A hollow complex structure bending and expanding welding integrated forming die and method under air pressure loading

Abstract

The application provides a hollow complex structure bending and expanding welding integrated forming die and method under gas pressure loading, and belongs to the field of sheet metal processing. The application effectively solves the problems of complex superplastic forming / diffusion bonding steps, multiple taking and heating, and uneven loading of curved surface sheet diffusion bonding, and can realize multiple steps of preforming, diffusion bonding and gas expanding forming at one time. The technical scheme of the application is as follows: the forming die comprises a male die as an upper die, a female die as a lower die and a ventilation sealing block as a gas inlet pipe during gas expanding, the upper surface of the female die is provided with a downwardly recessed die cavity, the lower surface of the male die is provided with a protrusion in accordance with the shape of the die cavity, and the gas expanding grooves corresponding to the rib positions of the hollow structure are formed in the lower surface of the male die, and the one-time gas inlet holes communicating with the gas expanding grooves are formed in the male die, and the outer hole openings of the one-time gas inlet holes are arranged on the side wall of the male die. The application realizes the integration of bending, diffusion bonding and gas expanding forming, and greatly improves the problems of time and resource waste caused by repeated furnace loading.

Description

Technical Field

[0001] This invention belongs to the field of metal sheet processing. Background Technology

[0002] To achieve lightweight structural designs, efficient material utilization, and improved thermal insulation, hollow structural components are increasingly used in aerospace and other fields, such as wings, engine blades, and rudders. Common manufacturing methods for hollow structures include investment casting, additive manufacturing, plastic forming / welding, and superplastic forming / diffusion bonding. Among these, superplastic forming / diffusion bonding can produce complex curved hollow structures at low cost and in large quantities, exhibiting good mechanical properties and dimensional accuracy.

[0003] In actual production, superplastic forming / diffusion bonding requires multiple processing steps, including preforming, diffusion bonding, and gas forming, necessitating multiple cooling and unloading processes followed by furnace heating, significantly reducing production efficiency. Furthermore, traditional pressure loading methods for superplastic forming / diffusion bonding of curved panel materials suffer from uneven pressure loading. Therefore, it is desirable to adopt a novel process method that completes multiple process steps such as preforming, diffusion bonding, and gas forming in one step, employing a new loading method for the pressure loading process of diffusion bonding on curved panel materials.

[0004] With the increasing demand for lightweighting in aerospace, new process methods are urgently needed to improve the efficiency of superplastic forming / diffusion bonding processes and broaden their application scope in order to achieve various complex structures.

[0005] In the publicly available technologies: CN110743957A, published on February 4, 2020, discloses a method for forming a four-layer structure of magnesium alloy. The method involves pretreatment; core plate preparation; stacking of sheet materials; superplastic forming of the face plate; diffusion bonding between core plates; superplastic forming of the core plate; diffusion bonding between the face plate and core plate; and demolding to create a four-layer hollow structure of magnesium alloy. Multiple vacuuming and gas filling processes are used to complete both forming and bonding within one cycle. However, this method is not suitable for superplastic forming / diffusion bonding of curved sheet materials that require bending, and the process is relatively cumbersome due to the need for multiple vacuuming cycles.

[0006] CN113042620A, published on June 29, 2021, discloses a method for the combined bending and bulging forming of aluminum alloy skin parts with small curvature. The entire process is divided into two parts: bending and bulging. First, the sheet metal is formed onto the bending surface, and then the mold is fully formed and fitted to the die using hydraulic bulging. This achieves integrated bending and bulging, but because it cannot achieve diffusion connection between the two layers of sheet metal, it is not suitable for forming double-layer hollow structures. Summary of the Invention

[0007] To address the above problems, this invention proposes an integrated forming mold and method for hollow complex structure bending expansion welding under air pressure loading. It effectively solves the problems of complex superplastic forming / diffusion bonding steps, the need for multiple part removal and heating, and uneven loading of curved panel material diffusion bonding. It can realize multiple steps of preforming, diffusion bonding, and air expansion forming in one go.

[0008] The technical solution of the present invention is as follows: the forming mold includes a punch 1 as an upper mold, a die 3 as a lower mold, and a vent sealing block 4 as an air inlet pipe during air expansion. The upper surface of the die 3 has a downwardly recessed cavity, and the lower surface of the punch 1 is protruding in a shape consistent with the shape of the cavity. An air expansion groove corresponding to the rib position of the hollow structural component is opened on the lower surface of the punch 1. A primary air inlet hole communicating with the air expansion groove is also opened inside the punch 1. The outer opening of the primary air inlet hole is located on the side wall of the punch 1. The lower surface edge of the punch 1 is provided with an upper slot for accommodating the venting sealing block 4, and the upper surface edge of the die 3 is provided with a lower slot for accommodating the venting sealing block 4. The upper and lower slots are positioned correspondingly, and after the mold is closed, they lock the venting sealing block 4 placed therein. The center of the venting sealing block 4 is provided with an air expansion inlet hole.

[0009] After mold closing, the venting sealing block 4 is held in place by the punch 1 and the die 3, achieving good positioning and airtightness to ensure subsequent processing results and prevent air leakage and pressure drop during diffusion welding gas pressure loading. More importantly, due to the presence of the air expansion groove, when there are gaps on the punch surface that prevent the sheet metal from being compacted, the gas pressure from the first venting can be used to pressurize the sheet metal, combined with the airtightness between the venting sealing block 4 and the punch 1, thereby effectively ensuring the subsequent bending forming effect.

[0010] The ratio of the rib width to the diameter of the primary air inlet is 50:1. This is to prevent the primary air inlet from affecting the surface morphology of the hollow structural component.

[0011] like Figure 3 As shown, the venting sealing block 4 has an air-filling channel inside, and the outer wall of the venting sealing block 4 is conical. The outer wall of the venting sealing block 4 has an annular protrusion and an annular groove, thereby forming two annular sealing positions. The inner wall of the upper slot has an upper semicircular groove 7 corresponding to the position of the annular protrusion and an upper semicircular protrusion ridge corresponding to the position of the annular groove. The inner wall of the lower slot has a lower semicircular groove corresponding to the position of the annular protrusion and a lower semicircular protrusion ridge corresponding to the position of the annular groove. Thus, after mold closing, the position of the vent sealing block 4 is fixed, and the two sealing structures effectively ensure a good airtight seal between the vent sealing block 4 and the punch 1 and the die 3.

[0012] The lower surface edge of the punch 1 is provided with an annular sealing groove, and the upper surface edge of the die 3 is provided with an annular sealing boss 5. This allows the die to press down on the sheet metal after it is placed in, thus sealing it and preventing air leakage and pressure drop during diffusion welding.

[0013] Follow these steps: Step 1: Treat the surface of the board by sanding it smooth and flat. Step 2: Place the board in alcohol and perform ultrasonic cleaning to remove impurities from the surface of the board. After ultrasonic cleaning, put it back into alcohol for cleaning again and blow it dry with an air gun. Step 3: Cover the surface of the sheet metal with green tape, and cut off the parts that need to be inflated, referring to the final molded part; Step 4: Spray solder resist and wait for it to solidify before removing the tape from the diffusion soldering section. Step 5: Place the first sheet metal, the vent sealing block, and the second sheet metal into the die cavity in sequence, so that the vent sealing block is located at the air vent of the hollow structural part, and complete the matching and positioning with the lower groove at the edge of the die cavity. Step 6: Fix the punch to the press head of the press with a pressure plate, fix the die to the platform of the press with a pressure plate, and insert thermocouples into the die and punch to measure the mold temperature; Step 7: Heat the forming mold to 480℃ at a rate of 10℃-30℃ / min and keep it at that temperature. Control the press head to press down so that the die and punch close. Use the press head to press and bend the sheet metal to perform the pre-forming process, forming the curved surface and the air vent. Step 8: Maintain a temperature of 480℃, introduce argon gas into the punch through the primary air inlet and maintain a pressure of 2 MPa for diffusion connection. The pressure holding time is 4 hours. After the process is completed, release the argon gas and return the gas pressure to zero. Step 9: Maintain a temperature of 480℃, introduce argon gas into the air vent through the vent sealing block and maintain a pressure of 2 MPa to allow the sheet material to expand and form internal flow channels. Maintain the pressure for 4 hours to set the shape.

[0014] Step 10: After the forming mold has cooled down, raise the pressure head to separate the punch and die, and remove the formed hollow structural part and the vent sealing block. Done.

[0015] The beneficial effects of this invention are as follows: I. The method of this invention for superplastic forming / diffusion bonding addresses the problem of the traditional forming process requiring multiple furnace loading, heating, cooling and unloading steps in the three steps of preforming bending, diffusion bonding and gas expansion forming. It innovates the equipment and process, realizing the integration of bending, diffusion bonding and gas expansion forming, and greatly improves the problem of time and resource waste caused by repeated furnace loading.

[0016] Second, the diffusion bonding method of this invention, which replaces traditional loading methods with pneumatic loading, enables diffusion bonding of curved structures. It also significantly improves the problem of uneven pressure loading caused by unevenness in the machine tool indenter and unevenness in the mold due to processing errors. Furthermore, the pneumatic loading method can adapt to diffusion bonding processes of plates of varying thicknesses, greatly expanding the equipment's application range.

[0017] Third, by setting up structures such as sealing ribs, sealing grooves, and ventilated sealing blocks, and in conjunction with the plastic deformation of the sheet material at high temperatures, the airtightness of the mold is achieved. High-pressure gas can be directly introduced for diffusion connection, eliminating the need for vacuuming and simplifying the forming process. For materials such as magnesium alloys that are prone to volatility under high temperature and vacuum, it is more convenient for superplastic forming / diffusion connection. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the diffusion zone and the expansion zone; Figure 2 Schematic diagram of the integrated bending expansion welding forming device; Figure 3 Longitudinal sectional view of the integrated bending and expansion welding forming device assembly; Figure 4 A cross-sectional view of the assembly of the integrated bending and expansion welding forming device; Figure 5 This is a schematic diagram of a pressure-loaded diffusion connection. Figure 6 This is a schematic diagram of the air-inflating molding process. In the diagram, 1 is the punch, 2 is the sheet metal, 3 is the die, 4 is the vent sealing block, 5 is the sealing boss, 6 is the primary air inlet, and 7 is the upper semi-circular groove. Detailed Implementation

[0019] To clearly illustrate the technical features of this patent, the following detailed description is provided through specific embodiments and in conjunction with the accompanying drawings.

[0020] like Figure 2-6 As shown, the forming mold in this case includes a punch 1 as an upper mold, a die 3 as a lower mold, and a vent sealing block 4 as an air inlet pipe during air expansion. The upper surface of the die 3 has a downwardly recessed cavity, while the lower surface of the punch 1 is protruding in a shape consistent with the cavity. An air expansion groove corresponding to the rib position of the hollow structural component is provided on the lower surface of the punch 1. A primary air inlet hole communicating with the air expansion groove is also provided inside the punch 1. The outer opening of the primary air inlet hole is located on the side wall of the punch 1. The lower surface edge of the punch 1 is provided with an upper slot for accommodating the venting sealing block 4, and the upper surface edge of the die 3 is provided with a lower slot for accommodating the venting sealing block 4. The upper and lower slots are positioned correspondingly, and after the mold is closed, they lock the venting sealing block 4 placed therein. The center of the venting sealing block 4 is provided with an air expansion inlet hole.

[0021] The ratio of the rib width to the diameter of the primary air inlet is 50:1. This is to prevent the primary air inlet from affecting the surface morphology of the hollow structural component.

[0022] The workpiece 2 to be formed consists of two stacked plates. During processing, the plates 2 need to be bent into a predetermined shape and then formed after diffusion welding. Figure 1 The diffusion connection area and the air-expanding forming area coated with solder resist are shown. Air expansion forming is then performed to form a hollow structural component. The hollow structural component has flow channels, and ribs are formed on the outer surface corresponding to the flow channels. Air vents connecting to the hollow flow channels are left at the edges of the hollow structural component. Specifically, during material feeding, the first sheet metal is placed in the die 3, then a vent sealing block 4 is placed at the air vent position, followed by the placement of another sheet metal. Finally, the mold is closed, and bending and expansion welding are initiated for integrated forming.

[0023] In the above, after the mold is closed, the vent sealing block 4 is stuck by the punch 1 and the die 3, thereby achieving good positioning and air sealing, so as to ensure the subsequent processing effect and prevent air leakage and air pressure drop during diffusion welding gas pressure loading.

[0024] More importantly, due to the presence of the air expansion groove, when there are gaps on the surface of the punch that prevent the sheet metal from being compacted, the gas pressure from the first ventilation can be used to pressurize the sheet metal. Combined with the air seal between the ventilation sealing block 4 and the punch 1, the diffusion welding effect (especially the diffusion welding effect at the edge positions on both sides of the flow channel) can be guaranteed, while further ensuring the bending forming effect.

[0025] like Figure 3 As shown, the venting sealing block 4 has an air-filling channel inside, and the outer wall of the venting sealing block 4 is conical. The outer wall of the venting sealing block 4 has an annular protrusion and an annular groove, thereby forming two annular sealing positions. The inner wall of the upper slot has an upper semicircular groove 7 corresponding to the position of the annular protrusion and an upper semicircular protrusion ridge corresponding to the position of the annular groove. The inner wall of the lower slot has a lower semicircular groove corresponding to the position of the annular protrusion and a lower semicircular protrusion ridge corresponding to the position of the annular groove. Thus, after mold closing, the position of the vent sealing block 4 is fixed, and the two sealing structures effectively ensure a good airtight seal between the vent sealing block 4 and the punch 1 and the die 3.

[0026] The lower surface edge of the punch 1 is provided with an annular sealing groove, and the upper surface edge of the die 3 is provided with an annular sealing boss 5. This allows the die to press down on the sheet metal after it is placed in, thus sealing it and preventing air leakage and pressure drop during diffusion welding.

[0027] Based on the above molding die, this case also proposes the following specific molding methods. Example

[0028] This embodiment features a ribbed rare-earth magnesium alloy panel. The panel is made of 2mm thick VW94 rare-earth magnesium alloy, with dimensions of 400mm × 281mm and a corner radius of 15mm.

[0029] Follow these steps: Step 1: Treat the surface of the board by sanding it smooth and flat. The sandpaper used is 400#, 800#, and 2000# sandpaper, which are used in sequence to polish the oxide layer on the surface of the magnesium alloy, so that the surface of the magnesium alloy has a metallic luster.

[0030] Step 2: Place the board in alcohol and perform ultrasonic cleaning to remove impurities from the surface of the board. After ultrasonic cleaning, put it back into alcohol for cleaning again and blow it dry with an air gun. Because magnesium alloys are prone to oxidation when heated, high-temperature gases cannot be used during the drying process. Alcohol, in addition to its cleaning function, also serves to prevent oxidation. Rubber gloves should be worn throughout the cleaning and drying process.

[0031] Step 3: Cover the surface of the sheet metal with tape, compare it with the final molded part, and use tape to cut off and tear off the parts that need to be inflated.

[0032] Step 4: Spray solder resist and wait for it to solidify before removing the tape from the diffusion soldering section. Because of the presence of solder resist, the air-expanded part will not be welded, which lays the foundation for the subsequent air-expanding forming process. The diffusion welding part can be welded normally, and after air-expanding forming, a hollow structural part can be obtained.

[0033] Step 5: Place the first sheet metal, the vent sealing block, and the second sheet metal into the die cavity in sequence, so that the vent sealing block is located at the air vent of the hollow structural part, and complete the matching and positioning with the lower groove at the edge of the die cavity. Step 6: Fix the punch to the press head of the press with a pressure plate, fix the die to the platform of the press with a pressure plate, and insert thermocouples into the die and punch to measure the mold temperature; Step 7: Heat the forming mold at a rate of 10℃-30℃ / min to 480℃ and keep it at that temperature. Control the press head to press down so that the die and punch close. Use the press head to press and bend the sheet metal to perform the pre-forming process, forming the curved surface and the air vent.

[0034] Step 8: Maintain a temperature of 480℃, introduce argon gas into the punch through the primary air inlet and maintain a pressure of 2 MPa for diffusion connection. The pressure holding time is 4 hours. After the process is completed, release the argon gas and return the gas pressure to zero. Argon is an inert gas. In addition to applying pressure, it can also prevent magnesium alloy from oxidizing. Since the punch must be curved and has an expansion groove to accommodate the ribs, the upper die cannot completely compact the workpiece during the forming process of the sheet from flat to curved. Step eight can ensure the diffusion welding effect (especially the diffusion welding effect at the edge position on both sides of the flow channel) while further ensuring the bending forming effect.

[0035] Step 9: Maintain a temperature of 480℃, introduce argon gas into the air vent through the vent sealing block and maintain a pressure of 2 MPa to allow the sheet material to expand and form internal flow channels. Maintain the pressure for 4 hours to set the shape.

[0036] Step 10: After the forming mold has cooled down, raise the pressure head to separate the punch and die, and remove the formed hollow structural part and the vent sealing block. Done.

[0037] In this way, the hollow structural component can be integrally formed by heating, bending, and welding in steps seven, eight, and nine above. The workpiece does not need to be removed, and subsequent processing can be completed, resulting in extremely high processing efficiency.

[0038] There are many specific ways to implement this invention. The above description is only a preferred embodiment of this invention. It should be noted that for those skilled in the art, several improvements can be made without departing from the principle of this invention, and these improvements should also be considered within the scope of protection of this invention.

Claims

1. A method for integral forming of hollow complex structures by bending and expansion welding under pneumatic loading, characterized in that, Based on a forming mold, the forming mold includes a punch (1) as an upper mold, a die (3) as a lower mold, and a vent sealing block (4) as an air inlet pipe during air expansion. The upper surface of the die (3) has a downward recessed mold cavity, and the lower surface of the punch (1) is protruding in a shape consistent with the shape of the mold cavity. An air expansion groove corresponding to the rib position of the hollow structural component is opened on the lower surface of the punch (1). A primary air inlet hole (6) communicating with the air expansion groove is also opened inside the punch (1). The outer opening of the primary air inlet hole is located on the side wall of the punch (1). The lower surface edge of the punch (1) is provided with an upper slot for accommodating the venting sealing block (4), and the upper surface edge of the die (3) is provided with a lower slot for accommodating the venting sealing block (4). The upper slot and the lower slot are positioned correspondingly, and after the mold is closed, they lock the venting sealing block (4) placed therein. The center of the venting sealing block (4) is provided with an air expansion inlet hole. The forming method is performed according to the following steps: Step 1: Treat the surface of the board by sanding it smooth and flat. Step 2: Place the board in alcohol and perform ultrasonic cleaning to remove impurities from the surface of the board. After ultrasonic cleaning, put it back into alcohol for cleaning again and blow it dry with an air gun. Step 3: Cover the surface of the sheet metal with tape, compare it with the final molded part, and use tape to cut off and tear off the parts that need to be inflated; Step 4: Spray solder resist and wait for it to solidify before removing the tape from the diffusion soldering section. Step 5: Place the first sheet metal, the vent sealing block, and the second sheet metal into the die cavity in sequence, so that the vent sealing block is located at the air vent of the hollow structural part, and complete the matching and positioning with the lower groove at the edge of the die cavity. Step 6: Fix the punch to the press head of the press with a pressure plate, fix the die to the platform of the press with a pressure plate, and insert thermocouples into the die and punch to measure the mold temperature; Step 7: Heat the forming mold to 480℃ at a rate of 10℃-30℃ / min and keep it at that temperature. Control the press head to press down so that the die and punch close. Use the press head to press and bend the sheet metal to perform the pre-forming process, forming the curved surface and the air vent. Step 8: Maintain a temperature of 480℃, introduce argon gas into the punch through the primary air inlet and maintain a pressure of 2 MPa for diffusion connection. The pressure holding time is 4 hours. After the process is completed, release the argon gas and return the gas pressure to zero. Step 9: Maintain a temperature of 480℃, introduce argon gas into the air vent through the vent sealing block and maintain a pressure of 2 MPa to allow the sheet material to expand and form internal flow channels. Maintain the pressure for 4 hours to set the shape. Step 10: After the forming mold has cooled down, raise the pressure head to separate the punch and die, and remove the formed hollow structural part and the vent sealing block. Done.

2. The method for integrated bending and expansion welding of a hollow complex structure under pneumatic loading according to claim 1, characterized in that, The ratio of the rib width to the diameter of the primary air inlet is 50:

1.

3. The method for integrated bending and expansion welding of a hollow complex structure under pneumatic loading according to claim 1, characterized in that, The ventilation sealing block (4) has an air-filling channel inside, and the outer wall of the ventilation sealing block (4) is conical. The outer wall of the ventilation sealing block (4) has an annular protrusion and an annular groove, thereby forming two annular sealing positions. The inner wall of the upper slot is provided with an upper semicircular groove (7) corresponding to the position of the annular protrusion and an upper semicircular protrusion corresponding to the position of the annular groove. The inner wall of the lower slot is provided with a lower semicircular groove corresponding to the position of the annular protrusion and a lower semicircular protrusion corresponding to the position of the annular groove.

4. The method for integrated bending and expansion welding of a hollow complex structure under pneumatic loading according to claim 1, characterized in that, The lower surface edge of the punch (1) is provided with an annular sealing groove, and the upper surface edge of the die (3) is provided with an annular sealing boss (5).

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