JPH0763694A - Nondestructive inspection apparatus for spot-welded part - Google Patents

Abstract

PURPOSE:To provide a nondestructive inspection apparatus with which whether a spot-welded part is good or not, can be judged nondestructively and in a noncontact manner and continuous and efficient inspection is made possible by a method wherein a nugget immediately after a spot welding operation is picked up by an infrared camera as the infrared image. CONSTITUTION:Two materials S1, S2 to be welded are stacked, their parts to be welded are sandwiched by electrodes 1a, 1b, a pressurization force and an electric current are applied, the electric current and the pressurization force are concentrated, and a nugget N as the welding part is formed at the contact face of the materials S1, S2 to be welded. When the material and the thickness of the materials S1, S2 are decided, the diameter of the nugget N controls the strength of a welding operation. In order to detect the size of the nugget N immediately after the welding operation, an infrared camera 2 for imaging of a welded trace is installed near the welding electrodes 1a, 1b, infrared rays generated by the nugget N and welding heat near it are taken in, and the size of the nugget N is detected on the basis of an infrared image reflecting a temperature distribution. Then, a welded area and a deformation degree are computed via an A/D converter 3 and a CPU 4, and whether a spot welding operation is good or not is judged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for inspecting whether a spot weld portion such as spot welding or projection welding is acceptable or not.

[0002]

2. Description of the Related Art Conventionally, spot welding such as that shown in FIG. 4 has been widely used for joining two thin plates (workpieces) W as a spot welding. The nugget N, which is a metal fusion part, is formed by sandwiching two workpieces W with a pair of electrodes 100 and energizing them. Conventionally, when inspecting whether or not the welding is properly performed, the nugget N is extracted. The part including the nugget N was cut, and the diameter of the nugget N was measured, and if it was equal to or larger than the reference value, it was considered to be acceptable, and it was estimated that the series of welding steps was properly performed.

Further, the electrode 100 for spot welding or the like is generally made of a copper alloy, and it is necessary to replace the electrode every predetermined number of weldings due to wear of the electrode itself. Then, every time the electrode is replaced, it may be inspected whether or not the welding by the electrode is properly performed. In that case, as shown in FIG. 5, two plate-shaped test pieces 102 are overlapped and tested. Welding was performed, the portion was cut, and the size of the nugget N was measured to determine whether the welding was successful or not, and thus the quality of the electrode.

On the other hand, as a nondestructive inspection method for spot welding points,
There is a non-destructive inspection method using ultrasonic waves. In this method, as shown in FIG. 6, the ultrasonic probe 103 is brought into contact with a welded portion to measure the plate thickness, and only the plate thickness T1 for one sheet is measured at a portion where welding is not performed. , Welding nugget N
The part (2) utilizes the fact that the plate thickness Tt of two sheets T1 + T2 is measured. The ultrasonic probe 103 is arbitrarily moved, the size of the welding nugget N is estimated, and the pass / fail of the welding is determined.

[0005]

However, the above-described destructive inspection by sampling has the drawback of destroying the welded product, cannot perform 100% inspection, and the inspection method using a test piece at the time of electrode replacement is cut. In addition to being troublesome, it simply estimates pass / fail of the welded product indirectly from the quality of the electrode. Further, although the ultrasonic non-destructive inspection method allows non-destructive inspection of all products, it has a drawback that the ultrasonic probe must be brought into contact with the material to be welded one by one, which makes the inspection troublesome.

An object of the present invention is to enable non-destructive and non-contact inspection of pass / fail of spot welds in spot welding, projection welding and the like.

[0007]

According to the present invention, there is provided an infrared camera for detecting the temperature condition of a nugget region immediately after spot welding, an image processing means for performing image processing of the infrared camera, and an image-processed nugget. It is provided with a pass / fail determination means for determining pass / fail of welding based on the temperature state of the region, and an output device for outputting the pass / fail result.

[0008]

In such an apparatus for inspecting spot welds, the nugget immediately after welding is captured as an infrared image by an infrared camera, and image processing is performed on the nugget to determine its characteristics to determine whether the welded part is acceptable or not. Output the result. Since the infrared camera can detect the size of the welding nugget in a non-contact and non-destructive manner, even if welding is performed on a large number of points one after another, all the points can be continuously inspected in a non-contact manner.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. A welding procedure and a device configuration will be described with reference to FIGS. Taking spot welding as an example, two materials to be welded S1 and S2 are superposed, and then the electrodes 1a and 1b are sandwiched between the welding points to apply pressure and energize, thereby concentrating the electric current and the applied pressure, and the welding target A nugget N that is a weld is formed on the contact surface between the materials S1 and S2. If the materials and plate thicknesses of the materials to be welded S1 and S2 are determined, the nugget diameter controls the welding strength of both. Further, in the state where proper welding is performed, the nugget diameter depends on the electrode tip diameter, and the nugget diameter dn = 0.9 to 1.1D (D: electrode tip diameter).
It is generally in the range of.

In this embodiment, in order to detect the size of the nugget N immediately after welding, an infrared camera 2 for photographing a welding trace is provided near the welding electrodes 1a and 1b. The infrared camera 2 captures infrared rays generated from the nugget N and its vicinity based on welding heat, and detects the size of the nugget N from an infrared image reflecting a temperature distribution. Connected to the computer 4.

In order to improve the image resolution, it is necessary to obtain an infrared image at the earliest possible stage after welding, so the infrared camera 2 is arranged near the electrodes 1a and 1b. For example, an infrared camera 2 on the arm or head of the welding robot
The infrared camera 2 can be configured to move together with the arm or head of the welding robot.
Alternatively, S2 and S2 may be sequentially moved after each welding at a certain point. The infrared camera 2 is preferably provided with a protector for protecting the camera lens from welding spatter, and the computer 4 can be installed at any place.

Next, the functional blocks of the equipment will be described with reference to FIG. Inside the infrared camera 2, an IR (infrared) / CCD 2a that is an image sensor, an amplifier 2b that amplifies a signal from the CCD 2a, a low-pass filter 2c that cuts a high frequency component of the amplified analog signal, and a signal is sampled. A sample hold circuit 2d and the like are incorporated.

In each cell of the IR / CCD 2a, a charge proportional to the amount of incoming infrared rays is stored. IR / CC
The D2a sequentially transfers and amplifies these charges to generate an analog signal 2e which becomes raster data of the screen. The high-frequency component of the generated analog signal 2e is cut by the low-pass filter 2c and becomes a smooth signal 2f. Next, the so-called PAM wave 2g is generated by the sample hold circuit 2d.

In general general-purpose CCDs, the light that can be detected is wide from visible rays to near infrared rays, but the resolution tends to deteriorate as the wavelength increases. Therefore, in order to improve the resolution of the infrared image corresponding to the nugget N, it is desirable to use IR (infrared) / CCD 2a.

The above-mentioned A / D converter 3 converts the video signal from the infrared camera 2 into A / D,
It is connected to the input interface unit 4a of the computer 4. The computer 4 uses this input interface unit 4
In addition to a, an image memory 4b as a work area, and a signal processing device 4 for executing various processes according to a program
c, a program memory 4d for storing the program,
Then, the output interface unit 4e for outputting the processing result and the like
Etc. are included. Further, a display monitor 5 is connected as an output device to the output interface section 4e, and information such as welding defects is displayed on the monitor 5.

The video signal from the infrared camera 2 is A /
The digital signal is A / D converted by the D converter 3 and becomes a digital signal representing the density. That is, 256-level density signals represented by, for example, 8 bits are applied to each of the pixels forming the determination pattern described later. These density signals are taken into the image memory 4b, and various image processing is performed by the signal processing device 4c including the CPU. The signal processing device 4c is sequentially driven by the program (4d).

Next, the flow of image processing will be described with reference to FIG. In step S1, the signal from the infrared camera 2 is digitized by the A / D converter 3, and the signal is captured in the image memory 4b as infrared image data, that is, a determination pattern in step S2. Then, in step S3, noise removal processing is performed. For each pixel, check the densities of the four adjacent pixels to the pixel of interest, and if all are below a certain density, consider that pixel of interest as noise and set the density of that pixel of interest to zero. To remove noise.

Next, as the binarization processing in step S4,
It is checked whether the density signal is above or below a certain threshold value or less than the threshold value for all the pixels of the judgment pattern. If the density signal is above the threshold value, it is set to 1, and if it is below the threshold value, it is set to 0. To a 1-bit signal. This processing is performed for the purpose of clarifying the contour of the infrared image and facilitating the measurement of the image.

The binarized determination pattern image is subjected to hole filling processing in step S5 in order to further clarify the image. This is to examine the densities of four pixels adjacent to the pixel of interest for each pixel whose density signal is 0 for the data whose contour has become clear after the binarization processing. When all are 1, the pixel of interest is regarded as a hole, the density of the pixel of interest is set to 1, and the pattern is filled. After this processing, the determination pattern is completed in step S6, and the data is used for the next image determination.

There are various other methods for the above noise removal processing and hole filling processing. For example, the contour of the aggregate of the density signals 1, that is, the boundary pixels are detected, the contour is reduced uniformly, and the contour is expanded again. There is also a method to remove small noise. Therefore, the description here is only an example.

The determination pattern clarified by the above-mentioned method is a portion which is considered to have been red-heated by the energization of the electrodes 1a and 1b and welded, that is, a portion corresponding to the nugget N. In step S7, the judgment pattern and the elevated temperature level are verified and compared with the reference data RD, and if it is at or above the level, it can be considered that sufficient welding has been performed. The item to be verified is the area of the determination pattern.
The area is obtained by counting the number of pixels whose density signal is 1, and when the area is equal to or larger than the reference area, it can be considered that there is a sufficient nugget area.

Next, the perimeter of the judgment pattern is calculated as a parameter for obtaining the pattern deformation degree. Then, the deformation degree of the determination pattern is calculated from the area and the perimeter of the determination pattern. For example, the absolute value of the difference between the areas of the perfect circles corresponding to the perimeter is calculated from the area of the actual determination pattern, and the area difference is compared with the reference value. If this difference is equal to or greater than a certain value, the determination pattern is determined to be a distorted shape.
In other words, even if there is a sufficient welding area, it cannot be said to be proper welding if the shape is distorted.

Since the shape of the electrode is generally round, it is unlikely that an extreme pattern deformation will occur, but when the electrode does not hit the surface of the material to be welded at a right angle during welding, or When the electrode is unevenly worn, pattern deformation may occur, so it is useful to consider the degree of deformation of the determination pattern. In this way, it is determined whether sufficient welding strength is secured by the welding area, and whether the correct welding pattern is formed is determined by the degree of deformation.

Based on the determination in step S7,
In step S8, the acceptance / rejection of the welded portion is displayed on an output device such as the monitor 5 to inform that effect. The manager of the welding process can check the monitor 5 to know the success or failure of the welding. Further, in the case of failure, it is possible to stop the spot welding apparatus 6 through the output interface section 4e of the computer 4 shown in FIG.
Further, an alarm device for alarming a welding failure with a buzzer sound or other sounds may be added.

[0025]

In the present invention, the nugget immediately after welding is captured as an infrared image of an infrared camera, and the pass / fail of the spot weld is determined based on this, so the inspection itself is nondestructive and noncontact. It can be efficiently performed without interfering with the welding process. Further, in continuous spot welding at a large number of points, continuous pass / fail inspection corresponding to the spot welding is also possible.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of the present invention together with a welding process.

FIG. 2 is a functional block diagram thereof.

FIG. 3 is a flowchart showing a flow of image signal processing.

FIG. 4 is an explanatory diagram of general spot welding.

FIG. 5 is a cross-sectional perspective view of a weld portion inspection using a conventional test piece.

FIG. 6 is an explanatory diagram of a conventional weld inspection using ultrasonic waves.

[Explanation of symbols]

 1a electrode 1b electrode 2 infrared camera 3 A / D converter 4 computer 4b image memory 4c signal processing device 4d program memory 5 monitor N nugget

Claims (1)

[Claims] 1. An infrared camera for detecting the temperature condition of a nugget region immediately after spot welding, an image processing means for performing image processing of the infrared camera, and a welding process based on the temperature condition of the image-processed nugget region. A non-destructive inspection device for spot welds, comprising: a pass / fail determination means for determining pass / fail; and an output device for outputting the pass / fail result.