WO2015189883A1

WO2015189883A1 - Laser welding method

Info

Publication number: WO2015189883A1
Application number: PCT/JP2014/065172
Authority: WO
Inventors: 雅徳宮城; 旭東張
Original assignee: 株式会社日立製作所
Priority date: 2014-06-09
Filing date: 2014-06-09
Publication date: 2015-12-17

Abstract

A laser welding method whereby an object being welded is bombarded by a laser and another heat source, wherein the object being welded is bombarded by the laser and the other heat source in a manner such that at least a portion of the weld pool formed by the laser bombardment and the weld pool formed by the other heat source overlap each other, and the object being welded is constantly bombarded by the laser at an area in front of the center of bombardment of the other heat source, in the direction in which the welding progresses.

Description

Laser welding method

The present invention relates to a laser welding method.

Laser welding has been used in recent years because it can be welded with higher penetration than conventional arc welding because it can be welded with deep penetration. The reason why welding with deep penetration is possible is that the laser has a higher power density than arc welding or the like, so that the metal irradiated with the laser instantaneously melts and evaporates. Due to the high reaction force due to the evaporation, the melting part is pushed down, and a space called a keyhole is formed. Since the laser can reach the inside of the material through the keyhole, welding with deep penetration is achieved.

However, even in laser welding, there are welding defects such as porosity (spatter), spatter (scattered matter), and cracks, and it is difficult to completely suppress these defects in current laser welding. As a solution to this problem, Patent Document 1 superimposes two laser beams with different condensing diameters, and periodically moves at least the laser beam with the smaller condensing diameter of the two laser beams in the same direction as the laser traveling direction. A method for reducing porosity by (weaving) has been proposed.

JP 2007-319878

∙ Spatter on the part surface may come off during assembly or product use. When the product is a fluid machine, the spatter that has been peeled off may flow along with the fluid, causing clogging in the middle of the flow path. Since clogging becomes more pronounced as the welded parts become smaller, it is required to reduce the occurrence of spatter, particularly among defects, when laser welding a small fluid machine.

However, in the method of Patent Document 1, surface defects due to sputtering are not sufficiently considered. The front part of the keyhole is a part where a laser or the like will be melted from now on, so even if spattering occurs, the surface of the welding object is not greatly affected. However, since the back of the keyhole is a part that will solidify, surface defects are more likely to occur than the front.

In Patent Document 1, since the laser B1 forming the keyhole is weaved starting from the irradiation center of the laser B2 having the larger condensing diameter (FIG. 2 of Patent Document 1), the laser B1 is moved backward in the laser traveling direction. When weaving, the molten pool behind the keyhole becomes smaller. Therefore, there is a problem that spatter is easily generated during welding.

An object of the present invention is to reduce the generation of spatter.

The above object is achieved by the invention described in the claims.

According to the present invention, the generation of spatter can be reduced.

Schematic diagram of longitudinal section of molten pool formed by laser Schematic diagram of longitudinal section of molten pool formed by laser Appearance of laser welding equipment Irradiation position relationship between the first laser and the second laser Schematic diagram of the molten pool formed by the first laser and second laser irradiation Cross-sectional shape schematic diagram during welding Schematic diagram of longitudinal section during welding Irradiation position relationship between the first laser and the second laser External view of laser welding equipment First and second laser irradiation position relationship and second laser scanning trajectory First and second laser irradiation position relationship and second laser scanning trajectory

FIG. 1A is a vertical (welding direction 13) cross-sectional schematic view of a weld pool 15 formed only by a laser. At the moment when the welding object 9 is irradiated with the laser, the metal is melted and evaporated to form a keyhole 14, and a molten pool 15 in which the metal is melted is formed around the keyhole 14. Since the pressure inside the keyhole 14 becomes high at the moment when the keyhole 14 is formed, the molten pool 15 receives a large force from the keyhole 14 and the solid metal around the molten pool 15. Reference numeral 17 denotes the flow of the molten pool.

When the area of the molten pool 15 is narrow, there is no escape place for the molten metal, and the molten metal jumps out of the molten pool 15 as the sputter 20 and adheres to the surface of the solid metal in the vicinity of the welded portion, which tends to cause surface defects. Alternatively, the molten metal is pushed out to the keyhole 14 side (19 in the figure), interferes with the laser, scatters outside the keyhole 14, and easily adheres to the surface of the solid metal near the weld.

In this embodiment, members are welded using both a laser that performs deep penetration welding and a heat source that heats and melts the periphery of the molten pool so as to expand the molten pool formed by laser irradiation. It is.

It should be noted that the present invention is not limited to the embodiments taken up here, and can be combined and improved as appropriate without departing from the scope of the invention.

FIG. 1B is a schematic vertical cross-sectional view of a molten pool formed using a laser and another heat source. In this embodiment, the molten pool 16 which melt | dissolved the circumference | surroundings of the molten pool 15 formed with a laser is further formed using another heat source. Then, by always irradiating the laser forward from the center of the irradiation range of the heat source, the keyhole 14 is always arranged at the front portion in the

molten pools

15 and 16 with respect to the welding progress direction 13, and the welding progresses. It is possible to form

molten pools

15 and 16 that are particularly widened behind the keyhole 14 with respect to the direction 13.

This makes it possible to expand the region where the molten metal that has received the pressure from the keyhole 14 can convect. Therefore, it is possible to reduce the occurrence of molten metal jumping out of the

molten pools

15 and 16 and to reduce the possibility that the molten metal is pushed into the keyhole 14 and interferes with the laser, so that sputtering can be suppressed. Even if spatter is generated, since the molten pool 16 is large, the spatter can drop into the molten pool and disappear. Therefore, almost no spatter adheres to the surface of the solid metal after the molten pool has solidified.

The heat source only needs to be able to melt the metal to be welded, and examples thereof include lasers, arcs, and plasmas. In particular, when a laser is used, a deep molten pool can be formed instantaneously, so that the range in which the molten metal near the keyhole can flow can be quickly expanded in the depth direction of the welding object. As a result, the escape area of the molten metal that has been subjected to pressure from the keyhole can be quickly formed. Further, since a fine region can be processed, it is preferable when it is desired to reduce the welded portion.

Hereinafter, embodiments in which a laser is used as a heat source will be described in detail with reference to the drawings. In addition, this invention is not limited to the Example taken up here, A combination and improvement are possible suitably in the range which does not change a summary.

FIG. 2 shows the appearance of the laser welding apparatus of Example 1. 1 is a first laser oscillator, 2 is a second laser oscillator, 3 is an optical fiber for a first laser, 4 is an optical fiber for a second laser, 5 is an optical head for a first laser, 6 Is an optical head for a second laser, 7 is a first laser, 8 is a second laser, 9 is an object to be welded, 10 is a processing table, 11 is a shield gas nozzle, and 12 is a shield gas.

In this example, the welding object 9 was 304 stainless steel. The first laser 7 was a fiber laser having a wavelength of about 1070 nm, and the second laser 8 was a semiconductor laser having a wavelength of about 900 nm. The welding direction is from left to right in the figure. The first laser was applied while being inclined 10 ° rearward from the irradiation axis of the second laser with respect to the welding progress direction. The shielding gas 12 was nitrogen gas.

The laser generated by the first laser oscillator 1 is sent to the optical head 5 for the first laser through the optical fiber 3 for the first laser. The first laser 7 is condensed by an optical head and irradiated to the welding object 9. The laser generated by the second laser oscillator 2 is sent to the optical head 6 for the second laser through the optical fiber 4 for the second laser. The second laser 8 is converted into a ring-shaped beam by the optical head, and is irradiated to the welding object 9.

FIG. 3 shows the irradiation position relationship between the first laser and the second laser. Reference numeral 13 denotes a welding progress method. The first laser 7 was arranged so as to irradiate inside the irradiation position of the second laser 8 and in front of the irradiation center so that the first laser 7 and the second laser 8 do not interfere with each other. Since the second laser 8 expands with the molten pool formed by the first laser 7, it is preferable that the irradiation area is larger than that of the first laser 7.

The shape of the first laser beam on the surface of the welding object 9 was a circle, and the beam diameter on the surface of the welding object 9 was 0.1 mm. The second laser beam shape was an elliptical ring shape, the major axis outer diameter was 10 mm, the minor axis outer diameter was 4 mm, and the ring width was 1 mm. The welding direction was from left to right in the figure.

FIG. 4 is a schematic view of a molten pool at a certain moment formed by the first laser irradiation and the second laser irradiation, and is a top view of the welding object. 14 is a keyhole formed by the first laser irradiation, 15 is a molten pool formed by the first laser irradiation, and 16 is a molten pool formed by the second laser irradiation. In the figure, the weld bead formed behind the molten pool is omitted as the welding operation proceeds.

In the present embodiment, by irradiating a ring-shaped second laser 8 around the first laser 7, the molten pool can be expanded as compared with the case where welding is performed only with the first laser 7 forming the keyhole. Is possible. The irradiation position of the second laser 8 may be the edge (outer edge) or the outer periphery of the molten pool 15 formed by the first laser 7, but the outer periphery of the second laser 8 does not overlap the outer edge of the molten pool 15. Is preferable because the second laser 8 makes it difficult for the molten metal to scatter.

In the present embodiment, the irradiation position of the first laser and the molten pool formed by the second laser are relatively fixed. As described above, the laser tends to cause sputtering when it hits the molten metal. While the first laser is irradiated to form the keyhole, the weld pool exists over a wide range of the welding object by the first laser and the second laser, so the laser and the molten metal do not interfere with each other. Thus, it is preferable not to roughen the surface of the molten pool. Therefore, by relatively fixing the irradiation position of the first laser and the molten pool formed by the second laser, it is possible to prevent the molten pool from undulating. It becomes difficult to enter. Therefore, the generation of spatter can be further suppressed.

FIG. 5 is a cross-sectional schematic view of the transverse (direction orthogonal to the welding progress direction) during welding, showing the AA cross section of FIG. 4, and FIG. 6 is a vertical (welding progress direction) cross-sectional schematic view of FIG. BB cross section is shown. Each of the

molten pools

15 and 16 has a larger melting area toward the surface of the welding object 9 and becomes narrower toward the inside. In this embodiment, the first laser 7 irradiates ahead of the irradiation center of the second laser 8 in the laser traveling direction. Thereby, the molten pool behind the keyhole 14 becomes large, and even if spatter occurs, it can fall into the molten pool and disappear.

In this embodiment, a fiber laser is used as the first laser and a semiconductor laser is used as the second laser, but the present invention is not limited to this. It is also possible to use a laser branched from one laser oscillator.

In this embodiment, the first laser is irradiated with an inclination of 10 ° with respect to the vertical direction of the surface of the welding object, but the irradiation angle is not limited to this.

In this embodiment, the beam shape of the first laser is a circle and the beam shape of the second laser is a ring shape, but the present invention is not limited to this.

Example 2 shows an example in which the beam shape of the second laser 8 is rectangular and the welding object 9 is copper. The rest of the system is the same as in the first embodiment. FIG. 7 shows the irradiation positional relationship between the first laser 7 and the second laser 8, and the

molten pools

15 and 16 formed by these lasers.

The distance between the first laser and the second laser was 1 mm. The first laser was a fiber laser having a beam diameter of 0.1 mm and a wavelength of about 1070 nm. As the second laser, a semiconductor laser having a rectangular shape with a beam shape of 1 mm × 4 mm and a wavelength of about 900 nm was used. Argon gas was used as the shielding gas.

In this embodiment, a rectangular second laser 8 is disposed behind the first laser 7. Unlike the first embodiment, the irradiation position of the first laser 7 is not in the irradiation region of the second laser 8, but is formed by irradiation of the molten pool 15 formed by the first laser 7 and the second laser 8. If the weld pool 16 to be overlapped in the welding direction, the weld pool 15 and the weld pool 16 are continuous and are expanded rearward from the keyhole. It may not be in the irradiation area.

When laser welding copper, molten metal may explode from the inside of the molten pool due to intense metal evaporation inside the keyhole. This is due in part to the fact that copper has a high thermal conductivity and the molten pool tends to be small. Therefore, the present embodiment can easily expand the molten pool rearward, and is preferable when the welding object is made of a material such as copper.

In this embodiment, the beam shape of the first laser is a circle and the beam shape of the second laser is a rectangle, but the present invention is not limited to this.

Example 3 shows an example in which the second laser 8 is scanned at high speed. FIG. 8 is a schematic external view of the laser welding apparatus. Reference numeral 18 denotes a scanner head. The first laser 7 was a fiber laser having a wavelength of about 1070 nm, and the second laser 8 was a semiconductor laser having a wavelength of about 900 nm. The first laser beam shape was a circle, and the beam diameter on the surface of the welding object 9 was 0.1 mm. The second laser beam shape was a circle, and the beam diameter on the surface of the welding object 9 was 2 mm. The first and second laser powers were constant. The elliptical shape was scanned with a period of 100 Hz with a major axis of 2 mm and a minor axis of 1 mm. The first laser was tilted by 10 ° for construction. The welding object was 304 stainless steel, and the shielding gas was nitrogen gas. The welding direction was left to right.

FIG. 9 shows the first and second laser irradiation position relationships and the scanning trajectory of the second laser. A broken line is a molten pool formed by each laser. The second laser 8 scans the periphery of the first laser 7 with an elliptical orbit at high speed, and simulates a ring-shaped laser as in the first embodiment so that the molten pool 15 is not interrupted. In this case, the center of the orbit of the second laser 8 becomes the irradiation center 21. The second laser 8 may be irradiated so as to trace the outer edge of the molten pool 14, but it is preferable to irradiate the outer periphery slightly away from the molten pool 14 because the molten metal is less likely to be scattered by the second laser 8. .

The same effect as in the above embodiment can be obtained by scanning the second laser 8 at high speed as in the present embodiment.

In this embodiment, the beam shapes of the first and second lasers are circles, but the present invention is not limited to this.

In this embodiment, the scanning trajectory of the second laser is elliptical and 100 Hz, but is not limited to this. The second laser power is constant, but can also be achieved by periodically varying the second laser power.

Example 4 shows an example in which the scanning orbit of the second laser 8 is changed and the welding object 9 is made of copper. The other apparatus system is the same as that of the third embodiment. The beam diameter of the first laser 7 was 0.1 mm, and the beam diameter of the second laser 8 was 1 mm. The second laser was periodically scanned at 50 Hz in a semi-elliptical shape behind the first laser. The semi-elliptical shape had a major axis of 3 mm and a minor axis of 1.5 mm, and was scanned 1 mm behind the first laser. Argon gas was used as the shielding gas.

FIG. 10 shows the first and second laser irradiation position relationships and the scanning trajectory of the second laser. A broken line is a molten pool formed by each laser. The molten pool is expanded by reciprocating the second laser 8 in a semi-elliptical shape behind the first laser 7. In this case, the center of gravity of the region surrounded by the trajectory of the second laser 8 and the start and end points of the second laser 8 is the irradiation center 21.

The second laser 8 may be irradiated so as to trace the outer edge of the molten pool 14, but it is preferable to irradiate the outer periphery slightly away from the molten pool 14 because the molten metal is less likely to be scattered by the second laser 8. .

In addition, by scanning the second laser 8 behind the irradiation position of the first laser 7, even if the surface of the molten pool is disturbed by the second laser 8, the second laser 8 is separated from the keyhole. The molten metal scattered by the laser 8 is difficult to enter the keyhole. Therefore, it is possible to suppress the occurrence of spatter when the first laser 7 hits the molten metal.

In this embodiment, the second laser is positioned behind the first irradiation position and scanned with a semi-elliptical orbit at 50 Hz. It is not limited to.

In the present embodiment, the second laser power is constant, but can also be achieved by periodically varying the second laser power.

DESCRIPTION OF SYMBOLS 1 1st laser oscillator 2 2nd laser oscillator 3 Optical fiber 4 for 1st laser Optical fiber 5 for 2nd laser Optical head 6 for 1st laser Optical head 7 for 2nd laser One laser 8 Second laser 9 Welding object 10 Processing table 11 Shield gas nozzle 12 Shield gas 13 Welding direction 14 Keyhole 15 Molten pool 16 Molten pool 17 Molten pool flow 18 Scanner head 19 Extruded into the keyhole Molten metal 20 Sputter 21 Irradiation center

Claims

In a laser welding method in which a welding object is joined by irradiating a laser and another heat source, at least a part of the molten pool formed by the irradiation of the laser overlaps with the molten pool formed by the irradiation of the other heat source. And irradiating the welding object with the laser and the other heat source, and always irradiating the laser in front of the welding progress direction from the irradiation center of the other heat source.
2. The laser welding method according to claim 1, wherein the other heat source is a laser.
2. The laser welding method according to claim 1, wherein an irradiation area of the other heat source is larger than that of the laser.
2. The laser welding method according to claim 1, wherein a relative position between the irradiation position of the laser and the molten pool formed by irradiation with the other heat source is fixed.
2. The laser welding method according to claim 1, wherein the other heat source irradiates an outer edge or an outer periphery of the molten pool formed by the laser irradiation.
2. The laser welding method according to claim 1, wherein the irradiation area of the other heat source is arranged behind the irradiation position of the laser.
2. The laser according to claim 1, wherein the laser is a first laser and the other heat source is a second laser, and the second laser scans an outer edge or an outer periphery of a molten pool formed by irradiation with the first laser. And a laser welding method.
8. The laser welding method according to claim 7, wherein the second laser performs reciprocal scanning behind the irradiation position of the first laser in the welding progress direction.