A method of profile pre-dispersion superplastic forming / diffusion bonding

Abstract

The application discloses a kind of profile pre-dispersion superplastic forming / diffusion connection method, belong to superplastic forming field.The present application solves the uneven wall thickness problem caused by excessive deformation of core plate when forming ultra-thin hollow multilayer structure by existing superplastic forming / diffusion connection method.The present application makes the core plate first undergo a large plastic deformation by the method of pre-expansion, releases the stress concentration in the material, then makes the protruding part undergo plastic deformation by positive expansion, because the core plate has undergone plastic deformation in the reverse expansion stage, the stress is more evenly distributed in the positive expansion stage, thereby avoiding the phenomenon of excessive deformation and thinning in local area, especially in high strain parts such as fillet, greatly improving the uniformity of wall thickness.The method provided by the present application includes the following steps:(1) core plate preforming and welding isolation rib;(2) panel forming;(3) core plate and panel combination;(4) core plate reverse expansion;(5) core plate superplastic forming.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of superplastic forming, and particularly relates to a type face pre-dispersion superplastic forming / diffusion bonding method. BACKGROUND

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

[0003] With the development of aerospace technology, materials are constantly required to reduce weight while pursuing performance, and 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 multi-layer structures, hexagonal honeycomb structures, triangular honeycomb structures, and spatial lattice structures such as pyramids and tetrahedrons. Superplastic forming / diffusion bonding is a combination of superplastic forming and diffusion bonding technology, which can accurately form hollow multi-layer complex structures with complex shapes. In addition, due to the slow forming rate and high forming temperature, no springback is generally generated after forming, and large-size integral structures can be easily prepared, with high design freedom. The microstructure after forming is a hot deformed structure, which has high and stable performance, and has been applied in the aerospace field. At present, superplastic forming / diffusion bonding technology has made great progress, but there are still some defects in the specialization of SPF / DB technology in the production of components, the advancement of process equipment, the quality of formed parts, the stability of forming, and product detection methods, which need to be further improved.

[0004] In the SPF / DB process of the ultra-thin hollow multi-layer structure, due to the characteristics of the multi-layer structure, there are many fillet regions in the part, and the fillet region is usually the most significant place of strain concentration. When the material passes through the fillet region of the core plate, the local strain rate is obviously higher than that of the flat region, because the fillet part needs to be stretched in multiple directions, and the geometry of the fillet causes stress and strain to concentrate in this area. During superplastic forming, the material needs to be stretched and expanded along the fillet, and due to the small curvature radius, the strain distribution is uneven, which causes the material to be over-stretched at the fillet, and finally leads to thinning; secondly, due to the large change in curvature of the fillet region, the material is prone to over-stretching during the forming process, especially during superplastic forming, which cannot effectively support the material like traditional cold working, so this over-stretching leads to serious thinning of the material at the fillet; in a multi-layer structure, if the material thickness of the core plate and the fillet of the core plate is seriously 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 much 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 superplastic forming / diffusion bonding is the key to superplastic forming / diffusion bonding technology. SUMMARY

[0005] The present application is to solve the problem of excessive thinning of the core plate of the ultra-thin hollow multi-layer structure during superplastic forming / diffusion bonding, and provides a profile pre-dispersion superplastic forming / diffusion bonding method.

[0006] The technical scheme of the present application is:

[0007] The object of the present application is to provide a profile pre-dispersion superplastic forming / diffusion bonding method, comprising:

[0008] Step 1: polish the plate flat, remove surface dirt, acid wash to remove impurities on the plate, wash with ethanol and dry for standby;

[0009] Step 2: take two plates treated in step 1 and place them on the core plate preforming mold to perform preforming to obtain a core plate;

[0010] Step 3: spray release agent on the core plate obtained in step 2 in a certain area, place a release bar in the core plate sprayed with release agent, and spot weld at the upper and lower ends of the release bar;

[0011] Step 4: place the final forming mold in the superplastic forming / diffusion bonding equipment, and heat the superplastic forming / diffusion bonding equipment to the process section temperature;

[0012] Step 5: Another two plates treated in step 1 are used as face plates, and the isolating agent is sprayed on a certain area of the face plates, and then the face plates are placed in the final forming die of the superplastic forming / diffusion bonding equipment which has reached the process section temperature;

[0013] Step 6: The temperature is raised again, and after the final forming die reaches the process section temperature, the superplastic forming of the face plates is carried out by blowing air;

[0014] Step 7: After the superplastic forming is completed, the face plates are taken out, and the isolating agent is cleaned and removed;

[0015] Step 8: The core plate containing the isolating ribs in step 3 is placed inside the face plate obtained in step 7 to obtain a combined plate;

[0016] Step 9: The combined plate is placed in the final forming die in the furnace cavity of the superplastic forming / diffusion bonding equipment, and after a period of temperature holding, air is blown between the core plate and the face plate to make the core plate bulge;

[0017] Step 10: After the bulging is completed, air is blown inside the core plate, and after a certain air pressure is reached, the temperature is maintained for 1 hour, and then the temperature is cooled down and the product is taken out.

[0018] Further limitation, the plate material in step 1 is titanium alloy.

[0019] Further limitation, 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] Further limitation, the concentration of hydrofluoric acid and nitric acid is 90%.

[0021] Further limitation, the pickling time in step 1 is 2 minutes.

[0022] Further limitation, the preforming in step 2 is carried out at room temperature.

[0023] Further limitation, the preforming process in step 2 uses a press to preform the plate, and the pressing speed of the press is 10 mm / min.

[0024] Further limitation, the area sprayed with the isolating agent in step 3 is: the isolating agent is not sprayed on the position where the isolating rib is placed and the sealing position of the core plate, and the isolating agent is sprayed on the remaining positions.

[0025] Further limitation, the core plate in step 3 forms a cavity, and the position of spot welding is located at both ends of the isolating rib and outside the cavity.

[0026] Further limitation, the process section temperature in step 4 is 860-940℃.

[0027] Further limitation, the process section temperature in step 4 is 920℃.

[0028] Further limit, the area of spraying the release agent in step 5 is only the sealing position of the panel.

[0029] Further limit, the holding time in step 6 is 10 min.

[0030] Further limit, the air pressure of the blowing process in step 6 and step 9 is both set as 2 MPa, and both gradually increase at a speed of 0.1 MPa / min, and both keep pressure for 30 min after reaching 2 MPa.

[0031] Further limit, the air pressure of the blowing process in step 10 is set as 2 MPa, and gradually increases at a speed of 0.1 MPa / min, and keeps pressure for 1 h after reaching 2 MPa.

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

[0033] The present application provides a profile pre-dispersion superplastic forming / diffusion bonding method, which can successfully realize the forming of ultra-thin hollow multi-layer structure parts, and the parts formed by the method do not have the problem of excessive thinning.

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

[0035] (2) The second stage of the method provided by the present application is the "positive bulging" stage. At this time, under the action of the traditional positive superplastic forming pressure, the core plate and other layers complete the final forming process together. Since the core plate has been plastically deformed once in the pre-dispersion stage, the stress is more uniformly distributed in the positive bulging stage, thereby avoiding excessive deformation and thinning in local areas, especially in the high-strain parts such as round corners.

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

[0037] (4) The present application partially releases the plastic deformation of the core plate at a lower pressure in the pre-dispersion stage, effectively reducing material damage caused by local stress concentration during the positive expansion process, reducing the problem of local material failure caused by excessive strain rate, avoiding excessive stretching of the core plate during final forming by deformation in the pre-expansion stage, reducing the problem of micro-cracks or material degradation caused by excessive deformation, thereby improving the overall quality of the forming.

[0038] (5) The present application is suitable for multi-layer hollow ultra-thin structural parts with complex geometric shapes or multi-rounded transitions. Through pre-dispersion, the forming stress of complex surfaces can be pre-distributed, making the thickness and mechanical properties of these complex regions more uniform. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 Figure 1 is a schematic diagram of the core plate reverse expansion stage and superplastic forming stage of Example 1;

[0040] Figure 2 Figure 1 is a schematic diagram of the core plate reverse expansion stage and superplastic forming stage of Example 1;

[0041] Figure 3 Figure 1 is a schematic diagram of the core plate reverse expansion stage and superplastic forming stage of Example 1;

[0042] Figure 4 Figure 1 is a schematic diagram of the core plate reverse expansion stage and superplastic forming stage of Example 1;

[0043] Figure 5 Figure 1 is a schematic diagram of the core plate reverse expansion stage and superplastic forming stage of Example 1;

[0044] Figure 6 Figure 1 is a schematic diagram of the core plate reverse expansion stage and superplastic forming stage of Example 1;

[0045] Figure 7 Figure 1 is a schematic diagram of the core plate reverse expansion stage and superplastic forming stage of Example 1;

[0046] Figure 8 Figure 1 is a schematic diagram of the core plate reverse expansion stage and superplastic forming stage of Example 1;

[0047] Figure 9 Figure 1 is a schematic diagram of the core plate reverse expansion stage and superplastic forming stage of Example 1;

[0048] Figure 1 is a schematic diagram of the core plate reverse expansion stage and superplastic forming stage of Example 1; DETAILED DESCRIPTION

[0049] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without the specific details set forth in this description. In other instances, well-known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present application.

[0050] Second, the "one embodiment" or "an embodiment" as used herein means a specific implementation, or a specific feature, structure, or characteristic within at least one implementation of the application. The various embodiments presented in this description are not necessarily mutually exclusive, and can be combined in any suitable manner. The terms "in one embodiment" and "in another embodiment" are not necessarily referring to the same embodiment.

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

[0052] Example 1

[0053] Step 1: The plate to be shaped is polished flat, and the surface oil is removed. The plate material is TA15 titanium alloy. The polishing stage ensures that the plate is smooth and has no obvious deformation. After polishing, the plate is pickled in a combined liquid with a composition of hydrofluoric acid: nitric acid: water (volume ratio) of 1:3:6 for 2 minutes to remove impurities. After completion, the plate is cleaned with anhydrous ethanol and dried for standby use.

[0054] Step 2: Take two plates treated in Step 1 and place them on the core plate preforming concave mold and core plate preforming convex mold in turn. Operate the main cylinder of the press at a speed of 10 mm / min to stop when the convex mold and concave mold are completely closed. Complete the preforming to obtain the core plate. The preforming is carried out at room temperature. The core plate preforming process is shown in Figure 4 .

[0055] Step 3: Spray the preformed core plate with release agent. The position where the release bar is placed is reserved and not sprayed with release agent (as shown in Figure 5 ). In addition, the sealing position of the core plate is not sprayed with release agent, and the rest of the position is sprayed with release agent. Place the release bar in the core plate after spraying the release agent, and spot weld the upper and lower ends to fix the release bar. The spot welding position is located at the two ends of the release bar 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: Place the final forming mold in the superplastic forming / diffusion bonding equipment, and heat the superplastic forming / diffusion bonding equipment to the process section temperature, which is the optimal superplastic forming temperature (920℃) of TA15 titanium alloy.

[0057] Step 5: Take another two plates treated in Step 1 as face plates, spray release agent in sealing position as shown in Figure 3 , and place the mold in the furnace cavity to reach the set temperature, as shown in Figure 2 ;

[0058] Step 6: When the face plates are placed in the furnace cavity in Step 5, the temperature will decrease because the furnace is opened, so the temperature is increased again. After the mold in the superplastic forming / diffusion bonding device reaches the set temperature (920°C), it is kept for 10 minutes, and then superplastic forming is performed by blowing air at a pressure of 2 MPa, which is gradually increased at a rate of 0.1 MPa / min, and kept for 30 min after reaching 2 MPa.

[0059] Step 7: After the superplastic forming in Step 6 is completed, the face plates are taken out and cleaned to remove the release agent thereon.

[0060] Step 8: Place the core plate treated in Step 3 inside the face plate after it is cooled in Step 7 to obtain a combined plate.

[0061] Step 9: Place the combined plate into the mold in the furnace cavity of the superplastic forming / diffusion bonding device, keep it at 920°C for 10 min, and then blow air between the core plate and the face plate to make the core plate bulge, with a pressure of 2 MPa, which is gradually increased at a rate of 0.1 MPa / min, and kept for 30 min after reaching 2 MPa.

[0062] Step 10: After the bulging is completed, blow air inside the core plate until the final forming is completed, with a pressure of 2 MPa, which is gradually increased at a rate of 0.1 MPa / min, and kept for 1 h after reaching 2 MPa. After forming, the plate is cooled with the furnace and taken out after cooling.

[0063] The process of Steps 9-10 is shown in Figure 1 .

[0064] The super-thin hollow four-layer structure part formed in this embodiment is shown in Figure 6 , 7 , which is composed of two face plates and two core plates, and the total thickness of the four-layer part is 1.3-2.0 m, because the thickness of each part changes during forming and is not a fixed value. As can be seen from the figure, the corner area is not excessively thinned. The super-thin plate itself cannot be deformed plastically, and it is very likely to be blown out, but under the typeface pre-dispersion method, the core plate deforms uniformly, and the corner area is not excessively thinned, so the multi-layer structure part has excellent performance.

[0065] Comparative Example 1

[0066] Step 1: polish the plate to be shaped flat, remove surface oil, the plate material is TA15 titanium alloy, the plate polishing stage should ensure that the plate is smooth and has no obvious deformation, after polishing, use a combined liquid with a composition of hydrofluoric acid: nitric acid: water (volume ratio) of 1:3:6 to pickle the plate for 2 min to remove impurities, then clean with anhydrous ethanol and dry for standby;

[0067] Step 2: take two plates treated in step 1 as core plates, according to the shape that the shaped part should have, analyze the stress condition of the core plate during superplastic forming and arrange the corresponding rib shape, do not spray release agent at the rib position, and spray release agent at the rest position;

[0068] Step 3: take another two plates treated in step 1 as face plates, cover them on the core plates from the upper and lower sides respectively, and then arrange the four plates in order and perform tube sealing welding;

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

[0070] Step 5: after the air tightness check is correct, place the four-layer plate after welding into the forming mold, place the mold in the superplastic forming / diffusion bonding equipment, and heat the superplastic forming / diffusion bonding equipment 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 920℃, keep warm for ten minutes, and blow air between the upper and lower face plates and the core plate to perform superplastic forming, the superplastic forming pressure is set to 2MPa, and the pressure is gradually increased at a speed of 0.1MPa / min, and after reaching 2MPa, keep pressure for 30min;

[0072] Step 7: blow air between the core plates, the superplastic forming pressure is set to 2MPa, and the pressure is gradually increased at a speed of 0.1MPa / min, and after reaching 2MPa, keep pressure for 1h;

[0073] Step 8: after the pressure keeping is finished, cool down with the furnace and take out the part.

[0074] The super-thin hollow four-layer structure part shaped by the comparative example is shown in Figure 8 The total thickness of the four-layer part is 1.3-2.0mm, because the thickness of each part will change during the forming process of the face plate and the core plate, and is not a fixed value. As can be seen from the figure, there is an excessive thinning phenomenon in the round corner area.

[0075] The buckling performance curve of the part shaped by example 1 and comparative example 1 is shown in Figure 9As shown, it can be seen that with the continuous increase of compressive strain, the stress of the two parts increases continuously, the part prepared by Comparative Example 1 starts to gradually lose stability at 75 MPa, while the part prepared by Example 1 reaches the instability strength at 78 MPa, and then the structure is gradually destroyed, and the structure is basically completely destroyed at about 20% of the strain, while the subsequent destruction strength of the part prepared by Example 1 is greatly enhanced compared with the part prepared by Comparative Example 1, which indicates that the anti-destruction ability of the part prepared by Example 1 using the reverse expansion technology is greatly enhanced compared with the part prepared without using the reverse expansion technology.

[0076] Although the present application has been disclosed in the preferred embodiments as above, it is not intended to limit the present application, and any person skilled in the art can make various modifications and modifications without departing from the spirit and scope of the present application, and therefore the protection scope of the present application should be defined by the claims.

Claims

1. A net shape pre-dispersion superplastic forming / diffusion bonding method, characterized by, The application relates to a method for manufacturing a titanium alloy composite plate. Step 1: polishing the plate to be flat, removing surface oil stains, pickling to remove impurities on the plate, washing with ethanol and drying for standby; Step 2: placing two plates treated in step 1 on a core plate preforming mold to perform preforming and obtain a core plate; Step 3: spraying isolating agent on a certain area of the core plate obtained in step 2, placing an isolating rib in the core plate sprayed with the isolating agent, and spot welding at both ends of the isolating rib; Step 4: placing a final forming mold in a superplastic forming / diffusion bonding device, and heating the superplastic forming / diffusion bonding device to a process section temperature; Step 5: taking another two plates treated in step 1 as face plates, spraying isolating agent on a certain area of the face plates, and then placing the face plates in the final forming mold in the superplastic forming / diffusion bonding device heated to the process section temperature; Step 6: re-heating, after the final forming mold reaches the process section temperature, keeping warm for a period of time, and blowing air to perform superplastic forming; Step 7: taking out the face plates after the superplastic forming is completed, and cleaning and removing the isolating agent; Step 8: placing the core plate with the isolating rib in step 3 into the face plates obtained in step 7 to obtain a composite plate; Step 9: placing the composite plate into the final forming mold in a furnace cavity of the superplastic forming / diffusion bonding device, keeping warm for a period of time, and blowing air between the core plate and the face plate to make the core plate reverse expand; Step 10: blowing air in the core plate after the reverse expansion is completed, keeping for 1 h after a certain air pressure is reached, and then cooling with the furnace and taking out the product; The certain area sprayed with the isolating agent in step 3 is that the isolating agent is not sprayed on the positions where the isolating rib is placed and the core plate is sealed, and the isolating agent is sprayed on the rest positions; The certain area sprayed with the isolating agent in step 5 is that the isolating agent is only sprayed on the sealing position of the face plate.

2. A method of profiled pre-dispersed superplastic forming / diffusion bonding according to claim 1, characterised in that, The plate material in step 1 is titanium alloy; The pickling liquid in step 1 is a mixed liquid composed of hydrofluoric acid, nitric acid and water in a volume ratio of 1:3:6, and the concentration of the hydrofluoric acid and the nitric acid is 90%; The pickling time in step 1 is 2 min.

3. A method of profiled pre-dispersed superplastic forming / diffusion bonding according to claim 1, wherein The preforming in step 2 is performed at room temperature. The preforming process in step 2 uses a press to preform the plate, and the press pressing speed is 10 mm / min.

4. A method of profiled pre-dispersed superplastic forming / diffusion bonding according to claim 1, wherein The core plate in step 3 forms a cavity, and the spot welding position is located at both ends of the isolating rib and outside the cavity.

5. A method of profiled pre-dispersed superplastic forming / diffusion bonding according to claim 1, wherein The process section temperature in step 4 is 860-940 DEG C.

6. A method of profiled pre-dispersed superplastic forming / diffusion bonding according to claim 1, wherein The process section temperature in step 4 is 920 DEG C.

7. A method of profiled pre-dispersed superplastic forming / diffusion bonding according to claim 1, wherein The keeping warm time in step 6 is 10 min.

8. A method of profiled pre-dispersed superplastic forming / diffusion bonding according to claim 1, wherein The air pressure in the blowing process in steps 6 and 9 is set to 2 MPa, is gradually increased at a speed of 0.1 MPa / min, is kept for 30 min after reaching 2 MPa.

9. A method of profiled pre-dispersed superplastic forming / diffusion bonding according to claim 1, wherein The air pressure in the blowing process in step 10 is set to 2 MPa, is gradually increased at a speed of 0.1 MPa / min, and is kept for 1 h after reaching 2 MPa.

Images