A method for cold stamping and thinning forming of thick metal plate and a die structure applied thereto

Abstract

The application discloses a kind of thick metal plate cold stamping thinning forming method and the die structure of application, the method includes the following steps: to be processed plate on stamping die stamping obtains forming intermediate piece;The drawing flanging of the forming intermediate piece is obtained on drawing die;The drawing intermediate piece is shaped on shaping die and is obtained shaping intermediate piece;The inner wall multichannel thinning of the shaping intermediate piece is carried out on thinning die, and after inner wall thinning to target size, further to the finish machining of appearance is obtained target product.The thick metal plate cold stamping thinning forming method and the die structure of application of the application can make inner wall material flow a lot and outer wall material flow a little, so that the wall thickness size of product can be more accurately controlled, and material utilization is improved, and material mechanical properties are improved.

Description

Technical Field

[0001] This invention relates to a method for cold stamping and thinning of thick metal sheets and the mold structure for its application, and more particularly to a method for cold stamping and thinning of thick metal sheets for forming a hat-shaped flexible wheel in a harmonic reducer and the mold structure for its application. Background Technology

[0002] Harmonic reducers, as precision transmission devices that utilize the controllable elastic deformation of flexible gears for motion and power transmission, possess outstanding advantages such as compact structure, small size, light weight, large reduction ratio, and high transmission accuracy. They are widely used in industrial robots, humanoid robots, aerospace, CNC machine tools, and medical devices. The flexspline is the most critical and fatigue-prone component in a harmonic reducer; its quality directly determines the reducer's load-bearing capacity, transmission accuracy, and service life. The top-hat flexspline, with its short axial dimension, compact structure, and ease of internal wiring, is particularly suitable for space-constrained applications (such as the wrist joint of a robot end effector). Furthermore, under high load conditions, its stress increase is significantly lower than that of a cup-shaped flexspline, making it the preferred structure for high-load harmonic reducers.

[0003] The top-hat type flexible gear is a thin-walled, cup-shaped flexible gear with a cylinder wall thickness typically ranging from 0.2 mm to 0.8 mm. The wall thickness tolerance must be controlled within ±0.01 mm, and the material is mostly medium-carbon alloy steel such as 40CrNiMo. To ensure the fatigue strength and life of the flexible gear, the forming process of its semi-finished product (before tooth machining) must simultaneously meet stringent requirements such as high material utilization, high dimensional accuracy, fine grain structure, and excellent metal flow line distribution.

[0004] Currently, the forming processes for top hat-shaped flexible wheel semi-finished products are mainly divided into the following three categories: I. Forging, hot forming, and precision machining processes The process involves hot forging of bar stock to obtain a flexible gear blank, followed by heat treatment and machining such as turning and gear hobbing. This process has the following significant drawbacks: 1. Most of the material is removed, resulting in extremely low material utilization (only about 3.6% in die forging process). 2. High-temperature forming leads to grain coarsening (25-40 μm, grain size only 6-8 grade), uneven microstructure, and easy oxidation and decarburization; 3. Subsequent machining operations are extensive and costly.

[0005] In addition, the forging process makes it difficult to form continuous and uniformly distributed metal flow lines along the cylinder axis, which has an adverse effect on the fatigue life of the flexible wheel.

[0006] II. Stamping Hot Forming Process This process uses hot stamping to form sheet metal into cylindrical semi-finished products. Although this process improves material utilization compared to forging, hot stamping still faces problems such as grain coarsening and uneven microstructure caused by high temperatures. Furthermore, the cylinder wall is usually not effectively thinned, resulting in poor wall thickness uniformity, large machining allowances, and ultimately, low material utilization. For thick metal sheets (2 mm to 8 mm), controlling material flowability during hot stamping is difficult, leading to a high defect rate.

[0007] III. Cold stamping forming process In recent years, to overcome the defects of hot forming, the industry has begun to explore cold stamping processes. For example, Chinese invention patent application number "2026100892209," entitled "A Flexible Gear, Its Manufacturing Method and Its Application in Harmonic Reducers," discloses a manufacturing method based on cold stamping. Specifically, it includes: sequentially heat-treating sheet metal, blanking, deep drawing stamping, and deep drawing-thinning stamping to obtain a semi-finished product with a machining allowance within 0.2 mm, followed by tempering, deep cooling, finishing, gear hobbing, and shot peening. This technology significantly improves material utilization and refines the grain size (to grade 11.5 or higher) through cold deformation combined with subsequent heat treatment. It also forms uniform metal flow lines extending from the bottom to the top of the cylinder, effectively improving the axial tensile strength and fatigue life of the flexible gear. However, the aforementioned existing cold stamping technology still faces the following technical bottlenecks in terms of precise wall thickness control: 1. Thinning methods primarily employ either "external wall thinning" or "overall thinning." In traditional processes, deep drawing-thinning dies typically control wall thickness through the gap between the punch and die. During thinning, the material flows more on the outer wall and less on the inner wall, resulting in wall thickness uniformity being limited by the die gap precision and material anisotropy. For deep cylindrical thin-walled parts such as top-hat shaped flexible wheels, the "brim" structure of the top-hat shaped flexible wheel makes internal wall thinning more suitable than external wall thinning. In existing cold stamping processes, inner wall forming largely relies on the passive extrusion of the punch, which cannot achieve a large-scale directional flow of material on the inner wall, often requiring a large machining allowance for the inner wall dimensions.

[0008] 2. Multi-pass thinning lacks a systematic mold structure design. When a large total thinning amount is required (e.g., from 4 mm to 1.25 mm, a thinning rate of nearly 70%), existing processes typically employ multiple independent drawing-thinning operations. Each time the mold is changed or the clearance is adjusted, the processes are scattered, resulting in large cumulative errors. Furthermore, the material hardens severely between each pass, making it prone to cracking. Although the concept of multi-pass progressive thinning has been proposed, a single-mold multi-pass continuous thinning structure using a "multi-stage annular step punch" combined with a "constant inner diameter die" has not yet been seen for inner wall thinning.

[0009] 3. In existing cold stamping thinning processes, large plastic deformation generates significant deformation heat, leading to increased die temperature and lubrication film failure, which in turn affects the dimensional stability and surface quality of the thinned workpiece. Although existing technologies occasionally mention cooling, they do not provide an integrated cooling structure or specific cooling parameters suitable for multi-pass inner wall thinning dies.

[0010] In summary, a cold stamping thinning method is urgently needed to address the challenges of producing thick metal sheets (2 mm to 8 mm thick) for the top-hat type flexible wheel of a harmonic reducer. This method enables the inner wall material to flow dominantly while the outer wall is subject to controlled constraints. By innovating the mold structure, multi-pass continuous and precisely controlled inner wall thinning can be achieved, thereby further reducing the wall thickness machining allowance and precisely controlling the wall thickness tolerance. Simultaneously, large plastic deformation can be used to refine the grains and improve mechanical properties. Summary of the Invention

[0011] This invention addresses the shortcomings of the prior art by providing a method for cold stamping and thinning of thick metal sheets for use in harmonic reducer flexures, as well as a mold structure for the application, which is particularly suitable for top hat-shaped flexures.

[0012] The method for cold stamping and thinning of thick metal sheets according to the present invention includes the following steps: Step 1: Stamp the sheet material to be processed on a stamping die to obtain a formed intermediate part; wherein, the sheet material to be processed is a thick metal sheet with a thickness between 2 mm and 8 mm; Step 2: The forming intermediate part is drawn and flanged on a drawing die to obtain a deep-drawn intermediate part; Step 3: The deep-drawn intermediate part is shaped and stamped on a forming die to obtain a shaped intermediate part; Step 4: The shaping intermediate part is thinned in multiple passes on the inner wall of the thinning mold, and after the inner wall is thinned to the target size, the outer shape is further refined to obtain the target finished product; The inner wall thinning process employs a punch with multiple thinning rings of progressively increasing outer diameter arranged from bottom to top on its outer circumference. This punch presses the shaped intermediate part into a thinning die with a fixed inner diameter. The thinning rings sequentially contact and compress the inner wall of the shaped intermediate part, causing the inner wall material to flow outwards and thin. The flow of the outer wall material is constrained by the thinning die, resulting in a less rapid flow than the inner wall material. Furthermore, the number of thinning rings on the outer circumference of the punch is 3 to 8 levels, and the outer diameter increment of each level of thinning ring is 0.1 mm to 0.5 mm from bottom to top.

[0013] In step two of the cold stamping thinning forming method for thick metal sheets of the present invention, when the forming intermediate part is placed on the deep drawing die, a blank holder is used to press down the periphery of the forming intermediate part, and then a punch is used to perform through stamping on the forming intermediate part to draw and flanging the forming intermediate part. Further, an ejector device is used to eject the deep-drawn intermediate part from the deep drawing die.

[0014] In step four of the cold stamping thinning forming method for thick metal sheets described in this invention, the forming intermediate part is placed on the thinning die of the thinning mold and pressed by the blank holder; then, the forming intermediate part is stamped by the punch thinning punch to thin the inner wall of the forming intermediate part in multiple passes. Further, a heat exchange medium between 0°C and 10°C is used to cool the forming intermediate part undergoing multiple inner wall thinning.

[0015] The mold structure for cold stamping and thinning of thick metal sheets according to the present invention includes a stamping mold for stamping the sheet to be processed into a forming intermediate part, a drawing mold for drawing and flanging the forming intermediate part into a drawing intermediate part, a forming mold for shaping and stamping the drawing intermediate part into a forming intermediate part, and a thinning mold for thinning the inner wall of the forming intermediate part in multiple passes. The thinning die includes a punch thinning pin, a thinning die, a pressure ring, and a cooling device. The outer periphery of the punch thinning rod is provided with multiple thinning rings with progressively increasing outer diameters from bottom to top; The thinning die has a constant inner diameter; The shaping intermediate part is pressed against the thinning die by the pressure ring. The punching thinning rod punches down, causing each thinning ring to contact and squeeze the inner wall of the shaping intermediate part in sequence, and pressing the shaping intermediate part into the thinning die. This causes the inner wall material of the shaping intermediate part to flow outward and thin, while the outer wall material is constrained by the thinning die and its flow rate is less than that of the inner wall material.

[0016] In the mold structure for cold stamping and thinning of thick metal sheets according to the present invention, the stamping mold includes a fixedly arranged stamping support mold base, and a forming die corresponding to the outer edge shape of the forming intermediate part is provided on the top of the stamping support mold base. And, a stamping punch that is configured to cooperate with the forming die, the stamping punch having a punch corresponding to the inner edge shape of the forming intermediate; It also includes a stamping blank assembly for pressing the periphery of the sheet metal to be processed against the stamping support die base; The punch penetrates the center of the stamping assembly and acts downwards on the sheet metal to be processed, thereby stamping to form the intermediate part.

[0017] In the mold structure for cold stamping and thinning of thick metal sheets according to the present invention, the deep drawing mold includes a fixedly arranged deep drawing support mold base, and the center of the deep drawing support mold base is provided with a through deep drawing hole corresponding to the outer edge shape of the deep drawing intermediate part; And, a drawing punch that mates with the drawing hole, the drawing punch having an outer edge corresponding to the inner edge shape of the drawing intermediate; It also includes a drawing blanking assembly for pressing the periphery of the forming intermediate against the drawing support die base, and an ejector assembly disposed below the drawing hole; The drawing punch plunges into the drawing hole to draw and flang the forming intermediate part to form a drawn intermediate part, and the ejector assembly ejects the drawn intermediate part from the drawing hole.

[0018] In the mold structure for cold stamping and thinning of thick metal sheets according to the present invention, the forming mold includes a forming support mold base, and the forming support mold base has a forming hole corresponding to the outer edge shape of the forming intermediate part; It also includes a shaping punch, which has a shaping punch corresponding to the inner edge shape of the shaping intermediate part, and a shaping ring groove distributed at the root of the shaping punch; The forming punch of the forming die punches downward into the forming hole, and the forming ring groove abuts against the top surface of the forming support die base, so as to form and stamp the deep-drawing intermediate part into a forming intermediate part.

[0019] In the mold structure for cold stamping and thinning of thick metal sheets described in this invention, the thinning mold further includes a matching ejector device; The ejector device ejects the shaping intermediate part, which has undergone multiple thinning processes on its inner wall, from the thinning die. The cooling device includes an inner wall cooling assembly for the shaping intermediate and an outer wall cooling assembly for the shaping intermediate. The cooling assembly for the inner wall of the forming intermediate part includes an axial fluid flow pipe arranged along the axial direction of the punch thinning rod. The axial fluid flow pipe has a fluid channel at the junction of two adjacent thinning rings. The heat exchange medium introduced from the outside flows through the axial fluid flow pipe and then flows out through the fluid channel. It then flows through the radial fluid flow groove opened on the top surface of the thinning ring and flows to the space between the inner wall of the forming intermediate part and the outer diameter of the thinning ring to cool the inner wall of the forming intermediate part. The cooling assembly for the outer wall of the shaping intermediate includes a cooling groove disposed at the bottom of the pressure ring. The heat exchange medium introduced from the outside flows through the cooling groove and then flows between the shaping intermediate and the inner wall of the thinning die to cool the outer wall of the shaping intermediate.

[0020] The technical effects of the cold stamping thinning forming method for thick metal sheets applied to the hat-shaped flexible wheel of a harmonic reducer, and the mold structure used in this invention, are as follows: (i) Achieve precise thinning dominated by the inner wall and improve the accuracy of wall thickness control.

[0021] This invention employs a punch with multiple annular steps on its outer periphery that progressively increase in outer diameter, in conjunction with a thinning die having a constant inner diameter. This causes the inner wall material to flow outward under pressure; while the outer wall material, constrained by the thinning die, flows less than the inner wall material. Compared to existing methods of thinning the outer wall of products (which result in a large flow of outer wall material and a small flow of inner wall material), this invention allows for a large flow of inner wall material and a small flow of outer wall material, thereby enabling more precise control of the product's wall thickness.

[0022] (ii) Reduce cumulative error by continuously thinning through multiple passes in one mold.

[0023] This invention features multiple thinning rings with progressively increasing outer diameters on a single thinning die. The thinning punch can complete multiple thinning passes in a single stroke. The process eliminates the need for die changes or multiple positioning operations, reducing accumulated errors between processes and improving processing efficiency and product consistency.

[0024] (iii) An integrated cooling system is adopted to effectively control thermal deformation during thinning.

[0025] This invention incorporates a cooling device within the thinning mold. The cooling medium cools the intermediate part undergoing multiple thinning passes on its inner wall, with the temperature of the heat exchange medium controlled between 0°C and 10°C. Directional cooling reduces thermal deformation during the thinning process, ensuring dimensional stability.

[0026] (iv) To achieve large plastic deformation of thick plates, refine grains, and improve mechanical properties and fatigue life.

[0027] This invention achieves large plastic deformation of thick plates by cold stamping with multiple inner wall thinning passes, and obtains fine grain strengthening effect by subsequent heat treatment. It achieves technical effects that are significantly better than traditional hot forming processes in terms of grain refinement, strength improvement and fatigue life extension.

[0028] (v) Particularly suitable for the manufacturing of semi-finished products of hat-shaped flexible wheels in harmonic reducers.

[0029] Because of the unique "brim" structure of the top hat-shaped flexible wheel, traditional outer wall thinning methods are difficult to position and easily damage the structural integrity. This invention, however, uses an inner wall thinning method, where the punch thinning pin presses downwards from inside the cylinder, and the outer wall is only constrained by the die, avoiding interference from the "brim" structure. This method is particularly suitable for the precision forming of deep-cylinder, thin-walled parts such as top hat-shaped flexible wheels, and is also applicable to other flexible wheel types that require inner wall thinning.

[0030] In summary, this invention, through innovations in thinning die structure, material flow control, cooling scheme, and process integration, achieves precise control over the cold stamping thinning process of thick metal sheets. It has achieved technical effects such as precise control of wall thickness, improved material utilization, grain refinement, and significant improvement in mechanical properties and fatigue life, demonstrating outstanding substantive features and significant progress. Attached Figure Description

[0031] Figure 1 This is a schematic flowchart of the cold stamping thinning forming method for thick metal sheets according to the present invention; Figure 2 This is a schematic diagram of the structure of the cold stamping thinning forming method for thick metal sheets described in this invention, which uses a stamping die for stamping. Figure 3 This is a schematic diagram of the structure of the forming intermediate in the cold stamping thinning forming method of thick metal sheet described in this invention; Figure 4 This is a schematic diagram of the structure of the cold stamping thinning forming method for thick metal sheets described in this invention, which uses a deep drawing die for deep drawing and flanging. Figure 5 This is a schematic diagram of the structure of the cold stamping thinning forming method for thick metal sheets described in this invention, which uses a forming die for forming. Figure 6A This is a schematic diagram of the structure of the cold stamping and thinning forming method for thick metal sheets described in this invention, which uses a thinning die for multi-stage thinning. Figure 6B This is a cross-sectional schematic diagram of the thinning die in the cold stamping thinning forming method for thick metal sheets described in this invention; Figure 7A , 7B 7C and 7D are schematic diagrams of the wall thickness state of the forming intermediate part after multiple thinning in the cold stamping thinning forming method of thick metal sheet described in this invention. Figure 8 This is a schematic diagram of the original austenite grain distribution of a thick metal sheet before it is processed using the cold stamping and thinning forming method for thick metal sheets described in this invention. Figure 9 This is a schematic diagram of the original austenite grain distribution after a thick metal sheet is processed using the cold stamping and thinning forming method for thick metal sheets described in this invention. Figure 10This is a schematic diagram of the microstructure of a thick metal sheet after it has been processed using the cold stamping and thinning method for thick metal sheets described in this invention and then subjected to quenching and tempering heat treatment. Detailed Implementation

[0032] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0033] like Figure 1 As shown, the cold stamping thinning method for thick metal sheets according to the present invention includes the following steps: Step 101: Stamp the sheet material to be processed on the stamping die to obtain the formed intermediate part.

[0034] In this step, the sheet material 10 to be processed is placed on a stamping die for stamping to obtain a formed intermediate part for use in subsequent processes. In this embodiment, the sheet material to be processed is a thick metal sheet with a thickness between 2 mm and 8 mm.

[0035] like Figure 2 , Figure 3 As shown, the stamping die specifically includes a fixedly disposed stamping support die base 13, and a forming die 131 corresponding to the outer edge shape of the forming intermediate part 20 is disposed on the top of the stamping support die base 13. It also includes a stamping punch 11 that cooperates with the forming die 131, the stamping punch 111 having a punch head 111 corresponding to the inner edge shape of the forming intermediate part 20. Furthermore, it includes a stamping pressure assembly 12 for pressing the periphery 110 of the sheet metal 10 to be processed against the stamping support die base 13. During processing, the sheet metal 10 to be processed is placed on the stamping support die base 13, and the stamping pressure assembly 12 presses down on the sheet metal 10. Then, the punch head 111 penetrates the center 121 of the stamping pressure assembly 12 and punches downwards onto the sheet metal 10 to form the forming intermediate part 20.

[0036] Step 102: The forming intermediate part is drawn and flanged on a drawing die to obtain a deep-drawing intermediate part.

[0037] In this step, the forming intermediate part 20 is placed on the deep drawing die for deep drawing and flanging, thereby obtaining the deep drawing intermediate part 30.

[0038] like Figure 4As shown, the deep drawing die specifically includes a fixedly disposed deep drawing support die base 23, the center of which is provided with a deep drawing hole 231 corresponding to the shape of the outer edge 301 of the deep drawing intermediate part 30. It also includes a deep drawing punch 21 that mates with the deep drawing hole 231, the deep drawing punch 21 having an outer edge 211 corresponding to the shape of the inner edge 302 of the deep drawing intermediate part 30. Furthermore, it includes a deep drawing blanking assembly 22 for pressing the periphery 301 of the deep drawing intermediate part 30 against the deep drawing support die base 23, and an ejector assembly 24 disposed below the deep drawing hole 231. During processing, the forming intermediate part 20 is placed on the deep drawing support die 23, and the periphery of the forming intermediate part 20 is pressed by the pressure assembly 22. Then, the deep drawing punch 21 is made to punch into the deep drawing hole 231 to draw and flang the forming intermediate part 20 to form the deep drawing intermediate part 30. Finally, the ejector assembly 24 is used to eject the deep drawing intermediate part 30 from the deep drawing hole 231.

[0039] Step 103: The deep-drawing intermediate part is shaped and stamped on a forming die to obtain a shaped intermediate part.

[0040] like Figure 5 As shown, the forming mold specifically includes a forming support mold base 32, which has a forming hole 321 corresponding to the shape of the outer edge 401 of the forming intermediate part 40. It also includes a forming punch 31, which has a forming punch 311 corresponding to the shape of the inner edge 402 of the forming intermediate part 40, and forming annular grooves 312 distributed at the root of the forming punch 311. During processing, the deep-drawing intermediate part 30 is placed on the forming support die base 32, and the forming punch 311 of the forming punch 31 is made to punch down into the forming hole 321. At the same time, the forming ring groove 312 is made to abut against the top surface of the forming support die base 32. With the help of the cooperation between the forming punch 311 and the forming hole 321, and the cooperation between the forming ring groove 312 and the corresponding retaining plate on the top of the forming support die base 32, the deep-drawing intermediate part 30 is formed and stamped into a forming intermediate part 40.

[0041] Step 104: The shaping intermediate part is thinned in multiple layers on the inner wall of the thinning mold, and after the inner wall is thinned to the target size, the outer shape is further refined to obtain the target finished product.

[0042] In this step, a thinning mold is used to perform multiple thinning processes on the inner wall of the shaping intermediate part 40 until the inner wall size of the shaping intermediate part 40 reaches the predetermined target size. Then, the outer shape of the shaping intermediate part 40 is further refined to obtain the target finished product.

[0043] like Figure 6A , Figure 6BAs shown, the thinning die specifically includes a punch thinning pin 520, with multiple thinning rings 52 of progressively increasing outer diameters arranged around the outer periphery of the punch thinning pin 520 (specifically, a first-stage thinning ring 521, a second-stage thinning ring 522, and a third-stage thinning ring 523 with progressively increasing outer diameters from bottom to top; the thinning rings 52 can be specifically set in multiple stages, for example, 3 to 8 stages, and the outer diameter of these thinning rings increases by 0.1 mm to 0.5 mm at each stage from bottom to top). It also includes a thinning die 51 (the thinning die has a fixed inner diameter) that is correspondingly matched with the multiple thinning rings, and a pressure ring 53 for pressing the forming intermediate part 40 against the thinning die 51; it also includes a matching cooling tank 54 and an ejector device 55.

[0044] The shaping intermediate part 40 is pressed against the thinning die 51 by the pressure ring 53. The pressure ring 53, as a core anti-wrinkle device, applies a controllable pressure force to the flange area 501 of the shaping intermediate part 40 to prevent wrinkling defects caused by tangential compressive stress, ensuring that the material can flow smoothly into the thinning die 51. The punch thinning shank 520 punches downwards, causing multiple thinning rings 52 to sequentially press the shaping intermediate part 40 into the thinning die 51 for inner wall thinning (e.g., ...). Figure 7A , Figure 7B , Figure 7C , Figure 7D As shown, multiple thinning rings 52 sequentially press the shaping intermediate part 40, causing the inner wall of the shaping intermediate part 40 to gradually thin, i.e., sequentially presenting the following characteristics. Figure 7A , Figure 7B , Figure 7C , Figure 7D(The wall thickness reduction state is shown). The thinning ring 52 acts as an active forming component, pressing the shaping intermediate 40 into the thinning die 51 to form a cylindrical shape. The thinning die 51 acts as a passive forming component, determining the outer diameter 502 of the shaping intermediate 40. During the thinning process, the shaping intermediate 40 is subjected to radial tensile stress (i.e., driving the material to flow into the thinning die 51) and tangential compressive stress (i.e. causing the material to compress in the circumferential direction). The combination of radial tensile stress and tangential compressive stress causes the material to elongate axially and contract radially, thereby reducing the wall thickness. In other words, by sequentially contacting and pressing the inner wall of the shaping intermediate 40 with each thinning ring, the inner wall material of the shaping intermediate 40 flows outward and thins, while the flow of the outer wall material is less than that of the inner wall material due to the constraint of the thinning die 51. To reduce the thermal deformation of the forming intermediate 40 during the inner wall thinning process, the present invention also employs a cooling device to cool the outer wall and inner wall of the forming intermediate 40 respectively. That is, the cooling device includes an inner wall cooling component and an outer wall cooling component of the forming intermediate. The cooling assembly for the inner wall of the forming intermediate part includes an axial fluid flow pipe 5210 arranged along the axial direction of the punch thinning rod 520. The axial fluid flow pipe 5210 has a fluid channel 5211 at the junction 5212 of two adjacent thinning rings. The heat exchange medium (temperature between 0 and 10°C) introduced from the outside flows through the axial fluid flow pipe 5210 and then flows out through the fluid channel 5211. It then flows through the radial fluid flow groove (not shown in the figure) opened on the top surface of the thinning ring and flows to the area between the inner wall of the forming intermediate part 40 and the outer diameter of the thinning ring to cool the inner wall of the forming intermediate part 40. At the same time, the heat exchange medium can also form lubrication between the thinning ring and the inner wall of the forming intermediate part to prevent the forming intermediate part from being scratched during the multi-stage thinning process. The cooling assembly for the outer wall of the shaping intermediate part includes a cooling groove 54 disposed at the bottom of the pressure ring 53. The heat exchange medium (temperature between 0 and 10°C) introduced from the outside flows through the cooling groove 54 and then flows to the space between the inner wall of the shaping intermediate part 40 and the thinning die 51 to cool the outer wall of the shaping intermediate part 40, while also having the effect of lubrication and friction reduction.

[0045] After the inner wall of the forming intermediate part 40 is thinned to the target size, the ejector device 55 ejects the forming intermediate part 40 from the thinning die 51. Compared to the thinning dies used in the prior art for processing cylindrical products, which thin the outer wall of the product (i.e., a large flow of material on the outer wall and a small flow of material on the inner wall), the thinning die in this embodiment, which can achieve multi-stage thinning of the inner wall, allows for a large flow of material on the inner wall and a small flow of material on the outer wall. This allows for more precise control of the product's wall thickness, improves material utilization, and enhances the material's mechanical properties. After the above-mentioned multi-stage thinning process, the outer shape can be further refined to improve product precision, ultimately obtaining a qualified target finished product.

[0046] Example 1 To further verify the technical effect of the present invention, an embodiment is provided here. A flexible wheel sample was prepared using a 4mm thick 40CrNiMo metal sheet as the material to be processed. The method described in this invention (including stamping, deep drawing and flanging, shaping, and multiple thinning of the inner wall to 1.25mm) was employed, along with subsequent heat treatment. A comparative test was conducted with a flexible wheel of the same specifications prepared using a traditional hot forming process (hot forging + machining). The results are as follows: (a) Comparison of grain structure.

[0047] Traditional thermoformed flexible wheels have a grain size of 25–40 μm and a grain size level of only 6–8. Their microstructure is characterized by coarse, uneven grains and localized mixed grain phenomena (such as…). Figure 8 (As shown). The flexible wheel prepared by the method of this invention, after large deformation thinning (4mm→1.25mm, cumulative thinning rate of about 68.75%) and subsequent heat treatment, has a grain size refined to 5-8μm, a grain size level of 11-12, and a microstructure characterized by uniform and fine equiaxed grains without obvious coarse grains (as shown). Figure 9 (As shown). The grain size is reduced to 1 / 4 to 1 / 5 of that of the traditional process, and the uniformity of the microstructure is significantly improved.

[0048] (II) Comparison of mechanical properties.

[0049] 1. Tensile strength: Traditional thermoformed flexible wheels have a tensile strength of 800-900 MPa, while the flexible wheels of this invention have a tensile strength of 1000-1150 MPa, representing an increase of 15%-30%.

[0050] 2. Yield strength: Traditional thermoformed flexible wheels have a yield strength of 650-750 MPa, while the flexible wheel of this invention has a yield strength of 950-1000 MPa.

[0051] 3. Impact toughness: Traditional hot-formed flexible wheels have low impact toughness and are prone to brittle fracture; the impact toughness of the flexible wheel of this invention is improved by 30% to 60%.

[0052] (III) Comparison of fatigue life Under rated loading conditions, the fatigue life of a conventional hot-formed flexible wheel is approximately 10. 7 ~10 8 Furthermore, the fatigue life of the flexible wheel prepared by this invention can reach 10... 9 The improvement is 5 to 10 times, representing a leap of an order of magnitude. Metallographic testing shows (e.g.) Figure 10 As shown in the figure, the flexible wheel of the present invention has fine and uniform grains, clear grain boundaries, no coarse grain regions, and a dense and continuous structure, while the conventional thermoformed flexible wheel has coarse grains of varying sizes, blurred grain boundaries, and banded structures and local coarse grain regions.

[0053] The comparative data above show that the present invention can achieve large plastic deformation of thick plates by cold stamping with multiple inner wall thinning, and obtain fine grain strengthening effect by subsequent heat treatment. It has achieved technical effects that are significantly better than traditional hot forming processes in terms of grain refinement, strength improvement and fatigue life extension.

[0054] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for cold stamping and thinning of thick metal sheets, characterized in that, Includes the following steps: Step 1: Stamp the sheet material to be processed on a stamping die to obtain a formed intermediate part; wherein, the sheet material to be processed is a thick metal sheet with a thickness between 2 mm and 8 mm; Step 2: The forming intermediate part is drawn and flanged on a drawing die to obtain a deep-drawn intermediate part; When the forming intermediate part is placed on the drawing die, the periphery of the forming intermediate part is pressed down by a pressure device, and then the forming intermediate part is drawn and flanged by a punch. Step 3: The deep-drawn intermediate part is shaped and stamped on a forming die to obtain a shaped intermediate part; Step 4: The shaping intermediate part is thinned in multiple passes on the inner wall of the thinning mold, and after the inner wall is thinned to the target size, the outer shape is further refined to obtain the target finished product; The shaping intermediate part is placed on the thinning die of the thinning mold and pressed by the pressure ring; then the shaping intermediate part is punched by the punch to thin the inner wall of the shaping intermediate part in multiple passes; at the same time, the inner wall and outer wall of the shaping intermediate part undergoing multiple inner wall thinning are cooled by a heat exchange medium between 0°C and 10°C. The inner wall thinning process employs a punch with multiple thinning rings of progressively increasing outer diameter arranged from bottom to top on the outer periphery. This punch presses the shaped intermediate part into a thinning die with a fixed inner diameter. The thinning rings sequentially contact and compress the inner wall of the shaped intermediate part, causing the inner wall material to flow outward and thin. The flow of the outer wall material is constrained by the thinning die and is therefore less than that of the inner wall material. The number of thinning rings on the outer periphery of the punch thinning rod is 3 to 8, and the outer diameter increment of each thinning ring from bottom to top is 0.1 mm to 0.5 mm.

2. The method for cold stamping and thinning of thick metal sheets as described in claim 1, characterized in that, The drawing intermediate part is ejected from the drawing die using an ejector device.

3. A mold structure for the cold stamping thinning forming method of thick metal sheet as described in claim 1, characterized in that, It includes a stamping die for stamping a sheet metal to be processed into a forming intermediate part, a drawing die for drawing and flanging the forming intermediate part into a drawing intermediate part, a forming die for shaping and stamping the drawing intermediate part into a forming intermediate part, and a thinning die for thinning the inner wall of the forming intermediate part in multiple passes. The thinning die includes a punch thinning pin, a thinning die, a pressure ring, and a cooling device. The thinning mold also includes a matching ejector device; The ejector device ejects the shaping intermediate part, which has undergone multiple thinning processes on its inner wall, from the thinning die. The cooling device includes an inner wall cooling assembly for the shaping intermediate and an outer wall cooling assembly for the shaping intermediate. The cooling assembly for the inner wall of the forming intermediate part includes an axial fluid flow pipe arranged along the axial direction of the punch thinning rod. The axial fluid flow pipe has a fluid channel at the junction of two adjacent thinning rings. The heat exchange medium introduced from the outside flows through the axial fluid flow pipe and then flows out through the fluid channel. It then flows through the radial fluid flow groove opened on the top surface of the thinning ring and flows to the space between the inner wall of the forming intermediate part and the outer diameter of the thinning ring to cool the inner wall of the forming intermediate part. The cooling assembly for the outer wall of the shaping intermediate includes a cooling groove disposed at the bottom of the pressure ring. The heat exchange medium introduced from the outside flows through the cooling groove and then flows to the space between the shaping intermediate and the inner wall of the thinning die to cool the outer wall of the shaping intermediate. The outer periphery of the punch thinning rod is provided with multiple thinning rings with progressively increasing outer diameters from bottom to top; The thinning die has a constant inner diameter; The shaping intermediate part is pressed against the thinning die by the pressure ring. The punching thinning rod punches down, causing each thinning ring to contact and squeeze the inner wall of the shaping intermediate part in sequence, and pressing the shaping intermediate part into the thinning die. This causes the inner wall material of the shaping intermediate part to flow outward and thin, while the outer wall material is constrained by the thinning die and its flow rate is less than that of the inner wall material.

4. The mold structure as described in claim 3, characterized in that, The stamping die includes a fixedly arranged stamping support die base, and the top of the stamping support die base is provided with a forming die corresponding to the outer edge shape of the forming intermediate part; And, a stamping punch that is configured to cooperate with the forming die, the stamping punch having a punch corresponding to the inner edge shape of the forming intermediate; It also includes a stamping blank assembly for pressing the periphery of the sheet metal to be processed against the stamping support die base; The punch penetrates the center of the stamping assembly and acts downwards on the sheet metal to be processed, thereby stamping to form the intermediate part.

5. The mold structure as described in claim 3, characterized in that, The drawing die includes a fixedly arranged drawing support die base, and the center of the drawing support die base is provided with a through drawing hole corresponding to the outer edge shape of the drawing intermediate part; And, a drawing punch that mates with the drawing hole, the drawing punch having an outer edge corresponding to the inner edge shape of the drawing intermediate; It also includes a drawing blanking assembly for pressing the periphery of the forming intermediate against the drawing support die base, and an ejector assembly disposed below the drawing hole; The drawing punch plunges into the drawing hole to draw and flang the forming intermediate part to form a drawn intermediate part, and the ejector assembly ejects the drawn intermediate part from the drawing hole.

6. The mold structure as described in claim 3, characterized in that, The shaping mold includes a shaping support mold base, which has shaping holes corresponding to the outer edge shape of the shaping intermediate part; It also includes a shaping punch, which has a shaping punch corresponding to the inner edge shape of the shaping intermediate part, and a shaping ring groove distributed at the root of the shaping punch; The forming punch of the forming die punches downward into the forming hole, and the forming ring groove abuts against the top surface of the forming support die base, so as to form and stamp the deep-drawing intermediate part into a forming intermediate part.

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