JP2002066777A - Laser machining head and processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize a laser machining by preventing a variation in a beam diameter on the surface of a laser irradiation object caused by the variation in the distance from a condenser lens to the surface of the laser irradiation object when irregularities exist on the surface of the laser irradiation object or when the diameter of a piping varies. SOLUTION: A contact 17 is installed on the further tips of a nozzle 15 installed on the tip of a lens holder 7 in which a condenser lens 13 being attached. The lens holder 7 is held movable back and forth relative to a processing head body 2 with an air cylinder 3 being interposed. Upon laser irradiation, the lens holder 7 and the air cylinder 3 are pushed out against a laser irradiation object 16 by the air pressure supplied to the air cylinder 3, so that the contact 17 is touched on the surface of the laser irradiation object 16 to keep the distance between the condenser lens 13 and the laser irradiation object 16 constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser processing head and a processing method for performing processing such as surface modification, welding, and cutting of a laser irradiation object by using a laser beam.

[0002]

2. Description of the Related Art Conventionally, in a preventive maintenance and repair technique for stress corrosion cracking generated in an object to be irradiated with laser, for example, a reactor pipe or the like, when a laser welding apparatus and a surface treatment apparatus by remote control are used, they are transmitted by an optical fiber. A method is used in which laser light is condensed by a condenser lens (convex lens) or the like, turned back by a mirror, and irradiated with laser light on the inner surface of the pipe.

[0003] This will be described with reference to FIG.
The laser beam L emitted from the laser beam L is converted into parallel light by a lens 55, turned back by a mirror 54, and then condensed via a lens 53. Predetermined beam diameter D1 on the surface of 56
Is irradiated so that a laser beam is formed.

[0004]

However, according to this method, the laser irradiation from the lens 53 is performed when the diameters of a plurality of pipes, which are the objects to be irradiated with laser, are changed or when the surface of the object to be irradiated has irregularities. Since the distance to the surface of the target 56 changes and the beam diameter D1 on the surface of the laser irradiation target 56 changes, the laser processing becomes unstable.

[0005] The present invention provides a laser processing method capable of realizing stable laser processing with a constant distance from the lens to the laser object surface even when the diameter of the pipe changes or the surface of the laser irradiation object has irregularities. It is an object to provide a head and a processing method.

[0006]

According to a first aspect of the present invention, there is provided a laser processing head comprising: a lens holder having a condensing lens for shaping a transmitted laser beam; A nozzle attached to the tip of the lens holder and having a laser emission port through which laser light can pass, a contact attached to the tip of the nozzle, and the lens holder inserted through an air cylinder so as to be relatively reciprocally movable. The air cylinder is provided with an air chamber whose volume can be expanded and reduced only in the axial direction, and air is supplied to this air chamber to expand the air chamber in the axial direction. The holder is extruded from the inside of the processing head body to the laser irradiation target side, and the contact is brought into contact with the surface of the laser irradiation target to collect. Distance from the lens to the laser irradiation surface of the object can be kept constant, it is possible to perform stable laser machining was.

According to a second aspect of the present invention, in the laser processing head, the air cylinder inserted between the lens holder and the processing head body may be connected to the air cylinder itself and the lens holder. Of the connection state between the air cylinder itself and the processing head body,
One of the coupling states is a reciprocally movable fitting state, and the air chamber is formed in the reciprocally movable fitting part.

Further, in the invention according to the third aspect of the present invention, all the connected states between the lens holder, the air cylinder and the body of the processing head are set to a relatively movable fitting state, and The air chamber is formed at a fitting portion between the lens holder and the air cylinder and at a fitting portion between the air cylinder and the processing head body.

Further, according to a fourth aspect of the present invention, in the laser processing head according to any one of the first to third aspects, the laser processing head is provided between the lens holder, the air cylinder and the processing head body. A restoring spring is provided between members that can relatively reciprocate, and when the air pressure in the air chamber is reduced, the lens holder or the air cylinder is housed in the laser processing head body by the restoring force of the spring. It is like that. According to the present invention, when the air pressure in the air cylinder is reduced, the lens holder and the air cylinder can be housed in the laser processing head body, and the lens holder and the air cylinder can be protected.

Further, the invention according to a fifth aspect of the present invention relates to a laser processing head, wherein a lens holder provided with a condenser lens for shaping the transmitted laser light, and a laser light mounted at the tip of the lens holder and through which the laser light can pass. A nozzle having a laser emission port, a contact attached to the tip of the nozzle, and a processing head body for holding the lens holder relatively reciprocally through an air cylinder. And the air cylinder inserted between the processing head body, the connection state between the air cylinder itself and the lens holder or the connection state between the air cylinder itself and the processing head body,
One of the coupling states is a reciprocally movable fitting state, and an air chamber that can be expanded and contracted only in the axial direction is formed in the reciprocally movable fitting part, and a restoring spring is provided. The lens holder is pushed out from the inside of the processing head body toward the laser irradiation object side by laser restoring force during laser irradiation, and the contact is brought into contact with the surface of the laser irradiation object.

Further, according to the invention relating to a laser processing head according to claim 6, in the laser processing head according to claim 5, the expandable and contractable air chamber expands when pressurized air is supplied, and The lens holder is housed in the processing head body side against the restoring force of the restoring spring.

Further, according to a seventh aspect of the present invention, in the processing head according to any one of the first to sixth aspects, the tip of the nozzle is provided on a surface of an object to be irradiated with laser. This is provided with a parallel shielding plate. According to the present invention, when performing laser processing on a laser irradiation target such as nuclear power plant equipment underwater,
Construction is possible without draining water from the furnace.

Further, the invention of a laser processing head according to claim 8 is an austenitic stainless steel which has been sensitized by a heat cycle at the time of welding using the laser processing head according to claims 1 to 7 and has deteriorated corrosion resistance. For steel,
In a laser processing method in which a laser is applied to the material surface of the sensitized portion, a method in which oxygen gas is mixed with nitrogen gas or an inert gas used as a shielding gas blown to the laser irradiated portion of the material surface during laser processing. In addition to preventing the occurrence of stress corrosion cracking of the material, it is possible to stabilize the laser absorptance of the laser irradiation part by mixing oxygen gas with nitrogen gas or inert gas used for shielding gas. As a result, laser processing can be stabilized.

Further, the invention according to a laser processing method according to a tenth aspect is the laser processing method according to the ninth aspect, wherein the oxygen concentration in the shielding gas is set to 0.5 to 2 wt%. Reduce the oxygen concentration in the shielding gas to 0.5
By setting the content to ２2 wt%, the laser absorptance of the laser irradiation part can be stabilized, and the laser processing can be stabilized.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A laser processing head and a processing method according to an embodiment of the present invention will be described below with reference to the drawings. (First Embodiment) A first embodiment will be described with reference to FIGS. FIG. 1 is a schematic diagram schematically showing a cross section of the laser processing head. This laser processing head 1
Has a cylindrical air cylinder 3 fitted smoothly and reciprocally in the axial direction inside a processing head body 2 formed in a cylindrical shape. It is configured such that it can be housed in the interior by the restoring force or air pressure, or can be fed out from the interior to the exterior.

An annular air chamber and a spring accommodating chamber are formed by utilizing a dimensional difference between an inner peripheral portion of the processing head body 2 and an outer peripheral portion of the air cylinder 3. In order to form the air chamber and the spring accommodating chamber, a flange-shaped seal portion 3-1 is protruded from the outer peripheral surface of the air cylinder 3 substantially at the center in the axial direction. Then, with respect to the inner peripheral portion of the processing head body 2, an annular fastener 2-2 is provided on the opening side thereof.
And a seal part 2-1 is provided inside the body.

A first air chamber 4 is formed between the seal parts 2-1 and 3-1 and a spring housing chamber 5 is formed between the seal part 3-1 and the annular fastener 2-2. By expanding or contracting the first air chamber 4, the air cylinder 3 is configured to be able to reciprocate in the axial direction with respect to the processing head body 2. Reference numeral 6 denotes a coil spring housed in the spring housing chamber 5, which is constantly compressed by the seal portion 3-1 and the annular fastener 2-2.

On the other hand, a cylindrical lens holder 7 is fitted to the inner peripheral portion of the air cylinder 3 smoothly and reciprocally only in the axial direction. Alternatively, it is configured such that it can be housed inside the air cylinder 3 or fed out from the inside to the outside by air pressure. Then, an annular second air chamber 8 is formed between the inner peripheral portion of the air cylinder 3 and the outer peripheral portion of the lens holder 7 by utilizing a difference between the two dimensions.

Incidentally, the lens holder 7 is a small cylindrical body having a long axial length on which a condenser lens described later is installed on the optical axis.
7-1 and a large cylindrical body 7-2 having an axial length shorter than that of the small cylindrical body 7-1 concentrically disposed outside thereof, and these small cylindrical bodies 7-1,
It has a shape in which one end of a large cylindrical body 7-2 is integrally connected. The outer periphery of the large cylinder 7-2 is the air cylinder 3
Is configured to fit smoothly with the inner peripheral portion of.

The inner peripheral portion of the air cylinder 3 is formed such that an annular second air chamber 8 is formed at the fitting portion between the inner peripheral portion of the air cylinder 3 and the large cylindrical body 7-2 of the lens holder 7. The inner diameter from the substantially central portion to the opening end in the axial direction is intentionally made larger than the outer diameter of the large cylindrical body 7-2 of the lens holder 7, and a seal is formed on the outer peripheral side of the large cylindrical body 7-2 on the opening side. The parts 7-3 are provided with seal parts 3-5 in the middle part of the inner peripheral part of the air cylinder 3, respectively.

The first and second air chambers 4 and 8 communicate with each other by one or a plurality of air communication passages 3-2, and a predetermined pressure is supplied from an air supply port 9 provided in the processing head body 2. Is supplied to the first air chamber 4 and the air communication passage.
Air of a predetermined pressure is also supplied to the second air chamber 8 through 3-2.

The annular groove formed between the small cylindrical body 7-1 and the large cylindrical body 7-2 is a spring storage chamber 10 for storing a coil spring 11, and the coil spring 11 is provided between the bottom of the groove and the air. The cylinder 3 is always compressed by an annular fastener 12 fitted to the inner peripheral portion of the open end of the cylinder 3.

Also, steps 3-3, 3-4 provided at the outer peripheral portion and the inner peripheral portion of the inner side end (upper part shown) of the air cylinder 3 are shown.
Constitute stoppers which act when the air cylinder 3 is extended and when the lens holder 7 is stored, respectively.

The lens holder 7 has a condensing lens 13 for shaping the laser light L and a glass 14 for protecting the lens (hereinafter referred to as a protective glass) 14 attached to an inner end thereof. The nozzle 15 through which the laser light L can pass is fixed. Further, a roller-shaped contact 17 that smoothly contacts the surface of the laser irradiation target 16 is fixed to the tip of the nozzle 15.

In the laser processing head thus configured, the laser light L transmitted into the processing head body 2
After being shaped by the condenser lens 13 and passing through the protective glass 14, the surface of the laser irradiation target 16 is irradiated from the exit of the nozzle 15.

FIG. 1 shows that air at a predetermined pressure is supplied to the two air chambers 4 and 8 and the air cylinder 3 is moved from the inside of the machining head body 2 against the restoring force of the coil springs 6 and 11. Also, a state is shown in which the lens holder 7 is extended from the inside of the air cylinder 3 to the outside.

FIG. 2 shows that the supply of air supplied to the air chambers 4 and 8 is stopped to release the pressure of the air, and the coil springs 6 and 11 are turned off.
3 shows a state in which the air cylinder 3 and the lens holder 7 are housed inside by the restoring force.

By the way, the shape of the melted portion formed on the surface of the laser irradiation object 16 by the laser irradiation depends on the condensing lens.
Since it is determined by the distance between the laser beam L and the surface of the laser irradiation object 16, in order to keep the shape of the surface modified layer formed by irradiating the laser beam L constant, the condensing lens 13
And the distance to the laser irradiation target 16 must always be kept constant.

According to this embodiment, the laser processing head 1
Is provided with a so-called copying mechanism in which the lens holder 7 is always drawn out to the laser irradiation target 16 side by the pressure of the air cylinder 3 and the contact 17 fixed to the tip of the nozzle 15 contacts the surface of the laser irradiation target 16 to copy. So,
Even when the surface of the laser irradiation target 16 has irregularities, the distance between the condenser lens 13 and the laser irradiation target 16 can always be kept constant, and stable laser processing can be performed.

Further, according to the present embodiment, the first air chamber 4, the second air chamber 8, and the air communication passage 3-
2 was formed at the fitting portion of the processing head body 2, the air cylinder 3, and the lens holder 7, and the processing head 1 was formed.
Can be reduced in size.

In the embodiment described above, in order to extend both the lens holder 7 and the air cylinder 3, a part of the fitting portion between the processing head 2 and the air cylinder 3 and the lens holder 7 and the air cylinder 3 The first and second air chambers are respectively provided in a part of the fitting portion with the first and second air chambers 3, and both air chambers are configured to expand in the axial direction by air pressure. Only one of them may be extended.

For example, when providing an air chamber only between the lens holder 7 and the air cylinder 3, the lens holder 7
When only the air cylinder 3 is provided and an air chamber is provided only between the air cylinder 3 and the processing head body 2, only the air cylinder 3 can be advanced without extending the lens holder 7.

In the embodiment described above, the air cylinder 3 and the processing head body 2 are described as cylinders, but it is not an essential requirement of the invention to form them as cylinders. For example, the air cylinder 3 may be formed in a shape that does not surround the entire circumference of the lens holder 7, for example, a semicircular cross section or a C-shape. In this case, the air chamber is naturally not annular,
It is half-moon shaped or C-shaped.

Further, the medium to be supplied to the air chamber is not necessarily air, and any kind of gas or liquid can be used as long as it can generate pressure against a spring and does not affect the processing.

(Second Embodiment) A second embodiment will be described with reference to FIGS. Note that elements corresponding to FIG. 1 and FIG. The major difference between this embodiment and the first embodiment is that
In the first embodiment, the air cylinder 3 and the lens holder 7 are extended from the processing head body side by the pressure of air,
In contrast to the housing by the restoring force of the coil spring, in the case of the present embodiment, the air cylinder and the lens holder are extended by the restoring force of the coil spring and housed by the pressure of air.

FIG. 3 is a schematic diagram showing a cross section of the outline of the laser processing head. The laser processing head 21 has a cylindrical air cylinder 23 fitted in a cylindrical processing head body 22 so as to smoothly reciprocate, that is, house and extend. Moreover, an annular groove having an appropriate depth in the axial direction from the opening end is formed in the inner peripheral portion of the machining head body 22.
22-1 is provided, this annular groove 22-1 and air cylinder 23
The first spring accommodating chamber 25 is formed by the outer peripheral surface of the first spring accommodating chamber. Reference numeral 26 denotes a coil spring housed in the first spring housing chamber 25.

A flange-like projection 23-1 is provided substantially at the center of the outer periphery of the air cylinder in the axial direction.
-1 is used as a holder for the coil spring 26, and the other is used as the processing head 22.
A stopper 32 fixedly provided at the opening end of the opening. In addition, the annular groove 22-1, the flange-like projection 23-1
And the stopper 32 form a first air chamber that can be expanded and reduced only in the axial direction. A flange-shaped stopper and holding member 23-2 is fixedly provided on the inner peripheral portion of the air cylinder 23 on the side opposite to the flange-shaped projection 23-1.

On the other hand, a cylindrical lens holder 27 is also installed inside the air cylinder 23 so as to be able to smoothly reciprocate (store and extend). Moreover, two annular grooves 27-1 having different depths are provided on the outer peripheral portion of the lens holder 27.
27-2 will be provided adjacently. The groove toward the annular groove 27-1 is made deep and wide.

The space defined by the outer peripheral portion of the flange-shaped projection 23-1, the inner peripheral portion of the lower portion of the processing head body 22 and the air cylinder holder 32 is defined as a first air chamber 24, and the annular groove 27-2 is A second air chamber 28 is formed by the inner peripheral portion of the cylinder 23 and the flange-shaped projection 23-2.
To form

The first air chamber 24 and the second air chamber 28 communicate with each other through an air communication port 23-3 provided in the air cylinder 23 itself. Reference numeral 29 denotes an air supply port provided in the processing head body 22 for supplying compressed air to the first air chamber 24.

The lens holder 27 has a condensing lens 33 for shaping the laser light L and a glass for protecting the lens (hereinafter referred to as a protective glass) 34 attached to the inner end thereof, and the laser light L can pass through the outer end. Nozzle 35 is fixed. Further, the nozzle 35 has a roller-shaped contact 37 that is in smooth contact with the surface of the laser irradiation object 36 fixed to the tip thereof.

During laser processing, the compressed air is not supplied from the air supply port 29, and the air cylinder 23 and the lens holder 27 are moved from the state shown in FIG. The air cylinder 23 and the state where the lens holder 27 is extended from the air cylinder 23 are maintained.

In this state, the laser beam L transmitted into the processing head body 22 is shaped by the condenser lens 33, passes through the protective glass 34, and irradiates the surface of the laser irradiation object 36 from the exit of the nozzle 35. It is configured to be.

By the way, the shape of the fused portion formed on the surface of the laser object by the laser irradiation is determined by the distance between the condenser lens 33 and the surface of the laser object 36.
In order to keep the shape of the surface modified layer formed by irradiating the laser beam L constant, it is necessary to always keep the distance between the condenser lens 33 and the laser irradiation target 36 constant.

According to this embodiment, the laser processing head 21
During laser processing due to the restoring force of the coil springs 26 and 31, the lens holder 27 is always extended to the laser irradiation target 36 side, and the contact 37 fixed to the tip of the nozzle 35 comes into contact with the surface of the laser irradiation target 36 to copy. Therefore, even if the surface of the laser irradiation target 36 has irregularities, the distance between the condenser lens 33 and the laser irradiation target 36 can be kept constant.

Also, after the end of the laser machining operation, FIG.
As shown in FIG. 2, by supplying air from the air supply port 29, compressed air is supplied to the first air chamber and the second air chamber through the air supply port 23-3, and the air cylinder 23
Then, the lens holder 27 is pushed up against the restoring force of the coil spring and housed in the processing head body 22. FIG. 4 shows this state.

(Third Embodiment) A third embodiment of the present invention will be described with reference to FIG. FIG. 5 is a schematic view showing a laser processing head suitable for performing laser processing in water.

When laser processing is performed in water, it is a general method to locally form a water-free space so that water does not enter the laser beam irradiation area and perform laser processing inside the space. As shown in FIG. 5, the laser processing head 41 of the present embodiment includes an underwater nozzle 45 at the tip of the lens holder 7.
Is used. This underwater construction nozzle 45 is substantially the same as the nozzle 8 or 28, but has a shielding plate 48 attached to the tip thereof so as to be parallel to the laser irradiation object.
Further, a contact 17 is attached to the tip.

When the shielding gas 46 is ejected from the same place as the laser light L emission port at the tip of the nozzle, a gap 47 is formed between the laser irradiation target 16 and the shielding plate 48. The distance between the underwater nozzle 45 and the object 16
17, the laser light irradiation range is always kept in a shield gas atmosphere, and stable laser processing can be performed.

For example, when the diameter of the exit at the tip of the underwater construction nozzle 45 is 7 mm, the flow rate of the shielding gas is 100 l / min, and the distance between the underwater construction nozzle 45 and the laser irradiation object 16 is 2 mm, the laser irradiation object 16 A gap of φ25 mm is formed on the surface, and stable laser processing can be performed even in water.

Also in this embodiment, when the lens holder 7 is extended, compressed air is supplied to the air cylinder, and when the lens holder 7 is stored in the processing head body, the air pressure may be reduced.

(Example 1) Hereinafter, a laser beam was irradiated to a sensitized stainless steel surface while flowing a shield gas, using the laser processing head shown in FIG. 1 used in the first embodiment. FIG. 6 shows an experimental result in the case where the surface is locally heated and melted, and the sensitized area of the heated and melted portion is surface-modified and thus desensitized.

The size of the molten layer formed on the surface of the laser object 16 by laser irradiation is determined by the absorptance of laser light and heat input. The larger the heat input to the stainless steel, the larger the formed heated / melted layer, and conversely, the smaller the heat input, the smaller the molten layer. Although the absorptance of the laser beam changes depending on the material and surface properties, the same material is greatly affected by the surface roughness of the material surface.

Therefore, the laser processing was performed using the laser processing head shown in FIG. 1 while changing the surface finishing method of the stainless steel and the type of the shielding gas, and a test was conducted on the depth of the molten layer formed on the stainless steel surface. Carried out.

The laser processing conditions were as follows: laser irradiation output 900W,
The application speed was 0.8 m / min, the shielding gas flow rate was 40 l / min, and the defocused beam was irradiated. The test results are as shown in FIG. Inert gas is often used as the shielding gas, but from the results of this test, the inert gas argon (A
When r) is used, the depth of the molten layer changes depending on the method of surface finishing.

On the other hand, when a gas in which 0.5 to 2% of oxygen (O ₂ ) was mixed with Ar was used as the shielding gas, no change was observed in the depth of the molten layer by any of the surface finishing methods. As a result, a stable molten layer was obtained.

[0057]

As described above, according to the present invention, since the contactor attached to the lens holder is always in contact with the laser irradiation object during laser irradiation, the condensing lens and the laser irradiation object Laser processing can be performed while always keeping the distance to the laser beam constant. As a result, it is possible to provide a laser processing head and a processing method capable of performing laser processing stably even when a laser irradiation target has a curvature such as an inner surface of a pipe or has irregularities.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a cross section of a laser processing head according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram when the laser processing head shown in FIG. 1 is housed.

FIG. 3 is a schematic view showing a laser processing head according to a second embodiment of the present invention in cross section.

FIG. 4 is a schematic diagram when the laser processing head shown in FIG. 2 is housed.

FIG. 5 is a schematic view showing a part of a third embodiment of the present invention.

FIG. 6 is a diagram showing the relationship between the surface roughness of a material and the depth of a molten layer formed by laser irradiation.

FIG. 7 is a schematic view of laser processing by a conventional apparatus.

[Explanation of symbols]

1,21 ... laser processing head, 2,22 ... processing head body,
3,23… Air cylinder, 4,24… First air chamber, 5,1
0,25 ... Spring storage chamber, 6,11,26 ... Coil spring, 7,27
... Lens holder, 8,28 ... Second air chamber, 9,29 ... Air supply port, 17,37 ... Contact, 13,33 ... Condenser lens, 14,34
... Protective glass, 15,35 ... Nozzle, 16,36 ... Laser irradiation target, 45 ... Underwater nozzle, 46 ... Shield gas ejection direction, 47 ... Void, 48 ... Shield plate.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seiichiro Kimura 2-4 Suehirocho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Inside the Toshiba Keihin Works (72) Inventor Hideyuki Minami 2-chome, Suehirocho, Tsurumi-ku, Yokohama-shi, Kanagawa 4 Toshiba Keihin Works (72) Inventor Hidenori Takahashi 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture F-term in Toshiba Yokohama Works 4F068 CA12 CB05 CD15 CJ01 CJ04 CJ05 CJ06 DB01

Claims (9)

[Claims] 1. A lens holder having a condensing lens for shaping transmitted laser light, a nozzle having a laser emission port mounted on a tip of the lens holder and allowing a laser beam to pass through, and a nozzle mounted on the tip of the nozzle. And a processing head body which holds the lens holder relatively reciprocally by inserting the lens holder through an air cylinder, wherein the air cylinder is capable of expanding and reducing the volume only in the axial direction of the air cylinder. Is provided, air is supplied to the air chamber to expand in the axial direction, and at the time of laser irradiation, the lens holder is pushed out from the inside of the processing head body toward the laser irradiation object side, and the contact is placed on the surface of the laser irradiation object. A laser processing head which is brought into contact with the laser processing head. 2. The laser processing head according to claim 1, wherein the air cylinder inserted between the lens holder and the processing head body is connected to the air cylinder itself and the lens holder or the air cylinder itself. And one of the coupling states between the processing head body and the coupling state is a reciprocally reciprocating fitting state,
And a laser processing head wherein the air chamber is formed in the reciprocating fitting portion. 3. The laser processing head according to claim 2, wherein all coupling states between the lens holder, the air cylinder, and the processing head body are set to a relatively movable fitting state, and the lens holder. And a fitting portion between the air cylinder and the air cylinder and a fitting portion between the air cylinder and the body of the processing head, wherein the air chamber is formed. 4. The laser processing head according to claim 1, wherein the laser processing head is reciprocally movable between the lens holder, the air cylinder, and the processing head body. A laser working head, wherein when the air pressure in the air chamber is reduced, the lens holder or the air cylinder is housed in the laser working head body by the restoring force of the spring. 5. A lens holder having a condensing lens for shaping transmitted laser light, a nozzle having a laser emission port mounted on the tip of the lens holder, and capable of passing laser light, and being mounted on the tip of the nozzle. And a processing head body that holds the lens holder relatively reciprocally by inserting the lens holder through an air cylinder, and the air cylinder inserted between the lens holder and the processing head body. The connection state between the air cylinder itself and the lens holder or the connection state between the air cylinder itself and the processing head body,
One of the coupling states is set to a reciprocally movable fitting state, an air chamber expandable and contractable in the axial direction is formed in the reciprocating fitting section, and a restoring spring is provided. The laser processing head characterized in that the laser holder is pushed out from the inside of the processing head body toward the laser irradiation target side by laser beam irradiation by the restoring force of the laser processing object, and the contact is brought into contact with the surface of the laser irradiation target object. 6. The laser processing head according to claim 5, wherein the expandable and contractible air chamber expands when pressurized air is supplied, and the lens holder opposes a restoring force of the restoring spring. A laser processing head configured to be accommodated in the processing head body side. 7. The processing head according to claim 1, wherein a tip end of said nozzle is provided with a shielding plate parallel to a surface of a laser irradiation object. Processing head. 8. An austenitic stainless steel which has been sensitized by a thermal cycle during welding using the laser processing head according to claim 1 and has deteriorated corrosion resistance.
In the laser processing method of irradiating a laser on the material surface of the sensitized part, oxygen gas is mixed with nitrogen gas or an inert gas used as a shielding gas blown to the laser irradiated part of the material surface during laser processing. Laser processing method. 9. The laser processing method according to claim 8, wherein the oxygen concentration in the shielding gas is 0.5 to 2 wt%.