JP7382026B2 - Laser spot welding method - Google Patents

Description

The present invention relates to a laser spot welding method.

Laser welding, in which a workpiece is irradiated with a laser and the material at the irradiated area is heated and melted by the light energy, has the advantage of non-contact, high-speed welding, and is increasingly replacing arc welding and resistance spot welding. As laser spot welding that replaces resistance spot welding, Patent Document 1 discloses a method in which a laser beam is scanned in a circular or spiral shape within a spot region in order to remove defects such as blowholes.

However, this type of welding method requires agile scanner operation to scan the beam within the spot area, which makes the control operation complicated and has the problem of lengthening the takt time by the amount of beam scanning. .

Japanese Patent Application Publication No. 2012-115876

The present invention was made in view of the above circumstances, and its purpose is to provide laser spot welding that can stably obtain joint strength with simple operation and avoid complicated control and increase in takt time. The purpose is to provide a method.

In order to solve the above problems, a laser spot welding method according to a first aspect of the present invention includes:
With the laser optical axis set in a predetermined area of multiple stacked metal plates,
a first step of irradiating the laser with a first defocus amount for a first time;
a second step of irradiating the laser with a second defocus amount for a second time;
including successively executing
the first time period is shorter than the second time period;
The first defocus amount is larger than the second defocus amount.

Further, the laser spot welding method according to the second aspect of the present invention includes:
With the laser optical axis set in a predetermined area of multiple stacked metal plates,
a first step of irradiating the laser with a first defocus amount for a first time;
a second step of irradiating the laser with a second defocus amount for a second time;
including successively executing
the first time period is shorter than the second time period;
The second defocus amount is larger than the first defocus amount.

In the laser spot welding method according to the first aspect of the present invention, before the second step (substantially basic irradiation) of irradiating the laser with a second defocus amount for a second time, the second defocus amount is A state in which a predetermined area is heated in advance by defocused irradiation by executing the first step (substantial defocused irradiation) of irradiating for a first time shorter than the second time with a larger first defocus amount. Then, the second step of basic irradiation can be performed, which has the advantage of suppressing spatter.

In the laser spot welding method according to the second aspect of the present invention, before the second step (substantial defocus irradiation) of irradiating a laser with a second defocus amount for a second time, a second defocus is applied. By performing the first step (substantial basic irradiation) of irradiating for a first time shorter than the second time with a first defocus amount smaller than the It is possible to shift to defocused irradiation in steps, which has the advantage of suppressing spatter.

In this way, in any aspect, if the operation is simple and does not involve scanning of the laser optical axis, the desired bonding strength and appearance can be obtained while suppressing spatter, and the complexity of control and increase in takt time can be avoided. It can be avoided.

FIG. 2 is a side sectional view showing laser spot welding according to the first embodiment of the present invention. It is a side sectional view showing laser spot welding concerning a 2nd embodiment of the present invention. It is a typical graph which shows the defocus amount in laser spot welding of each Example based on 1st Embodiment of this invention. It is a typical graph which shows the defocus amount in laser spot welding of each Example and comparative example based on 2nd Embodiment of this invention.

Embodiments of the present invention will be described in detail below with reference to the drawings.

(First embodiment)
FIG. 1 shows laser spot welding 10 according to a first embodiment of the present invention for three stacked metal plates 11, 12, and 13. The metal plates 11, 12, and 13 are not particularly limited, but are assumed to be thin steel plates with a thickness of 0.6 to 2.0 mm.

For the three metal plates 11, 12, 13, a protrusion (embossed, not shown) is pressed in advance on one of them (usually the metal plate 12, 13 below the gap), and the protrusion is pressed. or overlapped with a spacer (not shown) inserted between the metal plates, and held with a jig such as a clamp as necessary to adjust the spacing, and/ Alternatively, the press-formed products are stacked on each other with an unadjusted gap caused by springback in the flange portion, etc.

When performing laser spot welding 10, as shown in FIG. Laser irradiation La (substantially defocused irradiation) is performed for a predetermined time Ta (1/4 or less of the total irradiation time) at an irradiation diameter Sa) (first step).

This defocus amount da corresponds to the maximum area (minimum power density) or an irradiation area similar to it in the welding process, the power density is suppressed, and the irradiation time Ta is 1/4 or less of the total irradiation time. Therefore, at this stage, a melted part that penetrates the three metal plates 11, 12, 13 is not formed, and the irradiation area is expanded by heat conduction from the softened outermost metal plate 11 to the lower metal plates 12, 13. The whole is preheated (Wa).

Next, with the optical axis Lx fixed, focus control is performed using the optical system of the laser welding machine, and laser irradiation Lo (substantive basic irradiation) is performed for a predetermined time To at a defocus amount do (irradiation diameter So). Do it (second step).

This defocus amount do corresponds to the irradiation area with the minimum area (maximum power density) during the welding process, and the molten part is expanded from the center to the periphery of the irradiation area where the energy distribution is high, and the welded part is the most Sufficient penetration depth can be obtained to reach the metal plate 13 below, but since the metal plates 11, 12, and 13 are preheated in the first step (substantially defocused irradiation) prior to this, a rapid increase in penetration can be achieved. The temperature is relaxed and spatter generation is suppressed.

Note that when the metal plates 11, 12, and 13 have a surface treatment layer of a low melting point metal, the metal vapor generated in and around the molten part is transferred from the outermost metal plate 11 to the lower metal plate in the first step. Due to heat conduction (preheating Wa) to the metal plates 12 and 13, the heat is diffused and discharged through the gaps between the metal plates 11, 12, and 13.

(Second embodiment)
FIG. 2 shows laser spot welding 20 according to a second embodiment of the present invention for three stacked metal plates 11, 12, and 13. The configuration and arrangement of the metal plates 11, 12, and 13 are the same as in the first embodiment, and only the control of the defocus amount is different.

When carrying out the laser spot welding 20, as shown in FIG. Laser irradiation Lo (substantial basic irradiation) is performed for a predetermined time To (1/4 to 1/3 of the total irradiation time) at the irradiation diameter So), and three metal plates 11, 12, 13 is formed (first step).

This defocus amount do corresponds to the irradiation area with the minimum area (maximum power density) during the welding process, and corresponds to the irradiation area of the two metal plates 11 on the outermost side among the three metal plates 11, 12, 13 to be welded. , 12, and a sufficient penetration depth can be obtained even into the lowest metal plate 13.

Next, with the optical axis Lx fixed, focus control is performed using the optical system of the laser welding machine, and laser irradiation Lb (substantial defocus irradiation) is performed for a predetermined time Tb at a defocus amount db (irradiation diameter Sb). (second step).

This defocus amount db corresponds to the maximum area (minimum power density) or a similar irradiation area during the welding process, and laser irradiation Lb (substantial defocus irradiation) is performed over a wider area than the molten part Wo. By doing so, it is possible to expand the fusion zone while suppressing the rapid temperature rise in the center and the resulting spatter, and the final weld zone Wb can be obtained.

Note that when the metal plates 11, 12, and 13 have a surface treatment layer of a low-melting point metal, the metal vapor generated in the molten part and its surroundings causes heat transfer from the center to the periphery as described above. It is diffused and discharged through the gaps between the metal plates 11, 12, and 13.

In each of the above embodiments, a case has been described in which the defocus amount is changed by controlling the laser optical system, but the defocus amount is changed by mechanically moving the position of the laser processing head up and down (linear movement). You can also do that. Furthermore, in each of the above embodiments (FIGS. 1 and 2), a case was described in which a positive defocus amount was used in which the focus position (beam waist) was above (proximal to) the workpiece. A downward (distal) negative defocus amount can also be used.

(Example according to the first embodiment)
Next, in order to verify the effect of the laser spot welding 10 according to the first embodiment, the laser spot welding 10 was performed while changing the defocus amount da and the irradiation time Ta in the first step, and the situation of the welded part was examined. We conducted a comparative experiment.

In the experiment, the metal plates 11, 12, and 13 were steel plates with thicknesses t1 = 0.8 mm, t2 = 0.8 mm, and t3 = 1.0 mm from the outermost surface side (laser irradiation side) (total thickness 2.6 mm). ), laser irradiation was performed for a total of 0.4 seconds in the first and second steps at a laser output of 5 kW for each case where the gap g between the metal plates was 0 mm, 0.5 mm, and 1.0 mm.

(Example 1.1)
First, as shown by the symbol La1 in FIG. 3, laser irradiation La (first step) is performed with a defocus amount da = 65 mm (irradiation diameter Sa = 3.3 mm) and an irradiation time Ta = 0.1 seconds, and then, As shown by the symbol Lo, when laser irradiation Lo (second step) was performed with a defocus amount do = 44 mm (irradiation diameter So = 2.3 mm) and an irradiation time To = 0.3 seconds, the gap between the metal plates was In any case where g=0 mm, 0.5 mm, and 1.0 mm, no spatter occurred and welded parts with good appearance and strength were obtained.

(Example 1.2)
First, as shown by the symbol La2 in FIG. 3, laser irradiation La (first step) is performed with a defocus amount da = 55 mm (irradiation diameter Sa = 2.7 mm) and an irradiation time Ta = 0.1 seconds, and then, As shown by the symbol Lo, when laser irradiation Lo (second step) was performed with a defocus amount do = 44 mm (irradiation diameter So = 2.3 mm) and an irradiation time To = 0.3 seconds, the gap between the metal plates was When g=0 mm, spatter was observed on the back side. This is thought to be due to the fact that the defocus amount da=55 mm in the first step is insufficient and the energy density in the central portion is high. In each case where the gap g between the metal plates was 0.5 mm and 1.0 mm, welded parts with both external strength and strength within the allowable range were obtained.

(Example 1.3)
First, as shown by the symbol La3 in FIG. 3, laser irradiation La (first step) is performed with a defocus amount da = 65 mm (irradiation diameter Sa = 3.3 mm) and an irradiation time Ta = 0.05 seconds, and then, As shown by the symbol Lo, when laser irradiation Lo (second step) was performed with a defocus amount do = 44 mm (irradiation diameter So = 2.3 mm) and an irradiation time To = 0.35 seconds, the gap between the metal plates was In all cases where g=0 mm, 0.5 mm, and 1.0 mm, welded parts with good appearance and strength were obtained, although slight spatter was generated on the back side.

(Example 1.4)
First, as shown by the symbol La4 in FIG. 3, laser irradiation La (first step) is performed with a defocus amount da = 65 mm (irradiation diameter Sa = 3.3 mm) and an irradiation time Ta = 0.01 seconds, and then, As shown by the symbol Lo, when laser irradiation Lo (second step) was performed with a defocus amount do = 44 mm (irradiation diameter So = 2.3 mm) and an irradiation time To = 0.39 seconds, the gap between the metal plates was In all cases where g=0 mm, 0.5 mm, and 1.0 mm, welded parts with good appearance and strength were obtained, although slight spatter was generated on the back side.

(Example and comparative example according to the second embodiment)
Next, in order to verify the effect of the laser spot welding 20 according to the second embodiment, steel plates similar to those described above are used, and the gap g between the metal plates is 0 mm, 0.5 mm, and 1.0 mm. Laser spot welding 20 was performed with a laser output of 5 kW and the defocus amount db and the irradiation time Tb in the second step changed, and the conditions of the welded portion were compared.

(Example 2.1)
First, as shown by the symbol Lo in FIG. 4, laser irradiation Lo (first step) is performed with a defocus amount do = 44 mm (irradiation diameter So = 2.3 mm) and an irradiation time To = 0.1 seconds, and then, As shown by symbol Lb1, when laser irradiation Lb (second step) was performed with defocus amount db = 55 mm (irradiation diameter Sb = 2.7 mm) and irradiation time Tb = 0.3 seconds, the gap between the metal plates was Even when g was set to 0 mm, 0.5 mm, and 1.0 mm, welded parts with good appearance and strength were obtained, although slight spatter was observed.

(Example 2.2)
First, as shown by the symbol Lo in FIG. 4, laser irradiation Lo (first step) is performed with a defocus amount do = 44 mm (irradiation diameter So = 2.3 mm) and an irradiation time To = 0.1 seconds, and then, As shown by symbol Lb2, when laser irradiation Lb (second step) was performed with defocus amount db = 65 mm (irradiation diameter Sb = 3.3 mm) and irradiation time Tb = 0.3 seconds, the gap between the metal plates was Even when g was set to 0 mm, 0.5 mm, and 1.0 mm, welded parts with good appearance and strength were obtained, although slight spatter was observed.

(Comparative example)
As a comparative example, as shown by symbols Lo to Lo' in FIG. When the gap g=0 mm and 0.5 mm, spatter occurred on both the front side and the back side, and when the gap g between the metal plates was 1.0 mm, spatter also occurred on the back side.

In addition, in the above embodiment, the case where three metal plates are stacked and laser spot welded is shown, but depending on conditions such as laser output, two or four or more metal plates may be stacked and laser spot welded. is also possible. Further, although the experiment related to the above embodiment was conducted using three metal plates having a total thickness of 2.6 mm, it is also possible to weld a thickness smaller than that.

Further, in each of the above embodiments, a case is shown in which the outermost metal plate 11 is irradiated with a laser from vertically above, but workability within a practical range can be obtained at an irradiation angle of up to 40 degrees. Furthermore, it is also possible to weld metal plates tilted at any angle other than the horizontal plane.

Although several embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications and changes can be made based on the technical idea of the present invention.

11, 12, 13 Metal plate da, db, do Defocus amount La, Lb, Lo Laser irradiation Lx Laser optical axis Sa, Sb, So Laser irradiation diameter Wa Preheating Wb, Wo Welding part (molten part)

Claims (6)

A laser spot welding method, comprising:
With the laser optical axis set in a predetermined area of multiple stacked metal plates,
a first step of irradiating the laser with a first defocus amount for a first time;
a second step of irradiating the laser with a second defocus amount for a second time;
including successively executing
the first time period is shorter than the second time period;
the first defocus amount is larger than the second defocus amount;
Laser spot welding method. The first time is 1/4 or less of the total irradiation time of the first and second steps, and the first defocus amount is 1.25 to 1.5 of the second defocus amount. The laser spot welding method according to claim 1, wherein the laser spot welding method is twice as large. A laser spot welding method, comprising:
With the laser optical axis set in a predetermined area of multiple stacked metal plates,
a first step of irradiating the laser with a first defocus amount for a first time;
a second step of irradiating the laser with a second defocus amount for a second time;
including successively executing
the first time period is shorter than the second time period;
the second defocus amount is larger than the first defocus amount;
Laser spot welding method. The first time is 1/4 to 1/3 of the total irradiation time of the first and second steps, and the second defocus amount is 1.25 to 1/3 of the first defocus amount. The laser spot welding method according to claim 3, which is 1.5 times. The number of metal plates is 3, the total plate thickness is 2.6 mm or less, the gap between each plate is 0.5 mm or less, and the total irradiation time of the first to second steps is 0.2 to 1.0 seconds. The laser spot welding method according to any one of claims 1 to 4. The number of metal plates is 3, the total plate thickness is 2.6 mm or less, the gap between each plate is 0.5 to 1.0 mm, and the total irradiation time of the first to second steps is 0.25 to 0.5 mm. The laser spot welding method according to any one of claims 1 to 4, wherein the welding time is 5 seconds.