JP4780334B2 - Weld crack detection method - Google Patents

Description

  The present invention relates to a technique for detecting a weld defect, and more particularly, to a weld crack detection method for detecting a weld crack generated in a weld bead.

Conventionally, as a method for detecting a welding defect, for example, there is a method described in Patent Document 1. In this method, the weld bead is irradiated with slit-shaped light from an oblique direction, the irradiated slit light is imaged by a television camera, and the image is subjected to data processing to perform pass / fail judgment.
JP-A-5-71932

  However, according to the method described in Patent Document 1, the quality of the weld bead is determined based on the shape characteristics of the weld bead. Therefore, defects such as large swells, sink marks, or perforations can be detected, but they occur in the weld bead. It is difficult to detect weld cracks that are present, and in particular, it is impossible to detect minute weld cracks. In addition, since image recognition is performed using welding beats with large irregularities, it is easy to be affected by noise (disturbance), requiring troublesome data processing to cancel out noise components, and the complexity of the processing system is inevitable. There was also a problem.

  The present invention has been made in view of the above-described conventional problems. An object of the present invention is to provide a weld crack detection method capable of easily and reliably detecting a weld crack generated in a weld bead.

  In order to solve the above problems, a weld crack detection method according to the present invention is characterized by monitoring a temperature change of a workpiece during welding and determining the presence or absence of a weld crack based on the temperature change.

When welding a workpiece having a wide plate surface, the heat of welding conducts heat almost evenly in the left-right direction of the welded portion (weld bead), and there is no great difference in temperature change in the left-right direction of the welded portion. However, when welding is performed along the edge (side edge) of the workpiece, the movement of heat stops at the edge portion, so that heat is accumulated at the edge portion, and this accumulated heat is opposite to the edge, that is, Move (back flow) to the weld side. At this time, if a crack is generated in the weld bead, the inside of the crack becomes a heat insulating layer, so that the heat transfer to the opposite side through the weld bead is prevented. As a result, in the edge side portion from the welding line, a difference in temperature change occurs between the portion corresponding to the portion where the weld crack is generated and the portion corresponding to the portion where the weld crack is not generated. That is, in the part corresponding to the place where the weld crack is generated, the cooling is delayed more than the part corresponding to the place where the weld crack is not generated. The present invention has been made based on the above-described knowledge, and by monitoring the temperature change of the workpiece during welding as described above, the presence or absence of a weld crack can be easily and reliably detected from the temperature change. .
In the following, some aspects of the present invention will be illustrated and described.

  (1) During welding along the edge of the workpiece, the temperature change at the edge side from the welding line is monitored, and the presence or absence of a weld crack is determined based on the temperature change in the cooling process. Weld crack detection method.

  As described above, in the portion corresponding to the portion where the weld crack is generated, the cooling is delayed more than the portion corresponding to the portion where the weld crack is not generated. . In the weld crack detection method described in the item (1), since the presence or absence of the weld crack is determined based on the temperature change in the cooling process, the detection accuracy of the weld crack is increased, and the detection of a minute weld crack is also possible. .

  (2) The weld crack detection method according to item (1), characterized in that the presence or absence of a weld crack is determined in comparison with a temperature change in a case where no weld crack has occurred.

  In the weld crack detection method described in the item (2), the presence or absence of a weld crack can be easily determined by comparing with a change in temperature when the weld crack is not generated. In this case, the determination criterion for grasping the temperature change is arbitrary, and it may be determined by the cooling rate, by the time until the temperature falls to the predetermined temperature, or by the area inside the cooling curve. By setting appropriate threshold values for these values, the presence or absence of weld cracks can be easily determined.

  (3) The method for detecting a weld crack according to (1) or (2), wherein a temperature change is monitored by an infrared imaging device.

  According to the weld crack detection method described in the item (3), since the temperature change can be monitored over a wide area by the infrared imaging device, the presence or absence of the weld crack can be determined over the entire length of the weld bead, and reliability for quality assurance can be determined. Improves.

  (4) The method for detecting a weld crack according to (1) or (2), wherein a temperature change is monitored by a thermocouple.

  In the case of lap laser welding, weld cracks are likely to occur near the end of welding, so it is only necessary to centrally monitor the vicinity of the end of welding. In this case, a thermocouple is used as described in this section (4). Temperature changes can be monitored at low cost.

  (5) The welding crack detection method according to any one of (1) to (4), wherein the welding is a lap laser welding of a two-ply steel sheet.

  Since weld cracks are likely to occur in overlap laser welding of two-layer steel sheets, the present invention is particularly useful when applied to overlap laser welding as described in (5).

  According to the weld crack detection method of the present invention, a weld crack generated in a weld bead can be detected easily and reliably, which is extremely useful for quality assurance of a welded product.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 shows one embodiment of the present invention. In the present embodiment, when the flange portions 1a and 2a of the two thin steel plates 1 and 2 are overlapped and laser-welded, the presence or absence of weld cracks occurring in the weld bead 3 which is a welded portion is detected in parallel. is there. Here, the lap laser welding is intermittently performed along the welding line L close to the edges (side edges) of the flange portions 1a and 2a, and the welding torch 4 that emits laser light is connected to the welding line L. Move up in the welding direction F. The crack detection device 10 for detecting a weld crack is an infrared imaging device 11 arranged above the welding line L and an image captured by the infrared imaging device 11 is subjected to data processing, and the flange portions 1a and 2a are processed. An image data processing device 12 that obtains a temperature change curve at a site close to the edge, and a quality determination device 13 that determines the presence or absence of weld cracks in the weld bead 3 based on the temperature change curve obtained by the image data processing device 12. And a display device 14 that displays the determination result of the pass / fail determination device 13 on the screen.

  When a weld crack occurs in the weld bead 3 during the overlap laser welding so that the welding range by the welding torch 4 can be imaged over a wide area, as shown in FIG. 2, the edge side part corresponding to the place where the weld crack 5 has occurred There is a difference between the temperature change curve at P1 (here, the edge proximity portion) P1 and the temperature change curve at the edge side portion (edge proximity portion) P2 corresponding to the location where the weld crack 5 is not generated. FIG. 3 shows an example of the temperature change curve. The temperature change curve (represented by a dotted line) in the edge side portion P1 corresponding to the location where the weld crack 5 occurs is a location where the weld crack 5 does not occur. Compared with the temperature change curve (represented by a solid line) in the edge side portion P2 corresponding to, the cooling process is delayed. This is because the heat transfer from the edge side to the opposite direction is prevented by the weld crack 5 as described above.

  The infrared imaging device 11 constituting the crack detection device 10 is arranged at a position where a wide range of welding by the welding torch 4 can be imaged. Then, during welding, the infrared imaging device 11 images the welding range at high speed, and an image for each frame is sent to the image data processing device 12 at high speed. The image data processing device 12 sets a plurality of measurement points at a predetermined pitch in the welding direction F with respect to the image sent from the infrared imaging device 11, obtains a temperature change curve for each measurement point, and determines the result as good or bad. The data is sent to the determination device 13. The pass / fail judgment device 13 stores in advance a good temperature change curve of the edge side portion corresponding to the location where the weld crack 5 has not occurred, and the pass / fail judgment device 13 determines the good temperature change curve and the actual temperature change curve. The presence or absence of the weld crack 5 is determined by comparing the obtained temperature change curve. In this case, the pass / fail judgment device 13 sets appropriate thresholds for these values based on, for example, the cooling rate, the time until the temperature falls to a predetermined temperature, the area inside the cooling curve, etc. Pass / fail can be determined in relation to the value.

  As described above, in the present embodiment, the temperature change of the edge side portion is monitored by the infrared imaging device 11, the image captured by the infrared imaging device 11 is processed, and the presence or absence of the weld crack 5 is determined. Even a simple weld crack can be detected, and the reliability with respect to the detection accuracy is sufficiently high. Moreover, since the presence or absence of a weld crack is detected over the entire length of the weld bead 4, the reliability for quality assurance is improved.

  In the above embodiment, the temperature change of the edge proximity portion of the flange portions 1a and 2a is monitored. However, this monitoring portion (setting position) is arbitrary as long as it is an edge side portion from the welding line L. It may be a part slightly away from the edge. Moreover, in the said embodiment, although the example applied to welding of the flange parts 1a and 2a was shown, this welding object is arbitrary and a product general part may be sufficient. Furthermore, in the said embodiment, although the example applied to the lap welding was shown, as long as it is the aspect welded along the edge (side edge) of a workpiece | work, even if it is butt welding or fillet welding Good.

  Using a high-strength steel sheet having a thickness of 1.4 mm as a raw material, the two sheets were overlapped, and a part 5 mm away from the edge was overlapped and laser welded under the conditions of a laser output of 4 kW and a welding speed of 2 mm / min. In this lap laser welding, a plurality of thermocouples were attached to the edge proximate portion at a predetermined pitch in the welding direction in advance to monitor the temperature change, and an experiment was conducted on the relationship between the occurrence of weld cracking and the temperature change.

FIG. 5 shows the above experimental results. FIG. 5A shows a temperature change curve when no weld crack occurs, and FIG. 5B shows a temperature change curve when a weld crack occurs. Each represents. Thus, when the weld crack occurs, the cooling is significantly delayed as compared with the case where the weld crack does not occur. Incidentally, when compared with the time to drop to 400 ° C., while the time T _A in the case of weld crack is not generated (A) is about 3 seconds, the time T _B in the case of weld crack is generated (B) Is about 27 seconds, and a very large time difference is recognized between the two. Therefore, for example, it is clear that a weld crack can be reliably detected by the method of the present invention by setting an appropriate threshold value between the above-described times T _A and T _B.

1 is a perspective view schematically showing one embodiment of a welding crack detection method and apparatus according to the present invention. It is a top view which shows typically the generation | occurrence | production state of a weld crack. It is a graph which shows the difference of the cooling curve in the site | part (P1) corresponding to the location (P1) corresponding to the location where the weld crack generate | occur | produced, and the location where the weld crack does not generate | occur | produce. The experimental result of a weld crack is shown, (A) is a graph which shows the temperature change curve when a weld crack does not generate | occur | produce, (B) is a graph which respectively shows the temperature change curve when a weld crack occurs.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Thin steel plate 1a, 2a Flange part 3 Weld bead 4 Welding torch 5 Weld crack 10 Weld crack detection apparatus 11 Infrared imaging device 12 Image data processing apparatus 13 Pass / fail judgment apparatus 14 Display apparatus L Welding line

Claims (5)

  Welding crack detection characterized by monitoring the temperature change at the edge side from the welding line during welding along the edge of the workpiece and determining the presence or absence of weld cracking based on the temperature change in the cooling process Method.   The weld crack detection method according to claim 1, wherein the presence / absence of a weld crack is determined by comparing with a change in temperature when a weld crack does not occur, which is grasped in advance.   The method for detecting a weld crack according to claim 1 or 2, wherein a temperature change is monitored by an infrared imaging device.   The method for detecting a weld crack according to claim 1, wherein a temperature change is monitored by a thermocouple.   The welding crack detection method according to any one of claims 1 to 4, wherein the welding is a lap laser welding of two steel sheets.

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