Blanking method and device based on local heating

Abstract

The invention discloses a blanking method and device based on local heating. The device comprises an upper die unit, a lower die unit and a control system. A heating module and a first cooling module are integrated in a punch of the upper die unit; an active cooling module is integrated in a female die cutting edge area of the lower die unit. The working method comprises the steps that when the punch cuts into a plate to a preset depth, the annular to-be-separated material area at the cutting edge is instantly heated through the heating module, meanwhile, the lower portion of the area is intensively cooled through the active cooling module, and a temperature gradient with the high upper portion and the low lower portion is formed; and stamping separation is completed under the gradient guide. Through the synergistic effect of upper heating and lower cooling, the material performance of a shearing area is actively regulated and controlled in the blanking process, the technical problems that when high-strength materials are machined through a traditional blanking technology, the blanking force is large, and the fracture surface quality is poor are solved, and high-quality and low-load precision blanking is achieved.

Description

Technical Field

[0001] This invention belongs to the field of precision stamping and forming technology of metal sheets, specifically relating to a stamping method and apparatus based on local heating. Background Technology

[0002] Blanking is the most widely used sheet metal separation process in manufacturing. In traditional blanking, the punch and die edges apply shear force to the material, causing it to undergo elastic and plastic deformation. Cracks then initiate and propagate from the upper and lower cutting edges, eventually merging to achieve separation. This process creates four characteristic areas on the cross-section: a collapsed corner, a bright surface (band), a rough surface (fracture zone), and burrs. Burrs are caused by the failure of the upper and lower crack propagation paths to completely overlap, resulting in microscopic tearing of the material at the moment of separation. The presence of burrs not only affects the appearance, dimensional accuracy, and assembly performance of parts, but may also detach during use, causing serious malfunctions such as system wear, short circuits, or oil circuit blockages.

[0003] To control burrs, existing technologies mainly optimize in two directions: improving cross-sectional quality by controlling the die clearance on one side to 1%–3% of the plate thickness, maintaining the sharpness of the cutting edge, and applying an ultra-hard coating (such as TiAlN) to the cutting edge. However, these methods are costly, cannot change the fundamental mechanism of material separation, are extremely sensitive to die wear, and require frequent maintenance. Post-processing deburring involves adding steps such as vibratory grinding, sandblasting, electrolysis, thermal deburring, or manual grinding after blanking. This significantly increases production costs and cycle time, and may introduce secondary damage or dimensional changes. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects in the prior art and provide a punching method and apparatus based on local heating.

[0005] To achieve the above objectives, the technical solution of the present invention is to design a punching method based on local heating, comprising the following steps: S1: Place the sheet material on the lower mold and position it; S2: Drive the upper die to move the punch downwards to punch the sheet metal; S3: During the punching process, when the punch cuts into the sheet metal to the preset threshold H1, the local temperature control step is initiated; The local temperature control step includes: instantaneously heating the annular material area to be separated at the edge of the punch, while simultaneously implementing enhanced cooling on the lower part of the annular material area to form a temperature gradient that is higher at the top and lower at the bottom within the area; S4: Guided by the temperature gradient, the punch continues to descend to complete the punching, thus separating the material.

[0006] Preferably, the preset threshold H1 is 70% to 95% of the total thickness of the sheet. When the punch penetration depth is less than 70% of the sheet thickness, although the material has entered plastic deformation, the macroscopic shear band has not yet fully formed, and the stress concentration is insufficient. Applying heat at this time may be ineffective due to premature energy diffusion, and may also lead to increased collapse angle due to excessive material softening. When the penetration depth exceeds 95%, the microcracks inside the material may have already penetrated or are about to break naturally. Applying heat at this time is too late and cannot effectively intervene in the separation path. Setting H1 to 70% to 95% means that in the middle and late stages of the punching stroke, the material has accumulated sufficient plastic deformation energy and internal stress, and micro-damage (voids, microcracks) has already induced at the tip of the cutting edge but has not yet become unstable and expanded. At this time, instantaneous intervention of the energy field can most effectively promote the aggregation of micro-damage and the initiation of macroscopic cracks, while a strong temperature gradient can most effectively guide the newly initiated crack to expand along a predetermined path. Applying energy at the optimal time allows for the achievement of the most significant process effects (reduced power, improved quality) with minimal energy input (short heating time, relatively low power), avoiding the energy waste of heating too early and the ineffectiveness of heating too late.

[0007] Preferably, the heating involves raising the temperature of the upper part of the annular material region to above the material's dynamic recovery temperature or recrystallization temperature, but below its solidus temperature. The dynamic recovery temperature is the temperature at which the material softens during plastic deformation due to dislocation movement and recombination, causing a significant decrease in rheological stress. The recrystallization temperature is the temperature at which the material recrystallizes, softens completely, and experiences a significant decrease in strength. Setting the heating target above this temperature range is to fully soften the material and minimize its yield strength and shear strength, which is fundamental to reducing punching force. Simultaneously, strictly controlling the upper limit below the solidus temperature is to avoid melting. Above the dynamic recovery or recrystallization temperature, the material's plastic deformation capacity is enhanced, and deformation resistance is reduced, facilitating clean shear separation. Maintaining the material in a solid state ensures material continuity and controllable metallurgical structure; after cooling, the properties of the heated area (e.g., through phase transformation strengthening or aging) can sometimes even be improved, avoiding thermal damage.

[0008] Optionally, the heating energy can be applied using any one of high-frequency induction heating, pulsed laser heating, or plasma arc heating, and the heating effect is limited to a ring-shaped area with a width of 0.05–1 mm. High-frequency induction heating, pulsed laser heating, and plasma arc heating are selected as the energy source, and the heating effect is strictly limited to a ring-shaped area with a width of 0.05–1 mm. These three heating methods are all high-energy-density, fast-response heating technologies. High-frequency induction heating utilizes electromagnetic induction eddy currents for heating, and the heating depth is controllable; pulsed laser heating has the highest precision and the most concentrated energy; plasma arc heating has high power and relatively low cost. These methods are chosen to achieve the requirement of instantaneous heating, enabling the target area to be heated to the required temperature within milliseconds. Limiting the width of the area to 0.05–1 mm is to achieve localized heating. This width is slightly larger than or equal to the width of the final fracture shear band. If the heating area is too wide (1 mm), the energy is dispersed, the heat-affected zone is too large, and energy consumption increases. If the heat-affected zone is too narrow (<0.05mm), it is technically difficult to achieve stable and uniform heating, and the excessive concentration of heat input may lead to localized overheating or even vaporization. An extremely narrow heat-affected zone means that most areas of the part retain its original, excellent mechanical properties and microstructure, making it particularly suitable for parts with stringent requirements on the properties of the substrate. Furthermore, modern high-frequency power supplies, lasers, or plasma power supplies can achieve precise control of power and time, thereby ensuring the consistency of heating effects for each pulse.

[0009] Optionally, the enhanced cooling is achieved through an active cooling module installed within the die, which can be a semiconductor cooler array or a microchannel liquid cooling structure. The semiconductor cooler, based on the Peltier effect, rapidly cools the cold end to below ambient temperature upon energization, exhibiting extremely fast response and precise temperature control via current magnitude. The microchannel liquid cooling structure utilizes coolant flowing through channels ranging from tens to hundreds of micrometers in size, achieving ultra-high heat transfer efficiency due to its large specific surface area. This method solves the problem of achieving high-intensity cooling from one side (below) of the sheet metal during the punching process within a very short time, in conjunction with the instantaneous heating above, to create a steep temperature gradient. This rapid temperature drop instantly lowers the temperature of the lower part of the sheet metal at the start of heating, ensuring a sufficiently large temperature gradient, which is the physical basis for guiding the directional propagation of cracks. Active, intense cooling keeps the die cutting edge at a consistently low temperature, avoiding temperature rise, hardness reduction, and thermal wear caused by heat conduction and shear friction from above, significantly extending the die's lifespan.

[0010] Another technical solution of the present invention is to design a punching device based on local heating, including an upper die unit and a lower die unit. The upper die unit includes a punch, which integrates a heating module for locally heating the sheet metal and a first cooling module for cooling the punch body. The lower die unit includes a die, the cutting edge area of ​​which integrates an active cooling module for locally enhanced cooling of the sheet metal. The device also includes a control system electrically connected to the heating module and the active cooling module. This device achieves efficient separation by instantaneously and selectively heating an extremely narrow annular area near the punch cutting edge during the punching process, while simultaneously enhancing cooling of the lower part of the material, creating a strong temperature gradient between the upper and lower parts. This softens the upper material in the area to be separated, guiding cracks to propagate along a predetermined path. The punch is no longer a simple solid structure but integrates two functional modules: a heating module and a first cooling module. The heating module applies precise, localized heat to the sheet metal from above during the punching process. The first cooling module continuously cools the punch body, preventing excessive heat transfer from the heating module to the punch, which could lead to overheating, decreased hardness, or even thermal fatigue damage. The core of the lower die unit is the die cavity, which integrates an active cooling module in the area corresponding to the punch's cutting edge shearing region. This enhanced cooling unit actively and quickly absorbs heat from below the sheet metal. The control system is electrically connected to the heating and active cooling modules, precisely controlling the start / stop timing, energy level, and duration of heating and cooling based on the punching process (especially the punch's penetration depth). Precise heating from above softens the material, while powerful cooling from below maintains die rigidity and guides the thermal gradient, significantly reducing the shear force required for material separation (theoretically by 30%–70%). The separation path is also more controllable, resulting in a high-quality cross-section with a very high proportion of bright bands (up to 90% or more of the sheet thickness) and minimal burrs. This also significantly reduces die edge wear and extends die life. The entire device is compatible with existing punching machines.

[0011] Preferably, the heating module is a high-frequency induction heating module, which includes a high-frequency induction coil embedded inside the punch and a soft magnetic material magnetic ring surrounding the coil. The magnetic ring is used to focus the magnetic field on a narrow area around the end face of the punch.

[0012] A high-frequency current generates a high-frequency alternating magnetic field through a coil. The magnetic ring effectively focuses or guides the potentially divergent magnetic field lines to a very narrow annular region around the punch end face (i.e., the cutting edge). This region corresponds to the annular strip of material on the sheet metal that will be sheared. When the magnetic field passes through this region of the sheet metal, eddy currents are induced on the surface of the sheet metal. The Joule heating generated by these eddy currents causes the material to heat up rapidly. This method solves the problem of how to achieve efficient, precise, and rapid localized heating inside a punch with extremely limited space and subjected to huge mechanical loads. The focusing effect of the magnetic ring avoids magnetic field leakage and energy waste, ensuring that heat is applied only to the predetermined shearing strip. This method has extremely high heating efficiency and a very fast response speed (milliseconds), capable of heating the target area instantly as the punch moves to the preset depth, achieving true instantaneous heating. Simultaneously, induction heating is a non-contact heating method, avoiding direct contact with the high-temperature sheet metal and reducing the thermal impact on the punch body. The heating depth can be adjusted by the current frequency, thereby controlling the heating depth of sheet metal of different thicknesses. Furthermore, the structure is relatively compact, easy to integrate inside the punch, and allows for electromagnetic shielding.

[0013] Preferably, the punch is made of a material with a resistivity higher than 10^-7 Ω·m (such as certain high-strength mold steels, cemented carbide, or materials with special surface treatments), and the first cooling module is a cooling channel located inside the punch. High-resistivity materials can reduce eddy current heating during high-frequency induction and have a greater penetration depth than low-resistivity materials. Therefore, they can effectively reduce eddy currents induced by the induced magnetic field in the punch body, thereby minimizing the punch's own heating and ensuring that the heating energy mainly acts on the sheet metal rather than the mold. Simultaneously, the cooling channel inside the punch constitutes the first cooling module. The cooling medium (such as water, oil, or a special coolant) circulates within the channel, continuously carrying away heat that may be generated by thermal conduction or a small amount of eddy currents, maintaining the punch at a low and stable temperature. This ensures that the punch maintains sufficient hardness, strength, and dimensional stability under long-term repeated hot and cold alternating loads, preventing thermal softening, thermal deformation, or thermal fatigue cracks, thus guaranteeing the reliability and service life of the entire device. The closed-loop channel structure is simple and reliable, has high cooling efficiency, and is easy to connect to an external cooling system.

[0014] Furthermore, the upper mold unit is externally equipped with a multi-layer electromagnetic shielding structure, which includes a high conductivity layer and / or a high magnetic permeability layer. The high conductivity layer primarily attenuates high-frequency electromagnetic waves through reflection; the high magnetic permeability layer primarily attenuates low-frequency magnetic fields through absorption. This multi-layer combination can suppress electromagnetic field radiation outwards with a wide bandwidth and high efficiency. This prevents the strong electromagnetic field generated by the high-frequency induction heating module from causing electromagnetic interference to surrounding electrical equipment (such as the CNC system and sensors of the punching machine), affecting their normal operation, and improving product safety.

[0015] Optionally, the active cooling module is a semiconductor cooler array disposed within the die cavity, or a three-dimensional branched microchannel cooling network formed by additive manufacturing inside the die cavity. Multiple micro-semiconductor coolers are closely arranged and integrated above the cutting edge of the die cavity. When direct current is applied, the upper surface (cold end) of the cooler adheres to the die cavity cutting edge or contacts the underside of the substrate through a heat-conducting block, rapidly absorbing heat; the heat generated on the lower surface (hot end) is carried away by a heat sink (such as air cooling or liquid cooling). By controlling the magnitude and direction of the current, the cooling intensity and temperature can be precisely controlled. A second approach uses a three-dimensional branched microchannel cooling network. This is achieved using additive manufacturing (3D printing) technology to directly create a biomimetic tree-like or fractal microchannel network inside the die cavity. Driven by a pump, the coolant flows through these dense microchannels. Due to the small channel size and huge specific surface area, the heat exchange efficiency is extremely high, enabling rapid and uniform heat extraction from the die cavity cutting edge area. Semiconductor coolers offer fast response and precise temperature control, eliminating the need for complex fluid piping and making them suitable for compact applications. Microchannel cooling, on the other hand, boasts superior heat exchange capabilities, ideal for applications requiring extremely high cooling power. This active cooling module, in conjunction with the heating action above, instantly establishes an extremely high temperature gradient along the thickness of the sheet material (e.g., the upper annular zone is heated to several hundred degrees Celsius or even higher, while the adjacent lower region is cooled to room temperature or below). This strong gradient not only accelerates the downward transfer of heat (increasing the driving force of heat conduction), but more importantly, it creates an extreme difference in the mechanical properties of the material's shear zone—softer at the top and harder at the bottom—significantly promoting the directional propagation of shear deformation and cracks from top to bottom. This results in an extremely straight and bright separation surface while reducing the punching force. Simultaneously, the intense cooling protects the die cutting edge from the effects of heat conduction from above.

[0016] Furthermore, it also includes a multi-sensor detection system, including: a displacement sensor for real-time detection of punch displacement; a dynamic force sensor for real-time detection of punching force; and an infrared thermal imager for real-time monitoring of the temperature field of the heating area. The control system controls the start / stop and power of the heating module and the working status of the active cooling module in real time based on the feedback signal of the multi-sensor detection system.

[0017] The advantages and beneficial effects of this invention are as follows: 1. This invention creates a strong temperature gradient within the shear band, with higher temperatures at the top and lower temperatures at the bottom. This gradient not only softens the upper material to reduce the punching force, but more importantly, it acts as a physical guide, directing cracks to propagate stably from top to bottom along the relatively uniform, higher-temperature softened band, rather than randomly tearing at stress concentration points as in traditional punching. The direct result is an order-of-magnitude increase in the proportion of bright bands on the punched section, consistently reaching over 80% of the plate thickness, and even achieving nearly 100% bright band coverage. The surface roughness (Ra value) can be reduced by more than an order of magnitude. Simultaneously, burr height is effectively controlled.

[0018] 2. The process principle of this invention is universally applicable, its core being the active regulation of local material properties rather than relying on the material's inherent room-temperature plasticity. Therefore, it is not only applicable to materials with good traditional plasticity for achieving higher quality and lower loads, but more importantly, it opens up efficient separation pathways for a range of advanced materials that are difficult or even impossible to process using traditional stamping. For example, for high-strength martensitic and bainitic steels, it avoids the high wear and brittle fracture problems caused by their high hardness; this greatly expands the processing range of stamping processes, providing a reliable, efficient, and low-cost manufacturing solution for the engineering applications of new materials in areas such as structural lightweighting and performance enhancement.

[0019] 3. The main body of the device of this invention is a specially designed mold system. The entire system can be easily integrated into existing mechanical or hydraulic ordinary stamping presses without structural modifications to the press itself, resulting in relatively low modification costs and convenient upgrades. Its working process (depth monitoring, triggering heating / cooling, and completing the stamping) is fully automated by the control system. Process parameters (trigger depth, heating power, time, and cooling intensity) can be digitally set and stored, ensuring high repeatability and stability of the process. This makes it ideal for modern, automated, and flexible intelligent manufacturing production lines. This plug-and-play upgrade solution enables the rapid promotion and application of this innovative technology in the manufacturing industry, creating significant economic and social benefits. Attached Figure Description

[0020] Figure 1 This is a cross-sectional schematic diagram of a traditional stamped part; Figure 2 This is a flowchart of the punching method of the present invention; Figure 3 This is a schematic diagram of the punching device of the present invention.

[0021] In the figure: 1. Punch; 11. Cutting edge; 2. Heating module; 21. High-frequency induction coil; 22. Magnetic ring; 3. First cooling module; 4. Die; 5. Active cooling module; 51. Semiconductor cooler; 52. Heat sink; 6. Plate. Detailed Implementation

[0022] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0023] according to Figure 2 As shown, the present invention is a punching method based on local heating, comprising the following steps: Step S1: Place the sheet material on the lower mold and position it. First, based on the size and shape of the part to be processed, prepare a mold (including punch 1 and die 4) with the corresponding contour and install it on the blanking equipment. The sheet metal 6 to be blanked is transported to the working area and precisely placed on the upper surface of the die 4 in the lower die unit. Positioning is achieved through locating pins, locating blocks, or a vision positioning system on the die 4, ensuring that the blanking area of ​​the sheet metal 6 is perfectly aligned with the cavity of the die 4 and the cutting edge contour of the punch 1 in the horizontal plane. This step is fundamental to ensuring the accuracy of subsequent blanking and is no different from traditional blanking.

[0024] Step S2: Drive the upper die to move the punch downwards to punch the sheet metal. The blanking equipment (such as a mechanical press or hydraulic press) is started, and its slide drives the upper die unit (including punch 1) to begin descending. The cutting edge of punch 1 first contacts the upper surface of the sheet metal 6. As punch 1 continues to descend, it applies vertical pressure to the sheet metal 6, causing it to undergo elastic deformation, and then enters the plastic deformation stage. Under the combined action of punch 1 and the cutting edge of die 4, the sheet metal 6 begins to be squeezed, stretched, and bent, and a highly concentrated shear stress is generated in the cutting edge tip area. Plastic strain energy begins to accumulate inside the material and microscopic damage (such as dislocation entanglement and cavities) begins to form. This stage relies entirely on mechanical energy, and the blanking force increases approximately linearly or nonlinearly with the depth of cut. Displacement / pressure sensors monitor the downward displacement of punch 1 (or the displacement of the press slide) and the pressure value acting on the sheet metal in real time, and continuously transmit the data to the control system.

[0025] Step S3: During the punching process, when the punch cuts into the sheet metal to the preset threshold H1, the local temperature control step is initiated. This is the core step that distinguishes the method of this invention from traditional punching. The key to its implementation lies in a preset triggering condition and a set of synchronously executed composite energy field operations.

[0026] Trigger Judgment: The control system has a preset threshold H1 (the preset threshold H1 is 70% to 95% of the total thickness of the sheet). For example, for an 8mm thick DP780 steel sheet, H1 can be set to 85% of the total thickness of the sheet, i.e., 6.8mm. The control system continuously compares the real-time displacement data with the H1 value. When the sensor feedback shows that the depth of punch 1 into the sheet reaches exactly 6.8mm, it means that the punching process has entered the critical window period. At this time, the macroscopic shear band has been fully formed, sufficient plastic work has accumulated inside the material, and microscopic cracks may have already started to emerge, but the macroscopic cracks have not yet become unstable and propagated.

[0027] Instantaneous heating start-up: Once the triggering conditions are met, the control system immediately sends a command to the heating module 2 (e.g., a high-frequency induction heating power supply). Within milliseconds, the high-frequency power supply outputs a high-power (e.g., 50kW), short-duration (e.g., 20 milliseconds) high-frequency current (e.g., 200kHz) to the high-frequency induction coil 21 embedded in the end of the punch 1. The high-frequency alternating magnetic field generated by the coil 21 is focused by the soft magnetic material magnetic ring 22, penetrating the tiny gap between the punch 1 and the plate 6, and acting on a ring-shaped area on the plate with a width of approximately 0.5mm (a preferred value within the range of 0.05-1mm). This area is precisely the material strip to be separated directly below the punch cutting edge. The magnetic field induces strong eddy currents on the surface of the plate, converting electrical energy into heat energy according to Joule's law of heating. The heating goal is to rapidly raise the temperature of the material above this ring-shaped area to approximately 750°C within 20 milliseconds. For DP780 steel, its dynamic recovery temperature is approximately 600°C, its recrystallization temperature is approximately 700°C, and its solidus temperature is much higher than 1400°C. The set temperature of 750℃, above the recrystallization temperature, fully softens the material, significantly reducing the yield strength in this region, while remaining well below the solidus line, thus avoiding the risk of melting. The heating energy is strictly limited to a 0.5mm wide annular band, achieving extreme localization.

[0028] Synchronous Enhanced Cooling Start-up: When the heating command is issued (or, to ensure effective cooling below, cooling can be initiated at the beginning of the pressing and punching process), the control system sends a start command to the active cooling module 5. Taking a microchannel liquid cooling structure as an example, the external high-pressure coolant pump immediately starts, pumping low-temperature coolant (such as 20°C deionized water) at high pressure (such as 0.5MPa) into the three-dimensional branched microchannel cooling network formed by additive manufacturing inside the die 4. The coolant flows at high speed within the dense microchannels, instantly and efficiently removing heat from the cutting edge area of ​​the die 4 (i.e., the lower part of the plate 6 opposite the upper heating ring). If a semiconductor cooler array is used, all semiconductor cooler plates 51 are subjected to maximum operating current, and their cold end temperature rapidly drops to 0°C or even lower, strongly absorbing heat in close contact with the die cutting edge.

[0029] Formation of the temperature gradient: The direct physical effect of the aforementioned simultaneous heating from top to bottom operation is the instantaneous formation of a temperature gradient, higher at the top and lower at the bottom, within the 0.5mm wide annular shear band along the thickness direction of the sheet material. The upper material is heated to 750℃, while the lower material, due to rapid cooling, may remain below 50℃ or even lower. This temperature difference occurs within a thickness of less than 2mm, and the temperature gradient can reach hundreds of degrees Celsius per millimeter per second. This gradient field is the decisive factor guiding the subsequent material separation behavior.

[0030] Step S4: Guided by the temperature gradient, the punch continues to descend to complete the punching, separating the material. After a strong temperature gradient field is established, the punching process does not stop. The slide of the punching machine continues to drive punch 1 downwards. At this point, because the material at the top of the shear strip has been heated and softened (its strength may have dropped to 1 / 3 or even less of its room temperature strength), the force required to continue shearing this part of the material decreases significantly. Simultaneously, because the material at the bottom remains at a low temperature and high strength, the mechanical properties of the entire shear strip exhibit an extreme difference between soft at the top and hard at the bottom. In this state: The blanking force drops sharply: the total blanking force and stroke curve show a clear downward plateau after the trigger point, and the peak blanking force can be reduced by about 40%-50% compared with traditional cold blanking.

[0031] Directional crack propagation: Cracks preferentially initiate and propagate in the upper part of the softened zone, which has the lowest strength and the best plasticity. Below, the high-strength zone maintained by intense cooling makes it difficult for the crack to propagate downwards into the hard material; laterally, there is the unheated, high-strength base material; and above, there is the hard surface of the moving punch. Therefore, guided by both stress and temperature fields, the initiated crack is constrained and guided, propagating smoothly and rapidly from top to bottom almost strictly along the softened, relatively uniform annular band. This propagation path is the ideal pure shear plane.

[0032] Separation complete: The crack penetrates the entire annular band within milliseconds, and the material is completely separated. Punch 1 carries the punched scrap (or part) into the cavity of die 4. The separated cross-section exhibits an extremely wide bright band (up to 90% or more of the plate thickness), the fracture zone is extremely narrow and flat, and the burr height is significantly reduced.

[0033] After separation, the punching machine slide returns, the control system shuts off heating and enhanced cooling, all modules reset, and it prepares for the next work cycle.

[0034] according to Figure 3As shown, a blanking device for implementing the above method is described. The blanking device of this invention mainly consists of three parts: an upper die unit, a lower die unit, and a control system. The upper die unit is mounted on the slide of the blanking machine via an upper die holder and reciprocates up and down with the slide. The lower die unit is mounted on the worktable of the blanking machine via a lower die holder and remains fixed. The sheet material 6 to be processed is placed on the upper surface of the die 4 and precisely positioned by a locating pin or other locating mechanism.

[0035] The core of the upper die unit is the punch 1. The geometry (circular, rectangular, or irregular) of the punch 1 is determined according to the hole type or shape of the part to be punched. Unlike traditional punches, the punch 1 of this invention is a composite component integrating heating, cooling, and mechanical bearing functions. The base of the punch 1 is made of a die material with high hardness, high wear resistance, and high resistivity (preferably greater than 10^-7 Ω·m), such as cemented carbide, powder high-speed steel, or high-strength steel with a ceramic coating. Inside the punch 1, multiple annular closed cooling channels are machined or pre-embedded from its top downwards, forming the first cooling module 3. The cooling channels are arranged around the central area, and their inlet and outlet pipes (not shown in the figure) are led out from the upper die base and connected to an external water cooler or oil cooler to achieve coolant circulation. The coolant continuously flows through the channels, carrying away the heat of the punch body and keeping its overall temperature at a low level (usually below 80°C).

[0036] A heating module 2 is integrated at the end of the punch 1 (the working cutting edge). The heating module 2 mainly includes a high-frequency induction coil 21 and a soft magnetic material magnetic ring 22. The induction coil 21 is made of multiple turns of flat copper tube or Litz wire, and is embedded in an annular groove inside the end face of the punch. The copper tube itself can be cooled by water to prevent the coil from overheating. The magnetic ring 22 is made of high permeability, low loss soft magnetic ferrite or amorphous or nanocrystalline alloy. It tightly surrounds the outer periphery and the bottom of the coil 21, and its shape matches the coil. The function of the magnetic ring 22 is to constrain and guide the magnetic field lines. When a high-frequency power supply (usually in the frequency range of 50kHz~1MHz) supplies high-frequency alternating current to the coil 21, the generated alternating magnetic field is focused by the magnetic ring 22, so that most of the magnetic lines of force are concentrated and exit from the end of the magnetic ring 22 (i.e., the edge of the end face of the punch 1), acting on a very narrow annular area (usually 0.05-1mm wide) on the plate 6 directly below. (It is important to emphasize here that the punch and its tip are made of a high-resistivity material (resistivity higher than 10^-7 Ω·m) to suppress eddy current heating generated within the high-frequency magnetic field. Therefore, the punch tip does not generate excessive Joule heating due to high-frequency induction, thus affecting its punching performance.) This annular region coincides with the punching contour line and is precisely the material strip about to undergo shear separation. The magnetic field induces strong eddy currents on the surface of the sheet in this region, converting electrical energy into heat energy using the material's resistance. This causes the material in the upper part of the annular region to be rapidly heated to the target temperature (above the dynamic recovery temperature, but below the solidus) in a very short time (a few milliseconds to tens of milliseconds).

[0037] To protect the internal coil and flow channels of the punch 1 and to guide the magnetic field when necessary, the end face of the punch 1 can be constructed of multiple layers of material. The outermost layer is the cutting edge 11 that contacts the sheet metal, requiring extremely high hardness and wear resistance. It is typically a single piece of cemented carbide or diamond composite material with a resistivity higher than 10^-7 Ω·m. Above this is the mounting space for the magnetic ring 22 and the coil 21. The coil leads are led out through small holes on the side or center of the punch and connected to the high-frequency power supply output terminal fixed on the upper die base.

[0038] To prevent the strong electromagnetic field from the heating module 2 from interfering with the punching machine and its surrounding equipment, a multi-layered electromagnetic shielding structure is installed on the exterior of the upper die unit, especially around the upper die base and its components connected to the slider. This structure typically consists of an outer shell and an inner lining. The outer shell is generally made of highly conductive aluminum or copper plates, forming a reflective barrier for electromagnetic waves. On the inner side, a high-permeability absorbing material, such as ferrite tiles or magnetic rubber, may be attached to absorb low-frequency magnetic field components. The shielding structure should be well grounded to form a complete Faraday cage.

[0039] The core of the lower die unit is the die cavity 4. The die cavity 4 is fixed on the lower die base, and its cavity maintains a certain blanking clearance with the contour of the punch 1. The cutting edge of the die cavity 4 also needs high hardness and wear resistance. In the cutting edge area of ​​the die cavity 4, immediately above the cavity entrance, an active cooling module 5 is integrated.

[0040] The first implementation of the active cooling module 5: a semiconductor cooler array. A mounting step is machined around the cavity on the body of the die 4. Multiple small semiconductor coolers 51 are mounted on the step in a closely spaced arrangement, maintaining good contact with the die body via thermal grease or solder. To enhance the strength of the die 4 without being affected by the mounting step, multiple holes can be evenly distributed inside the semiconductor coolers 51 for multiple support pillars to pass through, thus providing auxiliary support; alternatively, the cooling effect of the semiconductor coolers 51 can be increased, allowing temperature conduction through the die 4, and then increasing the distance between them and the surface of the die 4 to enhance support strength. The cold side (upper surface) of each cooler 51 faces upwards, closely adhering to the die cutting edge area; the hot side (lower surface) faces downwards, connected to a heat sink consisting of heat dissipation fins and a fan, or connected to a liquid cooling block. The electrodes of all coolers 51 are connected in parallel or series to an external DC power supply and temperature controller. When cooling is required, the control system is powered on, and the cold surface of the cooling plate 51 begins to rapidly absorb heat, drawing away heat from the die cutting edge and the lower surface of the plate 6 in contact with it, causing its temperature to drop sharply, even below the ambient temperature. The heat sink 52 then dissipates the heat generated by the hot surface into the air or is carried away by liquid cooling.

[0041] The second implementation of the active cooling module 5: a three-dimensional branched microchannel cooling network. This scheme utilizes metal additive manufacturing technologies such as selective laser melting to integrally mold the die 4 with its complex internal flow channel structure. Inside the die 4, a three-dimensional branched microchannel network, mimicking the root system or vascular system of a tree, extends from the coolant inlet located on the side. The channels are densely distributed below the entire cutting edge bearing area of ​​the die. The coolant inlet and outlet are connected to an external high-pressure micro-volume coolant pump and heat exchanger via the lower die base. When the high-pressure coolant (deionized water or a special coolant) is pumped into the microchannel network, due to the extremely fine and densely distributed channels, there is a huge contact heat exchange area between it and the die metal, which can instantly remove the heat from the die cutting edge with extremely high efficiency, achieving ultra-strong cooling. The cooling capacity and temperature uniformity of this structure far exceed those of traditional drilled cooling channels.

[0042] The control system is typically based on a programmable logic controller (PLC) or an industrial computer (IPC), integrating a high-frequency induction heating power supply controller, a semiconductor cooler (or microchannel cooling pump) driver, a data acquisition module, and input / output interfaces. Displacement / pressure sensors (which can be optical scales, magnetic scales, or pressure sensors) are mounted on the punching machine slide or upper die holder to detect the downward displacement of punch 1 and / or the pressure signal acting on the sheet metal in real time, transmitting the signals to the control system. Operators can preset process parameters via a human-machine interface (HMI), including punching thickness, material type, heating trigger depth H1 (typically 70%–95% of the total sheet metal thickness), heating power (or target temperature), heating time, and cooling intensity.

[0043] The control system reads displacement sensor signals in real time according to a preset program. When the depth to which punch 1 cuts into sheet 6 reaches a preset threshold H1, the control system simultaneously sends trigger commands to the heating power controller and the active cooling module driver. The heating power controller immediately outputs a high-frequency current of specified power and duration to the high-frequency induction coil 21 to initiate local heating. At the same time, the active cooling module 5 (whether it is a semiconductor cooler array or a microchannel pump) immediately starts and enters the maximum cooling power operating state. The duration of heating and cooling can be a preset fixed value or dynamically adjusted according to the signal feedback from the pressure sensor (such as a downward trend). When the punching is completed (the punch passes through the sheet) or the pressure drops suddenly, the control system shuts down heating and enhanced cooling, and all modules return to standby mode.

[0044] The collaborative working process of the device and method of this invention can be summarized as follows: Initial mechanical loading stage: The punch 1 contacts and cuts into the plate 6 under mechanical force, inducing elastoplastic deformation and forming a shear stress concentration zone at the cutting edge. This stage is completely dominated by mechanical energy.

[0045] Critical State Perception and Judgment Stage: The control system monitors the stroke in real time through sensors, accurately capturing the moment when the punch penetration depth reaches the preset threshold H1 (e.g., 85% of the plate thickness). This depth corresponds to the critical state in the middle and late stages of material shear deformation, where microscopic damage has already occurred but macroscopic cracks have not yet propagated.

[0046] Multi-energy field instantaneous intervention phase: Once the critical depth is reached, the control system simultaneously triggers two actions: The high-frequency induction heating module 2 works instantly, precisely converting electromagnetic energy into heat energy, which is applied to the upper part of the extremely narrow annular shear band on the plate, causing its temperature to rise above the recrystallization temperature in milliseconds, achieving localized ultra-fast softening.

[0047] The active cooling module 5 inside the die is activated simultaneously, powerfully drawing heat from the lower part of the sheet metal shearing strip with extremely high power, causing the temperature in that area to drop sharply, even below room temperature, thus achieving localized ultra-fast cooling.

[0048] Along the thickness direction of the shear band in the sheet metal, an extremely steep temperature gradient field (hot at the top, cold at the bottom) and a corresponding mechanical property gradient field (soft at the top, hard at the bottom) are instantly constructed. Guided by this gradient field, the mechanical punching stroke continues. The shearing force required to shear the softened upper material decreases significantly, and the peak total punching force is significantly reduced. Cracks preferentially initiate in the softest, most ductile upper region. Under the constraint of the high-strength material below and the pull of the temperature gradient, the cracks are strictly constrained and guided, smoothly and directionally propagating from top to bottom along the relatively uniformly softened band, completing the separation. The separation path is controllable, resulting in a high-quality cross-section with a large proportion of bright bands and minimal burrs. Intense cooling also protects the die cutting edge, preventing thermal wear.

[0049] After separation, the control system shuts down the energy field, the punching machine returns to its original position, and all modules are reset, preparing for the next high-quality, high-efficiency, and low-consumption intelligent punching operation.

[0050] This invention upgrades the traditional passive and single mechanical punching process into an active, controllable, multi-field coupled intelligent precision separation process through the above-mentioned method and device, fundamentally solving the industry pain point of multiple burrs in the punching of high-strength materials.

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A punching method based on localized heating, characterized in that, Includes the following steps: S1: Place the sheet material on the lower mold and position it; S2: Drive the upper die to move the punch downwards to punch the sheet metal; S3: During the punching process, when the punch cuts into the sheet metal to the preset threshold H1, the local temperature control step is initiated; The local temperature control step includes: instantaneously heating the annular material area to be separated at the edge of the punch, while simultaneously implementing enhanced cooling on the lower part of the annular material area to form a temperature gradient that is higher at the top and lower at the bottom within the area; S4: Guided by the temperature gradient, the punch continues to descend to complete the punching, thus separating the material.

2. The method according to claim 1, characterized in that, The preset threshold H1 is 70% to 95% of the total thickness of the board.

3. The method according to claim 1, characterized in that, The heating is to raise the temperature of the upper part of the annular material region to above the material's dynamic recovery temperature or recrystallization temperature, but below its solidus temperature.

4. The method according to claim 1 or 3, characterized in that, The heating energy is applied in any one of high-frequency induction heating, pulsed laser heating, or plasma arc heating, and the heating effect is limited to an annular region with a width of 0.05-1 mm.

5. The method according to claim 1, characterized in that, The enhanced cooling is achieved through an active cooling module installed inside the mold, which is a semiconductor cooler array or a microchannel liquid cooling structure.

6. A punching apparatus for implementing the method according to any one of claims 1-5, comprising an upper die unit and a lower die unit, characterized in that: The upper die unit includes a punch (1), which integrates a heating module (2) for locally heating the sheet metal and a first cooling module (3) for cooling the punch body. The lower mold unit includes a die (4), and the cutting edge area of ​​the die (4) is integrated with an active cooling module (5) for localized strengthening and cooling of the sheet metal. The device also includes a control system electrically connected to the heating module (2) and the active cooling module (5).

7. The apparatus according to claim 6, characterized in that, The heating module (2) is a high-frequency induction heating module, which includes a high-frequency induction coil (21) embedded inside the punch (1) and a soft magnetic material magnetic ring (22) surrounding the coil. The magnetic ring (22) is used to focus the magnetic field on a narrow area around the end face of the punch.

8. The apparatus according to claim 7, characterized in that, The punch (1) is made of a material with a resistivity higher than 10^-7 Ω·m, and the first cooling module (3) is a cooling channel disposed inside the punch.

9. The apparatus according to claim 6, characterized in that, The upper mold unit is provided with a multi-layer electromagnetic shielding structure, which includes a high conductivity layer and / or a high magnetic permeability layer.

10. The apparatus according to claim 6, characterized in that, The active cooling module (5) is a semiconductor cooler array disposed in the concave mold (4), or a three-dimensional branched microchannel cooling network formed by additive manufacturing inside the concave mold.

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