KR20010057418A - Laser Welding Method Utilizing Multi Spot - Google Patents

Abstract

PURPOSE: A laser welding method is provided to obtain a deeper penetration as well as a 'V' shaped profile of the welding part by positioning a plurality of focal positions of laser beam inside a material in an optical axis direction. CONSTITUTION: In a welding method in which the material is jointed by melting a target material using laser, the laser welding method using an optical axis directional multi-focal method comprises the process of forming two or more focuses of laser beam by the laser at a position which is lower than the upper surface of the target material and higher than the lower surface of the target material in an optical axis direction, wherein an optical lens used in the laser has a shape in which the lens is divided into two lenses having different focal distances based on the straight line passing through the center, and an optical lens used in the laser has a shape in which two or more lenses having different focal distances in a concentric circle direction based on the center are integrated.

Description

Laser welding method using optical axis multi-focus method {Laser Welding Method Utilizing Multi Spot}

The present invention relates to a method of melting and welding a material with a laser, and more particularly, to a laser welding method capable of deeper penetration by forming two or more focal points in the optical axis direction.

Laser welding is a method of melt welding materials using high energy density by integrating laser light energy in a small area, and has been applied to places where precision and high quality welding is required, such as the electronic parts industry and the automotive industry. Current laser welding techniques have had commercial advantages primarily for thin plates (less than 3 mm thick) due to limitations in laser power. However, laser welding technology of thicker materials is required in shipbuilding and construction industries.

In laser welding, much research has been made on increasing penetration depth. For example, using a CW (Continuous Wave) 6kW CO ₂ laser, a maximum penetration depth of about 1 mm / min can be obtained at about 12 mm. When using high power laser, deep penetration can be obtained. In case of CW 20kW CO ₂ laser, 20mm penetration can be obtained at welding speed of 1m / min, but the laser itself is expensive and the system size is commercially available. It will be out of the available range.

In order to increase the depth of penetration, the method proposed to date has been proposed to connect two or three lasers in parallel (US 5325393, "Dual laser resonator and beam combiner"). In US 5325393, a method of synthesizing two types of lasers having different output laser wavelength bands is presented. An optical filter with different optical characteristics was used according to 1064nm and 1044nm input lasers having two wavelength bands of 1044nm and 1064nm, respectively. However, this method is inadequate for the synthesis of lasers having the same wavelength band output.

As another method, a method of arranging three laser welding heads so as not to interfere with each other has also been proposed (Toru Narikiyo et al, "YAG laser welding with combination system of three oscillators", ICALEO (1995), pp885,1995). When the three welding heads are used in combination, the volume and weight are so large that it is difficult to mount them on a robot or a computer numerical control (CNC), which is an obstacle to automation. In addition, the welds were irregular, inclined, and the penetration depth was minimal.

On the other hand, the focal position is an important process variable in laser welding. Wilgoss (Wilgoss et al, Weld. Met. Fabr. March 1979, pp 179, 1979) used a 6mm-thick stainless 310 material to change the focus position of a 5kW CO ₂ laser by 2.5mm. As a result of observing the welded cross section, the welded cross section is V-shaped if the focal point is deep below the surface, and the nail head-shaped welded part is created when the focal point is located on the surface. (See Figure 1).

Accordingly, an object of the present invention is to provide a laser welding method capable of obtaining a deeper penetration and at the same time obtaining a V-shaped weld cross section by placing a plurality of laser beam focal positions in the optical axis direction within a material. .

1 is a schematic diagram showing the shape change of the welded portion according to the focus position

Figure 2 (a) is a schematic diagram for explaining the focusing of the short focus laser welding method

(b) is a schematic diagram illustrating the focusing of a multifocal (two focus) laser welding method

3 (a) is a shape diagram of a conventional short focal optical lens

(b) is an optical lens showing an example of a multifocal lens according to the present invention

(c) is a diagram of an optical lens showing an example of a multifocal lens according to the present invention;

* Description of the symbols for the main parts of the drawings *

1 ... Welding material 2 ... Laser beam focus position

3 ... Welding material surface 4 ... Laser beam path

5 ... First focus in the optical axis 6 ... 2nd focus in the optical axis

The present invention for achieving the above object is a welding method for melting and bonding a target material using a laser, wherein the focus of the laser beam by the laser is lower than the upper surface of the target material and higher than the lower surface, the optical axis The present invention relates to a laser welding method using an optical axis direction multifocal method, characterized by forming two or more in the direction.

Hereinafter, the present invention will be described in detail.

The present invention focuses on the change of penetration according to the focal position, so that two or more multiple foci of the interior of the material are positioned for increasing the depth of penetration. Preferably, the first focal point is located near the surface of the material and the second or more focal points are located inside the material to improve the penetration depth. For example, the case in which the two positions are focused can be performed as shown in FIG. 2 (b), which is different from the conventional single focus method as shown in FIG. 2 (a).

In order to implement the multifocal as described above, for example, an optical lens as shown in FIG. 3 (b, c) may be proposed in which the existing optical lens as shown in FIG. 3 (a) is modified.

In the multifocal optical lens as shown in FIG. 3 (b), two focal points having different focal positions in the optical axis direction can be formed by dividing the focal length of the lens center by dividing the focal length from the lens center. That is, the multifocal lens may be formed as if the lens is divided into two lenses having different focal lengths based on a straight line passing through the center.

In addition, in the multifocal lens as shown in FIG. That is, the multifocal lens may be formed as having a form in which two or more lenses having different focal lengths in the concentric direction with respect to the center are integrated.

In addition to the above-mentioned multifocal lens, any one of the lenses capable of forming a multifocal lens in the optical axis direction may be applied to the present invention. That is, the present invention is not limited to FIG. 2 (b, c).

When the laser light is incident on the multifocal lens, the first focal point is formed near the surface of the material, and the second or more focal point is formed inside the material, and the material is welded by the high density laser beam. The first focal point creates a keyhole near the surface of the material, and serves to secure a space so that the laser beam energy corresponding to the second or more focal points is transmitted deeply inside the material.

On the other hand, since the energy density irradiated to the material is the most important process variable in laser welding, the depth of penetration can be obtained by placing a plurality of focal positions within the material.

In the multifocal welding method of the present invention, the distance between two focal points becomes an important variable. When the distance between the two focal points is smaller than the proper interval, the weld width tends to be wider than the increase of penetration depth, and when the distance between the two focal points is larger than the proper interval, the weld width in the depth direction is not constant. The experimentally determined focal spacing is considered to be about 2 to 4 times the depth of focus of the laser beam. However, such an appropriate interval is not limited to this because it may vary from laser system to laser system.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example

Welding was performed by applying a short focal length lens as shown in Fig. 3 (a) and a multifocal lens as shown in Fig. 3 (b) to the CO ₂ laser.

The laser used was 3kW continuous power, and the optical lens used for the single focus welding method was 7.5 inches in focal length, and the optical lens used for the multifocal welding method was shown in Fig. 3 (b), and the focal lengths were 7.5 inches and 7.578 inches, respectively. The distance between the two focal points was about 2mm. In addition, the same welding speed of 1mpm was applied. After welding, the depth of penetration in the case of the single focus welding method and the case of the multi focus welding method was measured, and the results are shown in Table 1 below.

Single focus welding Multifocal welding Laser power 3 kW 3 kW Welding speed 1 mpm 1 mpm Lens focal length 7.5 inches 7.7 inches + 7.578 inches Penetration depth 2.7 mm 3.3mm

As can be seen in Table 1, the depth of penetration is 2.7mm in the single-focal welding method, 3.3.mm was implemented in the multifocal welding method, which means that a better penetration depth can be obtained according to the present invention.

On the other hand, by applying the lens of the shape as shown in Fig. 3 (b), the welding was performed while changing the distance between the two focal points, when smaller than the proper interval, the weld width tended to be wider than the increase in penetration depth, proper interval In the larger case, the weld width in the depth direction was inconsistent. The focal length in this example was three times better than the Rayleigh length of the laser beam, and more preferably 2-4 times.

According to the present invention as described above, by placing a plurality of focal positions in the material in the laser welding, a method of increasing the depth of penetration by synthesizing a conventional high output laser and a method of geometrically arranging three welding heads Compared with this, it is easy to automate and excellent effect can be obtained in penetration increase.

Claims (4)

In the welding method of melting a target material by using a laser and bonding it, The laser welding method using the optical axis direction multifocal method, wherein the focus of the laser beam by the laser is formed at a position lower than the upper surface of the target material and higher than the lower surface in the optical axis direction. The method of claim 1, Optical lens used in the laser is a laser welding method using a multi-axis optical axis direction characterized in that it has a form divided into two lenses having a different focal length based on a straight line passing through the center The method of claim 1, The optical lens used in the laser is a laser welding method using an optical axis multifocal method characterized in that the two or more lenses having different focal lengths in a concentric circle direction with respect to the center is integrally formed. The method according to any one of claims 1 to 3, The focal length is a laser welding method using an optical axis direction multifocal method, characterized in that the interval between the shortest focus and the longest focus is 2 to 4 times the depth of focus of the laser beam.