JP2000210781A - Laser beam welding method and its equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser beam welding method and its laser beam welding equipment by which control having excellent management precision of weld quality is executed and a weld zone having sound and excellent quality is stably obtained. SOLUTION: The length L of the molten pool of an object W to be welded is obtained with an image processing means 6 based on an image photographed with a CCD camera 5, a command signal is transmitted to a laser beam oscillator 2 and a worktable 4 from a controller 7, and a laser output and a welding speed are adjusted. Thus, the ratio L/t of the length L of the molten pool to the plate thickness (t) of the object W is controlled so as to be set in the range of 1-3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser welding technique, and more particularly, to a laser welding method capable of performing a stable welding by monitoring a welding condition and obtaining a sound and good welded part quality, and The present invention relates to a welding device for automatically performing such laser welding.

[0002]

2. Description of the Related Art For example, Japanese Unexamined Patent Publication No. 5-77074 discloses that the strength of plasma generated during laser welding is used as a substitute characteristic of welding quality, and that the quality of welding is predicted by monitoring this during welding. There has been disclosed a technique for improving welding quality by making a determination and feeding it back to parameters mainly including a laser output and a welding speed.

[0003]

However, in the laser welding method described in the above publication, the state of the molten metal in the welded part is not directly monitored, but the information monitored is the intensity of the plasma. However, since it is merely a substitute for welding quality, it is difficult to respond with sufficient sensitivity to changes in welding quality, and the accuracy of prediction of welding quality is not sufficient. There is a problem that the laser welding may not be performed, which has been a problem in such a laser welding control technique.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the conventional laser welding control technology, and is capable of performing control with excellent welding quality control accuracy, and is sound and good. It is an object of the present invention to provide a laser welding method and a laser welding apparatus capable of stably obtaining a weld having a high quality.

[0005]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have studied the effects of laser welding conditions such as laser output and welding speed on welding quality, and the effects of laser welding conditions and the plate thickness of the material to be welded. As a result of diligent studies on the relationship between the two, the inventors focused on that the length of the molten pool during laser welding directly affects the quality after welding, and completed the present invention.

FIG. 2 illustrates the effect of the thickness t of the aluminum alloy and the length L of the molten pool (the direction of welding) on the welding quality in butt laser welding of aluminum alloy sheets. In the region where the ratio L / t of the length L of the molten pool to the plate thickness t of the material to be welded is less than 1, welding becomes unstable as shown by a mark in the figure, and spatter occurs frequently, resulting in a healthy sound. While welding becomes impossible,
In the region where the ratio L / t exceeds 3, as shown by the mark in the figure, the material to be welded is burnt out and welding cannot be performed, and the ratio L / L of the plate thickness t to the length L of the molten pool. t is 1
It has been found that by controlling to a range of 3, welding of good quality is possible.

[0007] The present invention is based on such knowledge, and the laser welding method according to claim 1 of the present invention provides:
The length of the molten pool in the direction of welding is 1 to 1
The laser output and / or the welding speed is controlled so as to be three times the range, and such a configuration in the laser welding method is a means for solving the above-mentioned conventional problems.

According to a second aspect of the present invention, there is provided a laser welding method, comprising:
The welding speed value expressed in units of minutes is in the range of 0.5 times to 3.0 times the value of the plate thickness of the work to be welded expressed in units of millimeters.
In the laser welding method according to the above, the laser output value per unit area expressed in units of kilowatt / square millimeter is changed from ten times the welding speed value expressed in units of meters / minute to ten times the welding speed value. The laser welding method according to claim 4, wherein the welding is a butt welding, wherein the welding is a butt welding.
In the laser welding method according to the first aspect, the object to be welded is an aluminum alloy. Further, in the laser welding method according to the sixth and seventh aspects, the additive element contained in the aluminum alloy is an element having a lower boiling point than aluminum. Yes, aluminum alloy is A5 in JIS standard
000 series or A7000 series alloy, and in a laser welding method according to claim 8, the thickness of the workpiece is 0.8 m.
The laser welding method according to claim 9, wherein the laser is a continuous oscillation type Nd:
It is characterized in that it is a YAG laser.

According to a tenth aspect of the present invention, there is provided a laser welding apparatus, comprising: a laser oscillator for generating a laser; a condensing means for condensing the laser from the laser oscillator and irradiating the object to be welded; Moving means for moving the workpiece relative to the light means, photographing means for photographing the molten pool at the welding point, and image processing means for measuring the size of the molten pool from an image obtained by the photographing means Characterized in that it comprises a control means for sending a command to increase or decrease the laser output and / or the welding speed based on the measurement result of the molten pool obtained by the image processing means to the laser oscillator or the moving means, respectively, Such a configuration in the welding apparatus is used as means for solving the above-mentioned conventional problems.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The laser welding method according to the present invention employs one of a laser output and a welding speed so that a molten pool length L is in a range of 1 to 3 times a plate thickness t of a workpiece. By controlling both of them, for example, when L / t exceeds 3, the laser output is reduced or the welding speed is increased so that L / t becomes 3 or less. When t is less than 1, the laser output is increased or the welding speed is reduced to control L / t to be 1 or more so that the welding state can be reduced without causing spatter or burn-through. The purpose is to stably maintain and obtain a sound and good weld. The reason why the L / t ratio is specified in the range of 1 to 3 is that if the L / t ratio is less than 1, welding becomes unstable and spatter occurs frequently, and If the ratio exceeds 3, the material to be welded will be burned off and welding cannot be performed.

The welding speed at this time is, as described in claim 2, a welding speed value V (m / min) expressed in units of meters / minute, and a welding speed expressed in units of millimeters. 0.5 to 3.0 times the value t (mm) of the thickness of the welded material, that is, 0.5t to 3.0.
It is desirable to set it in the range of t. This is because when the welding speed V in meters / minute is less than 0.5 times the plate thickness t in millimeters, the heat input to the workpiece becomes excessive and If the welding speed V exceeds 3.0 times the thickness t,
This is due to the fact that the heat input tends to be insufficient, and sufficient penetration cannot be obtained, and sound welding tends to be impossible.

The laser output is a laser output value P (kW / m) expressed in units of kilowatts / square millimeter as described in claim 3.
m ² ) ranges from 10 times the welding speed value V (m / min) in units of meters / minute to 10 times the welding speed value V plus 40, that is, 10 V to 10 V + 4.
It is desirable to set the range to 0. That is, the laser output value P per unit area expressed in units of kilowatt / square millimeter is the welding speed V expressed in units of meters / minute.
When the laser output value P per unit area exceeds 10 times the welding speed V plus 40, the spatter tends to occur frequently or burn off. It depends.

In the laser welding method according to the present invention, the ratio L / t of the molten pool length L to the plate thickness t is set to 1 to 3 as described above.
Since the molten pool length L is generally determined by both the welding speed V and the laser output P, the welding speed V and the laser output P per unit area are controlled.
Is controlled within the above range, the laser output P at that time is
Depending on the welding speed V and the welding speed V, L / t is not always in the range of 1 to 3, and the range described in claims 2 and 3 sets the ratio L / t of the molten pool length L to the plate thickness t to L / t. It is only a guide for controlling the range of 1-3.

The laser welding method according to the present invention is desirably applied to butt welding, as described in claim 4, and particularly good results can be obtained in butt welding. As described in Item 5, an aluminum alloy, particularly an additional element having a lower boiling point than aluminum as described in Item 6, for example, an aluminum alloy containing magnesium or zinc, specifically, specified in JIS A5000 series or A
It is desirable to apply to a 7000 series alloy. That is,
In these aluminum alloys, welding for maintaining the ratio L / t of the length L of the molten pool and the thickness t in the range of 1 to 3 in relation to the properties such as the specific gravity, viscosity and surface tension of the molten metal. This is because a decrease in the condition range is observed, and welding is facilitated.

The thickness range of the material to be welded in the laser welding method according to the present invention is preferably in the range of 0.8 mm to 5.0 mm. That is, when the material to be welded has a plate thickness of less than 0.8 mm, low output and high speed welding is performed, so that welding becomes unstable and burn-through easily occurs, and conversely, it exceeds 5.0 mm. In the case of a material to be welded having a large thickness, high-output low-speed welding is performed and the molten pool becomes large, so that burn-through tends to occur and a sound welded portion tends to be difficult to obtain. Further, the laser used in the laser welding method according to the present invention has a wide range of welding conditions for setting the range L / t of the length L to the thickness t of the molten pool to 1 to 3 in a weldable range, Particularly, since the welding efficiency can be improved by increasing the welding speed, it is desirable to use a continuous oscillation type Nd: YAG laser as described in the high-speed claim 9.

In carrying out the laser welding method according to the present invention, a welding apparatus as set forth in claim 10, that is, a laser oscillator, a condensing means for irradiating a laser from the oscillator to a welding position, and a condensing means. It is desirable to use a welding device having a moving means for relatively moving the workpiece relative to the means, a photographing means for photographing a molten pool at a welding point, an image processing means, and a control means. The size of the molten pool, in particular, the length L in the welding direction is measured from the image obtained by the photographing means by the image processing means, and a command signal is output from the control means to the laser oscillator and the moving means, and the command signal is inputted in advance. The laser output and the welding speed are feedback-controlled so that the value of L / t calculated from the thickness t of the material to be welded is always in the range of 1 to 3. I, it is possible to perform laser welding method according to the present invention completely automatically.

[0017]

In the laser welding method according to the first aspect of the present invention, the laser output and / or the laser output is set so that the length of the molten pool in the direction of welding progresses is in the range of 1 to 3 times the plate thickness of the workpiece. Since the welding speed is controlled, stable welding can be performed without generating spatter or burn-through, and a very excellent effect that a sound welded part having excellent quality can be obtained.

According to a second aspect of the present invention, there is provided a laser welding method comprising the steps of:
Since the welding speed value expressed in minutes is in the range of 0.5 times to 3.0 times the value of the thickness of the work piece when expressed in units of millimeters, Can determine the appropriate welding speed range, and can be used as a reference for controlling the welding speed so that the molten pool length becomes 1 to 3 times the plate thickness of the work to be welded. In the laser welding method according to claim 3, the laser output value per unit area expressed in units of kilowatt / square millimeter is from ten times the welding speed value expressed in units of meters / minute to the value of the welding speed value. Since it is set to be a value range obtained by adding 40 to 10 times, an appropriate laser output range can be obtained according to the welding speed, and the molten pool length is 1 to 3 times the plate thickness of the workpiece. Control the laser output so that It is a reference, according to claim 4
In the laser welding method according to the present invention, since the method is applied particularly to butt welding, it is possible to stably obtain a good weld without defects, and in the laser welding method according to claim 5, The laser welding method according to claims 6 and 7 is, for example, an aluminum alloy.
Alloy or an A7000 series alloy contains an additional element having a lower boiling point than aluminum in the aluminum alloy.
The range of welding conditions for increasing the ratio by three times becomes wider, and laser welding according to the present invention can be performed more easily.
Furthermore, in the laser welding method according to claim 8, the thickness of the workpiece is in the range of 0.8 mm to 5.0 mm, so that the laser welding according to the present invention can be performed without difficulty, Since the continuous wave Nd: YAG laser is used in the laser welding method according to the ninth aspect, the length of the molten pool is set to 1 to 3 of the plate thickness.
Since the range of the welding condition for holding twice is particularly widened on the high speed side, it is possible to perform the welding at a higher speed, and it is possible to improve the working efficiency.

According to a tenth aspect of the present invention, there is provided a laser welding apparatus, comprising: a laser oscillator; a laser condensing means; a moving means for moving a workpiece relative to the laser; a photographing means for photographing a molten pool; And the control means, the length L of the molten pool in the welding progress direction is determined based on the image obtained by the photographing means, and the ratio L is calculated based on the previously input plate thickness t of the workpiece. / T is calculated, and the laser output is increased or the welding speed is increased when L / t falls below a predetermined threshold so that the ratio L / t does not fall below 1 or exceeds 3. When the ratio L / t exceeds the threshold value, a command signal for decreasing the laser output or increasing the welding speed is transmitted to the laser oscillator or the moving means. For transportation Thus, the length L of the molten pool can always be automatically controlled within a range of 1 to 3 times the plate thickness t, and the laser welding method according to the present invention can be carried out fully automatically. It has an effect.

[0020]

EXAMPLES The present invention will be described below more specifically based on examples.

FIG. 1A shows an embodiment of a laser welding apparatus according to the present invention. The laser welding apparatus 1 shown in the figure has a laser oscillator 2, a collimation lens and a condenser lens. A condensing optical system 3 as a condensing means, a processing table 4 as a moving means for mounting and moving the workpiece W, and a photographing for photographing a molten pool of the workpiece W through a filter (not shown). CCD as a means
An image processing device 6 (image processing means) including the camera 5,
A control device 7 (control means) that sends a command signal to the laser oscillator 2 and the processing table 4 based on information from the image processing device 6 to increase or decrease the laser output and / or the moving speed (welding speed) of the processing table 4. It has.

In this embodiment, a continuous oscillation type Nd: YAG laser oscillator having an output of 4 kW is used as the laser oscillator 2 and guided to the condensing optical system 3 via a transmission fiber 8 having a diameter of 6 mm. A laser 9 imaged into a beam having a diameter of 0.3 mm using a collimating lens and a condensing lens having a focal length of 100 mm is fixed on the processing table 4 and irradiates the workpiece W.

The image processing device 6 processes the image as shown in FIG. 1B, for example, obtained by the CCD camera 5 to obtain a length parallel to the welding progress direction D of the molten pool P of the workpiece W. The measurement data is output to the control device 7.

The control unit 7 calculates the ratio L / t of the two from the molten pool length L input from the image processing unit 6 and the thickness t of the workpiece W input in advance. In order to increase the laser output to the laser oscillator 2 or the processing table 4 when L / t falls below a first threshold value (for example, 1.7) so that the value of L / t does not become smaller than 1. A control to output a command signal or a command signal for reducing the welding speed (there may be a case where both command signals are sent) to increase the ratio L / t of the length L of the molten pool to the thickness t of the plate. Is done automatically. When L / t exceeds a second threshold value (for example, 2.3) so that the value of this ratio does not exceed 3, a command signal for reducing the laser output or a welding speed is reduced. A command signal for speeding up is output (there may be a case where both command signals are sent), and control is performed such that the ratio L / t of the molten pool length L to the plate thickness t is reduced. Has become.

That is, according to the laser welding apparatus 1 having such a structure, the molten pool length L and the sheet thickness t can be determined by simply inputting the sheet thickness t of the workpiece W before welding. Since the ratio L / t is automatically controlled so as to always be in the range of 1 to 3 and is maintained at the size of the molten pool corresponding to the plate thickness t, stable welding without spatter and burn-through can be performed. A sound weld having an excellent appearance can be obtained.

Next, using such a welding apparatus 1, an aluminum alloy plate (JI
(SA5182) was subjected to butt welding under various welding conditions, and the relationship between the weld pool length L and the plate thickness t and the welding results was compared. In this case, the automatic control function of the laser welding apparatus 1 is released, and a constant laser output and
Welding was performed under a constant welding speed.

Table 1 shows the results.

[0028]

[Table 1]

As shown in Table 1, using the aluminum alloy plate having a plate thickness t = 2.0 mm, the welding speed V
= 3.0, 2.0, 4.0 (m / min), laser output per unit area P = 35, 30, 45 (kW / mm)
Examples 1 to 3 in which butt welding was performed under the welding conditions ² )
In the case of, the molten pool length L is 4.5 mm each.
(L / t = 2.25), 6. Omm (L / t = 3),
2.0 mm (L / t = 1), and a good weld without spatter or burn-through in any case could be obtained.

On the other hand, an aluminum alloy plate having a thickness of t = 2.0 mm was converted to V = 0.5 m / min (V / t = 0.2
In the case of Comparative Example 1 in which welding was performed at a welding speed of 5) and a laser output of P = 35 kW / mm ² , the length of the molten pool was L = 0.8 mm (L / t = 4), and the burnout was intermittent. Occurred, and sound welding was not possible.

In addition, the same aluminum alloy plate was subjected to the same laser output P and V = 9.0 m / min (V / t
= 4.5), and in the case of Comparative Example 2 where welding was performed at a high speed (P = 10V-55), and V = 3.0 m / min (V / t =
In the case of Comparative Example 3 in which welding was performed at a welding speed of 1.5) and a laser output (P = 10V-15) of P = 15 kW / mm ² , the length L of the molten pool was 1 mm or less (L).
/T≦0.5), and it was confirmed that spatter was generated and sound welding could not be performed.

Further, at a welding speed of V = 3.0 m / min and a laser output of P = 30 kW / mm ² , an aluminum alloy plate of t = 0.5 mm (V / t =
In the case of Comparative Example 4 where 6) was welded, burn-through occurred, and under the same welding conditions, the aluminum alloy plate of t = 10 mm (V / t = 0.3) was welded. In such a case, spatter was generated, and in all cases, sound welding was not possible.

[Brief description of the drawings]

FIG. 1A is a block diagram showing a structure of a laser welding apparatus according to an embodiment of the present invention. (B) It is a schematic diagram of the image | video by the imaging | photography means of the laser welding apparatus shown to Fig.1 (a).

FIG. 2 is a graph showing the effect of plate thickness and molten pool length on welding quality in butt laser welding of aluminum alloy plates.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser welding apparatus 2 Laser oscillator 3 Condensing optical system (condensing means) 4 Processing table (moving means) 5 CCD camera (photographing means) 6 Image processing apparatus (image processing means) 7 Control apparatus (control means) W Weldable Object L Length of molten pool t Thickness of workpiece

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) // B23K 103: 10 (72) Inventor Minoru Kasukawa 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd. F term (reference) 4E068 BA01 BE00 CA01 CA02 CA13 CB01 CC02 DA14 DB04

Claims (10)

[Claims] 1. A laser welding method comprising controlling a laser output and / or a welding speed such that a length of a molten pool in a welding traveling direction is in a range of 1 to 3 times a plate thickness of an object to be welded. 2. A welding speed value expressed in a unit of meter / minute is in a range of 0.5 times to 3.0 times a value of a plate thickness of a workpiece in a unit of millimeter. The laser welding method according to claim 1, wherein 3. The laser output value per unit area in units of kilowatts / square millimeter is increased from 10 times the welding speed value in units of meters / minute to 10 times the welding speed value by adding 40. The laser welding method according to claim 1, wherein the value is within a range of the calculated values. 4. The laser welding method according to claim 1, wherein the welding is a butt welding. 5. The laser welding method according to claim 1, wherein the workpiece is an aluminum alloy. 6. The laser welding method according to claim 5, wherein the additional element contained in the aluminum alloy is an element having a lower boiling point than aluminum. 7. The laser welding method according to claim 5, wherein the aluminum alloy is an A5000 or A7000 alloy according to JIS. 8. The thickness of the workpiece is 0.8 mm to 5.0 m.
The laser welding method according to any one of claims 1 to 7, wherein the range is m. 9. The laser welding method according to claim 1, wherein the laser is a continuous wave Nd: YAG laser. 10. A laser oscillator for generating a laser, a condensing means for converging a laser from the laser oscillator and irradiating the object to be welded, and a laser beam for converging the object to be welded with respect to the condensing means for irradiating the laser. Moving means for moving the molten pool at the welding point, a photographing means for photographing the molten pool at the welding point, an image processing means for measuring the size of the molten pool from an image obtained by the photographing means, and a molten pool obtained by the image processing means. A laser welding apparatus comprising control means for sending a command to increase or decrease a laser output and / or a welding speed based on a measurement result to a laser oscillator or a moving means, respectively.