Color-coated sheet residual stress detection method and system based on magnetic measurement method

Abstract

The invention relates to a color-coated sheet residual stress detection method and system based on a magnetic measurement method, and belongs to the technical field of metal material nondestructive detection methods and systems. According to the technical scheme, an attenuation coefficient k is calibrated through an unstressed calibration test block; a magnetic measurement sensor is used for detecting residual stress of different penetration depths twice or more, stress distribution results of corresponding depths are obtained respectively, and penetration depth control is achieved by adjusting excitation current frequency. Real residual stress is calculated based on the multi-section difference equation set; and separating a coating interference signal through a multi-section difference equation and dynamic attenuation coefficient calibration. The method has the beneficial effects that the difference equation is constructed through multiple detection results of different penetration depths, the non-magnetic coating interference is quantitatively eliminated in combination with the calibration process of the attenuation coefficient k, the detection precision is remarkably improved, and the method has the advantages of being high in anti-interference performance, standard in calibration process, suitable for industrial sites and the like.

Description

Technical Field

[0001] The present invention relates to a method and system for detecting residual stress of a color-coated plate based on a magnetic measurement method, and belongs to the technical field of nondestructive detection methods and systems for metal materials. Background Art

[0002] Color-coated steel sheets are a key material widely used in construction, home appliances, and other fields. Residual stress is easily generated in the substrate during processing, such as cold rolling, welding, and coating curing. The presence of residual stress can lead to substrate warping, reduced coating adhesion, and even cracking, directly impacting product reliability and service life. Therefore, accurately measuring residual stress in color-coated steel substrates is crucial for optimizing production processes and improving product quality.

[0003] Currently, magnetic measurement based on the inverse magnetostrictive effect is one of the mainstream technologies for residual stress detection. However, the non-magnetic coating of color-coated steel sheets significantly alters the distribution characteristics of the magnetic field, causing interference noise caused by the coating to be mixed into the detection signal. Existing technologies mainly use magnetic measurement signals at a single depth combined with empirical filtering to suppress coating interference, but this has the following key drawbacks:

[0004] Coating interference suppression relies on manual experience, and no quantitative compensation relationship based on physical models has been established, resulting in the detection results being greatly affected by the operator's subjective influence and poor repeatability; the correlation between penetration depth and signal attenuation is not fully utilized: the magnetic field attenuation law is not obtained through multi-depth detection, and the coating interference and the actual stress signal of the substrate cannot be effectively separated. Summary of the Invention

[0005] The purpose of the present invention is to provide a residual stress detection method and system for color-coated steel plates based on magnetic measurement. A differential equation is constructed through the detection results of multiple times at different penetration depths. Combined with the calibration of the attenuation coefficient k, the interference of non-magnetic coatings is quantitatively eliminated, and the detection accuracy is significantly improved. The method has the advantages of strong anti-interference ability, standardized calibration process, and applicability to industrial sites, effectively solving the above-mentioned problems existing in the background technology.

[0006] The technical solution of the present invention is: a method for detecting residual stress of a color-coated plate based on magnetic measurement, comprising the following steps:

[0007] (1) Calibrate the attenuation coefficient k using a stress-free calibration test block;

[0008] (2) Multi-depth magnetic measurement signal acquisition: a magnetic sensor is used to perform residual stress detection on the color-coated plate at two or more different penetration depths, and the stress distribution results of the corresponding depths are obtained respectively. The penetration depth is controlled by adjusting the excitation current frequency;

[0009] (3) Calculate the true residual stress based on a multi-segment difference equation system;

[0010] (4) The coating interference signal is separated through multi-segment differential equations and dynamic attenuation coefficient calibration.

[0011] The step (1) specifically includes the following steps:

[0012] Prepare a stress-free calibration test block made of the same material as the substrate to be tested, and spray a non-magnetic coating using the same process;

[0013] On the stress-free calibration block, the depths d1 to d n Conduct magnetic survey and measure the interference signals δ1, δ2, ..., δ at each depth n , use the recursive formula to perform layer-by-layer calibration calculation Or through piecewise fitting or dynamic weighting algorithm, establish the attenuation coefficient matrix k ij , representing the depth d j For depth d i The interference attenuation relationship.

[0014] In the step (2), the different penetration depths are d1, d2, ..., d n , and d i+1 >d i , corresponding to the stress distribution at depth σ i (x, y), where i = 1, 2, ..., n.

[0015] In step (2), the excitation current frequency is adjusted to achieve penetration depth control, and low frequency penetrates deeper. Frequency and current setting: according to the coating thickness-penetration depth model Where μ is the magnetic permeability and σ is the electrical conductivity, which determine the critical frequency. The smaller the frequency, the stronger the penetration.

[0016] In step (3), in the differential stress calculation,

[0017] Construct a multi-segment difference system:

[0018] Solve the true stress σ by the least squares method or iterative optimization algorithm true .

[0019] A residual stress detection system for color-coated plates based on magnetic measurement method comprises a high-precision signal measurement circuit of a multi-frequency excitation magnetic measurement sensor, a coating thickness measurement module and a signal processing unit, wherein the high-precision signal measurement circuit of the multi-frequency excitation magnetic measurement sensor and the coating thickness measurement module are respectively connected to the signal processing unit.

[0020] The coating thickness measurement module is an eddy current thickness gauge or a laser thickness gauge.

[0021] The signal processing unit includes an embedded processor and a filtering circuit, which are interconnected. The embedded processor is provided with an adaptive attenuation coefficient calibration module, a multi-depth difference calculation engine and a stress distribution trend visualization interface.

[0022] The beneficial effects of the present invention are: constructing a differential equation through the detection results of multiple times at different penetration depths, combining with the calibration of the attenuation coefficient k, quantitatively eliminating the interference of the non-magnetic coating, significantly improving the detection accuracy, and having the advantages of strong anti-interference ability, standardized calibration process, and applicability to industrial sites. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a flow chart of a method according to an embodiment of the present invention;

[0024] Figure 2 It is a schematic diagram of the calibration test block structure of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the invention implementation cases clearer, the technical solutions in the invention implementation cases will be clearly and completely described below in conjunction with the drawings in the implementation cases. Obviously, the implementation cases described are only a small part of the implementation cases of the present invention, rather than all the implementation cases. Based on the implementation cases in the present invention, all other implementation cases obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0026] A method for detecting residual stress of a color-coated steel plate based on magnetic measurement comprises the following steps:

[0027] (1) Calibrate the attenuation coefficient k using a stress-free calibration test block;

[0028] (2) Multi-depth magnetic measurement signal acquisition: a magnetic sensor is used to perform residual stress detection on the color-coated plate at two or more different penetration depths, and the stress distribution results of the corresponding depths are obtained respectively. The penetration depth is controlled by adjusting the excitation current frequency;

[0029] (3) Calculate the true residual stress based on a multi-segment difference equation system;

[0030] (4) The coating interference signal is separated through multi-segment differential equations and dynamic attenuation coefficient calibration.

[0031] The step (1) specifically includes the following steps:

[0032] Prepare a stress-free calibration test block made of the same material as the substrate to be tested, and spray a non-magnetic coating using the same process;

[0033] On the stress-free calibration block, the depths d1 to d nConduct magnetic survey and measure the interference signals δ1, δ2, ..., δ at each depth n , use the recursive formula to perform layer-by-layer calibration calculation Or through piecewise fitting or dynamic weighting algorithm, establish the attenuation coefficient matrix k ij , representing the depth d j For depth d i The interference attenuation relationship.

[0034] In the step (2), the different penetration depths are d1, d2, ..., d n , and d i+1 >d i , corresponding to the stress distribution at depth σ i (x, y), where i = 1, 2, ..., n.

[0035] In step (2), the excitation current frequency is adjusted to achieve penetration depth control, and low frequency penetrates deeper. Frequency and current setting: according to the coating thickness-penetration depth model Where μ is the magnetic permeability and σ is the electrical conductivity, which determine the critical frequency. The smaller the frequency, the stronger the penetration.

[0036] In step (3), in the differential stress calculation,

[0037] Construct a multi-segment difference system:

[0038] Solve the true stress σ by the least squares method or iterative optimization algorithm true .

[0039] A residual stress detection system for color-coated plates based on magnetic measurement method comprises a high-precision signal measurement circuit of a multi-frequency excitation magnetic measurement sensor, a coating thickness measurement module and a signal processing unit, wherein the high-precision signal measurement circuit of the multi-frequency excitation magnetic measurement sensor and the coating thickness measurement module are respectively connected to the signal processing unit.

[0040] The coating thickness measurement module is an eddy current thickness gauge or a laser thickness gauge.

[0041] The signal processing unit includes an embedded processor and a filtering circuit, which are interconnected. The embedded processor is provided with an adaptive attenuation coefficient calibration module, a multi-depth difference calculation engine and a stress distribution trend visualization interface.

[0042] Example:

[0043] 1. Equipment preparation: Place the magnetic residual stress detector on the workbench in the laboratory, ensure that the power connection is normal, turn on the device and preheat it for 30 minutes until the device is stable.

[0044] 2. Calibration test block preparation: Select the same material as the test color coated plate, the same coating process as the plate without stress treatment.

[0045] 3. Surface treatment of color coated plate: Use non-woven fabric to dip isopropyl alcohol (purity ≥ 99.5%) to wipe the surface in a single direction, remove grease and dust.

[0046] 4. Equipment calibration: Place the measurement probe group on the stress-free test plate, perform standby test, and start stress detection after observing stable current value.

[0047] 5. Frequency and current setting: According to the coating thickness-penetration depth model (μ is magnetic permeability, σ is electrical conductivity), determine the critical frequency, the smaller the frequency, the stronger the penetration.

[0048] 6. Calibration and verification of attenuation coefficient k: Detect with depth d n on the stress-free calibration test block, measure the interference signal δ n in the stress-free state. Calculate the attenuation coefficient according to the formula.

[0049] 7. Multi-depth stress detection: Adopt grid path planning, detection point spacing 30mm x 30mm, cover the transverse direction of the color coated plate, and perform multiple independent detections at different frequencies.

[0050] 8. Calibration curve fitting: Establish a three-dimensional calibration database of attenuation coefficient-depth-coating thickness (k-d-h), and generate a general calibration curve through polynomial fitting or interpolation algorithm.

[0051] 9. Stress calculation and visualization: Solve the real stress based on the difference equation, and output the smooth stress distribution map based on the Origin processing software.

[0052] The present application solves the problem of precision decline caused by coating in traditional magnetic measurement method by multiple magnetic measurements with different penetration depths, calibrates the interference attenuation coefficient k combined with the stress-free calibration test block, constructs the difference equation to eliminate the interference of non-magnetic coating, and has the advantages of strong anti-interference, standardized calibration process, and suitability for industrial site.

Claims

1. A method for detecting residual stress of color-coated steel sheets based on magnetic measurement, characterized in that The following steps are involved: (1) Calibrate the attenuation coefficient k using a stress-free calibration test block; (2) Multi-depth magnetic measurement signal acquisition: a magnetic sensor is used to perform residual stress detection on the color-coated plate at two or more different penetration depths, and the stress distribution results of the corresponding depths are obtained respectively. The penetration depth is controlled by adjusting the excitation current frequency; (3) Calculate the true residual stress based on a multi-segment difference equation system; (4) The coating interference signal is separated through multi-segment differential equations and dynamic attenuation coefficient calibration.

2. The method for detecting residual stress of a color-coated steel plate based on magnetic measurement according to claim 1, characterized in that: The step (1) specifically includes the following steps: Prepare a stress-free calibration test block made of the same material as the substrate to be tested, and spray a non-magnetic coating using the same process; On the stress-free calibration block, the depths d1 to d n Conduct magnetic survey and measure the interference signals δ1, δ2, ..., δ at each depth n , use the recursive formula to perform layer-by-layer calibration calculation Or through piecewise fitting or dynamic weighting algorithm, establish the attenuation coefficient matrix k ij , representing the depth d j For depth d i The interference attenuation relationship.

3. The method for detecting residual stress of a color-coated steel plate based on magnetic measurement according to claim 1, characterized in that: In the step (2), the different penetration depths are d1, d2, ..., d n , and d i+1 >d i , corresponding to the stress distribution at depth σ i (x, y), where i = 1, 2, ..., n.

4. The method for detecting residual stress of a color-coated steel plate based on magnetic measurement according to claim 1, characterized in that: In step (2), the excitation current frequency is adjusted to achieve penetration depth control, and low frequency penetrates deeper. Frequency and current setting: according to the coating thickness-penetration depth model Where μ is the magnetic permeability and σ is the electrical conductivity, which determine the critical frequency. The smaller the frequency, the stronger the penetration.

5. The method for detecting residual stress of a color-coated steel plate based on magnetic measurement according to claim 1, characterized in that: In step (3), in the differential stress calculation, Construct a multi-segment difference system: Solve the true stress σ by the least squares method or iterative optimization algorithm true .

6. A residual stress detection system for color-coated steel sheets based on magnetic measurement, characterized by: It comprises a high-precision signal measurement circuit of a multi-frequency excitation magnetic sensor, a coating thickness measurement module and a signal processing unit, wherein the high-precision signal measurement circuit of the multi-frequency excitation magnetic sensor and the coating thickness measurement module are respectively connected to the signal processing unit.

7. The residual stress detection system for color-coated steel sheets based on magnetic measurement according to claim 6, characterized in that: The coating thickness measurement module is an eddy current thickness gauge or a laser thickness gauge.

8. The residual stress detection system for color-coated steel sheets based on magnetic measurement according to claim 6, characterized in that: The signal processing unit includes an embedded processor and a filtering circuit, which are interconnected. The embedded processor is provided with an adaptive attenuation coefficient calibration module, a multi-depth difference calculation engine and a stress distribution trend visualization interface.

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