Laser transmission welding quality detection method based on flexible stress-strain sensor

Abstract

The application discloses a laser transmission welding quality detection method based on a flexible stress strain sensor, and comprises the following steps: laminating a light transmission layer film and a light absorption layer film; attaching a sensor array to the back of the light absorption layer film and connecting array units of the sensor array to a multi-channel data acquisition system; projecting laser for welding and synchronously collecting compressive stress characteristic parameters of the sensor array; performing off-line quality detection on weld samples prepared under different welding parameters, measuring weld depth characteristic parameters through an optical microscope; and establishing a multiple regression model of the compressive stress characteristic parameters and the weld depth characteristic parameters. The application arranges a flexible stress strain sensor array on the back of a weld, collects stress distribution information in a welding process in real time, and evaluates the internal quality of the weld through data processing and an established correlation model, so that an effective technical means is provided for realizing laser welding with high precision, high quality and high stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser welding, in particular to a laser transmission welding quality detection method based on a flexible stress-strain sensor. BACKGROUND

[0002] With the continuous development of precision manufacturing technology, laser transmission welding has been widely used in the fields of aerospace, automobile manufacturing, electronic packaging and medical devices due to its high precision, high efficiency, low deformation and other advantages. However, the quality of laser transmission welding is affected by many factors, including welding energy input, weld penetration, weld appearance, internal bubbles or cracks, etc., among which the slight changes in weld appearance and internal defects may directly affect the mechanical properties, reliability and service life of the welded joint.

[0003] Traditional weld quality detection methods mainly include optical microscopic measurement, ultrasonic detection, X-ray detection and laser confocal scanning. Although these methods can provide high-precision measurement, they have the following problems: the detection equipment is expensive, bulky and less adaptable to industrial site environment; the detection process is complex, and the adaptability to weld detection of complex curved surfaces or flexible structures is low; offline detection is usually required, making it difficult to realize real-time quality monitoring and feedback control during welding.

[0004] In recent years, flexible stress-strain film sensors have been widely used in structural health monitoring, human biological signal detection and other fields due to their high sensitivity, ability to conform to curved surfaces, low stiffness and easy integration. The introduction of flexible sensor technology into laser transmission welding weld quality detection is expected to achieve high-precision, real-time weld quality monitoring without affecting the weld structure. SUMMARY

[0005] The present application provides a laser transmission welding quality detection method based on a flexible stress-strain sensor to solve the problems in the prior art. By arranging a flexible stress-strain sensor array on the back of the weld, the appearance and stress distribution information during welding can be collected in real time, and combined with data analysis, high-precision, high-efficiency weld quality evaluation can be achieved.

[0006] To solve the above technical problems, the present application provides a laser transmission welding quality detection method based on a flexible stress-strain sensor, comprising the following steps:

[0007] S1, laminating a light transmission layer film and a light absorption layer film, and placing a gasket between them;

[0008] S2, attaching a flexible stress-strain sensor array to the side of the light absorption layer film away from the light transmission layer film, and connecting the array units of the sensor array to a multi-channel data acquisition system;

[0009] S3, laser projection welding is carried out along the predetermined welding seam path, and the stress characteristic parameters of the sensor array are synchronously collected through a multi-channel data collection system; wherein the center line of the predetermined welding seam path is aligned with the array unit center line of the sensor array;

[0010] S4, the welding seam samples prepared under different welding parameters are subjected to offline quality detection, and the welding seam depth characteristic parameters are measured through an optical microscope;

[0011] S5, a multivariate regression model is established between the stress characteristic parameters and the welding seam depth characteristic parameters, and the model formula is:

[0012] (1) ;

[0013] (2) ;

[0014] (3) ;

[0015] Wherein, P is the laser power, unit W; v is the welding speed, unit mm / s; sigma is the average stress, specifically the average stress of each sensor unit on the welding seam path, unit N; d is the average welding seam depth, unit pm; t is the film thickness of the light transmission layer, unit mm.

[0016] The present application sets a flexible stress and strain sensor array on the back of the welding seam, and establishes a corresponding relationship model between the stress characteristic parameters of the extracted sensor array and the actual welding seam depth through experimental calibration; formula 1 can predict the average stress of the welding seam when the welding seam is generated through power and welding speed, formula 2 can predict the average depth of the welding seam through power and welding speed, formula 3 is a matrix of formula 1 and formula 2, and the average stress can be predicted through power and welding speed, and the corresponding welding seam depth can be predicted from the average stress. By using this model, the real-time monitored stress data can be used to evaluate the morphology quality grade of the current welding seam.

[0017] Further, the preparation method of the flexible stress and strain sensor array comprises the following steps:

[0018] (1) spraying a mixed suspension of graphene nanosheets and polyurethane on a flexible substrate, and forming a graphene / polyurethane sensitive layer after drying;

[0019] (2) cutting a pre-patterned conductive film into a predetermined sensor array unit shape and size, and adhering the pre-patterned conductive film in an array on the graphene / polyurethane sensitive layer;

[0020] (3) pasting a fine wire in the array unit area through a conductive tape, to obtain a flexible stress and strain sensor array.

[0021] Further, the flexible substrate is a polyimide film with a thickness of 40-60 μm. The polyimide film has good flexibility, temperature resistance (> 200℃) and chemical stability.

[0022] Further, the concentration of graphene nanosheets in the mixed suspension is 0.5-5 wt%, preferably 1 wt%;

[0023] And / or, the solvent of the mixed suspension is N,N-dimethylformamide; the polyurethane in the mixed suspension acts as an adhesive.

[0024] Further, the temperature of the drying is 75-85℃, preferably 80℃, and the time is 1-3h, preferably 2h.

[0025] Further, the thickness of the graphene / polyurethane sensitive layer is 2.5-10 μm, preferably 5 μm.

[0026] Further, the pre-patterned conductive film is a pre-plated copper polyimide film, and the surface is engraved with a circuit pattern;

[0027] And / or, the electrode area of the pre-patterned conductive film is connected with the graphene / polyurethane sensitive layer through conductive adhesive or anisotropic conductive film.

[0028] Further, in S1, the light-transmitting layer film is a polycarbonate film;

[0029] And / or, the light-absorbing layer film is a polyethylene plastic film doped with 0.02-0.1 wt% carbon black, and the preferred concentration of carbon black is 0.05 wt%.

[0030] Further, before S3, the flexible stress-strain sensor is pre-processed: for the original signal collected from each channel, the direct current drift and high frequency noise are removed through a band-pass filter (0.1 Hz - 1 kHz), and the signal is converted into a stress value.

[0031] Further, in S3, the parameters of the laser transmission welding are: laser power 0.1-20 W, welding rate 1-5 mm / s.

[0032] The beneficial effects of the present application are:

[0033] The present application arranges a flexible stress-strain sensor array on the back of the weld, collects the stress distribution information in real time during the welding process, and evaluates the internal quality of the weld online through data processing and an established correlation model, providing an effective technical means for realizing high-precision, high-quality and high-stability laser welding. This technology can be widely applied in precision manufacturing, aerospace, microelectronic packaging and flexible electronic manufacturing fields, and provides important technical support for high-quality laser transmission welding. Attached Figure Description

[0034] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram showing the connection relationship of each component in the laser transmission welding quality detection method based on a flexible stress-strain sensor of the present invention.

[0036] Figure 2 This is a schematic diagram of the flexible stress-strain sensor array of Embodiment 1 of the present invention;

[0037] Figure 3 The sensor array in Embodiment 1 of this invention collects stress data;

[0038] Figure 4 These are images of offline weld depth measurement from Embodiment 1 of the present invention;

[0039] The labels in the diagram are as follows: 1. Transparent film, 2. Light-absorbing film, 3. Gasket, 4. Flexible stress-strain sensor array. Detailed Implementation

[0040] The technical solution of the present invention will be clearly and completely described below with reference to 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.

[0041] This embodiment provides a laser transmission welding quality inspection method based on a flexible stress-strain sensor, including the following steps:

[0042] S1. The light-transmitting layer film 1 and the light-absorbing layer film 2 are stacked together, with a spacer 3 placed between them; for example Figures 1-2 As shown, the gaskets are used to reduce the contact between the light-transmitting layer film and the light-absorbing layer film, and the thickness of each gasket can be the same or different.

[0043] S2. Attach the flexible stress-strain sensor array 4 to the side of the light-absorbing layer film away from the light-transmitting layer film, i.e. away from the laser incident side, and connect the array unit of the sensor array to the multi-channel data acquisition system.

[0044] The fabrication method of the flexible stress-strain sensor array includes the following steps:

[0045] (1) Spraying a mixed suspension of graphene nanosheets and polyurethane on a flexible substrate to form a graphene / polyurethane sensitive layer after drying;

[0046] (2) Cutting a pre-patterned conductive film into a predetermined sensor array unit shape and size, and adhering it in an array on the graphene / polyurethane sensitive layer;

[0047] (3) Adhering fine wires in the array unit area by conductive tape to obtain a flexible stress and strain sensor array;

[0048] S3, laser projection welding along a predetermined weld path, and synchronously collecting the compressive stress characteristic parameters of the sensor array by a multi-channel data acquisition system; wherein the center line of the predetermined weld path is aligned with the center line of the array unit of the sensor array;

[0049] S4, off-line quality detection of the weld samples prepared under different welding parameters, and measuring the weld depth characteristic parameters by an optical microscope;

[0050] S5, establishing a multiple regression model of the compressive stress characteristic parameters and the weld depth characteristic parameters, and the model formula is:

[0051] (1);

[0052] (2);

[0053] (3);

[0054] wherein P is the laser power, unit W; v is the welding speed, unit mm / s; σ is the average compressive stress, specifically the average value of the compressive stress of each sensor unit on the weld path, unit N; d is the average weld depth, unit μm; and t is the thickness of the light transmission layer film, unit mm.

[0055] As a preferred embodiment, the flexible substrate is a polyimide film with a thickness of 40-60 μm; the polyimide film has good flexibility, temperature resistance (>200℃) and chemical stability. The concentration of graphene nanosheets in the mixed suspension is 0.5-5 wt%, preferably 1 wt%; the solvent of the mixed suspension is N,N-dimethylformamide; and the polyurethane in the mixed suspension serves as an adhesive. The drying temperature is 75-85℃, preferably 80℃, and the time is 1-3 h, preferably 2 h. The thickness of the graphene / polyurethane sensitive layer is 2.5-10 μm, preferably 5 μm. The pre-patterned conductive film is a copper-plated polyimide film with a circuit pattern engraved on the surface; and the electrode area of the pre-patterned conductive film is connected to the graphene / polyurethane sensitive layer by conductive glue or an anisotropic conductive film.

[0056] As a preferred embodiment, in S1, the light-transmitting layer film is a polycarbonate film; and the light-absorbing layer film is a polyethylene plastic film doped with 0.02-0.1 wt% carbon black, preferably 0.05 wt% carbon black.

[0057] As a preferred embodiment, before S3, the flexible stress-strain sensor is pre-processed: for the original signal collected in each channel, a band-pass filter (0.1 Hz - 1 kHz) is used to remove the DC drift and high-frequency noise, and the signal is converted into a stress value.

[0058] As a preferred embodiment, in S3, the parameters of the laser transmission welding are: laser power 0.1-20 W, welding rate 1-5 mm / s.

[0059] Example 1

[0060] This example relates to a laser transmission welding quality detection method based on a flexible stress-strain sensor, comprising the following steps:

[0061] (1) Preparation of a high-sensitivity flexible stress-strain sensor array

[0062] A polyimide (PI) film with a thickness of 50 pm is selected as the flexible substrate.

[0063] A suspension of graphene nanosheet and polyurethane (PU) composite material (graphene concentration of about 1 wt%, dispersed in N,N-dimethylformamide DMF solvent, with the addition of PU adhesive) is uniformly sprayed on the PI flexible substrate by spraying. After spraying, it is dried in an 80°C oven for 2 h to form a graphene / PU composite sensitive film with a thickness of about 5 pm.

[0064] A commercially available pre-patterned conductive film: a copper-coated polyimide film with an etched circuit pattern on the surface. The pre-patterned conductive film is cut into the required shape and size of the sensor array. The cut pre-patterned conductive film is covered and adhered to the graphene / PU sensitive film, ensuring good contact between the electrode area of the conductive film and the sensitive layer, and conductive adhesive is used for bonding. In this example, the array is an 8x3 array, as shown in FIG. 1, the conductive film is cut into a sensing unit with a size of 3 mm x 3 mm, and the unit spacing is 3 mm. Figure 2

[0065] In the area of the electrode array, a thin conductive tape is used to paste a fine wire, which can realize electrical connection and mechanical fixation at the same time by using the conductivity and adhesion of the conductive tape itself. In order to enhance the connection reliability, slight pressure is applied at the conductive tape connection, and finally a flexible stress-strain sensor array containing 24 sensing array units is obtained, with a total size of about 50 mm x 20 mm. ​

[0066] (2) Sensor calibration

[0067] The prepared flexible stress-strain sensor array is pasted on a standard cantilever beam with a known elastic modulus. Different known loads are applied at the free end of the cantilever beam to produce different bending deformations, so that the sensors are subjected to different tensile or compressive stresses. A standard strain gauge is used to measure the actual stress value at the corresponding position on the surface of the cantilever beam simultaneously. The resistance change value of each array unit of the sensor array is recorded at the same time. The relationship curve between the resistance change rate of each sensing array unit and the actual stress is established, and the stress sensitivity coefficient of each sensing unit is calculated to ensure that the sensor array has good linearity and repeatability in the target stress range.

[0068] (3) Sensor installation and welding preparation

[0069] A 50 mm × 20 mm × 2 mm transparent polycarbonate (PC) film and a 50 mm × 20 mm × 2 mm black opaque polyethylene film containing 0.05wt% carbon black are prepared, as well as two thin spacers. The transparent PC film serves as the light-transmitting layer film, and the opaque polyethylene film serves as the absorbing layer film. Thin spacers are placed between the light-transmitting layer and the absorbing layer. Refer to Figure 1 The back of the absorbing layer (i.e. the side away from the laser incidence during welding) is cleaned in the area to be tested, and the center of the array unit of the sensor is aligned with the center position of the predetermined weld path of the absorbing layer. Gently press to ensure that the array unit of the sensor is tightly attached to the surface of the absorbing layer. The leads of the sensor array are led out from one side edge of the sensor to avoid interference in the welding area. High-temperature resistant tape is used to fix the edge of the sensor to prevent displacement during welding.

[0070] (4) Laser transmission welding and synchronous data acquisition

[0071] A pulsed laser with a wavelength of 980 nm is used, and the laser power varies from 0 W to 20 W. The welding speed varies from 1 mm / s to 5 mm / s, and linear welding is performed along the predetermined weld path. The sensor is first pre-processed: a band-pass filter is applied to the raw signals collected in each channel to remove DC drift and high-frequency noise, and the resistance change rate is converted to stress value. After the pre-processing is completed, the cable of the flexible sensor array unit is connected to a multi-channel data acquisition card, and the compressive stress change is measured. The sampling frequency of the data acquisition card is set to 5 kHz. The data acquisition card starts to collect the compressive stress signals of all 24 sensor channels at the same time as the laser starts welding. The on-off state of the laser and the welding parameters are recorded synchronously.

[0072] (5) Off-line quality detection of the weld samples prepared under different welding parameters (corresponding to different compressive stress characteristics); appearance inspection: observe whether the weld surface is continuous, uniform, has burning, bubbles, etc.; microscopic morphology: prepare a weld cross-section sample, and measure the weld depth d under an optical microscope.

[0073] Correlation model establishment: correlate the compressive stress characteristic parameters extracted in step (4) with the weld quality index weld depth represented in step (5). Through correlation analysis and regression analysis, a corresponding relationship model between the strain characteristic parameters and the weld quality index (weld depth) is established:

[0074] (1);

[0075] (2);

[0076] (3);

[0077] When P is 15W, v is 3mm / s, and t is 2mm, the compressive stress through the 8 array units in the center of the weld is as shown in Figure 3 , the average compressive stress σ is 1.491N; the actually measured weld depth is as shown in Figure 4 , and the average depth calculated for the actual weld depth is 283.86μm; the average weld depth calculated through formula (3) is 286.08μm, which is consistent with the evaluation.

[0078] (6) Online quality evaluation and feedback control

[0079] Real-time evaluation: in the subsequent welding process, the sensor data is collected in real time, processed and characteristic extracted through step (4), and then the characteristics are input into the correlation model established in step (5), so that the predicted quality information of the current welding point can be output in real time and online. At the same time, the evaluation results are displayed in real time on the monitoring interface, and when the predicted quality is lower than the set threshold or the defect characteristics are found, the system sends an alarm signal.

[0080] In summary, in the process of polymer laser transmission welding, the array units of the flexible stress and strain sensor close to the back of the welding part are used to perceive the local stress and strain changes caused by welding in real time, and through data processing and the established correlation model, the internal quality of the weld is evaluated online, which provides an effective technical means for realizing high-precision, high-quality and high-stability laser welding. At the same time, this method can be expanded to the quality monitoring of laser welding or other connection processes of other materials (such as thin metal, composite material, etc.), and only the sensor material, structure, welding process and correlation model need to be adjusted according to the specific application.

[0081] The present application is described in detail above with reference to specific embodiments and exemplary examples, but these are not to be understood as limiting the present application. It is understood by a person skilled in the art that various equivalent substitutions, modifications or improvements can be made to the technical solutions of the present application and the embodiments thereof without departing from the spirit and scope of the present application, and these all fall within the scope of the present application. The scope of protection of the present application is defined by the appended claims.

Claims

1. A laser transmission welding quality inspection method based on a flexible stress-strain sensor, characterized in that, Includes the following steps: S1. The light-transmitting layer film and the light-absorbing layer film are stacked together, and a spacer is placed between them; S2. Attach the flexible stress-strain sensor array to the side of the light-absorbing layer film away from the light-transmitting layer film, and connect the array units of the sensor array to the multi-channel data acquisition system. S3. Perform laser projection welding along the predetermined weld path, and synchronously acquire the compressive stress characteristic parameters of the sensor array through a multi-channel data acquisition system; wherein, the center line of the predetermined weld path is aligned with the center line of the array unit of the sensor array; S4. Offline quality inspection was performed on weld samples prepared under different welding parameters, and the weld depth characteristic parameters were measured by optical microscope. S5. Establish a multiple regression model between the compressive stress characteristic parameters and the weld depth characteristic parameters. The model formula is as follows: （1）； （2）； （3）； Where P is the laser power in W; v is the welding speed in mm / s; σ is the average compressive stress in N; d is the average weld depth in μm; and t is the thickness of the light-transmitting layer in mm.

2. The laser transmission welding quality inspection method based on a flexible stress-strain sensor as described in claim 1, characterized in that, The fabrication method of the flexible stress-strain sensor array includes the following steps: (1) A mixed suspension of graphene nanosheets and polyurethane is sprayed onto a flexible substrate and dried to form a graphene / polyurethane sensitive layer. (2) The pre-patterned conductive film is cut into the predetermined shape and size of the sensor array unit and adhered in an array on the graphene / polyurethane sensitive layer. (3) A flexible stress-strain sensor array is obtained by attaching thin wires to the array unit area with conductive tape.

3. The laser transmission welding quality inspection method based on a flexible stress-strain sensor as described in claim 2, characterized in that, The flexible substrate is a polyimide film with a thickness of 40-60 μm.

4. The laser transmission welding quality inspection method based on a flexible stress-strain sensor as described in claim 2, characterized in that, The concentration of graphene nanosheets in the mixed suspension is 0.5-5 wt%. And / or, the solvent of the mixed suspension is N,N-dimethylformamide.

5. The laser transmission welding quality inspection method based on a flexible stress-strain sensor as described in claim 2, characterized in that, The drying temperature is 75-85℃, and the time is 1-3 hours.

6. The laser transmission welding quality inspection method based on a flexible stress-strain sensor as described in claim 2, characterized in that, The thickness of the graphene / polyurethane sensitive layer is 2.5-10 μm.

7. The laser transmission welding quality inspection method based on a flexible stress-strain sensor as described in claim 2, characterized in that, The pre-patterned conductive film is a pre-copper-plated polyimide film with a circuit pattern engraved on its surface. And / or, the electrode region of the pre-patterned conductive film is connected to the graphene / polyurethane sensitive layer via conductive adhesive or anisotropic conductive film.

8. The laser transmission welding quality inspection method based on a flexible stress-strain sensor as described in claim 1, characterized in that, In S1, the light-transmitting layer film is a polycarbonate film; And / or, the light-absorbing layer film is a polyethylene plastic film doped with 0.02-0.1 wt% carbon black.

9. The laser transmission welding quality inspection method based on a flexible stress-strain sensor as described in claim 1, characterized in that, Before S3, the flexible stress-strain sensor undergoes signal preprocessing: the raw signal of each channel is processed by a bandpass filter to remove DC drift and high-frequency noise, and the signal is converted into a stress value.

10. The laser transmission welding quality inspection method based on a flexible stress-strain sensor as described in claim 1, characterized in that, In S3, the parameters for laser transmission welding are: laser power 0.1-20W, welding speed 1-5mm / s.

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