Infrared detection method for cold solder joint of spot welding of metal sheet

Abstract

A metal sheet spot welding spot pseudo soldering infrared detection method belongs to the technical field of welding spot pseudo soldering detection, and comprises the following steps: step 1, an infrared thermal imager is located right above a metal sheet, an initial temperature value T1 of the metal sheet is recorded, laser irradiates the metal sheet, and laser spots cover all welding spots; 2, when laser irradiation stops, the highest temperature value T2 of a metal sheet welding spot area is tested; step 3, carrying out tension test on the thin metal sheet and the thin metal sheet on the test piece, taking the test piece corresponding to the tension value meeting the user requirement as a qualified test piece, taking the qualified test piece corresponding to the lowest tension value meeting the user requirement as a standard, inversely checking T2 of the qualified test piece, and setting the T2 as a first detection threshold value; and 4, detecting the test piece to be tested, and when T2 of the test piece to be tested is greater than the first detection threshold value, regarding the test piece to be tested as an unqualified test piece, and when T2 is smaller than the first detection threshold value, regarding the test piece to be tested as a qualified test piece.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of spot welding detection, and particularly relates to a kind of metal sheet spot welding spot welding infrared detection method. BACKGROUND

[0002] On the mobile phone circuit board, various electromagnetic shielding covers are usually densely distributed, which are used to fix the PCB and suppress signal interference. These components are usually made of thin stainless steel, copper alloy and aluminum alloy; among them, the aluminum alloy shielding cover usually needs to be welded with a copper electrode sheet by laser spot welding method to facilitate welding and connection with the circuit board.

[0003] Laser spot welding has the advantages of precise control, small heat-affected zone, small deformation of workpiece after welding, and easy automation, and is widely used in the electronic industry.

[0004] Affected by factors such as laser parameter fluctuation and material surface oxidation and oil stain, such welding spots may have defects such as virtual welding and small fusion core, resulting in early failure of the product.

[0005] Precise resistance welding or ultrasonic welding is also widely used in the connection of two layers of metal sheets in the electronic industry, such as the tab welding of soft package lithium batteries, which also has similar welding spot defects.

[0006] The above-mentioned various welding spots are generally about 1mm in diameter and 0.1-1mm in thickness. The plate is thin and the welding spot is small. The existing ultrasonic, x-ray and AOI (automatic optical detection technology) detection methods cannot effectively detect such welding spot defects, which seriously affects the reliability of such products. SUMMARY

[0007] In order to solve the problem that the prior art cannot effectively detect and screen the virtual welding of spot welding between metal sheets, the present application provides an infrared non-destructive rapid detection method for the quality of laser, resistance or ultrasonic spot welding of metal sheets. The active thermal loading infrared detection method can realize rapid discrimination and screening of such welding spot defects, ensuring that the product quality meets the standard and has the characteristics of good consistency.

[0008] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0009] A kind of metal sheet spot welding spot welding infrared detection method, the spot welding spot is a welding spot of metal sheet welded on metal sheet, the size of the metal sheet is smaller than the size of the metal sheet;The infrared detection method comprises the following steps:

[0010] Step one, the infrared thermal imager is located directly above the metal sheet, first records the initial temperature value T1 of the metal sheet, then laser irradiates the metal sheet, and the laser spot covers all the welding spots;

[0011] Step two, the highest temperature value T2 of the metal sheet soldering point area is tested when the laser irradiation stops;

[0012] Step three, the metal sheet and metal sheet tensile test is carried out on the test piece, the test piece corresponding to the tensile value meeting the user's requirements is regarded as a qualified test piece, the T2 of the qualified test piece corresponding to the minimum tensile value meeting the user's requirements is inversely checked, and it is set as the first detection threshold value;

[0013] Step four, the test piece to be tested is detected, and when the T2 of the test piece to be tested is greater than the first detection threshold value, it is regarded as an unqualified test piece, and when it is less than the first detection threshold value, it is regarded as a qualified test piece.

[0014] Further, the area detected by the infrared thermal imager also includes the highest temperature T3 of the non-soldering point area of the metal sheet, and the T3 of the qualified test piece corresponding to the minimum tensile value meeting the user's requirements is inversely checked, and it is set as the second detection threshold value; the test piece to be tested is detected, and when the T3 of the test piece to be tested is greater than the second detection threshold value, and the T2 is less than the first detection threshold value, it is judged that the test piece is delaminated.

[0015] Further, in step one, the irradiation time of the laser is 0.3-2 seconds, and the power is set according to the temperature difference of 20-40℃ between T2 and T1 of the qualified test piece within the laser irradiation time.

[0016] Further, in step one, the size of the laser spot is less than or equal to the size of the metal sheet.

[0017] Further, in step two, the soldering point area of the metal sheet includes all soldering points, and the size of the soldering point area is less than the size of the metal sheet.

[0018] Further, the non-soldering point area of the metal sheet is the area irradiated by the laser.

[0019] Further, in step one, for an oval metal sheet, the laser spot is set to be oval; for a circular ring metal sheet, the laser spot is set to be a circular ring or a circle.

[0020] Further, the initial highest temperature T1 of the metal sheet of each test piece to be tested is tested, and if the T1 deviation value of each test piece to be tested exceeds ±3℃ (caused by the detection environment), the first detection threshold value and the second detection threshold value need to be adjusted accordingly.

[0021] Further, in the actual production process, the first detection threshold value is set to T2 minus 1-3℃.

[0022] Further, in the actual production process, the second detection threshold value is set to T3 plus 0.5-2℃. In this way, it can be ensured that the workpiece passing the detection is completely qualified.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] The product to be detected by the present application has a low individual value, and due to the limitation of the existing detection technology, destructive sampling methods (test tensile value) are mostly used. Once a substandard product is detected, the entire batch of products will be scrapped, resulting in considerable economic losses.

[0025] When the defective product flows into the production line of the customer, it will cause greater incalculable economic losses. The present application can detect defects such as virtual welding and too small welding core, etc., to ensure that the welding point quality meets the standards and has good consistency; the detection process of the present application is highly automated, and online production detection can be realized, with a speed of 1 second for detecting 1 piece. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a schematic diagram of an infrared detection system;

[0027] Figure 2 is a physical diagram of a shielding cover test piece A with an elliptical copper electrode piece in Example 1;

[0028] Figure 3 is an enlarged structural diagram of the elliptical copper electrode piece on test piece A in Example 1;

[0029] Figure 4 is a physical diagram of a shielding cover test piece B with a circular ring-shaped copper electrode piece in Example 1;

[0030] Figure 5 is an enlarged structural diagram of the circular ring-shaped copper electrode piece on test piece B in Example 1;

[0031] Figure 6 is a schematic diagram of the position of the elliptical laser spot irradiation area in test piece A in Example 1;

[0032] Figure 7 is a schematic diagram of the position of the circular laser spot irradiation area in test piece B in Example 1;

[0033] Figure 8 is a schematic diagram of the position of the three temperature measurement areas of the infrared thermal imager for test piece A in Example 1;

[0034] Figure 9 is a schematic diagram of the position of the three temperature measurement areas of the infrared thermal imager for test piece B in Example 1;

[0035] Figure 10 is a schematic diagram of the conditions for judging whether the welding point is qualified;

[0036] Figure 11 is a schematic diagram of the conditions for judging whether the welding point is unqualified;

[0037] Figure 12 is a schematic diagram of spot welding of cylindrical battery tab;

[0038] In the figure, 1, infrared thermal imager, 2, laser, 3, laser beam shaping device, 4, shielding cover, 5, copper electrode sheet, 6, welding spot, 7, laser spot irradiation area, 8, tab, 9, cylindrical battery. DETAILED DESCRIPTION

[0039] The technical solutions in the present application will be described clearly and completely below in combination with the drawings and examples. Obviously, the described examples are only a part of the examples of the present application, rather than all the examples. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0040] Example 1

[0041] A metal sheet spot welding spot virtual welding infrared detection method is used to detect the welding condition of a copper electrode sheet 5 on an electromagnetic shielding cover 4. The copper electrode sheet 5 is welded on the shielding cover 4 by laser spot welding, and the size of the copper electrode sheet 5 is smaller than that of the shielding cover 4. The used infrared detection system is shown in Figure 1 The infrared detection method comprises the following steps:

[0042] Step one, the laser 2 is located above the shielding cover 4 workpiece side, the laser 2 emits a beam of laser, the laser beam is irradiated on the copper electrode sheet 5 through the laser beam shaping device 3, so that the shape of the laser spot irradiation area 7 is the same as that of the copper electrode sheet 5, and the size of the laser spot irradiation area 7 is slightly smaller than that of the copper electrode sheet 5; the laser spot irradiation area 7 covers all the welding spots 6; the laser is used for heat loading, giving a heat pulse to the copper electrode sheet 5, and cannot irradiate on the shielding cover 4. If the shape of the copper electrode sheet 5 is oval (test piece A), as shown in Figure 2 and 3 , then the shape of the laser spot irradiation area 7 is also oval, as shown in Figure 6 . If the shape of the copper electrode sheet 5 is circular ring (test piece B), as shown in Figure 4 and 5 , then the shape of the laser spot irradiation area 7 is circular ring or circle (to reduce the design and control difficulty of the laser system), as shown in Figure 7 .

[0043] Step two, the infrared thermal imager 1 is located directly above the shielding cover 4 workpiece, and corresponding temperature measurement areas are set on the detection display interface of the infrared thermal imager 1; three temperature measurement areas are set on the thermal image corresponding to the test piece A, which are the temperature measurement area T1a on the shielding cover 4, the welding spot area (including all welding spots) T2a on the copper electrode sheet 5, and the non-welding spot area (also the laser irradiation area) T3a on the copper electrode sheet 5, as shown inFigure 8 As shown in the figure; the thermal image corresponding to the test piece B is provided with three temperature measuring areas, which are the temperature measuring area T1b on the shielding cover 4, the soldering point area (including all soldering points) T2b on the copper electrode sheet 5, and the non-soldering point area (also the laser irradiation area) T3b on the copper electrode sheet 5, as shown in the figure. Figure 9 As shown in the figure; set an appropriate laser output power size and time parameter, test a certain number of test pieces with normal parameter welding, when the laser irradiation stops, test the highest temperature T1 of the T1a / T1b temperature measuring area and the highest temperature T2 of the T2a / T2b temperature measuring area and the highest temperature T3 of the T3a / T3b temperature measuring area, respectively.

[0044] Step three, test the tensile force between the copper electrode sheet 5 and the shielding cover 4 of the batch of test pieces (destructive), the tensile force value of the good soldering points will be significantly greater than that of the defective soldering points with virtual soldering and has good consistency, the test pieces corresponding to the tensile force value range meeting the requirements of enterprises and users are regarded as qualified test pieces, and the test temperature parameters T1, T2 and T3 of these qualified test pieces are checked to obtain the detection temperature value interval of good qualified soldering points; take the qualified test pieces corresponding to the lowest tensile force value meeting the requirements of enterprises and users as the standard, check the T2 of the qualified test pieces, and set it as the first detection threshold value; in the actual production process, set the first detection threshold value as T2 minus 1~3℃, recorded as yt2a / yt2b.

[0045] Step four, detect the test pieces in the production detection, when the T2 of the test pieces is greater than the first detection threshold value, it is regarded as unqualified test pieces, and when it is less than the first detection threshold value, it is regarded as qualified test pieces, as shown in the figure. Figure 10

[0046] Take the qualified test pieces corresponding to the lowest tensile force value meeting the requirements of enterprises and users as the standard, check the T3 of the qualified test pieces, and set it as the second detection threshold value, in the actual production process, set the second detection threshold value as T3 plus 0.5~2℃, recorded as yt3a / yt3b; detect the test pieces, when the T3 of the test pieces is greater than the second detection threshold value, and the T2 is less than the first detection threshold value, it is judged as test piece disengaging, as shown in the figure. Figure 11

[0047] ​​T1a and T1b are temperature monitoring areas of the shielding cover 4, the measured T1 temperature value is an auxiliary test parameter, and the area is mainly set to ensure detection accuracy, and is used to monitor the initial temperature value of the shielding cover 4 (related to the detection site environment temperature, which will have a certain fluctuation range, and will undoubtedly have a certain influence on the detection result), and generally, the deviation value is ±3℃, and the detection parameter does not need to be changed, and when it exceeds ±3℃, the first detection threshold and the second detection threshold need to be compensated accordingly. For example: the T1a and T1b are 22℃ in the test of setting the detection threshold; the T1a and T1b are 27℃ in the actual production detection, the difference is +4℃, at this time, the first detection threshold and the second detection threshold need to be added by 4℃, and vice versa; (the ±3℃ fluctuation of T1 is very common, difficult to control, and has little effect on the detection result, so the detection parameter does not need to be adjusted frequently in production.)

[0048] T2a and T2b are main temperature monitoring areas, and each point welding spot is included, and is slightly smaller than the copper electrode piece.

[0049] T3a and T3b are auxiliary temperature monitoring areas, located on the copper electrode piece 5, and there is no spot welding spot in the area. The T3 temperature value is also an auxiliary test parameter, mainly used to identify the de-welding condition of the test piece.

[0050] Further, in step one, the laser output power size and time are mainly determined by the highest temperature T2 measured by T2a / T2b, small parameter power and short time, the highest temperature value T2 of T2a / T2b and the original temperature T1 are small, then the welding spot defect resolution is low; the large parameter power and long time may cause ablation oxidation to the test piece. Therefore, the irradiation time of the laser is generally set to 0.3-2 seconds, and the power is set according to the standard that the difference between T2 and T1 temperature values of the qualified test piece within the laser irradiation time is 20-40℃.

[0051] The same detection method can also be applied to the quality detection screening of the spot welding spot 6 of the similar cylindrical battery tab 8 connecting point, and the battery tab 8 is welded on the cylindrical battery 9. Figure 12

[0052] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description manner of the specification is only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that those skilled in the art can understand.​

Claims

1. A method for infrared detection of poor weld joints in spot welding of thin metal plates, characterized in that, The spot weld is a weld point where a thin metal sheet is welded onto a thin metal plate, and the size of the thin metal sheet is smaller than the size of the thin metal plate; the infrared detection method includes the following steps: Step 1: The infrared thermal imager is positioned directly above the metal sheet. First, the initial temperature value T1 of the metal sheet is recorded. Then, the metal sheet is irradiated with a laser, and the laser spot covers all the solder joints. Step 2: When laser irradiation stops, test the highest temperature value T2 in the weld joint area of ​​the metal sheet; Step 3: Perform tensile tests on the metal sheet and metal plate. The specimens that meet the tensile values ​​required by the user are considered qualified specimens. Using the qualified specimens that meet the minimum tensile values ​​required by the user as the standard, the T2 of the qualified specimens is checked backwards and set as the first detection threshold. Step 4: Test the test piece. If the T2 of the test piece is greater than the first detection threshold, it is considered an unqualified test piece; if it is less than the first detection threshold, it is considered a qualified test piece.

2. The infrared detection method for poor weld joints in spot welding of thin metal plates according to claim 1, characterized in that: The infrared thermal imager also detects the highest temperature T3 in the non-solder joint area of ​​the metal sheet. The T3 of the qualified test piece corresponding to the lowest tensile value required by the user is used as the standard, and it is set as the second detection threshold. When testing the test piece, if T3 of the test piece is greater than the second detection threshold and T2 is less than the first detection threshold, it is determined that the test piece has detached from the solder joint.

3. The infrared detection method for poor weld joints in spot welding of thin metal plates according to claim 1, characterized in that: In step one, the laser irradiation time is 0.3-2 seconds, and the power is set according to the standard that the temperature difference between T2 and T1 during the laser irradiation time of the qualified test piece is 20-40℃.

4. The infrared detection method for poor weld joints in spot welding of thin metal plates according to claim 1, characterized in that: In step one, the size of the laser spot is less than or equal to the size of the metal sheet.

5. The infrared detection method for poor weld joints in spot welding of thin metal plates according to claim 1, characterized in that: In step two, the solder joint area of ​​the metal sheet includes all solder joints, and the size of the solder joint area is smaller than the size of the metal sheet.

6. The infrared detection method for poor weld joints in spot welding of thin metal plates according to claim 2, characterized in that: The non-solder joint area of ​​the metal sheet is the area irradiated by the laser.

7. The infrared detection method for poor weld joints in spot welding of thin metal plates according to claim 1 or 4, characterized in that: In step one, for an elliptical metal sheet, the laser spot is set to be elliptical; for an annular metal sheet, the laser spot is set to be annular or circular.

8. The infrared detection method for poor weld joints in spot welding of thin metal plates according to claim 2, characterized in that: The initial maximum temperature T1 of the metal sheet to be tested is determined. If the overall deviation of T1 for each test piece exceeds ±3℃, the first and second detection thresholds need to be adjusted.

9. The infrared detection method for poor weld joints in spot welding of thin metal plates according to claim 1, characterized in that: In actual production, the first detection threshold is set to T2 minus 1~3℃.

10. The infrared detection method for poor weld joints in spot welding of thin metal plates according to claim 2, characterized in that: In actual production, the second detection threshold is set to T3 plus 0.5~2℃.

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