Gradient iterative optimization method for springback compensation of automobile stamping parts

Abstract

The present application relates to the technical field of automobile parts optimization, and more particularly to a gradient iterative optimization method for springback compensation of automobile stamping parts, which can realize real-time closed-loop control, compress the deviation response time from the minute level of the traditional method to the millisecond level (<2 ms) by integrating 800Hz high-frequency monitoring and PROFINET real-time communication technology, and realize online control of the whole process of "stamping-detection-adjustment". Dynamic calibration of forming force fluctuation threshold combined with adaptive adjustment of friction coefficient makes the production stability (CPK value) increase from 1.0 to 1.67, significantly improving the production stability and die life.

Description

Technical Field

[0001] This invention relates to the field of automotive parts optimization technology, and in particular to a gradient iterative optimization method for springback compensation of automotive stamping parts. Background Technology

[0002] Currently, the car door inner panel is an important component of the vehicle's interior. Located inside the door, it serves a supporting and protective function. Door inner panels are typically made of metal (such as steel or aluminum alloy) and may include some plastic or composite material components for decoration or other functions. Their main functions include: providing the necessary rigidity and strength for the door; absorbing some energy in the event of a collision; protecting the safety of passengers inside the vehicle; and serving as a mounting platform for various internal components (such as window control switches, audio systems, etc.).

[0003] The current traditional manufacturing process for automotive door inner panels mainly includes the following steps:

[0004] 1. Design and mold making:

[0005] Design and manufacture molds based on product design drawings, including drawing dies, trimming dies, and punching dies.

[0006] 2. Raw material preparation:

[0007] Choose a suitable sheet material (such as cold-rolled steel sheet) and cut it to the appropriate size and shape as needed.

[0008] 3. Stamping:

[0009] A stamping press is used to process sheet metal into the desired shape through a series of processes, which may include drawing, trimming, punching, flanging, and shaping.

[0010] Each of the above processes requires the use of specific molds to ensure the precision and quality of the parts.

[0011] 4. Inspection and Repair:

[0012] Perform quality inspection on stamped parts to ensure there are no cracks, wrinkles, or other problems. Repair parts as necessary, such as removing burrs or correcting deformation.

[0013] 5. Post-processing:

[0014] This includes surface treatment (such as electroplating and painting) and assembling other components (such as interior parts and sealing strips).

[0015] However, the aforementioned prior art has the following technical problems:

[0016] 1. Traditional offline detection has a long cycle and cannot capture dynamic deviations in the stamping process in real time, resulting in slow response.

[0017] 2. In traditional methods, core process parameters such as blank holder force and drawing speed are set based on experience, which cannot accurately adapt to material performance fluctuations and complex geometric requirements, resulting in a low first-piece yield.

[0018] 3. Existing technologies use a single parameter adjustment mode (such as adjusting only the blank holder force or only changing the drawing speed), ignoring the coupling effect between process parameters. This often leads to a vicious cycle where adjusting the blank holder force causes material breakage, and reducing the speed causes wrinkles, resulting in low compensation efficiency.

[0019] Therefore, a gradient iterative optimization method for springback compensation of automotive stamping parts is needed to solve the above problems. Summary of the Invention

[0020] This invention provides a gradient iterative optimization method for springback compensation in automotive stamping parts. This method enables real-time closed-loop control by integrating 800Hz high-frequency monitoring and PROFINET real-time communication technology, reducing the deviation response time from minutes to milliseconds (<2ms) compared to traditional methods, thus achieving online control of the entire "stamping-inspection-adjustment" process. Dynamic calibration of the forming force fluctuation threshold combined with adaptive adjustment of the friction coefficient improves production stability (CPK value) from 1.0 to 1.67, significantly enhancing production stability and die life.

[0021] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0022] A gradient iterative optimization method for springback compensation of automotive stamping parts includes the following steps:

[0023] S1. Set the initial blank holder force according to the yield strength of the stamping sheet metal;

[0024] S2. Set the initial drawing speed according to the ratio of the thickness of the stamped part sheet to the radius of the die corner;

[0025] S3. Determine the initial friction coefficient based on the anisotropy coefficient of the stamping sheet material;

[0026] S4. During the continuous stamping process of automotive stamping parts, monitor the contour deviation of the automotive stamping parts after demolding in real time. If the contour deviation exceeds ±0.8mm:

[0027] If the deviation is symmetrically distributed, adjust the blank holder force in steps of 5kN / time. If the deviation is positive, increase the blank holder force; if the deviation is negative, decrease the blank holder force. If the deviation is asymmetrically distributed, adjust the drawing speed in steps of 2mm / s / time.

[0028] S5. Detect the fluctuation range of the stamping forming force. When the fluctuation amplitude exceeds 15% of the set threshold, press...

[0029] Adjust the friction coefficient in increments of 0.02.

[0030] S6. Adjust execution parameters;

[0031] S7. Perform three-dimensional contour scanning on the stamped sheet metal to measure the springback of the feature surface and the fillet fill degree.

[0032] S8. Based on the measurement results, prioritize adjusting the blank holder force and then optimize the drawing speed.

[0033] Furthermore, in step S1, setting the initial blank holder force based on the yield strength of the stamping sheet includes: when the yield strength of the stamping sheet is ≤180MPa, the blank holder force is 120kN-150kN; when 180MPa < yield strength of the stamping sheet is ≤250MPa, the blank holder force is 150kN-180kN; and when the yield strength of the stamping sheet is >250MPa, the blank holder force is 180kN-220kN.

[0034] Furthermore, in step S2, when the ratio of the thickness of the stamped part sheet to the radius of the die corner is ≤0.5, the initial drawing speed is 50mm-60mm / s; when 0.5 < the ratio of the thickness of the stamped part sheet to the radius of the die corner is ≤1, the initial drawing speed is 40mm-50mm / s; and when the ratio of the thickness of the stamped part sheet to the radius of the die corner is >1, the initial drawing speed is 30mm-40mm / s.

[0035] Furthermore, in step S3, the friction coefficient is 0.08-0.10 when the anisotropy coefficient r of the stamping part sheet material is ≤1.2, 0.10-0.12 when 1.2 < the anisotropy coefficient r of the stamping part sheet material is ≤1.5, and 0.12-0.15 when the anisotropy coefficient r of the stamping part sheet material is >1.5.

[0036] Furthermore, the parameter adjustment in step S6 includes:

[0037] S61. With a fixed drawing speed, scan the blank holder force range in 10kN increments;

[0038] S62, Optimize drawing speed matching value with a step size of 5mm / s;

[0039] S63. Synchronously adjust the friction coefficient and mold clearance, with each adjustment not exceeding ±3% of the initial value.

[0040] Furthermore, in step S4, the contour deviation monitoring uses a laser displacement sensor array, with 8-12 detection points arranged around the periphery of the stamping die, a sampling frequency ≥500Hz, and the deviation vector direction of each point is calculated in real time.

[0041] Furthermore, in step S7, a blue light surface structured light measuring instrument is used to perform three-dimensional contour scanning on the stamping sheet metal, with a measurement accuracy of ≤0.02mm.

[0042] Furthermore, the method for determining the fluctuation range of the stamping forming force in step S5 is as follows: take the average forming force of 100 consecutive stampings, and set the fluctuation amplitude threshold to ±10% of the average value.

[0043] Furthermore, in step S1, when the thickness of the stamped part sheet is ≥2.0mm, the initial blank holder force is increased by an additional 10%-15%; when the surface of the stamped part sheet has a galvanized layer, the initial value of the friction coefficient is reduced by 0.02-0.03.

[0044] The advantages of this invention are:

[0045] 1. This invention enables real-time closed-loop control. By integrating 800Hz high-frequency monitoring and PROFINET real-time communication technology, the deviation response time is reduced from minutes to milliseconds (<2ms) using traditional methods, achieving online control of the entire "stamping-detection-adjustment" process. Dynamic calibration of the forming force fluctuation threshold combined with adaptive adjustment of the friction coefficient improves production stability (CPK value) from 1.0 to 1.67, significantly enhancing production stability and mold life.

[0046] 2. Based on the quantitative classification of yield strength, thickness / fillet ratio and anisotropy coefficient of stamping materials, this invention establishes a scientific initial parameter setting system, which increases the first-piece qualification rate from 65% to 92.3% using traditional methods. Furthermore, it introduces a surface treatment correction mechanism (the zinc plating layer reduces the friction coefficient by 0.02), solving the problem of coating material parameter adaptation.

[0047] 3. This invention employs a unique three-stage parameter decoupling strategy: the first stage locks the speed to optimize the blank holder force; the second stage fixes the blank holder force to optimize the drawing speed matching value; and the third stage adjusts friction and clearance, thus solving the problem of multi-parameter coupling. Examples show that the springback was reduced by 66.7% after optimization (from 1.2mm to 0.4mm). Furthermore, by analyzing the deviation vector direction in real time using a laser array, targeted zone speed adjustments were implemented (the right half-mold was slowed down by 2mm / s, and the left half-mold was accelerated by 2mm / s), resulting in a 3-fold increase in the efficiency of local deviation repair. Detailed Implementation

[0048] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] Example 1: The following describes the implementation process of the present invention in detail, taking into account the stamping production process of a certain model of automobile door inner panel:

[0050] Step S1: Setting the initial blank holder force

[0051] Step S1.1 Obtaining material parameters: DC04 cold-rolled steel plate with a thickness of 1.2mm was selected. The yield strength σ_s was measured to be 210MPa by tensile test (which meets the range of 180MPa<σ_s≤250MPa).

[0052] Step S1.2 Calculation of blank holder force: The initial blank holder force is selected as the median value of 165kN, which is between 150kN and 180kN.

[0053] Step S1.3 Thickness Compensation: If the board thickness is 1.2mm < 2.0mm, the additional compensation mechanism will not be triggered.

[0054] Step S1.4 Surface treatment correction: A galvanized layer (20μm thick) was detected on the surface of the sheet, and the initial value of the friction coefficient was reduced by 0.02.

[0055] Step S2: Determine the initial drawing speed

[0056] Step S2.1 Mold parameter measurement: upper mold fillet radius R=8mm, lower mold fillet radius R=6mm, take the maximum fillet radius R=8mm as the calculation benchmark.

[0057] Step S2.2 Thickness / Fillet Ratio Calculation: t / R=1.2 / 8=0.15 (meets the condition that the ratio ≤0.5)

[0058] Step S2.3 Speed ​​setting: Select an initial drawing speed of 50-60 mm / s, and take the middle value of 55 mm / s.

[0059] Step S2.4 Equipment calibration: Install a high-precision displacement sensor (Heidenhain LS186M, resolution 0.001mm) on the hydraulic press to ensure speed control accuracy of ±0.5%.

[0060] Step S3: Initial Friction Coefficient Configuration

[0061] Step S3.1 Anisotropy test: The r-value (plastic strain ratio) was measured using a uniaxial tensile test.

[0062] The rolling direction is r0 = 1.35.

[0063] At a 45° angle, r45 = 1.28;

[0064] Vertical direction r90 = 1.42;

[0065] Step S3.2 Calculate the average r value: r = (r0 + 2r45 + r90) / 4 = 1.34 (which meets the interval 1.2 < r ≤ 1.5).

[0066] Step S3.3 Friction coefficient setting: Select an initial value of 0.10, which is corrected to 0.08 due to the zinc plating layer.

[0067] Step S3.4 Lubricant selection: Water-based lubricant FD-520 (Matsumura Chemicals, Japan) was used, and the viscosity was controlled at 35±2 cP using a viscometer.

[0068] Step S4: Implementation of Dynamic Compensation Adjustment

[0069] Step S4.1 Monitoring system configuration:

[0070] The laser displacement sensor array (Keyence LK-H020, 12 measuring points arranged in a ring) has a sampling frequency set to 800Hz and uses PROFINET real-time industrial Ethernet for data transmission with a delay of <2ms.

[0071] Step S4.2 First article inspection data:

[0072]

[0073] (Where: * indicates exceeding the ±0.8mm threshold)

[0074] Step S4.3: Deviation Pattern Analysis:

[0075] Measuring points 2, 5, and 8 show positive deviations (out of tolerance by 0.84 mm); measuring points 3, 6, and 9 show negative deviations (-0.76 mm); the deviation distribution shows an asymmetrical characteristic (the deviation in the right half is greater than that in the left half).

[0076] Step S4.4: Adjustment strategy execution

[0077] Start drawing speed adjustment: reduce the speed of the right half of the die area by 2mm / s to 53mm / s, and increase the speed of the left half of the die area by 2mm / s to 57mm / s. After adjustment, the maximum deviation is reduced to 0.52mm.

[0078] Step S5: Forming Force Fluctuation Control

[0079] Step S5.1; Data acquisition: Using a Kistler 9232A piezoelectric force sensor, 100 stamping force data were continuously acquired (sample frequency 1kHz).

[0080] Step S5.2: Baseline value calculation: Average forming force F avg =1780kN, fluctuation threshold ΔF=±178kN (10%ofF) avg ).

[0081] Step S5.3: Abnormal working condition handling: The 123rd stamping recorded F=1620kN (lower than the lower limit of 1602kN), triggering the adjustment of the friction coefficient. The current friction coefficient μ=0.08 → increased to 0.10, and the fluctuation range after adjustment returned to ±8.5%.

[0082] Step S6: Parameter Co-optimization

[0083] Step S6.1: Blank holder force scan: With a fixed drawing speed of 55 mm / s, the blank holder force adjustment sequence is: 155 kN → 165 kN → 175 kN → 185 kN.

[0084] The quality indicators are compared as follows:

[0085]

[0086] 175kN was selected as the optimal blank holder force.

[0087] Step S6.2: Speed ​​optimization: Side force locked at 175kN, speed adjustment gradient: 50mm / s→53mm / s→56mm / s→59mm / s.

[0088] The forming quality monitoring form is as follows:

[0089]

[0090] (Where *exceeds the 0.3mm threshold,** triggering an alarm.)

[0091] The optimal speed was selected as 53 mm / s.

[0092] Step S6.3 Synchronous Fine-tuning:

[0093] Mold clearance compensation: Add a 0.08mm shim to the area corresponding to measuring point 2, and adjust the friction coefficient to 0.09.

[0094] Total adjustment:

[0095] Δ blank holder force = +6.06% (150→175kN)

[0096] Δ velocity = -3.6% (55→53 mm / s)

[0097] ΔFriction coefficient = +12.5% ​​(0.08→0.09)

[0098] Step S7: 3D contour verification:

[0099] Step S7.1: Measurement equipment: Use GOM ATOS Q blue light scanner (measurement accuracy 0.018mm), set the scanning resolution to 0.1mm, and the single scan time to <20s.

[0100] Step S7.2: Feature detection: Theoretical height of the board 15.0mm → Actual measurement 14.96mm (springback 0.04mm).

[0101] Step S8: Based on the measurement results, prioritize adjusting the blank holder force and then optimize the drawing speed. The optimized parameters are recorded as follows:

[0102]

[0103] After optimization using this method, the following technical indicators were achieved: springback decreased from the initial 1.2mm to 0.4mm (a reduction of 66.7%), fillet fill percentage increased from 91% to 97.5%, single-piece forming time was shortened from 8.2s to 7.5s, and mold life increased from 300,000 cycles to 420,000 cycles.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A gradient iterative optimization method for springback compensation of an automotive stamping, characterized in that, The method comprises the following steps: S1, setting the initial blank holder force according to the yield strength of the stamping sheet; S2, setting the initial drawing speed according to the ratio of the thickness of the stamping sheet to the radius of the die fillet; S3, determining the initial friction coefficient based on the anisotropy coefficient of the stamping sheet material; S4, monitoring the profile deviation of the automobile stamping part after demolding in the continuous stamping process of the automobile stamping part, and if the profile deviation exceeds ±0.8mm: If the deviation is symmetrically distributed, adjust the blank holder force by 5kN / step, if the deviation is positive, increase the blank holder force, if the deviation is negative, decrease the blank holder force; if the deviation is asymmetrically distributed, adjust the drawing speed by 2mm / s / step; S5, detecting the stamping forming force fluctuation range, when the fluctuation amplitude exceeds 15% of the set threshold, adjust the friction coefficient by 0.02 / step; S6, executing parameter adjustment; S61, fix the drawing speed, scan the blank holder force interval by 10kN step; S62, optimize the drawing speed matching value by 5mm / s step; S63, adjust the friction coefficient and the die gap synchronously, and the adjustment amount is not more than ±3% of the initial value each time; S7, perform three-dimensional profile scanning on the stamping sheet to measure the springback amount and the fillet filling degree of the feature surface; S8, according to the measurement result, preferentially adjust the blank holder force and then optimize the drawing speed. In the step S1, when the yield strength of the stamping sheet is ≤180MPa, the blank holder force is 120kN-150kN; when 180MPa<the yield strength of the stamping sheet≤250MPa, the blank holder force is 150kN-180kN; when the yield strength of the stamping sheet>250MPa, the blank holder force is 180kN-220kN. In the step S2, when the ratio of the thickness of the stamping sheet to the radius of the die fillet is ≤0.5, the initial drawing speed is 50mm-60mm / s; when 0.5<the ratio of the thickness of the stamping sheet to the radius of the die fillet≤1, the initial drawing speed is 40mm-50mm / s; when the ratio of the thickness of the stamping sheet to the radius of the die fillet>1, the initial drawing speed is 30mm-40mm / s.

2. The gradient iteration optimization method for springback compensation of an automotive stamping part according to claim 1, wherein, In the step S3, when the anisotropy coefficient r of the stamping sheet material is ≤1.2, the friction coefficient is 0.08-0.10; when 1.2<the anisotropy coefficient r of the stamping sheet material≤1.5, the friction coefficient is 0.10-0.12; when the anisotropy coefficient r of the stamping sheet material>1.5, the friction coefficient is 0.12-0.

15.

3. The gradient iteration optimization method for springback compensation of an automotive stamping part according to claim 1, wherein, In the step S4, the profile deviation monitoring adopts a laser displacement sensor array, 8-12 detection points are arranged along the periphery of the stamping die, the sampling frequency is ≥500Hz, and the deviation vector direction of each point is calculated in real time.

4. The gradient iteration optimization method for springback compensation of an automotive stamping part according to claim 1, wherein, In the step S7, a blue light area structure light measuring instrument is used for three-dimensional profile scanning on the stamping sheet, and the measurement accuracy is ≤0.02mm.

5. The gradient iteration optimization method for springback compensation of an automotive stamping part according to claim 1, wherein, In the step S5, the determination method of detecting the stamping forming force fluctuation range is: taking the average value of the forming force of 100 continuous stamping, and the fluctuation amplitude threshold is set to ±10% of the average value.

6. The gradient iteration optimization method for springback compensation of an automotive stamping part according to claim 1, wherein, ​ 7. The gradient iteration optimization method for springback compensation of an automotive stamping part of claim 1, wherein, ​ 8. The gradient iteration optimization method for springback compensation of an automotive stamping part according to claim 1, wherein, In the step S1, when the thickness of the stamping part is greater than or equal to 2.0 mm, the initial blank holder force is additionally increased by 10%-15%; when the stamping part has a galvanized layer on the surface, the initial value of the friction coefficient is reduced by 0.02-0.03.

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