Device and method for mold-free single-pass incremental forming of thin-wall deep-cavity part
By using hydraulic pre-expansion and material replenishment mechanisms, combined with composite loading trajectories, it is possible to form thin-walled deep cavity parts with a thickness of less than 1 mm in a single pass without molds. This solves the problems of extended production cycle and low efficiency caused by multi-pass forming, and improves forming limits and precision.
Patent Information
- Application Number
- CN202511963710.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-24
- Publication Date
- 2026-02-27
AI Technical Summary
Existing technologies require multiple forming passes when forming thin-walled parts with a thickness of less than 1 mm without molds, especially deep-cavity parts with a depth-to-diameter ratio of not less than 0.5. This results in longer production cycles, increased costs, and reduced efficiency, making it difficult to achieve efficient single-pass forming.
The process employs a hydraulic pre-expansion forming process and an active material replenishment mechanism. The hydraulic pre-expansion forming system initially distributes the sheet material to form a semi-ellipsoidal blank. During the forming process, a buffer replenishment stage is used to push the edge material of the sheet material towards the center, and a single-point progressive forming is achieved by combining a composite loading trajectory.
It achieves efficient forming of thin-walled deep-cavity parts with a single-pass forming thickness of less than 1 mm and a depth-to-diameter ratio of not less than 0.5, improves forming limits and geometric accuracy, reduces wrinkling and springback defects, and enhances process adaptability.
Smart Images
Figure CN121571540A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the technical field of metal sheet plastic forming methods, and relates to an apparatus for moldless single-pass incremental forming of thin-walled deep-cavity parts. This invention also relates to a method for moldless single-pass incremental forming of thin-walled deep-cavity parts. Background Technology
[0002] Progressive forming technology, as an emerging high-flexibility sheet metal forming technology, has attracted much attention in lightweight product prototyping and multi-variety small-batch production due to its advantages such as not requiring specialized molds and rapid and flexible forming. However, when using this technology to form thin-walled parts with a thickness of less than 1 mm without molds, and when the aspect ratio (the ratio of the part's forming depth to its opening radius) is not less than 0.5, such as deep-cavity parts like hemispherical or parabolic cone parts, this technology must employ a multi-pass forming process of three or more passes to prevent premature fracture caused by large material deformation. This multi-pass forming process not only deviates from the core advantage of "single-pass, high-efficiency" of the technology, but also forces the extension of the production cycle, increases manufacturing costs, and reduces production efficiency, which seriously restricts the widespread application of this technology in industrial production. Therefore, how to improve the forming limit of materials under large deformation in a single pass, and provide a method to efficiently manufacture thin-walled deep-cavity parts with a thickness of less than 1 mm and an aspect ratio of not less than 0.5 through a single pass forming, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention
[0003] The purpose of this invention is to provide a moldless single-pass progressive forming apparatus for thin-walled deep-cavity parts. This apparatus enables single-pass, high-efficiency forming of thin-walled deep-cavity parts with a thickness of less than 1 mm, and significantly improves their thickness uniformity.
[0004] Another object of the present invention is to provide a method for moldless single-pass progressive forming of thin-walled deep-cavity parts.
[0005] The first technical solution adopted in this invention is a device for moldless single-pass progressive forming of thin-walled deep cavity parts, including an oil cavity cylinder with an open upper end, a hollow upper pressure plate at the opening of the oil cavity cylinder, a sealing groove at the opening of the oil cavity cylinder, a sealing ring at the sealing groove, and a through hole on one side of the oil cavity cylinder, which is connected to a hydraulic pre-expansion forming system through a hydraulic hose.
[0006] The first technical solution of this invention is further characterized by: The upper pressure plate is connected to the oil chamber cylinder by threads.
[0007] The hydraulic pre-expansion system includes a needle valve, a check valve, a three-phase asynchronous motor, an oil suction filter, an air filter, a level gauge, and a hydraulic oil tank connected in sequence.
[0008] The hydraulic oil tank is also connected in sequence to an overflow valve and a pressure gauge.
[0009] The second technical solution adopted in this invention is a method for moldless single-pass progressive forming of thin-walled deep-cavity parts, which specifically includes the following steps: Step 1, Determine the target height for pre-bulging. H ; Step 2, based on the pre-bulging target height determined in Step 1 H Form a semi-ellipsoidal blank; Step 3: Start the CNC machine tool and make the forming tool perform single-point progressive forming on the surface of the semi-ellipsoidal blank according to the preset composite loading trajectory.
[0010] The second technical solution of the present invention is further characterized by: In step 1, the pre-bulging target height H Less than the limit height of the initial sheet material under pure hydraulic free bulging. .
[0011] The specific process of step 2 is as follows: Place the initial plate between the upper pressure plate and the oil chamber, and connect the pressure plate and the oil chamber with threads to press and fix the initial plate. Start the three-phase asynchronous motor in the hydraulic pre-expansion system to drive the hydraulic pump to draw hydraulic oil filtered by the suction filter from the hydraulic oil tank. Then, control the hydraulic pressure value by adjusting the needle valve and the relief valve and observing the pressure gauge. When the pressurized hydraulic oil enters the closed oil chamber, it will apply a uniform hydraulic force to the initial plate. When the stress generated in the initial plate by this pressure value exceeds the yield strength of the material, the initial plate will begin to undergo plastic deformation, that is, pre-expansion. At this time, continue to gradually increase the hydraulic pressure until the initial plate reaches the pre-expansion target height H set in step 1, forming a semi-ellipsoidal blank.
[0012] In step 3, the composite loading trajectory includes the buffer trajectory of the buffer replenishment stage and the spiral loading trajectory of the precision forming stage.
[0013] In step 3, the specific process of the buffer replenishment stage is as follows: the forming tool first travels a spiral trajectory in the non-forming area at the edge of the sheet, squeezing and pushing the material in the non-forming area at the edge of the sheet towards the forming area in the center, thus establishing a "material library".
[0014] In step 3, the specific process of the precision forming stage is as follows: after completing the buffer replenishment, the forming tool is switched to the spiral loading trajectory of the target part to perform progressive forming of the blank by pressing down layer by layer.
[0015] The beneficial effects of this invention are as follows: 1. This invention introduces a hydraulic pre-expansion forming process to initially allocate the thickness of the sheet metal, laying the foundation for subsequent material replenishment and progressive forming processes. Building upon this, the core breakthrough of this invention is solving the problem of insufficient material during the forming of thin-walled, deep-cavity parts. The material in the non-forming areas at the edge of the sheet metal is transformed into a "material library." Before formal forming, the forming tool travels a "buffer trajectory," actively and controllably pushing the material from the non-forming areas at the sheet metal edge towards the most vulnerable areas prone to thinning and cracking. This active material replenishment mechanism fundamentally solves the problem of premature sheet metal cracking caused by excessive material stretching in traditional processes, thereby significantly increasing the forming limit and forming depth of the part. Theoretically, as long as there is sufficient material at the edge, continuous replenishment can be achieved.
[0016] 2. By organically integrating hydraulic pre-expansion and material supply mechanisms, the material sources in the forming area can be broadened, and the thickness distribution of the formed parts can be more uniform. At the same time, the hydraulic flexible auxiliary support can provide continuous and controllable flexible support for the formed sheet throughout the forming process, effectively suppressing defects such as wrinkling and springback, and significantly improving the overall forming performance of the parts.
[0017] 3. In addition to material transfer, the buffer feeding stage of machining also achieves a "pre-forming" effect by the early pressing of the forming tool, which reduces the initial pressing amount in the subsequent precision forming stage of deep cavity parts. This can reduce local overstretching and height deviation caused by the direct pressing of the forming tool without buffer feeding, thereby further improving the geometric accuracy of the parts.
[0018] 4. By adjusting process parameters such as trajectory length, interlayer spacing, and downward pressure during the buffer replenishment stage, the amount of material transferred to the forming area can be precisely controlled, thereby adapting to the forming requirements of parts of different materials and sizes, and thus enhancing the adaptability of the process. Attached Figure Description
[0019] Figure 1 This is a schematic diagram of the device for moldless single-pass progressive forming of thin-walled deep-cavity parts according to the present invention; Figure 2 This is a schematic diagram of the device for forming thin-walled deep cavity parts without molds using the present invention, which forms a semi-ellipsoidal blank after hydraulic pre-expansion of the initial sheet material. Figure 3 This is a schematic diagram of the final contour and material transfer area of the molded hemispherical part formed by the moldless single-pass progressive forming device of the present invention. Figures 4(a) and 4(b) are schematic diagrams of the composite trajectory of the forming tool when forming a semi-ellipsoidal part using the moldless single-pass progressive forming device of the present invention. Figure 4(a) is the "buffer trajectory" of the forming tool in the non-forming area at the edge of the sheet metal. Figure 4(b) is the "loading trajectory" of the forming tool when forming the semi-ellipsoidal part. The combination of the "buffer trajectory" and the "loading trajectory" forms the composite trajectory of the semi-ellipsoidal part.
[0020] Figure 5(a) and Figure 5(b) are simulation and experimental results of forming a 1060 aluminum plate with an initial thickness of 1 mm and obtaining a hemispherical part with a radius of 35 mm by using the moldless single-pass progressive forming method of the present invention for thin-walled deep cavity parts; Figure 5(a) is the outline of the hemispherical part obtained by finite element simulation; Figure 5(b) is the outline of the hemispherical part obtained by experiment.
[0021] In the figure, 1. Upper pressure plate, 2. Oil chamber cylinder, 3. Sealing groove, 4. Sealing ring, 5. Forming tool, 6. Initial sheet metal, 7. Thread, 8. Needle valve, 9. Relief valve, 10. Pressure gauge, 11. Check valve, 12. Three-phase asynchronous motor, 13. Suction filter, 14. Air filter, 15. Level gauge, 16. Hydraulic oil tank, 17. Semi-ellipsoidal blank, 18. Non-forming area at the edge of the sheet metal, 19. Outline of the hemispherical part after progressive forming. Detailed Implementation
[0022] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.
[0023] Example 1 The present invention relates to a moldless, single-pass, progressive forming apparatus for thin-walled, deep-cavity parts, such as... Figure 1 As shown, the system includes an oil chamber cylinder 2 with an open top. A hollow upper pressure plate 1 is provided at the opening of the oil chamber cylinder 2. An initial plate 6 is horizontally positioned between the upper pressure plate 1 and the oil chamber cylinder 2. A sealing groove 3 is formed at the contact point between the oil chamber cylinder 2 and the initial plate 6, and a sealing ring 4 is provided at the sealing groove 3. A through hole is formed on one side of the oil chamber cylinder 2, which is connected to a hydraulic pre-expansion system via a hydraulic hose. The upper pressure plate 1 and the oil chamber cylinder 2 are connected by threads 7.
[0024] Example 2 The hydraulic pre-expansion system includes a needle valve 8, a check valve 11, a three-phase asynchronous motor 12, an oil suction filter 13, an air filter 14, a level gauge 15, and a hydraulic oil tank 16 connected in sequence. The hydraulic oil tank 16 is also connected in sequence to an overflow valve 9 and a pressure gauge 10.
[0025] Example 3 This invention discloses a moldless, single-pass incremental forming method for thin-walled, deep-cavity parts, aiming to organically integrate hydraulic flexible pre-expansion, active material supply, and single-point incremental forming technology. The method mainly includes the following general steps: Step 1, Determine the target height for pre-bulging. H ; Step 2, based on the pre-bulging target height determined in Step 1 H Form a semi-ellipsoidal blank; Step 3: Start the CNC machine tool and make the forming tool perform single-point progressive forming on the surface of the semi-ellipsoidal blank according to the preset composite loading trajectory.
[0026] Example 4 The specific process of step 1 is as follows: Based on the geometric parameters of the target hemispherical part and the material properties of the sheet metal used, combined with thin film theory and plastic instability criteria, a preliminary target height for pre-expansion is determined. H The target height H should be less than the theoretical limit height of the initial plate 6 under pure hydraulic free bulging. It is usually set to (in (where the radius is the bottom circle radius of the target part) to ensure that the material is in a stable deformation state during the pre-expansion stage and to avoid premature cracking of the sheet metal.
[0027] Example 5 The specific process of step 2 is as follows: Figure 1 The progressive hydraulic composite forming device shown is fixed to the worktable of a CNC machine tool by mounting bolts. This progressive hydraulic composite forming device includes a progressive forming system and a hydraulic pre-expansion system. The progressive forming system includes an upper pressure plate 1, an oil chamber cylinder 2, a sealing groove 3, a sealing ring 4, a forming tool 5, and connecting threads 7. The hydraulic pre-expansion system includes a needle valve 8, an overflow valve 9, a pressure gauge 10, a check valve 11, a three-phase asynchronous motor 12 (connected to a hydraulic pump), an oil suction filter 13, an air filter 14, a level gauge 15, a hydraulic oil tank 16, and hydraulic hoses. The hydraulic pre-expansion system is used to perform pressure-controlled hydraulic expansion of the initial clamped sheet material 6 and provides hydraulic flexible support for the forming sheet material during the progressive forming process.
[0028] The initial plate 6 is placed between the upper pressure plate 1 and the oil chamber 2, and pressed and fixed by the thread 7. The three-phase asynchronous motor 12 in the hydraulic pre-expansion system is started to drive the hydraulic pump to draw hydraulic oil filtered by the suction filter 13 from the hydraulic oil tank 16. The hydraulic pressure value is then controlled by adjusting the needle valve 8 and the relief valve 9 and observing the pressure gauge 10. When the pressurized hydraulic oil enters the sealed oil chamber 2, it will apply a uniform hydraulic force to the initial plate 6. When the stress generated in the plate by this pressure value exceeds the yield strength of the material, the plate begins to undergo plastic deformation, i.e., pre-expansion. At this time, the hydraulic pressure is gradually increased until the initial plate 6 reaches the pre-expansion target height set in step 1. H This forms a semi-ellipsoidal blank.
[0029] Example 6 Step 3 is as follows: Start the CNC machine tool and make the forming tool 5 perform single-point progressive forming on the surface of the semi-ellipsoidal blank according to the preset composite loading trajectory. The composite loading trajectory includes two stages: a) Buffering and replenishment stage: The forming tool 5 first travels a spiral trajectory within the non-forming area 18 at the edge of the sheet metal, extruding and pushing the material from the non-forming area 18 towards the forming area in the center, thus establishing a "material library". The length of this spiral trajectory needs to be determined comprehensively based on factors such as the material properties of the final part, forming depth, curvature, spiral layer spacing, and pitch.
[0030] b) Precision forming stage: After the buffer supply is completed, the forming tool 5 (a cylindrical bar with a ball end) is switched to the spiral loading trajectory of the target part to perform progressive forming of the blank by pressing down layer by layer, and finally obtain the target thin-walled deep cavity part.
[0031] Example 7 This embodiment takes the forming of a hemispherical part with a radius of 35mm using a 1060 circular aluminum plate with an initial thickness of 1mm and a radius of 50mm as an example. The specific implementation steps are as follows: Step 1, based on the geometric parameters (radius) of the target hemispherical part. Based on the material properties of the 1060 aluminum plate (35mm thick) and the material properties of the 1060 aluminum plate used, combined with thin film theory and the Swift plastic instability criterion, a safe target height for pre-expansion was initially determined. H .
[0032] Theoretical calculations show that the theoretical maximum height of this sheet material under hydraulic bulging is... Approximately 0.5 To ensure the material remains in a stable deformation state during the pre-expansion stage and prevent premature sheet cracking, in this embodiment, the target pre-expansion height H is set to 60% of the theoretical limit height, i.e.: H = 0.6 ≈0.6*(0.5 ) = 0.3 = 10.5mm Step 2, Figure 1 The progressive hydraulic composite forming device shown is fixed to the worktable of a CNC machine tool by mounting bolts.
[0033] Step 3: The initial sheet material 6, a 1mm thick, 50mm radius 1060 circular aluminum plate, is placed on top of the oil chamber cylinder 2, and its edges are clamped by the upper pressure plate 1 and the thread 7. The hydraulic pre-expansion system is activated, and by adjusting the overflow valve 9 and monitoring the pressure gauge 10, the expansion height of the central area of the initial sheet material 6 reaches the pre-expansion target height H=10.5mm set in Step 1, forming a shape as shown in the image. Figure 2 The semi-ellipsoidal thin-walled blank 17 is shown.
[0034] Step 4: Start the CNC machine tool and make the forming tool 5 perform single-point progressive forming on the semi-ellipsoidal blank 17 according to the preset composite loading trajectory (composed of the buffer trajectory in Figure 4(a) and the loading trajectory in Figure 4(b)). This process goes through the following two stages in sequence: Buffer replenishment stage: The CNC machine tool controls the forming tool 5 to start from the non-forming area (such as an area with a radius of 35mm to 45mm) at the edge of the sheet 6, and moves layer by layer from the outside to the inside along a spiral trajectory (see Figure 4(a)) with a layer spacing smaller than that of the subsequent precise forming stage. The main purpose of this stage is to replenish the material in the non-forming area at the edge of the sheet ( Figure 3 The non-forming area 18) at the edge of the sheet material is squeezed and pushed towards the center of the sheet material to reserve material for subsequent forming. This stage ends when the spiral trajectory reaches the end of the trajectory shown in Figure 4(a).
[0035] Precision forming stage of the hemispherical part: After the buffer replenishment stage is completed, the forming tool 5 moves to the boundary with radius R0 = 35mm, and its loading trajectory automatically switches to the loading trajectory of the hemispherical part (as shown in Figure 4(b), the outermost starting point of the spiral loading trajectory). Starting from this point, the tool head continues to progressively form the blank, ultimately obtaining the target thin-walled hemispherical part. The contour 19 of the progressively formed hemispherical part is as follows... Figure 3 As shown.
[0036] The effectiveness of this invention in solving the problems in the prior art is verified. By comparing the simulated and experimental profiles of the hemispherical parts in Figures 5(a) and 5(b), it can be found that the experimental results are in high agreement with the simulation results, verifying the reliability of this method. Furthermore, compared with traditional single-point incremental forming, the forming limit is improved by 52% and the geometric accuracy is improved by 9.5% when forming hemispherical parts using the method of this invention. This indicates that the method proposed in this invention can efficiently form thin-walled deep-cavity parts with a thickness of less than 1 mm and a depth-to-diameter ratio of not less than 0.5 through a single-pass forming process, solving the problems of low forming limit, poor accuracy, and easy breakage of thin-walled deep-cavity parts mentioned in the prior art.
Claims
1. An apparatus for dieless single pass incremental forming of thin-walled deep-cavity parts, characterized by: The oil cavity cylinder (2) comprises an upper opening, the upper pressing plate (1) is hollow and arranged at the opening of the oil cavity cylinder (2), the sealing groove (3) is arranged at the opening of the oil cavity cylinder (2), the sealing ring (4) is arranged at the sealing groove (3), and a through hole is formed in one side of the oil cavity cylinder (2) and connected with the hydraulic pre-expansion system through a hydraulic hose.
2. The apparatus for dieless single pass incremental forming of thin-walled deep-cavitated parts of claim 1, wherein: The upper pressing plate (1) is connected with the oil cavity cylinder (2) through the thread (7).
3. The apparatus for dieless single pass incremental forming of thin-walled deep-cavitated parts of claim 1, wherein: The hydraulic pre-expansion system comprises a needle valve (8), a one-way valve (11), a three-phase asynchronous motor (12), an oil suction filter (13), an air filter (14), a liquid level meter (15) and a hydraulic oil tank (16) connected in sequence.
4. The apparatus for dieless single pass incremental forming of thin-walled deep-cavitated parts of claim 3, wherein: The hydraulic oil tank (16) is further connected with an overflow valve (9) and a pressure gauge (10) in sequence.
5. A method for dieless single pass incremental forming of thin-walled deep-cavity parts, characterized in that: Specifically, the method comprises the following steps: Step 1, determining a pre- bulging target height H ; Step 2, pre- bulging target height determined according to step 1 H forming a half-ellipsoidal blank; Step 3: starting the numerical control machine tool, and making the forming tool (5) perform single-point incremental forming on the surface of the semi-ellipsoid blank according to the preset composite loading track.
6. The method of dieless single pass incremental forming of thin-walled deep-cavity parts according to claim 5, wherein: the pre- bulging target height in step 1 H less than the limit height of the initial sheet (6) under pure hydraulic free bulging .
7. The method of dieless single pass incremental forming of thin-walled deep-cavity parts according to claim 6, wherein: The specific process of the step 2 is as follows: the initial plate (6) is placed between the upper pressing plate (1) and the oil cavity cylinder (2), and the pressing plate (1) and the oil cavity cylinder (2) are connected through the thread to press and fix the initial plate (6), the three-phase asynchronous motor (12) in the hydraulic pre-expansion system is started to drive the hydraulic pump to extract the hydraulic oil filtered through the oil suction filter (13) from the hydraulic oil tank (16), and then the hydraulic pressure value is controlled by adjusting the needle valve (8) and the overflow valve (9) and observing the pressure gauge (10); when the hydraulic oil with pressure enters the sealed oil cavity cylinder (2), the initial plate (6) is subjected to uniform hydraulic action force, when the stress generated in the initial plate (6) exceeds the yield strength of the material, the initial plate (6) begins to deform plastically, that is, pre-expansion, and at this time, the hydraulic pressure is continuously increased until the initial plate (6) reaches the pre-expansion target height H set in the step 1 to form a semi-ellipsoid blank.
8. The method of dieless single pass incremental forming of thin-walled deep-cavity parts according to claim 7, wherein: In the step 3, the composite loading track comprises a buffer track in a buffer supplement stage and a spiral loading track in an accurate forming stage.
9. The method of claim 8, wherein: In the step 3, the specific process of the buffer supplement stage is as follows: the forming tool (5) first walks a spiral track in the non-forming area (18) of the plate edge to extrude and push the material in the non-forming area (18) of the plate edge to the center forming area to establish a "material library".
10. The method of dieless single pass incremental forming of thin-walled deep-cavity parts according to claim 9, wherein: In the step 3, the specific process of the accurate forming stage is as follows: after the buffer supplement is completed, the forming tool (5) is switched to the spiral loading track of the target part to perform layer-by-layer incremental forming on the blank.