JP4120254B2 - Laser welding quality evaluation apparatus, laser welding apparatus and method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser welding apparatus, and more particularly, to an apparatus used for evaluation and control by detecting a laser welding state with an AE sensor.
[0002]
[Prior art]
Conventionally, a technique has been proposed in which an AE (acoustic emission) wave generated during welding with a laser welding apparatus is detected, a welding state is evaluated from this detection signal, and welding is controlled.
[0003]
For example, Japanese Patent Application Laid-Open No. 1-210185 discloses an apparatus that attaches an AE sensor to a jig that holds an object to be welded, detects an AE wave generated in the object to be welded during welding, and determines whether the product is good or bad. Has been proposed.
[0004]
Japanese Laid-Open Patent Publication No. 6-1555056 proposes an apparatus for performing optimum welding control by attaching an AE sensor to a laser welding head (torch), detecting an AE wave generated at a welded portion through the welding head. Yes.
[0005]
Further, although not related to welding, as a similar example, Japanese Patent Application Laid-Open No. 64-40192 discloses AE associated with laser processing of a workpiece through one or a plurality of AE sensors fixed to the workpiece. A machining control method has been proposed in which a signal is detected, the AE signal is arithmetically processed, and the laser machining state is monitored and controlled in real time.
[0006]
[Problems to be solved by the invention]
In the apparatus disclosed in Japanese Patent Laid-Open No. 6-1555056, an AE wave generated in an object to be welded propagates to a welding head through an air layer and is detected by an AE sensor. Since the AE wave is greatly attenuated by the air layer, there is a problem that the S / N ratio is deteriorated in the detection by the AE sensor.
[0007]
In the techniques described in Japanese Patent Application Laid-Open Nos. 1-210185 and 64-40192, no air layer is interposed in the AE wave propagation path from the AE wave source to the AE sensor. Not. However, since the position of the AE sensor is fixed with respect to the work piece, when welding a relatively large work piece, the distance to the AE sensor and the AE wave propagation path change when the position of the welded portion changes. come. For this reason, if it is going to evaluate a welding state correctly about every place, there exists a problem that the process and mechanism which compensate the difference to the distance to an AE sensor and an AE wave propagation path are needed.
[0008]
The present invention has been made to solve such problems of the conventional apparatus.
[0009]
[Means for Solving the Problems]
A laser welding quality evaluation apparatus according to the present invention is an apparatus that detects an AE wave generated from a welded portion of an object to be welded by a laser welding apparatus by an AE sensor and evaluates the welding quality based on a detection signal of the AE sensor. A pressure roller that presses the vicinity of a welded portion of an object to be welded, the pressure roller being attached to a structural member of the laser welding apparatus, and the AE sensor is connected to the pressure roller or the structure An AE wave that is provided on a member and propagates from the vicinity of the weld to the pressure roller is detected by the AE sensor.
[0010]
In a preferred aspect of the present invention, the AE sensor is attached to a rotary shaft member of the pressure roller.
[0011]
In another preferred aspect of the present invention, the laser welding quality evaluation device irradiates a sound wave toward a welded portion of the workpiece and suppresses the undulation of the weld pool of the welded portion by the sound pressure of the sound wave. Irradiation means is provided.
[0012]
In another preferred aspect of the present invention, the AE sensor having a detection capability with a sensitivity center of substantially 500 kHz is used.
[0013]
A laser welding apparatus according to the present invention is a laser welding apparatus that welds a welded portion of an object to be welded by laser light emitted from a laser torch, and detects sound generated from the welded portion of the workpiece during welding by an AE sensor. A laser welding apparatus that controls processing parameters of the laser welding process based on a detection signal of the AE sensor, a pressure roller that presses the vicinity of a welded portion of an object to be welded, and is a structural member of the laser welding apparatus. A pressure roller attached to the pressure roller or the structural member, and the AE sensor detects an AE wave propagated from the vicinity of the weld to the pressure roller. To do.
[0014]
In a preferred aspect of the present invention, the AE sensor is attached to a rotary shaft member of the pressure roller.
[0015]
In another preferred aspect of the present invention, the laser welding apparatus irradiates a sound wave toward a welded portion of the workpiece, and a sound wave irradiation unit that suppresses the undulation of the weld pool of the welded portion by the sound pressure of the sound wave. Is provided.
[0016]
In another preferred aspect of the present invention, the AE sensor having a detection capability with a sensitivity center of substantially 500 kHz is used.
[0017]
In another preferred aspect of the present invention, the laser welding apparatus includes a sensor that detects a z-coordinate of the pressure roller, a moving unit that moves the pressure roller in the xy direction, and the addition detected by the sensor. and z coordinates and the x and y coordinates of the pressing roller obtained from the moving means of pressure rollers, the design shape data indicating a three-dimensional shape of the object to be welded, the control of the z-direction position of the pressure roller on the basis of And roller control means for performing.
[0018]
Further, the method according to the present invention is a welding method by a laser welding apparatus that welds a welded portion of a workpiece to be welded with a laser beam emitted from a laser torch, wherein the laser welding apparatus is used to press the vicinity of the welded portion of the workpiece. An AE sensor attached to a rotary shaft member of a pressure roller provided on the pressure roller detects an AE wave propagated from the vicinity of the weld to the pressure roller, and the laser welding is performed based on a detection signal of the AE sensor. The processing parameters of the welding process by the apparatus are controlled.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.
[0020]
FIG. 1 is a schematic diagram showing an overall configuration of a laser welding apparatus according to the present invention. In this figure, the direction perpendicular to the drawing sheet is the x-axis direction, the left-right direction of the figure is the y-axis direction, and the up-down direction is the z-axis direction. FIG. 2 is a diagram schematically showing a front cross section (a), a side cross section (b) of the laser torch 10 of this laser welding apparatus, and a state (c) of the laser output port viewed from below. It is. Hereinafter, the configuration of the laser welding apparatus of this embodiment will be described with reference to these drawings.
[0021]
In these drawings, a laser torch 10 is a device that outputs a laser beam for welding. The laser beam emitted from the laser 102 is focused by the lenses 104a and 104b. At the focal point of the focusing, the workpieces 30 such as two overlapped plates are heated by the laser beam and melted. The portion to be welded in this way is referred to as a welded portion 32. A protective plate 106 that transmits a laser beam is provided below the lens 104b in order to protect the lens and the like from splashes from the melting portion 32.
[0022]
The laser torch 10 is fixed to a support structure 14 that is driven up and down (that is, in the z-axis direction) by a hydraulic drive unit 12. The hydraulic drive unit 12 can move the support structure 14 up and down by supplying oil from the hydraulic device 16. The hydraulic drive unit 12 is attached to a welding robot (not shown). The welding robot is used to move the laser torch 10 in the x direction and the y direction. On the other hand, the hydraulic drive unit 12 is used to move the laser torch 10 in the z direction. By combining these two, it is possible to weld a workpiece having a somewhat complicated shape including irregularities. The relative height (z-axis direction position) of the laser torch 10 with respect to the welding robot can be detected by a height sensor 13 that detects the height of the cylinder of the hydraulic drive unit 12.
[0023]
A shaft support 18 is provided at the lower end of the support structure 14, and the shaft of the pressure roller 20 is supported by the shaft support 18. The pressure roller 20 is a member for pressing the work piece 30. The pressure roller 20 presses the vicinity of the welded portion 32, thereby improving the adhesion of a plurality of plates that are the workpieces 30 at the position of the welded portion 32. Both the pressure roller 20 and the shaft support portion 18 are formed of a material that easily propagates sound waves such as metal. Further, in order to minimize the reflection of sound waves at the interface between the pressure roller 20 and the shaft support portion 18, both are manufactured using materials having an acoustic impedance as close as possible.
[0024]
The drive control unit 26 is a control processor that controls movement in the x and y directions by the welding robot and movement in the z direction by the hydraulic drive unit 12. The drive control unit 26 receives the robot data including the information on the current xy coordinates of the torch 10 from the welding robot, and the height data including the information on the current height (z coordinate) of the torch 10 from the height sensor 13. From the storage device (not shown), design data indicating the three-dimensional shape of the workpiece is received. Based on the current three-dimensional position of the torch 10 indicated by the former two and the three-dimensional shape indicated by the design data, drive instruction data for the welding robot and drive instruction data for the hydraulic drive unit 12 are calculated. To supply each instruction data.
[0025]
The support structure 14 is biased relatively downward (relative to the shape of the work piece 30) by the hydraulic drive of the hydraulic drive unit 12 based on this drive instruction, so that the pressure roller 20 The weldment 30 is pressed.
[0026]
In the present embodiment, the AE sensor 22 is attached to the shaft support portion 18 that supports the rotation shaft of the pressure roller 20. The AE sensor 22 is attached such that its detection surface is in close contact with the shaft support 18. Therefore, the AE wave generated at the welded portion 32 of the workpiece 30 reaches the AE sensor 22 via the pressure roller 20 and the shaft support portion 18.
[0027]
Since the acoustic impedance differs greatly between the metal work piece 30 and air, the AE wave generated in the work piece 30 hardly propagates to the air layer, but the pressure roller 20 has an acoustic impedance on the work piece 30. Since they are close, the AE wave efficiently propagates to the pressure roller 20. Further, the AE wave is less attenuated in the pressure roller 20 than in the air layer. Further, since the shaft support portion 18 also has an acoustic impedance close to that of the pressure roller 20, the AE wave propagates efficiently between the two. Therefore, the AE wave reaches the AE sensor 22 with much less attenuation than when passing through the air layer. As a result, the S / N ratio of the detection signal of the AE sensor 22 can be improved.
[0028]
Further, when the AE sensor 22 is attached to the shaft support portion 18, the relative positional relationship of the AE sensor 22 with respect to the welded portion is constant no matter how the position of the welded portion is changed by the welding robot or the hydraulic drive unit 12. Therefore, there is an advantage that detection can always be performed under a certain condition.
[0029]
Note that, in place of attaching the AE sensor 22 to the shaft support portion 18, the S / N ratio can be greatly improved as compared with the case where the AE wave is detected through the air layer even if the AE sensor 22 is attached to the support structure 14 or the laser torch 10. However, it is most preferable to provide the AE sensor 22 here because the shaft support portion 18 is located closest to the welded portion 32 as a place where the relative positional relationship with respect to the welded portion 32 does not change. It can be said.
[0030]
As the AE sensor 22, it is preferable to use a sensor having a detection capability with a sensitivity center of about 500 kHz. This is based on experiments by the inventors of the present invention.
[0031]
In this experiment, the detection signals of the AE sensor were collected for various cases, such as when good welding was possible or when defects such as cracks occurred. As a result, a portion of the detection signal of the AE sensor below about 200 kHz gives a similar signal regardless of the welding state / quality, and this portion is caused by machine vibration or noise caused by welding shielding gas. It turned out to be the corresponding noise part. Conversely, the frequency component exceeding 200 kHz is a signal indicating the state / quality of welding.
[0032]
FIG. 3 shows the frequency analysis of the detection signal when the AE wave emitted from the welded part is detected by an AE sensor having a sensitivity center of 150 kHz in this experiment. As shown in this figure, in the range of 200 kHz or more, a signal exists up to nearly 600 kHz. Here, when an AE sensor having a sensitivity center of about 500 kHz is used, the sensitivity is improved from around 200 kHz, the highest sensitivity is obtained around 500 kHz, and a sensitivity distribution with sensitivity up to about 1 MHz is obtained. This is a sensitivity distribution suitable for detection of a signal representing welding quality. In this example, since a 150 kHz sensor is used, the sensitivity for high frequencies is low. However, considering various cases of actual welding, it is preferable that signals up to about 1 MHz can be detected.
[0033]
Such a detection signal of the AE sensor 22 is input to the welding evaluation processing unit 24. The welding evaluation processing unit 24 evaluates the quality / state of the welded part 32 based on the detection signal.
[0034]
As the evaluation process of the welding evaluation processing unit 24, for example, a process in which the welding result is evaluated as a non-defective product when the level of the detection signal is within a predetermined non-defective product level range, and a defective product is evaluated when the level falls outside the range. As the non-defective product level range, the level range of the detection signal when the welding quality is good may be determined in advance through experiments or the like and registered in the evaluation processing unit 24.
[0035]
FIG. 4 is an example of an experimental result for obtaining the non-defective product level range. When welding is performed on an object to be welded having the same material and thickness (3.00 mm) by changing the laser output in several stages. The change in the effective value of the level of the detection signal (AE signal) is shown together with the penetration depth of the welding result in each case. In this example, when the laser output is 0.5 kW, the penetration depth is 0.35 mm, and the penetration is insufficient. When the laser output is 2.0 kW, the penetration depth is 2.65 mm, which is a relatively good penetration state. At 4.0 kW, the depth of penetration is 3.00 mm and the back of the workpiece is completely melted, but it is slightly melted. And it turns out that the detection signal of the AE sensor during this period shows a mountainous change with a peak near the laser output of 2.0 kW indicating a good penetration state. From this experimental result, for example, it can be determined that the effective value level of the detection signal is 25 or more and 28 or less within the non-defective product level range.
[0036]
Of course, the example of FIG. 4 is merely an example. The method of penetration of the workpiece in welding depends on the combination of the materials of the plurality of members that are the workpiece and the amount of heat input per unit time to the workpiece. The amount of heat input per unit time depends on the laser output and the feed rate of the workpiece. Therefore, it is only necessary to conduct experiments by changing these conditions (material and heat input) in various ways, and obtain and register a good product level range under each condition in advance. As for the heat input, if some experiments are performed with a combination of typical laser output and feed rate, interpolation can be performed for other portions.
[0037]
In the present embodiment, in addition to this evaluation process, various conventional AE signal evaluation methods such as the evaluation process disclosed in Japanese Patent Laid-Open No. 6-1555056 described above can be used.
[0038]
Based on the result of the welding quality evaluation as described above by the welding evaluation processing unit 24, it is possible to automatically select defective products or provide the evaluation result to a subsequent process. In the latter case, in the post-process, it is possible to perform treatment such as reworking as necessary based on the evaluation result of each workpiece.
[0039]
The above is the evaluation and usage method for each workpiece (work), but even when welding one workpiece, the welding state at that time is determined from the real-time detection signal of the AE sensor 22. In addition, by controlling various processing parameters of the laser welding apparatus in accordance with the determination, the welding apparatus can be feedback-controlled so that good welding is performed. The processing parameters to be controlled include laser output, feed rate (welding speed), shield gas flow rate, assist gas flow rate, and the like. By controlling one or more of these based on the detection signal of the AE sensor 22, optimum control of the welding process is performed.
[0040]
As described above, the basic device configuration and the operation and effect of the present embodiment have been described. In the present embodiment, as an additional configuration, as shown in FIG. 2, the laser torch 10 includes three oscillators 110a, 110b, and 110c. It is also suitable to provide. These oscillators 110a to 110c are for suppressing the undulation of the surface of the molten pool (the portion where the metal is melted by the heat of welding) of the 30 welded portions 32 of the workpiece.
[0041]
That is, in laser welding, it has been found by conventional research that the surface of the weld pool is rippled at a frequency of about 1 to 2 kHz (Current Status and Future Technologies of Laser Welding) ), E. Beyer, A. Gasser, W. Gatzweiler and W. Sokolowski, "Plasma fluctuation in laser welding with CW-CO2 lasers," ICALEO, 1987, pp. 17-23.).
[0042]
The oscillators 110a to 110c shown here are intended to reduce this undulation with sound pressure generated by sound waves. By suppressing the undulations on the surface of the weld pool, the efficiency and quality of welding can be improved, and further improvement in the S / N ratio of the detection signal of the AE sensor 22 can be expected.
[0043]
Each oscillator 110a-110c emits the sound wave of the same frequency. For example, a sine wave of about 10 kHz is emitted from each of the oscillators 110a to 110c with respect to the above-described molten pool surface wave of 1 to 2 kHz. All of these oscillators 110 a to 110 c are arranged toward the welded portion 32 of the workpiece 30. Each oscillator 110a, 110b, 110c is driven by a drive signal having a phase different from each other by 1/3 period, like drive signals 200a, 200b, 200c shown in FIG. By such oscillation of each oscillator, a sound pressure almost always constant is always applied to the welded portion 32. The action of the sound pressure suppresses the wave motion on the surface of the molten pool.
[0044]
Strictly speaking, the oscillators 110a to 110c may output sound waves so as to have an equiphase interval as illustrated in FIG. Therefore, the phase difference of the drive signal applied to each oscillator may be determined based on the relationship between the arrangement positions of the oscillators 110a to 110c and the distance between the welds 32 so as to satisfy this requirement.
[0045]
Note that the oscillation frequency of the oscillators 110a to 110c is not limited to about 10 kHz illustrated. However, in order to avoid the mixing of noise into the AE sensor 22 as much as possible, it is preferable to use a low frequency with sufficiently low sensitivity in the sensitivity distribution of the AE sensor 22 (distribution centered at about 500 kHz in the above example). It is. A suitable frequency may be obtained in advance by experiments or the like.
[0046]
In the above example, three oscillators are used. However, a larger number (n) of oscillators are provided so that the surface of the molten pool is irradiated with a sound wave whose phase is shifted by 1 / n period. By doing so, the sound pressure acting on the molten ground surface can be made more constant.
[0047]
As described above, according to the apparatus of the present embodiment, since the AE wave can be detected via the pressure roller 20, it is high while performing suitable welding by bringing members of the workpieces into close contact with each other. The AE wave can be detected under the S / N ratio and under almost constant detection conditions, and the accuracy of the determination of the welding quality / state can be improved. In this embodiment, since the three-dimensional position of the pressure roller 20 can be controlled according to the design shape data of the workpiece, even a relatively complicated design shape with unevenness can be welded according to the shape. it can. In the present embodiment, since the laser torch 10 and the pressure roller 20 are both fixed to the common support structure 14, the distance between the torch 10 and the welded portion 32 of the work piece 30 is always constant. Can do. In this embodiment, by using an AE sensor having a central sensitivity of about 500 kHz, detection of a noise component of about 200 kHz or less can be greatly reduced, and an AE signal related to welding quality can be detected efficiently. Further, in the present embodiment, by providing the oscillators 110a to 110b that irradiate the welded portion 32 with sound waves, the surface of the welded portion 32 can be suppressed, and as a result, the welding efficiency can be improved and the AE signal can be detected. Further improvement of the S / N ratio can be achieved.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing an overall configuration of a laser welding apparatus according to the present invention.
FIG. 2 is a view for explaining details of a configuration of a laser welding apparatus according to the present invention.
FIG. 3 is a diagram illustrating an example of a frequency analysis result of a detection signal of an AE wave generated during welding by an AE sensor.
FIG. 4 is a diagram illustrating an example of a relationship between a laser output obtained in an experiment and an effective value level of an AE signal.
FIG. 5 is a diagram showing an example of drive signals given to three oscillators.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Laser torch, 12 Hydraulic drive part, 13 Height sensor, 14 Support structure, 16 Hydraulic device, 18 Shaft support part, 20 Pressure roller, 22 AE sensor, 24 Weld evaluation processing part, 26 Drive control part, 30 Welded 32 welds.

Claims (10)

An apparatus for detecting an AE wave generated from a welded portion of an object to be welded by a laser welding apparatus using an AE sensor and evaluating welding quality based on a detection signal of the AE sensor,
A pressure roller that presses the vicinity of the welded portion of the workpiece, and includes a pressure roller attached to the structural member of the laser welding apparatus;
The laser welding quality evaluation apparatus, wherein the AE sensor is provided on the pressure roller or the structural member, and an AE wave propagated from the vicinity of the welded portion to the pressure roller is detected by the AE sensor.   2. The laser welding quality evaluation apparatus according to claim 1, wherein the AE sensor is attached to a rotary shaft member of the pressure roller.   2. The laser welding quality according to claim 1, further comprising: a sound wave irradiation means for irradiating a sound wave toward a welded part of the workpiece and suppressing a wave of the weld pool of the welded part by a sound pressure of the sound wave. Evaluation device.   2. The laser welding quality evaluation apparatus according to claim 1, wherein the AE sensor has a detection capability substantially having a sensitivity center of 500 kHz. A laser welding apparatus for welding a welded portion of a workpiece by laser light emitted from a laser torch, wherein a sound generated from the welded portion of the workpiece during welding is detected by an AE sensor, and based on a detection signal of the AE sensor A laser welding apparatus for controlling processing parameters of a laser welding process,
A pressure roller that presses the vicinity of the welded portion of the workpiece, the pressure roller being attached to the structural member of the laser welding apparatus,
The laser welding apparatus according to claim 1, wherein the AE sensor is provided on the pressure roller or the structural member, and an AE wave propagated from the vicinity of the welding portion to the pressure roller is detected by the AE sensor.   6. The laser welding apparatus according to claim 5, wherein the AE sensor is attached to a rotary shaft member of the pressure roller.   6. The laser welding apparatus according to claim 5, further comprising a sound wave irradiation means for irradiating a sound wave toward a welded part of the workpiece and suppressing a wave of the weld pool of the welded part by a sound pressure of the sound wave. .   6. The laser welding apparatus according to claim 5, wherein the AE sensor has a detection capability substantially having a sensitivity center of 500 kHz. A sensor for detecting the z-coordinate of the pressure roller;
Moving means for moving the pressure roller in the xy direction;
And x and y coordinates of the pressing roller obtained from the z-coordinate, and the moving means of the pressure roller, wherein the sensor detects a design shape data indicating a three-dimensional shape of the object to be welded, the pressure roller on the basis of Roller control means for controlling the position of the z direction ,
The laser welding apparatus according to claim 5, comprising: A welding method by a laser welding apparatus for welding a welded portion of an object to be welded by laser light emitted from a laser torch,
AE propagated from the vicinity of the welded portion to the pressure roller by an AE sensor attached to the rotary shaft member of the pressure roller provided in the laser welding apparatus in order to press the vicinity of the welded portion of the workpiece. Detect waves,
Control processing parameters of the welding process by the laser welding apparatus based on the detection signal of the AE sensor.
Laser welding method.

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