High-strength large-diameter thick-wall end socket cold stamping die and variable blank holder force forming method

Abstract

The invention relates to an end socket cold stamping die, in particular to a high-strength large-diameter thick-wall end socket cold stamping die and a variable blank holder force forming method. The technical problem that the yield is low due to the fact that an existing end socket is wrinkled, swelled, thinned in wall thickness and the like during cold forming is mainly solved. An annular damping groove structure is arranged on the inner side of the upper end face of a female die ring in the die, and an annular damping boss is arranged on the lower end face of a blank holder; the damping boss is arranged in the damping groove structure when the blank holder abuts against the female die ring, and a gap is formed between the damping boss and the damping groove structure. The blank holder and the female die ring are of a damping structure, compared with a plane blank holder and a plane female die ring, the resistance of a plate entering the female die ring is increased, and the phenomena that the plasticity of materials is poor during forming at the normal temperature, and the end socket is prone to bulging in the forming process are avoided.

Description

Technical Field

[0001] This invention relates to a cold stamping die for end caps, specifically to a high-strength, large-diameter, thick-walled end cap cold stamping die and a variable pressure edge forming method. Background Technology

[0002] End caps, also known as end covers (plates), are components used to seal the ends of containers and isolate them from the media inside and outside. They are important components of containers and are widely used in basic industries of national economic development such as petroleum, chemical, electric power, atomic energy, nuclear industry, aerospace, environmental protection, boilers, pressure vessels, food and pharmaceutical, marine transportation, road transportation, and railway transportation.

[0003] There is a railway tank car for transporting liquefied petroleum gas. In this tank car, the main pressure-bearing component, the end cap, is as follows: Figure 1 As shown: This end cap is a standard elliptical end cap with the inner diameter as the reference. The material is Q345R-GB / T713, the nominal diameter is Φ3000mm, the nominal thickness is 22mm, the straight edge height is 50mm, the inner height is 800mm, the outer circumference deviation is +9~3mm, and the minimum wall thickness after forming is 19mm.

[0004] Currently, end caps are typically produced using either thermoforming or cold forming methods. Cold forming, in particular, is a method of forming end caps at room temperature using a die in a single stroke of a press. Compared to thermoforming, cold forming has the following characteristics: 1. It is formed at room temperature without heating, without oxide scale, with a beautiful appearance and no need for surface cleaning; during forming, the stress and strain of symmetrical parts are the same, and the shape is accurate, the dimensions are stable, and the interchangeability is good.

[0005] 2. High productivity, energy saving, clean work site, suitable for large-scale specialized production.

[0006] However, during the cold forming of existing heads, due to the high strength, poor plasticity, and large deformation resistance of the material, wrinkling, bulging, and thinning of the wall thickness are prone to occur, resulting in a low yield rate. Summary of the Invention

[0007] The purpose of this invention is to solve the technical problem that existing end caps suffer from wrinkling, bulging, and thinning of wall thickness during cold forming, resulting in a low yield rate. The invention provides a high-strength, large-diameter, thick-walled end cap cold stamping die and a variable pressure edge force forming method.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A high-strength, large-diameter, thick-walled end cap cold stamping die includes a punch, a die shank fixed at the center of the upper end of the punch, an annular punch connecting seat surrounding the die shank and placed on the punch, an annular support seat surrounding the punch connecting seat and placed on the punch, an annular lower die seat placed around the punch, an annular die ring provided on the lower die seat, and a pressure ring located above the die ring. Its special feature is: The upper end face of the die ring is provided with an annular damping groove structure, and the lower end face of the pressure ring is provided with an annular damping boss; the damping boss is placed in the damping groove structure when the pressure ring abuts against the die ring, and a gap is provided between the damping boss and the damping groove structure. The single-sided gap between the die ring and the punch is 25.1mm to 25.3mm.

[0009] Furthermore, the damping groove structure includes a damping groove and straight sections located at both ends of the damping groove; the two ends of the damping groove and the corresponding straight sections are respectively connected by arc-shaped transition sections. The damping groove is an arc-shaped groove with an arc radius R2 of 110mm to 120mm. The diameter Φ at the lowest point of the damping groove is 3470mm to 3490mm and the depth X1 is 53mm to 55mm. The radius R1 of the transition section is 85mm to 95mm; The depth X2 of the straight section is 20.8mm to 21.2mm; The inner side of the upper end face of the die ring is provided with a rounded corner, the radius of which is R3 and is 60mm to 70mm.

[0010] Furthermore, the damping groove is an arc-shaped groove with an arc radius R2 of R115mm, and the lowest point of the damping groove has a diameter Φ of 3480mm and a depth X1 of 54mm. The radius of the arc of the transition section, R1, is 90 mm; The depth X2 of the straight section is 21mm; The radius of the fillet on the inner side of the upper end face of the die ring is R3, which is 65mm.

[0011] Furthermore, the single-sided gap between the die ring and the punch is 25.25 mm.

[0012] Furthermore, the blank holder and the die ring are made of ductile iron QT600-3 with a Brinell hardness range of 225 to 270; the graphite spheroidization rate is greater than 90% and the graphite size grade is greater than or equal to 4.

[0013] Meanwhile, the present invention also provides a high-strength, large-diameter, thick-walled head forming method with variable pressure edge force, based on the aforementioned high-strength, large-diameter, thick-walled head cold stamping die, which is characterized by including the following steps: Step 1: Install the blank holder ring onto the blank holder slide of the press, and install the die ring onto the lower die base; Step 2: Place the pre-prepared blank into the groove of the die ring; Step 3: Start the press. The press will then perform its working process. S1. The stretching slide and the blank holder slide of the press drive the punch and blank holder ring to move downwards rapidly, respectively. S2. When the distance between the blank holder and the blank is 100mm, the stretching slider drives the punch to descend slowly, and the blank holder slider continues to descend to drive the blank holder to press the blank. S3. After the blank holder ring completes the blanking under the first set blanking force, the stretching slider drives the punch to continue moving downward. The punch contacts the blank and stretches it until the forming depth reaches the first set depth. As the punch continues to move downward, during the process of the forming depth changing from the first set depth to the second set depth, the blank holder force changes from the first set value to the second set value in a linear manner. During the process of the forming depth changing from the second set depth to the third set depth, the blank holder force changes from the second set value to the third set value in a linear manner. The first set value ranges from 3500t to 3800t, the second set value ranges from 2500t to 2800t, and the third set value ranges from 350t to 400t; The first set depth ranges from 600mm to 630mm, the second set depth ranges from 750mm to 770mm, and the third set depth ranges from 850mm to 870mm. S4. When the forming depth reaches the third set depth, the blank holder force of the third set value is used to hold the pressure for a set time to complete the stretching. S5. The stretching module drives the punch to move slowly upward. After the punch leaves the end cap, the stretching slider and the pressing slider move quickly upward to the starting position. Finally, the end cap is lifted by the ejector of the press and removed.

[0014] Further, in step S2, the first setting value is 3500t, the second setting value is 2500t, and the third setting value is 350t; The first set depth is 600mm, the second set depth is 750mm, and the third set depth is 850mm; In step S4, the set time is 3 seconds.

[0015] The beneficial effects of this invention are: 1. The blank holder and die ring adopt a damping structure, which increases the resistance of the sheet metal entering the die ring compared with the flat blank holder and die ring. This avoids the problem of poor plasticity of the material during forming at room temperature, which can easily cause bulging during the forming process of the end cap.

[0016] 2. Use blank holders and die rings with high Brinell hardness as working parts of the mold to improve the dimensional stability and service life of the working parts.

[0017] 3. The damping bosses prevent the blank from being placed off-center, ensuring that the sheet metal is pulled evenly into the die ring and that the sheet metal is deformed evenly.

[0018] 4. By setting a reasonable mold clearance, it is possible to avoid the jamming of the die ring and punch during the forming process, or the outward tilting of the straight edge of the end cap.

[0019] 5. The variable pressure force method, compared with the constant pressure force method, can avoid damage to the pressure ring during the head forming process. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the existing end cap structure; Figure 2 This is a schematic diagram of the assembly structure of an existing press and the head cold stamping die in this embodiment; Figure 3 This is a schematic diagram of the key parameters of the pressure ring and the die ring in the embodiments of the present invention; Figure 4 This is a curve of the variable pressure edge force in an embodiment of the present invention.

[0021] The attached figures are labeled as follows: 01-Flattening slider, 02-Stretching slider, 03-Ejector; 1-Punch, 2-Die shank, 3-Punch connecting seat, 4-Support seat, 5-Lower die seat, 6-Die ring, 7-Pressure ring, 8-Damping groove structure, 9-Damping boss. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] This invention provides a high-strength, large-diameter, thick-walled head cold stamping die, see [link to relevant documentation]. Figure 2The overall structure of the mold can be referenced from Chinese Patent CN114310157B, specifically including a punch 1, a mold shank 2 fixed at the upper center of the punch 1, an annular punch connecting seat 3 surrounding the mold shank 2 and placed on the punch 1, an annular support seat 4 surrounding the punch connecting seat 3 and placed on the punch 1, an annular lower mold seat 5 placed around the punch 1, an annular die ring 6 provided on the lower mold seat 5, and a pressure ring 7 located above the die ring 6.

[0024] This embodiment incorporates the following design based on existing molds: An annular damping groove structure 8 is provided on the inner side of the upper end face of the die ring 6, and an annular damping boss 9 is provided on the lower end face of the pressure ring 7. The damping boss 9 is placed in the damping groove structure 8 when the pressure ring 7 abuts against the die ring 6, and a gap is provided between the damping boss 9 and the damping groove structure 8.

[0025] See Figure 3 In this embodiment, specifically, the damping groove structure 8 includes a damping groove and straight sections located at both ends of the damping groove; the two ends of the damping groove and the corresponding straight sections are connected by arc-shaped transition sections.

[0026] The damping groove is an arc-shaped groove with a radius R2 of 110mm to 120mm, preferably 115mm in this embodiment. The diameter Φ at the lowest point of the damping groove is 3470mm to 3490mm, preferably 3480mm in this embodiment. The depth X1 of the damping groove (i.e., the vertical distance from the upper end face of the die ring 6 to the lowest point of the damping groove) is 53mm to 55mm, preferably 54mm in this embodiment. The radius R1 of the transition section is 85mm to 95mm, preferably 90mm in this embodiment. The depth X2 of the straight section is 20.8mm to 21.2mm, preferably 21mm in this embodiment. The inner side of the upper end face of the die ring 6 is provided with a rounded corner with a radius R3 of 60mm to 70mm, preferably 65mm in this embodiment.

[0027] A die clearance is provided between the die ring 6 and the punch 1. If the die clearance is too small (half the inner diameter of the die ring 6 minus the outer diameter of the punch 1), the die ring 6 and the punch 1 are prone to jamming during the forming process. If the die clearance is too large, the straight edge of the end cap pressed outward will tilt. For the case where the thickness of the straight edge sheet material of the end cap is large during the cold forming of thick plates, the die clearance is 25.1mm to 25.3mm. In this embodiment, it is preferably 25.25mm.

[0028] The blank holder 7 and the die ring 6 are the working parts of the mold. During forming, the sheet metal is subjected to severe friction with the die ring 6 and the blank holder 7. In order to improve the dimensional stability and service life of the working parts, the material is selected as ductile iron QT600-3 with a Brinell hardness range of 225 to 270; the graphite spheroidization rate is greater than 90% and the graphite size grade is greater than or equal to 4.

[0029] During the head forming process, to prevent wrinkles and bulges, the blank needs to be pressed down during the forming process. Typically, head forming uses a constant pressing force method, meaning the pressing force remains constant from the start to the end of forming. The advantage of constant pressing force is that the forming parameters are easy to set and operate. However, during the head forming process, as the blank is pulled into the die ring 6, the diameter of the pressing ring 7 and the die ring 6 in contact with the blank gradually decreases. Especially when the blank is completely pulled into the die ring 6, the pressing ring 7 experiences a very severe stress state, easily causing it to crack. Considering the characteristics of liquefied petroleum gas railway tank car heads—large diameter, thick wall, high material strength, and high pressing force—a method is used to protect the mold, such as... Figure 4 The variable blank holder force method shown uses different values ​​of blank holder force at different stages of forming, and the blank holder force gradually decreases as the forming depth increases.

[0030] Specifically, this embodiment describes a method for forming a high-strength, large-diameter, thick-walled end cap using variable pressure force, comprising the following steps: Step 1: Install the blank holder ring 7 on the blank holder slider 01 of the press, and install the die ring 6 on the lower die base 5. Set parameters such as the stroke of the stretch slider 02, the relative distance between the stretch slider and the blank holder slider 01, the stroke of the ejector cylinder, the forming speed, the total forming force, the ejection force, and the holding time. Set the blank holder force according to the variable blank holder force curve.

[0031] In this embodiment, the press used is a 40 / 85MN double-action press, which is a press with an upper and lower slider structure. The stretching slider 02 is the upper slider, and the stretching cylinder is fixed on the upper crossbeam, with a rated stretching force of 8500t. The pressing slider 01 is the lower slider, suspended on the stretching slider 02, and the pressing cylinder is fixed on the stretching slider 02, with a rated pressing force of 4000t. Both the stretching and pressing sliders 01 are guided by columns, with a maximum opening of 4500mm, a stroke of 3200mm, and a relative stroke of 1800mm between the two sliders. The outer diameter of the stretching slider 02 is Φ2700mm, the inner diameter of the frustum of the pressing slider 01 is Φ3220mm, and the worktable size is 4500×4500mm.

[0032] Step 2: Select the fixed-stroke forming mode on the press operation interface, raise the press slide to the highest position, and lay a 0.06mm polyethylene film on the part of the die ring 6 that contacts the sheet metal and the rounded corners. Place the pre-prepared Φ3800×22mm blank on the die ring 6, and apply lubricant to the annular area 420mm from the outer edge of the blank's upper surface.

[0033] Step 3: Start the press and perform semi-automatic pressing according to the set program. The working process is as follows: S1. The stretching slider 02 and the blank holder slider 01 of the press drive the punch 1 and the blank holder ring 7 to descend rapidly, respectively. S2. When the blank holder ring 7 is 100mm away from the blank, the stretching slider 02 drives the punch 1 to change to a slow downward speed, and the blank holder slider 01 continues to descend to drive the blank holder ring 7 to press the blank. After the blank holder ring 7 completes the blank holder pressing under the first set blank holder force, the stretching slider 02 drives the punch 1 to continue to descend. The punch 1 contacts the blank and stretches it until the forming depth reaches the first set depth. As the punch 1 continues to descend, the forming depth changes from the first set depth to the second set depth, and the first blank holder force changes from the first set value to the second set value in a linear manner. When the forming depth changes from the second set depth to the third set depth, the blank holder force changes from the second set value to the third set value in a linear manner. S3, see also Figure 4 After the blank holder ring 7 completes the blank holder pressing under the first set blank holder force, the stretching slider 02 drives the punch 1 to continue to descend. The punch 1 contacts the blank and stretches it until the forming depth reaches the first set depth. As the punch 1 descends, the forming depth changes from the first set depth to the second set depth, and the blank holder force changes from the first set value to the second set value linearly. The range of the first set value is 3500t to 3800t, and the range of the second set value is 2500t to 2800t. In this embodiment, the first set value is 3500t and the second set value is 2500t. The first set depth is 600mm to 630mm, and the second set depth is 750mm to 770mm. In this embodiment, the first set depth is 600mm and the second set depth is 750mm.

[0034] When the forming depth changes from the second set depth to the third set depth, the blank holder force changes linearly from the second set value to the third set value. The range of the third set value is 350t to 400t. In this embodiment, the third set value is 350t. The third set depth is 850mm to 870mm. In this embodiment, the third set depth is 850mm.

[0035] S4. When the forming depth reaches the third set depth, the blank holder force is held for a set time with the third set value. In this embodiment, the holding time is 3 seconds to complete the stretching. S5. The stretching module drives the punch 1 to move slowly upward. After the punch 1 is separated from the end cap, the stretching slider 02 and the pressing slider 01 move quickly upward to the starting position. Finally, the end cap is lifted by the ejector 03 of the press and then the end cap is forked out by the trolley.

[0036] The end caps manufactured using molds and variable pressure edge force forming methods are free of bulges and scratches, and their shape and dimensions meet the drawing requirements. Magnetic particle testing, ultrasonic testing, and radiographic testing revealed no surface cracks or internal defects, and their quality exceeds the requirements of GB25198. Compared with purchasing end caps, the above forming method is expected to save 0.6 million yuan in procurement costs per vehicle, resulting in a saving of 1.2 million yuan for 200 liquefied petroleum gas tank trucks.

[0037] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present invention should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A high-strength, large-diameter, thick-walled end cold stamping die, comprising a punch (1), a die shank (2) fixed at the center of the upper end of the punch (1), an annular punch connecting seat (3) surrounding the die shank (2) and placed on the punch (1), an annular support seat (4) surrounding the punch connecting seat (3) and placed on the punch (1), an annular lower die seat (5) placed around the punch (1), an annular die ring (6) provided on the lower die seat (5), and a blank holder (7) located above the die ring (6); Its features are: The upper end face of the die ring (6) is provided with an annular damping groove structure (8), and the lower end face of the pressure ring (7) is provided with an annular damping boss (9); the damping boss (9) is placed in the damping groove structure (8) when the pressure ring (7) abuts against the die ring (6), and a gap is provided between it and the damping groove structure (8). The single-sided gap between the die ring (6) and the punch (1) is 25.1 mm to 25.3 mm.

2. The high-strength, large-diameter, thick-walled head cold stamping die according to claim 1, characterized in that: The damping groove structure (8) includes a damping groove and straight sections at both ends of the damping groove; the two ends of the damping groove and the corresponding straight sections are connected by arc-shaped transition sections. The damping groove is an arc-shaped groove with an arc radius R2 of 110mm to 120mm. The diameter Φ at the lowest point of the damping groove is 3470mm to 3490mm and the depth X1 is 53mm to 55mm. The radius R1 of the transition section is 85mm to 95mm; The depth X2 of the straight section is 20.8mm to 21.2mm; The inner side of the upper end face of the die ring (6) is provided with a rounded corner with a radius of R3 of 60mm to 70mm.

3. The high-strength, large-diameter, thick-walled head cold stamping die according to claim 2, characterized in that: The damping groove is an arc-shaped groove with an arc radius R2 of R115mm. The lowest point of the damping groove has a diameter Φ of 3480mm and a depth X1 of 54mm. The radius of the arc of the transition section, R1, is 90 mm; The depth X2 of the straight section is 21mm; The radius of the fillet on the inner side of the upper end face of the die ring (6) is R3, which is 65mm.

4. A high-strength, large-diameter, thick-walled head cold stamping die according to any one of claims 1-3, characterized in that: The single-sided gap between the concave die ring (6) and the convex die (1) is 25.25 mm.

5. A high-strength, large-diameter, thick-walled head cold stamping die according to claim 4, characterized in that: The blank holder (7) and the die ring (6) are made of ductile iron QT600-3 with a Brinell hardness range of 225 to 270; the graphite spheroidization rate is greater than 90% and the graphite size grade is greater than or equal to 4.

6. A method for forming a high-strength, large-diameter, thick-walled end cap using variable pressure force, based on a cold stamping die for a high-strength, large-diameter, thick-walled end cap as described in any one of claims 1-5, characterized in that... Includes the following steps: Step 1: Install the blank holder (7) on the blank holder slider (01) of the press, and install the die ring (6) on the lower die holder (5); Step 2: Place the pre-prepared blank on the die ring (6); Step 3: Start the press. The press will then perform its working process. S1, the stretching slide (02) and the blank holder slide (01) of the press drive the punch (1) and the blank holder (7) to move downwards rapidly respectively; S2. When the blank holder (7) is 100mm away from the blank, the stretching slider (02) drives the punch (1) to change to a slow downward movement, and the blank holder slider (01) continues to move downward to drive the blank holder (7) to press the blank. S3. After the blank holder ring (7) completes the blanking under the first set blanking force, the stretching slider (02) drives the punch (1) to continue to descend. The punch (1) contacts the blank and stretches it until the forming depth reaches the first set depth. As the punch (1) continues to descend, during the process of the forming depth changing from the first set depth to the second set depth, the blanking force changes from the first set value to the second set value in a linear manner. During the process of the forming depth changing from the second set depth to the third set depth, the blanking force changes from the second set value to the third set value in a linear manner. The first set value ranges from 3500t to 3800t, the second set value ranges from 2500t to 2800t, and the third set value ranges from 350t to 400t; The first set depth ranges from 600mm to 630mm, the second set depth ranges from 750mm to 770mm, and the third set depth ranges from 850mm to 870mm. S4. When the forming depth reaches the third set depth, the blank holder force of the third set value is used to hold the pressure for a set time to complete the stretching. S5. The stretching module drives the punch (1) to move slowly upward. After the punch (1) leaves the end cap, the stretching slider (02) and the pressing slider (01) move quickly upward to the starting position. Finally, the end cap is lifted and moved out by the ejector (03) of the press.

7. The method for forming a high-strength, large-diameter, thick-walled end cap with variable pressure force according to claim 6, characterized in that: In step S2, the first setting value is 3500t, the second setting value is 2500t, and the third setting value is 350t; The first set depth is 600mm, the second set depth is 750mm, and the third set depth is 850mm; In step S4, the set time is 3 seconds.

Images