JP2000233290A - Method and device for monitoring weld zone of laser beam welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for monitoring laser beam welding capable of surely detecting a welding phenomenon in a deep part when performing deep penetration welding. SOLUTION: A material 4 to be welded is irradiated by a laser beam 1, and by detecting the optical characteristics of a weld zone by sensors 2, 3 arranged before and behind in the welding processing direction, a welding state is grasped. Respective sensors 2, 3 are arranged so that an angle formed by the beam axis L of the laser beam Δ1 and the optical axis O of the sensors 2, 3, becomes >=3 deg. and <=5 deg. at the irradiating point P of the laser beam on the surface of the material 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for monitoring a weld in laser beam welding and to a weld monitor for implementing the method.

[0002]

2. Description of the Related Art In laser beam welding, an attempt to grasp the welding state by detecting the optical characteristics of a welded portion and to estimate the welding quality based on the state is disclosed in, for example, JP-A-7-12753. Are also known as disclosed. In this method of monitoring a welded portion, a sensor is disposed obliquely above the welded portion behind and the welded portion is observed from this position. In the conventional welding part monitoring method described above, the angle between the beam axis of the laser beam and the optical axis of the sensor at the laser beam irradiation point on the surface of the workpiece is generally set to 25 ° or more. Generally, in a laser beam welding apparatus used, a focusing mirror having a focal length of 500 mm or less is used, and an F value (= focal length / beam diameter) is often 10 or less.
Since the beam is focused at a large angle, the sensor needs to be placed sideways to avoid interference with the beam or the focusing head. That is, it is necessary to increase the angle between the beam axis of the laser beam and the optical axis of the sensor.

[0003]

In recent years, as the output of a laser beam has been improved, attempts have been made to apply laser beam welding to a thick plate. However, when the penetration depth of the weld becomes deep, if the angle between the beam axis of the laser beam and the optical axis of the sensor is large as in the conventional case described above, even if a phenomenon near the welding surface can be detected, welding at the deep part There is a disadvantage that the phenomenon cannot be detected and a sufficient monitoring function cannot be performed. In addition, 1
Since detection is performed only by a single sensor, the amount of information that can be obtained is not sufficient, and there is a disadvantage that a sufficient monitoring function cannot be performed in this regard.

In particular, when deep penetration welding such as keyhole welding of a thick plate is performed, as shown in FIG. 4, a phenomenon occurs in which the deep portion of the keyhole is delayed backward in the welding progress direction. Detecting the penetration depth and shape and controlling the welding speed, laser output, wire supply, etc., will ensure the welding quality.However, in the conventional welding part monitoring method described above, as described above, In addition to the fact that a welding phenomenon cannot be detected in a deep portion, there is a disadvantage that such a delay phenomenon of a keyhole deep portion cannot be detected because the welded portion is detected by only one sensor. Further, as shown in FIG. 8, when the right and left heat conductions are different due to the difference in the plate thickness of the materials to be welded, a phenomenon occurs in which the keyhole is curved in the left and right direction in the welding progress direction. However, such a phenomenon cannot be detected by the above-described conventional method for monitoring a welded portion.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional drawbacks, and an object of the present invention is to make it possible to reliably detect a welding phenomenon in a deep portion when performing deep penetration welding. It is an object of the present invention to provide a method and apparatus for monitoring a weld in laser beam welding. It is another object of the present invention to provide a method and apparatus for monitoring a welded portion of laser beam welding, which can obtain a larger amount of detected information than before and monitor the welded portion with high accuracy.

[0006]

Means and Effects for Solving the Problems Claim 1
The method for monitoring a welded portion of laser beam welding is to irradiate a laser beam to a material to be welded, and to detect the optical characteristics of the welded portion by a sensor to grasp a welding state, and the method for monitoring a welded portion of laser beam welding as described above. At the laser beam irradiation point on the surface of the material to be welded, the angle between the beam axis of the laser beam and the optical axis of the sensor is set to 3 ° or more and 5 °.
The angle is set to less than or equal to °.

According to the first aspect of the present invention, the angle formed between the beam axis of the laser beam and the optical axis of the sensor is reduced even if the penetration depth of the weld is increased. Therefore, welding phenomena in deep parts can be detected. For example, in the case of keyhole welding, it is possible to estimate the penetration depth, detect insufficient penetration, and detect internal defects such as blowholes, thus contributing to high quality laser beam welding of thick plates.

According to a second aspect of the present invention, there is provided a laser beam welding monitoring method for irradiating a material to be welded with a laser beam and detecting a welding state by detecting an optical characteristic of the welded portion by a sensor. In the welding part monitoring method, the detection of the welding part by the sensor is performed in at least two directions from the front and the rear in the welding progress direction, and the welding state is grasped based on the detection results from both directions. It is characteristic.

According to the method for monitoring a welded portion of laser beam welding according to the second aspect of the present invention, the detection of the welded portion by the sensor is performed in at least two directions from the front and back in the welding advancing direction. Compared with the case where a weld is detected, the amount of information is increased, and high-precision monitoring can be performed, thereby contributing to high quality laser beam welding.

A third aspect of the present invention provides a method for monitoring a welded portion in laser beam welding, wherein a welded portion is detected by a sensor from both left and right sides in the welding progress direction.

According to the method for monitoring a weld portion of laser beam welding according to the third aspect, the amount of information is further increased, and more accurate monitoring can be performed, which contributes to the improvement of the quality of laser beam welding.

According to a fourth aspect of the present invention, there is provided a method for monitoring a welded portion of a laser beam according to the second or third aspect. The angle between the beam axis of the beam and the optical axis of the sensor is set to an angle of 3 ° or more and 5 ° or less.

According to the method for monitoring a welding portion of laser beam welding according to the fourth aspect, the phenomenon that the deep part of the keyhole is delayed backward in the welding progress direction or the keyhole is bent in the left and right direction in the welding progress direction. Can be detected, and the welding state in such a case can be grasped reliably. Therefore, it is possible to contribute to high quality laser beam welding of a thick plate.

According to a fifth aspect of the present invention, there is provided a welding portion monitoring apparatus for laser beam welding, which implements the welding portion monitoring method according to any one of the first to fourth aspects.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a specific embodiment of a method and apparatus for monitoring a weld in laser beam welding according to the present invention will be described in detail with reference to the drawings. First, in FIG. 1, reference numeral 1 denotes a laser beam, and a pair of sensors 2, 3 are disposed before and after the laser beam 1 in the welding progress direction. Reference numeral 4 denotes a material to be welded, and the sensors 2 and 3 are arranged with the optical axis directed to a laser beam irradiation point P on the surface of the material 4 to be welded. Each of these sensors 2 and 3 is composed of a light receiving element represented by a photodiode,
A wavelength of 0 nm to 1000 nm can be detected and 900 nm
It has a detection peak at a nearby wavelength. A characteristic of the present invention is that at the laser beam irradiation point P, the angle between the beam axis L of the laser beam 1 and the optical axis O of each of the sensors 2 and 3, that is, the detection angle α is 3 ° or more and 5 °. The point is that the angle is set to less than °.

By arranging the sensors 2 and 3 as described above, there is an advantage that a welding phenomenon at a deep welding position can be detected. For example, if the detection angle α is 25
When the keyhole diameter was 1 mm, only light emission with a depth up to 3.7 could be detected, whereas by setting the detection angle α as described above, FIG. As shown, assuming that the keyhole K is a cylinder having a diameter of 1 mm, when the detection angle α = 3 °, the depth is about 19 mm, and when the detection angle α = 5 °, the depth is about 11.4.
mm information is obtained. The detection angle α is set to 3 ° or more in order to prevent interference between the laser beam 1 and each of the sensors 2 and 3. That is, when the beam diameter incident on the condenser mirror is 60 mm and the focal length is 750 mm, the laser beam diameter becomes about 20 mm at a height position of 250 mm from the laser beam irradiation point P on the workpiece 4, If a photodiode having a diameter of 6 mm is to be installed close to the side, the detection angle α must be set to 3 ° or more.

Conventionally, a method has been adopted in which an observation hole is provided in the center of a converging mirror or a reflecting mirror, and a sensor is arranged coaxially with the beam axis of a laser beam. If an observation hole is provided at the center of the mirror, a portion of the laser beam having a high energy density at the center passes through the observation hole, causing power loss and damaging the sensor. If the output is used, it cannot withstand continuous use and is not practical.

FIG. 3 shows the relationship between the detected angle α and the obtained output level (voltage). As is clear from FIG. 3, the smaller the detected angle α, the higher the output level, that is, the higher the output level. The light emission amount is obtained. The reason why such a high light emission amount is obtained is because information from a deep portion of the welded portion is obtained in addition to information from the plasma near the welding surface. As a result of detecting welding phenomena in such a deep part, in the case of keyhole welding, it is possible to estimate the penetration depth, to detect insufficient penetration, and to detect internal defects such as blowholes. It can contribute to high quality laser beam welding.

The advantages of providing the sensors 2 and 3 at the front part and the rear part in the welding traveling direction as described above will be described. First, in the case of laser beam welding of a thick plate, as shown in FIG. 4, the deep portion of the keyhole K is delayed backward in the welding progress direction, and the keyhole K is bent. Then, when such a state is detected from before and after the sensors 2 and 3 arranged as described above, FIG.
As shown in (c), there is a difference between the detection areas K1 and K2 of the front and rear sensors 2 and 3. As a result, as shown in FIG. 6, the output Pf from the sensor 2 disposed in front is
The output Pb tends to be larger than the output Pb from the sensor 3 arranged behind. Therefore, as shown in FIG. 7, if the output difference (Pf-Pb) of the front and rear sensors 2 and 3 is taken, the penetration depth, the keyhole diameter, the delay of the keyhole, the distinction between penetration and non-penetration, and Since a certain relation is established between the output difference (Pf-Pb), the penetration depth, the keyhole diameter, the keyhole delay, the penetration and the non-penetration are determined based on the output difference (Pf-Pb). It is possible to estimate the distinction of penetration.
It is also possible to distinguish between a case where the diameter of the keyhole K is small and the penetration depth is deep, and a case where the diameter of the keyhole K is large and the penetration depth is shallow. For example, if the output difference (Pf-Pb) is larger than the reference value, it can be determined that the delay of the keyhole K has increased. If the output difference (Pf-Pb) becomes smaller than the reference value, That is, it can be determined that the delay of the keyhole K has become small.

In laser beam welding, as shown in FIG. 8, when the right and left heat conductions are different due to the different thicknesses of the materials to be welded 10 and 11, the keyhole K is formed. A phenomenon of bending in the left-right direction of the welding progress direction occurs. In order to detect such a phenomenon, sensors may be provided on both the left and right sides orthogonal to the welding progress direction in the same manner as described above. By doing so, the keyhole K
The presence / absence of bending and the bending direction can be detected by the same method as that for detecting the delay of (i.e., the difference between the outputs of the left and right sensors (Pf-Pb)).

As described above, according to the method for monitoring the welded portion of laser beam welding of the above embodiment, the detection angle α is set to an angle of 3 ° or more and 5 ° or less. As a result of the detection, in the case of keyhole welding, it is possible to estimate the penetration depth, detect insufficient penetration, and detect internal defects such as blowholes. In addition, since a plurality of sensors 2 and 3 are arranged toward the weld,
It is possible to detect the phenomenon that the deep part of the keyhole K is delayed backward in the welding progress direction, and it is also possible to detect the phenomenon in which the keyhole K bends in the left and right direction of the welding progress direction. it can. Therefore, it is possible to contribute to high quality laser beam welding of a thick plate.

The embodiment of the laser beam welding method for monitoring a welded portion of the present invention has been described above. The welded portion monitoring apparatus is used to carry out the above-described method. And a control unit for performing the above-described signal processing.
In the above embodiment, a plurality of sensors 2 and 3 are used, but the case where one sensor uses the detection angle α is also included in claim 1 of the present application, and in this case,
There is an advantage that a welding phenomenon in a deep part can be detected.
A case where the plurality of sensors 2 and 3 are used at an angle larger than the detection angle α is also included in claims 2 and 3 of the present application. In this case, the detection of the welded portion is performed from one direction. As compared with the case, the amount of information is increased, and high-precision monitoring can be performed, and there is an advantage that the quality of laser beam welding can be improved. Further, as shown in FIG. 9, the reflecting mirror 12 may be used. In this case,
The angle formed by the incident light O on the sensor 2 and the beam axis L of the laser beam at the laser beam irradiation point P is the detection angle α.
Called. Further, the sensors 2 and 3 are not limited to visible light, but may be any one of various ranges such as an infrared region and an ultraviolet region, and therefore various sensors other than the photodiode can be used.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an arrangement of sensors in one embodiment of a laser beam welding monitoring method of the present invention.

FIG. 2 is an explanatory diagram for explaining a visible region and an invisible region in a keyhole in the embodiment.

FIG. 3 is a graph showing a relationship between a detection angle of a sensor and an output level in the embodiment.

FIG. 4 is an explanatory diagram for explaining a delay phenomenon of a keyhole rearward in a welding advancing direction in the embodiment.

FIG. 5 is an explanatory diagram for explaining a visible region and an invisible region in a keyhole in the state of FIG. 4;

FIG. 6 is a graph schematically showing the relationship between the output of each sensor and the penetration depth obtained in the state of FIG. 4;

FIG. 7 is a graph schematically showing a relationship between an output difference between both sensors before and after and a penetration depth obtained in the state of FIG. 4;

FIG. 8 is an explanatory diagram for explaining a bending phenomenon of the keyhole in the left-right direction in the embodiment.

FIG. 9 is an explanatory diagram showing a modified example of the arrangement of the sensors.

[Explanation of symbols]

 Reference Signs List 1 laser beam 2 sensor 3 sensor 4 non-weld material P laser beam irradiation point L laser beam axis O optical axis of sensor K keyhole

Continued on the front page (72) Inventor Kaoru Adachi 3-1-1 Ueno, Hirakata City, Osaka Prefecture Inside the Production Technology Development Center, Komatsu Manufacturing Co., Ltd. (72) Taiichi Matsumoto 3-1-1 Ueno, Hirakata City, Osaka Prefecture No. F-term in Komatsu Manufacturing Technology Development Center (reference) 2G043 AA03 BA01 CA03 CA05 DA05 EA10 FA01 FA05 GA04 GB01 GB03 KA09 LA01 MA11 NA01 4E068 BA00 CA17 CC01 DA14

Claims (5)

[Claims] 1. A method for monitoring a welding portion in laser beam welding, comprising: irradiating a laser beam onto a material to be welded; and detecting an optical characteristic of the welded portion by a sensor to grasp a welding state. A welding part monitoring method for laser beam welding, wherein an angle formed by a beam axis of the laser beam and an optical axis of the sensor at a beam irradiation point is not less than 3 ° and not more than 5 °. 2. A method for monitoring a welded portion of laser beam welding, wherein a laser beam is applied to a material to be welded and optical characteristics of the welded portion are detected by a sensor to grasp a welding state. In at least two directions from the front and the back of the welding progress direction, and the welding state is grasped based on the detection results from both directions. 3. The laser beam welding monitoring method according to claim 2, further comprising the step of detecting a welding portion by a sensor from both left and right sides of the welding progress direction. 4. The sensor according to claim 1, wherein an angle between a beam axis of the laser beam and an optical axis of the sensor is 3 ° or more and 5 ° at a laser beam irradiation point on the surface of the workpiece.
The method for monitoring a welded portion in laser beam welding according to claim 2 or 3, wherein the angle is set as follows. 5. A welding part monitoring device for laser beam welding for implementing the welding part monitoring method according to any one of claims 1 to 4.