JP3407655B2 - Laser welding monitoring method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse laser welding monitoring apparatus most suitable for a monitoring apparatus of a pulse laser welding apparatus which locally emits a pulsed laser beam a predetermined number of times from a laser oscillator to perform seam welding on a work. It is about.

[0002]

2. Description of the Related Art Conventionally, in a pulse laser welding method in which a pulsed laser beam is locally emitted a predetermined number of times from a laser oscillator to perform seam welding on a work, the welding strength among welding quality in seam welding is It is necessary to satisfy both air tightness. In order to obtain good welding strength, the average power density (average laser power) of the laser beam is stably ensured, and in order to obtain good airtightness, the power density of the laser beam for each shot (for each shot) It is essential to ensure stable laser power).

Here, in the conventional monitoring method in seam welding using a pulse laser power source, the laser power for each shot is measured, and it is confirmed that the measured laser power is within a predetermined standard range. To ensure the welding quality, especially the welding strength and airtightness.

[0004]

However, in the conventional monitoring method, as shown in the graph of FIG. 9 and the graph of FIG. 10, even one shot per welding (one work piece) has a predetermined standard range, that is, an upper limit. Setting value (monitoring upper limit value for each shot) and lower limit setting value (monitoring lower limit value for each shot)
If the condition range between and is out of the range, even if the welding quality of the work is good, it is determined that the work is poor in airtightness or poor in welding strength.

As a result, in the case of pulse laser welding which requires welding strength and airtightness, in the case of seam welding having a narrow condition range satisfying the welding quality such as a fragile material, the graph shown in FIG. 10 is used. As described above, when the laser power for each shot is low, the welding strength is poor (or airtightness is poor), and when the laser power for each shot is high, welding cracks occur.
Many welding defects such as welding spatter (or welding cracks and airtightness due to spatter) occur.

Therefore, the number of defective welding quality products increases,
There is a problem that the defective welding rate becomes very high. In particular, in the mass production process, there are problems that welding quality defective products are likely to occur continuously, productivity is poor, and mass production is not suitable. Therefore, in order to avoid this, if the standard range that can satisfy the welding strength and airtightness, that is, the width between the upper limit setting value and the lower limit setting value is expanded, the welding quality of the workpiece cannot be guaranteed. Will occur.

Further, in seam welding to a work in which weld cracking is likely to occur, the pulse power is within the standard range (± 6%) of laser power per shot at which both welding strength and airtightness of welding quality can be judged to be good. The laser power of the laser power source is equal to the variation range (± 5%) of the laser power, and there is a problem in that the product is often judged to be defective in welding quality and processed. Therefore, in order to eliminate this problem,
There is a problem that an expensive pulse laser power source is required to prepare a pulse laser power source with a small variation range of laser power per welding (one work piece).
Here, in seam welding using a general pulse laser power source, as shown in FIGS. 11A and 11B, laser beams are welded by overlapping by 2 to 3 pulses, and 1 to 2 pulses ( Even if the laser power deviates from the predetermined standard range only by (shot), it does not particularly affect the welding quality of the work.

[0008]

It is an object of the present invention to prevent the welding quality from being treated as poor even though the welding quality is good, for example, in welding where the condition range is narrow, such as for materials that are prone to weld cracking. and to provide a laser welding monitoring how that can be. Another object is to provide a laser welding monitoring how even, less to be processed is determined that the weld quality defective products using inexpensive laser oscillator.

[0009]

According to the invention described in claim 1 SUMMARY OF THE INVENTION, together with the power density of the laser beam for each pulse measured by the measuring means determines whether out of the predetermined standard range When the power density of the laser beam for each pulse deviates from the specified range for a plurality of times in succession, it is determined that the welding quality of the work is defective, and the condition such as a material that easily causes welding cracks. Even in welding with a narrow range,
Even if the welding quality is good, it is possible to prevent the welding quality from being treated as poor. Further, even if an inexpensive laser oscillator is used, it is less likely that the product will be processed by determining that the welding quality is defective. According to the invention described in claim 2, the laser for each pulse measured by the measuring means.
The power density of the light beam is continuous from the first standard range multiple times.
When it comes off, the welding quality of the work, especially the airtightness, is poor.
To judge. And one pulse measured by the measuring means
Weld the workpiece based on the power density of each laser beam
The average power density of all the pulses
When the uniform power density is out of the second standard range, the work
It is judged that the welding quality, especially the welding strength, is poor.

According to the third aspect of the invention, the average power density of all the pulses for welding the work is calculated based on the power density of the laser beam for each pulse measured by the measuring means, and Weld the calculated workpiece
When the average power density of all the pulses that are out of the specified range is out of the specified range, by judging that the welding quality of the work is poor, even in welding in a narrow range of conditions such as materials where welding cracks are likely to occur, Even if the welding quality is good, it is possible to prevent the welding quality from being treated as poor. Further, even if an inexpensive laser oscillator is used, it is less likely that the product will be processed by determining that the welding quality is defective .

According to the invention described in claim 4, particularly
Despite good airtightness of seam welding to the
It is possible to prevent the denseness from being treated as defective.
Wear. Also, the welding strength of seam welding to the work is especially good.
Despite being good, the welding strength is treated as poor.
Can be prevented. According to the invention described in claim 5, conventionally, monitoring is performed by the average energy management width.
Because it was playing, there were many NG, but one shot
It is airtight when monitoring is performed in each energy management range.
A work processed as a defective product becomes a good product.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION [Structure of Embodiment] An embodiment of the present invention will be described based on an embodiment with reference to the drawings. here,
FIG. 1 is a diagram showing a schematic configuration of a pulse laser welding device equipped with a pulse laser welding monitoring device using a pulsed laser beam, and FIG. 2 is a diagram showing a main configuration of the pulse laser welding monitoring device. is there.

The pulse laser welding apparatus 1 of the present embodiment is a YA that continuously (seam) welds a round bar-shaped work (workpiece) W with a pulsed laser beam (laser beam).
A G (yag) laser processing apparatus and a pulse laser welding monitoring apparatus (hereinafter abbreviated as a monitoring apparatus) 2 that monitors (monitors) the welding quality of the workpiece W seam welded by this YAG laser processing apparatus are provided. In addition, on the same circumference of the work W, a welded portion 3 to be seam welded by receiving a pulsed laser beam emitted from the YAG laser processing apparatus is formed.

The YAG laser processing apparatus is also called a YAG pulse laser power supply, and is a YAG laser welding machine 4 for performing pulse laser welding, a power supply (not shown) for supplying electric power to the YAG laser welding machine 4, and YAG laser welding. A cooling water pump cooler (not shown) for cooling the machine 4 and a laser welding control device (not shown) for electronically controlling the YAG laser welding machine 4 are provided.

The structure of the YAG laser welding machine 4 will be briefly described with reference to FIG. YAG laser welder 4
Is equivalent to the laser welding means of the present invention, and is a laser oscillator 5 as a laser generating means for emitting a laser beam carrying welding energy in a pulsed form, and the laser beam is focused on one point on the work W for seam welding. An emitting lens 6 as a laser focusing means, an optical fiber 7 as a laser guiding means for guiding a laser beam from the laser oscillator 5 to the emitting lens 6, and a work moving means for detachably holding and rotating the work W. Work holding device (not shown).

A pulsed YAG (yttrium aluminum garnet) laser is used as the laser oscillator 5, the laser output is 3.5 J, and the oscillation pulse width is 2 mse.
In c, the focus is set at a position of 0.2 mm on the underfocus side from the outer peripheral surface of the work W. Other laser generating means such as a CO ₂ laser may be used as the laser oscillator 5.

Then, in this embodiment, the energy intensity of the laser beam in the YAG laser welding machine 4 is determined by two parameters (see FIG. 3 and the following formula 1). Further, tw in FIG. 3 is the oscillation pulse width (ms)
F represents the pulse emission period, and the shaded portion represents the energy intensity (also referred to as power density or oscillation energy intensity: hereinafter referred to as laser power).

[Formula 1] (laser power) = (laser waveform height) × (level correction coefficient)

The laser power of the YAG laser welding machine 4 is good enough to maintain both airtightness and welding strength in the welding quality of seam welding using a YAG laser processing device (YAG pulse laser power supply). Set to range. In this case, for example, the cross section of the work W having a cylindrical cross section is observed, and the degree of thermal influence is also considered. The energy width in the good range thus determined becomes equal to the control limit upper limit value and the control limit lower limit value of the measured value of the average laser power described later. Then, a control limit upper limit value and a control limit lower limit value, which will be described later, are determined from the energy variations at the lower limit value and the upper limit value.

FIG. 4 shows the laser power distribution when seam welding is performed at each set energy. In FIG. 4, A represents the conventional average energy management width, B represents the energy management width for each shot of the present invention, and C represents the energy distribution (± 3σJ / P) at 3.0 (J / P). )
, D is the energy distribution at 4.0 (J / P) (±
3σJ / P). Further, X represents 3.0 J / P (welding strength lower limit condition), Y represents 3.5 J / P (welding strength proper condition), and Z represents 4.0 J / P (welding strength upper limit condition).
Represents From FIG. 4, conventionally, since the average energy management width (A) was used for monitoring, NG frequently occurred. However, when monitoring is performed in the energy management width for each shot as in the present invention, the work W processed as an airtight defective product becomes a good product.

Next, the monitoring device 2 of this embodiment will be briefly described with reference to FIGS. 1 and 2. The monitoring device 2 corresponds to the laser welding monitoring device of the present invention, and is a well-known microcomputer including a CPU, a ROM, a RAM and the like, after the sensor signal from the optical sensor 10 is A / D converted by the measuring circuit 11. It is configured to be input to the microcomputer.

Then, the monitoring device 2 of this embodiment
Is a measuring circuit 11 for making the laser power output sent from the optical sensor 10 a measurement value corresponding to the laser power for each pulse, an arithmetic circuit 12 for arithmetically processing the energy intensity of the laser beam, and the energy intensity of the laser beam. A comparison circuit 13 as a comparison means for comparing the first and second standard ranges, a first monitor setting circuit 14 that stores the first standard range for airtightness, which is one of the welding qualities, and a welding quality. And a second monitoring setting circuit 15 for storing a second standard range for welding strength, and an alarm circuit 16 for outputting an alarm signal when the comparison circuit 13 determines that the welding is defective. It consists of The measuring circuit 11 and the arithmetic circuit 12 constitute the measuring means of the present invention.

The optical sensor 10 is a photodiode provided in the laser oscillator 5, and is light energy obtained by splitting, for example, 4% of the laser beam emitted from the laser oscillator 1 by the half mirror 17, that is, laser for each pulse. It is a light intensity detecting means for detecting light energy (also referred to as output energy or laser power output) corresponding to the laser power of the light beam.

As shown in FIG. 2, the measuring circuit 11 amplifies the optical energy from the optical sensor 10 to extract the laser waveform of the laser beam, and integrates the optical energy amplified by the amplifier 18. An integrating circuit 19 for obtaining the energy intensity of the laser beam for each pulse, and a sample holder 20 for holding the energy intensity (sample) of the laser beam for each pulse obtained by the integrating circuit 19.
And an A / D for A / D converting the energy intensity of the laser beam for each pulse held by the sample holder 20.
It is composed of a converter 21. The arithmetic circuit 12 is A
The laser power for each pulse is arithmetically processed from the measured value of the energy intensity of the laser beam for each pulse that is A / D converted by the / D converter 21, and the comparison circuit 13 sets the value so that the comparison can be performed.

The comparison circuit 13 is shown in the graph of FIG.
As shown in the graph, the laser power for each pulse is within the first standard range (greater than or equal to the monitoring lower limit value for each shot and less than or equal to the upper limit monitoring value for each shot) or out of the first standard range. Determine if there is. When the laser power setting value (average value / workpiece) of the YAG laser processing device (YAG pulse laser power supply) continuously falls below the monitoring lower limit value for each shot, or when the laser power setting value is the monitoring upper limit value for each shot. Welding defective product (NG) when continuously exceeded
To judge.

In addition, the comparison circuit 13 is, as shown in the graph of FIG. 5 and the graph of FIG.
It is determined whether the average laser power per piece is within the second standard range (good range of average laser power: above the average monitoring lower limit value and below the average monitoring upper limit value) or outside the second standard range. To do. If the average laser power for each welding is below the average monitoring lower limit value or above the average monitoring upper limit value, it is determined as a defective welding product (NG).

The first monitor setting circuit 14 sets and stores the first standard range in advance. In this embodiment, FIG.
As shown in the graph, the first standard range is a range equal to or higher than the monitoring lower limit value for each shot (for example, 180 W) and lower than the monitoring upper limit value for each shot (for example, 220 W).

The second monitor setting circuit 15 sets and stores the second standard range in advance. In this embodiment, FIG.
As shown in the graph, the average monitoring lower limit value (for example, 19
0 W) or more and the average monitoring upper limit value (for example, 210 W)
The following range is defined as a second standard range (good range of average laser power).

When the welding quality of the work W is judged to be defective based on the comparison result of the comparison circuit 13, the alarm circuit 16 directs a monitor or a lamp as a visual display means and a buzzer as a voice display means. Output signals such as alarms,
It is an output means for notifying the observer that the work W is a defective welding product.

[Monitoring Method of Embodiment] Next, a monitoring method of the monitoring device 2 of this embodiment will be briefly described with reference to FIGS. 1 to 8.

The pulsed laser beam emitted from the laser oscillator 5 is guided to the emission lens 6 through the optical fiber 7 and is focused by the emission lens 6 to a point on the surface of the workpiece W to be seam welded. Seam welding is performed by the focused welding energy. On the other hand, laser oscillator 5
The optical energy obtained by dispersing the laser beam emitted from the laser beam by the half mirror 17 is detected by the optical sensor 10, and the measurement circuit 11
Then, the arithmetic circuit 12 performs arithmetic processing to obtain the laser power for each pulse and the average laser power for each welding.

Conventionally, in the energy monitor built in the YAG laser welding machine, the threshold value can only be set to the lower limit value, the upper limit value, and the one level at a time. Therefore, if the lower limit value and the upper limit value of the condition range are simply set as the monitor level, the energy Since the variation exceeds the condition range, NG frequently occurs.

The welding quality was guaranteed by checking and confirming that the laser power for each shot was within a predetermined standard range. However, in the case of a YAG laser welding machine, if a temporal change such as a flash lamp is included, it will be long-term. In general, the laser power varies greatly from shot to shot. For this reason,
As shown in the graph of FIG. 10, when the condition range of the laser power per pulse that satisfies both the welding quality of the welding strength and the airtightness is narrow, the failure rate due to the NG determination is large (1
There is a problem that even one shot of the work is NG), and the number of works judged to be defective welding increases.

When the maximum level of variation in the condition range is set to the monitor level in consideration of the variation, although it deviates from the condition range, when welding is continuously performed with energy within the variation range, NG is Although it decreases, the airtightness of the work cannot always be guaranteed.

Therefore, the measured value of the laser power with respect to the set value of the laser power of the YAG laser welding machine 4 is obtained as a regression curve and a confidence interval (upper limit value of the confidence interval, lower limit value of the confidence interval), and the measured value of the laser power is obtained. The set U
The intersection between CL (w) (monitoring upper limit value for each shot) and the upper limit value of the confidence interval, and LCL (w) (monitoring lower limit value for each shot) set to the measured value of the laser power and the lower limit value of the confidence interval. By setting the laser power setting value of the YAG laser welding machine 4 between the intersection point with and, the wi is set to the i-th laser power in the seam welding of the work W with the pulsed laser beam. When the measured values are assumed, the welding quality is judged to be good when the following formulas (2) and (3) are satisfied, and the welding quality is not satisfied when the following formulas (2) and (3) are not satisfied. Judge as good product.

[0035]

[Equation 2]

[Equation 3]

That is, for the airtightness of welding quality,
A first standard range for each shot of a pulsed laser beam is provided, and the laser power for each shot reaches the lower limit set value for each shot, which is the lower limit setting value of the first standard range. If not, or if the number of unreached pulses during seam welding of one work W exceeds the monitoring upper limit value for each shot, which is the upper limit setting value of the first standard range, it is determined that airtightness is poor.

Here, regarding the airtightness of the welding quality, it is judged whether or not the adjacent pulsed laser beams are continuously lower than the monitoring lower limit value for each shot or whether the airtightness is poor. Become a material. That is, FIG. 7 (a)
As shown in, even if there are some shots with low energy intensity, air leakage does not occur if adjacent shots are normal. However, when shots with low energy are continuously generated, as shown in FIG. 7B, a gap S is formed between the shots and air leakage occurs.
However, when a large number of shots with low laser power occupy, it may be determined that the average laser power is NG.

For the welding strength of the welding quality, a second standard range of the average laser power during one welding of the pulsed laser beam is provided, and the average laser power during the welding of one product is When the average monitoring lower limit value of the second standard range is not reached, the welding strength is determined to be poor, whereby it is possible to reliably determine the airtightness and the welding strength, and to determine the non-defective product as a defective product. Like

Here, the quality judgment of the airtightness and the welding strength in each case is as shown in the following FIGS. 8 (a) to 8 (e). That is, in the first case of FIG.
The laser power for each shot during one welding is normal for all shots (pulses), and the airtightness and the welding strength are both good (OK). In the second case of FIG. 8B, the laser power for each shot during one welding is discontinuous and N
G (a small number), the airtightness is NG, and the welding strength is very good (OK).

In the third case of FIG. 8C, the laser power for each shot during one welding is continuous NG (a small number), the airtightness is NG, and the welding strength is judged to be good (O).
K). Further, in the fourth case of FIG. 8D, the laser power for each shot during one welding is discontinuous and NG (many), the airtightness is NG, and the welding strength is judged to be good (O).
K). Further, in the fifth case of FIG. 8E, the laser power for each shot during one welding is NG (a large number) continuously, and the airtightness and the welding strength are determined to be defective (NG).
Becomes

[Effects of the First Embodiment] As described above, in the monitoring device 2 of the present embodiment, the welding quality is divided into the airtightness and the welding strength. Even if the laser power of is out of the first standard range, if the laser power of the current shot is within the first standard range, the airtightness can be ensured, so that the laser power of each shot continues. It is judged that the airtightness is poor due to the deviation from the first standard range.

Moreover, with respect to the welding strength, even if the laser power of one shot deviates from the second setting range, the average laser power of all the shots of one workpiece to be welded is within the second standard range. In this case, since the welding strength can be secured, it is determined that the welding strength is poor because the average laser power is out of the second standard range, and thus the number of non-defective welding products that are determined to be defective welding is reduced. In addition, there is no defective welding product that is judged to be a good welding product.

That is, it is possible to reliably find a defective welding product without making a defective welding product into a defective welding product. Therefore, in the present embodiment, the welding strength and airtightness of the seam welding can be guaranteed, and reliable welding quality can be obtained. Further, the reliability of the monitoring method can be significantly improved, and the monitoring method enables reliable quality assurance. Further, even in the mass production process, defective welding products are unlikely to occur continuously, so that a monitoring method suitable for mass production can be provided.

[Modification] In the present embodiment, the welding quality of the work W is set so as to satisfy both welding strength and airtightness of the welding quality of the work W to be welded by seam welding using a pulse laser power source. However, the welding quality of the work W may be monitored so that either the welding strength or the airtightness of the welding quality is satisfied.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a schematic configuration of a pulse laser welding apparatus (Example).

FIG. 2 is a configuration diagram showing a main configuration of a pulse laser welding monitoring device (embodiment).

FIG. 3 is a waveform diagram showing the output energy of a YAG pulse laser power supply (Example).

FIG. 4 is a waveform diagram showing set energy of a YAG pulse laser power source (Example).

FIG. 5 is a graph showing NG judgment with respect to laser power for each shot (Example).

FIG. 6 is a graph showing a relationship between a measured laser power value and a laser power setting value (Example).

FIG. 7 (a) is a development view showing a good weld product of welding quality in seam welding, and FIG. 7 (b) is a development view showing a defective welding product of welding quality in seam welding (Example).

FIG. 8 (a) is a development view showing a good welding quality product of seam welding, FIG. 8 (b) is a development view showing a poor welding quality product of seam welding, and FIG. Fig. 3 is a development view showing defective welding products of welding quality, (d) is a development view showing defective welding products of welding quality of seam welding, and (e) is a development showing defective welding products of welding quality of seam welding. It is a figure (example).

FIG. 9 is a graph showing NG determination with respect to laser power for each shot (prior art).

FIG. 10 is a graph showing a relationship between an actually measured laser power value and a laser power setting value (prior art).

11A is a micrograph showing an appearance of a welded portion of a work, and FIG. 11B is a micrograph showing a cross section of the welded portion of the work.

[Explanation of symbols]

W work (workpiece) 1 pulse laser welding device 2 pulse laser welding monitoring device (laser welding monitoring device) 3 welded portion 4 YAG laser welding machine (laser welding means) 5 laser oscillator 6 emission lens 10 optical sensor 11 measurement Circuit (measurement means) 12 Arithmetic circuit (measurement means) 13 Comparison circuit (comparison means) 14 First monitoring setting circuit 15 Second monitoring setting circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-63-278687 (JP, A) JP-A-55-81096 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 26/00-26/30

Claims (5)

(57) [Claims] 1. A laser welding means for locally transmitting a pulsed laser beam from a laser oscillator a predetermined number of times to perform seam welding on a work, and (b) each pulse transmitted from the laser oscillator. Measuring means for measuring the power density of the laser beam, and (c) determining whether or not the welding quality of the work is defective based on the power density of the laser beam for each pulse measured by the measuring means. And a welding quality determining unit for measuring the welding quality by the measuring unit.
It is determined whether or not the power density of the laser beam for each pulse is out of a predetermined standard range, and the power density of the laser beam for each pulse measured by the measuring unit is continuously repeated a plurality of times from the predetermined standard range. The laser welding monitoring method is characterized in that the welding quality of the work is judged to be defective when the work is disengaged. 2. The laser welding monitoring method according to claim 1, wherein the welding quality determining means is a laser beam pattern for each pulse measured by the measuring means.
Determine whether the power density is out of the first standard range
Comparing means, the power of the laser beam for each pulse
When the density deviates from the first standard range multiple times in succession
First, it is determined that the welding quality of the work is poor.
Welding quality judgment means and the laser beam pattern for each pulse measured by the measuring means.
Based on the work density
The average power density of the
When the uniform power density is out of the second standard range,
Second welding quality judgment to judge that the welding quality of the peak is poor
Laser welding monitoring method is characterized in that a cross section. 3. A laser welding means for locally transmitting a pulsed laser beam a predetermined number of times from a laser oscillator to perform seam welding on a work, and (b) every pulse emitted from the laser oscillator. Measuring means for measuring the power density of the laser beam, and (c) determining whether or not the welding quality of the work is defective based on the power density of the laser beam for each pulse measured by the measuring means. And a welding quality determining unit for measuring the welding quality by the measuring unit.
Based on the power density of the laser beam for each pulse, while calculating the average power density of all the pulses for welding the workpiece, the average power density of all the pulses for welding the calculated workpiece from the predetermined standard range A laser welding monitoring method, characterized in that, when the work is disengaged, it is judged that the welding quality of the work is defective. 4. Any one of claims 1 to 3.
In the method for monitoring laser welding according to one of the above, the predetermined standard range is a range of seam welding on the workpiece.
A laser welding monitoring method, characterized in that it is within a condition range satisfying the denseness or within a condition range satisfying the welding strength of the seam welding to the work. 5. Any one of claims 1 to 4.
In the laser welding monitoring method described in one, monitoring is performed in the energy management width for each shot.
A laser welding monitoring method characterized by: