Document Type] Specificatioil
[Title of the Invention] LASER PROCESSlNG APPAIMI'US
['I'echnical Field of the Invention]
[OOOI ]
The present invention relates to a laser processing apparatus which irradiates
laser beams on a grain-oriented electromagnetic steel sheet used for the core of a
transformer or the like thereby refining magnetic domains.
[Related Art]
YO0021
A grain-oriented electromagnetic steel sheet is easily magnetized in the rolling
direction during the production of the steel sheet. Therefore, the grain-oriented
electromagnetic steel sheet is also called a unidirectional electromagnetic steel sheet.
The grain-oriented electromagnetic steel sheet is used as a material for forming the
core of an electrical device such as a transformer or a rotary machine.
When the grain-oriented electromagnetic steel sheet is magnetized, energy
loss such as core loss is generated. In recent years, due to the progress of global
warming, energy-saving electrical devices have been required worldwide. Therefore,
a technology for further reducing the core loss in a grain-oriented electromagnetic steel
sheet is necessary.
[0003]
Core loss is classified into eddy-current loss and hysteresis loss. Eddycurrent
loss is classified into classical eddy-current loss and anomalous eddy-current
loss. For reducing classical eddy-current loss, a grain-oriented electromagnetic steel
sheet which has an insulating coating film formed at the surface and has a small sheet
thickness is known. For example, Patent Document 1 mentioned bciow discloses a
grain-oriented electro~iiagrietics teel sheet which includes a glass Glm fo~.mcdo n the
surface of a steel sheet base steel material, and an insulating coating filni formed on the
surfacc of the glass coating film.
[0004]
For exarnplc, Patent Documents 2 and 3 mentioned below disclose a laser
magnetic domain control method capable of suppressing anomalous eddy-current loss.
Jn the laser magnetic domain control method, the surface of a grain-oriented
electromagnetic steel sheet in which an insulating coating film is formed is irradiated
with a laser beam and the laser beam is scanned substantially along a width direction
of the grain-oriented electromagnetic steel sheet (that is, a direction substantially
perpendicular to the rolling direction of the gain-oriented electromagnetic stecl sheet).
As a result, a number of residual strains are periodically formed along the rolling
direction on the surface of the grain-oriented electromagnetic steel sheet (that is, the
surface of the base steel material) such that magnetic domains of the grain-oriented
electromagnetic steel sheet are refined.
According to the laser magnetic domain control method, a thermal history
having a steep temperature gradient along a thickness direction is generated in the
outermost surface of the grain-oriented electromagnetic stecl sheet through the
scanning with the laser beam. Since the thermal histoly is given, residual strains are
generated on the surface of the base steel material of the grain-oriented
electromagnetic steel sheet, and circulating current magnetic domains are formed due
to the residual strains. Intervals between 180" domain walls are refined by the
circulating current magnetic domains, and as a result, anomalous eddy-current loss in
the grain-oriented electromagnetic steel sheet is reduced.
[OOOS]
As described above, intervals betwccn 180" domain walls arc rcfincd by the
circulating current magnetic domains formed on the surface of the base steel material,
and as a result, anomalous eddy-current loss is reduced. However, thc circulating
current magnetic domains formed on the surface of the base steel material cause an
increase in hysteresis loss. Therefore, in order to minimize core loss including eddycurrent
loss and hysteresis loss, it is effective to reduce the width of the circulating
current magnetic domains. For example, Patent Document 3 discloses a method in
which strong strains arc formed in a narrow region by using a TEMoo mode laser beam,
which enables a very small beam spot size by its excellent focusing characteristics,
such that circulating current magnetic domains which are narrow and havc sufficient
strength are obtained.
[0006]
In a laser irradiation process of the laser magnetic domain control method,
magnetic domain control is performed by forming the insulating coating film on the
glass coating film and emitting the laser beam toward the upper side of the insulating
coating film. Here, due to an increase in temperature caused by the laser beam
irradiation, defects may be generated on the insulating coating film and the glass
coating film. Here, defects mean film damage such as defective peeling, swelling,
alteration, and discoloration of the insulating coating film and the glass coating film.
In a case where defects are generated in the glass coating film, the steel sheet base steel
material is exposed to the outside, and there is concern that rust may be generated.
Therefore, in a case where defects are generated in the glass coating film, the
insulating coating film needs to be applied again, which causes an addition of a process
and an increase in production costs.
[0007]
During the production of the grain-onentcd elechomagnetlc steel sheet, many
heat treatments are performed, and the interlace structure and thickness of the glass
coating lilm or the insulating coating film may vary in the rolliilg direction and width
direction of the steel sheet basc steel material. Therelhre, it may be dirficult to
suppress the generation of defects in the glass coating film over the entire steel sheet
base steel material even when laser conditions are adjusted.
[Prior Art Document]
[Patent Document]
[0008]
[Patent Document 11 Japanese Unexamined Patent Application, First
Publication No. 2007-1 19821
[Patent Document 21 Japanese Unexamined Patent Application, First
Publication No. S59-33802
[Patent Document 31 PCT International Publication No. W020041083465
[Patent Document 47 Japanese Unexamined Patent Application, First
Publication No. S58-29592
{Patent Document 51 Japanese Unexamined Patent Application, First
Publication No. H2-52192
[Disclosure of the Invention]
[Problems to be Solved by the Invention]
[0009]
However, regarding laser magnetic domain control in the related art, a
property of a laser beam that is absorbed by a steel sheet varies depending on whether
or not an insulating coating film is transparent at the wavelength of the laser beam
which is emitted. In a case where the insulating coating film is opaque to the
wavelength orthe laser beam, the laser beam is absorbed by the insulating coaling fllm.
In addition, regarding the propagation of'a laser beam, it is lmown that as the
propagation distance (hereinafter, also referred to as a path length) of the laser beam
within a material that absorbs the laser beam increases, the absorbed lascr beam power
increases.
[OOl 01
In addition, in a case of laser magnetic domain control in which a laser beam
having a wavelength that is not transmitted by an insulating coating film is used, the
following problems have incurred. That is, in order to perform scanning the laser
beam rapidly and efficiently, an optical system which linearly scans a single laser beam
from a position at a predetermined height from the surface of a grain-oriented
electromagnetic steel sheet onto the grain-oriented electromagnetic steel sheet along a
width direction thereof is used.
In a case where this optical system is used, the laser beam is incident
perpendicular to the surface of the grain-oriented electromagnetic steel sheet at a center
portion ofthe laser scanning width. That is, in a case where the incident position of
the laser beam is coincident with the center portion of the laser scanning widlh, the
angle between the direction perpendicular (normal direction) to the surface of the
grain-oriented electromagnetic steel sheet and the propagation direction of the laser
beam (an incident angle 4 of the laser beam) becomes 0". On the other hand, as the
incident position of the laser beam approaches an end portion of the laser scanning
width, the incident angle + of the laser beam increases.
In such an optical system, as the incident position of the laser beam
approaches the end portion apart from the center portion ofthe laser scanning width (as
the incident angle + of the laser beam increases), the path length of the layer beam in
the i~lsulatingc oating film and the glass coating film increases, and thus the amount of
the laser beam absorbed by the insulatiilg coating film increases. Therefore, a higher
power is absorbed at the end portion of the laser scanning width in the steel shcet than
at thc center portion. Consequently, the risk of generating defects in the glass coating
film increases.
[OOll]
In order to solve this problem, reducing the absorptance of the laser beam at
the end portion of the laser scanning width may be considered. Regarding this, for
example, as disclosed in Patent Documents 4 and 5 mentioned above, a technology in
which the incident angle of a laser beam (linearly polarized light) is fixed to an angle
close to the Brewster's angle (for example, an angle of 45" or higher, referring to Claim
3 of Patent Document 4 and Claim 1 of Patent Documcnt 5) such that thc surface of a
processing object is irradiated with the laser beam in a state in which the absorptance
of the laser beam is always maximized has been hitherto known. However, a
technology for actively reducing the absorptance of a laser beam at a specific
irradiation position has not been required in the related art.
[00 121
The present invention has been made taking the foregoing circumstances into
consideration, and an object thereof is to provide a laser processing apparatus capable
of suppressing the generation of defects in a glass coating film.
[Means for Solving the Problem]
[OO13]
In order to achieve the object of solving the problems, the present invention
employs the following measures.
(1) An aspcct ofthe present invention provides a laser processing apparatus
for refining magnetic domains of a grain-oriented electrolllagnetic steel sheet by
setting a laser beam to be focused on the grain-oricnted e1cctroil:agnetic steel sheet and
scm:cd in a scanning direction, in which the laser beam focused on the grain-oriented
electromagnetic steel sheet is lincarly polarized light, and an angle between a linear
polarization direction and the scanning direction is higher than 45" and equal to or
lower than 90".
[0014]
(2) In the laser processing apparatus described in (I), a maximum incident
angle +MAX of the laser beam incident on the grain-oriented electromagnetic steel sheet
may satisfy the following conditional expression (1).
~ICOS~M5 1A.1X9 ...(1 )
[0015]
(3) In the laser processing apparatus described in (I) or (2), a wavelength of
the laser beam focused on the grain-oriented electromagnetic steel sheet may be higher
than 7 pm.
[0016]
(4) The laser processing apparatus described in any one of (1) to (3) may
further include a laser oscillator which emits the laser beam, and the laser oscillator
may he a COz laser which emits linearly polarized light.
[0017]
(5) In the laser processing apparatus described in any one of (I) to (4), a shape
of the laser beam focused on the grain-oriented electromagnetic steel sheet may be an
ellipse, and a minor axis direction of the ellipse may be perpendicular to the scanning
direction.
[Effects of the Invention]
1001 81
According to thc aspect, the generation of dcfccts in the glass coating film can
be suppressed.
[Bricf Description of the Drawings]
[0019]
FIG. 1 is a sectional view of a grain-oriented electromagnetic steel sheet 10
according to an embodiment of the present invention.
FIG. 2 is a flowchart showing an example of a production process of' the
grain-oriented electromagnetic steel sheet 10 according to an embodiment of the
present invention.
FIG. 3 is a schematic view showing an example of the configuration of a laser
processing apparatus 100 according to an embodiment of the present invention.
FIG. 4 is a schematic view showing an example of the configuration of a laser
irradiation device 106 according to an embodiment of the present invention.
FIG. 5 is a view showing a shape of a laser beam focused on the grainoriented
electromagnetic steel sheet 10.
FIG. 6 is a schematic view showing states of the laser beam incident on the
grain-oriented electromagnetic steel sheet 10.
FIG. 7A shows a path length el in an insulating coating film 16 and a path
length el' in a glass coating film 14 of the laser bcam incident on the insulating coating
film 16 at a center portion P1 of a laser scanning width L.
FIG. 7B shows a path length e2 in the insulating coating film 16 and a path
length e2' in the glass coating film 14 of the laser beam incident on the insulating
coating film 16 at an end portion P2 of the laser scanning width L.
FIG. 8 is a schematic view showing the relationship between a linear
polarization direction and a scanning direction of thc laser beam.
FIG. 9A is a vicw showing an clcctric field oscillation direction oS P-polarized
light in a case where linearly polarized light LB is incident on the surface of the grainoricnted
clectromagnctic steel sheet 10 at an incident angle +.
FIG. 9B is a view showing an electric field oscillation direction of S-polarized
light in a case where the linearly polarized light LB is incident on the surface of the
grain-oriented clectromagnetic steel sheet 10 at the incident angle +.
FIG. 10 is a graph showing the absorptances of P-polarized light and Spolarized
light of a laser beam at the upper surface ofa base steel material 12.
FIG. 11 is a view showing a modification example of the laser irradiation
device 106.
[Embodiment of the Invention]
[0020]
An embodiment of the present invention will be described in detail below
with reference to the accompanying drawings. In the specification and the drawings,
elements which have substantially the same functional configurations are denoted by
the same reference nu~ilerals,a nd corresponding descriptions will not be repeated.
[0021]

A grain-oriented electromagnetic steel sheet is an electromagnetic steel sheet
in which the easy magnetization axis of grains of ihe steel sheet ( direction of a
body-centered cubic crystal) is substantially aligned with the rolling direction in a
production process. In the grain-oriented electromagnetic steel sheet described above,
a number of magnetic domains of which the magnetization direction aligns with the
rolling direction are arranged and these magnetic domains are separated by domain
walls. The grain-oriented electromagnetic steel sheet is easily magnetized in the
rolling direction and is thus appropriate as the corc inatcrial of a transformer in which
the dircctions of hncs of magnetic forces are substantially constant.
A core for a transformer is roughly classified into a wound core and a stacked
core. In a production process of a wound core, a steel sheet is assembled into the
shape of the core while winding deformation is given thereto, and thereafter annealing
is performed on the resultant in order to remove strains introduced due to the
mechanical deformation. However, in the annealing process, as described above,
strains introduced due to laser irradiation are also removed, and thus an effect of
refining the magnetic domains is lost. On the other hand, in a production process of a
stacked core, an annealing process for strain removal described above is unnecessary.
Therefore, the grain-oriented electromagnetic steel sheet according to this embodiment
is particularly appropriate as the material of stacked cores.
[0022]
FIG. 1 is a sectional view of a grain-oriented electromagnetic steel sheet 10
according to this embodiment. As shown in FIG. 1, the grain-oriented
electromagnetic steel sheet 10 includes a steel sheet body (base steel material) 12, glass
i coating films 14 formed on both surfaces ofthe steel sheet body 12, and insulating
i
1 coating films 16 formed on the glass coating films 14.
The steel sheet body 12 is formed of an iron alloy containing Si. The
I
I composition of the steel sheet body 12 includes, as an example, Si: 2.5 mass% or more
and 4.0 mass% or less, C: 0.02 mass% or more and 0.10 mass% or less, Mn: 0.05
mass% or more and 0.20 mass% or less, acid-soluble Al: 0.020 mass% or more and
0.040 mass% or less, N: 0.002 mass% or more and 0.012 mass% or less, S: 0.001
mass% or more and 0.01 0 mass% or less, P: 0.01 mass% or more and 0.04 mass% or
less, and Fe and unavoidable impurities as the remainder. For example, the thickness
of the steel sheet body 12 is 0.1 mm or greater and 0.4 mm or smaller.
[0024]
For example, the glass coating film 14 is formed of conlplex oxides such as
forsterite (Mg2Si04), spinel (MgA1204), and cordierite (Mg2A14Si~O~~F).o r example,
the thickness of the glass coating film 14 is 1 pn.
[0025]
For example, the insulating coating film 16 is formed of a coating liquid
primarily containing colloidal silica and phosphate (magnesium phosphate, aluminum
phosphate, or the like), or a coating liquid in which alumina sol and boric acid are
mixed together. For example, the thickness of the insulating coating film 16 is 2 ym
or greater and 3 ym or smaller.
[0026]
In the grain-oriented electromagnetic steel sheet 10 having the abovedescribed
configuration, a laser beam is emitted toward the upper side of the insulating
coating film 16 such that residual strains are given to line-shaped regions substantially
perpendicular to the rolling direction. The line-shaped regions to which the residual
strains are given are formed at predetermined periods in the rolling direction. In
regions which exist between two line-shaped regions and are magnetized in the rolling
direction, magnetic domain widths in a direction substantially perpendicular to the
rolling direction are refined.
[0027]

A production method of the grain-orientcd electromagnetic steel sheet 10
accordiug to this embodinlent will be described with rererence to FIG. 2. FIG. 2 is a
flowchart showing an example of a production process of the grain-oriented
electromagnetic stcel sheet 10 according to this embodiment.
LO0281
As shown in FIG. 2, the production process of the grain-oriented
electromagnetic steel sheet 10 includes a casting process S2, a hot rolling process S4,
an annealing process S6, a coid rolling process S8, a decarburization annealing process
S10, an annealing separating agent applying process S12, a final finishing annealing
process S14, an insulating coating film forming process S16, and a laser irradiation
process S 18.
[0029]
In the casting process S2, molten steel which is adjusted lo have a
predetermined composition is supplied to a continuous casting machine to
continuously form an ingot. In the hot rolling process S4, hot rolling is performed by
heating the ingot to a predetermined temperature (for example, 1150°C to 1400°C).
Accordingly, a hot rolled material having a predetermined thickness (for example, 1.8
to 3.5 mm) is formed.
[0030]
In the annealing process S6, a heat treatment is performed on the hot rolled
material, for example, under the condition of a heating temperature of 750°C to
1200°C and a heating time 0230 seconds to 10 mintltes. In the cold rolling process
S8, the surface of the hot rolled material is pickled, and thereafter cold rolling is
performed thereon. Accordingly, a cold rolled material having a predetermined
thickness (for example, 0.1 to 0.4 rnm) is formed
[003 11
In the decal-hurization annealing proccss S10, a hcat treatment is performed on
the cold rolled material, for example, under the condition of a heating temperature of
700°C to 900°C and a heating time of 1 to 3 minutes, thereby forming the steel sheet
body 12. An oxide film primarily containing silica (Si02) is formed on the surface of
the steel sheet body 12. In the annealing separating agent applying process S12, an
annealing separating agent primarily containing magnesia (MgO) is formed on the
oxide layer of the steel sheet body 12.
[0032]
In the final finishing annealing process S14, the steel sheet body 12 to which
the annealing separating agent is applied is inserted into a batch type furnace in a state
of being wound in a coil shape and is subjected to a heat treatment. The heat
treatment conditions are, for example, a heating temperature of 1100°C to 1300°C and
a heating time of 20 to 24 hours. At this time, so-called Goss grains of which the
easy magnetization axis aligns with a transport direction (rolling direction) of the steel
sheet body 12 preferentially grow. As a result, a grain-oriented electromagnetic steel
sheet which has a high degree of crystal orientation (orientation) after the finishing
annealing can he obtained. In addition, in the final finishing annealing process S14,
the oxide layer and the annealing separating agent react with each other such that the
glass coating film 14 formed of forsterite (MgzSiOd) is formed on the surface of the
steel sheet body 12.
[0033]
In the insulating coating film forming process S16, the steel sheet body 12
which is wound in the coil shape is unwound and stretched into a plate shape so as to I
be transported. In addition, an insulating agent is applied onto the glass coating films
14 formed on both surfaces of the steel sheet body 12, and the resultant is balced,
thereby forming the insulating coating films 16. The steel sheet body 12 on which the
insulating coating films 16 are foimed is wound in a coil shape.
[0034]
In the laser irradiation process S18, the steel sheet body 12 which is wound in
the coil shape is unwound and stretched into a plate shape so as to be transported. In
addition, a laser beam is focused on and irradiates one surface of the steel sheet body
12 by a laser irradiation device, which will be described later, and the laser beam is
scanned substantially along the width direction of the clectromagnetic steel sheet
transported in the rolling direction (transport direction). Accordingly, line-shaped
strains which are substantially perpendicular to the rolling direction are formed on the
surface of the steel sheet body 12 at predetermined intervals in the rolling direction.
In addition, focusing and scanning of the laser beam may also be performed on both
surfaces including the front surface and the rear surface of the steel sheet body 12. In
addition, it is described above that the steel sheet body 12 on which the insulating
coating films 16 are formed is wound in the coil shape and is then subjected to the
laser irradiation process Sl8. However, laser irradiation may he performed
immediately after the Sormation of the insulating coating films and thereafter the steel
sheet body 12 may be wound in a coil shape.
[0035]
In the production process described above, the grain-oriented electromagnetic
steel sheet 10 in which the glass coating films 14 and the insulating coating films 16
are formed on the surface of the steel sheet body 12 and magnetic domains are
controlled by laser irradiltion is produced.
[0036]

An example of the configuration ofa laser processing apparatus 100 which
irradiates the grain-oriented electromagnetic steel sheet 10 with a laser beam to
generate residual strains will be described with refercnce to FIGS. 3 and 4. FIG. 3 is a
schematic view showing an example of the configuration of thc laser processing
apparatus 100 according to this embodiment. FIG. 4 is a schematic view showing an
example of the configuration of a single laser irradiation device 106.
[0037]
The laser processing apparatus 100 emits the laser beam toward the upper side
of the insulating coating film 16 of the grain-oriented elcctromagnetic steel sheet 10
transported in the rolling direction at a predetermined speed to generate line-shaped
strains which extend substantially perpendicular to the rolling direction. As shown in
FIG. 3, the laser processing apparatus 100 includes a number of laser oscillators 102, a
number of laser beam propagation paths 104, and a number of the laser irradiation
devices 106. In FIG. 3, three laser oscillators 102, three laser beam propagation paths
104, and three laser irradiation devices 106 are shown, and the configurations of the
threc are the same.
[0038]
For example, the laser oscillator 102 emits a laser beam with an output of 100
W or more. In addition, as described later, as the laser oscillator 102, an oscillator
which emits a laser beam at a wavelength of higher than 7 pm is preferable. As the
laser oscillator 102, for example, a COz laser with a laser beam wavelength of 10.6 pm
is uscd. Moreover, in this embodiment, the laser oscillator 102 emits a linearly
polarized laser beam having a predetermined polarization direction. The reason that
thc linearly polarized laser beam is used will be deqcribed later. The laser oscillator
102 may be either a continuous wave laser or a pulsed laser.
A lascr light having an electric lield component (linearly polarized
component) that oscillates only in one direction is ideal for the linearly polarized laser
in the present illvention. Strictly speaking, an electric field component that is
perpendicular to the linearly polarized component (orthogonal component) exists very
slightly. The ratio between the power of the linearly polarized component and the
power of the orthogonal component is dependent on the performance of a polarizing
beam splitter 124 described above and the performance of the laser oscillator 102.
When it is assumed that the power of the linearly polarized component is givcn by
PW1 and the power of the orthogonal component is given by PW2, and
(PWlI(PWl+PW2)) is defined as a degree of polarization, the linearly polarized light
in the present invention has a degree of polarization of 0.9 or higher and lower than 1 .O.
That is, in a case where a linearly polarized laser having a degree of polarization of 0.9
or higher and lower than 1.0 (90% or higher and lower than 100%) was used, the
results of Examples, which will be described later, were obtained. In addition, by
splitting the linearly polarized light using an orthogonal prism or the like, the
proportions of the linearly polarized components can be analyzed.
[0039]
The laser irradiation device 106 allows the laser beam propagated from the
laser oscillator 102 to the laser beam propagation path 104 to be focused on the grainoriented
electromagnetic steel sheet 10 such that the laser beam is scanned on the
grain-oriented electromagnetic stcel sheet 10 along a direction substantially
perpendicular to the rolling direction. A width which is scanned with the laser beam
by a single laser irradiation device 106 may be smaller than the sheet width of the
grain-oriented electromagnctic steel sheet 10. However, as shown in FIG 3, by
arrangmg a number of laser i~radiationd evices 106 in the sheet width direction, the
region of thc overall shect width of the grain-oriented electromagnetic steel sheet 10
can be scanned with the laser beam.
[0040]
As shown in FIG. 4, the laser irradiation device 106 includes a 1J2 plate 125, a
metallic mirror 126, a polygon mirror 128, and a parabolic mirror 130.
[0041]
The hi2 plate 125 is inserted to adjust the linear polarization direction by
changing its rotational angle. In a case where the linear polarization direction on the
steel sheet follows a predetermined direction, which will be described latcr, the hi2
plate 125 may be omitted. As an element for changing the linear polarization
direction, a Faraday rotator or the like may be used instead of the hi2 plate 125.
[0042]
In the above description, the laser beam emitted from the laser oscillator 102
is a linearly polarized light. However, the laser beam emitted from the laser oscillator
102 is not necessarily to be the linearly polarized light. In a case where the laser
beam emitted from the laser oscillator 102 is unpolarized light, a polarizing beam
splitter may be installed in front of the U2 plate 125 to convert the unpolarized light
into linearly polarized light. When the polarizing beam splitter is arranged to rotate
around the center axis of the laser beam, the linear polarization direction on the surface
of the steel sheet can be adjusted to be a predetermined direction even when the hi2
plate 125 is not installed. As described above, the linearly polarized laser beam can
propagate to the metallic mirror 126. The reason that the laser beam is the linearly
polarized light will be described later.
100431
The metallic mirror 126 is a mirror that squcezes and adjusts the beam
diameter ol'thc incident laser beam in the sheet width direction (see FIG. 5) oS the
grain-oriented electromagnetic steel sheet 10. As the melallic mirror 126, for
example, a cylindrical mirror or a parabolic minor having a curvature in a uniaxial
direction may be used. The laser beam reilected by the metallic mirror 126 is
incident on the polygon mirror 128 that rotates at a predetcrmined rotational speed.
[0044]
The polygon mirror 128 is a rotatable polyhedron and scans the laser beam on
the grain-oriented electromagnetic steel sheet 10 along the sheet width direction
thereof as the polygon mirror 128 rotates. While the laser beam is incident on one
side of the polyhedron of the polygon mirror 128, a single line-shaped region on the
grain-oriented electromagnetic steel sheet 10 along the sheet width direction is scanned
with the laser beam as the side rotates such that a residual strain is generated to the
line-shaped region. As the polygon mirror rotates, scanning of the laser beam is
repeatedly performed, and the grain-oriented electromagnetic steel sheet 10 is
simultaneously transported in the rolling direction. As a result, a region having a
line-shaped residual strain is periodically formed on the grain-oriented electromagnetic
steel sheet 10 in the rolling direction. The period of the line-shaped regions along the
rolling direction is adjusted by the transportation speed of the grain-oriented
electromagnetic steel sheet 10 and the rotational speed of the polygon mirror 128.
The parabolic mirror 130 is a mirror that squeezes and adjusts the beam
diameter of the laser beam reflected by the polygon mirror 128 in the rolling direction.
The laser beam reflected by the parabolic mirror 130 is focused on the surface of the
grain-oriented electromagnetic steel sheet 10.
[0046]
FIG. 5 is a view showing the shapc of the laser beam Socused on thc grainoriented
electromagnetic steel sheet 10. In this cmbodiinent, the shape of the focuscd
laser beam is an ellipse as shown in FIG. 5. The major axis direction of the ellipse is
parallel to the scanning direction of the laser beam, and the minor axis direction of the
ellipse is perpendicular to the scanning direction. In other words, the minor axis
direction of the ellipse is parallel to the rolling direction. By setting the shape of the
focused laser beam to be the ellipse, the time for irradiating one point on the grainoriented
electromagnetic steel sheet 10 with the laser beam increases. As a result, the
temperature of the grain-oriented electromagnetic steel sheet 10 can be increased
toward a deep position ofthe inside thereof, which is effective in reducing core loss.
Since the beam diameter in the sheet width direction is squeezed by the metallic mirror
126 and the beam diameter in the rolling direction is squeezed by the parabolic mirror
130, the shape of the focused laser beam becomes an ellipse. In addition, when the
shape of the focused laser beam is the ellipse, the area of the focused laser beam
increases compared to a case where the focused shape is a true circle, resulting in a
reduction in power density. As a result, a temperature gradient along the thickness
direction in the vicinity of the surface of the grain-oriented electromagnetic steel sheet
10 is prevented from becoming steep, which is effective in suppressing the generation
of defects in the glass coating film 14.
(00471
In the above description, a case where the shape of the laser beam focused on
the grain-oriented electromaglletic steel sheet 10 is an ellipse is exemplified, but the
present invention is not limited thereto. For example, the shape of the focuscd laser
beam lnay also be a true circle.
[0048]
In this embodiment, it is prcferable that the intcnsity distlibution of the laser
beam is set such that thc beam diameter (a width including 86% of thc integratcd
intcnsity) in the rolling direction becomes 200 pm or smaller. Accordingly, narrower
circulating current magnetic domains arc formed while further suppressing the
expansion of thermal conduction in the rolling direction, thereby significantly reducing
core loss. Furthermore, in order to reliably reduce core loss, it is more preferable that
the beam diameter be set to 120 llm or smaller.
[0049]

When the laser irradiation device 106 scans the surface ofthe grain-oriented
electromagnetic steel sheet 10 with the laser beam over a predetermined laser scanning
width, the states ofthe laser beam incident on the surface of the grain-oriented
electromagnetic steel sheet 10 at the center portion and the end portion of the laser
scanning width are different from each other.
[0050]
FIG. 6 is a schematic view showing the state of the laser beam incident on the
grain-oriented electromagnetic steel sheet 10. When the laser irradiation device 106
scans the laser beam over a predetermined laser scanning width L in the scanning
direction, as shown in FIG. 6, the state of the laser beam incident on a center portion P1
of the laser scanning width L is different from the state of the laser beam incident on
end portions P2 and P3 of the laser scanning width L. Specifically, the laser beam
reflected by the parabolic mirror 130 of the laser irradiation device 106 is incident
perpendicular to the surface (insulating coaling film 16) of the grain-oriented
electromagnetic steel sheet 10 at the center portion PI of the laser scanning width L.
On the other hand, the laser beam is obliquely incident on the surface ofthe giainoriented
elcctromagnctic stcel sheet 10 (incident at an incident angle 4 with respect to
the direciion normal to the surface) at both the end portions P2 and P3 ofthe laser
scanning width L.
That is, in a case where the incident position of the laser beam is coincident
with the center portion P1 of the laser scanning width L, the angle between the
direction perpendicular to (direction normal to) the surface of the grain-oriented
electromagnetic steel sheet 10 and the propagation direction of the laser beam (the
incident angle 4 of the laser beam) becomes 0". On the other hand, as the incident
position of the laser beam approaches the end portion P2 or P3 of the laser scanning
width L, the incident angle 4 of the laser beam increases.
[0051]
FIGS. 7A and 7B are schematic views showing path lengths of the laser beam
within the insulating coating film 16. FIG. 7A shows a path length el in the
insulating coating film 16 and a path length el' in the glass coating film 14 of the laser
beam incident on the insulating coating film 16 at the center portion P1 of the laser
scanning width L. FIG. 7B shows a path length e2 in the insulating coating film 16
and a path length e2' in the glass coating film 14 of the laser beam incident on the
insulating coating film 16 at the end portion P2 of the laser scanning width L. The
path lengths of the laser beam incident on the insulating coating film 16 at the end
portion P3 of the laser scanning width L are the same as those in FIG. 7B.
[0052]
The transmittance of the laser beam through the insulating coating film 16 and
the glass coating film 14 is e~pressed~bexyp (-aL) according to the Lambert-Beer law
which is well known. Isere. n is the absorption coefficient, and L is the path length.
As the path length L increases, the transmittance decreases. That is, as the path
length L incl.eases, the power of the laser beam absorbed inside the glass coating film
16 and inside the glass coating film 14 increases. As is apparent from FIGS. 7A and
7B, since the path length e2 (e2') is greater than the path length el (el '), the aliiount of
the laser beam absorbed by the insulating coating film 16 (the glass coating film 14) at
the end portion P2 (P3) of the laser scanning width L increases. As a result, a higher
power is supplied to the gain-oriented electromagnetic steel sheet 10 at the end
portion P2 (P3) of the laser scanning width L than at the center portion PI, the
temperature excessively increases, and defects are easily generated in the insulating
coating film 16 or the glass coating film 14.
[0053]
In this embodiment, in order to solve the above-described problems, the laser
beam focused on the surface (the insulating coating film 16) of the grain-oriented
electromagnetic steel sheet 10 is set to be linearly polarized light, and as shown in FIG.
8, the angle 8 between the linear polarization direction and the scanning direction of
the laser beam is set to be higher than 45" and equal to or lower than 90". FIG. 8 is a
schematic view showing the relationship between the linear polarization direction and
the scanning direction of the laser beam in a case where the incident angle c$ of the
laser beam is 0". As far as the angle 0 between the scanning direction of the laser
beam and the linear polarization direction is higher than 45" and equal to or lower than
90°, the relationship between the linear polarization direction and the scanning
direction of the laser beam may have a reflectional symmetry with respect to FIG 8.
[0054]
As in this embodiment, in a case where the angle 8 is set to be higher than 45O
and equal to or lower than 90°, as described later, the absorptance of the laser beam at
the end portions P2 and P3 of tlle laser scanning width L can be decreased. Therefore,
even when thc path length of the laser beam at the *nd portlons P2 and P3 of the laser
scanning width L incleases, an increase in the power absorbed by the insulating
coating filin 16 can be suppressed. As a result, the generation of defects in the glass
coating film 14 at the end portions P2 and P3 of the laser scanning width I, can be
suppressed.
[0055]

Here, the principle that the absorptance of the laser beam is decreased by the
angle 8 between the linear polarization direction and the scanning direction of the laser
beam is described.
[0056]
A portion of the laser beam incident on the grain-oriented electromagnetic
steel sheet 10 is reflected by the insulating coating film 16, and the remainder is
incident on the insulating coating film 16. A portion of the laser beam incident on the
insulating coating film 16 is absorbed inside the insulating coating film 16 and the
remainder reaches the upper surface of the glass coating film 14 such that a portion
thereof is reflected and the remainder thereof is incident on the glass coating film 14.
A portion of the laser beam incident on the glass coating film 14 is absorbed inside the
glass coating film 14 and the remainder reaches the upper surface of the steel sheet
body (hereinafter, also called base steel material) 12 such that a portion thereof is
reflected and the remainder thereof is absorbed by the surface of the steel sheet body
12. In addition, the power of the laser beam transmitted to the grain-oriented
electromagnetic steel sheet 10 is dependent on the absorptance of the laser beam
absorbed by the insulating coating film 16 and the like as described above. When the
absorptance of the laser beam at the insulating coating film 16 and the like is hlgh, the
power of the laser beam transmitted to the grain-oriented electroniagnetic steel sheet
10 increases.
[0057]
However, linearly polari~edli ght generally includes P-polarized light (also
called P wavcs) and S-polarized light (also called S waves). It is known that the
absorptance of P-polarized light and the absorptance of S-polarized light are different
from each other. Therefore, depending on the absorptances of the P-polarized light
and the S-polarized light into the insulating coating film 16 and the like, the power of
the laser bcam transmitted to the grain-oriented electromagnetic steel sheet 10 varies.
[0058]
FIG. 9A shows an electric field oscillation direction of P-polarized light in a
case where linearly polarized light LB is incident on the surface of the grain-oriented
electromagnetic steel sheet 10 at an incident angle 4. FIG. 9B shows an electric field
oscillation direction of S-polarized light in the case where the linearly polarized light
LB is incident on the surface of the grain-oriented electromagnetic steel sheet 10 at the
incident angle 4. As shown in FIGS. 9A and 9B, in a case where the linearly
polarized light LB is incident on the surface of the grain-oriented electromagnetic stcel
sheet 10 at the incident angle 4, the electric field oscillation direction of the Ppolarized
light and the electric field oscillation direction ofthe S-polarized light are
different from each other. Specifically, during scanning the linearly polarized light,
the electric field of the P-polarized light oscillates along the double arrow direction
shown in FIG. 9A, and the electric field of the S-polarized light oscillates along the
direction perpendicular to the figure as shown in FIG. 9B.
[0059]
FIG. 10 is a graph showing the absorptances of the P-polarized light and the
S-polarized liglit of the laser beam at the upper surrace of the base steel material 12
As shown in FIG. 10, the absorptance of the P-polarized liglit is higher than the
absorptance of the S-polarized liglit. In addition, as the incident angle 4 of the laser
beam (linearly polarized light) increases, the absorptance of the P-polarized light
increases, and the absorptance of the S-polarized light decreases. FIG. 10 shows the
absorptances at the uppcr surface of the base steel material 12, which remains after
removal of the insulating coating film 16 and the glass coating film 14 from the grainoriented
electromagnetic steel sheet 10. However, the absorptance at the upper
surface of the insulating coating film 16 and the absoiptance at the upper surface of the
glass coating film 14 have the same tendency as that of FIG. 10.
[0060]
In a case where the angle 8 between the linear polarization direction and the
scanning direction of the laser beam is On, only the P-polarized light is incident on an
incident surface (the surface of thc grain-oriented electromagnetic steel sheet 10). In
a case where the angle 0 is 45", the P-polarized light and the S-polarized light are
incident on the incident surface one half for each. In a case where the angle 8 is 90°,
only the S-polarized light is incident on the incident surface. Therefore, in a case
where the angle 0 is equal to or higher than 0" and lower than 45", the effect of the Ppolarized
light between the P-polarized light and the S-polarized light becomes
dominant, and as the incident angle + increases, the absorptance of the laser beam
increases. On the other hand, in a case where angle 0 is higher than 45" and equal to
or lower than 90°, the effect of the S-polarized light becomes dominant, and as the
incident angle 4 increases, the absorptance of the laser beam decreases.
[0061]
In this embodiment, foi reducing the absorptance of the lascr beam at the end
portions P2 and P3 of the laser scanning width L of the laser irradiation device 106, the
angle 8 between thc linear polarization direction and the scanning direction of the laser
beam is set to be higher than 45" and equal to or lower than 90". Accordingly, the
effect of the S-polarized light out of the P-polarized light and the S-polarized light
becomes dominant. Therefore, at the end portions P2 and P3 of the laser scanning
width L, even when the path length of the laser beam in the insulating coating film 16
and the glass coating film 14 increases, the amount of the laser beam absorbed by the
insulating coating film 16 and the glass coating film 14 can be reduced. As a result,
an increase in the temperature of the insulating coating film 16 and the like can be
suppressed, and thus the generation of defects of the glass coating film 14 at the end
porlions P2 and P3 of the laser scanning width L can be suppressed.
[0062]
Particularly, in a case where the angle 8 between the linear polarization
direction and the scanning direction of the laser beam is set to 70' or higher and 90" or
lower, the effect of the S-polarized light becomes more dominant, and the amount of
the laser beam absorbed by the insulating coating film 16 and the glass coating film 14
further decreases, and thus the generation of defects in the glass coating film 14 at the
end portions P2 and P3 of the laser scanning width L can be further suppressed.
[0063]
In addition, in this embodiment, it is even more preferable that the wavelength
of the laser beam lor scanning is higher than 7 pm. In a case where the wavelength of
thc laser beam is higher than 7 pm, the insulating coating film 16 is opaque to the laser
beam, and the laser beam is easily absorbed by the insulating coating film 16 and the
glass coating film 14. Therefore, in a case where a lascr beam at a wavelength in the
above-dcscribed range is focused on and scanned on the grain-oriented electronlagnetic
steel sheet 10, a higher power is likely to be absorbed by tlic insulating coating film 16
and the glass coating film 14 at the end portions P2 and P3 of the laser scanning width
when the laser beam is obliquely incident. Under this situation, as dcscribed above,
by setting the angle 0 to be higher than 45" and equal to or lower than 90°, the amount
of the laser beam reflected by the upper surface of each of the insulating coating film
16 and the glass coating film 14 at the end portions P2 and P3 of the laser scanning
width L increases, and the amount of the laser beam absorbed decreases. Therefore,
the power of the laser beam incident into the inside of each of the insulating coating
film 16 and the glass coating film 14 decreases. As a result, the power of the'laser
beam absorbed inside each of the insulating coating film 16 and the glass coating film
14 can be reduced, and thus the effectiveness of this embodiment can be further
reliably exhibited.
100641
In addition, the inventors discovered that when the magnification of a path
length with respect to a path length (el+el' of FIG. 7A, hereinafter, called reference
path length) in a case where the incident angle + of the laser beam is 0' is higher than
19%, as described above, even when the angle 0 between the linear polarization
direction and the scanning direction is set to be higher than 45" and equal to or lower
than 90°, the absorptance of the laser beam at the end portions P2 and P3 of the laser
scanning width L cannot be sufficiently reduced (in other words, defects are lilcely to
be generated in the glass coating film 14 at the end portions P2 and P3 of the laser
scanning width L).
It is thought that this is because when the magnification ofthe path lengtb
with respcct to the reference path length is higher than I9%, an increase in the amount
of the absorbed power due to an increase in the path length cannot be compensatcd by
a reduction of the absorplance of tllc laser beam (linearly polarized light)
Therefore, in order to reliably prevent the generation of defects in the glass
coating film 14 over the entire laser scanning width L, it is prcfcrable that the
maximum incident angle $MAX of the laser beam is set on the basis ol the following
conditional expression (1).
~/COS($M1.A19X ..~.(1 )
100651
In the conditional expression (I), the left side represents the magnification of
the path length (the path length at the maximum incident angle +MAXw) ith respect to
the reference path length. Therefore, using the conditional expression (I), the
maximum incident angle 4- at which the magnification with respect to the reference
path length is not higher than 19% can be obtained. According to the conditional
expression (I), it can be seen that it is preferable that the maximum incident angle
$MAX is 33" or lower. For example, in the laser irradiation device 106 which uses the
polygon mirror 128 shown in FIG. 4, when the number of sides of the polygon minor
128 is given by N, the maximum incident angle $MAX of the laser beam can be
expressed by 360°iiV. Therefore, it is preferable that in the laser irradiation device
106 shown in FIG. 4, N be 11 or higher.
[0066]
As shown in FIG. 11, a galvano mirror 140 may be used instead ofthe
polygon minor 128. The galvano mirror 140 is driven by a driving motor 141 to
rotate in arrow directions in the figure. As the galvano mirror 140 rotates, the grainoriented
electromagnciic steel sheet 10 is scannedwith the laser beam along the sheet
width dircction thereof (scanning direction). In this configuration, it is possible to
control the incident angle $ of the laser beam by contro1l:ng the rotational angle of the
galvano mirror 140. Thereforc, it is easy to set the maximum incident angle +MAx of'
the laser beam to an appropriate value by using the galvano minor 140.
[0067]
In addition, in the above-described embodiment, the laser oscillator 102 emits
the linearly polarized laser beam, but the present invention is not limited thereto. For
example, the laser oscillator 102 may emit an unpolarized laser beam, and a polarizer
such as a polarizing beam splitter which converts the unpolarized laser beam into
lincarly polarized light having a predetermined polarization direction may he provided
in front of the metallic mirror 126. Furthermore, the magnitude of the angle 8
described above may be adjusted by adjusting the rotational angle of the polarizing
beam splitter abound the center axis of the laser beam.
[0068]

As described above, the grain-oriented electromagnetic steel sheet 10 in
which a magnetic field is applied in the rolling direction has a structure in which a
number of magnetic domains having a magnetization dircction that substantially aligns
with the rolling direction are structured. Here, in order to achieve a further reduction
in the core loss of the grain-oriented electromagnetic steel sheet 10, it is effective to
refine the magnetic domains (reduce the magnetic domains in width) through laser
beam irradiation. Particularly, it is effective to obtain circulating current magnetic
domains which are narrow and have sufficient strength by generating a significant
temperature gradient along the thickness direction in a very narrow region that is
present in the vicinity of the uppermost layer of the grain-oriented electromagnetic
steel sheet 10 in the rolling direction.
[0069]
On thc othcr hand, when the tcruperature gradient along the thicltness
direction is increased, the temperature of the surface of the grain-oricntcd
electromagnetic steel sheet 10 increases. Duc to the teinpcrature increase, there may
be cases where defects such as defective peeling are generated in the insulating coating
Glm 16 or the glass coating film 14. Particularly in a case where defccts are
generated in thc glass coating film 14, the steel sheet body 12 is exposed to the outside
and there is concern that rust may be generated. Therefore, there is a need to prevent
the generation of defects in the glass coating film 14 while reducing the core loss of the
grain-oriented electromagnetic stecl sheet 10.
[0070]
According to this embodiment, not only the generation of defects can be
suppressed over the entire laser scanning width L, but also an effect of reducing core
loss can be obtained. That is, in a laser magnetic domain control method in which an
unpolarized laser beam is used in the related art, as described above, the power of the
laser beam absorbed at the end portions P2 and P3 of the laser scanning width L
increases due to an increase in the path lenglh, and thus defects are likely to be
generated in the insulating coating film 16 or the glass coating film 14. In order to
compensate for this, the power of the laser beam may be reduced. In this case, while
the generation of defects at the end portions P2 and P3 can be suppressed, the power of
the laser beam at the center portion P2 ofthe laser scanning width L also decreases,
which causes a problem of a reduction in the core loss reducing effect. On the other
hand, in this embodiment, as described above, in order to decrease the absorption of
the laser beam at the end portions P2 and P3 of the laser scanning width L, the grainoriented
electromagnetic steel sheet 10 is scanned with the linearly polarized light
including tlie S-polarized light ofwbich the absorptance decreases as the incident angle
6 increases. Here, at the center portion PI of the laser scanning width L,, since the
linearly polarized light is incidcni perpendicular to the surface of the grain-oriented
electromagnetic steel sheet 10 (the incident angle 4 shown in FIGS. 6 and 9 is small),
the absorptances of the P-polarized light and the S-polarized light at the center portion
P1 are substantially the same (see FIG 10). The fact that there is no difference in
absorptance between the P-polarized light and the S-polarized light which constitute an
unpolarized state means that employment of the S-polarized light hardly reduces the
absorptance. Therefore, in the laser processing apparatus 100 of this embodiment,
without a reduction of the power of the laser beam transmitted to the grain-oriented
electromagnetic steel sheet 10 at the center portion P1 of the laser scanning width L,
only the power of the laser beam absorbed at the end portions P2 and P3 can be
reduced. Accordingly, a reduction in core loss and the suppression of the generation
of defects can be realized over the entire laser scanning width L.
[0071]
In the above-described embodiment, as the laser oscillator 102 which emits a
laser beam at a wavelength of higher than 7 pm, the COz laser is used as an example,
but the present invention is not limited thereto. For example, as the laser oscillator
which emits a laser beam at a wavelength of higher than 7 pm, a fiber laser, Raman
fiber lasers, a quantum cascade laser, or the like may be used.
[0072]
In the above-described embodiment, as shown in FIG. 1, an example in which
the grain-oriented electromagnetic steel sheet 10 constituted by a three-layer structure
including the base steel material 12, the glass coating film 14, and the insulating
coating film 16 irradiated with the laser beam has been described. However, even for
a steel sheei having two layers including the base steel material 12 and the insulating
coating film 16 as the basic structure without the glass coating film 14, the laser
processing apparatus 100 of this embodiment exhibits an eflect of suppressing the
generation of defects in the insulating coating film 16 at thc end portions P2 aid 1'3 of
the laser scanning width L. This is because even when the glass coating fllm 14 is
absent, by employing the linearly polarized light as the laser beam and setting the
angle 0 to be in the above-described range, the amount of the laser beam absorbed by
the insulating coating film 16 at the end portions P2 and P3 of the laser scanning width
L can be reduced. As a grain-oriented electromagnetic steel sheet without the glass
coating film 14, a grain-oriented electromagnetic steel sheet in which the surface of a
base steel material has small roughness and is close to a mirror surface and thus
exhibits ultra-low core loss characteristics is known. In the grain-oriented
electromagnetic steel sheet having such ultra-low core loss characteristics, in order to
prevent the generation of rust caused by the exposure of the base steel material 12, it is
important that defects are not generated in the insulating coating film 16 during laser
beam irradiation. As described above, the laser processing apparatus 100 ofthis
embodiment is effective in suppressing the generation of defects.
[0073]

0
0
0
Number of pieces
where rust is generated
at cnd portion
0
" '-ximum
0
3
4
30
incident
angle +MAX
("1
24
~ / c o s + ~
1.09
100831
The results are shown in Tablc 2. When the maximum incident angle +MAX
was 33", although the generation of rust at the end portion of thc laser scauning width
was not confirmed, partial damage to the glass coating film 14 was confirmed. The
damaged portion was observed with an optical microscope, and damage to the glass
coating film 14 was present while the base steel material portion was not exposed to
the outside. This is considered to be the reason why rust was not generated. On the
other hand, it could be seen that when the maximum incident angle +- of the laser
beam was higher than 3 3 O , the number of pieces where rust was generated at the end
portion of the laser scanning width L was rapidly increased. It is thought that this is
because when the maximum incident angle +MAX of the laser beam was higher than 33",
the magnification of a path length with respect to the reference path length becomes
higher than 19%. That is, it was confirmed by the experiment that in order to reliably
prevent the generation of rust over the entire laser scanning width L, it is preferable
that the maximum incident angle +MAX of the laser beam is set on the basis of the
above-described conditional expression (1).
[0084]

As descried above, in the laser processing apparatus 100 according to this
embodiment, the angle 8 between the linear polarization direction of the light scanned
on the grain-oriented electromagnetic qteel sheet 10 and the scanning direction of the
laser beam is sct to be higher than 45" and equal to or lower than 90".
[OOSS]
Accordingly, the absorptance of the laser beam at the end portions P2 and P3
of the laser scanning width L of the glass coating film 14 can be reduced. Therefoic,
even though the path length of the laser bean1 at thc cild poi-tions P2 and P3 increases
due to oblique incidence, an increase in the power absorbed by the insulating coating
film 16 and the glass coating film 14 at thc end portions P2 and 1'3 can be suppressed.
As a result, the generation of defects in the glass coating film 14 at the end portions P2
and P3 of the laser scanning width L can be suppressed. Furthermore, as described
above, since the power of the laser beam absorbed at the center portion P1 of the laser
scanning width L is not reduced, the effect of reducing core loss at the center portion
P1 is not deteriorated. That is, reducing core loss and preventing the generation of
defects in the glass coating film 14 can be simultaneously realized over the entire laser
scanning width L.
[0086]
In the laser processing apparatus 100 according to this embodiment, since a
reduction in core loss and the suppression of defects in the glass coating film 14
described above can be achieved, the grain-oriented electromagnetic steel sheet 10
with low core loss can be produced while suppressing the generation of defects in the
glass coating film 14. Therefore, a cause of an increase in cost due to re-application
of the insulating coating film 16 caused by the generation of defects in the glass
coating film 14 can be excluded. As a result, the grain-oriented electromagnetic steel
sheet 10 with ultra-low core loss can be supplied at a lower cost. Furthermore, from
the viewpoint of realizing a reduction in energy consumption through the distribution
of the grain-oriented electromagnetic steel sheet 10 with ultra-low core loss worldwide,
a great economic effect is exhibited.
[0087]
While the preferred embodiment of the present invention has been described
in detail with ieference to the accompanying drawings, the piesent invention is not
limited to the examples. It should be notcd by those sltilled in the technical field to
which the present invention belongs that various changcs and modifications can bc
made without departing from the technical spirit described in the claims, and it should
be understood that these changes and nnodifications naturally belong to the technical
scope orthe present invention.
[Brief Description of the Reference Symbols]
[0088]
10: GRAIN-ORIENTED ELECTROMAGNETIC STEEL SHEE r
12: STEEL SHEET BODY
14: GLASS COATING FILM
16: INSULATING COATING FILM
100: LASER PROCESSING APPARATUS
102: LASER OSCILLATOR
104: LASER BEAM PROPAGATION PATH
106: LASER IRRADIATION DEVICE
125: W2 PLATE
126: METALLIC MIRROR
128: POLYGON MIRROR
130: PARABOLIC MIRROR
[Document Type] CLAIMS
1. A laser processing apparatus for refining rnagnctic domains of a grainoricntcd
clcctromagnctic steel sheet by setting a laser beam to be focused on the grainoriented
electromagnetic steel sheet and scanned in a scanning dircction,
wherein the laser beam focused on the grain-oriented electromagnetic steel
sheet is linearly polarized light, and
an angle between a linear polarization direction and the scanning direction is
higher than 45" and equal to or lower than 90".
2. The laser processing apparatus according to claim 1,
wherein a maximum incident angle $MAX of the laser beam incident on the
grain-oriented electromagnetic steel sheet satisfies the following conditional
expression (1).
3. The laser processing apparatus according to claim 1 or 2,
wherein a wavelength of the laser beam focused on the grain-oriented
electromagnetic steel sheet is higher than 7 pm.
4. The laser processing apparatus according to any one of claims 1 to 3,
further comprising:
a laser oscillator which emits the laser beam,
wherein the laser oscillator is a COz laser which emits linearly polarized light.
5. The h e r processing apparatus according to any one of claims 1 to 4,
wllerein a shape of the laser beam focused on the grain-oriented
electromagnetic steel sheet is an ellipse, and
a minor axis direction of the ellipse is perpendicular to the scanning direction.