JPH07214360A - Laser beam machining - Google Patents

Abstract

PURPOSE:To realize the uniform laser beam machining by providing a process to form the laser beam where the distribution of the laser beam intensity is of the ring shape including the hollow part, a process where the laser beam is converged, and a process where a work is irradiated with the laser beam at the position of the continuous shape without the hollow part. CONSTITUTION:A mask 3 is placed in the center of the laser beam 2 to shield the center part of the laser beam 2. The diameter of the laser beam is gradually reduced and the diameter of the center part also becomes smaller gradually on the downstream side of a lens 4 to converge the laser beam of the ring- shaped mode to the spot shape by using the machining lens 4. The inner edge of the ring-shaped distribution of the laser beam intensity is brought into contact with each other in the stage where the beam diameter is reduced, and the hollow condition is changed to the solid continuous shape. The laser beam in the ring- shaped mode is converged and the stacked works 5, 7 at the position where the hollow part disappears are irradiated with the laser beam. This constitution obtains the uniform energy distribution with wide area.

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 a laser beam having a ring-shaped energy distribution.

[0002]

2. Description of the Related Art When laser light is used, high energy density spots can be formed and can be used in various processing techniques. For example, a laser processing technique for cutting and welding a metal plate is known. A laser irradiation tool such as a trepanning head irradiates a processing object with laser light to perform processing such as cutting and welding.

By the way, there is welding that is difficult to carry out by such a general laser processing technique. One of them is lap spot welding of thin plates. In electronic devices and the like, it is desirable to stack two thin metal plates and perform spot welding.

This spot welding is required to have high welding strength and no weld 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 at the irradiation portion will melt over the entire thickness, and not only welding marks will be produced 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 weld strength is reduced.
In extreme cases, no welding is done.

Generally, a metal surface has a property of reflecting laser light. However, no matter how high the reflectance is, if the irradiation energy of the laser light is sufficiently high, the metal surface will melt. The once-melted metal surface sharply reduces the reflectance and absorbs the laser light more greatly.

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

[0007]

In lap spot welding of thin plates using a laser, it is not easy to simultaneously realize high welding strength and the absence of welding marks on the back surface of the weld.

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

[0009]

A laser processing method of the present invention comprises a step of forming a laser beam in which a light intensity distribution in a plane perpendicular to the traveling direction of light is a ring shape including a hollow portion,
The step of converging the laser beam and the process of irradiating the laser beam onto 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 the step of performing.

[0010]

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

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

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

[0013]

EXAMPLES Prior to the examples of the present invention, it will be considered why, according to the prior art, it was difficult to perform overlay spot welding of thin plates.

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

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

FIG. 6 (B) schematically shows a penetration shape in lap welding of thin plates. It is assumed that the thin plate-shaped workpieces 5 and 7 are overlapped with each other and a part thereof is irradiated with laser light to perform spot welding. Penetration shape 11
Shows the penetration shape when appropriate laser energy is applied. 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 increases and the energy applied to the workpieces 5 and 7 increases, the temperature rises particularly at the central portion of the beam, and like the penetration shape 12, the melted portion at the central portion. 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 the case where the light intensity of the laser beam is reduced. Since the energy applied to the workpieces 5 and 7 decreases, the penetration shape 13 becomes shallow and the melting area at the boundary between the workpieces 5 and 7 becomes narrow. Therefore, in the case of FIG. 6C, the welding strength is reduced.

The light intensity distribution shown in FIG. 6A is considered to occur almost generally when the laser light is focused. When spot welding is performed using this light intensity distribution, phenomena such as those shown in FIGS. 6B and 6C cannot be avoided due to variations in laser output.

The inventors of the present invention thought that if the light intensity at the central portion of the laser beam spot is made uniform, the melted shape can be relatively stabilized even if there is a laser output fluctuation. A ring-shaped mode laser beam is used to realize a flat light intensity distribution. However, the laser beam in the ring-shaped mode is not used as the ring-shaped mode, but is used in the state where the ring-shaped mode disappears.

FIG. 1 is a conceptual diagram schematically showing a laser processing method according to an embodiment of the present invention. FIG. 1 (A) schematically shows a state in which thin plates are superposed and spot welded using a laser beam. The laser beam 2 is given as a substantially parallel luminous flux. A mask 3 is placed at the center of the laser beam 2 to shield 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 condensed by the processing lens 4. Since the ring-shaped mode laser light is also formed from a parallel light flux, if it is focused by the lens 4, it is focused in a spot shape.

On the downstream side of the lens 4, the beam diameter becomes gradually smaller. The diameter of the central portion also gradually decreases.
An intermediate stage in which the beam diameter is reduced is indicated by P2. Eventually, when the beam diameter was reduced to some extent, the inner edges of the light intensity distribution of the ring-shaped mode laser beam touched each other,
The hollow state changes to a solid continuous shape. This state is indicated by P3.

A ring-shaped laser beam is focused, and a laser beam is applied to a processing object in which the processing objects 5 and 7 are superposed at a position where the hollow portion disappears. Figure 1 (B
1), (B2) and (B3) are at positions P1 and P, respectively.
2 shows the in-plane distribution of laser light at P3. Figure 1 (B
In 1) and (B2), the distribution of the laser beam is shown by the ring-shaped region 8, and the hollow region 9 which is not irradiated with the laser beam exists in the center thereof.

In the state of FIG. 1 (B3), the hollow region 9
Disappears, and a circular region 8a continuously irradiated with laser light is generated. 1 (C1), (C2), and (C3) schematically show the light intensity distributions of the laser light at the positions P1, P2, and P3, respectively. Figure 1 (C1), (C2), (C3)
In Fig. 1, the horizontal axis is shown in Fig. 1 (B1), (B2),
The X coordinate corresponding to the horizontal position of (B3) is taken, and the light intensity I is taken on the vertical axis. In the state of the position P1, a relatively wide ring-shaped light intensity distribution corresponding to the ring-shaped mode is generated.

At the position P2, the laser light is considerably condensed, the diameter of the ring is reduced, and the light intensity I is increased. In addition, in the figure, since the light intensity is schematically shown, the peak height is not faithful. In reality, the light intensity is further increasing.

Due to the progress of the focusing action, the ring-shaped mode no longer exists in the downstream side of the position P3, and a solid circular light intensity distribution is obtained. In this state, FIG.
As shown in 3), a continuous light intensity distribution is generated.

In the state where the inner edges of the rings are in contact with each other, 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-collecting state progresses, the light intensity distribution in the central portion eventually becomes almost flat. Further, when the position is below the focal position, a substantially flat light intensity distribution appears in the central part, and eventually the central part is dented and the ring mode is restored.

FIG. 2 schematically shows a state in which the laser beam in the ring-shaped mode is a circular mode in appearance and is condensed by the lens. The light intensity distribution in the ring mode is a combination of the left side portion 10a and the right side portion 10b, and as a result, a substantially flat light intensity distribution 10c is generated (the focused beam spot diameter is similar to the conventional diameter). In this state, if the laser output increases, the peaks of the light intensity distributions 10a and 10b appear most remarkably, but the combined light intensity distribution 10c shows little change due to the increase of the laser output.

Although FIG. 2 shows the energy intensity in a linear cross section, this phenomenon actually occurs in the ring portion on the plane. The light intensity distribution in the central portion according to the conventional technique shown in FIG. 6A greatly changes in the central portion of the light intensity distribution as the laser output changes. In contrast, the light intensity distribution shown in FIG. 2 has a circular light intensity. The peak portion of increases and decreases and the combined light intensity has a smaller increase and decrease level.

FIG. 3 shows the pulse waveform of the laser output.
FIG. 3A shows the pulse waveform of the laser output when performing normal pulse oscillation, as a function of time. When the pulse laser oscillates, its output sharply increases at the rising portion of the pulse and immediately attenuates to a substantially constant value. The output decreases sharply after the set pulse time.

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

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

This result indicates that rather than heating from room temperature to the molten state all at once, preheating is performed to increase the laser absorption rate due to the increase in the surface temperature of the workpiece and the formation of surface oxides, and thereafter It means that the laser beam is more stably absorbed and the stable welding result is obtained by heating to a high temperature to bring it into a molten state.

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

Since the radiated laser light has a substantially uniform energy intensity in a certain circular area, a uniform penetration is formed over a relatively wide area and a flat penetration surface 20 having a flat bottom surface is obtained. Since the penetration shape 20 shows a large area at the boundary between the workpieces 5 and 7, the welding strength is strong.

Further, since the bottom of the melted shape 20 is substantially flat, the melted shape 20 does not reach the back surface of the workpiece 7 even if it has a large area at the boundary between the workpieces 5 and 7. Therefore, welding marks are not generated on the workpiece 7, and an excellent appearance can be obtained.

In one example, a YAG laser was used as a laser, and a copper alloy plate having a thickness of 0.1 mm and a laminated plate having a thickness of 0.2 mm were superposed and spot welding was performed. The laser used was an Nd: YAG laser device, the output of which was 5
It was W. The pulse energy was 2.75 J / pulse, which had a two-step pulse waveform as shown in FIG. 3 (B). A photograph of the metal structure of the welded portion obtained by this spot welding is shown in FIG.

Laser light was emitted from the upper side, and a copper alloy plate having a thickness of 0.1 mm was arranged on the upper side. On the lower side, the thickness is 0.
A 2 mm laminated plate is arranged. In the photograph, only a part of the lower laminated plate is shown. The penetration shape projects downward from a 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. No welding marks were found on the back surface.

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

Optical components such as prisms, mirrors, and lenses may be used to convert to a ring mode. Further, although the case where the laser beam in the modified ring mode is used for spot welding has been described, the processing with 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 light intensity, the above-mentioned modified ring-shaped mode laser is effective. The laser is YAG
Not limited to lasers, various lasers can be used.

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

[0043]

Since a relatively uniform energy distribution can be obtained in a wide area, uniform laser processing can be performed in a wide area.

In the case of spot welding, the penetration shape is flattened, so that spot welding of superposed thin plates is also possible.

[Brief description of drawings]

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

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

FIG. 3 is a graph showing a pulse waveform of pulsed laser light.

FIG. 4 is a cross-sectional view showing a penetration shape in overlay 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 superposition spot welding according to a conventional technique.

[Explanation of symbols]

 2 laser beam 3 mask 4 lens 5, 7 workpiece 8 ring-shaped region 9 hollow region 8a modified ring-shaped region

Claims (3)

[Claims] 1. 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, and A laser processing method, comprising the step of irradiating a laser beam onto a workpiece to perform processing at a position where the light intensity distribution in a vertical plane has a continuous shape without a hollow portion. 2. The method according to claim 1, further comprising a step of controlling the light intensity of the laser beam with time in a pulse form, and controlling the waveform so that the light intensity is higher in the latter half of the pulse than in the former half of the pulse. Laser processing method. 3. The work piece is a laminated thin plate,
The laser processing method according to claim 1, wherein the processing is spot welding.