JP2002239761A - Method and device for monitoring laser beam welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a reliable monitoring the procedure of laser beam welding. SOLUTION: Normal/defective welding is decided in real time and nondestructively by capturing such various proxy signals as a plasma and heat which are generated during the laser beam welding, monitoring whether these are generated homogeneously or not, and comparing the signal with the preliminarily collected signal which is obtained in a case in which the welding is normally performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to laser welding monitoring in which the quality of welding is judged or monitored based on various proxy signals obtained during the course of laser welding.

[0002]

2. Description of the Related Art Various methods have been employed for inspecting welding quality. The property most strongly required in the case of a welded product is the strength of the joint.
The most reliable way to check the quality of the joint is to cut out the joint and perform a strength test. However, such a test in which the joint is destroyed naturally destroys the product itself, and thus cannot be applied to all products. Test the randomly extracted one,
We only expect that what was produced during the extraction would be of the same quality as itself. Because laser welding involves a combination of complex factors and a large amount of production, it is difficult to manage by laser inspection alone.
Some in-line monitoring is required.

However, when using laser processing at a production site, it is common to shorten the production tact and increase productivity because the laser equipment is expensive. Further, since the laser equipment is often operated unattended to reduce production costs, unless a means for immediately detecting the occurrence of a defect is provided, a large number of defective products will be held in a short time.
If the inspection means is low in reliability, even NG products are sent out as good products, or the equipment is stopped each time, resulting in very inefficient production.

Accordingly, a main object of the present invention is to perform highly reliable monitoring of welding quality in the course of laser welding.

[0005]

According to the laser welding monitoring method of the present invention, an area including an area which is acceptable as a non-defective product depending on the degree of failure between the 100% NG area and the 100% OK area, that is, an allowable area. Is provided. Although the quality control method of setting the upper and lower limits to be narrow and setting the upper and lower limits to be 100% NG when the upper and lower limits are exceeded is clear, the defect rate is increased and the yield is poor. A work whose measured value for a certain proxy signal belongs to the allowable area
Although it is not 100% NG, it is not 100% OK, but can be assigned to either depending on the set value. Therefore, by setting an allowable area inside the upper and lower limits that define the 100% NG area and setting the allowable area to an appropriate range, it is possible to suppress the NG rate while reliably eliminating 100% NG products. Become.
Further, for example, even for a work in which an abnormal measurement value is suddenly recorded and cannot be determined to be 100% OK, when the work as a whole is to be judged as a defect in welding quality when viewed as a whole welded part, Not always. Eliminating such a workpiece as an NG product means excluding a workpiece that should be treated as a good product, thereby deteriorating the yield.

[0006] By recording the measurement value obtained by the sensor in association with the time or distance component, the position of the abnormality or defect on the workpiece can be specified after welding.

According to the first aspect of the present invention, in monitoring welding quality using a measurement value obtained by a sensor in the course of laser welding, 100% of a measurement value plotted with respect to a welding time or a distance for each measurement value of each sensor. % NG
Along with setting upper and lower curves defining the area, providing an allowable area inside the upper curve and the lower curve respectively,
The probability of welding failure is calculated based on the total area value of the measured value curve portion protruding from the 100% OK region to the allowable region, and welding is performed based on the integrated value of the welding failure probability for all the measured values of the sensors. This is a laser welding monitoring method characterized by determining quality.

According to a second aspect of the present invention, when monitoring the welding quality using the measured values obtained by the sensors in the course of laser welding, 100% of the measured values plotted with respect to the welding time or distance for each measured value of each sensor. % NG
Along with setting upper and lower curves defining the area, providing an allowable area inside the upper curve and the lower curve respectively,
The probability of poor welding quality is calculated based on the integrated value of the time or distance of the measured value curve portion protruding from the 100% OK area to the allowable area, and the probability of poor welding is calculated for all the measured values of the sensors. This is a laser welding monitoring method characterized by determining the quality of welding quality based on a value.

According to a third aspect of the present invention, in monitoring welding quality using a measurement value obtained by a sensor during a laser welding process, upper and lower limits for defining a 100% OK region of the measurement value plotted with respect to welding time or distance. When a curve is set and the measured value curve approaches the upper / lower curve as much as possible without protruding from the 100% OK region, the measured value curve is integrated over the entire welding time or distance, and based on the integrated value. This is a method for monitoring laser welding, wherein the quality of the welding quality is determined by the method.

According to a fourth aspect of the present invention, when the measurement positions of a plurality of sensors are different, the time axis of the data from each sensor is corrected based on the distance between the measurement positions and the welding speed. And If the measurement positions of a plurality of sensors are different, the data from each sensor at a certain point in time is information on different positions and not information on the same measurement position, so by correcting the time axis of the data, More accurate and reliable monitoring becomes possible.

A laser welding monitoring apparatus according to the present invention is an apparatus for monitoring welding quality using a measurement value obtained from a sensor during a laser welding process as a proxy signal, wherein a plasma sensor and a temperature sensor are used in common. It is stored in a housing, and the light projected from the welded portion is split by a beam splitter to be incident on each of the sensors, and the temperature sensor is provided with a protector for shielding light incident from a molten ground. (Claim 5).

The intensity of the ultraviolet light of the plasma is measured by the plasma sensor, and the intensity of the infrared light at the welded portion is measured by the temperature sensor. This is advantageous, for example, when a plurality of sensors cannot be installed around the welded portion due to space restrictions. Further, by providing the temperature sensor with a protector that blocks the incident light from the melting point, it is possible to measure, for example, the temperature near the freezing point from which the molten pool has been removed.
As the temperature sensor, for example, a photodiode is used, and an electric signal corresponding to the intensity of infrared light received via the wavelength selection filter is obtained as a measured value. Here, the vicinity of the solidification point refers to a position where the molten pool is removed, that is, a position where the molten pool is slightly receded when viewed in the direction of progress of welding and where solidification is starting. It is known to use the temperature of the weld as a surrogate signal for monitoring, but conventionally, it is common practice to measure the temperature of the weld spot, ie, the weld pool, below the laser emission nozzle.
However, since the temperature of the molten pool itself is high, the range of its fluctuation is relatively large, and there is a problem that it is difficult to obtain a stable measured value. On the other hand, the temperature is lower near the freezing point than in the molten pool and the change is relatively slow, so that a stable measurement value can be obtained. As a result, highly reliable monitoring is realized.

[0013]

Embodiments of the present invention illustrated in the drawings will be described below.

First, the outline of laser welding will be described with reference to FIG. 6. Laser welding is welding performed by irradiating a laser beam, and a laser beam 1 emitted from a laser oscillator is guided to a processing head through a transmission optical system. Then, the light is irradiated on the workpiece 3 through the condensing optical system 2. If a laser beam is condensed, the power density at the focal point becomes very high. Therefore, when the laser beam is applied to the workpiece 3, its energy is absorbed and the surface temperature of the workpiece rapidly rises to reach the boiling point. . Once penetration occurs at a high power density, the absorptivity rises sharply and starts to evaporate, and the surrounding melt is pushed away by the pressure of the vapor to form a keyhole 7. Plasma 8 having high brightness is generated in the keyhole 7 and on the surface of the base material. In the figure, reference numeral 9 indicates a molten pool. During laser welding, fine molten metal called spatter scatters as indicated by reference numeral 4.

In the embodiment shown in FIG. 1, in a laser welding machine configured to irradiate a laser beam from a laser emission nozzle 16 to a workpiece, ie, a work 21, to perform laser welding, a temperature sensor 17 and a plasma sensor 18 are separately provided. And an external control device 24, a CRT 25, and a keyboard 26 are connected to the controller 23 having an AD board and an I / D board via an amplifier 22. As the temperature sensor 17, a well-known infrared sensor configured by housing a wavelength selection filter and a light receiving element (photodiode) in a housing can be used. As illustrated in the drawing, an optical fiber 17a is connected to a sensor head, and the tip of the optical fiber 17a is directed to a desired measurement position 21a. In addition, the sensor head of the temperature sensor 17 is disposed facing a welding portion. In addition, a light-shielding plate for removing disturbance may be provided. It is desirable that the measurement position 21a is set near the solidification point from which the molten pool has been removed. For example, when the emission nozzle 16 moves to the right in the drawing in the case of the irradiation system moving type, a predetermined distance (depending on the welding speed and laser output, depending on the welding speed and laser output) from the molten pool as viewed in the direction of movement of the emission nozzle 16. The temperature at the separated position is measured. The same applies to the case where the workpiece 21 moves to the left in the drawing in the workpiece moving type.

The plasma sensor 18 measures the intensity of the plasma generated at the weld based on the intensity of the ultraviolet light. Thereby, for example, it is possible to diagnose the presence or absence of a welding defect due to excessive evaporation of the base metal.

The embodiment shown in FIG.
7 ′ and the plasma sensor 18 ′ are stored in a common housing 31. By integrally disposing the temperature sensor 17 'and the plasma sensor 18' in this manner, the entire apparatus can be compactly assembled. Further, the arrangement is advantageous when the space around the laser emission nozzle 16 is restricted, such as when the workpiece 21 is a large three-dimensional workpiece. Inside the housing 31, there is further provided a mirror Md for receiving the reflected light from the welded portion 21a.
And a half mirror Me coaxial with the mirror Md, the reflected light from the welded portion 21a is split by the half mirror Me to be incident on the temperature sensor 17 'and the plasma sensor 18', respectively. I have. That is, the temperature sensor 17 'receives the light transmitted through the half mirror Me,
The plasma sensor 18 'receives the light reflected by the half mirror Me.

Further, a black protector 32 is provided at a stage preceding the temperature sensor 17 '. This black protector 32
2B, as shown in FIG. 2B, only the central portion 17 "of the temperature sensor 17 'is shielded (masked) to shield a portion of the reflected light from the welded portion corresponding to the molten pool.
To adjust the angle of d, remove the temperature sensor 17 '
A camera (not shown) is attached, and the protector 32 is installed by adjusting the CRT (25: see FIG. 1) so that only the center of the mirror can be seen. It is desirable that the position and area of the shield region of the protector 32 can be arbitrarily changed. For example, if the case of FIG. 2B is taken as an example, the shaded area shown by the oblique lines in the figure is not limited to the central part 17 ″ and can be changed in the vertical and horizontal directions of FIG. Further, the shield area is not limited to a circular shape as shown in the figure, and a protector in the form of a shutter movable in a vertical direction or a horizontal direction may be employed.

For monitoring the welding quality, various sensors are used in addition to the above-mentioned temperature sensor and plasma sensor. As an example, there is a shape sensor for determining a cross-sectional profile of a weld bead by a so-called light cutting method and measuring a bead width, penetration, and the like based on the profile (see Japanese Patent Application Laid-Open No. 10-296481).

Next, a method for judging the quality of welding based on the measurement data obtained by the various sensors as described above will be described.

Reference data for determination is created in advance as shown in FIG. That is, laser welding is performed, and measurement data plotted with respect to distance or time during the process is collected. Then, the quality of welding is determined, and O
In the case of K, it is recorded as OK data, and in the case of NG, it is NG
Record as data. When the data collection is completed in this way, the average value of the OK data is obtained and recorded as the reference data (curve Sr in FIG. 3A), and the upper and lower limit values of the reference data are set based on the NG data based on experience. (Curves Sa and Sb in FIG. 3A). The work whose measured data is in the region between the curves Sa and Sb is 100% OK. Next, as shown in FIG. 3B, upper and lower curves Sa,
The allowable regions Ga and Gb are set outside Sb. 100% NG for work whose measured data exceeds the allowable range Ga, Gb
Becomes Since the outside of the allowable regions Ga and Gb is the 100% NG region, the allowable regions Ga and Gb are inside the 100% NG region.

The determination of the actual welding quality will be described with reference to the flowchart shown in FIG. The measurement by various sensors is started at the same time as the start of welding, and data is collected sequentially. Then, it is determined whether or not the measurement data is 100% OK. 100% OK
If not, it is determined whether or not it is 100% NG. 100
If it is not% NG, the degree of NG is determined by a procedure described later. In each determination step, an NG signal is output to the external device when the output becomes 100% NG.

As one method for determining the degree of NG, as shown in FIG.
It is determined whether the integrated value (area value) of the area Gp protruding from the area b into the allowable area Ga or Gb is NG based on whether the integrated value (area value) is within the set range. As another method, as shown in FIG. 3D, of the measurement value curve Sp, the upper limit curve Sa or the lower limit curve Sb is used to determine the allowable area Ga or Gb.
Is determined to be NG based on whether or not the integrated value of the time or the distances ta, tb... As still another method, the measured data curve Sp is 1
Upper / lower limit curve Sa in the range not protruding from the 00% OK area
Or, when approaching to Sb without limit, since the probability of failure is high, if not 100% NG, the entire waveform of the measurement data curve Sp is integrated with respect to the entire welding time or distance, and the integrated value falls within the set range. The quality of the welding quality may be determined based on whether or not there is.

The above setting ranges and judgments are made for each sensor (measurement data). In the embodiment of FIG. 4, a comprehensive judgment is made after the welding is completed. That is, the probability of the failure of the measurement data by the temperature sensor, the plasma sensor, or the other sensors, that is, the% value with respect to the total integrated value of the region protruding into the allowable regions Ga and Gb is calculated, and the probability of the failure by each sensor is calculated. Whether the welding quality is good or not is comprehensively determined based on whether the sum is within a set range (for example, 100%, 120%, or the like). In this case, more accurate monitoring can be performed by weighting each sensor (measurement data) according to the work and the specification.

By recording the measurement value obtained by the sensor in association with the time or distance component, the position of the abnormality or defect on the workpiece can be specified after welding. However, the temperature sensor 17 of FIG.
When the measurement positions of a plurality of sensors are different from each other as in the case of the plasma sensor 18 and the like, the data from each sensor at a specific point in time is information on different positions and not information on the same measurement position. Therefore, by correcting the time axis of the data based on the distance between the measurement positions and the welding speed, more accurate and reliable monitoring can be performed. Such processing can be performed on a program of the control device.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an embodiment of a monitoring device.

FIG. 2A is a side view showing an embodiment of the monitoring device, and FIG. 2B is a front view of the protector.

FIG. 3 is a graph for explaining a quality determination method.

FIG. 4 is a flowchart for explaining data collection.

FIG. 5 is a flowchart for explaining a monitoring method.

FIG. 6 is a schematic view of a laser welding machine.

[Explanation of symbols]

 Reference Signs List 1 laser beam 3 workpiece (work) 4 spatter 7 keyhole 8 plasma 9 molten pool 16 laser emission nozzle 17, 17 'temperature sensor 18, 18' plasma sensor 21 work 21a measuring position 31 housing 32 protector Ga, Gb allowable area Sa Upper limit curve Sb Lower limit curve Sp Measured value curve ta, tb Time width

Continued on the front page F term (reference) 2G043 AA03 CA02 EA10 FA01 FA03 FA06 GA25 GB01 HA05 HA09 JA02 KA01 KA02 LA03 MA03 NA01 NA02 NA06 NA16 4E068 BA00 CA17 CB01 CC01 CC03

Claims (6)

[Claims] When monitoring welding quality using a measurement value obtained by a sensor during a laser welding process, a 100% NG area of a measurement value plotted with respect to a welding time or a distance is determined for each measurement value of each sensor. An upper and lower curve is set, an allowable area is provided inside each of the upper and lower curves, and a probability of a welding failure is determined based on a total area value of a measured value curve portion protruding from the 100% OK area to the allowable area. And calculating the welding quality based on an integrated value of the probability of poor welding with respect to the measured values of all the sensors. 2. In monitoring welding quality using a measurement value obtained by a sensor during a laser welding process, a 100% NG area of a measurement value plotted with respect to a welding time or a distance is determined for each measurement value of each sensor. An upper and lower curve is set, and an allowable area is provided inside each of the upper and lower curves, and welding is performed based on the integrated value of the time or distance of the measured value curve portion protruding from the 100% OK area to the allowable area. A method for monitoring laser welding, comprising calculating a probability of poor quality and determining the quality of welding quality based on an integrated value of the probability of poor welding with respect to the measured values of all sensors. 3. In monitoring welding quality using a measurement value obtained by a sensor in the course of laser welding, upper and lower curves are set which define a 100% OK region of the measurement value plotted with respect to welding time or distance, When the measured value curve approaches the upper / lower curve as much as possible without protruding from the 100% OK region, the measured value is integrated over the entire welding time or distance, and the quality of the welding quality is determined based on the integrated value. A method for monitoring laser welding, characterized by determining. 4. When the measurement positions of a plurality of sensors are different, zero point correction of a time axis of the sensors is performed based on a distance from a predetermined reference position to each sensor and a welding speed. 4. The monitoring method for laser welding according to any one of 1 to 3. 5. An apparatus for monitoring welding quality using a measurement value obtained from a sensor as a proxy signal in a process of laser welding, wherein a plasma sensor and a temperature sensor are stored in a common housing, and Of the projection light of the beam splitter and incident on each of the sensors,
A monitoring apparatus for laser welding, wherein the temperature sensor is provided with a protector for blocking incident light from the molten ground. 6. When the measurement positions of a plurality of sensors are different, zero point correction of the time axis of the sensors is performed based on a distance from a predetermined reference position to each sensor and a welding speed. 6. The monitoring device for laser welding according to 5.