U.S. patent application number 15/700695 was filed with the patent office on 2017-12-28 for laser cutting method.
This patent application is currently assigned to AMADA COMPANY, LIMITED. The applicant listed for this patent is AMADA COMPANY, LIMITED. Invention is credited to Hiroaki ISHIGURO, Akihiko SUGIYAMA.
Application Number | 20170368634 15/700695 |
Document ID | / |
Family ID | 47883378 |
Filed Date | 2017-12-28 |
United States Patent
Application |
20170368634 |
Kind Code |
A1 |
SUGIYAMA; Akihiko ; et
al. |
December 28, 2017 |
LASER CUTTING METHOD
Abstract
A laser cutting method and a laser cutting apparatus cut a
metallic work with a laser beam of a one-micrometer waveband. The
method and apparatus carry out the laser cutting of the work with a
ring beam RB passed through a focus position of a condenser lens 13
and having inner and outer diameters that tend to expand. The outer
diameter of the ring beam is in a range of 300 .mu.m (micrometers)
to 600 .mu.m, an inner diameter ratio of the same is in a range of
30% to 70%, and a focal depth of the condenser lens is in a range
of 2 mm to 5 mm.
Inventors: |
SUGIYAMA; Akihiko;
(Kanagawa, JP) ; ISHIGURO; Hiroaki; (Kanagawa,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
AMADA COMPANY, LIMITED |
Kanagawa |
|
JP |
|
|
Assignee: |
AMADA COMPANY, LIMITED
Kanagawa
JP
|
Family ID: |
47883378 |
Appl. No.: |
15/700695 |
Filed: |
September 11, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14344148 |
Mar 11, 2014 |
|
|
|
PCT/JP2012/073497 |
Sep 13, 2012 |
|
|
|
15700695 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23K 26/0869 20130101;
B23K 26/38 20130101; B23K 26/0734 20130101 |
International
Class: |
B23K 26/073 20060101
B23K026/073; B23K 26/38 20140101 B23K026/38; B23K 26/08 20140101
B23K026/08 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 16, 2011 |
JP |
2011-203416 |
Aug 10, 2012 |
JP |
2012-177867 |
Claims
1. A laser cutting method of cutting a work with a laser beam that
becomes a ring beam whose inner and outer diameters gradually
expand after passing a focus position of a condenser lens arranged
in a laser processing head, the laser beam including a first
portion in a region extending between the condenser lens and the
focus position of the condenser lens, the first portion of the
laser beam extends continuously within an area defined by and
entirely filling a perimeter of the first portion of the laser
beam, the perimeter of the first portion of the laser beam is
defined by a diameter of the first portion of the laser beam; and
the ring beam comprising a second portion of the laser beam, the
ring beam of the second portion of the laser beam extending within
an area defined between the outer diameter of the ring beam and the
inner diameter of the ring beam, the method comprising: providing
the laser beam; applying the first portion of the laser beam to a
surface of the work to carry out a piercing process; and
thereafter, applying the ring beam of the second portion of the
laser beam to the surface of the work to perform the cutting of the
work.
2. The laser cutting method according to claim 1, wherein after the
piercing process, the applying of the ring beam to the surface of
the work includes: moving a laser processing head toward the
surface of the work; and thereafter, moving the laser processing
head in a direction along the surface of the work.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This is a continuation of U.S. patent application Ser. No.
14/344,148, filed Mar. 11, 2014, which is a National Stage
Application of PCT/JP2012/073497, filed Sep. 13, 2012, which claims
the benefit of Japanese Patent Application No. 2012-177867, filed
Aug. 10, 2012, and of Japanese Patent Application No. 2011-203416,
filed Sep. 16, 2011. The disclosure of each of the above-identified
applications, including the specification, drawings, and claims, is
incorporated herein by reference in its entirety.
TECHNICAL FIELD
[0002] The present invention relates to a laser cutting method and
apparatus for cutting a metallic work with a laser beam of a
one-micrometer waveband, and particularly, to a method and an
apparatus for forming a laser beam into a ring beam and cutting a
work with the ring beam.
BACKGROUND ART
[0003] When cutting a metallic work with a laser beam, the laser
beam is condensed through a condenser lens into a spot of 100 .mu.m
(micrometers) to 500 .mu.m (micrometers) to increase energy density
and instantaneously heat the work to a metal melting point of 1500
degrees or over so that the work melts or sublimates. At the same
time, an assist gas is fed to remove melted material and cut the
work. When the work is a thick mild steel sheet (carbon steel
sheet), an oxygen gas is used as the assist gas to generate
oxidization reaction heat and utilize the heat as well for cutting
the work.
[0004] A laser beam of a one-micrometer waveband from a solid-state
laser or fiber laser realizes a very high optical energy
absorptance on a metallic work compared with a laser beam of a
ten-micrometer waveband from, for example, a CO2 laser. If the
one-micrometer waveband laser beam is used with an oxygen assist
gas to cut a mild steel sheet work, a melt width on a top face of
the work widens more than necessity to impair kerf control. In
addition, excessive burning (self-burning) may occur to deteriorate
the quality of the laser cutting.
[0005] Tests were conducted to compare changes in kerf width on a
top face of a work between the CO2 laser and the fiber laser by
equalizing spot diameters of laser beams emitted from the lasers,
by employing the same laser processing conditions (such as laser
output and oxygen gas pressure), and by changing a focus position
of each laser beam in a range of 0 mm to 6 mm from the top face of
the work. As illustrated in FIG. 2(A), the CO2 laser demonstrated
similar changes in both the kerf width and the focus position from
the top face of the work. On the other hand, as illustrated in FIG.
2(B), the fiber laser demonstrated larger changes in the kerf width
than in the focus position. Namely, the fiber laser provides
greater thermal effect on the work than the CO2 laser.
[0006] This means that the laser beam of a one-micrometer waveband
from the solid-state laser or fiber laser has a very high energy
density in the vicinity of the center of the laser beam, and
therefore, achieves a very high optical energy absorptance on a
work. When cutting a work with a laser beam according to a required
cut width, the laser beam is condensed to have a required spot
diameter. At this time, if an oxygen gas is used as an assist gas
for cutting the work, the work will easily cause self-burning to
expand a melt width on a top face of the work (for example, a mild
steel sheet) wider than the required cut width. Then, it is
difficult to properly conduct kerf control or stabilize the quality
of the cut work. It is required, therefore, for the laser cutting
work using the fiber laser and oxygen assist gas to realize the
same cutting quality as that realized by the CO2 laser.
[0007] For this, various tests were made and it was found that
forming a laser beam of the fiber laser into a ring beam and
cutting a work with the ring beam provide the same effect as that
provided by the CO2 laser.
[0008] A related art that forms a laser beam of the fiber laser
into a ring beam and cuts a work with the ring beam is disclosed in
WO2010/095744A1 (Patent Literature 1).
SUMMARY OF INVENTION
Problems to be Solved by Invention
[0009] FIGS. 1(A) and 1(B) schematically and conceptually
illustrates a laser cutting apparatus described in the Patent
Literature 1. The laser cutting apparatus 1 includes a laser
oscillator 3 such as a solid-state laser or a fiber laser. The
laser oscillator 3 is connected to a first end of a process fiber
5. A second end of the process fiber 5 is connected to a laser
processing head 7. The laser processing head 7 incorporates a
collimation lens (not illustrated) that forms a laser beam LB
emitted from an emission end (second end) of the process fiber 5
into a parallel beam. The laser processing head 7 also incorporates
a ring beam forming unit 9 that forms the parallel beam into a ring
beam. The ring beam forming unit 9 is made of a combination of a
conical axicon lens 11 and a condenser lens 13.
[0010] According to this configuration, an inner diameter r and an
outer diameter R of the ring beam RB gradually increase after
passing through a focus position F of the condenser lens 13.
Namely, on the lower side of the focus position F, the ring beam RB
increases its inner diameter r and outer diameter R as well as a
ratio between the inner diameter r and the outer diameter R.
[0011] A laser cutting method according to the invention described
in the Patent Literature 1 cuts a carbon steel sheet work such as a
mild steel sheet work by irradiating the work with a ring-shaped
laser beam (ring beam) to heat the work. To the heated part, the
related art jets an oxygen gas to burn the work and remove
combustion products and melted material from the work with the
kinetic energy of the oxygen gas, thereby cutting the work.
[0012] Namely, the laser cutting method described in the Patent
Literature 1 differs from the conventional laser cutting method
that uses energy of a laser beam to evaporate or melt a work and
cut the work. Instead, it resembles to a conventional gas cutting
method (refer to a paragraph 0020 of the Patent Literature 1).
[0013] According to the invention described in the Patent
Literature 1, a part of the work irradiated with the ring beam is
heated to about 900 to 1000 degrees centigrade without causing
evaporation or fusion. To the part of the work heated to this
temperature, an oxygen gas is jetted from a nozzle in the direction
of an axis of the ring beam to burn the work (mother material) and
produce fused material. The fused material and combustion products
are removed from the mother material by the kinetic energy of the
jetted oxygen gas, thereby cutting the work (mother material).
[0014] As mentioned above, the part of the work irradiated with the
ring beam is heated to 900 to 1000 degrees centigrade without
causing evaporation or fusion. To achieve this, the related art
sets an inner diameter of the ring beam to 0.5 mm to 2 mm and an
outer diameter thereof to 1.5 mm to 3 mm (refer to paragraphs 0029
and 0030 of the Patent Literature 1).
[0015] The invention described in the Patent Literature 1 heats the
work surface to 900 to 1000 degrees centigrade with the ring beam
and cuts the work with the jetted oxygen gas and the combustion
heat produced by continuation of the burning of the work itself.
The oxygen gas is sufficiently fed into a cut groove of the work to
blow continuously produced combustion and fusion materials. The
outer diameter of the ring beam is set to 1.5 mm to 3 mm to
thermally cut even a thick sheet. The width of the cut groove is
wide such as 1 mm or greater.
[0016] A laser cutting process on a work is carried out by
condensing a laser beam through a condenser lens into a spot of 100
.mu.m to 500 .mu.m. According to the thickness and the like of the
work, the position of the spot (a focus position of the condenser
lens) is changed to a top face of the work, above the top face,
below the top face, or any other location and the work is cut with
the laser beam. The width of a cut groove formed by the laser
cutting on the work is, even in a wider case, about 0.3 mm to 0.6
mm.
[0017] When the fiber laser is used to cut a work such as a mild
steel sheet, a laser beam from the fiber laser is condensed to a
spot of 100 .mu.m to 500 .mu.m. The fiber laser has a
one-micrometer waveband and achieves a high optical energy
absorption on the work and a very high energy density at the center
of the laser beam. If oxygen and/or air is used as an assist gas
like the case of the CO2 laser, the fiber laser will cause
self-burning of the work to enlarge the width of a cut groove more
than required. Therefore, cutting a work such as a mild steel sheet
with the use of the fiber laser is required to provide the same
cutting result as with the CO2 laser even if oxygen and/or air is
used as an assist gas.
Means to Solve Problems
[0018] In consideration of the problems of the related art
mentioned above, a technical aspect of the present invention
provides a laser cutting method of cutting a work of metallic
material with a laser beam of a one-micrometer waveband. The method
carries out the laser cutting of the work with a ring beam passed
through a focus position of a condenser lens and having inner and
outer diameters that tend to expand, wherein the outer diameter of
the ring beam is in a range of 300 .mu.m to 600 .mu.m and an inner
diameter ratio of the same is in a range of 30% to 70%.
[0019] Another technical aspect of the present invention provides a
laser cutting method of cutting a work with a laser beam that tends
to become a ring beam whose inner and outer diameters expand after
passing a focus position of a condenser lens arranged in a laser
processing head. The method applies a non-ring part of the laser
beam to a surface of the work to carry out a piercing process, and
thereafter, changes the laser beam applied to the surface of the
work to the ring beam to carry out the laser cutting of the
work.
BRIEF DESCRIPTION OF DRAWINGS
[0020] FIGS. 1(A) and 1(B) are explanatory views schematically and
conceptually illustrating a configuration of a laser cutting
apparatus according to a related art.
[0021] FIGS. 2(A) and 2(B) are explanatory views illustrating spot
diameter and top face kerf relationships of a CO2 laser and fiber
laser, in which FIG. 2(A) illustrates the spot diameter and top
face kerf width relationship of the CO2 laser and FIG. 2(B)
illustrates that of the fiber laser.
[0022] FIGS. 3(A) and 3(B) are explanatory views illustrating test
results about a preferable inner diameter ratio of a ring beam
according to an embodiment of the present invention, in which FIG.
3(A) illustrates a relationship among outer beam diameter, inner
diameter ratio, and cut quality and FIG. 3(B) illustrates a
relationship among outer beam diameter, inner diameter ratio, and
focal depth for preferable cut.
[0023] FIGS. 4(A) and 4(B) are explanatory views illustrating a
relationship between beam diameter and top face kerf when cutting a
work with a fiber laser beam, in which FIG. 4(A) is with a standard
condenser lens and FIG. 4(B) is with a ring beam.
[0024] FIG. 5 is an explanatory view illustrating an operation to
shift a piercing process to a cutting process.
[0025] FIGS. 6(A)-6(C) are explanatory views schematically and
conceptually illustrating configurations of laser processing heads
according to embodiments of the present invention.
[0026] FIGS. 7(A)-7(C) are explanatory views schematically and
conceptually illustrating sectional shape and energy density
relationships of a laser beam and ring beam.
MODE OF IMPLEMENTING INVENTION
[0027] Embodiments of the present invention will be explained with
reference to the drawings. The configuration, concept, and scheme
of a laser cutting apparatus according to each embodiment of the
present invention are similar to those of the laser cutting
apparatus 1 of the related art explained above. Accordingly,
elements having like functions are represented with like reference
marks to omit overlapping explanations.
[0028] The laser processing method according to the above-mentioned
related art heats a work to 900 to 1000 degrees centigrade and jets
an oxygen gas to a heated part of the work to burn and melt the
heated part with combustion heat. Namely, the related art uses the
combustion heat of the work itself to cut the work, and therefore,
material of the work is limited to iron (carbon steel).
[0029] Thermal cut of steel is carried out by utilizing a
temperature difference between a melting point of iron oxide of
1380 degrees centigrade and a melting point of pure iron of 1535
degrees centigrade. Namely, material of a work is burned to
generate oxidization heat, the oxidization heat melts iron oxide,
and the melted material is blown with gas pressure. These steps are
continued to cut the work.
[0030] As mentioned above, the laser cutting method according to
the related art uses combustion heat of a work itself to melt the
work. The related art first heats the work with a laser beam to a
temperature at which the work causes an oxidization combustion
reaction, and thereafter, continuously jets an oxygen gas so that
the work burns to produce combustion heat to melt the work. Even if
the laser beam emitted to a melted part of the work is stopped, the
work that may be very thick can be cut (this case is of a gas
cutting process).
[0031] Returning to the laser cutting process, the condenser lens
13 condenses the laser beam LB and irradiates a metallic work with
the laser beam to melt or sublimate an irradiated part of the work.
An assist gas is jetted toward the irradiated part to remove melted
or sublimated material and cut the work. If the work is made of
steel and is relatively thick, oxygen and/or air is used as the
assist gas to use oxidization reaction heat of the work as well to
cut the work.
[0032] Using oxygen and/or air as the assist gas to utilize
oxidization reaction heat of the work causes no significant problem
if the laser beam LB is of a CO2 laser. When the laser beam LB is
of a fiber laser whose wavelength is in a one-micrometer band
(10-micrometer band in the case of the CO2 laser), the wavelength
thereof is short compared to that of a beam of the CO2 laser and
achieves a very high energy absorptance on the work. Accordingly,
using oxygen and/or air as the assist gas for a relatively thick
work causes excessive burning that makes it difficult to keep a
proper cut width on a top face of the work.
[0033] To deal with this, various tests were made and it was found
that even the fiber laser using oxygen and/or air as an assist gas
is able to cut a work similar to the CO2 laser if the laser beam LB
is formed into a ring beam to disperse and decrease energy density
of the laser beam LB. With the use of a fiber laser of the same
output, a standard condenser lens and a condenser lens for forming
a ring beam were tested to find relationships between spot diameter
and kerf width on a top face of a work. Results of the tests are
illustrated in FIGS. 4(A) and 4(B). In FIGS. 4(A) and 4(B), a 0-mm
focus position agrees with the top face of the work, a minus focus
position is below the top face of the work, and a plus focus
position is above the top face of the work.
[0034] As is apparent from the test results in FIGS. 4(A) and 4(B),
cutting a steel sheet with the laser beam LB of the fiber laser and
the assist gas of oxygen and/or air with the use of the standard
condenser lens widens the top face kerf twice as large as the spot
diameter of the laser beam LB. On the other hand, the ring beam RB
formed from the laser beam LB is effective to suppress the top face
kerf to about 1.5 times as large as the spot diameter or
smaller.
[0035] When the ring beam RB formed from the laser beam LB
irradiates a work, the work is heated but sometimes is not melted,
as described in the Patent Literature 1. If the work is not melted,
an assist gas made of, for example, nitrogen is unable to remove
melted material, and therefore, the work is unable to be cut.
[0036] Accordingly, the ring beam RB emitted to a work to cut the
work must have a beam diameter that is able to melt the work, and
when using oxygen and/or air as an assist gas, the ring beam RB
must have a beam diameter to suppress a top face kerf to be small
compared to a focus diameter of the beam. Namely, the ring beam RB
formed from the laser beam LB to cut a work must have a proper
diameter at a position to irradiate the work. It is preferable to
properly set a relationship (inner diameter ratio (%)) between an
outer diameter and an inner diameter of the ring beam RB at a
position where the ring beam RB irradiates the work.
[0037] The fiber laser ring beam RB is formed and used at a
position below the focus position F of the condenser lens 13.
Accordingly, a work to be cut with the laser is so positioned that
a top face of the work is below the focus position.
[0038] Tests were conducted with the fiber laser ring beam RB to
cut a work made of SS400-19t under the conditions of 600 mm/min in
cutting speed, 3500 W in output, 1000 Hz in frequency, 80% in duty,
0.06 MPa in oxygen gas pressure, and 0 mm to +6 mm in focus
position range. Test results are illustrated in FIGS. 3(A) and
3(B).
[0039] When the spot diameter of the ring beam RB emitted to the
work is 200 .mu.m or smaller, the kerf width is narrow, a flow of
the assist gas is bad, and the laser cutting is difficult. When the
spot diameter is 700 .mu.m or greater, self-burning occurs and the
kerf width on the work top face is hardly controlled to a required
value. When the spot diameter is 300 .mu.m, it is possible to cut
the work. However, as the work becomes thicker, it becomes
difficult to cut the work. When the spot diameter is in a range of
400 .mu.m to 500 .mu.m, processibility is quite good. When the spot
diameter is 600 .mu.m, it is possible to cut the work. However, a
cut face has rough streaks and self-burning easily occurs.
[0040] For the spot diameters of 300 .mu.m, 450 .mu.m, and 600
.mu.m, cutting tests were conducted to determine a range of inner
diameter ratios. Results of the tests in connection with surface
roughness on a laser cut sectional face of each test piece at a
position 2 mm from a top face are illustrated in FIG. 3(A). As is
apparent in FIG. 3(A), in the cases of the spot diameters of 300
.mu.m, 450 .mu.m, and 600 .mu.m, it is preferable that the inner
diameter ratio is in a range of about 23% to 70%. If the inner
diameter ratio is 20% or lower, or 70% or greater, the surface
roughness gradually worsens.
[0041] Tests were made to find a relationship between focal depth
and inner diameter ratio. In connection with the focal depth, the
position of the condenser lens 13 is vertically adjusted at 1-mm
pitch to confirm a focus width to be able to cut a work. Results of
the tests are illustrated in FIG. 3(B). Applying the range of inner
diameter ratios illustrated in FIG. 3(A) to FIG. 3(B) makes it
clear that a preferable focal depth (Rayleigh length) is in a range
of 2 mm to 5 mm.
[0042] As is apparent from the above explanation, the fiber laser
is usable to form the ring beam RB and cut a work with the ring
beam RB and assist gas of oxygen and/or air so that oxidization
reaction heat (combustion heat) of the work is also used to cut the
work. At this time, the outer diameter of the ring beam is set to
300 .mu.m to 600 .mu.m and the inner diameter ratio thereof to 30%
to 70%, to suppress self-burning of the work and perform the laser
cutting similar to the CO2 laser. At the same time, a condenser
lens having a focal depth (Rayleigh length) of 2 mm to 5 mm is used
to properly carry out the laser cutting of the work.
[0043] As is already understood from the above, a laser cutting
apparatus according to an embodiment of the present invention
includes a laser oscillator, a process fiber having a first end
connected to the laser oscillator, a laser processing head provided
with a collimation lens that forms a parallel beam from a laser
beam emitted from a second end of the process fiber, and a ring
beam forming unit that forms the parallel beam into a ring beam.
The ring beam forming unit includes a condenser lens that provides
the ring beam with an outer diameter in a range of 300 .mu.m to 600
.mu.m and an inner diameter ratio in a range of 30% to 70%. The
condenser lens has a focal dept of 2 mm to 5 mm.
[0044] As mentioned above, using a fiber laser to cut a carbon
steel work with oxygen and/or air as an assist gas provides a good
cut result if a laser beam from the fiber laser is formed into a
ring beam RB having an outer diameter in the range of 300 .mu.m to
600 .mu.m and an inner diameter ratio in the range of 30% to
70%.
[0045] When cutting a work with a laser, a piercing process is
needed as an initial laser process. When piercing the work,
spatters from a pierced location of the work must be prevented from
adhering to a lens. To realize this, a gap G between a laser
processing head H and the surface of a work W illustrated in FIG. 5
is preferable to be large. After the completion of the piercing,
the laser processing head H is moved toward the work W to decrease
the gap and it is preferable to maintain the decreased gas when
moving the laser processing head H along the surface of the work to
cut the work W with a laser beam.
[0046] As mentioned above, the ring beam forming unit forms a laser
beam into a ring beam after the focus position of the condenser
lens. If the gap G between the work W and the laser processing head
H is large, the piercing will be carried out with the ring beam.
This is not preferable because the ring beam has a low energy
density. If the laser processing head H is moved toward the work W
to reduce the gap G, a part of the ring beam adjacent to the focus
position of the condenser lens or a non-ring part of the laser beam
(above the focus position) will carry out the piercing. This is not
preferable because it is unable to prevent spatters from the
piercing location from adhering to the lens.
[0047] For the laser processing head having the ring beam forming
unit for forming a laser beam into a ring beam, it is preferable
that the piercing of a work is carried out in the vicinity of the
focus position F. On the other hand, it is preferable that the
cutting of the work is carried out at a position A illustrated in
FIG. 6 where the ring beam RB formed from the laser beam LB has an
outer diameter in the range of 300 .mu.m to 600 .mu.m and an inner
diameter ratio in the range of 30% to 70%.
[0048] As is understood from FIG. 6, bringing the focus position F
closer to the surface of the work results in bringing the laser
processing head H closer to the work surface and bringing the
position A closer to the work surface results in separating the
laser processing head H away from the work surface. Accordingly,
the laser processing head H illustrated in FIG. 6 is configured so
that the focus position F is adjustable with respect to the laser
processing head H in the direction of an optical axis.
[0049] A laser processing head HA schematically and conceptually
illustrated in FIG. 6(A) includes, between the emission end of the
process fiber 5 and a ring beam forming unit 9, a collimate lens CL
that is positionally adjustable along an optical axis of a laser
beam LB so that the beam diameter of the laser beam LB made
incident to the ring beam forming unit 9 is freely adjustable. More
precisely, it includes a position adjusting unit 21 to adjust the
position of the collimate lens CL along the optical axis. The
position adjusting unit 21 has a nut member 23 arranged at a part
of the collimate lens CL and a threaded member 25 screwed into the
nut member 23. The threaded member 25 is linked to a servo motor 29
that is arranged at a proper position on a housing 27 of the laser
processing head HA.
[0050] Under the control of a controller (not illustrated), the
servo motor 29 is turned in a normal or reverse direction to adjust
the position of the collimate lens CL in the direction of the
optical axis of the laser beam LB. The configuration of the
position adjusting unit 21 is not limited to that mentioned above.
For example, a proper linear actuator such as a linear motor may be
adopted to adjust the position of the collimate lens CL. Namely,
the position adjusting unit 21 may have an optional
configuration.
[0051] The ring beam forming unit 9 may be configured in the same
manner as the related art illustrated in FIG. 1(B). In FIG. 6, the
ring beam forming unit 9 has an axicon lens 11 integrated with a
condenser lens 13. As schematically, conceptually, and
exaggeratedly illustrated in FIG. 6(C), the axicon lens 11 and
aspherical condenser lens 13 are integrated into one by laying the
condenser lens 13 over a conical face 11F of the axicon lens 11. In
other words, an apex of the axicon lens 11 is left and the conical
face 11F is formed into an annular convex face.
[0052] The axicon lens 11 and condenser lens 13 may be integrated
together by joining a flat face of the axicon lens 11 and a flat
face of the condenser lens 13 together.
[0053] When the collimate lens CL is brought closer to the emission
end of the process fiber 5 away from the ring beam forming unit 9,
the diameter of the laser beam LB transmitted through the collimate
lens CL increases and enters the ring beam forming unit 9. This
results in elongating a focal length. Then, the laser processing
head HA keeps a large gap and irradiates the work surface with a
part of the laser beam LB adjacent to the focus position F to
conduct the piercing of the work.
[0054] When the collimate lens CL is moved away from the emission
end of the process fiber 5, i.e., closer to the ring beam forming
unit 9, the focal length is shortened. As a result, the laser
processing head HA keeps a small gap and irradiates the work
surface with a part of a ring beam RB adjacent to the position A to
conduct the cutting of the work.
[0055] A laser processing head HB illustrated in FIG. 6(B) has
another configuration. The laser processing head HB has a concave
mirror CM to bend and reflect a parallel laser beam LB transmitted
through a collimate lens CL toward a ring beam forming unit 9. The
concave mirror CM has a proper actuator AC such as a fluid pressure
mechanism to freely change a curvature of a concave reflection face
of the mirror.
[0056] This configuration is able to reflect the parallel laser
beam LB transmitted through the collimate lens CL toward the ring
beam forming unit 9 by enlarging or reducing the diameter of the
laser beam LB to be made incident to the ring beam forming unit 9
to a required value, thereby adjusting a focal length. Accordingly,
this configuration provides an effect similar to that provided by
the laser processing head HA mentioned above.
[0057] As is already understood from the above, the laser
processing heads HA and HB are each provided with the beam diameter
adjusting unit capable of freely adjusting the diameter of the
laser beam LB to be made incident to the ring beam forming unit
9.
[0058] The laser beam LB transmitted through the ring beam forming
unit 9 is condensed at the focus position F as schematically
illustrated in FIG. 7(A), and below the focus position F, is formed
into the ring beam RB.
[0059] A sectional shape of the laser beam LB transmitted through
the ring beam forming unit 9 has, as illustrated in FIG. 7(B), a
minimum beam diameter at the focus position F and is not annular
but solid at the focus position F. On the upper side (the ring beam
forming unit 9 side) of the focus position F, the laser beam LB is
solid and has a larger diameter than at the focus position F. On
the lower side of the focus position F, the laser beam LB gradually
increases its diameter and forms the ring beam RB that is
hollow.
[0060] An energy density distribution of the laser beam at each
position is illustrated in FIG. 7(C). At the focus position F, the
energy density is sharp, large, and high. The energy density on the
upper side of the focus position F is smaller and lower than at the
focus position F. The energy density around the position A on the
lower side of the focus position F where the ring beam RB is formed
is smaller and lower than at the focus position F and is circularly
distributed.
[0061] When cutting a work, a non-ring part of the laser beam LB in
the vicinity of the focus position F is used to pierce the surface
of the work. At this time, the beam diameter adjusting unit is
operated to adjust the diameter of the laser beam LB to be made
incident to the ring beam forming unit 9 and the laser processing
head HA (HB) is widely separated away from the work surface to
secure a wide gap. This suppresses the entering of spatters from a
piercing spot into the laser processing head HA (HB).
[0062] After the piercing of the work, the beam diameter adjusting
unit is operated to adjust the diameter of the laser beam LB to be
made incident to the ring beam forming unit 9 and the laser
processing head HA (HB) is moved toward the work to secure a
smaller gap between the work and the laser processing head. As a
result, a part of the ring beam RB in the vicinity of the position
A is applied to the work surface and the assist gas of oxygen
and/or air is fed to cut the work.
[0063] As is understood from the above explanation, cutting a work
(carbon steel sheet) with a fiber laser beam with the use of oxygen
and/or air as an assist gas is preferably carried out by forming
the laser beam LB into the ring beam RB. When carrying out a
piercing process as an initial process of the laser beam cutting, a
gap between the laser processing head and the surface of the work
is kept wide so that a non-ring part of the laser beam LB (around
the focus position F of the condenser lens 13) is applied to the
work surface.
[0064] As mentioned above, the gap is kept wide and the non-ring
part of the laser beam LB is used to pierce the work. Namely, a
part of the laser beam LB where energy density is high is used to
efficiently pierce the work. The wide gap is able to suppress the
entering of spatters caused during the piercing into the laser
processing head.
[0065] After the piercing, the laser beam LB is formed into the
ring beam RB and the gap between the laser processing head and the
work is narrowed and kept thereat. At the same time, the assist gas
of oxygen and/or air is used to cut the work with the laser beam.
In this way, the present invention excellently achieves the laser
cutting process.
EFFECTS OF INVENTION
[0066] The present invention forms a laser beam of a one-micrometer
waveband into a ring beam having an outer diameter in a range of
300 .mu.m to 600 .mu.m and an inner diameter ratio in a range of
30% to 70%, thereby equalizing energy density levels at the center
of the laser beam and suppressing energy density. Setting the inner
diameter ratio within the range of 30% to 70% results in setting
the energy density to a proper level. The present invention is able
to use oxygen and/or air as an assist gas without causing
self-burning, and therefore, is able to solve the problems of the
related art mentioned above.
UNITED STATES DESIGNATION
[0067] In connection with United States designation, this
international patent application claims the benefit of priority
under 35 U.S.C. 119(a) to Japanese Patent Applications No.
2011-203416 filed on Sep. 16, 2011 and No. 2012-177867 filed on
Aug. 10, 2012 whose disclosed contents are cited herein.
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