A high-precision control method for pre-forming bulging of a large-size welded blank with a high diameter-thickness ratio

Abstract

This application relates to the field of integral manufacturing of large space tanks, and specifically discloses a high-precision control method for preforming bulging of large-size welded plates with a high diameter-to-thickness ratio, including: using a first set of molds to perform multiple pressing processes on the entire surface of the sheet metal; using a second set of molds to perform multiple pressing processes on the entire surface of the sheet metal; both the first set of molds and the second set of molds correspond to the same opening diameter, and the opening diameter is 800-1000 mm; the radius of curvature corresponding to the first set of molds is greater than the radius of curvature corresponding to the second set of molds, and the radius of curvature corresponding to both the first set of molds and the second set of molds is determined by the opening diameter and the chord height difference H, where H = δ + (60-80) mm, and δ is the thickness of the sheet metal. The solution of this application realizes precise trajectory control of point control with small pressure in multiple passes, reduces the frequency of mold replacement, achieves a forming accuracy control within 1.5 mm, and improves the bulging forming accuracy of large-size welded plate structural parts with a high diameter-to-thickness ratio.

Description

Technical Field

[0001] The present application relates to the technical field of integral manufacturing of large aerospace storage tanks, and particularly to a high-precision control method for pre-forming bulging of large-size high-diameter-to-thickness ratio welded plates. Background Art

[0002] The storage tank is a core component of the rocket body structure of a launch vehicle, and its volume accounts for about two-thirds of the entire rocket. The storage tank is both a structural component and a functional component, with a harsh working environment and very strict manufacturing quality requirements. For many years, due to the limitations of domestic basic industrial conditions and the forming equipment capabilities, in the absence of large-width plates, large-tonnage and large-specification forming equipment, the manufacturing scheme for the bottom of the storage tank of the existing launch vehicles is welding. Since the number of parts is relatively large and the manufacturing process of a single part is complex, with the development of space technology, international market competition, and the urgent need for high-density launches of models, many problems and inadaptabilities have emerged in the current bottom manufacturing process.

[0003] The core components of the rocket with the largest launch capacity in China and the next-generation heavy launch vehicle to be key developed both contain cryogenic storage tanks with a diameter of 5 meters. However, due to the limitations of process equipment, the bottom of the 5-meter diameter storage tank all adopts a top cover + segmented spherical shell welded structure. On the one hand, the domestic spinning forming technology started relatively late, and the spinning forming technology for the bottom of the 5-meter diameter storage tank is still blank in China. On the other hand, due to the limitations of domestic sheet metal processing capabilities, it is currently difficult to purchase ultra-large size plates. Therefore, the raw materials for the bottom of the 5-meter diameter storage tank need to be formed by welding, and then bulging and spinning forming processes are carried out. Due to defects such as low strength of the welded joint and porosity in the weld zone, stress concentration is likely to occur, resulting in weld cracks. Currently, there is still a blank in the high-precision bulging forming of large-size welded plate structures in China. Summary of the Invention

[0004] The present application provides a high-precision control method for pre-forming bulging of large-size high-diameter-to-thickness ratio welded plates, which performs point control of precise trajectory control forming with small pressure in multiple passes, reduces the frequency of die replacement, and finally realizes that the forming accuracy is controlled within 1.5 mm, greatly improving the bulging forming accuracy of large-size high-diameter-to-thickness ratio welded plate structural parts.

[0005] In a first aspect, a bulging pre-forming method is provided, characterized by comprising:

[0006] Using a first set of dies to perform multiple pressing processes on the entire surface of the sheet metal;

[0007] Using a second set of dies to perform multiple pressing processes on the entire surface of the sheet metal;

[0008] Both the first set of dies and the second set of dies correspond to the same opening diameter, and the opening diameter is 800 - 1000 mm;

[0009] The radius of curvature corresponding to the first set of dies is greater than the radius of curvature corresponding to the second set of dies. The radii of curvature corresponding to the first set of dies and the second set of dies are both determined by the opening diameter and the chord height difference H. The chord height difference H is the height difference from the center of the bottom surface of the female die to the center of the opening of the female die, and the chord height difference H satisfies: H = δ + (60 - 80) mm, where δ is the thickness of the sheet metal.

[0010] Compared with the prior art, the solution provided by this application at least includes the following beneficial technical effects:

[0011] The above-mentioned dies can achieve a gradual change in curvature and achieve precise surface control and point control of large components of tailor-welded blanks, solve the problem of stress concentration at the mutation point, solve the problems such as poor accuracy in the spinning tail top area and poor forming rigidity and easy backflipping, and lay a foundation for the high-precision forming of the integral spinning of the bottom of a large storage tank.

[0012] Combined with the first aspect, in some implementation manners of the first aspect, the radii of curvature corresponding to the first set of dies and the second set of dies satisfy any one of the following:

[0013] The radius of curvature corresponding to the first set of dies is 2500 mm, and the radius of curvature corresponding to the second set of dies is 1900 mm;

[0014] The radius of curvature corresponding to the first set of dies is 1900 mm, and the radius of curvature corresponding to the second set of dies is 1500 mm;

[0015] The radius of curvature corresponding to the first set of dies is 1500 mm, and the radius of curvature corresponding to the second set of dies is 1250 mm.

[0016] The transition amount of the radius of curvature between different dies can be different, which is beneficial to realizing a smooth transition of the bulging forming process.

[0017] Combined with the first aspect, in some implementation manners of the first aspect, the process of performing multiple pressing processes on the entire surface of the sheet metal includes:

[0018] Adjust the position of the sheet metal in the die so that the center mark of the sheet metal is aligned with the center of the die, and perform pre-pressing at the center mark of the sheet metal.

[0019] Taking the center mark of the sheet metal as the center, perform circumferential pressing on the sheet metal, including:

[0020] Feed axially N pre-pressing step lengths from the center mark. After each feed of the pre-pressing step length, perform circumferential pressing along the circle with the center mark as the center and the feed position as the radius until the entire surface of the sheet metal is pressed.

[0021] Precision trajectory control forming is carried out in multiple passes to reduce the frequency of die replacement. Finally, the forming accuracy is controlled within 1.5 mm, greatly improving the bulging forming accuracy of large-sized tailor-welded plates with a high diameter-thickness ratio.

[0022] Combined with the first aspect, in some implementation manners of the first aspect, the multiple pressing processes include multiple full-surface pressing operations, and the pre-pressure of the multiple pressing processes satisfies at least one of the following:

[0023] The pre-pressure of the first full-surface pressing is 2 - 3 Mpa;

[0024] The pre-pressure of the second full-surface pressing is 3.5 - 5 Mpa;

[0025] The pre-pressure increment between two adjacent full-surface pressings is 2 Mpa.

[0026] The reasonable increase in pre-pressure is beneficial to achieving uniform forming of the sheet metal with a relatively small number of full-surface pressing times, and avoiding process problems such as weld defects.

[0027] Combined with the first aspect, in some implementation manners of the first aspect, during the circumferential pressing process, the distance L between two adjacent hammers is 1 / 3 - 1 / 2 of the die opening radius.

[0028] The reasonable drop hammer spacing is beneficial to achieving uniform forming of the sheet metal with a relatively small number of drop hammer times, and avoiding process problems such as weld defects.

[0029] Combined with the first aspect, in some implementation manners of the first aspect, the pre-pressing step size is 300 - 500 mm.

[0030] The reasonable drop hammer feed is beneficial to achieving uniform forming of the sheet metal with a relatively small number of drop hammer times, and avoiding process problems such as weld defects.

[0031] Combined with the first aspect, in some implementation manners of the first aspect, the multiple pressing processes include multiple full-surface pressing operations, and the initial pressurization directions of two adjacent full-surface pressing operations differ by 90°.

[0032] The initial pressurization directions of two adjacent full-surface pressing operations differ by 90°, which is beneficial to improving the processing uniformity.

[0033] Combined with the first aspect, in some implementation manners of the first aspect, the method further includes:

[0034] Performing circumferential spot pressing and trimming with the first mutation point as the center;

[0035] Performing axial trimming on the first mutation point.

[0036] Precision trajectory control forming is carried out with a small pressure, achieving a forming accuracy control within 1.5 mm, which greatly improves the bulging forming accuracy of large-size welded blanks with a high diameter-thickness ratio structural parts.

[0037] Combined with the first aspect, in some implementation manners of the first aspect, the circumferential point pressing trimming satisfies:

[0038] The distance between the trimming position and the first mutation point is 400 - 600 mm;

[0039] The pre-pressure of the circumferential point pressing trimming is 1 - 2 Mpa;

[0040] The distance between two adjacent hammers is 150 - 250 mm.

[0041] The parameter setting of the small pressure point control forming is reasonable, which is beneficial to optimizing the process and improving the sheet metal forming quality.

[0042] Combined with the first aspect, in some implementation manners of the first aspect, the axial direction is the connection line between the newly generated second mutation point and the first mutation point after the circumferential point pressing trimming.

[0043] Formulate the trimming trajectory to axially release the stress, and the mutation point can be pushed out towards the edge of the sheet metal. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of the welding process of the bottom of the storage tank.

[0045] Figure 2 It is a schematic diagram of the bulging forming structure.

[0046] Figure 3 It is a schematic diagram of the bulging forming structure

[0047] Figure 4 It is a schematic diagram of the drop hammer position.

[0048] Figure 5 It is a schematic diagram of the local mutation point trimming method.

[0049] Figure 6 It is an enlarged view of the mutation point. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0050] The present application will be further described in detail below with reference to the drawings and specific embodiments.

[0051] When bulging forming an industrial head for a pressure vessel, large pressure and multiple dies are generally used for forming. During forming, pressure is applied to the entire surface for forming, and the forming surface is not easy to accurately control, and the forming accuracy is relatively low, which cannot meet the high-precision forming requirements. During the forming process, it is necessary to replace the dies multiple times to form the required profile, greatly increasing the production cost and labor cost.

[0052] However, for the high-precision requirements of the 5-meter large-size storage tank structural parts of launch vehicles, the traditional manufacturing methods are far from meeting the needs. Large-size structural parts are prone to distortion and deformation during the forming process, and the roundness is not easy to control. It is difficult to form the required profile by simple bulging or simply changing the mold. At the same time, based on the basic characteristics of the bulging forming equipment and mold design, the bulging forming belongs to a low-precision rough machining forming process, which also makes it extremely difficult to control the high precision of the bulging forming.

[0053] The main processes of spin forming are: welding prefabrication → bulging preforming → spin forming. Bulging forming can reduce the deformation amount of subsequent spin forming, prevent instability during subsequent spin forming, and preform the blank into a necked-in shape, which can prevent excessive warping of the blank edge during spin forming. Therefore, the control degree of the profile accuracy of bulging forming directly determines the success or failure of spin forming.

[0054] Figure 2 This application provides an accurate control method for bulging preforming. According to the size characteristics of the large-size high-diameter-to-thickness ratio electron beam welded plate and the product accuracy requirements, using the multi-pass gradual curvature forming technology, the accurate trajectory control forming is carried out in multiple passes with small pressure to achieve accurate surface control and point control. Finally, the forming accuracy is controlled within 1.5 mm, and the part products that meet the high-precision requirements of the spin forming tail top area are produced, greatly improving the bulging forming accuracy of the large-size high-diameter-to-thickness ratio welded plate structural parts. In addition, the frequency of mold replacement can be reduced. The specific technical solution of the multi-pass gradual curvature forming technology is as follows.

[0055] (1) Mold design

[0056] This application considers the thickness δ of the welded plate and the product curvature radius R, and selects and matches the preforming mold to facilitate local surface control and point control forming.

[0057] As Figure 3 shown, according to the arc requirement of the part forming profile, on the basis of the standard mold opening diameter (the diameter of the concave mold opening contour) R1000 mm, the chord height difference H = δ + (60 - 80) mm is selected, and multiple concave mold curvature radii SR 下 min are determined using the chord height difference and three points to form a circle. The chord height difference H is the height difference from the center of the bottom surface of the concave mold to the center of the concave mold opening. Multiple concave molds can be used in turn from large to small according to the curvature radius SR 下 min. For the concave mold with a relatively large curvature radius, the change of the curvature radius SR 下 min can be transitioned according to 400 - 700 mm, for example, transitioned according to 600 mm. For the concave mold with a relatively small curvature radius, the curvature radius SR 下The min change can transition in the range of 150 - 350 mm, for example, transitioning by 250 mm.

[0058] In some embodiments, the designed radius of curvature SR 下 min of the female dies 1, 2, 3, and 4 decreases in sequence. The radius of curvature SR 下 min of female die 1 can be SR2500 mm. The radius of curvature SR 下 min of female die 2 can be SR1900 mm. The radius of curvature SR 下 min of female die 3 can be SR1500 mm. The radius of curvature SR 下 min of female die 4 can be SR1250 mm.

[0059] To ensure sufficient deformation of the sheet metal, the radius of curvature SR 上 of the male die = SR 下 min - (20 - 30).

[0060] (2) Multi - pass variable - curvature forming control

[0061] 1) Marking and measurement

[0062] As Figure 4 shown, determine and mark the center point. Perform "cross" scribing along the weld and perpendicular to the weld direction. The intersection of the scribed lines can be used as the center - point mark. Measure and record the thickness values of the welded blank along the weld and perpendicular directions (a total of 4 quadrants). Mark the mutation areas where the thickness deviation value is greater than 1.5 mm.

[0063] 2) Press forming

[0064] ① Execute the first pressing process on the entire surface of the sheet metal. The pre - pressure of the first pressing process can be 2 - 3 Mpa.

[0065] Specifically, adjust the position of the sheet metal in the die so that the center - point mark on the sheet metal aligns with the die center. Apply a pre - pressure of 2.5 Mpa at the center - point mark to cause obvious plastic deformation. After pressing, the deformation amount of the sheet metal can be observed.

[0066] After that, circumferential uniform pressing can be performed. Feed axially the first pre - pressing step length (which can take a value of 300 - 500 mm, for example, 400 mm) from the center - point mark of the sheet metal, and perform circumferential uniform pressing along the circle defined by the center - point mark as the center and the first pre - pressing step length as the radius. The position schematic diagram between every two hammers is as Figure 4 shown. The center of the latter hammer falls near the edge of the former hammer, and L is controlled to be 1 / 3 - 1 / 2 of the die opening radius. Thus, the overall roundness and smoothness of the product can be effectively controlled. After completing each circle of pressing, continue to feed axially outward the first pre - pressing step length until the entire surface of the sheet metal is pressed.

[0067] Each time the sheet metal is pressed, the sheet metal can be rotated to adjust the placement orientation and position of the sheet metal relative to the die. By spraying at the edge of the vertical weld as a subsequent rotation mark, it is convenient to position the rotation of the sheet metal.

[0068] ② Measure the surface gap with a template.

[0069] Specifically, the thickness reduction can be measured by a thickness gauge. When measuring, it can be measured in a total of 4 quadrants along the weld direction and the direction perpendicular to the weld, and the data is recorded.

[0070] ③ Observe the weld morphology on the inner and outer surfaces with a magnifying glass, pay attention to whether cracks occur, and record the data.

[0071] ④ Perform the second pressing process on the entire surface of the sheet metal. The pre-pressure of the second pressing process can be 3.5 - 5 Mpa.

[0072] Specifically, when performing the second pressing process, rotate the sheet metal so that the initial pressurization orientation of the second pressing process is 90° to the initial pressurization orientation of the first pressing process. When the center mark of the sheet metal aligns with the center of the die, the orientation of the sheet metal relative to the die in the second pressing process can be 90° to the orientation of the sheet metal relative to the die in the first pressing process. Apply a pre-pressure of 4 Mpa at the center mark.

[0073] After that, circumferential uniform pressing can be performed. Feed the second pre-pressing step length (for example, 300 - 500 mm) axially from the center mark of the sheet metal, and perform circumferential uniform pressing along the circle defined with the center mark as the center and the second pre-pressing step length as the radius. To make the initial pressurization orientation of the second pressing process 90° to the initial pressurization orientation of the first pressing process, the connection line between the starting position of each circle in the second pressing process and the center mark is 90° to the connection line between the starting position of each circle in the first pressing process and the center mark. The schematic diagram of the position between every two hammers is as Figure 4 shown. The center of the latter hammer falls near the edge of the former hammer, and L is controlled to be 1 / 3 - 1 / 2 of the radius of the die plane. Thus, the overall roundness and smoothness of the product can be effectively controlled. After each circle of pressing is completed, continue to feed the first pre-pressing step length axially outward until the entire surface of the sheet metal is pressed.

[0074] ⑤ Record the data and observe the weld morphology according to the method in steps ② - ③. If there is no abnormality, continue the pressing.

[0075] ⑥ With 2 MPa as the variable pressure increment, the pressing process is cyclically executed. The specific manner of the pressing process can refer to step ① or ④ above. After pressing is completed, the surface gap measurement can be performed according to step ② above, that is, measure the gap between the sheet metal and the template. Until the surface gap does not change significantly,

[0076] Replace with the next set of molds with a smaller radius of curvature.

[0077] ⑦ After replacing the mold, re - execute the above steps ① - ⑥.

[0078] 3) Precision forming of local mutation points with small pressure

[0079] Since the part is a large - size structural part, there are obvious differences in strength between the weld area and the homogeneous base material area. After multiple passes of pre - pressing forming, it is extremely easy to produce quadrant asymmetry and local surface distortion during the forming process, and the phenomenon of local mutation due to the inability to release stress concentration, that is, the deformation amounts in the direction along the weld and perpendicular to the weld are quite different.

[0080] In the general process, it is necessary to replace the mold with large pressure for multiple passes for the product, that is, to achieve a smooth transition of the overall curved surface with large pressure at the edge. However, this brings new adjustments to the anti - deformation ability of the weld, and it is extremely easy to cause stress concentration in the weld due to excessive forming force, resulting in cracking.

[0081] To ensure high - precision forming of the product, weak - pressure focus control is adopted, and it is necessary to form the local mutation points. As shown in the following figure:

[0082] ① According to the observation results, mark the mutation points on the sheet metal.

[0083] Figure 5 、 Figure 6 The light - gray area shows the mutation points. During the forming process, markings are made to facilitate the operator's observation and operation.

[0084] ② Conduct circumferential point - pressing trimming within the range of a radius of r (which can take values from 400 to 600 mm, for example, 500 mm) from the center of the mutation point to achieve circumferential stress release.

[0085] It is possible to give priority to trimming the end close to the center. Defining the trimming sequence can effectively weaken the inward movement of the mutation point and restrict the forming balance point. The weak pressure is selected as a small pressure of 1 - 2 Mpa (for example, 1.5 MPa) to weaken the surface - contact effect and achieve focus forming. The distance between the centers of two adjacent drop hammers can be 150 - 250 mm (for example, 200 mm).

[0086] ③ Trim along the axial direction.

[0087] Formulate the trimming trajectory to release the stress axially, and the mutation point can be pushed towards the edge of the sheet metal. Specifically, after circumferential point - pressing trimming around the mutation point, new mutation points may be formed around the mutation point. The line connecting the center of the new mutation point and the center of the initial mutation point can be the direction of this axial trimming. During the hammering process, frequently measure the deformation amount at the mutation point to control the deformation amount within 1.5 mm.

[0088] Although the present invention is disclosed above in preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims of the present invention.

Claims

1. A preforming method for a drum, characterized in that, Including: Using a first set of dies, performing multiple pressing processes on the entire surface of the sheet metal; Using a second set of dies, performing multiple pressing processes on the entire surface of the sheet metal; The first set of dies and the second set of dies both correspond to the same opening diameter, and the opening diameter is 800 - 1000 mm; The radius of curvature corresponding to the first set of dies is greater than the radius of curvature corresponding to the second set of dies. The radii of curvature corresponding to the first set of dies and the second set of dies are both determined by the opening diameter and the chord height difference H. The chord height difference H is the height difference from the center of the bottom surface of the concave die to the center of the opening of the concave die, and the chord height difference H satisfies: H = δ+(60 - 80) mm, where δ is the thickness of the sheet metal; Performing multiple pressing processes on the entire surface of the sheet metal includes: Adjusting the position of the sheet metal in the die so that the center mark of the sheet metal is aligned with the center of the die, and performing pre-pressing at the center mark of the sheet metal; Centering on the center mark of the sheet metal, performing circumferential pressing on the sheet metal, including: Feeding N pre-pressing step lengths axially from the center mark. After each feeding of the pre-pressing step length, performing circumferential pressing along the circle with the center mark as the center and the feeding position as the center until the entire surface of the sheet metal is pressed; during the circumferential pressing process, the distance L between adjacent hammers is 1 / 3 - 1 / 2 of the opening radius of the die; the multiple pressing processes include multiple full-surface pressing operations, and the initial pressing azimuths of adjacent two full-surface pressing operations differ by 90°; The method further includes: performing circumferential point pressing and trimming centered on the first mutation point; performing axial trimming on the first mutation point; the axial direction is the connection line between the newly generated second mutation point and the first mutation point after the circumferential point pressing and trimming.

2. The method according to claim 1, wherein The radii of curvature corresponding to the first set of dies and the second set of dies satisfy any one of the following: The radius of curvature corresponding to the first set of dies is 2500 mm, and the radius of curvature corresponding to the second set of dies is 1900 mm; The radius of curvature corresponding to the first set of dies is 1900 mm, and the radius of curvature corresponding to the second set of dies is 1500 mm; The radius of curvature corresponding to the first set of dies is 1500 mm, and the radius of curvature corresponding to the second set of dies is 1250 mm.

3. The method according to claim 1, wherein The multiple pressing processes include multiple full-surface pressing operations, and the pre-pressures of the multiple pressing processes satisfy at least one of the following: The pre-pressure of the first full-surface pressing is 2 - 3 Mpa; The pre-pressure of the second full-surface pressing is 3.5 - 5 Mpa; The pre-pressure increment between adjacent two full-surface pressings is 2 Mpa.

4. The method according to claim 1, wherein The pre-pressing step length is 300 - 500 mm.

5. The method according to claim 1, wherein The circumferential point pressing and trimming satisfies: The distance between the trimming position and the first mutation point is 400 - 600 mm; The pre-pressure of the circumferential point pressing and trimming is 1 - 2 Mpa; The distance between adjacent hammers is 150 - 250 mm.

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