Forming method for large-size ultra-high strength steel deep cavity integral head

Abstract

A forming method for a large-size ultra-high-strength steel deep-cavity integral head relates to the technical field of head forming, specifically to the field of ultra-high-strength steel processing, and particularly to a forming method for a large-size ultra-high-strength steel deep-cavity integral head, which comprises the following steps: upsetting forming, selecting an ultra-high-strength steel bar, heating and holding the bar, and performing axial upsetting on a hydraulic press to obtain a cake blank after upsetting; placing the obtained cake blank on a rolling lower die horizontally arranged on an axial closed-die rolling forming device for forming. The present invention adopts the method of upsetting - axial closed-die rolling - drawing - machining to form in one heat treatment. Compared with the current process route, the production cycle is shortened by 50%, the material utilization rate reaches more than 40%, the manufacturing cost is reduced by more than 30%, the anisotropic performance consistency can reach more than 95%, and the residual deformation amount during welding with the cylinder section can be reduced by 80%; at the same time, the number of circumferential welds can be reduced, and the manufacturing accuracy, load-bearing performance and product reliability can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of head forming, specifically to the field of ultra-high strength steel processing, and particularly to a forming method for a large-size ultra-high strength steel deep cavity integral head. Background Art

[0002] Head: The bottom of the barrel of a solid rocket engine shell, which is the main load-bearing component of the segmented connection section. It is the part with the most complex stress condition, the highest reliability requirement, the greatest manufacturing difficulty, and the longest manufacturing cycle in the engine shell. The head belongs to a thin-walled variable-wall-thickness special-shaped part with an ellipsoidal shape and a flange joint. It is the installation reference for the nozzle assembly and also the welding reference for connecting with the cylinder body. The shape consistency and manufacturing reliability of the head part have a significant impact on the overall performance, reliability, manufacturing cycle, and manufacturing cost of the engine.

[0003] Axial Closed Die Rolling (ACDR) is a three-way severe plastic deformation technology independently developed in China. During the forming process, the upper die inclines at a specific angle to contact the blank locally. While the upper die presses down, the lower die rotates to drive the blank and the upper die to rotate. Due to the rotation of the workpiece for forming, there is an obvious linear velocity difference between the core and the edge, and at the same time, there is an angular velocity difference due to the different contact areas of the upper and lower end faces. Thus, while the forging is continuously locally formed, compression and torsion composite deformation are achieved.

[0004] For large-size deep cavity heads, the split welding method is generally used for manufacturing. The manufacturing process is to manufacture the sphere, transition ring, and flange joint separately. Among them, the sphere is formed by sheet metal stretching, the transition ring is formed by ring rolling, and the flange joint is formed by die forging. Then, the transition ring, sphere, and flange are welded into a head part by ring welding. The entire manufacturing process involves multiple processes such as drawing, ring rolling, die forging, and welding, with a long production and manufacturing cycle. In particular, the head has a circumferential weld, which affects the reliability of the engine. Whether it is hot-rolled or cold-rolled sheet, there are obvious anisotropies in its longitudinal and transverse properties. The tangential and normal stress states and stress levels of the rolled sheet during the rolling process are different, resulting in obvious warping deformation of the head part during subsequent heat treatment and welding, seriously affecting the assembly accuracy and production efficiency of the engine shell. Moreover, the sphere is formed by sheet metal stretching, with uneven wall thickness and obvious springback, requiring additional correction or machining by increasing the allowance.

[0005] The heads of the ultra-high strength steel metal shells of foreign large solid engines all adopt a seamless integral head structure, which is machined integrally from die forgings. For example, the metal shells of the solid engines of the US space shuttle booster with a diameter of 3.7m and the European Ariane 5 rocket booster with a diameter of Ф3.5m both adopt a machined structure after integral hot forming with a seamless structure.

[0006] Changzhou Heshida Co., Ltd. has carried out a series of studies on bowl-shaped thin-walled parts. Based on the problems that metals have poor plasticity, high strength, small elastic modulus, low thermal conductivity, large deformation resistance at room temperature, and serious metal springback, which result in large forming loads for such parts, difficult wall thickness control, and extremely high requirements for the accuracy of production equipment, an eccentric forming device and method for bowl-shaped thin-walled parts with low load and precise forming are provided. This method can produce thin-walled bowl-shaped parts with an opening diameter of 500 mm grade under the rated load. The forming load is only 1 / 15 - 1 / 30 of the stamping process and 1 / 2 - 1 / 5 of the ordinary continuous local loading method. The thin-walled bowl-shaped parts prepared by this forming method have precise dimensions and accurate unilateral allowances, solving the technical problem of difficult wall thickness control caused by serious springback, and are especially suitable for producing large bowl-shaped thin-walled parts of titanium alloy and alloy steel.

[0007] Problems existing in the above prior art are as follows:

[0008] (1) For domestic medium and large solid rocket engines, the heads of the metal casings of the solid engines all adopt welded structure heads, which are formed by welding parts such as joints, stamping heads, and fork rings. This leads to welding deformation, stress concentration, and a decrease in the structural accuracy of the heads. The existence of weld defects reduces the load-bearing capacity of the structure, thus affecting the structural reliability of the engine. In addition, due to the long production process of the welded structure head, the production efficiency is low, and it cannot meet the production and delivery requirements.

[0009] (2) When using an eccentric forming device and method to produce bowl-shaped thin-walled parts, during the deformation process, since the convex die contacts the inner wall of the workpiece, the equipment needs to bear a large lateral force during the forming process. As the overall size of the bowl-shaped part increases and the inner wall of the bowl-shaped part decreases, the lateral force received becomes larger and larger, and the integrity of the head forming cannot be guaranteed. Summary of the Invention

[0010] To solve the above problems, the present invention provides an axial closed die rolling forming technology (Axial Closed Die Rolling, abbreviated as ACDR) based on the principle of continuous compression-torsion composite deformation, to complete the high-quality, high-efficiency, high-reliability, and low-cost manufacturing of large-sized heads, and to achieve low-load, high-efficiency, isotropic, and overall precision forming of large-sized head forgings, a forming method for large-sized ultra-high-strength steel deep cavity integral heads.

[0011] A forming method for large-sized ultra-high-strength steel deep cavity integral heads of the present invention is characterized by including the following steps:

[0012] The first step is upsetting forming. Select ultra-high-strength steel bars, heat the bars to 1100 - 1150 °C, and keep them warm for 4 - 5 h, then perform axial upsetting on a hydraulic press to obtain a cake blank after upsetting.

[0013] In the second step, axial closed-die rolling forming is carried out. The obtained cake blank is placed on the rolling lower die horizontally arranged on the axial closed-die rolling forming equipment. There is an annular first groove on the rolling lower die. The outer diameter of the first groove is the same as the outer diameter of the skirt of the finished head. The side of the first groove facing the center of the rolling lower die is smoothly transitionally connected to the surface of the rolling lower die facing the rolling upper die. The rolling upper die is in horizontal contact with the blank. The included angle between the axis of the rolling upper die and the axis of the rolling lower die is 9°. During the axial rolling forming process, the rolling lower die rotates actively, driving the cake blank and the rolling upper die to rotate by means of frictional force. At the same time, the rolling upper die makes a feeding movement downward along the axis. Through the periodic local contact between the rolling upper die and the blank, continuous and stable forming of the workpiece is realized, and a thin plate blank is obtained by deformation.

[0014] In the third step, the thin plate blank is placed in the drawing female die and kept stationary. The drawing male die is fixed on the upper crossbeam of the hydraulic press. The drawing male die moves vertically downward toward the drawing female die at a constant speed. When the thin plate blank is drawn to the required size, the drawing is completed. Then the drawn part is machined to the required size to obtain the required deep cavity head, and the depth / diameter of the deep cavity head > 0.1.

[0015] Preferably, in the second step, during the axial rolling forming process, the rolling lower die rotates actively at a rotational speed of 0.5 - 1 rad / s, and the rolling upper die makes a feeding movement downward along the axis at a speed of 3 - 6 mm / s.

[0016] Preferably, in the first step, during the upsetting process, the upsetting upper die moves vertically downward at a constant speed of 6 - 8 mm / s to upset the bar.

[0017] Preferably, in the third step, the drawing male die moves vertically downward toward the drawing female die at a constant speed of 3 mm / s to realize the drawing of the thin plate blank.

[0018] Or preferably, an annular second groove is arranged at the position corresponding to the first groove on the surface of the rolling upper die facing the rolling lower die. The side of the second groove facing the center of the rolling upper die is smoothly transitionally connected to the surface of the rolling upper die facing the rolling lower die.

[0019] Preferably, the ultra-high strength steel bar is D406A alloy.

[0020] The present invention forms in one heat treatment by means of upsetting - axial closed - die rolling - drawing - machining. Through statistical analysis, compared with the current process route, the production cycle is shortened by 50%, the material utilization rate reaches over 40%, the manufacturing cost is reduced by over 30%, the anisotropy of properties can reach over 95%, and the residual deformation during welding with the cylinder section can be reduced by 80%. At the same time, the number of circumferential welds can be reduced, which can improve the manufacturing accuracy, load - bearing performance and product reliability. Axial closed - die rolling forming is currently the most ideal forming technology for the integral manufacturing of large - size isotropic heads, which can effectively meet the manufacturing requirements of large - size heads for isotropy, integral forming, suppressing welding deformation, high efficiency and low cost. Brief Description of the Drawings

[0021] Figure 1 is the forming process of the existing deep - cavity flange.

[0022] Figure 2 is the process schematic diagram of the present invention.

[0023] Figure 3 is the physical drawing of the formed head. Detailed Embodiment

[0024] A forming method for a large - size ultra - high - strength steel deep - cavity integral head of the present invention is characterized by comprising the following steps:

[0025] The first step is upsetting forming. Select ultra - high - strength steel bars, heat the bars to 1100 - 1150 °C, and keep them at this temperature for 4 - 5 h. Then, perform axial upsetting on a hydraulic press to obtain a cake - shaped blank after upsetting.

[0026] The second step is axial closed - die rolling forming. Place the obtained cake - shaped blank on the rolling lower die horizontally arranged on the axial closed - die rolling forming equipment. There is a circular first groove on the rolling lower die, and the outer diameter of the first groove is the same as the outer diameter of the skirt of the finished head. The side of the first groove facing the center of the rolling lower die is smoothly transitionally connected to the surface of the rolling lower die facing the rolling upper die. The rolling upper die is in horizontal contact with the blank, and the included angle between the axis of the rolling upper die and the axis of the rolling lower die is 9°. During the axial rolling forming process, the rolling lower die rotates actively, driving the cake - shaped blank and the rolling upper die to rotate by means of frictional force. At the same time, the rolling upper die makes a feeding movement downward along the axis. Through the periodic local contact between the rolling upper die and the blank, continuous and stable forming of the workpiece is realized, and a thin - plate blank is obtained through deformation.

[0027] The third step is to place the thin - plate blank in the drawing female die and keep it stationary. The drawing male die is fixed on the upper crossbeam of the hydraulic press. The drawing male die moves vertically downward towards the drawing female die at a constant speed. When the thin - plate blank is drawn to the required size, the drawing is completed. Then, the drawn part is machined to the required size to obtain the required deep - cavity head, where the depth / diameter of the deep - cavity head > 0.1.

[0028] In the second step, during the axial rolling forming process, the rolling lower die rotates actively at a speed of 0.5 - 1 rad / s, and the rolling upper die moves downward axially at a speed of 3 - 6 mm / s.

[0029] In the first step, during the upsetting process, the upsetting upper die moves vertically downward at a constant speed of 6 - 8 mm / s to upset the bar.

[0030] In the third step, the drawing punch moves vertically downward at a constant speed of 3 mm / s towards the drawing die to realize the drawing of the thin plate blank.

[0031] On the surface of the rolling upper die facing the rolling lower die, a circular second groove is provided at the position corresponding to the first groove. The side of the second groove facing the center of the rolling upper die is smoothly transitionally connected to the surface of the rolling upper die facing the rolling lower die.

[0032] The ultra-high strength steel bar is D406A alloy.

[0033] Example:

[0034] First step, upsetting forming. Select a φ300×400 mm D406A ultra-high strength steel bar, heat the bar to 1150 °C, and keep it warm for 4 h, then perform axial upsetting. The upsetting upper die moves vertically downward at a constant speed of 6 mm / s, upset to a height of 115 mm to obtain a cake blank.

[0035] Second step, axial closed-die rolling forming. Place the obtained cake blank on the rolling lower die of a 45000 MN axial closed-die rolling forming equipment. A circular first groove is provided on the rolling lower die. The outer diameter of the first groove is the same as the outer diameter of the skirt of the finished head. The side of the first groove facing the center of the rolling lower die is smoothly transitionally connected to the surface of the rolling lower die facing the rolling upper die. The axis angle between the rolling upper die and the rolling lower die is 9°. The depth of the first groove is 20 mm. During the axial rolling forming process, the rolling lower die rotates actively at a speed of 0.5 rad / s, and drives the cake blank and the rolling upper die to rotate by the action of friction; at the same time, the rolling upper die moves downward axially at a speed of 3 mm / s. Through the periodic local contact between the upper die and the blank, continuous and stable forming of the workpiece is realized, and it is deformed to a diameter of φ990 mm and a thickness of 35 mm to obtain a thin plate blank.

[0036] Third step, place the thin plate blank in the corresponding drawing die and keep it stationary; the drawing punch is fixed on the upper crossbeam of the hydraulic press and moves vertically downward at a constant speed of 3 mm / s. When the drawing punch moves to the set stroke of 200 mm, the drawing is completed to obtain a D406A ultra-high strength steel integral head forging that meets the dimensional requirements, as Figure 2 shown, and then the required head size is obtained after machining.

[0037] For the present invention, the forming process is significantly reduced; welding deformation is reduced, there are fewer circumferential welds, and stability is improved; production efficiency is greatly enhanced.

[0038] By adopting the process method of "upsetting - axial closed - die rolling - drawing - machining", a D406A ultra - high strength steel head with an outer diameter of 790 mm is successfully prepared. Through experimental analysis, all mechanical properties meet the requirements, and the difference in three - dimensional properties is ≤5%. The present invention realizes the transformation and application of this technology in large - size deep - cavity forgings with an outer diameter of 790 mm.

[0039] The following table shows the relevant data measured from the chord - wise, radial, and axial specimens taken at the skirt part of the D406A ultra - high strength steel head: From the perspective of the stability of three - dimensional properties, the difference in three - dimensional properties can reach ≤5%.

[0040] Table Mechanical Properties of Integrally Formed D406A Heads

[0041]

Claims

1. A method for forming a large-size ultra-high strength steel deep cavity integral head, characterized in that: The steps include: The first step is upsetting. Ultra-high strength steel bars are selected and heated to 1100-1150°C. After keeping the temperature for 4-5 hours, axial upsetting is performed on a hydraulic press to obtain a cake blank. The second step is axial closed rolling forming, the obtained cake blank is placed on a horizontally arranged rolling lower die on the axial closed rolling forming equipment, the rolling lower die is provided with a first annular groove, the outer diameter of the first groove is the same as the outer diameter of the skirt of the finished head, the side of the first groove facing the center of the rolling lower die is smoothly connected with the side of the rolling lower die facing the rolling upper die; the rolling upper die is in horizontal contact with the blank, and the angle between the axis of the rolling upper die and the axis of the rolling lower die is 9°; During the axial rolling forming process, the rolling lower die rotates actively, and the friction force drives the cake blank and the rolling upper die to rotate; at the same time, the rolling upper die feeds downward along the axial direction, and the workpiece is continuously and stably formed through the periodic local contact between the rolling upper die and the blank, and the thin plate blank is obtained by deformation; The third step is to place the sheet metal blank in the drawing die and keep it still; the drawing punch is fixed on the crossbeam of the hydraulic press, and the drawing punch moves vertically downward toward the drawing die at a constant speed. When the sheet metal blank is drawn to the required size, the drawing is completed, and then the drawn part is machined to the required size to obtain the required deep cavity head, and the depth / diameter of the deep cavity head is greater than 0.1; A second annular groove is arranged on a surface of the rolling upper die facing the rolling lower die at a position corresponding to the first groove, and the second groove smoothly transitions to a surface of the rolling upper die facing the rolling lower die on one side facing the center of the rolling upper die.

2. A method for forming a large-size ultra-high strength steel deep cavity integral head as claimed in claim 1, characterized in that: In the second step, during the axial rolling forming process, the rolling lower die actively rotates at a speed of 0.5-1 rad / s, and the rolling upper die feeds downward in the axial direction at a speed of 3-6 mm / s.

3. A method for forming a large-size ultra-high strength steel deep cavity integral head as claimed in claim 1, characterized in that: In the first step, during the upsetting process, the upsetting upper die moves vertically downward at a constant speed of 6-8 mm / s to upset the bar.

4. A method for forming a large-size ultra-high strength steel deep cavity integral head as claimed in claim 1, characterized in that: In the third step, the drawing punch moves vertically downward toward the drawing die at a constant speed of 3 mm / s to achieve drawing of the thin plate blank.

5. A method for forming a large-size ultra-high strength steel deep cavity integral head as claimed in claim 1, characterized in that: The ultra-high strength steel bar is D406A alloy.

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