JPH08122051A - Method for measuring nugget of spot welding part - Google Patents

Abstract

PURPOSE: To grasp an entire picture quickly by calculating the tendency of temperature increase from a temperature distribution detected by an infrared camera and measuring the size of the nugget of a spot welding part. CONSTITUTION: A reverse side 2 of a spot welding member 1 is heated by a gas burner 3. An infrared camera 5 is laid out on the surface side 4 of the member 1 to pick up the image of the temperature change of the surface 4. When the reverse side 2 is heated by the burner 3, heat with Gauss distribution is given to the reverse side 2 for a certain specified time with the welding part of the member 1 as the center. In the heat conduction to the surface 4 due to the heating, a part which is surely welded indicates the maximum conduction, and if the thermal image of the surface 4 is picked up after heating has been completed, the central part of the temperature distribution becomes the maximum-temperature region. By obtaining the temperature inclination by performing the first-order differentiation of the temperature distribution from the thermal image, it is judged that a part where the absolute value of inclination is maximized is corona bond diameter. Further, by performing the second-order differentiation, a position where the value is maximized is judged to be the nugget diameter, thus accurately and quickly obtaining the entire picture of nugget.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring spot welds using a thermography method in which spot welds are locally heated and the joints are measured non-destructively from surface temperature changes. Is.

[0002]

2. Description of the Related Art A spot weld is placed in water and the water distance from a focusing probe is set so that the beam focus is located below the spot weld and the spot weld is ultrasonically applied. The measuring method is, for example, JP-A-6-138.
It is disclosed in Japanese Patent Publication No. 100.

[0003]

By the way, in the above-described method for measuring spot welds by ultrasonic waves, the size of the nugget forming portion can be accurately measured.
Since the scanning graph of the interface echo in each direction is obtained by finely scanning in the Y direction and the Y direction at a constant pitch, it takes a lot of time for the measurement and the probe must be operated in water. There is a problem that it must be.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to heat a spot welding portion and to detect a temperature change of the heating portion with an infrared camera. An object of the present invention is to provide a method for measuring a nugget in a spot-welded portion, which can detect an accurate whole image of the nugget in a short time by detecting and determining the nugget portion.

[0005]

In order to achieve the above object, a method for measuring a nugget of a spot welded portion according to the present invention calculates a tendency of temperature rise from a temperature distribution detected by an infrared camera, and calculates the calculated value. The method of measuring the size of the nugget at the spot welded part is adopted.

Then, the back surface of the central portion of the spot welded portion is heated with a gas burner for a certain period of time, and the temperature distribution on the surface side after a predetermined period of time is detected by the infrared camera, from the temperature distribution detected by the infrared camera. A method of calculating the tendency of temperature rise and measuring the size of the nugget at the spot welded portion from the calculated value can be adopted.

Further, the spot welds are located in the middle, electrodes are installed on both sides, and a current is passed through the electrodes for a short time, and the surface side of the spot welds due to the change of the Jule heat generated at that time. Detecting the temperature distribution of the infrared camera after a predetermined time, calculating the tendency of temperature rise from the temperature distribution detected by the infrared camera, and measuring the size of the nugget of the spot weld from the calculated value. It can also be adopted.

[0008]

[Operation] When the back surface of the center of the spot weld is heated with a gas burner for a certain period of time, or when the spot weld is positioned in the middle and electrodes are installed on both sides and a current is applied to the electrode for a short time. In the vicinity of the spot weld, the heating rate varies depending on the degree of welding between the non-welded part and the welded part or within the welded part.Therefore, the temperature change with the infrared camera at the time when a predetermined time has elapsed after heating. The temperature increase tendency is calculated from the detected temperature distribution, and the corona bond portion and the nugget diameter are determined from this.

[0009]

An embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows one embodiment in which a spot welded portion according to the present invention is heated and a temperature change of the heated portion is detected by an infrared camera. In the figure, 1 is a spot welding member, and the back surface 2 of the spot welding member 1 is heated by a gas burner 3. An infrared camera 5 is arranged on the front surface 4 side of the spot welding member 1, and the temperature change of the surface 4 of the spot welding member 1 is photographed by the infrared camera 5. In the present invention, the rear surface and the front surface of the spot welding member are unified so that the side to which the infrared camera is directed is the front surface and the opposite side is the rear surface. Further, 6 is a heat insulating material which covers the surface 4 of the spot welding member 1 excluding the measuring portion in order to avoid the direct influence of the flame of the gas burner 3 on the infrared camera 5, and 7 is an image processor. .

When the back surface 2 of the spot welding member 1 is heated by the gas burner 3, a heat quantity having a Gaussian distribution is given to the back surface 2 for a certain period of time centering on the welded portion of the spot welding member 1. The heat conduction to the surface 4 of the spot welding member 1 due to this heating varies depending on the degree of welding between the non-welded portion and the welded portion or within the welded portion, and the surely welded portion exhibits the highest heat conduction. Then, for example, 0.2 seconds after the end of the heating, the surface 4 of the spot welding member 1 is photographed from the surface 4 side of the spot welding member 1 by the infrared camera 5.
When the thermal image of the above is taken, the temperature distribution has a temperature distribution such that the central portion has the highest temperature range as shown in FIG.

Therefore, the temperature distribution from the imaged thermal image is used to perform a first derivative to know the distribution of the temperature gradient, and the position at which the absolute value of the gradient is maximum is determined as the corona bond diameter. Then, the second derivative is further performed, and the maximum position is determined as the nugget diameter.

FIG. 2 shows another embodiment in which the spot welding portion according to the present invention is heated and the temperature change of the heating portion is detected by an infrared camera. In the figure, the substantially welded center portion 12 of the spot welding member 11 is positioned in the middle and the electrodes 1 are provided on both sides thereof.
3, 14, 15, and 16 are installed, respectively. An infrared camera 18 is arranged on the surface 17 side of the spot welding member 11, 19 is an image processor, 20 is a controller, and 21 is a power source. In the figure, the electrode 13 on the surface 17 side of the spot welding member 11 is shown. , 15 are connected to the power source 21, and the electrodes 14, 16 on the back surface 22 side of the spot welding member 11 are insulated by the insulating materials 23, 24, respectively.
Insulated. Therefore, the electrodes 13 and 15 are energized, and the current flows on the surface 17 side of the spot welding member 11. When the electrodes 14 and 16 are connected to the power supply 21 and the electrodes 13 and 15 are insulated, a current flows on the back surface 22 side of the spot welding member 11, and the electrodes 13, 16 or 14, 15 are connected to the power supply 21. When the other electrodes are insulated from each other, the current flows between the front surface and the back surface of the spot welding member 11.

As described above, when the welding center portion 12 of the spot welding member 11 is positioned in the middle and a current is passed through the electrodes on both sides for a short time, the current passes through the welding center portion 12, and this current flows. In the spot-welded member 11, the non-welded portion and the welded portion or the welded portion also generate different Jule heat because the current density varies depending on the degree of welding. Therefore, when a thermal image of the surface 17 of the spot welding member 11 is taken by the infrared camera 18 from the surface 17 side of the spot welding member 11 after, for example, 0.2 seconds after the heating by the jule heat is completed, the temperature distribution is as shown in FIG. As shown in Nos. 4, 5, and 6, different temperature distributions are shown depending on the current flow method.

That is, FIG. 4 is an outline of the temperature distribution when the electrodes 14 and 16 are connected to the power source 21 and the electrodes 13 and 15 are insulated, and a current is applied to the back surface 22 side of the spot welding member 11. FIG. 5 is an outline of the temperature distribution when the electrodes 13 and 15 are connected to the power source 21 and the electrodes 14 and 16 are insulated, and a current is passed to the surface 17 side of the spot welding member 11, and FIG. , 16 or 14, 15 for power supply 2
1 is a schematic diagram showing the temperature distribution when the other electrodes are connected to each other and an electric current is passed through the spot welding member 11 from the front surface 17 side to the rear surface 22 side or from the rear surface 22 side to the front surface 17 side.

As a means for arithmetically processing the temperature distribution thus obtained, for example, when an electric current as shown in FIG. 4 is applied to the back surface 22 side of the spot welding member 11, first, a section taken along the line AA in FIG. The temperature curve is shown in the upper part of FIG. Then, this curve is first-order differentiated to know the distribution of the slope as shown in the middle part of FIG. 7, and the interval C at which the absolute value of this slope is the maximum is determined as the corona bond diameter, and the second-order differentiation is performed to perform the second-order differentiation. The curve shown in the lower part is obtained, and the interval N between the maximum positions is determined as the nugget diameter.

The method of heating the spot-welded portion in this manner and measuring the size of the nugget by detecting the temperature change of the heated portion with an infrared camera, and the method of spot-welding by ultrasonic waves described in the above-mentioned prior art. The size of the nugget diameter was judged by contrasting with the method of measuring the nugget of the part, but no particular difference was found between them.

[0017]

According to the present invention, the spot weld is heated,
The temperature change of the heating part is detected by an infrared camera, the tendency of the temperature rise is calculated from the temperature distribution detected by the camera, and the size of the nugget of the spot weld is measured from the calculated value. You can easily know the whole picture of the nugget in a short time.

Moreover, the spot weld is heated by a gas bar.
Since the image of the temperature distribution can be easily obtained by turning on or off the electricity and the image of the temperature distribution can be obtained in the atmosphere, it is not necessary to use water as in the conventional example, and its operation is easy.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an apparatus suitable for use in a method for measuring a nugget of a spot welded portion according to the present invention.

FIG. 2 is a configuration diagram similar to FIG. 1 of another embodiment.

FIG. 3 is a temperature distribution diagram of spot welds obtained by the measuring method according to the present invention.

FIG. 4 is a temperature distribution diagram similar to FIG. 3 of another embodiment.

FIG. 5 is a temperature distribution diagram similar to FIG. 3 of still another embodiment.

FIG. 6 is a temperature distribution diagram similar to FIG. 3 of still another embodiment.

FIG. 7 is an explanatory diagram calculated from the temperature distribution obtained in FIG.

[Explanation of symbols]

 1,11 Spot welding member 2,22 Rear surface of spot welding member 3 Gas burner 4,17 Surface of spot welding member 5,18 Infrared camera 12 Central part of spot welding portion 13, 14, 15, 16 Electrode

Claims (3)

[Claims] 1. A method for heating a spot-welded portion and detecting a temperature change in the heated portion with an infrared camera to measure the size of a nugget, wherein a temperature rise tendency is detected from a temperature distribution detected by the infrared camera. A method of calculating and measuring the size of the nugget of the spot welded portion from the calculated value. 2. A method for heating a spot weld and detecting a temperature change in the heated portion with an infrared camera to measure the size of the nugget, wherein the back surface of the center of the spot weld is fixed by a gas burner. After heating for a period of time, the temperature distribution on the surface side after a predetermined time is detected by the infrared camera, the tendency of temperature rise is calculated from the temperature distribution detected by the infrared camera, and the nugget of the spot weld is calculated from the calculated value. How to measure size. 3. A method of heating a spot weld and detecting a temperature change of the heated portion with an infrared camera to measure the size of a nugget, wherein the spot weld is positioned in the middle and electrodes are installed on both sides. Then, an electric current is passed through the electrode for a short time, and the temperature distribution on the surface side of the spot welding portion due to the change of the Jule heat generated at that time is detected by the infrared camera after a predetermined time, and detected by the infrared camera. A method of calculating the tendency of temperature increase from the obtained temperature distribution and measuring the size of the nugget of the spot welded portion from the calculated value.