[0067] The shearing release of the side connecting strip by the forming bending punch is achieved through the misalignment movement between the specially designed shearing edge on its side wall and the corresponding edge on the lower die assembly. As the slider descends steadily, the shearing edge of the forming bending punch gradually approaches and passes the mating edge of the lower die. This process is similar to the closing action of scissors, applying concentrated shear stress to the side connecting strip using the extremely small gap between the upper and lower edges (typically 5% to 8% of the material thickness). When this stress exceeds the shear strength of the metal material, the side connecting strip breaks and separates along the edge trajectory, thereby releasing the physical constraint of the strip skeleton on the shielding product and completing the shearing release.

[0068] The bending of the product sidewall by the forming bending punch is achieved through the forming radius (R-angle) at the bottom of the punch and the relative movement between the sidewall plane and the lower die insert. Simultaneously or slightly before the shearing edge cuts off the connecting strip, the bottom edge of the forming bending punch contacts the product sidewall in its pre-bent state. As the punch continues to press down at a constant low speed, it forces the product sidewall to undergo plastic rotational deformation around the radius of the lower die insert, gradually bringing it closer to the vertical direction. During this process, because the side connecting strip is not completely broken or has just broken at the initial stage of bending, the lateral tension it provides balances the bending moment, ensuring that the sidewall bends along the predetermined bending line, rather than undergoing overall lateral displacement or warping.

[0069] Specifically, S3 includes the following sub-steps S31-S33.

[0070] S31. Control the slider to descend and use the pre-set angled or wavy shearing edge on the side wall of the forming bending punch to cut into the side connecting strip in a point contact manner; at the moment of cutting, the vertical stamping impact force is converted into a tangential shearing force along the metal sheet plane of the side connecting strip, and the integrity of the stress transmission structure of the side connecting strip is destroyed in advance before the bending action causes lateral tensile deformation of the metal sheet of the side connecting strip.

[0071] S32. As the slider continues to descend, driving the product sidewall to bend and deform, the shearing blade advances downward synchronously and cuts off the side connecting strip. During this process, the vertical advance speed of the shearing cut point is kept synchronized with the sinking speed of the bending neutral layer, thereby decoupling the lateral tensile stress of the strip skeleton on the product sidewall in real time and preventing necking or tearing of the bending edge in the plastic deformation zone.

[0072] S33. While the shearing blade cuts the side connecting strip, the vacuum generator in the lower die assembly is activated to establish a negative pressure field below the shearing fracture surface. Using the pneumatic suction force generated by the negative pressure field, the cut continuous shearing waste is pulled out of the bending and forming station along the preset vacuum suction channel direction to prevent the waste from being trapped in the fitting gap between the die assemblies during the pressure holding process in subsequent steps.

[0073] The side connecting strip is chosen to be destroyed and cut off first in steps S31 and S32 because it acts as a rigid bridge between the strip skeleton and the product, generating a significant constraint effect during bending. If the side connecting strip is not cut off at this point but is left to be cut off in a later process, the strip skeleton remains fixed while the product sidewall needs to undergo significant displacement and rotation during the bending process driven by the forming punch. This relative motion causes the connecting strip to be stretched violently, thus applying a huge reverse tensile stress to the sidewall undergoing plastic deformation. This tensile stress can cause the material at the root of the sidewall to thin (necking), and in severe cases, it can tear directly. Furthermore, the forced bending can lead to unpredictable springback, severely affecting dimensional accuracy. Conversely, if it is cut off too early before bending, the product will lose its positioning support and is prone to shifting at the moment of punch contact. Therefore, cutting it off simultaneously during the bending deformation of the product sidewall, either before or at the very beginning of the deformation, utilizes the positioning function of the connecting strip in the initial contact stage and releases the constraint in time before harmful tensile stress is generated.

[0074] The so-called bending neutral layer refers to a layer of metal fibers located between the inner compression zone and the outer tension zone during the bending deformation of a metal sheet. Its length remains constant before and after bending, neither elongating nor shortening. S32 emphasizes that the vertical advance speed of the shearing cut point is synchronized with the sinking speed of the bending neutral layer, meaning that the shearing action closely follows the natural flow rhythm of the material. This is similar to precise cutting in surgery, where the feed speed of the blade matches the displacement speed of the tissue, thereby achieving real-time decoupling of lateral tensile stress and ensuring that the product's sidewalls are bent and formed under ideal conditions free from tension interference.

[0075] The reason why continuous shearing waste is generated when cutting the side connecting strip is that, in order to ensure a clean cut and reduce burrs, the shearing process is not a simple break, but a shearing separation similar to punching. Especially when using an angled or wavy shearing edge for point contact cutting, there is a punching gap between the cutting edge and the lower die. The shearing process actually "cuts" a small section of material (i.e., the connecting bridge itself or some of its fragments) from the side connecting strip, rather than a seamless separation. This separated metal entity is the continuous shearing waste.

[0076] Taking the processing of a 0.15mm thick nickel-plated copper shield as an example, when the slider drives the upper die downwards, the wavy cutting edge (designed at a 1.5° angle) on the side of the forming bending punch first cuts into the side connecting strip in a point-contact manner. At this moment, the bending has just begun, and the side wall only displaces slightly downwards. At the instant the cutting edge penetrates, the vertical impact force is converted into a horizontal shearing force, and cracks begin to appear on the surface of the connecting strip, blocking the stress transmission path. As the slider continues to press down, the side wall bends further, and the cutting edge moves downwards synchronously to completely cut off the connecting strip. At this moment, the tiny strip-shaped waste generated by the breakage of the connecting strip is instantly sucked into the waste suction channel of the lower die under the action of gravity and negative pressure field, preventing the waste from being pressed onto the precision-formed surface when the die is closed and pressure is maintained. The entire process is completed within tens of milliseconds, achieving precise coordination of positioning, decoupling, and waste removal.

[0077] S4. When the slider reaches the bottom dead center, the servo pressure holding program is executed to control the slider to stop moving and maintain the preset pressure holding time. During this pressure holding time, the mold device maintains the forced extrusion state on the pre-made warped corner, and utilizes the creep characteristics of the metal material to make the warped corner material flow fully and fill the bending joint to form a seamless closed structure.

[0078] The servo pressure holding program described here refers to the control logic that relies on the high response of the servo motor and its closed-loop control system of the servo press to forcibly lock the motor rotation angle or maintain a constant torque output at a specific position in the slide's stroke. Unlike traditional mechanical presses, which are limited by the kinematic characteristics of the crank-connecting rod mechanism and must pass through the bottom dead center instantaneously, the servo pressure holding program gives the slide the ability to remain at the bottom dead center for an extended period. Controlling the slide to stop moving and maintain this position for a period of time is to create a continuous, steady-state high-pressure environment in the most tightly closed state of the mold cavity. This is because the deformation of metal materials is not a purely instantaneous behavior, especially in cases involving complex volume forming and micro-filling, where material flow has a significant time dependence.

[0079] In the cold-pressing environment of this embodiment, the creep characteristics of metallic materials manifest as a continuous plastic deformation phenomenon caused by dislocation movement and grain boundary slip within the metal crystal under constant stress. This microscopic rearrangement requires a sufficient time window to complete and cannot be fully achieved in an instantaneous impact. If the slider returns immediately after reaching the bottom dead center, the remaining elastic potential energy within the metallic material is not effectively released, and the microscopic plastic filling is not yet complete, leading to springback and the reappearance of gaps after unloading.

[0080] Taking the processing of nickel-plated copper shields as an example, when the slider is at the bottom dead center, the lateral extrusion force exerted by the forming bending punch and the lower die forming groove on the pre-formed warped corner reaches hundreds of tons. Under this continuous high pressure, the originally hard metal exhibits properties similar to a high-viscosity fluid, and the metal material of the pre-formed warped corner gradually creeps towards the bending joint where resistance is least. As the holding time progresses, the material gradually fills the micro-texture and negative angle space of the inner wall of the forming groove until the geometric gaps are completely eliminated. This time-accumulated plastic flow ensures that the final formed shield sidewall joints achieve a physical closure at the airtight level.

[0081] Optionally, the holding time in step S4 is set to 50ms to 100ms. In step S4, a micron-level displacement sensor installed in the mold is used to monitor the closing height in real time. If the closing height deviation caused by thermal expansion exceeds ±0.005mm, the servo control system automatically adjusts the bottom dead center position of the slider to ensure that the extrusion pressure of the forced filling is constant.

[0082] Setting the holding time to 50ms to 100ms represents an optimal balance between the physical time window required for the micro-rheological changes in the metallic material and the cycle time of high-speed continuous production using progressive dies. For shielding sheet materials with a thickness typically between 0.15mm and 0.2mm, under extremely high closing pressure, it usually takes tens of milliseconds for lattice slip and dislocation movement to reach rheological equilibrium from the initial excitation. If the holding time is less than 50ms, the stress relaxation inside the metal is often insufficient, and the residual elastic potential energy will cause springback after unloading, causing the physically closed gap to open slightly again. If the holding time exceeds 100ms, although it can further eliminate residual stress, its marginal contribution to forming quality decreases, and it will significantly reduce the strokes per minute (SPM) of the entire stamping line, affecting production efficiency. Therefore, this time setting ensures reliable zero-gap forming without sacrificing production capacity.

[0083] The significance of real-time monitoring of the closing height lies in establishing a precise compensation mechanism for environmental variables. During continuous stamping, the die components experience temperature increases due to frequent frictional heat generation and the accumulation of heat from metal deformation. According to the principle of thermal expansion and contraction of metals, the die steel undergoes volume expansion, causing a micrometer-level elongation in the effective vertical dimension of the upper and lower die components. This thermal expansion effect directly alters the actual closing gap of the die; that is, with the slider position unchanged, thermal expansion leads to a larger actual indentation depth, resulting in drastic fluctuations in extrusion pressure. For forced filling processes relying on mechanical interference, a deviation of ±0.005mm may mean an indentation depth error exceeding 20% ​​(10%-15% of the indentation amount relative to 0.15mm material), leading to over-pressure deformation or insufficient pressure for filling. By receiving real-time data from sensors through the servo control system, when thermal expansion causes the actual gap to decrease, the system automatically fine-tunes and raises the bottom dead center position of the slider; conversely, it lowers it. This dynamic closed-loop control ensures that the actual physical extrusion applied to the precast corner remains constant regardless of whether the mold is in a cold or hot state, thus guaranteeing the consistency of the filling quality of products in mass production.

[0084] Specifically, S4 includes the following sub-steps S41-S43.

[0085] S41. Control the slider to reach the bottom dead center position at a near-zero final speed, so that the hard limit step and the limit post in the mold are rigidly closed; at the same time, apply the initial impact pressure to the root of the bend through the indentation ribs set on the forming bending punch, and establish a high pressure stress field in the closed space formed by the pre-made warp and the forming groove.

[0086] In this step, controlling the slider to reach the bottom dead center position at a near-zero final velocity is a soft-landing strategy achieved using the electronic cam function of the servo press. The bottom dead center position refers to the lowest limit position that the press slider can reach during its reciprocating stroke, and it is also the geometric position where the closing gap between the upper and lower die components is the smallest and the locking force is the largest. Traditional crank presses typically have a high tangential velocity when passing through the bottom dead center, which causes a huge rigid collision sound and reaction impact force to be generated at the moment of contact of the hard limit structure. This impact not only accelerates the fatigue damage of the die limit post, but also causes micron-level elastic vibration of the die components, destroying the dimensional stability of precision molding. Through nonlinear deceleration control, the slider's velocity is reduced to an extremely low level just before contacting the hard limit, eliminating inertial kinetic energy and ensuring that the die completes the final locking in a quasi-static and stable state.

[0087] The bend root specifically refers to the inner rounded transition area at the connection between the main body of the shield's top surface and the bend edge of the side wall. This area is where stress is most concentrated and geometry is most critical during bending deformation. At the instant the rigid limiting step and the limiting post rigidly close, although the slider stops macroscopic movement, due to the pre-designed mechanical interference fit, the indentation rib on the forming bending punch is forced to penetrate the metal surface layer at the bend root. This penetration action instantly establishes extremely high hydrostatic pressure, i.e., a high-pressure stress field, within the tiny enclosed space formed by the pre-made upturned corner and the forming groove. This stress field breaks the elastic equilibrium of the metal material, providing the necessary initial driving energy for subsequent directional plastic flow of the material towards the joint. For example, when processing a 0.2mm thick stainless steel shield, the slider begins to decelerate sharply at a distance of 0.1mm from the bottom dead center, eventually gently contacting the limiting post at a speed close to 0mm / s. At this point, the indentation rib has embedded approximately 0.025mm into the bend root, successfully establishing an internal stress environment exceeding the material's yield strength within the closed cavity.

[0088] Specifically, S41 includes the following sub-steps S411-S413.

[0089] S411. Within the micro-range before the slider reaches the bottom dead center, a non-linear deceleration program is executed to dissipate the kinetic energy of the slider below the impact threshold, ensuring that the hard limit step and the limit post do not generate inertial impact that causes elastic vibration of the mold assembly when they contact and lock; wherein, the micro-range is 0.05mm-0.1mm.

[0090] S412. By using the rigid locking of the hard limiting step and the limiting post, the final closing height between the forming bending punch and the lower die forming groove is forcibly set, so that the mold cavity size at the final closing height is smaller than the original thickness of the shielding material to be processed, so as to create a mechanical interference state in the closed space.

[0091] S413. Based on the aforementioned mechanical interference state, the indentation ribs on the driving forming bending punch penetrate into the metal surface layer at the root of the bend. By utilizing the penetration action, the local contact pressure of the metal surface layer is instantly increased to above the yield strength of the metal material, so as to physically activate the phase transition potential energy of the material from elastic deformation to plastic flow, and complete the establishment of a high-pressure stress field.

[0092] In this step, the nonlinear deceleration program means that the slider's speed change no longer follows a linear uniform deceleration law, but is controlled according to a specific smooth curve. For example, the system can use an S-shaped speed curve or a cosine deceleration curve, so that after the slider enters the micro-range of 0.05mm to 0.1mm, the speed smoothly decreases from the process setting value to near zero. The impact threshold refers to the maximum instantaneous impact force or vibration amplitude that the mold structure can withstand without causing significant elastic deformation or dynamic oscillation. For example, the vibration amplitude is set to not exceed 2 micrometers. The rigid locking of the hard limit step and the limit post occurs when the slider reaches the bottom dead center and stops descending. Its purpose is to provide an absolute physical stopping reference for the mold, preventing the slider from excessively pressing down due to control errors and causing the mold to collapse. If the slider impacts the hard limit structure at a high speed, the huge kinetic energy is instantly converted into a shock wave, which will cause the mold components to experience high-frequency reciprocating elastic vibration at the micrometer level. This vibration will disrupt the stability of the indentation depth and may even cause the gap that has just closed to open again.

[0093] The movement of the indentation ribs on the forming bending punch and the rigid limiting structure follows the mechanical logic of geometric interference drive and rigid limiting lock. During the mold structure design phase, the height difference between the rigid limiting step and the limiting post is precisely calculated and set so that when the two rigidly contact each other—that is, when the mold is closed to the bottom dead center—the vertical distance between the top of the indentation rib on the bottom surface of the forming bending punch and the corresponding surface of the lower mold assembly is strictly less than the original thickness of the shielding metal material to be processed. This dimensional difference creates a mechanical interference state within the mold cavity.

[0094] In terms of timing, when the servo press drives the slide to perform the downward stamping stroke, the process is as follows: First, the forming and bending punch brings the indentation rib into contact with and begins to press into the metal surface at the root of the bend. At this time, the hard limit step has not yet contacted the limit post, and the mold is still in a slightly open state. Subsequently, driven by the huge closing load of the servo press, the slide continues to be forced downward, overcoming the deformation resistance of the metal material, forcing the indentation rib to further penetrate into the metal. Finally, when the slide reaches the preset bottom dead center position, the hard limit step and the limit post rigidly collide and lock. At the same instant of this rigid locking, based on the aforementioned geometric interference design, the indentation rib is forced to remain at the preset penetration depth, usually 10% to 15% of the material thickness. Therefore, the penetration of the indentation rib into the metal surface does not occur during the continued movement after the hard limit rigid locking, but rather at the end of the dynamic stroke when the slide approaches and finally reaches the hard limit locking position. The function of the hard limit structure is to physically cut off the movement of the slider, preventing material breakage or mold damage due to excessive intrusion, thereby precisely locking the indentation depth at the threshold that produces the best work hardening effect and is sufficient to activate plastic flow, and successfully establishing a high-pressure stress field in the closed space.

[0095] S42. During the first pressure holding period while keeping the slider position locked, the high-pressure stress field is used to force the metal lattice at the pre-formed corner to slip, generating directional plastic flow pointing towards the inner joint of the bend, until the flowing metal material completely fills the negative angle space of the shaping groove; wherein, the preset pressure holding time consists of a continuous first pressure holding period and a second pressure holding period.

[0096] In this embodiment, the preset holding time is subdivided into a first holding period and a second holding period, based on the staged characteristics of the rheological behavior of metallic materials during strong constraint molding. Holding at the bottom dead center is not a static state, but a dynamic and evolving physical process. The first holding period mainly corresponds to the active filling stage, during which the material undergoes visible volume migration and geometric changes; while the second holding period mainly corresponds to the stress relaxation and stabilization stage, during which the material undergoes rearrangement of its internal microstructure and dissipation of elastic potential energy. This time-segmentation allows the servo control system to apply differentiated monitoring and control strategies for the physical characteristics of different stages, thereby ensuring full filling while precisely controlling springback.

[0097] During the first holding period, the slider is in a rigidly locked state under closed-loop position control, and the volume of the mold cavity remains constant. Although the mold assembly stops moving macroscopically, the metal material inside the cavity is in a state of intense plastic flow driven by the high-pressure stress field established by S41. Due to the local pressure generated by the indentation ribs far exceeding the material's yield limit, the metal lattice in the pre-formed warp corner area is forced to slip. Constrained by the boundary of the rigid wall on the outer side of the forming groove, this lattice slip cannot extend to the outside of the mold, but can only be transformed into directional plastic flow pointing towards the inner joint of the bend and the negative angle space of the forming groove. This process is essentially a secondary redistribution of the redundant metal volume stored in the pre-formed warp corner within the constant volume cavity until the flowing metal completely fills the V-shaped gaps and negative angle spaces generated by the bending geometry, achieving a dense closure in the physical structure.

[0098] Specifically, S42 includes the following sub-steps S421-S423.

[0099] S421. When the precast warp corner begins to deform under pressure, the negative angle or right angle inner wall of the shaping groove is used as a rigid boundary to block the outward expansion deformation path of the warp corner material, and the original extension trend of the material along the tangential direction is forcibly transformed into a reverse flow vector pointing to the inner rounded corner area of ​​the bend.

[0100] S422. Maintain a constant volume constraint during the first pressure holding period, and use the pressure gradient formed between the high-pressure zone at the indentation rib at the root of the bend and the low-pressure zone at the gap of the bend joint to drive the metal material in the plastic state to migrate from the high-pressure zone to the low-pressure zone along the reverse flow vector.

[0101] S423. By filling the natural geometric gaps at the inner rounded corners of the bend through the volume migration until the migrated metal material completely fits the right-angle vertex of the shaping groove, the bend angle of the shield is reconstructed from a rounded transition shape to a microscopic orthogonal right-angle closed shape, thereby physically cutting off the leakage channel of electromagnetic waves.

[0102] This invention constructs a complete physical process of blocking, driving, and reconstructing at the micro-rheological level. In S421, when the preformed corner is subjected to a vertical closing pressure, the metallic material instinctively tends to extend towards the external free space where resistance is least. At this time, the inner wall of the shaping groove acts as an absolutely rigid physical barrier, effectively intercepting the outward expansion path of the material. This geometric constraint forces the shear slip bands inside the material to change direction, forcibly guiding the material volume that might otherwise form external burrs into the void region inside the mold.

[0103] In S422, the pressure distribution difference within the closed cavity becomes the driving force for material flow. The indentation ribs, acting as local loading points, create an extremely high-pressure zone at the root of the bend, far exceeding the material's yield strength, while the geometric gap at the bend joint, unfilled, remains in a relatively low-pressure state. Under the constant volume constraint of the first holding period, this significant pressure gradient drives the plastic metal, like a high-viscosity fluid, to undergo mass transfer along a predetermined reverse flow vector. This process is not simple elastic compression, but a substantial volume transfer.

[0104] In S423, continuous volume migration ultimately eliminates the natural geometric gaps that are unavoidable due to the bending radius in traditional bending processes. As the metal material gradually fills the gaps and tightly fits the apex of the shaping groove, the corner morphology of the shield's sidewalls undergoes a qualitative change, reconstructing from an open structure with rounded transitions into a sharply angled microscopic orthogonal right-angled structure. This structurally dense closure completely blocks the path of high-frequency electromagnetic waves to penetrate or diffract at a physical level.

[0105] For example, when processing a 0.2 mm thick nickel-plated copper shield, the pre-formed corners open outwards by approximately 4 degrees. When the mold closes, the 89-degree negative angle inner wall of the lower mold insert prevents the corners from deforming outwards, forcing approximately 0.01 cubic millimeters of redundant metal material to flow inwards. Driven by the localized high pressure generated by the indentation ribs, this portion of metal flows towards the natural gap with a radius of 0.1 mm on the inner side of the bend. After approximately 30 milliseconds of plastic flow, the metal completely fills the gap and adheres to the right angle of the mold, resulting in a sharp right-angle shape on the outer side of the final shield. Testing showed that its electromagnetic shielding effectiveness was significantly improved by a decibel compared to traditional rounded-corner bending products.

[0106] S43. During the subsequent second pressure holding period, the attenuation rate of the forming load is monitored in real time using a pressure sensor. When the forming load is detected to decrease from its peak and tend to stabilize, and the rate of change is lower than the preset threshold, it is determined that the elastic rebound stress inside the metal material has been converted into plastic deformation. At this time, the locking state of the slider is released, and the final shaping is completed.

[0107] In this step, the forming load refers to the reaction force exerted on the mold components (such as rigid restraint structures or forming bending punches) by the metal material due to extrusion deformation while the mold remains closed and locked. Macroscopically, it manifests as the real-time tonnage value read by the pressure sensor. This value is not static but rather a direct external representation of the micro-stress state within the metal. During the second holding pressure period, since the slider position is rigidly locked, the geometric volume of the mold cavity remains constant, and the change in the forming load at this time depends entirely on the evolution of the internal stress of the material.

[0108] Monitoring the attenuation rate of the forming load aims to accurately determine the stress relaxation process through quantitative methods. Under constant strain (i.e., constant mold closing height), the elastic rebound stress inside a metallic material gradually decreases over time; this phenomenon is called stress relaxation. The physical mechanism lies in the gradual transformation of high-energy elastic lattice distortion within the material into stable plastic deformation through dislocation climb and slip, leading to a gradual decrease in the external pressure required to maintain the same deformation. Therefore, the attenuation rate of the forming load (i.e., the derivative of force with time) directly reflects the activity level of this transformation. When the attenuation rate is high, it indicates that the material is in a stage of intense stress release; if the mold is opened at this point, the residual elastic potential energy will cause significant rebound. When the attenuation rate approaches zero or falls below a preset threshold, it indicates that stress relaxation is nearing its limit, and the internal structure has reached rheological equilibrium; at this point, opening the mold yields optimal dimensional accuracy.

[0109] Elastic rebound stress exhibits a non-linear, negatively correlated relationship with time, typically displaying an exponential decay curve. In the initial stage of pressure holding, the stress decreases rapidly; as time progresses, the rate of decrease gradually slows and tends towards a stable value (residual stress). This invention utilizes this physical law to upgrade time control to state control.

[0110] For example, when processing a certain type of stainless steel shield, the pressure sensor reading is 200 tons the instant the slider reaches the bottom dead center. After entering the second holding pressure period, as the crystal lattice rearranges, the reading rapidly drops to 195 tons within the first 10 ms, at which point the decay rate is relatively fast. Subsequently, the reading decreases slowly, reaching 192 tons at 60 ms, at which point the rate of change is extremely small, below the system's set threshold of 0.05 t / ms. Based on this, the control system determines that the elastic stress has been effectively converted into plastic deformation and immediately instructs the slider to return to its original position. This mechanism avoids excessive springback due to insufficient holding pressure time and also prevents unnecessary long holding pressure periods from affecting production efficiency.

[0111] Specifically, S43 includes the following sub-steps S431-S433.

[0112] S431. During the second pressure holding period, a piezoelectric sensor is used to collect real-time load signals in the mold closed state at a sampling frequency of kilohertz, and a low-pass filtering algorithm is used to filter out mechanical vibration noise from the servo motor to construct a denoised force-time characteristic curve that reflects the internal stress state of the metal material.

[0113] S432. Perform real-time differential operation on the noise reduction force-time characteristic curve to calculate the decay rate of the forming load over time; compare the decay rate with a preset stress relaxation convergence threshold, and determine that the metal material has reached a rheological equilibrium state and the bending springback potential energy has been completely dissipated only when the absolute value of the decay rate is continuously less than the stress relaxation convergence threshold and the duration reaches a preset confirmation time window.

[0114] S433. Once the rheological equilibrium state is determined, the original pressure holding time is interrupted, and the slider is controlled to start a micro-return action with a non-linear S-shaped speed curve. While releasing the mold locking force, the instantaneous release of the mold elastic deformation energy caused by the sudden unloading of the load is avoided, which would impact the already shaped shield product.

[0115] The denoised force-time characteristic curve refers to the physical quantity change spectrum after being purified by digital signal processing technology. In actual stamping operations, the raw signal collected by piezoelectric sensors is often superimposed with electromagnetic noise generated by the high-frequency rotation of the servo motor and the slight vibration interference of the mechanical transmission chain, presenting a jagged waveform full of burrs. After removing these high-frequency noises by using a low-pass filtering algorithm (such as a Butterworth filter with a cutoff frequency set to 200Hz), a smooth and continuous curve is obtained. This curve realistically depicts the physical process of the die closing force monotonically decreasing over time, accurately reflecting the true trajectory of stress relaxation within the metal material. For example, the raw signal may show the load fluctuating at high frequency between 199.8 tons and 200.2 tons, while the denoised curve shows the load stabilizing at 200.0 tons and slowly decreasing.

[0116] Real-time differentiation of the curve essentially calculates the slope of load change between adjacent sampling points. The control system reads the denoised load value at extremely short time intervals (e.g., 1 millisecond) and calculates the instantaneous rate of change at the current moment using a difference formula. For example, if the load is 195.00 tons at time t1 and 194.95 tons at time t2 (1 ms later), the decay rate is -0.05 tons / millisecond. The preset stress relaxation convergence threshold is a very small value (e.g., 0.01 tons / millisecond), representing the critical state where the internal stress activity of the material tends to be static. The preset confirmation time window (e.g., 10 milliseconds) is a continuous verification condition set to prevent misjudgment caused by occasional signal fluctuations. When the absolute value of the decay rate is less than 0.01 tons / millisecond for 10 consecutive milliseconds, it indicates that the load decrease is no longer caused by macroscopic rheology but has entered a microscopic stabilization period, meaning that the metal has reached rheological equilibrium and the elastic potential energy driving the rebound has been completely dissipated.

[0117] A nonlinear S-shaped velocity curve refers to a situation where the slider's speed does not increase nonlinearly during the initial return stroke, but rather its acceleration itself changes continuously (i.e., the jerk is controlled). The slider starts slowly with extremely low acceleration, its speed rising parabolically, and then accelerates rapidly after leaving the mold contact area. This motion mode avoids the rigid impact caused by sudden speed changes. For example, the slider does not accelerate from 0 to 10 mm / s instantaneously, but moves only a micrometer-level distance in the first 5 milliseconds, allowing the hundreds of tons of elastic deformation energy accumulated in the mold to be released smoothly like deflating a vent, avoiding the shock wave from an instantaneous energy burst damaging the delicate right-angled structure of the shield.

[0118] During the processing of high-strength stainless steel shielding covers, the system collects load data at high frequency during the second pressure holding period. After filtering out motor noise, it is found that the load rapidly decreases from 200 tons to 190 tons within the first 20ms. At this time, the attenuation rate calculated by the derivative far exceeds the threshold, and the system maintains pressure holding. Subsequently, the load decrease slows down and stabilizes at around 188 tons at 65ms. The calculated attenuation rate is below 0.005 tons / ms for 10 consecutive ms, and the system determines that stress relaxation is complete. Immediately afterwards, the slider performs an S-shaped return stroke. The first 2mm of the stroke takes a relatively long time to ensure the flexible release of the mold's elastic potential energy. The final shielding cover produced has perfect sidewall verticality and no springback deformation.

[0119] The following is a complete example of the production cycle sequence. This example takes the production of a shield made of nickel silver (0.2mm thick), requiring a sidewall height of 2.0mm and zero gaps at the four corners. It details the changes in the product's position and shape, as well as the specific actions performed by the mold, in every millisecond-level action from material feeding to the end of molding.

[0120] Phase 1: Feeding and Positioning (Time Point: T0 - T100ms). In this phase, the servo feeder drives the conveyor belt skeleton to move one step.

[0121] Action performed: The side connecting belt pulls the semi-finished shielding cover horizontally at high speed into the mold forming station. Subsequently, the guide pin inside the mold is inserted into the positioning hole of the material strip, and the forming and unloading float is in a high position lifted by the spring.

[0122] Product position: The product is suspended above the lower mold assembly, and then precisely sits on the top surface of the forming and stripping float under the action of the guide pin.

[0123] Product form: At this point, the product's sidewalls are in a pre-bent state (approximately 80°), with the pre-formed upturned corners at the ends of the sidewalls opening outwards by about 4°, maintaining a "trumpet" shape. The side connecting strips are intact, firmly connecting the product to the material strip skeleton.

[0124] Second stage: Flexible pressing (time point: T100ms - T150ms). In this stage, the servo press slide descends rapidly from the top dead center, performing non-linear deceleration before approaching the product.

[0125] Action: The upper mold assembly decelerates, making a low-speed "soft landing" to contact the product. The bottom surface of the upper mold cooperates with the forming and stripping float to overcome the spring force of the lower mold and clamp the product as it moves downwards synchronously.

[0126] Product position: The product's Z-axis degree of freedom is locked, and it sinks into the lower mold cavity along with the float, but has not yet contacted the lower mold insert.

[0127] Product form: The top surface is flattened and corrected, but the side walls and connecting strips have not undergone further deformation. At this time, the side connecting strips remain connected, serving to help prevent the plane from rotating.

[0128] The third stage: synchronous continuous shearing and bending (time point: T150ms - T300ms). In this stage, the slider advances at a constant low speed (e.g., 20mm / s) and enters the core forming zone.

[0129] Action performed: The wavy shearing edge (1.5° bevel) of the forming bending punch sidewall begins to contact the side connecting strip. At the same time, the lower die vacuum generator is activated, and negative pressure is established in the waste suction channel.

[0130] Product form changes: At the moment of entry: the shearing edge penetrates the connecting strip in a point-contact manner, the vertical impact is converted into tangential shearing force, and the connecting strip begins to show cracks, but has not yet completely separated.

[0131] Deformation process: The punch continues to press down, driving the product's sidewall to bend vertically around the fillet of the lower die insert. At this time, the shearing cut-off point moves downward with the punch, its speed synchronized with the sinking speed of the neutral layer during sidewall bending. The side connecting strip is completely cut off before the sidewall is about to experience destructive tensile stress.

[0132] Waste stripping: The cut-off thin strips of waste are instantly sucked into the lower mold channel by negative pressure and completely leave the forming area.

[0133] Product position: The side wall of the product rotates and bends relative to the main body of the top surface, with the angle gradually approaching 90° from 80°.

[0134] Phase 4: Rigid locking and stress field establishment (time point: T300ms - T310ms). In this phase, the slider reaches the micro-range (0.1mm) before reaching the bottom dead center, and the speed drops to near zero.

[0135] Action performed: The rigid limiting step inside the mold collides rigidly with the limiting post and locks in place to prevent overpressure on the mold. At the same time, the indentation rib (0.03mm high) at the bottom of the forming bending punch is forced into the metal surface at the root of the bend.

[0136] Product position: The product is fully pressed into the lower mold shaping groove.

[0137] Product form: Due to the mold cavity volume being smaller than the material volume (mechanical interference), the pre-formed warped corners are forcibly blocked by the 89° negative angle inner wall of the shaping groove, preventing outward expansion. The intrusion of the indentation ribs causes local yielding of the root material, establishing high-pressure rheological conditions.

[0138] Phase 5: Servo pressure holding and creep filling (time points: T310ms - T400ms). In this phase, the slider stops moving and maintains a pressure holding state for approximately 90ms.

[0139] Perform the following actions: First phase (first 40ms): The mold maintains high pressure constraint. Driven by the pressure gradient, the pre-formed warped metal material undergoes directional plastic flow like a high-viscosity fluid, gradually filling the V-shaped geometric gaps on the inside of the bend.

[0140] Second period (last 50ms): Pressure sensor monitors in real time. The forming load slowly decreases from 200 tons to 195 tons and tends to stabilize (the decrease rate is below the threshold), indicating that the elastic rebound stress inside the metal has been converted into permanent plastic deformation.

[0141] Product form: The prefabricated upturned corners have completely disappeared, transforming into solid metal that fills the joints. The side wall joints have changed from an open state to a microscopically orthogonal right-angled closed state, achieving zero gaps.

[0142] Phase 6: Flexible Return and Discharge (Time Point: T400ms - T500ms). In this phase, the system determines rheological balance and instructs the slider to return.

[0143] Action: The slider starts with an S-shaped speed curve, slowly releasing the mold locking force to avoid elastic impact. It then accelerates upward to the top dead center.

[0144] Product position: The forming and stripping float pushes the finished product out of the lower mold under the action of spring force.

[0145] Product form: The final product exhibits perfectly vertical sidewalls, with tight seams at all four corners, no springback or pressure marks, and clean breaks in the side connecting strips. At this point, the product has completely detached from the material strip skeleton (or retains only a weak connection for subsequent air separation at a later station), completing a single stamping cycle.

[0146] 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.

[0147] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is used as an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above.

[0148] 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 shield case progressive die apparatus having a zero gap bending forming function, characterized by, The application relates to a die assembly for manufacturing a shielding cover, which comprises a lower die assembly, an upper die assembly, an elastically arranged forming and stripping floating block and a forming and bending punch. The lower die assembly is a fixed die base, the upper die assembly is arranged above the lower die assembly and can reciprocate vertically relative to the lower die assembly; the forming and stripping floating block is elastically arranged in the lower die assembly to support a shielding cover product to be processed and provide an elastic floating stroke in the vertical direction; and the forming and bending punch is fixedly arranged on the upper die assembly and located directly above the forming and stripping floating block. The side wall of the forming and bending punch is provided with a shearing blade, which is located at a vertical projection position corresponding to a side edge connecting band of the shielding cover product, so that when the upper die assembly drives the forming and bending punch to perform a bending stroke, the shearing blade cooperates with a corresponding blade on the lower die assembly to cut or partially cut the side edge connecting band, so as to maintain the positioning connection between the product and a material band skeleton during the forming process. The lower die assembly is provided with a shaping groove at a pre-bent angle position corresponding to a bending angle of the shielding cover product, and the shaping groove has a negative angle or a right angle inwardly-contracted inner wall profile; when the upper die assembly is lowered to a lower dead point relative to the lower die assembly, the forming and bending punch and the shaping groove of the lower die assembly form a closed extrusion cavity, and the volume of the closed extrusion cavity is smaller than the volume of the metal material containing the pre-bent angle, so that the pre-bent angle is subjected to lateral extrusion by the closing locking force of the upper die assembly, and the metal material at the pre-bent angle is forced to flow plastically and backfill to the bending joint, so as to physically close the side wall gap of the shielding cover.

2. The shield case progressive die apparatus having a zero-gap bending forming function according to claim 1, wherein, The forming and bending punch is provided with a hard limiting step, and the lower die assembly is provided with a corresponding limiting column; the height difference between the hard limiting step and the limiting column is set to be 10%-15% of the material thickness when the die is closed, so as to cooperate with the material flow of the pre-bent angle to lock the bending angle.

3. The shield case progressive die apparatus having a zero-gap bending forming function according to claim 1, wherein, The lower die assembly is provided with a vacuum waste suction channel directly below the shearing blade, and the shearing blade is designed as a 1-2 wave-shaped oblique blade, which is used to prevent the cut-off connecting waste from jumping up and being clamped into the shaping groove when the side face cutting action occurs.

4. A shield zero gap forming method characterized by, The application further discloses a manufacturing method of the die assembly. S1. A shielding cover semi-finished product with a pre-bent angle is conveyed into the die through a side edge connecting band; S2. The slide block of a servo press is controlled to slow down, and the product plate is pressed by the forming and stripping floating block; wherein the slide block is a power output component of the servo press, which is connected with the upper die assembly and drives the upper die assembly to reciprocate vertically relative to the lower die assembly; S3. The slide block is controlled to descend at a constant low speed, and the shearing release of the side edge connecting band and the bending of the product side wall are synchronously completed by the forming and bending punch. S4. When the slider reaches the lower dead point, a servo pressure maintaining program is executed to control the slider to stop moving and maintain a preset pressure maintaining time; during the pressure maintaining time, the mold device maintains the forced extrusion state of the pre-bent angle, uses the creep characteristics of the metal material to make the bent angle material flow and fill the bending joint, and forms a seamless closed structure.

5. The shield zero gap forming method of claim 4, wherein, The pressure maintaining time in the S4 step is set to 50 ms to 100 ms; In the S4 step, a micro-level displacement sensor installed in the mold is used to monitor the closing height in real time, and if the deviation of the closing height caused by thermal expansion exceeds ±0.005 mm, the position of the lower dead point of the slider is automatically adjusted through the servo control system to ensure that the extrusion force for forced caulking is constant.

6. The shield zero gap forming method of claim 4, wherein, The S4 includes the following sub-steps: S41. Control the slider to approach the zero end point speed to reach the lower dead point position, so that the hard limit step and the limit column in the mold are rigidly closed; at the same time, the initial impact pressure is applied to the bending root by the indentation protruding rib arranged on the forming bending punch, and a high pressure stress field is established in the closed space formed by the pre-bent angle and the shaping groove; S42. In the first pressure maintaining period with the position of the slider being locked, the high pressure stress field is used to force the metal lattice at the pre-bent angle to slip and generate directional plastic flow pointing to the inside joint of the bending, until the flowing metal material completely fills the negative angle space of the shaping groove; wherein the preset pressure maintaining time is composed of a continuous first pressure maintaining period and a second pressure maintaining period; S43. In the subsequent second pressure maintaining period, the pressure sensor is used to monitor the attenuation rate of the forming load in real time; when it is monitored that the forming load decreases from the peak value and tends to be stable, and the change rate is lower than the preset threshold, it is determined that the elastic rebound stress inside the metal material has been converted into plastic deformation, at which time the locking state of the slider is released, and the final shaping is completed.

7. The shield zero-gap forming method of claim 6, wherein, The S41 includes the following sub-steps: S411. In the micro-distance range before the slider reaches the lower dead point, a non-linear deceleration program is executed to dissipate the kinetic energy of the slider below the impact threshold, so as to ensure that the inertial impact of the hard limit step and the limit column does not cause elastic vibration of the mold assembly when they are in contact and locked; wherein the micro-distance range is 0.05 mm-0.1 mm; S412. The hard limit step and the limit column are used to forcibly set the final closing height between the forming bending punch and the lower mold shaping groove, so that the mold cavity size at the final closing height is smaller than the original thickness of the material to be processed, so as to construct a mechanical interference state in the closed space; S413. Based on the mechanical interference state, the indentation protruding rib on the forming bending punch invades the metal surface layer of the bending root, and the local contact pressure of the metal surface layer is instantaneously increased to above the yield strength of the metal material by the invasion action, so as to physically activate the phase change potential of the material from elastic deformation to plastic flow, and complete the establishment of the high pressure stress field.

8. The shield zero-gap forming method of claim 6, wherein, The S42 includes the following sub-steps: S421. When the pre-bent corner starts to be plastically deformed, the negative angle or right angle inner wall of the shaping groove is used as a rigid boundary to block the outward expansion of the corner material, and the material's original tangential extension is forced to change into a reverse flow vector pointing to the inside of the corner; S422. The constant volume constraint during the first holding period is maintained, and the pressure gradient between the high pressure area at the bending root indentation protrusion and the low pressure area at the bending seam gap drives the plastic metal material to migrate from the high pressure area to the low pressure area along the reverse flow vector; S423. The natural geometric gap at the inside corner of the bend is filled by the volume migration, and the metal material migrates completely to the right angle vertex of the shaping groove, reconstructing the shield bend corner from a circular arc transition to a micro-orthogonal right angle closed form, thereby physically cutting off the electromagnetic wave leakage channel.

9. The shield zero-gap forming method of claim 6, wherein, The S43 includes the following sub-steps: S431. During the second holding period, a piezoelectric sensor is used to collect real-time load signals under the closed mold state at a sampling frequency of kilohertz, and a low-pass filtering algorithm is used to filter out mechanical vibration noise from the servo motor, and a denoising force-time characteristic curve reflecting the internal stress state of the metal material is constructed; S432. The denoised force-time characteristic curve is differentiated in real time to calculate the decay rate of the forming load with time; the decay rate is compared with the preset stress relaxation convergence threshold value, and only when the absolute value of the decay rate is continuously less than the stress relaxation convergence threshold value and the holding time reaches the preset confirmation time window, it is determined that the metal material has reached the rheological equilibrium state, and the bending rebound potential energy has been dissipated; S433. Once the rheological equilibrium state is reached, the original holding time is interrupted, and the slider is controlled to start a small amount of return motion with a nonlinear S-shaped velocity curve, releasing the mold locking force while avoiding the impact on the shaped shield product caused by the instantaneous release of the mold elastic deformation energy due to the sudden unloading of the load.

10. The shield zero-gap forming method of claim 4, wherein, The S3 includes the following sub-steps: S31. Control the slider to descend, and use the preset bevel or wavy shear edge of the forming bend punch side wall to cut into the side edge connecting band in a point contact manner; at the moment of cutting, convert the vertical punching impact force into a tangential shear force along the plane of the metal plate of the side edge connecting band before the bending action causes lateral tensile deformation of the metal plate of the side edge connecting band, and pre-damage the integrity of the stress transmission structure of the side edge connecting band; S32. As the slider continues to descend to drive the product side wall to deform, the shear edge advances downward and cuts off the side edge connecting band; in this process, the vertical advancing speed of the shear cutting point is kept synchronized with the sinking speed of the bending neutral layer, thereby decoupling the lateral tensile stress of the product side wall from the material band skeleton in real time, preventing necking or tearing of the bending edge in the plastic deformation zone; S33. While the cutting blade is cutting off the side edge connecting strip, the vacuum generating device in the lower die assembly is started to establish a negative pressure field under the shearing fracture surface; the aerodynamic suction force generated by the negative pressure field is used to pull the cut-off connecting shearing waste along the preset direction of the vacuum suction channel from the bending forming station to be oriented and peeled off, so as to prevent the waste from being clamped into the matching gap between the mold assemblies during the subsequent pressure maintaining process.

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