KR20030017016A - Method and apparatus for estimating welding quality in high frequency electric resistance welding - Google Patents

Abstract

PURPOSE: A method and an apparatus for judging quality of high frequency electric resistance welding are provided to more accurately judge quality of welding in manufacturing a steel pipe. CONSTITUTION: A CCD camera(14) obtains an image of an observation area(13) nearby a V convergence welding point based on the V convergence welding point. An image board(15) converts an analog image signal into a digital image signal. An image processing and analyzing part(16) extracts a welding part heating area by using the digital image signal. A welding quality judging part(17) judges an accident of welding by using the welding part heating area. A welding quality judging result display part(18) reporting the result from the welding quality judging part to a worker.

Description

METHOD AND APPARATUS FOR ESTIMATING WELDING QUALITY IN HIGH FREQUENCY ELECTRIC RESISTANCE WELDING}

The present invention relates to a welding quality determination method and apparatus for high frequency electric resistance welding used to manufacture a steel pipe.

The high frequency electric resistance welding is a welding method in which a high frequency current of about 300 to 1000 kHz is applied to the welded material, and a compression is applied to a welded portion heated by resistance heat generated at this time. A representative example to which this welding method is applied is a process of manufacturing a steel pipe by sequentially forming a steel strip as shown in FIG. The high frequency electric resistance welding method is a high frequency induction welding method in which a high frequency current is induced and heated by using an induction coil 2 as shown in FIG. 1 (a) according to a method of applying a high frequency current to the welded material 1; As in b), there is a high frequency resistance welding method in which the contactor 3 is brought into contact with the welded material 1 to directly supply current.

In Fig. 1, 4 is a welding point, 5 is a welding part, 6 is a pressure roll, and 7 is an impeller.

The characteristics of the high frequency electric resistance welding method is that the heat effect is small and the welding speed is increased because the resistance heat is concentrated in the welded section due to the skin effect and proximity effect generated by the use of high frequency. The productivity is much higher than the welding process.

Oil and gas pipes and mechanical structural steel pipes made by this welding method require high quality, and welding defects must be strictly managed because defects in welding parts can result in major accidents or environmental disasters.

For this reason, an automatic heat input control method has been proposed and used to automatically adjust the amount of heat input to the weld in order to reduce the frequency of weld defects in the steel pipe manufactured by the high frequency electric resistance welding method. Fig. 2 shows an overview of this method, which includes a traveling speed signal S1 of the welded material 1, a pressing force signal S2 for the welding portion 5, a current heat input signal S3, and the like. Is fed back to the computing unit (8), and the computing unit (8) generates a welding zone heating width target value and a current heating width signal (S5) corresponding to the current situation from the feedback signals to the welding controller (9). It is a way to send. However, this method has the problem that the heating width of the welding part, which is a feedback signal, is greatly influenced by the noise over time, and it is also active for the variation of the welding point converged to the V type because the measurement position of the heating width is fixed and measured. It has the disadvantage of not coping.

The present invention is to provide a new and useful welding quality determination method and apparatus using the image information on the heating phenomenon of the weld in order to solve the above conventional problems, the welding point that best represents the welding phenomenon using a vision system Acquiring a nearby image; acquiring image information on a heating area that is correlated with welding quality and having low noise from the acquired image; and determining weld quality from the image information on the heating area. It is to provide a method comprising a step and an apparatus for performing the method.

1 is a schematic diagram of steel pipe manufacturing by high frequency electric resistance welding;

2 is a configuration diagram of a conventional automatic heat input control apparatus;

3 is a configuration diagram of an apparatus for determining welding quality of high frequency electric resistance welding according to the present invention;

4 is a flowchart of a welding quality determining method according to the present invention;

5 is a graph showing a correlation between a welded heating area and weld defects;

Figure 6 is a view showing the image acquisition and the heating area extraction according to the weld in sequence.

Explanation of symbols on the main parts of the drawings

DESCRIPTION OF SYMBOLS 1 Welding material 11 Contact 12 Pressing roll

13: observation area 14: CCD camera 15: image board

16: image processing and analysis unit 17: welding quality determination unit

18: welding quality determination result display unit 19: heating area

Hereinafter, the method and apparatus of the present invention for achieving the above object will be described in more detail with reference to the accompanying drawings. Figure 3 shows the overall configuration of the apparatus according to the present invention, which is a welding quality determination apparatus of high frequency electric resistance welding including a vision system for extracting image information of the welding phenomenon, Figure 4 is correlated with the welding quality The image information acquisition and analysis algorithm is shown.

First, FIG. 3 is a device used to carry out the method of the present invention, wherein 11 is a contact tip for supplying a high frequency current from the welding power source to the welded material 1 to be welded, and 12 is a high frequency current. Is a squeeze roll that presses and joins a locally heated section, and 13 is a region near the V convergent welding point, which is the part that best describes the welding phenomenon and provides the most information in high frequency electric resistance welding. 14 is a CCD camera configured to observe the area near the welding point in a vertical direction in order to derive a correlation between image information and welding quality, and 15 is a CCD camera 14. The image board converts the acquired image into a digital signal for processing and analysis on a computer.16 is divided and welded using a digital image signal. The digital image processing and analysis unit is responsible for calculating points and calculating the heating area, and 17 is the heating area including the current heating area and the preset allowable range, which is information obtained through digital image processing and image analysis. Is a welding quality judging unit for judging the welding quality, and 18 is a welding for informing the worker of the heating area and the allowable heating area range of the welding unit input to the welding quality judging unit 17 and the determination result of the welding quality judging unit. Quality judgment result display unit.

In the present invention, the image to evaluate the welding phenomenon uses an image based on the welding point converged to the V-shape. When the image of the welded area that was heated based on this V-converging weld point was used as the characteristic value, it was found that the standard deviation of the signal was small and correlated with the weld defect.

Fig. 5 shows the relationship between the welding area and the welding area proposed in the present invention in the production of steel pipes for a 10 mm thick steel pipe material. Condition 1 is a welding condition where the V convergence angle of the weld is 5 degrees and the welding speed is 16 m / min.Condition 2 is a welding condition where the V convergence angle is 5 degrees and the welding speed is 20 m / min. In Condition 3, Condition 3 is the result of welding under the welding condition of V converging angle of 6 degrees and welding speed of 16m / min. Regardless of welding speed or V convergence angle, it can be seen that the heating area increases linearly with increasing welding power under any condition. For this material and thickness, the welding area shows good welding quality at 100 ~ 200mm ² . If it is out of the area, it shows a weld defect. From this, it is shown that if the reference heating area and tolerance are set for a certain material or thickness, the quality of welding can be judged easily by monitoring the occurrence of welding defect when it is out of this tolerance range.

4 shows a process of digital image processing and welding quality determination of a weld according to the present invention, and FIG. 6 acquires an image of a weld using the apparatus of FIG. 3 and the digital image processing and image analysis algorithm of FIG. An example of extracting the heating area is shown. First, an appropriate heating area and an allowable range are set according to the material and thickness of the object to be welded, and the welding image is acquired from the CCD camera 14 and the image board 15 at the start of welding. The first image acquired by the weld is a black and white image having a gray distribution as shown in FIG. Next, the threshold value is determined using the histogram of the image area acquired by the image processing and analysis unit 16, and the heated area and the background area are divided based on the threshold value. It is treated as 0 and the area above the threshold (heated area) is treated as 255. In this process, a binarized image as shown in FIG. 6B is obtained. Next, in the image processing and analysis unit 16, an edge is obtained from line profile (Line1, Line2) information for two lines as shown in FIG. 6 (c) in order to find a V convergence welding point from the binarized image. After detecting the point, the equation of two straight lines forming the V convergence angle is obtained and the V convergent welding point is calculated from the equations of these two straight lines. Next, the heating area 19 is calculated by setting the ROI (region of interest) 10 mm above and below and 25 mm before and after the V convergence welding point calculated as described above (Fig. 6 (d)). Next, the welding quality determining unit 17 determines that the welding quality is good when the currently calculated heating area falls within the preset allowable range, and determines that the welding quality is bad when out of the allowable range. Finally, the welding quality determination result display unit 18 informs the operator of the current welding quality result in real time and provides information so that the current welding process state can be easily monitored.

The welding quality judgment is explained in more detail. First, the standard welding area and allowable range according to the material and thickness of the welded material are set in advance, and compared with the welding area obtained through image processing and image analysis during actual welding. If it is out of the allowable range, it is judged to be a welding defect, and it is within the allowable range and is judged to be good. In addition, when welding is performed at a constant speed and the image information acquisition period is also constant, for example, 1/30 second, the position of the welding defect determination is calculated based on the information on the welding starting point, and the number of defect determination is accumulated to determine the total welding defect length. Calculate Then, the percentage of weld defects is calculated from the ratio of the number of welding good judgment and the number of welding failure judgment at the end of welding.

The present invention calculates the heating area for a certain area near the welding point of the V-converging type and the preset reference value and tolerance according to the material and thickness of the welded material when welding the steel pipe by the high frequency electric resistance welding method as described above. With regard to the limit, it is possible to make a more accurate determination of welding quality by providing real-time information on the position, the number of deviations, and the length of deviations outside the allowable limits during welding.

Claims (2)

In the high frequency electric resistance welding applied to steel pipe manufacturing, a CCD camera 14 which acquires an image of a certain region near the welding point based on the V convergence welding point, and an analog image signal from the CCD camera 14 are digitally imaged. The image board 15 which converts the signal into a signal, the image processing and analysis unit 16 which extracts the welded heating area by using the digital image signal from the image board 15, and the weld abnormality using the welded heating area. The welding quality determination unit 17 for determining nothing, and the welding quality determination result display unit 18 for informing the operator of the result output from the welding quality determination unit 17, the high frequency electric resistance welding Welding quality determination device. A method for determining the welding quality of high frequency electric resistance welding, the method comprising: setting a reference value and a permissible range of a heating area for a region near the V-converging welding point according to the thickness and material of the welded material; Calculating a V convergence welding point using the image information, calculating a heating area of a predetermined region near the V convergence welding point, and setting a reference value and a tolerance set in advance in the heating area reference value and setting an allowable range thereof. Comparing and determining the heating area calculated in the step and calculating the heating area of a certain area near the V convergence welding point to determine the presence or absence of welding abnormality, and the position and deviation of the position outside the allowable limit during welding after welding A welding quality determination method of high frequency electric resistance welding comprising the step of evaluating the number of times, the deviation length.