A process and apparatus for improving sheet metal pressing indentation
By combining S-shaped path loading and flexible buffer pads, the problem of deep indentations on the surface of the sheet material in traditional pressing processes is solved, achieving efficient sheet material forming and improved surface quality, while reducing production costs and time.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHENGXI SHIPYARD
- Filing Date
- 2026-04-22
- Publication Date
- 2026-07-14
AI Technical Summary
When thickened steel plates are used in structural parts such as the tower frame of wind turbine towers, the traditional V-shaped die pressing process results in obvious indentations on the surface of the plates, affecting surface quality and performance. In addition, a lot of manual grinding is required, which is costly and may affect the structural integrity.
Progressive forming is achieved by using an S-shaped path loading method, combined with a flexible buffer layer. By increasing the width of the upper mold and using segmented loading, stress concentration is reduced. The S-shaped path loading method is used for progressive forming, and a flexible buffer layer is laid on the shoulder of the lower mold. Combined with transverse staggered pressure compensation, the stress field distribution is optimized.
It effectively reduces the indentation depth on the board surface, lowers sanding time and cost, improves board surface integrity and production efficiency, and reduces structural damage.
Smart Images
Figure CN122377967A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of wind tower manufacturing technology, specifically to a process and apparatus for improving the pressing indentation of sheet metal. Background Technology
[0002] Thickened steel plates are typically used in structural components such as the tower frame of wind turbine towers to meet strength design requirements. Currently, when pressing thickened plates with a thickness of ≥75mm, the traditional V-shaped die structure is commonly used for pressure forming. However, in actual production, it has been found that under this process, obvious local indentations easily appear in the pressure-bearing area of the plate, with a maximum indentation depth of about 0.6mm, which seriously affects the surface quality and subsequent performance of the plate.
[0003] During the sheet metal bending process, the sheet metal first undergoes elastic deformation under the pressure of the punch, and then enters the plastic deformation stage. During this process, the sheet metal is squeezed and slipped against the shoulder of the V-groove of the die, forming sliding friction. As the punch continues to press down, the sheet metal gradually comes into contact with the inner surface of the V-groove of the die until the stroke ends and the die comes into contact with the sheet metal, at which point a clear indentation line will be formed on the surface of the sheet metal.
[0004] Indentation damages the flatness of the board surface, requiring a lot of manual labor for sanding and correction, with sanding time for a single set of boards taking about 8 hours; the production cycle and cost are high, and excessive sanding may also cause structural integrity problems, so it is necessary to improve the pressing process.
[0005] The causes of indentation problems also include the degree of mold matching, the width of the V-groove of the die and the thickness of the sheet metal; as a result, under the same punch conditions, the smaller the width of the V-groove, the greater the contact pressure between the sheet metal and the shoulder of the V-groove, and the more obvious the indentation; the size of the radius of curvature (R-angle) of the shoulder of the V-groove of the die directly affects the pressure distribution of the friction pair, the smaller the R-angle, the greater the pressure on the sheet metal, and the deeper the indentation; in addition, the rigid contact of traditional devices lacks buffering. Summary of the Invention
[0006] The purpose of this invention is to overcome the shortcomings of the prior art and solve at least one of the problems described in the background art.
[0007] To achieve the above objectives, the technical solution provided by the present invention is as follows.
[0008] A process for improving indentation in sheet metal pressing, characterized by comprising the following steps: S1. Design the upper mold to match the thickness parameters of the material to be processed, so that the width of the upper mold is increased to 8 to 10 times the thickness of the material. S2. Lay a flexible cushioning pad at the shoulder of the V-groove of the lower mold; S3. The S-shaped path loading method is used to progressively form the sheet metal. The punch is reciprocated along the length of the sheet metal. In each reciprocating stroke, it advances forward step by step according to the preset step interval. At the same time, the downward depth of the punch is controlled to increase in each reciprocating cycle. S4. After the S-shaped path loading is completed, perform transverse staggered pressing. The punch is offset by a preset distance along the width direction of the sheet metal to supplement the pressing of the interval area between the loading paths in the previous stage. S5. The punch is reset to the center position of the sheet metal, and the final shaping and pressing are performed. After holding the pressure, the punch is unloaded.
[0009] As a preferred technical solution, the S-shaped path includes: the punch first descends to induce an initial bending deformation of the sheet metal to 30% to 40% of the target angle; then the punch advances forward along the length of the sheet metal at a step interval D. Each complete reciprocating stroke is defined as one unit S-shaped operation. At the beginning of each unit S-shaped operation, the depth of the punch descends increases by 2 to 3 mm based on the previous cycle. At the end of each unit S-shaped operation, the punch is raised to a height of 3 to 5 mm away from the surface of the sheet metal.
[0010] As a preferred technical solution, the step spacing D is determined according to the following relationship between the plate thickness t and the target bending angle θ: D=(3~6)×t×sin ; The turning angle α of the S-shaped path is determined based on the board width W and the step spacing D according to the following relationship: α=arctan(W / (2D))×(0.6~0.8).
[0011] As a preferred technical solution, during the S-shaped path loading process, the turning length L of a unit S-shaped operation is determined according to the step spacing D and the number of unit S-shaped operations n according to the following relationship: L = n × D, where n is an integer and its value ranges from 5 to 8; At the end of each turning length L, the loading path direction of the punch is reversed to form an S-shaped turning point, and the arc transition radius R of the turning point is set to 15 to 25 mm.
[0012] As a preferred technical solution, in step S3, when the punch travels to the end of the plate, a second layer of S-shaped loading is performed in reverse along the original S-shaped path. The downward depth of the punch in the second layer of S-shaped loading is increased by 1 to 2 millimeters compared with the first layer, and the step spacing is adjusted to D×1.2 to 1.5 times.
[0013] As a preferred technical solution, in step S4, the distance by which the punch is offset along the width direction of the sheet metal during transverse staggered pressing is 30% to 40% of the punch width, the downward depth of the punch is controlled at 80% to 90% of the final forming depth, and the pressing path is advanced from one edge of the sheet metal to the other edge in a unidirectional progressive manner.
[0014] As a preferred technical solution, in step S2, the flexible buffer layer is made of polyurethane rubber material, with a Shore hardness controlled within the range of 75A to 85A, and its thickness is determined according to the following relationship based on the thickness t of the plate: h = (0.12~0.16) × t, The width of the flexible cushioning layer covers 30 to 50 millimeters on each side of the shoulder of the V-shaped groove.
[0015] As a preferred technical solution, in step S5, the final pressing time T is determined according to the following relationship between the plate thickness t and the target bending angle θ: T = (0.3~0.5) × t × , During the pressure holding process, a staged pressure release method is adopted, and the return speed of the punch is controlled within the range of 8 to 12 mm / s.
[0016] A sheet metal pressing apparatus for implementing the process described in any of the above technical features includes a punch and a lower die, and also includes an S-shaped bending mechanism, wherein the S-shaped bending mechanism includes a transverse moving unit, a longitudinal moving unit and a path control unit; The lateral movement unit is used to drive the punch to move back along the length of the plate. The longitudinal moving unit is used to drive the punch to step off along the width direction of the sheet metal; The path control unit is connected to the lateral movement unit and the longitudinal movement unit, and is used to control the movement of the two units to make the punch form an S-shaped loading trajectory.
[0017] As a preferred technical solution, the S-shaped bending mechanism further includes a loading depth adjustment unit, which is connected to the punch and is used to adjust the downward depth of the punch during the loading process of the S-shaped path; The path control unit has a built-in path planning module, which automatically calculates the step spacing, turning angle, turning length and loading depth increasing curve of the S-shaped path based on the sheet material parameters.
[0018] The advantages and beneficial effects of this invention are as follows: By improving the pressing process and device structure, the problem of deep indentations easily generated during the pressing of thickened plates is solved. In traditional processes, when the plate is pressed, the stress is concentrated in a narrow area on the shoulder of the die. Coupled with the lack of cushioning in rigid contact, this results in indentations up to 0.6 mm deep on the plate surface, requiring 8 hours of manual grinding for each set of plates. This invention uses an S-shaped path loading method, allowing the punch to move back and forth on the plate surface, applying pressure gradually in segments. This disperses the stress to multiple points of application, preventing stress from accumulating continuously in a single location. Simultaneously, a flexible buffer layer is laid on the shoulder of the lower die, preventing rigid contact between the plate and the metal die and reducing indentation. After adopting this invention, the original 0.6 mm deep indentations are essentially eliminated, leaving only slight contact marks on the plate surface. Minimal or no grinding is needed to meet quality requirements, and the grinding time for a single set of plates is reduced from 8 hours to just a few minutes, directly saving on grinding labor costs. Furthermore, due to reduced excessive grinding, the surface integrity and thickness of the plate are better preserved, and the production cycle is also shortened. Attached Figure Description
[0019] Figure 1 This is a demonstration of the effects of the process embodiments and comparative examples shown in this invention.
[0020] Figure 2 This is a schematic diagram of the structure of the device shown in this invention. Detailed Implementation
[0021] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, it should be noted that, for ease of description, only the parts relevant to this application are shown in the accompanying drawings, not the entire structure. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.
[0022] The terms “comprising” and “having”, and any variations thereof, used in this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.
[0023] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly or implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.
[0024] This invention provides a process for improving indentation during sheet metal pressing. By optimizing the stress field distribution and contact interface conditions during the pressing process, indentation is reduced. The process includes the following steps: First, the upper die is designed to match the thickness parameters of the sheet metal to be processed, increasing the width of the upper die to 8 to 10 times the thickness of the sheet metal. Second, a flexible buffer layer is laid at the shoulder of the V-groove of the lower die. Then, the sheet metal is progressively formed using an S-shaped path loading method, with the punch reciprocating along the length of the sheet metal. In each reciprocating stroke, the punch advances forward gradually according to a preset step interval, while controlling the downward depth of the punch to increase in each reciprocating cycle. Next, after the S-shaped path loading is completed, lateral staggered pressing is performed, with the punch offset by a preset distance along the width of the sheet metal to supplement the pressing of the interval areas between the previous stage loading paths. Finally, the punch is reset to the center position of the sheet metal for final shaping pressing, and the pressure is held before unloading.
[0025] Indentations during sheet metal bending essentially stem from stress concentration and frictional damage at the contact interface. When the punch contacts the sheet metal, the contact stress is inversely proportional to the contact width. Traditional narrow-width dies, due to their small contact area, generate higher contact stress under the same pressing force, leading to localized yielding on the sheet metal surface and the formation of indentations. Simultaneously, during the sheet metal bending deformation process, the shoulder of the lower die's V-groove acts as a support point, forming a sliding friction pair with the back of the sheet metal. The combined effect of the friction coefficient and the normal pressure determines the degree of surface damage.
[0026] This invention reduces the maximum compressive stress at the contact interface by increasing the contact area of the upper mold. By introducing a flexible buffer layer at the shoulder of the lower mold, the contact area is increased using the deformation characteristics of the elastic material, and some impact energy is absorbed through the material's damping properties, thereby reducing the frictional shear stress on the back of the sheet metal. The S-shaped loading method effectively avoids the stress accumulation mode of traditional one-time loading. By decomposing the total deformation into multiple cycles, stress redistribution occurs after each local loading, preventing stress from continuously concentrating at a single location and forming indentations.
[0027] In the aforementioned basic process steps, when the upper die width is too small, the contact area is narrow, the stress peak is high, and local indentation is easily formed. When the upper die width is too large, although it can further reduce stress, it may be limited by equipment space and die manufacturing process. Through finite element simulation analysis and extensive process experiments, controlling the upper die width within the range of 8 to 10 times the thickness of the plate material can achieve the best stress dispersion effect under existing equipment conditions. Taking a 75mm thick plate as an example, the upper die width is designed to be 600mm to 750mm.
[0028] To achieve S-shaped path loading, the punch first descends to induce initial bending deformation of the sheet metal to 30% to 40% of the target angle. Subsequently, the punch advances forward along the length of the sheet metal in steps D. Each complete reciprocating stroke is defined as one unit S-shaped operation. At the beginning of each unit S-shaped operation, the punch's descent depth increases by 2 to 3 mm from the previous cycle. At the end of each unit S-shaped operation, the punch rises to a height of 3 to 5 mm above the sheet metal surface. This loading method controls the plastic flow process of the material through a segmented and gradual approach. When the initial deformation reaches 30% to 40% of the target angle, the sheet metal is in the elastic deformation and early plastic deformation stage, and a stable stress field has not yet formed inside the material. Starting S-shaped loading at this point effectively guides stress distribution. The design of the punch detaching from the sheet metal surface at the end of each unit S-shaped operation allows the sheet metal to complete the rebalancing of internal stresses under unloading conditions, similar to the stress relaxation process of the material, and reduces the accumulation of residual stress.
[0029] In some embodiments, the step spacing D is determined based on the sheet thickness t and the target bending angle θ according to the following relationship: D = (3~6) × t × sin(θ / 2). During the V-bending process, the contact point between the sheet and the lower die shoulder moves with the change of bending angle, and the trajectory length of the contact point has a clear geometric relationship with the sheet thickness and bending angle. The step spacing D essentially determines the degree of overlap between two adjacent loading operations along the length of the sheet. An excessively large step spacing will lead to discontinuity in the loading area, forming an insufficiently deformed area; an excessively small step spacing will reduce processing efficiency. sin(θ / 2) reflects the influence of the bending angle on the length of the contact area. The larger the bending angle, the longer the deformation area of the sheet in the V-groove, and the required step spacing should also be increased accordingly. At the same time, the turning angle α of the S-shaped path is determined based on the sheet width W and the step spacing D according to the following relationship: α = arctan(W / (2D)) × (0.6~0.8). The turning angle α determines the offset rate of the S-shaped path in the width direction of the sheet metal. When the above formula is satisfied, the loading areas of adjacent reciprocating strokes have an overlap rate of 20% to 30% in the width direction, thus ensuring uniform force distribution in the width direction of the sheet metal. Taking a sheet metal with a width of 1000mm and a step spacing of 80mm as an example, the theoretical turning angle is about 80.5°. After multiplying by a coefficient of 0.6 to 0.8, it is controlled between 48° and 64°, which can ensure effective overlap without causing unstable punch movement due to excessively sharp turning.
[0030] The turning length L of a unit S-shaped operation is determined based on the step distance D and the number of unit S-shaped operations n according to the following relationship: L = n × D, where n is an integer ranging from 5 to 8. The turning length L determines the length of each continuous loading segment, and n is set to 5 to 8 to achieve a balance between processing efficiency and stress dispersion effect. It should be noted that L is limited by the actual length Lp of the sheet metal. If the value of n is too small, the turning will be too frequent, affecting processing efficiency; if the value of n is too large, the single continuous loading segment will be too long, weakening the stress dispersion effect. At the end of each turning length L, the loading path direction of the punch reverses to form an S-shaped turning point, and the arc transition radius R of the turning point is set to 15 to 25 mm. When the punch movement direction reverses, if a right-angle turning is used, it will cause a sudden change in instantaneous acceleration, generating an impact force on the sheet metal surface; by setting an appropriate arc transition radius, the punch can maintain a smooth speed change during the turning process.
[0031] When the punch reaches the end of the sheet metal, a second layer of S-shaped loading is applied in reverse along the original S-shaped path. The punch's downward depth in the second layer of S-shaped loading is increased by 1 to 2 millimeters compared to the first layer, and the step spacing is adjusted to D × 1.2 to 1.5 times. The stress state at the end of the sheet metal is unique; due to the lack of continuous material constraint, its stress distribution differs from the middle region, easily leading to stress concentration or insufficient deformation. By applying a second layer of S-shaped loading in reverse, a cross-loading path can be formed, allowing areas not sufficiently deformed in the first layer to be processed in the second layer. The appropriately increased step spacing in the second layer is intended to correct localized uneven areas, rather than re-loading the entire sheet. Therefore, a wider step spacing ensures the correction effect without causing excessive reloading. The 1 to 2 millimeter increase in downward depth takes into account the work hardening effect of the material after the first layer of loading, requiring slightly higher pressure to achieve the same deformation effect.
[0032] Lateral staggered pressure compensation involves: the punch offsetting along the width of the sheet metal by 30% to 40% of its width, resulting in a 20% to 40% overlap between the pressure compensation area and the S-shaped path loading area; the punch's downward depth during pressure compensation is controlled at 80% to 90% of the final forming depth, and the pressure compensation path advances unidirectionally from one edge of the sheet metal to the other. The technical purpose of lateral staggered pressure compensation is to eliminate any gaps that may be left by the S-shaped path loading. Although the S-shaped path design considers the overlap rate, slight stress differences may still exist due to the anisotropy and local non-uniformity of the sheet metal material during actual processing. Lateral offset pressure compensation is equivalent to a second stress field renormalization in the vertical direction, making the stress distribution more uniform. The offset amount is controlled at 30% to 40% of the punch width, ensuring sufficient overlap between the pressure compensation area and the original loading area without completely repeating the original path. The design of controlling the downward depth to 80% to 90% of the final forming depth does not require reaching the final forming depth; stress normalization of the surface layer is sufficient.
[0033] In some embodiments, to optimize the material selection and geometric parameters of the flexible cushioning pad, the flexible cushioning pad is made of polyurethane rubber with a Shore hardness controlled within the range of 75A to 85A. The thickness is determined according to the sheet thickness t using the following relationship: h = (0.12~0.16) × t. Polyurethane rubber, as a high-molecular elastic material, has excellent compression resilience and wear resistance. The design formula for thickness h reflects the positive correlation between the pad thickness and the sheet thickness, because thicker sheets require greater pressing force, thus requiring a thicker cushioning layer to absorb energy. Taking a 75mm thick sheet as an example, the pad thickness is controlled between 9mm and 12mm, which provides sufficient cushioning space without causing insufficient punch stroke or excessive pad deformation that affects molding accuracy. The width of the flexible cushioning pad covers 30 to 50 mm on each side of the V-groove shoulder, ensuring that all potential contact areas between the back of the sheet and the lower die are protected by the cushioning layer.
[0034] The final holding time T for shaping and pressing is determined based on the sheet thickness t and the target bending angle θ according to the following relationship: T = (0.3~0.5) × t × (θ / 90), in seconds. The holding time is designed based on the physical mechanisms of material creep and stress relaxation. Even after the sheet reaches the predetermined deformation, residual stress still exists internally. If this residual stress is not fully released, it will cause elastic recovery after unloading, affecting molding accuracy and potentially leading to surface microcracks. The holding process provides time for the material's creep deformation, allowing internal stress to be gradually released through the movement of micro-dislocations. The holding time is proportional to the sheet thickness because thicker sheets have a greater stress gradient and require a longer time to achieve stress equilibrium; it is also proportional to the bending angle because a larger bending angle results in greater sheet deformation and a higher level of residual stress. For example, for a 75mm thick sheet with a 90° bending angle, the holding time is controlled within the range of 20 to 30 seconds. In addition, a staged pressure relief method is adopted during the pressure holding process. First, 50% to 60% of the pressure is relieved and held for 5 to 8 seconds, and then the remaining pressure is completely relieved.
[0035] The invention also provides a sheet metal pressing device. This device includes a frame, a hydraulic drive system, a control system, a punch, and a lower die that cooperates with the punch. An S-shaped bending mechanism is added, which includes a lateral movement unit, a longitudinal movement unit, and a path control unit. The lateral movement unit is mounted on the frame and drives the punch to move back and forth along the length of the sheet metal. It typically uses a servo motor with a ball screw drive mechanism or a linear motor to achieve high-precision position control. The longitudinal movement unit is connected to the lateral movement unit and drives the punch to move in a stepwise manner along the width of the sheet metal. It also uses a servo drive system to ensure positioning accuracy. The path control unit is electrically connected to the control system and controls the lateral and longitudinal movement units to cooperate according to preset S-shaped path parameters, so that the punch forms a continuous S-shaped loading trajectory on the surface of the sheet metal.
[0036] From a control engineering perspective, the S-shaped bending mechanism is essentially a two-dimensional motion control system that needs to address the synchronization and coordination of two motion axes. The core function of the path control unit is trajectory planning and interpolation calculation. The control system first automatically calculates the key parameters of the S-shaped path based on the input sheet metal parameters (thickness, length, width, target bending angle), including the step spacing D, turning angle α, turning length L, and loading depth increment curve.
[0037] In some embodiments, the S-shaped bending mechanism further includes a loading depth adjustment unit connected to the punch, used to adjust the downward depth of the punch according to a preset incremental step size during the S-shaped path loading process. The loading depth adjustment unit can be an independent vertical motion axis or a proportional valve control system linked to the hydraulic system. During the S-shaped path loading process, the loading depth adjustment unit needs to work in conjunction with the lateral and longitudinal movement units to form a three-dimensional spatial motion trajectory.
[0038] The present application will be further explained and illustrated below with reference to the embodiments.
[0039] Example 1 A process for improving indentation in sheet metal pressing includes the following steps: S1. Design the upper mold to match the thickness parameters of the material to be processed, so that the width of the upper mold is increased to 8 times the thickness of the material.
[0040] S2. A flexible cushioning pad is laid at the shoulder of the V-shaped groove of the lower mold. The flexible cushioning pad is made of polyurethane rubber material with a Shore hardness of 80A, a thickness of 0.14 times that of the plate thickness, and a width covering 40mm on each side of the shoulder of the V-shaped groove.
[0041] S3. The sheet metal is progressively formed using an S-shaped path loading method. The punch first descends to induce an initial bending deformation of the sheet metal to 35% of the target angle. Then, loading is performed according to preset S-shaped path parameters: the step distance D is calculated using the formula D=10×t×sin(θ / 2); the turning angle α is calculated using the formula α=arctan(W / (2D))×0.7; the turning length L of a unit S-shaped operation is 6×D, and the arc transition radius at the turning point is R=20mm. The punch advances forward along the length of the sheet metal at a step distance D. Each complete reciprocating stroke is defined as one unit S-shaped operation. At the beginning of each unit S-shaped operation, the punch's descent depth increases by 2.5mm from the previous cycle. At the end of each unit S-shaped operation, the punch rises to a height of 4mm above the sheet metal surface. When the punch reaches the end of the sheet metal, a second layer of S-shaped loading is performed in reverse along the original S-shaped path. The descent depth of the punch in the second layer of S-shaped loading is 1.5mm greater than the first layer, and the step distance is adjusted to D×1.3 times.
[0042] After loading the S4 and S-shaped paths, perform lateral staggered pressure replenishment. The distance the punch is offset along the width of the sheet metal is 35% of the punch width, and the downward depth of the punch is controlled at 85% of the final forming depth. The pressure replenishment path advances from one edge of the sheet metal to the other edge in a unidirectional progressive manner.
[0043] S5. The punch returns to the center of the sheet metal for final shaping and pressing. The holding time T is calculated using the formula T=0.4×t×(θ / 90). During the holding process, a staged pressure release method is adopted, and the punch return speed is controlled at 10 mm / s.
[0044] In this embodiment, the 75mm thickened board pressed using the above process has a maximum indentation depth of 0.04mm, which is almost invisible to the naked eye. The sanding time for a single set of boards is reduced from 8 hours in the traditional process to 10 minutes, and the sanding labor cost is reduced from 248 yuan / set to 5 yuan / set. Based on the GE107-set project, the direct savings in sanding costs are approximately 26,000 yuan.
[0045] Example 2 A process for improving indentation in sheet metal pressing includes the following steps: S1. Design the upper mold to match the thickness parameters of the material to be processed, so that the width of the upper mold is increased to 9 times the thickness of the material.
[0046] S2. A flexible cushioning pad is laid at the shoulder of the V-shaped groove of the lower mold. The flexible cushioning pad is made of polyurethane rubber material with a Shore hardness of 75A, a thickness of 0.12 times that of the plate thickness, and a width covering 30mm on each side of the shoulder of the V-shaped groove.
[0047] S3. The sheet metal is progressively formed using an S-shaped path loading method. The punch first descends to induce an initial bending deformation of the sheet metal to 30% of the target angle. Then, loading is performed according to preset S-shaped path parameters: the step distance D is calculated using the formula D=8×t×sin(θ / 2); the turning angle α is calculated using the formula α=arctan(W / (2D))×0.6; the turning length L of a single S-shaped operation is 5×D, and the arc transition radius at the turning point is R=15mm. The punch advances forward along the length of the sheet metal at a step distance D. At the beginning of each single S-shaped operation, the punch's descent depth increases by 2.0mm from the previous cycle. At the end of each single S-shaped operation, the punch rises to a height of 3mm above the sheet metal surface. When the punch reaches the end of the sheet metal, a second layer of S-shaped loading is performed in reverse along the original S-shaped path. The descent depth of the punch in the second layer of S-shaped loading is 1.0mm greater than the first layer, and the step distance is adjusted to D×1.2 times.
[0048] After loading the S4 and S-shaped paths, perform lateral staggered pressure replenishment. The distance the punch is offset along the width of the sheet metal is 30% of the punch width, and the downward depth of the punch is controlled at 80% of the final forming depth. The pressure replenishment path advances from one edge of the sheet metal to the other edge in a unidirectional progressive manner.
[0049] S5. The punch returns to the center of the sheet metal for final shaping and pressing. The holding time T is calculated using the formula T=0.3×t×(θ / 90). During the holding process, a staged pressure release method is adopted, and the punch return speed is controlled at 8 mm / s.
[0050] In this embodiment, the maximum indentation depth of the 50mm thick plate after being pressed using the above process is 0.03mm. The sanding time for a single set of plates is reduced from 5 hours in the traditional process to 8 minutes, and the sanding labor cost is reduced from 155 yuan / set to 4 yuan / set. Based on a batch production of 200 sets, the direct savings in sanding costs are approximately 30,000 yuan.
[0051] Example 3 A process for improving indentation in sheet metal pressing includes the following steps: S1. Design the upper mold to match the thickness parameters of the material to be processed, so that the width of the upper mold is increased to 10 times the thickness of the material.
[0052] S2. A flexible cushioning pad is laid at the shoulder of the V-shaped groove of the lower mold. The flexible cushioning pad is made of polyurethane rubber material with a Shore hardness of 85A, a thickness of 0.16 times that of the plate thickness, and a width covering 50mm on each side of the shoulder of the V-shaped groove.
[0053] S3. The sheet metal is progressively formed using an S-shaped path loading method. The punch first descends to induce an initial bending deformation of the sheet metal to 40% of the target angle. Then, loading is performed according to preset S-shaped path parameters: the step distance D is calculated using the formula D=12×t×sin(θ / 2); the turning angle α is calculated using the formula α=arctan(W / (2D))×0.8; the turning length L of a single S-shaped operation is 8×D, and the arc transition radius at the turning point is R=25mm. The punch advances forward along the length of the sheet metal at a step distance D. At the beginning of each unit S-shaped operation, the punch's descent depth increases by 3.0mm from the previous cycle. At the end of each unit S-shaped operation, the punch rises to a height of 5mm above the sheet metal surface. When the punch reaches the end of the sheet metal, a second layer of S-shaped loading is performed in reverse along the original S-shaped path. The descent depth of the punch in the second layer of S-shaped loading is 2.0mm greater than the first layer, and the step distance is adjusted to D×1.5 times.
[0054] After loading the S4 and S-shaped paths, perform lateral staggered pressure replenishment. The distance the punch is offset along the width of the sheet metal is 40% of the punch width, and the downward depth of the punch is controlled at 90% of the final forming depth. The pressure replenishment path advances from one edge of the sheet metal to the other edge in a unidirectional progressive manner.
[0055] S5. The punch returns to the center position of the sheet metal for final shaping and pressing. The holding time T is calculated according to the formula T=0.5×t×(θ / 90). During the holding process, a staged pressure release method is adopted, and the return speed of the punch is controlled at 12 mm / s.
[0056] In this embodiment, the maximum indentation depth of the 100mm thick plate after being pressed using the above process is 0.06mm. The sanding time for a single set of plates is reduced from 12 hours in the traditional process to 20 minutes, and the sanding labor cost is reduced from 372 yuan / set to 10 yuan / set. Based on a batch production of 50 sets, the direct savings in sanding costs are approximately 18,000 yuan.
[0057] Comparative Example 1 A process for improving indentation in sheet metal pressing includes the following steps: S1. A traditional narrow upper mold is adopted, with the upper mold width being 3.5 times the thickness of the sheet material. The working surface of the upper mold has right-angled edges without rounded transitions.
[0058] S2, The lower mold V-groove shoulder has no flexible buffer pad.
[0059] S3. The punch is directly lowered to the final forming position using a one-time loading method, without segmented loading, S-shaped path, or pressure holding process.
[0060] In this comparative example, the 75mm thickened board, pressed using the above process, achieved a maximum indentation depth of 0.62mm. Each set of boards requires 8 hours of manual sanding, with a labor cost of 248 yuan per set. The springback of the board after forming is approximately 2.8°.
[0061] Comparative Example 2 A process for improving indentation in sheet metal pressing includes the following steps: S1. A traditional narrow upper mold is adopted, with the upper mold width being 3.5 times the thickness of the sheet material.
[0062] S2. A flexible cushioning pad is laid at the shoulder of the V-shaped groove of the lower mold. It is made of ordinary industrial rubber with a Shore hardness of 60A and a thickness of 5mm.
[0063] S3. The punch is loaded into position in one go, and then moves directly down to the final forming position without segmented loading or an S-shaped path.
[0064] In this comparative example, the maximum indentation depth of the 75mm thickened plate after being pressed using the above process is 0.38mm. Each set of plates requires 4.5 hours of sanding, with a sanding labor cost of 140 yuan per set. The cushioning layer undergoes permanent deformation after 20 uses.
[0065] Comparative Example 3 A process for improving indentation in sheet metal pressing includes the following steps: S1. A traditional narrow upper mold is adopted, with the upper mold width being 3.5 times the thickness of the sheet material.
[0066] S2, The lower mold V-groove shoulder has no flexible buffer pad.
[0067] S3. A segmented loading method is adopted, with the material being pressed down gradually in three stages to the final forming position. After each loading is completed, the pressure is maintained for 10 seconds. There is no S-shaped path loading, and the punch is always located in the center of the sheet metal.
[0068] In this comparative example, the maximum indentation depth of the 75mm thickened board after being pressed using the above process is 0.29mm. Each set of boards requires 3 hours of sanding, with a sanding labor cost of 93 yuan per set. The depth of the friction marks on the back of the board is approximately 0.22mm.
[0069] Comparative Example 4 A process for improving indentation in sheet metal pressing includes the following steps: S1. Design the upper mold to match the thickness parameters of the material to be processed, so that the width of the upper mold is increased to 9 times the thickness of the material.
[0070] S2. A flexible buffer pad layer is laid at the shoulder of the V-shaped groove of the lower mold. It is made of polyurethane rubber material with a Shore hardness of 80A and a thickness of 10.5mm.
[0071] S3. A linear reciprocating loading method is adopted. The punch moves back and forth in a straight line along the length of the sheet metal, with a fixed step distance of 500mm and no S-shaped path turning angle. The punch descends 2.5mm in each reciprocating stroke, but there is no second layer of reverse loading and no lateral staggered pressure.
[0072] S4. After the punch is reset, perform final shaping and pressing, hold pressure for 20 seconds, and then unload.
[0073] In this comparative example, the 75mm thickened board, after being pressed using the above process, had a maximum indentation depth of 0.18mm, but the surface of the board showed regular striped marks with periodic fluctuations in depth. Each set of boards required 1.2 hours of sanding, with a sanding labor cost of 37 yuan per set.
[0074] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.
Claims
1. A process for improving indentation during sheet metal pressing, characterized in that, Includes the following steps: S1. Design the upper mold to match the thickness parameters of the material to be processed, so that the width of the upper mold is increased to 8 to 10 times the thickness of the material. S2. Lay a flexible cushioning pad at the shoulder of the V-groove of the lower mold; S3. The S-shaped path loading method is used to progressively form the sheet metal. The punch is reciprocated along the length of the sheet metal. In each reciprocating stroke, it advances forward step by step according to the preset step interval. At the same time, the downward depth of the punch is controlled to increase in each reciprocating cycle. S4. After the S-shaped path loading is completed, perform transverse staggered pressing. The punch is offset by a preset distance along the width direction of the sheet metal to supplement the pressing of the interval area between the loading paths in the previous stage. S5. The punch is reset to the center position of the sheet metal, and the final shaping and pressing are performed. After holding the pressure, the punch is unloaded.
2. The process according to claim 1, characterized in that, In step S3, the specific operation of loading the S-shaped path is as follows: the punch first moves downward to induce an initial bending deformation of the sheet metal to 30% to 40% of the target angle; then the punch moves forward along the length of the sheet metal at a step interval D. Each complete reciprocating stroke is defined as one unit S-shaped operation. At the beginning of each unit S-shaped operation, the downward depth of the punch increases by 2 to 3 mm based on the previous cycle. At the end of each unit S-shaped operation, the punch is raised to a height of 3 to 5 mm away from the surface of the sheet metal.
3. The process according to claim 2, characterized in that, The step spacing D is determined according to the plate thickness t and the target bending angle θ according to the following relationship: D=(3~6)×t×sin(θ / 2); the turning angle α of the S-shaped path is determined according to the plate width W and the step spacing D according to the following relationship: α=arctan(W / (2D))×(0.6~0.8).
4. The process according to claim 3, characterized in that, During the loading process of the S-shaped path, the turning length L of the unit S-shaped operation is determined according to the following relationship between the step spacing D and the number of unit S-shaped operations n: L=n×D, where n is an integer and the value ranges from 5 to 8; at the end of each turning length L, the loading path direction of the punch is reversed to form an S-shaped turning point, and the arc transition radius R of the turning point is set to 15 to 25 mm.
5. The process according to claim 2, characterized in that, In step S3, when the punch travels to the end of the plate, the second layer of S-shaped loading is performed in reverse along the original S-shaped path. The downward depth of the punch in the second layer of S-shaped loading is increased by 1 to 2 millimeters compared with the first layer, and the step spacing is adjusted to D×1.2 to 1.5 times.
6. The process according to claim 1, characterized in that, In step S4, during the transverse staggered pressing, the distance by which the punch is offset along the width direction of the sheet metal is 30% to 40% of the punch width, the downward depth of the punch is controlled at 80% to 90% of the final forming depth, and the pressing path is advanced from one edge of the sheet metal to the other edge in a unidirectional progressive manner.
7. The process according to claim 1, characterized in that, In step S2, the flexible buffer pad is made of polyurethane rubber material, with a Shore hardness controlled within the range of 75A to 85A. The thickness is determined according to the thickness t of the plate according to the following relationship: h = (0.12~0.16) × t. The width of the flexible buffer pad covers 30 to 50 mm on each side of the shoulder of the V-shaped groove.
8. The process according to claim 1, characterized in that, In step S5, the final pressing holding time T is determined according to the plate thickness t and the target bending angle θ according to the following relationship: T=(0.3~0.5)×t×(θ / 90). During the pressing process, a graded pressure release method is adopted, and the punch return speed is controlled within the range of 8 to 12 mm / s.
9. A sheet metal pressing apparatus for performing the process according to any one of claims 1 to 8, comprising a punch and a lower die, characterized in that, It also includes an S-shaped bending mechanism, which includes a lateral moving unit, a longitudinal moving unit, and a path control unit; the lateral moving unit is used to drive the punch to move backward along the length of the sheet metal; the longitudinal moving unit is used to drive the punch to move in a stepwise offset along the width of the sheet metal; the path control unit is connected to the lateral moving unit and the longitudinal moving unit, and is used to control the coordinated action of the two to make the punch form an S-shaped loading trajectory.
10. The sheet metal pressing device according to claim 9, characterized in that, The S-shaped bending mechanism also includes a loading depth adjustment unit, which is connected to the punch and is used to adjust the downward depth of the punch during the loading process of the S-shaped path; the path control unit has a built-in path planning module, which automatically calculates the step spacing, turning angle, turning length and loading depth increment curve of the S-shaped path according to the sheet material parameters.