LASER PROCESSING APPARATUS AND LASER IRRADIATION METHOD
5 Field of the Invention
[0001]
The present invention relates to a laser processing apparatus and a laser
irradiation method in which magnetic domains are controlled by applying a laser beam to
a grain-oriented electrical steel sheet used for transformer cores and the like.
10 Priority is claimed on Japanese Patent Application No. 2012-246305, filed
November 8, 2012, the content of which is incorporated herein by reference.
Description of Related Art
[0002]
15 A grain-oriented electrical steel sheet has a characteristic of easily allowing the
penetration of the magnetic lines of force with respect to the rolling direction during the
manufacture of a steel sheet (having an easy magnetization direction along the rolling
direction) (henceforth, also referred to as a one-oriented electrical steel sheet), and is
used as a material constituting an iron core of electric devices such as a transformer and a
20 rotator. In the grain-oriented electrical steel sheet used for iron cores, there has been a
demand to reduce the energy loss (core loss) during magnetization. In particular,
recently, in response to the intensifying global warming, there has been a global demand
for energy saving in electric devices. As a result, there has been a desire to stably
produce grain-oriented electrical steel sheets in which the core loss is reduced as much as
25 possible.
2
[0003]
The core loss is classified into an eddy-current loss and a hysteresis loss.
Furthermore, the eddy-current loss can be classified into a classical eddy-current loss and
an anomalous eddy-current loss. To reduce the classical eddy-current loss, there has
5 been provided a thin grain-oriented electrical steel sheet having an insulation film on the
sheet surface. As the grain-oriented electrical steel sheet having an insulation film
formed thereon, for example, as described in Patent Document 1, a steel sheet having a
double-layered structure in which the surface of a base steel sheet (metal section) is
coated with a glass film and the glass film is coated with an insulation film has been
10 proposed and put into practical use.
[0004]
In addition, to suppress the anomalous eddy-current loss, for example, as
described in Patent Documents 2 and 3, there has been proposed a laser magnetic domain
control method in which a laser beam is focused and emitted above an insulation film,
15 and the electrical steel sheet is scanned substantially in a width direction of the electrical
steel sheet with the laser beam (that is, in a direction substantially perpendicular to the
rolling direction) so that a region periodically having residual strain in the rolling
direction is provided, thereby reducing a magnetic domain size. According to the laser
magnetic domain control method, the scanning and irradiation of a laser beam imparts a
20 temperature history having a strong temperature gradient with respect to the sheet
thickness direction to the outermost layer region of the steel sheet, the temperature
history generates surface strain, the surface strain causes closure domains, the closure
domains reduce the 180° domain wall spacing, and particularly, the anomalous
eddy-current loss is reduced.
25 [0005]
3
The closure domains imparted through the laser magnetic domain control reduce
the 180° domain wall spacing, and decrease the anomalous eddy-current loss, but also
cause an increase in the hysteresis loss. Therefore, from the viewpoint of reducing the
total core loss, it is effective to narrow the widths of the closure domains. As an
5 invention following this technical idea, for example, Patent Document 3 discloses a
method in which strong strain is formed in a narrow region using a TEMoo mode laser
beam having an excellent focusability, and narrow closure domains having a sufficient
intensity are obtained.
[0006]
10 Meanwhile, in a laser irradiation step in the laser magnetic domain control
method, the magnetic domains are controlled by forming an insulation film on a glass
film, and radiating a laser beam above the insulation film. However, in this method,
there have been cases in which the irradiation of a laser beam increases the temperature,
and the increase in the temperature generates flaws in the insulation film and the glass
15 film. Here, the flaws refer to film damage such as the exfoliation, uplift, property
change, and color change of the insulation film and the glass film. In a case in which
flaws are generated in the glass film, the metal section below the film becomes exposed
to the outside, and there is a concern that rust may be generated. Therefore, in a case in
which flaws are generated in the glass film, it is necessary to apply the insulation film
20 again. In such a case, the addition of a step increases the manufacturing costs.
[0007]
In the manufacture of the grain-oriented electrical steel sheet, a number of
thermal treatments are carried out, and thus there are cases in which the interface
structure or thickness of the glass film or the insulation film becomes uneven in the
25 rolling direction and the width direction of the metal section of the steel sheet. As a
4
result, there have been cases in which, even when the laser conditions are adjusted, it is
difficult to suppress the generation of flaws in the glass film throughout the entire steel
sheet.
5 Patent Citation
[0008]
[Patent Document 1]
Publication No. 2007-119821
[Patent Document 2]
10 Publication No. S59-33802
[Patent Document 3]
WO2004/083465
[Patent Document 4]
Publication No. Hl-51527
15
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0009]
As described above, to efficiently manufacture a grain-oriented electrical steel
20 sheet having low core loss, it is necessary to suppress the generation of flaws in a glass
film, and to form narrow closure domains having a sufficient intensity in a metal section
of the steel sheet. However, the suppression of the generation of flaws and the
formation of the closure domains are conflicting concepts. That is, to form narrow and
deep closure domains, it is effective to increase the gradient of a temperature distribution
25 with respect to the sheet thickness direction which is formed near the outermost layer of
Japanese Unexamined Patent Application, First
Japanese Unexamined Patent Application, First
Pamphlet of International Publication No.
Japanese Examined Patent Application, Second
5
the steel sheet during the scanning and irradiation of a laser. However, when the
temperature gradient is great, the temperature at a laser be am-irradiated section on the
steel sheet surface becomes high, and thus a risk of flaws being generated in the glass
film increases. There is a demand for optimizing the laser irradiation conditions in
5 consideration of the above-described conflicting relationship, but techniques capable of
sufficiently satisfying both requirements have not yet been found.
[0010]
For example, when magnetic domains are controlled using the TEMoo mode
laser beam disclosed in Patent Document 3, it is possible to form narrow closure domains
10 having a sufficient intensity due to the high focusability, which is the characteristic of the
TEMoo mode, and a temperature distribution in which the temperature becomes high in
the middle section. Meanwhile, in this method, since the beam intensity is high near the
center, compared with a case in which the TEMoo mode is not used, there has been a
problem in that flaws are likely to be generated. As a method for suppressing the
15 generation of the above-described flaws, for example, Patent Document 4 discloses a
method in which the beam is provided with an elliptic shape that is long in the scanning
direction of the laser beam. However, according to the method in which the laser beam
having the above-described elliptic shape is used, while the generation of flaws is
suppressed, the heating time becomes long. Therefore, there has been a tendency thai
20 the widths of the closure domains become great due to the influence of thermal
conduction in a direction perpendicular to the scanning direction of the laser beam, and
there has been a problem that the reduction of the core loss is difficult.
[0011]
The present invention has been made in consideration of the above-described
25 problems. An object of the present invention is to provide a laser processing apparatus
6
and a laser irradiation method in which it is possible to suppress the generation of flaws
in a glass film while reducing the core loss of a grain-oriented electrical steel sheet.
Methods for Solving the Problem
5 [0012]
(1) That is, according to an aspect of the present invention, there is provided a
laser processing apparatus for reducing a magnetic domain size of a grain-oriented
electrical steel sheet by focusing a laser beam on the grain-oriented electrical steel sheet
and scanning the grain-oriented electrical steel sheet in a scanning direction with the
10 laser beam, including a laser oscillator emitting the laser beam; and a laser irradiation
unit applying the laser beam transmitted from the laser oscillator to the grain-oriented
electrical steel sheet, in which, the laser irradiation unit has a structure providing an
intensity distribution of the laser beam focused on the grain-oriented electrical steel sheet
on a cross-section in a direction perpendicular to the scanning direction on the
15 grain-oriented electrical steel sheet so as to satisfy lb/la < 2, where, when the integral of
the intensity distribution is calculated from the centroid of the intensity distribution in
each of the first direction and the second direction which are both perpendicular to the
scanning direction, Rai is the distance between the centroid of the intensity distribution
and a position at which the intensity integration value from the centroid of the intensity
20 distribution in the first direction is 43% of the total intensity integration value, Ra2 is the
distance between the centroid of the intensity distribution and a position at which the
intensity integration value from the centroid of the intensity distribution in the second
direction is 43% of the total intensity integration value, a beam intensity lai is the
intensity corresponding to Rai, the beam intensity Ia2 is the intensity corresponding to
25 Ra2, la is the average value of the beam intensity lai and the beam intensity Ia2 and lb is
7
the beam intensity of the laser beam at the centroid of the intensity distribution.
[0013]
(2) In the laser processing apparatus according to (1), furthermore, the structure
of the laser irradiation unit provides a C direction intensity distribution of the laser beam
5 focused on the grain-oriented electrical steel sheet on a cross-section in the scanning
direction on the grain-oriented electrical steel sheet so as to satisfy 1.5 < Id/Ic < 10,
where, when the integral of the C direction intensity distribution is calculated from the
centroid of the C direction intensity distribution in each of the third direction and the
fourth direction which are both along the scanning direction, Rci is the distance between
10 the centroid of the C direction intensity distribution and a position at which the intensity
integration value from the centroid of the C direction intensity distribution in the third
direction is 43% of the total C direction intensity integration value, Rc2 is the distance
between the centroid of the C direction intensity distribution and a position at which the
intensity integration value from the centroid of the C direction intensity distribution in
15 the fourth direction is 43% of the total C direction intensity integration value, a beam
intensity Icj is the intensity corresponding to Rci, a beam intensity Ic2 is the intensity
corresponding Rc2, Ic is the average value of the beam intensity ICJ and the beam
intensity Ic2 and Id is the beam intensity of the laser beam at the centroid of the C
direction intensity distribution.
20 [0014]
(3) In the laser processing apparatus according to (1) or (2), lb/la may be within
a range of 1.0 to 2.0.
[0015]
(4) In the laser processing apparatus according to any one of (1) to (3), when the
25 average value of Rai and Ra2 is represented by Ra, Ra may be within a range of 5 um to
8
100 urn.
[0016]
(5) In the laser processing apparatus according to (4), Ra may be within a range
of 5 umto 60 um.
5 [0017]
(6) In the laser processing apparatus according to any one of (1) to (5), when a
wavelength of the laser beam is represented by X in units of um, a beam parameter
product of the laser beam focused on the grain-oriented electrical steel sheet may be
within a range of 7Jn to 10 mm-mrad.
10 [0018]
(7) In the laser processing apparatus according to any one of (1) to (6), the laser
oscillator may be a fiber laser or a disc laser.
[0019]
(8) In the laser processing apparatus according to any one of (1) to (7), a spot
15 shape of the laser beam focused on the grain-oriented electrical steel sheet may be an
ellipse, and a short axis direction of the ellipse may be perpendicular to the scanning
direction.
[0020]
(9) According to another aspect of the present invention, there is provided a laser
20 irradiation method including a laser irradiation step for decreasing a magnetic domain
size of a grain-oriented electrical steel sheet by focusing a laser beam on the
grain-oriented electrical steel sheet and scanning the grain-oriented electrical steel sheet
in a scanning direction with the laser beam, in which, lb/la is 2.0 or less in the intensity
distribution of the laser beam focused on the grain-oriented electrical steel sheet on a
25 cross-section in a direction perpendicular to the scanning direction on the grain-oriented
9
electrical steel sheet, where, when the integral of the intensity distribution is calculated
from the centroid of the intensity distribution in each of the first direction and the second
direction which are both perpendicular to the scanning direction, Rai is the distance
between the centroid of the intensity distribution and a position at which the intensity
5 integration value from the centroid of the intensity distribution in the first direction is
43% of the total intensity integration value, Ra2 is the distance between the centroid of
the intensity distribution and a position at which the intensity integration value from the
centroid of the intensity distribution in the second direction is 43% of the total intensity
integration value, a beam intensity lai is the intensity corresponding to Raj, the beam
10 intensity Ia2 is the intensity corresponding to Ra2, la is the average value of the beam
intensity la] and the beam intensity la2 and lb is the beam intensity of the laser beam at
the centroid of the intensity distribution.
[0021]
(10) In the laser irradiation method according to (9), furthermore, Id/Ic falls
15 within a range of 1.5 to 10 in a C direction intensity distribution of the laser beam
focused on the grain-oriented electrical steel sheet on a cross-section in the scanning
direction on the grain-oriented electrical steel sheet, where, when the integral of the C
direction intensity distribution is calculated from the centroid of the C direction intensity
distribution in each of the third direction and the fourth direction which are both along
20 the scanning direction, Rci is the distance between the centroid of the C direction
intensity distribution and a position at which the intensity integration value from the
centroid of the C direction intensity distribution in the third direction is 43% of the total
C direction intensity integration value, Rc2 is the distance between the centroid of the C
direction intensity distribution and a position at which the intensity integration value
25 from the centroid of the C direction intensity distribution in the fourth direction is 43% of
5
10
the total C direction intensity integration value, a beam intensity Ici is the intensity
corresponding to Rcj, a beam intensity 1C2 is the intensity corresponding RC2, Ic is the
average value of the beam intensity Ici and the beam intensity IC2 and Id is the beam
intensity of the laser beam at the centroid of the C direction intensity distribution.
Effects of the Invention
[0022]
According to the above-described aspects of the present invention, it becomes
possible to suppress the generation of flaws in a glass film while reducing the core loss of
10 a grain-oriented electrical steel sheet.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023]
FIG. 1 is a cross-sectional view of a grain-oriented electrical steel sheet 10
15 according to the present embodiment.
FIG. 2 is a flowchart showing an example of a step for manufacturing the
grain-oriented electrical steel sheet 10 according to the present embodiment.
FIG. 3 is a schematic view showing a constitution of an example of a laser
processing apparatus 100 according to the present embodiment.
20 FIG. 4 is a schematic view showing a constitution of an example of a laser
irradiation unit 106 according to the present embodiment.
FIG. 5 is a schematic view showing a beam parameter product (BPP).
FIG. 6 is a view showing a spot shape of a laser beam on the grain-oriented
electrical steel sheet 10.
25 FIG. 7 is a view showing the intensity distribution of a laser beam according to
11
the present embodiment on a cross-section perpendicular to the laser beam scanning
direction.
FIG. 8 is a view showing the intensity distribution of the laser beam according to
a comparative example on the cross-section perpendicular to the laser beam scanning
5 direction.
FIG. 9 is a schematic view showing thermal conduction occurring in a direction
orthogonal to the scanning direction from each wing region A according to the
comparative example.
FIG. 10 is a view showing a modified example of the intensity distribution of the
10 laser beam according to the present embodiment.
FIG 11 is a view showing the intensity distribution of the laser beam according
to the present embodiment on the cross-section perpendicular to the laser beam scanning
direction.
FIG. 12 is a view showing the intensity distribution of the laser beam according
15 to the comparative example on the cross-section perpendicular to the laser beam scanning
direction.
FIG. 13 is a schematic view showing the intensity distribution of the laser beam
according to the present embodiment.
20 DETAILED DESCRIPTION OF THE INVENTION
[0024]
Hereinafter, embodiments of the present invention will be described in detail
with reference to the accompanying drawings. In the present specification and the
drawings, components having substantially the same constitution and function will be
25 given the same reference symbol, and will not be repeatedly described.
12
[0025]

A grain-oriented electrical steel sheet refers to an electrical steel sheet in which
the easy magnetization axes (in a <100> direction of a body-centered cubic crystal) of
5 crystal grains in the steel sheet substantially align along a rolling direction in a
manufacturing step. The grain-oriented electrical steel sheet has a structure in which
magnetic domains magnetized in the rolling direction are arrayed in multiple rows with a
magnetic wall interposed therebetween. The grain-oriented electrical steel sheet is
easily magnetized in the rolling direction, and is thus suitable for a core material of a
10 transformer in which the directions of the magnetic lines of force are almost constant.
[0026]
FIG. 1 is a cross-sectional view of a grain-oriented electrical steel sheet 10
according to the present embodiment. As shown in FIG. 1, the grain-oriented electrical
steel sheet 10 includes a base steel sheet (metal section) 12, glass films 14 formed on
15 both surfaces of the base steel sheet 12, and insulation films 16 formed on the glass films
14. Transformers are roughly classified into laminated core transformers and toroidal
transformers. For the toroidal transformers, a steel sheet is changed toroidally in shape
by a bending deformation so as to have a transformer shape, and then is annealed to
remove strain introduced due to the mechanical deformation (stress-relief annealing step).
20 In this annealing step, even strain introduced by the laser irradiation as described above
is released, and the magnetic domain refinement effect is lost. Meanwhile, in the
manufacture of the laminated core transformers, the strain-relief annealing step is not
required. Therefore, the grain-oriented electrical steel sheet 10 according to the present
embodiment is particularly suitable as a material for the laminated core transformers.
25 [0027]
13
The base steel sheet 12 is constituted of an iron alloy containing Si. An
example of the chemical composition of the base steel sheet 12 is Si: 2.5 mass% to 4.0
mass%, C: 0.02 mass% to 0.10 mass%, Mn: 0.05 mass% to 0.20 mass%, acid-soluble Al:
0.020 mass% to 0.040 mass%, N: 0.002 mass% to 0.012 mass%, S: 0.001 mass% to
5 0.010 mass%, and P: 0.01 mass% to 0.04 mass% with the balance of Fe and impurities.
The thickness of the base steel sheet 12 is, for example, within a range of 0.2 mm to 0.3
mm.
[0028]
The glass film 14 is constituted of a multiple oxide, for example, forsterite
10 (Mg2Si04), spinel (MgA^C^), or cordierite (Mg2Al4Si5Oi6). The thickness of the glass
film 14 is, for example, 1 um.
[0029]
The insulation film 16 is formed by, for example, baking a coating solution
mainly including colloidal silica and a phosphate (magnesium phosphate, aluminum
15 phosphate, or the like) or a coating solution that is a mixture of an alumina sol and boric
acid. The thickness of the insulation film 16 is, for example, within a range of 2 um to
3 um.
[0030]
In the grain-oriented electrical steel sheet 10 in the above-described constitution,
20 a laser beam is focused, is emitted above the insulation film 16, and the grain-oriented
electrical steel sheet is scanned substantially in a width direction (a direction
substantially orthogonal to a rolling direction) of the grain-oriented electrical steel sheet
being transported in the rolling direction (transportation direction) with the laser beam.
Temperature gradients in the sheet thickness direction and the sheet width direction,
25 which are caused by the irradiation of the laser beam, impart residual strain in linear
14
regions almost orthogonal to the rolling direction. The linear regions imparted with the
residual strain are generated in predetermined periods in the rolling direction, and in
regions which are interposed between two linear regions and are magnetized in the
rolling direction, the magnetic domain widths in a direction substantially orthogonal to
5 the rolling direction are reduced.
Hereinafter, in some cases, the above-described grain-oriented electrical steel
sheet will be referred to as the grain-oriented electrical steel sheet according to the
present embodiment.
[0031]
10
A method for manufacturing the grain-oriented electrical steel sheet 10
according to the present embodiment will be described with reference to FIG. 2. FIG. 2
is a flowchart showing an example of a step for manufacturing the grain-oriented
electrical steel sheet 10 according to the present embodiment.
15 [0032]
The step for manufacturing the grain-oriented electrical steel sheet 10, as shown
in FIG. 2, includes a casting step S2, a hot rolling step S4, an annealing step S6, a cold
rolling step S8, a decarburization annealing step S10, an annealing separator coating step
SI2, a final annealing step SI4, an insulation film formation step SI6, and a laser
20 irradiation step SI8.
[0033]
In the casting step S2, molten steel adjusted to have a predetermined
composition is supplied to a continuous casting machine, and a slab is continuously
formed. In the hot rolling step S4, the slab is heated to a predetermined temperature
25 (for example, 1150°C to 1400°C), and is hot-rolled. As a result, a hot-rolled sheet
15
having a predetermined thickness (for example, 1.8 mm to 3.5 mm) is obtained.
[0034]
In the annealing step S6, a thermal treatment (annealing) is carried out on the
hot-rolled sheet under conditions of, for example, a heating temperature within a range of
5 750°C to 1200°C and a heating time within a range of 30 seconds to 10 minutes. In the
cold rolling step S8, the surface of the hot-rolled sheet is pickled, and then cold rolling is
carried out. As a result, a cold-rolled sheet having a predetermined thickness (for
example, 0.15 mm to 0.35 mm) is obtained.
[0035]
10 In the decarburization annealing step S10, a thermal treatment (decarburization
annealing) is carried out on the cold-rolled sheet under conditions of, for example, a
heating temperature within a range of 700°C to 900°C and a heating time within a range
of 1 minute to 3 minutes, thereby obtaining the base steel sheet 12. According to the
decarburization annealing step, an oxide layer mainly including silica (SiCh) forms on
15 the surface of the base steel sheet 12. In the annealing separator coating step SI 2, an
annealing separator mainly including magnesia (MgO) is applied onto the oxide layer on
the surface of the base steel sheet 12.
[0036]
In the final annealing step SI4, the base steel sheet 12 onto which the annealing
20 separator has been applied is coiled in a coil shape, is put into a batch-type furnace, and a
thermal treatment (final annealing) is carried out. The thermal treatment conditions are,
for example, a heating temperature within a range of 1100°C to 1300°C and a heating
time within a range of 20 hours to 24 hours. At this time, so-called Goss grains which
have easy magnetization axes in the transportation direction (rolling direction) of the
25 base steel sheet 12 preferentially grow. As a result, a grain-oriented electrical steel
16
sheet having a high crystal orientation (crystal alignment) is obtained after the final
annealing. In addition, in the final annealing step S14, the oxide layer and the annealing
separator react to each other, and the glass film 14 made of forsterite (Mg2Si04) forms on
the surface of the base steel sheet 12.
5 [0037]
In the insulation film formation step S16, the base steel sheet 12 which has been
coiled in a coil shape is uncoiled, is stretched in a sheet shape, and is transported. In
addition, an insulating material is applied onto the glass films 14 formed on both surfaces
of the base steel sheet 12, and is baked, thereby forming the insulation films 16. The
10 base steel sheet 12 on which the insulation films 16 are formed is coiled in a coil shape.
[0038]
In the laser irradiation step S18, the base steel sheet 12 which has been coiled in
a coil shape is uncoiled, is stretched in a sheet shape, and is transported. In addition, a
laser beam is focused and a single surface of the base steel sheet 12 is irradiated with the
15 laser beam using a laser in-adiation unit according to the present embodiment described
below, and the grain-oriented electrical steel sheet is scanned substantially in a width
direction (a direction substantially orthogonal to the rolling direction) of the
grain-oriented electrical steel sheet being transported in the rolling direction
(transportation direction) with the laser beam. Therefore, linear strain almost
20 orthogonal to the rolling direction is formed on the surface of the base steel sheet 12 at
predetermined intervals in the rolling direction. The focusing and scanning of the laser
beam may be carried out only on the front or back surface of the base steel sheet 12, or
may be carried out on both the front and back surfaces. In addition, in the above
description, it is described that the base steel sheet 12 on which the insulation films 16
25 are formed is coiled in a coil shape, and then is sent to the laser irradiation step SI8, but
17
it is also possible to cany out the laser irradiation immediately after the formation of the
insulation films, and then coil the base steel sheet in a coil shape.
[0039]
As described above, the glass films 14 and the insulation films 16 are formed on
5 the surfaces of the base steel sheet 12, and are irradiated with the laser beam, thereby
manufacturing the grain-oriented electrical steel sheet 10 in which magnetic domains are
controlled.
[0040]
Constitution of the laser processing apparatus>
10 With reference to FIGS. 3 and 4, a constitution of an example of the laser
processing apparatus 100 (hereinafter, in some cases, referred to as the laser processing
apparatus according to the present embodiment) that irradiates the grain-oriented
electrical steel sheet 10 with a laser beam according to the present embodiment so as to
impart the residual strain will be described. The laser processing apparatus 100
15 according to the present embodiment is used to irradiate the grain-oriented electrical steel
sheet 10 with a laser beam in the laser irradiation step SI8. FIG. 3 is a schematic view
showing a constitution of an example of the laser processing apparatus 100 according to
the present embodiment.
[0041]
20 The laser processing apparatus 100 emits a laser beam above the insulation film
16 in the grain-oriented electrical steel sheet 10 being transported in the rolling direction
at a certain speed, thereby imparting linear strain almost orthogonal to the rolling
direction. The laser processing apparatus 100, as shown in FIG. 3, includes a plurality
of laser oscillators 102, a plurality of transmission fibers 104, and a plurality of laser
25 irradiation units 106. In FIG. 3, three laser oscillators 102, three transmission fibers 104,
18
and three laser irradiation units 106 are shown, and the respective constitutions are the
same. In the present embodiment, a case in which three laser oscillators, three
transmission fibers, and three laser irradiation units are provided will be described, but
the number of the units is not limited as long as the steel sheet can be scanned with the
5 laser beam throughout the entire sheet width.
FIG 4 is a schematic view shown a constitution of an example of the laser
irradiation unit 106.
[0042]
The laser oscillator 102 emits, for example, a high-output laser beam. The
10 transmission fiber 104 is an optical fiber that transmits a laser beam emitted from the
laser oscillator 102 to the laser irradiation unit 106.
[0043]
Regarding the type of the laser oscillator 102, from the viewpoint of an excellent
focusability and a capability of forming narrow closure domains, a fiber laser or a disc
15 laser is preferred. The fiber laser or the disc laser has a wavelength in a near-ultraviolet
to near-infrared range (for example, a 1 urn band), and is thus capable of transmitting a
laser beam using an optical fiber. When a laser beam is transmitted using an optical
fiber, a more compact laser processing apparatus 100 can be realized. In addition, when
the laser beam from the fiber laser or the disc laser is transmitted using an optical fiber,
20 compared with a CO2 laser or an YAG laser incapable of transmitting a laser beam using
an optical fiber, it becomes easier to control the beam intensity distribution at a position
of the spot described below, which is preferable. In addition, the laser oscillator 102
may be a continuous wave laser or a pulse laser.
[0044]
25 In a portion which is irradiated with the laser beam in the grain-oriented
19
electrical steel sheet 10, it is necessary to ensure a depth of focus to appropriately form
magnetic domains in a case in which the vibration or the like of a steel sheet surface in a
direction perpendicular to the steel sheet surface is generated. To ensure the depth of
focus, as described below, the beam quality parameter product of the laser beam is
5 preferably 10 (mm-mrad) or less. When the fiber laser or the disc laser is used as the
laser oscillator 102, it is possible to set the beam quality parameter product within the
above-described range.
[0045]
A method for quantitatively evaluating the beam qualities will be described.
10 The spot radius of the laser beam and the depth of focus of the laser beam are dependent
on the beam qualities. The beam qualities are generally quantified using a beam
parameter product (BPP).
[0046]
FIG. 5 is a schematic view showing the beam parameter product (BPP). In FIG
15 5, the laser beam that has passed through a lens is focused to a beam diameter with a
radius r, and then is enlarged again. In addition, the laser beam is focused at an angle 0.
In this case, the beam parameter product (BPP) is expressed by Equation (1) described
below in units of mm-mrad.
BPP=rx9 -(1)
20 [0047]
In addition, in this case, the depth of focus (DOF) is expressed by Equation (2)
described below using BPP in units of mm.
DOF=2000xr2/BPP--- (2)
Here, it is found that, when BPP is set to 10 (mm-mrad) or less, even in a case in
25 which r is set to 0.06 mm to obtain a narrower closure domain width, it is possible to
20
ensure a DOF of 0.7 mm or more. When a DOF of 0.7 mm or more is ensured, even in
a case in which the grain-oriented electrical steel sheet 10 vibrates in a direction
perpendicular to the sheet surface, it is effective to appropriately reduce magnetic domain
size. The lower limit value of BPP is }JTI (mnvmrad) when the wavelength of the laser
5 beam is X (um).
[0048]
The description will be continued with reference back to FIG. 3. The laser
irradiation unit 106 focuses the laser beam transmitted from the laser oscillator 102 using
the transmission fiber 104 on the grain-oriented electrical steel sheet 10 and scans the
10 grain-oriented electrical steel sheet 10 with the focused laser beam. The width to be
scanned with the laser beam by the laser irradiation unit 106 may be narrower than the
sheet width of the grain-oriented electrical steel sheet 10. When the laser irradiation
units 106 are arrayed in multiple rows in the sheet width direction as shown in FIG. 3, it
is possible to scan the entire sheet width of the grain-oriented electrical steel sheet 10
15 with the laser beam.
[0049]
The laser irradiation unit 106, as shown in FIG. 4, includes a laser head 122, a
collimator lens 124, a metal mirror 126, a polygon mirror 128, and a paraboloid mirror
130.
20 [0050]
The laser head 122 emits the laser beam transmitted using the transmission fiber
104 at a predetermined divergence angle. The collimator lens 124 alters the laser beam
emitted from the laser head 122 to a collimated beam.
[0051]
25 The metal mirror 126 is a mirror to reduce and adjust the beam diameter of the
21
incident laser beam in the sheet width direction (refer to FIG. 3) of the grain-oriented
electrical steel sheet 10. As the metal mirror 126, it is possible to use, for example, a
columnar mirror or a paraboloid mirror which has curvature in a single axis direction.
The laser beam reflected on the metal mirror 126 is incident on the polygon mirror 128
5 rotating at a predetermined rotation speed.
[0052]
The polygon mirror 128 is a rotatable polyhedron, and moves the laser beam in
the sheet width direction of the grain-oriented electrical steel sheet 10 by being rotated.
While the laser beam is incident on one surface of the polyhedron of the polygon mirror
10 128, a linear region is scanned with the laser beam substantially in a sheet width direction
on the grain-oriented electrical steel sheet 10 in accordance with the rotation of the
surface. As a result, residual strain is imparted to the linear region. In accordance
with the rotation of the polygon mirror 128, scanning is repeated with the laser beam, and
simultaneously, the grain-oriented electrical steel sheet 10 is transported in the rolling
15 direction. As a result, regions having linear residual strain are periodically formed on
the grain-oriented electrical steel sheet 10 in the rolling direction. Meanwhile, the
period of the linear regions in the rolling direction is adjusted using the transportation
speed of the grain-oriented electrical steel sheet 10 and the rotation speed of the polygon
mirror 128.
20 [0053]
The paraboloid mirror 130 is a mirror to reduce and adjust the beam diameter of
the laser beam reflected on the polygon mirror 128 in the rolling direction. The laser
beam reflected by the paraboloid mirror 130 is focused on the surface of the
grain-oriented electrical steel sheet 10.
25 [0054]
22
FIG. 6 is a view showing the spot shape of the laser beam on the grain-oriented
electrical steel sheet 10. In the present embodiment, the spot shape of the laser beam is
an elliptical shape as shown in FIG. 6, and has a long axis along the scanning direction of
the laser beam LB (the long axis and the scanning direction of the laser beam LB are
5 almost parallel to each other) and a short axis substantially orthogonal to the scanning
direction (that is, almost 90°, and cases of being not strictly 90° are also included).
When the spot shape is set to an elliptical shape as described above, the heating time by
the irradiation with the laser beam at one point on the steel sheet becomes long. As a
result, the temperatures at deep positions inside the grain-oriented electrical steel sheet
10 10 can be increased, and the core loss can be effectively reduced. Regarding a spot
shape of the laser beam, an elliptical spot can be obtained by reducing the beam diameter
in the scanning direction of the laser beam LB using the metal mirror 126, and reducing
the beam diameter in a direction orthogonal to the scanning direction using the
paraboloid minor 130. In a case in which the grain-oriented electrical steel sheet 10 is
15 scanned with the laser beam LB in the width direction while the grain-oriented electrical
steel sheet is transported in the rolling direction, the scanning direction seen from the
laser irradiation unit 106 and the scanning direction seen from the grain-oriented
electrical steel sheet 10 are different from each other. The scanning direction of the
laser beam LB in the present embodiment refers to the scanning direction seen from the
20 grain-oriented electrical steel sheet 10.
[0055]
In the above description, the spot shape of the laser beam on the grain-oriented
electrical steel sheet 10 is set to an elliptical shape, but is not limited thereto. For
example, the spot shape of the laser beam may be an exact circle shape.
25 [0056]
23
In addition, in the above description, the laser oscillator 102 is the fiber laser or
the disc laser, but is not limited thereto. For example, the laser oscillator 102 may be a
CO2 laser. In this case, the laser beam is transmitted from the laser oscillator 102 to the
laser irradiation unit 106 using a mirror or the like in place of the optical fiber.
5 [0057]

Meanwhile, the grain-oriented electrical steel sheet 10 to which a magnetic field
is applied in the rolling direction, as described above, has a structure in which magnetic
domains magnetized in the rolling direction are arrayed in multiple rows. Here, to
10 further reduce the core loss of the grain-oriented electrical steel sheet 10, it is effective to
reduce the magnetic domain size (narrow the magnetic domains) by irradiating with the
laser beam. To reduce the magnetic domain size, it is particularly effective to form
narrower closure domains having a sufficient intensity by imparting a great temperature
gradient with respect to the sheet thickness direction to extremely narrow regions along
15 the rolling direction near the outermost layer of the grain-oriented electrical steel sheet
10.
[0058]
To increase the temperature gradient, it is necessary to increase the temperature
of the surface of the grain-oriented electrical steel sheet 10. However, when the
20 temperature of the surface is increased, there are cases in which the temperature increase
causes flaws, such as the exfoliation of films, in the insulation film 16 or the glass film
14. Particularly, in a case in which flaws are generated in the glass film 14, the base
steel sheet 12 is exposed to the outside, and there is a concern that rust may be generated,
which is not desirable.
25 [0059]
24
Therefore, in the present embodiment, to realize both the reduction of the core
loss of the grain-oriented electrical steel sheet 10 and the prevention of the generation of
flaws in the glass film 14, as described below, the intensity distribution of the laser beam
on the surface of the grain-oriented electrical steel sheet 10 is set so that predetermined
5 conditions are satisfied.
[0060]

The setting of the intensity distribution of the laser beam on the surface of the
10 grain-oriented electrical steel sheet 10 of the present embodiment will be described with
comparison with comparative examples.
[0061]
FIG. 7 is a view showing the intensity distribution of the laser beam according to
the present embodiment. FIG. 8 is a view showing the intensity distribution of the laser
15 beam according to a comparative example. Both FIGS. 7 and 8 show the distributions
of the beam intensity I (the output power of the laser beam per unit area) on a
cross-section perpendicular to the scanning direction of the laser beam passing through
the centroid of the laser beam with respect to the scanning direction. The horizontal
axis in FIGS. 7 and 8 indicates the distance x from the centroid of the intensity
20 distribution (the definition of the x axis is shown in FIG. 6). Here, the centroid of the
intensity distribution with respect to the scanning direction is defined as, when the
scanning direction of the laser beam is defined as the y axis, the centroid position y of the
intensity integration value (this integration value serves as a function of y) obtained by
the integral of the intensity distribution of the laser beam, which serves as functions of x
25 and y, along the x axis with respect to individual y values. Meanwhile, the comparative
25
example shown in FIG. 8 is an intensity distribution in a case in which a so-called TEMoo
mode laser beam is focused on the grain-oriented electrical steel sheet 10. The TEMoo
mode refers to a mode showing the Gaussian distribution in which the maximum beam
intensity is present in the central section of the intensity distribution as shown in FIG. 8.
5 [0062]
In the case of the comparative example, as shown in FIG. 8, the beam intensity is
distributed in a wide range in a direction orthogonal to the scanning direction (the x-axis
direction), and wing regions A are present in both sides of the intensity distribution (that
is, both sides of the intensity distribution smoothly extend). In a case in which the wing
10 regions A are present as described above, thermal conduction easily occurs from the wing
regions A in a direction orthogonal to the scanning direction of the laser beam.
[0063]
FIG. 9 is a schematic view showing thermal conduction occurring in a direction
orthogonal to the scanning direction from the wing region A in the intensity distribution
15 of the laser beam according to the comparative example. When the laser beam LB is
moved in the scanning direction as shown in FIG. 9, thermal conduction occurs in a
direction orthogonal to the scanning direction from the wing region A. Therefore,
regions in which the temperature increases spread in a wide range in a direction
orthogonal to the scanning direction, and the closure domain widths are likely to widen.
20 As a result, the reduction of the core loss of the grain-oriented electrical steel sheet 10 is
hindered.
[0064]
On the contrary, in the case of the intensity distribution of the laser beam
according to the present embodiment, as shown in FIG. 7, the widths of the wing regions
25 in the intensity distribution are narrow, and the beam intensity is distributed in a narrow
26
range in a direction orthogonal to the scanning direction. Therefore, the occurrence of
thermal conduction in a direction orthogonal to the scanning direction from the wing
region is suppressed, and the closure domain widths become narrow. As a result,
compared with the comparative example, it becomes possible to further reduce the core
5 loss of the grain-oriented electrical steel sheet 10.
[0065]
In the intensity distributions of the laser beam shown in FIGS. 7 and 8, distances
Rai and Ra2, a beam intensity lai, a beam intensity Ia2, and a beam intensity lb are
defined as described below. The distance Rai represents the distance from the centroid
10 of the intensity distribution to a position on the x axis at which the intensity integration
value obtained by the integral of the intensity distribution from the centroid of the
intensity distribution in the —x direction (the first direction, the left direction on the paper
in FIG. 7) is 43% of the total intensity integration value. In addition, the distance Ra2
represents the distance from the centroid of the intensity distribution to a position on the
15 x axis at which the intensity integration value obtained by the integral of the intensity
distribution from the centroid of the intensity distribution in the +x direction (the second
direction, the right direction on the paper in FIG. 7) is 43% of the total intensity
integration value. That is, in FIG. 7, the area of the hatched region indicated by Raj and
Ra2 accounts for 86% (43%+43%) of the value obtained by the integral of the entire
20 intensity distribution in FIG. 7 (this definition shall also apply to FIG. 8). In addition,
the beam intensity lai represents the beam intensity at the position of the distance Rai,
and the beam intensity Ia2 represents the beam intensity at the position of the distance
Ra2. The average value of lai and Ia2 is represented by la. Meanwhile, in a case in
which the laser beam is bilaterally symmetric, Rai and Ra2, and lai and Ia2 become equal.
25 The beam intensity lb represents the beam intensity at the centroid of the intensity
27
distribution.
[0066]
In the intensity distribution of the laser beam according to the comparative
example shown in FIG. 8, lb/la is 2.8. On the contrary, in the intensity distribution of
5 the laser beam according to the present embodiment shown in FIG. 7, to suppress the
peak of the intensity and suppress thermal conduction in a direction orthogonal to the
scanning direction, lb/la is set to 2.0 or less, preferably within a range of 1.0 to 2.0.
When the intensity distribution of the laser beam on the surface of the grain-oriented
electrical steel sheet 10 is set so that lb/la falls within a range of 1.0 to 2.0, the
10 occurrence of thermal conduction is suppressed, and it becomes possible to significantly
reduce the core loss.
Ib/Ia can be appropriately adjusted through, in the laser processing apparatus,
for example, a change in the type of the laser beam and/or the selection of the metal
mirror 126 or the paraboloid mirror 130 having appropriate curvature (focal length).
15 [0067]
In addition, in the present embodiment, when the average value of Rai and Ra2
is represented by Ra, the intensity distribution of the laser beam is set so that Ra is 100
fim (0.1 mm) or less. Therefore, narrower closure domains are formed while the
distance of thermal conduction in a direction orthogonal to the scanning direction is
20 further diminished, and thus it is possible to more significantly reduce the core loss. To
reliably reduce the core loss, it is more desirable to set Ra to 60 um or less. When Ra
reaches less than 5 um, the depth of focus becomes too shallow, which is not desirable.
[0068]
According to a laser beam having the intensity distribution of the laser beam
25 according to the present embodiment, it is possible to suppress the generation of flaws in
28
the glass film 14. In a case in which the intensity distribution of the laser beam is the
Gaussian distribution as shown in FIG. 8, high beam intensity (the beam intensity lb
shown in FIG. 8) appears at the center section of the intensity distribution. In such a
case, the beam intensity becoming too high at the center section of the intensity
5 distribution locally increases the temperature on the surface of the grain-oriented
electrical steel sheet 10, and there is a concern that flaws may be generated in the glass
film 14.
[0069]
On the contrary, in a case in which the intensity distribution of the laser beam
10 has an intensity distribution as shown in FIG. 7, the beam intensity distribution appears in
a substantially rectangular shape, and thus, compared with the comparative example, the
beam intensity (the beam intensity lb shown in FIG. 7) does not become too high at the
center section. Therefore, it is possible to reduce a local temperature increase on the
surface of the grain-oriented electrical steel sheet 10, and thus it is possible to suppress
15 the generation of flaws in the glass film 14.
[0070]
In the above description, the intensity distribution of the laser beam according to
the present embodiment is described to look like a distribution as shown in FIG. 7, but
the intensity distribution of the laser beam is not limited thereto. For example, FIG. 10
20 is a view showing a modified example of the intensity distribution of the laser beam
according to the present embodiment. In an intensity distribution as shown in FIG. 10,
the beam intensities at both end sections of the distribution are slightly higher than the
beam intensity at the center section. Therefore, lb/la becomes less than 1, and therefore
2.0 or less. This intensity distribution shown in FIG. 10 is the same as the intensity
25 distribution shown in FIG. 7 in that no wing regions are present in either side of the
29
intensity distribution. Therefore, similar to the intensity distribution shown in FIG. 7,
the distance of thermal conduction in a direction orthogonal to the scanning direction is
decreased, and it is possible to significantly reduce the core loss. That is, when lb/la is
2.0 or less, the distance of thermal conduction in a direction orthogonal to the scanning
5 direction is decreased, and it is possible to significantly reduce the core loss. In a case
in which the center of the intensity distribution is lower than the edge sections, and lb/la
reaches less than 1.0, the temperatures at the edge sections easily increase, and thus there
is a tendency that the distance of thermal conduction in a direction orthogonal to the
scanning direction becomes great. From this viewpoint, lb/la is desirably 1.0 or more.
10 [0071]
In addition, FIGS. 7 to 9 shown above show cases in which the spot shape of the
laser beam is an elliptical shape, but the spot shape is not limited thereto. For example,
even in a case in which the spot shape of the laser beam is an exact circle shape, when
lb/la is set to be 2.0 or less, it is possible to reduce the core loss, and suppress the
15 generation of flaws in the glass film 14.
[0072J
In a case in which the laser beam focused and moved in the present embodiment
is seen on a cross-section in the scanning direction of the laser beam passing through the
centroid of the laser beam with respect to a direction orthogonal to the scanning direction,
20 the laser beam intensity distribution (C direction intensity distribution) appears in a shape
as shown in FIG. 11. FIG. 11 is a view in which, in a case in which the scanning
direction of the laser beam is indicated along the y axis, the beam intensity I is indicated
along the vertical axis, and the distance y from the centroid of the intensity distribution is
indicated along the horizontal axis. Here, the centroid of the laser beam with respect to
25 a direction orthogonal to the scanning direction is defined as the centroid position x of
30
the intensity integration value (this integration value serves as a function of y) obtained
by the integral of the intensity distribution of the laser beam, which serves as functions of
x and y, along the y axis with respect to individual x values.
In the intensity distribution of the laser beam in FIG. 11, the distance from the
5 centroid of the intensity distribution to a position on the y axis at which the intensity
integration value obtained by the integral of the intensity distribution from the centroid of
the intensity distribution in the -y direction (the third direction, the left direction on the
paper in FIG. 11) is 43% of the total intensity integration value is represented by Rcj, the
distance from the centroid of the intensity distribution to a position on the y axis at which
10 the intensity integration value obtained by the integral of the intensity distribution from
the centroid of the intensity distribution in the +y direction (the fourth direction, the right
direction on the paper in FIG. 11) is 43% of the total intensity integration value is
represented by R.C2 (that is, in FIG. 11, the area of the hatched region accounts for 86% of
the value obtained by the integral of the entire intensity distribution in FIG. 11), the beam
15 intensity at the position of the distance Rci is represented by Ici, the beam intensity at the
position of the distance Rc2 is represented by Ic2, the average value of Ici and IC2 is
represented by Ic, and the beam intensity at the centroid of the intensity distribution is
represented by Id, Ic and Id satisfy Id/Ic > 1.5.
The comparative example shown in FIG. 12 is an intensity distribution in a case
20 in which the beam intensity distribution is close to a so-called top flat distribution. In
such a case, Id/Ic is less than 1.5. In the top flat-type intensity distribution, an abrupt
temperature increase on the surface of the grain-oriented electrical steel sheet occurs in
response to an abrupt rise in the spatial intensity distribution, and flaws become likely to
be generated in the films due to a thermal shock.
25 When Id/Ic is 1.5 or more, the intensity distribution smoothly rises, and the
31
abrupt temperature increase on the surface of the grain-oriented electrical steel sheet is
suppressed, and thus flaws are not easily generated in the films, which is preferable.
When Id/Ic becomes too great, the intensity at the centroid section becomes too
high, and therefore it is desirable to set Id/Ic to 10 or less.
5 [0073]
FIG. 13 is a schematic view showing the beam intensity of the laser beam in
which the distribution of the beam intensity I on a cross-section perpendicular to the
scanning direction of the laser beam is as in FIG. 7, and the distribution of the beam
intensity I on a cross-section in the scanning direction of the laser beam is as in FIG. 11.
10 [0074]

The present examples and the comparative examples will be described to
confirm the effectiveness of the examples according to the present embodiment described
above.
15 [0075]
First, a slab having a chemical composition of Si: 3.0 mass%, C: 0.05 mass%,
Mn: 0.1 mass%, acid-soluble Al: 0.02 mass%, N: 0.01 mass%, S: 0.01 mass%, and P:
0.02 mass% with the balance of Fe and impurities was prepared. Hot rolling was
carried out on this slab at 1280°C, thereby obtaining a 2.3 mm-thick hot-rolled sheet.
20 Next, a thermal treatment was carried out on the obtained hot-rolled sheet under
conditions of 1000°Ol minute (a heating temperature of 1000°C and a soaking time of
1 minute). After the thermal treatment, a pickling was carried out on the hot-rolled
sheet, and cold rolling was carried out, thereby obtaining a 0.23 mm-thick cold-rolled
sheet. Decarburization annealing was carried out on this cold-rolled sheet at 800°C for
25 2 minutes. Next, an annealing separator mainly including magnesia was applied to both
32
surfaces of the cold-rolled sheet that had been subjected to the decarburization annealing.
In addition, the cold-rolled sheet onto which the annealing separator had been applied
was coiled in a coil shape, was put into a batch-type furnace, and final annealing was
carried out at 1200°C for 20 hours. Therefore, a steel sheet (the base steel sheet 12)
5 having glass films formed on both surfaces was manufactured. Next, an insulating
material made of aluminum phosphate was applied onto the glass films 14, and then
baking (850°Cxl minute) was carried out, thereby forming the insulation films 16.
[0076]
In addition, the base steel sheet 12 on which the insulation films 16 and the glass
10 films 14 were formed was irradiated with a laser beam, and strain was imparted to the
surface of the base steel sheet 12.
[0077]
The laser irradiation unit 106 shown in FIG. 1 was used as a laser irradiation unit,
the intensity distribution of the laser beam on the steel sheet surface was set to an
15 elliptical shape, and the long axis of the ellipse was aligned in the scanning direction of
the laser beam on the steel sheet surface. In addition, to compare the present example
and the comparative example, tests were carried out under a variety of conditions in
which lb/la, Ra, and Id/Ic, which are defined as described above, were differed with
respect to the intensity distributions of the beam on a cross-section in the scanning
20 direction of the laser beam and a cross-section in a direction perpendicular to the
scanning direction by changing a variety of conditions such as the type of a fiber laser
that was used as the laser oscillator 102, the core diameter of the optical fiber, the focal
length of the collimator lens, the focal lengths of the metal mirror 126 and the paraboloid
mirror 130, and the distances from these optical elements to the steel sheet surface.
25 Regarding the irradiation conditions, the scanning speed Vc was set to 160 m/s, the
33
irradiation pitch PL was set to 5 mm, and the wavelength X of the laser beam was set to
1.08 urn.
[0078]
lb/la was experimentally obtained as described below. First, the beam intensity
5 distribution at the steel sheet surface position was measured using a commercially
available focused laser beam evaluation instrument. Next, the beam intensity
distribution on the short axes of the ellipses of the measured elliptical laser beam spots,
that is, a cross-section perpendicular to the scanning direction of the laser beam passing
through the centroid of the laser beam with respect to the scanning direction of the laser
10 beam was obtained. Finally, Rai, Ra2, Ra which is the average value of Rai and Ra2,
and la were obtained, and lb/la was computed.
Simultaneously, the beam intensity distribution on the long axes of the ellipses
of the measured elliptical laser beam spots, that is, a cross-section in the scanning
direction of the laser beam passing through the centroid of the laser beam with respect to
15 a direction orthogonal to the scanning direction of the laser beam was obtained, Rci, Rc2,
Re which is the average value of Rci and Rc2, and Ic were obtained, and Id/Ic was
computed.
Meanwhile, in the laser beam used in the present example, Rai was equal to Ra2,
and Rci was equal to Rc2.
20 [0079]
Apart of the laser-treated steel sheet and a laser-untreated section of the steel
sheet sampled from the same coil were put into a single sheet tester (SST), and a core
loss W17/50 (W/kg) was evaluated. Wn/50 represents the core loss at a frequency of 50
Hz and a maximum magnetic flux density of 1.7T. As test specimens for the SST
25 measurement, rectangular specimens cut into sizes of a steel sheet width direction length
34
of 100 mm and a steel sheet rolling direction length of 500 mm were used. The core
loss improvement ratio (%) of the laser-treated steel sheet is defined on the basis of the
core loss of the laser-untreated section of the steel sheet sampled from the same coil.
[0080]
5 In addition, whether or not rust was generated by the generation of flaws in the
glass film 14 was determined through a humidity cabinet test. The humidity cabinet test
was carried out in accordance with JIS K2246-5.34, and the test conditions were set to a
temperature of 50°C, a humidity of 98%, and a test time of 72 hours. After that,
whether or not rust was generated in the laser-irradiated section was visually checked.
10 For individual conditions, 10 rectangle specimens having sizes of a steel sheet width
direction length of 100 mm and a steel sheet rolling direction length of 500 mm were cut
out, and evaluation was carried out on the basis of the number of specimens on which
rust is generated.
[0081]
15 The test results are described in Table 1. In Examples 1 to 5 in which lb/la was
2.0 or less, a sufficient core loss improvement ratio of 12% or more was obtained. In
addition, there was no specimen on which rust was generated, and the generation of flaws
in the glass film 14 by the laser irradiation was suppressed.
Example 6 is an example in which the steel sheet surface was set to the focal
20 position of the metal mirror 126. In this case, the C direction intensity distribution
became close to the top flat distribution, and Id/Ic was 1.3. When Example 6 is
compared with Examples 3 and 4 having the same lb/la, the core loss was improved to
the same extent, but there were two samples on which rust was generated. From the
above-described results, it is found that Id/Ic is desirably set to 1.5 or more since flaws
25 are not easily generated in the films.
35
In addition, when Example 1 and Examples 2 to 6 are compared with each other,
it is found that Id/Ic is desirably set to be greater than lb/la since the core loss is further
improved.
[0082]
5 Comparative Example 1 is an example in which the TEMoo mode laser (laser
beam) was used. In Comparative Example 1, lb/la was 2.8, and the core loss
improvement ratio was 10.2%. While a core loss improvement of 12% or more is
required to satisfy the target product grade, Comparative Example 1 failed to achieve the
target in terms of the core loss improvement ratio. Furthermore, in Comparative
10 Example 1, rust was generated in the glass film 14 in two specimens out of 10.
[0083]
Comparative Example 2 as well is an example in which the TEMoo mode laser
(laser beam) was used. When Ra (Rai and Ra2) was decreased using the good
focusability of the TEMoo mode as in Comparative Example 2, a core loss improvement
15 of 12% or more was obtained. However, in a case in which the TEMoo mode laser was
used with a reduced Ra, it is found that rust was generated in all 10 samples, and flaws
are significantly generated in the glass films 14 by the laser irradiation. In a case in
which a laser is used under the conditions of Comparative Example 2, it becomes
necessary to coat the insulation films 16 again, and thus the manufacturing costs
20 significantly increase.
[0084]
[Table 1]
[0085]
From the above-described test results, it is found that, when lb/la is set to 2.0 or
less as in the present example, not only a sufficient core loss-improving effect but also an
5 effect that suppresses the generation of flaws in the glass film 14 is obtained. In
addition, it is found that, when Id/Ic is set to 1.5 or more, the generation of flaws can be
further suppressed.
[0086]
As described above, in the intensity distribution on a cross-section in a direction
10 perpendicular to the scanning direction of the laser beam, when the distances from the
centroid of the intensity distribution to the positions at which the intensity integration
value from the centroid of the intensity distribution is 43% of the total intensity
integration value are represented by Rai and Ra2, the intensities of the laser beam
corresponding to Rai and Ra2 are respectively represented by Iaj and Ia2, the average
15 value of Iaj and Ia2 is represented by la, and furthermore, the intensity of the laser beam
at the centroid of the intensity distribution is represented by lb, the laser processing
apparatus 100 according to the present embodiment is constituted so that Tb/Ia is 2.0 or
less. Therefore, it is possible to set the intensity distribution of the laser beam on the
37
surface of the grain-oriented electrical steel sheet 10 to an optimal shape. As a result, it
is possible to reduce thermal conduction in a direction orthogonal to the scanning
direction when the laser beam is moved in the scanning direction. Therefore, even in a
case in which the spot shape is made to be elliptical to form closures domains having a
5 sufficient intensity, and accordingly, the irradiation time with the laser beam at one point
on the grain-oriented electrical steel sheet 10 becomes long, it becomes possible to limit
an increase in the closure domain width caused by thermal conduction. As a result, it
becomes possible to further reduce the core loss of the grain-oriented electrical steel
sheet 10.
10 [0087]
In addition, in the intensity distribution of the laser beam according to the
present embodiment, it is possible to restrict the beam intensity lb from becoming too
high at the centroid of the intensity distribution, and thus it is possible to limit the local
temperature increase on the surface of the grain-oriented electrical steel sheet 10, and
15 consequently, it is possible to inhibit the generation of flaws in the glass films 14.
[0088]
According to the laser processing apparatus 100 according to the present
embodiment, since the core loss is reduced, and flaws in the glass films are decreased, it
is possible to stably manufacture the grain-oriented electrical steel sheet 10 having low
20 core loss with a favorable yield. As a result, not only does it become possible to supply
the grain-oriented electrical steel sheet 10 having low core loss at a lower price, but it is
also possible to reduce the energy consumption by widely distributing the grain-oriented
electrical steel sheet 10 having low core loss across the globe. Therefore, significant
economic effects are exhibited.
25 [0089]
38
Thus far, the preferred embodiment and examples of the present invention have
been described in detail with reference to the accompanying drawings, but the present
invention is not limited thereto. It is needless to say that a person skilled in the art can
conceive of a variety of modified examples and corrected examples within the scope of
5 the technical ideas described in the claims, and those examples are also, surely,
interpreted to be included in the technical scope of the present invention.
Industrial Applicability
[0090]
10 According to the present invention, it becomes possible to suppress the
generation of flaws in the glass films while reducing the core loss of the grain-oriented
electrical steel sheet.
Reference Symbol List
15 [0091]
10: GRAIN-ORIENTED ELECTRICAL STEEL SHEET
12: BASE STEEL SHEET
14: GLASS FILM
16: INSULATION FILM
20 100: LASER PROCESSING APPARATUS
102: LASER OSCILLATOR
104: TRANSMISSION FIBER
106: LASER IRRADIATION UNIT
122: LASER HEAD
25 124: COLLIMATOR LENS
39
126: METAL MIRROR
128: POLYGON MIRROR
130: PARABOLOID MIRROR

What is claimed is:
1. A laser processing apparatus for reducing a magnetic domain size of a grain-oriented
electrical steel sheet by focusing a laser beam on the grain-oriented electrical steel sheet
5 and scanning the grain-oriented electrical steel sheet in a scanning direction with the
laser beam, the laser processing apparatus comprising:
a laser oscillator emitting the laser beam; and
a laser irradiation unit applying the laser beam transmitted from the laser
oscillator to the grain-oriented electrical steel sheet,
10 wherein the laser irradiation unit has a structure providing an intensity
distribution of the laser beam focused on the grain-oriented electrical steel sheet on a
cross-section in a direction perpendicular to the scanning direction on the grain-oriented
electrical steel sheet so as to satisfy lb/la < 2, where, when an integral of the intensity
distribution is calculated from a centroid of the intensity distribution in each of a first
15 direction and a second direction which are both perpendicular to the scanning direction,
Rai is a distance between the centroid of the intensity distribution and a position at which
an intensity integration value from the centroid of the intensity distribution in the first
direction is 43% of a total intensity integration value, Ra2 is a distance between the
centroid of the intensity distribution and a position at which an intensity integration value
20 from the centroid of the intensity distribution in the second direction is 43%o of the total
intensity integration value, a beam intensity Iaj is an intensity corresponding to the Rai,
the beam intensity Ia2 is an intensity corresponding to the Ra2, la is an average value of
the beam intensity lai and the beam intensity Ia2 and lb is a beam intensity of the laser
beam at the centroid of the intensity distribution.
25
41
2. The laser processing apparatus according to Claim 1,
wherein the structure of the laser irradiation unit provides a C direction intensity
distribution of the laser beam focused on the grain-oriented electrical steel sheet on a
cross-section in the scanning direction on the grain-oriented electrical steel sheet so as to
5 satisfy 1.5 < Id/Ic < 10, where, when an integral of the C direction intensity distribution
is calculated from a centroid of the C direction intensity distribution in each of a third
direction and a fourth direction which are both along the scanning direction, Rci is a
distance between the centroid of the C direction intensity distribution and a position at
which an intensity integration value from the centroid of the C direction intensity
10 distribution in the third direction is 43% of a total C direction intensity integration value,
Rc2 is a distance between the centroid of the C direction intensity distribution and a
position at which an intensity integration value from the centroid of the C direction
intensity distribution in the fourth direction is 43% of the total C direction intensity
integration value, a beam intensity Ici is an intensity corresponding to the Rci, a beam
15 intensity Ic2 is an intensity corresponding the RC2, Ic is an average value of the beam
intensity Ici and the beam intensity Ic2 and Id is a beam intensity of the laser beam at the
centroid of the C direction intensity distribution.
3. The laser processing apparatus according to Claim 1 or 2,
20 wherein the lb/la is within a range of 1.0 to 2.0.
4. The laser processing apparatus according to any one of Claims 1 to 3,
wherein Ra is within a range of 5 urn to 100 urn, where the Ra is an average
value of the Rai and the Ra2.
25
42
5. The laser processing apparatus according to Claim 4,
wherein the Ra is within a range of 5 um to 60 um.
6. The laser processing apparatus according to any one of Claims 1 to 5,
5 wherein a beam parameter product of the laser beam focused on the
grain-oriented electrical steel sheet is within a range of )Jn to 10 mm-mrad, where X is a
wavelength of the laser beam in units of um,
7. The laser processing apparatus according to any one of Claims 1 to 6,
10 wherein the laser oscillator is a fiber laser or a disc laser.
8. The laser processing apparatus according to any one of Claims 1 to 7,
wherein a spot shape of the laser beam focused on the grain-oriented electrical
steel sheet is an ellipse, and
15 a short axis direction of the ellipse is perpendicular to the scanning direction.
9. A laser irradiation method comprising a laser irradiation step for reducing a magnetic
domain size of a grain-oriented electrical steel sheet by focusing a laser beam on the
grain-oriented electrical steel sheet and scanning the grain-oriented electrical steel sheet
20 in a scanning direction with the laser beam,
wherein lb/la is 2.0 or less in an intensity distribution of the laser beam focused
on the grain-oriented electrical steel sheet on a cross-section in a direction perpendicular
to the scanning direction on the grain-oriented electrical steel sheet, where, when an
integral of the intensity distribution is calculated from a centroid of the intensity
25 distribution in each of a first direction and a second direction which are both
43
perpendicular to the scanning direction, Rai is a distance between the centroid of the
intensity distribution and a position at which an intensity integration value from the
centroid of the intensity distribution in the first direction is 43% of a total intensity
integration value, Ra2 is a distance between the centroid of the intensity distribution and
5 a position at which an intensity integration value from the centroid of the intensity
distribution in the second direction is 43% of the total intensity integration value, a beam
intensity Iai is an intensity corresponding to the Rai, the beam intensity Ia2 is an intensity
corresponding to the Ra2, la is an average value of the beam intensity lai and the beam
intensity Ia2 and lb is a beam intensity of the laser beam at the centroid of the intensity
10 distribution.
10. The laser irradiation method according to Claim 9,
wherein Id/Ic falls within a range of 1.5 to 10 in a C direction intensity
distribution of the laser beam focused on the grain-oriented electrical steel sheet on a
15 cross-section in the scanning direction on the grain-oriented electrical steel sheet, where,
when an integral of the C direction intensity distribution is calculated from a centroid of
the C direction intensity distribution in each of a third direction and a fourth direction
which are both along the scanning direction, RCJ is a distance between the centroid of the
C direction intensity distribution and a position at which an intensity integration value
20 from the centroid of the C direction intensity distribution in the third direction is 43% of
a total C direction intensity integration value, Rc2 is a distance between the centroid of
the C direction intensity distribution and a position at which an intensity integration
value from the centroid of the C direction intensity distribution in the fourth direction is
43% of the total C direction intensity integration value, a beam intensity Ici is an
25 intensity corresponding to the Rci, a beam intensity Ic2 is an intensity corresponding the
44
RC2, Ic is an average value of the beam intensity Ici and the beam intensity IC2 and Id is a
beam intensity of the laser beam at the centroid of the C direction intensity distribution.