A method for real-time imaging and quality evaluation of resistance spot welding joints

Abstract

The application particularly relates to a real-time imaging and quality evaluation method of a resistance spot welding joint, which comprises the following steps: collecting an ultrasonic A-scan signal of the resistance spot welding joint; and performing real-time imaging and quality evaluation of the resistance spot welding joint according to the ultrasonic A-scan signal of the resistance spot welding joint.The real-time imaging and quality evaluation method of the resistance spot welding joint has the characteristics of intuitive imaging, simple operation, accurate evaluation result and wide use by using a matrix distributed ultrasonic probe to perform real-time imaging and quality evaluation of the resistance spot welding joint.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic nondestructive testing technology for resistance spot welding, and in particular to a method for real-time imaging and quality assessment of resistance spot welded joints. Background Technology

[0002] Resistance spot welding is one of the main processing techniques used for connecting body parts, and its quality directly affects the safety performance of the vehicle body. Traditional destructive inspections—such as tensile testing and metallography—are no longer sufficient to meet the needs of automakers to ensure the quality of resistance spot welds. Therefore, using non-destructive testing techniques to evaluate resistance spot weld quality has become the mainstream inspection method for automakers. Ultrasonic testing is the most commonly used method for assessing resistance spot weld quality. Its main principle is to use the reflection and transmission of sound waves propagating in the weld nugget area to detect internal defects in the weld. At the same time, by designing appropriately sized probes, the size of the weld nugget can be evaluated, and then the overall quality of the resistance spot weld can be analyzed.

[0003] Existing ultrasonic testing systems for resistance spot welding use A-scan or C-scan imaging methods, resulting in unintuitive imaging results that fail to accurately reflect the morphological characteristics of the resistance spot weld joint. Furthermore, they do not consider the influence of weld nugget thickness when assessing resistance spot weld quality, relying solely on indentation depth or plate thickness reduction rate to determine weak welds. On the other hand, existing ultrasonic testing systems for resistance spot welding consider welds with good surface quality. Since resistance spot welding commonly uses conical or spherical electrodes, there will be obvious indentations on the surface of the resistance spot weld joint. Moreover, due to the influence of electrode wear, the indentations on the surface of the resistance spot weld joint exhibit irregular morphological characteristics, leading to a large error in the assessed weld nugget diameter. Summary of the Invention

[0004] Therefore, it is necessary to address the problems of unintuitive imaging and large errors in the existing ultrasonic testing of resistance spot welded joints, and to provide a real-time imaging and quality assessment method for resistance spot welded joints. This method uses a matrix distributed ultrasonic probe to perform real-time imaging and quality assessment of resistance spot welded joints, and has the characteristics of intuitive imaging, simple operation, accurate assessment results, and wide applicability.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for real-time imaging and quality assessment of resistance spot welded joints includes the following steps: acquiring ultrasonic A-scan signals of the resistance spot welded joint, and performing real-time imaging and quality assessment of the resistance spot welded joint based on the ultrasonic A-scan signals.

[0007] Furthermore, the real-time imaging and quality assessment method for the resistance spot welded joint includes the following steps:

[0008] Step 1: Acquire ultrasonic A-scan signals from the resistance spot welded joint; Based on the ultrasonic A-scan signals from the resistance spot welded joint, determine the array elements at the edge of the weld nugget, identify the outer array elements at the edge of the weld nugget as the outer array elements of the weld nugget, and identify the inner array elements at the edge of the weld nugget as the inner array elements of the weld nugget.

[0009] Step 2: Assemble all the edge elements of the molten core and take the center of all the edge elements of the molten core as the center of the molten core; calculate the proportion of the molten core area within the effective coverage area of ​​each edge element of the molten core based on the ultrasonic A-scan signal of each edge element of the molten core; determine the molten core edge point of each edge element of the molten core based on the proportion of the molten core area within the effective coverage area of ​​each edge element of the molten core.

[0010] Step 3: Interpolate between each edge point of the weld nugget to draw the cross-sectional shape of the weld nugget. Fill the weld nugget, the transition area between the weld nugget and the single-layer plate and the single-layer plate with different colors. The colors of the weld nugget, the transition area between the weld nugget and the single-layer plate and the single-layer plate are uniformly transitioned. Perform color imaging analysis on the resistance spot weld joint.

[0011] Step 4: Determine the edge points of defects within the melt core based on the ultrasonic A-scan signal of the array elements within the melt core; perform interpolation between the edge points of defects within the melt core to draw the morphology of defects within the melt core; fill the defects within the melt core with a color different from the filling color of the melt core; and perform color imaging analysis on the defects within the melt core.

[0012] Step 5: Calculate the thickness of the single-layer plate of the resistance spot weld joint based on the distance between the first and second echoes of the single-layer plate bottom surface in the ultrasonic A-scan signal of the resistance spot weld joint surface and the bottom of the resistance spot weld joint, for single-layer plate thickness calibration.

[0013] Step 6: Calculate the molten core area ratio based on the molten core area ratio of each edge element and the molten core area ratio of the elements within the molten core, and combine this with the effective coverage area of ​​a single element to calculate the molten core cross-sectional area. Then, use the equivalent circle method to determine the type of the edge element based on its position. Finally, calculate the molten core diameter through integration to outline the specific contour of the molten core edge.

[0014] Step 7: Calculate the indentation depth of the resistance spot weld joint based on the ultrasonic A-scan signal between the coupling layer of the inner array element of the fusion core and the surface of the resistance spot weld joint.

[0015] Step 8: Calculate the thickness of the resistance spot weld joint fusion zone based on the ultrasonic A-scan signals from the surface and bottom of the resistance spot weld joint of the inner array element of the fusion core.

[0016] Step 9: Collect the ultrasonic A-scan signals of all array elements in the weld core, extract multiple ultrasonic echoes of the resistance spot weld joint, and calculate the attenuation coefficient of the resistance spot weld joint.

[0017] Step 10: Collect the ultrasonic A-scan signals of all array elements in the weld nugget, analyze and determine whether there is an echo exceeding 20% ​​FSH between the first and second ultrasonic echoes of the resistance spot weld joint. If so, it is determined to be a defect echo, and the amplitude of the defect echo and the corresponding array element position are recorded.

[0018] Step 11: Based on the calculation results of steps 6-10, evaluate the quality of the resistance spot weld joint.

[0019] Further, in step 1, ultrasonic A-scan signal acquisition of the resistance spot welded joint includes the following steps: a matrix ultrasonic probe is used to completely cover the resistance spot welded joint, and each element of the matrix ultrasonic probe independently transmits and receives ultrasonic signals to acquire ultrasonic A-scan signals of the resistance spot welded joint; the ultrasonic A-scan signal includes ultrasonic echo position and ultrasonic echo amplitude.

[0020] Further, in step 1, the center frequency of the matrix ultrasound probe is 15MHz, the element spacing of the matrix ultrasound probe is (1×1)mm, and the effective coverage area of ​​the array elements of the matrix ultrasound probe is 1mm. 2 The resistance spot welded joint is formed by resistance spot welding two single-layer plates.

[0021] Further, in step 1, based on the ultrasonic A-scan signal of the resistance spot welded joint, the edge array elements of the weld nugget are determined, and the outer array elements of the weld nugget edge are determined as the outer array elements of the weld nugget, and the inner array elements of the weld nugget edge are determined as the inner array elements of the weld nugget. This includes the following steps:

[0022] The ultrasonic A-scan signals of the first echo of each array element coupling layer, the first echo of the surface of the resistance spot weld joint, and the first echo of the bottom of the resistance spot weld joint were extracted.

[0023] The location of the edge element of the weld nugget is determined by the ultrasonic A-scan signals of the first echo on the surface and the first echo at the bottom of the resistance spot weld joint, and the ultrasonic A-scan signals of the edge element of the weld nugget are classified.

[0024] Based on the ultrasonic A-scan signals of the classified molten core edge array elements, determine whether each array element belongs to the molten core edge array element;

[0025] When the identified edge elements of the melting core form a closed shape, the determination of the edge elements of the melting core stops, and the outer edge elements of the melting core are determined as outer edge elements of the melting core, and the inner edge elements of the melting core are determined as inner edge elements of the melting core.

[0026] Furthermore, the ultrasonic A-scan signals of the edge elements of the molten core are classified as follows:

[0027] When the array element is at the edge of the resistance spot weld joint, obvious single-layer plate bottom surface echo or molten core bottom surface echo will appear in the ultrasonic A-scan signal of the array element.

[0028] When the first echo at the bottom of the resistance spot weld is determined to be the bottom echo of a single-layer plate, there is a first echo N of the molten core after the position of the first echo at the bottom of the resistance spot weld, which is defined as the first type of molten core edge array element.

[0029] When the first echo at the bottom of the resistance spot weld is the bottom surface echo of the weld nugget, there is a first echo P of a single-layer plate in front of the first echo position at the bottom of the resistance spot weld, which is defined as the second type of weld nugget edge array element.

[0030] When the tilt angle of the edge portion of the resistance spot welded joint is greater than 10°, the first echo amplitude at the bottom of the resistance spot welded joint is less than 15%FSH and cannot be effectively identified, and is defined as the third type of weld nucleus edge array element.

[0031] When there are pores and incomplete penetration defects at the edge of the weld nugget, the ultrasonic reflected echo amplitude of the resistance spot weld joint exhibits a "Napoleon hat" phenomenon, which first increases and then decreases. This phenomenon is defined as the fourth type of weld nugget edge array element.

[0032] When the surface indentation at the edge of the resistance spot weld joint has a raised or irregular shape, the ultrasonic waves are scattered. The echo energy received by the array element is less than the set value, or even cannot effectively receive this part of the ultrasonic echo signal. This is defined as the fifth type of weld core edge array element.

[0033] Further, in step 2, the proportion of the molten core area within the effective coverage area of ​​each molten core edge element is calculated based on the ultrasonic A-scan signal of each molten core edge element, including the following steps:

[0034] The proportion of the molten core area within the effective coverage area of ​​the edge array elements for the first, second, and third types of molten cores is calculated based on the ratio of the ultrasonic reflection amplitude of the molten core in the molten zone to the ultrasonic reflection amplitude of the single-layer plate in the unmelted zone, according to the formula for calculating the ultrasonic reflection amplitude and the transmitted sound pressure amplitude. The proportion of the molten core area within the effective coverage area of ​​the edge array elements for the fourth type of molten core is 1. The proportion of the molten core area within the effective coverage area of ​​the edge array elements for the fifth type of molten core is determined based on the depth of the indentation on the surface of the resistance spot weld joint.

[0035] When the indentation depth on the surface of the resistance spot welded joint is ≤0.1mm, the proportion of the weld nugget area within the effective coverage area of ​​the edge array element of the fifth type of weld nugget is taken as 1;

[0036] When the indentation depth on the surface of the resistance spot welded joint is 0.1-0.2mm, the proportion of the weld nugget area within the effective coverage area of ​​the fifth type of weld nugget edge array element is taken as 0.9.

[0037] When the indentation depth on the surface of the resistance spot welded joint is >0.2mm, the proportion of the weld nugget area within the effective coverage area of ​​the fifth type of weld nugget edge array element is taken as 0.8.

[0038] Further, in step 4, the defect edge points within the melt nugget are determined based on the ultrasonic A-scan signal of the elements within the melt nugget, including the following steps:

[0039] Based on the ultrasonic A-scan signal of the array elements inside the molten core, the array elements with defect echoes inside the molten core are screened out.

[0040] The percentage of defect area in the melt core is calculated based on the ultrasonic echo amplitude of the defect echo array element in the melt core and the ultrasonic echo amplitude of the array element in the melt core. The percentage of defect area in the melt core is equal to the ratio of the sum of the ultrasonic echo amplitudes of the defect echo array element in the melt core to the sum of the ultrasonic echo amplitudes of all array elements in the melt core.

[0041] The edge points of defects within the melt core are determined based on the proportion of the defect area within the melt core.

[0042] Furthermore, in step 9, the attenuation coefficient α of the resistance spot weld joint is calculated according to the following formula:

[0043]

[0044] In the formula, m and n are the ultrasonic echo numbers of the bottom wave, respectively; B m B n δ represents the height of the m-th and n-th bottom waves, respectively; δ is the ultrasonic echo loss, with each ultrasonic echo loss being approximately (0.5–1.0) dB; x is the thickness of the single-layer plate.

[0045] Further, step 11, based on the quantitative calculation results of the characteristic parameters in steps 6-10, evaluates the quality of the resistance spot weld joint, including the following steps:

[0046] The quality of resistance spot welded joints is classified into qualified, overheated, incomplete penetration, weld nugget diameter too small, weld nugget thickness too small, and poor weld.

[0047] The criteria for judging the quality of resistance spot welded joints as qualified are: defect area / weld area ≤ 0.1, indentation depth ≤ 1 / 3 of the thickness of the first single-layer plate, attenuation coefficient ≥ 0.8, weld nugget thickness ≥ 80%d, and weld nugget diameter ≥ Where d represents the sum of the thicknesses of the two single-layer plates;

[0048] The criteria for judging the quality of resistance spot welded joints as overheated are: defect area / melt area ≤ 0.1, indentation depth > 1 / 3 of the thickness of the first single-layer plate, and attenuation coefficient ≥ 2.0;

[0049] The criteria for judging the quality of resistance spot welded joints as incomplete penetration are: defect area / melt nugget area > 0.1, indentation depth ≤ 1 / 3 of the thickness of the first single-layer plate, attenuation coefficient ≥ 0.8, and melt nugget area thickness ≥ 80%d;

[0050] The criterion for judging the quality of resistance spot welded joints as having a weld nugget diameter that is too small is: defect area / weld nugget area ≤ 0.1;

[0051] The criteria for judging the quality of resistance spot welded joints with insufficient weld nugget thickness are as follows: indentation depth ≤ 1 / 3 of the first single-layer plate thickness, attenuation coefficient < 0.8, weld nugget thickness < 80%d, and weld nugget diameter ≥ ;

[0052] The criteria for judging the quality of resistance spot welded joints as poor welds are: indentation depth ≤ 1 / 4 of the thickness of the first single-layer plate, attenuation coefficient < 0.8, and weld nugget thickness < 80%d.

[0053] Beneficial technical effects of the present invention:

[0054] The present invention provides a real-time imaging and quality assessment method for resistance spot welded joints. A matrix ultrasonic probe completely covers the resistance spot welded joint, eliminating the need for scanning devices and ensuring convenient and accurate positioning. It realistically displays the morphological characteristics of the resistance spot welded joint, providing intuitive imaging. The introduction of an attenuation coefficient as a quantitative assessment basis for the weld nugget thickness effectively assesses weld joints with weld nugget thicknesses less than the standard requirements. Utilizing image recognition and quantitative assessment modes based on feature parameters significantly reduces the professional requirements for testing personnel. The method offers diversified evaluation indicators, resulting in more accurate assessment results. It has a wide range of applications, particularly suitable for ultrasonic quality testing of resistance spot welded joints with deep or irregular surface indentations. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of the location of ultrasound A-scan signals;

[0056] Figure 2 This is a real-time image of a resistance spot welded joint. Detailed Implementation

[0057] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0058] See Figure 1-2 This embodiment provides a method for real-time imaging and quality assessment of resistance spot welded joints, including the following steps: acquiring ultrasonic A-scan signals of the resistance spot welded joint, and performing real-time imaging and quality assessment of the resistance spot welded joint based on the ultrasonic A-scan signals of the resistance spot welded joint.

[0059] In this embodiment, the real-time imaging and quality assessment method for resistance spot welding joints includes the following steps:

[0060] Step 1: Acquire ultrasonic A-scan signals from the resistance spot welded joint; Based on the ultrasonic A-scan signals from the resistance spot welded joint, determine the array elements at the edge of the weld nugget, identify the outer array elements at the edge of the weld nugget as the outer array elements of the weld nugget, and identify the inner array elements at the edge of the weld nugget as the inner array elements of the weld nugget.

[0061] Step 2: Assemble all the edge elements of the molten core and take the center of all the edge elements of the molten core as the center of the molten core; calculate the proportion of the molten core area within the effective coverage area of ​​each edge element of the molten core based on the ultrasonic A-scan signal of each edge element of the molten core; determine the molten core edge point of each edge element of the molten core based on the proportion of the molten core area within the effective coverage area of ​​each edge element of the molten core.

[0062] Step 3: Interpolate between each edge point of the weld nugget to draw the cross-sectional shape of the weld nugget. Fill the weld nugget, the transition area between the weld nugget and the single-layer plate and the single-layer plate with different colors. The colors of the weld nugget, the transition area between the weld nugget and the single-layer plate and the single-layer plate are uniformly transitioned. Perform color imaging analysis on the resistance spot weld joint.

[0063] Step 4: Determine the edge points of defects within the melt core based on the ultrasonic A-scan signal of the array elements within the melt core; perform interpolation between the edge points of defects within the melt core to draw the morphology of defects within the melt core; fill the defects within the melt core with a color different from the filling color of the melt core; and perform color imaging analysis on the defects within the melt core.

[0064] Step 5: Calculate the thickness of the single-layer plate of the resistance spot weld joint based on the distance between the first and second echoes of the single-layer plate bottom surface in the ultrasonic A-scan signal of the resistance spot weld joint surface and the bottom of the resistance spot weld joint, for single-layer plate thickness calibration.

[0065] Step 6: Calculate the molten core area ratio based on the molten core area ratio of each edge element and the molten core area ratio of the elements within the molten core, and combine this with the effective coverage area of ​​a single element to calculate the molten core cross-sectional area. Then, use the equivalent circle method to determine the type of the edge element based on its position. Finally, calculate the molten core diameter through integration to outline the specific contour of the molten core edge.

[0066] Step 7: Calculate the indentation depth of the resistance spot weld joint based on the ultrasonic A-scan signal between the coupling layer of the inner array element of the fusion core and the surface of the resistance spot weld joint.

[0067] Step 8: Calculate the thickness of the resistance spot weld joint fusion zone based on the ultrasonic A-scan signals from the surface and bottom of the resistance spot weld joint of the inner array element of the fusion core.

[0068] Step 9: Collect the ultrasonic A-scan signals of all array elements in the weld core, extract multiple ultrasonic echoes of the resistance spot weld joint, and calculate the attenuation coefficient of the resistance spot weld joint.

[0069] Step 10: Collect the ultrasonic A-scan signals of all array elements in the weld nugget, analyze and determine whether there is an echo exceeding 20% ​​FSH between the first and second ultrasonic echoes of the resistance spot weld joint. If so, it is determined to be a defect echo, and the amplitude of the defect echo and the corresponding array element position are recorded.

[0070] Step 11: Based on the calculation results of steps 6-10, evaluate the quality of the resistance spot weld joint.

[0071] In this embodiment, step 1, which involves acquiring ultrasonic A-scan signals from the resistance spot welded joint, includes the following steps:

[0072] A matrix ultrasonic probe is used to completely cover the resistance spot weld joint. Each element of the matrix ultrasonic probe independently transmits and receives ultrasonic signals to acquire the ultrasonic A-scan signal of the resistance spot weld joint.

[0073] The ultrasound A-scan signal includes the ultrasound echo location and ultrasound echo amplitude.

[0074] In this embodiment, in step 1, the center frequency of the matrix ultrasound probe is 15MHz, the element spacing of the matrix ultrasound probe is (1×1)mm, and the effective coverage area of ​​the array elements of the matrix ultrasound probe is 1mm. 2 The resistance spot welded joint is formed by resistance spot welding of two single-layer plates. The thickness of the single-layer plate is (1.7+1)mm, and the material of the single-layer plate is DP590 duplex steel commonly used in car bodies.

[0075] In this embodiment, step 1 involves determining the edge array elements of the weld nugget based on the ultrasonic A-scan signal of the resistance spot weld joint, identifying the outer array elements of the weld nugget edge as the outer array elements of the weld nugget, and the inner array elements of the weld nugget edge as the inner array elements of the weld nugget, including the following steps:

[0076] The ultrasonic A-scan signals of the first echo D0 of each array element coupling layer, the first echo D1 of the surface of the resistance spot welded joint, and the first echo D2 of the bottom of the resistance spot welded joint are extracted.

[0077] The location of the edge element of the weld nugget is determined based on the ultrasonic A-scan signals of the first echo D1 on the surface of the resistance spot welded joint and the first echo D2 at the bottom of the resistance spot welded joint, and the ultrasonic A-scan signals of the edge element of the weld nugget are classified.

[0078] Based on the ultrasonic A-scan signals of the classified molten core edge array elements, determine whether each array element belongs to the molten core edge array element;

[0079] When the identified edge elements of the melting core form a closed shape, the determination of the edge elements of the melting core stops, and the outer edge elements of the melting core are determined as outer edge elements of the melting core, and the inner edge elements of the melting core are determined as inner edge elements of the melting core.

[0080] In this embodiment, in step 1, the ultrasonic A-scan signals of the edge array elements of the molten core are classified as follows:

[0081] When the array element is at the edge of the resistance spot weld joint, obvious single-layer plate bottom surface echo or molten core bottom surface echo will appear in the ultrasonic A-scan signal of the array element.

[0082] When the first echo D2 at the bottom of the resistance spot weld is determined to be the bottom echo of a single-layer plate, there is a first echo N of the weld nugget after the position of the first echo D2 at the bottom of the resistance spot weld, which is defined as the first type of weld nugget edge array element.

[0083] When the first echo D2 at the bottom of the resistance spot welded joint is the bottom surface echo of the weld nugget, there is a first echo P of a single-layer plate in front of the position of the first echo D2 at the bottom of the resistance spot welded joint, which is defined as the second type of weld nugget edge array element.

[0084] When the tilt angle of the edge portion of the resistance spot welded joint is greater than 10°, the amplitude of the first echo D2 at the bottom of the resistance spot welded joint is less than 15%FSH and cannot be effectively identified. It is defined as the third type of weld nugget edge array element.

[0085] When there are pores and incomplete penetration defects at the edge of the weld nugget, the ultrasonic reflected echo amplitude of the resistance spot weld joint exhibits a "Napoleon hat" phenomenon, which first increases and then decreases. This phenomenon is defined as the fourth type of weld nugget edge array element.

[0086] When the surface indentation at the edge of the resistance spot weld joint has a raised or irregular shape, the ultrasonic waves are scattered. The echo energy received by the array element is less than the set value, or even cannot effectively receive this part of the ultrasonic echo signal. This is defined as the fifth type of weld core edge array element.

[0087] In this embodiment, step 2, calculating the proportion of the melt core area within the effective coverage area of ​​each melt core edge element based on the ultrasonic A-scan signal of each melt core edge element, includes the following steps:

[0088] The edge element of the melt core indicates that the element is located at the edge of the melt core. Therefore, the ultrasonic A-scan signal of the edge element of the melt core includes the ultrasonic A-scan signal of the unmelted single-layer plate and the ultrasonic A-scan signal of the melt core in the molten zone.

[0089] The proportion of the melt core area within the effective coverage area of ​​the edge array elements of the first, second, and third types of melt cores is calculated based on the ratio of the ultrasonic reflection amplitude of the melt core in the molten zone to the ultrasonic reflection amplitude of the single-layer plate in the unmelted zone, according to the calculation formula of ultrasonic reflection amplitude and transmitted sound pressure amplitude.

[0090] The ultrasonic echo amplitude of the edge array elements of the fourth and fifth types of molten cores is not calculable. Since the defect exists inside the molten core, the diameter of the molten core includes the size of the defect portion. Therefore, the proportion of the molten core area within the effective coverage area of ​​the edge array elements of the fourth type of molten core is 1.

[0091] The proportion of the weld nugget area within the effective coverage area of ​​the edge array element of the fifth type of weld nugget is determined based on the depth of the indentation on the surface of the resistance spot weld joint;

[0092] When the indentation depth on the surface of the resistance spot welded joint is ≤0.1mm, the proportion of the weld nugget area within the effective coverage area of ​​the edge array element of the fifth type of weld nugget is taken as 1;

[0093] When the indentation depth on the surface of the resistance spot welded joint is 0.1-0.2mm, the proportion of the weld nugget area within the effective coverage area of ​​the fifth type of weld nugget edge array element is taken as 0.9.

[0094] When the indentation depth on the surface of the resistance spot weld joint is greater than 0.2 mm, the proportion of the weld nugget area within the effective coverage area of ​​the fifth type of weld nugget edge array element is taken as 0.8.

[0095] In this embodiment, step 4, determining the defect edge point within the melt core based on the ultrasonic A-scan signal of the array elements within the melt core, includes the following steps:

[0096] Based on the ultrasonic A-scan signal of the array elements inside the molten core, the array elements with defect echoes inside the molten core are screened out.

[0097] The percentage of defect area in the melt core is calculated based on the ultrasonic echo amplitude of the defect echo array element in the melt core and the ultrasonic echo amplitude of the array element in the melt core. The percentage of defect area in the melt core is equal to the ratio of the sum of the ultrasonic echo amplitudes of the defect echo array element in the melt core to the sum of the ultrasonic echo amplitudes of all array elements in the melt core.

[0098] The edge points of defects within the melt core are determined based on the proportion of the defect area within the melt core.

[0099] In this embodiment, in step 6, the effective coverage area of ​​a single array element is 1 mm. 2 The area ratio of the melt core to the inner array element is 1. Based on the ratio of the melt core area between the melt core edge and the inner array element, the effective area of ​​the melt core is calculated to be 26.96 mm. 2 Equivalent to a circle, the diameter of the melt core was calculated to be 5.86 mm.

[0100] In this embodiment, in step 7, the D1-D0 values ​​within all weld nuggets are calculated, and the maximum value is taken to represent the indentation depth of the resistance spot weld joint. The indentation depth of the resistance spot weld joint is calculated as (1.65-0.83)×1480 / 5900=0.21mm.

[0101] In this embodiment, in step 8, the values ​​of D2-D1 of all the elements in the fusion core are calculated, and the minimum value is taken to represent the thickness of the fusion core area of ​​the resistance spot welded joint. The thickness of the fusion area of ​​the resistance spot welded joint is calculated to be 3.30-1.65=1.65mm.

[0102] In this embodiment, in step 9, there are multiple ultrasonic echoes from the weld joint within the weld nugget. There are 11 array elements with defect-free echo interference. The first three ultrasonic echoes from the weld joint within the weld nugget are extracted, and the attenuation coefficient of the ultrasonic echo from each array element weld joint is calculated according to the acoustic energy attenuation formula. The calculated value is 1.496±0.305. The attenuation coefficient α of the resistance spot weld is calculated according to the following formula:

[0103]

[0104] In the formula, m and n are the ultrasonic echo numbers of the bottom wave, respectively; B m B n δ represents the height of the m-th and n-th bottom waves, respectively; δ is the ultrasonic echo loss, with each ultrasonic echo loss being approximately (0.5–1.0) dB; x is the thickness of the single-layer plate.

[0105] In this embodiment, in step 10, defect echo signals were found in 6 array elements, with a defect depth of 1.85 mm. Based on the formula for calculating the ultrasonic reflection amplitude and transmitted sound pressure amplitude, the defect area ratio can be calculated to be 18%, and thus the defect area is calculated to be 4.85 mm. 2 Based on the area, the radius of the circular defect is calculated to be 1.24 mm.

[0106] In this embodiment, step 11, evaluating the quality of the resistance spot weld joint based on the calculation results of steps 6-10, includes the following steps:

[0107] The quality of resistance spot welded joints is classified into qualified, overheated, incomplete penetration, weld nugget diameter too small, weld nugget thickness too small, and poor weld.

[0108] The criteria for judging the quality of resistance spot welded joints as qualified are: defect area / weld area ≤ 0.1, indentation depth ≤ 1 / 3 of the thickness of the first single-layer plate, attenuation coefficient ≥ 0.8, weld nugget thickness ≥ 80%d, and weld nugget diameter ≥ Where d represents the sum of the thicknesses of the two single-layer plates;

[0109] The criteria for judging the quality of resistance spot welded joints as overheated are: defect area / melt area ≤ 0.1, indentation depth > 1 / 3 of the thickness of the first single-layer plate, and attenuation coefficient ≥ 2.0;

[0110] The criteria for judging the quality of resistance spot welded joints as incomplete penetration are: defect area / melt nugget area > 0.1, indentation depth ≤ 1 / 3 of the thickness of the first single-layer plate, attenuation coefficient ≥ 0.8, and melt nugget area thickness ≥ 80%d;

[0111] The criterion for judging the quality of resistance spot welded joints as having a weld nugget diameter that is too small is: defect area / weld nugget area ≤ 0.1;

[0112] The criteria for judging the quality of resistance spot welded joints with insufficient weld nugget thickness are as follows: indentation depth ≤ 1 / 3 of the first single-layer plate thickness, attenuation coefficient < 0.8, weld nugget thickness < 80%d, and weld nugget diameter ≥ ;

[0113] The criteria for judging the quality of resistance spot welded joints as poor welds are: indentation depth ≤ 1 / 4 of the thickness of the first single-layer plate, attenuation coefficient < 0.8, and weld nugget thickness < 80%d.

[0114] In this embodiment, defect echo signals were found in 6 array elements, with a defect depth of 1.85 mm. Based on the formula for calculating the amplitude of ultrasonic reflection and transmission sound pressure, the defect area ratio was calculated to be 18%, and therefore the defect area was calculated to be 4.85 mm. 2 Since the defect area / melt area is greater than 0.1, the quality assessment of this resistance spot weld is incomplete penetration, meaning that there is an incomplete penetration defect inside the melt.

[0115] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for real-time imaging and quality assessment of resistance spot welds, characterized in that, Includes the following steps: Step 1: Acquire ultrasonic A-scan signals from the resistance spot welded joint; Based on the ultrasonic A-scan signals from the resistance spot welded joint, determine the array elements at the edge of the weld nugget, identify the outer array elements at the edge of the weld nugget as the outer array elements of the weld nugget, and identify the inner array elements at the edge of the weld nugget as the inner array elements of the weld nugget. Step 2: Assemble all the edge elements of the molten core and take the center of all the edge elements of the molten core as the center of the molten core; calculate the proportion of the molten core area within the effective coverage area of ​​each edge element of the molten core based on the ultrasonic A-scan signal of each edge element of the molten core; determine the molten core edge point of each edge element of the molten core based on the proportion of the molten core area within the effective coverage area of ​​each edge element of the molten core. Step 3: Interpolate between each edge point of the weld nugget to draw the cross-sectional shape of the weld nugget. Fill the weld nugget, the transition area between the weld nugget and the single-layer plate and the single-layer plate with different colors. The colors of the weld nugget, the transition area between the weld nugget and the single-layer plate and the single-layer plate are uniformly transitioned. Perform color imaging analysis on the resistance spot weld joint. Step 4: Determine the edge points of defects within the melt core based on the ultrasonic A-scan signal of the array elements within the melt core; perform interpolation between the edge points of defects within the melt core to draw the morphology of defects within the melt core; fill the defects within the melt core with a color different from the filling color of the melt core; and perform color imaging analysis on the defects within the melt core. Step 5: Calculate the thickness of the single-layer plate of the resistance spot weld joint based on the distance between the first and second echoes of the single-layer plate bottom surface in the ultrasonic A-scan signal of the resistance spot weld joint surface and the bottom of the resistance spot weld joint, for single-layer plate thickness calibration. Step 6: Calculate the molten core area ratio based on the molten core area ratio of each edge element and the molten core area ratio of the elements within the molten core, and combine this with the effective coverage area of ​​a single element to calculate the molten core cross-sectional area. Then, use the equivalent circle method to determine the type of the edge element based on its position. Finally, calculate the molten core diameter through integration to outline the specific contour of the molten core edge. Step 7: Calculate the indentation depth of the resistance spot weld joint based on the ultrasonic A-scan signal between the coupling layer of the inner array element of the fusion core and the surface of the resistance spot weld joint. Step 8: Calculate the thickness of the resistance spot weld joint fusion zone based on the ultrasonic A-scan signals from the surface and bottom of the resistance spot weld joint of the inner array element of the fusion core. Step 9: Collect the ultrasonic A-scan signals of all array elements in the weld core, extract multiple ultrasonic echoes of the resistance spot weld joint, and calculate the attenuation coefficient of the resistance spot weld joint. Step 10: Collect the ultrasonic A-scan signals of all array elements in the weld nugget, analyze and determine whether there is an echo exceeding 20% ​​FSH between the first and second ultrasonic echoes of the resistance spot weld joint. If so, it is determined to be a defect echo, and the amplitude of the defect echo and the corresponding array element position are recorded. Step 11: Based on the calculation results of steps 6-10, evaluate the quality of the resistance spot weld joint.

2. The resistance spot weld joint real-time imaging and quality assessment method of claim 1, wherein, In step 1, ultrasonic A-scan signal acquisition is performed on the resistance spot welded joint, including the following steps: a matrix ultrasonic probe is used to completely cover the resistance spot welded joint, and each element of the matrix ultrasonic probe independently transmits and receives ultrasonic signals to acquire ultrasonic A-scan signals of the resistance spot welded joint; the ultrasonic A-scan signal includes ultrasonic echo position and ultrasonic echo amplitude.

3. The resistance spot welding joint real-time imaging and quality assessment method of claim 2, wherein, In step 1, the matrix ultrasonic probe has a center frequency of 15 MHz, an element spacing of (1x1) mm, and an effective coverage area of 1 mm 2 The resistance spot welded joint is formed by resistance spot welding of two single-layer plates.

4. The resistance spot welding joint real-time imaging and quality assessment method of claim 1, wherein, In step 1, based on the ultrasonic A-scan signal of the resistance spot welded joint, the edge array elements of the weld nugget are determined. The outer array elements of the weld nugget edge are identified as the outer array elements of the weld nugget, and the inner array elements of the weld nugget edge are identified as the inner array elements of the weld nugget. This includes the following steps: The ultrasonic A-scan signals of the first echo of each array element coupling layer, the first echo of the surface of the resistance spot weld joint, and the first echo of the bottom of the resistance spot weld joint were extracted. The location of the edge element of the weld nugget is determined by the ultrasonic A-scan signals of the first echo on the surface and the first echo at the bottom of the resistance spot weld joint, and the ultrasonic A-scan signals of the edge element of the weld nugget are classified. Based on the ultrasonic A-scan signals of the classified molten core edge array elements, determine whether each array element belongs to the molten core edge array element; When the identified edge elements of the melting core form a closed shape, the determination of the edge elements of the melting core stops, and the outer edge elements of the melting core are determined as outer edge elements of the melting core, and the inner edge elements of the melting core are determined as inner edge elements of the melting core.

5. The resistance spot welding joint real-time imaging and quality assessment method of claim 4, wherein, The ultrasonic A-scan signals of the fusion core edge elements are classified as follows: When the array element is at the edge of the resistance spot weld joint, obvious single-layer plate bottom surface echo or molten core bottom surface echo will appear in the ultrasonic A-scan signal of the array element. When the first echo at the bottom of the resistance spot weld is determined to be the bottom echo of a single-layer plate, there is a first echo N of the molten core after the position of the first echo at the bottom of the resistance spot weld, which is defined as the first type of molten core edge array element. When the first echo at the bottom of the resistance spot weld is the bottom surface echo of the weld nugget, there is a first echo P of a single-layer plate in front of the first echo position at the bottom of the resistance spot weld, which is defined as the second type of weld nugget edge array element. When the tilt angle of the edge portion of the resistance spot welded joint is greater than 10°, the amplitude of the first echo at the bottom of the resistance spot welded joint is less than 15%FSH and cannot be effectively identified. This is defined as a third type of weld nugget edge array element. When there are pores and incomplete penetration defects at the edge of the weld nugget, the ultrasonic reflected echo amplitude of the resistance spot weld joint exhibits a "Napoleon hat" phenomenon, which first increases and then decreases. This phenomenon is defined as the fourth type of weld nugget edge array element. When the surface indentation at the edge of the resistance spot weld joint has a raised or irregular shape, the ultrasonic waves will be scattered. The echo energy received by the array element is less than the set value, or even cannot effectively receive this part of the ultrasonic echo signal. This is defined as the fifth type of weld core edge array element.

6. The resistance spot welding joint real-time imaging and quality assessment method of claim 1, wherein, In step 2, the proportion of the molten core area within the effective coverage area of ​​each edge element is calculated based on the ultrasonic A-scan signal of each edge element, including the following steps: The proportion of the molten core area within the effective coverage area of ​​the edge array elements for the first, second, and third types of molten cores is calculated based on the ratio of the ultrasonic reflection amplitude of the molten core in the molten zone to the ultrasonic reflection amplitude of the single-layer plate in the unmelted zone, according to the formula for calculating the ultrasonic reflection amplitude and the transmitted sound pressure amplitude. The proportion of the molten core area within the effective coverage area of ​​the edge array elements for the fourth type of molten core is 1. The proportion of the molten core area within the effective coverage area of ​​the edge array elements for the fifth type of molten core is determined based on the indentation depth on the surface of the resistance spot weld joint. When the indentation depth on the surface of the resistance spot welded joint is ≤0.1mm, the proportion of the weld nugget area within the effective coverage area of ​​the fifth type of weld nugget edge array element is taken as 1. When the indentation depth on the surface of the resistance spot welded joint is 0.1-0.2mm, the proportion of the weld nugget area within the effective coverage area of ​​the fifth type of weld nugget edge array element is taken as 0.

9. When the indentation depth on the surface of the resistance spot weld joint is greater than 0.2 mm, the proportion of the weld nugget area within the effective coverage area of ​​the fifth type of weld nugget edge array element is taken as 0.

8.

7. The resistance spot welding joint real-time imaging and quality assessment method of claim 1, wherein, In step 4, the defect edge points within the melt core are determined based on the ultrasonic A-scan signal of the array elements within the melt core, including the following steps: Based on the ultrasonic A-scan signal of the array elements inside the molten core, array elements with defect echoes inside the molten core are screened out. The percentage of defect area in the melt core is calculated based on the ultrasonic echo amplitude of the defect echo array element in the melt core and the ultrasonic echo amplitude of the array element in the melt core. The percentage of defect area in the melt core is equal to the ratio of the sum of the ultrasonic echo amplitudes of the defect echo array element in the melt core to the sum of the ultrasonic echo amplitudes of all array elements in the melt core. The edge points of defects within the melt core are determined based on the proportion of defect area within the melt core.

8. The method for real-time imaging and quality assessment of resistance spot welded joints according to claim 1, characterized in that, In step 9, the resistance spot weld joint attenuation coefficient is calculated as follows: In the formula, , These represent the number of ultrasonic echoes from the bottom wave; , The first and the Second wave height; The ultrasound echo loss is approximately (0.5–1.0) dB per echo. The thickness of a single-layer board.

9. The method for real-time imaging and quality assessment of resistance spot welded joints according to claim 1, characterized in that, Step 11, based on the calculation results of steps 6-10, evaluate the quality of the resistance spot weld joint, including the following steps: The quality of resistance spot welded joints is classified into qualified, overheated, incomplete penetration, weld nugget diameter too small, weld nugget thickness too small, and poor weld. The criteria for judging the quality of resistance spot welded joints as qualified are: defect area / melt nugget area ≤ 0.1, indentation depth ≤ 1 / 3 of the thickness of the first single-layer plate, attenuation coefficient ≥ 0.8, and melt nugget thickness ≥ 80%. d , melt core diameter ≥ ,in d This represents the sum of the thicknesses of the two single-layer plates; The criteria for judging the quality of resistance spot welded joints as overheated are: defect area / melt nugget area ≤ 0.1, indentation depth > 1 / 3 of the thickness of the first single-layer plate, and attenuation coefficient ≥ 2.0; The criteria for judging incomplete penetration in resistance spot welding joints are: defect area / melt nugget area > 0.1, indentation depth ≤ 1 / 3 of the first single-layer plate thickness, attenuation coefficient ≥ 0.8, and melt nugget thickness ≥ 80%. d ; The criterion for judging the quality of resistance spot welded joints as having a weld nugget diameter that is too small is: defect area / weld nugget area ≤ 0.1; The criteria for judging the quality of resistance spot welded joints with insufficient weld nugget thickness are: indentation depth ≤ 1 / 3 of the thickness of the first single-layer plate, attenuation coefficient < 0.8, and weld nugget thickness < 80%. d , melt core diameter ≥ ; The criteria for judging a resistance spot weld as a poor weld are: indentation depth ≤ 1 / 4 of the thickness of the first single-layer plate, attenuation coefficient < 0.8, and weld nugget thickness < 80%. d .

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