JP2002126885A - Monitoring method for laser welding quality and monitoring method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser welding quality monitoring method and device capable of conducting with excellent accuracy the quality determination of a welded part in lap welding of a surface treatment steel material provided with a covered layer of a substance with a melting point lower than that of a base material. SOLUTION: In the laser welding quality monitoring method in a laser lap welding method in which at least one lapping face becomes the covered layer of the substance with the melting point lower than that of the base material, by using the fact that the low frequency component strength peak-a peak value SL(t) in 30 Hz or below of a key hole emission signal detected by a light sensor makes the relational expression |SL(t)|>Th1 established against a threshold Th1 previously set at the time of occurrence of welding anomaly in over lap gap, the anomaly caused by the lap gap fluctuation amount is detected with excellent accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for monitoring laser welding.

[0002]

2. Description of the Related Art In assembling an automobile body, lap welding is often performed between steel materials, such as galvanized steel plates, in which at least one welding surface has a coating layer of a substance having a lower melting point than its base material. Conventionally, such lap welding was performed by spot welding or the like.
Since rigidity can be increased and welding processing can be performed from only one side, an example of adopting laser welding which can achieve diversification of member shapes is increasing. However, in laser lap welding of galvanized steel sheet, some abnormality occurred in the plate holding mechanism,
If the galvanized steel sheets adhere too much, zinc, which has a lower melting point than the base metal, may boil rapidly, causing the molten metal to be scattered as spatter and causing serious welding abnormalities. If the overlapping gap is excessively large due to abnormalities in the plate holding mechanism, the molten metal is drawn between the plates due to evaporation recoil, surface tension, etc., and the welded portion becomes concave-shaped underfill or drawn molten metal Causes a dynamic change in the direction of the welding line, which may cause a welding abnormality or the like.

[0003] If the overlapping gap amount becomes an abnormal value in this way, there is a possibility that a welding abnormality may occur.
It is necessary to do some welding quality inspection. In the conventional production line, inspectors visually inspected the quality after welding was completed.However, shortening the inspection process and improving inspection accuracy to improve production efficiency, the number of cases where online welding quality inspection is increasing is increasing. ing.

[0004] Examples of online welding quality inspection include measuring the plasma emission intensity as disclosed in JP-A-11-114683 and setting an allowable maximum value and an allowable minimum value based on the plasma emission intensity data measured during normal welding in advance.
There is a method of monitoring whether the plasma emission intensity at the time of actual welding is within the range of the allowable value, and setting a case where the plasma emission intensity deviates from this range as a welding abnormality. This method is based on the premise that there is a correlation between the plasma emission intensity and the normal / abnormal welding, and if there is no correlation, attempts to increase reliability by supplementing with a combination with other sensor signal intensities.

[0005]

In the case of lap welding of steel materials having at least one welding surface having a coating layer of a substance having a lower melting point than that of the base material, such as galvanized steel sheet, abnormalities caused by the lap gap amount may be caused. The welding phenomenon that occurs differs greatly depending on whether the overlap gap is too large or too small. For this reason, it is difficult to uniquely determine whether welding is normal or abnormal only based on the light emission intensity from the keyhole portion. As described above, when the overlap gap is too small, zinc, which has a lower melting point than the base metal, boils rapidly, causing the weld metal to be scattered as spatter. If the overlap gap is too large, the molten metal is drawn between the plates due to evaporation recoil, surface tension, etc., and the weld is formed in a concave shape, or the drawn molten metal changes dynamically in the direction of the weld line. Usually, the light emission intensity often decreases, but when a dynamic change occurs, the light emission intensity increases, and there is a possibility that the situation will not change from the normal state. For this reason, it is necessary to determine the welding quality by performing a welding phenomena which causes a welding abnormality by finding some discriminating factor other than the light emission intensity.

[0006]

Means for Solving the Problems To solve the above-mentioned problems, the present inventors have found that when the overlap gap is too small, zinc, which has a lower melting point than that of the base material, boils rapidly and scatters the weld metal as spatter. When the overlapping gap is too large, the molten metal is drawn between the plates due to evaporation recoil, surface tension, etc., and the weld is formed in a concave shape, or the drawn molten metal moves in the direction of the weld line. The present invention is based on the fact that there is a difference in the change frequency of the keyhole light emission intensity in a phenomenon that causes a significant change, and based on this, the present invention has been completed.

The gist of the present invention is as follows.

(1) In a laser welding quality monitoring method in a laser lap welding method in which at least one overlapping surface becomes a coating layer of a substance having a lower melting point than that of a base material, a keyhole emission signal detected by an optical sensor is detected. 3
When the low-frequency component intensity peak-to-peak value SL (t) at 0 Hz or lower is a relational expression | SL with respect to a predetermined threshold value Th1 when a welding abnormality occurs when the overlap gap is excessively large.
(T) A laser welding quality monitoring method characterized by accurately detecting an abnormality caused by the overlap gap variation amount by using the fact that |> Th1 holds.

(2) In a laser welding quality monitoring method in a laser lap welding method in which at least one overlapping surface becomes a coating layer of a substance having a lower melting point than its base material, a keyhole emission signal detected by an optical sensor is detected. 1
The high-frequency component intensity peak-to-peak value SH (t) at 00 Hz or more is expressed by the relational expression | S with respect to a predetermined threshold value Th2 when a welding abnormality occurs when the overlap gap is too small.
H (t) |> Th2 holds, and a preset threshold value Th3 when a welding abnormality occurs when the overlap gap is excessive.
A laser welding quality monitoring method characterized by accurately detecting an abnormality caused by the lap gap variation amount by using the relational expression | SH (t) | <Th3 holds.

(3) In a laser welding quality monitoring apparatus in a laser lap welding apparatus in which at least one of the overlapping surfaces becomes a coating layer of a substance having a lower melting point than that of a base material, radiation is emitted from a keyhole formed at a welding processing point. A / D board for converting a detection value signal from the sensor head into digital data, and a low-frequency signal of 30 Hz or less obtained by capturing the digital data and separating the digital data by frequency filtering. When the frequency component intensity peak-peak value SL (t) has a relational expression | SL (t) |> Th1 with respect to a predetermined threshold value Th1 when welding abnormality occurs when the overlap gap is excessive, and at a frequency of 100 Hz or more. High frequency component intensity peak-to-peak value SH (t) may be The relational expression | SH (t) |> Th2 holds for the threshold value Th2 set in advance, and the relational expression | SH (SH) for the threshold value Th3 set in advance when a welding abnormality occurs when the overlap gap is excessive. t) | <Th
3. A laser welding quality monitoring apparatus, comprising: a computer that accurately detects an abnormality caused by the overlap gap variation amount by using the fact that the condition 3 is satisfied.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

FIG. 1 shows a DC signal obtained by AC-coupling a signal obtained by receiving a keyhole light emission by a photodiode when laser welding is performed while continuously changing a lap gap in lap welding between galvanized steel sheets. This is the signal component excluding the minute. FIG. 2 shows a sample 5 used at the time of the laser welding of FIG. 1 described above. In the vicinity 2 of the welding start point and the vicinity 4 of the welding end point, the lap gap 1 between the galvanized steel sheets 6 is too small. In the vicinity 3 of the center, the overlap gap 1 is excessively large. In the example shown in FIG. 1, the intensity change 1 of the light emission signal from the keyhole received by the photodiode is large near the welding start point 2 and near the welding end point 4 and small near the center 3. This is due to the welding start point 2 where the overlap gap 1 is too small and the welding end point 4 near the welding end point.
In, the emission intensity increases just before the molten metal is pushed up by the zinc vapor and blown off, and after being blown off,
This is because the difference in signal intensity increases because the molten metal disappears. In the vicinity of the welding center 3 where the overlap gap 1 is excessively large, the molten metal is drawn between the plates due to evaporation recoil, surface tension, etc., so that the molten metal falls from the surface of the base material, and the light emitting area of the molten metal as viewed from the surface Is reduced, so that the difference in signal intensity is also reduced. In the range where the overlap gap is appropriate, the difference in the intensity of the light emission signal is an intermediate value between the two. Therefore, the welding quality can be monitored by monitoring the difference in the intensity of the light emission signal.

However, in the example shown in FIG. 3, there is a portion where the signal intensity difference is large even in the vicinity of the welding center where the overlap gap is excessive, and the method of monitoring the welding quality based on the magnitude of the signal intensity difference described above. Is not applicable.
This appears near the base metal surface as the molten metal once drawn into the gap is pulled back by surface tension etc.,
This instantaneous emission intensity also increases. When this phenomenon occurs, the molten metal may be pulled back, causing anomalies such as scattered spots with insufficient welding amount.

FIGS. 4, 5, 6 and 7 each show a part of the signal waveform of FIG. 3 in an enlarged manner. FIG. 4 shows a signal waveform in a normal bead, that is, a proper overlapping gap range, and FIG. 6 shows a signal waveform at a place where a lot of pits and porosity is generated due to scattering of molten metal, FIG. 6 shows a signal waveform at a place where molten metal falls due to an excessive gap and is underfilled, and FIG. This is a signal waveform at a location where the molten metal is pulled back by the surface tension and appears on the surface of the base material due to an excessive gap as described above. Comparing the waveforms of FIG. 5 and FIG. 7, the frequency of the signal fluctuation is significantly different. The signal fluctuation frequency of FIG. 5 is mainly composed of 100 Hz to 200 Hz, and the signal of FIG. 7 is composed of the frequency of 10 Hz to 30 Hz.

Therefore, the present inventors perform frequency processing on the light emission signal intensity signal from the keyhole, and perform discrimination processing by dividing the signal intensity component into a signal intensity component at 100 Hz or more and a signal intensity component at 30 Hz or less. We have invented a method to accurately detect welding abnormalities caused by the gap amount and monitor welding quality online. FIG.
Fig. 8 shows a signal obtained by capturing a keyhole light emission with a photodiode and removing a DC component by AC coupling. Fig. 8 shows a signal waveform obtained by extracting a component having a frequency of 30 Hz or less, and Fig. 9 shows a signal obtained by extracting a component having a frequency of 100 Hz or more. FIG. In FIG. 8, the signal intensity peak near the center of the weld is shown.
While the peak value (hereinafter referred to as the PP value) increases, the signal intensity PP value near the welding start point and the end point and the signal intensity PP near the center in the waveform of FIG. The ratio with the value is relatively increased as compared with the waveform of FIG. Signal intensity PP value SL (t) of a keyhole emission signal of 30 Hz or less at a proper overlap gap
And the average value SH_AV of the signal intensity PP value SH (t) of the component of 100 Hz or more, and the determination threshold values Th1, Th2, and Th3 are determined,
Th1 = SL_AV + α (α is a constant), Th2 = S
H_AV + β (β is a constant), Th3 = SH_AV + γ
(Γ is a constant). With respect to the time variation SL (t) of the signal intensity PP value composed of components of 30 Hz or less, | SL
(T) It is possible to determine that the region where |> Th1 is a welding abnormality due to an excessive overlap gap. Similarly, FIG.
, The signal intensity P-
In the area where | SH (t) |> Th2 is overlapped with the P value SH (t), welding abnormality due to an excessively small gap, | SH
The region where (t) | <Th3 is overlapped and a welding abnormality due to an excessive gap is determined, and the region where Th3 <| SH (t) | <Th2 is determined to be normal.

An embodiment of the present invention will be described with reference to FIG. The laser monitoring device according to the present invention includes an electric diaphragm mechanism 8, a variable density liquid crystal filter 9, and a condenser lens 1.
0, a photodiode 11, a photodiode amplifier 12, an A / D board 13, a D / A board 14, an electric diaphragm controller 16, a variable density liquid crystal filter controller 15, and a computer 17,
Is installed outside or inside the laser torch 7. When the sensor head unit 18 is installed outside the laser torch 7, the angle is set as high as possible with respect to the base material. When the sensor head unit 18 is installed inside, the optical axis is coaxial with the irradiation laser.

Radiation light and plasma light radiated from a keyhole formed at a processing point are adjusted in light quantity by an electric diaphragm mechanism 8 and a variable density liquid crystal filter 9, and are coupled to a light receiving surface of a photodiode 11 by a condenser lens 10. Image. The output signal of the photodiode 11 is amplified by the photodiode amplifier 12 and becomes a signal voltage suitable for the input dynamic range of the A / D board 13 in the computer 17. The output of the D / A board is connected to an electric diaphragm controller 16 and a variable density liquid crystal filter controller 15, and controls the electric diaphragm mechanism 8 and the variable density liquid crystal filter 9, respectively.

The output signal of the photodiode amplification amplifier 12 is converted into digital data by an A / D converter 13 and taken into a computer 17, and the photodiode output signal frequency is 100H by FIR filter processing.
The difference between the maximum value and the minimum value of 10 to 1000 pieces of data in the vicinity of a certain point of interest in a set range movable in the time direction is extracted while extracting the intensity difference between the component equal to or greater than z and the component equal to or less than 30 Hz. Intensity PP value,
The signal strength PP value of the component that is higher than 100 Hz is SH
(T) and the signal intensity PP of the component below 30 Hz
Let the value be SL (t). The high frequency component signal strength SH
Appropriate threshold values Th1 to Th3 are provided for (t) and the low-frequency component signal strength SL (t), and the welding quality is determined based on the determination logic shown in Table 1.
According to the present invention, it was possible to accurately detect a welding abnormality.

[0019]

[Table 1]

[0020]

As described above, according to the present invention, it is possible to accurately detect a welding abnormality caused by a lap gap amount in laser lap welding and evaluate welding quality online.

[Brief description of the drawings]

FIG. 1 is a diagram showing a typical waveform example of a keyhole emission intensity signal when laser welding is performed by partially changing an overlap gap in overlap welding of galvanized materials.

FIG. 2 is a view showing a sample for lap welding between galvanized materials in which the lap gap is partially changed.

FIG. 3 is a diagram showing an example of a waveform in which a keyhole emission intensity signal is increased even when the gap is excessive when laser welding is performed by partially changing an overlap gap in overlap welding of galvanized materials.

FIG. 4 is a diagram showing a waveform in which a keyhole emission intensity signal in a region where an overlap gap is appropriate is expanded in a time direction.

FIG. 5 is a diagram illustrating a waveform obtained by enlarging a keyhole emission intensity signal in a time direction when an abnormality occurs in a region where an overlap gap is too small.

FIG. 6 is a diagram illustrating a waveform obtained by enlarging a keyhole emission intensity signal in a time direction when an underfill occurs in a region where an overlap gap is excessive.

FIG. 7 is a diagram illustrating a waveform obtained by enlarging a keyhole emission intensity signal in a time direction when a welding abnormality occurs in a region where an overlap gap is excessive.

8 is a diagram showing a signal waveform obtained by extracting a component having a signal frequency of 100 Hz or more in FIG.

9 is a diagram showing a signal waveform obtained by extracting a component having a signal frequency of 30 Hz or less in FIG. 3;

FIG. 10 is a diagram showing an overall configuration diagram of a laser welding monitoring device according to an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF REFERENCE NUMERALS 1 Partially changed lap gap 2 Near welding start point 3 Near center 4 Near welding end point 5 Sample of galvanized steel sheet with partially changed lap gap 6 Galvanized steel sheet 7 Laser torch 8 Electric drawing mechanism 9 Concentration conversion type liquid crystal filter DESCRIPTION OF SYMBOLS 10 Condensing lens 11 Photodiode 12 Amplifying amplifier for photodiode 13 A / D board 14 D / A board 15 Density conversion type liquid crystal filter controller 16 Electric diaphragm controller 17 Computer 18 Sensor head part

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasutomo Ichiyama 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technology Development Division (72) Inventor Takashi Tanaka 20-1 Shintomi, Futtsu City Nippon Steel Corporation (72) Inventor Masahiro Ohara 1 in Nishinoshi, Oita, Nippon Steel Corporation Oita Works (72) Inventor Yoshinao Tanaka 2-6 Otemachi, Chiyoda-ku, Tokyo 3. Inside Nippon Steel Corporation (72) Inventor Koji Nomura 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Takefumi Shiga 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation F term (reference) 4E068 BF00 CA17 CA18 CB02 CC01 DA14 DB14

Claims (3)

[Claims] 1. A laser welding quality monitoring method in a laser lap welding method in which at least one overlapping surface becomes a coating layer of a substance having a lower melting point than that of a base material, wherein a keyhole emission signal detected by an optical sensor has a frequency of 30 Hz. Low frequency component intensity peak-peak value SL in:
(T) is a relational expression | SL with respect to a predetermined threshold value Th1 when a welding abnormality occurs when the overlap gap is excessive.
(T) A laser welding quality monitoring method characterized by accurately detecting an abnormality caused by the overlap gap variation amount by using the fact that |> Th1 holds. 2. A laser welding quality monitoring method in a laser lap welding method in which at least one superposed surface becomes a coating layer of a substance having a lower melting point than that of a base material, wherein a keyhole emission signal detected by an optical sensor is 100 Hz.
High-frequency component intensity peak-peak value SH described above
(T) is a relational expression | SH with respect to a predetermined threshold value Th2 when welding abnormality occurs when the overlap gap is too small.
(T) |> Th2 is satisfied, and the relational expression | SH (t) | <Th3 is satisfied with respect to a threshold value Th3 set in advance when a welding abnormality occurs when the overlap gap is excessive. A laser welding quality monitoring method characterized by accurately detecting an abnormality caused by a gap fluctuation amount. 3. A laser welding quality monitoring apparatus in a laser lap welding apparatus in which at least one superposed surface becomes a coating layer of a substance having a lower melting point than that of a base material, radiation is emitted from a keyhole formed at a welding processing point. Radiation
A sensor head section for detecting plasma light, an A / D board for converting a detection value signal from the sensor head section into digital data, a low-frequency component intensity peak at 30 Hz or lower, which is obtained by capturing the digital data and separating the digital data by a frequency filter process. The relational expression | SL (t) |> Th1 is established with respect to a threshold value Th1 set in advance when a welding abnormality occurs when the peak value SL (t) is too large in the overlap gap.
And the high-frequency component intensity peak-peak value SH (t) at or above 100 Hz satisfies the relational expression | SH (t) |> Th2 with respect to a threshold value Th2 set in advance when a welding abnormality occurs when the overlap gap is too small. Further, utilizing the fact that the relational expression | SH (t) | <Th3 is satisfied with respect to a threshold value Th3 set in advance when a welding abnormality occurs when the overlap gap is excessive, the abnormality caused by the overlap gap fluctuation amount is accurately detected. A laser welding quality monitoring device comprising a computer for detecting.