JP2003129135A - Low iron loss unidirectional electrical steel sheet manufacturing method - Google Patents

Abstract

A high-efficiency grooving method that does not require laser modification in high-speed linear scanning laser grooving. SOLUTION: A periodic groove is formed on a surface of a unidirectional electrical steel sheet by a laser beam linear scanning process in a direction substantially perpendicular to a rolling direction to subdivide a magnetic domain, thereby reducing iron loss characteristics. The laser time waveform is a continuous wave and the laser focusing shape is an ellipse having a long axis in the scanning direction of the laser beam. In the above manufacturing method,
Input power P (W), laser beam scanning speed V (mm /
s), when the elliptical minor axis a (mm) and elliptical major axis b (mm) of the laser focusing shape are set, the instantaneous power density Pd (W / mm ² ) = P / (πab) of the laser beam at the processing point, The energy density of the laser beam at the processing point is defined as Ud (J / mm ² ) = P / (V × a), and is adjusted to be included in the range of 0.8 ≦ Ud ≦ 3.3 when 50000 ≦ Pd ≦ 250,000.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a manufacturing method for forming a groove by laser processing, and in particular, by forming a groove on the surface of a unidirectional electrical steel sheet by laser processing, it has excellent magnetic characteristics capable of withstanding strain relief annealing. And a method for manufacturing a grain-oriented electrical steel sheet.

[0002]

2. Description of the Related Art For grain-oriented electrical steel sheets, it is desired to reduce iron loss from the viewpoint of energy saving. As a method, a method of subdividing a magnetic domain by laser irradiation has already been disclosed in Japanese Patent Publication No. 58-265405. This method reduces iron loss by introducing stress strain into the grain-oriented electrical steel sheet by the reaction force of the thermal shock wave generated by irradiating the laser beam and subdividing the magnetic domain to suppress the increase in hysteresis loss. This is intended to reduce the current loss. However, this method has a problem that the strain introduced by laser irradiation disappears during annealing, and the domain refinement effect is lost. Therefore, this method can be used for a laminated iron core transformer that does not require strain relief annealing, but cannot be used for a wound iron core transformer that requires strain relief annealing treatment.

Therefore, as a method of improving the magnetic properties of grain-oriented electrical steel sheets in which the effect of reducing the iron loss value remains even after strain relief annealing, a shape change exceeding the stress strain level is applied to the steel sheet to change the magnetic permeability and the magnetic domain. Various methods have been proposed for subdividing. For example, a method of pressing a steel plate with a tooth profile roll to form groove-shaped or point-shaped depressions on the surface of the steel sheet (see Japanese Patent Publication No. 63-04804) and a method of forming depressions on the surface of the steel sheet by chemical etching (US Patent No. 4750949
(See Japanese Patent Publication No. 7-220913), or a method of forming point-slots on the surface of a steel sheet with a Q-switch CO ₂ laser (Japanese Patent Laid-Open No. 7-220913)
(See the official gazette).

[0004]

However, among the above-mentioned conventional techniques, the mechanical method using the tooth profile roll causes the tooth profile to wear in a short period of time because the hardness of the electromagnetic steel sheet is high. Further, from the viewpoint of high-speed processing, it is difficult to achieve a line speed of 100 mpm or more, which is required in a general steel manufacturing process. The chemical etching method does not have a problem that the tooth profile is worn, but it requires masking, etching, and mask removing steps, and thus has a problem that the steps are more complicated than mechanical methods. The method of forming the dot-slots on the steel sheet with the Q-switch CO ₂ laser does not cause the wear of the tooth profile and the process is complicated because it forms the dents in a non-contact manner, and high-speed processing is possible. There is a problem that it is necessary to add a special Q-switch device to the laser oscillation device. In addition, a pulse-shaped time waveform is used instead of a continuous wave for groove formation by a laser of the related art. This is because it generally requires as high a power density as possible to form the grooves in the steel sheet, so that the Q switch
Due to the very high peak power of CO ₂ lasers.

On the premise of a steel plate speed of 100 mpm, a high beam scanning speed of 10 m / s or more is required to form grooves periodically in a direction substantially perpendicular to the rolling direction, that is, the moving direction. When a Q-switched CO ₂ laser is used at a beam scanning speed of 10 m / s, a typical pulse-time width of the Q-switched laser is about 10 μs, and the focused beam moves 100 μm in this pulse-time. When grooving, the focused beam diameter is focused to about 100 μm. Therefore, in this case, the focused beam diameter is equivalently doubled, and the power density is equivalently 1/2. In addition, since the pulse of the Q-switched laser is composed of an initial spike part and a tail part where the laser power is extremely high within the pulse time width, the power density fluctuates if the focused beam moves within the pulse time. Therefore, it is difficult to form a groove having a uniform depth in the scanning direction. further,
The groove formed by pulse processing becomes a dot array hole, but in order to form a continuous dot array, a high repetition frequency is required, and a higher laser output is required as the speed becomes higher.

On the other hand, if the laser time waveform is a continuous wave,
Although the power density does not fluctuate over time, the power density is low, so in order to process the groove depth required for improving iron loss characteristics under high speed scanning of 10 m / s or more, the condensing diameter must be made even smaller. However, it was industrially difficult due to the limitation of the light collecting performance.
It is possible to increase the laser power to increase the power density, but there is a cost problem for industrial equipment.

The present invention forms a groove by laser processing,
It is an object of the present invention to provide an inexpensive and stable laser groove processing method capable of high-speed processing, in a method of manufacturing a grain-oriented electrical steel sheet for improving heat-resistant magnetic properties.

[0008]

According to the present invention, a groove is formed on the surface of a unidirectional magnetic steel sheet by linear scanning of a laser beam in a direction substantially perpendicular to the rolling direction, In a method of subdividing magnetic domains to improve iron loss characteristics, a low iron loss characteristic is characterized in that the laser time waveform is a continuous wave and the laser focusing shape is an ellipse having a major axis in the scanning direction of the laser beam. It is a method of manufacturing a grain-oriented electrical steel sheet.

According to the present invention, in the above manufacturing method, the input power P (W) and the scanning speed V of the laser beam (mm /
s), the elliptic minor axis a (mm) and the elliptic major axis b (mm) of the laser focusing shape, the instantaneous power density Pd (W / mm ² ) = P / (πab) of the laser beam at the processing point, The laser beam energy density Ud (J / mm ² ) = P / (V × a) at the processing point is defined, and it is included in the range of 0.8 ≦ Ud ≦ 3.3 at 50000 ≦ Pd ≦ 250,000. Is a method for producing a low iron loss unidirectional electrical steel sheet.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to examples.

FIG. 5 is a block diagram used in the method for producing a low iron loss unidirectional electrical steel sheet of the present invention.

Grooves 3 are formed at intervals PL in the rolling direction while the laser beam LB is scanned at a speed V in the width direction of the electromagnetic steel plate 1 moving at a speed v. In order to supply the processing point assist gas, the assist gas supply nozzle 2 is installed perpendicular to the rolling direction and parallel to the groove. The beam converging shape of the ellipse is adjusted so that the minor axis a is in the rolling direction and the major axis b is the direction perpendicular to the rolling direction, that is, the scanning direction of the laser beam.

The inventors of the present invention have examined the relationship between the workability due to the converging shape, that is, the depth of the groove, and the iron loss improvement rate due to the subdivision of the magnetic domain, which is caused by the converging shape. The diameter a in the rolling direction, that is, the length of the ellipse minor axis is 0.1 mm, the diameter b in the direction perpendicular to the rolling direction, that is, the length of the ellipse major axis is 0.2 mm, and the scanning speed is changed to change the groove depth and iron. The loss was measured. For comparison, the beam focusing diameter is a = b = 0.
A round having a size of 1 mm was also performed. As other fixed conditions, the groove pitch PL in the rolling direction is 3 mm, the assist gas is air, the assist gas direction is perpendicular to the rolling direction,
Installed in parallel with the groove, adjust the assist gas pressure component in the scanning direction to 0.06 to 0.15 MPa at the processing point,
Grooving is performed on both sides of the steel sheet under the same conditions. Figure 2 shows the relationship between the scanning speed and the groove depth per side.

In FIG. 2, comparing the circular condensing and the elliptical condensing, for example, at the same beam scanning speed of 10 m / s, the circular condensing has a groove of 16 μm in depth, while the elliptical condensing has 25.
Since the groove processing of μm is done, elliptical focusing is
It can be seen that the processing efficiency is high. This is because the laser is a heat source with a very high energy density, but the irradiation beam has an energy distribution, so at the laser irradiation part, the part that evaporates when it exceeds the melting temperature and evaporates by being heated to the evaporation temperature in a short time. There can be a portion that does not reach the temperature range, that is, a portion that remains in the melting temperature range. Grooving by continuous wave laser causes evaporation and scattering of melted material by assist gas,
It is considered that the grooves are formed by the scattering due to the processing reaction force. In the case of beam scanning irradiation, the beam is irradiated to the same point during time t = (ellipse major axis b / beam scanning speed V).

Therefore, since the elliptical condensing shape whose converging shape is long in the scanning direction of the laser beam is melted for a longer time than the circular condensing shape, it is considered that the groove becomes deep at the same beam scanning speed. That is, from the viewpoint of power density, the groove is formed more efficiently in elliptical focusing, though it is lower than in circular focusing.

FIG. 3 shows the improvement rate (%) of groove depth (μm) per side and iron loss W17 / 50 (W / kg) = (iron loss before laser irradiation−iron loss after laser irradiation) / The relationship is iron loss before laser irradiation x 100. Iron loss after laser irradiation is the value measured after strain relief annealing at 800 ° C for 4 hours. In addition, W17
/ 50 indicates the iron loss when the frequency is 50 Hz and the maximum magnetic flux density is 1.7T. When the groove depth per surface is in the range of 0 μm to 15 μm, the magnetic domain refining effect gradually increases, and the improvement rate becomes maximum at 15 μm. If the groove depth per one surface exceeds 15 μm, the cross-sectional area decreases as the number of voids in the groove increases, and the magnetic flux density decreases, so iron loss begins to deteriorate and the improvement rate also decreases. When the iron loss improvement rate of 2% or more is the lower limit of the improvement effect, the groove depth range is 5 μm to 23 μm. From Fig. 3, in order to achieve an iron loss improvement rate of 10%, the groove depth per side is approximately 15 µm, so the scanning speed at which this processing is possible is
From Fig. 2, elliptical focusing is 17.
It is 5 m / s, and it can be seen that the processing efficiency is improved, which is advantageous for speeding up.

The present inventors have made various changes to the elliptical shape (minor axis a, major axis b), beam scanning speed V, and input power P in order to realize processing with higher efficiency and improved iron loss. The loss improvement rate was measured. As a fixed condition, PL = 3 mm. FIG. 1 shows the range in which the iron loss improvement is obtained, that is, the improvement rate of 2% or more, with the horizontal axis representing the instantaneous power density Pd and the vertical axis representing the energy density Ud. Instantaneous power density Pd is input power P (W) / condensing shape area πab (mm ² ),
In order to achieve the same improvement rate, the smaller this value is, the smaller the input power is and the larger the condensing diameter is.
It is cost effective. Energy density Ud is input power
P (W) / (laser beam scanning speed V (mm / sec) × axial length a (mm) perpendicular to the scanning line direction of the elliptical focusing shape), and Ud = Pd × t. t = b / V corresponds to the irradiation time. When Pd is the same to achieve the same improvement rate,
When Ud is smaller, t is smaller, that is, V is larger, so that the machining efficiency is high, which is advantageous for high-speed machining.

In the region A in which Ud is smaller than 0.8 in FIG. 1, the irradiation time t is short, so that the groove is shallow and the iron loss cannot be improved.
Further, in the region B where Ud is larger than 3.3, the irradiation time t is long, so the groove becomes too deep, and the iron loss improvement rate decreases. Pd is 50
Groove processing does not occur in the area C smaller than KW / mm ² . This is because the instantaneous energy is too small to heat up to the evaporation / melting temperature range. In the region D where Pd is 250 KW / mm ² or more, although the groove is formed, the generated plasma becomes very large, the absorption of laser light becomes remarkable by the plasma, the processing efficiency deteriorates, and the required power increases. Not preferable. On the other hand, when Pd and Ud are in the region E other than the above, there is an iron loss improving effect, and good electromagnetic characteristics are obtained. Furthermore, by making the condensing shape oval, compared with circular condensing, Pd became smaller, but Ud
As a result, the iron loss can be improved more efficiently, which is very advantageous in terms of industry and cost.

For example, of the iron loss improvement obtained in FIG.
Input power is 2 KW, minor axis a is fixed to 0.1 mm (Pd is reduced by the reciprocal of major axis b of elliptical focusing), and iron loss improvement value of 10% is achieved, that is, groove depth per side is 15 μm. FIG. 4 shows the relationship between the elliptic ratio = the major axis b / the minor axis a and the beam scanning speed V as the processing conditions. The ellipticity ratio of 1 corresponds to circular focusing, and the range in which the beam scanning speed is higher than this (Ud is reduced by the reciprocal number of the processing speed V), that is, the range of the ellipticity ratio is greater than 1 and 5 or less, and the processing efficiency is improved. Higher speed is possible.

[0020]

As described above, according to the present invention,
High-speed linear scanning laser grooving enables highly efficient grooving without laser modification. As a result, it is possible to speed up the production of the low iron loss grain-oriented electrical steel sheet and reduce the cost.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an iron power improvement range of an instantaneous power density and an energy density of a low iron loss unidirectional electrical steel sheet manufacturing method using a laser of the present invention.

FIG. 2 is an explanatory diagram comparing the relationship between the beam scanning speed and the processing depth in the present invention and the conventional circular light condensing as a light condensing shape.

FIG. 3 is an explanatory diagram showing the relationship between groove depth and iron loss improvement rate.

FIG. 4 is an explanatory diagram showing a relationship between a beam scanning speed and an elliptic ratio of a converging shape that achieves a groove depth of 15 μm.

FIG. 5 is an explanatory view showing a method for producing a low iron loss unidirectional electrical steel sheet using a laser according to the present invention.

[Explanation of symbols]

1 ... Electromagnetic steel sheet 2 ... Assist gas supply nozzle 3 ... Processed groove a ... Short axis of elliptical focusing b ... Long axis of elliptical focusing LB ... laser beam V ... Beam scanning speed v ... Steel plate speed PL ... Pitch of groove

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Claims (2)

[Claims] Claim: What is claimed is: 1. A linear groove is formed on the surface of a unidirectional electrical steel sheet by laser beam linear scanning to form a periodic groove in a direction substantially perpendicular to the rolling direction to subdivide a magnetic domain to thereby reduce iron loss. In the method for improving characteristics, a method for producing a low iron loss unidirectional electrical steel sheet, wherein the laser time waveform is a continuous wave and the laser focusing shape is an ellipse having a major axis in the laser beam scanning direction. 2. The input power P (W), the scanning speed V of the laser beam (mm / s), and the ellipse minor axis a (m) of the laser focusing shape.
m) and elliptic major axis b (mm), the instantaneous power density Pd (W / mm ² ) = P / (πab) of the laser beam at the processing point,
Energy density Ud (J / mm ² ) of laser beam at processing point
= P / (V × a), and when 50000 ≦ Pd ≦ 250,000,
The method for producing a low iron loss unidirectional electrical steel sheet with a laser according to claim 1, wherein the method falls within the range of 0.8≤Ud≤3.3.