Hot gas bulging forming system and hot gas bulging forming method

Abstract

A hot gas bulging forming system and a hot gas bulging forming method. The forming system comprises a tube bender device (1), a loading device (2), a preforming device (3), a heating device (4), a bulging quenching device (5) and an unloading device (6) which are arranged in sequence. The heating device comprises a heating cavity (407), wherein an electrode chuck (404) for clamping an end of a metal tube is provided in the heating cavity; the electrode chuck is connected to an IGBT induction heating apparatus (402); an infrared thermometer (406) is provided in the heating cavity; and the infrared thermometer and the IGBT induction heating apparatus are both in communication connection with a controller. By means of the hot gas bulging forming system and forming method, it is convenient to heat materials of different thicknesses and tubes of complex shapes, and the heating rate of the materials of different coatings can also be adjusted by the controller on the basis of coating characteristics, thereby protecting the coatings to the greatest extent and obtaining better surface quality of products. The hot gas bulging forming system and forming method are widely applicable, involve a high heating speed, and greatly improve the heating efficiency.

Description

Hot gas expansion forming system and hot gas expansion forming method

[0001] This application claims priority to Chinese Patent Application No. 2025100109163, filed on January 3, 2025, entitled "Hot Air Inflation System and Hot Air Inflation Method", the entire contents of which are incorporated herein by reference; and also claims priority to Chinese Patent Application No. 2025119316517, filed on December 19, 2025, entitled "Hot Air Inflation System and Hot Air Inflation Method", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to the field of metal tube forming technology, and in particular to a hot gas expansion forming system and a hot gas expansion forming method. Background Technology

[0003] Hot-formed metal tubing, also known as hot air forming, is a special forming process that involves heating hollow tubing to a specific temperature, forming it under high pressure within a mold, and then quenching it. This process can increase the product's strength from 400-600 MPa to 2000 MPa. This technology is widely used in automotive A-pillars, B-pillars, crash beams, and rear towing beams. The use of hot air forming in vehicles is increasing, with higher requirements for corrosion resistance and coatings. The hot air forming process generally includes bending, pre-forming, heating, bulging, and laser cutting.

[0004] In existing technologies, walking beam furnaces or box furnaces are generally used in the heating process. Walking beam furnaces use rollers to move raw materials step-by-step into the continuous furnace, heating the workpiece through upward heat radiation from the bottom layer. This method is widely used in sheet metal hot stamping production lines. Box furnaces heat the raw materials inside through heat conduction. Each chamber of a box furnace has heating tubes arranged in both the upper and lower layers, heating the workpiece through upward heat radiation from the bottom layer and downward heat radiation from the top layer. Both of these heating methods are radiant heating, and their heating rate is directly related to the thickness of the sheet metal, resulting in a longer heating time. Summary of the Invention

[0005] In view of this, the present invention provides a hot gas expansion forming system, which facilitates heating of materials of different thicknesses and complex shapes of pipes, has a wide range of applications, and a fast heating speed, which greatly improves heating efficiency.

[0006] The present invention also provides a method for hot gas expansion molding.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A hot gas expansion forming system includes a pipe bending device, a feeding device, a preforming device, a heating device, an expansion quenching device, and a unloading device arranged in sequence. The heating device includes a heating chamber, in which an electrode clamp for clamping the end of a metal pipe is provided. The electrode clamp is connected to an IGBT induction heating device. An infrared thermometer is provided in the heating chamber. Both the infrared thermometer and the IGBT induction heating device are communicatively connected to a controller.

[0009] Optionally, the heating device includes a main frame, on which a heating platform is provided, and the electrode clamp is disposed on the heating platform;

[0010] A sealing plate is provided around and on top of the heating platform. The sealing plate is connected to the main frame, and the sealing plate and the heating platform form the heating cavity.

[0011] Optionally, a dry gas dew point control component is provided inside the heating chamber;

[0012] The dry gas dew point control component includes a dew point sensor and a gas delivery component. The dew point sensor is disposed inside the heating chamber and is communicatively connected to the controller. The gas delivery component is used to deliver dry gas to the heating chamber.

[0013] Optionally, the gas delivery assembly includes a dry gas source connected through an inlet pipe and a porous exhaust pipe. The porous exhaust pipe is disposed inside the heating chamber, and the dry gas source is disposed outside the heating chamber. A flow control valve is provided at the inlet end of the porous exhaust pipe. The porous exhaust pipe is provided with a plurality of exhaust through holes, which are arranged along the length of the porous exhaust pipe and are oriented towards the metal pipe.

[0014] The drying gas source is used to hold the drying gas, which is either air or nitrogen.

[0015] Optionally, a first handling robot is provided between the feeding device and the preforming device. The first handling robot is used to transfer the metal pipe from the feeding device to the preforming mold cavity of the preforming device.

[0016] A second transport robot is provided between the preforming device and the heating device. The second transport robot is used to transfer the metal tube from the preforming mold cavity to the heating cavity. After the metal tube is heated, the second transport robot is used to transfer the metal tube from the heating cavity to the bulging mold cavity of the bulging quenching device.

[0017] A third transport robot is provided between the bulging and quenching device and the unloading device. The third transport robot is used to transfer the metal tube from the bulging mold cavity to the unloading conveyor belt of the unloading device.

[0018] Optionally, a lifting door is provided on the side wall of the sealing plate, and the width of the lifting door is greater than the length of the metal pipe.

[0019] As can be seen from the above technical solution, the hot gas expansion forming system provided by this invention uses an IGBT induction heating device as the heating power source. The IGBT induction heating device powers the electrode clamps that hold the ends of the metal tube. When the metal tube is not demagnetized, the useful work of heating is mainly induction heating. As the tube temperature rises, the metal tube gradually demagnetizes, and the useful work of heating changes from induction heating to resistance heating. The demagnetization temperature varies depending on the material of the metal tube. This hot gas expansion forming system of the present invention uses induction and resistance heating of the tube itself, rather than radiation heating. Its heating speed is adjusted by the input current and is independent of the sheet thickness, making it convenient for heating materials of different thicknesses and complex-shaped tubes. It has a wide range of applications and a fast heating speed. The hot gas expansion forming system of the present invention uses induction heating and resistance heating in the heating process, which greatly improves heating efficiency, reduces energy consumption, and can heat complex-shaped metal tubes.

[0020] The present invention also provides a hot gas expansion forming method, comprising the following steps:

[0021] S1. Use a pipe bending machine to bend and shape the metal pipe;

[0022] S2. Transfer the bent and shaped metal tube to the feeding device, which positions the metal tube.

[0023] S3. The metal pipe is picked up from the feeding device and fed into the preforming mold cavity of the preforming device to preform the metal pipe;

[0024] S4. The metal tube in the preformed mold cavity is sent into the heating chamber of the heating device for heating. The metal tube is clamped on the electrode clamp and heated by the IGBT induction heating device. The controller controls the IGBT induction heating device to perform heating.

[0025] S5. The heated metal tube is fed into the expansion mold cavity of the expansion quenching device to complete the expansion quenching.

[0026] S6. The expanded and cooled metal tube is fed into the feeding device for feeding.

[0027] Optionally, the heating process in step S4 includes:

[0028] S401. Preheating process: Adjust the power on-state ratio of the IGBT induction heating device, and the metal tube heats up at 10-18°C per second for 0-3 seconds.

[0029] S402. During the rapid heating process, the power on-state ratio of the IGBT induction heating device is adjusted so that the metal tube heats up at 20-24°C per second for 3-30 seconds, so that the temperature of the metal tube reaches 550-650°C.

[0030] S403. During the slow heating process, when the coating on the metal pipe is an aluminum-silicon coating, the metal pipe heats up at less than 10°C per second, and the metal pipe heats up from 600-650°C to 750°C.

[0031] When the coating on the metal pipe is a hot-dip galvanized layer, the temperature of the metal pipe rises by less than 5°C per second, and the temperature of the metal pipe rises from 550-600°C to 650°C.

[0032] S404. When the coating on the metal pipe is an aluminum-silicon plating layer, the metal pipe heats up at 18-20°C per second, and the metal pipe heats up from 750°C to 840°C.

[0033] When the coating on the metal pipe is a hot-dip galvanized layer, the metal pipe heats up at 18-22°C per second, and the metal pipe heats up from 650°C to 750°C.

[0034] S405. When the coating on the metal pipe is an aluminum-silicon plating layer, the metal pipe is heated from 840°C to 925°C at a rate of 5-7°C per second.

[0035] When the coating on the metal pipe is a hot-dip galvanized layer, the metal pipe is heated from 750°C to 850°C at a rate of 5 to 7°C per second.

[0036] S406, during the austenitizing process, when the coating on the metal pipe is an aluminum-silicon plating layer, the metal pipe is heated by 1-2°C per second, and the metal pipe is heated from 925°C to 950°C and then kept at that temperature.

[0037] When the coating on the metal pipe is a hot-dip galvanized layer, the metal pipe heats up by less than 1°C per second, and the metal pipe is kept warm after being heated from 880°C to 890°C.

[0038] Optionally, in step S403, the heating time is 30 to 55 seconds;

[0039] In step S404, the heating time is 55-60 seconds;

[0040] In step S405, the heating time is 60-75 seconds;

[0041] In step S406, the heating time is 75-100 seconds and the heating and holding time is 100-180 seconds.

[0042] Optionally, dry gas is introduced into the heating chamber to control the dew point of the heating chamber and ensure that the dew point of the heating chamber meets the requirements.

[0043] The hot gas expansion forming method of the present invention uses the above-described hot gas expansion forming system for forming, and therefore has the advantages of the above-described system, which will not be elaborated here. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 is a simplified structural diagram of the hot gas expansion forming system provided in an embodiment of the present invention;

[0046] Figure 2 is a schematic diagram of the hot gas expansion forming system provided in an embodiment of the present invention;

[0047] Figure 3 is a schematic diagram of the heating device provided in an embodiment of the present invention;

[0048] Figure 4 is a schematic diagram of the process window of the hot gas expansion forming method provided in the embodiment of the present invention;

[0049] Figure 5 is a schematic diagram of the bulging quenching device provided in an embodiment of the present invention;

[0050] Figure 6 is a circuit diagram of the heating system of the IGBT induction heating device provided in an embodiment of the present invention;

[0051] Figure 7 is a schematic diagram of the porous exhaust pipe provided in an embodiment of the present invention;

[0052] Figure 8 is a schematic diagram of the structure of the dew point sensor and the porous exhaust pipe installed in the heating chamber according to an embodiment of the present invention.

[0053] The components include: 1. Pipe bending device; 2. Feeding device; 3. Pre-forming device; 4. Heating device; 401. Main frame; 402. IGBT induction heating equipment; 403. Support leg; 404. Electrode chuck; 405. Drying gas dew point control component; 4051. Dew point sensor; 4052. Multi-hole exhaust pipe; 4053. Flow control valve; 4054. Air inlet port; 4055. Exhaust through hole; 406. Infrared thermometer; 407. Heating chamber; 408. Heating table; 5. Expansion quenching device; 501. Lower mold; 502. Oil cylinder; 503. Plug; 504. Upper mold; 6. Feeding device; 7. Metal pipe; 8. Second handling robot; 9. Third handling robot; 10. First handling robot. Detailed Implementation

[0054] This invention discloses a hot gas expansion forming system, which facilitates heating of materials of different thicknesses and complex shapes, has a wide range of applications, and provides fast heating speed, greatly improving heating efficiency.

[0055] The present invention also discloses a hot gas expansion forming method.

[0056] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] Referring to Figures 1 to 3, the hot gas expansion forming system of the present invention includes a pipe bending device 1, a feeding device 2, a preforming device 3, a heating device 4, an expansion quenching device 5, and a unloading device 6 arranged sequentially. The heating device 4 includes a heating chamber 407, within which an electrode chuck 404 for clamping the end of the metal pipe 7 is disposed. The electrode chuck 404 is connected to an IGBT induction heating device 402. An infrared thermometer 406 is disposed within the heating chamber 407. Both the infrared thermometer 406 and the IGBT induction heating device 402 are communicatively connected to a controller.

[0058] The bending device 1, feeding device 2, preforming device 3, bulging and quenching device 5, and unloading device 6 are all commonly used devices in existing technologies. Generally, the bending device 1 is a bending machine; for large-arc bends, a die can also be used for pressure bending. The feeding device 2 is used to position the metal tube 7, ensuring the robot can stably grasp it; it contains a part identification sensor. The preforming device 3 preforms the bent metal tube 7, preparing it for the next bulging step, ensuring the preformed tube 7 can be smoothly placed into the bulging cavity of the bulging and quenching device 5. The heating device 4 heats the metal tube 7 according to a pre-set program. The bulging and quenching device 5 is used for bulging and quenching the metal tube 7. The controller is a PLC.

[0059] In the hot gas expansion forming system of this invention, the heating power source in the heating device 4 is an IGBT induction heating device, which is the power source for the electrode clamp 404 that clamps the end of the metal tube 7. When the metal tube 7 is not demagnetized, the useful work of heating includes induction and resistance heating, with induction heating being the primary useful work. As the temperature of the metal tube 7 rises, it gradually demagnetizes, and the useful work of heating changes from induction heating to resistance heating. The demagnetization temperature varies depending on the material of the metal tube 7. This hot gas expansion forming system of the present invention uses induction and resistance heating of the tube itself, rather than radiation heating. Its heating speed is adjusted by the input current and is independent of the sheet thickness, making it convenient for heating materials of different thicknesses and complex-shaped tubes. It has a wide range of applications and a fast heating speed. The hot gas expansion forming system of the present invention uses induction heating and resistance heating in the heating process, which greatly improves heating efficiency, reduces energy consumption, and can heat complex-shaped metal tubes. The hot gas expansion forming system of the present invention can adjust the heating rate of materials with different coatings according to the coating characteristics by the controller, thereby maximizing the protection of the coating, obtaining better product surface quality, and avoiding product surface peeling.

[0060] In one embodiment, the demagnetization temperature of the metal tube 7 is 750 degrees Celsius. When the heating temperature is below 750 degrees Celsius, the metal tube 7 is in a non-demagnetized state; when the heating temperature is above 750 degrees Celsius, the metal tube 7 is in a demagnetized state. This demagnetization temperature is determined by the material of the metal tube 7 and its temperature may fluctuate.

[0061] Specifically, the heating device 4 includes a main frame 401, as shown in Figure 3. A heating platform 408 is mounted on the main frame 401, and an electrode clamp 404 is mounted on the heating platform 408. To form a sealed chamber, a sealing plate is provided around and on top of the heating platform 408. The sealing plate is connected to the main frame 401, and the sealing plate and the heating platform 408 enclose a heating cavity 407, thereby facilitating the control of the temperature and atmosphere within the heating cavity 407. A support leg 403 is provided at the bottom of the main frame 401.

[0062] To improve resistance to hydrogen embrittlement and oxidation, a dry gas dew point control component 405 is installed inside the heating chamber 407. Specifically, the dry gas dew point control component 405 includes a dew point sensor 4051 and a gas delivery component, as shown in Figures 7 and 8. The dew point sensor 4051 is located inside the heating chamber 407 and is communicatively connected to the controller. The gas delivery component is used to deliver dry gas to the heating chamber 407. The dew point sensor 4051 is an instrument used to detect the dew point temperature of the heating chamber 407. The controller controls the amount of airflow delivered by the gas delivery component based on the detection value of the dew point sensor 4051.

[0063] Specifically, the gas delivery assembly includes a dry gas source connected via an inlet pipe and a porous exhaust pipe 4052. The porous exhaust pipe 4052 is disposed within the heating chamber 407, while the dry gas source is disposed outside the heating chamber 407. The inlet port 4054 of the porous exhaust pipe 4052 is connected to the inlet pipe. A flow control valve 4053 is provided at the inlet end of the porous exhaust pipe 4052. The porous exhaust pipe 4052 is provided with a plurality of exhaust through holes 4055, as shown in Figure 7. The plurality of exhaust through holes 4055 are arranged along the length direction of the porous exhaust pipe 4052, and the exhaust through holes 4055 are oriented towards the metal pipe 7. The opening position of the exhaust through holes 4055 is aligned with the lower part of the metal pipe 7, and the port of the porous exhaust pipe 4052 away from the inlet port 4054 is sealed. Preferably, the multiple exhaust holes 4055 are evenly distributed along the length of the porous exhaust pipe 4052, and the length of the porous exhaust pipe 4052 with exhaust holes 4055 is greater than the length of the metal pipe 7. By providing multiple exhaust holes 4055, the dry gas can be evenly diffused into the heating chamber 407, maintaining the dew point temperature of the heating chamber 407.

[0064] The drying gas source is used to hold drying gas, which can be air or nitrogen. A dew point sensor 4051 is used to detect the dryness level within the heating chamber 407, i.e., to perform humidity detection. The controller controls the opening of the flow control valve 4053 based on the dew point temperature detected by the dew point sensor 4051, thereby controlling the flow rate of the drying gas and achieving dew point control. Preferably, the dew point sensor 4051 is mounted on the heating platform 408. In one embodiment, the dew point temperature within the heating chamber 407 is controlled between -5°C and -25°C.

[0065] To facilitate the transfer of metal tubing 7 between different devices, a first transport robot 10 is installed between the feeding device 2 and the preforming device 3; a second transport robot 8 is installed between the preforming device 3 and the heating device 4; and a third transport robot 9 is installed between the bulging and quenching device 5 and the unloading device 6. The first transport robot 10 transfers the metal tubing 7 from the feeding device 2 to the preforming cavity of the preforming device 3. The second transport robot 8 transfers the metal tubing 7 from the preforming cavity to the heating cavity 407. After heating, the second transport robot 8 transfers the metal tubing 7 from the heating cavity 407 to the bulging cavity of the bulging and quenching device 5. The third transport robot 9 transfers the metal tubing 7 from the bulging cavity to the unloading conveyor belt of the unloading device 6.

[0066] To facilitate the placement of the metal tube 7 into the heating chamber 407, a lifting door is provided on the side wall of the sealing plate, and the width of the lifting door is greater than the length of the metal tube 7.

[0067] The present invention also provides a hot gas expansion forming method, comprising the following steps:

[0068] S1. Use a pipe bending machine to bend and shape the metal pipe 7.

[0069] There are two main methods for bending and forming: stretch bending and push bending. The equipment used is a pipe bending machine. For pipes with large arcs, a mold can also be used for pressure bending. This step is for pre-forming preparation, ensuring that the bent pipe can be smoothly placed into the pre-forming mold cavity.

[0070] S2. Transfer the bent metal tube 7 to the feeding device 2, and position the metal tube 7.

[0071] The feeding device 2 positions the metal pipe 7 to ensure that the handling robot stably grasps the metal pipe 7 and sends it into the preforming mold cavity. The feeding device 2 is equipped with a part identification sensor and a light grating protection human-machine engineering system.

[0072] S3. The metal pipe 7 is picked up from the feeding device 2 and fed into the preforming mold cavity of the preforming device 3. The preforming device 3 preforms the metal pipe 7.

[0073] The bent metal tube 7 is pre-formed to prepare for the next step of bulging and to ensure that the pre-formed workpiece can be smoothly placed into the bulging mold cavity.

[0074] S4. The metal tube 7 in the preformed mold cavity is sent into the heating chamber 407 of the heating device 4 for heating. The metal tube 7 is clamped on the electrode chuck 404 and heated by the IGBT induction heating device 402. The controller controls the IGBT induction heating device 402 to heat according to the set program.

[0075] S5. The heated metal pipe 7 is fed into the expansion mold cavity of the expansion quenching device 5 to complete the expansion quenching.

[0076] The forming cavity is equipped with an upper mold 504 and a lower mold 501, as shown in Figure 5. A hydraulic cylinder 502 is mounted on the lower mold 501, and a plug 503 is connected to the drive end of the cylinder 502. A transport robot delivers the heated metal tube 7 from the heating table 408 into the forming cavity. The press drives the upper mold 504 downwards to close with the lower mold 501. Simultaneously, the hydraulic cylinder 502 on the mold pushes the plug 503. At the moment the mold is fully closed, the plug 503 is pushed into place, sealing both ends of the metal tube 7. The plug 503 has an air inlet. After mold closure, high-pressure nitrogen or air is injected through the air inlet on the plug 503 to complete the forming process. The high-pressure gas is maintained at 60-70 MPa for 1-2 seconds. Cooling water is circulated through the mold insert for 10-15 seconds for cooling. This holding time is adjusted according to the thickness of the part to ensure that the temperature of the metal tube 7 exiting the mold is below 80°C. Finally, the mold is opened and the part is removed.

[0077] The metal tube 7 is expanded under high-pressure gas, and its outer surface is completely in contact with the mold. The cooling channels inside the mold rapidly cool the mold and the metal tube 7, specifically at a cooling rate of 27℃ / s, achieving rapid cooling of the metal tube 7. The interior of the metal tube 7 is transformed into a uniform martensitic structure. The metallographic structure of the metal tube 7 after hot gas expansion is not less than 95% martensite.

[0078] After hot gas expansion forming, the surface of the metal tube 7 is covered with a coating of 30-40 μm. The coating has a four-layer structure. From the outermost layer of the coating to the microstructure of the steel substrate, the microstructure is as follows: a surface layer containing Al oxides and brittle Fe2Al5 in continuous distribution, an intermetallic compound FeAl layer, an intermediate layer containing brittle Fe2Al5 phase, and an interdiffusion layer.

[0079] S6. The expanded and cooled metal tube 7 is fed into the feeding device 6 for feeding.

[0080] The handling robot grabs the expanded and cooled metal tube 7 out of the mold cavity and sends it onto the unloading conveyor belt on the unloading device 6.

[0081] Further, the heating process in step S4 includes: S401, preheating process: adjusting the power activation ratio of the IGBT induction heating device to avoid electrode arcing, the metal tube heats up at 10-18°C per second for 0-3 seconds. The device power is activated at 20-40%, allowing for a stable contact between the metal tube 7 and the electrode clamp 404. The metal tube 7 is at room temperature, for example, 10-20°C, and heats up to 45-80°C after 3 seconds. S402, rapid heating process: adjusting the power activation ratio of the IGBT induction heating device 402 to 80%-95%, the metal tube 7 heats up at 20-24°C per second for 3-30 seconds, bringing the temperature of the metal tube 7 to 550-650°C. This stage aims for rapid heating to shorten the heating time. S403, slow heating process. When the coating on metal pipe 7 is an aluminum-silicon coating, the temperature of metal pipe 7 increases by less than 10°C per second, from 600-650°C to 750°C, with a heating time of 30-55 seconds. When the coating on metal pipe 7 is a hot-dip galvanized layer, the temperature of metal pipe 7 increases by less than 5°C per second, from 550-600°C to 650°C, with a heating time of 30-55 seconds. During this step, the equipment power is turned on at 40%-60%. The temperature should not rise too quickly in this step, mainly to facilitate the fusion and protection of the coating on metal pipe 7. S404, Second stage rapid heating process. When the coating on metal pipe 7 is an aluminum-silicon coating, the temperature of metal pipe 7 increases by 18-20°C per second, from 750°C to 840°C. When the coating on metal pipe 7 is a hot-dip galvanized layer, the temperature of metal pipe 7 increases by 18-22°C per second, from 650°C to 750°C. The heating time for this step is 55-60 seconds. During this step, the equipment power is operated at 70%-95%. This step is for coating protection and pre-alloying. S405. When the coating on metal pipe 7 is an aluminum-silicon coating, the temperature of metal pipe 7 increases from 840°C to 925°C, at a rate of 5-7°C per second. When the coating on metal pipe 7 is a hot-dip galvanized layer, the temperature of metal pipe 7 increases from 750°C to 850°C, at a rate of 5-7°C per second; in this step, austenitization begins. The heating time for this step is 60-75 seconds. During this step, the equipment power is operated at 60%-80%. The heating time for this stage can be appropriately increased or decreased according to the temperature difference of metal pipe 7. S406, during the austenitizing process, when the coating on the metal pipe 7 is an aluminum-silicon plating layer, the metal pipe 7 heats up at 1-2°C per second, from 925°C to 950°C, and then holds at that temperature. During this time, the equipment power is operated at 30%-60%. When the coating on the metal pipe 7 is a hot-dip galvanized layer, the metal pipe 7 heats up at less than 1°C per second, from 880°C to 890°C, and then holds at that temperature. During this time, the equipment power is operated at 20%-50%. In this step, the heating time is 75-100 seconds, and the heating and holding time is 100-180 seconds. This stage is a slow heating and holding process.After heating is complete, the power is cut off, and the robot's manipulator picks up the part and transfers it to the bulging mold cavity. The process window for heating time and temperature is shown in Figure 4. The above control process is controlled by a controller. The metal tube 7 is heated from room temperature, and its heating temperature and time are limited within the KLMN graph in Figure 4. The coordinates of the extreme points of the KLMN graph are: K (25 seconds, 950°C), L (100 seconds, 950°C), M (180 seconds, 880°C), N (75 seconds, 880°C). The heating rate is as per step S4. The seconds mentioned above are all time points on the time axis. For example, the heating time in step S402 is 3 to 30 seconds, that is, heating from 3 seconds to 30 seconds, with a heating time period of 27 seconds.

[0082] During the heating process of the heating device 4, dry gas is introduced into the heating chamber 407 to control the dew point of the heating chamber 407, ensuring that the dew point of the heating chamber 407 meets the requirements, and to prevent hydrogen embrittlement and oxidation.

[0083] The hot gas expansion forming method of this invention utilizes the induction and resistance heating of the metal tube 7 itself, with the heating rate adjusted by the input current. Heating a steel tube with a diameter of φ50, a thickness of 2mm, and a length of 2m from room temperature can reach 950℃ within 30 seconds, demonstrating rapid heating. The heating time for automotive hot gas expansion parts does not exceed 3 minutes. The heating power source is an IGBT induction heating device 402. When the metal tube 7 is not demagnetized (below 750℃), the useful work is performed by the induction heating current. When the metal tube 7 is demagnetized (above 750℃), the useful work is performed by the resistance heating current. The heating rate is precisely controlled by a PLC and an infrared thermometer 406, better protecting the coating layer of the metal tube 7. This hot gas expansion forming method of the present invention does not require different process windows or defined heating parameters based on the thickness of the tube, thus meeting the material performance requirements of different coating thicknesses. It controls the heating rate to meet the coating structure of the finished product, maximizing corrosion resistance requirements. It is simple to use and facilitates stable product quality control. The hot air expansion forming method of the present invention can be modified by adding heating units according to the production plan or the number of cavities in the mold, thereby completing multiple outputs such as two-piece, three-piece, or four-piece production. The equipment is highly flexible and easy to use.

[0084] The heating system circuit diagram of the IGBT induction heating device 402 is shown in Figure 6. Specifically, it is a series resonant circuit as used in existing technology. It eliminates the large and bulky filter reactor, reducing losses; the filter is handled by capacitor C1. The thyristor T1 acts as a switch here, turning on when the capacitor C1 is charged to a certain voltage. The frequency conversion circuit consists of two IGBTs. The conduction loss of the IGBTs is comparable to that of the thyristor, while the switching loss is lower. Therefore, the frequency conversion current loss is approximately 3%. The output circuit of this device is characterized by a series resonant circuit formed by the induction coil and the compensation capacitor connected in series. The characteristic of this circuit is that the current flowing through the IGBT is equal to the current flowing through the induction coil and the compensation capacitor, while the voltage across the induction coil is approximately 100V, the induced voltage. The IGBT is a fully controllable power device; its switching on and off is directly controlled by its gate, independent of the power factor and Q value of the oscillation circuit. Therefore, it can start successfully regardless of the load. The series resonant medium-frequency induction heating furnace with IGBT frequency conversion has advantages such as a high power factor (≥0.95), significant energy savings (10%–30% compared to traditional series medium-frequency furnaces), and successful start-up under any load. The useful power ratio of inductive heating can be finely adjusted by changing the frequency of the resonant circuit.

[0085] In the description of this solution, it should be understood that the terms "upper", "lower", "vertical", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this solution.

[0086] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this solution, "multiple" means two or more, unless otherwise explicitly specified.

[0087] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0088] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A hot air expansion forming system, characterized in that, The device includes a pipe bending device, a feeding device, a preforming device, a heating device, an expansion quenching device, and a unloading device arranged in sequence. The heating device includes a heating chamber, in which an electrode clamp for clamping the end of the metal pipe is provided. The electrode clamp is connected to an IGBT induction heating device. An infrared thermometer is provided in the heating chamber. Both the infrared thermometer and the IGBT induction heating device are communicatively connected to a controller.

2. The hot gas expansion forming system according to claim 1, characterized in that, The heating device includes a main frame, on which a heating platform is provided, and the electrode clamp is disposed on the heating platform. A sealing plate is provided around and on top of the heating platform. The sealing plate is connected to the main frame, and the sealing plate and the heating platform form the heating cavity.

3. The hot gas expansion forming system according to claim 2, characterized in that, The heating chamber is equipped with a dry gas dew point control component. The dry gas dew point control component includes a dew point sensor and a gas delivery component. The dew point sensor is disposed inside the heating chamber and is communicatively connected to the controller. The gas delivery component is used to deliver dry gas to the heating chamber.

4. The hot gas expansion forming system according to claim 3, characterized in that, The gas delivery assembly includes a dry gas source connected through an inlet pipe and a porous exhaust pipe. The porous exhaust pipe is disposed inside the heating chamber, and the dry gas source is disposed outside the heating chamber. A flow control valve is provided at the inlet end of the porous exhaust pipe. The porous exhaust pipe is provided with a plurality of exhaust through holes, which are arranged along the length of the porous exhaust pipe and are oriented toward the metal pipe. The drying gas source is used to hold the drying gas, which is either air or nitrogen.

5. The hot gas expansion forming system according to claim 1, characterized in that, A first transport robot is provided between the feeding device and the preforming device. The first transport robot is used to transfer the metal pipe from the feeding device to the preforming mold cavity of the preforming device. A second transport robot is provided between the preforming device and the heating device. The second transport robot is used to transfer the metal tube from the preforming mold cavity to the heating cavity. After the metal tube is heated, the second transport robot is used to transfer the metal tube from the heating cavity to the bulging mold cavity of the bulging quenching device. A third transport robot is provided between the bulging and quenching device and the unloading device. The third transport robot is used to transfer the metal tube from the bulging mold cavity to the unloading conveyor belt of the unloading device.

6. The hot gas expansion forming system according to claim 2, characterized in that, A lifting door is provided on the side wall of the sealing plate, and the width of the lifting door is greater than the length of the metal pipe.

7. A method for hot gas expansion molding, characterized in that, Includes the following steps: S1. Use a pipe bending machine to bend and shape the metal pipe; S2. Transfer the bent and shaped metal tube to the feeding device, which positions the metal tube. S3. The metal pipe is picked up from the feeding device and fed into the preforming mold cavity of the preforming device to preform the metal pipe; S4. The metal tube in the preformed mold cavity is sent into the heating chamber of the heating device for heating. The metal tube is clamped on the electrode clamp and heated by the IGBT induction heating device. The controller controls the IGBT induction heating device to perform heating. S5. The heated metal tube is fed into the expansion mold cavity of the expansion quenching device to complete the expansion quenching. S6. The expanded and cooled metal tube is fed into the feeding device for feeding.

8. The hot gas expansion forming method according to claim 7, characterized in that, The heating process in step S4 includes: S401. Preheating process: Adjust the power on-state ratio of the IGBT induction heating device, and the metal tube heats up at 10-18°C per second for 0-3 seconds. S402. During the rapid heating process, the power on-state ratio of the IGBT induction heating device is adjusted so that the metal tube heats up at 20-24°C per second for 3-30 seconds, so that the temperature of the metal tube reaches 550-650°C. S403. During the slow heating process, when the coating on the metal pipe is an aluminum-silicon coating, the metal pipe heats up at less than 10°C per second, and the metal pipe heats up from 600-650°C to 750°C. When the coating on the metal pipe is a hot-dip galvanized layer, the temperature of the metal pipe rises by less than 5°C per second, and the temperature of the metal pipe rises from 550-600°C to 650°C. S404. When the coating on the metal pipe is an aluminum-silicon plating layer, the metal pipe heats up at 18-20°C per second, and the metal pipe heats up from 750°C to 840°C. When the coating on the metal pipe is a hot-dip galvanized layer, the metal pipe heats up at 18-22°C per second, and the metal pipe heats up from 650°C to 750°C. S405. When the coating on the metal pipe is an aluminum-silicon plating layer, the metal pipe is heated from 840°C to 925°C at a rate of 5-7°C per second. When the coating on the metal pipe is a hot-dip galvanized layer, the metal pipe is heated from 750°C to 850°C at a rate of 5 to 7°C per second. S406, during the austenitizing process, when the coating on the metal pipe is an aluminum-silicon plating layer, the metal pipe is heated by 1-2°C per second, and the metal pipe is heated from 925°C to 950°C and then kept at that temperature. When the coating on the metal pipe is a hot-dip galvanized layer, the metal pipe heats up by less than 1°C per second, and the metal pipe is kept warm after being heated from 880°C to 890°C.

9. The hot gas expansion forming method according to claim 8, characterized in that, In step S403, the heating time is 30 to 55 seconds; In step S404, the heating time is 55-60 seconds; In step S405, the heating time is 60-75 seconds; In step S406, the heating time is 75-100 seconds and the heating and holding time is 100-180 seconds.

10. The hot gas expansion forming method according to claim 7, characterized in that, Dry gas is introduced into the heating chamber to control the dew point of the heating chamber and ensure that the dew point of the heating chamber meets the requirements.

Images