JP2017113778A - Laser welding method - Google Patents

Abstract

A laser welding method capable of butt-welding stainless plate materials with good processing quality using a laser beam having a wavelength in the 1 μm band is provided. A pair of stainless steel plate members having a plate thickness of 0.8 mm to 2.0 mm are butted against each other without a gap. The value obtained by dividing the melting time required for the plate material to melt at the peak power density by the travel time required for the beam spot with an area corresponding to 86% of the heat energy from the center of the beam spot to move by one diameter. is multiplied by the plate thickness ratio as the first index. A second index is obtained by dividing the melting time required for the plate material to melt at the average power density by the moving time, multiplying the ratio of the peak power density to the average power density and the plate thickness ratio. Using a laser beam with a wavelength in the 1 μm band, the conditions that the ratio of the peak power density to the average power density is 50% or more, the first index is 0.82% or less, and the second index is 0.25% or less A pair of plates are butt welded together. [Selection drawing] Fig. 1

Description

  The present invention relates to a laser welding method in which a stainless steel plate material is butt welded with a laser beam.

As a laser oscillator for emitting laser light used in a laser processing machine, there are various oscillators such as a CO ₂ laser oscillator, a fiber laser oscillator, and a direct diode laser oscillator (DDL oscillator).

The CO ₂ laser oscillator is large in size and high in cost. In contrast, fiber laser oscillators and DDL oscillators can reduce the size of the apparatus and have a low running cost. Therefore, in recent years, fiber laser oscillators and DDL oscillators are widely used in laser processing machines.

JP-A-5-208285

The wavelength of the laser light emitted from the CO ₂ laser oscillator is about 10 μm, whereas the wavelength of the laser light emitted from the fiber laser oscillator or the DDL oscillator is about 1 μm. Therefore, the laser light emitted from the fiber laser oscillator or the DDL oscillator has a small beam waist and a high power density, and thus is suitable for processing a thin plate material at high speed.

  A laser processing machine using a fiber laser oscillator or a DDL oscillator is widely used as an application for cutting a plate material or spot welding a plate material. There is a demand for a laser processing machine using a fiber laser oscillator or a DDL oscillator to be used for butt welding by joining the end portions of two plate members without gaps or with a gap of a predetermined interval.

  When the inventor butt-welded a stainless steel plate material using a laser processing machine using a fiber laser oscillator or a DDL oscillator, for example, there were many events in which a hole was formed at the beginning of a bead and the processing quality was poor. This is presumably because the laser light emitted from the fiber laser oscillator or the DDL oscillator has a small beam waist and a high power density, so that heat energy tends to concentrate in a small region.

  Therefore, it is difficult to butt-weld the plate material with good processing quality using the laser light having a wavelength emitted by the fiber laser oscillator or the DDL oscillator in the 1 μm band. There is a need for a laser welding method capable of butt welding a stainless steel plate with good processing quality using a laser beam having a wavelength of 1 μm band.

  An object of the present invention is to provide a laser welding method capable of butt-welding a stainless steel plate with good processing quality using a laser beam having a wavelength of 1 μm band.

  In order to solve the above-described problems of the prior art, the present invention uses a laser beam having a wavelength of 1 μm band, the plate thickness of the stainless steel plate is 0.8 mm to 2.0 mm, and ends of the pair of plate materials The first area corresponding to 3% of the total thermal energy of the beam spot from the center of the beam spot among the beam spots of the laser light irradiated to the plate member with the gaps butted together The power density at is the peak power density, and the melting time required for the plate material to melt at the peak power density corresponds to 86% of the total heat energy of the beam spot from the center of the beam spot. The thickness obtained when the beam spot of the second area to be divided by the moving time required to move by one diameter is based on a plate thickness of 1.0 mm Is the first index, and the peak power is calculated by dividing the melting time required for the plate material to melt at the average power density in the second area by the moving time. The ratio of the peak power density divided by the power density and the average power density multiplied by the thickness ratio is used as a second index, and the ratio of the peak power density to the average power density is 50% or more. The laser welding method is characterized in that the pair of plate members are butt-welded under the condition that the first index is 0.82% or less and the second index is 0.25% or less.

Further, in order to solve the above-described problems of the conventional technology, the present invention uses a laser beam having a wavelength of 1 μm band, the plate thickness of the stainless steel plate is 0.8 mm to 2.0 mm, and the pair of plate materials Of the laser beam irradiated to the plate material, 4% of the circumference of the circle contacting the gap is abutted between the end portions of the plate material with a gap of 0.1 mm to 0.3 mm. The power density in the first area multiplied by the plate thickness is defined as the peak power density, and the melting time required for the plate to melt at the peak power density is calculated from the center of the beam spot to the total heat energy of the beam spot. The first area is divided by the second area to a value obtained by dividing the beam spot having the second area corresponding to 86% of the thermal energy by the movement time required for moving by one diameter. The average power density in the third area, which is the portion of the beam spot of the second area that is irradiated to the surface of the plate material, is obtained by multiplying the square root of the obtained value by the first index. A ratio of the peak power density obtained by dividing the average power density by the peak power density to the value obtained by dividing the melting time required for melting by the moving time, and the first area. Multiplied by the square root of the value divided by the second area as a second index, and the beam spot diameter of the second area obtained by dividing the gap interval by the beam spot diameter of the second area, The ratio with the gap is less than 60%, the ratio between the peak power density and the average power density is 50% or more, the first index is 0.82% or less, and the second index is 0.19% or less. The pair of the above Provided is a laser welding method characterized by butt welding plate materials.

  In the above laser welding method, the beam profile of the laser beam is preferably a top hat type.

  According to the laser welding method of the present invention, a stainless steel plate material can be butt welded using a laser beam having a wavelength of 1 μm.

It is a perspective view showing the example of the whole composition of the laser beam machine of one embodiment. It is a figure which shows schematic structure at the time of comprising the laser oscillator 11 in FIG. 1 with the fiber laser oscillator 11F. It is a figure which shows schematic structure at the time of comprising the laser oscillator 11 in FIG. 1 with the direct diode laser oscillator 11D. It is a conceptual diagram which shows the state irradiated with a laser beam when a pair of board | plate materials are faced | butted without a gap, and when it faces | matches with a gap of a predetermined space | interval. It is a conceptual diagram which shows the beam spot irradiated to a pair of board | plate material when a pair of board | plate materials are faced | butted without a gap, and when it faces | matches with a gap of a predetermined space | interval. It is a conceptual diagram for demonstrating in detail the state of the beam spot irradiated to a pair of board | plate material at the time of facing a pair of board | plate material with a gap of 0.4 mm. It is a figure for demonstrating the definition of the peak power density at the time of facing a pair of board | plate material with a gap. It is a conceptual diagram which shows the state which the beam spot of 86% of beam spots center side moves only one diameter, when a pair of board | plate materials are faced | matched without the gap. It is a conceptual diagram which shows the state which the beam spot of 86% of the center side of a beam spot moves only one diameter, when a pair of board | plate materials are faced | matched with a gap. It is a figure which shows the determination result of processing quality when a pair of board | plate material is butt-welded using the laser beam which has a top hat type beam profile. It is a figure which shows the determination result of the processing quality when a pair of board | plate material is butt-welded using the laser beam which has a Gaussian beam type beam profile.

  Hereinafter, a laser welding method according to an embodiment will be described with reference to the accompanying drawings. In this embodiment, a case where a fiber laser oscillator or a DDL oscillator is used as a laser oscillator that emits laser light having a wavelength of 1 μm band will be described. The wavelength of the laser light emitted from the fiber laser oscillator is generally 1060 nm to 1080 nm, and the wavelength of the laser light emitted from the DDL oscillator is generally 910 nm to 950 nm. These wavelengths are referred to as the 1 μm band.

  In FIG. 1, a laser processing machine 100 includes a laser oscillator 11 that generates and emits laser light, a laser processing unit 15, and a process fiber 12 that transmits the laser light to the laser processing unit 15. The laser beam machine 100 butt-welds the plate materials W1 and W2 with the laser beam emitted from the laser oscillator 11. The plate materials W1 and W2 may be abutted without a gap or with a gap having a predetermined interval.

  The laser oscillator 11 is a fiber laser oscillator or a DDL oscillator. However, any laser oscillator that emits laser light having a wavelength of 1 μm may be used other than a fiber laser oscillator or a DDL oscillator. The process fiber 12 is mounted along X-axis and Y-axis cable ducts (not shown) arranged in the laser processing unit 15.

  The laser processing unit 15 includes a processing table 21 on which the plate materials W1 and W2 are placed, a portal-type X-axis carriage 22 that is movable in the X-axis direction on the processing table 21, and a perpendicular to the X-axis on the X-axis carriage 22. And a Y-axis carriage 23 that is movable in the Y-axis direction. Further, the laser processing unit 15 has a collimator unit 29 fixed to the Y-axis carriage 23.

  The collimator unit 29 collimates the laser light emitted from the output end of the process fiber 12 into a parallel light beam to make a substantially parallel light beam, and the laser light converted into the substantially parallel light beam is perpendicular to the X axis and the Y axis. And a bend mirror 25 that reflects downward in the Z-axis direction. The collimator unit 29 includes a condenser lens 27 that condenses the laser light reflected by the bend mirror 25 and a processing head 26.

  The collimator lens 28, the bend mirror 25, the condenser lens 27, and the processing head 26 are fixed in the collimator unit 29 with the optical axis adjusted in advance. In order to correct the focal position, the collimating lens 28 may be configured to move in the X-axis direction.

  The collimator unit 29 is fixed to a Y-axis carriage 23 that is movable in the Y-axis direction. The Y-axis carriage 23 is provided on an X-axis carriage 22 that is movable in the X-axis direction. Therefore, the laser processing unit 15 can move the position at which the plate material W1 is irradiated with the laser light emitted from the processing head 26 in the X-axis direction and the Y-axis direction.

  With the above configuration, the laser processing machine 100 transmits the laser light emitted from the laser oscillator 11 to the laser processing unit 15 through the process fiber 12, and the laser light at the boundary between the plate materials W1 and W2 where the respective ends are abutted. Can be butt welded to the plate materials W1 and W2.

  When the plate materials W1 and W2 are butt-welded, shield gas is injected to the plate materials W1 and W2. The main role of the shielding gas in butt welding is to prevent the metal from being oxidized in the process where the metal is generally melted and solidified into a bead shape. In addition, the evaporated metal (metal vapor) is blown away. The main component of the shielding gas is nitrogen or argon gas. As a method for ejecting the shield gas, there is a method in which the gas is ejected from a plurality of locations divided into main and sub. In addition, in FIG. 1, illustration is abbreviate | omitted about the structure which injects shielding gas.

  A robot type laser processing machine may be used instead of the laser processing machine 100 shown in FIG.

  FIG. 2 shows a schematic configuration when the laser oscillator 11 is constituted by a fiber laser oscillator 11F. In FIG. 2, each of the plurality of laser diodes 110 emits laser light having a wavelength λ. The excitation combiner 111 combines the laser beams emitted from the plurality of laser diodes 110 with a spatial beam.

  The laser light emitted from the excitation combiner 111 is incident on the Yb-doped fiber 113 between the two fiber Bragg gratings (FBGs) 112 and 114. The Yb-doped fiber 113 is a fiber in which a rare earth Yb (ytterbium) element is added to the core.

  The laser light incident on the Yb-doped fiber 113 repeats reciprocation between the FBGs 112 and 114, and laser light having a wavelength λ ′ of approximately 1060 nm to 1080 nm, which is different from the wavelength λ, is emitted from the FBG 114. Laser light emitted from the FBG 114 is incident on the process fiber 12 via the feeding fiber 115 and the beam coupler 116. The beam coupler 116 includes lenses 1161 and 1162.

  The process fiber 12 is composed of one optical fiber, and the laser light transmitted through the process fiber 12 is not combined with other laser light until the plate materials W1 and W2 are irradiated.

  FIG. 3 shows a schematic configuration when the laser oscillator 11 is constituted by a DDL oscillator 11D. In FIG. 3, a plurality of laser diodes 117 emit laser beams having different wavelengths λ1 to λn, respectively. The wavelengths λ1 to λn are 910 nm to 950 nm as described above.

  The optical box 118 spatially combines the laser beams having the wavelengths λ1 to λn emitted from the plurality of laser diodes 117. The optical box 118 includes a collimating lens 1181, a grating 1182, and a condensing lens 1183.

  The collimating lens 1181 collimates the laser light with wavelengths λ1 to λn. The grating 1182 bends the direction of the collimated laser beam by 90 degrees and makes it incident on the condenser lens 1183. The condensing lens 1183 collects the incident laser light and makes it incident on the process fiber 12.

  The process fiber 12 is composed of one optical fiber, and the laser light transmitted through the process fiber 12 is not combined with other laser light until the plate materials W1 and W2 are irradiated.

  Next, it will be considered how to butt-weld the plate materials W1 and W2 with good processing quality using a laser beam having a wavelength of 1 μm band.

  FIG. 4A conceptually shows a state in which laser light is irradiated when the plate members W1 and W2 that are abutted without a gap are viewed from the side. Laser light is applied to the surfaces of the plate materials W1 and W2 and heat is input. FIG. 4B conceptually shows a state in which the laser beams are irradiated when the plate members W1 and W2 that are abutted with a gap of a predetermined interval are viewed from the side. The laser light is applied to the surfaces and side surfaces of the plate materials W1 and W2 to be heat input.

  Therefore, the conditions for welding with good processing quality differ between the butt welding without gap shown in FIG. 4A and the butt welding with gap shown in FIG. 4B. In this embodiment, SUS304 is used as a stainless steel plate material, and plate materials having thicknesses of 0.8 mm, 1.0 mm, 1.5 mm, and 2.0 mm are butt welded without gaps and butt welded with gaps, resulting in good processing quality. It was verified whether it was bad or bad.

  In order to improve the processing quality of butt welding, it is necessary to form a back bead on the back surfaces of the plate materials W1 and W2. It is assumed that the processing quality is good when a hole is not formed in the plate materials W1 and W2, the metal is melted from the front surface to the back surface, and a back bead is formed on the back surface.

  In order to weld the plate materials W1 and W2, it is necessary that a stainless steel molten pool and a keyhole be formed. The average power density of the beam spot mainly contributes to the formation of the molten pool. The peak power density of the beam spot mainly contributes to the formation of the keyhole.

  FIG. 5A shows a state in which the beam spot Bs is located at the butt portion of the plate materials W1 and W2 in the butt welding without gap. Of the area of the beam spot Bs, what actually contributes to the melting of the material is an area corresponding to approximately 86% of the total thermal energy from the center of the beam spot Bs. The 86% portion of the beam spot Bs is referred to as a beam spot Bs86. The average power density of the beam spot Bs is the average power density of the beam spot Bs86.

  The peak portion of the beam spot Bs is an area corresponding to approximately 3% of the total heat energy from the center of the beam spot Bs in the area of the beam spot Bs. The peaked portion will be referred to as peak Bs03. The peak power density is an average power density of the peak Bs03.

  FIG. 5B shows a state in which the beam spot Bs is located at the butt portion of the plate materials W1 and W2 in the butt welding with a gap. In butt welding with a gap, the peak Bs03 is located in the gap and does not contribute much to the melting of the plate materials W1 and W2. Therefore, in butt welding with a gap, it is necessary to regard the density of the portion different from the peak Bs03 as the peak power density.

  FIG. 6 shows a state in which the beam spot Bs is located at the abutting portion of the plate materials W1 and W2 when the gap interval is 0.4 mm. When the gap interval is 0.4 mm, a circle having an area corresponding to about 45% of the total heat energy from the center of the beam spot Bs in the area of the beam spot Bs abuts the plate materials W1 and W2. ing. The 45% portion of the beam spot Bs is referred to as a beam spot Bs45.

  It is considered that 2% of the outer periphery of the beam spot Bs45 contributes to melting the end portion of the plate material W1, and 2% contributes to melting the end portion of the plate material W2. A 2% portion of the outer periphery of the beam spot Bs45 is an arc C4502. Assuming that the plate thickness of the plate members W1 and W2 is th, an area of 2 × C4502 × th contributes to melting the plate members W1 and W2, as shown in FIG. The density of power input by an area of 2 × C4502 × th can be regarded as the peak power density in butt welding with a gap.

  Although not shown, when gap intervals are 0.1 mm, 0.2 mm, and 0.3 mm, circles with areas corresponding to thermal energy of approximately 3%, 11%, and 25% from the center of the beam spot Bs, respectively. Abuts against the plate materials W1 and W2. Therefore, when the gap is 0.1 mm, 0.2 mm, and 0.3 mm, the area of 2 × 2% × th of the outer circumference of the circle corresponding to the thermal energy of 3%, 11%, and 25%, respectively, This contributes to melting the plate materials W1 and W2.

  Similarly, when the gap interval is 0.1 mm, 0.2 mm, and 0.3 mm, 2 × 2% × th of the outer circumference of the circle corresponding to the thermal energy of 3%, 11%, and 25%, respectively. The density of power input by the area is the peak power density.

  In FIG. 6, the average power density of the beam spot Bs that contributes to melting the plate materials W1 and W2 is originally hatching that is a portion of the beam spot Bs86 that is irradiated on the surfaces of the plate materials W1 and W2. This is the average power density of the part marked with. The calculation of the average power density of the hatched portion is complicated. Therefore, taking the case where the gap is 0.4 mm as an example, the average power density of the portion excluding the beam spot Bs45 from the beam spot Bs86 is set as the average power density of the beam spot Bs in the butt welding with a gap.

  Of course, the average power density of the hatched portion of the beam spot Bs86 may be obtained. Since the average power density of the portion excluding the beam spot Bs45 from the beam spot Bs86 and the average power density of the hatched portion are not significantly different, the average power density of the portion excluding the beam spot Bs45 from the beam spot Bs86 is It can be regarded as the average power density of the hatched part.

  FIG. 8 shows a state where the beam spot Bs86 moves by one diameter of the beam spot Bs86 in the butt welding without gap. When the beam spot Bs86 moves by one diameter, there is heating to prepare for melting of the stainless steel, a molten pool is formed on the surface side just before the peak Bs03 arrives, and a keyhole is formed when the peak Bs03 arrives.

  When the peak Bs03 passes, a molten pool is formed on the back surface side, and when the beam spot Bs86 passes, the molten stainless steel is solidified as a back bead.

  FIG. 9 shows a state in which the beam spot Bs86 moves by one diameter of the beam spot Bs86 in the butt welding with a gap. Again, the case where the gap is 0.4 mm is taken as an example. In FIG. 9, a molten pool is formed on the surface side immediately before the portion having the area of 2 × C4502 × th described in FIG. 7 arrives, and a keyhole is formed when the portion reaches. When that portion passes, a molten pool is formed on the back side, and when the beam spot Bs86 passes, it becomes a back bead and the molten stainless steel hardens.

  Here, the melting temperature of stainless steel (SUS304) is 1400 to 1450 ° C. SUS304 corresponds to AISI standard 304 or UNS standard 30400, and is also called 18-8 stainless steel. SUS304 contains carbon (C), silicon (Si), manganese (Mn), nickel (Ni), chromium (Cr), Ni is 8 wt% or more and Cr is 18 wt% or more. Some stainless steel. Different types of stainless steel contain different chemical components and their properties change, but at the same time the melting temperature range also changes. The time t required for the stainless steel to melt is expressed by the following formula (1).

In formula (1), c is specific heat (J / kg · ° C.), ρ is density (kg / m ³ ), λ is thermal conductivity (W / m · ° C.), A is absorptance (%), and Pd is Power density (W / m ² ), T is a melting temperature (° C.), and T 0 is a temperature (° C.) before heat input. In these, Kelvin K may be used instead of Celsius. In addition, the heat input by the laser beam to stainless steel shall be conducted from the surface layer surface of material.

  If stainless steel is heated too much, it takes too much time to dissipate heat, resulting in holes. If there is not enough heat input, no molten pool or keyhole will be formed. Therefore, when the beam spot Bs86 moves as shown in FIG. 8, the melting time at the power density (peak power density) at the peak Bs03 per moving time required for the beam spot Bs86 to move by one diameter is: This is an important factor in realizing butt welding with good processing quality.

  Similarly, when the beam spot Bs86 moves as shown in FIG. 9, the power density (peak power) in the area of 2 × C4502 × th per moving time required for the beam spot Bs86 to move by one diameter. The melting time in (density) is an important factor in realizing butt welding with good processing quality.

  8 and 9, (melting time at peak power density) / (movement time required for the beam spot Bs 86 to move by one diameter) is represented by Expression (2). (Melting time at average power density) / (movement time required for the beam spot Bs86 to move by one diameter) is represented by Equation (3). The definition of the peak power density in Formula (2) and the average power density in Formula (3) is as described above.

  First, the case where the DDL oscillator 11D is used will be described. The beam profile of the laser light emitted from the DDL oscillator 11D is a top hat type.

  In the butt welding without gap, the index 1 is obtained by multiplying the formula (2) by the thickness ratio. The plate thickness ratio is based on a plate thickness of 1.0 mm. If the plate thickness is 0.8 mm, the plate thickness ratio is 0.8, and if the plate thickness is 1.5, the plate thickness ratio is 1.5. Further, an index 2 is obtained by multiplying the expression (3) by the ratio of the peak power density (peak Pd) and the average power density (average Pd) and the plate thickness ratio. The ratio of the peak Pd to the average Pd is a value obtained by dividing the average Pd by the peak Pd.

  In butt welding with a gap, the index 1 is obtained by multiplying the formula (2) by the square root of (2 × 2% × th area) / (area of the beam spot Bs86). The square root of (2 × 2% × th area) / (area of beam spot Bs86) is referred to as an area ratio. The index 2 is obtained by multiplying the expression (3) by the ratio of the peak Pd and the average Pd and the area ratio.

  FIG. 10 shows the thicknesses of the plate materials W1 and W2 of 0.8 mm, 1.0 mm, 1.5 mm, and 2.0 mm, and the following in each of the gaps 0 mm, 0.1 mm, 0.2 mm, 0.3 mm, and 0.4 mm. And the determination result of whether the processing quality is good or bad. FIG. 10 shows the indexes 1 and 2, the ratio between the diameter of the beam spot Bs86 and the gap interval, and the ratio between the peak Pd and the average Pd.

  As a result of the verification of whether the processing quality is good or defective by the inventor, as shown in FIG. 10, the portion that is not hatched, the processing quality is good, and the portion that is hatched is The processing quality was found to be poor.

  From FIG. 10, in the butt welding with a gap, the ratio of the diameter of the beam spot Bs86 obtained by dividing the gap interval by the diameter of the beam spot Bs86 and the gap needs to be less than 60%. In the butt welding without a gap, the ratio of the diameter of the beam spot Bs86 to the gap is 0% and less than 60%. In both butt welding without a gap and butt welding with a gap, the ratio of the peak Pd to the average Pd needs to be 50% or more.

  In butt welding without a gap, it is necessary that the index 1 is 0.82% or less and the index 2 is 0.25% or less. In butt welding with a gap, it is necessary that the index 1 is 0.82% or less and the index 2 is 0.19% or less.

  Next, a case where the fiber laser oscillator 11F is used will be described. The beam profile of the laser light emitted from the fiber laser oscillator 11F is a Gaussian beam type. FIG. 11 shows the same verification result as FIG.

  From FIG. 11, in the butt welding with a gap, the ratio of the diameter of the beam spot Bs86 obtained by dividing the gap interval by the diameter of the beam spot Bs86 and the gap needs to be less than 60%. In the butt welding without a gap, the ratio of the diameter of the beam spot Bs86 to the gap is 0% and less than 60%. In both the butt welding without a gap and the butt welding with a gap, the ratio of the peak Pd to the average Pd is less than 50% and needs to be a positive value.

  In the butt welding without a gap, it is necessary that the index 1 is 0.70% or less and the index 2 is 0.58% or less. In butt welding with a gap, it is necessary that the index 1 is 0.70% or less and the index 2 is 0.69% or less (however, negative is impossible).

  By the way, even when the fiber laser oscillator 11F is used, by using a beam shaper, the beam profile of the laser beam emitted from the fiber laser oscillator 11F is set to the top hat type similar to the laser beam emitted from the DDL oscillator 11D. be able to.

  In this case, even if the fiber laser oscillator 11F is used, the condition shown in FIG. 10 is a condition for realizing good processing quality.

  The present invention is not limited to the embodiment described above, and various modifications can be made without departing from the scope of the present invention.

11 Laser oscillator 11D Direct diode laser oscillator (DDL oscillator)
11F Fiber laser oscillator 100 Laser processing machine W1, W2 Plate material

Claims (3)

Using a laser beam with a wavelength of 1 μm,
The plate thickness of the stainless steel plate is 0.8 mm to 2.0 mm,
Abutting the ends of the pair of plate members without a gap,
The power density in the first area corresponding to 3% of the total thermal energy of the beam spot from the center of the beam spot among the beam spots of the laser beam irradiated on the plate material is defined as the peak power density. The beam spot having the second area corresponding to 86% of the total thermal energy of the beam spot from the center of the beam spot is the melting time required for the plate material to melt at the peak power density. Is obtained by multiplying the value divided by the moving time required to move by one diameter by the plate thickness ratio with respect to the plate thickness of 1.0 mm as the first index,
The peak power density obtained by dividing the average power density by the peak power density to a value obtained by dividing the melting time required for the plate material to melt at the average power density in the second area by the moving time, and the peak power density The ratio of the average power density and the plate thickness ratio are multiplied by the second index,
Under the condition that the ratio of the peak power density and the average power density is 50% or more, the first index is 0.82% or less, and the second index is 0.25% or less, the pair of plate materials A laser welding method characterized by butt welding. Using a laser beam with a wavelength of 1 μm,
The plate thickness of the stainless steel plate is 0.8 mm to 2.0 mm,
The end portions of the pair of plate members are abutted with a gap of 0.1 mm to 0.3 mm,
Among the beam spots of the laser beam irradiated to the plate material, the power density in the first area obtained by multiplying 4% of the circumference of the circle in contact with the gap by the plate thickness of the plate material is defined as the peak power density, and the plate material However, the melting time required for melting at the peak power density is one beam spot having a second area corresponding to 86% of the total thermal energy of the beam spot from the center of the beam spot. The value obtained by dividing the value obtained by dividing the moving time required to move by the diameter by the square root of the value obtained by dividing the first area by the second area is used as the first index.
The melting time required for the plate to melt at the average power density in the third area, which is the portion of the beam spot of the second area irradiated on the surface of the plate, is divided by the moving time. Multiplied by the ratio of the peak power density obtained by dividing the average power density by the peak power density and the average power density, and the square root of the value obtained by dividing the first area by the second area. As the second indicator,
The ratio of the beam spot diameter of the second area divided by the diameter of the beam spot of the second area and the gap is less than 60%, and the ratio of the peak power density to the average power density is The laser welding method, wherein the pair of plate members are butt-welded under a condition of 50% or more, the first index is 0.82% or less, and the second index is 0.19% or less.   3. The laser welding method according to claim 1, wherein a beam profile of the laser beam is a top hat type.

Images