A method and a die for correcting the rebound of a side wall of a beam member

Abstract

A method for correcting the curling rebound of the sidewall of a beam-type component is proposed. This method uses the condition that the component (1) is in the yielding stage at the moment of unloading after forming as a constraint. Based on the mutual transmission of forces between the microstructures during material deformation under stress, the method optimizes the mold structure to achieve the same stress sign between the outermost and innermost layers of the component's sidewall at that moment. This reduces the thickness stress difference in the sidewall region (2), thus correcting the curling rebound of the sidewall. This invention provides a method and mold for correcting the curling rebound of the sidewall of a beam-type component. Without altering the component structure or requiring complex mold design, it addresses the essence of sidewall curling and establishes a solution, effectively correcting the curling rebound of the sidewall of a beam-type component.

Description

Technical Field

[0001] This invention belongs to the field of cold stamping forming of sheet metal, specifically relating to a method and a correction mold for correcting the curling and rebound of the sidewall of a beam-type component. Background Technology

[0002] During sheet metal forming, due to elastic deformation, a certain degree of elastic recovery, known as stamping rebound, occurs when the part is unloaded or removed from the mold. This rebound is the most significant factor determining the forming accuracy of stamped parts. The rebound of a part is closely related to the strength, elastic modulus, and structural design of the material used. In recent years, with the automotive industry's increasing demands for vehicle safety and energy conservation, high-strength steel and even ultra-high-strength steel sheets have become increasingly popular and widely used due to their dual advantages of weight reduction and improved safety. However, because ultra-high-strength steel has significantly increased strength, the rebound problem of stamped parts has become increasingly prominent, making rebound control an urgent issue.

[0003] Body structural components, especially high-strength parts, are mostly beam-type parts. When using traditional stamping methods, backlash, particularly sidewall curling, is a common problem. Backlash control methods include adjusting stamping process parameters, multiple rounds of die surface compensation, and optimizing component or mold structure design. However, these measures are often insufficient to completely control backlash or are prohibitively costly. Furthermore, some solutions lack universal applicability.

[0004] The invention application with application number CN200910067556.1 discloses "a method for controlling the springback of ultra-high strength steel stamped parts." The method describes a mold structure mainly composed of a punch, a die, and a top plate. The bottom surface of the punch and the upper surface of the top plate are made into double-arc surfaces. During forming, the punch moves downwards, and the sheet metal is pressed against the arc bottom surface of the punch by the top plate, causing elastic deformation of the sheet metal along the arc of the punch. During unloading, the reverse springback deformation generated by the bent double-arc surface can compensate for the springback deformation of the side walls of the stamped part. By controlling the arc curvature, springback can be reduced or even eliminated. This method is suitable for beam-type parts with no complex top surface features. However, the actual operation is relatively complex, the degree of double-arc surface needs repeated experimentation, and the punch and die need to be adjusted simultaneously during adjustment, resulting in poor matching.

[0005] The invention application with application number CN201410134106.0 discloses a "stamping device for controlling the curling and springback of the sidewall of a stamped part". From top to bottom, it includes an upper die base, a die cavity, a pressure ring driven by an air ejector rod, a punch matching the die cavity, and a lower die base. The upper die base is fixedly connected to the die cavity and moves synchronously. The punch is fixedly connected to the lower die base. The punch includes a first stamping part and a second stamping part from top to bottom. The first stamping part and the second stamping part are smoothly transitioned by a transition curve. The gap between the outer contour of the sidewall of the first stamping part and the sidewall of the die cavity is 1.2-1.6 times the thickness of the plate to be stamped. The gap between the outer contour of the sidewall of the second stamping part and the sidewall of the die cavity is 0.8-0.9 times the thickness of the plate to be stamped. The projection length of the transition curve in the stamping direction is 2-3 times the thickness of the plate to be stamped. This device designs the die structure during the stamping process to change the die clearance, resulting in different clearances for the sheet metal at different forming depths. This reduces the stress difference between the inner and outer layers of the material, effectively controlling the sidewall curling and rebound of the part, and improving the forming accuracy and quality of the part. However, when stamping parts with large thickness or high yield strength, the friction between the second stamping part, the die, and the stamped part increases significantly. This can easily cause wear on the second stamping part on the punch and the die, resulting in damage to the stamped part. Long-term use of this device will greatly reduce its control effect on the sidewall curling and rebound of the stamped part.

[0006] Invention application CN201110380742.8 discloses "a method and system for springback correction processing of beam-type molds." The method includes: determining mold surface parameters based on preset beam-type workpiece surface parameters; fabricating a first beam-type mold using mold processing equipment based on the mold surface parameters; fabricating a first test workpiece using the first beam-type mold; obtaining the surface parameters of the first test workpiece using springback analysis equipment; comparing the surface parameters of the first test workpiece with the preset beam-type workpiece surface parameters to obtain the workpiece springback amount; performing springback compensation on the mold surface parameters of the first beam-type mold based on the workpiece springback amount to obtain compensated mold surface parameters; fabricating a second beam-type mold based on the compensated mold surface parameters; determining the final mold surface parameters when the surface parameters of the test workpiece and the preset beam-type workpiece meet the workpiece qualification requirements; and fabricating the final beam-type mold based on the final mold surface parameters. This method compensates for the mold surface, which is a post-processing adjustment, resulting in long debugging costs and a long cycle.

[0007] Chinese invention application CN201380045002.6 discloses "a method and analysis device for suppressing springback of stamped parts." The method for suppressing springback of stamped parts includes the following steps: an analysis model generation step, in which an analysis model of the component is generated using planar and / or three-dimensional elements; a stress state setting step, in which a stress state is set that causes springback in each element of the generated analysis model; a rigidity contribution part detection step, in which shape optimization analysis is performed on the analysis model with the stress state set in the stress state setting step, and parts contributing significant rigidity are detected; and a rigidity improvement step, in which units for improving the rigidity of the component are implemented based on the parts detected in the rigidity contribution part detection step. However, the measures to improve rigidity involve modifications to the parts, requiring negotiation with the vehicle body designer, and thus face certain difficulties in widespread adoption.

[0008] Invention application CN201110287803.6 discloses "a forming mold for processing high-tensile sheet metal parts". The forming mold includes an upper mold base, a pressure core, an upper mold fixing plate, a lower mold base, a punch, a pressure plate, and an upper mold cutting block. The upper mold fixing plate is disposed between the upper mold base and the upper mold cutting block. At least one first nitrogen spring is disposed between the pressure core and the upper mold base, and at least two second nitrogen springs are disposed between the pressure plate and the lower mold base. Locking units are fabricated on the pressure plate and the upper mold cutting block. During forming, the sheet metal locked between the pressure core and the locking units will undergo sufficient tensile plastic deformation, overcoming the large springback after forming. However, this mold structure only has the pressure plate pressing the material before reaching the bottom, therefore requiring that the part not have flange surface compression. Furthermore, this solution requires the pressure plate to have a delayed return function, making the setup relatively complex. Summary of the Invention

[0009] To address the above problems, this invention provides a method and mold for correcting the curling and rebound of the sidewalls of beam-type components. The specific technical solution is as follows:

[0010] A method for correcting the curling and rebound of the sidewalls of beam-type components, characterized in that:

[0011] The constraint condition is that the sheet metal (1) is in the yield stage at the time of unloading after forming.

[0012] Based on the mutual transmission of forces between tissues when the material is deformed by stress, the stress of the outermost and innermost layers of the component sidewall is controlled to be the same at this moment by optimizing the force application method of the mold structure. In this way, the sidewall curling rebound is corrected by reducing the thickness stress difference in the sidewall region (2).

[0013] A method for correcting the curling and rebound of the sidewalls of beam components according to the present invention is characterized in that:

[0014] The optimization of the mold structure is achieved by symmetrically setting a pair of protrusions (4) on the flange part (3) of the punch and setting grooves at corresponding positions on the die.

[0015] A method for correcting the curling and rebound of the sidewalls of beam components according to the present invention is characterized in that:

[0016] The top corners of the protrusions are all rounded, and the top of the grooves is also rounded accordingly.

[0017] A method for correcting the curling and rebound of the sidewalls of beam components according to the present invention is characterized in that:

[0018] The location of the protrusion is determined according to the following formula:

[0019] ΔL≥(1 / 2W)+t+R+a,

[0020] In the formula,

[0021] ΔL: Distance between the center line of the protrusion and the boundary line of the component, in mm;

[0022] W: Width of the protrusion, unit: mm;

[0023] t: Original thickness of sheet metal, unit: mm;

[0024] R: Rounded corner;

[0025] a: Adjust the parameter, the range is between 5-7mm.

[0026] A method for correcting the curling and rebound of the sidewalls of beam components according to the present invention is characterized in that:

[0027] The radius of the rounded corner of the raised top is the same as that of the corresponding rounded corner of the groove top, and is limited to a value greater than or equal to 3 times the thickness of the sheet material.

[0028] A method for correcting the curling and rebound of the sidewalls of beam components according to the present invention is characterized in that:

[0029] The aforementioned "achieving the same stress sign for the outermost and innermost layers of the component's sidewall at a given moment through optimized mold structure force application" is implemented through the following steps:

[0030] S1: Based on the numerical solution method, the stresses on the outermost and innermost layers of the component sidewalls at the time of loading and unloading of the mold with unoptimized structure are calculated, and the corresponding strain values ​​are determined based on the calculations as the initial strain values.

[0031] S2: Based on the stress-strain curve, with the goal of the stresses of the outermost and innermost layers of the sidewall having the same sign at the moment of unloading after the component is formed, the outermost stress value, innermost stress value, and corresponding strain value generated by the mold loading with structural optimization settings at the corresponding moment are determined through iterative calculation. This strain value is taken as the final strain value; and the difference between the final strain value and the initial strain value is taken as the strain increment value corresponding to the target.

[0032] S3: Finalize the mold structure optimization based on the strain increment value.

[0033] A method for correcting the curling and rebound of the sidewalls of beam components according to the present invention is characterized in that:

[0034] The numerical solution method is the finite element method, and the iterative calculation is based on the finite element method.

[0035] A method for correcting the curling and rebound of the sidewalls of beam components according to the present invention is characterized in that:

[0036] Step S2 specifically involves: using the initial strain value calculated in step S1 as the initial value, and continuously increasing the strain value to approximate the target until the target converges, and determining the corresponding strain value and stress value based on the strain increment at this time.

[0037] A method for correcting the curling and rebound of the sidewalls of beam components according to the present invention is characterized in that:

[0038] Step S3 is completed according to the following formula:

[0039] H = Δε × L,

[0040] 1 / 2≤W / H≤1,

[0041] In the above formula,

[0042] H: Height of the protrusion, in mm;

[0043] Δε: The strain increment corresponding to the target;

[0044] L: Sheet cross-sectional line length, unit: mm;

[0045] W: Width of the protrusion, unit: mm.

[0046] A method for correcting the curling and rebound of the sidewalls of beam components according to the present invention is characterized in that:

[0047] The stress in the sidewalls is characterized by the average stress in the sidewall region.

[0048] A method for correcting the curling and rebound of the sidewalls of beam components according to the present invention is characterized in that:

[0049] The sidewall area is divided into regions along the length of the component, and steps S1-S3 are performed based on each region.

[0050] The division of the region is determined based on the distribution of the thickness stress difference.

[0051] A method for correcting the curling and rebound of the sidewalls of beam components according to the present invention is characterized in that:

[0052] The division of regions is determined based on the distribution of the thickness stress difference, specifically as follows:

[0053] SS1: Calculate the outermost and innermost stress values ​​at each location to determine the thickness stress difference at each location;

[0054] SS2: Starting from the initial position at any end of the sidewall region, compare the thickness stress difference at each position after that position with the thickness stress difference at the initial position until the comparison result is greater than a set value, then divide the region before that position into the same region.

[0055] SS3: Take the position after this location as the starting position for determining the next region. Starting from this starting position, calculate the difference between the thickness stress difference and the thickness stress difference at each subsequent location until the comparison result is greater than the set value. Then, divide the region before this location into another identical region. Repeat this process until the division of all sidewall regions is completed.

[0056] A method for correcting the curling and rebound of the sidewalls of beam components according to the present invention is characterized in that:

[0057] The aforementioned stress sign is achieved by transforming the compressive stress in the innermost layer into tensile stress while keeping the tensile stress in the outermost layer unchanged.

[0058] A mold for correcting the curling and rebound of the sidewall of a beam-type component, characterized in that:

[0059] By symmetrically setting a pair of protrusions (4) on the flange part (3) of the punch and setting grooves at corresponding positions on the die, the optimization of the mold structure is established. According to the optimization, when the forming is completed and unloaded, the stress of the outermost and innermost layers of the side wall area (2) of the component has the same sign, thereby completing the correction of the side wall curling rebound by reducing the thickness stress difference of the side wall area (2).

[0060] According to the present invention, a sidewall curling rebound correction mold for beam-type components is characterized in that:

[0061] The top corners of the protrusions are all rounded, and the top corners of the grooves are correspondingly rounded.

[0062] According to the present invention, a sidewall curling rebound correction mold for beam-type components is characterized in that:

[0063] The location of the protrusion is determined according to the following formula:

[0064] ΔL≥(1 / 2W)+t+R+a,

[0065] In the formula,

[0066] ΔL: Distance between the center line of the protrusion and the boundary line of the component, in mm;

[0067] W: Width of the protrusion, unit: mm;

[0068] t: Original thickness of sheet metal, unit: mm;

[0069] R: Rounded corner;

[0070] a: Adjust the parameter, the range is between 5-7mm.

[0071] According to the present invention, a sidewall curling rebound correction mold for beam-type components is characterized in that:

[0072] The radius of the rounded corner of the raised top is the same as that of the corresponding rounded corner of the groove top, and is limited to a value greater than or equal to 3 times the thickness of the sheet material.

[0073] According to the present invention, a sidewall curling rebound correction mold for beam-type components is characterized in that:

[0074] The size of the protrusion is determined according to the following formula:

[0075] H = Δε × L,

[0076] 1 / 2≤W / H≤1,

[0077] In the above formula,

[0078] H: Height of the protrusion, in mm;

[0079] Δε: The strain increment corresponding to the stresses of the outermost and innermost layers of the component's sidewall region having the same sign at the moment of unloading after forming is complete;

[0080] L: Sheet cross-sectional line length, unit: mm;

[0081] W: Width of the protrusion, unit: mm.

[0082] According to the present invention, a sidewall curling rebound correction mold for beam-type components is characterized in that:

[0083] The strain increment Δε in the formula is determined according to the following:

[0084] First, based on the numerical solution method, the stresses on the outermost and innermost layers of the component sidewalls at the time of loading and unloading of the mold with unoptimized structure are calculated, and the corresponding strain values ​​are determined based on the calculations as the initial strain values.

[0085] Secondly, based on the stress-strain curve, with the goal of the stresses of the outermost and innermost layers of the sidewall having the same sign at the moment of unloading after the component is formed, the outermost stress value, innermost stress value, and corresponding strain value generated by the mold loading with structural optimization settings at the corresponding moment are determined by iterative calculation. This strain value is taken as the final strain value; and the difference between the final strain value and the initial strain value is taken as the strain increment value corresponding to the target.

[0086] According to the present invention, a sidewall curling rebound correction mold for beam-type components is characterized in that:

[0087] The numerical solution method is the finite element method, and the iterative calculation is based on the finite element method.

[0088] According to the present invention, a sidewall curling rebound correction mold for beam-type components is characterized in that:

[0089] Using the initial strain value as the initial value, the calculation approximates the target by continuously increasing the strain value until the target converges. The strain increment at this point is the strain increment Δε.

[0090] According to the present invention, a sidewall curling rebound correction mold for beam-type components is characterized in that:

[0091] The stress in the sidewalls is characterized by the average stress in the sidewall region.

[0092] According to the present invention, a sidewall curling rebound correction mold for beam-type components is characterized in that:

[0093] The sidewall region is divided into regions along the length of the component, and stress and strain calculations are performed based on each region.

[0094] The division of the region is determined based on the distribution of the thickness stress difference.

[0095] According to the present invention, a sidewall curling rebound correction mold for beam-type components is characterized in that:

[0096] The division of regions is determined based on the distribution of the thickness stress difference, specifically as follows:

[0097] SS1: Calculate the outermost and innermost stress values ​​at each location to determine the thickness stress difference at each location;

[0098] SS2: Starting from the initial position at any end of the sidewall region, compare the thickness stress difference at each position after that position with the thickness stress difference at the initial position until the comparison result is greater than a set value, then divide the region before that position into the same region.

[0099] SS3: Take the position after this location as the starting position for determining the next region. Starting from this starting position, calculate the difference between the thickness stress difference and the thickness stress difference at each subsequent location until the comparison result is greater than the set value. Then, divide the region before this location into another identical region. Repeat this process until the division of all sidewall regions is completed.

[0100] According to the present invention, a sidewall curling rebound correction mold for beam-type components is characterized in that:

[0101] The aforementioned stress sign is achieved by transforming the compressive stress in the innermost layer into tensile stress while keeping the tensile stress in the outermost layer unchanged.

[0102] This invention discloses a method and correction mold for correcting the curling and rebound of the sidewall of a beam-type component. Starting from the essence of sidewall curling, it calculates the stress difference between the inner and outer layers of the sidewall region before rebound using the finite element method, and calculates the required subsequent deformation based on the stress-strain curve of the stamped sheet material. This ensures that the inner and outer layer stresses in the sidewall region have the same sign, thereby greatly reducing the thickness-wise stress difference in the sidewall region. This stress sign is achieved by optimizing the mold structure to change the nature of one of the stresses through force application. Specifically, a set of protrusions penetrating the longitudinal direction of the component are arranged outside the trimming line of the part on the punch and die of the stamping mold for the beam-type component. When the sheet material is stamped to the contact between the convex and concave surfaces at the protrusion locations, deformation occurs at that location and is transmitted to the sidewall for subsequent deformation. This invention provides a method and correction mold for correcting the curling and rebound of the sidewall of a beam-type component without changing the component structure or making complex designs to the mold structure. Attached Figure Description

[0103] Figure 1 This is a schematic diagram illustrating the implementation steps of the present invention;

[0104] Figure 2 This is a schematic diagram of the rebound correction method of the present invention on the stress-strain curve;

[0105] Figure 3 This is a schematic diagram of the mold structure before sheet metal deformation in this invention;

[0106] Figure 4 This is a schematic diagram of the sheet metal after deformation in this invention;

[0107] Figure 5 for Figure 4Enlarged diagram of the protruding part;

[0108] Figure 6 This is a schematic diagram of the region division in the working principle of the present invention;

[0109] Figure 7 A schematic diagram comparing the present invention with conventional methods.

[0110] In the picture,

[0111] 1-Component;

[0112] 2-Side wall region;

[0113] 3-Flange portion on the punch;

[0114] 4-Protrusion;

[0115] 5-Upper mold base;

[0116] 6-Lower mold base;

[0117] 7-Die;

[0118] 8-Punch;

[0119] 9-Pressure plate;

[0120] 10 - Part boundary line;

[0121] 11-Elastic element;

[0122] 12-Sectional profile of the part before rebound;

[0123] 13-Cross-section profile after rebound in traditional stamping methods;

[0124] 14- Cross-sectional profile after rebound using the present invention. Detailed Implementation

[0125] The following is a detailed description of a method for correcting the curling and rebound of the sidewall of a beam component according to the present invention, and a correction mold, with reference to the accompanying drawings and specific embodiments.

[0126] A method for correcting the curling and rebound of the sidewalls of beam-type components, using the condition that the sheet metal (1) is in the yielding stage at the moment of unloading after forming as the constraint.

[0127] Based on the mutual transmission of forces between tissues when the material is deformed by stress, the stress of the outermost and innermost layers of the component sidewall is controlled to be the same at this moment by optimizing the force application method of the mold structure. In this way, the sidewall curling rebound is corrected by reducing the thickness stress difference in the sidewall region (2).

[0128] in,

[0129] The optimization of the mold structure is achieved by symmetrically setting a pair of protrusions (4) on the flange part (3) of the punch and setting grooves at corresponding positions on the die.

[0130] in,

[0131] The top corners of the protrusions are all rounded, and the top of the grooves is also rounded accordingly.

[0132] in,

[0133] The location of the protrusion is determined according to the following formula:

[0134] ΔL≥(1 / 2W)+t+R+a,

[0135] In the formula,

[0136] ΔL: Distance between the center line of the protrusion and the boundary line of the component, in mm;

[0137] W: Width of the protrusion, unit: mm;

[0138] t: Original thickness of sheet metal, unit: mm;

[0139] R: Rounded corner;

[0140] a: Adjust the parameter, the range is between 5-7mm.

[0141] in,

[0142] The radius of the rounded corner of the raised top is the same as that of the corresponding rounded corner of the groove top, and is limited to a value greater than or equal to 3 times the thickness of the sheet material.

[0143] in,

[0144] The aforementioned "achieving the same stress sign for the outermost and innermost layers of the component's sidewall at a given moment through optimized mold structure application" is specifically implemented according to the following steps (see...). Figure 1 ):

[0145] S1: Based on the numerical solution method, the stresses on the outermost and innermost layers of the component sidewalls at the time of loading and unloading of the mold with unoptimized structure are calculated, and the corresponding strain values ​​are determined based on the calculations as the initial strain values.

[0146] S2: Based on the stress-strain curve, with the goal of the stresses of the outermost and innermost layers of the sidewall having the same sign at the moment of unloading after the component is formed, the outermost stress value, innermost stress value, and corresponding strain value generated by the mold loading with structural optimization settings at the corresponding moment are determined through iterative calculation. This strain value is taken as the final strain value; and the difference between the final strain value and the initial strain value is taken as the strain increment value corresponding to the target.

[0147] S3: Finalize the mold structure optimization based on the strain increment value.

[0148] in,

[0149] The numerical solution method is the finite element method, and the iterative calculation is based on the finite element method.

[0150] in,

[0151] Step S2 specifically involves: using the initial strain value calculated in step S1 as the initial value, and continuously increasing the strain value to approximate the target until the target converges, and determining the corresponding strain value and stress value based on the strain increment at this time.

[0152] in,

[0153] Step S3 is completed according to the following formula:

[0154] H = Δε × L,

[0155] 1 / 2≤W / H≤1,

[0156] In the above formula,

[0157] H: Height of the protrusion, in mm;

[0158] Δε: The strain increment corresponding to the target;

[0159] L: Sheet cross-sectional line length, unit: mm;

[0160] W: Width of the protrusion, unit: mm.

[0161] in,

[0162] The stress in the sidewalls is characterized by the average stress in the sidewall region.

[0163] in,

[0164] The sidewall area is divided into regions along the length of the component, and steps S1-S3 are performed based on each region.

[0165] The division of the region is determined based on the distribution of the thickness stress difference.

[0166] in,

[0167] The division of regions is determined based on the distribution of the thickness stress difference, specifically as follows:

[0168] SS1: Calculate the outermost and innermost stress values ​​at each location to determine the thickness stress difference at each location;

[0169] SS2: Starting from the initial position at any end of the sidewall region, compare the thickness stress difference at each position after that position with the thickness stress difference at the initial position until the comparison result is greater than a set value, then divide the region before that position into the same region.

[0170] SS3: Take the position after this location as the starting position for determining the next region. Starting from this starting position, calculate the difference between the thickness stress difference and the thickness stress difference at each subsequent location until the comparison result is greater than the set value. Then, divide the region before this location into another identical region. Repeat this process until the division of all sidewall regions is completed.

[0171] in,

[0172] The aforementioned stress sign is achieved by transforming the compressive stress in the innermost layer into tensile stress while keeping the tensile stress in the outermost layer unchanged.

[0173] A sidewall curling rebound correction mold for beam-type components is established by symmetrically setting a pair of protrusions (4) on the flange part (3) of the punch and setting grooves at corresponding positions on the die to optimize the mold structure. According to the optimization, when the forming is completed and unloaded, the stress of the outermost and innermost layers of the sidewall region (2) of the component has the same sign, thereby completing the correction of sidewall curling rebound by reducing the thickness stress difference of the sidewall region (2).

[0174] in,

[0175] The top corners of the protrusions are all rounded, and the top corners of the grooves are correspondingly rounded.

[0176] in,

[0177] The location of the protrusion is determined according to the following formula:

[0178] ΔL≥(1 / 2W)+t+R+a,

[0179] In the formula,

[0180] ΔL: Distance between the center line of the protrusion and the boundary line of the component, in mm;

[0181] W: Width of the protrusion, unit: mm;

[0182] t: Original thickness of sheet metal, unit: mm;

[0183] R: Rounded corner;

[0184] a: Adjust the parameter, the range is between 5-7mm.

[0185] in,

[0186] The radius of the rounded corner of the raised top is the same as that of the corresponding rounded corner of the groove top, and is limited to a value greater than or equal to 3 times the thickness of the sheet material.

[0187] in,

[0188] The size of the protrusion is determined according to the following formula:

[0189] H = Δε × L,

[0190] 1 / 2≤W / H≤1,

[0191] In the above formula,

[0192] H: Height of the protrusion, in mm;

[0193] Δε: The strain increment corresponding to the stresses of the outermost and innermost layers of the component's sidewall region having the same sign at the moment of unloading after forming is complete;

[0194] L: Sheet cross-sectional line length, unit: mm;

[0195] W: Width of the protrusion, unit: mm.

[0196] in,

[0197] The strain increment Δε in the formula is determined according to the following:

[0198] First, based on the numerical solution method, the stresses on the outermost and innermost layers of the component sidewalls at the time of loading and unloading of the mold with unoptimized structure are calculated, and the corresponding strain values ​​are determined based on the calculations as the initial strain values.

[0199] Secondly, based on the stress-strain curve, with the goal of the stresses of the outermost and innermost layers of the sidewall having the same sign at the moment of unloading after the component is formed, the outermost stress value, innermost stress value, and corresponding strain value generated by the mold loading with structural optimization settings at the corresponding moment are determined by iterative calculation. This strain value is taken as the final strain value; and the difference between the final strain value and the initial strain value is taken as the strain increment value corresponding to the target.

[0200] in,

[0201] The numerical solution method is the finite element method, and the iterative calculation is based on the finite element method.

[0202] in,

[0203] Using the initial strain value as the initial value, the calculation approximates the target by continuously increasing the strain value until the target converges. The strain increment at this point is the strain increment Δε.

[0204] in,

[0205] The stress in the sidewalls is characterized by the average stress in the sidewall region.

[0206] in,

[0207] The sidewall region is divided into regions along the length of the component, and stress and strain calculations are performed based on each region.

[0208] The division of the region is determined based on the distribution of the thickness stress difference.

[0209] in,

[0210] The division of regions is determined based on the distribution of the thickness stress difference, specifically as follows:

[0211] SS1: Calculate the outermost and innermost stress values ​​at each location to determine the thickness stress difference at each location;

[0212] SS2: Starting from the initial position at any end of the sidewall region, compare the thickness stress difference at each position after that position with the thickness stress difference at the initial position until the comparison result is greater than a set value, then divide the region before that position into the same region.

[0213] SS3: Take the position after this location as the starting position for determining the next region. Starting from this starting position, calculate the difference between the thickness stress difference and the thickness stress difference at each subsequent location until the comparison result is greater than the set value. Then, divide the region before this location into another identical region. Repeat this process until the division of all sidewall regions is completed.

[0214] in,

[0215] The aforementioned stress sign is achieved by transforming the compressive stress in the innermost layer into tensile stress while keeping the tensile stress in the outermost layer unchanged.

[0216] Working process and principle

[0217] During the drawing process of body beam components, as the sheet metal flows through the rounded corners of the die, the sidewall area of ​​the sheet metal undergoes continuous bending deformation. This manifests as the transformation of tensile and compressive stresses on the outermost and innermost layers of the sheet metal along its thickness direction. Figure 2As shown, after the stamping reaches its limit, the outermost metal layer in the entire sidewall region experiences significant tensile stress along the material flow direction, while the innermost metal layer experiences significant compressive stress. This large stress difference in thickness causes the entire sidewall region to be subjected to a bending moment that leads to reverse curling during unloading, which is particularly pronounced for beam-type components. Based on this, the present invention provides a method and correction die for correcting sidewall curling rebound in beam-type components. By setting secondary stretching feature ribs (i.e., protrusions) on the traditional drawing die structure, deformation at these feature rib locations before the punch and die closes causes a certain amount of stretching in the sidewall of the component. This alters the stress distribution in the thickness direction of the sidewall, ensuring that the stresses in the outermost and innermost layers of the sidewall are of the same sign during unloading after the stamping reaches its limit, thereby reducing the stress difference in the thickness direction and minimizing sidewall curling rebound. The specific steps are as follows:

[0218] 1) For the thickness stress difference Δσ of the material i Defined as the outermost stress σ along the flow direction of the sheet metal. i-U With the innermost layer stress σ i-L The difference is denoted as Δσ. i =σ i-U- σ i-L .

[0219] 2) Perform stamping forming analysis on the target beam-type component to obtain the outermost stress σ in the sidewall region before unloading when the component is fully formed. i-U Innermost layer stress σ i-L Thickness stress difference Δσ i Distribution of [something].

[0220] According to the analysis, the outermost layer stress σ i-U Innermost layer stress σ i-L They should belong to tensile stress and compressive stress with opposite signs, respectively.

[0221] 3) Thickness stress difference Δσ i Acquisition (see) Figure 6 First, define a sheet metal coordinate system, where x represents the longitudinal direction of the component, y represents the sheet metal flow direction, and z represents the sheet metal thickness direction. The sheet metal must contain at least three layers of properties in the thickness direction: an outermost layer, a middle layer, and an innermost layer. Then, through finite element analysis, obtain the outermost stress σ at different positions Pn(xn,yn) before unloading from the component in its final formed state. i-U Innermost layer stress σ i-L Let them be denoted as (xn, yn, σ) i-U (xn, yn, σ) i-L Furthermore, the thickness stress difference Δσ at this location is obtained. i denoted as (xn, yn, Δσ) iThe next step is to divide the component into 3 to 5 regions along its longitudinal x-axis based on the thickness stress difference, and calculate the average value of the outermost and innermost stresses for each region. The division of regions along the longitudinal x-axis is mainly based on the fact that the thickness stress difference varies greatly at different locations. Therefore, the thickness stress difference obtained along the x-axis of the component is screened and divided into 3 to 5 regions according to the size of the difference. Subsequent steps are performed for each region. If the difference is within 100 MPa, multiple regions are not divided.

[0222] 4) Calculate the average values ​​of the outermost and innermost stresses in the non-rounded corner areas of the sidewalls, i.e., where the sheet metal has flowed through the rounded corners of the die punch and die.

[0223] 5) Calculate the above average stress value based on the stress-strain relationship of the material used in the stamping component. The corresponding outermost strain ε i-U and the innermost strain ε i-L .

[0224] The stress-strain relationship of the material can be the result of static tensile test on actual stamped sheet metal, or it can be a theoretical formula fitted based on the test results.

[0225] 6) By combining the stress and strain states of the outermost and innermost layers, a subsequent strain increment Δε is applied along the sheet flow direction in the sidewall region to reduce the thickness stress difference.

[0226] Based on the stress-strain curve, the estimated strain increment Δε should ensure that the original innermost layer stress is reduced from compressive stress. Evolved into tensile stress The original outermost layer stress continues along the stress-strain trajectory from Evolved to The stress direction remains unchanged. (That is: First, based on the numerical solution method, the stresses on the outermost and innermost layers of the component's sidewalls at the time of unloading from the unoptimized mold loading process are calculated, and the corresponding strain values ​​are determined as initial strain values. Second, based on the stress-strain curve, with the goal of the stresses on the outermost and innermost layers of the sidewalls at the time of unloading from the unoptimized mold loading process being of the same sign, the outermost and innermost stress values ​​and corresponding strain values ​​generated by the mold loading process with optimized structure at the corresponding time are determined through iterative calculation. This strain value is used as the final strain value. The difference between the final strain value and the initial strain value is used as the strain increment value corresponding to the target. The iteration specifically involves: using the calculated initial strain value as the initial value, the calculation approximates the target by continuously increasing the strain value until the target converges, and the corresponding strain value and stress value are determined based on the strain increment at this time.) The corresponding thickness stress difference is determined by Δσ.i Reduce to Δσ d .

[0227] The subsequent strain increment Δε should ensure that the material re-enters the yielding stage, which can be determined by the theoretical position of the stress value on the stress-strain curve.

[0228] 7) The main body of the mold includes a die (7), a punch (8), a pressure plate (9), and protrusions (4) in the areas corresponding to the punch, die and component beam. The characteristic is that the sheet metal before deformation (i.e. the formed component 1) is placed on the pressure plate (9), and the pressure plate (9) is provided with an elastic element (11) to provide pressure. During operation, the upper die seat (5) installed on the pressure source drives the die (7) to move downward, press the sheet metal on the pressure plate (9), and maintain a certain pressure to move downward. When the sheet metal contacts the punch (8), the sheet metal begins to deform. When the die (7) continues to move downward to the lower side of the sheet metal and the protrusion (4) on the punch (8), the secondary tensile deformation of the sheet metal begins to occur at this position. As the die (7) continues to move downward, the amount of tensile deformation increases and is transmitted to the side wall area, realizing the subsequent deformation of the side wall area, thereby reducing the thickness stress difference on the side wall. This structure can correct the curling rebound of the component formed by stamping metal sheet.

[0229] The protrusions are symmetrically designed on the left and right sides of the beam-like components (see this section). Figure 3 , 4 Its corresponding dimensions are as follows:

[0230] The top of the protrusion has rounded corners on the left and right sides, with rounded corner sizes of R3 and R4 respectively; it is a concave feature on the die (7) side, with a width ≥ W+2t and a height ≥ H+2t, and rounded corners on the bottom left and right sides, with rounded corner sizes of R1 and R2 respectively, where t is the original thickness of the sheet metal (see Figure 5 ).

[0231] The height H of the protrusion is determined based on the strain increment Δε, specifically: H≈Δε*section line length, where the section line length is the contour length from the left end to the right end of the target part corresponding to the position of the tensile feature. If the contour length differs along the longitudinal direction of the part, the corresponding feature height H will change accordingly, but a smooth transition must be ensured (this point corresponds to the aforementioned area division). Simultaneously, to ensure a certain tensile feature strength, the ratio of the protrusion width W to the feature height H is set to 1 / 2 ≤ W / H ≤ 1.

[0232] The fillet sizes R1, R2, R3, and R4 should be no less than 3t to ensure that no material forming defects occur at these locations during actual stamping. In the initial design, it is preferable to have the four fillet radii be the same, and the fillet radii can be adjusted later during the adjustment of the rebound correction effect.

[0233] The center line of the protrusion should be a certain distance from the boundary line (8) of the part. This distance should be no less than (1 / 2W+t+R1+5~7)mm, so as to take into account both material utilization and the shape of the part itself.

[0234] Example

[0235] This embodiment provides a method and mold for correcting the curling and rebound of the sidewalls of beam-type components. To illustrate the effectiveness of the proposed method, a representative structure for beam-type components and a stamping mold were designed, i.e., the part's cross-sectional shape is as follows: Figure 4 The beam shown has a uniform cross-section, a height of 100mm, a top width of 200mm, a side draft angle of 10°, and top and bottom corner radii of 8mm. The part in this embodiment is made of a high-strength steel with a tensile strength of 980MPa, a thickness of 1.2mm, and a sheet size of 580*500mm rectangle, with the length direction aligned with the rolling direction. The method and die structure proposed in this invention are described in comparison to a commonly used drawing process for this type of part.

[0236] Based on this embodiment, a method and mold for correcting the curling rebound of the sidewall of a beam-type component according to the present invention are described in detail below:

[0237] A method for correcting the rebound curling of the sidewall of a beam-type component includes the following steps:

[0238] For the thickness stress difference Δσ of the material i Defined as the outermost stress σ along the flow direction of the sheet metal. i-U With the innermost layer stress σ i-L The difference is denoted as Δσ = σ i-U -σ i-L .

[0239] A stamping forming analysis was performed on the component, using a traditional drawing forming process. The punch, die, and blank holder were defined, and a blank holder force of 3 MPa was set. Finally, the outermost stress σ in the sidewall region before unloading in the component's fully formed state was obtained. i-U Innermost layer stress σ i-L Thickness stress difference Δσ i The distribution of stress. Specifically, the stress σ in the outermost layer of the sheet metal. i-U For tensile stress and innermost layer stress σ i-L For compressive stress, the two have opposite signs.

[0240] Calculate the average values ​​of the outermost and innermost stresses in the non-rounded corner areas of the sidewalls, i.e., where the sheet metal has flowed through the rounded corners of the die punch and die. For the part in this embodiment, the calculation Approximately 1089 MPa The pressure is approximately -1105 MPa, and the corresponding thickness stress difference is Δσ.i =2194MPa

[0241] The average stress value was further calculated based on the stress-strain relationship of the material used in the stamping component. The corresponding outermost strain ε i-U and the innermost strain ε i-L The values ​​are 0.032 and 0.031, respectively. In this embodiment, the values ​​are inferred based on the material stress-strain data obtained from the standard tensile test.

[0242] Further combining the stress and strain states of the outermost and innermost layers, by applying a subsequent strain increment Δε along the sheet flow direction in the sidewall region, and based on the stress-strain curve, it is estimated that a strain increment Δε = 0.02 can reduce the original innermost layer stress from compressive stress. Evolved into tensile stress The original outermost layer stress continues along the stress-strain trajectory from Evolved to σ d-U =1256MPa, stress direction remains unchanged, corresponding thickness stress difference is due to Δσ i =2194MPa decreased to Δσ d =98MPa.

[0243] The corresponding correction mold, such as Figure 3 , 4 As shown, the main body of the mold includes a die, a punch, a pressure plate, and protrusions at specific positions on the punch and die. Before deformation, the sheet metal is placed on the pressure plate, and an elastic element providing pressure is provided under the pressure plate. During operation, the upper die holder mounted on the pressure source drives the die downward, pressing the sheet metal onto the pressure plate and maintaining a certain pressure as it moves downward. When the sheet metal contacts the punch, it begins to deform. When the die continues to descend to the lower side of the sheet metal and the protrusion on the punch, secondary tensile deformation of the sheet metal begins at this position. As the die continues to descend, the amount of tensile deformation increases and is transmitted to the sidewall area, realizing subsequent deformation of the sidewall area, thereby reducing the thickness stress difference on the sidewall. This structure can correct the curling and rebound of parts formed by stamping metal sheets.

[0244] The relevant dimensions of the protrusion, including position, height, width, and the limit of the rounded corners, are all set according to the explanation in the principle section. The cross-sectional line length of this embodiment is measured to be approximately 500mm, so the height H is approximately 10mm. The width W is set to 10mm, the four rounded corners to be 4mm, and the distance from the part boundary line to be 15mm.

[0245] The mold structure parameters obtained using this invention were re-imported into the stamping analysis software for analysis and verification. Figure 7The figure shows a comparison between the rebound profile obtained using the method of this invention and the rebound profile obtained using the conventional method. Reference numeral 14 represents the rebound profile obtained using the method of this invention, reference numeral 12 represents the profile of the component before rebound, and reference numeral 13 represents the rebound profile obtained after stamping using the conventional method. As can be seen from the figure, the profile 12 before rebound is the designed profile of the part. Compared with the rebound profile 13 obtained after stamping using the conventional method, the rebound profile 14 obtained using the method of this invention has better overlap with the designed profile of the part, i.e., the profile of the component before rebound. It can be seen that the method proposed in this invention can largely correct the sidewall curling and rebound of beam-type components.

[0246] This invention discloses a method and correction mold for correcting the curling and rebound of the sidewall of a beam-type component. Starting from the essence of sidewall curling, it calculates the stress difference between the inner and outer layers of the sidewall region before rebound using the finite element method. Based on the stress-strain curve of the stamped sheet, it calculates the required subsequent deformation to ensure that the inner and outer layer stresses in the sidewall region have the same sign, thereby greatly reducing the thickness-wise stress difference in the sidewall region. This stress sign is achieved by optimizing the mold structure to change the nature of one of the stresses through force application. Specifically, a set of protrusions penetrating the longitudinal direction of the component are arranged outside the trimming line of the part on the punch and die of the stamping mold. When the sheet metal is stamped to the contact between the convex and concave surfaces at the protrusion locations, deformation occurs at that location and is transmitted to the sidewall for subsequent deformation. This invention effectively corrects the curling and rebound of the sidewall of a beam-type component without changing the component structure or requiring complex mold design.

Claims

1. A method for correcting the rebound curling of the sidewall of a beam-type component, characterized in that: The constraint condition is that the sheet metal (1) is in the yield stage at the time of unloading after forming. Based on the mutual transmission of forces between tissues when materials are deformed under stress, the stress of the outermost and innermost layers of the component sidewall is the same at the time of unloading after forming by optimizing the mold structure. In this way, the sidewall curling rebound is corrected by reducing the thickness stress difference in the sidewall area (2). The aforementioned optimization of the mold structure is achieved by symmetrically setting a pair of protrusions (4) on the flange portion (3) of the punch and setting grooves at corresponding positions on the die. The aforementioned method of controlling the stress sign of the outermost and innermost layers of the component sidewall at the moment of unloading after forming, achieved by optimizing the mold structure, is specifically implemented through the following steps: S1: Based on the numerical solution method, the stresses on the outermost and innermost layers of the component sidewalls at the time of loading and unloading of the mold with unoptimized structure are calculated, and the corresponding strain values ​​are determined based on the calculations as the initial strain values. S2: Based on the stress-strain curve, with the goal of the stresses of the outermost and innermost layers of the sidewall having the same sign at the moment of unloading after the component is formed, the outermost stress value, innermost stress value and corresponding strain value generated by the mold loading with structural optimization settings at the corresponding moment are determined by iterative calculation, and this strain value is used as the final strain value. The difference between the final strain value and the initial strain value is taken as the strain increment value corresponding to the target. S3: Finalize the mold structure optimization based on the strain increment value. Step S3 is completed according to the following formula: ， 1 / 2≤W / H≤1, In the above formula, H: Height of the protrusion, in mm; : The strain increment corresponding to the target; : Sheet metal section line length, unit: mm; W: Width of the protrusion, unit: mm The top corners of the protrusions are all rounded, and correspondingly, the top of the groove is rounded. The location of the protrusion is determined according to the following formula: ， In the formula, Distance between the center line of the protrusion and the boundary line of the component, in mm; W: Width of the protrusion, unit: mm; Original sheet thickness, unit: mm; R: Rounded corner; Adjust the parameters, the range is between 5-7mm.

2. The method for correcting the curling and rebound of the sidewall of a beam component according to claim 1, characterized in that: The radius of the rounded corner of the raised top is the same as that of the corresponding rounded corner of the groove top, and is limited to a value greater than or equal to 3 times the thickness of the sheet material.

3. The method for correcting the curling and rebound of the sidewall of a beam component according to claim 1, characterized in that: The numerical solution method is the finite element method, and the iterative calculation is based on the finite element method.

4. The method for correcting the curling and rebound of the sidewall of a beam component according to claim 1, characterized in that: Step S2 specifically involves: using the initial strain value calculated in step S1 as the initial value, and continuously increasing the strain value to approximate the target until the target converges, and determining the corresponding strain value and stress value based on the strain increment at this time.

5. The method for correcting the curling and rebound of the sidewall of a beam component according to claim 1, characterized in that: The stress in the sidewalls is characterized by the average stress in the sidewall region.

6. The method for correcting the curling and rebound of the sidewall of a beam component according to claim 1, characterized in that: The sidewall area is divided into regions along the length of the component, and steps S1-S3 are performed based on each region. The division of the region is determined based on the distribution of the thickness stress difference.

7. The method for correcting the curling and rebound of the sidewall of a beam component according to claim 6, characterized in that: The division of regions is determined based on the distribution of the thickness stress difference, specifically as follows: SS1: Calculate the outermost and innermost stress values ​​at each location to determine the thickness stress difference at each location; SS2: Starting from the initial position at any end of the sidewall region, compare the thickness stress difference at each position after that position with the thickness stress difference at the initial position until the comparison result is greater than a set value, then divide the region before that position into the same region. SS3: Take the position after this location as the starting position for determining the next region. Starting from this starting position, calculate the difference between the thickness stress difference and the thickness stress difference at each subsequent location until the comparison result is greater than the set value. Then, divide the region before this location into another identical region. Repeat this process until the division of all sidewall regions is completed.

8. The method for correcting the curling and rebound of the sidewall of a beam component according to claim 1, characterized in that: The aforementioned stress sign is achieved by transforming the compressive stress in the innermost layer into tensile stress while keeping the tensile stress in the outermost layer unchanged.

9. A mold for correcting the curling and rebound of the sidewall of a beam-type component, characterized in that: The main body of the mold includes a die, a punch, a pressure plate, and protrusions at specific positions on the punch and die. Before deformation, the sheet metal is placed on the pressure plate. An elastic element that provides pressure is provided under the pressure plate. During operation, the die is driven downward by the upper mold seat installed on the pressure source. A pair of protrusions (4) symmetrically arranged on the flange part (3) of the punch and grooves are set at corresponding positions on the die to optimize the mold structure. Based on the optimization, when the forming reaches the unloading time, the stress of the outermost and innermost layers of the side wall area (2) of the component has the same sign, thereby completing the correction of the side wall curling rebound by reducing the thickness stress difference of the side wall area (2). The apex corners of the protrusions are all rounded, and correspondingly, the apex corners of the grooves are rounded. The location of the protrusion is determined according to the following formula: ， In the formula, Distance between the center line of the protrusion and the boundary line of the component, in mm; W: Width of the protrusion, unit: mm; Original sheet thickness, unit: mm; R: Rounded corner; Adjust the parameters; the range is between 5-7mm. The size of the protrusion is determined according to the following formula: ， 1 / 2≤W / H≤1, In the above formula, H: Height of the protrusion, in mm; The strain increment corresponding to the stress in the outermost and innermost layers of the component's sidewall region at the moment of unloading after forming is complete; : Sheet metal section line length, unit: mm; W: Width of the protrusion, unit: mm The strain increment in the formula Determined according to the following: First, based on the numerical solution method, the stresses on the outermost and innermost layers of the component sidewalls at the time of loading and unloading of the mold with unoptimized structure are calculated, and the corresponding strain values ​​are determined based on the calculations as the initial strain values. Secondly, based on the stress-strain curve, with the goal of the stresses of the outermost and innermost layers of the sidewall having the same sign at the moment of unloading after the component is formed, the outermost stress value, innermost stress value and corresponding strain value generated by the mold loading with structural optimization settings at the corresponding moment are determined by iterative calculation, and this strain value is taken as the final strain value. The difference between the final strain value and the initial strain value is taken as the strain increment value corresponding to the target.

10. A mold for correcting the curling and rebound of the sidewall of a beam component according to claim 9, characterized in that: The radius of the rounded corner of the raised top is the same as that of the corresponding rounded corner of the groove top, and is limited to a value greater than or equal to 3 times the thickness of the sheet material.

11. A beam-type component sidewall curling rebound correction mold according to claim 9, characterized in that: The numerical solution method is the finite element method, and the iterative calculation is based on the finite element method.

12. A mold for correcting the curling and rebound of the sidewall of a beam component according to claim 9, characterized in that: Using an initial strain value as the initial value, the calculation approximates the target by continuously increasing the strain value until the target converges. The strain increment at this point is the strain increment. .

13. A mold for correcting the curling and rebound of the sidewall of a beam component according to claim 9, characterized in that: The stress in the sidewalls is characterized by the average stress in the sidewall region.

14. A beam-type component sidewall curling rebound correction mold according to claim 9, characterized in that: The sidewall region is divided into regions along the length of the component, and stress and strain calculations are performed based on each region. The division of the region is determined based on the distribution of the thickness stress difference.

15. A beam-type component sidewall curling rebound correction mold according to claim 14, characterized in that: The division of regions is determined based on the distribution of the thickness stress difference, specifically as follows: SS1: Calculate the outermost and innermost stress values ​​at each location to determine the thickness stress difference at each location; SS2: Starting from the initial position at any end of the sidewall region, compare the thickness stress difference at each position after that position with the thickness stress difference at the initial position until the comparison result is greater than a set value, then divide the region before that position into the same region. SS3: Take the position after this location as the starting position for determining the next region. Starting from this starting position, calculate the difference between the thickness stress difference and the thickness stress difference at each subsequent location until the comparison result is greater than the set value. Then, divide the region before this location into another identical region. Repeat this process until the division of all sidewall regions is completed.

16. A mold for correcting the curling and rebound of the sidewall of a beam component according to claim 9, characterized in that: The aforementioned stress sign is achieved by transforming the compressive stress in the innermost layer into tensile stress while keeping the tensile stress in the outermost layer unchanged.

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