A stamping process applied to Q235 carbon steel

Abstract

The present application relates to a kind of stamping process applied to Q235 carbon steel, first prepare the sheet of Q235 carbon steel material;Then the sheet is placed on the special die of stamping after being evenly smeared with lubricating oil on both sides;After that, the sheet is preliminarily compressed and positioned by pressing plate;Start the special die of stamping, the main cylinder pressure of press is 7000KN~8000KN, the slider speed is 40mm / s~50mm / s, the slider runs to the bottom, and the pressure holding time is 5s~15s;Start the hydraulic ejector rod to eject the sheet after pressing. The present application solves the technical problem of realizing the deep-width ratio of 0.37 of Q235 carbon steel cold stamping technology by optimizing the die structure, box bottom parameters and stamping process parameters. The box bottom can be precisely formed at one time, without subsequent welding, which realizes the three benefits of process route simplification, production efficiency leap and product quality strengthening.

Description

Technical Field

[0001] This invention relates to the field of metal stamping, and more specifically to a stamping process applied to Q235 carbon steel. Background Technology

[0002] Q235 steel, as one of the most common carbon structural steels, is widely used in the manufacture of building structures, general mechanical parts, supports, and shells due to its low cost, moderate strength, good plasticity, and weldability. However, its general reputation for "moderate strength" and "good plasticity" presents a significant challenge for its application in the field of deep stamping, where the stamping depth is relatively shallow.

[0003] Deep stamping is a process that subjects a flat blank to a complex stress state of tension and compression under the action of a die, thereby forming a hollow part. This process places extremely high demands on parameters such as the material's overall plasticity, tensile strength to yield strength ratio, plastic strain ratio, and thickness anisotropy. The inherent limitations of Q235 steel in this regard are mainly reflected in: 1. Relatively high yield strength and low yield-to-tensile strength ratio: Although the yield strength (≥235MPa) of Q235 steel is lower than that of low-alloy high-strength steel, it is significantly higher than that of deep-drawing steel (such as SPCC and DC01). More importantly, its yield-to-tensile strength ratio (yield strength / tensile strength) is relatively high. A high yield-to-tensile strength ratio means that the plastic deformation range from the start of yielding to fracture is shorter, the forming potential is limited, and early fracture is more likely to occur during deep drawing, making it difficult to achieve deep drawing with large deformation.

[0004] 2. Lower plastic strain ratio (r value) and higher anisotropy (Δr value): The r value reflects the sheet's ability to resist thinning during stretching. Deep-drawing steels typically achieve high r values ​​(>1.5) through refining and controlling grain orientation. Q235 steel, as a general-purpose steel, usually has an r value close to or slightly below 1. This indicates that during deformation, its tendency to thin in the thickness direction is similar to its tendency to extend in the surface direction, resulting in poor resistance to thinning, a larger limiting drawing coefficient, and an inability to achieve greater depths. Simultaneously, its anisotropy index Δr value is unstable, easily causing a noticeable "earing" phenomenon at the nozzle of stamped parts. This not only increases scrap but also creates stress concentration points at the ear root, becoming the origin of tensile cracking.

[0005] Limitations of chemical composition and microstructure: Q235 steel has a relatively high carbon content (0.14%~0.22%) and contains certain amounts of manganese, silicon, and other elements. Its microstructure after rolling is typically ferrite + pearlite. The cementite phase in pearlite has high hardness and poor plasticity, making it prone to becoming the initiation site of microcracks during stamping deformation, accelerating crack propagation, and thus limiting the overall deformation capacity of the material.

[0006] Currently, when deep drawing is required, if the part has a complex shape or a large depth, the industry usually avoids using Q235 steel directly, and instead adopts the following alternatives: Material upgrade: Directly select higher-priced deep-drawing cold-rolled steel sheets (such as SPCD, SPCE, DC04, DC06, etc.). These steels undergo special metallurgical and processing techniques (such as aluminum killing, vacuum degassing, annealing), resulting in extremely low yield strength, high r-value, and elongation. However, this undoubtedly significantly increases raw material costs, negating the core economic advantages of Q235 steel.

[0007] Adding intermediate annealing: A recrystallization annealing process is added between multiple drawing operations to eliminate work hardening caused by previous processes and restore the material's plasticity. This method is effective, but it leads to production interruptions, longer production cycles, increased energy consumption, and may cause surface quality problems such as oxidation and decarburization, resulting in a significant increase in overall costs.

[0008] Hot forming (hot stamping): Q235 steel sheet is heated to above its recrystallization temperature and then stamped, taking advantage of the material's characteristic of a sharp decrease in yield strength and a significant increase in plasticity at high temperatures. However, this method requires a heating furnace, high-temperature resistant molds, and a corresponding cooling system, resulting in huge equipment investment, complex processes, severe surface oxidation of parts, and difficulty in controlling dimensional accuracy.

[0009] In summary, existing technologies face a dilemma: while minimizing part costs, there is a desire to use economical Q235 steel, but its inherent mechanical properties severely limit its application in deep stamping processes, making it impossible to achieve deep stamping. Existing solutions directly negate the cost advantage of Q235 and introduce new complexities and drawbacks.

[0010] Oil-immersed transformers are core equipment in power systems. Their oil tanks primarily house the transformer body and insulating oil, providing a sealed protection against external moisture and air intrusion. They are generally made of Q235 steel. The oil tanks need to be leak-proof, resistant to high temperatures and high voltages, thus requiring high precision in welding. However, because the tank body is an assembly of steel plate components, the weld seams are long, ranging from several meters to over ten meters. Each long weld seam must be completed in one continuous operation, demanding exceptional concentration from the welder and resulting in low processing efficiency. Existing transformer tank shells have either quadrilateral or hexagonal bottom shapes, and the bottom plate has a high flange height. Current forming methods mostly involve bending, requiring full welds at the forming and joining points to ensure no leakage. This operation requires multiple steps and coordination among various trades, making it labor-intensive and time-consuming.

[0011] Given the difficulty in guaranteeing the stability of finished product quality and production efficiency with existing processes, and in the face of increasingly fierce market competition, developing an innovative cold stamping process specifically for Q235 steel—one that requires no expensive equipment investment, does not rely on multiple intermediate annealing processes, and can significantly tap its plasticity potential to achieve greater depth stamping—is of great practical significance and economic value for expanding the application range of Q235 steel and reducing the manufacturing cost of deep-drawn parts. This invention aims to overcome this long-standing technical bottleneck. Summary of the Invention

[0012] The purpose of this invention is to provide a stamping process for Q235 carbon steel to solve the technical problem that Q235 carbon steel cannot achieve a large depth of stamping in the prior art.

[0013] To achieve the above objectives, the present invention provides the following technical solution: A stamping process for Q235 carbon steel includes the following steps: The first step is to prepare Q235 carbon steel sheets; The second step is to evenly apply lubricating oil to both sides of the sheet material and place it on the stamping position of the stamping die. The stamping die includes an upper die assembly, a die core, a lower die assembly, and a hydraulic ejector rod. A pressure plate is floating at the lower end of the upper die assembly. The die core includes an upper die cavity and a lower punch. A die hole is provided in the middle of the die cavity. The telescopic end of the hydraulic ejector rod faces upward. There are arc transition sections between adjacent sides of the die hole and between adjacent sides of the punch. The side and top surfaces of the punch are rounded. The third step is to press down the pressure plate to initially press and position the material sheet; The fourth step is to start the special stamping die to drive the upper die assembly and the groove downward to achieve the pressing process. During the pressing process, the main cylinder pressure of the press is 7000KN~8000KN, the slide speed is 40mm / s~50mm / s, and the pressure holding time after the slide reaches the bottom is 5s~15s. Fifth step: Activate the hydraulic push rod to eject the formed sheet.

[0014] Furthermore, the upper mold assembly includes a nitrogen cylinder with its telescopic end facing downwards, and the pressure plate is installed below the telescopic end of the nitrogen cylinder. In the third step, the output thrust of the nitrogen cylinder is 28KN-32KN.

[0015] Furthermore, the mold core also includes a pressure ring, the die is fixed on the upper mold assembly, the pressure ring can float relative to the lower mold assembly, the lower mold assembly includes a guide post that can guide the floating of the pressure ring; the pressure ring is provided with a pressure hole in the middle, the size of the pressure hole is larger than the size of the pressure plate so that the pressure plate can pass through the middle.

[0016] Furthermore, the size of the pressing hole is the same as the size of the die hole.

[0017] Furthermore, the upper mold assembly includes an upper mold base plate, an upper pad block, and an intermediate pad plate that are fixedly connected, with the upper pad block placed between the upper mold base plate and the intermediate pad plate; the mold core also includes a lower pad block for adjusting the distance between the die cavity and the intermediate pad plate, with the lower pad block fixedly connected to the die cavity.

[0018] Furthermore, the lower mold assembly also includes a lower mold base plate, a lower mold pad, a lower mold upper plate, and a lower mold fixing plate. The lower mold base plate, lower mold pad, lower mold upper plate, lower mold fixing plate, and guide post are fixedly connected. The pressure ring, the die, and the lower pad are all provided with guide holes, and the guide holes cooperate with the guide post to float along it.

[0019] Furthermore, the pressure during the hydraulic push rod ejection process is 700KN~800KN, and the ejection speed is 150mm / s~200mm / s.

[0020] Furthermore, before placing the sheet material on the stamping die, an elastic layer is provided on both sides of the sheet material. The thickness of the elastic layer is 2mm to 5mm. The elastic layer can be peeled off from the formed product after stamping.

[0021] Further, the part to be formed includes a base plate and an upper flange. The cross-sectional shape of the base plate is a rounded rectangle. The length of the blank in the first step is L1=L2+2H2, the width is W1=W2+2H2, and the thickness is TK1=TK2, where L2 is the length of the part to be formed, W2 is the width of the part to be formed, H2 is the depth of the part to be formed, and TK2 is the wall thickness of the part to be formed. The radius of the arc transition section between two adjacent sides of the die hole is R2≥0.05W2, the radius of the arc transition section between two adjacent sides of the punch is R3=R2-TK2, and the side and top surfaces of the punch are rounded with a radius R1≥0.05*min(H2,W2).

[0022] Furthermore, the part to be formed includes a base plate and an upper flange. The cross-sectional shape of the base plate is a hexagon formed by the truncated angle of an equilateral triangle, with rounded transitions between adjacent sides of the hexagon. The blank material cut in the first step is a rounded equilateral triangle. The width B1 of the blank material is 1.23 to 1.3 times the width B2 of the base plate, and the thickness TK1 = TK2, where TK2 is the wall thickness of the part to be formed. The radius R2 of the rounded transition section between adjacent sides of the die hole is ≥0.03B2, and the radius R3 of the rounded transition section between adjacent sides of the punch is R3 = R2 - TK2. The side and top surfaces of the punch are rounded, with a radius R1 ≥0.015B2.

[0023] Compared with the prior art, the beneficial effects of the present invention are: 1. Under cold stamping conditions, Q235 carbon steel can only be stamped to a relatively shallow depth. When forming parts with a depth-to-width ratio greater than 0.2 using cold stamping, wrinkling or tearing of the parts often occurs. This invention overcomes the technical challenge of achieving a depth-to-width ratio of 0.37 in cold stamping of Q235 carbon steel by synergistically optimizing the mold structure, box bottom parameters, and stamping process parameters, thus avoiding wrinkling or tearing of the box bottom during cold stamping. The box bottom can be precisely formed in one step without subsequent welding, achieving a triple benefit of simplified process route, leapfrog production efficiency, and enhanced product quality: avoiding welding defects, ensuring ultra-high consistency and stability of quality; reducing processing steps, and significantly reducing production costs and time.

[0024] 2. The nitrogen cylinder and pressure plate in the mold structure pre-position the material sheet. When the upper mold assembly drives the entire die to press down, the edge of the material sheet is clamped between the pressure ring and the die, which avoids wrinkles on the four sides of the material sheet and improves the quality of the finished product.

[0025] 3. Apply lubricating oil and an elastic layer before loading the sheet onto the machine. This helps protect the sheet surface, improves stamping performance, and facilitates waste removal. Attached Figure Description

[0026] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a three-dimensional structural diagram of the stamped box bottom according to Embodiment 1 of the present invention; Figure 2 This is a front view of the stamping die in Example 1; Figure 3 This is a left view of a stamping die; Figure 4 This is a three-dimensional structural diagram of the stamped box bottom according to Embodiment 2 of the present invention; Figure 5 This is a schematic diagram of the bottom plate of the box in Embodiment 2; Figure 6 This is a schematic diagram of the structure of the sheet material in Example 2; Figure 7 This is a flowchart of the stamping process of the present invention; In the diagram: 100, square box bottom; 11, base plate; 12, top flange; 200, triangular box bottom; 1. Upper mold base plate; 2. Upper pad block; 3. Nitrogen cylinder; 4. Intermediate pad plate; 5. Lower pad block; 6. Die; 7. Hydraulic ejector rod; 8. Lower mold base plate; 9. Lower mold pad block; 10. Lower mold upper plate; 11. Lower mold fixing plate; 12. Pressure ring; 13, 14. Guide pillars. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0028] Example 1 of the stamping process of the present invention applied to Q235 carbon steel: A stamping process applied to Q235 carbon steel, used for stamping forming such as... Figure 1 The square box base 100 shown includes a base plate 11 and upturned edges 12 around the base plate. The dimensions of the square box base are as follows: length L2 = 750 mm, width W2 = 380 mm, depth H2 = 140 mm, and wall thickness TK2 = 4 mm. The stamping of the above square box base includes the following steps: The first step is to prepare a Q235 carbon steel plate with a thickness of TK1=4mm, a length of L1=980mm, and a width of W1=620mm as the material sheet according to the dimensions and specifications of the bottom of the box to be processed. The second step is to evenly apply lubricating oil to both sides of the sheet and place it on a special stamping die; The structure of stamping special dies is as follows Figures 2 to 4 As shown, it includes an upper mold assembly, a lower mold assembly, and a mold core.

[0029] The upper mold assembly includes a fixedly connected upper mold base plate 1, an upper pad block 2, and an intermediate pad plate 4. The fixed end of the nitrogen cylinder 3 is mounted on the upper mold base plate 1, and the telescopic end—the retractable movable part—extends out of the intermediate pad plate 4 and is fixed with a pressure plate. The pressure plate is a rectangular flat plate structure, and its outer contour shape is consistent with the cross-sectional shape of the punch. The upper pad block 2 is used to increase the distance between the upper mold base plate 1 and the intermediate pad plate 4.

[0030] The mold core includes a lower pad 5, a die 6, a pressure ring 12, and a punch. The lower pad 5 and the die 6 are fixed together by bolts. The function of the lower pad 5 is to ensure that the distance between the die 6 and the intermediate pad 4 matches the extension and retraction distance of the nitrogen cylinder 3. The pressure ring 12 is floatingly mounted on the lower mold assembly. The internal die cavity structure of the die 6 matches the outer contour dimensions of the square box bottom to be formed, and the outer contour shape of the punch matches the inner contour dimensions of the square box bottom to be formed. The sheet material is placed between the die 6 and the punch so that when the die 6 moves downward, the periphery of the sheet material is squeezed into the space between the die 6 and the punch to complete the forming process.

[0031] The upper end face of the punch has a rounded corner with a radius of 7mm between it and the side face. There is an arc transition section with a radius of 15mm between two adjacent sides of the punch. There is an arc transition section with a radius of 19mm between two adjacent sides of the die.

[0032] The lower mold assembly includes a lower mold base plate 8, a lower mold pad 9, a lower mold upper plate 10, a lower mold fixing plate 11, and a guide post 14. The lower mold base plate 8, lower mold pad 9, lower mold upper plate 10, and lower mold fixing plate 11 are fixed as one unit, and the guide post 14 ensures the positional accuracy of the four components. Simultaneously, a pressure ring 12 is fitted onto the guide post 14. The die 6 and the lower pad 5 also have guide holes that match the shape of the guide post 14 and allow them to move along the guide post 14. The die 6 and the lower pad 5 can move together with the upper mold assembly. A pressure hole is provided on the pressure ring 12, the size of which is larger than the size of the pressure plate to allow it to pass through. In this embodiment, the size of the pressure hole is equal to the size of the mold hole, and its function is to press the material sheet around its perimeter, preventing uncontrolled deformation of the material sheet during the molding process and thus avoiding wrinkling of the upper flange 12 after molding. The fixed part of the hydraulic ejector rod 7 is fixed on the lower mold base plate 8, and the ejector rod part corresponds to the position of the pressure ring 12, so that when it extends upward, it pushes the pressure ring 12 and the formed material sheet together to be ejected.

[0033] The third step is to set an elastic layer on both the Q235 carbon steel plate and the punch. The thickness of the elastic layer is 2mm, and it can be peeled off from the formed product after stamping. Step 4: Nitrogen cylinder 3 drives the pressure plate to extend, and performs preliminary pressing and positioning of the middle part of the material sheet. The output thrust of nitrogen cylinder 3 is 30KN. Step 5: Start the press to drive the upper die assembly and the die downwards, forcing part of the material of the sheet into the gap between the die and the punch, thus achieving the forming process. During the forming process, the main cylinder pressure of the press is 7000KN, the slide speed is 50mm / s, and the pressure holding time after the slide reaches the bottom is 5s.

[0034] Step 6: Start the hydraulic ejector rod 7 to eject the formed sheet along with the pressure ring. During the ejection process, ensure that the pressure of the hydraulic ejector rod is 800KN and the ejection speed is 200mm / s.

[0035] The depth-to-width ratio k of the square box bottom formed by stamping in this invention is k=H2 / W2=140 / 380=0.37.

[0036] Embodiment 2 of a stamped transformer oil tank of the present invention: The difference between Example 2 and Example 1 is that: Example 2 is used for stamping and forming, such as... Figure 4 The hexagonal box base 200 shown has a wall thickness TK2 = 4mm and a depth H2 = 140mm. Its outline is formed by the truncated angle of an equilateral triangle. The width of the base plate is B2 = 637mm, where B2 refers to the distance between the two parallel straight edges. The radius of the arc transition section between two adjacent straight edges in the upper flange is R2 = 20mm, and the radius of the fillet between the outer wall of the base plate and the outer wall of the upper flange is R1 = 10mm.

[0037] Meanwhile, the material sheet cut in the first step is an equilateral triangle with rounded corners, with the following dimensions: thickness of 4mm, width B1=785mm, the width of the material sheet refers to the distance from the top of the rounded corner to the opposite side, and the radius of the rounded corner is 444mm.

[0038] The shapes of the die and punch in the stamping die match the shape of the triangular box bottom.

[0039] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims and not by the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A stamping process applied to Q235 carbon steel, characterized in that: The steps include: First, prepare Q235 carbon steel sheets; The second step is to evenly apply lubricating oil to both sides of the sheet material and place it on the stamping position of the stamping die. The stamping die includes an upper die assembly, a die core, a lower die assembly, and a hydraulic ejector rod. A pressure plate is floating at the lower end of the upper die assembly. The die core includes an upper die cavity and a lower punch. A die hole is provided in the middle of the die cavity. The telescopic end of the hydraulic ejector rod faces upward. There are arc transition sections between adjacent sides of the die hole and between adjacent sides of the punch. Rounded corners are provided between the side and top surfaces of the punch. The third step is to press down the pressure plate to initially press and position the material sheet; The fourth step is to start the special stamping die to drive the upper die assembly and the groove downward to achieve the pressing process. During the pressing process, the main cylinder pressure of the press is 7000KN~8000KN, the slide speed is 40mm / s~50mm / s, and the pressure holding time after the slide reaches the bottom is 5s~15s. Fifth step: Activate the hydraulic push rod to eject the formed sheet.

2. The stamping process for Q235 carbon steel according to claim 1, characterized in that: The upper mold assembly includes a nitrogen cylinder with its telescopic end facing downwards. The pressure plate is installed below the telescopic end of the nitrogen cylinder. In the third step, the output thrust of the nitrogen cylinder is 28KN-32KN.

3. The stamping process applied to Q235 carbon steel according to claim 2, characterized in that: The mold core also includes a pressure ring. The die is fixed on the upper mold assembly. The pressure ring can float relative to the lower mold assembly. The lower mold assembly includes a guide post that can guide the floating of the pressure ring. The pressure ring has a pressure hole in the middle. The size of the pressure hole is larger than the size of the pressure plate so that the pressure plate can pass through the middle.

4. The stamping process for Q235 carbon steel according to claim 3, characterized in that: The size of the pressing hole is the same as the size of the die hole.

5. The stamping process for Q235 carbon steel according to claim 3, characterized in that: The upper mold assembly includes an upper mold base plate, an upper pad block, and an intermediate pad plate that are fixedly connected, with the upper pad block placed between the upper mold base plate and the intermediate pad plate; the mold core also includes a lower pad block for adjusting the distance between the die cavity and the intermediate pad plate, with the lower pad block fixedly connected to the die cavity.

6. The stamping process for Q235 carbon steel according to claim 3, characterized in that: The lower mold assembly also includes a lower mold base plate, a lower mold pad, a lower mold upper plate, and a lower mold fixing plate. The lower mold base plate, lower mold pad, lower mold upper plate, lower mold fixing plate, and guide post are fixedly connected. The pressure ring, the die, and the lower pad are all provided with guide holes. The guide holes cooperate with the guide post to float along it.

7. The stamping process applied to Q235 carbon steel according to claim 1, characterized in that: The pressure during the hydraulic jacking process is 700KN~800KN, and the jacking speed is 150mm / s~200mm / s.

8. The stamping process applied to Q235 carbon steel according to claim 1, characterized in that: Before placing the sheet material on the stamping die, an elastic layer is provided on both sides of the sheet material. The thickness of the elastic layer is 1mm to 5mm. The elastic layer can be peeled off from the formed product after stamping.

9. A stamping process for Q235 carbon steel according to any one of claims 1 to 8, characterized in that: The part to be formed includes a base plate and an upper flange. The cross-sectional shape of the base plate is a rounded rectangle. The length of the blank in the first step is L1=L2+2H2, the width is W1=W2+2H2, and the thickness is TK1=TK2, where L2 is the length of the part to be formed, W2 is the width of the part to be formed, H2 is the depth of the part to be formed, and TK2 is the wall thickness of the part to be formed. The radius of the arc transition section between two adjacent sides of the die hole is R2≥0.05W2, and the radius of the arc transition section between two adjacent sides of the punch is R3=R2-TK2. The side and top surfaces of the punch are rounded, and the radius of the rounded corner is R1≥0.05*min(H2,W2).

10. A stamping process for Q235 carbon steel according to any one of claims 1 to 8, characterized in that: The part to be formed includes a base plate and an upper flange. The cross-sectional shape of the base plate is a hexagon formed by the truncated angle of an equilateral triangle. The adjacent sides of the hexagon are rounded. The blank material cut in the first step is a rounded equilateral triangle. The width B1 of the blank material is 1.23 to 1.3 times the width B2 of the base plate. The thickness TK1 of the blank material is equal to TK2, where TK2 is the wall thickness of the part to be formed. The radius R2 of the rounded transition section between adjacent sides of the die hole is ≥0.03B2. The radius R3 of the rounded transition section between adjacent sides of the punch is R3 = R2 - TK2. The side and top surfaces of the punch are rounded with a radius R1 ≥0.015B2.

Images