System and method for regulating and controlling plate bulging strain microcell

Abstract

The invention provides a system and a method for regulating and controlling a plate bulging strain microcell. The system comprises a hydraulic bulging device, a multi-axis movement system, an online vision measurement system, a control system and a low-temperature medium spraying device, a plate is arranged in the hydraulic bulging device, and the low-temperature medium spraying device is installed at the tail end of the multi-axis movement system. Signals generated by the on-line vision measurement system are input into the control system, and the control system outputs the signals to the multi-axis movement system and the low-temperature medium injection device. According to the method and the device, the strength difference, the hardening difference and the ductility difference of the light alloy in different temperature intervals are utilized, and the method and the device capable of realizing strain microcell regulation and control are designed; different from preposed regulation and control measures in the prior art, such as integral heating, integral ultralow-temperature freezing and preset local heating and cooling measures, the strain evolution trend and rule of the plate can be monitored in real time.

Description

Technical Field

[0001] The present invention relates to the technical field of metal sheet plastic forming, and in particular to a system and method for regulating and controlling sheet metal bulging strain micro-regions. Background Art

[0002] With the increasing demand for complex sheet metal forming and lightweighting in the automotive, aviation, and aerospace sectors, light alloy sheet metal, with its advantages of low density, high specific strength, and high specific stiffness, holds broad application prospects in these fields. However, light alloy sheet metal has low strength and elongation, and its hardening index is significantly lower than that of high-strength steel and stainless steel. Therefore, it struggles to meet the large deformation requirements of complex curved surface components, often leading to premature necking instability and cracking in localized areas.

[0003] Traditionally, in order to improve the formability of light alloy sheets, the forming process is often designed as a multi-pass deformation process of step-by-step small deformation + re-annealing. The areas where strain hardening occurs are softened again through annealing to avoid concentrated instability. However, this greatly increases the forming cycle and manufacturing cost of light alloy parts, making it difficult to meet the needs of mass production.

[0004] Some scholars have improved some of the forming properties by changing the microstructure of alloy sheets. Patent document CN118064815A proposes a method using high strain rate rolling and recrystallization heat treatment to significantly refine the grains of magnesium alloy sheets, thereby improving strength and elongation. Patent document CN1099940094 uses gradient die deformation to control the texture orientation of magnesium alloy sheets, weaken the texture, and improve the formability of the sheets. However, the actual problem is that the material hardening index n value of these solutions does not increase significantly, and the sheets still tend to undergo concentrated necking instability, making it impossible to control the local strain trend.

[0005] Research has shown that the strength of light alloy materials decreases with increasing temperature from room temperature, but increases with decreasing temperature at low temperatures. Some researchers, leveraging the principle that decreasing strength facilitates forming, have employed hot forming to improve the hot forming properties of light alloy sheets. However, while this approach increases elongation, it reduces the hardening exponent, n, resulting in excessive localized thinning of parts, often exceeding 30%, resulting in significant differences in part wall thickness compared to the sheet, and reduced load-bearing performance.

[0006] Patent document CN112658088B uses hot forming equipment and step-by-step hot press forming to address the cracking problem of titanium alloy parts. Patent document CN109985955B proposes a hot air expansion deep drawing method to alleviate the severe bottom thinning and uneven deformation problems in the original hot deep drawing process. Patent document CN116351944B proposes a curved surface tension-compression composite hot forming method that uses a flexible heating elastic pad to uniformly preheat the sheet. However, hot forming has a long manufacturing cycle and high cost, which cannot meet the urgent needs of rapid product development and weight reduction.

[0007] In the Chinese patent document CN116351944B, a method for integrated progressive forming with ultra-low temperature cooling in divided steps is proposed. For solution-aged plates, combined with the layer-by-layer processing characteristics of the single-point progressive forming process, the entire plate is first cooled to below -100°C. When a certain layer is processed, ultra-low temperature fluid and gas are sprayed into the area to maintain the plasticizing effect during the ultra-low temperature progressive forming process. This is a preset supplementary cooling measure. Patent document CN202011435530.0 is for solution-treated plates, the entire plate is cooled to below -100°C, and a multi-point punch is used to form complex aluminum-lithium alloy components. Patent document CN111940585A provides a solution for cooling the mold and plate to below -123°C for the solution-treated plate drawing forming process. However, the actual problem is that these solutions are all preset supplementary cooling measures, which cannot monitor the strain growth law and trend in real time, and cannot control the local strain trend in areas where concentrated necking instability occurs. Summary of the Invention

[0008] In view of the defects in the prior art, the purpose of the present invention is to provide a system and method for micro-region control of plate bulging strain.

[0009] According to the present invention, a system for micro-region control of plate bulging strain is provided, comprising: Hydraulic bulging device, multi-axis motion system, online visual measurement system, control system and cryogenic medium injection device; A sheet material is arranged in the hydraulic bulging device, and a low-temperature medium injection device is installed at the end of the multi-axis motion system; the signal generated by the online visual measurement system is input into the control system, and the control system outputs the signal to the multi-axis motion system and the low-temperature medium injection device.

[0010] Preferably, the hydraulic bulging device includes a blank holder, a pressure port, a sealing plate and a hydraulic source; The boost port is connected to the sealing plate, and the hydraulic source applies high-pressure liquid medium to the sheet material through the boost port, and the sheet material is fixed between the blank holder and the sealing plate; the blank holder is used to apply clamping force to seal the liquid medium between the sheet material and the sealing plate.

[0011] Preferably, the multi-axis motion system includes a universal three-dimensional multi-axis CNC machine tool structure, a universal track-type multi-axis robotic arm structure, and a universal inverted multi-axis robotic arm structure.

[0012] Preferably, the control system includes a general numerical control system for input and output of strain processing and trajectory planning signals.

[0013] Preferably, the cryogenic medium injection device includes a cryogenic solenoid valve, a liquid nitrogen spray gun and a liquid nitrogen tank; the cryogenic solenoid valve is used to receive instructions from the control system to open or close the cryogenic medium injection device.

[0014] According to the present invention, a method for micro-region control of plate bulging strain is provided, comprising: Step S1: printing a grid on the outer surface of the plate to be formed; Step S2: placing the sheet in a hydraulic bulging device, applying initial liquid pressure under the sheet to start bulging; Step S3: enabling the online visual measurement system to collect strain data and point cloud data in real time and send them to the control system; Step S4: The control system receives strain data and point cloud data, and automatically plans a movement path when it identifies that a certain point or local strain reaches a target area strain safety threshold; Step S5: The multi-axis motion system drives the terminal cryogenic medium spraying device to locate the starting spraying point, and locally freezes the area based on the cryogenic medium spraying device according to the planned movement path; Step S6: Repeat steps S3-S5 to monitor and control the global strain growth trend of the plate in real time until it reaches a preset value; Step S7: The plate is made to maintain a global nearly uniform strain to reach the final forming height, completing the strain micro-region control process.

[0015] Preferably, the process of printing the grid includes: -Square grids are printed using screen printing; - Printing dot grids using electrochemical etching; -The square grid is printed using laser etching.

[0016] Preferably, the control system can automatically start measurement according to a preset fixed time interval; the safety threshold includes a maximum value and a safety value of the strain data and the point cloud data.

[0017] Preferably, after receiving the control system instruction, the cryogenic solenoid valve in the cryogenic medium injection device injects liquid nitrogen in the gas-liquid mixed phase into the local micro-region, thereby strengthening the local region and suppressing the non-uniform necking deformation of the region.

[0018] Preferably, the working parameters of the low-temperature medium injection device have been saved in the control system database, and the plate is strengthened after ultra-low temperature freezing, which suppresses the increase of non-uniform strain in the area; the working parameters include injection height, injection pressure and movement rate parameters.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention utilizes the strength, hardening, and ductility differences exhibited by light alloys in different temperature ranges to design a method and device that can achieve micro-area strain control. Different from the existing pre-control methods, such as integral heating, integral ultra-low temperature freezing, and preset local heating and cooling measures, the present invention can monitor the strain evolution trends and patterns of sheet metal in real time.

[0020] 2. The present invention can regulate the strength and hardening index of the micro-area in real time according to the strain deformation law of the sheet material, thereby suppressing the non-uniform concentrated instability and cracking of the sheet material; the provided micro-area strain regulation scheme does not require reaching ultra-low temperatures of -100°C or below, and can achieve the effect of suppressing concentrated instability by controlling the spray distance and residence time. Therefore, the liquid nitrogen consumption is much lower than that of the existing technology.

[0021] 3. Compared with the existing technology, the plate maintains a global nearly uniform strain to reach the final forming height, and the wall thickness uniformity and forming limit are greatly improved; real-time monitoring and control of strain micro-zones will elevate the existing sheet metal forming technology to an intelligent level, and has good application prospects.

[0022] Other beneficial effects of the present invention will be explained through the introduction of specific technical features and technical solutions in the specific implementation methods. Those skilled in the art should be able to understand the beneficial technical effects brought about by the introduction of these technical features and technical solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings: Figure 1 This is a schematic diagram of the method for controlling the micro-area strain of plate bulging according to the present invention.

[0024] Figure 2 This is a schematic diagram of the device structure for realizing micro-area control of plate bulging strain in the present invention.

[0025] Description of reference numerals: Hydraulic bulging device 1 blank holder 101 Multi-axis motion system 2 boost port 102 Online vision measurement system 3 sealing plate 103 Control system 4 hydraulic source 104 Cryogenic medium injection device 5 Cryogenic solenoid valve 501 Liquid nitrogen spray gun 502 Liquid nitrogen tank 503 DETAILED DESCRIPTION The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several changes and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0026] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a method and device for realizing real-time control of the micro-zone of plate bulging strain, which can effectively solve the problems of low hardening ability, concentrated necking instability and cracking in local large deformation areas of light alloy plates during large plastic deformation.

[0027] Reference Figure 1 As shown, the present invention provides a method for achieving micro-region control of plate bulging strain, comprising the following steps: Step S1: printing a grid on the outer surface of the plate to be formed.

[0028] As a further technical solution, in step S1, the square grid is printed by screen printing; As a further technical solution, in step S1, the spot grid is printed using an electrochemical etching method; As a further technical solution, in step S1, a square grid is printed using a laser etching method; As a further technical solution, this technical solution is applicable to different heat treatment states of various types of plates.

[0029] Step S2: placing the plate with the printed grid in a bulging tool, applying initial liquid pressure under the plate, and starting bulging; The hydraulic source 104 applies high-pressure liquid medium to the sheet material through the boost port 102. The sheet material is fixed between the blank holder 101 and the sealing plate 103. The blank holder 101 is used to apply clamping force to seal the liquid medium between the sheet material and the sealing plate 103.

[0030] Step S3, the online visual measurement system 3 collects strain and point cloud data in real time; Every 1-60 seconds, the online visual measurement system 3 automatically starts measuring to obtain the strain and point cloud data of the plate surface.

[0031] Step S4: The control system 4 automatically plans a movement path after identifying that a certain point or local strain reaches the target area strain safety threshold based on the strain data received from the online visual measurement system 3; The control system 4 identifies that the difference between the maximum value of the target area strain data and the safety value reaches the set threshold, automatically plans the movement path, and the multi-axis motion system 2 moves to the starting injection point according to the path. The specific steps are: 1. When the difference between the maximum value and the safety value of the strain data in the target area of ​​a certain strain analysis (DIC) image reaches a set threshold, the judgment condition is met and the hydraulic source 104 is controlled to stop pressurization; 2. The control system 4 extracts the sheet metal contour and strain maximum coordinate points obtained by the current online visual measurement system 3; 3. Convert the sheet metal contour and the maximum strain coordinate points into discrete surfaces and generate process trajectories on the discrete surfaces; 4. The trajectory is automatically converted into G code recognized by the machine tool and output to the multi-axis motion system 2. The multi-axis motion system 2 moves to the starting injection point according to the trajectory.

[0032] Step S5: The multi-axis motion system 2 drives the terminal low-temperature medium spraying device 5 to locate to the starting spraying point. According to the planned spraying path, the low-temperature medium spraying device 5 performs local freezing on the area.

[0033] The cryogenic solenoid valve 501 in the cryogenic medium injection device 5 receives instructions from the control system 4 and sprays a gas-liquid mixture of liquid nitrogen into a localized micro-region, strengthening the region and suppressing non-uniform necking deformation. Parameters such as injection height, injection pressure, and movement rate are stored in the control system 4 database. The sheet material undergoes ultra-low temperature freezing, strengthening it and suppressing the increase in non-uniform strain in the region. The specific steps for implementing micro-region cryogenic injection control are as follows: 1. The multi-axis motion system 2 reads the G code, starts from zero, and moves to the starting injection point along the trajectory; 2. Parameters such as injection height, injection pressure, and movement rate have been saved in the control system database and called in the G code program.

[0034] 3. After reaching the starting injection point, the injection start instruction in the G code is activated, and the low-temperature solenoid valve 501 on the low-temperature medium injection device 5 receives the signal, adjusts the injection pressure, and starts to inject the gas-liquid mixed medium to cool the micro-area.

[0035] 4. After reaching the end injection point, the end instruction in the G code takes effect, and the low-temperature solenoid valve 501 on the low-temperature medium injection device 5 receives the signal and closes the injection passage.

[0036] 5. Multi-axis motion system 2 returns to zero point; 6. Control the hydraulic source 104 to continue to slowly increase the pressure.

[0037] Step S6: repeat steps S3-S5 to monitor and control the global strain growth trend of the plate in real time; Step S7: The plate maintains a global nearly uniform strain to reach the final forming height, completing the strain micro-region control process.

[0038] Reference Figure 2As shown, the present invention also provides a device for micro-region control of sheet metal bulging strain, enabling intelligent monitoring and control of the overall strain growth trend of the sheet metal. The device comprises a hydraulic bulging device 1, a multi-axis motion system 2, an online visual measurement system 3, a control system 4, and a cryogenic medium injection device 5.

[0039] A sheet material is arranged in the hydraulic bulging device 1, a low-temperature medium injection device 5 is installed at the end of the multi-axis motion system 2, the signal of the online visual measurement system 3 is input to the control system 4, the control system 4 outputs the signal to the multi-axis motion system 2, and the control system 4 outputs the signal to the low-temperature medium injection device 5.

[0040] The hydraulic bulging device 1 includes a blank holder 101, a pressurizing port 102, a sealing plate 103, and a hydraulic source 104. The pressurizing port 102 is connected to the sealing plate 103. The hydraulic source 104 applies high-pressure liquid medium to the sheet material through the pressurizing port 102. The sheet material is fixed between the blank holder 101 and the sealing plate 103. The blank holder 101 is used to apply a clamping force to seal the liquid medium between the sheet material and the sealing plate 103.

[0041] As a further technical solution, the multi-axis motion system 2 is composed of a common three-dimensional multi-axis CNC machine tool structure on the market; As a further technical solution, the multi-axis motion system 2 is composed of a common rail-type multi-axis robotic arm structure on the market; As a further technical solution, the multi-axis motion system 2 is composed of a common inverted multi-axis robotic arm structure on the market; As a further technical solution, the online visual measurement system 3 is composed of binocular visual point cloud recognition and strain processing modules. The commercial plate global strain measurement system DIC has this function.

[0042] As a further technical solution, the control system 4 contains signal input and output functions such as strain processing and trajectory planning, and is developed from a general-purpose CNC system on the market.

[0043] As a further technical solution, the cryogenic medium spraying device 5 is composed of a cryogenic solenoid valve 501, a liquid nitrogen spray gun 502 and a liquid nitrogen tank 503. The cryogenic solenoid valve 501 receives instructions from the control system 4 to open and close the spraying device.

[0044] The present invention utilizes the strength, hardening and ductility differences exhibited by light alloys in different temperature ranges to design a method and device that can achieve strain micro-area regulation; different from the existing pre-regulation means, such as integral heating, integral ultra-low temperature freezing, and preset local heating and cooling measures, the present invention can monitor the strain evolution trends and laws of sheet metal in real time.

[0045] The above are basic embodiments of the present invention. The technical solution of the present invention will be further described below through one or several preferred embodiments.

[0046] Example 1 This embodiment provides a method for micro-region control of bulging strain of aluminum alloy plates. The method utilizes the characteristics of large temperature differences inducing differences in plate strength and hardening ability to achieve the purpose of intelligently monitoring and controlling the global strain growth trend of the plate during the hydraulic bulging process of the plate.

[0047] The hydraulic bulging device 1 is provided with a sheet material, and a multi-axis motion system 2 is provided outside. A cryogenic medium injection device 5 is installed at the end, and an online visual measurement system 3 monitors the sheet material bulging process in real time. The sheet material is annealed 2219 aluminum alloy with a thickness of 4mm and a diameter of 2300mm. The online visual measurement system 3 transmits the strain and point cloud data to the control system 4, and the control system 4 outputs a signal to the multi-axis motion system 2. The cryogenic solenoid valve 501 in the cryogenic medium injection device 5 receives an instruction from the control system 4 and injects liquid nitrogen in a gas-liquid mixed phase into a local micro-region, thereby strengthening the local region and suppressing the non-uniform necking deformation of the region. The specific steps are as follows: S1. Print a grid on the outer surface of the 2219 aluminum alloy plate using screen printing to print a square grid; In this embodiment, the plate is annealed 2219 aluminum alloy with a thickness of 4 mm and a diameter of 2300 mm.

[0048] S2, placing the plate with the printed grid in the bulging tool, applying initial liquid pressure under the plate to start bulging; like Figure 2 As shown, in this embodiment, the hydraulic bulging device 1 consists of a blank holder 101, a pressurizing port 102, a sealing plate 103, and a hydraulic source 104. The pressurizing port 102 is connected to the sealing plate 103, and the hydraulic source 104 applies high-pressure liquid medium to the sheet material through the pressurizing port 102. The sheet material is fixed between the blank holder 101 and the sealing plate 103. The blank holder 101 is used to apply the clamping force to seal the liquid medium between the sheet material and the sealing plate 103.

[0049] In this embodiment, the pressure increase rate is set to 0.1 MPa / min. S3, online visual measurement system 3 collects strain and point cloud data in real time; In this embodiment, a commercially available online visual measurement system 3 (DIC) for global sheet metal strain is used. This optical measurement system provides three-dimensional, full-field, contactless measurement of the contour, displacement, and strain of any material. The online visual measurement system 3 is mounted above the hydraulic bulging device 1. The system sequentially captures a series of images before and after deformation, compares and calculates the motion and deformation information of each grid area, and calculates global displacement and strain information. In this embodiment, a single image is captured every 10 seconds to obtain strain and point cloud data on the sheet metal surface, which is then transmitted to the control system 4.

[0050] S4, the control system 4 automatically plans a movement path after identifying that a certain point or local strain reaches the target area strain safety threshold based on the received visual measurement system strain data; In this embodiment, the control system 4 monitors the strain concentration growth area and issues instructions to the multi-axis motion system 2. The specific steps are: 1. When the difference between the maximum value and the safety value of the strain data in the target area of ​​a certain strain analysis (DIC) image reaches a set threshold of 0.05, the judgment condition is met and the hydraulic source 104 is controlled to stop pressurization; 2. The control system 4 extracts the sheet metal contour and strain maximum coordinate points obtained by the current online visual measurement system 3; 3. Convert the sheet metal contour and the maximum strain coordinate points into discrete surfaces and generate process trajectories on the discrete surfaces; 4. The trajectory is automatically converted into G code recognized by the machine tool and output to the multi-axis motion system 2. The multi-axis motion system 2 moves to the starting injection point according to the trajectory.

[0051] S5. The multi-axis motion system 2 drives the terminal low-temperature medium spraying device 5 to locate at the starting spraying point. According to the planned spraying path, the low-temperature medium spraying device 5 performs local freezing on the area.

[0052] In this embodiment, the multi-axis motion system 2 adopts a commercial inverted robot gantry machine tool structure. A low-temperature medium injection device 5 is installed at the end of the robot. The specific steps for implementing micro-area low-temperature value injection control are as follows: 1. The multi-axis motion system 2 reads the G code, starts from zero, and moves to the starting injection point along the trajectory; 2. Parameters such as injection height, injection pressure, and movement rate have been saved in the control system database and called in the G code program.

[0053] In this embodiment, the spray height is called to be 20 mm, the spray pressure is called to be 0.3 MPa, and the moving speed is called to be 100 mm / min.

[0054] 3. After reaching the starting injection point, the injection start instruction in the G code is activated, the low-temperature solenoid valve 501 on the low-temperature medium injection device 5 receives the signal, adjusts the injection pressure to 0.3 MPa, and starts to inject the gas-liquid mixed medium to cool the micro-zone.

[0055] 4. After reaching the end injection point, the end instruction in the G code takes effect, and the low-temperature solenoid valve 501 on the low-temperature medium injection device 5 receives the signal and closes the injection passage.

[0056] 5. Multi-axis motion system 2 returns to zero point; 6. Control the hydraulic source 104 to continue to slowly increase the pressure.

[0057] S6. Repeat S3-S5 to monitor and control the global strain growth trend of the plate in real time; S7. The plate maintains a global nearly uniform strain to reach the final forming height, completing the strain micro-area control process.

[0058] In this embodiment, the final forming height of the bulging part is measured and compared with the bulging parameters of the sheet metal without real-time strain micro-area regulation, as shown in Table 1.

[0059] Table 1 Comparison of micro-area control effects of bulging strain on 2219 (O state, 4mm) sheet

[0060] Compared with the existing technology, the plate maintains a global nearly uniform strain to reach the final forming height, and the wall thickness uniformity and forming limit are greatly improved; real-time monitoring and control of strain micro-areas will elevate the existing sheet metal forming technology to an intelligent level, and has good application prospects.

[0061] Those skilled in the art will appreciate that, in addition to implementing the system and its various devices, modules, and units provided by the present invention in purely computer-readable program code, it is entirely possible to implement the same functions of the system and its various devices, modules, and units provided by the present invention in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; the devices, modules, and units for implementing various functions can also be considered as both software modules implementing the method and structures within the hardware component.

[0062] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

Claims

1. A system for micro-region control of sheet metal bulging strain, characterized in that: include: A hydraulic bulging device (1), a multi-axis motion system (2), an online visual measurement system (3), a control system (4), and a cryogenic medium injection device (5); The data collected by the online visual measurement system (3) include strain and point cloud data of the plate surface; The control system (4) extracts the plate contour and the coordinate points of the maximum strain value according to the strain and point cloud data of the plate surface and converts them into discrete surfaces, and generates a process trajectory on the discrete surfaces; The cryogenic medium injection device (5) injects the cryogenic medium according to the generated process trajectory to complete local freezing; The cryogenic medium sprayed by the cryogenic medium spraying device (5) includes liquid nitrogen; A sheet material is arranged in the hydraulic bulging device (1), and a low-temperature medium injection device (5) is installed at the end of the multi-axis motion system (2); a signal generated by the online visual measurement system (3) is input to the control system (4), and the control system (4) outputs a signal to the multi-axis motion system (2) and the low-temperature medium injection device (5).

2. The system for micro-area control of sheet metal bulging strain according to claim 1, characterized in that: The hydraulic bulging device (1) comprises a blank holder (101), a pressurizing port (102), a sealing plate (103) and a hydraulic source (104); The boost port (102) is connected to the sealing plate (103), and the hydraulic source (104) applies high-pressure liquid medium to the sheet material through the boost port (102). The sheet material is fixed between the blank holder (101) and the sealing plate (103); the blank holder (101) is used to apply a clamping force so that the liquid medium is sealed between the sheet material and the sealing plate (103).

3. The system for micro-region control of sheet metal bulging strain according to claim 1, characterized in that: The multi-axis motion system (2) comprises a universal three-dimensional multi-axis CNC machine tool structure, a universal track-type multi-axis robotic arm structure, and a universal inverted multi-axis robotic arm structure.

4. The system for micro-region control of sheet metal bulging strain according to claim 1, characterized in that: The control system (4) includes a general numerical control system for inputting and outputting strain processing and trajectory planning signals.

5. The system for micro-region control of sheet metal bulging strain according to claim 1, characterized in that: The cryogenic medium injection device (5) comprises a cryogenic solenoid valve (501), a liquid nitrogen spray gun (502) and a liquid nitrogen tank (503); the cryogenic solenoid valve (501) is used to receive instructions from the control system (4) to open or close the cryogenic medium injection device (5).

6. A method for micro-region control of sheet metal bulging strain, based on the system for micro-region control of sheet metal bulging strain according to any one of claims 1 to 5, characterized in that: include: Step S1: printing a grid on the outer surface of the plate to be formed; Step S2: placing the sheet material in the hydraulic bulging device (1), applying initial liquid pressure under the sheet material, and starting bulging; Step S3: enabling the online visual measurement system (3) to collect strain data and point cloud data in real time and sending the data to the control system (4); Step S4: The control system (4) receives the strain data and the point cloud data, and automatically plans a moving path when it is identified that a certain point or a local strain reaches a target area strain safety threshold; Step S5: The multi-axis motion system (2) drives the terminal low-temperature medium injection device (5) to locate the starting injection point, and locally freezes the area based on the low-temperature medium injection device (5) according to the planned moving path; Step S6: Repeat steps S3-S5 to monitor and control the global strain growth trend of the plate in real time until it reaches a preset value; Step S7: The plate is made to maintain a global nearly uniform strain to reach the final forming height, completing the strain micro-region control process.

7. The method for micro-region control of sheet metal bulging strain according to claim 6, characterized in that: The process of printing a grid includes: -Square grids are printed using screen printing; - Printing dot grids using electrochemical etching; -The square grid is printed using laser etching.

8. The method for controlling micro-area strain of sheet metal bulging according to claim 6, characterized in that: The control system (4) can automatically start measurement according to a preset fixed time interval; the safety threshold includes a maximum value and a safety value of the strain data and the point cloud data.

9. The method for controlling micro-area strain of sheet metal bulging according to claim 6, characterized in that: After receiving the instruction from the control system (4), the cryogenic solenoid valve (501) in the cryogenic medium injection device (5) injects liquid nitrogen in the gas-liquid mixed phase into the local micro-region, thereby strengthening the local micro-region and suppressing the non-uniform necking deformation of the local micro-region.

10. The method for controlling micro-area strain of sheet metal bulging according to claim 9, characterized in that: The working parameters of the low-temperature medium injection device (5) have been saved in the control system (4) database. The plate is strengthened after ultra-low temperature freezing, which suppresses the increase of non-uniform strain in the area. The working parameters include injection height, injection pressure and movement rate parameters.

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