JP6418005B2 - Undercut defect detection method, undercut defect detection device, and fillet arc welding method - Google Patents

Description

  The present invention relates to a method for detecting weld defects during arc welding, and more particularly to a method for detecting undercut defects online in arc welding.

  In the case of automatic welding, if the dimensional accuracy of the groove is poor, undercutting may occur due to the movement trajectory of the welding torch being deviated from the center of the groove even if the welding line is copied.

  Therefore, after the welding operation is completed, the operator detects the undercut defect by visually observing the appearance shape around the welded portion. However, when an operator visually detects an undercut defect, skill is required to find the undercut defect, an error is likely to occur in the quality determination, and much labor is required for repair. In addition, when the undercut defect is detected by visual inspection after the welding operation is completed, if an undercut defect is found, the periphery of the defective part is excised, and after repair welding, the repetitive operation of detecting the defect again The cost and work man-hours increased, and the welding cost was high.

  For this reason, it has been desired to detect in real time defects that occur during welding. That is, it has been desired to monitor the information on the welded part in real time during welding, detect an undercut defect, and immediately determine whether or not to continue welding. Under such circumstances, various proposals have been made regarding detection (on-line detection) of welding defects around a welded part during welding.

  In Patent Document 1, in arc welding, the welding voltage at the time of arc welding is monitored, and the perforation is detected by detecting the moment when a certain deviation or more has occurred from the specified value set from the data at the time of normal welding. Technology is disclosed.

  In Patent Document 2, a relational expression between a current change amount ΔI and a distance change amount ΔL from the torch to the base material to be welded is identified by test welding, and in actual welding, the welding current I is detected and detected from the target current. By calculating the current change amount ΔI and substituting the calculated current change amount ΔI into the relational expression, the distance change amount ΔL from the target distance from the torch to the base material to be welded is calculated, and the calculated distance change A technique is disclosed in which the tip position of the torch is feedback-controlled so as to reduce the amount ΔL, and the occurrence of defects is suppressed without shifting the target position.

  In Patent Document 3, slit light is irradiated to a groove part to be welded, the slit light reflected on the surface of the groove part is imaged, and an image of the imaged slit light is image-processed to obtain a light cutting line. A technique is disclosed that suppresses the occurrence of defects by extracting and recognizing the position and shape of the groove portion from the obtained optical cutting line and welding an accurate target position.

  The technique disclosed in Patent Document 1 has a problem that the voltage fluctuation is small and cannot be monitored in a welding defect other than a hole defect, and the technique disclosed in Patent Document 2 is misaligned in a groove with poor cutting accuracy. There is a problem that an undercut defect occurs, and the technique disclosed in Patent Document 3 uses an optical cutting method device, which can detect an undercut defect but is very expensive and difficult to put into practical use. there were.

JP 2014-046316 A JP 2014-030841 A JP, 2014-032076, A

  An object of the present invention is to provide a method capable of detecting an undercut defect on-line in arc welding in view of the above-described state of the art.

  Therefore, the present inventors diligently studied a method for solving the above problems. When performing fillet arc welding, a camera was installed diagonally above the welding direction of the fillet arc welding device in the reverse direction, and the periphery of the weld was observed. High-intensity light was observed at the location corresponding to the weaving reversal position. When this light was investigated in detail, it was found that the arc light was reflected by an undercut defect. And it discovered that the presence or absence of an undercut defect could be detected and determined online by detecting this reflected light during fillet arc welding.

The present invention has been made based on the above findings, and the gist thereof is as follows.
(1) A method of detecting an undercut defect during welding when welding a fillet arc while weaving a welding torch, and a camera around the welded portion immediately after solidification among the welded portion surrounding fillet arc welding When the reflected light of the arc light that is brighter than the surroundings observed at the place corresponding to the reversing position of the weaving is detected, the undercut defect has occurred. A method of detecting an undercut defect, characterized by: determining.
(2) An apparatus for detecting an undercut defect during welding when performing fillet arc welding while weaving the welding torch, and imaging around the welded portion immediately after solidification among the welded portion during fillet arc welding An undercut defect detection device comprising: a camera for displaying an image captured by the camera, and a display device capable of monitoring the presence or absence of reflected light of arc light.
(3) A method of automatically performing fillet arc welding while weaving the welding torch, wherein an undercut defect has occurred during the fillet arc welding by the undercut defect detection method described in (1) above. When this is detected, the fillet arc welding method is characterized in that the fillet arc welding is stopped, and the fillet arc welding is performed by changing the welding position of the welding torch.

  According to the present invention, in fillet arc welding, an undercut defect that cannot be detected by voltage monitoring can be detected on-line regardless of the dimensional accuracy of the groove. Can be detected and determined.

It is a figure which shows the outline of the method of adjusting the welding aim position of the center of weaving and performing fillet arc welding. It is a figure which shows the mode during fillet arc welding, and the cross section of a weld bead. (A) shows the part which shines with high brightness around the welded part immediately after welding during fillet arc welding, and (b) shows the cross section (optical micrograph) of the weld bead including the part shined with high brightness. It is a figure which shows the cross section (optical microscope photograph) of the welding bead containing the part which was shining with high brightness | luminance when adjusting the welding aim position of the center of weaving and performing fillet arc welding. It is a figure which shows the relationship between the welding aim position of the center of weaving, and the depth of an undercut defect.

Hereinafter, the welding defect detection method of the present invention (hereinafter referred to as “the detection method of the present invention”) will be described.
The detection method of the present invention is a method for detecting an undercut defect that occurs during fillet arc welding when performing fillet arc welding of a joining portion or a crossing portion of two plates. In particular, of the surroundings of the welded part during fillet arc welding, the surroundings including the reversing position of the weaving around the welded part immediately after solidification are imaged with a camera, the reflected light of the arc light is monitored, and it corresponds to the reversing position of the weaving This is a detection method in which it is determined that an undercut has occurred when the reflected light of high-intensity arc light from a spot to be detected is detected.

  The inventors of the present invention, when the welding operation is completed, detect the undercut defect by visual inspection or the like, require skill to find the undercut defect, easily cause an error in the quality determination, and greatly repair. Since it takes time, we studied a method for easily detecting the occurrence of undercut defects online. First, with respect to the welding progress direction of the arc welding apparatus, a camera was installed obliquely above the reverse traveling direction, fillet arc welding of the T-shaped joint was performed, and the periphery of the welded part during arc welding was observed. As a result, high brightness light was confirmed around the welded part immediately after welding. When the part which was shining after completion | finish of welding work was confirmed, the undercut defect had arisen. From this, it was guessed that the high-intensity light around the welded part immediately after welding was arc light reflected by the undercut defect.

  Therefore, the present inventors intentionally adjust the welding target position of the welding torch so that an undercut defect is likely to occur during fillet arc welding, and the high brightness light around the welded part immediately after welding. In order to confirm the relationship with the undercut defect, the following test was performed.

  FIG. 1 shows an outline of a method for performing fillet arc welding by adjusting the welding target position at the center of the weaving. First, the shape of the test plate used for fillet arc welding will be described with reference to FIG. In the test, the steel plate 1 and the steel plate 2 are used as test plates, the steel plate 2 is used for the steel plate 1, and the fillet arc welding is performed using the welding torch 3. YM-24T was used for the welding wire. Both the steel plate 1 and the steel plate 2 have a length of 200 mm in the depth direction of the paper (hereinafter referred to as “length direction”). The steel plate 2 has a length of 50 mm in the length direction and the direction perpendicular to the plate thickness direction (hereinafter referred to as “width direction”). Moreover, the steel plate 2 has an inclined portion of 10 mm in the width direction and 5 mm in the plate thickness direction at the end of the weld. This is to simulate welding from the state after the lower layer is formed in the multi-layer welding.

  Next, welding conditions for fillet arc welding will be described. First, the welding target position of the welding torch 3 will be described. The welding target position 4 can be set to 0 to +7 at 1 mm intervals in the inclination direction of the welded portion end of the steel plate 2 with the welded end portion of the steel plate 2 being set to 0. In the test, the welding target position 4 is set to +1, the frequency is set to 50 Hz with the welding target position 4 as the center, the welding torch 3 is weaved, and the fillet arc welding is performed in the length direction of the steel plates 1 and 2. Went. Other welding conditions were set to a current of 270 A, a voltage of 30 V, and a welding speed of 18 cm / min.

  Next, a method for observing high-luminance light around the welded part immediately after welding will be described. During fillet arc welding, the periphery of the welded portion including the weaving reversal position of the steel plate 1 around the welded portion immediately after solidification was imaged with a camera to observe high-luminance light. The camera was a CCD camera equipped with a band-pass filter that allows only light in the wavelength range of 940 nm ± 4 nm. And this camera was installed in the diagonally upward direction of welding reverse progress with respect to the welding part, and the steel plate 1 around the welding part immediately after solidification was imaged. The imaging condition was 2000 frames / second.

  The state during fillet arc welding in this test and the formed weld bead will be described. FIG. 2 shows a state during fillet arc welding and a cross-sectional view of the weld bead. FIG. 2A shows a diagram of a portion that shines with high brightness around the welded portion immediately after welding during fillet arc welding, and FIG. 2B shows a cross section of the weld bead including the portion that shines with high brightness. The figure is shown.

  As shown in FIG. 2 (a), during fillet arc welding, arc 6 is generated from the tip of the wire 5 provided on the welding torch 3 in the fillet arc welding of the steel plate 1 and the steel plate 2 and melted. A pond 7 is formed. A weld bead 8 is formed behind the molten pool 7 with respect to the welding direction, and a portion 9 that emits light with higher brightness than the surrounding steel plate 1 is observed in the form of dots on the top of the weld bead 8 immediately after solidification. However, high-intensity light was not observed on the welded portion in front of the molten pool 7 and on the upper portion of the weld bead 8 that is about 5 cm or more away from the molten pool 7.

  The portion 9 that emits high-intensity light is made to correspond to the position in the longitudinal direction of the weld bead 8, and in the longitudinal direction of the weld bead 8 so as to include the portion 9 that emits high-intensity light after completion of fillet arc welding. Cut vertically. The cut cross-sectional image is an image shown in FIG. As shown in FIG. 2B, an undercut was formed in a section surrounded by a dotted line in the cross section observed with the optical microscope. Therefore, it was confirmed that the portion 9 that emits light with higher luminance than the surrounding steel plate 1 is a portion where the undercut defect shines by reflecting the arc light. In addition, there is a portion corresponding to the reversing position of the weaving in the vicinity of the undercut defect, and when the welding target position at the center of the weaving is not appropriate, an undercut defect is formed at a position corresponding to the reversing position of the weaving. I found out.

  Next, in order to confirm the depth of the undercut defect that can be observed as high-intensity light around the welded part immediately after welding, the following test was performed.

  Five sets of test plates similar to the test plate shown in FIG. Then, the welding target position 4 is set to 5 levels from +3 to +7, the frequency is set to 50 Hz around each welding target position 4, and the welding torch 3 is weaved. Fillet arc welding was performed in the direction to prepare five test pieces. Other welding conditions were common to each group, and were set to a current of 270 A, a voltage of 30 V, and a welding speed of 18 cm / min.

  In addition, the observation of high-intensity light around the welded part immediately after welding uses the same camera and bandpass filter as the above-described test of the correspondence between the high-intensity light around the welded part immediately after welding and the undercut defect. The steel sheet 1 around the welded part immediately after solidification was imaged with a camera. The imaging condition was 2000 frames / second.

  FIG. 3 shows a cross-sectional view of a weld bead that is observed with an optical microscope including a portion that shines with high brightness around the welded part when fillet arc welding is performed by adjusting the welding target position at the center of the weaving. FIG. 3 also shows a cross-sectional view of a weld bead including a portion shining with high brightness around the welded portion when the fillet arc welding is performed with the above-mentioned welding target position 4 being +1. FIG. 3 shows that the undercut defect is reduced by moving the welding target position from +1 to +7. That is, when the welding target position is +7, it can be seen that the welding target position is an appropriate welding target where no undercut defect occurs.

  FIG. 4 shows the relationship between the welding target position at the center of the weaving and the depth of the undercut defect. In addition, the white circle is the relationship between the welding target position and the undercut depth where the bright part was observed, and the welding target position and the undercut depth where the black circle was not observed as the bright part. It is a relation to. As a result, even when the welding target position was set to +6 and the fillet arc welding was performed, even a very shallow undercut defect of about 0.1 mm was observed to shine with high brightness. . Here, the undercut depth was obtained by measuring the distance between the surface of the steel plate 1 and the deepest point of the undercut.

From the above, among the welded parts during fillet arc welding, the surroundings including the reversal position of the weaving of the steel sheet 1 around the welded part immediately after solidification are imaged by the camera, and the reflected light of the arc light with higher brightness than the surrounding steel sheet 1 It was found that even under shallow defects can be detected online by detecting.
In addition, since high-speed cameras and bandpass filters are expensive, a similar experiment was performed by installing a neutral density filter instead of a bandpass filter on a commercially available home digital camera. As a result, it was confirmed that an undercut defect was detected in a commercially available home digital camera as well.

  The present invention has reached the inventions described in the above (1) to (3) through the examination process as described above, and the necessary requirements and preferable requirements will be further described in order for the present invention. .

First, the detection method of the present invention will be described.
The detection method of the present invention is a method for detecting an undercut defect that occurs during welding during fillet arc welding while weaving a welding torch of a welded joint. The surrounding area including the reversing position of the weaving of the steel plate around the welded part is imaged with a camera, and the arc light reflected from the steel sheet is monitored, and the periphery of the position observed at the position corresponding to the reversing position of the weaving of the steel sheet This is a method for determining that a welding defect has occurred when the reflected light of arc light with higher brightness is detected. Undercuts generated from either the steel plate 1 side or the steel plate 2 side in FIG. 1 can be observed.

(Fillet arc welding)
The detection method of the present invention is a method that is performed when fillet arc welding is performed on a crossing portion of a steel plate and a steel plate. The welding method of fillet arc welding is not particularly limited, and a commonly used welding method can be adopted as long as welding is performed while weaving the welding torch. A welding wire can also be used regardless of the wire component. Conventional welding conditions such as current and voltage may be used. When the shielding gas is used, the shielding gas may be Ar gas, CO ₂ gas, and a mixed gas thereof.

(Welded steel plate)
The thickness of the steel sheet to be welded is not particularly limited. However, in fillet arc welding of a steel sheet having a thickness of 6 mm or more, a welding method in which the welding torch is gradually moved in the welding progress direction while weaving may be employed. The detection method of the present invention is a method for detecting an undercut defect formed close to the weaving reversal position when the welding target position at the center of the weaving is not appropriate. It is effective when used in meat arc welding. The shape of the steel sheet to be welded should have at least a plate-like portion, and the whole may not be a plate, and includes, for example, a shape steel and a steel pipe.

  Moreover, the component composition of the steel plate to be welded is not particularly limited. As described above, the detection method of the present invention is based on the detection of the reflected light of the arc light from the undercut defect. Therefore, the component composition of the steel plate and the weld metal to be welded is limited to this limit. There is no need to make adjustments according to the desired mechanical properties. Stainless steel or aluminum may be used.

(Camera installation location)
An undercut defect can be imaged by installing the camera in the reverse direction of welding of the welded portion so as to image the periphery including the weaving reversal position around the welded portion immediately after solidification. The welded part immediately after solidification is a welded part within a range of about 5 cm from the rear of the molten pool. And a camera is installed in the position which can image the undercut defect produced around the welding part immediately after solidification, and does not necessarily need to monitor arc light, a molten pool, and a weld bead. Therefore, the distance (for example, 150 mm to 300 mm) between the welded portion and the welding camera may be adjusted so that the periphery including the reversal position of the weaving of the steel sheet enters the field of view of the camera. In addition, it is preferable to install a camera obliquely above the steel plate around the welded portion in the reverse direction of welding of the welded portion because it is easy to detect an undercut defect.

(Monitoring of arc reflected light)
The arc light reflected from the steel plate is imaged by a camera and displayed on a display device for monitoring. It is determined that an undercut defect has occurred when the reflected light of arc light having a higher luminance than the periphery of the portion observed at the portion corresponding to the reversal position of the weaving of the steel plate is confirmed. Since the reflected light of the arc light from the said part is high-intensity, it can confirm easily and can determine the occurrence of an undercut defect even if it is not a skilled worker. In addition, the undercut defect that affects the joint strength of the weld is an undercut defect that is formed in the final pass. When welding, and when one-pass welding of a crossing portion of a steel plate and the like is performed, the reflected light of the arc light may be monitored during one-pass fillet arc welding.

Next, the undercut defect detection apparatus of the present invention (hereinafter referred to as “detection apparatus of the present invention”) will be described.
The detection apparatus of the present invention is an apparatus for detecting an undercut defect that occurs during fillet arc welding. Among the surroundings of the weld during fillet arc welding, the reversing position of the weaving of the steel plate around the weld immediately after solidification is detected. It is an apparatus having a camera that captures the surroundings and a display device that displays an image captured by the camera.

(camera)
The detection apparatus of the present invention has a camera that images the periphery of the welded part including the reversal position of the weaving of the steel plate around the welded part immediately after solidification during fillet arc welding. It can be set as the camera which has sensitivity to infrared region, such as a digital video camera. The camera preferably includes a lens for imaging, and a neutral density filter or the like is attached to the lens. This is because the arc light is too strong. In fillet arc welding, when a pulse current is used, a camera that can be observed with a frame number more than twice the pulse frequency should be used so that the arc light emitted at the pulse frequency can be imaged. preferable. For example, when fillet arc welding is performed by weaving at 50 Hz, the imaging condition of the camera is exemplified at 2000 frames / second.

(Band pass filter)
It is also preferable to attach a band-pass filter to the camera and pick up an image with the camera through only light of a specific wavelength. However, since the radiation from this high-luminance part is mainly light in a wavelength region of 600 nm or less, when photographing using a bandpass filter that selectively transmits a region having a wavelength longer than red, the plasma around the arc The portion is relatively suppressed, and the appearance around the weld can be better observed. If the bandpass filter can also transmit infrared light, a clearer image can be obtained by detecting reflected light of the arc light from the undercut when using an imaging device having sensitivity up to the infrared region, such as a CCD camera. Can be obtained. When a commercially available home digital camera is used, a clear image can be obtained even using a neutral density filter.

(Display device)
The image picked up by the camera is displayed on a display device such as a liquid crystal display, for example. The display device is not particularly limited as long as the operator can confirm the displayed image.

Next, the fillet arc welding method of the present invention (hereinafter referred to as “the welding method of the present invention”) will be described.
When the welding method of the present invention detects that an undercut defect has occurred by the detection method of the present invention during fillet arc welding automatically based on a predetermined welding target position while weaving the welding torch. The fillet arc welding is performed by stopping fillet arc welding and changing the welding target position of the welding torch.

  When welding is performed while automatically weaving using a welding robot or the like, the welding torch is advanced based on a predetermined welding target position or in combination with welding line tracing. However, if the groove center is misaligned, or if the misalignment is beyond the range that can be covered by welding line scanning even when welding line scanning is used, the welding torch cannot follow the groove change. Undercut may occur.

  Therefore, when an undercut defect is detected by the detection method of the present invention, fillet arc welding is stopped, the welding target position is changed to an appropriate position, for example, the welding target position is changed to +7 in FIG. Perform again. This eliminates the need for repair welding around the undercut defect after completion of the welding operation.

  According to the present invention, in fillet arc welding, an undercut defect that cannot be detected by voltage monitoring can be detected on-line regardless of the dimensional accuracy of the groove. Can be detected and determined. Therefore, the present invention has high industrial applicability.

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Steel plate 3 Welding torch 4 Welding aim position 5 Wire 6 Arc 7 Weld pool 8 Weld bead 9 Part which emits high-intensity light (undercut)

Claims (3)

  This is a method for detecting undercut defects during welding when fillet arc welding while weaving the welding torch. Of the surroundings of the welded part during fillet arc welding, the area around the welded part immediately after solidification is imaged with a camera. When the reflected light of the arc light is monitored and the reflected light of the arc light having a higher brightness than the surrounding area observed at the position corresponding to the reversal position of the weaving is detected, it is determined that the undercut defect has occurred. An undercut defect detection method characterized by the above.   An apparatus for detecting undercut defects during welding when performing fillet arc welding while weaving the welding torch, and a camera for imaging the periphery of the welded portion immediately after solidification among the welded portion during fillet arc welding An undercut defect detection device comprising: a display device capable of displaying an image picked up by the camera and monitoring the presence or absence of reflected light of arc light.   A method of automatically performing fillet arc welding while weaving a welding torch, wherein an undercut defect is detected by the undercut defect detection method according to claim 1 during the fillet arc welding. By the way, the fillet arc welding method is characterized in that the fillet arc welding is stopped and the fillet arc welding is performed by changing the welding position of the welding torch.