Profile pre-dispersion superplastic forming / diffusion bonding method

Abstract

The invention discloses a molded surface pre-dispersion superplastic forming / diffusion bonding method, and belongs to the field of superplastic forming. The method solves the problem that when an ultrathin hollow multilayer structure is formed through an existing superplastic forming / diffusion bonding method, the wall thickness is not uniform due to excessive deformation of a core plate. According to the method, the core plate is subjected to large plastic deformation through a pre-reverse expansion method, stress concentration in a material is released, then the protruding part is subjected to plastic deformation through forward expansion, the core plate is subjected to plastic deformation in the reverse expansion stage, stress is more evenly distributed in the forward expansion stage, and therefore the situation that in a local area, the stress concentration in the material is reduced is avoided. And particularly, the phenomena of excessive deformation and thinning of high-strain parts such as fillets and the like are avoided, so that the uniformity of the wall thickness is greatly improved. The method provided by the invention comprises the following steps: (1) pre-forming a core plate and welding isolation ribs; (2) panel forming; (3) combining the core plate and the panel; (4) carrying out reverse expansion on the core plate; and (5) superplastic forming of the core plate.

Description

Technical Field

[0001] The invention belongs to the field of superplastic forming, and in particular relates to a mold surface pre-dispersed superplastic forming / diffusion connection method. Background Art

[0002] Superplastic forming / diffusion bonding (SPF / DB) is an important technology in modern material processing, especially in the aerospace, automotive and electronics industries. The combination of these two technologies is used to manufacture high-performance parts with complex shapes, high strength and light weight, especially for some multi-layer structures in the aerospace field, which are manufactured using superplastic forming / diffusion bonding technology.

[0003] With the development of aerospace technology, materials are constantly required to reduce weight while pursuing performance. In this context, hollow structures have emerged. Commonly used hollow structures mainly include honeycomb sandwich structures, corrugated plate three-layer structures, grid hollow structures, four-layer plate hollow structures, pigeon egg hollow structures, hollow tube multilayer structures, hexagonal honeycomb structures, triangular honeycomb structures, and space lattice structures such as pyramids and tetrahedrons. Superplastic forming / diffusion bonding combines superplastic forming with diffusion bonding technology, which can accurately form hollow multilayer complex structures with complex shapes. In addition, due to the slow forming rate and high forming temperature, there is generally no rebound after forming, and it is convenient to realize the preparation of large-size integral structures. The design freedom is large, and the structure after forming is a thermal deformation structure with high and stable performance. It has been applied in the field of aerospace. At present, superplastic forming / diffusion bonding technology has made great progress, but SPF / DB technology still has certain defects in the degree of specialized production of components, the advancement of process equipment, the quality of formed parts, the forming stability, and product testing methods, which need to be further improved.

[0004] In the SPF / DB process of ultra-thin hollow multi-layer structure, due to the characteristics of multi-layer structure, there are many fillet areas in the parts, and the fillet area is usually the place where strain concentration is most significant. When the material passes through the fillet area of ​​the core plate, the local strain rate is significantly higher than that of the plane area, because the fillet part needs to be extended in multiple directions, and the geometric shape of the fillet makes the stress and strain concentrate in this area. During superplastic forming, the material needs to be stretched and expanded along the fillet, and due to the small radius of curvature, the strain distribution is uneven, resulting in excessive stretching of the material at the fillet, which eventually leads to thinning; secondly, due to the large change in curvature of the fillet area, the material is prone to excessive stretching during the forming process, especially in the superplastic forming process, it is impossible to effectively support the material like traditional cold working, so this excessive stretching leads to serious thinning of the material at the fillet; in the multi-layer structure, if the material thickness of the core plate and the fillet of the core plate is severely thinned, the strength and stiffness of the entire structure will be significantly reduced, especially in ultra-thin workpieces, this uneven thickness problem causes the local area to bear stress far higher than the design stress, forming a stress concentration point, and at the same time significantly reducing the tensile strength and bending stiffness of these areas. Therefore, solving the problem of excessive thinning of the core plate of the ultra-thin hollow multi-layer structure during the superplastic forming / diffusion bonding process is the key to superplastic forming / diffusion bonding technology. Summary of the invention

[0005] In order to solve the problem of excessive thinning of the core plate of an ultra-thin hollow multi-layer structure during superplastic forming / diffusion bonding, the present invention provides a surface pre-dispersed superplastic forming / diffusion bonding method.

[0006] The technical solution of the present invention:

[0007] The object of the present invention is to provide a surface pre-dispersed superplastic forming / diffusion bonding method, comprising:

[0008] Step 1: Grind the plate to make it smooth, remove the oil stains on the surface, pickle it to remove impurities on the plate, wash it with ethanol and blow it dry for later use;

[0009] Step 2: Take two plates processed in step 1 and place them on a core plate preforming mold for preforming to obtain a core plate;

[0010] Step 3: spraying an isolation agent on a certain area of ​​the core plate obtained in step 2, placing isolation ribs in the core plate sprayed with the isolation agent, and spot welding the upper and lower ends of the isolation ribs;

[0011] Step 4: placing the final forming die in a superplastic forming / diffusion bonding device, and heating the superplastic forming / diffusion bonding device to a process section temperature;

[0012] Step 5: Take two more plates processed in step 1 as panels, spray a release agent on a certain area of ​​the panels, and then place them in the final forming mold in the superplastic forming / diffusion bonding equipment that has reached the process section temperature;

[0013] Step 6: Heat up again, and after the final forming mold reaches the process section temperature, keep warm for a period of time, and blow air to perform superplastic forming on the panel;

[0014] Step 7: After the superplastic forming is completed, the panel is taken out and the release agent is cleaned and removed;

[0015] Step 8: placing the core board containing the isolation ribs in step 3 inside the panel obtained in step 7 to obtain a composite board;

[0016] Step 9: Place the combined sheet into the final forming mold in the furnace chamber of the superplastic forming / diffusion bonding equipment, keep warm for a period of time, and then blow air between the core sheet and the panel to make the core sheet expand;

[0017] Step 10: After the reverse expansion is completed, blow air inside the core board, maintain it for 1 hour after reaching a certain air pressure, then cool it with the furnace and take out the parts after cooling down.

[0018] It is further defined that the plate material in step 1 is titanium alloy.

[0019] It is further defined that the liquid used in the pickling process in step 1 is a mixed liquid composed of hydrofluoric acid, nitric acid and water in a volume ratio of 1:3:6.

[0020] It is further defined that the concentration of the hydrofluoric acid and the nitric acid are both 90%.

[0021] It is further defined that the pickling time in step 1 is 2 minutes.

[0022] It is further defined that the preforming in step 2 is performed at room temperature.

[0023] It is further defined that in the preforming process in step 2, a press is used to preform the sheet material, and the pressing speed of the press is 10 mm / min.

[0024] It is further defined that the area where the isolation agent is sprayed in step 3 is: except for the position where the isolation ribs are placed and the sealing position of the core plate, the isolation agent is sprayed on the remaining positions.

[0025] It is further defined that in step 3, the core plate forms a cavity, and the spot welding positions are located at both ends of the isolation ribs and outside the cavity.

[0026] It is further defined that the process section temperature in step 4 is 860-940°C.

[0027] It is further defined that the process section temperature in step 4 is 920°C.

[0028] It is further defined that the area where the release agent is sprayed in step 5 is sprayed only at the sealing position of the panel.

[0029] It is further defined that the holding time in step 6 is 10 minutes.

[0030] It is further defined that the air pressure in the blowing process in step 6 and step 9 is both set to 2 MPa, and is gradually increased at a speed of 0.1 MPa / min, and the pressure is maintained for 30 minutes after reaching 2 MPa.

[0031] It is further defined that the air pressure during blowing in step 10 is set to 2 MPa, and is gradually increased at a speed of 0.1 MPa / min, and the pressure is maintained for 1 hour after reaching 2 MPa.

[0032] The beneficial effects of the present invention are:

[0033] The present invention provides a mold surface pre-dispersed superplastic forming / diffusion bonding method, which can successfully realize the forming of ultra-thin hollow multi-layer structure parts, and the parts formed by this method do not have the problem of excessive thinning. Compared with the prior art, the present invention has the following advantages:

[0034] (1) The first stage of the method provided by the present invention is the "pre-dispersion" stage, that is, before the superplastic forming begins, the core plate is subjected to external force for pre-reverse bulging. During this process, the core plate material is formed into an initial shape through pre-bulging, which partially releases the stress concentration in the material and geometrically disperses the strain of the core plate in subsequent forming in advance.

[0035] (2) The second stage of the method provided by the present invention is the "positive expansion" stage. At this time, under the action of traditional positive superplastic forming pressure, the core plate and other layers complete the final forming process. Since the core plate has undergone plastic deformation once in the pre-dispersion stage, the stress is more evenly distributed in the positive expansion stage, thereby avoiding excessive deformation and thinning in local areas, especially high-strain areas such as fillets.

[0036] (3) The present invention makes the strain distribution of the core plate more uniform by pre-dispersion, especially effectively reduces local thinning in rounded corners and other stress concentration areas, greatly improves the uniformity of wall thickness in the multi-layer structure, and avoids the rupture of the part wall due to local excessive thinning. This has an important impact on the overall mechanical properties of the multi-layer structure, helps to improve the fatigue strength and structural stability of the parts, and realizes the preparation of high-quality ultra-thin parts.

[0037] (4) In the pre-dispersion stage of the present invention, the plastic deformation of the core plate is partially released under relatively low pressure, which effectively reduces the material damage caused by local stress concentration during the positive expansion process and reduces the local material failure problem caused by excessive strain rate. Through the deformation in the pre-expansion stage, the core plate avoids excessive stretching during the final forming, reduces the microcracks or material degradation problems caused by excessive deformation, and thus improves the overall forming quality.

[0038] (5) The present invention is suitable for multi-layer hollow ultra-thin structural parts with complex geometric shapes or multi-radius transitions. By pre-dispersion, the forming stress of the complex curved surface can be pre-distributed, so that the thickness and mechanical properties of these complex areas are more consistent. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of the core plate reverse expansion stage and superplastic forming stage in Example 1;

[0040] Figure 2 This is a schematic diagram of the individual forming of the panel in Example 1;

[0041] Figure 3 This is a schematic diagram of the spraying of the release agent on the panel of Example 1;

[0042] Figure 4 This is a schematic diagram of the core plate preforming process of Example 1;

[0043] Figure 5 This is a schematic diagram of the spraying of the core plate isolation agent in Example 1;

[0044] Figure 6 This is a digital photo of the four-layer structure part formed in Example 1;

[0045] Figure 7 This is a digital photo of the interior of the four-layer structure part formed in Example 1;

[0046] Figure 8 This is a digital photo of the four-layer structure part formed in Comparative Example 1;

[0047] Fig. 9 This is a comparison diagram of the buckling performance of parts formed in Example 1 and Comparative Example 1;

[0048] In the figure, 1-panel, 1-1-upper panel, 1-2-lower panel, 2-isolation ribs, 3-core plate, 4-upper die of the final forming die, 5-lower die of the final forming die, 6-core plate pre-forming die, 7-core plate pre-forming die. DETAILED DESCRIPTION

[0049] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0050] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0051] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, and methods used are conventional materials, reagents, and methods in the art, unless otherwise specified, and can be obtained by those skilled in the art through commercial channels.

[0052] Example 1

[0053] Step 1: Grind the sheet to be formed to remove oil stains on the surface. The sheet material is TA15 titanium alloy. During the grinding stage, the sheet should be smooth and free of obvious deformation. After grinding, pickle the sheet with a liquid containing hydrofluoric acid: nitric acid: water (volume ratio) of 1:3:6 for 2 minutes to remove impurities. After that, clean it with anhydrous ethanol and blow it dry for later use.

[0054] Step 2: Take two pieces of plate processed in step 1, place them on the core plate preforming die and the core plate preforming punch in sequence, operate the main cylinder of the press machine to press down at a speed of 10mm / min until the punch and die are completely closed, and then stop, completing the preforming to obtain the core plate. The preforming is carried out at room temperature. The schematic diagram of the core plate preforming process is shown in Figure 4 As shown;

[0055] Step 3: Spray the isolation agent on the preformed core board, and reserve the location for the isolation ribs without spraying the isolation agent (such as Figure 5 As shown), in addition, the sealing position of the core plate is not sprayed with an isolating agent, and the other positions are sprayed with an isolating agent. After the isolating agent is sprayed, an isolating rib is placed in the core plate, and the isolating rib is fixed by spot welding at the upper and lower ends. The spot welding position is located at both ends of the isolating rib and outside the cavity formed by the core plate, which does not affect the internal diffusion connection. The current during spot welding is 12500A and the power-on time is 0.25s.

[0056] Step 4: placing the final forming die in a superplastic forming / diffusion bonding device, and heating the superplastic forming / diffusion bonding device to a process section temperature, which is the optimal superplastic forming temperature (920°C) of TA15 titanium alloy;

[0057] Step 5: Take two more boards that have been processed in step 1 to use as panels. Figure 3 As shown in the figure, spray the isolation agent on the sealing position and place it in the mold in the furnace cavity that reaches the set temperature. Figure 2 As shown;

[0058] Step 6: When the panel is put into the furnace cavity in step 5, the temperature will drop because the furnace is opened, so it needs to be heated again. After the mold in the superplastic forming / diffusion bonding equipment reaches the set temperature (920℃), keep it warm for ten minutes, blow air for superplastic forming, and set the superplastic forming pressure to 2MPa, gradually increase it at a speed of 0.1MPa / min, and keep the pressure for 30min after reaching 2MPa;

[0059] Step 7: After the superplastic forming in step 6 is completed, the panel is taken out and the release agent on it is cleaned and removed;

[0060] Step 8: placing the core board processed in step 3 inside the panel cooled in step 7 to obtain a composite board;

[0061] Step 9: Put the assembled plates back into the mold in the furnace chamber of the superplastic forming / diffusion bonding equipment. After keeping it at 920℃ for 10 minutes, blow air between the core plate and the panel to make the core plate swell. The air pressure during blowing is 2MPa, and it is gradually increased at a speed of 0.1MPa / min. After reaching 2MPa, keep the pressure for 30 minutes.

[0062] Step 10: After the reverse expansion is completed, air is blown inside the core plate until it is finally formed. The air pressure during blowing is 2MPa, and it is gradually increased at a speed of 0.1MPa / min. After reaching 2MPa, the pressure is maintained for 1 hour. After forming, it is cooled with the furnace and the parts are taken out at a lower temperature.

[0063] The process diagram of steps 9 to 10 is as follows Figure 1 shown.

[0064] The ultra-thin hollow four-layer structure parts formed in this embodiment are as follows Figure 6 , 7 As shown in the figure, four layers means that the part is composed of two layers of face plates and two layers of core plates. The total thickness of the four-layer part is 1.3 to 2.0 m. This is because the thickness of the face plates and core plates will change during the forming process and is not a fixed value. As can be seen from the figure, the fillet area is not excessively thinned. Ultra-thin sheets themselves cannot undergo large plastic deformation and are very likely to be blown apart. However, under the pre-dispersion method of the mold surface, the core plate deforms evenly, the fillet area is not excessively thinned, and the multi-layer structure parts have excellent performance.

[0065] Comparative Example 1

[0066] Step 1: Grind the sheet to be formed to remove oil stains on the surface. The sheet material is TA15 titanium alloy. During the grinding stage, the sheet should be smooth and free of obvious deformation. After grinding, pickle the sheet with a liquid containing hydrofluoric acid: nitric acid: water (volume ratio) of 1:3:6 for 2 minutes to remove impurities. After that, clean it with anhydrous ethanol and blow it dry for later use.

[0067] Step 2: Take two plates processed in step 1 as core plates, analyze the stress of the core plates during superplastic forming and arrange the corresponding rib shapes according to the shape of the formed parts, do not spray the isolation agent on the rib parts, and spray the isolation agent on the remaining parts;

[0068] Step 3: Take two more plates processed in step 1 as panels, and cover them on the core plate from the upper and lower sides respectively. Arrange the four plates neatly and then seal and weld the air pipes;

[0069] Step 4: Put the sealed four-layer plate into water and blow air to check the air tightness;

[0070] Step 5: After the air tightness check is correct, the welded four-layer plate is placed in the forming mold, the mold is placed in the superplastic forming / diffusion bonding equipment, and the superplastic forming / diffusion bonding equipment is heated to the process section temperature, which is the optimal superplastic forming temperature of TA15 (920℃);

[0071] Step 6: After the mold in the superplastic forming / diffusion bonding equipment reaches the set temperature of 920°C, keep the temperature for ten minutes, ventilate the upper and lower panels and the core plate for superplastic forming, and set the superplastic forming pressure to 2MPa, gradually increase it at a rate of 0.1MPa / min, and maintain the pressure for 30 minutes after reaching 2MPa;

[0072] Step 7: Ventilate between the core plates, set the superplastic forming pressure to 2MPa, gradually increase at a rate of 0.1MPa / min, and maintain the pressure for 1h after reaching 2MPa;

[0073] Step 8: After the pressure holding is completed, cool down with the furnace and take out the parts at a lower temperature.

[0074] The ultra-thin hollow four-layer structure parts formed in this comparative example are as follows Figure 8 As shown in the figure, the total thickness of the four-layer part is 1.3-2.0 mm. This is because the thickness of the face plate and the core plate will change during the forming process and is not a constant value. As can be seen from the figure, there is excessive thinning in the fillet area.

[0075] The buckling performance curves of the parts formed in Example 1 and Comparative Example 1 are as follows: Fig. 9As shown, it can be seen that with the continuous increase of the compressive strain, the stress on the two parts continues to increase. The part prepared in comparative example 1 begins to gradually become unstable at 75MPa, while the part prepared in example 1 reaches the instability strength at 78Mpa, and then the structure is gradually destroyed. When the strain reaches about 20%, the structure is basically completely destroyed, and the subsequent destructive strength of the part prepared in example 1 is greatly enhanced compared with that of the part prepared in comparative example 1, indicating that the part prepared in example 1 using the reverse expansion technology has a better ability to resist destruction than the parts prepared without the reverse expansion technology.

[0076] Although the present invention has been disclosed as above in the preferred embodiment, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for pre-dispersed superplastic forming / diffusion bonding of a mold surface, characterized in that: include: Step 1: Grind the plate to make it smooth, remove the oil stains on the surface, pickle it to remove impurities on the plate, wash it with ethanol and blow it dry for later use; Step 2: Take two plates processed in step 1 and place them on a core plate preforming mold for preforming to obtain a core plate; Step 3: spraying an isolation agent on a certain area of ​​the core plate obtained in step 2, placing isolation ribs in the core plate sprayed with the isolation agent, and spot welding the two ends of the isolation ribs; Step 4: placing the final forming die in a superplastic forming / diffusion bonding device, and heating the superplastic forming / diffusion bonding device to a process section temperature; Step 5: Take two more plates processed in step 1 as panels, spray a release agent on a certain area of ​​the panels, and then place them in the final forming mold in the superplastic forming / diffusion bonding equipment that has reached the process section temperature; Step 6: Heat up again, and after the final forming mold reaches the process section temperature, keep warm for a period of time, and blow air for superplastic forming; Step 7: After the superplastic forming is completed, the panel is taken out and the release agent is cleaned and removed; Step 8: placing the core board containing the isolation ribs in step 3 inside the panel obtained in step 7 to obtain a composite board; Step 9: Place the combined sheet into the final forming mold in the furnace chamber of the superplastic forming / diffusion bonding equipment, keep warm for a period of time, and then blow air between the core sheet and the panel to make the core sheet expand; Step 10: After the reverse expansion is completed, blow air inside the core board, maintain it for 1 hour after reaching a certain air pressure, then cool it with the furnace and take out the parts after cooling down.

2. A method for pre-dispersed superplastic forming / diffusion bonding of molded surfaces according to claim 1, characterized in that: In step 1, the plate material is titanium alloy; The liquid used for pickling in step 1 is a mixed liquid consisting of hydrofluoric acid, nitric acid and water in a volume ratio of 1:3:6, and the concentrations of hydrofluoric acid and nitric acid are both 90%; The pickling time in step 1 is 2 minutes.

3. A method for pre-dispersed superplastic forming / diffusion bonding of molded surfaces according to claim 1, characterized in that: The preforming in step 2 is carried out at room temperature; In the preforming process in step 2, a press is used to preform the sheet material, and the pressing speed of the press is 10 mm / min.

4. A method for pre-dispersed superplastic forming / diffusion bonding of molded surfaces according to claim 1, characterized in that: The area where the isolation agent is sprayed in step 3 is: except for the position where the isolation ribs are placed and the sealing position of the core plate, the isolation agent is sprayed on the remaining positions; In step 3, the core plate forms a cavity, and the spot welding positions are located at both ends of the isolation ribs and outside the cavity.

5. A method for pre-dispersed superplastic forming / diffusion bonding of molded surfaces according to claim 1, characterized in that: The process section temperature in step 4 is 860-940°C.

6. A method for pre-dispersed superplastic forming diffusion / dispersion connection of a mold surface according to claim 1, characterized in that: The process section temperature in step 4 is 920°C.

7. A method for pre-dispersed superplastic forming diffusion / dispersion connection of a mold surface according to claim 1, characterized in that: The area where the release agent is sprayed in step 5 is sprayed only on the sealing position of the panel.

8. A method for pre-dispersed superplastic forming / diffusion bonding of molded surfaces according to claim 1, characterized in that: The holding time in step 6 is 10 min.

9. A method for pre-dispersed superplastic forming / diffusion bonding of molded surfaces according to claim 1, characterized in that: The air pressure in the blowing process in step 6 and step 9 was set to 2 MPa, and was gradually increased at a speed of 0.1 MPa / min. After reaching 2 MPa, the pressure was maintained for 30 minutes.

10. A method for pre-dispersed superplastic forming / diffusion bonding of molded surfaces according to claim 1, characterized in that: The air pressure during blowing in step 10 is set to 2 MPa, and is gradually increased at a speed of 0.1 MPa / min. After reaching 2 MPa, the pressure is maintained for 1 hour.

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