Numerical control forward and reverse four-roller roll bending machine and roll bending method

Abstract

The invention provides a numerical control forward and reverse four-roller roll bending machine and a roll bending method. Comprising a machine frame, a lower roller shaft rotationally arranged on the machine frame, an upper roller shaft vertically spaced from the lower roller shaft, a lifting adjusting mechanism fixedly arranged on the machine frame, connected with the upper roller shaft and used for adjusting the position of the upper roller shaft, a first driving assembly driving the upper roller shaft to rotate and a second driving assembly driving the lower roller shaft to rotate. The first turnover transmission mechanism is fixedly arranged on the machine frame and used for driving the upper side roller to turn around the upper roller shaft, and the second turnover transmission mechanism is fixedly arranged on the machine frame and used for driving the lower side roller to turn around the lower roller shaft. The upper side roller and the lower side roller are driven by the first turnover transmission mechanism and the second turnover transmission mechanism to press the plate in the forward direction or the reverse direction and are matched with the upper roller shaft and the lower roller shaft to achieve roll bending of the plate in different directions and with different curvatures, and pre-bending of the end of the plate and forming of the variable-curvature complex plate are achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal plate processing, in particular to a numerical control positive and negative four-roll roll bending machine and a roll bending method. BACKGROUND

[0002] In the field of metal plate processing, roll bending forming is one of the core processes for realizing the geometric shape processing of plate structure parts, and is widely used in the aerospace, automobile manufacturing, pressure vessel, engineering machinery, shipbuilding and other industries. As a common bending forming equipment, the four-roll roll bending machine is widely used in the production of pressure vessels, pipeline manufacturing, steel structure parts and other products by virtue of its structure configuration of "upper roller + lower roller + double side roller", which realizes the curvature change by clamping the plate and adjusting the position of the side roller. However, with the continuous improvement of the plate forming precision and the demand for complex shape processing in modern industry, the existing four-roll roll bending machine gradually exposes many technical bottlenecks in actual application, and it is difficult to meet the requirements of high precision and diversification.

[0003] The forming principle of the existing four-roll roll bending machine determines that it is more suitable for the processing of cylindrical surface or circular arc parts with single curvature. At the same time, the single movement dimension of the side roller leads to the lack of complex shape forming capability. The existing side roller only has the lifting degree of freedom along the fixed guide rail. For the forming of complex profiles such as S-type and double curvature surface, it needs to be processed step by step by adjusting the roller position multiple times, which not only is cumbersome to operate, but also the transition area of each roll bending section is prone to "dead folding" or curvature mutation, which cannot guarantee the smoothness of the curved surface. For example, when processing S-type ventilation pipeline, the traditional four-roll roll bending machine needs to be positioned and adjusted at least three times, and after forming, it needs to rely on subsequent numerical control milling correction, which increases the processing cost. Therefore, it is a technical problem to be solved in the field to develop an improved technology of four-roll roll bending machine that can overcome the above technical bottlenecks. SUMMARY

[0004] The present application aims to overcome the problem that the existing four-roll roll bending machine cannot directly realize the plate forming of S-type and other asymmetric multi-curvature, and step-by-step processing is prone to "dead folding" or curvature mutation, and provides a numerical control positive and negative four-roll roll bending machine and a roll bending method, which realizes the continuous forming of plate variable curvature shape through the adjustable upper roller shaft and the upper side roller and lower side roller arranged around the upper roller shaft and lower roller shaft.

[0005] To achieve the above objectives, the present invention provides a CNC forward and reverse four-roll bending machine, comprising a frame, a lower roller shaft rotatably mounted on the frame, an upper roller shaft spaced vertically from the lower roller shaft, a lifting adjustment mechanism fixed to the frame and connected to the upper roller shaft for adjusting the position of the upper roller shaft, a first drive assembly for driving the upper roller shaft to rotate, and a second drive assembly for driving the lower roller shaft to rotate. The machine is characterized by further including an upper side roller, a lower side roller, a first rotational transmission mechanism fixed to the frame for driving the upper side roller to rotate around the upper roller shaft, and a second rotational transmission mechanism fixed to the frame for driving the lower side roller to rotate around the lower roller shaft. The upper and lower side rollers are dynamically adjusted in position through the first and second rotational transmission mechanisms and cooperate with the upper and lower roller shafts to adapt to bending of sheet metal in different directions and with different curvatures.

[0006] Furthermore, the first rotational transmission mechanism includes a first gear assembly connected to the upper side roller and a first pin assembly cooperating with the first gear assembly for locking the first gear assembly, and the second rotational transmission mechanism includes a second gear assembly connected to the lower side roller and a second pin assembly cooperating with the second gear assembly for locking the second gear assembly.

[0007] Furthermore, the first rotational transmission mechanism also includes a third drive assembly fixed to the frame. The first gear assembly is a planetary gear set. The first gear assembly includes an internal gear ring fixed to the frame, a sun gear rotatably mounted on the frame and coaxial with the internal gear ring, and planet gears meshing with the internal gear ring and the sun gear. The sun gear is connected to the third drive assembly. One end of the upper roller is fixedly connected to the planet gear, and the other end is fitted with a first limiting connector. The first limiting connector is rotatably connected to the upper roller shaft.

[0008] Furthermore, the first pin assembly includes a first positioning flange fixed to the end face of the sun gear and having multiple positioning holes, and a first pin slidably disposed on the frame for inserting into the positioning holes of the first positioning flange.

[0009] Furthermore, the second rotational transmission mechanism also includes a fourth drive assembly fixed to the frame. The second gear assembly includes a small gear connected to the fourth drive assembly and a large gear meshing with the small gear. The large gear is rotatably connected to the lower roller shaft via a bearing. A second limiting connector is fixedly connected to the end face of the large gear. One end of the second limiting connector is rotatably connected to the lower roller shaft, and the other end is connected to the lower side roller. The ends of the lower roller shaft and the lower side roller away from the second gear assembly are connected via a third limiting connector.

[0010] Furthermore, the second pin assembly includes a second positioning flange fixed to the other end face of the large gear and having multiple positioning holes, and a second pin slidably disposed on the frame for inserting into the positioning holes of the second positioning flange.

[0011] Furthermore, the frame includes a first mounting frame, a second mounting frame, and a base plate. The first and second mounting frames are disposed on the upper surface of the base plate. The second drive assembly and the second rotational transmission mechanism are fixed to the first mounting frame. The first drive assembly is connected to the first mounting frame through a lifting adjustment mechanism. The first rotational transmission mechanism is fixed to the second mounting frame. The lifting adjustment mechanism includes a lifting assembly disposed at the bottom of the second mounting frame and a hoisting assembly connected to the first drive assembly. The lifting assembly and the hoisting assembly move synchronously to drive the upper roller to move up and down.

[0012] Furthermore, the second mounting frame has a guide hole at its bottom. The lifting assembly includes a guide post that slides with the guide hole and a lifting hydraulic cylinder fixed to the base plate and connected to the bottom of the second mounting frame. The hoisting assembly includes a hoisting seat connected to the first drive assembly and the end of the upper roller shaft. A hoisting hydraulic cylinder is connected between the hoisting seat and the first mounting frame.

[0013] Furthermore, the first mounting frame has a lower limit groove adapted to the movement trajectory of the lower roller, and the second mounting frame has an upper limit groove adapted to the movement trajectory of the upper roller. The end of the lower roller is slidably disposed in the lower limit groove, and the end of the upper roller is slidably disposed in the upper limit groove.

[0014] A rolling bending method, using a CNC forward and reverse four-roll rolling bending machine as described in any one of claims 1-9, is characterized by comprising the following steps:

[0015] S1. Plate feeding: Insert one end of the plate between the upper roller shaft and the lower roller shaft, so that the end of the plate extends beyond the edge of the lower roller shaft. The upper roller shaft presses the plate tightly under the drive of the lifting and adjusting mechanism.

[0016] S2. End pre-bending: The upper and lower rollers are driven to rotate by the first and second rotational transmission mechanisms, so that the upper and lower rollers clamp the end of the sheet material that extends beyond the edge of the lower roller shaft. The second drive assembly drives the lower roller shaft to rotate, so that the end of the sheet material is bent to the target curvature under the clamping of the upper and lower rollers. After the end of the sheet material is pre-bent, the upper and lower rollers disengage from the sheet material and return to their original positions.

[0017] S3. Plate feeding: The upper and lower roller shafts start to rotate under the drive of the first and second drive components, driving the plate to feed continuously.

[0018] S4. Variable curvature forming: The target curvature of the sheet is divided into m continuous intervals (m≥2) according to the rate of curvature change. Based on the sheet thickness and the target curvature of the m continuous intervals, the downward pressure of the upper roller shaft and the positions of the upper and lower rollers are dynamically adjusted to adapt to the dynamic requirements of variable curvature bending.

[0019] S5, Unloading and Reset: The upper roller shaft rises, the upper and lower side rollers retract to their original positions, and the lower roller shaft continues to rotate to deliver the formed sheet material.

[0020] The beneficial effects of this invention are:

[0021] This invention features an upper roller that presses against the sheet material from above, achieving forward bending; and a lower roller that presses against the sheet material from below, achieving reverse bending. The cooperation of the upper and lower rollers allows for both forward and reverse bending of the sheet material, forming continuous S-shaped or other forward and reverse curvature shapes. Furthermore, the upper and lower rollers can be rotated clockwise or counterclockwise to press the sheet material at different positions on either side of the roller shaft, creating arbitrary variable curvature arcs. Compared to existing bending machines that can only bend in one direction, this invention integrates multiple bending processes into a single machine. Unlike traditional bending machines, which require transferring the sheet material to another machine or flipping it via a conveyor after each bending operation, this reduces auxiliary time, shortens overall processing time, and improves production efficiency, making it suitable for mass production.

[0022] This invention allows for precise adjustment of the height of the upper roller shaft via a lifting and adjusting component. Combined with the independently driveable upper and lower side rollers that surround the upper and lower roller shafts, it enables clamping and pre-bending of the end of the sheet material. Furthermore, this invention can flexibly adjust the bending parameters (the downward pressure of the upper roller shaft, the positions of the upper and lower side rollers, etc.) according to the requirements of different thicknesses, materials, and target curvatures, to achieve sheet material forming with variable curvature and high forming accuracy, making it suitable for scenarios requiring complex forming curvatures.

[0023] The upper roller of this invention is driven by a planetary gear set. Planetary gear transmission features precise transmission ratio and high load-bearing capacity, enabling smooth and precise rotation of the upper roller around its axis. The lower roller is driven by the meshing of a large gear and a small gear, which offers high transmission efficiency and controllable speed, ensuring stability during rotation. Furthermore, the planetary gear set, the large gear, and the small gear are equipped with pin assemblies, allowing for quick and precise locking after the upper and lower rollers have been positioned. This improves structural stability, achieves efficient coordination with the upper and lower roller axes, and enhances the continuity and consistency of sheet metal bending. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly described below.

[0025] Figure 1 This is a rear view of the present invention.

[0026] Figure 2 This is an isometric view of the present invention.

[0027] Figure 3 for Figure 1 CC section view.

[0028] Figure 4 This is a schematic diagram of the second rotational transmission mechanism of the present invention.

[0029] Figure 5 for Figure 4 Enlarged view of point A.

[0030] Figure 6 This is a schematic diagram of the first rotary transmission mechanism of the present invention.

[0031] Figure 7 for Figure 6 Enlarged view of point B.

[0032] Explanation of reference numerals in the attached figures

[0033] 1. Upper roller shaft; 2. Lower roller shaft; 3. Upper side roller; 4. Lower side roller; 5. First drive assembly; 6. Second drive assembly; 7. First rotational transmission mechanism; 8. Second rotational transmission mechanism; 9. First mounting frame; 10. Second mounting frame; 11. Auxiliary baffle; 12. Base plate; 13. Lifting assembly; 14. Hoisting assembly; 15. Upper roller shaft mounting seat; 16. Lower roller shaft mounting seat; 17. First limiting connector; 18. Second limiting connector; 19. Lifting adjustment mechanism; 20. Frame; 21. First gear assembly; 22. Second gear assembly; 23. First pin assembly; 24. Second pin assembly 25. First positioning flange; 26. Second positioning flange; 27. Third drive assembly; 28. Fourth drive assembly; 29. ​​Internal gear ring; 30. Sun gear; 31. Planetary gear; 32. First pin; 33. Second pin; 34. Pinion; 35. Gear; 36. Guide hole; 37. Guide post; 38. Lifting hydraulic cylinder; 39. Hoisting hydraulic cylinder; 40. Hoisting seat; 41. Auxiliary feeding ramp; 42. Upper limit groove; 43. Lower limit groove; 44. Third limit connector; 45. First limit seat; 46. First locking hydraulic cylinder; 47. Second limit seat; 48. Second locking hydraulic cylinder. Detailed Implementation

[0034] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0035] Please refer to Figures 1 to 7As shown, this embodiment of a CNC forward and reverse four-roll bending machine includes a frame 20, an upper roller shaft 1, a lower roller shaft 2, an upper side roller 3, a lower side roller 4, a lifting and adjusting mechanism 19, a first drive assembly 5, a second drive assembly 6, a first rotational transmission mechanism 7, and a second rotational transmission mechanism 8. The lower roller shaft 2 is rotatably mounted on the frame 20. The upper roller shaft 1 is located above the lower roller shaft 2 and is parallel to and spaced apart from it. The gap between the upper roller shaft 1 and the lower roller shaft 2 allows the sheet metal to pass through. The first drive assembly 5 is fixed to the frame 20 and connected to the upper roller shaft 1 to drive its rotation. The second drive assembly 6 is fixed to the frame 20 and connected to the lower roller shaft 2 to drive its rotation. The first drive assembly 5 and the second drive assembly 6 include a motor and a reducer. The lifting and adjusting mechanism 19 is fixed to the frame 20 and includes a lifting assembly 13 and a hoisting assembly 14, which are respectively connected to both ends of the upper roller shaft 1. The lifting assembly 13 and the hoisting assembly 14 move synchronously to drive the upper roller shaft 1 to move up and down. The upper side roller 3 and lower side roller 4 are arranged parallel to and spaced apart from the upper roller shaft 1 and lower roller shaft 2. The first rotary transmission mechanism 7 is fixed to the frame 20 to drive the upper side roller 3 to rotate around the upper roller shaft 1. The second rotary transmission mechanism 8 is fixed to the frame 20 to drive the lower side roller 4 to rotate around the lower roller shaft 2. The upper side roller 3 and lower side roller 4 are dynamically adjusted in position through the first rotary transmission mechanism 7 and the second rotary transmission mechanism 8, and can adapt to rolling of the sheet metal in different directions and with different curvatures in cooperation with the upper roller shaft 1 and lower roller shaft 2. The upper roller shaft 1 and lower roller shaft 2 have a diameter of 200mm, are made of 40Cr, and have a surface hardness of HRC55. The upper side roller 3 and lower side roller 4 have a diameter of 80mm, and are made of the same material and have the same surface hardness as the upper roller shaft 1 and lower roller shaft 2. The upper side roller 3 and lower side roller 4 rotate 270° around the upper roller shaft 1 and lower roller shaft 2. In another embodiment, the parameters of the upper roller 1 and the lower roller 2, the upper side roller 3 and the lower side roller 4, and the rotation angle of the upper side roller 3 and the lower side roller 4 can be adjusted according to factors such as the thickness of the sheet material and the material. This embodiment does not impose specific limitations.

[0036] The frame 20 includes a first mounting bracket 9, a second mounting bracket 10, and a base plate 12. The first mounting bracket 9 and the second mounting bracket 10 are disposed on the upper surface of the base plate 12. A second drive assembly 6 and a lifting assembly 14 are fixedly mounted on the first mounting bracket 9. The lifting assembly 14 includes a lifting seat 40 fixedly connected to one end of the first drive assembly 5, and a lifting hydraulic cylinder 39 fixed between the lifting seat 40 and the first mounting bracket 9. A jacking assembly 13 is disposed between the second mounting bracket 10 and the base plate 12. The second mounting bracket 10 has a guide hole 36 at its bottom. The jacking assembly 13 includes a guide post 37 that slides with the guide hole 36 and a jacking hydraulic cylinder 38 fixed to the base plate 12 and connected to the bottom of the second mounting bracket 10. The first mounting frame 9 has a lower limit groove 43 adapted to the movement trajectory of the lower roller 4, and the second mounting frame 10 has an upper limit groove 42 adapted to the movement trajectory of the upper roller 3. The end of the lower roller 4 is slidably disposed in the lower limit groove 43, and the end of the upper roller 3 is slidably disposed in the upper limit groove 42. The second mounting frame 10 is fixedly provided with an upper roller shaft mounting seat 15. One end of the upper roller shaft 1 is rotatably supported on the upper roller shaft mounting seat 15 through a self-aligning roller bearing, and the other end of the upper roller shaft 1 is rotatably connected to the lifting seat 40 through a self-aligning roller bearing. A lower roller shaft mounting seat 16 is fixedly provided on the upper surface of the base plate 12. One end of the lower roller shaft 2 is rotatably supported on the lower roller shaft mounting seat 16 through a self-aligning roller bearing, and the other end is connected to the output end of the second drive assembly 6. The first rotating transmission mechanism 7 is fixed to the second mounting frame 10. One end of the upper roller 3 is connected to the first rotating transmission mechanism 7, and the other end is rotatably equipped with a first limiting connector 17. The first limiting connector 17 is rotatably connected to the upper roller shaft 1 through a self-aligning roller bearing. The second rotating transmission mechanism 8 is fixed to the first mounting frame 9. One end of the lower roller 4 is connected to the second rotating transmission mechanism 8, and the other end is rotatably equipped with a third limiting connector 44. The third limiting connector 44 is rotatably connected to the lower roller shaft 2 through a self-aligning roller bearing. An auxiliary baffle 11 is fixedly provided on the front edge of the base plate 12 to isolate the operator from the roller shaft. The top of the auxiliary baffle 11 is provided with an auxiliary feeding slope 41 extending along the gap between the upper roller shaft 1 and the lower roller shaft 2 to support the plate to be bent and prevent the bending accuracy from being affected by gravity.

[0037] The first rotary transmission mechanism 7 includes a third drive assembly 27, a first gear assembly 21, and a first pin assembly 23. The third drive assembly 27 includes a motor and a reducer. The first gear assembly 21 is a planetary gear set, including an internal gear ring 29 fixed to the second mounting bracket 10, a sun gear 30 rotatably mounted on the second mounting bracket 10 and coaxial with the internal gear ring 29, and planet gears 31 meshing with the internal gear ring 29 and the sun gear 30. The sun gear 30 is connected to the output end of the third drive assembly 27, and the planet gears 31 are fixedly connected to one end of the upper side roller 3. The first pin assembly 23 includes a first positioning flange 25, a first pin 32, a first limit seat 45, and a first locking hydraulic cylinder 46. The first positioning flange 25 is fixed to the end face of the sun gear 30 and has multiple positioning holes. The first limiting seat 45 and the first locking hydraulic cylinder 46 are fixed to the second mounting bracket 10. The first pin 32 is slidably disposed on the first limiting seat 45 and connected to the output end of the first locking hydraulic cylinder 46 for insertion into the positioning hole of the first positioning flange 25, thereby locking the upper side roller 3.

[0038] The second rotary transmission mechanism 8 includes a fourth drive assembly 28, a second gear assembly 22, and a second pin assembly 24. The fourth drive assembly 28 includes a motor and a reducer. The second gear assembly 22 includes a pinion 34 connected to the output end of the fourth drive assembly 28 and a large gear 35 meshing with the pinion 34. The large gear 35 is rotatably connected to the lower roller shaft 2 via a self-aligning roller bearing. A second limiting connector 18 is fixedly provided on the end face of the large gear 35. One end of the second limiting connector 18 is rotatably connected to the lower roller shaft 2, and the other end is connected to the lower side roller 4. The second pin assembly 24 includes a second positioning flange 26, a second pin 33, a second limiting seat 47, and a second locking hydraulic cylinder 48. The second positioning flange 26 is fixed to the other end face of the large gear 35 and has multiple positioning holes. The second limiting seat 47 and the second locking hydraulic cylinder 48 are fixed to the first mounting bracket 9. The second pin 33 is slidably disposed on the second limiting seat 47 and connected to the output end of the second locking hydraulic cylinder 48 for insertion into the positioning hole of the second positioning flange 26, thereby locking the lower side roller 4.

[0039] This embodiment discloses a roll bending method, which is performed using the CNC forward and reverse four-roll roll bending machine described above, and specifically includes the following steps:

[0040] S1. Plate feeding: Insert one end of the plate to be bent between the upper roller 1 and the lower roller 2, so that the end of the plate extends beyond the edge of the lower roller 2. The plate at the supply end is supported on the auxiliary feeding slope 41. The upper roller 1 is pre-pressed by the lifting adjustment mechanism 19.

[0041] S2, End pre-bending: The upper roller 3 and lower roller 4 are driven to rotate by the first rotational transmission mechanism 7 and the second rotational transmission mechanism 8, so that the upper roller 3 and lower roller 4 clamp the end of the plate that extends beyond the edge of the lower roller shaft 2. The second drive assembly 6 drives the lower roller shaft 2 to rotate, so that the end of the plate is bent to the target curvature under the clamping of the upper roller 3 and lower roller 4. After the end of the plate is pre-bent, the upper roller 3 and lower roller 4 are disengaged from the plate and reset.

[0042] S3, Plate feeding: The upper roller 1 and the lower roller 2 start to rotate under the drive of the first drive assembly 5 and the second drive assembly 6, driving the plate to be fed continuously. The upper roller 1 and the lower roller 2 rotate in opposite directions and have the same angular velocity.

[0043] S4. Variable curvature forming: The target curvature of the sheet is divided into m continuous intervals (m≥2) according to the rate of change of curvature. Based on the sheet thickness and the target curvature of the m continuous intervals, the downward pressure of the upper roller 1 and the positions of the upper side roller 3 and the lower side roller 4 are dynamically adjusted to adapt to the dynamic requirements of variable curvature bending. The sheet can pass through the gaps between the upper roller 1 and the lower roller 2, between the upper roller 1 and the upper side roller 3, and between the lower roller 2 and the lower side roller 4 to complete the forming of complex curvatures.

[0044] S5, Unloading and Reset: The upper roller shaft 1 rises, the upper side roller 3 and the lower side roller 4 retract to their original positions, and the lower roller shaft 2 continues to rotate to deliver the formed sheet material.

[0045] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A CNC forward and reverse four-roll bending machine, comprising a frame (20), a lower roller shaft (2) rotatably mounted on the frame (20), an upper roller shaft (1) spaced vertically from the lower roller shaft (2), a lifting adjustment mechanism (19) fixed to the frame (20) and connected to the upper roller shaft (1) for adjusting the position of the upper roller shaft (1), a first drive assembly (5) for driving the upper roller shaft (1) to rotate, and a second drive assembly (6) for driving the lower roller shaft (2) to rotate, characterized in that: It also includes an upper side roller (3), a lower side roller (4), a first rotational transmission mechanism (7) fixed to the frame (20) for driving the upper side roller (3) to rotate around the upper roller shaft (1), and a second rotational transmission mechanism (8) fixed to the frame (20) for driving the lower side roller (4) to rotate around the lower roller shaft (2). The upper side roller (3) and the lower side roller (4) are driven by the first rotational transmission mechanism (7) and the second rotational transmission mechanism (8) to press against the plate in the positive or negative direction and cooperate with the upper roller shaft (1) and the lower roller shaft (2) to achieve rolling bending of the plate in different directions and with different curvatures.

2. The CNC forward and reverse four-roll bending machine according to claim 1, characterized in that: The first rotational transmission mechanism (7) includes a first gear assembly (21) connected to the upper side roller (3) and a first pin assembly (23) cooperating with the first gear assembly (21) for locking the first gear assembly (21). The second rotational transmission mechanism (8) includes a second gear assembly (22) connected to the lower side roller (4) and a second pin assembly (24) cooperating with the second gear assembly (22) for locking the second gear assembly (22).

3. The CNC forward and reverse four-roll bending machine according to claim 2, characterized in that: The first rotational transmission mechanism (7) further includes a third drive assembly (27) fixed to the frame (20). The first gear assembly (21) is a planetary gear set. The first gear assembly (21) includes an internal gear ring (29) fixed to the frame (20), a sun gear (30) rotatably mounted on the frame (20) and coaxial with the internal gear ring (29), and a planetary gear (31) meshing with the internal gear ring (29) and the sun gear (30). The sun gear (30) is connected to the third drive assembly (27). One end of the upper roller (3) is fixedly connected to the planetary gear (31), and the other end is fitted with a first limiting connector (17). The first limiting connector (17) is rotatably connected to the upper roller shaft (1).

4. The CNC forward and reverse four-roll bending machine according to claim 2 or 3, characterized in that: The first pin assembly (23) includes a first positioning flange (25) fixed to the end face of the sun gear (30) and having multiple positioning holes, and a first pin (32) slidably disposed on the frame (20) for inserting into the positioning holes of the first positioning flange (25).

5. The CNC forward and reverse four-roll bending machine according to claim 2, characterized in that: The second rotational transmission mechanism (8) further includes a fourth drive assembly (28) fixed to the frame (20). The second gear assembly (22) includes a small gear (34) connected to the fourth drive assembly (28) and a large gear (35) meshing with the small gear (34). The large gear (35) is rotatably connected to the lower roller shaft (2) through a bearing. A second limiting connector (18) is fixedly connected to the end face of the large gear (35). One end of the second limiting connector (18) is rotatably connected to the lower roller shaft (2) and the other end is connected to the lower side roller (4). The ends of the lower roller shaft (2) and the lower side roller (4) away from the second gear assembly (22) are connected through a third limiting connector (44).

6. The CNC forward and reverse four-roll bending machine according to claim 2 or 5, characterized in that: The second pin assembly (24) includes a second positioning flange (26) fixed to the other end face of the large gear (35) and having multiple positioning holes, and a second pin (33) slidably disposed on the frame (20) for inserting into the positioning holes of the second positioning flange (26).

7. The CNC forward and reverse four-roll bending machine according to claim 1, characterized in that: The frame (20) includes a first mounting frame (9), a second mounting frame (10), and a base plate (12). The first mounting frame (9) and the second mounting frame (10) are disposed on the upper surface of the base plate (12). The second drive assembly (6) and the second rotation transmission mechanism (8) are fixed on the first mounting frame (9). The first drive assembly (5) is connected to the first mounting frame (9) through a lifting adjustment mechanism (19). The first rotation transmission mechanism (7) is fixed on the second mounting frame (10). The lifting adjustment mechanism (19) includes a lifting assembly (13) disposed at the bottom of the second mounting frame (10) and a hoisting assembly (14) connected to the first drive assembly (5). The lifting assembly (13) and the hoisting assembly (14) move synchronously to drive the upper roller (1) to move up and down.

8. The CNC forward and reverse four-roll bending machine according to claim 7, characterized in that: The second mounting frame (10) has a guide hole (36) at the bottom. The lifting assembly (13) includes a guide post (37) that slides with the guide hole (36) and a lifting hydraulic cylinder (38) that is fixed to the base plate (12) and connected to the bottom of the second mounting frame (10). The hoisting assembly (14) includes a hoisting seat (40) that is connected to the end of the first drive assembly (5) and the upper roller (1). The hoisting seat (40) is connected to the first mounting frame (9) by a hoisting hydraulic cylinder (39).

9. The CNC forward and reverse four-roll bending machine according to claim 7, characterized in that: The first mounting frame (9) has a lower limit groove (43) adapted to the movement trajectory of the lower side roller (4), and the second mounting frame (10) has an upper limit groove (42) adapted to the movement trajectory of the upper side roller (3). The end of the lower side roller (4) is slidably disposed in the lower limit groove (43), and the end of the upper side roller (3) is slidably disposed in the upper limit groove (42).

10. A roll bending method, performed using a CNC forward and reverse four-roll roll bending machine as described in any one of claims 1-9, characterized in that: Includes the following steps: S1. Plate feeding: Insert one end of the plate between the upper roller shaft (1) and the lower roller shaft (2) so that the end of the plate extends beyond the edge of the lower roller shaft (2). The upper roller shaft (1) presses the plate under the drive of the lifting adjustment mechanism (19). S2, End pre-bending: The upper roller (3) and lower roller (4) are driven to rotate by the first rotational transmission mechanism (7) and the second rotational transmission mechanism (8), so that the upper roller (3) and lower roller (4) clamp the end of the plate that extends beyond the edge of the lower roller shaft (2). The second drive assembly (6) drives the lower roller shaft (2) to rotate, so that the end of the plate is bent to the target arc under the clamping of the upper roller (3) and lower roller (4). After the end of the plate is pre-bent, the upper roller (3) and lower roller (4) are disengaged from the plate and reset. S3, Plate feeding: The upper roller shaft (1) and the lower roller shaft (2) start to rotate under the drive of the first drive assembly (5) and the second drive assembly (6), driving the plate to feed continuously; S4. Variable curvature forming: The target curvature of the sheet is divided into m continuous intervals (m≥2) according to the curvature change rate. Based on the sheet thickness and the target curvature of the m continuous intervals, the downward pressure of the upper roller shaft (1) and the positions of the upper side roller (3) and the lower side roller (4) are dynamically adjusted to adapt to the dynamic requirements of variable curvature bending. S5, Unloading and Reset: The upper roller shaft (1) rises, the upper side roller (3) and the lower side roller (4) retract to their original positions, and the lower roller shaft (2) continues to rotate to send out the formed sheet.

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