Pulsed laser welding apparatus and welding method

Abstract

This invention provides a laser welding apparatus and welding method that can improve product quality by reducing the effects of thermal shrinkage, such as warping. [Solution] The laser welding apparatus 1 includes a laser oscillator 2 that irradiates a laser beam B in the thickness direction of multiple stacked metal plates 11, 11, and a pulse generator 3 connected to the laser oscillator 2 that emits a pulse voltage signal. The pulse generator 3 sets the duty cycle of the laser beam B irradiated from the laser oscillator 2 by controlling the on / off state of the pulse voltage signal P.

Description

Technical Field

[0001] The present invention relates to a laser welding apparatus and a welding method.

Background Art

[0002] Conventional laser welding apparatuses weld a plurality of members to be welded (hereinafter also referred to as base materials) to each other by irradiating at least two of the members with a pulsed laser beam. For example, by adopting a laser welding method comprising a first step of irradiating at a constant pulse pitch such that adjacent weld beads overlap, and a second step of irradiating between the weld beads under the same conditions, a configuration that improves welding strength is known (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of Invention

Problems to be Solved by the Invention

[0004] In general, laser welding using a laser welding apparatus locally melts and solidifies the base materials, so thermal shrinkage occurs in the cooling step after welding. For example, there are cases where two long plate-shaped metal plates are stacked as base materials and laser-welded along the longitudinal direction. In this case, the energy amount of the laser beam input to the metal plate on the surface facing the laser welding apparatus side is larger than that of the metal plate on the back surface, and the melting amount of the base materials increases. For this reason, there is a difference in the amount of longitudinal shrinkage from the metal plate on the back surface during cooling, and a bending moment is applied to cause warping (longitudinal bending) deformation, which causes a problem that thermal strain adversely affects product accuracy.

[0005] Furthermore, conventional welding techniques, which involve two separate processes, have the problem of increasing the welding time and thus raising manufacturing costs. Therefore, further improvements are needed to provide high-quality products using a universally applicable distortion reduction method.

[0006] The present invention aims to provide a laser welding apparatus and welding method that can improve product quality by reducing the effects of thermal shrinkage such as warping. [Means for solving the problem]

[0007] The laser welding apparatus of the present invention comprises a laser oscillator that irradiates a laser beam in the thickness direction of multiple stacked metal plates, and a pulse generator connected to the laser oscillator that generates a pulse voltage signal. The pulse generator is characterized by controlling the on / off state of the pulse voltage signal to set the duty cycle of the laser beam irradiated from the laser oscillator. [Effects of the Invention]

[0008] The present invention provides a laser welding apparatus and welding method that can improve product quality by reducing the effects of thermal shrinkage such as warping. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows the overall configuration of a welding system in an embodiment of the present invention. [Figure 2] This graph compares the square wave of the embodiment with a sine wave and a triangular wave. [Figure 3] This table shows the evaluation of appearance quality when the duty cycle is changed for each laser beam frequency. [Figure 4] This is a plan view of the surface of a metal plate that exploded due to laser beam irradiation. [Figure 5] This is a plan view showing an example of a metal sheet material with good surface appearance quality. [Figure 6]This graph shows the amount of distortion in each waveform as an improvement rate from continuous oscillation. [Figure 7] This is a cross-sectional view at the VV line position in Figure 1, showing the welding process between metal plates of the base material. [Figure 8] This is a schematic cross-sectional view showing the extent of the melted area due to heat conduction when welding metal plates of the base material using a continuous wave. [Modes for carrying out the invention]

[0010] Hereinafter, an embodiment of the present invention, a laser welding apparatus 1, will be described. As shown in Figure 1, the laser welding apparatus 1 irradiates a pulsed laser beam (pulsed wave laser beam) B to weld at least two or more metal plate materials 11, 11 (hereinafter also referred to as base materials), such as aluminum alloy materials, to each other. Then, the welded portion 20 of the two metal plates 11, 11 that was melted by irradiation with laser beam B solidifies upon cooling to become an integrated product 10 which is a structural component of the vehicle body.

[0011] The laser welding apparatus 1 includes a laser oscillator 2 that irradiates a laser beam B in the thickness direction H of multiple stacked metal plates 11, 11. A fiber optic cable 7 is connected to the laser oscillator 2, and an irradiation unit 4 is provided at the end of the fiber optic cable 7 to irradiate a laser beam B. The laser beam B generated by the laser oscillator 2 is then irradiated from the irradiation unit 4 via the fiber optic cable 7 in a desired direction, for example, toward the welded portion 20 of the metal plate material 11.

[0012] In this embodiment, an arm robot 5 is provided as a moving mechanism. The arm robot 5 has a multi-jointed movable arm 6. The irradiation unit 4 is attached to the tip of the movable arm 6. The movable arm 6 can move the irradiation unit 4 along the longitudinal direction L of the metal plate material 11 at a preset constant moving speed. The laser welding apparatus 1 of the embodiment is set such that the moving speed of the laser beam B irradiated from the irradiation unit 4 to the welded portion 20 is 1.5 m / min. In this manner, the laser beam B irradiated from the irradiation unit 4 moves along the longitudinal direction L of the metal plate material 11 at a preset constant moving speed, whereby the laser welding apparatus 1 can input a uniform amount of energy from one side surface of the metal plate material 11 in the plate thickness direction H.

[0013] Further, the laser welding apparatus 1 includes a pulse generator 3 connected to the laser oscillator 2. The pulse generator 3 is configured to oscillate a pulse voltage signal P to the laser oscillator 2. The pulse generator 3 can perform on-off control on a voltage signal with a frequency of 0.01 μHz to 5 MHz. Thereby, the duty ratio of the laser beam B irradiated from the laser oscillator 2 can be set to be between 1% and 100%, and the laser beam B with a frequency of 1 kHz to 10 kHz can be generated. Here, the duty ratio (also referred to as duty cycle) is the proportion of time during which a pulse is on in a pulse signal that repeats at a constant cycle, and is expressed as a percentage (%) obtained by dividing the pulse width (τ) of the ON time by the cycle (T). For example, in the pulse oscillation shown in Figure 2, the time during which the pulse is on in one cycle T is 1 / 2, and the duty ratio is 50 (%). A duty ratio of 100% is equivalent to continuous oscillation.

[0014] Figure 2 shows the laser output output from the laser oscillator 2. At the top of Figure 2, a general continuous oscillation laser output is shown. In the laser welding apparatus 1 of the embodiment, the ON / OFF time of the pulse voltage signal P oscillated by the pulse generator 3 is controlled, so that the duty ratio of the laser output oscillated from the laser oscillator 2 can be set to any value between 1% and 100%.

[0015] That is, the laser welding apparatus 1 of the embodiment can use the pulse generator 3 to increase or decrease the time during which the pulse is ON within one cycle T, that is, the pulse width (τ) of the ON time. Thereby, the duty ratio of the laser beam B emitted from the irradiation unit 4 of the laser oscillator 2 can be set to any value between 1% and 100%. Therefore, compared with the general continuous oscillation shown at the top in FIG. 2, adjustment to reduce the input energy of the laser beam B can be easily performed. Note that FIG. 2 shows, as comparative examples of laser output, waveforms of a sine wave and a triangular wave having the same cycle T as that of pulse oscillation.

[0016] FIG. 3 shows evaluation results when laser welding is performed using the laser welding apparatus 1 of the embodiment. Here, the results of evaluating the laser beams B with different duty ratios irradiated onto the metal plate material 11 for each frequency are described. Here, as the evaluation conditions, a base material formed by stacking two metal plate materials 11 made of an aluminum alloy (A6061, thickness t=2 mm) is used uniformly. Then, the to-be-welded portion 20 of the metal plate material 11 was irradiated with the pulsed laser beam B in the plate thickness direction H at a moving speed of 1.5 m / min (see FIG. 1). Further, the frequency of the laser beam B was tested at each of the frequencies 1, 4, 7, and 9.99 kHz, with the duty ratio set to 50, 60, 70, 80, and 90 for each combination.

[0017] Warping (longitudinal bending) deformation due to thermal shrinkage was measured and evaluated using a laser displacement gauge for the portion with the largest deformation amount at the intermediate part in the longitudinal direction L. The circles in FIG. 3 indicate samples that fall within the desired deformation amount and have good appearance quality (see FIG. 5). The crosses in FIG. 3 indicate cases where spatter occurs on the surface of the metal plate material 11 due to the irradiation of the laser beam B, resulting in poor appearance quality (NG) (see FIG. 4). When spatter occurs, the input energy amount that provides the desired joint strength cannot be obtained, which is regarded as a welding defect.

[0018] As a result, it was found that by reducing the duty cycle to 50-90%, the warping (longitudinal bending) deformation due to thermal shrinkage was reduced to the desired deformation amount. However, if the duty cycle is reduced, explosives may occur on the surface of the metal plate 11, resulting in poor appearance quality (NG), and the desired welding strength may not be achieved. Therefore, by setting the frequency of the laser beam B generated by the laser oscillator 2 to a higher value of 1 to 10 kHz, the duty cycle can be further reduced, thereby decreasing the amount of input energy.

[0019] In other words, the laser welding apparatus 1 of the embodiment increases the frequency as the duty cycle decreases. For example, the frequency of laser beam B is set to 9.99 kHz, approaching 10 kHz. This allows the duty cycle to be set to 50%, reducing the amount of base material melted on the surface of the metal plate material 11 on the irradiation unit 4 side, and suppressing warping during cooling without causing explosions. As a result, the welded product 10 has good product accuracy and appearance quality, and the desired weld strength can be obtained.

[0020] Furthermore, with the laser welding apparatus 1 of this embodiment, laser welding is completed by irradiating the part to be welded 20 with the laser beam B only once. Therefore, compared to conventional techniques that perform welding in two stages, the time required for welding can be shortened, and an increase in manufacturing costs can be suppressed.

[0021] Furthermore, in the laser welding apparatus 1 of this embodiment, as shown in Figure 6, the frequency of the laser beam B can be set to 7 kHz when the duty cycle is set to 60%. As a result, the laser welding apparatus 1 can reduce the warpage from 1.72 mm to 1.51 mm, which is the amount of warpage in the case of continuous oscillation. Therefore, the improvement rate increases to -12.2%, further improving product accuracy.

[0022] For example, as shown in Figure 7, in the case of continuous oscillation, heat is transferred to the surface of the metal plate 11 located on the irradiation unit 4 side, causing the base material around the energy input unit 21 to melt more than the metal plate 11 on the back side (see Figure 8). In contrast, in the laser welding apparatus 1 of the embodiment, by setting the laser beam B to a rectangular wave and lowering the duty cycle, the amount of heat transferred within the surface metal plate material 11 can be reduced, thereby reducing the amount of melting of the welded part 20 on the irradiation unit 4 side. Therefore, when the laser beam B is a rectangular wave, the difference in vertical shrinkage between it and the metal plate material 11 on the back surface during cooling is not as large compared to the case of continuous oscillation. Thus, by performing laser welding using the laser welding apparatus 1 of the embodiment, thermal distortion such as warping (vertical bending) deformation can be suppressed, and product accuracy can be improved.

[0023] Furthermore, by making the laser beam B a rectangular wave, the amount of energy input to the base material can be reduced. As a result, the laser welding apparatus 1 of this embodiment can achieve improvement rates in each frequency band that are equivalent to or better than the improvement rates of -2.9% and -6.4% obtained when reducing warpage using sinusoidal waves and triangular waves (see Figure 2). Therefore, by connecting a pulse generator 3 that produces a rectangular wave pulse voltage signal P to a conventionally used laser oscillator 2, it can be applied in a general way. Thus, the laser welding apparatus 1 of this embodiment exhibits practically beneficial effects, such as being able to provide high-quality products 10 using the distortion reduction method described above.

[0024] As described above, the laser welding apparatus 1 is equipped with a laser oscillator 2 that irradiates a laser beam B in the thickness direction of multiple stacked metal plates 11, 11. The laser welding apparatus 1 is also equipped with a pulse generator 3 connected to the laser oscillator 2 that emits a pulse voltage signal P. The pulse generator 3 controls the on / off state of the pulse voltage signal P to set the duty cycle and frequency of the laser beam B irradiated from the laser oscillator 2.

[0025] As a result, the laser welding apparatus 1 of the present invention can reduce the effects of thermal shrinkage such as warping and improve the quality of the product 10. More specifically, the laser beam B irradiated from the laser oscillator 2 onto the metal plate material 11 can be given the desired input energy by setting the duty cycle and frequency with the pulse voltage signal P generated from the pulse generator 3. Therefore, for example, the amount of energy of the laser beam B directed onto the surface of the metal plate material 11 can be reduced to decrease the effects of thermal contraction such as warping. Furthermore, the laser welding apparatus 1 can reduce the time required for laser welding. Therefore, it can suppress increases in manufacturing costs.

[0026] Furthermore, the duty cycle of the pulse voltage signal P only needs to be set to 50-90%. Therefore, the desired bond strength can be efficiently obtained. Furthermore, the frequency of the laser beam B emitted from the laser oscillator 2 only needs to be set to 1 to 10 kHz. Therefore, even when the duty cycle of the pulse voltage signal P is low, no explosions or other damage occur on the surface of the metal plate material 11. Consequently, it is possible to improve the appearance quality while obtaining the desired bonding strength.

[0027] Furthermore, by setting the pulse frequency and duty cycle of the laser beam B irradiated onto the metal plate material 11, the amount of energy supplied to one side of the metal plate material 11 can be easily adjusted, thereby reducing thermal distortion such as warping. Furthermore, the existing laser oscillator 2 can be used. This allows for practical benefits such as suppressing increases in equipment costs and reducing the manufacturing cost of the product.

[0028] The present invention is not limited to the embodiments described above, and various modifications are possible. The embodiments described above are illustrative examples provided to facilitate understanding of the present invention, and are not necessarily limited to those comprising all the configurations described. Furthermore, it is possible to replace parts of the configuration of one embodiment with those of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. In addition, it is possible to delete parts of the configuration of each embodiment, or to add or replace other configurations. Possible modifications to the above embodiments are as follows, for example.

[0029] In the embodiments described, an example has been described in which the irradiation unit 4 is provided at the tip of the movable arm of the robotic arm. However, the invention is not limited to this, and a moving mechanism may be used in which two metal plates 11, 11 are stacked on a base and placed on the base, and the part to be welded 20 is moved together with the base. Alternatively, the moving mechanism may be configured to use the robotic arm 5 and the base in combination to move the part to be welded 20 of the metal plate 11 relative to the irradiation unit 4.

[0030] Furthermore, in this embodiment, the duty cycle and frequency of the irradiated laser beam B are set, but this is not limited to this, and at least one of the duty cycle and frequency of the irradiated laser beam B may be changed and set. Also, the duty cycle of the laser beam B irradiated from the irradiation unit 4 of the laser oscillator 2 can be set to any value between 50 and 90 (%). However, this is not limited to this. For example, the duty cycle may be high, such as 99% close to 100%, or even 90% or more, and may be less than 50% as long as it does not explode. In other words, the value of the duty cycle of the laser beam B set by the pulse generator 3 is not particularly limited. [Explanation of Symbols]

[0031] 1. Laser welding equipment 2. Laser Oscillator 3. Pulse Generator 10 products 11 Metal plate material B Laser beam P pulse voltage signal

Claims

1. A laser oscillator that irradiates a laser beam in the thickness direction of multiple stacked metal plates, The laser oscillator is connected to a pulse generator that generates a pulse voltage signal, The laser welding apparatus is characterized in that the pulse generator controls the pulse voltage signal on and off to set the duty cycle and frequency of the laser beam irradiated from the laser oscillator.

2. The laser welding apparatus according to claim 1, characterized in that the duty cycle of the pulse voltage signal is set to 50 to 90%.

3. The laser welding apparatus according to claim 1, characterized in that the frequency of the laser beam emitted from the laser oscillator is set to 1 to 10 kHz.

4. The laser welding apparatus according to claim 3, characterized in that the laser beam is set to have a frequency that increases as the duty cycle decreases.

5. The laser welding apparatus according to claim 1, characterized in that the metal plate material is a vehicle body frame component.

6. The laser welding apparatus according to claim 1, characterized in that the metal plate material is an aluminum alloy material.

7. A welding method using a laser welding apparatus according to claim 1, characterized by setting the duty cycle and frequency of the laser beam to be irradiated.

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