JP2880061B2 - Laser processing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser processing technique, and more particularly to a laser processing technique using laser light having a ring-shaped energy distribution.

[0002]

2. Description of the Related Art When a laser beam is used, a spot having a high energy density can be formed and can be used for various processing techniques. For example, a laser processing technique for performing cutting, welding, and the like of a metal plate is known. The object to be processed is irradiated with laser light from a laser irradiation tool such as a trepanning head to perform processing such as cutting and welding.

[0003] By the way, there is a welding that is difficult to perform by such a general laser processing technique. One of them is lap spot welding of thin plates. In electronic equipment and the like, it is desired that two thin metal sheets are overlapped and spot-welded.

[0004] This spot welding is required to have high welding strength and no welding marks on the back surface after welding. Since the object to be welded is a thin plate, if the energy density of the irradiation laser beam is set too high, the thin plate of the irradiated portion is melted over the entire thickness, and not only welding marks are formed but also holes may be formed. Also, if the energy density of the irradiation laser light is too low,
The penetration depth of the weld is insufficient, and the welding strength is reduced.
In extreme cases, no welding is performed.

Generally, a metal surface has a property of reflecting laser light. However, no matter how high the reflectivity is, if the irradiation energy of the laser beam is sufficiently high, the metal surface will melt. Once melted, the metal surface sharply reduces the reflectivity and absorbs the laser light even more.

In the case of overlapping spot welding of thin plates, unless the energy density of the laser beam to be irradiated is properly controlled,
It will be difficult to obtain the desired penetration depth. When the object to be welded is a thin plate, the control of the energy level of the laser beam becomes even more important.

[0007]

It is not easy to simultaneously achieve high welding strength and no welding marks on the back surface of a welded portion in spot welding of thin plates using a laser.

An object of the present invention is to provide a laser processing technique excellent in processing quality. Another object of the present invention is to
It is an object of the present invention to provide a laser welding method which has high control of penetration depth and shape, and can obtain high welding strength and excellent back surface shape of a welded portion.

[0009]

According to one aspect of the present invention, there is provided a step of forming a laser beam having a ring-shaped light intensity distribution in a plane perpendicular to a light traveling direction, including a hollow portion;
A step of controlling the waveform so that the time change of the light intensity of the laser beam is pulse-like, and the latter half of the pulse has a higher light intensity than the former half of the pulse; and Irradiating the laser beam onto a workpiece at a position where the light intensity distribution in a plane perpendicular to the traveling direction of the workpiece has a continuous shape without a hollow portion to perform processing. You. According to another aspect of the present invention, a step of forming a ring-shaped laser beam having a light intensity distribution in a plane perpendicular to a light traveling direction including a hollow portion, and a step of condensing the laser beam, Irradiating the laser beam on the workpiece at a position where the light intensity distribution in a plane perpendicular to the light traveling direction has a continuous shape without a hollow portion, and performing the processing, Is a superposed thin plate, and the processing is spot welding.

[0010]

When a laser beam having a ring-shaped light intensity distribution is condensed, the shape of the ring gradually becomes smaller, and the central portion not irradiated with the laser beam eventually disappears.

As described above, a laser beam having a ring-shaped mode is condensed, and laser processing is performed in a state where the laser beam is not in the ring-shaped mode, whereby high processing accuracy can be obtained.

It is considered that when the ring-shaped mode changes to a mode in which the hollow portion disappears, the light intensity distribution of the laser beam can be made flat over a relatively large area.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the embodiment of the present invention, why the conventional technique makes it difficult to perform spot welding of thin plates by overlapping is considered.

FIG. 6A is a graph schematically showing a light intensity distribution in a laser spot. The horizontal axis indicates the radial position R of the beam, and the vertical axis indicates the light intensity I. The light intensity distribution is as shown in the figure.

When the beam intensity increases, the half width does not change much, and the peak height of the light intensity increases. Therefore, the central part of the laser spot is greatly affected by the increase and decrease of the light intensity.

FIG. 6B schematically shows a penetration shape in lap welding of thin plates. It is assumed that the workpieces 5 and 7 in a thin plate shape are superimposed, and a part thereof is irradiated with laser light to perform spot welding. Penetration shape 11
Indicates a penetration shape when an appropriate laser energy is given. In the case of this penetration shape, the welding strength is high and welding marks do not appear on the surface of the workpiece 7.

By the way, when the light intensity of the laser beam is increased and the energy given to the workpieces 5 and 7 is increased, the temperature rise is particularly high at the center of the beam, and the melted portion at the center like the penetration shape 12 Reaches the back surface of the workpiece 7. In this state, welding marks are formed on the back surface of the workpiece.

FIG. 6C shows a case where the light intensity of the laser beam is reduced. Since the energy given to the workpieces 5 and 7 decreases, the penetration shape 13 becomes shallow, and the fusion area at the boundary between the workpieces 5 and 7 becomes narrow. Therefore, in the case of FIG. 6C, the welding strength is reduced.

It is considered that the light intensity distribution shown in FIG. 6A generally occurs when laser light is focused. In the case of spot welding using this light intensity distribution, phenomena as shown in FIGS. 6B and 6C are unavoidable due to variations in laser output.

The present inventors have thought that if the light intensity at the center of the laser beam spot is made uniform, the penetration shape can be relatively stabilized even if the output of the laser fluctuates. In order to achieve a flat light intensity distribution, a ring-shaped mode laser beam is used. However, the laser beam in the ring mode is not used as the ring mode, but used in a state where the ring mode has disappeared.

FIG. 1 is a conceptual view schematically showing a laser processing method according to an embodiment of the present invention. FIG. 1A schematically shows a state in which a thin plate is overlapped and spot-welded using a laser beam. The laser beam 2 is provided as a substantially parallel light beam. A mask 3 is placed at the center of the laser beam 2 to block the center of the laser beam 2. On the downstream side of the mask 2, the energy distribution of the laser beam has a hollow ring shape having a hollow portion. This state is indicated by P1. The laser beam in the ring mode is focused by the processing lens 4. Since the laser light in the ring-shaped mode is also formed from a parallel light beam, if it is condensed by the lens 4, it is condensed in a spot shape.

On the downstream side of the lens 4, the beam diameter gradually decreases. The diameter of the central part also becomes smaller gradually.
An intermediate stage in which the beam diameter is reduced is indicated by P2. Eventually, at the stage where the beam diameter has been reduced to some extent, the inner edges of the light intensity distribution of the laser beam in the ring-shaped mode come into contact with each other,
The state changes from the hollow state to a solid continuous shape state. This state is indicated by P3.

A laser beam in a ring-shaped mode is condensed, and a laser beam is applied to a workpiece on which workpieces 5 and 7 are superimposed at a position where the hollow portion has disappeared. FIG. 1 (B
1), (B2) and (B3) correspond to the positions P1 and P, respectively.
2 shows the in-plane distribution of laser light at P3. FIG. 1 (B
In (1) and (B2), the distribution of the laser beam is indicated by a ring-shaped region 8, and a hollow region 9 not irradiated with the laser beam exists in the center of the ring-shaped region.

When the state shown in FIG.
Disappears, and a circular area 8a continuously irradiated with laser light is generated. 1 (C1), (C2), and (C3) schematically show the light intensity distributions of the laser light at positions P1, P2, and P3, respectively. FIG. 1 (C1), (C2), (C3)
In FIG. 1, the abscissa axis represents FIGS. 1B1, B2,
The X coordinate corresponding to the horizontal position (B3) is taken, and the light intensity I is taken on the vertical axis. In the state at the position P1, a ring-shaped light intensity distribution having a relatively wide width is generated corresponding to the ring-shaped mode.

At the position P2, the laser light is considerably focused, the diameter of the ring is reduced, and the light intensity I is increased. It should be noted that, in the figure, since the light intensity is schematically shown, the height of the peak is not true. In practice, the light intensity is further increasing.

The light condensing action proceeds, and no ring-shaped mode exists any more downstream of the position P3, resulting in a solid circular light intensity distribution. In this state, FIG.
A continuous light intensity distribution occurs as shown in 3).

When the inner edge of the ring starts to contact, the light intensity at the original peak position of the ring-shaped mode is higher than the light intensity at the central portion, and the light intensity distribution is concave at the central portion. .

As the light condensing state progresses, the light intensity distribution at the central portion becomes almost flat. Further, below the focal position, a substantially flat light intensity distribution appears at the center, and the center is eventually dented, returning to the ring mode.

FIG. 2 schematically shows a state in which a laser beam in a ring-shaped mode has a circular mode in appearance and is converged by a lens. In the light intensity distribution of the ring-shaped mode, the left portion 10a and the right portion 10b are combined, and as a result, a substantially flat light intensity distribution 10c is generated (the focused beam spot diameter is the same as the conventional diameter). In this state, if the laser output is increased, it appears most remarkably at the peaks of the light intensity distributions 10a and 10b, but the combined light intensity distribution 10c shows little change due to the increase in the laser output.

FIG. 2 shows the energy intensity in a linear cross section, but this phenomenon actually occurs at the ring portion on a plane. The light intensity distribution in the central portion according to the prior art shown in FIG. 6A greatly changes in the central portion of the light intensity distribution with a change in the laser output, whereas the light intensity distribution shown in FIG. The peak portion of the light intensity increases / decreases, and the increase / decrease level of the combined light intensity decreases.

FIG. 3 shows a pulse waveform of the laser output.
FIG. 3A shows a pulse waveform of the laser output as a function of time when normal pulse oscillation is performed. When the pulse laser oscillates, its output sharply increases at the rising edge of the pulse, and immediately attenuates to take a substantially constant value. After the set pulse time, the output sharply decreases.

The present inventors performed superposition spot welding using the laser light in the modified ring mode shown in FIGS. 1 and 2 and the pulse waveform shown in FIG. Was.

For further improvement, a pulse having a waveform shown in FIG. 3B was used. In the pulse waveform of FIG. 3 (B), when the output rises, it first stabilizes at a certain value,
Eventually, the output is further increased and stabilized again at a high output. By using the pulse waveform controlled in such a manner, a better result was obtained in the overlap spot welding.

The result is that, rather than raising the temperature from room temperature to the molten state at once, preheating is performed, and the laser absorption rate is increased by increasing the surface temperature of the workpiece and forming surface oxides. Heating to a high temperature to form a molten state indicates that the laser beam is more stably absorbed and a stable welding result can be obtained.

FIG. 4 schematically shows a typical example of the penetration shape obtained in such lap spot welding. The workpieces 5 and 7 are superimposed, and spot welding is performed by irradiating laser light in a modified ring mode from the upper surface.

The laser light to be irradiated has a substantially uniform energy intensity in a certain circular area, so that a uniform penetration is formed over a relatively large area, and a wide penetration shape 20 with a flat bottom surface is obtained. Since the penetration shape 20 has a large area at the boundary between the workpieces 5 and 7, the welding strength is high.

Also, since the bottom of the penetration shape 20 is substantially flat, the penetration shape 20 does not reach the back surface of the workpiece 7 even if the boundary between the workpieces 5 and 7 has a large area. Accordingly, no weld marks are formed on the workpiece 7, and an excellent appearance can be obtained.

In one example, spot welding was performed by using a YAG laser as a laser and superposing a 0.1 mm thick copper alloy plate and a 0.2 mm thick laminated plate. The laser used was a Nd: YAG laser device whose output was 5
W. The pulse energy was 2.75 J / pulse, and had a two-step pulse waveform as shown in FIG. FIG. 5 shows a photograph of the metal structure of the welded portion obtained by the spot welding.

The laser beam was applied from above, and a copper alloy plate having a thickness of 0.1 mm was placed on the upper side. On the lower side, a thickness of 0.
A 2 mm laminate is arranged. The photograph shows only a part of the lower laminate. The penetration shape protrudes downward from the copper alloy plate having a thickness of 0.1 mm in a wide area, but the projection height is 0.03 mm or less. High welding strength was obtained by this welding. Also, no welding marks were observed on the back surface.

Although a case has been described in which a mask is arranged at the center of a coherent laser beam in order to form a ring mode laser, a ring mode laser can be formed in other forms. For example, a ring mode laser as disclosed in JP-A-63-16893 may be used.

The mode may be converted to a ring mode by using optical components such as a prism, a mirror, and a lens. Although the case where the laser beam in the modified ring mode is used for performing the spot welding has been described, the processing using the laser beam in the modified ring mode can be applied to other laser processing. When it is desired to perform laser processing with a uniform laser beam intensity, the laser in the above-mentioned modified ring mode is effective. The laser is YAG
Not limited to lasers, various lasers can be used.

The present invention has been described in connection with the preferred embodiments.
The present invention is not limited to these. For example,
It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0043]

As described above, since a relatively uniform energy distribution can be obtained over a wide area, uniform laser processing can be performed over a wide area.

In the case of spot welding, since the penetration shape is flattened, it is also possible to perform spot welding in which thin plates are overlapped.

[Brief description of the drawings]

FIG. 1 is a schematic view for explaining a laser processing method according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram showing the effect of fluctuations in laser output in the embodiment of FIG.

FIG. 3 is a graph showing a pulse waveform of a pulse laser beam.

FIG. 4 is a cross-sectional view showing a penetration shape in lap spot welding.

FIG. 5 is a micrograph showing a metal structure of a cross section of a sample obtained by performing lap welding of thin plates.

FIG. 6 is a graph and a cross-sectional view for explaining overlap spot welding according to a conventional technique.

[Explanation of symbols]

 2 Laser beam 3 Mask 4 Lens 5, 7 Workpiece 8 Ring-shaped area 9 Hollow area 8a Modified ring-shaped area

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B23K 26/00-26/18

Claims (2)

(57) [Claims] A step of forming a laser beam having a ring-shaped light intensity distribution in a plane perpendicular to the light traveling direction including a hollow portion; and a temporal change in the light intensity of the laser beam in a pulse shape; A step of controlling the waveform so that the latter half of the pulse has a higher light intensity than the former half of the pulse; a step of condensing the laser beam; and a light intensity distribution in a plane perpendicular to the light traveling direction. Irradiating the workpiece with the laser beam on the workpiece at a position where the workpiece has a continuous shape. A step of forming a ring-shaped laser beam having a light intensity distribution in a plane perpendicular to the light traveling direction including a hollow portion; a step of condensing the laser beam; Irradiating the laser beam onto the workpiece at a position where the light intensity distribution in the vertical plane has a continuous shape without a hollow portion, and performing the processing, wherein the workpiece is a laminated thin plate. A laser processing method, wherein the processing is spot welding.