JP7144225B2 - Spot weld inspection method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for inspecting spot welds, and more particularly to a method for inspecting spot welds for detecting internal cracks in welded joints by X-ray CT scanning.

As shown in FIG. 5, the resistance welded joint 10 is formed by sandwiching and pressurizing two superimposed high-tensile steel plates 11A and 11B between a pair of upper and lower welding electrodes (not shown) of a spot welding device. By energizing between the electrodes, the contact portions of the high-tensile steel plates 11A and 11B are melted and formed. A nugget (weld metal) 21 is formed in the spot welded portion 20 of the high-tensile steel plates 11A and 11B, and a heat-affected zone 22 is formed around the nugget 21 . In FIG. 5, reference numeral 23 denotes a solid-phase-welded corona bond portion generated around the nugget 21, reference numeral 25 denotes a sheet separation, and reference numeral 26 denotes a steel plate 11A that is pressed by a pair of welding electrodes. , 11B.

It is known that LME cracks (liquid metal embrittlement cracks) caused by hot-dip galvanization occur during welding in galvanized high-strength steel sheets that have been developed in recent years. LME cracks include HAZ cracks that occur in the heat affected zone 22. Outer cracks, such as cracks formed from the outside of the weld zone toward the nugget 21, and cracks in the plate thickness direction from the end of the corona bond 23. and an inner crack formed toward the

Of these cracks, inner cracks that occur inside the joint cannot be visually confirmed from the outside, and are considered particularly important because they become stress concentration areas and cause a decrease in joint strength.

Conventionally, with regard to such cracks, the presence or absence of cracks has been confirmed by a cut check of the spot welded portion 20 after spot welding. However, in the cut check, there is a problem that it is only possible to grasp information on cracks in a cross section cut by chance, and joint strength cannot be evaluated appropriately.

In order to deal with such problems, various inspection methods described in Patent Documents 1 to 3 have been proposed. The inspection method of Patent Document 1 obtains the size of the nugget diameter from the ultrasonic waves oscillated from the ultrasonic probe, compares it with the normal nugget diameter stored in advance, and inspects the presence or absence of abnormality in spot welding. there is In addition, the inspection method of Patent Document 2 uses an X-ray transmission image obtained by irradiating a welded portion of an object to be inspected with X-rays to determine the structure boundary surface between the base metal and the melted portion where the structure has changed due to the welding heat. A transmission image is detected, and the size and shape of the nugget are detected from the density and shape of the transmission image of the tissue boundary surface to inspect the quality of spot welding. In the inspection method of Patent Document 3, the quality of the welded state is judged by calculating the joint area from the shading of the cross-sectional photograph of the laser welded portion taken with an X-ray CT device and comparing it with a preset area.

JP-A-62-119453 JP-A-8-247749 JP 2009-105193 A

However, the inspection method of Patent Document 1 scans a contact that emits ultrasonic waves from the outer region of the recessed portion of the spot welded portion to the outer region on the opposite side through the center of the welded portion to determine whether or not there is a nugget. Since the size is detected, only the information on the scanning line can be obtained, and there is a possibility that the information is not necessarily sufficient to appropriately determine the presence or absence of an abnormality in spot welding. The inspection method of Patent Document 2 inspects the quality of the welded portion from an X-ray transmission image of the spot welded portion, and the inspection method of Patent Document 3 is based on the contrast of the cross-sectional photograph of the laser welded portion obtained by an X-ray CT device. However, there is room for improvement as there is no mention of cracks in the weld, especially internal cracks that affect joint strength.

The present invention has been made in view of the above-mentioned problems, and its object is to accurately and quantitatively grasp cracks in spot welds, especially inner cracks, by non-destructive inspection using an inspection method using X-ray CT scanning. An object of the present invention is to provide an inspection method for spot welds.

The above objects of the present invention are achieved by the following configurations.
(1) performing an X-ray CT scan on a resistance welded joint in which the steel plates are superimposed;
a step of blackening the base material portion, the weld metal, and the heat-affected zone in the slice image obtained by the X-ray CT scan, and whitening the other portions;
a step of removing or blackening at least one of the whitened portion of the whitened portion, the white portion of the sheet separation, the white portion of the indentation portion, and the white portion continuous from the joint surface;
A step of detecting the white portion inside the joint as an inner crack;
A method for inspecting a spot weld, comprising:
(2) performing an X-ray CT scan on the resistance welded joint in which the steel plates are superimposed;
a step of color-coding the slice image obtained by the X-ray CT scan with a first color for the base material portion, the weld metal, and the heat-affected zone, and a second color for the other portions;
removing or discoloring to the first color at least one of the second color that is continuous from the sheet separation, the indentation, and the joint surface;
detecting the second color inside the joint as an internal crack;
A method for inspecting a spot weld, comprising:

According to the method for inspecting spot welds of the present invention, it is possible to non-destructively and accurately quantitatively grasp internal cracks inside welded joints, which were difficult to detect by conventional cross-sectional macro observation inspection methods.

It is a figure which shows the inspection procedure by the inspection method of the spot-welded part of 1st Embodiment of this invention. It is a figure which shows the inspection procedure by the inspection method of the spot-welded part of 2nd Embodiment of this invention. It is a figure which shows the inspection procedure by the inspection method of the spot-welded part of 3rd Embodiment of this invention. It is a figure which shows the inspection procedure by the inspection method of the spot-welded part of 4th Embodiment of this invention. 1 is a cross-sectional view schematically showing a resistance welded joint; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, each embodiment of a method for inspecting spot welds according to the present invention will be described in detail based on the drawings.

(First embodiment)
In the inspection method of the present embodiment, first, an X-ray CT is performed along a predetermined direction perpendicular to the plate thickness of the steel plates 11A and 11B on the resistance welded joint 10 having the spot welded portion 20 as shown in FIG. scan. As a result, an X-ray CT scan image is provided, which is an aggregate of a plurality of cross-sectional images (hereinafter referred to as slice images) cut at equal intervals in a predetermined direction.

In an X-ray CT scan, the areas where X-rays are transmitted are white, the areas where X-rays are completely blocked are black, and the areas where some X-rays are transmitted or blocked are shaded according to the amount of X-rays transmitted. displayed in gray with Therefore, in the slice image of the resistance welded joint 10, as shown in FIG. 1, the base material portion 11 of the steel plates 11A and 11B, the weld metal (nugget) 21, and the heat affected zone 22 (see FIG. 5) are black or gray. Indentations 26, cracks including inner cracks 24, and sheet separations 25 are displayed in white or gray.

By subjecting the slice image 31 obtained by this X-ray CT scan to binarization processing using a threshold value set for the numerical value indicating the density of the image, the base material portion 11, the weld metal 21, and the heat-affected The part 22 is blackened and the other parts are whitened. As a result, an intermediate processed image 32 is obtained in which the impression portion 26, the inner crack 24, and the sheet separation 25 are displayed in white.

Then, the intermediate processed image 32 is trimmed to remove the impression portion 26 and the sheet separation 25, and an inspection image 33 is created in which only the inner crack 24 remains as a white portion. In addition, when there is an outer crack displayed by a white portion continuous from the surface, image processing is performed so as to blacken the outer crack. Similarly, if there are cracks or pores that do not penetrate to the surface and are displayed by white portions inside the nugget 21, image processing is performed so as to blacken these portions. However, when the outer crack extends to the corona bond portion 23, it is treated as an inner crack 24 and is not blackened. As a result, only the inner crack 24 is displayed as a white portion in the inspection image 33 .

The above-described processing is similarly performed on a plurality of slice images 31 of X-ray CT scan images, and the presence or absence of inner cracks 24 is inspected. Among the inner cracks 24 shown as white portions in the inspection image 33, when there is a crack with a maximum crack length of 0.2 mm or more in the plate thickness direction that affects the joint strength, it is determined that the weld is defective.

Since the inspection is performed based on the slice image 31 obtained by the X-ray CT scan in this way, the inner crack 24, which is difficult to be accurately detected by the conventional nondestructive inspection, can be quantitatively determined nondestructively with high accuracy.
Further, based on the plurality of slice images 31, the maximum crack length (the circumference of the inner crack 24) in the plane perpendicular to the thickness direction of the inner crack 24 can be calculated. Therefore, the welding state can be determined by considering not only the maximum crack length in the plate thickness direction of the inner crack 24 but also the circumferential length. The welded state is not limited to the above, and may be determined based on the area and volume of the inner crack 24 .

(Second embodiment)
Next, a method for inspecting spot welds according to the second embodiment will be described with reference to FIG.
This embodiment performs an X-ray CT scan on the resistance welded joint 10, performs a binarization process on a slice image 31 obtained by the X-ray CT scan, and creates an intermediate processed image 32. are the same as in the first embodiment. Therefore, in FIG. 2, the slice image 31 and intermediate processed image 32 of the second embodiment are substantially the same as those of the first embodiment.

On the other hand, in the present embodiment, among the portions displayed in white in the intermediate processed image 32, the indentation portion 26 and the sheet separation 25 are blackened to create an inspection image 33 in which only the inner crack 24 is displayed as a white portion. do. If there are external cracks displayed as white portions continuous from the surface, cracks or pores inside the nugget 21, these portions are blackened as in the first embodiment.

Among the inner cracks 24 displayed as white portions in the inspection image 33, when there is a crack with a maximum crack length of 0.2 mm or more in the plate thickness direction, it is determined that the weld is defective.
Other configurations and actions are the same as those of the first embodiment.

(Third embodiment)
Next, a method for inspecting spot welds according to the third embodiment will be described with reference to FIG. The method for inspecting a spot welded portion according to the present embodiment is an inspection method for a case where a minute inner crack 24A is present inside the spot welded portion 20 .

First, an X-ray CT scan is performed on the resistance welded joint 10 to obtain a slice image 31 shown in FIG. At this time, the fine inner crack 24A is displayed in darker gray than the indentation portion 26, the sheet separation 25, and the relatively large inner crack 24, because the amount of X-ray transmission is small.

Then, by subjecting this slice image 31 to binarization processing, the base material portion 11, the weld metal 21, and the heat-affected zone 22 are blackened, and the other portions (indentation portion 26, inner crack 24, and sheet A first intermediate processed image 32A is created by whitening the separation 25). At this time, since the minute inner crack 24A is displayed as dark gray in the slice image 31, it may be blackened by the binarization process and may not be displayed.

Such minute inner cracks 24A that cannot be whitened by the binarization process are manually whitened using image processing software, so that even the minute inner cracks 24A are displayed in white. 2 Create an intermediate processed image 32B.

Next, among the portions displayed in white in the second intermediate processed image 32B, the impression portion 26 and the sheet separation 25 are blackened to create an inspection image 33 in which only the inner cracks 24 and 24A are displayed as white portions. . If there are external cracks displayed as white portions continuous from the surface, cracks or pores inside the nugget 21, these portions are blackened as in the first embodiment. As a result, the inner cracks 24 and minute inner cracks 24A inside the resistance welded joint 10 can be displayed as white portions, and the inner cracks 24 and minute inner cracks 24A can be detected.

Among the inner cracks 24 and 24A shown as white portions in the inspection image 33, when there is a crack with a maximum crack length of 0.2 mm or more in the plate thickness direction, it is determined that the weld is defective.
Other configurations and actions are the same as those of the first embodiment.

(Fourth embodiment)
Next, a method for inspecting spot welds according to the fourth embodiment will be described with reference to FIG. Since the inner crack 24 always occurs inside the sheet separation 25, in the spot welded portion inspection method of the present embodiment, only the inner portion surrounded by the sheet separation 25 and the indentation portion 26 is subjected to an X-ray CT scan. A slice image 31 is created. Therefore, the sheet separation 25 is not displayed in this slice image 31 .

Then, in the same manner as in the inspection method of the spot welded portion of the first embodiment, the slice image 31 is subjected to binarization processing to blacken the weld metal 21 and the heat-affected zone 22, and to whiten the other portions. A processed image 32 is created. Furthermore, if there is an indentation portion 26, a white portion continuous from the surface, and a white portion inside the nugget 21, the white portion is also blackened to create an inspection image 33 in which only the inner crack 24 is displayed. This allows internal cracks 24 inside the resistance welded joint 10 to be detected.

According to the method for inspecting a spot welded portion of the present embodiment, the range of X-ray CT scanning is set to a narrow range, so efficient X-ray CT scanning is possible.
Other configurations and actions are the same as those of the first embodiment.

It should be noted that the present invention is not limited to the above-described embodiments, and can be modified, improved, etc. as appropriate.
For example, in each of the above-described embodiments, slice images obtained by X-ray CT scanning have been described as being configured in two colors, black and white. Often, black and white can also be displayed in reverse. Furthermore, the base metal portion, weld metal, and heat-affected zone are displayed in a first color, and the other portions are displayed in a second color. You may make it

As described above, this specification discloses the following matters.
(1) performing an X-ray CT scan on a resistance welded joint in which the steel plates are superimposed;
a step of blackening the base material portion, the weld metal, and the heat-affected zone in the slice image obtained by the X-ray CT scan, and whitening the other portions;
a step of removing or blackening at least one of the whitened portion of the whitened portion, the white portion of the sheet separation, the white portion of the indentation portion, and the white portion continuous from the joint surface;
A step of detecting the white portion inside the joint as an inner crack;
A method for inspecting a spot weld, comprising:
According to this configuration, it is possible to non-destructively and accurately quantitatively grasp inner cracks inside the joint, which was difficult with the conventional cross-sectional macroscopic observation and inspection method.

(2) By binarizing the slice image obtained by the X-ray CT scan, the base metal portion, the weld metal, and the heat-affected zone are blackened, and the other portions are whitened. The method for inspecting spot welds according to (1), characterized in that:
According to this configuration, by setting the threshold value for the binarization process to an appropriate value, the base material portion, the weld metal, and the heat-affected zone can be appropriately blackened, and the other portions can be whitened. , inner cracks can be detected more accurately.

(3) The spot welded portion according to (2), further comprising a step of manually performing whitening processing using image processing software for minute cracks that cannot be whitened by the binarization processing. inspection method.
According to this configuration, even minute cracks that cannot be whitened by binarization can be reliably detected as cracks.

(4) The method for inspecting spot welds according to any one of (1) to (3), wherein the X-ray CT scan is performed on the resistance welded joint in a range inside the sheet separation.
According to this configuration, the X-ray CT scan range can be narrowed, and internal cracks inside the joint can be efficiently detected.

(5) The resistance welded joint is determined to be defective when there is a crack with a maximum crack length of 0.2 mm or more in the plate thickness direction among the cracks inside the joint. (1) The inspection method for spot welds according to any one of (4).
According to this configuration, it is possible to determine the quality of the resistance welded joint based on the size of the inner crack that affects the joint strength.

(6) performing an X-ray CT scan on the resistance welded joint in which the steel plates are superimposed;
a step of color-coding the base material portion, the weld metal, and the heat-affected zone in a first color and the other portions in a second color in the slice image obtained by the X-ray CT scan;
removing or discoloring to the first color at least one of the second color that is continuous from the sheet separation, the indentation, and the joint surface;
detecting the second color inside the joint as an internal crack;
A method for inspecting a spot weld, comprising:
According to this configuration, the slice image obtained by the X-ray CT scan is color-coded into the first color and the second color according to the amount of X-ray transmission, and is processed. Cracks can be quantified non-destructively and accurately.

10 resistance welded joint 11 base metal portion 20 spot welded portion 21 nugget (weld metal)
22 Heat-affected zone 24 Inner crack 24A Minute inner crack 25 Sheet separation 26 Impression 31 Slice image

Claims (6)

performing an X-ray CT scan on the resistance welded joint in which the steel sheets are superimposed;
a step of blackening the base material portion, the weld metal, and the heat-affected zone in the slice image obtained by the X-ray CT scan, and whitening the other portions;
a step of removing or blackening the white portion of the sheet separation, the white portion of the indentation portion, and the white portion continuous from the joint surface, among the whitened portions;
A step of detecting the white portion inside the joint as an inner crack;
A method for inspecting a spot weld, comprising: The slice image obtained by the X-ray CT scan is binarized to blacken the base metal portion, the weld metal, and the heat-affected zone, and whiten the other portions. The method for inspecting a spot weld according to claim 1. 3. The method for inspecting spot welds according to claim 2, further comprising the step of manually performing whitening processing using image processing software for minute cracks that cannot be whitened by the binarization processing. . 4. The method for inspecting spot welds according to claim 1, wherein the X-ray CT scan is performed for a range inside the sheet separation of the resistance welded joint of steel. The resistance welded joint is determined to be defective when there is a crack with a maximum crack length of 0.2 mm or more in the plate thickness direction among the cracks inside the joint. 5. The method for inspecting spot welds according to any one of 1 to 4. performing an X-ray CT scan on the resistance welded joint in which the steel sheets are superimposed;
a step of color-coding the base material portion, the weld metal, and the heat-affected zone in a first color and the other portions in a second color in the slice image obtained by the X-ray CT scan;
removing or discoloring to the first color the portions of the second color that are continuous from the sheet separation, the indentation and the joint surface;
detecting the second color inside the joint as an internal crack;
A method for inspecting a spot weld, comprising:

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