JP2984962B2 - Pulse laser welding method and laser device for aluminum alloy - 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 method for welding an aluminum alloy using a pulse laser beam.

[0002]

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

[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 from the molten boundary surface MB in the material to be welded W2 on the back side (lower side) to the inside of the molten metal portion MG and crossing the joining surface BS.
R tends to occur. Such a crack CR is a welding defect that significantly reduces the joining strength of the welded portion and impairs the welding quality. Further, when seam welding is performed by the above-mentioned conventional pulse laser welding method, as shown in FIG. 11, cracks CR1, CR2 similar to those in the case of spot welding inside molten metal portions MG1, MG2,. ,…
There is a problem that the cracks CR1, CR2,... Are connected in the seam welding direction and easily develop into large cracks or cracks.

[0004] As described above, the reason that cracks tend to occur in the welded portion in pulsed laser welding of aluminum alloys is that a small amount of a liquid film forming a low melting point eutectic is formed, and tensile strain is rapidly added thereto. Probably, but the details have not been elucidated yet. In any case, as described above, the occurrence of cracks that traverse the joint surface of the material to be welded or are connected in the seam welding direction makes the significance of using the pulse laser welding method to join the aluminum alloy diminished.
Therefore, it is required to establish the optimum pulse laser beam irradiation conditions for welding aluminum alloys.

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

[0006]

In order to achieve the above-mentioned object, a method according to the present invention comprises the steps of:
Laser welding method for welding aluminum alloys
And in the laser output waveform per time or per cycle
The relationship where all or some of the peak values are gradually lower
A plurality of pulsed laser beams
The next pal while the melt by the keyhole maintains the keyhole
Laser output and time for laser beam irradiation
Irradiate the aluminum alloy weld at a distance
With the laser energy of the plurality of pulsed laser beams.
It was a method of joining gold.

[0007] Further , the apparatus of the present invention includes the above-described pallet of the present invention.
Laser equipment for implementing laser welding method
A laser medium, an excitation light source, and an optical resonator.
Turn on the light source and use the laser based on the light energy.
Laser that oscillates and outputs laser light from medium and optical resonator
An oscillating unit and a plurality of capacitors connected in parallel to the pump light source.
A laser bank, and the plurality of
The plurality of capacitors to oscillate and output the pulsed laser light.
Discharge the banks sequentially or alternately at the time intervals
And a laser power supply section for performing the operation.

[0008]

According to the present invention, all of the laser output waveforms
Relationship where the peak value of each part or part is gradually reduced
Multiple pulsed laser beams in the
It is applied to the contact. Here, these pulse trains
All of the light contributes to the welding and is
The next pulsed laser while the fusion zone holds the keyhole
Light is irradiated. As a result, the molten metal portion of the weld is
As a result of the solidification,
Minimized.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a configuration of a YAG laser for performing a pulse laser welding method according to an embodiment of the present invention. In the laser oscillation section of the YAG laser, a YAG rod 12 is provided in parallel with the excitation lamp
Is pulse-lit, the light energy causes the YAG rod 12 to oscillate laser, and the pulsed laser light LB emitted from both end faces of the YAG rod 12 is turned into a pair of resonance mirrors 1.
The reflection is repeated between 4 and 16, and after amplification, it is output to the outside.

The power supply device for the YAG laser includes two laser power supply circuits 20 and 50 having different current control methods as a circuit for supplying a lamp current for pulsatingly driving the excitation lamp 10 of the laser oscillation section. A lamp current I1 controlled to a desired waveform is generated from the first laser power supply circuit 20 by the switching operation of the switching element, and each has an independent peak value from the second laser power supply circuit 50 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 configured as follows. The input terminal of the three-phase full-wave rectifier circuit 22 is connected to the three-phase AC input terminals (U, V, W). The output terminal of the three-phase full-wave rectifier circuit 22 is a smoothing capacitor 2
4. It is connected to the electrode terminal of the excitation lamp 10 via a switching transistor 26 for waveform control, a coil 28 for smoothing, a capacitor 30, and a diode 32. The diode 34 connected in parallel with the capacitor 30 with the coil 28 interposed therebetween constitutes a return circuit for returning the electromagnetic energy stored in the coil 28.

The PWM control signal SA from the switching controller 36 is provided at the base of the switching transistor 26.
Is provided via the drive circuit 38 as a switching control signal. The switching transistor 26 is turned on / off at a high frequency by the PWM control signal SA, so that a pulse width modulated chopper waveform DC current is obtained at its collector terminal. The DC current having the chopper waveform is converted into an envelope waveform DC current 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.

The switching control unit 36 for performing the PWM control as described above receives a start signal ED for instructing start / end of the first lamp current I1 and a current waveform reference signal Fi representing a desired current waveform. 80. A current path of the first laser power supply circuit 20 is provided with a current sensor 40 composed of, for example, a toroidal coil. Based on an output signal of the current sensor 40, a current value measuring circuit 42 detects the current of the first lamp current I1. The measured value is determined. The switching control unit 36 includes a current value measurement circuit 42
From the current measurement MI 1
PWM control is performed in a feedback manner 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 operation of the switching transistor 26 provided between the rectifier circuit 22 and the excitation lamp 10 is performed by PWM control, so that a desired waveform is controlled. The obtained first lamp current I1 is obtained. However, in the first laser power supply circuit 20, a desired current waveform is generated in such a manner that the DC of the substantially constant level from the rectifier circuit 22 is chopped by the switching transistor 26 in small steps. Has a limit,
Pulses with relatively large current peak values are not obtained. However, regarding this point, the second
Of the laser power supply circuit 50, the laser power supply device as a whole can obtain a pulse-shaped lamp current having a practically arbitrary current waveform and a peak value. In addition, the first laser power supply circuit 20 can be configured by an inverter type power supply circuit.

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

The voltages 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 charging control unit 66 includes:
The charge voltage setting values FV1 and FV2 are received from the main control unit 80, and the charge voltage detection values MVC1 and MVC2 are changed to the respective set values FV1 and FVC1.
Control signals CS1 and CS2 control ON / OFF of the switching transistors 54A and 54B for charging via the driving 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 signals TM1 and TM1 from the main control unit 80.
Each capacitor 58 at a predetermined timing according to TM2.
Control signals CD1, C1 so as to start the discharge of A, 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
A, 54B and the charge control unit 66 charge the first and second capacitors 58A, 58B to predetermined preset charging voltages, respectively, and the first and second discharge transistors 60A, 60B and the discharge control unit 70 Accordingly, the capacitors 58A and 58B can be discharged instantaneously at any timing set in advance.
Therefore, by repeatedly charging and discharging the capacitors 58A and 58B alternately at short time intervals, a plurality (series) of pulses each controlled to a desired peak value once or within the lamp current duration per cycle. A current can be generated as the second lamp current I2. The number of capacitors can be three or more.

The main control unit 80 controls and supervises the operations of the first and second laser power supply circuits 20 and 50 as described above, and also outputs the first lamp current I1 from the set value input unit 82. The peak value of each pulse in the waveform set value and the second lamp current I2 and their lamp current I2
Various settings such as a combination pattern set value of 1, I2 and the like are taken in, and a trigger circuit 84 for applying a 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. In the case where spot welding is performed on a material to be welded made of an aluminum alloy, in the above-described laser power supply device, for example, a pulse laser beam defined by time-output characteristics as shown in FIG. The output waveform is set and input. This output waveform is 3.4 kW
, Each pulse width is 4 msec, and each peak value is 1.5
Four pulse output waveforms LB (1) to LB (4) of kW , 1.2 kW , 1.0 kW , and 0.6 kW (second output waveform) are separated by an interval of 1 msec (intermittent time). It can be seen as overlapping. When the main control unit 80 captures such an output waveform set value from the set value input unit 82, at the time of spot welding, the first laser power supply circuit 20 outputs a first output waveform corresponding to the first output waveform as described below. The second laser power supply circuit 50 generates the second lamp current
Is controlled so as to generate the second lamp current 12 corresponding to the output waveform of FIG.

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

In the second laser power supply circuit 50, at time t0
Previously, the charging control section 66 was operated to turn on the charging transistors 54A and 54B, and the capacitors 58A and 58B
To the first and second pulse output waveforms LB (1),
The battery is charged in advance to a set voltage corresponding to the peak value of LB (2). Then, at time t0, the discharge control unit 70
Is turned on, and the first capacitor 58A is discharged. Due to the discharge of the capacitor 58A, as shown in FIG. 2A, the first pulse output waveform LB (1) has a first peak value PI1.5 corresponding to the set peak value (1.5 kW ). Pulse current I2
(1) is generated. Then, 4 msec from time t0
At time t4 after the lapse of time, the discharge control unit 70 turns off the transistor 60A to stop discharging the first capacitor 58A, and ends the first pulse current I2 (1). next,
At time t5 after a lapse of 1 msec from time t4, the discharge control unit 70 turns on the second discharging transistor 60B and discharges the second capacitor 58B. Due to the discharge of the capacitor 58B, the set peak value (1 .1) of the second pulse output waveform LB (2) as shown in FIG.
A second pulse current I2 (2) having a peak value PI1.2 corresponding to 2 kW ) is generated. Then, at time t5
At time t9 after a lapse of 4 msec from discharge control unit 70
Turns off the transistor 72A, stops discharging the first capacitor 58B, and ends the second pulse current I2 (2). On the other hand, during the discharging of the second capacitor 58B,
The charge controller 66 charges the first capacitor 58A to a set voltage. As a result, 1 msec from time t9
At time t10 after the lapse of time, when the discharge control unit 70 turns on the first discharging transistor 72A, the first capacitor 58A is discharged, and the set peak value (1. 0 kW ) corresponding to the peak value PI1.
A third pulse current I2 (3) having zero is generated.
Similarly, during the period from time 15 to time 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 (0.6 kW ) 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) constituting the second output waveform during the lamp current duration.
Pulse currents I2 (1), I2 (2), I2 (3),
I2 (4) is generated intermittently with a fixed intermittent 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 supplied sequentially.

Therefore, the excitation lamp 10 has the structure shown in FIG.
As shown in FIG. 2C, the first lamp current I1 (FIG. 2B) from the first laser power supply circuit 20 is replaced with the second lamp current I2 from the second laser power supply circuit 50 (FIG. 2B). (A)) flows, and the YAG rod 12 outputs a pulse 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 pulse laser beam LB obtained as described above. In FIG. 4, the peak values of the pulses LB (1) to LB (4) are sequentially
That is, not only does the peak value of LB (1), LB (2), LB (3), and LB (4) drop, but also the peak value itself of each pulse LB (i) decreases with time. This latter decrease (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 due to the fact that the peak value of the discharge current of the capacitors 58A and 58B at 50 actually decreases with time.

In the spot welding, when such a pulse laser beam LB is applied to the welded portions of the workpieces W1 and W2 made of an aluminum alloy, as shown in FIG. Small cracks cr occur on the surface of the MG. The cracks cr on the surface portion are on the front side (upper side).
In the material to be welded W1 and does not cross the joint surface BS, so that it does not cause welding defects. in this way,
According to the pulse laser welding method of the present embodiment, four pulses LB (1) to LB (4) in one laser output waveform.
Are intermittently repeated and the four pulses LB
By irradiating a pulsed laser beam LB having a relationship that the peak values of (1) to LB (4) become gradually lower to the welded portion of the aluminum alloy, a high quality welded joint substantially free of weld cracks can be obtained.

The reason why cracking of the weld is prevented or minimized by the method of this embodiment has not been elucidated yet, but 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 per cycle, the workpieces W1, W2 to be irradiated with the pulse laser beam LB are irradiated. In the welded portion of the above, the next pulse LB (i) is maintained while the fused portion by the previous pulse LB (i) maintains the keyhole.
(i + 1), the molten metal M
It solidifies so that G is folded. As a result, only a small crack cr which stops in the workpiece W1 on the front side is generated, and a large crack (C
R) is considered not to occur.

FIGS. 6 to 8 show the operation when the pulse laser welding method of this embodiment is applied to seam welding of an aluminum alloy. In seam welding, as shown in FIG. 6, the same combined lamp current (I1 + I2) as in spot welding is used.
May be supplied to the excitation lamp 10 and the welded part may be moved little by little by moving the workpiece and the laser beam spot relatively in the seam welding direction each time each pulsed laser beam LB is irradiated. Then, as shown in FIG. 7, cracks cri generated on the surface of each molten metal portion MGi by the irradiation of each pulsed laser beam LBi are removed by the molten metal portion MGi by the next irradiation of the pulsed laser beam LBi + 1. As a result, the molten metal portion MG by the irradiation of the last pulsed laser beam LBN
Small cracks crN remain only on the surface of N. FIG. 8 is a schematic plan view showing this state. In order to prevent cracking crN in the final molten metal portion MGN, a method of adjusting the alloy composition so as to become a eutectic component having a high melting point is considered.

As described above, in the seam welding according to the pulse laser welding method of the present embodiment, four pulses LB (1) to LB (4) are intermittently repeated in the laser output waveform per cycle. And the four pulses LB (1) to L
By irradiating the weld portion of the aluminum alloy with the pulsed laser beam LB having a relationship in which the peak value of B (4) gradually decreases, a high quality welded joint substantially free of weld cracks can be obtained.

In the above-described embodiment, the number of pulses included in the laser output waveform at one time or per cycle is four. However, this is merely an example, and an arbitrary number of pulses is selected. It is possible. In addition, in the present invention, the basic requirement is that the peak values of the plurality of pulses sequentially become lower. However, the condition does not necessarily have to be satisfied among all the pulses, and the pulse value is not necessarily required for most of the pulses. Or during some of the 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. Also, an arbitrary value can be selected as a whole or individually for the output value or the length of the intermittent time between pulses.
Various waveforms can be selected for the peak level of each pulse.

[0030]

As described above, according to the present invention,
One or all of the laser output waveforms per cycle
Or some of the peak values are gradually lower.
Pulsed laser light by the previous pulsed laser light
The next pulse rate while the weld maintains the keyhole
Laser output and time interval to irradiate
Irradiate the welded part of the aluminum alloy and
Metallurgically with the laser energy of multiple pulsed laser beams
Because of joining, there is no welding defect such as welding peeling.
A high quality welded joint can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a main part of a YAG laser for performing a pulse laser welding method according to one 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 illustrating an example of an output waveform of a pulse laser beam set and input in the laser power supply device according to the embodiment.

FIG. 4 is a measurement waveform chart showing an example of an output waveform of a pulse laser beam obtained by a YAG laser in an example.

FIG. 5 is a cross-sectional view showing a cross-sectional structure of a weld obtained by spot welding by a pulse laser welding method according to an example.

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

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

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 example.

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]

 Reference Signs List 10 excitation lamp 12 YAG rod 20 first laser power supply circuit 26 switching transistor 36 switching control unit 50 second laser power supply circuit 54A, 54B charging transistor 58A, 58B capacitor 60A, 60B discharging transistor 66 charging control unit 70 discharging Control unit 80 Main control unit 82 Set value input unit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A 57-82492 (JP, U) JP-B 48-25829 (JP, B1) (58) Fields investigated (Int. Cl. ⁶ , DB name) B23K 26/00-26/06

Claims (6)

(57) [Claims] 1. An aluminum alloy using a pulsed laser beam.
In the pulsed laser welding method for welding gold , the entire laser output waveform per cycle or per cycle
Or some of the peak values are gradually lower.
Pulsed laser light by the previous pulsed laser light
The next pulse rate while the weld maintains the keyhole
Laser output and time interval to irradiate
Irradiating the welded part of the aluminum alloy,
Metallurgically with the laser energy of multiple pulsed laser beams
Pulse welding of aluminum alloy characterized by joining
User welding method. 2. The method according to claim 1, wherein said pulse laser light is substantially intermittent.
Laser light with a preset laser output value that is not zero
And irradiating the welding portion with the welding portion.
Laser welding method for the aluminum alloy described above. 3. Each of the plurality of pulsed laser beams
The feature is that the pulse width is selected to an arbitrary value.
The pulse laser welding method according to claim 1 or 2, wherein 4. Each of the plurality of pulsed laser beams
It is unique that the pulse waveform is selected to be an arbitrary waveform.
The pulse laser welding method according to claim 1 or 2, wherein
Law. 5. A pulse laser welding method according to claim 1.
A laser device for implementing the method, comprising: a laser medium, an excitation light source, and an optical resonator;
Illuminating the laser medium based on the light energy
Oscillation that oscillates and outputs laser light from an optical resonator
And a plurality of capacitor vans connected in parallel to the pump light source.
A plurality of pulse trains from the laser oscillation unit.
To oscillate and output laser light.
Tanks that discharge the inks sequentially or alternately at the time intervals described above.
And a power supply unit. 6. The pulse laser welding method according to claim 2.
A laser device for implementing the method, comprising: a laser medium, an excitation light source, and an optical resonator;
Illuminating the laser medium based on the light energy
Oscillation that oscillates and outputs laser light from an optical resonator
And a plurality of capacitor vans connected in parallel to the pump light source.
A plurality of pulse trains from the laser oscillation unit.
To oscillate and output laser light.
The first or second discharge is performed sequentially or alternately at the time intervals.
Laser power supply section, a rectifier circuit that converts AC voltage of commercial frequency to DC,
Waves connected in series between the rectifier circuit and the excitation light source
Switching means for shape control, said laser output
The switching means is turned on at a high frequency during the period of the waveform.
Turn off and apply a DC current with a preset waveform to the excitation
A second laser power supply for supplying the electromotive light source
A laser device characterized by the above-mentioned.