A laser ultrasonic detection method and system for laser precision spot welding quality

Abstract

The present invention provides a laser ultrasonic detection method and system for laser precision spot welding quality, which relates to the technical field of precision machining quality detection methods, including a laser, a dichroic mirror, a convex mirror, a displacement platform, a laser vibrometer, a first photodetector, a signal processing system, a computer, a CCD camera, adjusting the laser settings, focusing on the surface of the test piece through the convex mirror, recording the propagation signal of the ultrasonic longitudinal wave in the upper plate before welding, and recording the propagation signal of the ultrasonic longitudinal wave in the test piece after welding. The present invention has high detection efficiency and accurate and reliable detection results.

Description

Technical Field

[0001] The invention belongs to the technical field of precision machining quality detection methods, and specifically relates to a laser ultrasonic detection method and system for laser precision spot welding quality. Background Art

[0002] Laser welding technology uses high-energy laser pulses to heat tiny areas of materials. The energy of laser radiation diffuses into the material through heat conduction, melting the material to form a specific molten pool to achieve the purpose of welding. Laser welding technology does not require contact during the welding process, avoiding damage to the device surface caused by contact between the tool and the device surface. It has high processing accuracy and is a new type of microelectronic packaging and interconnection technology. It is suitable for the production and processing of various tiny core devices and is widely used in electronic communications, transportation, medical care, military and other fields.

[0003] There are a huge number of solder joints in electronic components, and the size of solder joints is small (100-500μm). During the welding process, defects such as cold solder joints, leaking solder joints, and pores may occur, which will cause fatal harm to the entire welded workpiece. At the same time, the quality of each solder joint must be qualified to ensure its normal function after the packaging is completed. Therefore, there is an urgent need for a fast and effective non-destructive testing method to conduct online detection of solder joint quality to ensure the quality of laser precision welding. At present, conventional testing methods include appearance testing, tensile testing, metallographic testing, infrared spectroscopy monitoring, and traditional high-frequency ultrasonic testing. Appearance testing can only detect appearance defects that can be observed with a microscope, and cannot detect internal defects in welding; tensile testing can intuitively judge the welding strength, and metallographic testing can accurately observe the morphology of the internal molten pool of welding, but these two methods are destructive and are only suitable for failure analysis, not for welding quality testing. Infrared spectroscopy monitoring collects plasma, reflected light, and temperature signals generated during welding to jointly predict welding quality. This detection method is effective in the welding process of large components, but the misjudgment rate is too high in the welding process of solder joints with a size of 100-500μm. Traditional ultrasonic nondestructive testing technology uses piezoelectric transducers as ultrasonic excitation and detection probes, but this detection technology has the following problems: the piezoelectric transducer needs to be in close contact with the sample, and an appropriate amount of ultrasonic coupling agent needs to be applied between the two, which cannot meet the high-speed processing of laser spot welding; the piezoelectric transducer is large in size and cannot meet the local detection of welds with a diameter of about 0.5mm; the bandwidth of the piezoelectric transducer is generally less than 20MHz, and the longitudinal resolution is low (-0.3mm), which cannot meet the weld detection of metal sheets with a total thickness of about 0.3-0.5mm. Laser ultrasonic testing uses laser excitation and reception of ultrasonic waves. It is a long-distance non-contact nondestructive testing technology with the advantages of wide bandwidth (up to 1GHz), high detection resolution (-0.1mm horizontally, -0.05mm vertically), and high detection efficiency. It can be integrated with the optical system of laser welding and is the most promising detection technology for online detection of laser precision spot welding quality.

[0004] At present, laser ultrasonic testing technology has realized the detection of defects, morphology and microstructure in metals, semiconductors, composite materials and ceramic materials, especially in harsh environments such as high temperature, high pressure, strong radiation and strong corrosion. It has an irreplaceable role and has been widely used in many fields such as aerospace aircraft maintenance, chip quality inspection, precision instrument inspection, and national defense military facility maintenance. Especially in the field of online inspection, this technology has successfully realized the surface quality inspection of laser welding process and the thickness inspection of steel pipe manufacturing, fully demonstrating its advantages in non-contact rapid inspection, but the laser ultrasonic online inspection technology for laser precision spot welding quality is still in a blank state.

[0005] Therefore, there is an urgent need to provide a laser ultrasonic detection method and system for laser precision spot welding quality with high detection efficiency and accurate and reliable detection results. Summary of the invention

[0006] The purpose of the present invention is to provide a laser ultrasonic detection method and system for laser precision spot welding quality in view of the shortcomings of the existing laser ultrasonic detection method and system for laser precision spot welding quality.

[0007] The present invention provides the following technical solutions:

[0008] A laser ultrasonic detection system for laser precision spot welding quality comprises a laser, a dichroic mirror, a convex mirror, a displacement platform, a laser vibrometer, a first photoelectric detector, a signal processing system, a computer and a CCD camera.

[0009] Preferably, the laser vibrometer comprises a detection laser and a second photodetector.

[0010] Preferably, the test piece is placed on the upper surface of the displacement platform.

[0011] A laser ultrasonic detection method for laser precision spot welding quality, applied to a laser ultrasonic detection system for laser precision spot welding quality, includes the following detection steps:

[0012] S1: According to the thickness and material of the test piece, taking into account the ultrasonic excitation efficiency and non-destructiveness to the test piece, select the laser for laser precision spot welding quality inspection, and determine the single-side and transmission inspection methods according to the placement of the test piece;

[0013] S2: Connect the laser, the dichroic mirror, the convex mirror, the displacement platform, the laser vibrometer, the first photodetector, the signal processing system, the computer and the CCD camera through a data cable;

[0014] S3: Use a CCD camera to monitor the focal point position of the laser on the surface of the test piece and adjust the optical path to ensure that the excitation point and the receiving point coincide on the surface of the test piece or the line connecting the two is parallel to the thickness direction of the test piece;

[0015] S4: For the unfused area, the ultrasonic wave excited by the upper surface of the upper plate propagates inside the upper plate and then reflects the ultrasonic echo at the bottom surface of the upper plate. For the fused area, since a mechanical bond has been formed between the two, the ultrasonic wave can pass through the fusion area and enter the lower plate, and the ultrasonic echo is reflected at the bottom surface of the lower plate. There is a significant difference in the time required for the ultrasonic echo to return to the upper surface of the upper plate. The propagation time of the ultrasonic echo at the solder joint can be measured to determine whether it is well fused, thereby screening out the test pieces with poor solder joints and leaked solder joints.

[0016] S5: Adjust the laser settings to emit a laser with a wavelength of 1064nm. When testing on one side, use a dichroic mirror to change the laser propagation direction and focus it on the surface of the test piece through a convex mirror.

[0017] S6: Adjust the laser vibrometer to emit a laser with a wavelength of 532nm, focus on the surface of the test piece, and record the vibration displacement of the surface of the test piece caused by the ultrasonic wave. The frequency is 1GHz, and the ultrasonic longitudinal wave signal is collected by averaging 128 times and input into the signal processing system;

[0018] S7: Record the propagation signal of the ultrasonic longitudinal wave in the upper plate before welding, and determine its propagation time t0;

[0019] S8: Record the propagation signal of the ultrasonic longitudinal wave in the test piece after welding, and determine its propagation to the test piece t1. When the ultrasonic longitudinal wave does not propagate to the lower layer after welding, there is a phenomenon of false welding or leaking welding, and the signal processing system gives an alarm instruction;

[0020] S9: When two plates in the sample are welded together, the C-scan imaging technology is used to detect the three-dimensional profile of the weld; the echo signal of the ultrasonic longitudinal wave at the interface between the weld area and the substrate is used to detect the distance between the interface and the surface by moving the detection laser according to the propagation time of the ultrasonic echo, thereby depicting the three-dimensional profile of the entire molten pool;

[0021] S10: The zero point and scanning mode, step length, range and other parameters of the displacement platform are set by computer, the scanning area is imaged according to the longitudinal wave echo time tij and amplitude Aij, and the welding contour is displayed on the computer, so as to comprehensively evaluate the quality of laser precision spot welding.

[0022] The beneficial effects of the present invention are:

[0023] 1) It adopts non-contact method of exciting and receiving ultrasonic waves, which is suitable for online detection of laser precision spot welding quality and has high detection efficiency;

[0024] 2) The frequency of high-frequency broadband laser can reach 200MHz, and the detection accuracy of laser vibrometer can reach sub-nanometer level, so the imaging resolution can reach nanometer level and the detection accuracy is high;

[0025] 3) Based on the dual-wave mixing technology of photorefractive crystal dynamic holographic diffraction grating, the adaptive heterodyne interference optical system and improved Kalman filter are used to filter out strong electromagnetic interference, which can filter out the influence of external low-frequency vibration on the interference optical path, and the reliability of data acquisition is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0027] Figure 1 It is a schematic diagram of the single-side detection of the present invention;

[0028] Figure 2 It is a schematic diagram of transmission detection of the present invention;

[0029] Figure 3 This is a schematic diagram of the detection principle of false solder joints and leak solder joints in the present invention;

[0030] Figure 4 The C-scan imaging detection principle diagram and scanning path of the entire molten pool in the present invention;

[0031] Figure 5 The principle of the laser and pattern working at the detection site (left) and the welding position mark of the detection pattern (right);

[0032] Figure 6 These are the waveforms detected at different welding positions.

[0033] The markings in the figure are: 1. Laser; 2. Dichroic mirror; 3. Convex mirror; 4. Laser vibrometer; 5. Detection laser; 6. Second photodetector; 7. First photodetector; 8. Signal processing system; 9. Test piece; 10. Displacement platform; 11. CCD camera; 12. Computer; 13. Upper plate of test piece; 14. Lower plate of test piece; 15. Unfused area; 16. Fused area; 17. Scanning path. DETAILED DESCRIPTION

[0034] like Figures 1 to 6 As shown, a laser ultrasonic detection system for laser precision spot welding quality includes a laser 1, a dichroic mirror 2, a convex mirror 3, a displacement platform 10, a laser vibrometer 4, a first photodetector 7, a signal processing system, a computer 12 and a CCD camera 11.

[0035] The laser vibrometer 4 includes a detection laser 5 and a second photodetector 6. The test piece 9 is placed on the upper surface of the displacement platform 10.

[0036] A laser ultrasonic detection method for laser precision spot welding quality, applied to a laser ultrasonic detection system for laser precision spot welding quality, includes the following detection steps:

[0037] S1: According to the thickness and material of the test piece 9, taking into account the ultrasonic excitation efficiency and the non-destructiveness of the test piece 9, the laser 1 is selected to perform laser precision spot welding quality inspection, and the single-side inspection method and the transmission inspection method are determined according to the placement of the test piece 9;

[0038] S2: Connect the laser 1, the dichroic mirror 2, the convex mirror 3, the displacement platform 10, the laser vibrometer 4, the first photodetector 7, the signal processing system, the computer 12 and the CCD camera 11 through a data line;

[0039] S3: Use the CCD camera 11 to monitor the focus position of the laser on the surface of the test piece 9 and adjust the optical path to ensure that the excitation point and the receiving point coincide on the surface of the test piece 9 or the line connecting the two is parallel to the thickness direction of the test piece 9;

[0040] S4: For the unfused area 15, the ultrasonic wave excited by the upper surface of the upper plate propagates inside the area and the ultrasonic echo is reflected on the bottom surface of the upper plate. For the fused area 16, since a mechanical bond has been formed between the two, the ultrasonic wave can pass through the fusion area and enter the lower plate, and the ultrasonic echo is reflected on the bottom surface of the lower plate. There is a significant difference in the time required for the ultrasonic echo to return to the upper surface of the upper plate. The propagation time of the ultrasonic echo at the solder joint can be measured to determine whether it is well fused, thereby screening out the test pieces with poor solder joints and leaked solder joints.

[0041] S5: Adjust the laser 1 setting to emit a laser with a wavelength of 1064 nm. During single-side detection, use a dichroic mirror to change the laser propagation direction and focus it on the surface of the test piece 9 through a convex mirror 3.

[0042] S6: Adjust the laser vibrometer 4 to emit a laser with a wavelength of 532 nm, focus on the surface of the test piece 9, and record the vibration displacement of the surface of the test piece 9 caused by the ultrasonic wave. The frequency is 1 GHz, and the ultrasonic longitudinal wave signal is collected by averaging 128 times and input into the signal processing system;

[0043] S7: Record the propagation signal of the ultrasonic longitudinal wave in the upper plate before welding, and determine its propagation time t0;

[0044] S8: Record the propagation signal of the ultrasonic longitudinal wave in the test piece 9 after welding, and determine the propagation of the test piece 9t1. When the ultrasonic longitudinal wave does not propagate to the lower plate after welding, there is a phenomenon of cold welding or leaking welding, and the signal processing system gives an alarm instruction;

[0045] S9: When two plates in the sample are welded together, the C-scan imaging technology is used to detect the three-dimensional profile of the weld; the echo signal of the ultrasonic longitudinal wave at the interface between the weld area and the substrate is used to detect the distance between the interface and the surface by moving the detection laser according to the propagation time of the ultrasonic echo, thereby depicting the three-dimensional profile of the entire molten pool;

[0046] S10: The zero point and scanning mode, step length, range and other parameters of the displacement platform 10 are set through the computer 12, the scanning area is imaged according to the longitudinal wave echo time tij and amplitude Aij, and the welding contour is displayed on the computer 12, so as to comprehensively evaluate the quality of laser precision spot welding.

[0047] Example

[0048] During the detection process, the computer 12 first sends a command to the laser 1 to excite a high-frequency broadband laser (wavelength of 1064nm), and uses a dichroic mirror 2 to change the laser propagation direction by 90°. The laser is focused on the surface of the test piece to be tested through a convex mirror 3. Due to the thermoelastic effect, a high-frequency broadband ultrasonic longitudinal wave is generated in the test piece, and the position of the laser focus point on the test piece surface is displayed in real time using a CCD camera 11. The longitudinal wave propagates along the thickness direction of the test piece to the bottom surface and is reflected. When the reflected wave propagates to the surface of the test piece, the surface vibrates. The laser vibrometer 4 (wavelength of 532nm) uses the principle of light interference to measure the displacement signal generated by the vibration of the test piece. The displacement platform 10 can be controlled by the computer 12 to perform a C scan on the test piece, and the signal is input into the signal processing system through the USB interface. The system software based on the MATLAB language in the computer 12 completes the control of the entire detection system and the real-time display of the ultrasonic detection results, so as to realize the online detection of the quality of laser precision spot welding on the same side of the sample.

[0049] Transmission laser ultrasonic testing device Figure 2 As shown, the detection process is the same as the above-mentioned single-side method, and ultrasonic waves can be excited on one side of the test piece and received on the other side.

[0050] The main functions of the detection software based on MATLAB programming in the above-mentioned computer 12 include ultrasonic signal data acquisition, filtering, wavelet transform, sound-time cross-correlation algorithm, C-scan imaging, welding depth and area quantitative analysis, etc., which can realize the detection and evaluation of laser precision welding quality.

[0051] The laser 1 is used to excite ultrasonic waves (longitudinal waves) in the welded parts, and the fiber laser vibrometer 4 detects the weak displacement of the welded parts surface caused by the longitudinal waves. The integrated linkage multi-information fusion technology of active visual measurement and laser ultrasonic non-destructive testing is adopted to realize micron-level imaging of the surface morphology, material defects, microstructure and stress distribution of precision laser welding, and complete three-dimensional reconstruction imaging of typical defects, including: broadband high-frequency laser 1, fiber laser vibrometer 4, test piece 9 and displacement platform 10, signal processing and imaging system, connected to computer 12 via data line.

[0052] During the detection process, the computer 12 first sends a command to the laser 1 to excite a high-frequency broadband laser (wavelength of 1064nm), uses a dichroic mirror 2 to change the laser propagation direction by 90°, and uses a convex mirror 3 to focus the laser on the surface of the test piece 9 to be tested. Due to the thermoelastic effect, a high-frequency broadband ultrasonic longitudinal wave is generated in the test piece 9, and the CCD camera 11 is used to display the position of the laser focus point on the surface of the test piece 9 in real time. The longitudinal wave propagates in the test piece 9 along its thickness direction to the bottom surface and is reflected. When the reflected wave propagates to the surface of the test piece 9, it causes the surface to vibrate. The laser vibrometer 4 (wavelength of 532nm) uses the interference principle of light to measure the displacement signal generated by the vibration of the test piece 9. The displacement platform 10 can be controlled by the computer 12 to perform a C scan on the test piece 9, and input into the signal processing system through the USB interface. The system software based on the MATLAB language in the computer 12 completes the control of the entire detection system and the real-time display of the ultrasonic detection results, so as to realize the online detection of the quality of laser precision spot welding on the same side of the sample. Transmission laser ultrasonic detection device such as Figure 2 As shown, the detection process is the same as the above-mentioned single-side detection, and ultrasonic waves can be excited on one side of the test piece 9 and received on the other side.

[0053] The main functions of the detection software based on MATLAB programming in the above-mentioned computer 12 include ultrasonic signal data acquisition, filtering, wavelet transform, sound-time cross-correlation algorithm, C-scan imaging, welding depth and area quantitative analysis, etc., which can realize the detection and evaluation of laser precision welding quality.

[0054] It can realize online detection of spot welding quality with high detection efficiency and accurate and reliable detection results. At the same time, this detection technology is not limited to laser precision spot welding quality detection, but is also suitable for residual stress measurement and structural mechanical properties testing of metal welding and heat treatment under extreme environments such as high temperature and high pressure.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A laser ultrasonic detection method for laser precision spot welding quality, characterized in that: Based on a laser ultrasonic detection system for laser precision spot welding quality, the detection system includes a laser, a convex mirror, a displacement platform, a laser vibrometer, a first photoelectric detector, a signal processing system, a computer and a CCD camera; The laser vibrometer comprises a detection laser and a second photodetector; The test piece is placed on the upper surface of the displacement platform, and the detection steps include: S1: According to the thickness and material of the test piece, taking into account the ultrasonic excitation efficiency and non-destructiveness to the test piece, select the laser for laser precision spot welding quality inspection, and determine the single-sided and transmission inspection methods according to the placement of the test piece. In the case of single-sided inspection, the inspection system also includes a dichroic mirror; S2: Connect the laser, convex mirror, displacement platform, laser vibrometer, first photodetector, signal processing system, computer, CCD camera, and dichroic mirror for unilateral detection through data cables; S3: Use a CCD camera to monitor the focal point position of the laser on the surface of the test piece and adjust the optical path to ensure that the excitation point and the receiving point coincide on the surface of the test piece or the line connecting the two is parallel to the thickness direction of the test piece; S4: For the unfused area, the ultrasonic wave excited by the upper surface of the upper plate propagates inside the upper plate and then reflects the ultrasonic echo at the bottom surface of the upper plate. For the fused area, since a mechanical bond has been formed between the two, the ultrasonic wave can pass through the fusion area and enter the lower plate, and the ultrasonic echo is reflected at the bottom surface of the lower plate. There is a significant difference in the time required for the ultrasonic echo to return to the upper surface of the upper plate. The propagation time of the ultrasonic echo at the solder joint can be measured to determine whether it is well fused, thereby screening out the test pieces with false solder joints and leaked solder joints. S5: Adjust the laser settings to emit a laser with a wavelength of 1064nm. When testing on one side, use a dichroic mirror to change the laser propagation direction and focus it on the surface of the test piece through a convex mirror. S6: Adjust the laser vibrometer to emit a laser with a wavelength of 532nm, focus it on the surface of the test piece, and record the vibration displacement of the surface of the test piece caused by the ultrasonic wave. The sampling frequency is 1GHz, and the ultrasonic longitudinal wave signal is collected by averaging 128 times and input into the signal processing system; S7: Record the propagation signal of the ultrasonic longitudinal wave in the upper plate before welding, and determine its propagation time t0; S8: Record the propagation signal of the ultrasonic longitudinal wave in the test piece after welding, and determine its propagation time t1. If the ultrasonic longitudinal wave does not propagate to the lower plate after welding, there is a phenomenon of cold welding or leaking welding, and the signal processing system gives an alarm instruction; S9: When two plates in the sample are welded together, the C-scan imaging technology is used to detect the three-dimensional profile of the weld; the echo signal of the ultrasonic longitudinal wave at the interface between the welding area and the substrate is used, and the distance between the interface and the surface is detected by moving the detection laser according to the propagation time of the ultrasonic echo, thereby depicting the three-dimensional profile of the entire molten pool; S10: The zero point, scanning mode, step length and range parameters of the displacement platform are set by computer, the scanning area is imaged according to the longitudinal wave echo time tij and amplitude Aij, and the weld contour is displayed on the computer, so as to comprehensively evaluate the quality of laser precision spot welding.

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