Ultrasonic assisted sheet forming limit test apparatus and operating method under cryogenic conditions

Abstract

The application provides an ultrasonic-assisted plate forming limit test device and operation method under a deep cooling condition, which comprises a loading device outer box, a hydraulic cylinder, a loading device guide column, a hydraulic cylinder piston, an ultrasonic equipment fixing plate, a spring, a limiting block, a blank holder sliding block, a blank holder ring fixing plate, a liquid nitrogen barrel, a liquid cooling pump, a vacuum heat insulation pipe, thermal insulation material, a concave die fixing plate, a glass cover plate, a CCD camera, a camera support, a forming device outer box, a forming device guide column, a nitrogen storage box, an air compression pump, a concave die, a blank holder ring, a split ultrasonic punch, an amplitude varying rod, an ultrasonic wave generator, a transducer, a flange plate, a force sensor, a check valve, a fixing support, a non-contact temperature sensor, an experimental plate and an air suction device; the application combines the ultrasonic vibration device with the split ultrasonic punch, reduces the requirement for the low-temperature resistance of the overall ultrasonic vibration equipment, and cools the plate and the split ultrasonic punch by using the liquid cooling mold, so that the forming area is always in a deep cooling environment.

Description

Technical Field

[0001] This invention relates to the field of special energy field assisted sheet metal forming and processing technology, and in particular to the ultrasonic-assisted sheet metal forming limit testing device and operating method under cryogenic conditions. Background Technology

[0002] Forming limit testing, as a method to investigate the ultimate deformation degree of sheet metal under different strain paths, is widely used in the study of sheet metal forming performance. By conducting hemispherical (Nakajima) / cylindrical (Marciniak) punch bulging experiments on specimens of different sizes and geometries, the surface strain of the specimen before fracture is obtained, and the corresponding forming limit curves / graphs are plotted to guide the stamping forming process of sheet metal. With the continuous development of materials technology and the increasing complexity of stamped parts requirements, traditional plastic forming methods have become insufficient to meet production demands, leading to difficulties in controlling the forming quality and precision of parts and hindering mass production. Therefore, it is necessary to utilize special energy fields such as ultrasonic vibration fields, temperature fields, and electromagnetic fields for assisted forming. In recent years, cryogenic forming has been considered an advanced method to improve the quality of formed parts, and its combination with ultrasonic energy fields holds promise for obtaining high-performance formed parts. Therefore, it is necessary to develop corresponding special energy field-assisted forming limit testing devices and explore their working mechanisms to characterize the forming performance of sheet metal under complex special energy fields, providing theoretical guidance for the stamping forming process of sheet metal.

[0003] Traditional forming limit tests are mainly conducted at room temperature. Compared with forming at room temperature, some materials have better plastic deformation capabilities in cryogenic environments. Currently, existing cryogenic processes commonly employ methods such as overall cryogenic treatment and cryogenic treatment followed by forming. These cooling methods are usually complex to operate, require expensive equipment, and cannot stably and precisely control the cryogenic temperature.

[0004] The existing technology has the following problems: 1) Existing forming limit testing equipment cannot realize the study of sheet forming performance under multiple special energy fields such as cryogenic field and ultrasonic field; 2) The traditional cryogenic first and then forming process has defects such as uneven temperature during the transfer process and complicated operation, while the existing overall cryogenic process consumes a lot of liquid nitrogen, has low cooling efficiency, and is costly. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide an ultrasonic-assisted sheet metal forming limit testing device under cryogenic conditions, which combines an ultrasonic vibration device with a split ultrasonic punch to reduce the requirements for the overall ultrasonic vibration equipment's low-temperature resistance; and uses a liquid-cooled mold to cool the sheet metal and the split ultrasonic punch, so that the forming area is always in a cryogenic environment.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a cryogenic ultrasonic-assisted plate forming limit testing device, comprising a loading device outer casing, a hydraulic cylinder, a loading device guide column, a hydraulic cylinder piston, an ultrasonic equipment fixing plate, a spring, a limit block, a pressure block slider, a pressure ring fixing plate, a liquid nitrogen tank, a liquid cooling pump, a vacuum insulation tube, a first insulation material, a die fixing plate, a glass cover, a CCD camera, a camera bracket, a forming device outer casing, a forming device guide column, a nitrogen storage tank, an air compressor pump, a die, a pressure ring, a split ultrasonic punch, an amplitude transformer, a second insulation material, an ultrasonic generator, a transducer, a flange, a force sensor, a check valve, a fixing bracket, a non-contact temperature sensor, an experimental plate, and a suction device; The split-type ultrasonic punch is mounted on an amplitude transformer rod, which is connected by threads. The amplitude transformer rod and transducer are an integral structure mounted on an ultrasonic equipment mounting plate. The transducer and the ultrasonic equipment mounting plate are connected by a flange. The ultrasonic equipment mounting plate is locked and fixed to the hydraulic cylinder piston by four sets of bolts and nuts, and is also fixed to the limit block and the pressure block by springs. The limit block and the pressure block are connected by threads. The pressure block has a through hole for mounting the loading device guide post. Under the cooperation of the loading device guide post and the pressure block, the displacement of the hydraulic cylinder piston on the pressure ring is controlled, and a certain pressure is applied to the pressure area of ​​the experimental material under the action of the pressure ring. The pressure ring fixing plate, the die fixing plate, and the forming... The guide column of the device is a single unit, and the pressure ring fixing plate and the die fixing plate are respectively connected to the pressure ring and the die by threads. Both the die and the pressure ring have slots / holes for liquid nitrogen flow channels to achieve deep cryogenic treatment of the experimental material. They are also connected to the liquid cooling pump through vacuum insulation pipes and check valves. A glass cover and a non-contact temperature sensor are installed on the top of the die. The non-contact temperature sensor is fixed to the outer surface of the die fixing plate with low-temperature resistant tape and is used to measure and provide feedback on the real-time temperature of the experimental material. The liquid cooling pump is connected to the non-contact temperature sensor through leads. The non-contact temperature sensor monitors the temperature of the upper surface of the experimental material in real time throughout the processing and transmits the temperature information to the liquid cooling pump.

[0007] In a preferred embodiment, when the liquid-cooled mold starts working, the liquid-cooling pump controls the liquid nitrogen tank to release liquid nitrogen to begin cooling. A non-contact temperature sensor sends a feedback signal to the liquid-cooling pump. After receiving the feedback signal, the liquid-cooling pump controls the output flow rate of the liquid nitrogen tank, switches the power on and off, and stabilizes the temperature of the upper surface of the experimental plate at the target temperature. At the same time, the suction device absorbs the escaping nitrogen through the air holes in the pressure ring fixing plate and the die fixing plate, preventing excessive air pressure in the closed forming device. It also works with the second insulation material to prevent low-temperature nitrogen from contacting the transducer, thus avoiding the transducer temperature from dropping below the critical operating temperature and damaging the ultrasonic vibration equipment.

[0008] In a preferred embodiment, when the ultrasonic vibration device starts working, the ultrasonic generator inputs a high-frequency current into the transducer, which converts it into mechanical vibration output. The corresponding amplitude is then applied to the experimental plate through the split ultrasonic punch via the amplitude transformer. The ultrasonic amplitude value transmitted to the experimental plate by the split ultrasonic punch is adjusted by adjusting the power of the ultrasonic generator. The compression degree of the spring can be controlled by adjusting the position of the limiting block in the guide column of the loading device, thereby controlling the magnitude of the pressing force applied to the experimental plate by the pressing ring. The relative distance between the pressing slider and the transducer is also adjusted to avoid over-displacement and damage to the transducer.

[0009] This invention also provides an operating method for an ultrasonic-assisted sheet metal forming limit testing device under cryogenic conditions. Using this device, the required experimental sheet metal is first placed on a blank holder, and a hydraulic piston pushes a blank holder slider to fix the sheet metal in the mold. After the die and blank holder are closed, the liquid cooling pump is turned on, and a target temperature is set. A non-contact temperature sensor controls the operation of the liquid cooling pump to cool the experimental sheet metal to the target temperature. Simultaneously, an air compressor is turned on to control the suction device to absorb nitrogen gas escaping from the mold, preventing excessive internal pressure in the forming device and preventing the low-temperature nitrogen gas from contacting the transducer. After reaching the target temperature... After turning on the ultrasonic generator and setting the amplitude, the split ultrasonic punch is pushed by the hydraulic piston to perform a forming limit test on the sheet metal. Once the force sensor detects that the pressure exceeds the preset value, the CCD camera is turned on to record the deformation process of the sheet metal until it breaks. Then, the hydraulic piston stops moving, and the liquid cooling pump, ultrasonic generator, and CCD camera are turned off. Then, the hydraulic piston returns, and after the die and the pressure ring separate, the power of the air compressor is increased to quickly absorb the vaporized liquid nitrogen to prevent injury from low-temperature nitrogen gas when removing the part. After observing from the glass cover above the device that the vaporized liquid nitrogen has completely disappeared, the suction device is turned off, the formed experimental sheet metal is removed, and the experiment ends.

[0010] Compared with the prior art, the present invention has the following beneficial effects: This device can perform ultrasonic vibration-assisted sheet metal forming limit testing under cryogenic conditions, solving the problem that existing forming limit testing devices can only perform forming under simple working conditions.

[0011] The liquid-cooled mold in this device directly cools the experimental plate and the split ultrasonic punch. Combined with the insulation material covering the mold, the cooling area is concentrated inside the mold, improving liquid nitrogen utilization and solving the problem of high liquid nitrogen loss during overall cryogenic processes. Furthermore, the experimental plate uses the same mold for both cooling and forming, avoiding the uneven temperature field that occurs during the transfer process in a cryogenic-then-forming process. Cooling holes near the plate in the liquid-cooled mold quickly bring it to the target temperature, improving cooling efficiency.

[0012] By using a split ultrasonic punch structure, the requirements for the overall ultrasonic vibration device's low-temperature resistance can be reduced, which not only improves the service life of the ultrasonic vibration equipment but also reduces maintenance costs.

[0013] The suction device, driven by an air compressor pump and mounted on the side of the liquid-cooled mold, absorbs nitrogen gas escaping from the mold, preventing excessive pressure inside the enclosed forming device. Simultaneously, combined with the insulation material within the pressure slider, it prevents low-temperature nitrogen gas from contacting the transducer and damaging the ultrasonic vibration equipment. After testing, the suction device quickly absorbs the vaporized liquid nitrogen, preventing injury from low-temperature nitrogen gas when handling the sheet material.

[0014] The non-contact temperature sensor is installed near the top glass cover of the sample, which can monitor and provide feedback on the temperature of the upper surface of the experimental plate in real time. It can also avoid damage to the equipment caused by liquid nitrogen vaporization. At the same time, the non-contact temperature sensor is directly connected to the liquid cooling pump, which is conducive to closed-loop control of the forming temperature of the experimental plate.

[0015] Applications: Research on the forming performance of sheet metal used in complex ultra-low temperature conditions in fields such as national defense equipment, aerospace, transportation, and biomedical devices. Attached Figure Description

[0016] Figure 1 This is an overall structural diagram of the ultrasonic-assisted forming limit testing device under cryogenic conditions according to a preferred embodiment of the present invention; Figure 2 This is a cross-sectional view of a liquid-cooled mold according to a preferred embodiment of the present invention; Figure 3 This is a cross-sectional view of a split ultrasonic punch according to a preferred embodiment of the present invention. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0018] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0019] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application; as used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise; furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0020] An ultrasonic-assisted sheet metal forming limit testing device under cryogenic conditions, as shown in the attached document. Figure 1As shown; Appendix Figure 2 Appendix Figure 3 These are cross-sectional views of the liquid-cooled mold and the split-type ultrasonic punch, respectively. The overall equipment structure includes: 1. Loading device outer casing, 2. Hydraulic cylinder, 3. Loading device guide post, 4. Hydraulic cylinder piston, 5. Ultrasonic equipment fixing plate, 6. Spring, 7. Limiting block, 8. Pressure edge slider, 9. Pressure edge ring fixing plate, 10. Liquid nitrogen tank, 11. Liquid cooling pump, 12. Vacuum insulation tube, 13. First insulation material, 14. Die fixing plate, 15. Glass cover, 16. CCD camera, 17. Camera bracket, 18. Forming device outer casing, 19. Forming device guide post, 20. Nitrogen storage tank, 21. Air compressor pump, 22. Die, 23. Pressure edge ring, 24. Split-type ultrasonic punch, 25. Amplitude rod, 26. Second insulation material, 27. Ultrasonic generator, 28. Transducer, 29. Flange, 30. Force sensor, 31. Check valve, 32. Fixing bracket, 33. Non-contact temperature sensor, 34. Experimental plate, 35. Suction device.

[0021] The split-type ultrasonic punch 24 is mounted on the amplitude transformer 25, and the two are connected by threads. The amplitude transformer 25 and the transducer 28 are an integral structure mounted on the ultrasonic equipment mounting plate 5. The transducer 28 is connected to the ultrasonic equipment mounting plate 5 through the flange 29. The ultrasonic equipment mounting plate 5 is locked and fixed to the hydraulic cylinder piston 4 by four sets of bolts and nuts, and is also fixedly connected to the limit block 7 and the pressure block slider 8 by the spring 6. The limit block 7 and the pressure block slider 8 are connected by threads. The pressure block slider 8 is provided with a through hole for mounting the loading device guide post 3. Under the cooperation of the loading device guide post 3 and the pressure block slider 8, the displacement control of the hydraulic cylinder piston 4 on the pressure ring 23 can be realized, and under the action of the pressure ring 23, a certain pressure is applied to the pressure area of ​​the experimental plate 34. The pressure ring fixing plate 8, the die fixing plate 14, and the forming device guide post 18 are an integral unit, and the pressure ring fixing plate 9 and the die fixing plate 14 are respectively connected to the pressure ring 23 and the die 22 by threads. Both the die 22 and the pressure ring 23 have internal slots / holes for liquid nitrogen flow channels to achieve deep cryogenic treatment of the experimental plate 34. They are also connected to the liquid cooling pump 11 via a vacuum insulation pipe 12 and a check valve 31. A glass cover plate 15 and a non-contact temperature sensor 33 are installed on the top of the die 22. The non-contact temperature sensor 33 is fixed to the outer surface of the die fixing plate 14 with low-temperature resistant tape and is used to measure and provide feedback on the real-time temperature of the experimental plate 34. The liquid cooling pump 11 is connected to the non-contact temperature sensor 33 via a lead wire. The non-contact temperature sensor 33 monitors the temperature of the upper surface of the experimental plate 34 in real time throughout the processing and transmits the temperature information to the liquid cooling pump 11.

[0022] When the liquid-cooled mold starts working, the liquid cooling pump 11 controls the liquid nitrogen tank 10 to release liquid nitrogen to begin cooling. The non-contact temperature sensor 33 sends a feedback signal to the liquid cooling pump 11. After receiving the feedback signal, the liquid cooling pump 11 controls the output flow rate of the liquid nitrogen tank 10, switches the power on and off, and stabilizes the temperature of the upper surface of the experimental plate 34 at the target temperature. At the same time, the suction device 35 absorbs the escaping nitrogen through the air holes in the pressure ring fixing plate 9 and the die fixing plate 14, preventing excessive air pressure in the closed forming device. It also works with the second insulation material 26 to prevent low-temperature nitrogen from contacting the transducer 28, thus preventing the temperature of the transducer 28 from dropping below the critical operating temperature (-40℃) and damaging the ultrasonic vibration equipment.

[0023] When the ultrasonic vibration equipment starts working, the ultrasonic generator 27 inputs a high-frequency current into the transducer 28, which converts it into mechanical vibration output. The amplitude is then transmitted via the amplitude transformer 25 to the experimental plate 34 through the split ultrasonic punch 24. The ultrasonic amplitude value transmitted to the experimental plate 34 by the split ultrasonic punch 24 is adjusted by regulating the power of the ultrasonic generator 27. Adjusting the position of the limiting block 7 within the guide post 3 of the loading device controls the compression of the spring 6, thereby controlling the pressure force applied by the pressure ring 23 to the experimental plate 32. It also adjusts the relative distance between the pressure slider 8 and the transducer 28 to prevent over-displacement and damage to the transducer 28.

[0024] First, the experimental plate 34 to be formed is placed on the blank holder 23. The blank holder slider 8 is pushed by the hydraulic piston 4 to fix the plate in the mold. After the die 22 and the blank holder 23 are closed, the liquid cooling pump 11 is turned on and the target temperature is set. The non-contact temperature sensor 33 controls the operation of the liquid cooling pump to cool the experimental plate 34 to the target temperature. At the same time, the air compressor pump 21 is turned on to control the air intake device 35 to absorb the nitrogen gas escaping from the mold, preventing excessive air pressure and low-temperature nitrogen gas from contacting the transducer 28. After the target temperature is reached, the ultrasonic generator 27 is turned on and the amplitude is set. The split ultrasonic punch is pushed by the hydraulic piston 4 to perform a forming limit test on the plate. After the force sensor 30 senses that the pressure exceeds the preset value, the CCD camera 16 is turned on to start recording the deformation process of the plate until the plate breaks. Then, the movement of the hydraulic piston 4 is stopped, and the liquid cooling pump 11, ultrasonic generator 27 and CCD camera 16 are turned off. Then, the hydraulic piston 4 returns to its original position. After the die 22 and the pressure ring 23 separate, the power of the air compressor pump 21 is increased to quickly absorb the vaporized liquid nitrogen, preventing injury from low-temperature nitrogen gas during part removal. After observing from the glass cover 15 above the device that the vaporized liquid nitrogen has completely disappeared, the suction device 35 is turned off, the formed experimental plate 34 is removed, and the experiment ends.

Claims

1. A device for testing the forming limit of sheet metal under cryogenic conditions, characterized in that... The system includes a loading device outer casing, hydraulic cylinder, loading device guide column, hydraulic cylinder piston, ultrasonic equipment fixing plate, spring, limit block, pressure block slider, pressure ring fixing plate, liquid nitrogen tank, liquid cooling pump, vacuum insulation tube, first insulation material, die fixing plate, glass cover, CCD camera, camera bracket, forming device outer casing, forming device guide column, nitrogen storage tank, air compressor pump, die, pressure ring, split ultrasonic punch, amplitude transformer, second insulation material, ultrasonic generator, transducer, flange, force sensor, check valve, fixing bracket, non-contact temperature sensor, experimental plate, and suction device. The split-type ultrasonic punch is mounted on an amplitude transformer rod, which is connected by threads. The amplitude transformer rod and transducer are an integral structure, mounted on an ultrasonic equipment mounting plate. The transducer is connected to the ultrasonic equipment mounting plate via a flange. The ultrasonic equipment mounting plate is locked and fixed to the hydraulic cylinder piston by four sets of bolts and nuts, and is also fixed to the limit block and the pressure block slider by springs. The limit block and the pressure block slider are connected by threads. The pressure block slider has a through hole for mounting the loading device guide post. Under the cooperation of the loading device guide post and the pressure block slider, the displacement of the hydraulic cylinder piston on the pressure ring is controlled, and pressure is applied to the pressure area of ​​the experimental material under the action of the pressure ring. The pressure ring fixing plate, the die fixing plate, and the forming... The guide column of the device is a whole, and the pressure ring fixing plate and the die fixing plate are respectively connected to the pressure ring and the die by threads; the die and the pressure ring have slots or holes for liquid nitrogen flow channels to achieve deep cryogenic treatment of the experimental plate. At the same time, they are connected to the liquid cooling pump through vacuum insulation pipe and check valve; a glass cover plate and a non-contact temperature sensor are set on the top of the die. The non-contact temperature sensor is fixed to the outer surface of the die fixing plate with adhesive tape. It is used to measure and feedback the real-time temperature of the experimental plate. At the same time, the liquid cooling pump is connected to the non-contact temperature sensor through lead wire. The non-contact temperature sensor monitors the temperature of the upper surface of the experimental plate in real time throughout the processing and transmits the temperature information to the liquid cooling pump. When the liquid-cooled mold starts working, the liquid-cooling pump controls the liquid nitrogen tank to release liquid nitrogen to begin cooling. The non-contact temperature sensor feeds back a signal to the liquid-cooling pump. After receiving the feedback signal, the liquid-cooling pump controls the output flow rate and power supply of the liquid nitrogen tank to stabilize the temperature of the upper surface of the experimental plate at the target temperature. At the same time, the suction device absorbs the escaping nitrogen through the air channels in the pressure ring fixing plate and the die fixing plate to prevent excessive air pressure in the closed forming device. It also works with the second insulation material to prevent nitrogen from contacting the transducer, thus avoiding the transducer temperature from dropping below the critical operating temperature and damaging the ultrasonic vibration equipment.

2. The ultrasonic-assisted sheet metal forming limit testing device under cryogenic conditions according to claim 1, characterized in that, When the ultrasonic vibration equipment starts working, the ultrasonic generator inputs a high-frequency current into the transducer, which converts it into mechanical vibration output. The amplitude is then applied to the experimental plate by the split ultrasonic punch via the amplitude transformer. The ultrasonic amplitude value transmitted to the experimental plate by the split ultrasonic punch is adjusted by adjusting the power of the ultrasonic generator. The spring compression can be controlled by adjusting the position of the limiting block in the guide column of the loading device, thereby controlling the magnitude of the pressing force applied to the experimental plate by the pressing ring. The distance between the pressing slider and the transducer can also be adjusted to avoid over-displacement and damage to the transducer.

3. The operation method of the ultrasonic-assisted sheet metal forming limit testing device under cryogenic conditions, characterized in that... Using the cryogenic ultrasonic-assisted sheet metal forming limit testing device described in claim 1, the experimental sheet metal to be formed is first placed on the blank holder ring, and the blank holder slider is pushed by the hydraulic cylinder piston to fix the sheet metal in the mold; after the die and blank holder ring are closed, the liquid cooling pump is turned on, the target temperature is set, and the operation of the liquid cooling pump is controlled by a non-contact temperature sensor to cool the experimental sheet metal to the target temperature. At the same time, the air compressor pump is turned on to control the air suction device to absorb the nitrogen gas escaping from the mold, preventing excessive air pressure inside the forming device and nitrogen gas from contacting the transducer; after the target temperature is reached, the ultrasonic generator is turned on and the amplitude is set. Then, the hydraulic cylinder piston pushes the split ultrasonic punch to perform a forming limit test on the sheet metal. After the force sensor detects that the pressure exceeds the preset value, the CCD camera is turned on to record the deformation process of the sheet metal until the sheet metal breaks. At this point, the movement of the hydraulic cylinder piston is stopped, and the liquid cooling pump, ultrasonic generator, and CCD camera are turned off. Then, the hydraulic cylinder piston returns, and after the die and the pressure ring separate, the power of the air compressor pump is increased to quickly absorb the vaporized liquid nitrogen to prevent nitrogen gas from injuring people when removing the part. After observing from the glass cover above the device that the vaporized liquid nitrogen has completely disappeared, the suction device is turned off, the formed experimental sheet metal is removed, and the experiment ends.

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