JPH06210472A - Pulse laser welding method for aluminum alloy - Google Patents

Abstract

PURPOSE:To join an aluminum alloy without a weld defect such as a weld crack, etc., by irradiating with a pulse laser beam. CONSTITUTION:Four pulses LB (1) to LB (4) are repeated with an intermittent time (for instance, lmsec) in a laser output waveform per one time or one cycle. The peak values of these pulses LB (1) to LB (4) go down successively, that is, in order of LB (1), LB (2), LB (3), and LB (4). When the weld zone of a material to be welded, being made of an aluminum alloy, is irradiated with such a pulse laser beam LB, a crack does not occur except for only on the surface part of a molten metal part in a weld zone. The crack occurred on this surface part does not cross the joint surface of the material to be welded, and it is not a weld defect.

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 method for welding an aluminum alloy using pulse laser light.

[0002]

2. Description of the Related Art Aluminum alloys are lightweight, corrosion resistant,
It is widely used in aircraft, automobiles, ships, high-speed vehicles, vacuum devices, electric / electronic equipment products, etc. because of its excellent workability, high specific strength, and low temperature characteristics. Recently, a pulse laser welding method has been attracting attention as a welding method for joining aluminum alloys used for such structures, devices, products, etc. with high accuracy, high quality and high speed. The pulse laser welding method is a welding method in which a laser beam having a pulsed output waveform is applied to a welded portion of a material to be welded, the welded portion is melted with laser energy and metallurgically joined, and generally YAG. A laser is used. Conventionally, as shown in FIG. 9, welding was performed by irradiating a welded portion of an aluminum alloy with a pulsed laser beam having a standard rectangular output waveform.

[0003]

However, when spot welding is performed by the conventional pulse laser welding method as described above,
In the welded portion, as shown in FIG. 10, a crack C extending inside the molten metal portion MG starting from the molten boundary surface MB in the backside (lower side) workpiece W2 and traversing the joint surface BS.
R tends to occur. Such cracks CR are welding defects that significantly weaken the joint strength of the welded portion and impair the welding quality. When seam welding is performed by the above-mentioned conventional pulse laser welding method, as shown in FIG. 11, cracks CR1 and CR2 similar to those in the case of spot welding are formed inside the molten metal portions MG1, MG2, ... Corresponding to each pulse. Not only is it easy to get ...
These cracks CR1, CR2, ... are connected in the seam welding direction, and there is a problem that large cracks or cracks easily develop.

As described above, in pulse laser welding of an aluminum alloy, cracks are likely to occur in the welded portion because a small amount of a liquid film forming a eutectic having a low melting point is generated and tensile strain is rapidly added thereto. It is possible, but the details have not been clarified yet. In any case, if a crack that crosses the joint surface of the material to be welded or is connected to the seam welding direction occurs as described above, the significance of using the pulse laser welding method for joining the aluminum alloy is diminished.
Therefore, it is required to establish optimum irradiation conditions of pulsed laser light for welding aluminum alloys.

The present invention has been made in view of the above problems, and an object thereof is to provide a pulse laser welding method for joining aluminum alloys without causing welding defects such as welding cracks.

[0006]

In order to achieve the above-mentioned object, the pulse laser welding method for aluminum alloy according to the present invention has a plurality of pulses intermittently in a laser output waveform per one cycle or one cycle. A method of irradiating the welded portion of the aluminum alloy with pulsed laser light that is repeated and has a relationship in which the peak values of all or part of the plurality of pulses are gradually lowered.

In the present invention, the pulse width of each of the plurality of pulses, the pulse waveform, the length of the interruption time between the pulses, and the output during the interruption time are selected or controlled to any values according to welding conditions. It is possible to

[0008]

When a plurality of pulses are repeated intermittently within the laser output waveform once or per one cycle, in the welded portion of the workpiece to be irradiated with the pulsed laser light, the melted portion due to the preceding pulse is generated. Irradiation with the next pulse while maintaining the keyhole results in the molten metal portion of the weld being convoluted and solidified, resulting in prevention or minimization of cracking.

[0009]

Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 shows a structure of a YAG laser for carrying out a pulse laser welding method according to an embodiment of the present invention. In the laser oscillation section of this YAG laser, a YAG rod 12 is provided in parallel with the excitation lamp 10, and the lamp 10
Is pulse-lit, the YAG rod 12 oscillates with the light energy, and the pulsed laser light LB emitted from both end faces of the YAG rod 12 is paired with the resonant mirror 1.
The reflection is repeated between 4 and 16 and is amplified and then output to the outside.

This YAG laser power supply device is provided with two laser power supply circuits 20 and 50 having different current control methods as a circuit for supplying a lamp current for pulse-lighting the excitation lamp 10 of the laser oscillator. The first laser power supply circuit 20 generates a lamp current I1 controlled to a desired waveform by the switching operation of the switching element, and the second laser power supply circuit 50 has an independent peak value by a capacitor bank. A lamp current I2 consisting of a series of pulse currents is generated.

The first laser power supply circuit 20 is constructed as follows. The input terminals of the three-phase full-wave rectifier circuit 22 are connected to the three-phase AC input terminals (U, V, W). The output terminal of the three-phase full-wave rectifier circuit 22 is the smoothing capacitor 2
4, the switching transistor 26 for waveform control, the coil 28 for smoothing, the capacitor 30, and the diode 32 are connected to the electrode terminal of the excitation lamp 10. The diode 34, which is connected in parallel with the capacitor 30 with the coil 28 interposed therebetween, constitutes a return circuit for returning the electromagnetic energy accumulated in the coil 28.

At the base of the switching transistor 26, the PWM control signal SA is supplied from the switching control unit 36.
Is provided as a switching control signal via the drive circuit 38. The PWM control signal SA turns on / off the switching transistor 26 at a high frequency, so that a pulse-width-modulated DC current having a chopper waveform is obtained at its collector terminal. The DC current of the chopper waveform is changed to the DC current of the envelope waveform corresponding to the pulse width by passing through the smoothing coil 28 and the capacitor 30, and this DC current is excited via the diode 32 as the first lamp current I1. It is supplied to the lamp 10.

In the switching control section 36 for performing the PWM control as described above, the main control section receives the starting signal ED for instructing the start and end of the first lamp current I1 and the current waveform reference signal Fi representing the desired current waveform. Given from 80. In addition, a current sensor 40 including, for example, a toroidal coil is provided in the current path of the first laser power supply circuit 20, and the current value measuring circuit 42 determines the current of the first lamp current I1 based on the output signal of the current sensor 40. Measured values are required. The switching control unit 36 includes a current value measuring circuit 42.
From the current measurement value MI1 from this current measurement value M
PWM control is performed by a feedback method so that I1 follows the current waveform reference signal Fi from the main controller 80.

As described above, in the first laser power supply circuit 20, the switching transistor 26 provided between the rectifier circuit 22 and the excitation lamp 10 is PWM-controlled to perform a switching operation so that a desired waveform is controlled. The obtained first lamp current I1 is obtained. However, the first laser power supply circuit 20 generates a desired current waveform by chopping the direct current at a substantially constant level from the rectification circuit 22 with the switching transistor 26 in small steps, so that the magnitude of the current value is large. Has a limit,
A pulse with a relatively large current peak value is not obtained. However, regarding this point, the second
Since the laser power supply circuit 50 of FIG. 2 supplements (carries), the laser power supply device as a whole is capable of obtaining a pulsed lamp current having an arbitrary current waveform and peak value in practical use. Note that the first laser power supply circuit 20 can also be configured with an inverter power supply circuit.

The second laser power supply circuit 50 is a capacitor type power supply circuit having two capacitor banks.
Three-phase full-wave rectifier circuit 5 for three-phase AC input terminals (U, V, W)
The two input terminals are connected, and the output terminal of the three-phase full-wave rectifier circuit 52 is connected via charging first and second switching transistors 54A and 54B and first and second charging coils 56A and 56B. Connected to the first and second capacitors 58A and 58B for charging and discharging, and the terminals of these capacitors 58A and 58B are connected via the first and second switching transistors 60A and 60B and the diodes 62A and 62B for discharging. Are commonly connected to the electrode terminals of the excitation lamp 10. Each capacitor 58A,
58B is, for example, 10,000 to 200 so that it can store a large amount of electric energy that can be used for laser processing.
It has a capacitance of 00 μF.

The voltage between the terminals of the capacitors 58A and 58B, that is, the charging voltages VC1 and VC2 are detected by the charging voltage detection circuit 64, and the respective charging voltage detection values MVC1 and MV are detected.
C2 is given to the charge control unit 66. The charge control unit 66
The charging voltage set values FV1 and FV2 are received from the main control unit 80, and the charging voltage detection values MVC1 and MVC2 are set to the set values FV1 and FV1, respectively.
The control signals CS1 and CS2 control ON / OFF of the charging switching transistors 54A and 54B through the drive circuits 68A and 68B so that the charging of the capacitors 58A and 58B is stopped when the voltage reaches FV2. The discharge control unit 70 receives the timing signal TM1, from the main control unit 80.
Each capacitor 58 at a predetermined timing according to TM2
Control signals CD1 and C to start the discharge of A and 58B
D2 controls on / off of the discharge switching transistors 60A and 60B via the drive circuits 72A and 72B.

As described above, in the second laser power supply circuit 50, the first and second charging transistors 54 are provided.
The first and second capacitors 58A and 58B are respectively charged by the A and 54B and the charge control unit 66 to arbitrary preset charging voltages, and the first and second discharge transistors 60A and 60B and the discharge control unit 70 are charged. The capacitors 58A and 58B can be instantly discharged at preset arbitrary timings.
Therefore, by repeatedly charging and discharging both capacitors 58A and 58B alternately at short time intervals, a plurality of (series) pulses each controlled to a desired peak value once or within the lamp current duration per one cycle. The current can be generated as a second lamp current I2. The number of capacitors may be three or more.

The main controller 80 controls or supervises the operations of the first and second laser power supply circuits 20 and 50 as described above, and the current of the first lamp current I1 from the set value input unit 82. The peak value of each pulse in the waveform setting value and the second lamp current I2 and their lamp current I
Various setting values such as a combination pattern setting value of 1 and I2 are taken in, and the trigger circuit 84 for applying the trigger TR to the lamp 10 is controlled. The laser power supply device is also provided with a simmer circuit (not shown) for stabilizing the discharge path in the excitation lamp 10.

Next, the operation of the YAG laser in this embodiment will be described. When spot welding is performed on a material to be welded made of an aluminum alloy, in the above-described laser power supply device, the set value input unit 82 outputs pulsed laser light defined by time-output characteristics as shown in FIG. 3, for example. Output waveform is set and input. This output waveform is 3.4KW
On the constant output waveform (first output waveform) of, each pulse width is 4 msec, and each peak value is 1.5
Four pulse output waveforms LB (1) to LB (4) (second output waveform) of KW, 1.2KW, 1.0KW, and 0.6KW overlapped with an interval (interruption time) of 1msec. Can be seen. When the main control unit 80 takes in such an output waveform set value from the set value input unit 82, during spot welding, as described below, the first laser power supply circuit 20 receives the first output waveform corresponding to the first output waveform. 1 lamp current I
1 is generated and the second laser power supply circuit 50 is controlled to generate the second lamp current I2 corresponding to the second output waveform.

In the first laser power supply circuit 20, time t0
At this time, the switching control unit 36 starts the operation, and the switching transistor 26 performs the switching operation by the PWM control, so that the current according to the current waveform reference signal Fi corresponding to the first output waveform, that is, (B) in FIG. A first lamp current I1 as shown in
1 is supplied to the excitation lamp 10 without interruption during the lamp current duration (20 msec) from time t0 to time t20.

In the second laser power supply circuit 50, time t0
The charging control unit 66 previously operated to turn on the charging transistors 54A and 54B, and the capacitors 58A and 58B.
Are the first and second pulse output waveforms LB (1), L
Charge in advance to the set voltage corresponding to the peak value of B (2). Then, at time t0, the discharge control unit 70 turns on the first discharge transistor 60A to discharge the first capacitor 58A. This discharge of the capacitor 58A causes the first pulse output waveform L to be changed as shown in FIG.
A first pulse current I2 (1) having a peak value PI1.5 corresponding to the set peak value (1.5 KW) of B (1) is generated. Then, at time t4 4 msec after time t0
Then, the discharge control unit 70 turns off the transistor 60A to stop the discharge of the first capacitor 58A and terminates the first pulse current I2 (1). Next, from time t4, 1 mse
At time t5 after c has elapsed, the discharge control unit 70 turns on the second discharging transistor 60B to turn on the second capacitor 5B.
Discharge 8B. This discharge of the capacitor 58B causes the second pulse output waveform LB as shown in FIG.
A second pulse current I2 (2) having a peak value PI1.2 corresponding to the set peak value (1.2 KW) of (2) is generated. Then, at time t9, which is 4 msec after time t5.
Then, the discharge control unit 70 turns off the transistor 72A to stop the discharge of the first capacitor 58B and terminates the second pulse current I2 (2). On the other hand, the second capacitor 58
During the discharge of B, the charging control unit 66 controls the first capacitor 58
Charge A to the set voltage. As a result, time t9
At time t10 after 1 msec has elapsed, the discharge control unit 70 turns on the first discharge transistor 72A.
The capacitor 58A of is discharged, and the third pulse output waveform L
A third pulse current I2 (3) having a peak value PI1.0 corresponding to the set peak value (1.0 KW) of B (3) is generated. Similarly, during the period from time 15 to t19, the second capacitor 58B is discharged and the fourth pulse output waveform LB
A fourth pulse current I2 (4) having a peak value PI0.6 corresponding to the set peak value (0.6KW) of (4) is generated.

As described above, in the second laser power supply circuit 50, the four pulse output waveforms (set values) LB (1) to LB (4) forming the second output waveform during the lamp current duration.
Corresponding to 4 pulse currents I2 (1), I2 (2), I2 (3),
I2 (4) is generated intermittently with a constant interruption time (1 msec), and these pulse currents I2 (1) to I2 (4) collectively constitute the second lamp current I2, and the excitation lamp 10 Are sequentially supplied.

Therefore, the excitation lamp 10 is shown in FIG.
As shown in (C), the first lamp current I1 from the first laser power supply circuit 20 ((B) in FIG. 2) and the second lamp current I2 from the second laser power supply circuit 50 (see FIG. 2). (A)) overlaps with the lamp current, and the YAG rod 12 outputs a pulsed laser beam LB having a laser output waveform corresponding to the combined ramp current (I1 + I2).

FIG. 4 shows an example of the measured values of the output waveform of the pulsed laser beam LB obtained as described above. In FIG. 4, the peak values of the pulses LB (1) to LB (4) are
That is, not only LB (1), LB (2), LB (3), and LB (4) decrease in this order, but also the peak value of each pulse LB (i) itself decreases with the passage of time. This latter decrease (the decrease in the peak value itself of each pulse LB (i)) is caused by the peak value of each pulse current I2 (1) to I2 (4) in the second lamp current I2, that is, the second laser power supply circuit. This is because the peak value of the discharge current of the capacitors 58A and 58B at 50 actually decreases with the passage of time.

In spot welding, when such a pulsed laser beam LB is applied to the welds of the materials W1 and W2 to be welded made of an aluminum alloy, the welded metal is melted at the welds as shown in FIG. Small cracks cr occur on the surface of the MG. Such surface cracks cr are on the front side (upper side).
It does not cause welding defects because it stops inside the welded material W1 and does not cross the joint surface BS. in this way,
According to the pulse laser welding method of this embodiment, four pulses LB (1) to LB (4) are included in the laser output waveform per one time.
Are repeated intermittently, and these four pulses LB
By irradiating the welded portion of the aluminum alloy with the pulsed laser light LB in which the peak values of (1) to LB (4) are gradually lowered, a high quality welded joint having substantially no weld cracks can be obtained.

The reason why the cracking of the weld is prevented or minimized by the method of this embodiment has not yet been clarified, but it is considered as follows. That is, when a plurality of pulses LB (1) to LB (4) are intermittently repeated in the laser output waveform once or in one cycle, the workpieces W1 and W2 to be irradiated with the pulsed laser beam LB are welded. In the welded part, the next pulse LB while the melted part by the previous pulse LB (i) maintains the keyhole.
By irradiating (i + 1), the molten metal part M of the welded part
Solidify as G is folded. As a result, only small cracks cr that stop in the welded material W1 on the front side are generated, and large cracks (C
It is considered that R) does not occur.

6 to 8 show the operation when the pulse laser welding method of this embodiment is applied to seam welding of aluminum alloy. In seam welding, as shown in Fig. 6, the combined lamp current (I1 + I2) is the same as in spot welding.
Is supplied to the excitation lamp 10, and the welded material and the laser beam spot are moved relative to each other in the seam welding direction each time the pulsed laser light LB is irradiated to gradually move the welded portion. Then, as shown in FIG. 7, the crack cri generated on the surface portion of each molten metal portion MGi by the irradiation of each pulse laser beam LBi is removed by the molten metal portion MGi by the irradiation of the next pulse laser light LBi + 1, As a result, the molten metal part MG by the irradiation of the last pulsed laser beam LBN
A small crack crN remains only on the surface of N. FIG. 8 is a schematic plan view showing this state. In order to prevent the crack crN in the final molten metal portion MGN, a method of adjusting the alloy composition so that the eutectic component has a high melting point may be considered.

As described above, in seam welding by the pulse laser welding method of this embodiment, four pulses LB (1) to LB (4) are intermittently repeated in the laser output waveform per cycle, And those four pulses LB (1) to L
By irradiating the welded portion of the aluminum alloy with the pulsed laser light LB in which the peak value of B (4) is gradually lowered, a high quality welded joint having substantially no weld cracks can be obtained.

In the above-described embodiment, the number of pulses included in the laser output waveform per one cycle or one cycle is four, but this is merely an example, and an arbitrary number of pulses is selected. It is possible. Further, in the present invention, it is a basic requirement that the peak values of the plurality of pulses be sequentially reduced, but the condition does not necessarily have to be satisfied among all the pulses, and during the majority of the pulses. It is sufficient that the condition is satisfied at or between some pulses. It is also possible to set the pulse width of each pulse to an individual value instead of a uniform value,
For example, the pulse width may be sequentially reduced or sequentially increased. Further, it is possible to select an arbitrary value for the value of the output at the interruption time between the pulses or the length of the interruption time as a whole or individually.
Also, various waveforms can be selected for the peak level of each pulse.

[0030]

As described above, according to the pulse laser welding method of the present invention, a plurality of pulses are intermittently repeated in the laser output waveform once or in one cycle,
And since it was arranged to irradiate the welded portion of the aluminum alloy with pulsed laser light in which the respective peak values of all or part of the plurality of pulses are gradually lowered,
It is possible to obtain a high quality welded joint without welding defects such as weld cracks.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a main part of a YAG laser for carrying out a pulse laser welding method according to an embodiment of the present invention.

FIG. 2 is a waveform diagram of a current of each part in the laser power supply device according to the embodiment.

FIG. 3 is a diagram showing an example of an output waveform of pulsed laser light that is set and input in the laser power supply device according to the embodiment.

FIG. 4 is a measurement waveform diagram showing an example of an output waveform of pulsed laser light obtained by the YAG laser in the example.

FIG. 5 is a sectional view showing a sectional structure of a welded portion obtained by spot welding by a pulse laser welding method according to an embodiment.

FIG. 6 is a diagram showing a waveform of a lamp current supplied from the laser power supply device of the embodiment to the excitation lamp when seam welding is performed.

FIG. 7 is a cross-sectional view showing a cross-sectional structure of a welded portion obtained by seam welding by a pulse laser welding method according to an embodiment.

FIG. 8 is a schematic plan view showing a surface state of a welded portion obtained by seam welding by a pulse laser welding method according to an embodiment.

FIG. 9 is a diagram showing an output waveform of pulse laser light by a conventional typical pulse laser welding method.

FIG. 10 is a sectional view showing a sectional structure of a welded portion obtained by spot welding by a conventional pulse laser welding method.

FIG. 11 is a schematic plan view showing a surface state of a welded portion obtained by seam welding by a conventional pulse laser welding method.

[Explanation of symbols]

 10 Excitation Lamp 12 YAG Rod 20 First Laser Power Supply Circuit 26 Switching Transistor 36 Switching Control Section 50 Second Laser Power Supply Circuit 54A, 54B Charging Transistor 58A, 58B Capacitor 60A, 60B Discharging Transistor 66 Charging Control Section 70 Discharging Control unit 80 Main control unit 82 Set value input unit

Claims (5)

[Claims] 1. A plurality of pulses are intermittently repeated in a laser output waveform per one cycle or one cycle, and peak values of all or a part of the plurality of pulses are sequentially lowered. A pulse laser welding method for an aluminum alloy, which comprises irradiating a weld portion of the aluminum alloy with a pulsed laser beam. 2. The pulse laser welding method according to claim 1, wherein the pulse width of each of the plurality of pulses is selected to an arbitrary value. 3. The pulse laser welding method according to claim 1, wherein each pulse waveform of the plurality of pulses is selected as an arbitrary waveform. 4. The pulse laser welding method according to claim 1, wherein the length of each interruption time between the plurality of pulses is selected to an arbitrary value. 5. The pulse laser welding method according to claim 1, wherein the output during each interruption time between the plurality of pulses is selected to an arbitrary value.