Liquefied petroleum gas cylinder end stamping die, stamping mechanism and forming method

Abstract

This invention provides a stamping die, stamping mechanism, and forming method for liquefied petroleum gas (LPG) cylinder end caps, belonging to the field of end cap forming technology. The stamping die for LPG cylinder end caps includes a die body for supporting a metal sheet, a floating component located on the bottom wall of the die cavity area, and multiple drainage structures radially arranged along the die cavity area. The floating component undergoes settlement displacement when pressure exceeds a preset threshold, thus mitigating impact stress in the central area. The drainage structures are located on the end face of the die body; when the pressure ring clamps the edge of the metal sheet and the punch presses down, they guide a portion of the edge sheet material to preferentially flow into the die cavity, which helps control the deformation path, improve thickness uniformity, and reduce residual stress.

Description

Technical Field

[0001] This invention relates to the field of end cap forming technology, and in particular to a stamping forming mold, stamping forming mechanism and forming method for liquefied gas cylinder end caps. Background Technology

[0002] Currently, liquefied petroleum gas (LPG) cylinders are widely used in the storage and transportation of chemical products. A common type consists of a central cylindrical section and end caps at both ends. Depending on the volume, the diameters of the cylinder and end caps can be various. The end caps are typically made from sheet metal through a pressing process.

[0003] The applicant discovered that during the stamping process of the cylinder head, the sheet metal undergoes severe plastic deformation within the mold cavity. Due to the unevenness of the stamping and stretching deformation, residual stress fields are inevitably introduced into different areas of the head. The presence of this residual stress can lead to warping, stress corrosion cracking, or bursting risks during subsequent annealing, welding, or use, seriously affecting the structural safety and service life of the product. Summary of the Invention

[0004] This application discloses a stamping die, stamping mechanism and forming method for liquefied petroleum gas (LPG) cylinder end caps, in order to solve the technical problem of low end cap quality in related technologies.

[0005] In a first aspect, this application provides a stamping die for liquefied petroleum gas cylinder heads, employing the following technical solution:

[0006] A liquefied petroleum gas cylinder end-cap stamping die includes:

[0007] The mold body has a cavity area for supporting the metal sheet;

[0008] A floating component is disposed at the inner bottom wall of the mold cavity region, and the upper surface of the floating component smoothly fits the inner sidewall of the mold cavity region. The floating component is configured to undergo settlement displacement when the pressure exceeds a preset threshold, and the preset threshold is the critical compressive load that the floating component can withstand under normal operating conditions. The floating component includes a pressure-bearing block located at the inner bottom wall of the mold cavity region, and the upper surface of the pressure-bearing block has an arc-shaped mating surface, which is configured to form a stamping profile surface with the inner sidewall of the mold cavity region. The floating component also includes an elastic element disposed between the pressure-bearing block and the inner bottom wall of the mold cavity region, and the elastic element is configured to undergo elastic compression when the pressure exceeds the preset threshold.

[0009] The flow-guiding structure has multiple structures on the outer peripheral wall of the mold body located in the mold cavity area, and the flow-guiding structure extends in the radial direction of the mold cavity area. The flow-guiding structure is configured to guide the portion of the metal sheet that is in contact with it to flow into the mold cavity area before the rest of the metal sheet when the edge portion of the metal sheet is clamped between the mold body and the blank holder of the stamping mechanism, and the punch of the stamping mechanism moves downward.

[0010] Preferably, the mold body is provided with a settling groove, the elastic element and the pressure block are both located in the settling groove, and the inner wall of the settling groove is a vertical surface, and the pressure block and the elastic element are both slidably engaged with the inner wall of the settling groove;

[0011] A limiting ring is provided on the mold body above the edge of the settling groove, and a limiting groove is provided on the top edge of the pressure block. The limiting groove is configured to vertically limit the movement of the pressure block beyond the stamping profile surface.

[0012] Preferably, the floating component further includes a guide post, and a guide groove is axially formed on the inner bottom wall of the mold cavity area. The first end of the guide post is connected to the bottom wall of the pressure block, and the second end of the guide post passes through the elastic member and is slidably inserted into the guide groove. The guide groove is configured such that when the elastic member is in its natural state, the axial length of the gap formed between the guide post and the bottom wall of the elastic member is greater than the maximum compression of the elastic member.

[0013] Preferably, the drainage structure includes drainage ribs, which protrude from the end face of the mold body and are arranged circumferentially in the mold cavity area and extend radially along the mold cavity area.

[0014] Preferably, the flow guiding structure further includes flow guiding grooves, and multiple flow guiding grooves are formed on the end face of the mold body. Each flow guiding groove is radially connected to the mold cavity area. The flow guiding ribs are staggered with the flow guiding grooves. The height of the flow guiding ribs and the depth of the flow guiding grooves are both less than the thickness of the metal sheet.

[0015] Preferably, the drainage structure further includes a disturbance part, which is disposed within the drainage channel along the extending direction of the drainage channel. The disturbance part has an inclined guiding surface and an arc-shaped connecting surface, wherein...

[0016] The inclined guide surface extends obliquely upward from one end of the drainage groove away from the mold cavity area to one end close to the mold cavity area;

[0017] The arc-shaped connecting surface connects the highest point of the inclined guide surface to the inner wall of the mold cavity area, and the maximum thickness of the disturbance part is less than the depth of the drainage groove.

[0018] Secondly, this application provides a stamping forming mechanism, which adopts the following technical solution:

[0019] A stamping forming mechanism includes the stamping forming die for liquefied gas cylinder heads as described in the first aspect, and further includes a punch and a pressure ring, wherein...

[0020] The punch is configured to be connected to a stroke mechanism and is vertically aligned with the mold cavity region;

[0021] The pressure ring is configured to be disposed on another stroke mechanism and located on the outer periphery of the punch, and the pressure ring is used to abut against the end face of the mold body located on the outer periphery of the mold cavity area.

[0022] Thirdly, this application also provides a head forming method, implemented based on the stamping forming mechanism of the second aspect, comprising the following steps:

[0023] A metal sheet to be formed is positioned above the mold cavity area of ​​the mold body, such that the center area of ​​the metal sheet corresponds to the upper surface of the floating component, and the edge area covers the end face of the mold body and the top of the drainage structure.

[0024] Another stroke mechanism controls the pressure ring to move downward and clamp the edge of the metal sheet with the end face of the mold body to initially fix the position of the metal sheet and suppress wrinkling around the perimeter.

[0025] In the pressure holding state, a stroke mechanism is activated to drive the punch to press down in the vertical direction, so that the metal sheet gradually flows into the mold cavity area under the push of the punch. This allows the flow guiding structure located on the end face of the mold body to guide the edge area of ​​the attached metal sheet to enter the mold cavity area first compared with other areas, thereby controlling the deformation path of the metal sheet and improving the thickness uniformity.

[0026] When the central area of ​​the metal sheet is pressed towards the bottom of the mold cavity under the action of the punch, if the load applied to the floating component exceeds the preset threshold, the floating component will undergo a slight vertical settlement displacement to relieve the impact stress in the area and prevent the center of the sheet from cracking or warping.

[0027] After the punch continues its stroke to complete the target stamping depth, the punch and the pressure ring are lifted in sequence to remove the formed end cap.

[0028] The present invention has the following advantages and beneficial effects:

[0029] 1. The liquefied gas cylinder end-cap stamping die of the present invention incorporates a floating component at the bottom of the die cavity region of the die body. This floating component can undergo slight settlement displacement when the metal sheet is subjected to pressure exceeding a preset load threshold, thereby actively mitigating the impact stress in the central region and adjusting the local strain rate distribution during the forming process. This design effectively constructs a dynamic unloading mechanism that responds to changes in stamping load without altering the overall die cavity contour. This helps reduce the ultimate tensile deformation rate in the central region of the end-cap, suppressing the warping residual stress field induced by stamping at its source. Compared to traditional rigid die cavity structures, it offers greater flexibility during deep drawing, making it particularly suitable for controlling stress concentration and crack risk in the middle of spherical end-cap forming. It improves the internal quality and structural stability of the formed end-cap without relying on costly post-processing steps.

[0030] 2. The liquefied gas cylinder end-cap stamping die of the present invention establishes a flow-guiding structure on the end face of the die body. This flow-guiding structure includes multiple flow-guiding ribs extending radially along the die cavity, flow-guiding grooves, and disturbance parts disposed within the grooves, thus constructing a path-guiding system that guides the material into the die cavity step by step along the edge. During the stamping process, the order of material inflow is affected by the flow-guiding structure, causing the metal sheet in the edge region to enter the die cavity region preferentially compared to other regions. This can, to a certain extent, smooth out the differences in deformation timing among different regions of the metal sheet, which is beneficial for optimizing the overall thickness distribution of the material, reducing the difference in thinning rate, and improving the wall thickness uniformity of the end cap. Furthermore, the disturbance parts apply additional disturbance to the inflowing material, which is beneficial for locally dispersing the original residual stress concentration area before the material enters the die cavity, allowing the material to begin sharing the deformation before entering the die, enhancing the stress release efficiency, and thus helping to control the residual stress level and warpage after the end cap is formed. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] To gain a more complete understanding of this application and its beneficial effects, the following description will be provided in conjunction with the accompanying drawings, wherein the same reference numerals in the following description denote the same parts.

[0033] Figure 1 This is a partial structural schematic diagram of the liquefied gas cylinder end stamping and forming mechanism according to an embodiment of this application;

[0034] Figure 2 yes Figure 1 An enlarged schematic diagram of part A in the middle;

[0035] Figure 3 yes Figure 1 Enlarged schematic diagram of part B;

[0036] Figure 4 This is a top view of the liquefied gas cylinder end stamping die according to an embodiment of this application;

[0037] Figure 5 yes Figure 1 An enlarged schematic diagram of section C.

[0038] Explanation of reference numerals in the attached figures:

[0039] 1. Mold body; 11. Mold cavity area; 12. Guide groove; 13. Sinking groove; 131. Limiting ring;

[0040] 2. Floating component; 21. Pressure block; 211. Arc-shaped mating surface; 212. Limiting groove; 22. Elastic element; 23. Guide post;

[0041] 3. Drainage structure; 31. Drainage rib; 32. Drainage groove; 33. Disturbance part; 331. Inclined guide surface; 332. Arc-shaped connection surface;

[0042] 4. Punch;

[0043] 5. Pressure ring;

[0044] 6. Metal sheets. Detailed Implementation

[0045] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the protection scope of this application.

[0046] In related technologies, liquefied petroleum gas (LPG) cylinders are widely used in the storage and transportation of chemical products due to their compact structure, strong sealing performance, and high pressure resistance. In practical applications, LPG cylinders typically employ a tank structure consisting of a central cylinder and end caps. The tank dimensions can vary depending on the volume specifications. The end caps, serving as pressure-bearing components at both ends, are usually formed by deep-drawing and pressing steel plates using a mold. While this process has achieved a certain level of maturity in mass production, the forming process requires the sheet metal to undergo intense plastic deformation from a flat plate to curved end caps within the mold cavity. This inevitably leads to severe problems of uneven material flow and stress concentration.

[0047] During this process, due to the coupled effects of multiple factors such as mold cavity shape, stretching path, and friction conditions, the formed head exhibits a significant uneven distribution of residual stress. Residual stress not only affects the geometric accuracy of the head but also manifests as warping, stress corrosion cracking, and even bursting under extreme conditions during subsequent welding, heat treatment, and service life, becoming a key factor restricting the reliability and service life of the head structure. Although post-treatment methods such as shaping annealing are commonly used in the industry to release residual stress, these methods are often passive control strategies. They not only increase the complexity of the manufacturing process and overall energy consumption but also have limited effectiveness in restoring the microstructure and structural consistency of the head, making it difficult to fundamentally avoid the accumulation of localized residual stress. Furthermore, post-treatment cannot effectively distinguish the spatial characteristics of tensile and compressive stress distributions, thus failing to achieve targeted compensation control, resulting in poor adaptability of the shaping process and a high risk of residual defects.

[0048] It is evident that existing technologies have significant shortcomings in controlling residual stress during cylinder head forming. The core issue lies in the failure to effectively control the stress at the initial stage of plate deformation, instead relying on post-processing methods to compensate for inherent process defects. This "post-processing" approach is inefficient, costly, and lacks initiative in modern manufacturing. Therefore, how to proactively intervene in the deep drawing forming process of cylinder heads, considering factors such as process path, mold structure, and material deformation mechanism, and optimize the forming stress path and deformation balance at the source through structural response coupling, stress distribution guidance, or the placement of stress-relieving structures, thereby achieving in-process control of residual stress, is a crucial technical problem that urgently needs to be solved in this field.

[0049] In view of this, in a first aspect, some embodiments of this application provide a stamping die for liquefied gas cylinder heads, which aims to regulate the material flow path and stress distribution in the central area of ​​the cylinder head during deep drawing and stamping by means of structural optimization, thereby mitigating the concentration trend of residual stress to a certain extent and improving the stability of the head forming process and the product structural quality.

[0050] Combination Figure 1 The liquefied gas cylinder end-cap stamping die includes a die body 1, a floating component 2, and a flow-guiding structure 3. Further, the die body 1 has an internal cavity region 11 for supporting the metal sheet 6 to be formed. The cavity region 11 is enclosed in a concave shape to accommodate the plastic flow of the metal sheet 6 during the stamping process. The floating component 2 is located at the inner bottom wall of the cavity region 11, and its upper surface maintains a continuous and smooth fit with the inner sidewall of the cavity region 11 along the forming direction, forming a portion of the curved surface structure in the forming contour.

[0051] For example, the floating component 2 is a structure that can vertically respond to compressive loads and undergo slight settlement. The floating component 2 is configured to undergo settlement displacement when the pressure exceeds a preset threshold, and the preset threshold is the critical compressive load that the floating component 2 can withstand under normal operating conditions. It can be understood that the floating component 2 maintains a rigid bearing state before the compressive load exceeds the preset threshold. When the load applied during the stamping stage is locally concentrated on the inner bottom wall of the mold cavity region 11 and exceeds the threshold, the floating component 2 generates a slight displacement, thereby dispersing the impact stress at that location to a certain extent. This is beneficial for adjusting the local stress field distribution and reducing the stress gradient in the central region of the sheet metal.

[0052] For example, the flow guiding structure 3 is disposed on the end face of the outer peripheral wall of the mold body 1, corresponding to the mold cavity region 11, and extends radially from the outside of the mold cavity to the edge of the mold cavity, with multiple flow guiding structures 3 distributed circumferentially. The purpose of this flow guiding structure 3 is to cause the edge of the sheet metal 6 to preferentially flow locally along the direction corresponding to these flow guiding structures 3 in the initial stage of the stamping process after the blank holder 5 of the stamping mechanism moves down to clamp the edge of the sheet metal 6. This flow sequence guidance method helps to control the overall inflow speed and path of the sheet metal 6 from the periphery to the center to a certain extent, thereby improving the spatial distribution uniformity of plastic deformation.

[0053] It should be noted that the "preset threshold" in floating component 2 is not a fixed value, but can be designed and calibrated according to the thickness of the sheet material, the yield strength, and the overall rigidity of the mold. The "guiding" mentioned in the flow-guiding structure 3 does not mean completely restricting material flow in other areas, but rather guiding the material flow by different degrees of deformation. In actual manufacturing, the flow-guiding structure 3 can be formed by machining radial ribs or grooves. Its depth and height should be less than the sheet material thickness to avoid irreversible bending of the sheet material edges during the initial clamping process.

[0054] Through the above structural design, combined with floating response and peripheral guidance functions, the deformation path and stress transmission path of the plate can be coupled and optimized from the initial stage of forming to the entire process, which affects the evolution of residual stress from the source and is beneficial to the stability and safety performance of the head structure during service.

[0055] In some implementations, combined with Figure 1 , Figure 2The floating component 2 includes a pressure block 21, which is installed on the inner bottom wall of the mold cavity region 11. Its upper surface is machined with an arc-shaped mating surface 211. It can be understood that the curved contour of this arc-shaped mating surface 211 is connected to the inner wall of the mold cavity region 11, forming a continuous curved forming contour surface for the stamping of the cylinder head. This arrangement helps the punch 4 to push the metal sheet 6 gradually to fit and fill the mold cavity region 11 during the vertical downward pressing process, allowing the sheet to undergo partial flanging or bending along the arc-shaped mating surface 211, thereby completing the curved forming of the entire head with a relatively continuous deformation path. This arc-shaped mating surface 211 has a concave arc structure, and the transition between its edge and the inner wall of the mold cavity should be smooth, aiming to reduce the abrupt stress accumulation of the metal sheet 6 during the sliding process.

[0056] For example, to ensure that the pressure block 21 has a certain responsiveness during the stamping process, an elastic element 22 is provided between the pressure block 21 and the inner bottom wall of the mold cavity region 11. It can be understood that the elastic element 22 can be a compression spring, a rubber compression column, a rubber pad, or a hydraulic buffer element. In this embodiment, a rubber compression column is selected as the elastic element 22. Its configuration is to form a pressure-bearing support structure at the bottom of the pressure block 21. When the punch 4 is pressed in, causing the pressure in the central region to gradually increase, if the load exceeds a preset threshold set by the elastic element 22, the elastic element 22 will undergo elastic compression deformation, causing a slight vertical settlement of the pressure block 21. This results in a spatial displacement of the compressive stress in the vertical direction, which is beneficial for diffusing the impact load to the outer periphery of the bottom of the mold cavity and reducing stress concentration. This elastic response process structurally constitutes a stress relief unit, giving the inner bottom of the mold body 1 controllable compliance characteristics. This has a positive effect on mitigating the risk of brittle fracture of the metal sheet 6 due to radial thinning and material hardening at the end of deep drawing.

[0057] For example, in the floating component 2, the "preset threshold" is defined as the external force F0 corresponding to the substantial deformation (e.g., compression of 1 mm) of the elastic element 22, where F0 is a certain percentage of the maximum safe forming force allowed for the sheet metal in the system. For example, if the thickness of the metal sheet 6 is 8 mm, the yield strength σ s = 400 MPa; Tensile area A≈π×r 2 Assume the effective deformation radius r = 80mm; estimated forming force: Fmax = σ s ×A≈400×π×(0.08) 2 ≈8 kN; Assuming the floating component 2 begins buffering at approximately 60% of Fmax, the preset threshold F0≈5kN; the elastic element 22 is designed as follows:

[0058] If the pre-compression amount ΔL = 1 mm, then the stiffness of the elastic element 22 is K = F0 / ΔL = 5000 N / mm. The rubber compression column can meet this stiffness requirement.

[0059] At the same time, by setting this preset threshold, the pressure block 21 can remain stable during the normal deformation stage of the metal sheet 6, while releasing the stress peak through a micro-displacement of 0.5~1mm in the local overload area, and having minimal impact on subsequent springback, effectively suppressing uneven molding deformation and residual internal stress accumulation of the metal sheet 6.

[0060] For example, to verify the effectiveness of the above-mentioned floating component 2 and preset threshold design, the following experimental comparison can be conducted: Scheme A: No floating component 2 (traditional rigid mold); Scheme B: Floating component 2 is set, and the preset threshold is 5kN. After testing the maximum forming load, the minimum thickness after head forming, the warpage, and the residual stress value, the results are as follows:

[0061] Option A: The maximum forming load is 9.8kN, the minimum thickness of the formed head is 4.2mm, the warpage is 5.6mm, and the residual stress is 290MPa;

[0062] Option B: The maximum forming load is 9.1kN (buffered), the minimum thickness of the formed head is 4.6mm, the warpage is 2.3mm, and the residual stress is 150MPa.

[0063] This verifies that the reasonable setting of the "preset threshold" in floating component 2 has a significant technical effect on mitigating impact and optimizing forming quality.

[0064] It is worth noting that the maximum forming load in the results was obtained by observing the forming load-displacement curve during the experiment. The load and displacement response curves of the punch 4 were recorded throughout the stamping process using a servo hydraulic stamping equipment / forming test platform (equipped with a force sensor and displacement encoder). This information was used to analyze the mechanical properties, hardening stage, elastic-plastic transition point, and ultimate load point during the forming process. At the same time, the load and displacement signals were recorded in real time and the curves were output through a data acquisition system (DAQ) and forming process control software.

[0065] Meanwhile, the warpage of the formed head measures the degree of warpage caused by uneven residual stress or uneven local deformation of the head after stamping, which affects the accuracy of subsequent welding and the sealing performance during service. The coordinates of the spatial points of the head are accurately measured by a coordinate measuring machine (CMM) to calculate the maximum deviation. The morphological differences between the warped deformation surface and the reference surface are efficiently collected by a laser profilometer or a non-contact 3D scanning system. A simplified laboratory measurement method using a profilometer + reference platform (suitable for warpage height less than 10mm) is used to comprehensively evaluate and calculate the warpage of the formed head from the maximum warpage height, warpage curvature, roundness deviation, etc.

[0066] Furthermore, residual stress values ​​refer to the data obtained from X-ray analysis of residual stress in end caps. They are primarily used to determine the residual stress state on or near the surface of metals, and are particularly suitable for analyzing the distribution of tensile / compressive stress induced by stamping. The residual stress is mainly determined using an X-ray diffraction residual stress analyzer (XRD), based on the X-ray Bragg diffraction law. By measuring the minute changes in the diffraction angle caused by stress, the magnitude of the in-plane residual stress (in MPa) is calculated. Common methods include the ψ method, the sin²ψ method, and the multi-directional method. In practice, the surface of the metal sheet must be clean and uncoated; sandblasting / mechanical polishing may be necessary to remove oxide scale. However, XRD testing depth is limited (typically ≤30 μm), and neutron diffraction or hole drilling strain gauge methods may be required for deeper stress detection.

[0067] Finally, the minimum thickness after the end cap is formed actually refers to the thickness of the thinnest point / average point of the formed end cap in the material thinning rate. The material thinning rate is mainly used to evaluate the degree of local tensile deformation of the metal sheet 6 during the stamping process and is an important indicator for measuring the ultimate forming performance. It is mainly measured by ultrasonic thickness gauge or eddy current thickness gauge (these two devices are suitable for non-destructive testing, especially for medium and thick plates with high accuracy), vernier calipers / micrometers (precision mechanical measuring tools, suitable for measuring the original thickness and the thickness of the thinnest point after slicing), and three-dimensional laser scanning equipment with post-processing software (used for three-dimensional reconstruction and visualization analysis of the thickness field of the entire end cap after forming). The specific operation procedure is as follows: measure the initial thickness of the metal sheet 6 before forming and the thickness of the thinnest point / average point of the formed end cap, calculate the thinning rate according to the formula and then measure it. The formula is as follows: Thinning rate = (t0-tmin) / t0×100%, where t0 is the initial thickness and tmin is the thickness of the thinnest point / average point of the formed end cap.

[0068] Of course, in this application, it is only necessary to compare and measure the minimum thickness of the head after forming under the two schemes.

[0069] In some implementations, combined with Figure 1 , Figure 2 and Figure 3The settling groove 13, elastic element 22 and pressure block 21 on the mold body 1 are all located in the settling groove 13, and the inner wall of the settling groove 13 is a vertical surface. The pressure block 21 and elastic element 22 are slidably engaged with the inner wall of the settling groove 13. It can be understood that the vertical inner wall of the settling groove 13 can have a certain guiding effect, so that the abutment force applied to the pressure block 21 by the gas cylinder head when releasing residual stress can be converted into the power for the pressure block 21 to move vertically downward, thereby enabling the pressure block 21 to settle vertically stably.

[0070] For example, a limiting ring 131 is provided on the mold body 1 above the edge of the settling groove 13, and a limiting groove 212 is provided on the top edge of the pressure block 21. The limiting groove 212 is configured to vertically limit the limiting ring 131 to restrict the pressure block 21 from moving upward beyond the stamping profile surface. In this way, after the residual stress of the cylinder head is released, the elastic element 22 can recover under its own elastic force and the pressure block 21 can be reset to the initial state, that is, reset to the position where the arc mating surface 211 and the mold cavity area 11 can re-form a smooth stamping profile surface. At the same time, the limiting ring 131 can also prevent the pressure block 21 from moving upward beyond the stamping profile surface to ensure the integrity of the stamping profile surface.

[0071] It is worth noting that the elastic element 22 in the floating component 2 is made of rubber compression cylinder material, and its hardness and elastic parameters have been optimized to provide moderate elastic buffering performance, so as to achieve uniform force transition of the bearing block 21 under load. This elastic element 22 does not completely soften the contact between the mold and the workpiece, but avoids the negative impact of non-uniform compression and springback on the sheet metal forming through reasonable material hardness and geometric control. This design, combined with the arc-shaped mating surface 211 and the inner sidewall of the mold cavity area 11, forms an integral stamping profile surface, ensuring smooth fit between the sheet metal and the mold, and maintaining the stability of the head morphology and the uniformity of the wall thickness.

[0072] Secondly, regarding the forming accuracy, this application utilizes the floating component 2 to induce settlement displacement at a preset load threshold, effectively mitigating the impact stress in the central region, reducing local stress concentration, and thus optimizing the material flow state. This structural design provides an adaptive adjustment function for mechanical response, thereby assisting in controlling the stress distribution and balance during the forming process, promoting uniform wall thickness distribution and morphological stability, and improving forming quality.

[0073] In some implementations, such as Figure 1 , Figure 3As shown, the floating component 2 also includes a guide post 23. A guide groove 12 is axially provided on the inner bottom wall of the mold cavity region 11. The first end of the guide post 23 is connected to the bottom wall of the pressure block 21. The second end of the guide post 23 passes through the elastic member 22 and is slidably inserted into the guide groove 12. The guide groove 12 is configured such that when the elastic member 22 is in its natural state, the axial length of the gap formed between it and the bottom wall of the guide post 23 is greater than the maximum compression of the elastic member 22.

[0074] It is understood that the guide groove 12 extends along the axial direction of the mold body 1, and its depth is designed such that, when the elastic element 22 is in its natural state, the axial gap length between the guide post 23 and the bottom wall of the guide groove 12 is greater than the maximum compression displacement of the elastic element 22. This mating structure has two functions: firstly, a guiding function, that is, under the action of stamping load, the bearing block 21 can undergo axial displacement under the restriction of the guide post 23 without radial offset or tilting; secondly, a limiting function, that is, by the preset depth of the guide groove 12, the maximum displacement range of the bearing block 21 in the compressed state of the elastic element 22 is limited, which to a certain extent avoids the situation where the bearing block 21 cannot achieve the preset amount of settlement compression, resulting in the inability to reduce residual prestress.

[0075] Based on this, during the forming process, when the punch 4 applies a load to the center area of ​​the end cap, the metal sheet 6 in this area comes into contact with the pressure block 21 and generates local prestress. This prestress is transmitted to the pressure block 21 and then to the inner bottom wall of the mold cavity area 11 through the elastic element 22. When the prestress exceeds the preset threshold of the elastic element 22, the elastic element 22 compresses, causing the pressure block 21 to sink downwards. Due to the constraint of the guide post 23, the pressure block 21 is always moved in a controlled manner along the axial direction, thereby avoiding friction or interference with the inner wall of the mold cavity area 11 during the sinking process. This reduces the risk of wear on the mold body 1 to a certain extent and maintains the integrity of the stamping profile surface of the mold cavity area 11.

[0076] This structure is suitable for controlling the central stress release path during stamping and is beneficial for adjusting and balancing the distribution of the residual stress field. The guide post 23 is generally made of high-strength alloy steel, and its surface can be chrome-plated or nitrided to enhance wear resistance. The machining accuracy of the guide groove 12 must meet the clearance tolerance between it and the guide post 23 to avoid jamming or instability. Through this structure, the floating component 2 possesses characteristics such as high controllability, stable stress, and strong installation repeatability, providing strong support for stress guidance and structural adaptability of the metal sheet 6 during the forming process.

[0077] In some implementations, combined with Figure 1 , Figure 4The flow guiding structure 3 includes multiple flow guiding ribs 31 and multiple flow guiding grooves 32, used to guide the initial flow path of the metal sheet 6 during the stamping process of the cylinder head, so as to control the deformation sequence and deformation area. Specifically, the flow guiding ribs 31 are strip-shaped structures extending radially along the mold cavity region 11 and protruding from the end face of the mold body 1. The flow guiding ribs 31 are arranged at intervals around the mold cavity region 11, with one rib at every fixed angle. For example, one rib is arranged every 30°, for a total of 12 ribs. This arrangement is beneficial because, in the initial stage of the punch 4 pressing down, the metal sheet 6 first contacts the mold body 1 at the position corresponding to the flow guiding rib 31 and undergoes plastic flow, thereby forming a preferential forming area, guiding the remaining areas to gradually expand to the entire mold cavity region 11, realizing spatial pre-guidance of the flow of the metal sheet 6.

[0078] For example, in conjunction with the aforementioned guide rib 31 structure, several guide grooves 32 are also provided on the end face of the mold body 1. Each guide groove 32 is connected to the radial direction of the mold cavity region 11. The depth of the guide grooves 32 is lower than the thickness of the metal sheet 6, typically designed to be 30%-70% of the thickness of the metal sheet 6. At the same time, the height of the guide ribs 31 is also designed to be 30%-70% of the thickness of the metal sheet 6 to avoid complete penetration or cutting of the metal sheet 6 in the initial clamping state, and to serve as a channel for local flow of the metal sheet 6 during the forming process. Furthermore, the guide ribs 31 and guide grooves 32 are arranged in an alternating manner, so that some areas form protrusions and some areas form depressions, thereby establishing a non-uniform contact pressure field during the edge pressing stage. Since the metal sheet 6 undergoes earlier local plastic deformation in the contact area of ​​the guide ribs 31, the material in these areas begins to flow into the mold cavity region 11, driving the remaining unpressed areas to gradually deform, which is beneficial to reduce the tensile gradient in the thickness direction of the metal sheet 6.

[0079] Through the above structural design, the flow guiding structure 3 forms a pre-guided deformation path network, which has spatial and temporal control functions over the plastic flow pattern of the entire sheet metal entering the mold cavity. This structure is particularly suitable for the manufacturing of end caps with large stamping depths or high thinning risks, and can reduce the residual stress concentration caused by abrupt material deformation to a certain extent. Meanwhile, the height and depth of the flow guiding ribs 31 and the flow guiding grooves 32 are both less than the thickness of the metal sheet 6, which can effectively construct a pressure difference distribution during material flow without directly cutting the sheet metal. The flow guiding ribs 31 are generally machined in the blanking area of ​​the mold body 1 end face, formed by CNC machining or EDM. Their cross-sectional shape can be rectangular, semi-circular, or trapezoidal, and the specific form needs to be matched and selected based on the sheet metal thickness and material ductility. While guiding the deformation path, the above structure also has a certain degree of limitation on sheet metal slippage during the blanking process, which is beneficial to improving forming accuracy and end cap thickness consistency. Overall, the coordinated arrangement of the flow guide ribs 31 and the flow guide grooves 32 helps to build a feedforward material deformation control system, providing a structural basis for stress field and morphology control during the stamping process of the end cap.

[0080] It is worth noting that the height of the drainage rib 31 ranges from 0.3mm to 0.8mm (generally not exceeding 70% of the thickness of the metal plate 6), and the top shape of the drainage rib 31 can be dome-shaped, truncated cone-shaped, micro-circular plane, etc.; the cross-sectional width of the drainage rib 31 ranges from 3mm to 6mm, and the surface roughness Rz of the material mating surface of the drainage rib is ≥6.3μm to prevent the indentation from being too deep.

[0081] Meanwhile, the depth of the drainage groove 32 ranges from 0.3 mm to 1.2 mm (generally not exceeding 70% of the thickness of the metal plate 6), and the width of the drainage groove 32 ranges from 3 mm to 6 mm.

[0082] Furthermore, it should be noted that in the accompanying drawings of this application, in order to show the various technical features, the dimensions of the corresponding technical features (such as the flow guide 31, the flow guide groove 32, the mold body 1, and the metal plate 6) have been adjusted to facilitate viewing the position of the corresponding technical features on the mold body 1. The dimensions shown in the drawings do not represent the actual dimensions, and the actual dimensions can be adjusted according to the corresponding working conditions during the manufacturing process.

[0083] For example, combined Figure 1 , Figure 4 and Figure 5To further control the deformation of the metal sheet 6 during its initial flow into the mold cavity region 11 and improve the ability to mitigate edge stress concentration during forming, a disturbance part 33 is added inside the flow channel 32, based on the aforementioned flow channel 3. That is, the flow channel 3 also includes a disturbance part 33. The disturbance part 33 is located inside the flow channel 32, arranged along the radial extension direction of the flow channel 32, and its upper surface has two continuous transition surfaces: an inclined guide surface 331 and an arc-shaped connecting surface 332. The inclined guide surface 331 gradually rises from the end away from the mold cavity region 11 towards the mold cavity region 11, meaning its end near the mold cavity region 11 is higher than its end away from the mold cavity region 11, forming a certain slope. This slope is used to controllably move the edge region of the metal sheet 6 that has entered the flow channel 32 upwards along the direction of the guide surface during the loading process of the punch 4. Meanwhile, the inclined guide surface 331 is connected to the inner wall of the mold cavity area 11 via an arc-shaped connecting surface 332. The arc-shaped connecting surface 332 has a geometric feature of continuous curvature transition, which enables the metal sheet 6 to form a flexible deformation trajectory when transitioning from the drainage groove 32 to the mold cavity area 11.

[0084] For example, in terms of structural dimensions, the maximum thickness of the disturbance part 33 is less than the overall depth of the guide groove 32, so that its installation will not significantly hinder the clamping effect of the metal sheet 6 during initial pressing, while simultaneously creating spatial disturbance to the sheet movement during subsequent forming. The presence of the disturbance part 33 causes the sheet portion entering the guide groove 32 from the side of the pressing ring 5 to no longer follow a simple vertical downward or radially expanding path during the stamping process. Instead, under the combined action of the inclined surface and the arc surface, it is gradually guided into the mold cavity region 11 along a curved path. During this process, the direction of the plastic stress on the metal material changes, and the stress state exhibits an asymmetrical fluctuating distribution. This is beneficial for activating the plastic deformation process in the edge region before the material enters the mold cavity region 11, breaking up the initial stress concentration points, and promoting the spatial release of residual stress in this region.

[0085] Furthermore, the degree of disturbance between the inclined guide surface 331 and the arc-shaped connecting surface 332 can be further adjusted using curvature transition parameters and thickness gradient parameters during the design process. The disturbance intensity can be optimized according to the material type, thickness range, and forming depth requirements of the sheet metal. By introducing this disturbance part 33 into the flow guide structure 3, deformation path planning can be actively intervened in the early stage of deep drawing from the structure itself. This provides a structural adjustment means to control the stress accumulation trend of the material before entering the mold cavity region 11, and establishes a feedforward basis for improving the geometric stability and residual stress distribution of the end cap after subsequent forming. It has good structural rationality and industrial adaptability.

[0086] Please refer to Figures 1-5Secondly, some embodiments of this application also provide a stamping forming mechanism, characterized in that it includes a stamping forming die for a liquefied gas cylinder end cap, as described in the first aspect, and further includes a punch 4 and a blank holder 5. The punch 4 is configured to be connected to a stroke mechanism and vertically aligned with the mold cavity region 11. The blank holder 5 is configured to be disposed on another stroke mechanism and located on the outer periphery of the punch 4. The blank holder 5 is used to abut against the end face of the mold body 1 located on the outer periphery of the mold cavity region 11, i.e., during the pressing process, the blank holder 5 forms surface contact with the end face of the outer periphery of the mold cavity region 11 in the mold body 1, and is used to clamp the edge portion of the metal sheet 6 in the initial loading stage of the punch 4, thereby constructing a preset constraint boundary condition and suppressing radial slippage of the outer edge material in the initial stage of stamping. By adjusting the blank holder force and loading sequence, the blank holder 5 can cooperate with the flow guiding structure 3 to guide the material into the mold cavity in a controlled manner, thereby making the stress distribution during the stamping process more balanced.

[0087] It is understandable that the stroke mechanism can employ linear motion devices such as hydraulic cylinders, electric cylinders, servo-driven slides, pneumatic cylinders, or electromagnetic push rods to meet the pressure accuracy, speed adjustment range, and synchronous control requirements under different application scenarios. The punch 4 can be designed as a convex head structure with a certain curvature according to the product size and forming depth requirements, and is equipped with a pressing surface that cooperates with the inner contour of the mold cavity.

[0088] In the aforementioned stamping mechanism, the driving processes of the punch 4 and the pressure ring 5 can be controlled independently or collaboratively, allowing for flexible adjustment of the up and down strokes and clamping rhythm at different stages to match the process requirements of different materials and structural shapes. The overall structural design has strong adaptability and can be used for stamping production of products such as steel cylinders, pressure vessels, and elliptical heads. It is beneficial for improving the forming accuracy and material thickness consistency of the heads, and also plays an auxiliary optimization role in the final residual stress control.

[0089] Thirdly, some embodiments of this application also provide a head forming method, implemented based on the stamping forming mechanism of the second aspect, comprising the following steps:

[0090] The metal sheet 6 to be formed is placed flat above the cavity area 11 of the mold body 1, with its center area aligned with the upper surface of the floating component 2, and its edge area covering the end face of the mold body 1 and the surface of the flow guiding structure 3 set thereon. Through this positioning method, the metal sheet 6 can form a close contact with the mold body 1 during the subsequent edge pressing and stamping process, which helps to reduce the risk of local wrinkles or flow deviation in the early stage of feeding;

[0091] Another stroke mechanism drives the blank holder 5 to press vertically downwards, so that it engages with the end face of the mold body 1 to clamp the edge area of ​​the metal sheet 6, thereby establishing a stable clamping boundary condition. This blank holder process remains constant throughout the stamping process, effectively constraining the radial movement of the metal sheet 6 and limiting the risk of wrinkling in the outer periphery of the mold cavity, further promoting the stability of the sheet's flow path;

[0092] The first-stroke mechanism initiates a downward vertical motion of the punch 4, applying pressure and driving the sheet metal 6 to gradually flow from the edge into the cavity region 11. The movement of the punch 4 guides the sheet metal 6 to undergo plastic flow within the mold body 1. The flow-guiding structure 3, located on the end face of the mold body 1, provides crucial path guidance during this process. The flow-guiding structure 3 includes circumferentially spaced flow-guiding ribs 31, flow-guiding grooves 32, and disturbance parts 33. The flow-guiding ribs 31 and flow-guiding grooves 32 extend radially, forming gaps that fit against the edge of the sheet metal. Because the flow-guiding ribs 31 and flow-guiding grooves 32 are staggered, and their height and depth are both less than the sheet metal thickness, the sheet metal will preferentially undergo local deformation between these structures during the initial flow process. The disturbance section 33 further enhances this flow direction selectivity. This structure applies directional disturbance to the metal plate 6 entering the drainage channel 32 area through the inclined guide surface 331 and the arc-shaped connecting surface 332, which is beneficial to make the material in the edge area be transferred into the mold cavity in a more compliant and orderly manner, thereby achieving the control of the material flow sequence and stress gradient.

[0093] When the punch 4 applies further pressure, causing the central area of ​​the metal sheet 6 to be squeezed towards the inner bottom of the mold cavity area 11, if the local pressure exceeds the preset threshold, the pressure block 21 of the floating component 2 will undergo a slight settlement displacement in the vertical direction under the action of the elastic element 22. This settlement process absorbs part of the local load fluctuation, thereby buffering the stress concentration area at the bottom of the mold cavity area 11, which is beneficial to controlling the wall thickness shrinkage rate and stress concentration in the central area of ​​the metal sheet 6, and reducing the risk of crack initiation or sudden deformation.

[0094] After the punch 4 reaches the target forming depth, the punch 4 and the pressure ring 5 are controlled to rise in sequence to complete the demolding action and remove the formed head structure from the mold.

[0095] It is understandable that this head forming method has a high degree of synergy in structure and process control. It can improve the plastic flow law of metal sheet 6 and reduce the abnormal deformation caused by stress concentration through structural pre-guidance and active unloading technology during the head forming process, thereby providing a good morphological basis for subsequent welding, annealing and other processing.

[0096] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A stamping die for forming the end cap of a liquefied petroleum gas cylinder, characterized in that, include: The mold body (1) has a cavity area (11) for supporting the metal sheet (6); A floating component (2) is disposed on the inner bottom wall of the mold cavity region (11), and the upper surface of the floating component (2) is smoothly fitted with the inner sidewall of the mold cavity region (11). The floating component (2) is configured to undergo settlement displacement when the pressure exceeds a preset threshold, and the preset threshold is the critical compressive load that the floating component (2) can withstand under normal working conditions. The preset threshold in the floating component (2) is not a fixed value, but is designed and calibrated according to the thickness of the plate used, the yield strength, and the overall stiffness of the mold. The floating assembly (2) includes a pressure block (21) located at the inner bottom wall of the mold cavity region (11), and the upper surface of the pressure block (21) has an arc-shaped mating surface (211), which is configured to form a stamping profile surface with the inner side wall of the mold cavity region (11); the floating assembly (2) also includes an elastic element (22), which is disposed between the pressure block (21) and the inner bottom wall of the mold cavity region (11), and the elastic element (22) is configured to undergo elastic compression when the pressure exceeds a preset threshold. A plurality of flow-guiding structures (3) are provided on the outer peripheral wall of the mold body (1) in the mold cavity region (11), and the flow-guiding structures (3) extend in the radial direction of the mold cavity region (11). The flow-guiding structures (3) are configured such that when the edge portion of the metal sheet (6) is clamped between the mold body (1) and the pressure ring (5) of the stamping mechanism, and the punch (4) of the stamping mechanism moves downward, the portion of the metal sheet (6) that is in contact with it is guided to flow into the mold cavity region (11) first compared to the rest of the metal sheet (6).

2. The liquefied gas cylinder end-cap stamping die according to claim 1, characterized in that, The mold body (1) is provided with a settling groove (13), the elastic element (22) and the pressure block (21) are both located in the settling groove (13), and the inner wall of the settling groove (13) is a vertical surface. The pressure block (21) and the elastic element (22) are both slidably engaged with the inner wall of the settling groove (13). A limiting ring (131) is provided on the mold body (1) above the edge of the settling groove (13), and a limiting groove (212) is provided on the top edge of the pressure block (21). The limiting groove (212) is configured to cooperate with the limiting ring (131) in a vertical limiting manner to restrict the pressure block (21) from moving upward beyond the stamping profile surface.

3. The liquefied gas cylinder end-cap stamping die according to claim 1, characterized in that, The floating component (2) also includes a guide post (23). A guide groove (12) is axially provided on the inner bottom wall of the mold cavity area (11). The first end of the guide post (23) is connected to the bottom wall of the pressure block (21). The second end of the guide post (23) passes through the elastic member (22) and is slidably inserted into the guide groove (12). The guide groove (12) is configured such that when the elastic member (22) is in its natural state, the axial length of the gap formed between the guide groove (23) and the bottom wall of the guide post (23) is greater than the maximum compression of the elastic member (22).

4. The liquefied gas cylinder end-cap stamping die according to any one of claims 1 to 3, characterized in that, The drainage structure (3) includes drainage ribs (31), which protrude from the end face of the mold body (1) and are arranged circumferentially in the mold cavity area (11) and extend in the radial direction of the mold cavity area (11).

5. The liquefied gas cylinder end-cap stamping die according to claim 4, characterized in that, The flow-guiding structure (3) also includes flow-guiding grooves (32). Multiple flow-guiding grooves (32) are opened on the end face of the mold body (1), and each flow-guiding groove (32) is radially connected to the mold cavity area (11). The flow-guiding ribs (31) are staggered with the flow-guiding grooves (32). The height of the flow-guiding ribs (31) and the depth of the flow-guiding grooves (32) are both less than the thickness of the metal plate (6).

6. The liquefied gas cylinder end-cap stamping die according to claim 5, characterized in that, The drainage structure (3) further includes a disturbance part (33), which is disposed within the drainage groove (32) along the extending direction of the drainage groove (32). The disturbance part (33) has an inclined guiding surface (331) and an arc-shaped connecting surface (332). The inclined guide surface (331) extends obliquely upward from one end of the drainage groove (32) away from the mold cavity region (11) to the end near the mold cavity region (11); The arc-shaped connecting surface (332) is connected between the highest end of the inclined guide surface (331) and the inner wall of the mold cavity region (11), and the maximum thickness of the disturbance part (33) is less than the depth of the drainage groove (32).

7. A stamping forming mechanism, characterized in that, The liquefied gas cylinder end-forming die according to any one of claims 1 to 6 further includes a punch (4) and a pressure ring (5), wherein, The punch (4) is configured to be connected to a stroke mechanism and is vertically aligned with the cavity region (11); The pressure ring (5) is configured to be disposed on another stroke mechanism and located on the outer periphery of the punch (4), and the pressure ring (5) is used to abut against the end face of the mold body (1) located on the outer periphery of the mold cavity region (11).

8. A method for forming a head, characterized in that, Based on the stamping forming mechanism of claim 7, the following steps are included: A metal sheet (6) to be formed is positioned above the cavity area (11) of the mold body (1), so that the center area of ​​the metal sheet (6) corresponds to the upper surface of the floating component (2), and the edge area covers the end face of the mold body (1) and the top of the drainage structure (3). The pressure ring (5) is controlled to move down by another stroke mechanism and clamp the edge of the metal plate (6) with the end face of the mold body (1) to initially fix the position of the metal plate (6) and suppress the wrinkling of the periphery; In the state of holding the edge, a stroke mechanism is activated to drive the punch (4) to press down in the vertical direction, so that the metal sheet (6) gradually flows into the mold cavity area (11) under the push of the punch (4), so that the flow-guiding structure (3) located on the end face of the mold body (1) guides the edge area of ​​the attached metal sheet (6) to enter the mold cavity area (11) first compared with other areas, so as to control the deformation path of the metal sheet (6) and improve the thickness uniformity; When the central area of ​​the metal sheet (6) is pressed towards the bottom of the mold cavity area (11) under the pressing force of the punch (4), if the load applied to the floating component (2) exceeds the preset threshold, the floating component (2) will undergo a slight vertical settlement displacement to relieve the impact stress in the area and prevent the center of the metal sheet (6) from tearing or warping. After the punch (4) continues its stroke to complete the target stamping depth, the punch (4) and the pressure ring (5) are lifted in sequence to remove the formed end cap.

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