Infrared nondestructive testing method based on dipulse differential excitation
The infrared nondestructive testing method based on dual-pulse differential excitation solves the problems of slow detection speed and low sensitivity of micro-weld joints by utilizing the synergistic effect of pre-excitation and main excitation. It enables rapid and efficient defect detection of weld joints made of dissimilar materials and is suitable for online inspection.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-25
- Publication Date
- 2026-03-24
AI Technical Summary
Existing non-destructive testing methods for micro-weld joints suffer from slow testing speed, low sensitivity, and inability to perform online testing. In particular, internal defects such as incomplete welds and lack of fusion are easily generated in weld joints made of dissimilar materials. Furthermore, existing equipment is expensive or poses a radiation risk.
An infrared nondestructive testing method using dual-pulse differential excitation is employed. A thermal background field is established by pre-excitation with a first laser pulse, and the main excitation is performed with a second laser pulse. Two thermal images are recorded and differential calculations are performed. The differential thermal images are then used to determine solder joint defects.
It significantly improves the detection signal-to-noise ratio and sensitivity, can quickly identify micron-level defects, has a fast detection speed, is suitable for online detection, and has low equipment cost and does not require radiation protection.
Smart Images
Figure CN121721086A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to an infrared nondestructive testing method based on dual-pulse differential excitation, belonging to the field of defect detection technology. Background Technology
[0002] With the rapid development of new energy vehicles, high-end consumer electronics, and aerospace, the application of laser micro-spot welding structures using dissimilar materials (such as copper and steel) is becoming increasingly widespread. The quality of such welds directly determines the reliability and safety of the product. However, due to the significant differences in the physical properties of dissimilar materials (such as melting point, thermal conductivity, and coefficient of thermal expansion), the welding process is highly susceptible to internal defects such as incomplete welds and lack of fusion.
[0003] Currently, non-destructive testing methods for this type of micro-solder joint have significant limitations:
[0004] X-ray inspection is insensitive to two-dimensional planar defects perpendicular to the X-ray direction (such as incomplete fusion), and the equipment is expensive, poses radiation safety risks, and is difficult to integrate into online production lines. Ultrasonic inspection requires a coupling agent, which can contaminate precision electronic components, and the inspection speed is slow, failing to meet the cycle time requirements of online full inspection. Traditional single-pulse infrared inspection, for high thermal conductivity materials such as copper and aluminum, causes the heat generated by a single pulse excitation to dissipate rapidly, resulting in extremely weak thermal anomaly signals caused by tiny defects, low signal-to-noise ratio, and defects easily being drowned out by background noise. Although traditional differential techniques such as phase-locked-phase thermal imaging can suppress some noise, they require multiple cycles of thermal excitation and data acquisition, resulting in slow inspection speeds and failing to achieve millisecond-level rapid inspection.
[0005] Therefore, there is an urgent need for a micro-weld joint defect detection solution that can balance high speed, high sensitivity, and suitability for online detection. Summary of the Invention
[0006] To address the issues of weak thermal response signals and low signal-to-noise ratio in existing nondestructive testing of micro-solder joints, this invention provides an infrared nondestructive testing method based on dual-pulse differential excitation.
[0007] The present invention provides an infrared nondestructive testing method based on dual-pulse differential excitation, comprising:
[0008] The test specimen is first excited by a first laser pulse to generate a stable initial temperature rise in the test specimen area of the solder joint, and the first excitation thermal image is recorded; after a set time interval, the test specimen is second excited by a second laser pulse, and the second excitation thermal image is recorded; the energy density of the second laser pulse is greater than the energy density of the first laser pulse;
[0009] A differential thermal image is obtained by performing a differential thermal image on the second excitation thermal image and the first excitation thermal image; the presence of defects in the weld area to be tested is determined based on the differential thermal image.
[0010] According to the infrared nondestructive testing method based on dual-pulse differential excitation of the present invention, the ratio of the energy density of the second laser pulse to the energy density of the first laser pulse ranges from 10:1 to 3:1.
[0011] According to the infrared nondestructive testing method based on dual-pulse differential excitation of the present invention, the power of the first laser pulse is 8~10W and the power of the second laser pulse is 20~30W.
[0012] According to the infrared nondestructive testing method based on dual-pulse differential excitation of the present invention, the laser spot diameter of the two laser pulses is 0.5~2mm, and the laser waveform is a rectangular wave.
[0013] According to the infrared nondestructive testing method based on dual-pulse differential excitation of the present invention, the set duration is 10 to 30 ms.
[0014] According to the infrared nondestructive testing method based on dual-pulse differential excitation of the present invention, the method for performing differential operations on the second excitation thermal image and the first excitation thermal image is as follows:
[0015] The differential thermal image is obtained by subtracting the corresponding chronological image sequence from the chronological image sequence in the second excitation thermal image.
[0016] According to the infrared nondestructive testing method based on dual-pulse differential excitation of the present invention, the method for determining whether there are defects in the area of the weld joint to be tested based on the differential thermal image is as follows:
[0017] The maximum differential temperature value in the differential thermal image is selected and compared with the differential temperature threshold. If the maximum differential temperature value is greater than the differential temperature threshold, it is determined that there is a defect in the area of the weld point to be tested.
[0018] According to the infrared nondestructive testing method based on dual-pulse differential excitation of the present invention, the differential temperature threshold ranges from 10°C to 50°C.
[0019] According to the infrared non-destructive testing method based on dual-pulse differential excitation of the present invention, a laser is used to emit laser pulses and an infrared thermal imager is used to acquire thermal images.
[0020] The laser spot emitted by the laser pulse coincides with the center of the field of view of the infrared thermal imager.
[0021] The beneficial effects of this invention are as follows: The method of this invention enables rapid online identification of defects in micro-weld joints made of dissimilar materials. It applies a dual-pulse laser sequence with a predetermined energy ratio and interval to the workpiece under test. The first pulse is used for pre-excitation to establish a thermal background field, and the second pulse is used for main excitation to elicit the nonlinear thermal response of the defect. Subsequently, the thermal image sequences after the two excitations are acquired and differentially processed to effectively suppress background noise and maximize the contrast of the defect area. This invention significantly improves the signal-to-noise ratio, accuracy, and efficiency of detecting internal defects in micro-weld joints made of highly thermally conductive and highly reflective materials.
[0022] This invention employs dual-pulse differential excitation technology, significantly enhancing the thermal response signal in defect areas through the synergy of pre-excitation and main excitation, thus solving the problem of low signal-to-noise ratio in the detection of micro-defects in high thermal conductivity materials. Compared with existing single-pulse infrared detection, this invention significantly improves detection sensitivity, enabling the identification of micron-level defects; greatly increases detection speed, controlling single-point detection time to within 1 second; exhibits excellent anti-interference capabilities, effectively suppressing surface emissivity inhomogeneity and environmental reflection interference; and achieves quantitative evaluation of solder joint quality, providing a reliable basis for product quality control. Compared with existing X-ray detection, this invention requires no radiation protection, has lower equipment costs, and is more suitable for online detection applications. Attached Figure Description
[0023] Figure 1 This is a flowchart of the infrared nondestructive testing method based on dual-pulse differential excitation described in this invention;
[0024] Figure 2 This is a schematic diagram of a system for implementing the method of the present invention. Detailed Implementation
[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.
[0026] Specific Implementation Method 1: Combination Figure 1 As shown, this invention provides an infrared nondestructive testing method based on dual-pulse differential excitation, comprising:
[0027] The test specimen is first excited by a first laser pulse to generate a stable initial temperature rise in the test specimen area of the solder joint, and the first excitation thermal image is recorded; after a set time interval, the test specimen is second excited by a second laser pulse, and the second excitation thermal image is recorded; the energy density of the second laser pulse is greater than the energy density of the first laser pulse;
[0028] A differential thermal image is obtained by performing a differential thermal image on the second excitation thermal image and the first excitation thermal image; the presence of defects in the weld area to be tested is determined based on the differential thermal image.
[0029] Furthermore, the ratio of the energy density of the second laser pulse to that of the first laser pulse ranges from 10:1 to 3:1.
[0030] As an example, the power of the first laser pulse is 8~10W, and the power of the second laser pulse is 20~30W.
[0031] As an example, the laser spot diameters of both laser pulses are 0.5~2mm, and the laser waveforms are rectangular waves.
[0032] As an example, the set duration is 10 to 30 ms.
[0033] The specific duration of the interval between the two laser pulses is determined based on the thermal conductivity of the material.
[0034] Furthermore, the method for performing differential calculations between the second-excitation thermal image and the first-excitation thermal image is as follows:
[0035] The differential thermal image is obtained by subtracting the corresponding chronological image sequence from the chronological image sequence in the second excitation thermal image.
[0036] The method for determining whether there are defects in the area of the weld point under test based on differential thermal imaging is as follows:
[0037] The maximum differential temperature value in the differential thermal image is selected and compared with the differential temperature threshold. If the maximum differential temperature value is greater than the differential temperature threshold, it is determined that there is a defect in the area of the weld point to be tested; otherwise, the weld point is determined to be qualified.
[0038] In this embodiment, the differential temperature threshold ranges from 10°C to 50°C.
[0039] In this embodiment, a laser is used to emit laser pulses, and an infrared thermal imager is used to acquire thermal images;
[0040] The laser spot emitted by the laser pulse coincides with the center of the field of view of the infrared thermal imager.
[0041] Combination Figure 2As shown, the system for implementing the method of the present invention may include a pulsed laser 1, an infrared thermal imager 2, an arbitrary waveform generator 3, a synchronous control system 4, a computer 5, a test piece 6, and a work platform 7. The synchronous control system 4 issues a command to trigger the arbitrary waveform generator 3 to emit a first laser pulse through the pulsed laser 1 to pre-excite the test piece 6, and simultaneously triggers the infrared thermal imager 2 to start acquiring data. After a preset interval, a second laser pulse is emitted again to mainly excite the test piece, and simultaneously triggers the infrared thermal imager 2 to start acquiring data. Finally, the thermal image data is transmitted to the computer 5 for differential calculation and quality judgment. The test piece 6 is fixed on the work platform 7.
[0042] The testing process is as follows:
[0043] Place the test piece on the workbench, adjust the laser irradiation position, and position the infrared thermal imager directly at the solder joint of the test piece. Use the first laser pulse to excite the area of the solder joint to be tested. The energy density of the first pulse is E1.
[0044] After a preset interval Then, a second laser pulse is used to excite the same area. The energy density of the second laser pulse is E2, and E2>E1.
[0045] The first laser pulse with lower energy heats the workpiece surface uniformly, resulting in a mild and stable initial temperature rise. The second laser pulse with higher energy excites the workpiece surface a second time. An infrared thermal imager is used to record the thermal images of the two laser excitations.
[0046] The final thermal image is obtained by performing a difference operation on the two thermal images.
[0047] Under the same parameters, the final thermal image of the test piece is compared with the thermal image of a test piece with no solder joint defects to determine whether there are defects in the solder joints of the test piece.
[0048] The ratio of E1:E2 can be selected between 1:3 and 1:6.
[0049] The first laser pulse has a power of 8W, and the second laser pulse has a power of 20W. The laser spot diameter is 2mm.
[0050] The value ranges from 10 to 20 milliseconds.
[0051] Example:
[0052] Taking the quality inspection of the copper-steel shielding cover on a smartphone chip as an example, the process includes the following steps:
[0053] Step 1: Fix the test piece onto the dedicated stage and secure it with clamps. Ensure that the laser spot coincides with the center of the infrared thermal imager's field of view.
[0054] Step 2: Set the dual-pulse excitation parameters: Set the energy density of the first laser pulse E1 to 8 J / cm², and the energy density of the second laser pulse E2 to 32 J / cm² (energy ratio E1:E2 = 1:5), with the interval time... The ms time was set to 15ms. This parameter was determined based on the thermal diffusivity of copper and optimized through pre-experimentation. The power of the first laser pulse was 8W, the power of the second laser pulse was 20W, and the spot diameter was 2mm.
[0055] Step 3: Start the detection process. The synchronous control unit first triggers the laser to emit the first pulse to pre-excite the solder joint area of the shielding cover, and the infrared thermal imager starts to collect data simultaneously, obtaining the first thermal image sequence S1; after waiting for 15ms, the synchronous control unit triggers the laser again to emit a second pulse with higher energy for main excitation, and the infrared thermal imager continues to collect data, obtaining the second thermal image sequence S2.
[0056] Step 4: The image processing unit performs differential processing on the acquired thermal image sequence: Select thermal image frame F2 25 ms after the second pulse excitation from sequence S2; perform differential operation: differential thermal image = F2 - F1, to obtain a differential thermal image with high signal-to-noise ratio.
[0057] Step 5: Determine solder joint quality based on differential thermal images. Extract the characteristic parameters from the image: maximum differential temperature value. Set quality criterion thresholds: ;like If the weld does not meet the standard, the weld is considered defective; otherwise, it is considered acceptable.
[0058] Comparative experiments have verified that the signal-to-noise ratio of the method of this invention is 50% higher than that of the single-pulse method, the detection sensitivity is significantly improved, it can identify micron-level defects, and the detection speed is less than 1 second, realizing rapid detection of defects in high thermal conductivity materials.
[0059] The method of this invention is based on active infrared thermography technology and is particularly suitable for online rapid identification of internal defects in weld joints of dissimilar materials such as copper and steel.
[0060] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.
Claims
1. An infrared nondestructive testing method based on dual-pulse differential excitation, characterized in that... include: The first laser pulse is used to excite the test area of the weld point on the specimen for the first time, so that the test area of the weld point generates a stable initial temperature rise, and the first excitation thermal image is recorded. After a set interval, a second laser pulse is used to excite the weld area of the test piece a second time, and the second excitation thermal image is recorded; the energy density of the second laser pulse is greater than the energy density of the first laser pulse; A differential thermal image is obtained by performing a differential thermal image on the second excitation thermal image and the first excitation thermal image; the presence of defects in the weld area to be tested is determined based on the differential thermal image.
2. The infrared nondestructive testing method based on dual-pulse differential excitation according to claim 1, characterized in that, The ratio of the energy density of the second laser pulse to that of the first laser pulse ranges from 10:1 to 3:
1.
3. The infrared nondestructive testing method based on dual-pulse differential excitation according to claim 1, characterized in that, The power of the first laser pulse is 8~10W, and the power of the second laser pulse is 20~30W.
4. The infrared nondestructive testing method based on dual-pulse differential excitation according to claim 1, characterized in that, Both laser pulses have laser spot diameters of 0.5~2mm and laser waveforms are rectangular waves.
5. The infrared nondestructive testing method based on dual-pulse differential excitation according to claim 1, characterized in that, The set duration is 10 to 30 ms.
6. The infrared nondestructive testing method based on dual-pulse differential excitation according to claim 1, characterized in that, The method for performing differential calculations between the second-excitation thermal image and the first-excitation thermal image is as follows: The differential thermal image is obtained by subtracting the corresponding chronological image sequence from the chronological image sequence in the second excitation thermal image.
7. The infrared nondestructive testing method based on dual-pulse differential excitation according to claim 6, characterized in that, The method for determining whether there are defects in the area of the weld point under test based on differential thermal imaging is as follows: The maximum differential temperature value in the differential thermal image is selected and compared with the differential temperature threshold. If the maximum differential temperature value is greater than the differential temperature threshold, it is determined that there is a defect in the area of the weld point to be tested.
8. The infrared nondestructive testing method based on dual-pulse differential excitation according to claim 7, characterized in that, The differential temperature threshold ranges from 10°C to 50°C.
9. The infrared nondestructive testing method based on dual-pulse differential excitation according to claim 1, characterized in that, Laser pulses are emitted using a laser, and thermal images are acquired using an infrared thermal imager; The laser spot emitted by the laser pulse coincides with the center of the field of view of the infrared thermal imager.